Acta Limnologica Brasiliensia, 2010, vol. 22, no. 2, p. 133-146 doi: 10.4322/actalb.02202003 Aquatic macrophytes in natural and managed wetlands of Rio Grande do Sul State, Southern Brazil Macróitas aquáticas em áreas úmidas naturais e manejadas do Rio Grande do Sul, sul do Brasil Ana Silvia Rolon, Henrique Flores Homem and Leonardo Maltchik Ecologia e Conservação de Ecossistemas Aquáticos, Universidade do Vale do Rio dos Sinos – UNISINOS, CEP 93022-000, São Leopoldo, RS, Brazil Abstract: Aim: his study gathers the main results obtained from studies regarding dynamic of aquatic macrophyte community in natural and managed wetlands of Southern Brazil. We analyzed the aquatic macrophytes diversity in wetlands of Southern Brazil, the environmental factors that determine the structure of the aquatic macrophyte community in fragmented wetlands, the efects of loods on the dynamics of macrophytes, and the contributions to the rice ield for the conservation of aquatic macrophytes; Methods: he information was obtained from several researches carried in several spatial scales and diferent wetlands types over the last 10 years in Southern Brazil; Results: he studies have reported the occurrence of approximately 250 species of aquatic macrophytes. Wetland area, habitat diversity, altitude and hydroperiod were determinant for macrophyte richness and composition in wetlands of Southern Brazil. Furthermore, lood events, long or short-term ones, are strongly associated to the structure of the aquatic macrophyte community. he rice ield systems of Southern Brazil (crops and irrigation channel) shelter a representative number of species of macrophyte found at natural wetlands in this region. he agricultural practices adopted over rice cultivation cycle in the rice ields have inluenced the macrophyte richness and biomass. he diferent hydrological management practices adopted after the harvesting period (presence or lack of water surface) did not inluence the macrophyte richness and biomass, however it inluenced the species composition; Conclusions: he increasing process of wetland degradation (e.g. fragmentation, lood control and rice ield expansion) presents a threat to the conservation aquatic macrophyte species. Keywords: aquatic plant, diversity, conservation, Neotropical region. Resumo: Objetivo: Este estudo reúne os principais resultados obtidos em trabalhos sobre a dinâmica da comunidade de macróitas aquáticas em áreas úmidas naturais e manejadas do sul do Brasil. Nós analisamos a diversidade de macróitas aquáticas do sul do Brasil, os fatores ambientais que determinam a estrutura da comunidade de macróitas aquáticas nas áreas úmidas, o efeito das inundações na dinâmica da comunidade e a contribuição dos arrozais para a conservação das macróitas aquáticas; Métodos: As informações foram obtidas de vários trabalhos realizados em diversas escalas espaciais e diferentes tipos de áreas úmidas ao longo dos últimos 10 anos no sul do Brasil; Resultados: Os estudos têm reportado a ocorrência de aproximadamente 250 espécies de macróitas aquáticas. O tamanho da área úmida, diversidade de habitats, altitude e hidroperíodo foram determinantes para a riqueza e a composição de espécies em áreas úmidas do sul do Brasil. Além disso, os eventos de inundação, de longa ou curta duração, estão fortemente relacionados à estrutura da comunidade de macróitas. Os sistemas orizícolas sul do Brasil (lavouras e canais de irrigação) abrigam um número representativo de espécies de macróitas aquáticas encontradas em áreas úmidas naturais dessa região. As práticas agrícolas adotadas ao longo do ciclo de cultivo nos arrozais inluenciaram a biomassa e a riqueza de macróitas. As práticas de manejo adotadas no período póscolheita (presença ou ausência de água supericial) não inluenciaram a riqueza e a biomassa de macróitas, mas inluenciaram a composição de espécies; Conclusões: O aumento do processo de degradação das áreas úmidas (e.g. fragmentação, controle de inundações e expansão de arrozais) constitui uma ameaça a conservação das espécies de plantas aquáticas. Palavras-chave: planta aquática, diversidade, conservação, região Neotropical. Biological Limnology e-mail: asrolon@gmail.com, hfhomem@gmail.com, maltchik@unisinos.br 134 Rolon, AS., Homem, HF. and Maltchik, L. 1. Introduction Wetlands are important sites for biological conservation because they support a rich biodiversity and present high productivity (Mitsch and Gosselink, 2000). However, biodiversity in wetlands has been reduced worldwide (Shine and Klemm, 1999) – a loss of more than 50% of these ecosystems in the last century due to human activities (Shine and Klemm, 1999). Subtropical and tropical wetlands have come under increasing pressure since the 1950s, and the wetland loss in South America over the 90’s decade was estimated at 6% of total wetlands of continent (OECD, 1996). he impact of wetland loss on biodiversity was veriied by the decline of populations of several wetland-dependent species (Millennium Ecosystem Assessment, 2005). he fragmentation of wetlands is one of the main problems related to the conservation of the biodiversity. he change in the landscape has caused a reduction in the area and connectivity of natural habitats. Understanding the biodiversity patterns in fragmented wetlands of the Southern Brazil is extremely important to guide policies for biodiversity conservation. he principle that a large area supports more species (Arrhenius, 1921; Rosenzweig, 1995) has been put into practice in conservational planning. By assuming wetlands to be ecological islands surrounded by terrestrial habitats, the relationships among species richness and wetland size were extensively used for wetland management (Hall et al., 2004). Agriculture is one of the main human activities responsible for the decline of natural wetlands throughout the world, being the conservation of the species jeopardized by the impact of irrigated agriculture expansion (Millennium Ecosystem Assessment, 2005). Rice is the most important cereal crop in the developing world (Juliano, 1993). In 2003, approximately 151 million ha of land were cultivated with rice worldwide (FAOSTAT, 2008). Biodiversity conservation in agricultural landscape is an ecological challenge (Marshall et al., 2003). Several studies have demonstrated the contribution of managed ecosystems, like as, rice ields and irrigation channels, providing