Floodplain wetlands of eastern India in a changing climate: Trophic characterization, ecological status, and implications for fisheries

India is endowed with vast floodplain wetland resources (0.5 million ha), which provide both livelihood and nutritional security to much of the rural populace. These biologically sensitive ecosystems are threatened by a range of anthropogenic and climatic factors. Assessment of their ecological vulnerability, and of the environmental threats that they face, is essential both in evaluating the health of these ecosystems and in developing sustainable management strategies for conservation and fisheries enhancement. In this context, eight wetlands in the Ganga basin were studied for two consecutive years across the seasons and were characterized ecologically based on chlorophyll a, primary productivity, and trophic state index. A warming temperature (+0.20 – +0.47 °C) and a decreasing total annual rainfall (257–580 mm) have been observed along the Ganga basin in the last three decades. The chlorophyll a (mean ± S.E.) content of the water varied from 4.08±1.04 to 38.0±14.11 µg l-1. The high primary productivity, gross primary productivity/plankton respiration ratio and trophic state index correlated positively with the high fish yield in the wetlands. Analysis of data based on Carlson's method revealed five wetlands in the eutrophic category, whereas based on Lamparelli's method, two wetlands fall into the eutrophic category. The Lamparelli TSI value ranged from 54.1 in Majharia to 65.8 in Kararia among the wetlands. The Bishnupur wetland in West Bengal and Kararia wetland in Bihar were found to be eutrophic due to cascading sewage incursion from nearby towns. These altered ecosystems with high TSI values were prudently exploited by selecting suitable fish species for high fish production, and a fish yield of 1200 kg ha-1 yr-1 was achieved in Bishnupur. The study revealed that eutrophic wetlands can be strategically managed for maintaining both ecosystem services and fish production. Careful selection of suitable fish species and stocking rate is crucial. The planned disposal and treatment of sewage is recommended to maintain the ecological health of floodplain wetlands for sustainable fisheries management in the context of a changing climate.