Seasonal variability of aquatic chemistry and phytoplankton communities in a shallow floodplain lake of the Daugava River, Latvia

Seasonal changes of water level, aquatic chemistry and phytoplankton composition of the Daugava's floodplain lake Grivas was studied in 1999. Significant influence of the Daugava's floods on the lake's water level was found. Filling, drainage and isolation phases in hydrological regime of the lake were distinguished. The Daugava's flood water influx in April caused considerable water level rising and dilution of the lake's water column. Small diatoms and greens formed the spring maximum at the highest water level. After the floods, concentration of total diluted solids and nutrients increased, typical planktonic algae species were replaced by epiphytic and benthic species and rich macrophyte vegetation developed as in other shallow lakes.