Chapter 5: Benthic Invertebrates in the Middle Paraná River Floodplain (Argentina).

ZILLI, FLORENCIA; MONTALTO LUCIANA

Floodplains: Physical Geography, Ecology and Societal Interactions.

Nova Science Publishers, Inc.

Lugar: New York; Año: 2011; p. 99 - 126

The large rivers in South America are characterized by extensive floodplains and the river-floodplain systems are regulated by the flood pulse regime and the hydrological connectivity, which determine high habitat heterogeneity and a wide spectrum of resources for benthic invertebrates. The floodplain environments range from secondary channels of different discharge and flowing regime (intermittent flow, permanent flow), to shallow lakes with different geomorphologic origin, shape, position in relation to active channels and connectivity degree and fluvial or lacustrine wetlands. The connectivity degree, macrophytes cover, riparian leaf litter, availability of detritus in the bottom sediments determine high habitat heterogeneity at different temporal and spatial scales in the Middle Paraná River floodplain. The high spatial variability (patches, mesohabitat, regional/landscape scales) and the temporal fluctuations of the system (flood pulses magnitude, duration and frequency, seasonality, etc.), determine a high taxonomic and functional diversity of benthic invertebrates and large amounts of available benthic resources for aquatic and aquatic-terrestrial food webs. Lateral gradients are found among mesohabitats with increasing richness, abundance, biomass and secondary production from the main channel to secondary channels, lakes with different connectivity degree and wetlands. The secondary channels show differences in the benthic invertebrate assemblages among the central strip and the banks, in relation to detritus inputs, granulometry and hydraulic stability degree. The lakes offer a high heterogeneity in relation to their connectivity degree (mainly at the landscape level). Besides high levels of environmental complexity and significant differences in the benthos assemblages may be found inside each lake at the patches scale in relation to their area and shore development (embayment, irregularities, debris dams, etc.). A gradient from the permanent water bodies to the terrestrial zones may be observed in the marginal wetlands in terms of physical and chemical microhabitats and invertebrates assemblages. Moreover, the taxa found in the benthos of marginal wetlands can develop desiccation strategies to survive during the drought phase. Despite the importance of floodplain habitats and their natural dynamics for the biodiversity of the system and for the human economic activities, many large rivers have been greatly disturbed by damming and engineering, resulting in a degradation of floodplain-river function and connectivity. Further research on floodplain function and its biota is necessary to evaluate the impact of anthropogenic activities and to develop restoration and management strategies.