Climate Impact on Dissolved Organic Carbon Composition in a North‐Temperate Peatland and Recipient Surface Water

Abstract

AbstractClimate may regulate dissolved organic carbon (DOC) composition across the peat‐water interface, but experimental evidence is scarce. We manipulated the climate in peatland and recipient surface water mesocosms to reflect four different climate warming scenarios. In half of the mesocosms, the water level was managed to avoid drought, after which responses were recorded during two annual cycles. It was hypothesized that warming and drought increase the aromaticity and humic‐like fluorescence character of DOC, and that this change propagate to recipient waters. Pore water DOC concentrations increased with temperature and peaked in hydrologically unmanaged mesocosms. Aromaticity increased as expected after drought in the warmest scenario (+3.2°C), but the overall evidence for hypothesized changes in DOC aromaticity and fluorescence composition (%) was limited. In managed warming scenarios, one aromatic humic component expectedly increased together with microbially derived humic fluorescence, whereas two other humic‐like components decreased. In the unmanaged mesocosms which were exposed to drought, water level exerted an overriding control of humic DOC; for example, as the microbially derived humic fluorescence diminished after drought in all climate scenarios. In the surface water recipients, warming had nearly no impact on humic‐like fluorescence, but there were decreases in protein‐like fluorescence. Overall, this experiment revealed no conclusive support for the hypothesized aromatization and humification of peatland‐derived DOC in response to drought or warming. Nonetheless, both factors increase the quantity of DOC in peatland pore waters and affect composition in complex ways, calling for further investigation of chemical and functional traits of peatland DOC in a changing environment.