habitats for establishment of aquatic organisms (Elphick, 2000; Goulder, 2008; Herzon and Helenius, 2008). Wetland studies are important in Brazil, mainly because we are referring to a country with the highest rates of biodiversity and freshwater ecosystems (Agostinho et al., 2005; Lewinsohn and Prado, 2005). he hydrological characteristic of Southern Brazil is the high diversity and Acta Limnologica Brasiliensia density of wetlands; approximately 11% of total area of Rio Grande do Sul State (Maltchik et al., 2003). In Southern Brazil, approximately 72% of wetlands are smaller than 1 km2 (Maltchik, 2003). his strong fragmentation is due to agricultural expansion, mainly irrigated rice fields (Gomes and Magalhães, 2004). Conservative estimates indicate that approximately 90% of wetlands have disappeared in Southern Brazil (Maltchik, 2003). he increasing process of degradation of these ecosystems presents a threat to the aquatic biodiversity conservation in Southern Brazil, including the aquatic macrophytes. his study gathers the main results obtained from several studies carried out over the last 10 years to identify the spatial and temporal dynamics of aquatic macrophytes in wetlands of Rio Grande do Sul. he main goals were to: (1) carry out a survey of the aquatic macrophytes diversity in wetlands of Rio Grande do Sul; (2) analyse the efects of environmental factors that determine the structure of the aquatic macrophytes in fragmented wetlands, (3) investigate the efects of loods on the dynamics of macrophytes, and (4) analyse the contributions to the rice ield for the conservation of aquatic macrophytes. This study gathers information obtained from several researches carried in several spatial scales and diferent wetlands types (e.g. marshes, shallow lakes, oxbow lakes and rice ields). Such information may be used as base for planning the conservational guidelines and the sustainable use of the wetlands of Southern Brazil. 2. Methods he inluence of environmental variables on the macrophyte richness and composition of the species was analysed in three spatial scales: the Rio Grande do Sul State (Rolon and Maltchik, 2006), the middle part of the Coastal Plain (Rolon et al., 2008), and the Rio do Sinos basin (Maltchik et al., 2002). Such studies were carried along eight years (2000-2007). he efect of loods on the structure of the macrophyte community was investigated in wetlands of the Rio dos Sinos basin between 2000 and 2005 (Maltchik et al., 2004, 2005, 2007; Schott et al., 2005). he diversity and the dynamics of aquatic macrophytes in rice ields in Southern Brazil were assessed in six rice ields (Rolon and Maltchik, 2010) and in four irrigation channels (unpublished data) of the Coastal Plain of Rio Grande do Sul between 2006 and 2007. he survey of aquatic macrophyte biodiversity was carried between 2000 and 2009. 2010, vol. 22, no. 2, p. 133-146 Aquatic macrophytes in natural and managed wetlands... 135 3. Results and Discussion 3.1. Diversity of aquatic macrophytes in wetlands of Southern Brazil Our studies carried recently in wetlands in Southern Brazil, which focused on diferent spatial scales, have reported the occurrence of approximately 250 species of aquatic macrophytes (Maltchik et al., 2002; Bertoluci et al., 2004; Rolon et al., 2004; Rolon et al., 2008) (Table 1). he species richness of aquatic macrophytes of Rio Grande do Sul is estimated around 500 species (Irgang and Gastal, 1996); however, such estimation was based on a larger number of habitats, including the estuarine wetlands and the great lakes of the Coastal Plain. he assemblage of aquatic macrophyte from wetlands of Southern Brazil is represented by a variety of biological types (submerged, loating, emergent and amphibious) and taxonomic groups, since macro-algae until angiosperms. he emergent species are dominant in wetlands of Southern Brazil and in this group, Cyperaceae, Poaceae and Asteraceae are the outstanding families. he highest level of dominance in number of emergent species in relation to the number of hydrophyte species (loating and submerged) in the wetlands is related to the shallowness of the wetlands as well as to the intermittent character of some systems. Some species of aquatic macrophyte such as Luziola peruviana, Ludwigia peploides, Polygonum punctatum and Nymphoides indica are among the most frequent species of the wetlands of Southern Brazil (Rolon et al., 2004). Nevertheless, the majority of the species has presented low occurrence rate, indicating high spatial variability in the macrophyte community. Such spatial variability (β-diversity) is a very important characteristic for the wetlands conservation. he distribution of aquatic macrophytes occurs heterogeneously in Rio Grande do Sul (Figure 1). he areas with high diversity of aquatic macrophytes are at the middle part of the Coastal Plain of Rio Grande do Sul, while the areas with low diversity are distributed along the Upland at the Northern part of the state. The differences in the richness of aquatic macrophytes at the wetlands may result from the environmental heterogeneity in the landscape scale (e.g. altitude variations, size of the ecosystems, hydroperiod, connectivity and environmental matrix) or in micro-scales (e.g. habitat diversity and physic-chemical conditions of the water and sediment). Figure 1. Distribution of aquatic macrophyte richness in wetlands of Rio Grande do Sul State. he large points represent wetlands with high diversity of aquatic macrophytes and small points represent poor-richness wetlands. 