Characteristics of the allochthonous organic matter in Finnish forest lakes and reservoirs

Alloktonisen orgaanisen aineen ominaisuuksista suomalaisissa metsäjärvissä ja tekoaltaiss

Comparative study on the estimation of humic matter in natural waters

Luonnonvesien humuspitoisuuden arviointi eri menetelmill

The effect of water quality on the mercury concentration of northern pike (Esox Iucius, L.) in Finnish forest lakes and reservoirs

Veden laadun vaikutus hauen elohopeapitoisuuteen Suomen metsäjärvissä ja tekoaltaiss

Regional Variability and Drivers of Below Ice CO2 in Boreal and Subarctic Lakes

Northern lakes are ice-covered for considerable portions of the year, where carbon dioxide (CO2) can accumulate below ice, subsequently leading to high CO2 emissions at ice-melt. Current knowledge on the regional control and variability of below ice partial pressure of carbon dioxide (pCO(2)) is lacking, creating a gap in our understanding of how ice cover dynamics affect the CO2 accumulation below ice and therefore CO2 emissions from inland waters during the ice-melt period. To narrow this gap, we identified the drivers of below ice pCO(2) variation across 506 Swedish and Finnish lakes using water chemistry, lake morphometry, catchment characteristics, lake position, and climate variables. We found that lake depth and trophic status were the most important variables explaining variations in below ice pCO(2) across the 506 lakes(.) Together, lake morphometry and water chemistry explained 53% of the site-to-site variation in below ice pCO(2). Regional climate (including ice cover duration) and latitude only explained 7% of the variation in below ice pCO(2). Thus, our results suggest that on a regional scale a shortening of the ice cover period on lakes may not directly affect the accumulation of CO2 below ice but rather indirectly through increased mobility of nutrients and carbon loading to lakes. Thus, given that climate-induced changes are most evident in northern ecosystems, adequately predicting the consequences of a changing climate on future CO2 emission estimates from northern lakes involves monitoring changes not only to ice cover but also to changes in the trophic status of lakes.Peer reviewe

Lakes as nitrous oxide sources in the boreal landscape

Abstract Estimates of regional and global freshwater N2O emissions have remained inaccurate due to scarce data and complexity of the multiple processes driving N2O fluxes the focus predominantly being on summer time measurements from emission hot spots, agricultural streams. Here we present four-season data of N2O concentrations in the water columns of randomly selected boreal lakes covering a large variation in latitude, lake type, area, depth, water chemistry and land use cover. Nitrate was the key driver for N2O dynamics, explaining as much as 78% of the variation of the seasonal mean N2O concentrations across all lakes. Nitrate concentrations varied among seasons being highest in winter and lowest in summer. Of the surface water samples 71% were oversaturated with N2O relative to the atmosphere. Largest oversaturation was measured in winter and lowest in summer stressing the importance to include full year N2O measurements in annual emission estimates. Including winter data resulted in four-fold annual N2O emission estimates compared to summer only measurements. Nutrient rich calcareous and large humic lakes had the highest annual N2O emissions. Our emission estimates for Finnish and boreal lakes are 0.6 Gg and 29 Gg N2O-N y-1, respectively. The Global Warming Potential (GWP) of N2O cannot be neglected in the boreal landscape, being 35% of that of diffusive CH4 emission in Finnish lakes.peerReviewe

Coupled biogeochemical cycles and ecosystem services

Human activities disturb the biogeochemical cycles often resulting in limited eco-system services. The cycles of biologically active elements are also coupled to each other which is rarely acknowledged in ecosystem studies. Many of the regulating and maintenance services are linked to element cycles driven by micro-organisms, but these have often been omitted in ecosystem service studies. In the present publication the terminology of ecosystem services are used to help to define and describe the coupled biogeochemical processes and to highlight their importance in both terrestrial and aquatic ecosystems. The extended abstracts offer fresh viewpoints on biogeochemical cycles and on the management of their fluxes. The abstracts may also function as basis for new themes for research