Implications of Altered Hydrology for Substrate Quality and Trace Gas Production in a Poor Fen Peatland

Core Ideas Long‐term hydrological alterations influenced peat substrate quality. Peat lability was greatest from inundated sites. Long‐term drainage produced degraded peat quality. Peat quality and lability were specific to microforms. Northern peatlands are forecast to experience changes in surface temperatures and precipitation patterns in the next century, with implications for their long‐term water table position. Because peatlands are a large global C sink, it is important to investigate how multidecadal changes to hydrology will influence peat quality and C cycling. We examined peat substrate quality along a gradient of long‐term water table alterations (reference, wet, and dry) across a peatland complex in northern Michigan with Fourier‐transformed infrared (FTIR) spectroscopy, aerobic and anaerobic incubations, and elemental analyses. Peat substrate quality was determined by the intrinsic differences between hummock and lawn peat, in addition to being affected by changes in hydrology. These factors altered decomposition processes and created differences in vegetation communities and structure across the long‐term water table gradient. Our data suggest that peat from inundated sites is the most labile and that long‐term drainage results in degraded peat quality. There may be interactive effects of climate change for increased trace gas production if wet sites drain, particularly if lawn microforms are dominant. Wet hummocky peatlands might be more resistant to increased trace gas production if the depth to water table changes with climate. These results indicate that peatlands impacted by long‐term water table changes will experience shifts in substrate quality with concurrent changes in greenhouse gas emissions and highlight the need to incorporate microtopography in assessing the sensitivity of mineralization processes.