An isotopic model for the origin of autochthonous organic matter contained in the bottom sediments of a reservoir

Abstract

Geochemical analysis of surface sediment samples collected in 2005 and 2006 was used to evaluate the potential sources of the organic matter present in sediments of southeast Poland's Solina Reservoir. Statistical analysis of sediment variables (carbon to nitrogen ratio, and the carbon 13 and nitrogen 15 isotope ratios) determined for the organic fraction indicated significant spatial variability with respect to sources of organic matter. A binary mixing model was developed from literature sources to predict the relative contributions of allochthonous and autochthonous production to sediment organic matter. Autochthonous production was shown to account for 60–75% of bulk sedimentation in the lacustrine parts of the reservoir, near the dam. In contrast, autochthonous production accounted for only 25% of sedimentation in the riverine zone receiving stream inputs. Statistical analysis identified the δ15N of organic matter as the best predictor of the source of organic matter. Multiple regression analysis indicated that two water-quality variables (nitrate and dissolved silica) were significantly related to the δ15N signature of organic matter. This led to a conclusion that limnetic nitrate and dissolved silica concentrations were regulating organic matter production in the Solina Reservoir.