Popular Science: 104.6 km from the confluence, or what is the water quality of Slapy Reservoir?
The authors compared water quality data from various data sources. They have analyzed 23 parameters from the Vltava River Basin Authority (SOE) database since 1995 and data from their own measurements between 2012–2013. To determine the main sources of pollution (whether point or surface pollution), they used the flow rate.
From a long-term perspective, a decline in several parameters have occurred since 1995 in the profiles of Kosova Hora and Radíč, especially nitrogen compounds. The total concentration of phosphorus has also decreased, but when comparing the concentrations in 2015–2016 with the quality classes according to the Czech Technical Standard (I.-unpolluted, II .-slightly polluted, III.-polluted, IV.-heavily polluted, V.-very heavily polluted), it is still possible to evaluate the water in selected profiles as ranging from polluted (III. class) to heavily polluted (IV class), especially in connection with high concentrations of nitrogen, phosphorus and total organic carbon.
The water quality of the last profile on the Mastník stream watercourse before the Slapy Reservoir can be classified as heavily polluted, mainly due to chlorophyll-α and total phosphorus concentrations.
An evaluation of their own monitoring showed that only two of the six profiles fell under category III. (polluted), while the others were classified as category IV. (heavily polluted) and V. (very heavily polluted), mainly because of the low dissolved oxygen concentrations, high CODMn (chemical oxygen demand) and high concentrations of ammoniacal nitrogen as the biggest problem.
The high concentrations of nitrates were registered especially in the autumn and winter, when this nutrient is not consumed by plants and, at the same time, there is a general flush from agricultural areas to the stream. Phosphate concentrations were mainly influenced by the flow rate, dilution occurred at higher water levels, indicating a point source of pollution, especially municipal waste water.
The results of the study are very alarming. The water quality of the Mastník stream, which also significantly influences the water quality in the Slapy Reservoir, is still very low. The worse water quality is mainly connected to intensive agriculture activities in the basin and the presence of smaller municipalities that still don‘t have their own wastewater treatment plant. Another factor that supports increasing water eutrophication with cyanobacteria and algae growth is, among other factors, climate change, particularly rising water temperatures and changes in the amount and annual distribution of precipitation. The authors see hope in the construction of wastewater treatment plants and land consolidation of the agricultural soil to a reduction in land erosion.