Analysis of the effects of Dniester reservoirs on the state of the Dniester river by Zoï Environment Network

Анализ влияния водохранилищ днестровских ГЭС на состояние Днестра

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

GEF project “Enabling Transboundary Cooperation and Integrated Water Resources Management in the Dniester River Basin” UNDP • OSCE • UNECE

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

Report of the Moldovan-Ukrainian expert group Thematic supplement to the Transboundary Diagnostic Analysis of the Dniester River Basin Vienna • Geneva • Kyiv • Chisinau 2019

The report was prepared as a part of Global Environment Facility (GEF) project “Enabling Transboundary Cooperation and Integrated Water Resources Management in the Dniester River Basin” by members of Moldovan-Ukrainian expert group on the analysis of the effects of Dniester reservoirs on the Dniester river, namely Vasyl Hrebin, Volodymyr Hubanov, Oksana Huliaieva, Gabriel Gilca, Elena Zubcov, Anatolii Kalashnyk, Vitaly Kolvenko, Ruslan Melian, Mikhail Penkov, Ilia Trombitki, and Oleksandr Usov. The GEF project is being implemented by the United Nations Development Program (UNDP) and the Organization for Security and Cooperation in Europe (OSCE) in collaboration with the United Nations Economic Commission for Europe (UNECE) . Comments and suggestions were provided by Gherman Bejenaru (Austrian Development Agency), Leonid Kalashnyk (OSCE) , Bo Libert (UNECE), participants in the meetings of the bilateral Commission on the Sustainable Use and Protection of the Dniester River Basin held in Chisinau on September 17, 2018 and in Kyiv on April 4, 2019 , as well as by the participants of the second meeting of the Steering Committee for GEF project "Enabling Transboundary Cooperation and Integrated Water Resources Management in the Dniester River Basin" held in Odessa on December 18, 2018. Coordination of the expert group and technical editing of the report: Nickolai Denisov (Zoï Environment Network). Organizational support of the expert group: Anna Zhovtenko, Natalia Kozenko, Nadejda Mazur (OSCE), Hanna Plotnykova (OSCE / UNECE). General coordination of GEF project “Enabling Transboundary Cooperation and Integrated Water Resources Management in the Dniester River Basin”: Tamara Kutonova (OSCE). Translation from original Russian version into English: Artyom Klimenko. Layout and graphic design: Yulia Madinova. Cover design: Carolyn Daniel (Zoï Environment Network), Yulia Madinova. Illustration on the cover: Mikhail Larionov, "Les poissons" (Tiraspol, 1906) © 2019, ProLitteris, Zurich. Photo © 2019, Centre Pompidou, MNAM-CCI, Dist. RMN-Grand Palais / Philippe Migeat © OSCE 2019 The content, opinions, assessments, and conclusions expressed in this publication are those of authors and do not necessary reflect the official views of organizations and countries involved in the implementation or financing of the project. The designations used and the information given are not an expression of any opinion on part of these organizations and countries about the legal status of any country or any territories, cities and areas under its jurisdiction, or about the delimitation of its borders. Although every effort has been taken to ensure high quality of the publication, the authors and implementors of the project accept no liability whatsoever for the completeness and accuracy of information, possible errors, or possible implications of the use of information, conclusions, and recommendations contained in this publication. We apologize for any possible errors and omissions in the text. Publication is printed on FSC and PEFC certified paper.

TABLE OF CONTENTS INTRODUCTION

CHAPTER 1. DESCRIPTION OF RESERVOIRS AND HYDROMORPHOLOGICAL EFFECTS OF THEIR CONSTRUCTION

CHAPTER 2. IMPACT OF STRUCTURAL CHANGES ON THE AQUATIC ENVIRONMENT AND BIOTIC COMMUNITIES 2.1. Impact on the suspended sediment regime 2.2. Effect on physico-chemical conditions 2.3. Impact on aquatic organisms

14 15 17 19

CHAPTER 3. DAILY RUNOFF FLUCTUATIONS AND THEIR IMPACT ON THE STATE OF TRANSBOUNDARY SECTION 3.1. Description of daily runoff fluctuations 3.2. Impact on physico-chemical characteristics of water 3.3. Impact on aquatic organisms

28 28 31 32

CHAPTER 4. LONG-TERM CHANGES AND INTRA-ANNUAL REDISTRIBUTION OF RUNOFF 4.1. Long-term changes in the natural runoff 4.2. Intra-annual redistribution of runoff by reservoirs 4.3. The impact of hydrological changes on the state of biotic communities in the lower Dniester 4.4. Provision of basic water supply functions

33 34 36 42 43

CHAPTER 5. CONCLUSION

REFERENCES

ANNEX I. Taxonomic composition of the fish fauna in the Dniester basin before and after the regulation of runoff

ANNEX II. Water consumption in the basin downstream of HPP-2 (mln m3 per year)

LIST OF ILLUSTRATIONS 1.1

Physical map of the Dniester basin

1.2

Linear layout of hydropower stations and reservoirs

2.1

Average annual flow rate of suspended sediment at Zalishchyky o/p and the downstream of Dubossary HPP downstream (2) in 1959-1980

2.2

Average annual flow rate of suspended sediment at Zalishchyky and downstream of Dniester HPP (Mogilev-Podolsky) in 1990–2015

2.3

Average monthly flow rate of suspended sediment for 1994-2015, downstream of Dniester HPP: Mogilev-Podolsky (1), Grushka (2), downstream of Dubossary HPP

2.4

Average annual flow rate of suspended sediment for 1994 - 2015 downstream of Dniester HPP: Mogilev-Podolsky, Grushka, downstream of Dubossary HPP

2.5

Average long-term annual variation in the water temperature of downstream of Dniester HPP-1, at Mogilev-Podolsky and Grushka o/p(s) from 1990 to 2015

2.6

Difference in the average monthly water temperature at Camenca o/p in 1990–2015 compared with 1951-1980

2.7

Number of fish species in Naslavcea-Camenca area in 1950-1959 and 1996–2000

2.8

Commercial fishing in Dubossary reservoir by years and tons

2.9

Averaged commercial fishing pattern in Dubossary Reservoir in the 1960s and 2000s

2.10 Catch of aquatic biological resources in Dniester estuary, the lower reaches of the Dniester River and the floodplain system in Odessa region in 1983 - 2017, tons 2.11 Structure of commercial catches in Dniester estuary, the lower reaches of the Dniester River and the flood plain system in 1983 and 2017, tons

3.1

Amplitude of diurnal fluctuations in the water level downstream of Dniester HPP-2 (Naslavcea-1) and Dubossary HPP (Vadul-lui-Voda - 2) in the second half of 2018

3.2

Measured flow rate (m3/s) and flow velocity (m/s) in Mogilev-Podolsky (2012 and 2013)

3.3

Oxygen and temperature stratification in the dam section of the Dniester reservoir and dissolved oxygen fluctuations downstream of HPP-2 dam during the day (special case - autumn 2014: 1 – 2 km, 2 – 57 km, 3 – 83 km from HPP-2 dam)

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

3.4

Daily dynamics of dissolved oxygen content in transboundary section of the Dniester (2 km from HPP-2 dam) in the absence of oxygen stratification in the Dniester reservoir during environmental release (spring 2015)

4.1

Difference integral curves of Dniester average annual water flow in sections of individual hydrological posts

4.2

Multi-year changes in the maximum water flow rate during spring floods at Zalishchyky o/p (m3/s)

4.3

Change in average monthly water flow rates in 1990–2015 in relation to natural runoff due to regulation

4.4

Change in average monthly water flow rate in relation to natural runoff for different periods of reservoirs and HPPs commissioning

4.5

Change in the minimum and maximum runoff in Mogilev-Podolsky in 1990–2015 compared with 1951-1980

4.6

Intra-annual distribution of average monthly water flow rates for 1990–2015 at Bendery and Mogilev-Podolsky o/p(s)

4.7

Long-term characteristics of spring flood periods at Zalishchyky o/p and ecological and reproduction release at Dniester HPP-1 site

4.8

Long-term changes in the volume of water runoff during spring flood at Zalishchyky o/p and the total runoff volume during spring flood (including environmental releases) in HPP-1 upstream

4.9

Number of nests of glossy ibis and little heron in the Dniester delta from 1972 to 2009

4.10 Water consumption in the Dniester basin downstream of HPP-2 for 1965–2017 and a forecast until 2028, by type of water usage and basin countries, million m3 per year

LIST OF TABLES 1.1

Morphometric characteristics of Dniester reservoirs

2.1

Comparison of characteristics for the dominant macroinvertebrate groups in the transboundary area before and after the construction of Dniester hydropower complex

2.2

Comparison of characteristics for the dominant macroinvertebrate groups in Dubossary reservoir downstream area (Vadul-lui-Voda district ) before and after its construction

2.3

Comparison of current characteristics of phytoplankton in river sections downstream of Dniester and Dubossary reservoirs

2.4

Comparison of characteristics of zooplankton in sections of the river downstream of Dniester and Dubossary reservoirs before and after the construction of Dniester hydropower complex

2.5

Species diversity of Dniester fish before and after the creation of reservoirs

5.1

Effects of the construction and operation of reservoirs and recommendations for further actions

LIST OF INSERTS

2.1

Methodology issues of the analysis of structural changes impact

2.2

Features of thermal and oxygen regime of the Dniester reservoir

2.3

List of dominant macroinvertebrate species in the transboundary area before and after the construction of Dniester hydropower complex

3.1

Methodology issues of daily runoff fluctuations

3.2

Transformation of release at a transboundary site

4.1

Methodology issues of long-term runoff changes analysis

4.2

Water balance of the Dniester reservoir

4.3

Eco-reproductive release

4.4

Analysis of the situation at the Chisinau water intake and proposed remedial measures

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

INTRODUCTION This analysis of impact of construction and operation of the cascade of reservoirs at Dniester HPPs and PSPPs on the hydrological regime and ecosystem of the lower part of the Dniester basin as well as on basic water management functions was produced by a mixed expert group representing research, design, economic and environmental organizations and institutions of the Republic of Moldova1 and Ukraine within the framework of GEF project “Enabling Transboundary Cooperation and Integrated Water Resources Management in the Dniester River Basin”. This analysis is based on the available evidence, including published sources, data of hydrological, hydrochemical and hydro-biological observations by governmental agencies of Moldova and Ukraine, as well as historical data and information of research and industrial organizations in both countries. The activities of the group followed common principles of collaboration established at the meeting on hydropower issues held under the aegis of GEF project in Chisinau on 15 April 2018:

good faith;

desire for dialogue;

no stress on political aspects of the problems;

respect for colleagues’ opinions;

patience;

flexibility in negotiating issues and opinions.

In analyzing data and drawing conclusions, the expert group strove as much as possible to achieve consensus among the members. To ensure more open discussions, the meetings of the group followed Chatham House rules to maximize dissemination of information about work progress and results without reference to members and specific sources of the views expressed2. Over the course of 2018-2019, the group had three working meetings. During the first meeting held on 18 – 19 June 2018 in Kyiv3 general methodological issues of the group’s work were discussed and generally agreed upon, including the periodization of the analysis (consideration of the periods before the construction of reservoirs and after filling and commissioning), the identification of the main sections for analysis (the near-dam transboundary section, the middle and lower reaches of the Dniester), the choice of observation posts and the periodicity of hydrometeorological data for analysis, as well as the preliminary list of hydrological, hydrochemical and hydrobiological indicators for analysis, taking into account EU recommendations and evidence. Based on the results of the meeting, a final composition and structure of the group was established and its Terms of Reference prepared. 1

Hereinafter referred to as Moldova

"When a meeting, or part thereof, is held under the Chatham House Rule, participants are free to use the information received, but neither the identity nor the affiliation of the speaker(s), nor that of any other participant, may be revealed”: https://www.chathamhouse.org/ chatham-house-rule.

Project of the Global Environment Facility “Enabling Transboundary Cooperation and Integrated Water Resources Management in the Dniester River Basin”. Working meeting of the expert group to analyze the impact of reservoirs of Dniester HPPa on the state of the Dniester River Basin: city of Kyiv, Ukraine, 18 - 19 June 2018. Summary of the meeting.

INTRODUCTION

At the second working meeting held on 14 September 2018 in Chisinau4, the group discussed the results of the preliminary exchange of data and its analysis in respect of changes in the runoff, temperature and oxygen regimes, the state of macroinvertebrate communities, long-term dynamics, and current water needs in the basin. According to the results of the meeting, it was proposed to supplement the hydrological analysis on intraday fluctuations in flow rate and water level, characteristics of the spring flood regime and water balance of reservoirs. It was also suggested to use complementary information in hydrochemical analysis and supplement the database of hydrobiological information for analysis with the data from the Institute of Zoology of Moldova and the available materials on the state of fish communities of the Dniester, avifauna and ecosystems of the Dniester floodplains. Finally, it was agreed to expand the analysis of water use by reconstructing long-term data on water consumption by Moldova and Ukraine in the middle and lower reaches of the Dniester and its expert forecast. At the third working meeting held on April 3, 2019 in Kyiv, the leaders and deputies of expert subgroups discussed and clarified the draft of this report. The draft results of the analysis were presented at the first and second sessions of the Commission on Sustainable Use and Protection of the Dniester River Basin in Chisinau on 18 September 2018, and in Kyiv on 4 April 2019, as well as at the second meeting of the Steering Committee of the project “Enabling Transboundary Cooperation and Integrated Water Resources Management in the Dniester River Basin” in Odessa on 18 December 2018 . The final results and conclusions of the analysis conducted by the expert group were included in a short form in the Dniester Transboundary River Basin Management Plan, as well as prepared and published in the form of this report. In the substantial part of this report, the effects of the construction and operation of reservoirs are divided into two categories: caused mainly by structural modifications (physical rearrangement of the drainage network, channel and floodplain of the Dniester – Chapter 2); and caused by changes in the runoff due to its redistribution and regulation by storage reservoirs (explored in Chapters 3 and 4). The conclusion contains an overview of the major changes brought about by the construction and operation of the Dniester reservoirs, as well as the recommendations of the group on future studies and remedial measures. It should be noted that the task of the expert group was to analyze the impact of the operation of hydropower facilities. However, this is not the only reason for changes in the hydrological regime and biotic communities of the Dniester. They are also influenced by climate change, industrial and domestic pollution, construction, coastal protection, changes in the status of the catchment basin, the spread of invasive species, and other factors. The Dniester Transboundary River Basin Management Plan, amongst other things, considers the impact of those factors.

Global Environment Facility Project “Enabling Transboundary Cooperation and Integrated Water Resources Management in the Dniester River Basin”. Working meeting of the expert group on the analysis of the impact of Dniester reservoirs on the state of the Dniester basin: Chisinau, the Republic of Moldova, September 14 , 2018. Meeting summary.

