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Drained organic soils are large sources of anthropogenic greenhouse gases (GHG) in many European and Asian countries. In Germany, they account for more than 7% of the national GHG emissions. Carbon dioxide (CO2) forms the vast majority of emissions from these soils and is thus the main target for mitigation measures. Bog peatlands are mainly found in North-Western Germany and frequently used for high-intensity grassland use. Further, former peat extraction areas are restored for nature protection. While restoration has decades of tradition, paludiculture and active water management in agriculture are comparatively new.Here, we will compile data on GHG exchange of bog peatlands and highlight recent results on water management by ditch blocking and subsurface irrigation, on Sphagnum paludiculture and on restored bog peatlands. Groundwater levels are usually considered as the major control for both CO2 and methane (CH4) emissions. The effects of water management on CO2 emissions are strongly depending on the site. Surprisingly, raising the groundwater level by subsurface irrigation in a grassland under bog peat to levels considered as acceptable even in restoration projects did not only fail to reduce CO2 emissions, but raised them compared to deeply drained control parcel. These results might be explained by an interaction of increased soil moisture in the topsoil and improved nutrient retention during phases of high soil temperatures and, at the same time, by limitations of microbial activity due to low soil moisture at the control parcels. However, at a second grassland site with subsurface irrigation, this did not occur, but a combination with grassland renewal caused extremely high nitrous oxide emissions. In contrast, both re-wetting for restoration purposes and Sphagnum farming reliably reduce GHG emission or may even lead to a carbon sink. Here, the effects of the groundwater level on CO2 and, even more, on CH4 emissions in a Sphagnum farming experiment were partially overridden by vegetation development dynamics.

The vast majority of peatlands in the North German Plain are cultivated as grassland. Intensive drainage measures are a prerequisite for conventional agricultural use of peatlands, but this practice causes high emissions of greenhouse gases (GHG), mainly carbon dioxide (CO2). Thus, raising the water levels is necessary to reduce or stop CO2 emissions. Water management options such as submerged drains (SD) and ditch blocking (DB) are discussed as a potential compromise between maintaining the trafficability for intensive grassland use and reducing the GHG emissions. Furthermore, grassland renewal is regularly practiced to improve the fodder quality for dairy farming; however, this might cause additional release of GHGs, especially nitrous oxide (N2O). Here, we present results of a four-year study on the GHG emissions from an intensively used grassland on fen peat equipped with SD and DB. Additionally, the effect of grassland renewal by shallow ploughing and direct sowing was evaluated.The target groundwater levels were set to -0.30 m below ground. In the first year, the water management system was optimized. In the following years, mean annual water levels at the parcels with SD were -0.23 m and at the parcels with DB -0.37 m. The groundwater level at the SD parcels was around 0.18 m higher than at the conventionally drained control parcels. Thus, water management by SD enabled us to even surpass the target water levels. However, year two and three of the study were dryer than usual, the differences between the SD parcels and the control parcels are expected to be lower in wet years. DB, in contrast, raised the water levels only marginally.During the first three years, control parcels with ditch drainage emitted 27-49 t CO2-eq. ha-1 a-1. This is within the typical range of emissions from grasslands on fen peat in Germany. On average, the parcels with SD showed slightly lower emissions than the drained control parcels, but these were highly variable (16-60 t CO2-eq. ha-1 a-1). Due to similar groundwater levels the emissions from the parcel with DB (23-43 t CO2-eq. ha-1 a-1) were comparable to the drained control parcels. Reasons for the high CO2 emissions despite increased groundwater levels by SD remain so far unclear. Both types of grassland renewal lead to higher N2O emissions during the first year after renewal. Afterwards, effects became ambiguous. Results from the fourth measurement year (2020) will be presented as well. So far, the data seems to support the results of the previous years.

During the last century, drainage turned the majority of the bogs and fens in Germany into productive agricultural land, causing substantial emissions of greenhouse gases (GHG). The project ‘SWAMPS’ focuses both on maintaining the trafficability for conventional intensive grassland use and on the reduction of GHG emissions by managing the groundwater level by submerged drains and blocked ditches. Here, we aim to evaluate the interaction of water table management and a severe mice infestation on the emissions of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4).We set up two field sites on both fen and bog peat in North-Western Germany. Submerged drains were installed at a distance of 4 to 5 m and with a target ditch level of 45 to 50 cm below mean soil surface. On the parcels with blocked ditches, the target ditch level is adjusted at 30 to 35 cm. The control parcels are drained by ditches and/or drainage pipes. Since 2017, diurnal CO2 flux measurement campaigns have been realised once every three to four weeks with transparent and opaque chambers and a portable gas analyser. CH4 and N2O samples are taken biweekly and additionally more frequently after fertilizer application.However, our experimental design was disrupted when, after an extremely dry summer and a dry and mild winter, the mice population grew strongly in 2019. We monitored both the number of mouse holes and the damage by mice. At the bog site, nearly no grass was left at the control site at the end of the year, while at the fen site, less, but still significant damage was observed. In this year, this was typical for the situation in North-Western Germany, where around 150,000 ha of grassland were severely damaged by mice. The sites with water table management were less effected by mice, but as food became scarce, they started to move into these wetter areas as well.Despite higher water levels, CO2 emissions in 2019 were partially higher than in previous years, especially at those sites affected by mice. With this presentation, we would like to discuss the effects of mice damage on soil respiration and on possibilities to disentangle water management effects from this (experimental and agricultural) calamity.