The distribution and isotopic composition of carbon and nitrogen as indicators of organic-matter fluxes in the Solina Reservoir (south-east Poland)

Abstract

The feasibility of using carbon and nitrogen isotope ratios of sediment organic matter (OM) to elucidate the source and fate of bottom sediment was studied in the Solina Reservoir (south-east Poland). Horizontal and vertical changes in OM, total organic carbon (TOC) and total nitrogen (TN) content, as well as δ15N and δ13C values, in bottom sediments were analysed to establish the extent to which these sediments are terrestrial or internal in origin. Increased proportions of TOC along with slight decreases in TN were noted in the surface layer of shallow water sediment compared with the profundal sites. Upstream shallower C : N and δ15N values amounted to ~15 and ~2‰, respectively, pointing to the allochthonous origin of the OM. In turn, profundal C : N ratios of less than 10 and δ15N values of ~4‰ indicated autochthonous sediment. Values for δ13C did not differ between stations and ranged from –27.39 to –27.66‰. It is therefore suggested that the sediment from the upper shallower stations contains more allochthonous, refractory OM, whereas the profundal stations have planktonic OM enriching the sediment. This combined with the vertical distribution observed for δ15N signalled an intensification of eutrophication over the past few years.