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

CHAPTER 1

DESCRIPTION OF RESERVOIRS AND HYDROMORPHOLOGICAL EFFECTS OF THEIR CONSTRUCTION

Source: Strategic Directions ... 2015

Fig. 1.1. Physical map of the Dniester basin

CHAPTER 1. DESCRIPTION OF RESERVOIRS AND HYDROMORPHOLOGICAL EFFECTS OF THEIR CONSTRUCTION

The reservoirs of the Dniester hydropower stations are multipurpose and provide for the irrigation needs, water supply, flood control, electricity generation, shipping, recreation, etc. Three river reservoirs and a reservoir of a pump-storage power plant (PSPP) were built along the length of the river.

Dniester HES-1 Dniester HES-2

The Dubasari Dam mouth of Dniester

Soroca Zalishchyky

Bender

Mohyliv-Podilskyi Dniester HAES

Mayaky

Vadul lui Vodă

Naslavcea

Fig. 1.2. Linear layout of hydropower stations and reservoirs Table 1.1 Morphometric characteristics of Dniester reservoirs

Indicator

Dniester reservoir

Buffer reservoir Before PSPP commiss

After PSPP commiss

The upper pond of the PSPP

Dubossary Reservoir

Normal retaining level (NRL), m

121,0

72,0

77,1

229,50

28,0

Forced retaining level, m

125,0

82,0

30,0

Dead volume, m

102,5

67,0

67,6

215,50

24,2

Area of the water table at NRL, km2

136,0

5,9

7,3

2,61

67,5

Volume of the reservoir at NRL, mln m3

2657

31,0

58,1

41,43

266,0

Useful volume, mln m

1907

23,4

31,8

32,70

163,4

Length, km

194,0

19,8

2,90

127,5

Average width, m

701,0

298,0

369,0

900,0

529,0

Maximum depth, m

54,0

9,0

17,1

29,75

19,5

Average depth, m

19,5

5,3

6,7

15,90

4,54

Data Sources: Draft Rules, 2017; Certification, 1983

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

Restructuring of river ecosystems and the following ecosystem changes in the mouth of the Dniester started in 1955 with the construction of Dubossary HPP. Filled in 1954 - 1956, Dubossary reservoir, according to its design (Certification, 1983), is used to carry out seasonal runoff regulation, weekly runoff regulation during the low-flow period, and during flood period, daily runoff regulation. The purpose of the reservoir is to meet the needs of hydropower, irrigation, fisheries, and water supply. It is a medium-sized reservoir with shallow depths. The second wave of significant changes in the 1980s is linked to the commissioning of the Dniester hydropower complex (currently referred to as the Dniester cascade of HPPs and PSPPs) (Fig. 1.1). The Dniester reservoir commissioned in December 1981 carries out seasonal (with multi-year elements) regulation of the Dniester runoff (Rules, 1987). Characteristic features of the reservoir are its significant length and depth, relatively small width and great tortuosity. According to the main morphometric characteristics (Table 1), it belongs to a category of large riverbed foothill deep water bodies (Avakyan, 1987). The purpose of the reservoir is flood control, water consumption, hydropower generation, and irrigation. The buffer reservoir, a technical reservoir, commissioned in 1987 by building an overflow dam 20 kilometers downstream of Dniester HPP-1, is used for alignment of the flow rate of water coming from Dniester reservoir (Regulation 1987). In the late 1990s and early 2000s, the reconstruction of buffer hydropower complex was carried out in order to commission Dniester HPP-2. In the early 2000s, the construction of PSPP resulted in changes of morphometric characteristics of the buffer reservoir (Table. 1 .1). Following the launch of the first PSPP unit in 2009, the reservoir has been used as the lower pond of PSPP. The buffer reservoir provides daily and weekly regulation and belongs to the small, shallow channel reservoir category. On the right bank of the buffer reservoir, a PSPP upper pond was created. During nighttime, when power demands are low, water is pumped up from the buffer reservoir, while during morning and evening peak demands the water is discharged back, passing through hydropower units. According to morphometric characteristics, the reservoir can be classified as a fillable reservoir with average depths.

CHAPTER 2

IMPACT OF STRUCTURAL CHANGES ON THE AQUATIC ENVIRONMENT AND BIOTIC COMMUNITIES METHODOLOGY ISSUES OF THE ANALYSIS OF IMPACT OF STRUCTURAL CHANGES The analysis of hydrochemical and hydrophysical changes was focused on studying the content of oxygen dissolved in water, its temperature, and - as a characteristic of changes in solid runoff - the flow rate of suspended sediment. For analysis, we used information from Hydrometeorological Center of Ukraine, State Hydrometeorological Service of Moldova and Hydrometeorological Center of Tiraspol: on average monthly and average annual flow rate of suspended sediment, from observation posts in

Zalishchyky, Mogilev-Podolsky, Grushka, the upstream of Dubossary hydropower plant; on average monthly water temperatures, from observation posts at the upstream of HPP-1 (buffer

reservoir), Mogilev-Podolsky, Grushka, Camenca, and the upstream of Dubossary HPP; on water-dissolved oxygen, from observation posts at the upstream of Dniester HPP-1, Naslavcea,

Otach, and Soroki. Two periods are considered in the study: before the construction of HPP-1 dam (1951–1980) and its period of operation (1990–2015). The period from 1980 to 1990 is excluded from the analysis due to the filling of Dniester reservoir during these years, the construction and commissioning of HPP-2, and also based on the characteristics of the climate cycle. The period of 1990–2015 coincides with the current phase of climate change, which is directly reflected in hydrophysical changes. When analyzing hydrobiological changes, we used available information on species diversity, dominant species, quantitative indicators of the presence of hydrobionts (abundance, biomass) along with additional indicators (biotic indices, saprobity indices, etc.). The sources of information were monographs and research summarizing the results of field hydrobiological studies before and after the creation of reservoirs, as well as data of hydrobiological monitoring by State Hydrometeorological Service of the Republic of Moldova (Naslavcea, Otaci, Soroca, Rezina, Dubossary reservoir upstream and downstream of Dubossary, Dubossary reservoir upstream, Vadul-lui-Voda and Bendery). To calculate the characteristics of the dominant macroinvertebrate groups, the ASTERICS software http://www.aqem.de/ was used.

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

2.1. IMPACT ON THE SUSPENDED SEDIMENT REGIME A characteristic feature of the solid runoff at the unregulated upper and middle Dniester is its intra-annual variability, which significantly depends on water content (correlation coefficient 0.71–0.84) (Melnik, 2006, 2010). The bulk of suspended sediment is formed during the spring flood and rain floods. Monthly average values vary widely - from 0.21 to 2400 kg/s (State Cadastre, rivers). From the 1950s to this day, there has been a downward trend in the amount of sediment in the unregulated river flow; according to some estimates, the decrease is up to 40% (Melnik, 2010; State Cadastre, rivers). Prior to the regulation of the runoff, some 3.5–6 million tons/year of suspended solids arrived at the mouth of the Dniester (Hydrobiological, 1992; Ecosystem, 1990). With the commissioning of the Dubossary reservoir, about 90% of suspended sediments in the lower reaches of the river (Figure 2.1.) (Hydrological Yearbook) became intercepted, which resulted in active silting of the reservoir: from 1955 to 1981 its total volume decreased by 45% and useful volume, by 23% (Certification, 1983). The inflow of sediment to the transboundary section of the river and to the Dubossary reservoir was significantly reduced due to the construction of Dniester reservoir (Fig. 2.2), and the current volume of solid runoff downstream of the dam of Dubossary reservoir is practically unchanged throughout the year regardless of water content (State Cadastre, rivers). Dniester reservoir also intercepts an average of 90% of the suspended sediment entering it (Hydrological Yearbook), but its siltation is less intense: since 1981, the total volume has decreased by only 11% anduseful volume, by 4.7% (Draft Rules, 2017). Along the length of reservoir sediment, deposition occurs in different ways: the maximum flow rate (up to 60% of the received suspensions) is observed within 120-150 kilometers upstream of the dam, the smallest deposition of sediments occurs in the tail and the dam sections (Gulyaeva, 2009).

Fig. 2.1. Average annual flow rate of suspended sediment (kg/sec) at Zalishchyky (1) and Dubossary HPP downstream (2) in 1959-1980.

Fig. 2.2. Average annual flow rate of suspended sediment (kg/sec) at Zalishchyky o/p (1) and Dniester HPP (Mogilev-Podolsky) downstream (2) in 1990–2015.

Sources: Hydrological Yearbook 1951–1977; State Cadastre, rivers 1978–2015.

CHAPTER 2. IMPACT OF STRUCTURAL CHANGES ON THE AQUATIC ENVIRONMENT AND BIOTIC COMMUNITIES

Such distribution directly affects the chemical composition of bottom sediments in the middle section of Dniester reservoir (Boyko, 1999), since the largest amount of absorbed pollutants – up to 70% - falls on the medium silt fractions there (Denisova, 1975). Active deposition of suspended solids also leads to significant clarification (increased transparency) and a change in the color of water (Gulyaeva, 2013). In contrast to Dubossary reservoir, an increase in the content of suspended matter in water is observed downstream of the Dniester dam during high water season and spring floods as compared to low water periods (State Cadastre, rivers). Downstream of the reservoirs, only a partial restoration of the suspended matter content in the water takes place and the flow rate increases to 0.1 kg/s per kilometer of the channel. At a distance of 148 kilometers from the dam of the HPP-2 in the region of o/p Hruska some years mean monthly values may reach 80-90 kg/s, while multiyear monthly and annual average flow rate of suspended solids ranges from 5 to 25 -30 kg/s (Figs. 2.3 - 2.4).

Fig. 2.3. Average monthly flow rate of suspended sediment (kg/sec) for 1994-2015, Dniester HPP downstream: Mogilev-Podolsky (1), Grushka (2), Dubossary HPP downstream (3)

kg/s 25 20 15

3 1

5 2014

2012

2010

2008

2006

2004

2002

2000

1998

1996

1994

Fig. 2.4. Average annual flow rate of suspended sediment for 1994 - 2015 downstream of Dniester HPP: Mogilev-Podolsky (1), Grushka (2), Dubossary HPP downstream (3)

Thus, today no more than 1–1.2 million tons/year of suspended solids arrive at the mouth of the Dniester (State Cadastre, rivers), which is three to six times less than before the regulation of runoff5.

The above estimates relate to the total runoff of suspended solids, including solid particles of various origins and sizes (clay, silt, sand, etc.). In the framework of this study, the long-term variability of the runoff of individual sediment fractions was not explored, since it would require a detailed analysis of data on particle size distribution for different time periods. In general, solid runoff downstream of reservoirs is determined by both volume and composition of sediment entering the reservoirs: light fractions are less actively precipitated. According to the data of Zalishchyky observation post, at the beginning of the 2000s the share of sand fractions in the solid runoff upstream of Dniester reservoir amounted to 5–10%. One-way extraction of sand and gravel from the Dniester riverbed also affects the redistribution and volumes of solid runoff (there are no quantitative estimates here).

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

2.2. EFFECT ON PHYSICO-CHEMICAL CONDITIONS The temperature regime of the river is largely determined by the design features of Dniester HPP-1 dam (water is taken from 27–43 meters depth),as well as the thermal regime of Dniester reservoir (Insert 2.2).

FEATURES OF THERMAL AND OXYGEN REGIME OF DNIESTER RESERVOIR Water masses are present in Dniester reservoir for four to five months. As a result, all water quality indicators are formed in the reservoir itself. A characteristic feature of its thermal regime is the separation of reservoir water mass in the summer period into three horizontal layers, the thickness of each of which is unstable and depends on hydrometeorological conditions. The upper layer (epilimnion) with a thickness of up to 10 meters arises, in particular, due to the low velocities of runoff and wind currents as well as weak wind-wave mixing. The largest vertical temperature drop (1-3 ° C/m) in the summer is most often observed at a depth of 10 to 20 meters (State Cadastre, lakes). The passage of floods leads to significant mixing of water throughout the entire depth and the formation of a picture atypical for the summer period lacking distinct thermal layers. Similar to the temperature regime, the oxygen content of the river section downstream of Dniester cascade of HPPs and the PSPPs is affected by dissolved oxygen content in the deep water masses of Dniester reservoir entering HPP upstream. In summer and early autumn, there are no oxygen sources in the lower layer of the reservoir (hypolimnion), and due to the aerobic decomposition of suspended organic matter it is actively consumed. Therefore, the reserves of dissolved oxygen accumulated in the winter-spring period are gradually depleted in this zone. The largest vertical difference in oxygen concentration usually coincides with the thermocline layer.

The presence of a buffer reservoir and PSPP upper reservoir only smoothens out the influence of Dniester reservoir on the water temperature but it does not make a significant contribution to its increase (Shevtsova, 2008). The greatest influence on the thermal regime of the river section is observed directly downstream of HPP-2 dam in June (temperature decrease by 7.5–8 degrees) and November (temperature increase by 5.5–6 degrees). Downstream, water temperature gradually approaches its natural values (Fig. 2.5).

Fig. 2.5. Average long-term annual variation in water temperature of Dniester HPP-1 downstream (1), at Mogilev-Podolsky (2) and Grushka o/p(s) (3) from 1990 to 2015 (1-12 at the y axis stand for months). Sources: Hydrological Yearbook of Ukraine 1990–2015; State Water Cadastre of the Republic of Moldova, 1978–2015.

CHAPTER 2. IMPACT OF STRUCTURAL CHANGES ON THE AQUATIC ENVIRONMENT AND BIOTIC COMMUNITIES

The heating of the water in the river bed section occurs more intensively (0.3–0.4 degrees per 10 kilometers) than cooling (0.2–0.3 degrees per 10 kilometers). In Camenca, according to many years of observations, in summer the deviation of the water temperature from its natural values does not exceed 2.7 degrees (Fig. 2.6). In reservoirs, water heats more intensively than in river areas. As a result, in the upper portion of Dubossary reservoir (town of Rybnitsa-Rezina) water temperature corresponds to natural values. The thermal regime of the Lower Dniester is outside the influence zone of the reservoirs of Dniester cascade of HPPs and PSPPs (State Cadastre, rivers).

degree

Fig. 2.6. Difference in the average monthly water temperature at Camenca o/p in 1990–2015 compared with 1951-1980. (the x axis represents months and the y axis, degrees).

