Effects of Altered Deposition Chemistry On Dissolved Organic Carbon, Pore Water Nutrients, and Microbial Enzyme Activities in a Northern Peatland.

Exports of dissolved organic carbon (DOC) from lakes and streams have increased throughout Europe and North America over the past several decades. One possible cause is altered deposition chemistry; specifically, rising nitrogen (N) inputs which can increase the activity of carbon-acquiring enzymes produced by the microbial community, and decreasing sulfate (S) inputs leading to changes in ionic strength and DOC solubility. To further investigate the relationship between deposition chemistry and DOC export in peatlands, a field experiment was conducted to compare the pore water chemistry and peat microbial enzyme activity of mesocosms receiving nitrate and/or sulfate amendments to mesocosms receiving no additions. To investigate how peatlands respond during recovery from increased inputs of S, mesocosms were also installed in an area of the same peatland that was previously amended with S. Added N did not change DOC concentration or microbial enzyme allocation. The lack of response could be due to possible phosphorus (P) limitation of the microbial community, the short length of the study, or the time lag between amendments and samplings, during which enzymes and/or DOC concentration may have changed and returned to baseline. Added S decreased DOC concentration and increased DOC aromaticity. Both N and S amendments decreased total dissolved phosphorus (TDP) concentration. TDP was elevated in the area of the peatland recovering from S amendment. This increase, which was reflected in microbial enzyme activity, could have shifted the microbial community from P limitation to N limitation.