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

Abstract

Climate 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 degrees 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.It is well known that peatlands leach organic carbon into recipient freshwaters, affecting their water quality. We hypothesized that warming and drying of peatlands make the material that leaches out from the peat more aromatic and brownish-colored. Such a browning would, chemically, be comparable to what happens in a fruit or vegetable that becomes brown faster due to air exposure or being taken out from the fridge. This hypothesis was tested in a laboratory experiment with peatland and receiving surface water ecosystems in glass tanks, in which the climate and water level were manipulated. Warming increased the concentrations and fluxes of dissolved organic carbon, but the "brownness" of the leached material generally did not change. Nonetheless, we found that different groups of fluorescent organic compounds either increased or decreased because of the combined influence of climate and water level. Thus, despite lacking support for our overall hypothesis, peatland leachate responses to climate change and water level clearly exist but are more complex than what could be expected. Our study underscores the importance of further characterization of the organic matter that leaches from peatlands in a changing environment, and how the freshwater network is affected.Water level variations strongly modulate the climate warming impact on dissolved organic carbon (DOC) composition in peatland mesocosms The climatic and hydrological impacts on the aromaticity of peatland DOC are weak in laboratory settings

Published in

Journal of Geophysical Research: Biogeosciences
2024, volume: 129, number: 6, article number: e2023JG007807
Publisher: AMER GEOPHYSICAL UNION

SLU Authors

• Salimi, Shokoufeh

  • Lund University

• Sparkes, Bradley

  • Lund University

Global goals (SDG)

SDG6 Clean water and sanitation
SDG13 Climate action
SDG15 Life on land

UKÄ Subject classification

Climate Science
Geosciences, Multidisciplinary

Publication identifier

• DOI: https://doi.org/10.1029/2023JG007807

Permanent link to this page (URI)

https://res.slu.se/id/publ/130817