5 3 1

-1 -3 -5

9 10 11 12

Sources: Hydrological Yearbook 1951-1977; State Water Cadastre of the Republic of Moldova, 1978–2015

The oxygen regime in the river section downstream of Dniester cascade of HPPs and PSPPs is affected by dissolved oxygen content in deep-water masses of Dniester reservoir entering the upstream of the hydropower plant (Insert 2.2). In winter and spring, there is no oxygen deficiency in the lower layer; however, in summer and early autumn its concentration may drop to zero. Nevertheless, the increased flow turbulence in the buffer reservoir, in PSPP upper reservoir and in the upstream of HPP-2 leads to fairly rapid re-saturation of water with oxygen. According to monitoring data6, the concentration of water-dissolved oxygen at the transboundary site mainly varies between 7–12 mg/dm3. Currently, in areas of the river with intensive development of macrophytes (upstream of Volchinets village) in the absence of wastewater sources in the daytime, there have been cases of a decrease in oxygen content to 56 - 64% saturation (Zubkov, 2007). In addition to the parameters listed above, the joint Moldovan-Ukrainian hydrochemical expedition in 2011 (Meliyan, 2011) also noted a rather sharp decrease in the acid reaction (pH) of water in the buffer reservoir compared to Dniester reservoir: from 8.1–8.2 to 7.6 with subsequent increase in the downstream section of the river to 8.1 at the entrance to Dubossary reservoir. In Dubossary reservoir, further alkalization of water was noted (probably associated with vital processes of aquatic vegetation): up to 8.3 upstream and downstream of the dam. The expedition, based on one-time sampling along the river, also found the absence of any noticeable effect of channel reservoirs on the content of water-soluble organic substances (value of chemical oxygen consumption) and a number of other parameters, including salt composition (sulfates, chlorides, dry residue), biogens (mineral forms of nitrogen and phosphorus), petroleum products, heavy metals, some organic pesticides and polyaromatic hydrocarbons.

http://dnister.meteo.gov.ua/ua/water_quality and Hydrochem. Yearbook. EQMD.

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

2.3. IMPACT ON AQUATIC ORGANISMS HIGHER AQUATIC VEGETATION In 1945-1948, higher aquatic vegetation was very poorly developed in the Dniester, although plants were distributed throughout the river (Yaroshenko, 1957). Prior to construction of Dubossary reservoir in the middle reaches of the Dniester in the section between the town of Soroca and the village of Cioburciu one could find only single specimens of several species of macrophytes (pondweed, watermilfoil, hornwort). In the upper and lower reaches of the Dniester, the shore vegetation of hornwort, watermilfoil, and various species of pondweed had developed relatively well (Yaroshenko, 1957). The construction and operation of reservoirs caused a decrease in maximum flow rates and increased water transparency in the lower sections of the bed, which contributed to massive development of higher aquatic vegetation in the middle reaches and gave macrophytes the opportunity to get firmly rooted. By 1991, the higher aquatic vegetation, represented mainly by hydatophytes (plants wholly or mostly submerged in water), appeared along the entire river from Naslavcea to Dubossary. As a result, the number of macrophyte species developing in the Naslavcea-Camenca section increased from several to 26, in the Dubossary reservoir to 43, and the degree of overgrowing of the water area increased from 0.7-1% to 10-15% in the 1980s and up to 85% at present time (Sharapanovskaya, 1999, Smirnova-Garaeva, 1980, data from the Institute of Zoology of Moldova). Massive development of higher aquatic vegetation in the middle reaches of the river, mainly caused by the construction of Dniester cascade, has diverse effects. On the one hand, plant communities provide new substrates and habitats for other aquatic organisms, contribute to oxygenation of water during photosynthesis and are involved in the processing of pollution, etc. On the other hand, the processes of aquatic vegetation and periphyton rotting lead to secondary pollution of water with organic substances and a decrease in waterdissolved oxygen content (Zubkov, 2007). The redistribution of runoff and the associated decrease in the flow velocity at the confluence of the Dniester and Glubokoy Turunchuk into the Dniester estuary contributed to a 9.5 km2 increase in the area of water caltrop Trapeta natantis and yellow pond lily Nuphareta luteae formations, both of which are listed in the Green Book of Ukraine. The regulation of runoff did not have a negative impact of some species of macrophytes in the Lower Dniester listed in the Red Books of Ukraine and Moldova: floating moss Salvinia natans (L.) All., water chestnut Trapa natans L. and floating heart Nymphoides peltata (S.G. Gmel.) O. Kuntze. However, the development of macrophytes worsened the living conditions of fish: the death of large masses of macrophytes in the delta flood lakes in autumn and winter accelerates the course of natural successions, leads to siltation and a decrease in the depth of water bodies while increasing the likelihood of die-offs due to falling levels of water-dissolved oxygen.

MACROINVERTEBRATES Comparison of modern features7 of dominant macroinvertebrate groups in the transboundary section of the river downstream of Dniester cascade (according to data of the Institute of Zoology and Surface Water Quality Yearbook of the Republic of Moldova on hydrobiological elements of EQMD) with those from before the Calculation of characteristics was performed using ASTERICS software ( http://www.aqem.de/ ), which allows us to calculate more than 60 parameters for macrobenthos invertebrate communities.

CHAPTER 2. IMPACT OF STRUCTURAL CHANGES ON THE AQUATIC ENVIRONMENT AND BIOTIC COMMUNITIES

construction of reservoirs (according to Yaroshenko, 1957) made it possible to draw a number of conclusions on changes that took place (Tables 2.1 and 2.2). Table 2.1 Comparison of characteristics for the dominant macroinvertebrate groups in the transboundary area before and after the construction of Dniester hydropower complex

Number of ind./m2

Biomass, g/m2

Wealth of taxa EPT [%]а

Saprobity

1945–1951b

2500

21,4

2016–2017c

12000–18000

24–150

4,8–5,6

Years

Proportion of species related to a particular substrate [%] silt

sand

gravel

rocks

veg.

2,10

2,11

18–21

4–14

4–5

13–19

31–34

Jacquard Similarity Index <10%

a – EPT-Taxa - relative number of species (%) Ephemeroptera, Plecoptera, Trichoptera (mayflies, stoneflies, caddisflies). b – Averaged data for the section from Galich to Soroca. c – Averaged data for the section from Naslavcea to Soroca. Data sources: Yaroshenko, 1957; Yearbook of Surface Water Quality of the Republic of Moldova on hydrobiological elements of EQMD and the data of the Institute of Zoology of the Academy of Sciences of Moldova (Mungiu, 2017)

Table 2.2 Comparison of characteristics for the dominant macroinvertebrate groups in the Dubossary reservoir downstream area (Vadul-lui-Voda district ) before and after its construction*

Years

Number Biomass, Wealth of taxa ind./m2 g/m2 EPT [%]а

Saprobity

Proportion of species related to a particular substrate [%] silt

sand

gravel

rocks

veg.

1945–1951

2300

20,3

14,3

1,98

2016

11200

9,3

2,12

Jacquard Similarity Index ≈7–17%

а – EPT-Taxa - relative number of species (%) Ephemeroptera, Plecoptera, Trichoptera (mayflies, stoneflies, caddisflies). * The river in the Vadul-lui-Voda area is prominently influenced by the polluted Reut tributary

Data sources: Yaroshenko, 1957; data of the Institute of Zoology of the Academy of Sciences of Moldova (Mungiu, 2017)

Between the two periods, a radical change in the species composition of the dominant group of macroinvertebrates in the transboundary area was observed (Jacquard species similarity index <10%; Insert 2.3). Today, in the dominant core of macroinvertebrate communities the largest proportion of species (34%) belongs to the species of the phytophilic group (associated with aquatic plants), while before the construction of reservoirs species of the lithophilic group (associated with a solid substrate, rocks) were predominant (52%). First of all, these changes are a consequence of the massive development of macrophytes in this section of the river. There is also a significant (from 5% to 21%) increase in the number of pelophilic species (associated with silts).

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

LIST OF DOMINANT MACROINVERTEBRATE SPECIES IN THE TRANSBOUNDARY AREA BEFORE AND AFTER CONSTRUCTION OF DNIESTER HYDROPOWER COMPLEX Beforeа

After

Alboglossiphonia heteroclite (Linnaeus, 1761)

b

Anopheles sp.

b

Baetis sp.



c

Bithynia tentaculata (Linnaeus, 1758)

 b, c

Chaoborus sp.

b

Chironomus plumosus-Gr.

a

Chironomidae Gen. sp.

b

Cricotopus sylvestris-Gr.



c

Elmidae Gen. sp.

b

Erpobdella sp.

b

Esperiana esperi (Férussac , 1823)



Gammarus kischineffensis (Schellenberg 1937)

b

Haliplus ruficollis (De Geer, 1774)

b

Heptagenia sp.



Hydropsyche sp.



Lepidostoma hirtum (Fabricius, 1775)

b

Lithoglyphus naticoides (C. Pfeiffer, 1828)



Monodiamesa bathyphila (Kieffer, 1918)



Oligochaeta Gen. sp.

c

b

Ophidonais serpentina (Muller, 1774)



Orthocladiinae Gen. sp.



Physella acuta (Draparnaud, 1805)

 b, c

Pisidium casertanum ssp.

 b, c

Polypedilum scalaenum-Gr.



Radix sp.



Rheotanytarsus sp.



Stagnicola corvus (Gmelin, 1791) Theodoxus danubialis ssp.

b 

Theodoxus fluviatilis ssp. Thienemannimyia lentiginosa (Fries, 1823)

b

 b, c 

Valvata piscinalis ssp.

b

Valvata pulchella Studer, 1789

c

a – According to Yaroshenko, 1957. b – Data of EQMD of SGS of Moldova (2016). c – Data of the Institute of Zoology of the Academy of Sciences of Moldova

CHAPTER 2. IMPACT OF STRUCTURAL CHANGES ON THE AQUATIC ENVIRONMENT AND BIOTIC COMMUNITIES

In the river downstream of HPP-2 and Dubossary reservoir water area, rheophilic or typical river aquatic species are being displaced by typical limnophilic ones (Cricotopus algarum (Kieffer, 1911), Cricotopus sylvestris (Fabricius,1794), Chaetogammarus warpachowskyi (Sars, 1894), Limnomysis benedeni Czerniavsky, 1882, Physella integra (Haldeman, 1841), Lymnaea peregra (O.F. Müller, 1774), Eudiaptomus gracilis (Sars G.O., 1863) and E. graciloides (Lilljeborg, 1888)) (Zubkov, 2007)). Due to the reduction in the number of mayfly specimens, a decrease in % of EPT wealth has been observed (from 21% to 5%). A direct comparison of the diversity of macroinvertebrate species in the transboundary section of the river before and after the construction of reservoirs is not possible. At the same time, from indirect

data8 it can be assumed that the total number of species has not changed significantly.

The total number of macroinvertebrates increased from 2.5 to 18–24 thousand ind./m2, while their biomass changed from 31 to 24 - 150 g/m2. Due to a favorable oxygen regime for macroinvertebrate communities, the saprobity indices used to assess the degree of pollution of water bodies with organic substances remained at the same level as before the construction of Dniester reservoirs (about 2.1, which corresponds to the II quality class or “good condition”). The same changes, albeit less stark, are also observed in the macroinvertebrate communities of Dniester channel downstream of Dubossary reservoir (Table 2.2). In the Dniester, there are identifiable risk zones for degradation of macrobenthos macroinvertebrate communities, which include Naslavcea site (in samples from 2016, 25 taxa were recorded) and the section of the river downstream of Soroca affected by wastewater (18 taxa were recorded in 2016 ) (Mungiu, 2017).

PLANKTON The quantitative indicators of phyto- and zooplankton in the channel downstream of Dniester hydropower complex and Dubossary reservoir are close to each other. Moreover, the current abundance of zooplankton in the riverbed is comparable to that of before the construction of reservoirs (Tables 2.3 and 2.4). Table 2.3 Comparison of current characteristics of phytoplankton in the river sections downstream of Dniester and Dubossary reservoirs Sites

Years

Number, cells / ml

Biomass, mg / L

Saprobity

Number of species

Naslavcea, Ataky

2011–2017

330

0,82

1,91

Vadul lui voda

2011–2017

350

0,63

1,99

Data sources: Yearbook of Surface Water Quality of the Republic of Moldova on hydrobiological elements of EQMD

According to the long-term data (Yaroshenko, 1957), 123 forms are represented in the section from Galich to Soroca. The combination of EQMD of Moldova data for 2017 (Naslavcea station) and data from two stations (Naslavcea and Valcinet) for 2016 (Mungiu, 2017) indicates the presence of 76 species.

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

Table 2.4 Comparison of characteristics of zooplankton in sections of the river downstream of Dniester and Dubossary reservoirs before and after the construction of Dniester hydropower complex Sites Naslavcea, Ataky

Vadul lui voda

Years

Abundance, ind./m3

Biomass, mg /L

Saprobity

Number of species

1947–1951

2300

n/a

2011–2017

4000

22,1

1,65

1947–1951

1800

n/a

2009–2012

3500

7,3

1,72

* n/a. – no available data.

Data sources: Yaroshenko, 1957; Surface Water Quality Yearbook of the Republic of Moldova on hydrobiological elements of EQMD

At the same time, according to the Institute of Zoology of the Academy of Sciences of Moldova for 2015-2017, in the area from Naslavcea to Camenca the production of zooplankton during the vegetation season is virtually absent.

ICHTHYOFAUNA Under the influence of numerous factors, which are seen as related9 and unrelated to the construction and operation of reservoirs10, Dniester fish communities have undergone significant changes. The species diversity of Dniester fish before and after the creation of reservoirs according to data of various authors is presented in Table 2.5. Table 2.5 Species diversity of Dniester fish before and after the creation of reservoirs Source

Dniester as a whole

Middle section

Dubossary Res.

Lower section

Prior to 1954 Berg, 1948–1949

74 а

Burnashev et al. , 1954

81 а

Burnashev et al. , 1955

Tomnatic, 1964

Ecosystem, 1990

Yaroshenko, 1951 Yaroshenko, 195 7

37 а 49 б

Blockage of migratory fish migration paths by reservoir dams; changes in bottom substrate and feed base; changes in the temperature regime and atypical daily fluctuations in the level and temperature of water (chapter 3) in transboundary section; changes, compared with natural, in timing and regime of spring floods (chapter 4).

Diking and cutting off of oxbows and wetland floodplains, stocking, breaches of the ichthyofauna protection regime, pollution, etc.

CHAPTER 2. IMPACT OF STRUCTURAL CHANGES ON THE AQUATIC ENVIRONMENT AND BIOTIC COMMUNITIES

Bulat, 2017

62 б

1996–2017 Snigirev, 2012

Bulat, 2017

Usatîi, 2004

а – Quoted from Tomnatic, 1964. b - Only the channel of the Dniester. c – At the same time, only seven species were present in the control catches of 2017–2018 made directly downstream of HPP-2 dam site near Naslavcea: three-spined stickleback, dace, bleak, baleen, roach, mustard, and sculpin (Bulat et al., 2018)

60 50 Rare

Frequent 30

In mass Numerous

Episodic

10 0 1950–1959

1996–2000

Fig. 2.7. The number of fish species in Naslavcea-Camenca area in 1950-1959 and 1996–2000. * The graph shows the total number of species found for all years of the indicated periods. With the commissioning of Dubossary reservoir in 1955, the number of species in it decreased from 53 to 42 by 1959 (Tomnatic, 1964). Since the decrease in the number of fish species in the reservoir occurred primarily due to the loss of migratory species (Tomnatic, 1964), it can be assumed that similar changes occurred in the upper part of this section.

