In this paper we show the quantitative and relative importance of phosphorus (P) losses from agri... more In this paper we show the quantitative and relative importance of phosphorus (P) losses from agricultural areas within European river basins and demonstrate the importance of P pathways, linking agricultural source areas to surface water at different scales. Agricultural P losses are increasingly important for the P concentration in most European rivers, lakes, and estuaries, even though the quantity of P lost from agricultural areas in European catchments varies at least one order of magnitude (<0.2 kg P ha(-1) to >2.1 kg P ha(-1)). We focus on the importance of P for the implementation of the EU Water Framework Directive and discuss the benefits, uncertainties, and side effects of the different targeted mitigation measures that can be adopted to combat P losses from agricultural areas in river basins. Experimental evidence of the effects of some of the main targeted mitigation measures hitherto implemented is demonstrated, including: (i) soil tillage changes, (ii) treatment of soils near ditches and streams with iron to reduce P transport from source areas to surface waters, (iii) establishment of buffer zones for retaining P from surface runoff, (iv) restoration of river-floodplain systems to allow natural inundation of riparian areas and deposition of P, and (v) inundation of riparian areas with tile drainage water for P retention. Furthermore, we show how river basin managers can map and analyze the extent and importance of P risk areas, exemplified by four catchments differing in size in Norway, Denmark, and the Netherlands. Finally, we discuss the factors and mechanisms that may delay and/or counteract the responses of mitigation measures for combating P losses from agricultural areas when monitored at the catchment scale.
fuse sources as the influence of P from point sources has decreased considerably in most countrie... more fuse sources as the influence of P from point sources has decreased considerably in most countries due to im- In this paper we show the quantitative and relative importance of proved wastewater treatment (European Environment phosphorus (P) losses from agricultural areas within European river
Haderslev Dam is a 272 ha lake in southern Denmark with a high recreational value. For decades th... more Haderslev Dam is a 272 ha lake in southern Denmark with a high recreational value. For decades the lake has been severely eutrophicated due to excessive phosphorus loading. Major point sources were cut off in the early 1990s and an upstream wetland was recreated. However, the ecological quality remains unsatisfactory. In this study we estimate the importance of agriculture on diffuse phosphorus (P) input to the lake by modelling combined with independent estimates for contributions from scattered dwellings not connected to a sewer and from background losses. We apply a newly developed Danish P index to the lake catchment for mapping of risk areas for diffuse phosphorus losses. For risk areas we suggest mitigation measures and estimate the effect of the mitigation measures on the total P loading of the lake as well as the associated costs.
The Mike 11-TRANS modelling system was applied to the lowland Gjern river basin in Denmark to ass... more 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 degrees 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.
An important step in the implementation of the Water Framework Directive is to define and charact... more An important step in the implementation of the Water Framework Directive is to define and characterize the natural status, designated as the reference condition (RC). Here we present the results of a type-specific screening for reference stream sites in Denmark using two different approaches. First, we performed a screening applying physicochemical, hydro-morphological and pressure criteria at the catchment, reach and site level of a total of 128 sites a priori selected by the regional water authorities as representing the best sites in Denmark. Second, we performed a GIS screening of all mapped streams in Denmark (26,000 km representing app. 90% of all Danish streams) using solely land use characteristics in the catchment area to target the search for larger stream sites to comply with the WFD requirements of type-specificity. Among the 128 sites we did not find any that fulfilled all criteria applied at the catchment, reach and site level using recommended RC threshold values and only three sites using threshold values that were less strict. Similarly very few km (<1%) of the GIS screened streams fulfilled catchment land use criteria, suggesting that the potential of identifying RC sites in Denmark is very limited. The lack of success in the screening process clearly demonstrates a need for alternative methods to establish RC for Danish streams. We propose a combined approach that includes the development of a guiding image for RC for all the stream biota needed to evaluate the ecological quality. This guiding image should be based on historical data, expert knowledge and investigations in streams situated in countries that are subjected to less intense land use and, at the same time, share both topographical and climatic similarities with Denmark, e.g. the Baltic countries.
This article presents a comparative study of modelled changes in nutrient losses from two Europea... more This article presents a comparative study of modelled changes in nutrient losses from two European catchments caused by modifications in agricultural practices. The purpose was not to compare the actual models used, but rather to assess the uncertainties a manager may be faced with after receiving decision support from consultants using different models. Seven modelling teams were given the same data about two catchments and their management characteristics and were asked to model the same changes in management practices using the model of their own choice. This can potentially cause accumulated 'errors' due to differences in the modelling teams' interpretation of relevant processes and definitions of boundary conditions (inputs). The study was carried out within the framework of the EUROHARP project, which aimed at harmonising procedures for quantifying diffuse losses of nitrogen and phosphorus from agriculture. Models are important for assessing river basin management plans (RBMPs) as required e.g. under the EC Water Framework Directive and Action Plans under the EC Nitrates Directive. This article illustrates some challenges with respect to interpreting such modelling results. The selected management scenarios include changes in fertiliser application levels, changes in livestock numbers and changes in land-use and crop rotation systems. Seven models were applied for the same scenarios in the Enza catchment in Italy and the Zelivka catchment in the Czech Republic. All models had been calibrated and validated with respect to historical data of climatic conditions, water quality and discharge measurements. The modelling results reveal a variation in predicted effects of the management scenarios, causing different conclusions with respect to choice of best management practice for reducing nutrient losses. The study demonstrates that it is important that care is taken by modellers and involved decision makers throughout the entire modelling process, both with regard to a common understanding of the problem definition, understanding of boundary conditions, and uncertainty of outputs and interpretation of results.
