Impact of two different flood pulses on planktonic communities of the largest floodplain lakes of the Daugava River (Latvia)

Abstract

An impact of two different flood pulses on phyto- and zooplankton communities of the two largest floodplain lakes of the Daugava River were studied in the spring and summer of 2005. Samples of phyto- and zooplankton were taken at weekly and biweekly intervals. At the end of March, a medium size pulse of spring flood was observed. At the beginning of May, it was followed by an unusually high pulse of flush floods caused by heavy rainstorms in the local drainage area. An overall increase of biomass and the number of taxa of planktonic communities during the filling and drainage phases of the spring floods was stated. The pulse of the flush floods resulted in a lower total biomass and higher species diversity, and can be regarded as a disturbance event. The high species diversity represented by a hump-shaped pattern caused by an intermediate disturbance that was measured by the rate of water level change during the floods according to Intermediate Disturbance Hypothesis (IDH). This study reflected both linear and a slight hump-shaped relationships between the rate of water level change and the number of phytoplankton and zooplankton taxa.