Data Sources: Usatîi, 2004; Tomnatic, 1957; Reports of the Institute of Zoology of the Academy of Sciences of Moldova

In Naslavcea – Camenca section in 1996–2000, 42 fish species were recorded, including previously absent invasive species; among them 25 species from Cyprinidae family, –five from Percidae and Gobiidae, –two from Sobitidae and Gasterosteidae, and one each from Acipenseridae, Esocidae and Siluridae. According to (Burnashev et al., 1955 ); Until 1955, 47 species had been found in Khotin - Dubossary section (Fig. 2.7).

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

tons 120 100

Fig. 2.8. Commercial fishing in Dubossary reservoir by years, tons

80 60

Data source: data from the State Fisheries Service of the Republic of Moldova (Usatîi et al., 2016)

40 20

1950

1960

1970

1980

1990

2000

2010

2020

Presently, commercial fish species have almost disappeared from the river in Moldova. Prior to HPP construction in Naslavcea – Camenca section, the main commercial species of fish were sterlet, common carp, zanthe, catfish, sneep, and barbel (Yaroshenko, 1957). Today, commercial fish species are almost completely replaced by low-value short-cycle and invasive species, while three-spined stickleback, mustard, and bleak dominate (Bulat, 2018, Bulat et al., 2017). In Dubossary reservoir, recorded fishing catches significantly decreased, and their structure changed (Figs. 2.8–2.9).

Capr

1960s

2000s

Bream

4,8 14,3

7,0

0,0

1,6 0,8

Roach

0,0

3,5 0,3

Crucian Vimba

1,3 0,4 24,5

0,9

0,8

Asp

4,8 9,6

0,8

Pike perch

0,2 0,1 0,0

Catfish Blue bream

1,3

2,4 1,4

0,3

Perch

Fig. 2.9. Averaged fishing pattern in Dubossary Reservoir in the 1960s and 2000s Data source: State Agency for Fish Protection of the Republic of Moldova; Usatîi et al., 2016

Before regulation of the Dniester runoff, Dniester estuary, the floodplain system of the delta, and the lower section of the middle Dniester were a single ecosystem with rich ichthyofauna, spawning grounds for rheophilic,

CHAPTER 2. IMPACT OF STRUCTURAL CHANGES ON THE AQUATIC ENVIRONMENT AND BIOTIC COMMUNITIES

lithophilic, phytophilic, and psammophilic fish species, as well as their feeding grounds. The construction of Dubossary HPP divided the Dniester basin into two isolated sections and led to significant changes in the structure of the ichthyocenosis of the Lower and Middle Dniester. Due to lack of fish passage structures, the dam of Dubossary reservoir interdicts migration routes of spawning anadromous sturgeon species: beluga Huso huso (Linnaeus, 1758), stellate sturgeon Acipenser stellatus (Pallas, 1771), Russian sturgeon Acipenser gueldenstaedtii (Brandt et Ratzeburg, 1833), which led to a drastic reduction in their numbers, and the thorn sturgeon Acipenser nudiventris Lovetskiy was classified as an extinct species. In the Dniester estuary, zanthe Vimba vimba (Linnaeus, 1758) almost disappeared from fishing catches, and in the late 90s, in the Dniester delta, apparently, due to the deterioration of spawning conditions, previously abundant sabre fish Pelecus cultratus (Linnaeus, 1758) completely disappeared. The increase in water transparency in the Dniester due to sediment deposition in Dniester and Dubossary reservoirs stimulated the growth of macrophytes in the flooded lakes and the Dniester bed, which caused a reduction in the number of spawning grounds for lithophilic and psammophilic fish species. The situation is worsened by the extraction of gravel and sand in the Dniester channel, which as a whole led to a significant decrease in the number of four rare and endangered fish species: carp Rutilus frisii (Nordmann, 1840), sterlet Acipenser ruthenus (Linnaeus, 1758), large chop Zingel zingel (Linnaeus, 1766) and small chop Zingel streber (Linnaeus, 1758). Impoverishment of the species composition of the fish fauna of the Lower Dniester in its delta part was also due to the disappearance in the Dniester estuary of several marine species: the Black Sea sprat Sprattus sprattus phalericus (Risso, 1827), anchovy Engraulis encrasicholus ponticus (Alexandrov, 1927), Black Sea salmon Salmo trutta labrax (Pallas, 1814), garfish Belone belone euxini (Gunther, 1866), whiting Odontogadus merlangus (Linnaeus, 1758), bluefin Pomatomus saltatrix (Linnaeus, 1766), kalkan flounder Scophthalmus maeoticus (Pallas, 1814), and in the 1960s, of mackerel Scomber scombrus (Linnaeus, 1758). During the same period, for the unidentified reason, another previously abundant commercial species Percarina demidofii (Nordmann, 1840) practically disappeared from the Dniester estuary and was listed in the Red Book of Ukraine, while crucian carp Carassius carassius (Linnaeus, 1758) almost disappeared in the Dniester delta. At the same time, an increase in the number of fish species in the Lower Dniester basin can be explained by the directed introduction of some commercial species: silver carp Hypophthalmichthys molitrix (Valenciennes, 1844), bighead carp Hypophthalmichthys nobilis (Richardson, 1845), grass carp Ctenopharyngodon Idella (Valenciennes, 1844), black carp Mylopharygodon piceus (Richardson, 1846), so-iuy mullet Lisa haematocheila (Temminck & Schlegel, 1845), channel catfish Ictalurus punctatus (Rafinesque, 1818), as well as due to the penetration of the three invasive species: sunfish Lepomis gibbosus (Linnaeus, 1758), topmouth gudgeon Pseudorasbora parva (Temminck & Schlegel, 1842) and amur sleeper Perccottus glenii (Dybowski, 1877).

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

tons 2500 2000 1500 1000 500

1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017

Fig. 2.10. Catch of aquatic biological resources in Dniester estuary, the lower reaches of the Dniester River and the floodplain system in Odessa region in 1983 - 2017, tons Data source: Statistics of Odesarybvod Department

1983

46 232

143

Prussian carp Common bream

2017

186

Heckelii

272

Common carp Zandler

184

Bighead carp

175

Other species

2068

Fig. 2.11. Structure of commercial catches in Dniester estuary, the lower reaches of the Dniester River and the flood plain system in 1983 and 2017, tons Data source: Statistics of Odesarybvod» Department

As a result, structure and volumes of commercial catches, which are currently dominated by phytophilic species, have changed substantially in the Lower Dniester, with the Prussian carp Carassius auratus gibelio (Bloch, 1782) (Figs. 2.10–2.11) becoming predominant commercial fish. The significant growth in fish catches in the lower reaches of the Dniester in 2015 - 2017 is associated with an increased catch of the Prussian carp and increased fishing intensity in Dniester estuary, as well as the prohibition of commercial fishing in the Republic of Moldova, including its Transdniestrian region.

ГЛАВА 2. ВЛИЯНИЕ СТРУКТУРНЫХ ИЗМЕНЕНИЙ НА ВОДНУЮ СРЕДУ И БИОТИЧЕСКИЕ СООБЩЕСТВА

CHAPTER 3

DAILY RUNOFF FLUCTUATIONS AND THEIR IMPACT ON THE STATE OF TRANSBOUNDARY SECTION METHODOLOGY ISSUES OF DAILY RUNOFF FLUCTUATIONS To account for daily runoff fluctuations, modern hourly water discharge rates data of Dniester HPP-1 and HPP-2 for 2017–2018 were used. Data were provided by PJSC Ukrhydroenergo and PJSC Nizhnednistrovskaya HPP. The analysis of intraday fluctuations in water level was based on the data for the second half of 2018, retrieved from the automated posts in Naslavcea, Soroka, and Vadul-lui-Voda. These are the only hydrological data series of hourly fluctuations in water level available at three posts simultaneously; therefore, the data array for this period is represented by the most complete series of observations. To assess the transformation of release waves and physico-chemical indicators, we used data from publications of Ukrainian NAS Institute of Hydrobiology.

3.1. DESCRIPTION OF DAILY RUNOFF FLUCTUATIONS During normal operation of the cascade in the absence of floods, depending on the needs, the hydraulic units of Dniester HPP-1 are switched on one, two (less often – three or four) times a day. The total duration of operation varies from two to twelve hours a day. The water flow rate to the buffer reservoir can vary from 200 to 1700 m3/s, while the highest water flow rate in the downstream of HPP (flow rates of HPP-1) is observed in the evening. Dniester HPP-2 operates 24 hours a day. Water can pass through turbines of electric generators or get discharged through spillways without generating electricity. According to hourly data for 2017-2018, the maximum amplitude (variation) values for the water flow rate during the day to the upstream of HPP-2 amounted to 380 m3/s during high water. Reducing flow rate to the upstream of HPP-2 to less than 100 m3/s is not allowed throughout the entire year. During river floods and high water, the cascade of Dniester HPPs and PSPPs modifies its operation: HPP-1 operates anywhere from 12 to 24 hours a day, while HPP-2, working around the clock, discharges water through turbines and spillways simultaneously. In case high water flow rate exceeds 5700 m3/s, the nuclear power plant limits its operations up to a halt (Draft Rules, 2017). For most of the year, the cascade operates in normal mode and performs releases that are uneven in comparison with natural flow rate during the day. According to the Draft Rules (2017), water level fluctuations during the day in the upstream of HPP-2 (outside the flood period) cannot exceed 20 centimeters. Based on the automated

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

hydrological post operational data11 in the second half of 2018, the average downstream amplitude of diurnal fluctuations in the water level near Naslavcea was about 30 centimeters, the minimum value in the normal mode was four centimeters, and the maximum value was 60–65 cm/day (Fig. 3.1). Maximum amplitude of diurnal fluctuations during floods reached 135 centimeters. In Soroka, due to the transformation of releases, the amplitude of fluctuations in water level is reduced by 55%. Downstream of Dubossary HPP, according to operational data from the automated hydrological post in Vadullui-Voda12, the second half of 2018 saw daily fluctuation amplitude of the water level of about 18 centimeters with its minimum value in the normal mode being one centimeter and maximum being 40-60 cm/day. During floods, the maximum amplitude of water level fluctuations reached 137 centimeters (Fig. 3.1).

Fig. 3.1. Amplitude of diurnal fluctuations in the water level downstream of Dniester HPP-2 (Naslavcea-1) and Dubossary HPP (Vadul-lui-Voda - 2) in the second half of 2018 Source: Data from automated stations http://nistru.meteo.gov.ua/en/autoposts_operational_data/

In addition to fluctuations in the water level, there is also a temporal variability of the hydrodynamic characteristics of the flow (Fig. 3.2): depending on the volume of the release, the flow velocity in Mogilev-Podolsky can vary from 0.40 to 2.75 m/s (State Cadastre, rivers).

http://nistru.meteo.gov.ua/en/autoposts_operational_data/

Same as above.

CHAPTER 3. DAILY RUNOFF FLUCTUATIONS AND THEIR IMPACT ON THE STATE OF TRANSBOUNDARY SECTION

Fig. 3.2. Measured flow rate (m3/s) and flow velocity (m/s) in Mogilev-Podolsky (2012 and 2013)

TRANSFORMATION OF RELEASE AT A TRANSBOUNDARY SITE Calculation of the propagation of release and flood waves is one of the most difficult problems of river hydraulics. In this regard, field measurements of the unsteady movement of water are of great importance. In October 2014 and April 2015 at the Institute of Hydrobiology of the National Academy of Sciences of Ukraine, a number of hourly field observations of the water level was carried out at four sections located at different distances from HPP-2 dam (2.3 km, 27 km, 57 km, 83.4 km) . The measurement results showed tthe following: as the distance from the dam increases, the velocity of the wave crest decreases from 4.6 to 2.9 km/h; as the distance from the dam increases, the waveform (release hydrograph) changes: wave height

decreases by more than 75%, maximum intensity of level change decreases by 85% (from 30 to 4 cm/h), duration of the level rise and fall phases increases (from 3 to 12 hours); depending on natural conditions, at a distance of up to 27 kilometers from HPP-2, the wave can expand

by 16-50%. In the autumn low-water season, the greatest wave transformation was observed at a distance of 27–57 kilometers from HPP-2; the process of wave transformation is significantly affected by the water level (average depth) in the

river and the amount of release through the dam: during the spring discharge, the transformation was twice as intense as in the autumn low-water season. The results of the analysis, approximated in quantitative terms, give only a qualitative description of these phenomena. It should be noted that the release waves carry a significant amount of “new” water and thus can perform a flushing function in a transboundary area that is exposed to significant anthropogenic load in the summer-autumn period. Source: O.A. Gulyaeva

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

3.2. IMPACT ON PHYSICO-CHEMICAL CHARACTERISTICS OF WATER As already noted in paragraph 2.2, the thermal and oxygen stratifications in Dniester reservoir during the summerautumn period have a great influence on the physico-chemical parameters of the water downstream of HPP-1 and HPP-2 dams. In this period, during synchronous releases of HPP -1 and HPP-2, spikes in water temperature and dissolved oxygen concentration, which are often not captured by regular observations, can be observed in the transboundary section. The data of episodic observations (Fig. 3.3) show that the temperature can fluctuate within three degrees, and the dissolved oxygen content can decrease to 2–4 mg/dm3, after which the initial values are restored (Analysis, 2008; Gulyaeva, 2016 ). Daily fluctuations of other water quality indicators are possible; however, additional specialized studies are required to give a definitive answer.

Fig. 3.3. Oxygen and temperature stratification in the dam section of the Dniester reservoir (a) and dissolved oxygen fluctuations downstream of HPP-2 dam during the day (special case - autumn 2014: 1 – 2 km, 2 – 57 km, 3 – 83 km from the HPP-2 dam) (b) In the absence of thermal and oxygen stratifications in the Dniester reservoir, the releases of hydropower plants have practically no effect on intraday fluctuations in physicochemical parameters in the transboundary section of the river (Fig. 3.4).

CHAPTER 3. DAILY RUNOFF FLUCTUATIONS AND THEIR IMPACT ON THE STATE OF TRANSBOUNDARY SECTION

Fig. 3.4. Daily dynamics of dissolved oxygen content in transboundary section of the Dniester (2 km from HPP-2 dam) in the absence of oxygen stratification in Dniester reservoir during environmental release (spring 2015)

3.3. IMPACT ON AQUATIC ORGANISMS Diurnal water level fluctuations in cross-border section of the river downstream of HPP-2 cause periodic draining of parts of the channel that may lead to partial demise of aquatic organisms in drained areas and also adversely affect the environment and productivity of fish spawning13.

Members of the expert group disagreed on the effect of diurnal fluctuations on higher aquatic vegetation and the content of dissolved oxygen. Due to the lack of field data, special field studies are needed to quantify the impact.