In this paper we show the quantitative and relative importance of phosphorus (P) losses from agri... more In this paper we show the quantitative and relative importance of phosphorus (P) losses from agricultural areas within European river basins and demonstrate the importance of P pathways, linking agricultural source areas to surface water at different scales. Agricultural P losses are increasingly important for the P concentration in most European rivers, lakes, and estuaries, even though the quantity of P lost from agricultural areas in European catchments varies at least one order of magnitude (<0.2 kg P ha(-1) to >2.1 kg P ha(-1)). We focus on the importance of P for the implementation of the EU Water Framework Directive and discuss the benefits, uncertainties, and side effects of the different targeted mitigation measures that can be adopted to combat P losses from agricultural areas in river basins. Experimental evidence of the effects of some of the main targeted mitigation measures hitherto implemented is demonstrated, including: (i) soil tillage changes, (ii) treatment of soils near ditches and streams with iron to reduce P transport from source areas to surface waters, (iii) establishment of buffer zones for retaining P from surface runoff, (iv) restoration of river-floodplain systems to allow natural inundation of riparian areas and deposition of P, and (v) inundation of riparian areas with tile drainage water for P retention. Furthermore, we show how river basin managers can map and analyze the extent and importance of P risk areas, exemplified by four catchments differing in size in Norway, Denmark, and the Netherlands. Finally, we discuss the factors and mechanisms that may delay and/or counteract the responses of mitigation measures for combating P losses from agricultural areas when monitored at the catchment scale.
fuse sources as the influence of P from point sources has decreased considerably in most countrie... more fuse sources as the influence of P from point sources has decreased considerably in most countries due to im- In this paper we show the quantitative and relative importance of proved wastewater treatment (European Environment phosphorus (P) losses from agricultural areas within European river
Haderslev Dam is a 272 ha lake in southern Denmark with a high recreational value. For decades th... more Haderslev Dam is a 272 ha lake in southern Denmark with a high recreational value. For decades the lake has been severely eutrophicated due to excessive phosphorus loading. Major point sources were cut off in the early 1990s and an upstream wetland was recreated. However, the ecological quality remains unsatisfactory. In this study we estimate the importance of agriculture on diffuse phosphorus (P) input to the lake by modelling combined with independent estimates for contributions from scattered dwellings not connected to a sewer and from background losses. We apply a newly developed Danish P index to the lake catchment for mapping of risk areas for diffuse phosphorus losses. For risk areas we suggest mitigation measures and estimate the effect of the mitigation measures on the total P loading of the lake as well as the associated costs.
The Mike 11-TRANS modelling system was applied to the lowland Gjern river basin in Denmark to ass... more 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 degrees 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.
An important step in the implementation of the Water Framework Directive is to define and charact... more An important step in the implementation of the Water Framework Directive is to define and characterize the natural status, designated as the reference condition (RC). Here we present the results of a type-specific screening for reference stream sites in Denmark using two different approaches. First, we performed a screening applying physicochemical, hydro-morphological and pressure criteria at the catchment, reach and site level of a total of 128 sites a priori selected by the regional water authorities as representing the best sites in Denmark. Second, we performed a GIS screening of all mapped streams in Denmark (26,000 km representing app. 90% of all Danish streams) using solely land use characteristics in the catchment area to target the search for larger stream sites to comply with the WFD requirements of type-specificity. Among the 128 sites we did not find any that fulfilled all criteria applied at the catchment, reach and site level using recommended RC threshold values and only three sites using threshold values that were less strict. Similarly very few km (<1%) of the GIS screened streams fulfilled catchment land use criteria, suggesting that the potential of identifying RC sites in Denmark is very limited. The lack of success in the screening process clearly demonstrates a need for alternative methods to establish RC for Danish streams. We propose a combined approach that includes the development of a guiding image for RC for all the stream biota needed to evaluate the ecological quality. This guiding image should be based on historical data, expert knowledge and investigations in streams situated in countries that are subjected to less intense land use and, at the same time, share both topographical and climatic similarities with Denmark, e.g. the Baltic countries.
This article presents a comparative study of modelled changes in nutrient losses from two Europea... more This article presents a comparative study of modelled changes in nutrient losses from two European catchments caused by modifications in agricultural practices. The purpose was not to compare the actual models used, but rather to assess the uncertainties a manager may be faced with after receiving decision support from consultants using different models. Seven modelling teams were given the same data about two catchments and their management characteristics and were asked to model the same changes in management practices using the model of their own choice. This can potentially cause accumulated 'errors' due to differences in the modelling teams' interpretation of relevant processes and definitions of boundary conditions (inputs). The study was carried out within the framework of the EUROHARP project, which aimed at harmonising procedures for quantifying diffuse losses of nitrogen and phosphorus from agriculture. Models are important for assessing river basin management plans (RBMPs) as required e.g. under the EC Water Framework Directive and Action Plans under the EC Nitrates Directive. This article illustrates some challenges with respect to interpreting such modelling results. The selected management scenarios include changes in fertiliser application levels, changes in livestock numbers and changes in land-use and crop rotation systems. Seven models were applied for the same scenarios in the Enza catchment in Italy and the Zelivka catchment in the Czech Republic. All models had been calibrated and validated with respect to historical data of climatic conditions, water quality and discharge measurements. The modelling results reveal a variation in predicted effects of the management scenarios, causing different conclusions with respect to choice of best management practice for reducing nutrient losses. The study demonstrates that it is important that care is taken by modellers and involved decision makers throughout the entire modelling process, both with regard to a common understanding of the problem definition, understanding of boundary conditions, and uncertainty of outputs and interpretation of results.
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Papers by Hans Andersen