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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - PALAEO (Palaeolimnological assessment of methane emissions from lakes in changing environment using stable isotopes)

Teaser

Summary

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 â€“ 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 infor

Work performed

During the first year of the project, the aim was to collect sedimented Daphnia ephippia and chironomid head capsule samples from areas representing different trends in climate warming and degree of anthropogenic impacts. Therefore the first year of the project mostly included sampling lake sediments from Denmark to Greenland and collecing remains of sedimented invertebrate remains (mainly ephippia and head capsules) from diffrent depths of the sediment cores to represent past environmental conditions and methane concentrations of the lakes. In addition to these \'fresh\' sediment samples, previously collected and stored sediment cores were used to sub-sample more lakes from wider geographical region. These ephippia and head capsule samples were then carefully prepared for stable isotope analyses of carbon, nitrogen, hydrogen and oxygen, which will provide information on past methane concentrations, food web structure and temperatures. In addition to ephippia and chironomid samples, direct greenhouse gas (methane, carbon dioxide and nitrous oxide) measurements were done in the mesocosms of an artificial shallow lake experiment, where temperatures and nutrient concetrations are experimantally raised to mimic expected climate change effects. Similar direct gas emission measurements were done on lakes in Greenland. The first sets of prepared ephippia and head capsule samples were analysed for stable isotopes from Danish and Greenlandic lake sediments but there is not yet enough data to publish these results. More samples and data will be needed from a greater number of lakes covering a wider geographical area. The results obtained thus far nonetheless create confidence on the applicability of the selected methods and preparation techniques.

Final results

In addition to the scientific objectives, an important objective of the project was to enhance the skills and career prospects of the experienced researcher. This was done by discussing potential future plans and funding possibilities. The goal was to start preparing for time after the Marie Curie fellowship as soon as possible and to make a competitive application for a funding securing the upcoming years and giving greater independency of the researcher. Also, as the first year of the fellowship was mostly aimed for collecting samples, there was not yet enough data to write papers from the present work. However, the experienced researcher continued some earlier work and took on new collaboration during the first year. These produced four papers published in peer-reviewed international journals in 2016. In addition to this, the experienced researcher made new contacts and networks by visiting other research groups to plan and discuss issues related to the project, which is fundamental for the future career development of the fellow. Also, the fellow was awarded significant research funding from his home country during the first year of the project.