Recent environmental changes in alpine Lake Kotlaničko as revealed by sedimentary diatom assemblages (Dinaric Alps, Bosnia and Herzegovina)

Alpine regions are among the most sensitive ecosystems to climate warming, with alpine lakes being particularly affected by this forcing. However, none of these lakes in Bosnia and Herzegovina are regularly sampled or monitored, resulting in extremely scarce data and a largely unknown history of these lakes. We used a paleolimnological approach to identify and examine the main drivers of change in Lake Kotlaničko, located in the alpine tundra zone of the Zelengora Mountains in southeastern Bosnia and Herzegovina. We investigated changes in diatom assemblages using a 23 cm long sedimentary record and found a pronounced increase since the 1960s of planktonic diatoms (mainly Lindavia radiosa ) relative to tychoplanktonic and benthic species. This change in diatom assemblage composition is likely associated with stronger thermal stratification due to longer ice-free seasons induced by rising regional air temperatures. In addition, the more recent period (since 2002) covered by the sedimentary record is marked by the occurrence of the planktonic Asterionella formosa , a taxon commonly found in mesotrophic to eutrophic lakes. The longer inferred periods of thermal stratification, combined with increased nutrients as revealed by the diatoms, suggest shifts in lake habitat and that Lake Kotlaničko has undergone important changes over the last ~ 65 years.