Costs and Potential of Raising the Groundwater Table As a Greenhouse Gas Mitigation Option for Grasslands in Peatland Areas.

In Northern Germany, agricultural production accounts for >30% of total anthropogenic GHG emissions. Of these, more than 40% are derived from the drainage of peatland for their use in intensive dairy agriculture. The most effective mitigation tool for these emissions is an increment of groundwater tables. In the presented study we calculated the effect of a proposed higher groundwater table in a fen area (21.700 ha) in two scenarios (S_I: 10 cm and S_II: 20 cm groundwater elevation) on GHG emissions and costs of the proposed mitigation tool. Land-use on organic soils in that area is divided into 71% intensive grassland production (G_I; 3-4 silage cuts), 24% extensive grassland production (G_E; 1-2 silage cuts per year) and 5% of non-use (N_U) due to waterlogged soils. Results showed that due to higher groundwater tables GHG emissions were reduced by 9 (S_I) and 21 (S_II) t CO₂-_eq / ha / year. The share of land-use for G_I, G_E and N_U in the study area changed to 27/44/29% in S_I and 5/22/73% in S_II, respectively, thus shifting the dominant management form from intensive grasslands to fallow. The economic loss for dairy farms was estimated with 115 (S_I) and 372 (S_II) € / ha / year, being equivalent to costs of 11.9 (S_I) and 16.7 (S_II) € / t CO_2eq / year. We conclude that the proposed groundwater elevation would considerably reduce the GHG emissions from the agricultural sector by 9–20% in the state. Economic costs as result of lower total milk yields expressed in € / t CO_2eq savings are lower compared to other mitigation tools. However, costs per farm were not evenly distributed. Small farms classes (<60 ha) are more affected than larger farm classes (>200 ha), which would accelerate the structural change of dairy farms in that area.