3.2. Environmental gradients and macrophyte diversity in fragmented wetlands of Southern Brazil he area is one of the main environmental parameters related to the richness of aquatic macrophyte (Oertli et al., 2002; Jones and Maberly, 2003; Dahlgren and Ehrlén, 2005). In Southern Brazil, the macrophyte richness, in general, is conditioned by wetland area in diferent spatial scales (Maltchik et al., 2002; Rolon and Maltchik, 2006; Rolon et al., 2008). he high species richness in larger areas may be the direct result of an increase in potential areas for colonization (the area efect per se, Kohn and Walsh, 1994; Ricklefs and Lovette, 1999). However, there are other hypotheses for the joint increase of species richness and area. he habitat diversity hypothesis suggests that the number of species increases as area increases because the number of habitat rises (Kohn and Walsh, 1994; Ricklefs and Lovette, 1999). However, it is diicult to assess the independent efects of area and habitat diversity on richness because usually they are highly correlated (Ricklefs and Lovette, 1999). In wetlands of Coastal Plain of Southern Brazil, it was noticed that both area per se and habitat diversity determined macrophyte species richness (Rolon et al., 2008). The altitude was a limiting factor for the macrophyte richness in Southern Brazil wetlands (Rolon and Maltchik, 2006). Nevertheless, the effect of altitude on macrophyte richness was correlated to the area efects, making it diicult to assess the proportional contribution of each of these variables to species richness (Rolon and Maltchik, 2006). he connectivity of the wetlands is another factor related to the variation of altitude in Southern Brazil and it is possibly important for the structure 136 Rolon, AS., Homem, HF. and Maltchik, L. Acta Limnologica Brasiliensia Table 1. Aquatic macrophyte species in wetlands of Southern Brazil. Family Charophyta CHARACEAE Briophyta SPHAGNACEAE RICCIACEAE Pteridophyta EQUISETACEAE LYCOPODIACEAE MARSILEACEAE PTERIDACEAE SALVINIACEAE Magnoliophyta THELYPTERIDACEAE ACANTHACEAE ALISMATACEAE AMARANTHACEAE APIACEAE ARACEAE ARALIACEAE ASTERACEAE Species Nitella sp.1 Nitella sp.2 Nitella sp.3 Nitella sp.4 Sphagnum sp. Riccia stenophylla Spruce Ricciocarpus natans (L.) Corda Equisetum giganteum L. Lycopodium alopecuroides L. Marsilea ancylopoda A. Braun Regnellidium diphyllum Lindm. Acrostichum sp. Azolla iliculoides Lam. Salvinia herzogii de la Sota Salvinia minima Bak. Thelypteris sp. Hygrophila brasiliensis (Spr) Lindau Hygrophila guaianensis Nees Hygrophila helodes Nees Echinodorus grandilorus (Cham & Schl.) Michx. Echinodorus longiscapus Arech. Echinodorus tenellus (Mart.) Buch. Sagittaria montevidensis Cham & Schl. Alternanthera brasiliana (L.) Kuntze Alternanthera philoxeroides (Mart.) Gris. Centella asiatica (L.) Urb. Eryngium eburneum Decne. Eryngium horridum Malme Eryngium pandanifolium Cham & Schl. Eryngium sp. Lilaeopsis brasiliensis (Glaziou) Affolter Lilaeopsis carolinensis Coutter & Rose Colocasia esculenta (L.) Schott. Lemna minuta Kunth Lemna valdiviana Phil. Pistia stratiotes L. Spirodela intermedia W. Koch Wolfia brasiliensis Wedell Wolfiella lingulata (Hegelm.) Hegelm. Wolfiella oblonga (Phil.) Hegelm. Zantedeschia aethiopica (L.) Spr. Hydrocotyle bonariensis Lam. Hydrocotyle ranunculoides L. f. Hydrocotyle verticillata Thumb Aster squamatus (Spreng.) Hier. Baccharis microcephala (Less.) DC. Baccharis trimera (Less.) DC. Bidens laevis (L.) B.S.P. Bidens pilosa L. Conyza pampeana (Parodi) Cabrera 2010, vol. 22, no. 2, p. 133-146 Aquatic macrophytes in natural and managed wetlands... Table 1. Continued... Family Magnoliophyta BEGONIACEAE CABOMBACEAE CAMPANULACEAE CERATOPHYLLACEAE CLEOMACEAE COMMELINACEAE CONVOLVULACEAE CYPERACEAE Species Cotula coronopifolia L. Enydra anagallis Gardner Eupatorium sp Gymnocoronis spilanthoides (Don.) DC. Hypochoeris sp Jaegeria hirta (Lag.) Less. Mikania micrantha H. B. K. Mikania sp. Pluchea sagittalis (Lam.) Cabr. Senecio bonariensis H. & A. Senecio brasiliensis Less. Senecio jurguensii Less. Senecio tweediei Hook & Arn. Vernonia nudilora Less. Begonia cucullata Willd. Cabomba caroliniana A. Gray Pratia hederacea (Cham.) G. Don Ceratophyllum demersum L. Cleome hassleriana Chodat Commelina diffusa Burm. f Floscopa glabrata (Kunth) Hassk. Ipomoea cairica (L.) Sweet. Androtrichum trigynum (Spreng.) H.Pfeiff. Bulbostylis capillaris (L.) C.B. Clarke Carex sp. Cyperus barrosianus Herter Cyperus berroi (C. B. Cl.) Barros Cyperus difformis L. Cyperus esculentus L. Cyperus ferax Rich. Cyperus giganteus Vahl. Cyperus haspan L. Cyperus hermaphroditus (Jacq.) Stand. Cyperus imbricatus Retz. Cyperus intricatus Schr. & Schult. Cyperus laetus Kunth Cyperus lanceolatus Poir. Cyperus luzulae (L.) Retz Cyperus megapotamicus Kunth Cyperus polystachyos Rottb. Cyperus prolixus H.B.K. Cyperus relexus Vahl Cyperus sesquilorus (Torrey) Mattf. & Kük Cyperus surinamensis Rottb. Eleocharis acutangula (Roxb) Schult. Eleocharis bonariensis Nees Eleocharis elegans (Kunth) Roem. & Schult. Eleocharis interstincta (Vahl) Roem. & Schult. Eleocharis maculosa (Vahl) Roem & Schult Eleocharis minima Kunth Eleocharis radicans (Poir.) Kunth Eleocharis sellowiana Kunth Eleocharis viridans Kük. ex Osten 137 138 Rolon, AS., Homem, HF. and Maltchik, L. Acta Limnologica Brasiliensia Table 1. Continued... Family Magnoliophyta DROSERACEAE ERIOCAULACEAE EUPHORBIACEAE FABACEAE HALORAGACEAE HALORAGACEAE HYDROCHARITACEAE JUNCACEAE LAMIACEAE LENTIBULARIACEAE LIMNOCHARITACEAE LINDERNIACEAE LYTHRACEAE MAYACACEAE Species Fimbristylis autumnalis (L.) Roem. & Schult. Fimbristylis dichotoma (L.) Vahl. Fimbristylis sp. Fimbristylis squarrosa Vahl Kyllinga odorata Vahl Kyllinga vaginata Lam. Oxycaryum cubense (Poepp. & Kunth) Palla Rhynchospora barrosiana Guagl. Rhynchospora brittonii Gale Rhynchospora corymbosa (L.) Britton Rhynchospora holoschoenoides (Rich.) Herter Schoenoplectus californicus (C.A. Mey.) Soják Scirpus sp. Scirpus submersus C. Wright Drosera brevifolia Pursh Eriocaulon modestum Kunth Sebastiania commersoniana (Baill.) L.B. Smith & R.J. Downs Sebastiania schottiana (M. Arg.) M.Arg. Bauhinia foricata Link Desmodium adscendens (Sw.) DC. Erythrina crista-galli L. Inga uruguensis Hook. & Arn. Mimosa bimucronata (DC) O Kze Sesbania punicea (Cav.) Benth Sesbania virgata (Cav.) Pers. Vigna longifolia (Benth.) Verdc. Vigna luteola (Jacq.) Benth. Laurembergia tetrandra (Schott ex Spreng.) Kanitz Myriophyllum aquaticum (Vell.) Verdcourt Proserpinaca palustris L. Egeria densa Planch. Limnobium laevigatum (Humb. & Bonpl. ex Willd.) Heine Najas microdon A. Br. Juncus bufonius L. Juncus capillaceus Lam. Juncus dombeyanus Gay Juncus effusus L. Juncus marginatus Rostk. Juncus microcephalus H.B.K. Juncus pallescens Lam. Juncus scirpoides Lam. Juncus sellowianus Kunth Hyptis balansae Briq. Hyptis fasciculada Benth. Utricularia foliosa L. Utricularia gibba L. Utricularia inlata Walter Utricularia praelonga A.St.-Hil. & Girard Utricularia subulata L. Utricularia tricolor A. St.