| Swedish lakes are transforming in ways that in many cases are already visible by eye as a change in lake water color, from blue to green and brown, due to increased concentrations of nutrients and terrestrially derived dissolved organic matter (DOM) from runoff. Such changes can be linked to increased temperature and precipitation, but can also be linked to land use change, such as intensified coniferous forestry and clearcutting. Given that increased loading of DOM can have major effects on ecosystem functions such as biomass production, tracking the impact of land use on nutrient and DOM loading and subsequent effects on aquatic ecosystem diversity and function may be key to prioritize conservation actions at the land-water interface.
For efficient nature management of lakes it is important to study how land use and natural gradients interactively affect biogeochemistry, biodiversity and functioning, as this informs about which practice and management option that could have the greatest positive effect on biodiversity on the local scale. Here, we therefore outline a research program aiming to identify how variation in forest type and cover, variation in DOM loading and nitrogen fertilization - all linked to land use and different forestry practices - may impact lake-biodiversity and productivity. We specifically ask: (1) How do land use and vegetation type interact with lake characteristics in affecting biodiversity of plankton, invertebrates and fish? (2) How do different combinations of forest fertilizers and DOM affect plankton community composition and production depending on lake chemistry and associated water colour?
To this end, we will use existing data from environmental monitoring carried out in Sweden to analyze how land use and vegetation type, together with various environmental variables and lake characteristics, affect the composition and diversity of organisms in lakes. To more mechanistically understand how forest practices indirectly affect lake communities via changes in nutrient and DOM loading, and how this depends on local lake characteristics, we will set up enclosure experiments in selected lake pairs, consisting of brown and clear lakes. The proposed project will produce knowledge needed for adaptive management at the land-lake interface aiming to maintain and restore food web functioning in lakes, taking natural biogeochemical gradients into account. We also see this proposal as a first novel step towards a long term research program to develop the knowledge-base and guidelines needed to better integrate land use, forest and lake conservation management.
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