CO₂ exchange and Carbon balance in two grassland sites on eutrophic drained peat soils

International audienceIn this study we investigated the role of intensive and extensive dairy farm practices on CO2 exchange and the carbon balance of peatlands by means of eddy covariance (EC) measurements. Year long EC measurements were made in two adjacent farm sites on peat soil in the western part of the Netherlands. One site (Stein) is a new meadow bird reserve and is managed predominantly by mowing in June and August. The second site (Oukoop) is an intensive dairy farm. Minimum ecosystem flux of the grass sward (range ?2 to ?34 ?mol CO2 m?2 s?1) showed a close and similar linear relationship with Leaf Area Index (LAI; range 1 to 5) except in maturing hay meadows, where minimum ecosystem flux did not decrease further. Apparent quantum yield varied between ?0.02 and ?0.08 (mean ?0.045) ?mol CO2 ?mol?1 photons at both sites and was significantly correlated with LAI during the growth season. Ecosystem Respiration at 10°C (R10) calculated from the year round data set was 3.47 ?mol CO2 m?2 s?1 at Stein and 3.64 ?mol CO2 m?2 s?1 at Oukoop. Both sites were a source of carbon in winter and a sink during summer, with net ecosystem exchange varying between 50 to 100 mmol CO2m?2 d?1 in winter to below ?400 mmol CO2 m?2 d?1 in summer. Periodically both sites became a source after mowing. Net annual ecosystem exchange (NEE) for Stein was ?8.4 g C m?2 a?1 and for Oukoop 122.4 g C m?2 a?1, the difference between the sites was mainly due a difference in GEP (101 g C m?2 a?1). However when biomass removal, manure applications and estimates of methane emissions are taken into account, both eutrophic peat meadows are a strong source for C ((462 g C m?2 a?1 and 465 g C m?2 a?1 at Stein and Oukoop, respectively)