Aspects of peat conservation and water management

An extended water regime model was used for calculating the evapotranspiration, groundwater recharge, and peat mineralization (CO ₂ and N release) for various fen locations with grassland utilization in dependence on the groundwater level. The results show that an increasing groundwater level leads to a strong decline of the actual evapotranspiration E_t. For example, increasing the groundwater level from 30 to 120 cm diminishes the E_t by up to 230 mm a^-1. A positive groundwater recharge only takes place at groundwater levels of 90 cm and more. At smaller distances the capillary rise into the rooting zone during the summer months is greater than the water seepage during the winter months, so that a negative groundwater recharge-balance is reached in the course of a year. The CO₂- and the N-release, as well as the annual decline in peat thickness, increase significantly with rising groundwater levels. The results show, that varying the groundwater level can influence the water regime and the peat mineralization significantly. The lower the groundwater level the less is the peat decomposition. The demand for a groundwater level as small as possible is, however, limited by an agricultural utilization of the fens. Choosing the optimum groundwater level should consider the aims (1) peat mineralization, (2) gas emission (CO₂, CH₄, N ₂O), and (3) crop production. If a grassland utilization is supposed to be made possible and all three aims above are given equal importance, the groundwater level should be maintained at 30 cm. At this distance, about 90% of the optimum plant output can be reached. The peat mineralization can be reduced to 30 to 40% of the maximum peat mineralization. The gas emission amounts to 50-60% of the maximum value.