Kaasut

Pilot Study Brings New Insights into the Climate Impact of Lakes

The project investigates the regional variation of methane and carbon dioxide emissions between surface waters and the atmosphere, as well as water quality in two lakes in Southern Finland. The goal is to better understand the role of littoral waters in the overall greenhouse gas balance of lakes. The project aims to determine the spatial variation in concentrations of methane and carbon dioxide released from lake surface waters, and how local land use and other hydrological features influence carbon cycling and greenhouse gas emissions. The research findings will be made directly applicable to environmental governance, for example by providing open-access spatial datasets. Kaasut is the first part of a three-phase research programme.

Increasing load impacts the carbon balance of lakes

Diffuse loading of nutrients and organic matter into Finnish lakes has increased, largely due to changes in land use and climate. As a result, lakes may experience eutrophication, darkening, increased turbidity, and sedimentation. These changes affect the lakes’ carbon balance, that is, the extent to which water bodies absorb or release carbon into the atmosphere. Research conducted in the SAARI project on Finland’s southern coastal areas has shown that the amount of organic matter strongly influences surface water concentrations of methane and carbon dioxide. The Kaasut project now investigates whether the same pattern holds true in lakes. If it does, it could mean that greenhouse gas emissions from lake surface waters have been significantly underestimated.

Little is known about environmental variation within lakes

Finland has approximately 56,000 lakes larger than one hectare, with a combined surface area of over 30,000 square kilometers. This is nearly 10% of the country’s total land area. Most Finnish lakes are irregularly shaped and shallow, with an average depth of just seven meters. This suggests that significant variation may occur not only between different lakes but also within individual lakes – in terms of lake type, environmental pressures, condition, and functioning.

Most Finnish lakes have been classified based on the assumption that observations made mainly in their central parts represent the lake as a whole. However, since most Finnish lake waters are shallow, measurements taken in deep and offshore areas do not accurately reflect the true variation in lake condition and processes. Nutrient and organic matter concentrations are generally higher in shallow, nearshore waters than in open water areas. Furthermore, littoral waters tend to warm more frequently and intensely than offshore waters, which especially accelerates the formation and release of methane into the atmosphere.