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Popular Science: 104.6 km from the confluence, or what is the water quality of Slapy Reservoir?

In recent decades, there has been a significant improvement in the surface water quality of the main streams of the Czech Republic, mainly because of the decrease of heavy industry and due to the construction of wastewater treatment plants in municipalities over 2000 inhabitants. However, the surface water quality of small rivers is still very low, because they are often found in agricultural areas, which are still affected by fertilizers and other pollutants and many of them also do not yet have wastewater treatment plants. One of these is the Mastník stream in the Central Bohemian Region, which flows into the Vltava River’s Slapy Reservoir. Luboš Mrkva and Bohumír Janský from the Department of Physical Geography and Geoecology at our Faculty have focused on the development and current state of the water quality of this important water body.

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.

Extensive eutrophication in Mastník Bay, which is already affected by the slap of the Slapy reservoir. Photo: Luboš Mrkva.

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.

Mrkva, L., Janský, B. (2018): Surface water quality in the Mastnik stream catchment area: The situation in the Czech countryside. Geografie, 123/4, s. 479–505.

Kateřina Fraindová


Published: Sep 01, 2019 04:10 PM

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