Sediment organic matter (OM) and its stable carbon and nitrogen isotopes were studied in 12 Slovenian mountain lakes in the Julian Alps. The lakes have different catchment areas and display a range of trophic states. Surface sediment atomic C/N ratios ranged from 8.4 to 13.2. Based on these C/N ratios, we concluded that autochthonous OM dominates in these lakes and constitutes approximately 65–92% of the total OM. Higher contributions of autochthonous OM sources were observed in lakes above the tree line. Relatively constant C/N ratios in the deeper sediments suggest that degradation processes are most intense in the upper few centimetres of the sediments and/or that remaining OM is relatively resistant to further degradation. Surface sediment δ13C and δ15N values ranged from −36.1 to −14.1‰ and from −5.2 to +1.1‰, respectively. In sediment cores from seven lakes, higher δ13C and lower δ15N values characterize oligotrophic lakes situated above the tree line, whereas the reverse is true for eutrophic lakes below the tree line that are also exposed to more anthropogenic impact. Carbon and nitrogen biogeochemical cycling differs considerably among the lakes. Stratigraphic shifts in carbon, total nitrogen, C/N ratios and stable C and N isotopes in cores record changes in inputs, and hence water column processes, as well as alterations in loading to the lakes. The stratigraphic variations are also the result of post-depositional diagenetic changes in the upper few centimetres of sediment. All the lakes show impacts from recent increases in atmospheric deposition of dissolved inorganic nitrogen. Application of sediment OM analysis thus proved to be useful to reconstruct paleoecological changes in sensitive mountain lake ecosystems that are either natural and/or anthropogenically derived.
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This research was carried out as a part of the Slovene National Research Projects Z1-3342, J1-6509, J1-6717 and research programmes P0-0531-0106, P1-0143 and P0-0504-0105 funded by the Slovenian Research Agency. We thank A. Brancelj, B. Čermelj, M. Šiško, S. Lukančič, T. Mezek and U. Žibrat (National Institute of Biology) and S. Žigon (Jožef Stefan Institute) for their valuable help during sampling and analyses. The valuable comments of M. Brenner, three anonymous reviewers and editorial handling of H. Eggermont are much appreciated. Special thanks are given to A. R. Byrne for editorial corrections.
Guest editors: Hilde Eggermont, Martin Kernan & Koen Martens / Global change impacts on mountain lakes
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Vreča, P., Muri, G. Sediment organic matter in mountain lakes of north-western Slovenia and its stable isotopic signatures: records of natural and anthropogenic impacts. Hydrobiologia 648, 35–49 (2010). https://doi.org/10.1007/s10750-010-0148-4
- Alpine lakes
- Atmospheric deposition
- C/N ratios
- Julian Alps
- Nitrogen, stable isotopes