-Hil. Hydrocleys nymphoides (Willd.) Buch. Micranthemum umbrosum (Walter) Blake Cuphea carthagenensis (Jacq.) Macbride Mayaca luviatilis Aubl. 2010, vol. 22, no. 2, p. 133-146 Aquatic macrophytes in natural and managed wetlands... Table 1. Continued... Family Magnoliophyta MELASTOMATACEAE MENYANTHACEAE MORACEAE MYRSINACEAE NYMPHAEACEAE ONAGRACEAE ORCHIDACEAE OXALIDACEAE PHYLLANTHACEAE PLANTAGINACEAE POACEAE Species Mayaca sellowiana Kunth Tibouchina asperior (Cham) Cogn. Tibouchina cisplatensis Cogn. Nymphoides indica (L.) Kuntze Ficus organensis Miq. Myrsine parvifolia A. DC. Nymphaea Ludwigia decurrens Walt Ludwigia grandilora (Michx.) Greuter & Burdet Ludwigia leptocarpa (Nutt.) Hara Ludwigia longifolia (DC.) Hara. Ludwigia multinervia (Hook. & Arn.) Ramam. Ludwigia peploides (Kunth) P.H. Raven Ludwigia peruviana (L.) H. Hara Habenaria sp. Oxalis corniculata L. Phyllanthus sellowianus M. Arg. Bacopa lanigera (C & S) Wettst. Bacopa monnierii (L.) Penn. Bacopa tweedii (Benth.) Parodi Callitriche heterophylla Pursh Callitriche rimosa Fasset Mecardonia tenella (Cham. & Schlecht.) Pennell Plantago australis Lam. Andropogon bicornis L. Briza minor L. Digitaria sp. Echinochloa polystachya (H.B.K.) Hitchc. Echinochloa sp Eragrostis hypnoides (Lam.) Britton, Sterns & Poggenb. Eragrostis sp. 1 Eragrostis sp. 2 Erianthus angustifolius Nees Hymenachne amplexicaulis (Rudge) Nees Imperata brasiliensis Trin. Ischaemum minus J.Presl Leersia hexandra Sw. Luziola peruviana Gmelin Oryza sp. Panicum grumosum Nees Panicum prionitis Nees Panicum racemosum (P. Beauv.) Spreng. Panicum repens L. Panicum rivulare Trin. Panicum sp. 1 Panicum sp. 2 Panicum sp. 3 Panicum sp. 4 Paspalum acuminatum Raddi Paspalum distichum L. Paspalum modestum Mez Paspalum pumilum Nees Paspalum sp Paspalum vaginatum Sw. 139 140 Rolon, AS., Homem, HF. and Maltchik, L. Acta Limnologica Brasiliensia Table 1. Continued... Family Magnoliophyta POLYGALACEAE PONTEDERIACEAE POTAMOGETONACEAE RANUNCULACEAE RUBIACEAE SALICACEAE SOLANACEAE THYMELAEACEAE TYPHACEAE XYRIDACEAE ZINGIBERACEAE of the macrophyte community. In Rio Grande do Sul, regions of low altitude, such as the Coastal Plain and the Central Depression, present high density of wetlands (Maltchik et al., 2003) and are places of high richness of aquatic macrophytes (Figure 1). On the other hand, the low richness in the wetlands of the Upland may be result of the presence of small and isolated wetlands. he hydrological luctuation and hydroperiod are important attributes for macrophyte richness (Rolon and Maltchik, 2006; Maltchik et al., 2007). Macrophyte richness was signiicantly higher in permanent wetlands than in intermittent ones. Furthermore, the smallest and the highest species Species Piptochaetium sp. Polygala leptocaulis Torr. & A.Gray Polygonum acuminatum H.B.K. Polygonum ferrugineum Wedd. Polygonum hidropiperoides Michx. Polygonum lapathifolium L. Polygonum meissnerianum Cham & Schl. Polygonum persicaria L. Polygonum punctatum Ell. Polygonum setaceum Baldw. Polygonum sp. Polygonum stelligerium Cham. Rumex obovatus Danser Eichhornia azurea (Sw.) Kunth Eichhornia crassipes (Mart.) Solms Heteranthera limosa (Sw.) Willd Heteranthera reiniformis Ruiz & Pavon Heteranthera zosterifolia Mart. Pontederia cordata L. Potamogenton sp. Potamogeton ferrugineus Hagstr. Potamogeton spirilliformis Hagstr. Ranunculus apiifolius Persoon. Ranunculus bonariensis Poir. Ranunculus lagelliformis Smith Cephalanthus glabratus (Spreng.) K. Schum. Diodia alata Nees & Mart. Diodia saponariifolia (Cham & Schl.) K. Schum. Hedyotis salzmannii (DC.) Steud. Salix humboldtiana Willd. Solanum americanum Mill. Solanum capsicoides All. Solanum glaucophyllum Desf. Daphnopsis racemosa Griseb. Typha dominguensis Pers. Typha latifolia L. Xyris jupicai L.C.Rich Hedychium coronarium Koenig richness coincided with the lowest and the highest precipitation periods. Brose (2001) noticed that the hydroperiod can be more important than the area to predict the macrophyte richness in intermittent wetlands, where the water loss leads to local extinctions and/or dormancy of hydrophytes, which remain in the permanent wetlands. However, the recovery of the species richness following water table re-establishment is relatively fast in the intermittent wetlands, indicating that dormancy is probably an important plant strategy in these ecosystems. The composition of aquatic macrophytes was determined, as for the richness, by several environmental attributes such: area, diversity of 2010, vol. 22, no. 2, p. 133-146 Aquatic macrophytes in natural and managed wetlands... the habitats, altitude, water conductivity and nutrient concentration (Rolon and Maltchik, 2006; Rolon et al., 2008). A more detailed study in wetlands of Coastal Plain of Rio Grande do Sul has indicated that the structural characteristics of the ecosystem (area and diversity of habitat) and the water chemical conditions inluenced independently the composition of the aquatic macrophytes, presenting additive effects on the macrophyte composition (Rolon et al., 2008). Wetland hydroperiod has also influenced macrophyte composition (Rolon et al., 2008). Among the species typical from permanent wetlands are some euhydrophytes (e.g., Azolla filiculoides, Hydrocotyle ranunculoides, Myriophyllum aquaticum, Salvinia herzogii and Utricularia foliosa). Identifying the main environmental factors that determine the structure of aquatic macrophyte community is essential for establishing the guidelines for the biodiversity conservation of Southern Brazil. Proposals regarding the conservation of biodiversity normally prioritize large areas, with high species richness, high connectivity and occurrence of endemic species. The area was a determining factor for the richness and for the structure of the macrophyte composition in Southern Brazil, indicating that this factor should be considered in the management of the wetlands in Southern Brazil. However, other factors, such as, altitude, habitat diversity and hydroperiod, should be considered. 