Comparing chamber and eddy covariance based net ecosystem CO₂ exchange of fen soils

Abstract

Due to their high emission potential, the reporting of CO2 emissions from peatlands requires exact emission factors for different land use categories. Recently used emission factors are mainly based on CO2 flux measurements by chamber techniques or the micrometeorological eddy covariance (EC) method. However, evidence about the reliability and comparability of annual CO2 balances based on these methods is scarce. Therefore, manual chamber measurements of ecosystem respiration (RECO) and net ecosystem exchange (NEE) were conducted for two years (March 2012–April 2014) to model annual balances of two sites on fen soils with different land use intensity in northern Germany: an unutilized and rewetted grassland (UG) and an intensively utilized wet grassland (GW). Simultaneously, EC measurements of NEE were conducted on the sites. Two reasons for occasionally great deviations in NEE between the methods could be observed: (1) the accordance of both methods was most hampered during transition periods such as the beginning of the growing season and the onset of regrowth after a grassland defoliation due to different spatial scales of EC and chamber measurements and (2) RECO and gross primary production (GPP) partitioned from EC NEE measurements were systematically lower than those from the chamber‐based model, which could be a result of the EC energy balance gap. Differences were more pronounced for the managed site GW as a result of more frequent regrowth periods. It is concluded that the EC and chamber method can show comparable results for the CO2 exchange of grasslands on fen soils when the limitations of both methods are known and considered for the reporting of emission factors. These limitations are due to energy balance closure and potentially biased footprints for EC and a restricted representativeness especially during early stages of plant development for the chamber method.

The Effect of Fertilization on Biomass and Metabolism in North Carolina Salt Marshes: Modulated by Location‐Specific Factors

“…However, nighttime decoupling could also be the result of extrapolating R measured during the day to nighttime in the chambers, assuming no diel variability in S. alterniflora respiration. Other studies similarly have observed minor differences in magnitude of chamber and tower flux measurements with a slight bias toward greater CO 2 fluxes from chambers than towers (Krauss et al, 2016; Poyda et al, 2017; Wang, Liu, et al, 2013) (Figure S4).…”

Sub-soil irrigation does not lower greenhouse gas emission from drained peat meadows

“…Campaign-wise fitting of Reco and GPP models can best represent the original data sets, while pooling data for a longer period can provide better model fitness and less bias toward single measurements (Huth et al, 2017;Poyda et al, 2017). However, in this study, different responses of vegetation and soil processes to drought, especially to the extreme drought in 2018, caused abnormal data points that do not fit the classic models, resulting in the generally poor performances of annual models.…”

Methane and Carbon Dioxide Fluxes in a Temperate Tidal Salt Marsh: Comparisons Between Plot and Ecosystem Measurements

“…CH 4 fluxes were recorded concurrently with NEE measurements using semi‐transparent chambers. Similar chambers are commonly used for greenhouse gas flux measurements to study land‐atmosphere interaction (Limmer et al., 2018; Poyda et al., 2017; Tong et al., 2010).…”

“…CH 4 fluxes were recorded concurrently with NEE measurements using semi-transparent chambers. Similar chambers are commonly used for greenhouse gas flux measurements to study land-atmosphere interaction (Limmer et al, 2018;Poyda et al, 2017;Tong et al, 2010). These chamber measurements were taken using a closed loop sampling design with chamber air circulated through an ultra-portable greenhouse gas analyzer (LGR; Los Gatos Research, Model 915-0011, San Jose, CA) capable of reading both CH 4 and CO 2 (Limmer et al, 2018).…”