Water quality in Tatra Mountains lakes

We have studied recovery of high elevation lakes in the Tatra Mountains from atmospheric acidification since the 1980s. Thirty lakes differing in pH, alkalinity and catchment characteristics (like vegetation, soil, and scree cover) have been sampled for water composition annually since the early 1990s. Lake water composition is rapidly improving (decreasing concentrations of strong acid anions like sulphate, nitrate, and chloride, while increasing pH and alkalinity) due to reduction in atmospheric pollution in Europe. In addition to decreasing acidic deposition, the lake water recovery has been increasingly affected by climate change, accelerating since the middle 2000s. The associated increase in rainfall intensity and annual number of days without snow, along with air temperatures fluctuating around the freezing point elevates the physical erosion of rocks, especially in high-elevation, steep, and scree-rich areas where rocks are not thermally insulated and stabilized by soils. Weathering of exposed accessory calcite in the eroded granodiorite bedrock is a source of calcium and bicarbonate. Their liberation significantly supports alkalinity and pH increase in lakes. In contrast, sulphur-bearing minerals contribute to lake water sulphate and partly mitigate its deposition-related decrease associated with reduced acidic deposition. In addition, elevated precipitation and an increase in rainfall intensity reduce water residence time in soils, and consequently affect nitrogen retention in catchments and terrestrial export of nitrate. All effects are more important in scree-rich than in soil-rich catchments. The climate effects on changes in the water composition of lakes recovering from acidic deposition thus depends on elevation and cover of soil and scree in catchments.

Kopáček J., Kaňa J., Porcal P., Stuchlík E. (2021):Diverse effects of accelerating climate change on chemical recovery of alpine lakes from acidic deposition in soil-rich versus scree-rich catchments. Environmental Pollution 284, 117522