The Middle Paraná River: Limnology of a Subtropical Wetland

IRIONDO, MARTÍN; PAGGI, JUAN CÉSAR; PARMA, MARÍA JULIETA

Springer

Lugar: Heidelberg (Alemania); Año: 2006 p. 378

978-3-540-70623-6

The great Parana basin (2,600,000 Km2) covers a large portion of the Neotropical Realm, extending from the Andes to the Atlantic coast and connecting the central regions of South America along 2200 kilometers in a North-South direction. Most of the basin is under subtropical climates, which range from desertic in the West to humid in the East.  The Middle Parana is a broad, complex floodplain extending along 600 kilometers in the heart of the interior lowlands of the continent. Such system of river channels, shallow lakes, islands and wetlands remains unoccupied by man and basically unaltered. From a systemic point of view,  his area can be considered as the most important link and collector of the fluvial chain that conveys huge volumes of nutrients, sediments and salts from the continent to the South Atlantic ocean.  The influence of the Parana in the Atlantic has been important. It has been calculated that a sediment deposit  400 m thick and one million square kilometers in area was accumulated in the platform and nearby oceanic bottom in the last two million years, with a similar amount of dissolved salts contributed by the river to the ocean.  This book contains the recent advances in the knowledge of the most important segment of the Parana river, organised according to the scientific structure of the National Institute of Limnology of Argentina (INALI-CONICET-UNL). It integrates contributions  from specialists in Physical Geography, Geomorphology, Fluvial Hydraulics, Geochemistry and several branches of Ecology: Phytoplankton, Macrophytes, Zooplankton, Bentos, Littoral Communities, Fishes, Amphibians, Reptiles and Birds. Such a diverse variety of approaches can hardly be syntesized by an unique word, although we authors believe that the classical term "Limnology" still works.   The volume is organized in four sections. Part I contains the physical and chemical characteristics of the system and related regions. The first two chapters describe the physical geography of the river basin and the geomorphology of the floodplain. Chapter 1  describe the physical geography of the whole Paraná basin, with its geological and climatic components and location in South America; limnological connections with the Amazon basin are developed. Chapter 2 sinthesizes the geomorphology of the flood plain named Middle Paraná, wich is characterized by several well defined gemorphological units, each of them with different ecological meaning. Chapter 3 develop a characterization of shape, size and depth for more than fifteen hundred lakes inside the plain by using techniques of Quantitative Geomorphology. It is really important to know the main parameters of a “mean lake” in that region with thousands of water bodies. Chapter 4 describes the complex dynamics of water  in selected lakes of the plain during floods and low waters, a mechanism that reverse in some epochs and varies among years. The sediment budget, discriminating Andean sources from geological old terranes and the main channel-floodplain inter-relationships along tens of years is present in Chapter 5.  A comprehensive study of the geochemistry of the Parana river and related systems is developed in Chapter 6 , considering the influence of El Niño years and other factors.     Parts II and III deal with aquatic communities of vegetables and invertebrates related to the lentic and lotic environments of the floodplain and the main channel of the studied complex of ecosystems. All these chapters include a synthetic description of the composition and abundance of these communities and also an analysis of their functional and distributional variations in relation to the dominant environmental factors, that is to say those directly or indirectly associated with the flood-pulse. All these chapters deal with  traditionally important conceptual areas of the limnological knowledge but  stressing about the particularities of these communities in a subtropical floodplain. In the Chapter 7, devoted to phytoplankton of the main channel and the alluvial plain, the spatiotemporal changes of this community, associated to the hydrosedimentological regime, are described and discussed. It is also analyzed the essential role of the floodplain in maintaining algal populations and incorporating them towards or from the lotic environments. The complex combination of lenitic and lotic environments with different conditions of flux and water quality located between the floodplain and the main channel are closely associated to the composition, number of species, diversity, density and biovolume of the assemblages inhabiting these environments. The more clear differences are shown during isolation periods. In the Chapter 8 the authors, stress about the important role of macrophytes mainly Eichhornia crassipes and Paspalum repens because their contribution to the productivity and to the physical structure of the system as habitat and refuge of a number organisms. Also the importance of drifting vegetation as dispersal mean and distribution of nutrients is discussed. The next chapter (Chapter 9), which deals with zooplankton, concludes that the assemblages of lotic environments of the Paraná River shows characteristics similar to most rivers in the world such as the dominance of small organisms and also that its density is low, comparable to that of other South American rivers. The influence of the flood pulse on zooplankton of floodplain lakes would be related to their degree of connection with the river. Between lotic and lentic environments there are at least two gradients in regard to diversity and abundance of zooplankton, one of then associated to the relative influence of the physical and biological control and the other one related to the level of environmental heterogeneity. In the main channel, biological mechanisms to control zooplankton populations would be less important than physical mechanisms of control. The composition and abundance of benthic invertebrates of the Middle Paraná River-floodplain complex, which is a mosaic of habitats undergoing succession, is described and discussed in the Chapter 10. Environmental factors, which mainly control benthic structure and composition, are flood pulses, groundwater seepage, hydraulic parameters, hydrological connectivity degree, macrophytes cover and water quality. In spite the great amount of organic matter accumulated on the bottom of floodplain environments the ´gathering-collectors´ functional group is dominant in the main being the ´shredders´ present only in the floodplain. In the central strip of the higher channels the assemblages are characterized by the dominance of species endemic to the Neotropical region, mainly Narapa bonettoi. The littoral communities of floodplain environments of the Middle Paraná River are treated in the Chapter 11, they include a group of complexes of high biological diversity and abundant populations. Macrocrustaceans constitude an important group and with active participation in the community structure and biomass. Dominant species of this group are prawns of the genera Macrobrachium, Palaemonetes, and crabs belonging to family Trichodactylidae. Biological and ecological aspects are discussed, mainly growth, reproduction, spatial distribution and trophic ecology. Co-adaptation of the assemblages of macrocrutaceans are also analyzed under the functional context imposed in the Paraná River from its formation, habitat characteristics and stability degree, being the product of a joint organic evolution      Part IV deal with vertebrate animal life. Chapter 12 show the high fish diversity and productivity in this section of the Parana River and summarizes information about migratory displacements, reproductive strategies and life histories, participation of the fish species in the complex trophic webs and data of metabolism and responses to hypoxia. The objectives of Chapter 13 are present information about the diversity and natural history (tadpole and adult characteristics, habitat use and reproductive traits) of anurans commonly found in riparian areas of the Middle Parana River. The factors that determine the presence of anuran species in ponds are part of a complex network of relationships that acts sinergically. The purpose of Chapter 14 is to analyze the reptile community in the floodplain, including aspects of species richness, ecological traits and environmental variables. A total of 71 reptile species were recorded in the Middle Parana River and the snakes are the richest reptile group with 49 taxa, that they occupy all type of habitats and substrates, including various species adapted to live in the water. Finally, Chapter 15 presents data of ecology of birds in the middle section of the river in relation to thopic and functional groups, seasonal dynamics and characteristics of the reproductive biology.         Acknowledgements: The Editors are very grateful to the National Council of Scientific and Technical Research (CONICET) of Argentine Republic for the financial assistance from the Program PIP N° 02195 under the direction of  MSc. María Julieta Parma