Climate change is arguably the greatest environmental challenge facing mankind. Robust predictions of the impacts of climate change and the development of appropriate socio-economic responses depend on a better understanding of the global carbon cycle. Many aspects of the cycle are already well constrained, but some elements remain highly uncertain, particularly the role of fresh waters. It has become evident in recent years that the role of fresh waters in the global carbon cycle, in particular as significant sources of greenhouse gases such as methane, has been severely underestimated. This is partly due to the absence of long-term data sets of methane emissions from lakes, which makes predictions and modelling of lake ecosystem responses to future climate change extremely difficult. Latest models agree that future warming and precipitation trends will be amplified at high northern latitudes, with the most severe increases in the Arctic followed by boreal and then temperate regions. This project will combine a unique experimental system, contemporary field observations and state-of-the-art palaeolimnology to develop, validate and apply methods to track long-term methane dynamics in lakes. Hence this proposal aims to provide completely novel insights into the long-term dynamics of methane concentrations and emissions from lakes in response to past climatic variation and anthropogenic impact. Lakes are an important component in the global carbon budget although their role as major sources of greenhouse gases has long been underestimated. In this project we will sample and analyse sediment cores from the Arctic (Greenland), boreal (Finland) and temperate (Denmark) regions. Sampling from such regions that have shown large climate variations (Arctic, boreal) and highly variable degree of human impact (boreal, temperate) will provide unique data for modelling how methane emissions from lakes will be affected under future warming scenarios. The different spatial and temporal scales are linked by a consistent methodology using stable isotope analysis applied to sedimented chitinous invertebrate remains, which have the potential to reflect past methane concentrations in the water. These cores also provide information on past environmental and ecological conditions, such as temperature, nutrient levels and community structure. In addition, these data will allow the assessment of the relative importance of multiple pressures (climate warming, eutrophication) in driving the increases of methane emissions from lakes in different regions. This makes the project a highly novel study linking change in the environment and ecosystem structure to long-term change in a key ecosystem process with global significance – methane production and emissions. The main objectives of the project are to study i) how methane dynamics in lakes from the Arctic, boreal and temperate regions are affected by climate change and/or anthropogenic impacts through increasing temperatures and enhanced nutrient and dissolved organic carbon runoff from catchments; and ii) the importance of multiple pressures (climate warming, eutrophication) and the relative importance of each individual stressor in driving the increases of methane emissions from lakes in different regions. Therefore this project will yield results that provide important insights about the responses of lake ecosystem methane fluxes to changes in climate or increasing human impact. While having crucial global importance on climate change scenarios and carbon cycle, it will also have more regional and applied emphasis on current debate on the potential environmental impacts of different land-use practises. Also, it will deliver new information to assess the importance of multiple pressures (climate warming, eutrophication), and the relative importance of each individual stressor, in driving the increases of CH4 emissions from lakes in different regions. Hence the project will produce valuable new information for conservation purposes and policymakers within the EU and more globally.
