Long-Term Changes Of The Physico-Chemical Conditions In Alte Donau

The long-term development of physico-chemical changes will be described here from the early twentieth century till recent years with the main focus on the past three decades. Four periods can be distinguished: the eutrophication phase dominated by phytoplankton meaning high contents of phosphorus and low water transparency. By applying the RIPLOX treatment (restoration) algal biomass, particulate matter and nutrients dropped down, but also some chemical parameters temporary changed, like chloride, calcium and nitrate. When macrophytes recovered pH values raised significantly, moreover influenced by low buffering capacity. To encounter this process flushing from the impoundment Neue Donau was carried out periodically, representing a further impact on physico-chemical development. Currently Alte Donau indicates stable mesotrophic conditions with low annual mean concentrations of TP and chl-a and high transparency.