Michael Trepel

Quantifying nitrogen retention in surface flow wetlands for environmental planning at the landscape-scale

Surface flow wetlands are valued highly for their high nutrient retention potential and their unique biodiversity. At present, there are an increasing number of activities aimed at restoring these sites as multifunctional landscape entities. The success of wetland restoration is however clearly dependent on the site selection to achieve the specific restoration goals. This study first presents a tool to identify the most suitable areas for the restoration of surface flow wetlands for water quality improvement in a given catchment and secondly compares three different mathematical equations in order to quantify the effect of nitrogen retention when restoring the previously selected, most suitable wetland sites. For site selection, a score system was developed which is linked to a Geographical Information System. The score system combines information from a given catchment in eight data layers including soil substrate, actual land use, relief features, hierarchical drainage basin classification, river proximity and socio-economic factors. The score system was applied to a potential use situation in the Neuwuhrener Au watershed (40 km2) in northern Germany belonging to the Baltic Sea drainage basin. Three areas were identified as most suitable for the restoration of surface flow wetlands. Their potential effect on nitrogen retention was evaluated using three different equations: (I) a linear relation between wetland load and a wetland; (II) an exponential equation between wetland load and wetland area; and (III) an exponential equation between wetland load and hydraulic retention time. The linear approach calculates increasing wetland retention with increasing upstream catchment area and appears to overestimate nitrogen retention in wetlands located more downstream. The two exponential equations calculated nitrogen retention in the three wetlands in the same order of magnitude. The results from the siting procedure and the prediction of nitrogen removal rates are useful for decision makers in wetland planning to base their decision on best available data and knowledge. The model comparison allows the incorporation of uncertainty in the decision progress which is seen as a necessary requirement when quantifying biological processes in environmental planning.

A GIS-Based Score System for Siting and Sizing of Created or Restored Wetlands: Two Case Studies

Water bodies are impacted by watershed loads in terms of nutrients and xenobiotics. This impact impairs the designated uses of the water body. Often preventive actions and end-of-pipe treatments do not reach the acceptable load to ensure the water quality standard in the water body. Wetlands are suitable tools for improving the self-purification capacity of a water system and can be used as a tool to reduce pollutant loads in a river network.This paper presents a methodology for the Siting and Sizing of created or restored wetlands at the watershed level, based on Geographical Information Systems (GIS) technique and estimations of wetland required area. The final outputs of the methodology are a Land Score System for Siting and a first rough estimation for the Sizing. The combination of these two elements is expected to be useful as a planning tool for watershed management and wetland planning.In order to assess the reliability of the procedure two very different case-studies are considered.

Denitrification in drained and rewetted minerotrophic peat soils in Northern Germany (Pohnsdorfer Stauung)

This study was conducted to assess the nitrogen removal potential of a minerotrophic peatland in Northern Germany, where hydrological conditions were partly restored in the beginning of the 1990s. Actual denitrification and the effect of nitrate (NO3-) and glucose additions on denitrification rates were determined in two flooded and one drained histosols in spring and summer 1998. In the flooded soils, denitrification was insignificant, but the drained field emitted significant rates. Additions of NO3- stimulated denitrification at all sites in spring and summer, whereas glucose additions had no effect. Low NO3- concentration in floodwater was obviously limiting denitrification in the flooded soils. In the drained soil, a coupled nitrification/denitrification might explain the low, but significant denitrification rates. No spontaneous production of nitrous oxide occurred in the flooded soils, whereas at the drained site an increase in spontaneous nitrous oxide concentration was measured during incubation in the summer samples. The suggested introduction of NO3- rich water from a stream flowing through the area would apparently induce denitrification in the flooded fields. (Less)

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.

Biologische Erfolgskontrolle Gewässerunterhaltung

Die Erfolgskontrolle zur Gewasserunterhaltung an funf Pilotstrecken in Schleswig-Holstein zeigt, dass es durch Einfuhrung einer Stromstrichmahd zu positiven Veranderungen der Wasserpflanzenbestande und einzelner Strukturparameter kommt. Auf die hiermit verbundene Erhohung der Lebensraumvielfalt hat die Wirbellosenfauna mit signifikanten Zunahmen fliesgewassertypischer Arten und einer Verbesserung des okologischen Zustands reagiert.