Effect of prolonged summer on two ox-bow lakes

Abstract

Physicochemical as well hydrobiological investigations were made in two large tropical ox-bow lakes at monthly intervals during the period of two annual cycles of which the second one experienced an unusual drought. The monthly mean concentrations of total alkalinity, hardness, chloride, phosphate and nitrate of water were greatly increased during the drought-affected second year compared with the first year. Prolonged summer in the region caused about 5 – 25-fold increases in chlorophyll a concentration of nanoplankton and net plankton, respectively. Phytoplankton peaks were less developed during the first year, whereas the summer peak was greatly enlarged during the drought affected second year. There was about a twofold rise in the numbers of zooplankton during the second year as compared with the first year. Benthic invertebrates, on the other hand, were reduced in numbers. Fish production was relatively less during the drought affected second year than during the first year.