Hydrological connectivity, surface water quality and distribution of fish species within sub-locations of an urban oxbow lake, East India

Ecological processes and distribution of biodiversity within river floodplains are driven by the hydrological regime of the area. The relationship between fish abundance/diversity and surface water quality at four impact points of the Sashadanga oxbow lake was examined based on hydrological connectivity (distance of lake sections from parent channel; density of buffer vegetation and hydrological phases of seasons). Fish sample populations (n = 1440) belonging to 10 orders showed greater numerical abundance in the pre-and post-flooding phases. Oxbow sites proximal to the parent channel showed higher comprehensive pollution index (CPI), higher dominance and lower species evenness during the pre-monsoon (minor flooding) and vice versa during the monsoon and post-monsoon (greater flooding periods). Diversity descriptors using curve/asymptote based on Hill’s numbers indicate significant site-specific fish diversity within the oxbow lake at different seasons. Discriminant analysis revealed that change in temperature, turbidity and concentration of inorganic nitrogen were significant predictors in differentiating the quality of the different sites of the lake. Principal component analysis (PCA) revealed that the relative abundance of each species order across sites was significantly influenced by changes in seasons and physicochemical parameters, and showed a weak association with the density of buffer vegetation at sites. Depending on the distance of oxbow areas to the parent channel, the combination of periodic flooding, riparian buffer and lake morphology define the degree of hydrological connectivity which in turn affects the composition and abundance of fish communities at different points of the lake.