Trophic webs in Mediterranean freshwater environments through Stabel Isotope Analysis (S.I.A.) of carbon and nitrogen: Lake Sos Canales (Sardinia, Italy)

Reservoirs are complex man-made ecosystems, with environmental traits intermediate between rivers and lakes. Previous studies highlighted that eutrophication is the most important issue of Sardinian reservoirs. Studies on zooplankton were, in this context, addressed to understand whether and how peculiar traits of these environments, also related to their trophic status, might influence transfer of matter and energy through the food web. A preliminary study on 15 Sardinian reservoirs led to the decision of choosing Lake Sos Canales to apply carbon and nitrogen Stable Isotope Analysis (S.I.A) for investigating the role and seasonality of different sources sustaining pelagic food web. Between October 2010 and October 2011 suspended particulate matter (SPM), zooplankton and fish were collected. SPM was strongly affected by hydrological seasonal dynamics of the reservoir. Results of SPM isotopic signature were used to quantify contribution of different sources to zooplankton consumers. Results on crustacean zooplankton taxa highlighted common seasonal patterns and taxa-specific roles in matter and energy transfer to upper levels of the trophic web. The fish community was constituted by two allochthonous species, only one relying upon pelagic food sources. Data showed that paths of transfer of matter and energy and trophic interactions between fish species were peculiar of these environments, intensely affected by hydrological stressors.