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

CHAPTER 4

LONG-TERM CHANGES AND INTRA-ANNUAL REDISTRIBUTION OF RUNOFF METHODOLOGY ISSUES OF THE ANALYSIS OF LONG-TERM RUNOFF CHANGES In order to analyze the changes in the hydrological regime, a fundamental agreement was reached on the following points: just like in the analysis of structural changes impact (Chapter 2), two periods are considered: the period

before the construction of HPP-1 dam (1951-1980) and the period of its operation (1990-2015); to assess the hydrological regime features in 1990–2015, shorter time periods are considered: the period

after the launch of HPP-1 and the operation of HPP-2 reservoir in the buffer mode before HPP-2 was put into operation; the period after the launch of HPP-2 (1999-2002) before the launch of PSPP (1st unit in the end of 2009); and the period of 2012–2018 after the commissioning of PSPP upper reservoir; to assess the impact of reservoirs on runoff, daily data of State Hydrometeorological Center of Ukraine

from two main hydrological sites, Zaleshchyky and Mogilev-Podolsky, are used. To get a comprehensive picture, daily data from Bendery River Post in Moldova are used as well. The calculations were carried out using the Indicators of Hydrological Alteration recommended by Guidelines No. 31 “Accounting for Environmental Runoff Requirements” on the implementation of European Parliament and European Council Directive on framework conditions for water policy activities. To analyze the characteristics of spring floods as well as ecological and reproductive release, we used longterm data about the regime and resources of surface waters (Water Cadastre of Ukraine) as well as daily water flow data at Dniester HPP-1 site. Analysis of Dniester reservoir water balance is based on the calculations of Novodnistrovsk lake station. As a part of the of water use analysis, its condition was assessed in the Moldavian part of the Dniester River basin (including the left bank) and in Odessa region in 1951–1980 and during the period of operation of the reservoirs (1990–2015). We analyzed the existing water supply and sanitation systems, the dynamics and prospects of irrigation development. We also summarized annual reports form 2-TP “Vodkhoz”, as well as strategic and policy documents in the field of water supply, treatment and management in Moldova and Odessa region of Ukraine. For the analysis of hydrobiological changes, available information on the species composition, abundance, biomass of aquatic organisms, aquatic and semi-aquatic birds was used. The information was derived from monographs and research articles summarizing the results of field hydrobiological studies before and after the creation of the reservoirs, as well as hydrobiological monitoring data of State Hydrometeorological Service of the Republic of Moldova, State Fish Protection Service of the Republic of Moldova and the statistical data of the Odessarybvod.

CHAPTER 4. LONG-TERM CHANGES AND INTRA-ANNUAL REDISTRIBUTION OF RUNOFF

4.1. LONG-TERM CHANGES IN THE NATURAL RUNOFF The long-term course of the Dniester runoff is characterized by the alternation of high water and low water years. For existing historical series of observations, from 1880 to 2015, the average yearly below normal water runoffs14 were repeatedly observed in series of 3–6 years, and above normal, up to nine consecutive years. In the long-term course of runoff prior to 1946, short low water periods were observed15 to be replaced by more high-water ones. Long low water phase in 1916 – 1964 was balanced out by a high-water period in 1965 – 1981. Long-term annual runoff fluctuations comprise a full cycle from 1982 to 2010. From 2011 to present, a low-water phase of the Dniester runoff is observed (Fig. 4.1).

Fig. 4.1. Difference integral curves of Dniester average annual water flow in sections of individual hydrological posts Data Sources: Hydrological Yearbook 1951 - 1977; State Cadastre rivers 1978 - 2015.

On average, the seasonal distribution of runoff in Dniester HPP-1 site is as follows (Draft Rules, 2017):

38% - in spring (March – May), when the main part of the runoff is formed due to melting of snow in the Carpathian part of the basin;

27% - in summer (June – August), which accounts for the bulk of rain floods;

19% – in fall (September – November);

16% - in winter (December – February).

Climate change affects the cyclicity of the runoff. In recent decades, they manifest themselves in increased (compared to the 1950-1980) cold season runoff, which is most likely due to the restructuring of synoptic processes and an increase in rainfall in the autumn, as well as milder winters with thaws. The unstable nature of the snow cover, shallow soil freezing depth all contribute to infiltration of melt water and the transfer of surface runoff to underground. This leads to an increase in winter low water runoff. Over the past decades, the The runoff norm is understood as the average runoff value over a multi-year period of such duration, which, if increased, will have practically no effect on the obtained value, meaning it will remain within the margin of error. If the average value is determined over a short series of observations or there is a suspicion that the series is not representative, such a value is called the long-term average value but not the norm.

The graph shows not the absolute values of the runoff, but the result of a usual conversion into "integral-difference curves" used in hydrology. A section of such a curve with an upward slope corresponds to a high-water phase of cyclical flow fluctuations (or generally a phase of increased values), and a section with a downward slope corresponds to a low-water phase (or a phase of reduced values). Fracture points of the curve indicate the beginning or the end of the cycle.

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

minimum average daily water flow rate has increased by 73% (the minimum average monthly water flow rate has increased to a lesser extent - less than 20%) (State Cadastre, rivers). Significantly smaller changes are characteristic of the maximum water flow rate, which in 80% of cases is not due to melting of snow but rather to rain floods: the maximum average daily water flow rate increased by only 4%, and the maximum monthly average, by less than 2% (State Cadastre, rivers) Climate changes contribute to a decrease in the maximum flow rates during spring floods for both the Dniester and its tributaries; the last significant spring flood of the rivers of the basin was observed in 1996 (State Cadastre, rivers; Ovcharuk, 2013). Despite a slight decrease in the last decades of maximum spring flood water flow rates of the Dniester (Fig. 4.2), the flood runoff volume during for this period remained virtually unchanged.

Fig. 4.2. Multi-year changes in the maximum water flow rate during spring floods at Zalishchyky site (m3/s) Data sources: Hydrological Yearbook 1941 - 1977; State Cadastre, rivers 1978 – 2015

The average long-term runoff volume during the flood period amounts to about 1.9 km3, the average flow rate is 380 m3/s, and the maximum values vary significantly – from 167 m3/s to 2810 m3/s. River floods can begin as early as February and end in late May with an average duration of about two months. Often the flood comes in several waves, which is especially pronounced during the early ice break-up and subsequent return of the cold weather. The course of the flood can be complicated, and runoff volume can increase due to rainfall; in such cases, the second peak of the flood often exceeds the first.

CHAPTER 4. LONG-TERM CHANGES AND INTRA-ANNUAL REDISTRIBUTION OF RUNOFF

Днестровская ГЭС ДнестровскаяOF ГЭС-2 Дубоссарская ГЭС 4.2. INTRA-ANNUAL REDISTRIBUTION RUNOFF BY RESERVOIRS

устье Днестра

Comparative analysis of the annual runoff variation of the Dniester done by the year of commissioning of Сороки Бендеры Маяки hydropower plants and reservoirs (1990-1998 – HPP-1 operation; 1999-2008 –HPP-1 and HPP-2 operation, Залещики Могилев-Подольский Вадул луй Водэ 2009-2015 –HPP-1, HPP-2 and PSPP operation) showed that the annual runoff in the downstream of the Днестровская ГАЭС Наславча cascade almost always coincides with the value of the total inflow of water into the reservoirs. The decrease in the annual runoff of the Dniester downstream of the cascade of HPPs and PSPPs (MogilevPodolsky) amounts to 3.2–6.6% and is due to additional evaporation from the surface of reservoirs, the presence of intakes in this section of the river (Insert 4.2), and also possibly the insufficient accuracy of regular runoff observations due to diurnal fluctuations. According to the authors of a detailed study of karst processes taking place град in the region of the Middle Dniester (Axiom, 2002), possible karst influences on the runoff characteristics 3 of the Dniester and its tributaries in the vicinity of HPP-1 and HPP-2 cascade can only result in runoff increase due to leakage of underground water through a system of tectonic disturbances from the Prut basin side. 1 % 100

-1

Reservoirs of the Dniester complex ensure intra-annual redistribution of runoff. When accumulating or discharging -3 water, their influence in the80maximum flow rate during floods and high water, 1 2 3 is4 manifested 5 6 7 primarily 8 9 10 in11a decrease 12 -5 in a decrease in spring flow rate in general (except in May, when ecological and reproductive release as well as is carried out – see below) and in an increase in summer-autumn 60low water flow rates (Fig. 4.3). 40 % 20

Fig. 0 4.3. Change in average monthly water flow rates (%) in 1990–2015 in relation to -10 natural runoff due to regulation

0 -10 -20

Data source: State Cadastre, rivers 1978–2015. -20

-30 1

9 10 11 12

A similar situation is observed when considering changes with respect to the time of commissioning of reservoirs and hydropower plants (Fig. 4.4): 1990– 1998 –HPP-1 operation; 1999-2008 –HPP-1 and HPP-2 operation; 2009-2015 –HPP-1, HPP-2 and PSPP operation. The main regulator of the Dniester runoff is HPP-1 Dniester reservoir. It receives the discharge of the upper Dniester and its tributaries: Zbruch, Zhvanchik, Smotrytch, Studenitsa, Ushitsa and Kalyus (lateral inflow accounts for 19 - 23% of the total inflow). In most cases, the buffer reservoir and the upper reservoir of PSPP are only involved in daily flow rate regulation. Comparison of data from hydrological posts in Zalishchyky and Mogilev-Podolsky (including lateral inflow) for 1951-1980 and 1990-2015 shows that after the creation of reservoirs, minimum average runoff increased by 102-118% and the minimum average, by 35-42%. At the same time, a decrease of 20–25% in the maximum daily average and 15% in the maximum average monthly water flow rate is observed16 (Fig. 4.5). These changes are also partly due to the transformation of unregulated runoff parameters over the indicated period – compare to information in the previous section.

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

WATER BALANCE OF DNIESTER RESERVOIR The water balance equation can be represented in the following general form: Wпр + Wб + Wбр + Wос + Wп - WГЭС - WфГЭС - Wфложе - Wис - Wсп = ∆Wак, where Wпр – Dniester tributary (h/p Zalishchyky); Wб – measured lateral inflow; Wбр – estimated lateral inflow from the area where water flow rate is not measured; Wос – precipitation in the reservoir water table; it is determined from precipitation observational data by stations and posts (the water table area of the reservoir, which varies with changing water level, is taken into account) Wп – discharges from enterprises; WГЭС – runoff through hydropower facilities of HPP-1; WфГЭС – filtration through the dam body; Wфложе – filtration in the reservoir bed; Wис – evaporation of the reservoir water surface; calculated using hydrometeorological observations on the banks and water area of the reservoir, accounting for changes in the area size of the reservoir water surface; Wсп –withdrawal of water for economy needs; Wак – accumulation of water in reservoir basin.

The upper Dniester runoff is the main contributor to the water balance inflow. According to observations of Hydrometeorological Center of Ukraine, an average of 6–8 km3 of river water flows into the reservoir each year. Some years, the inflow can reach 12 km3/year. Some dry years, the runoff of the upper Dniester does not exceed 4–5 km3/year. The second largest component of the water balance is the lateral inflow. The volume of discharges from enterprises, including household wastewater, is given according to the data provided by water-using enterprises and departments of the water supply network in Kamenets-Podolsky and Khotin. It is rather small and averages at 15-17 million m3/ year. The annual rainfall affecting the reservoir water table averages at 500–600 millimeters (70–80 million m3). Essentially, the outflow component of the water balance is formed due to discharge into the buffer reservoir, which makes up 80–97% of the total inflow to reservoirs. Evaporation from the water table of the Dniester reservoir amounts to 700-800 millimeters per year, which causes an annual loss of up to 95-105 million m3 (1-2% of water inflow). The flow rate of the filtration through the body of HPP-1 dam averages at 7 m3/ s (220–225 million m3/ year). Filtration in the reservoir bed does not exceed 3%. The abstraction of water for household needs from Dniester reservoir ranges within 35–45 million m3 / year. Data source: Lake station Novodnistrovsk HMC Ukraine

CHAPTER 4. LONG-TERM CHANGES AND INTRA-ANNUAL REDISTRIBUTION OF RUNOFF

m3/s

-30

-60

-90

-120

-150 1991-1998

1999-2008

2009-2015

Fig. 4.4. Change in average monthly water flow rate in relation to natural runoff for different periods of reservoirs and HPPs commissioning Data Source: State Cadastre, rivers 1978–2015.

As these calculations show, the general trend is towards the decrease in the absolute value of the changes with an increase in the averaging period. When comparing the data form posts in Mogilev-Podolsky and Bendery between 1990 and 2015, the same patterns are observed – an increase in the minimum and a decrease in the maximum runoff. The forms of runoff hydrograph at these posts are also quite similar (Fig. 4.6).

устье Днестра Сороки

Бендеры

Могилев-Подольский

Маяки

Вадул луй Водэ

аславча ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

% 100

9 10 11 12

Fig. 4.5. Change in the minimum and maximum runoff (%) in Mogilev-Podolsky in 1990–2015 compared with 1951-1980.

80 60

1 - average daily minimum runoff, 2 - minimum runoff (average for 3 days),

3 - minimum runoff (average for 7 days), 20

4 - average monthly minimum runoff, 5 - minimum runoff (average for 90 days),

6 - average daily maximum runoff, 7 - maximum runoff (average for 3 days),

-10

8 - maximum runoff (average for 7 days), 9 - average monthly maximum runoff,

-20 1

9 10 11 12

м3/s 500

10 - maximum runoff (average for 90 days)

400

300

1 200

2 100

Fig. 4.6. Intra-annual distribution of average monthly water flow rates for 1990–2015 at Bendery (1) and Mogilev-Podolsky (2) o/p In spring (usually in April – May) an ecological and reproductive release from the Dniester reservoir is carried out (Insert 4.3). The release begins when the water temperature in the Dniester delta reaches 10–12 °С. In most cases, such values are observed in the second decade of April. The release lasts for an average of 30 days. When determining the course of release, the Interdepartmental Commission of Ukraine for coordinating the operation

CHAPTER 4. LONG-TERM CHANGES AND INTRA-ANNUAL REDISTRIBUTION OF RUNOFF

of Dnieper and Dniester reservoirs generally adheres to the following schedule: an increase in the short term (up to 6–8 days) flow rates up to average daily values of 450–500 m3/s; maintaining this level for 10-12 days; and subsequent gradual decrease. The volume of release averages at 0.9–1.2 km3; the minimum required volume, according to the studies of Ukrainian NAS Institute of Hydrobiology (Shevtsova, 2003), is 0.8 km3.

ENVIRONMENTAL AND REPRODUCTIVE RELEASE Ecological and reproductive release is designed to maintain the environmental sustainability of the natural river system. Its parameters are set annually by Interdepartmental Commission of Ukraine to coordinate the operation of the Dnieper and Dniester reservoirs. Compliance with the release schedule is ensured by NEC Ukrenergo and PJSC Ukrhydroenergo. Analysis and control of the hydrological situation in the Dniester basin during the release period is carried out by State Water Resources Agency of Ukraine. It should be noted that at the state level in Ukraine there is no mechanism for monitoring the effectiveness of environmental and reproductive releases and, accordingly, no key environmental indicators have been identified the assessment of which could indicate its effectiveness. As part of its own monitoring programs, Dniester Delta ecosystem is monitored by Lower Dniester National Nature Park. The value of ecological reproductive release does not include the volume of water to ensure economic and other activities.

