Flushing meadows : the influence of management alternatives on the greenhouse gas balance of fen meadow areas

The degradation of peatlands is a major and growing source of anthropogenic greenhouse gas (GHG) emissions, and small changes in the management of peatlands can lead to drastic changes in GHG emissions and changes in carbon storage and in the past have indeed done so. GHG emissions from peatlands and the subsidence of peat soils can both probably be decreased by rewetting peatland and by restoring peatland by reducing the intensity of agricultural land use on peat soils. It might even be possible for these agricultural peatlands to revert to being sinks of GHGs. To test whether agricultural peat areas can be turned into GHG sinks and carbon sinks if they are restored and whether GHG emissions can at least be reduced by reducing management intensity and rewetting, a landscape-scale experiment measuring GHG emissions and carbon releases was started in 2005

Release of CO2 and CH4 from lakes and drainage ditches in temperate wetlands

Shallow fresh water bodies in peat areas are important contributors to greenhouse gas fluxes to the atmosphere. In this study we determined the magnitude of CH4 and CO2 fluxes from 12 water bodies in Dutch wetlands during the summer season and studied the factors that might regulate emissions of CH4 and CO2 from these lakes and ditches. The lakes and ditches acted as CO2 and CH4 sources of emissions to the atmosphere; the fluxes from the ditches were significantly larger than the fluxes from the lakes. The mean greenhouse gas flux from ditches and lakes amounted to 129.1 ± 8.2 (mean ± SE) and 61.5 ± 7.1 mg m-2 h-1 for CO2 and 33.7 ± 9.3 and 3.9 ± 1.6 mg m-2 h-1 for CH4, respectively. In most water bodies CH4 was the dominant greenhouse gas in terms of warming potential. Trophic status of the water and the sediment was an important factor regulating emissions. By using multiple linear regression 87% of the variation in CH4 could be explained by PO4 3- concentration in the sediment and Fe2+ concentration in the water, and 89% of the CO2 flux could be explained by depth, EC and pH of the water. Decreasing the nutrient loads and input of organic substrates to ditches and lakes by for example reducing application of fertilizers and manure within the catchments and decreasing upward seepage of nutrient rich water from the surrounding area will likely reduce summer emissions of CO2 and CH4 from these water bodie

Spatial and temporal variation of methane emissions in drained eutrophic peat agro-ecosystems: drainage ditches as emission hotspots

International audienceOur research investigates the spatial and temporal variability of methane (CH4) emissions in two drained eutrophic peat areas (one intensively managed and the other less intensively managed) and the correlation between CH4 emissions and soil temperature, air temperature, soil moisture content and water table. We stratified the landscape into landscape elements that represent different conditions in terms of topography and therefore differ in moisture conditions. There was great spatial variability in the fluxes in both areas; the ditches and ditch edges (together 27% of the landscape) were methane hotspots whereas the dry fields had the smallest fluxes. In the intensively managed site the fluxes were significantly higher by comparison with the less intensively managed site. In all the landscape element elements the best explanatory variable for CH4 emission was temperature. Neither soil moisture content nor water table correlated significantly with CH4 emissions, except in April, where soil moisture was the best explanatory variable

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

In 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. Maximum photosynthetic uptake of the grass sward (range 2 to 34 mu 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 maximum photosynthetic uptake did not increase further. Apparent quantum yield varied between 0.02 and 0.08 (mean 0.045) mu mol CO₂ mu mol(-1) photons at both sites and was significantly correlated with LAI during the growth season. Ecosystem Respiration at 10 degrees C (R-10) calculated from the year round data set was 3.35 mu mol CO₂ m(-2) s(-1) at Stein and 3.69 mu 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 CO₂ m(-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 -5.7 g C m(-2) a(-1) and for Oukoop 133.9 g C m(-2) a(-1). When biomass removal, manure applications and estimates of methane emissions ware taken into account, both eutrophic peat meadows are a strong source for C around 420 g C m(-2) a(-1)

Agricultural peatlands: towards a greenhouse gas sink - a synthesis of a Dutch landscape study

It is generally known that managed, drained peatlands act as carbon (C) sources. In this study we examined how mitigation through the reduction of the intensity of land management and through rewetting may affect the greenhouse gas (GHG) emission and the C balance of intensively managed, drained, agricultural peatlands. Carbon and GHG balances were determined for three peatlands in the western part of the Netherlands from 2005 to 2008 by considering spatial and temporal variability of emissions (CO2, CH4 and N2O). One area (Oukoop) is an intensively managed grass-on-peatland area, including a dairy farm, with the ground water level at an average annual depth of 0.55 (±0.37) m below the soil surface. The second area (Stein) is an extensively managed grass-on-peatland area, formerly intensively managed, with a dynamic ground water level at an average annual depth of 0.45 (±0.35) m below the soil surface. The third area is a (since 1998) rewetted former agricultural peatland (Horstermeer), close to Oukoop and Stein, with the average annual ground water level at a depth of 0.2 (±0.20) m below the soil surface. During the measurement campaigns we found that both agriculturally managed sites acted as C and GHG sources and the rewetted former agricultural peatland acted as a C and GHG sink. The ecosystem (fields and ditches) total GHG balance, including CO2, CH4 and N2O, amounted to 3.9 (±0.4), 1.3 (±0.5) and -1.7 (±1.8) g CO2-eq m-2 d-1 for Oukoop, Stein and Horstermeer, respectively. Adding the farm-based emissions to Oukoop and Stein resulted in a total GHG emission of 8.3 (±1.0) and 6.6 (±1.3) g CO2-eq m-2 d-1, respectively. For Horstermeer the GHG balance remained the same since no farm-based emissions exist. Considering the C balance (uncertainty range 40–60%), the total C release in Oukoop and Stein is 5270 and 6258 kg C ha-1 yr-1, respectively (including ecosystem and management fluxes), and the total C uptake in Horstermeer is 3538 kg C ha-1 yr-1. Water bodies contributed significantly to the terrestrial GHG balance because of a high release of CH4. Overall, this study suggests that managed peatlands are large sources of GHGs and C, but, if appropriate measures are taken, they can be turned back into GHG and C sinks within 15 years of abandonment and rewetting. The shift from an intensively managed grass-on-peat area (Oukoop) to an extensively managed one (Stein) reduced the GHG emissions mainly because N2O emission and farm-based CH4 emissions decreased