3.3. Flood and macrophyte community dynamics in natural wetlands The floodplain systems are representative wetlands in Southern Brazil. The flood pulse concept suggests that the lood is an important event on the community structure and functioning of river-floodplain system (Junk et al., 1989). he looding event is a complex variable, which encompasses several attributes (e.g. duration, frequency, amplitude and timing), which can afect the biota in diferent ways. According to Casanova and Brock (2000), the lood compromised the penetration of light and the ability of emergent plants to reach the surface by increasing the water depth. herefore, the lood pulse can export the aquatic plants across the river-loodplain system. he duration of the lood is an important agent of biological stability in wetland systems (Turner and Dale, 1998). Several studies have investigated the impact of the long-term loods in the aquatic vegetation in large river-loodplain systems (Junk, 1989; Ferreira, 2000; Padial et al., 2009); however, 141 information regarding the efect of short-term loods on the structure of aquatic macrophytes is still rare in the literature. he changes of the environmental conditions due to long-term loods may change the structure of the macrophyte community by replacing the species, changing the richness and varying the biomass or the relative abundance of the species. In a shallow lake associated to the river loodplain, the stability of the macrophyte community was jeopardized after long-term loods (38 days), presenting alterations in both richness and total biomass of macrophytes (Maltchik et al., 2004). While short or very short-term floods (1 to 3 days) changed the biomass of the aquatic macrophyte assemblage, they did not modify the species richness (Schott et al., 2005; Maltchik et al., 2007). Another important property of lood disturbance on community stability in aquatic ecosystems is the lood frequency. In Southern Brazil, the increase of the lood frequency, even the short-term ones, has reduced significantly the resistance of the macrophyte community (Maltchik et al., 2005). Furthermore, the absence of dominance was observed only in the shallow lake with the highest number of lood events (Maltchik et al., 2005). he decrease of resistance of the community may be related to the recurrence of loods, since the shortest interval between lood events may hinder the growth of the macrophyte and as consequence its reestablishment (Maltchik et al., 2005, 2007). he number of macrophyte species with modiied biomass after the looding events increased with the recurrence of loods in a loodplain palustrine wetland of Southern Brazil (Maltchik et al., 2007). While no species had their biomass modiied after the irst lood, the biomass of one and three species of macrophytes were modiied after the subsequent loods (Maltchik et al., 2007). he hydrological luctuation and connectivity provided by the lood events afect the macrophyte diversity (Santos and homaz, 2007). Furthermore, flood and drawdown events affect directly the establishment and survival of aquatic plants (Blanch et al., 1999; Seabloom et al., 2001). he degree of tolerance of species to hydrological extremes (loods and drawdown events) determines the structure of macrophyte communities (Van Geest et al., 2005a, b). he alternation of hydrological phases (with loods, without loods and drawdown) has inluenced the richness, biomass and the composition of aquatic macrophytes in several wetland types in Southern Brazil 142 Rolon, AS., Homem, HF. and Maltchik, L. (Maltchik et al., 2005, 2007; Schott et al., 2005). In general, the lower richness of aquatic macrophyte was associated to the period of occurrence of loods (Maltchik et al., 2005, 2007; Schott et al., 2005). According to Gopal and Junk (2000), the hydrological fluctuation contributes to a high biodiversity in loodplain systems. he increase in the species richness in a subtropical palustrine wetland resulted of the resistance of several species during both hydrological extremes (flood and drought) and the establishment of new species along the drawdown phase (Maltchik et al., 2007). he variation of the macrophyte biomass along the hydrological phases occurred differentially between the wetland types of Southern Brazil. While in some systems, the biomass was lower in looded periods (Malchik et al., 2005); in others, the biomass was higher in the period without the presence of the surface water (Schott et al., 2005). According to Neiff (1975), while the peak of biomass of some macrophyte species occurs over the lood period, other species show high biomass values at low water level. hese variations in the biomass peaks of species determine the dynamics of community biomass in floodplain systems. Maltchik et al. (2007) have noticed that the biomass peak of Eichhornia azurea during the lood phase and the biomass peak of Luziola peruviana and Eleocharis interstincta during the drawdown phase have contributed to maintain the mean biomass of macrophytes similar between both hydrological phases. hese results have indicated that the lood events, long or short-term ones, are strongly associated to the structure of the aquatic macrophyte community in several wetland types. hus, any alteration in the hydrological regime (duration, frequency, etc.) will present several implications for the composition, richness and abundance of the aquatic macrophytes in wetlands of Southern Brazil. 3.4. Rice fields and irrigation channels Rice ields have been recognized worldwide as having potential value for many aquatic species (Bambaradeniya and Amerasinghe, 2003; Elphick and Oring, 2003). Several new practices have been proposed to foster biodiversity conservation on agricultural wetlands as the management of water depth, ditches, and post-harvest straw (Bird et al., 2000; Tourenq et al., 2003; Manley et al., 2005). For instance, Californian rice producers usually lood their plantations after harvesting to accelerate straw decomposition. he intentional loods of rice Acta Limnologica Brasiliensia ields had a positive efect on waterbird richness (Elphick and Oring, 1998). In Southern Brazil, during the fallow phase, the agricultural land is drained and used to raise cattle. However, some rice ields are maintained looded because they are located at lower areas susceptible to lood due to heavy rains in the winter. In this sense, the rice ields can be categorized as looded or dry, according to the unintentional hydrological management practice after harvesting. In looded rice ields, the surface water was present during all phases of the cycle, except in the tillage phase, whereas in the dry rice ields, the surface water was present only during the growing season (rice emergence and tillering). Accordingly, rice ields can be viewed as managed wetlands. he rice ield systems of Southern Brazil (crops and irrigation channel) shelter a representative number of species of macrophyte found