The main difficulty in agreeing on the regulations for environmental releases is the lack of synchronization of water inflow into the Dniester reservoir during the spring flood with the established dates for the ecological and reproductive releases (Fig. 4.7). This often leads to significant spring triggering of the Dniester reservoir and a decrease in the water level in it, which is detrimental to the fish of the reservoir itself, especially in its upper section. If there are contradictions between water requirements of the Dniester delta and Dniester reservoir, especially in dry years, the delta, which is more important for the conservation and reproduction of valuable hydrobiocenoses, takes precedence (Shevtsova, 2003)17.

At the same time, the possibility and necessity of optimizing the timeframe, duration and maximum flow rates of ecological-reproductive release remain. In the interests of the fisheries in the Middle Dniester and Dniester floodplains, the optimal maximum flow rates, according to a number of different estimates, should be in the range of 400–500 to 700–750 m3/s (Restoration, 2016).

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

Fig. 4.7. Long-term characteristics of spring flood periods at Zalishchyky o/p and ecological and reproduction release at Dniester HPP-1 site It should be noted that the total (including ecological-reproductive release) volume of water passing during spring floods through the HPP-1, on average, coincides with the volume of spring flood runoff at Zalishchyky o/p. (Fig. 4. 8). The maximum flow rate at HPP-1 is observed in the second decade of March and can reach 1000 - 1500 m3/s (State Cadastre, rivers 1978 - 2015).

Fig. 4.8. Long-term changes in the volume of water runoff during spring flood at Zalishchyky o/p (1) and the total runoff volume during spring flood (including environmental releases) in HPP-1 upstream (2). * Lines three and four are mean annual values .

CHAPTER 4. LONG-TERM CHANGES AND INTRA-ANNUAL REDISTRIBUTION OF RUNOFF

4.3. THE IMPACT OF HYDROLOGICAL CHANGES ON THE STATE OF BIOTIC COMMUNITIES IN THE LOWER DNIESTER The commissioning of Dniester complex affected the seasonal distribution of the Dniester runoff, thereby changing the spawning conditions of almost all ecological groups of fish. Because of the degradation of flood lakes due to a decrease in water exchange mudminnow Umbra krameri (Walbaum, 1792), an indigenous species of the Dniester delta listed in the Red Books of Moldova, Ukraine and Europe, saw a sharp decrease. persons 2000

1500

1000

500

1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

persons 600 500 400 300 200 100

1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

Fig. 4.9. Number of nests of glossy ibis and little heron in the Dniester delta from 1972 to 2009 Data Source: Schegolev, 2016

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

The regulation of the Dniester runoff significantly affects the condition of aquatic and semi-aquatic birds. The species composition and abundance of birds in the Dniester delta during nesting and migration periods largely depend on the hydrological conditions of the year, flooding of floodplain meadows in the spring, and the flooding of the plains. Significant fluctuations in the number of semi-aquatic birds are characteristic of the Dniester delta. In the wake of runoff regulation, the abundance and nesting conditions in the Dniester delta for colonial semiaquatic birds (little cormorant, night heron, great white, little, pond and purple heron, glossy ibis and spoonbill), as well as the presence of forage biotopes for a number of migratory species, are primarily defined by ecological releases from the Dniester reservoir. In dry years, when the maximum flow rates of ecological releases amount to 400–450 m3/s, a decrease in the number of gray goose and mallard is observed. Under such conditions, the numbers of spoonbill and previously abundant glossy ibis are also reduced (Fig. 4 .9). The flooding of the plains also largely affects the placement of the gray goose and the mute swan nests in the Dniester delta. At the same time, runoff regulation does not affect the abundance of some species of fish-eating birds - the great cormorant and the white pelican, whose numbers in the Dniester delta have grown in recent years to approximately 10,000 and 2,000 individuals, respectively.

4.4. PROVISION OF BASIC WATER SUPPLY FUNCTIONS The Dniester reservoirs play an important role in providing water resources to the regions of Ukraine (Chernivtsi, Khmelnitsky, Ternopol, Vinnitsa, Odessa regions) and the Republic of Moldova (including the Transdniestrian region). In the area of the Dniester reservoir, the main consumers are the utility enterprises of Novodnistrovsk, Kamenets-Podolsky, Khotin and smaller settlements of Ukraine. In most cases, before reaching a drawdown level of 114 meters18 the reservoir ensures uninterrupted operation of water intakes. As indicated in subsection 4.2, due to the accumulation of water resources in the reservoir of Dniester cascade of HPPs (and to a lesser extent, in Dubossary reservoir)19 the minimum runoff increases, providing a guaranteed flow rate of 100 m3/s, sufficient for intakes of the Middle and Lower Dniester (designed around the flow rate of 80 m3/s). In Moldova, the Dniester provides 63% of drinking water in the amount of 73 to 78 million m3 of water per year. The largest volume of water per capita (43.7 m3/ year) is consumed in Chisinau. In recent years, there have been issues related to lower water levels at a number of water intakes (in Chisinau and the Transnistrian region). However, upon closer examination such issues normally turned out to be unrelated to the hydrological regime (Insert 4.4).

According to the draft Rules for the Operation of Reservoirs of the Dniester cascade of HPPs and PSPPs, the minimum elevations of water intakes at Kamenets-Podolsky (108.65 m) and Khotin (111.0 m) must be taken into account when the Dniester reservoir falls below 114.7 meters.

According to the Operation Rules of Dubossary Reservoir, sanitary and navigation release to the upstream should collectively amount to 60 m3/s.

CHAPTER 4. LONG-TERM CHANGES AND INTRA-ANNUAL REDISTRIBUTION OF RUNOFF

ANALYSIS OF THE SITUATION AT CHISINAU WATER INTAKE AND PROPOSED REMEDIAL MEASURES Since the 1980s, according to SA Apă-Canal Chişinău Operational Service, the water intake at the Dniester main pumping station (MPS), which supplies water to the city of Chisinau, occasionally operated with water levels in the river being well below design parameters, which jeopardized guaranteed water supply in Chisinau as well as other settlements receiving water from this group water supply system. To determine the causes of falling water level and design remedial measures, the Aquaproject Institute used its own data, as well as the archival data of the institutes and organizations of Moldgiprostroy, Chisinaugorproject, Moldgiprovodkhoz, Bendery River Port OJSC, SA Apă-Canal Chişinău, Agenţia Apele Moldovei, ÎS Direcţia Bazinieră de Gospodărire a Apelor, State Design Institute "Soyuzvodkanalproekt" Minsk, SRL GEOVANMAX. In addition, in September- December 2016, depth measurements at eight sections of the Dniester were made, as well as one-hour connection of the water edge, and vertical and planned referencing to state geodetic network in the water intake area. Measurements were carried out at the same sites where SC GEOVANMAX SRL had conducted measurements in 2002, 2008, and 2009. To analyze the dynamics of changes in the river channel at the water intake, 2016 measurement data were laid over the previously obtained data. In sections No. 2 and No. 8 more detailed hydraulic and hydro-technical calculations were performed. As a result of the calculations, it was established that with a current channel profile at the water intake, the existing minimum flow rates do not meet design parameters necessary for the operation of the pumping station: 8.5 meters (hereinafter using the Baltic elevation system) with minimal sanitary and environmental releases of Dubossary HPP of 80 m3/s and 9.0 meters, with guaranteed releases during the vegetative season of 120 m3/s. The decrease in the estimated water level at the water intake site is caused by the following factors: the embankment of the Dniester channel in order to protect settlements and floodplain agricultural

lands from flooding; the construction by Bendery River Shipping Company (starting in 1958) of underwater directional dams

(transverse dikes, jetties) on the left bank in order to ensure navigation, which led to the erosion of the bed and the right bank of Dniester; long-term extraction of sand and gravel from the riverbed, including the area of the water intake, violation of the natural river base level in the downstream of Dubossary reservoir due to construction

of Dubossary HPP. These changes led to the drop of the riverbed level at MPS water intake by 3-5 meters.

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

Changes in riverbed and water levels at the Chisinau MPS water intake Year

Riverbed level, м

1968 1994

Water level at different flow rates, m 80 m3/s

120 m3/s

8,08

9,83

10,24

3,85

8,01

8,55

2002

3,64

7,45

8,20

2008

3,49

7,30

7,97

2016

3,03

7,91

8,43

m 13 L = 17.6 km

L = 4.17 km

11 10

5 4 3

8.41

H 120 m3/s

7.69

H 80 m3/s

MPS section

H 80 m3/s

∆ 5-6 m

Chisinau-Dubossary bridge

H 120 m3/s

∆ 1.2 m

2 1 0 section #

5 52

Distance, m

4 3в 3б 3а 33

2а

10 13 17 17 17

2 30

1 8 31

6 72

Riverbed level 1968

Riverbed level 2008

Water level at H 120 m3/s

Riverbed level 1994

Riverbed level 2016

Water level at H 80 m3/s

Riverbed level 2002

Longitudinal profile and changes in minimum riverbed levels in the area of water intake

CHAPTER 4. LONG-TERM CHANGES AND INTRA-ANNUAL REDISTRIBUTION OF RUNOFF

Since 1994 alone, the cross-section of the Dniester riverbed at the pumping station (site 3) has increased by 91.0 m2, which given minimal flow rates in the river inevitably leads to a local decrease in water levels at the water intake site. In section No. 2a, 30 meters downstream of the MPS axis, a lowering of the floor by 0.5–2.0 meters was observed in the center of the river and on the right bank. The analysis also showed a deepening of the river floor at the highway bridge in Dubossary from 1962 to 1990 by 4-6 meters and at the highway bridge near the city of Vadul-lui-Voda from 1978 to 2008, by 1.4 meters. Therefore, in the studied area at Dubossary HPP dam and near the city of Vadul-lui-Voda, there is an ongoing trend towards the deformation of the channel, lowering the riverbed and as a result the water level during minimal releases. The “Aquaproject” Institute proposed to carry out hydrotechnical measures to increase water level at the water intake site. These include creation of an underwater foundation sill made of cylindrical stone gabions, i.e. factory-made double torsion mesh bags filled with rubble stone in the riverbed, in section No. 8 downstream of the MPS water intake. The suggested foundation sill will not affect wintering pits and spawning grounds, thereby preserving the existing conditions for the development of Dniester hydrobionts. Hydromorphometric and hydraulic calculations show that a foundation sill with a crest mark of 6.6 meters will ensure the water level of 8.5 meters at the water intake site with the flow rate from Dubossary HPP of 80 m3/s and 9.0 meters with the flow rate of 120 m3/s. That will ensure uninterrupted operation of the MPS water intake and guarantee water supply to the city of Chisinau. Source: Acvaproiect SRL

The Dniester water is essential to the operation of industrial enterprises, in particular the Moldavian State District Power Plant. Its return consumption for cooling of electric generators (after use, the water is returned to the Turunchuk sleeve through the Cuciurgan estuary) amounts to an average of 555 million m3 of water per year (State Water Cadastre of the Republic of Moldova) and can be brought up to 835 million m3 per year when six power units are operating. In Odessa region of Ukraine, the cities of Odessa, Yuzhny, Chernomorsk, Belyaevka, Teplodar and settlements of Belyaevsky, Ovidiopolsky and Limansky districts with a population of 1.26 million people located in a radius of 100 kilometers from Odessa water intake get their drinking water from the Dniester. Except for emergencies at water pipelines, no interruptions in water supply in Odessa in the last decade have been recorded. According to LLC “Infox”, the branch of “Infoxvodokanal”, the reduction in release volumes in the Dniester reservoir during offshore winds reducing Dniester water levels at the intake area also increases water treatment costs20. An analysis of the potential threat to Odessa water intake as a result of a prolonged runoff decline during periods of strong surge winds requires additional research. In Moldova, as well as in Odessa and Vinnitsa regions of Ukraine, the Dniester water is used for irrigation. Since the 1990s, the area of irrigated lands has decreased significantly (in Moldova from 100–240 to less than 20–35 thousand hectares); however, in the recent years, interest in irrigated agriculture has grown again, which has led to an increase in size of irrigated areas. In the next decade, total water consumption in the Republic of Moldova and Odessa region of Ukraine is expected to increase from 392 million m3 in 2018 to 925 million m3 by 2028 (Fig. 4.10). The results of observations made at the nearest hydrological observation post in Mayaky, which is under the influence of surge phenomena, show that commissioning of the Dniester cascade of HPPs and PSPPs had almost no effect on the average annual water level values.

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

(а)

(b)

Fig. 4.10. Water consumption in the Dniester basin downstream of HPP-2 for 1965–2017 and a forecast until 2028, by (a) type of water usage, and (b) basin countries, million m3 per year * Without taking into account water consumption downstream of HPP-2 in Vinnytsia and Cherkasy regions of Ukraine and the return consumption of Moldovan PSPP.

Data Sources: Water Use Report ...; Government of the Republic of Moldova, 2011; archives of the Ministry of Land Reclamation and Water Resources of the MSSR; Agency “Apele Moldovei”; Lower Dniester National Natural Park; Department of Water Resources of Odessa region; expert forecast (M.S. Penkov, A.N. Kalashnik)

CHAPTER 4. LONG-TERM CHANGES AND INTRA-ANNUAL REDISTRIBUTION OF RUNOFF

Nevertheless, the estimated total irrigated area of 550 thousand hectares used as a basis for existing Rules of operation of Dniester hydropower complex reservoirs will not be attained in the next 20-30 years. In the long term, however, such an area will need to be provided with water for the expanded production of highly profitable fruits and vegetables and other crops, necessary for the economic and social development of rural communities. At the same time, the irrigation norm of 4420 m3/ha included in the calculations is unjustifiably high and can be significantly reduced, thus releasing the necessary volume of water for the spring ecologicalreproductive release not included in the initial calculation. Existing experience shows that the regulation of minimal runoff, especially in extremely dry years, will continue to be critical in the years to come21. At the same time, it is necessary to retain the capability to regulate river floods in the summer period in order to protect from flooding the agricultural lands, which in many villages are the only source of people’s livelihood.

Therefore, an analysis of the situation in an extremely dry year of 2007 emphasizes the need for reservoirs to ensure guaranteed water consumption, which exceeded the natural inflow in July - August with irrigation of only 35 thousand hectares, much less than can be expected in the future.

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

CHAPTER 5

CONCLUSION Analysis of vast body of data conducted by an expert group enabled us to identify significant changes of hydrological, hydrochemical, and hydrobiological indicators described in detail in the report and summarized below. Some indicators and processes for which, according to the available data, no significant changes were found, remained outside the summary table and recommendations. These include:

oxygen regime downstream of reservoirs;

total number of species and indices of saprobity for macroinvertebrate communities;

zooplankton abundance;

total number of fish species within the basin and its large sections;

average annual runoff;

the volume of spring runoff downstream of the cascade in comparison with natural floods.

