Short and long term dynamics of nutrients, potamoplankton and primary productivity in an alpine river (Danube, Austria)
Dokulil, Martin T.
An outline of nutrient concentrations and biotic processes in the Austrian stretch of the River Danube is presented for different time windows, from daily to long-term. Today, the river is mostly fragmented by dams. The remaining free-flowing section of the river is compared to impounded sections with reduced flow. Concentrations of nutrients, turbidity and chlorophyll-a depend on discharge, light and temperature. Concentrations of phosphorus and nitrogen increased between 1960 and 1980, declining thereafter to values typical for the late fifties of the last century, due to efforts at sewage treatment in the entire catchment. The river plankton is characterized by large biovolumes of small centric diatoms. Biovolumes and chlorophyll-a show little variation along the river and are generally insignificantly influenced by the river impoundments, but gross-photosynthetic rates are higher and extend to greater depths whenever flow is reduced near the dams. Rates of net-photosynthesis and production per unit area are negative most of the time due to high respiration rates in the water column. Both biomass and production of the phytoplankton are controlled by light availability, as is typical for turbulent turbid systems.