For additional info:
http://person.au.dk/en/hea@dmu.dk/

My research interests are:

• Modelling of nutrient losses at the farm and catchment scale
• Simplified indices for identifying risk areas for diffuse nutrient losses
• Mitigation measures to reduce diffuse nutrient losses

Selected publications:
Andersen, H.E., Kronvang, B., Larsen, S.E., Hoffmann, C.C., Jensen, T.S. & Rasmussen, E.K. (2006) Climate-change impacts on hydrology and nutrients in a Danish lowland river basin. - Science of the Total Environment 365: 223-237.

The Mike 11–TRANS modelling system was applied to the lowland Gjern river basin in Denmark to assess climate-change impacts on hydrology and nitrogen retention processes in watercourses, lakes and riparian wetlands. Nutrient losses from land to surface waters were assessed using statistical models incorporating the effect of changed hydrology. Climate-change was predicted by the ECHAM4/OPYC General Circulation Model (IPCC A2 scenario) dynamically downscaled by the Danish HIRHAM regional climate model (25 km grid) for two time slices: 1961–1990 (control) and 2071–2100 (scenario). HIRHAM predicts an increase in mean annual precipitation of 47 mm (5%) and an increase in mean annual air temperature of 3.2 °C (43%).

The HIRHAM predictions were used as external forcings to the rainfall-runoff model NAM, which was set up and run for 6 subcatchments within and for the entire, Gjern river basin. Mean annual runoff from the river basin increases 27 mm (7.5%, p < 0.05) when comparing the scenario to the control. Larger changes, however, were found regarding the extremes; runoff during the wettest year in the 30-year period increased by 58 mm (12.3%). The seasonal pattern is expected to change with significantly higher runoff during winter. Summer runoff is expected to increase in predominantly groundwater fed streams and decrease in streams with a low base-flow index. The modelled change in the seasonal hydrological pattern is most pronounced in first- or second-order streams draining loamy catchments, which currently have a low base-flow during the summer period. Reductions of 40–70% in summer runoff are predicted for this stream type.

A statistical nutrient loss model was developed for simulating the impact of changed hydrology on diffuse nutrient losses (i.e. losses from land to surface waters) and applied to the river basin. The simulated mean annual changes in TN loads in a loamy and a sandy subcatchment were, respectively, + 2.3 kg N ha- 1 (8.5%) and + 1.6 kg N ha- 1 (6.9%).

The rainfall-runoff model and the nutrient loss model were chained with Mike 11–TRANS to simulate the combined effects of climate-change on hydrology, nutrient losses and nitrogen retention processes at the scale of the river basin. The mean annual TN export from the river basin increased from the control to the scenario period by 7.7%. Even though an increase in nitrogen retention in the river system of 4.2% was simulated in the scenario period, an increased in-stream TN export resulted because of the simulated increase in the diffuse TN transfer from the land to the surface-waters.

Andersen, H.E. & Kronvang, B. (2006) Modifying and evaluating a P index for Denmark. - Water, Air and Soil Pollution 174: 341-353.

The European Union recently adopted the Water Framework Directive aiming at protecting and enhancing the status of aquatic ecosystems. The Water Framework Directive mandates EU member states to develop river basin management plans for each river basin. Consequently, water district managers need tools for identifying critical source areas within a catchment in order to target cost-effective remedial measures. The P Index could be well suited for screening large areas because of its low demand for input data and manpower compared to mechanistic, process based models. The P Index needs to be modified to local or regional conditions in order to incorporate all potential P loss pathways. In Denmark tile drains and leaching are considered major P loss pathways. We modified the Pennsylvania P Index to reflect Danish conditions. The Pennsylvania P Index and the modified Danish P Index were applied on a 1000 km[2] catchment. In order to test the P Indices we examined their capability to correctly rank measured annual diffuse total P losses from twelve sub-catchments within the 1000 km[2] catchment. Both P Indices, calculated on a sub-catchment basis, correlated with total P losses. The Danish P Index, however, performed distinctly better than the Pennsylvania P Index and explained 85% of the variation in measured diffuse total P losses.

Andersen, H.E., Kronvang, B. & Larsen, S.E. (2005) Development, validation and application of Danish empirical phosphorus models. - Journal of Hydrology 304: 355-365.

Phosphorus (P) is the limiting nutrient for algae growth in most Danish lakes and coastal waters. Discharge of P from point sources has been reduced greatly, however, no trend in diffuse P loss has been detected. In spite of the overall reduction in P discharge, the ecological condition of most lakes and coastal waters does not comply with the objectives set by regional authorities. Thus, in order to achieve ‘good ecological status’ of surface waters, as required by the EU Water Framework Directive, there is a future need to reduce diffuse P loss. Consequently, water district managers will need tools for assessing diffuse P losses at the catchment scale. They will also need tools to help them select for each specific catchment the appropriate measures to reduce P losses. We suggest that empirical phosphorus models can be an important part of such a tool. A number of international empirical phosphorus models are reviewed. The development, validation and application of six Danish empirical phosphorus models for total phosphorus (TP), particulate phosphorus (PP) and dissolved reactive phosphorus (DRP) is described as a case study. Manageable parameters relating to agricultural practices are generally absent in the international models reviewed. In the Danish models such parameters play a relatively minor role compared to non-manageable parameters like soil type and hydrology. The importance of validating empirical models and of uncertainty assessments on model predictions is stressed.