However, the available data was found to be insufficient for reliable analysis of a number of processes and trends. For such cases, the group suggests conducting additional studies to fill in specific information gaps, also summarized below. Alongside the studies mentioned below, additional more detailed research may be needed for the issues not covered by this study, such as the impact of existing and planned facilities of Dniester PSPP on the state of aquatic communities downstream of the hydrocomplex, and the impact of water intake conditions and water level fluctuations in the Dniester reservoir on the condition of the fish stock and rare and endangered species. Finally, based on the results of the analysis, a number of recommendations for addressing specific problems has been given. These recommendations are preliminary and may be taken into consideration and further developed during the preparation and implementation of the Strategic Action Plan within the framework of GEF project “Enabling Transboundary Cooperation and Integrated Water Resources Management in the Dniester River Basin “, as well as the Dniester River basin Management Plans as a part of Moldova and Ukraine commitment to the requirements of Directive 2000/60/EU on the framework conditions for activities in the field of water policy22. In the same context, the distribution of responsibilities for financial support and the implementation of compensation measures to restore and improve the condition of the Dniester basin requires further analysis. During the discussion among experts on this analysis, a proposal was made to abandon the use of the Dniester for hydropower in principle and to begin gradual liquidation of the existing reservoirs. The expert group was not able to reach consensus on this issue, which ultimately requires strategic and political decisions at the intersection of the interests of energy, water use, and environmental protection. However, expert group members are ready to contribute to the further research of these problems and their solutions. The study of the necessity and feasibility of building fish passage facilities through dams of Dniester HPPs was excluded from the final recommendations. Members of the expert group unanimously agreed that the current state of fish communities of the Black Sea does not allow for the recovery of anadromous fish in the Dniester. In addition, the real effectiveness of existing facilities for commercial species is small.

CHAPTER 5. CONCLUSION

Table 5.1 Effects of the construction and operation of reservoirs and recommendations for further actions Main effects of the construction and operation of reservoirs

Recommendations for exploring opportunities or taking corrective measures

Recommendations for conducting additional research

Impact of structural changes resulting from the construction of reservoirs on the aquatic environment and biotic communities Decreased suspended solid runoff downstream of reservoirs up to the Dniester delta

Study of long-term changes in runoff and balance of heavy particle-size fractions of river sediments (sand and gravel)

Development of a strategy for regulating solid runoff (sediment) in the Dniester basin

Change in the thermal regime of the transboundary section downstream of HPP-2

Studying the possibility of water discharge from various depths of the Dniester reservoir

The development of macrophytes, the overgrowing of the channel and flood lakes

Quantitative assessment of the extent of channel bedding and its implications (oxygen regime, secondary pollution)

An increase in the stocking of the Lower Dniester by an obligate phytophage, grass carp Ctenopharyngodon idella

Change in the species composition of invertebrates (replacement of rheophilic species with limnophilic species), increasing the total number and biomass of macroinvertebrates, worsening the living conditions of sensitive taxa (decreasing EPT index)

Standardized sampling of macroinvertebrates from various substrates and banks at different distances from the HPP-2 dam and downstream of Dubossary reservoir (in the Reut River influence zone). Study of the size and age structure of populations of dominant mollusk species depending on temperature changes

Decreased cross-border zooplankton production

Spatial and quantitative assessment of the state of zooplankton at different distances from dams

Change in the species composition of ichthyofauna, reduction in stocks of commercial species, reduction in the number of rare and endangered species

Analysis of the prevalence of invasive Preventing the spread of invasive and invading species in the Dniester species basin

Influence of diurnal runoff fluctuations on the state of transboundary site Uneven intraday runoff fluctuations downstream of HPP-2

Study of the intraday runoff fluctuations over a longer (representative) period of time. Study of intraday variations in water quality in the downstream of HPP-2

Setting up bilateral automated monitoring of the level and flow rate of water downstream of HPP-2. Inclusion of restrictions on the minimum value of instant release at HPP-2 in the Operating Rules of Dniester Reservoirs

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

Uneven intraday fluctuations in temperature, water level, and drainage of channel parts in the transboundary section

Study of the dependence of aquatic communities and aquatic organisms downstream of HPP2 on daily fluctuations in water level

Long-term changes and intra-annual redistribution of runoff Reduction of maximum flow rate in reservoirs’ downstreams (flood control)

Development of modeling for an accurate forecast of the hydrological situation

Increase in the minimal runoff in reservoirs’ downstreams and ensuring guaranteed flow rates at water intakes and the needs of irrigated lands

Regular updates of medium- and longterm forecasts of water consumption in the Dniester basin. Study of the water intake related problems on the left bank of the Dniester (including degradation of the stream channel) and the city of Odessa (possible impact of surge phenomena at low flow rates)

Strict enforcement of the Operating Rules for guaranteed water supply and irrigated agriculture in dry years. Implementation of the “Aquaproject” Institute proposal to ensure the water level at the Chisinau water intake

Cutting off the peak flow rates and transformation of the spring flood regime during environmental and reproductive releases. Deterioration of fish spawning conditions, bird habitats, ecosystem conditions in the Dniester delta due to a decrease in flooding of the plains

Quantitative analysis (modeling) of the processes of flooding of floodplains at different runoff volumes and surge and offshore phenomena. Studies to update data on species diversity and ichthyofauna production, occurrence of rare and endangered fish species, assessment of fish stocks and the status of spawning grounds of the lower Dniester

Steps to enable water level rise of the Dniester reservoir to the top mark (dam repair, removal of existing dams and prevention of the construction of new facilities between FRL and SRL). Further optimization of regular flushing of the riverbed and floodplains and of the spring ecological and reproductive release. Development of measures for the protection of rare and endangered fish species of the Lower Dniester, restoration of spawning grounds, and regulation of commercial and recreational fishing. Incentivization of fish-breeding enterprises for stocking of natural reservoirs with zanthe, sabrefish, and other commercial and rare species. Creation of artificial meadow spawning grounds in the Dniester basin to ensure spawning of phytophilic species.

REFERENCES Avakyan A. B. Reservoirs / Avakyan A. B., Satalkin V.P., Sharapov V.A. - Moscow: Mysl, 1987. 325 p. Aksiom S. D., Khilchevsky V.K. Sulfate karst inflow into chemical storage of natural waters in the Dniester basin. - K.: Nika-Center, 2002. - 204 p. Analysis of the variability of the chemical composition of the Dniester waters in Naslavcea / N. Goryacheva, V. Gladky, G. Duka [et al.]. // Management of the basin of the transboundary river Dniester and the Water Framework Directive of the European Union: Mater. Int. conf. (Chisinau, 2–3 October 2008). - Chisinau: Eco-Tiras, 2008. - P. 111−115. Bezhenaru G., Denisov N., Penkov M. Prospects for the use of water resources of the Dniester basin, 2015. Berg L.S. Freshwater fish of the USSR and neighboring countries. - M.; L .: Publishing house of the Academy of Sciences of the USSR, 1948-1949. - Part 1-3. - 1382 p. Boyko T. Asociation of important metals near the coastal inlets of the Dniester water reservoir / T. Boyko, V. Kosmus, G. Rudko // Geology and geochemistry of combustible fossils. - 1999.– No. 4. - P. 166–184. Bulat D.E., Bulat Dm., Usatyi M.A., Trombitsky I.D., Zubkova E.I. Long-term dynamics of the ichthyofauna of the middle section of the Dniester River and the Dubossary reservoir // Biodiversity and factors affecting the ecosystems of the Dniester / Mat. Int. conf. (with international participation), Tiraspol, 16 - 17 Nov 2018 – Tiraspol: Eco - TIRAS , 2018. - P. 38-41. Burnashev M.S., Chepurnov V.S., Dolgiy V.N. Fishes and fisheries of the Dniester River. – Journ. of KIshinev State University. - vol. XIII, 1954. Burnashev M.S., Chepurnov V.S., Rakitin N.P. Fish of Dubossary reservoir and the development of fishing. – Journ. of Kishinev State University. - vol. XX, 1955. - P. 3-31. Restoring communication between the Dniester River and estuary floodplains / V.V. Gubanov, V.B. Egoraschenko, V.A. Zaitsev, E.A. Lukyanchenko, D.A. Onishchenko and N.A. Stepanko / Report for UNECE and OSCE in the framework of the component “Climate Change and Security in the Dniester River Basin” of the project “Climate Change and Security in Eastern Europe, Central Asia and the South Caucasus”, 2016 . - 42 p. Hydrobiological regime of the Dniester and its reservoirs / [Sirenko L.A., Evtushenko N.Yu., Komarovsky F.Ya. Et al]; ed. by L.P. Braginsky . - K.: Naukova Dumka, 1992. -- 356 p. Hydrological Yearbook. Volume 2. Basin of the Black and Azov Seas (without the Caucasus). Issue 1. - K., 1951-1977. State Water Cadastre of the Republic of Moldova. Annual data on the regime and resources of land surface waters, 1993–2015.

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Gulyaeva O. A. Ecological and hydrological characteristics of the reservoirs of the Dniester energy complex / O. A. Gulyaeva // Hydrobiological journal. - 2013. - T. 49. - No. 6. P. 92–105. Gulyaeva O. A. Features of the formation of the oxygen regime of the Middle Dniester / Academician L.S. Berg is 140 years old: a collection of scientific articles. – Bendery: Eco - TIRAS, 2016. - P. 338–342 Gulyaeva O.A. [Field data collected as a part of the research concducted under President’s Scholarships for Young Scientists of NAS of Ukraine (2014-2016) “Release regime of the Dniester hydropower complex and its impact on the ecosystem components of cross-border section of the Dniester River”]. Gulyaeva O. O. Sedimentation regime of the Dniester reservoir // Hydrology, Hydrochemistry and Hydroecology. - K .: VGL “ Obrii ”, 2009. - Volume 16. - P. 103–107. Denisova A. I. The role of bottom sediments in the processes of self-cleaning and selfpollution of water bodies / A. I. Denisova, E. P. Nakhshina, I. K. Palamarchuk // Self-cleaning, bioproductivity and protection of water bodies and watercourses of Ukraine. - K., 1975. P. 86−87. State water cadastre. Yearly data on the regime and resources of surface water bodies. Part 2. Lakes and reservoirs. - Volume 2. Issue 1. Basins of Western Bug, Danube, Dniester, South Bug, 1978–2015. State water cadastre. Yearly data on the regime and resources of surface water bodies. Part 1. Rivers and channels. - Volume 2. Issue 1. Basins of Western Bug, Danube, Dniester, South Bug, 1978–2015. Dolgii V.N. Ichthyofauna of Dniester and Prut basins. Kishinev Shtiintsa, 1993. - 322 p. Yearbook: surface water quality of the Republic of Moldova according to the hydrobiological elements of the Environmental Quality Monitoring Department (EQMD), 1990-2015. Yearbook: surface water quality of the Republic of Moldova according to the hydrobiological elements of the Environmental Quality Monitoring Department (EQMD) for 2008–2017. Zubkov E. Influence of hydro construction on the ecological state of the Dniester River // Academos, nr. 2 - 3 (7), September 2007. - p. 53 - 57. Melian R. (ed.) 2011. Joint Moldovan-Ukrainian hydro chemical expedition of 2011 to the Dniester River (Dniester III project). Report. - Chisinau. Melnik S.V. Spatial-temporal dynamics of turbidity in the basin of the Upper Dniester // Ukrainian Hydrometeorological Journal. - 2010. - No. 7. - P. 177–182. Melnik S.V. Suspended sediment runoff in the Dnister / S.V. Melnik // Hydrology, Hydrochemistry and Hydroecology. - K .: VGL “Obrii”, 2006. - Volume 11. - P. 207–212.

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Munzhiu O.V., I.K. Toderash, I.V. Shubernetskiy. Investigation of zoobenthos of the Dniester in Moldova in 2016 // Integrated management of transboundary Dniester River basin: a platform for cooperation and current challenges: Mat. of Int. conf. - Tiraspol, October 26–27, 2017 / Tiraspol: Eco-TIRAS, 2017 .-- P. 269–273. Ovcharuk V.A. Statistical parameters of the hourly series of maximum water flow rates and water strata during spring floods in the Dnieper river basin / V.A. Ovcharuk, A.V. Traskova // Bulletin of the Odessa State Ecological University. - 2013. - Iss. 16. - P. 141–148. Report on water use in the Republic of Moldova. Form No. 2TP-Vodkhoz: 1963–1988 Certification of reservoirs. Rules for the operation of the Dubossary reservoir. - Chisinau, 1983. - 105 p. Decree of the Government of the Republic of Moldova dated March 20, 2014 No. 199 “On approval of the Strategy for water supply and sanitation (2014–2028)”. The rules of operation of the reservoirs of the Dniester hydropower complex. - M: Min. of the water management of the USSR, 1987. - 50 p. Government of the Republic of Moldova, 2011. Decision No. 751 dated 05.10.2011 on the approval of the Program for the Development of Water Management and Land Reclamation in the Republic of Moldova for 2011 - 2020 // Monitorul Oficial No. 170-175, article No. 830, 10/14/2011. Draft Rules for the operation of reservoirs of the Dniester cascade of HPPs and PSPPs at FRL 77.10 buffer reservoir. - Kharkov, PJSC “Ukrhydroproject”. - 732–39 - V48. - 2017. - 108 p. Smirnova-Garaeva N.V. Aquatic vegetation of the Dniester and its economic importance. Chisinau: Shtiintsa, 1980. - 136 p. Snigirev S. M. Ichtiofauna of the Lower Dniester basin // Bulletin of the A. A. Brauner Museum Fund I. I. Metchnikoff ONU, 2012. - Vol. IX. - No. 3. - P. 1-32. Strategic directions of adaptation to climate change in the Dniester basin. ENVSEC, UNECE, OSCE, 2015. - 72 p. Tomnatik E.N. Ichthyofauna of the Dubossary reservoir, its change and ways to increase the stocks of commercial fish // Dubossary reservoir. - M.: Publishing House of the USSR Academy of Sciences, 1964. - P. 175–209. Tomnatik E.N. Direction of ichthyofauna formation in the Dubossary reservoir in the first two years of formation // Bul. Of Mold. Branch of the USSR Academy of Sciences, 1957. No. 8 (41). - P. 67–81. Sharapanovskaya T.D. Ecological problems of the Middle Dniester. - Chisinau: Ecological Society “BIOTICA”, 1999. - 88 p. Shevtsova L.V. Environmentally sound operation of the Dniester reservoir as a factor in preserving the ecosystem of the Dniester delta / L. V. Shevtsov, N. Y. Babich, V. V. Semchenko // Gidrobiol. journal - 2003. - V. 39. - No. 4. - P. 11-23.

