Using Automatic Chambers to Disentangle the Role of Vegetation in CO2 and CH4 Emissions From a Rewetted Fen Peatland

Peatland rewetting can reduce CO₂ emissions but unintendedly increase CH₄ emissions from drained peatlands. The magnitude of these emissions depends on factors such as time since rewetting, nutrient availability, vegetation type and water table fluctuations. In this study, we used automatic chambers to measure CO₂ and CH₄ emissions in a rewetted fen peatland under (a) grass-dominated and (b) Juncus sp. dominated vegetation plots. Our objectives were to (1) quantify CO₂ and CH₄ emissions, (2) identify how emissions were affected by vegetation type, and (3) relate emissions to changes in water table.

The study was conducted in the Nørreå valley in central Denmark. Autochambers (ECOFlux; DMR A/S) measuring gas fluxes first in transparent and then in dark mode in the same plot, were placed in a small area with mixed vegetation and connected to a multiplexer system which allowed simultaneous CO₂ and CH₄ flux measurements. We used a LGR-ICOS^TM GLA131-GGA microportable gas analyzer (ABB Ltd.), and a LI-7810 trace gas analyzer (LI-COR, Inc.). Three autochambers were placed in grass-dominated plots, while three others were placed in Juncus sp. dominated plots. Axillary data on soil temperature, soil moisture, water table depth (WTD), and photosynthetic active radiation (PAR) were obtained within each chamber. Gas flux measurements were performed five to six times per day per chamber from 1^st of May to 10^th of November 2024. Biomass development was estimated with biweekly light reflectance measurements and the RVI vegetation index was calculated using a RapidSCAN CS-45 (Holland Scientific Inc., Lincoln, NE, USA). At the end of the study period, the aboveground vegetation was harvested and analyzed for dry matter content, total C (TC) and total N (TN). Additionally, peat cores were collected at six depth increments (0-10, 10-20, 20-40, 40-60, 60-80, and 80-100 cm), and the soil samples were analyzed for TC, TN, field bulk density, pH, Fe, and microbial composition. Preliminary findings suggest that CH₄ emissions is higher from the Juncus than from the grass-dominated vegetation, but the effect of vegetation type on both CO₂ and CH₄ emissions depends on WTD, soil temperature, peat physicochemical characteristics and microbial composition. Findings from this study will provide valuable information on how high frequency WTD along with automatic chamber measurements can contribute to the understanding of peatland rewetting and management strategies in order to minimize greenhouse gas emissions during the rewetting process.