We studied the effects of catchment characteristics (soil type and land use) on the concentration and quality of dissolved organic matter (DOM) in river water and on the bacterial degradation of terrestrial DOM. The share of organic soil was the strongest predictor of high concentrations of dissolved organic carbon, nitrogen, and phosphorus (DOC, DON, and DOP, respectively), and was linked to DOM quality. Soil type was more important than land use in determining the concentration and quality of riverine DOM. On average, 5-9 % of the DOC and 45 % of the DON were degraded by the bacterial communities within 2-3 months. Simultaneously, the proportion of humic-like compounds in the DOM pool increased. Bioavailable DON accounted for approximately one-third of the total bioavailable dissolved nitrogen, and thus, terrestrial DON can markedly contribute to the coastal plankton dynamics and support the heterotrophic food web.
<p>Natural ecosystems play an important role in regulating greenhouse gas (GHG) fluxes between land and water surfaces and the atmosphere. To evaluate the full GHG balance of a region, fluxes from natural ecosystems such as undrained mires, lakes and rivers, should be included in the GHG accounting together with fluxes from forestry, agricultural and anthropogenic activities. We present a method for collating regional GHG balances including natural ecosystem processes, to support strategies for climate change mitigation and adaptation. Our study area is Kokem&#228;enjoki river basin (SW Finland), which includes two eLTER sites (Lammi and Hyyti&#228;l&#228;/SMEAR). Empirical data of these sites are used for model developments and calibrations as well as regional extrapolation. We report spatially explicit estimates on sources and sinks of GHG such as carbon dioxide and methane, and nitrous oxide for some ecosystems, and aggregate the regional balance from vertical fluxes of these elements. Spatial data sources include CORINE land use data, soil map, lake and rivers shorelines, national forest inventory data, as well as statistical data on anthropogenic activities. The regionally aggregated vertical balance will be compared to observed total lateral flux to the Bothnian Sea. We quantify the fluxes on the basis of empirical evidence from eLTER site information, literature, as well as on calculations with a forest growth and gas exchange model (PREBAS).</p><p>&#160;</p><p>Acknowledgements and funding:</p><p>Irina Bergstr&#246;m, Markus Haakana, Antti Ihalainen and Kari Minkkinen</p><p>eLTER H2020 GA 654359</p><p>IBC-Carbon Academy of Finland SRC 2017/312559</p><p>SOMPA Academy of Finland SRC 2017/312912</p><p>oGIIR</p><p>Freshabit LIFE IP LIFE14/IPE/FI/023</p>
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