SUBFOSSIL DIATOM COMMUNITIES FROM BANSKÁ ŠTIAVNICA RESERVOIRS MIRROR VEGETATION CHANGES IN THE CATCHMENT

 

Lucia SOCHULIAKOVÁ¹, Katarína TRNKOVÁ², Ladislav HAMERLÍK^{1, 3} , Peter BITUŠÍK¹

¹ Katedra biológie a ekológie Fakulty prírodných vied UMB, Tajovského 40, SK-974 01 Banská Bystrica, e-mail:lucia.sochuliakova@umb.sk 
² Katedra životného prostredia Fakulty prírodných vied UMB, Tajovského 55, SK-974 01 Banská Bystrica
³ Institute of Geological Sciences, Polish Academy of Sciences, Twarda 51/55, 00-818 Warsaw, Poland

  

Abstract

We present the results of the analysis of sediment cores from two man-made reservoirs, remains of a unique mining hydro-energetic system, located in a former mining region in the surroundings of Banská Štiavnica (Central Slovakia). The significance of the reservoirs as energy sources has changed during their existence and in the present they are used for recreation, angling and flood protection purposes (Veľká Richňava reservoir), or as a drinking water supply (Rozgrund reservoir). To understand the relationship between the catchment vegetation and lake biota, we analysed changes in diatom (aquatic) and pollen (terrestrial) remains preserved in the lake sediment. The top/ bottom paleolimnological approach was used to compare the bottom part of the sediment referring to the post-initial lake conditions (beginning of the 20^th century) with the surface part representing current conditions (after 2000). We found a certain level of synchronicity between the responses of both proxies indicating that diatom communities could be influenced by land-use changes in the catchment. In Veľká Richňava, the period with the dominance of pollen assemblage indicating grazing co-occurred with diatom species tolerating high nutrient levels, such as that of the Stephanodiscus genus. In the recent samples, the catchment vegetation has changed from herb dominated flora to forest and simultaneously Cyclotella species became dominant referring to decreased nutrient concentrations in the reservoir. In Rozgrund the most dominant diatoms in the bottom sediments, Fragilaria gracilis and Asterionella formosa have also been replaced by Cyclotella taxa in the recent sediments indicating lower phosphorus concentrations. In both reservoirs, there was a similar trend of terrestrial vegetation from the dominance of herbs (i.e. meadows, pastures) towards increasing afforestation in the catchment. At the same time, diatoms indicate lower trophy in the present relative to past, most likely connected to decreasing nutrient concentrations as a result of the changes in terrestrial vegetation. Thus, we conclude that this phenomenon should be taken into consideration when future management actions are proposed, since restoration of pastures in the catchment will lead to higher trophy of reservoirs.

 

Key words: Bacillariohyceae, pollen, palaeolimnology, Veľká Richňava, Rozgrund, land-use, eutrophication, World Heritage site UNESCO, Banská Štiavnica, Central Europe