The Lower Paraguay River-floodplain habitats in the context of the Fluvial Hydrosystem Approach

EDMUNDO C. DRAGO, KARL M. WANTZEN & ALDO R. PAIRA

Ecohydrology & Hydrobiology

UNESCO (Venice, Italy) & International Centre for Ecology-Warsaw, Institute of Freswater Biology-Cracow. Polish Academy of Sciences.

Lugar: Warsaw; Año: 2007

1642-3593

Abstract The Lower Paraguay River is a segment of the Paraguay-Paraná hydrosystem, the most important N-S fluvial corridor of South America. We report herein the first description of the physical structure of their aquatic habitats along 390 km from Asunción city (Paraguay) to the confluence with the Paraná River. The hierarchical ordination of the Fluvial Hydrosystem Approach (FHA) was used to determine the relationships between the hydrogeomorphological processes and the types of habitats patches, and the hydrological connectivity between lotic and lentic environments. The Lower Paraguay is a meandering functional sector where five functional sets were identified: (a) main channel, (b) floodplain channel, (c) floodplain lentic environment, (d) tributary, and (f) aquatic-terrestrial transition zone. These functional sets encompassed twenty one functional units and sixty one major mesohabitats. In the longitudinal as well as in the lateral dimension, the relatively homogeneous habitats of the main channel contrasted with the heterogeneous floodplain habitats. We attribute this riverine habitat diversity to the changes in the channel-floodplain morphology and in the strength, duration and frequency of their hydrological connectivity, caused e.g. by geologic controls, shiftings of the river channel, tributaries effects, or by multi-year periods of higher or lower inundation-drought phases. Furthermore, as a result of the variable river-floodplain-tributary complex, several types of fluvial-lacustrine boundaries and ecotones are developed. Key words: Large river, Lower Paraguay, floodplain, physical habitat, connectivity, boundaries, ecotones.