Response of emergent macrophytes to hydrological changes in a shallow lake, with special reference to nutrient cycling

Abstract

The effect of water level reduction on nutrient concentrations and productivity of emergent macrophytes was analyzed in a shallow, polymictic lake, located in Central-Western Poland. The water level was regulated for irrigation purposes from 1974 to 2002, with an average amplitude of 0.85 m. In 2002, the water level was reduced by 0.60 m during winter time and by 0.40 m in summer time. Nutrient concentrations, nitrogen, phosphorus, and potassium standing stocks and aboveground biomass production were compared among four vegetation types along with a moisture gradient in the littoral zone. This study was conducted in the littoral zone of Lake Niepruszewskie during the growing seasons in 1999–2001 (1st period with high water level) and 2005–2008 (2nd period with low water level). The reduction of water level resulted in a negative effect on biomass production and nutrient concentrations. Stoichiometric indexes, like N:P and N:K ratios, indicate that the shift in nutrient limitation due to changes in hydrological conditions caused a reduction of the nutrient uptake by vegetation and affected productivity. The decrease in the aboveground biomass production was more marked at sites that were less affected by drainage, i.e., permanently flooded. However, in drawdown areas, plant growth decreased. Species including Phragmites australis and Carex acutiformis coped better with the reduction of water levels than Typha angustifolia and Glyceria maxima.