Effect of river connectivity on hydrochemistry, sediment enzyme activity and biotic communities of wetlands

Abstract

Wetlands associated with floodplains of the Ganges and Brahmaputra river systems cover an estimated 0.2 million ha and play a vital role in the fisheries, rural economy and environment. In recent years, most wetlands in the states of Bihar, Assam and West Bengal in India have lost connectivity with their parent rivers due to natural and anthropogenic changes. These changes are causing rapid shrinkage of valuable wetlands and threatening their biodiversity and ecological function. The present study was conducted to assess the effect of river connectivity on the hydrochemistry, sediment enzyme activity, and biotic communities of these wetlands. One wetland area having link channels (open) connecting the main river, and another without link channels (closed), were selected from each of the Ganges and Brahmaputra basins for the study. Comparative analysis of open and closed, ecologically distinct wetlands of the Ganges basin revealed greater seasonal reduction in water depth and higher water conductivity (p < 0.04), nutrients (Ca+2, Mg+2, SiO3-Si), sediment microbial activity (p < 0.004), phosphorous cycling enzymes (p < 0.001), carbon cycling enzymes (p < 0.01), organic matter, conductivity, and plankton and macrozoobenthos (p < 0.01) density in the closed wetland. However, the open wetland showed higher diversity of plankton and macrozoobenthos. A profound impact of connectivity on wetland fisheries was observed in the Brahmaputra basin in Assam, where a higher percentage of catch comprised of indigenous fish species with lower fish yield was noted in the open wetland.