Lake biota response to human impact and local climate during the last 200years: A multi-proxy study of a subalpine lake (Tatra Mountains, W Carpathians)

Element content, loss-on-ignition, chironomid analysis and 210Pb dating were applied on a sediment core from a subalpine Tatra lake (Popradské pleso) to reveal the response of aquatic biota to eutrophication induced by human activities in the lake catchment. The lead dating indicates that the 0–8cm section of the core represents the past ca 200years, ending at ~1814AD. Comparing the key changes of the proxies with human activities that are historically well documented, four phases of the recent lake development were distinguished: (1) a pre-tourism phase, (2) a phase of increasing touristic activity and early cottage development, (3) a phase of eutrophication, and (4) a phase of post-eutrophication. Neither touristic activity, nor early cottage development around the lake (1st and 2nd phases) had considerable influence on the chironomid assemblage structure or organic content of the lake. The most significant change both in chironomid assemblage structure and loss-on-ignition occurred during the 3rd phase, when a big tourist hotel was built close by the lake and started contaminating it via direct wastewater input. However, the structure of the chironomid assemblage has not changed significantly over time and the dominating taxa remained the same during the whole period. Parallel with the nutrient signal of the paleo assemblage, a secondary signal has been identified as the ratio of rheophilic taxa on total abundance that did not correlate with the sediment's organic content, and is most likely driven by local climatic oscillations. Changes of most of metal elements concentrations reflected rather bigger scale changes of industrial activities than local scale human disturbances. Our results indicate that hydromorphological properties can moderate the impact of organic pollution on the lake biota. [Display omitted] •We examined a short sediment core representing the last 200years of a subalpine lake.•Direct organic pollution induced changes in the structure of the lake biota.•Climatic oscillations were detected by comparing rheophilic taxa and instrumental measurements.•Elements analysed originated both from local and regional sources.•Hydromorphological properties can influence the impact of organic pollution on the lake biota.