Impact of riverine connectivity on ecology and fisheries of selected floodplain wetlands in Assam

Abstract

Ecology and fisheries in two floodplain wetlands (beels) located in Nagaon district of Assam viz., Samaguri beel (N 26° 25' 36" and E 92° 51' 27"; 60 ha; seasonally open) and Sibasthan-Potakolong beeI (N 26° 30' 37" and E 92° 52' 22"; 92 ha; closed) in relation to riverine connection are discussed. Physico-chemical parameters of water indicated better water quality regimes in Samaguri than Sibasthan-Potakolong beel. Total phosphorous (ug/l), chlorophyll-a (ug/l) and net primary productivity was slightly higher in Samaguri (53.7-83.3; 18.7-63.2 and 930.5-1008.0) than Sibasthan-Potakolong beel (30.3-142.2; 14.2-23.8; 538.4-880.0). T-test showed Chl-a, pH and dissolved oxygen was significantly (p<0.05) different between the beels. Trophic Status Index indicated eutrophic conditions (60-70) of the beels. Soil was sandy-clayey in nature. Phytoplankton population was higher in Samaguri than Sibasthan-potakolong beel mainly because of low macrophyte infestation and competition for nutrient and space. Macrophyte coverage as well as macrophyte-associated fauna was higher during the monsoon seasons. Abundance of benthos was found to be higher in Sibasthan-Potakolong beel in winter season. Average fish yield rate was higher in Samaguri (698 kg/ha/yr) than Sibasthan-Potakolong beel (483 kg/ha/yr); supplementary stocking was practiced in both the beels. Higher fin-fish diversity (53nos.) was recorded in Samaguri than Sibasthan-Potakolong beel (42nos.) apparently because of riverine input in the former. Cypriniformes dominated the diversity in both the beel. Stocked fishes contributed 55% of the total catch in Samaguri, whereas it was 70% in Sibasthan-Potakolong beel. Among indigenous fishes, Indian river shad (35%) and small catfishes (10%) dominated the catch in Samaguri and Sibasthan-Potakolong beel, respectively. The study indicated that the seasonal riverine connectivity had positive influence on ecology and fin fish diversity of the beels.