at wetlands in this region. Along the cultivation cycle, which covers the cultivated and non-cultivated phases (fallow phases), was registered the presence of 88 species of aquatic macrophytes in six rice crops (Rolon et al., 2010) and 59 species in four irrigation channels (unpublished data). This macrophyte richness is similar to the results veriied in rice ields in Asia and Europe (Vasconcelos et al., 1999; Bambaradeniya et al., 2004). However, the number of species was smaller than in wetlands of Southern Brazil (153 species - Rolon and Maltchik, 2006) and in wetlands adjacent to the study rice ields (105 species - Rolon et al., 2008). Among the frequent species in the rice ield systems, the outstanding species are Bulbostylis capillaris, Limnobium laevigatum, Ludwigia peploides, Luziola peruviana, Salvinia herzogii and Salvinia minima. Approximately 70% of the aquatic species were registered in the wetlands of Coastal Plain of Rio Grande do Sul State (Rolon and Maltchik, 2006; Rolon et al., 2008). However, the macrophyte composition in rice ields and in irrigation channels was diferent from that on natural wetlands, mainly due to the high dominance of grasses and sedges (Rolon et al., 2008). he dominance of grasses and sedges veriied in rice ields and irrigation channels (c.a. 50% of total species) is greater than the one found in most of the natural areas. he high dominance of grasses and sedges was also observed in rice ields of Sri Lanka (Bambaradenya et al., 2004). Furthermore, in the irrigation channels, hydrophytes (loating and submerged species) corresponded to 51% of all macrophyte species and emergent corresponded to 2010, vol. 22, no. 2, p. 133-146 Aquatic macrophytes in natural and managed wetlands... 49% of macrophyte diversity. In natural wetlands, the hydrophytes represented only a small part of the community (c.a. 25% of species – Rolon et al., 2004). he morphology of the channels limits the establishment of emergent species to the littoral zone and the mean depth of 60 cm in the studied channels has provided more availability of habitats for the establishment of hydrophytes. he agricultural practices adopted over rice cultivation cycle in the rice ields have inluenced the macrophyte richness and biomass. he macrophyte richness and biomass in the tillage phase was lower than the two fallow phases and the end of the growing season. he low richness and biomass at the tillage phase can be a consequence of soil drainage, machine use and herbicide application. The absence of water during tillage phase suppressed the macrophyte species with low tolerance to drought and the use of machinery causes the revolving of soil and serious mechanical damages on plants. Furthermore, the control of aquatic macrophytes with herbicide (glyphosate) carried out during the tillage phase and in the beginning of the growing season was very evident, since most of the collected plants along the cultivation periods showed signs of tissue death. he irrigation channels, on the other hand, have not sufered the impact of the management practices adopted along the cultivation cycle, and the richness and biomass of macrophyte in such systems were constant over the year. One of the factors that may have contributed for the stability of the macrophyte assemblage was the permanence of the surface water along the whole period studied. he diferent hydrological management practices adopted after the harvesting period (presence or lack of water surface) did not inluence the macrophyte richness and biomass in the present study, however it has inluenced the species composition. Like as in natural wetlands (Maltchik et al., 2007; Rolon et al., 2008), hydroperiod and water fluctuations are important determining factors for the macrophyte composition in rice ields. During uncultivated period (fallow phases), looded and dry rice ields showed differences regarding the macrophyte composition, some hydrophytes (Azolla filiculoides, Salvinia minima, Ricciocarpus natans, Spirodella intermedia and Lemna valdiviana) characterized the looded rice ields and some amphibian species (Bulbostylis capillaris, Centella asiatica, Hydrocotyle ranunculoides and Panicum spp.) discriminated the dry rice ields. he variation in species composition between looded and dry rice ields may contribute 143 to the similarity of richness and abundance of macrophytes in rice fields under different management practices. he diference in the species composition of looded and dry rice ields is an important result concerning the conservation of biodiversity. Keeping the areas looded and dry within the same farm could maximize habitats for the aquatic organisms up to 30% and should be considered as a strong conservational action. Rice ields must not be viewed as surrogate systems for natural wetlands, given that natural wetlands are complex systems that have several functions (e.g. aquifer recharging, climatic stability and water storage). Furthermore, the macrophyte richness in rice ields is lower than in Southern Brazil wetlands, and the macrophyte composition was diferent from that on natural wetlands mainly due to the high dominance of grasses and sedges. However, the habitats provided by rice fields could contribute to increase the connectivity in a fragmented landscape, like as, Southern Brazil. he dispersion of macrophyte species is carried out by asexual or sexual propagules. Some macrophyte species reached their reproductive stages (lowers, seeds and oospores production). he production of sexual propagules could provide seeds for the seed bank formation in theses systems and contribute to the maintenance of genetic diversity of the populations, therefore, conserving the aquatic species of this region. It is worth highlighting that a great portion of the observed species in rice ields (47%) was limited to one phase along the cultivation cycle, not able to reach the end of their life cycles in these ecosystems, but can providing asexual propagules. Furthermore, the network of irrigation channels can be used as ecological corridors for aquatic organisms dispersion (Armitage et al., 2003; Mazerolle, 2004). 