A food web model of Lake Garda as a management tool within the context of climate changes.

Abstract

Freshwater ecosystems support enormous biodiversity and provide key ecosystem services. However, alteration of natural flow regimes, nutrient loading and climate forcing have resulted in major impacts on water quality, food webs and productivity. Lake Garda, the largest of the deep southern subalpine lakes, experienced, during the last 40 years, a significant tendency to an increase of phosphorus content and water temperatures (0.035 °C/year in the upper 50 m layer). The objective of the thesis was to characterize trophic interactions and energy fluxes within the Lake Garda food web and to evaluate their temporal dynamics, considering effects of fisheries and climate change, using an Ecopath with Ecosim (EwE) mass-balanced model composed by 22 functional groups. According to the model outputs, ecotrophic efficiency is generally higher for fish groups and lower for zooplankton and primary producers, indicating that bottom-up control is the dominant pattern in the lake. At the current status, primary production required for total catch is 88.43 t/km2, which corresponds to 4.23% of total primary production (2090 t/km2/year). Dynamic simulations based on temperature increase scenarios show that, with constant primary production, effects on the different groups in terms of relative biomass are mixed, whereas, with increased primary production, effects are significantly positive for most groups, with an increase in the total biomass of the system up to 20%.