Transparent automated CO2 flux chambers reveal spatial and temporal patterns of net carbon fluxes from managed peatlands

Abstract

Degradation of peatlands as a consequence of drainage is responsible for approximately 30 % of the global greenhouse gas emissions from land-use and land-use change. Measuring CO2 exchange between peatland ecosystems and the atmosphere is important to gain insights into carbon processes in both the soil and vegetation, and to determine to what extent ecosystems are a net carbon (C) source or sink. Here, we aim to demonstrate and discuss the value and applicability of automated chambers (AC) to determine the net carbon fluxes of a managed peatland ecosystem from a spatial and temporal perspective at different scales. To achieve this, we deployed four custom-developed AC systems for 3.5 years to determine the net ecosystem carbon balance (NECB) at two selected research sites that each consisted of a conventional agricultural control parcel and a treatment parcel with subsoil irrigation and drainage (SSI) aiming to raise the water table depth (WTD). Complementary, for one parcel the temporal C-flux dynamics determined with AC were compared with eddy covariance (EC) flux measurements. With a high half-hourly temporal flux coverage of 89 % on average for all AC sites, we found positive NECBs indicating net C-losses that occurred for 97 % from May until October. Furthermore, during the summer period harvesting cycles dominated short-term temporal airborne CO2 flux dynamics measured with AC. We found that spatial water management treatments raised average summer WTD from 0.54 to 0.30 m and from 0.65 to 0.58 m at the two sites. The effect of this was captured well in the measured NECB with reducing average annual emissions of 24.0 ± 2.1 and 14.3 ± 2.2 t CO2 ha−1 yr−1 by both 9.3 ± 3.2 t CO2 ha−1 yr−1. AC also reflected spatial flux patterns within the parcel with higher fluxes at deeper average summer WTDs. On a field scale, we found distinct temporal flux patterns for AC and EC that can be explained by the different spatial coverage and land management differences. Long-term NECB estimates for AC and EC showed overlapping confidence intervals and thus no significant differences, but a slightly higher NECB for EC was found likely due to additional carbon sources within the footprint. Local groundwater heterogeneity strongly affected peatland C-losses and should therefore be well represented in the measurement set-up when upscaling chamber C-fluxes to ecosystem scale. To conclude, AC measurements provided a complete comprehension of peatland C-fluxes, and EC measurements can contribute to that on a field scale.

Keywords

• Automated chambers
• ecosystem C-losses
• Eddy covariance
• Peatlands
• CO2 emissions
• Groundwater level