3.5. Macrophyte conservation he macrophyte richness related in this study (250 species) is a representative portion of richness estimated by Irgang and Gastal (1996) for wetlands of Rio Grande do Sul (400 to 500 species). At the wetlands of Southern Brazil, several environmental characteristics were determinant for the macrophyte richness and composition, such as, size, habitat diversity, altitude, hydroperiod, and lood maintenance. With regard to the conservation, the area may be an important criterion to be considered when choosing the priority areas for conservation. However, the inluence of the habitat diversity must be considered, since several small 144 Rolon, AS., Homem, HF. and Maltchik, L. wetlands have presented high habitat diversity and as consequence high macrophyte diversity. Although the richness is an important attribute for conservation, the diference in the composition of the species between the wetlands (β-diversity) gives us better information concerning the conservation of the regional diversity of the species. Hence, the gradients – size, altitude and hydroperiod – that were determinant for the composition of the species should be preserved. Furthermore, the lood events, long or short-term ones, are strongly associated to the structure of the aquatic macrophyte community in several wetland types. Any alteration in the hydrological regime (duration, frequency, etc.) will present several implications for the composition, richness and abundance of the aquatic macrophytes in wetlands of Southern Brazil. Actions concerning the minimization of the impact of the agricultural activities on the conservation of biodiversity are extremely relevant. Conservation of species in agroecosystems has attracted attention, mainly in Europe – where agricultural policy pays farmers to modify their farming practice to increase environmental beneits (CEC, 1985). he conservation of the macrophyte species in rice ield may be an important strategy for biodiversity conservation in areas that the natural wetlands were converted into rice fields. Such strategy would minimized the agricultural impacts on aquatic plants diversity in Southern Brazil, where more than 90% of wetland systems have already been lost and the remaining ones are still at high risk due to the expansion of rice production. References AGOSTINHO, AA., THOMAZ, SM. and GOMES, LC. 2005. Conservation of the biodiversity of Brazil’s inland waters. Conservation Biology, vol. 19, no. 3, p. 646-652. A R M I TA G E , P D . , S ZO S Z K I E W I C Z , K . , BLACKBURN, JH. and NESBITT, I. 2003. Ditch communities: a major contributor to loodplain biodiversity. Aquatic Conservation: Marine and Freshwater Ecosystems, vol. 13, no. 2, p. 165-185. ARRHENIUS, O. 1921. Species and area. Journal of Ecology, vol. 9, no. 1, p. 95-99. Acta Limnologica Brasiliensia associated with an irrigated rice agroecosystem in Sri Lanka. Biodiversity and Conservation, vol. 13, no. 9, p. 1715-1753. BERTOLUCI, VDM., ROLON, AS. and MALTCHIK, L. 2004. Diversidade de macróitas aquáticas em áreas úmidas do município de São Leopoldo, Rio Grande do Sul, Brasil. Pesquisas: Botânica, vol. 55, p. 187-199. BIRD, JA., PETTYGROVE, GS. and EADIE, JM. 2000. The impact of waterfowl foraging on the decomposition of rice straw: mutual beneits for rice growers and waterfowl. Journal of Applied Ecology, vol. 37, no. 5, p. 728-741. BLANCH, SJ., GANF, GG. and WALKER, KF. 1999. Tolerance of riverine plants to looding and exposure by water regime. Regulated Rivers: Research & Management, vol. 15, no. 1-3, p. 43-62. BROSE, U. 2001. Relative importance of isolation, area and habitat heterogeneity for vascular plant species richness of temporary wetlands in east-German farmland. Ecography, vol. 24, no. 6, p. 722-730. CASANOVA, MT. and BROCK, MA. 2000. How do depth, duration and frequency of looding inluence the establishment of wetland plant communities? Plant Ecology, vol. 147, no. 2, p. 237-250. Commission of the European Communities - CEC. 1985. Perspectives for the Common Agricultural Policy. Brussels: Communication from the Commission to the Council and the Parliament. COM(85) 333 inal. DAHLGREN, JP. and EHRLÉN, J. 2005. Distribution patterns of vascular plants in lakes – the role of metapopulation dynamics. Ecography, vol. 28, no. 1, p. 49-58. ELPHICK CS. and ORING, LW. 1998. Winter management of Californian rice fields for waterbirds. Journal of Applied Ecology, vol. 35, no. 1, p. 95-108. ELPHICK, CS. 2000. Functional equivalency between rice fields and seminatural wetland habitats. Conservation Biology, vol. 14, no. 1, p. 181–191. ELPHICK, CS. and ORING, LW. 2003. Conservation implications of flooding rice fields on winter waterbird communities. Agriculture, Ecosystems & Environment, vol. 94, no. 1, p. 17-29. FAOSTAT. 2008. FAO Statistical Databases. Available from: <http://faostat.fao.org>. BAMBARADENIYA, CNB. and AMERASINGHE, FP. 2003. Biodiversity associated with the rice field agroecosystem in Asian countries: a brief review. Sri Lanka: International Water Management Institute – IWMI. 24 p. IWMI Working Paper, no. 63. FERREIRA, LV. 2000. Efects of looding duration on species richness, loristic composition and forest structure in river margin habitat in Amazonian blackwater floodplain forests: implications for future design of protected areas. Biodiversity and Conservation, vol. 9, no. 1, p. 1-14. BAMBARADENIYA, CNB., EDIRISINGHE, JP., SILVA, DN., GUNATILLEKE, CVS., RANAWANA, KB. and WIJEKOON, S. 2004. Biodiversity GEEST, GJ. van, COOPS, H., ROIJACKERS, RMM., BUIJSE, AD. and SCHEFFER, M. 2005a. Succession of aquatic vegetation driven by reduced 2010, vol. 22, no. 2, p. 133-146 Aquatic macrophytes in natural and managed wetlands... water-level luctuations in loodplain lakes. Journal of Applied Ecology, vol. 42, no. 2, p. 251-260. GEEST, GJ. van, WOLTERS, H., ROOSEN, FCJM., COOPS, H., ROIJACKERS, RMM., BUIJSE, AD. and SCHEFFER, M. 2005b. Water-level luctuations affect macrophyte richness in floodplain lakes. Hydrobiologia, vol. 539, no. 1, p. 239-248. GOMES, AS. and MAGALHÃES Jr., AMD. 2004. Arroz Irrigado no Sul do Brasil. Pelotas: Embrapa. 900 p. GOPAL, B. and JUNK, WJ. 2000. Biodiversity in wetlands: an introduction. In GOPAL, B., JUNK, WJ. and DAVIES, JA. (Eds.). Biodiversity in Wetlands: Assessment, Function and Conservation. Leiden: Backhuys Publishers. p. 1-10. GOULDER, R. 2008. Conservation of aquatic plants in artiicial watercourses: Are main drains a substitute for vulnerable navigation canals? Aquatic Conservation: Marine and Freshwater Ecosystems, vol. 18, no. 2, p. 163-174. HALL, DL., WILLIG, MR., MOORHEAD, DL., SITES, RW., FISH, EB. and MOLLHAGEN, TR. 2004. Aquatic macroinvertebrate diversity of playa wetlands: the role of landscape and island biogeographic characteristics. Wetlands, vol. 24, p. 77-91. HERZON, I. and HELENIUS, J. 2008. Agricultural drainage ditches, their biological importance and functioning. Biological Conservation, vol. 141, no. 5, p. 1171-1183. IRGANG, BE. and GASTAL Jr., CVS. 1996. Macrófitas aquáticas da Planície Costeira do RS. Porto Alegre. 