Study on the suspended particulate matter of a Mediterranean artificial lake (Sos Canales Lake) using Stable Isotope Analysis of carbon and nitrogen

Stable isotope analysis of carbon (C) and nitrogen (N) was used to study the nature and origin of the suspended particulate matter (SPM) in a small Mediterranean reservoir, Lake Sos Canales (SC). The δ13C and δ15N isotopic ratios, physical-chemical parameters, nutrients and phytoplankton were analyzed ca. monthly over a hydrological year on the vertical profile at two stations (lacustrine and riverine). SPM quantity and composition were related to the hydrological annual dynamic. In Mediterranean reservoirs, water-level fluctuation is one of the most important stressors, largely dependent on the strong seasonality of climate and water exploitation for human uses. Mediterranean reservoirs show different phases during a hydrological year, alternating empty and low water level (summer-autumn), re-filling (winter-spring) and high water (spring-summer) phases. Isotopic ratios of C and N were similar on the vertical profile and at the two stations during the low water phase, but differed during the re-filling and high water phases. Significant correlations were found between δ15N and water level, and between δ13C and temperature in the surface layer at the lacustrine station. An unusual δ13C distribution along the water column during the re-filling phase was interpreted on the basis of phytoplankton species composition, mainly due by Gymnodinium uberrimum.