Late Holocene evolution of a dystrophic Tatra Lake: natural trophic changes revealed by multi-proxy data

Abstract. Dystrophic lakes, characterized by dark-colored water, low transparency, and low pH, are relatively common in the mountainous and lowland regions of temperate and boreal zones. The occurrence of dystrophic conditions depends on hydrological, climatic, and biological factors, including surface and groundwater inflows and outflows, precipitation, air temperature, and vegetation within the lake's catchment. A change in any of these factors can lead to either an increase or a decrease in the degree of lake dystrophy. In this study, we present changes in the trophic status of a small forest lake located in the lower part of the Tatra Mountains (1,089 m a.s.l.; Western Carpathians, Poland). The lake is located within the Tatra National Park, and its natural dystrophic character is one of the features protected under the park's conservation objectives. We aimed to determine whether these dystrophic conditions are of natural origin and have persisted over a long period. To investigate this, we analysed a 1.4-m sediment core spanning the last 3,150 years using a range of geochemical and paleobiological methods, including elemental analysis, stable carbon and nitrogen isotope analyses, and analyses of diatom and Cladocera assemblages. Changes in the species composition of diatoms and Cladocera indicate that dystrophic conditions did not persist throughout the entire study period. The lake was dominated by species characteristic of meso-oligotrophic and oligotrophic water bodies, with only a brief period during which species indicative of dystrophic conditions appeared, coinciding with a low-water phase around 2700–2350 cal. yr BP. Permanent dystrophic conditions became established no earlier than approximately 950 cal. yr BP, which is relatively late compared with many lowland lakes.