290 p. JONES, JI., LI, W. and MABERLY, SC. 2003. Area, altitude and aquatic plant diversity. Ecography, vol. 26, no. 4, p. 411-420. JULIANO, BO. 1993. Rice in human nutrition. Philippines: Food and Agriculture Organization –FAO, International Rice Research Institute – IRRI. 162 p. JUNK, WJ. 1989. Flood tolerance and tree distribution in central Amazonia. In HOLM-NIELSEN, LB., NIELSEN, IC. and BALSLEV, H. (Eds.). Tropical Forest Botanical Dynamics, Speciation and Diversity. London: Academic Press. p. 47-64. KOHN, DD. and WALSH, DM. 1994. Plant species richness – the efect of island size and habitat diversity. Journal of Ecology, vol. 82, no. 2, p. 367-377. LEWINSOHN, TM. and PRADO, PI. 2005. How many species are there in Brazil? Conservation Biology, vol. 19, no.3, p. 619-624. MALTCHIK, L. 2003. hree new wetlands inventories in Brazil. Interciencia, vol. 28, no. 7, p. 421-423. MALTCHIK, L., COSTA, ES., BECKER, CG. and OLIVEIRA, AE. 2003. Inventory of wetlands of Rio Grande do Sul (Brazil). Pesquisas: Botânica, vol. 53, p. 89-100. 145 MALTCHIK, L., OLIVEIRA, GR., ROLON, AS. and STENERT, C. 2005. Diversity and stability of aquatic macrophyte community in three shallow lakes associated to a loodplain system in the South of Brazil. Interciencia, vol. 30, no. 3, p. 166-170. MALTCHIK, L., ROLON, AS. and GROTH, c. 2002. Diversidade de macróitas aquáticas em áreas úmidas da Bacia do Rio dos Sinos, Rio Grande do Sul. Pesquisas: Botânica, vol. 52, p. 143-154. MALTCHIK, L., ROLON, AS. and SCHOTT, P. 2007. Efects of hydrological variation on the aquatic plant community in a loodplain palustrine wetland of Southern Brasil. Limnology, vol. 8, no. 1, p. 23-28. MALTCHIK, L., ROLON, AS., GUADAGNIN, DL. and STENERT, C. 2004. Wetlands of Rio Grande do Sul, Brazil: a classiication with emphasis on plant communities. Acta Limnologica Brasiliensia, vol. 16, no. 2, p. 137-151. MANLEY, SW., KAMINSKI, RM., REINECKE, KJ. and Gerard, PD. 2005. Agronomic implications of waterfowl management in Mississippi riceields. Wildlife Society Bulletin, vol. 33, no. 3, p. 981–992. MARSHALL, EJP., BROWN, VK., BOATMAN, ND., LUTMAN, PJW., SQUIRE, GR. and WARD, LK. 2003. he role of weeds in supporting biological diversity within crop ields. Weed Research, vol. 43, no. 1, p. 77-89. MAZEROLLE, MC. 2004. Drainage ditches facilitate frog movements in a hostile landscape. Landscape Ecology, vol. 20, no. 5, p. 579-590 Millennium Ecosystem Assessment. 2005. Ecosystems and human well-being: wetlands and water. Washington: World Resources Institute. 80 p. MITSCH, WJ. and GOSSELINK, JG. 2000. Wetlands. New York: John Wiley and Sons. 920 p. NEIFF, JJ. 1975. Fluctuaciones anuales en la composition itocenotica y biomasa de la hidroita en lagunas isleñas del Parana Medio. Ecosur, vol. 2, no. 4, p. 153-183. OERTLI, B., JOEY, DA., CASTELLA, E., JUGE, R., CAMBIN, D. and LACHAVANNE, JB. 2002. Does size matter? he relationship between pond area and biodiversity. Biological Conservation, vol. 104, no. 1, p. 59-70. Organization for Economic Co-operation and Development - OECD. 1996. Guidelines for aid agencies for improved conservation and sustainable use of tropical and subtropical wetlands. Paris: OECD. PADIAL, AA., CARVALHO, P., THOMAZ, SM., BOSCHILIA, SM., RODRIGUES, RB. and KOBAYASHI, JT. 2009. he role of an extreme lood disturbance on macrophyte assemblages in a Neotropical loodplain. Aquatic Sciences, vol. 71, no. 4, p. 389-398. RICKLEFS, RE. and LOVETTE, IJ. 1999. he roles of island area per se and habitat diversity in the species- 146 Rolon, AS., Homem, HF. and Maltchik, L. area relationships of four Lesser Antillean faunal groups. Journal of Animal Ecology, vol. 68, no. 6, p. 1142-1160. ROLON, AS. and MALTCHIK, L. 2006. Environmental factors as predictors of aquatic macrophyte richness and composition in wetlands of Southern Brazil. Hydrobiologia, vol. 556, no. 1, p. 221-231. ROLON, AS. and MALTCHIK, L. 2010. Does looding of rice ields after cultivation contribute to wetland plant conservation in southern Brazil? Applied Vegetation Science, vol. 13, no. 1, p. 26-35. ROLON, AS., LACERDA, T., MALTCHIK, L. and GUADAGNIN, DL. 2008. The influence of area, habitat and water chemistry on richness and composition of macrophyte assemblages in southern Brazil wetlands. Journal of Vegetation Science, vol. 19, no. 2, p. 221-228. ROLON, AS., MALTCHIK, L. and IRGANG, B. 2004. Levantamento de macrófitas aquáticas em áreas úmidas do Rio Grande do Sul, Brasil. Acta Biologica Leopoldensia, vol. 26, no. 1, p. 17-35. ROSENZWEIG, ML. 1995. Species diversity in space and time. Cambridge: Cambridge University Press. 460 p. SANTOS, AM. and THOMAZ, SM. 2007. Aquatic macrophyte diversity in lagoons of a tropical loodplain: he role of connectivity an water level. Austral Ecology, vol. 32, no. 2, p. 177-190. Acta Limnologica Brasiliensia SCHOTT, P., ROLON, AS. and MALTCHIK, L. 2005. he dynamics of macrophytes in an oxbow lake of the Sinos River basin in south Brazil. Verhandlungen. Internationale Vereinigung fuer theoretische und angewandte Limnologie, vol. 29, no. 2, p. 815-820. SEABLOOM, EW., MALONEY, KA. and VALK, AG. van der. 2001. Constraints on the establishment of plants along a luctuating water-depth gradient. Ecology, vol. 82, no. 8, p. 2216-2232. SHINE, C. and KLEMM, C. 1999. Wetlands, water and the law: using law to advance wetland conservation and wise use. Gland: IUCN. 348 p. TOURENQ, C., SADOUL, N., BECK, N., MESLÉARD, F. and MARTIN, JL. 2003. Efects of cropping practices on the use of rice ields by waterbirds in the Camargue, France. Agriculture, Ecosystems & Environment, vol. 95, no. 2-3, p. 543-549. TURNER, MG. and DALE, VH. 1998. Comparing large and infrequent disturbances: what have we learned? Ecosystems, vol. 1, no. 6, p. 493-496. VASCONCELOS, T., TAVARES, M. and GASPAR, N. 1999. Aquatic plants in the rice ields of the Tagus valley, Portugal. Hydrobiologia, vol. 415, no. 1, p. 59-65. Received: 24 February 2010 Accepted: 12 August 2010