Ecohydrological characterisation of a degenerated valley peatland in Northern Germany for use in restoration

Abstract

Present environmental policy aims to restore wetlands for multifunctional purposes and requires quantitative information on the spatially interrelated biohydrochemical processes which allow wetlands to regulate water- and nutrient flow on different scales. For this purpose, this study presents an ecohydrological system analysis as a basis for a future management concept of the Eider valley peatland. This study combines field data with existing knowledge to set up different modelling techniques to study hydrological processes and nitrogen transformations. The Eider valley of northern Germany is a riverine freshwater wetland of 150 ha. Mire genesis was dominated first by river water inflow from the upstream catchment area, and in a later successional stage by groundwater inflow at the mire margins. Drainage, land use intensification and river regulation have resulted in severe degeneration of the peatland. Altering of the water flow patterns led to the mobilisation of nutrients and resulted in eutrophication of the sites. Abandonment of the mown or grazed sites led to the establishment of species poor Urtica dioica stands. The scenario calculations of the nitrogen budget of the peatland with a process oriented nitrogen model indicate that a water level increase of 30 cm is not sufficient to reduce peat loss due to oxidation. On the basis of the system analysis, restoration prospects for the Eider valley peatland are discussed where the historical subsurface flow pattern can be a long term restoration goal. Due to irreversible changes in peat hydraulic conductivities combined with subsidence, it is only possible to restore surface flow on top of the peat. Raising river water level will result in a shallow lake system. The limnic stage is a draw-back in the genesis of the valley, but necessary for the restoration of wetlands as self-evolving landscape entities.