Physicochemical Differentiation of the Muskau Arch Pit Lakes in the Light of Long-Term Changes

Thirteen pit lakes of the Muskau Arch (Western Poland) were studied in the summer season of 2016. The lakes display great geomorphological and hydrochemical diversity. The aim of the study was to characterize temporal changes in the physicochemical conditions of the pit lakes over the last 30 years (1986–2016) and to determine the main factors influencing their evolution. All the lakes were characterized in terms of the same set of physicochemical parameters measured and used for comparative analysis with literature data from the years 1986 and 1992. The results showed significant temporal differentiation in terms of morphometric features and most of the physicochemical characteristics. pH, EC, Ca2+, Mg2+ and total Fe were among the most significantly differentiating parameters. A similar pattern of changes was found for most of the lakes, suggesting natural fluctuations. Despite the differences in values of thermal and oxygen profiles, there were also similarities in lake stratification. Additionally, meromictic conditions were found in 4 lakes. In some of the lakes a negative effect of neutralization and fertilization of the water was observed. Our results showed that the Muskau Arch lakes are subject to dynamic hydrogeological and hydrochemical changes. In addition to natural changes, human-caused transformations were among the key factors responsible for the differentiation of the physicochemical conditions.