Identification of anthropic impact on the food web using carbon and nitrogen stable isotopes as chemical markers. Case study:

JULIETA GRIBOFF; MICHA HORACEK; DANIEL WUNDERLIN; MAGDALENA MONFERRAN

Insbruck

Encuentro; 13th Austrian stable isotope user group meeting (SINA); 2014

Stable isotopes have been used to trace the impact of anthropic activities, mainly untreated sewage discharges, in three reservoirs presenting different degrees of eutrophication. The main goal of our research was finding chemical-isotopic markers that could be used to link anthropic pollution with changes in different compartments in reservoirs, namely water, sediment, and different levels of the food web (plankton, shrimps and fish).Thus, we measured ¦Ä13C and ¦Ä15N values in various organisms (from primary producers to upper consumers) to understand the influence of the different anthropogenic activities on the environment and the possibility to distinguish regions with different types of contamination, as well as areas of greater or lesser risk for food production. Study site samplings were carried out during the wet season (April 2014), after a massive rain event in three lakes in C¨®rdoba, Argentina: San Roque, Los Molinos and R¨ªo Tercero lakes. San Roque Lake supplies drinking water to C¨®rdoba city, and is also intended for recreational use. It is surrounded by cities and settlements which are not fully connected to the public sewage system. Los Molinos Lake provides water to the Southeastern area of the city of C¨®rdoba and is used for recreational activities and irrigation. In the surrounding agriculture, mainly corn and sorghum are produced. R¨ªo Tercero Lake is the largest artificial reservoir in the province of C¨®rdoba, and it is used for water supply and industrial activities, as well as for providing cooling water for a nuclear power plant. We collected water, sediment, plankton, shrimp (Palaemonetes argentinus) and fish (Odontesthes bonariensis) from each lake. Stable isotope analyses were performed in an Isotope Ratio Mass Spectrometer (IRMS), connected with an elemental analyzer (both Thermo Fisher Scientific). Results showed distinctive patterns in ¦Ä13C and ¦Ä15N between the lakes under study, allowing the identification of lakes more exposed to anthropogenic sewage. San Roque Lake showed the highest ¦Ä15N values for all the samples, indicating the most prominent influence of sewage on the lake ecology. Further research studies are being conducted to confirm this preliminary result, providing an interesting alternative to link sewage discharges with levels of stable isotopes in biota, including edible fish; thus, pointing out risk for people drinking water or eating fish from such impacted lakes.