Annual balances of CH4 and N2O from a managed fen meadow using eddy covariance flux measurements

Annual terrestrial balances of methane (CH4) and nitrous oxide (N2O) are presented for a managed fen meadow in the Netherlands for 2006, 2007 and 2008, using eddy covariance (EC) flux measurements. Annual emissions derived from different methods are compared. The most accurate annual CH4 flux is achieved by gap filling EC fluxes with an empirical multivariate regression model, with soil temperature and mean wind velocity as driving variables. This model explains about 60% of the variability in observed daily CH4 fluxes. Annual N2O emissions can be separated into background emissions and event emissions due to fertilization. The background emission is estimated using a multivariate regression model also based on EC flux data, with soil temperature and mean wind velocity as driving variables. The event emissions are estimated using emission factors. The minimum direct emission factor is derived for six fertilization events by subtracting the background emission, and the IPCC default emission factor of 1% is used for the other events. In addition, the maximum direct emission factors are determined for the six events without subtracting the background emission. The average direct emission factor ranges from 1.2 to 2.8%, which is larger than the IPCC default value. Finally, the total terrestrial greenhouse gas balance is estimated at 16 Mg ha-1 year-1 in CO2-equivalents with contributions of 30, 25 and 45% by CO2, CH4 and N2O, respectively

Comparison of chamber and eddy covariance-based CO2 and CH4 emission estimates in a heterogeneous grass ecosystem on peat

Fluxes of methane (CH4) and carbon dioxide (CO2) estimated by empirical models based on small-scale chamber measurements were compared to large-scale eddy covariance (EC) measurements for CH4 and to a combination of EC measurements and EC-based models for CO2. The experimental area was a flat peat meadow in the Netherlands with heterogeneous source strengths for both greenhouse gases. Two scenarios were used to assess the importance of stratifying the landscape into landscape elements before up-scaling the fluxes measured by chambers to landscape scale: one took the main landscape elements into account (field, ditch edge ditch), the other took only the field into account. Non-linear regression models were used to up-scale the chamber measurements to field emission estimates. EC CO2 respiration consisted of measured night time EC fluxes and modeled day time fluxes using the Arrhenius model. EC CH4 flux estimate was based on daily averages and the remaining data gaps were filled by linear interpolation. The EC and chamber-based estimates agreed well when the three landscape elements were taken into account with 16.5% and 13.0% difference for CO2 respiration and CH4, respectively. However, both methods differed 31.0% and 55.1% for CO2 respiration and CH4 when only field emissions were taken into account when up-scaling chamber measurements to landscape scale. This emphasizes the importance of stratifying the landscape into landscape elements. The conclusion is that small-scale chamber measurements can be used to estimate fluxes of CO2 and CH4 at landscape scale if fluxes are scaled by different landscape element

Methane emissions in two drained peat agro-ecosystems with high and low agricultural intensity

Methane (CH4) emissions were compared for an intensively and extensively managed agricultural area on peat soils in the Netherlands to evaluate the effect of reduced management on the CH4 balance. Chamber measurements (photoacoustic methods) for CH4 were performed for a period of three years in the contributing landscape elements in the research sites. Various factors influencing CH4 emissions were evaluated and temperature of water and soil was found to be the main driver in both sites. For upscaling of CH4 fluxes to landscape scale, regression models were used which were specific for each of the contributing landforms. Ditches and bordering edges were emission hotspots and emitted together between 60% and 70% of the total terrestrial CH4 emissions. Annual terrestrial CH4 fluxes were estimated to be 203 (±48%), 162 (±60%) and 146 (±60%) kg CH4 ha-1 and 157 (±63%), 180 (±54%) and 163 (±59%) kg CH4 ha-1 in the intensively managed site and extensively managed site, for 2006, 2007 and 2008 respectively. About 70% of the CH4 was emitted in the summer period. Farm based emissions caused per year an additional 257 kg CH4 ha-1 and 172 kg CH4 ha-1 for the intensively managed site and extensively managed site, respectively. To further evaluate the effect of agricultural activity on the CH4 balance, the annual CH4 fluxes of the two managed sites were also compared to the emissions of a natural peat site with no management and high ground water levels. By comparing the terrestrial and additional farm based emissions of the three sites, we finally concluded that transformation of intensively managed agricultural land to nature development will lead to an increase in terrestrial CH4 emission, but will not by definition lead to a significant increase in CH4 emission when farm based emissions are include