Limno-Chemical Characteristics of a Scroll Meander Depression in Comparison with Other Sectors of a Floodplain Wetland of Assam, India

Floodplain wetlands (beel) in Assam constitute a major fishery resource of the region. Spatio-temporal variability of six common limno-chemical parameters viz. water temperature, pH, dissolved oxygen, free carbon dioxide, specific conductivity and total alkalinity were determined monthly during 2001-02 at surface and bottom of deep scroll meander in comparison with those at shallow areas of Samaguri beel, Nagaon, Assam, India. Shallow zone was infested with submerged macrophytes throughout the year, whereas deep zone was devoid of them. All the parameters varied widely across the zones especially bottom of scroll meander depression, which behave differently as compared to all other sectors. Trophogenic activity in surface of shallow zone and tropholytic activity in bottom of deep zone controlled the limno-chemical parameters. Establishment of riverine connectivity in monsoon played a major role in controlling those parameters especially in bottom of the deep zone by enhanced mineralization of bottom organic matter as evidenced by sharp increase of sp. conductivity. Meander depression is characterized with lower temperature, acidic pH, anoxic water, higher sp. conductivity, higher free CO2 concentration and higher total alkalinity. Surface of the deep zone with low variability of the parameters may provide better limno-chemical environment for fishes as compared to all other sectors for survival and growth.