Legacy of the past

The Blanice River is important for several reasons. The upper part of the catchment area falls largely in various areas reserved for nature protection such as the Šumava Protected Landscape Area. From an ecological perspective, the river is also important because it houses the most abundant population of the critically endangered freshwater pearl mussel (Margaritifera margaritifera) in Central Europe.

One of the Blanice River tributaries is the Tetřívčí Brook. Photo: K. Fraindová.

The upper Blanice River basin has undergone several transformations in the past. In the second half of the 20^th century, large-scale interventions were undertaken to drain water from the landscape as quickly as possible. This involved a subsurface agricultural drainage system consisting of a network of narrow trenches and underground channels or pipes/tubing. Ditches were also built in the forests which are still partially functional today. In addition to the change in hydrology, it appears that such interventions also have an impact on water quality. Recent measures, such as the construction of wastewater treatment plants and the decrease in arable land, have made major contributions to improving water quality. Nevertheless, have these measures been sufficient to render the river a safe source of drinking water and a suitable home for freshwater pearl mussel populations?

Following the implementation of these measures, an improvement in water quality in addition to a decreasing trend of nitrogen and phosphorus compounds in the water in the main stream was recorded between 2003 and 2019. The water quality has been continually assessed according to Czech technical standards, and it is rated ‘very clean’ to ‘clean’ according to most parameters. 

The upper Blanice River is home to the freshwater pearl mussel which is on the IUCN (International Union for Conservation of Nature) Red List of Threatened Species. Photo: K. Fraindová.

However, some sites are still experiencing increased pollution. Most of the pollution in the upper Blanice River catchment area is directly related to anthropogenic activities. These include subsurface drainage which causes high levels of total phosphorus and iron and electrical conductivity (concentration of electrolytes in water = ionic dissolved substances). There is also the municipal solid waste landfill, Libínské sedlo, where high levels of chloride, basic cations, and ammonia nitrogen have been discovered. High nitrate nitrogen values are commonly associated with areas of cattle and sheep grazing where surface flushing can occur, particularly when animals have close access to streams. Natural sources of water pollution include peat bogs in the upper parts of the catchment area. They have higher concentrations of organic matter and total phosphorus and a lower pH, together with higher concentrations of metals, specifically Al and Fe.

Additionally, the water quality is still suboptimal at most sites for freshwater pearl mussels. The values for electrical conductivity, calcium, total phosphorus, nitrate-nitrogen, and the magnesium-to-calcium ratio frequently exceed upper critical limits. Such results refer to the baseflow, i.e., ‘normal water level’ in the river. However, even higher values can be observed during rainfall-runoff events. Heavy rainfall events have caused a greater release of aluminium, with values up to ten times higher, reaching up to 1 mg.l⁻¹, which is a direct threat for the freshwater pearl mussel population. For organic matter and total phosphorus, values have increased 3–5 times over the baseflow figures.

Overall, the results of this study highlight that even in near-natural catchments in landscape-protected areas, previous and current interventions are reflected acutely in water quality changes which are also closely linked to changes in hydrological conditions. In the future, it would be useful to conduct more detailed research on water quality changes during different rainfall-runoff conditions in relation to various landscape characteristics and anthropogenic activities to understand the main sources of pollutants and to develop appropriate strategies to protect water quality in vulnerable ecosystems.

Kateřina Fraindová

Fraindová, K., Matoušková, M., Kliment, Z., Vlach, V. (2022): Changes and dynamics of headwaters chemistry on the boundary of nature protected areas: Example of upper Blanice River catchment, Czechia. Geografie, 127, 2, 99–126. https://doi.org/10.37040/geografie.2022.001