Benthic invertebrates in the Middle Paraná River floodplain (Argentina)

ZILLI, FLORENCIA L. Y MONTALTO, LUCIANA

Floodplains: Physical Geography, Ecology and Societal Interactions

Nova Science Publishers, Inc.

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. The Middle Paraná River has built a wide fringing floodplain. The river-floodplain systems are regulated by the flood pulse regime and the connectivity, which determine high habitat heterogeneity and resources for benthic macroinvertebrates. The floodplain environments range from secondary channels of different discharge and flowing regime (intermittent or permanent flow), lakes with different connectivity degree, shape, position in relation to active channels and origin, and fluvial or lacustrine wetlands. The connectivity, macrophytes cover, riparian leaf litter, availability of detritus in the bottom sediments (conditioning level by microbiota, percentage of dissolved and particulate fractions, chemical quality, etc.) determine high habitat heterogeneity at different temporal and spatial scales in Middle Paraná River floodplain. The high spatial variability (patches, mesohabtitat, regional/landscape levels) and the temporal fluctuations (flood pulses magnitude and frequency, seasonality, etc.) of the system, determine a high benthic invertebrate taxonomic and functional diversity and wide spectrum of available benthic the resources for aquatic and aquatic-terrestrial food webs. Higher taxonomic richness, abundance, biomass and secondary production are found among secondary channels-lakes with different connectivity degree and marginal wetlands. The secondary channels show differences of benthic invertebrate assemblages among the central strip and the banks, in relation to detritus inputs, granulometry and hydraulic stability degree. The lakes have a high heterogeneity in relation to connectivity degree (landscape level). Besides high levels of environmental complexity and significant differences in the benthos assemblages may be found inside each shallow lake in relation to their area and shore development (embayment, irregularities) at the patches level. A gradient from the permanent water bodies to the terrestrial zones may be observed in the marginal wetlands in terms of microhabitats and invertebrates assemblages. Moreover, the taxa found in the benthos of wetlands 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 regional economy, 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 biota is an important tool for evaluating the impact of not sustainable anthropogenic activities and to develop restoration and management strategies.