| Swedish lakes and streams are subjected to long-term change due to slowly progressing processes that act over large spatiotemporal scales. Among these are the ongoing changes in climate/cryosphere, the recovery from decades of anthropogenic acidification, the large-scale increase in water color (a.k.a. brownification), declines in total phosphorus concentrations, and the continued atmospheric deposition of nitrogen and contaminants. These long-term changes have repercussion on the base of food webs of lakes and subsequently on consumers on higher trophic levels. Many of these long-term changes have been archived in the stable isotopic signatures of fish scales and bones, and in their muscle tissue.
The objective of this study is to unravel the long-term changes in the food webs (trophic pathways) of different lake types and link these to ongoing large-scale environmental change. We will do this by analyzing (1) stable isotopes in archived scales and bones and (2) stable isotopes and biomarker fatty acids of banked muscle tissue samples of of key fish species (Arctic char, perch, pike). Samples available at the Museum of Natural History and at the Institute of Freshwater Research at Drottningholm date back to the late 1960s, thus covering almost 50 years of gradual environmental change. We hypothesize that the long-term processes such as acidification and subsequent recovery, brownification (forest lakes) and oligotrophication (Arctic/alpineaffects the base of the food web of these lakes and anticipate that these changes can be detected in the change in isotopic signatures and biomarker fatty acids in archived fish samples (i.e. scales and/or opercular bones, as well as dorsal muscle tissue).
We anticipate that the results will provide an integrated measure of the relative change in the trophic position of key fish species. The results will therefore provide important information about the changing baselines for these lakes that can be used in assessment protocols. The concept of changing baselines is central in ecological assessment, as it provides a measure of the gradual change due to climate change of pristine (or near-pristine) ecosystems, that serves as the baseline in assessments protocols. Our results will further be of great help for the interpretation of temporal changes in the concentrations of persistent organic pollutants and mercury, contaminants that are regularly analyzed in national monitoring plans. The results can also be used in the ongoing upcoming assessments of change in the Arctic within the Convention of Arctic Flora and Fauna that has been signed by all pan-Arctic countries, including Sweden. The research outlined here has thus relevance for practical management of water bodies and is relevant for the Oscar and Lilli Lamm foundation.
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