Composition and origin of organic matter in surface sediments of Lake Sarbsko: A highly eutrophic and shallow coastal lake (northern Poland) |
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| Authors: | Micha? Woszczyk Achim Bechtel Reinhard Gratzer Maciej J Kotarba Miko?aj Kokociński Jens Fiebig Roman Cie?liński |
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| Institution: | aDepartment of Quaternary Geology & Paleogeography, Adam Mickiewicz University, Dzi?gielowa 27, 61-680 Poznań, Poland;bDepartment of Applied Geosciences & Geophysics, University of Leoben, Peter-Tunner-Str. 5, A-8700 Leoben, Austria;cDepartment of Environmental Analyses, Cartography and Economical Geology, AGH University of Science and Technology, Mickiewicza 30, 30-059 Kraków, Poland;dDepartment of Hydrobiology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznań, Poland;eDepartment of Geosciences – Palaeontology, J.W. Goethe-University, Altenhöfer Allee 1, 60438 Frankfurt a. M., Germany;fDepartment of Hydrology, University of Gdańsk, Ba?yńskiego 4, 80-952 Gdańsk, Poland |
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| Abstract: | We present an organic geochemical study of surface sediments of Lake Sarbsko, a shallow coastal lake on the middle Polish Baltic coast. The aim was to provide evidence concerning the origin of the organic matter (OM) and its compositional diversity in surface deposits of this very productive, highly dynamic water body. The content and composition of the OM in the bottom sediments were investigated at 11 sampling stations throughout the lake basin. OM sources were assigned on the basis of bulk indicators total organic carbon (TOC), total nitrogen (TN), δ13CTOC and δ15N and extractable OM yield], biomarker composition of extractable OM and compound-specific C isotope signatures. The source characterization of autochthonous compounds was verified via phytoplankton analysis. The distribution of gaseous hydrocarbons in the sediments, as well as temporal changes in lake water pH, the concentration of DIC (dissolved inorganic carbon) and δ13CDIC were used to trace OM decomposition.The sedimentary OM is composed mainly of well preserved phytoplankton compounds and shows minor spatial variability in composition. However, the presence of CH4 and CO2 in the bottom deposits provides evidence for microbial degradation of sedimentary OM. The transformation of organic compounds in surface, bottom and pore waters via oxidative processes influences carbonate equilibrium in the lake and seasonally favours precipitation or dissolution of CaCO3.The data enhance our understanding of the relationships between the composition of sedimentary OM and environmental conditions within coastal ecosystems and shed light on the reliability of OM proxies for environmental reconstruction of coastal lakes. |
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