A paleolimnological investigation of the impact of catchment dynamics on pelagic communities in a deep sub-alpine lake (L. Iseo)

Catchment area changes (e.g. river hydrology, nutrient loads, land use), driven by climatic variation or anthropic activities, can have a strong impact on lake ecosystems. In particular extreme flood events can bring a lot of material in lake basin affecting water transparency and consequently impacting on the biocenosis. In previous studies has been verified that this phenomenon is amplified in lakes with a large ratio between drainage basin and lake area. Lake deposits provide ideal archives to study the past catchment dynamics and the answer of lake ecosystems. In particular, subfossil Cladocera remains are a valuable biological proxy, able to provide information on lake responses to hydrology- and climate-related environmental perturbations. Lithological analyses combined with subfossil remains can reveal responses of lake ecosystems to changes in the catchment area. The aim of this work is a paleolimnological reconstruction of human, climate and hydrological impacts on a deep subalpine lake (Lake Iseo, northern Italy) during the XX century. We study the lithological parameters and Cladocera and diatoms subfossil remains record in an 80 cm long sediment core spanning from the early 1920s to 2014. We compare the sediment records with historical information on major hydrological events during the last century, and with climate-related limnological data. As already observed in other lakes, the sediment records of Lake Iseo suggest that catchment related processes are able to decisively affect the food web dynamics and the lake functionalities. In particular, we observed that a series of flood events in the period between the ‘70s and ‘80s resulted in a decrease in the Cladocera total abundance and a prevalence of the littoral species over the pelagic one. The decline of the pelagic species has been attributed to the transport of inorganic material from the catchment area to the lake.