• Simon Vang Pedersen
4. term, Environmental Engineering, Master (Master Programme)
Torsted Lake in Northern Jutland, Denmark, is a wetland which was restored in November 2016. A 5 ha shallow lake and a 48 ha surrounding wetland was established by removing existing drainage infrastructure and creating meandering inlets and outlets. Parts of the new lake were deepened through excavation. Three methods were used to estimate the annual denitrification of the system. The first method was entirely based on empirical data from comparable systems, and was used to assess the theoretical input and removal of nitrogen. With the second method, direct field measurements of flow and nitrogen concentrations in the in- and outlets were used to calculate the input of nitrogen, and an empirical model was subsequently used to estimate the denitrification. The third method was entirely based on field measurements during four months prior to and following the restoration, and denitrification was derived from a mass balance of nitrogen in the system. The degree to which denitrification in the lake can be optimized by enrichment of the sediment with organic carbon was also assessed. By laboratory analysis the potential denitrification was estimated for substrates with varying concentrations of easily degradable organic carbon (topsoil, straw, sawdust, charcoal, and sand). To assess whether soil amendment is viable in the long term, the rate of sedimentation in the lake was measured using sediment traps. Prior to restoration, no measurable amount of denitrification was present in the area. Four months after the works finished, the denitrification was found at a rate of 40 kg N ha−1, and expected to rise further to 60–80 kg N ha−1 within the first year. In regards to the analysed substrates, the topsoil is the most economically viable for amendment, potentially increasing denitrification in the lake by 25 %. However, this approach will only increase the denitrification of the entire system by 3 %, as most of the denitrification happens in areas where water percolates through the soil, and within 7–10 years, natural sedimentation in the lake will have superseded the effect.
Publication date10 Jun 2017
Number of pages45
ID: 259464318