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Shevtsova L.V. Hydrobiological assessment of the impact of the Dniester pump storage power plant on the river’s water ecosystems according to the national and international EIA systems / Management of the Dniester transboundary river basin and the Water Framework Directive Mat. of Int. conf. - Chisinau, 2 - October 3, 2008, city of - Chisinau : Eco - TIRAS . the C. 288-290. Schegolev I.V., Schegolev S.I., Schegolev E.I. Endangered wetland birds in the deltas of the Black Sea rivers / Works on bird ecology. Volume 1. - Odessa: Prof. I. I. Puzanov Fund for the Protection and Revival of Wildlife “Natural Heritage.”, 2016. - 256 p. Ecosystem of the Lower Dniester in conditions of increased anthropogenic impact / [Gorbatenky GG, Zelenin A. M., Chorik F. P. et al.]. - Chisinau: Shtiintsa, 1990. - 206 p. Yaroshenko M.F. Hydrofauna of the Dniester. - M.: Publishing House of the Academy of Sciences of the USSR, 1957. - 168 p. Yaroshenko, M.F., Ganya, I.M., Valkovskaya, O.P., and Naberezhny, A.M., On the Ecology and Commercial Importance of Some Dniester Fish, Bul. Of Mol. Branch of USSR Academy of Sciences. - Chisinau, 1951. - P. 273 - 298. Acvaproiect SRL. [Longitudinal and transverse profiles of the Dniester river at the Chisinau main water intake site for 2016 and a change in the longitudinal profile since 1968. Prepared as part of the activities of SA Apă-Canal Chișinău “Măsuri hidrotehnice prioritare ce garantează funcționarea prizei de apă pentru alimentarea cu apă a or. Chișinău la debitele minimale din r. Nistru”]. [BIOTICA EA] Assessment of the possibility of creating a regulated spawning ground on the right bank of the Dniester. Draft report for the OSCE [2015]. - 46 p. Bulat, Dumitru. Ihtiofauna Republicii Moldova: amenințări, tendințe și recomandări de reabilitare: Monografie / Dumitru Bulat; Acad. de Științe a Moldovei, Inst. De Zoologie al Acad. de Științe a Moldovei. – Chișinău: S. n., 2017 (Tipog. «Foxtrot»). - 343 p. Usatîi, Ad., Usatîi, M., Șaptefrați, N., Dadu, A. Resursele piscicole naturale ale Republicii Moldova. ed. Balacron, Chișinău, 2016. 124 p. Usatîi M. Evoluția, conservarea și valorificarea durabilă a diversității ihtiofaunei ecosistemelor acvatice ale Republicii Moldova. Teza de dr. hab. In șt. biol. ... pe spec. 03.00.18 – Hidrobiologie. Chişinău, 2004.

ANNEX I.

TAXONOMIC COMPOSITION OF THE FISH FAUNA IN THE DNIESTER BASIN BEFORE AND AFTER THE REGULATION OF RUNOFF Species Ord. Petromyzontiformes Fam. Petromyzontidae Ukrainian brook lamprey Eudontomyzon mariae (Berg, 1931) Ord. Acipenseriformes Fam. Acipenseridae Starry sturgeon Acipenser stellatus (Pallas, 1771) Sturgeon Huso huso (Linnaeus, 1758) Russian sturgeon Acipenser gueldenstaedtii (Brandt et Ratzeburg, 1833) Thorn sturgeon Acipenser nudiventris (Lovetsky, 1828) Sterlet Acipenser ruthenus (Linnaeus, 1758) Ord. Anguilliformes Fam. Anguillidae European eel Anguilla anguilla (Linnaeus, 1758) Ord. Clupeiformes Fam. Clupeidae Black Sea shad Alosa tanaica (Grimm, 1901) Pontic shad Alosa immaculata (Bennett, 1835) Azov shad Alosa maeotica (Grimm, 1901) Black Sea sprat Clupeonella cultriventris (Nordmann, 1840) Ord. Salmoniformes Fam. Salmonidae Brown trout Salmo trutta fario (Linnaeus, 1758) Fam. Thymallidae European grayling Thymallus thymallus (Linnaeus, 1758) Ord. Esociformes Fam. Esocidae Northern pike Esox lucius (Linnaeus, 1758) Fam. Umbridae Mudminnow Umbra krameri (Walbaum, 1792) Ord. Cypriniformes Fam. Cyprinidae European carp Cyprinus carpio (Linnaeus, 1758 Crap) Crucian carp, Carassius carassius (Linnaeus, 1758) Goldfish Carassius auratus (Linnaeus, 1758) Common barbel Barbus barbus (Linnaeus, 1758) Romanian barbel Barbus petenyi (Heckel, 1852) Tench Tinca tinca (Linnaeus, 1758) Common nase Chondrostoma nasus (Linnaeus, 1758) Gudgeon Gobio gobio (Linnaeus, 1758)

Before regulation, Dniester as a wholea

After regulation Lowlands Middle and the Dniesterb estuaryc



  



 

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 

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ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

Species Ukrainian gudgeon Gobio sarmaticus (Berg, 1949) Carpathian gudgeon Gobio carpathicus (Vladykov, 1925) Northern whitefin gudgeon Romanogobio belingi (Slastenenko, 1934) Kessler's gudgeon Romanogobio kessleri (Dybowski, 1862) Stone moroko Pseudorasbora parva (Temminck &Schlegel, 1846) Common bream Abramis brama (Linnaeus, 1758) White-eye bream Ballerus sapa (Pallas, 1814) Blue bream Ballerus ballerus (Linnaeus, 1758) White bream Blicca bjoerkna (Linnaeus, 1758) Zanthe Vimba vimba (Linnaeus, 1758) Common roach Rutilus rutilus (Linnaeus, 1758) Azov roach Rutilus heckelii (Nordmann, 1840) Black Sea roach Rutilus frisii (Nordmann, 1840) European bitterling, common bitterling Rhodeus amarus (Bloch, 1782) Asp Aspius aspius (Linnaeus, 1758) Sabrefish Pelecus cultratus (Linnaeus, 1758) Common chub Squalius cephalus (Linnaeus, 1758) Ide Leuciscus idus (Linnaeus, 1758) Common minnow Phoxinus phoxinus (Linnaeus, 1758) Common dace Leuciscus leuciscus (Linnaeus, 1758) Dnieper chub Petroleuciscus borysthenicus (Kessler, 1859) Common rudd Scardinius erythrophthalmus (Linnaeus, 1758) Silver carp Hypophthalmichthys molitrix (Valenciennes, 1844) Bighead carp Hypophthalmichthys nobilis (Richardson, 1844) Grass carp Ctenopharyngodon idella (Valenciennes, 1844) Black carp Mylopharyngodon piceus (Richardson, 1846) Sunbleak Leucaspius delineatus (Heckel, 1843) Common bleak Alburnus alburnus (Linnaeus, 1758) Pontian shemaya Alburnus sarmaticus (Freyhof et Kottelat, 2007) Riffle minnow Alburnoides bipunctatus (Bloch, 1782) Fam. Balitoridae Stone loach Barbatula barbatula (Linnaeus, 1758) Fam. Cobitidae Siberian loach Cobitis melanoleuca (Nichols, 1925) Azov loach Cobitis tanaitica (Bacescu et Mayer, 1969) Spined loach Cobitis taenia (Linnaeus, 1758) Danube loach Cobitis elongatoides (Bacescu et Maier, 1969) Northern golden loach Sabanejewia baltica (Witkowski, 1994) Balkan golden loach Sabanejewia balcanica (Karaman, 1922) European weather loach Misgurnus fossilis (Linnaeus, 1758) Ord. Siluriformes Fam. Siluridae Wels catfish Silurus glanis (Linnaeus, 1758 Somn) Ord. Gadiformes Fam. Lotidae Burbot Lota lota (Linnaeus, 1758) Ord. Gasterosteiformes Fam. Gasterosteidae Ukrainian stickleback Pungitius platygaster (Kessler, 1859) Three-spined stickleback Gasterosteus aculeatus (Linnaeus, 1758) Ord. Sygnathiformes Fam. Sygnathidae

Before regulation, Dniester as a wholea 

After regulation Lowlands Middle and the b Dniester estuaryc   



 



  



   

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ANNEX I. TAXONOMIC COMPOSITION OF THE FISH FAUNA IN THE DNIESTER BASIN BEFORE AND AFTER THE REGULATION OF RUNOFF

Species Black-striped pipefish Syngnathus abaster (Risso, 1827) Straightnose pipefish Nerophis ophidion (Linnaeus, 1758) Broadnosed pipefish Syngnathus typhle (Linnaeus, 1758) Ord. Atheriniformes Fam. Atherinidae Big-scale sand smelt Atherina boyeri (Risso, 1810) Ord. Perciformes Fam. Percidae European perch Perca fluviatilis (Linnaeus, 1758 Biban) Zander Sander lucioperca (Linnaeus, 1758) Volga pikeperch Sander volgensis (Gmelin, 1789) Ruffe Gymnocephalus cernuus (Linnaeus, 1758) Donets ruffe Gymnocephalus acerina (Gmelin, 1789) Streber Zingel streber (Siebold, 1863) Common zingel Zingel zingel (Linnaeus, 1766) Common percarina Percarina demidoffii (Nordmann, 1840) Fam. Gobiidae Kessler's goby Neogobius kessleri (Guenther, 1861) Mushroom goby Ponticola eurycephalus (Kessler, 1874) Racer goby Babka gymnotrachelus (Kessler, 1857) Round goby Neogobius melanostomus (Pallas, 1814) Tubenose goby Proterorhinus marmoratus (Pallas, 1814) Monkey goby Neogobius fluviatilis (Pallas, 1814) Toad goby Mesogobius batrachocephalus (Pallas, 1814) Grass goby Zosterisessor ophiocephalus (Pallas, 1814) Black goby Gobius niger (Linnaeus, 1758) Longtail dwarf goby Knipowitschia longecaudata (Kessler, 1877) Brauner's tadpole-goby Benthophiloides brauneri (Beling & Iljin, 1927) Black Sea tadpole-goby Benthophilus nudus (Berg, 1898) Stellate tadpole-goby Benthophilus stellatus (Sauvage, 1874) Fam. Centrarchidae Pumpkinseed Lepomis gibbosus (Linnaeus, 1758) Fam. Odontobutidae Chinese sleeper Perccottus glenii (Dybowski, 1877) Ord. Scorpaeniformes Fam. Cottidae European bullhead Cottus gobio (Linnaeus, 1758) Alpine bullhead Cottus poecilopus (Heckel, 1837) Ord. Mugiliformes Fam. Mugilidae Flathead grey mullet Mugil cephalus (Linnaeus, 1758) Leaping mullet Liza saliens (Risso, 1810) Golden grey mullet Liza aurata (Risso, 1810) Redlip mullet Lisa haematocheila (Temminck & Schlegel, 1845) Ord. Pleuronectiformes Fam. Pleuronectidae European flounder Platichthys flesus (Linnaeus, 1758) a - According to Berg, 1949.

b - According to Bulat, 2017.

Before regulation, Dniester as a wholea 

After regulation Lowlands Middle and the b Dniester estuaryc 

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c - According to Snigirev, 2012.

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ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

ANNEX II

WATER CONSUMPTION IN THE BASIN DOWNSTREAM OF HPP-2 (MLN M3 PER YEAR) Year 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997

Total 250 260 265 279 290 305 320 338 357 374 388 405 423 440 461 481 503 521 542 562 588 612 628 640 656 698 675 673 613 583 575 545 514

Water supply Including UKRb MOLa 150 100 155 105 160 105 165 114 172 118 185 120 195 125 208 130 222 135 234 140 246 142 260 145 275 148 290 150 306 155 322 159 338 165 350 171 365 177 380 182 400 188 418 194 430 198 440 200 451 205 488 210 466 209 466 207 408 205 380 203 374 201 346 199 317 197

Total 109 118 129 140 155 168 183 196 211 229 245 263 280 299 318 336 350 369 392 423 468 492 516 536 519 707 349 576 461 588 362 267 137

Irrigation Including MOLa UKRb 89 20 96 22 104 25 112 28 120 35 129 39 139 44 149 47 160 51 174 55 187 58 200 63 212 68 226 73 240 78 255 81 265 85 280 89 298 94 325 98 367 101 387 105 408 108 426 110 409 110 587 120 269 80 466 110 361 100 473 115 292 70 207 60 97 40

Total water consumption Including Total MOLa UKRb 359 239 120 378 251 127 394 264 130 419 277 142 445 292 153 473 314 159 503 334 169 534 357 177 568 382 186 603 408 195 633 433 200 668 460 208 703 487 216 739 516 223 779 546 233 817 577 240 853 603 250 890 630 260 934 663 271 985 705 280 1056 767 289 1104 805 299 1144 838 306 1176 866 310 1175 860 315 1405 1075 330 1024 735 289 1249 932 317 1074 769 305 1171 853 318 937 666 271 812 553 259 651 414 237

ANNEX II. WATER CONSUMPTION IN THE BASIN DOWNSTREAM OF HPP-2 (MLN M3 PER YEAR)

Year 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018c 2019c 2020c 2021c 2022c 2023c 2024c 2025c 2026c 2027c 2028c

Total 508 434 366 338 332 327 325 328 330 332 332 328 325 324 324 323 319 319 320 320 324 331 340 348 357 369 385 399 405 417 445

Water supply Including UKRb MOLa 313 195 244 190 206 160 178 160 172 160 167 160 165 160 168 160 170 160 172 160 172 160 168 160 165 160 164 160 164 160 163 160 159 160 159 160 160 160 160 160 164 160 168 163 172 168 176 172 180 177 184 185 188 197 192 207 196 209 205 212 230 215

Total 93 81 67 59 61 64 60 57 56 68 59 59 59 60 59 59 59 61 61 61 68 75 112 138 204 250 296 342 388 434 480

Irrigation Including MOLa UKRb 63 30 61 20 48 19 40 19 42 19 45 19 41 19 38 19 38 18 50 18 41 18 41 18 39 20 40 20 39 20 39 20 39 20 39 22 39 22 39 22 43 25 45 30 72 40 88 50 144 60 180 70 216 80 252 90 288 100 324 110 360 120

Total water consumption Including Total MOLa UKRb 601 376 225 515 305 210 433 254 179 397 218 179 393 214 179 391 212 179 385 206 179 385 206 179 386 208 178 400 222 178 391 213 178 387 209 178 384 204 180 384 204 180 383 203 180 382 202 180 378 198 180 380 198 182 381 199 182 381 199 182 392 207 185 406 213 193 452 244 208 486 264 222 561 324 237 619 364 255 681 404 277 741 444 297 793 484 309 851 529 322 925 590 335

a - Excluding return water consumption of CJSC “Moldavskaya GRES”. b - Odessa region, excluding water consumption in the Vinnitsa and Cherkasy regions of Ukraine. c - Expert assessment. Data Sources: Water Use Report ...; Government of the Republic of Moldova, 2011; archives of the Ministry of Land Reclamation and Water Resources of the MSSR; Agency “Apele Moldovei”; Lower Dniester National Natural Park; Department of Water Resources of Odessa region; expert estimates and forecast (M.S. Penkov, A.N. Kalashnik).

ANALYSIS OF THE EFFECTS OF DNIESTER RESERVOIRS ON THE STATE OF THE DNIESTER RIVER

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