Assessing groundwater denitrification spatially is the key to targeted agricultural nitrogen regulation.

Globally, food production for an ever-growing population is a well-known threat to the environment due to losses of excess reactive nitrogen (N) from agriculture. Since the 1980s, many countries of the Global North, such as Denmark, have successfully combatted N pollution in the aquatic environment by regulation and introduction of national agricultural one-size-fits-all mitigation measures. Despite this success, further reduction of the N load is required to meet the EU water directives demands, and implementation of additional targeted N regulation of agriculture has scientifically and politically been found to be a way forward. In this paper, we present a comprehensive concept to make future targeted N regulation successful environmentally and economically. The concept focus is on how and where to establish detailed maps of the groundwater denitrification potential (N retention) in areas, such as Denmark, covered by Quaternary deposits. Quaternary deposits are abundant in many parts of the world, and often feature very complex geological and geochemical architectures. We show that this subsurface complexity results in large local differences in groundwater N retention. Prioritization of the most complex areas for implementation of the new concept can be a cost-efficient way to achieve lower N impact on the aquatic environment.

N-Map: High-resolution groundwater N-retention mapping and modelling by integration of geophysical, geological, geochemical, and hydrological data.

A key aspect of protecting aquatic ecosystems from agricultural nitrogen (N) is to locate (i) farmlands where nitrate leaches from the bottom of the root zone and (ii) denitrifying zones in the aquifers where nitrate is removed before entering the surface water (N-retention). N-retention affects the choice of field mitigation measures to reduce delivered N to surface water. Farmland parcels associated with high N-retention gives the lowest impact of the targeted field measures and vice versa. In Denmark, a targeted N-regulation approach is currently implemented on small catchment scale (approx. 15 km2). Although this regulatory scale is much more detailed than what has been used previously, it is still so large that regulation for most individual fields will be either over- or under-regulated due to large spatial variation in the N-retention. The potential cost reduction for farmers is of up to 20-30% from detailed retention mapping at the field scale compared to the current small catchment scale. In this study, we present a mapping framework (N-Map) for differentiating farmland according to their N-retention, which can be used for improving the effectiveness of targeted N-regulation. The framework currently only includes N-retention in the groundwater. The framework benefits from the incorporation of innovative geophysics in hydrogeological and geochemical mapping and modelling. To capture and describe relevant uncertainties a large number of equally probable realizations are created through Multiple Point Statistical (MPS) methods. This allows relevant descriptions of uncertainties of parts of the model structure and includes other relevant uncertainty measures that affects the obtained N-retention. The output is data-driven high-resolution groundwater N-retention maps, to be used by the individual farmers to manage their cropping systems due to the given regulatory boundary conditions. The detailed mapping allows farmers to use this information in the farm planning in order to optimize the use of field measures to reduce delivered agricultural N to the surface water and thereby lower the costs of the field measures. From farmer interviews, however, it is clear that not all farms will have an economic gain from the detailed mapping as the mapping costs will exceed the potential economic gains for the farmers. The costs of N-Map is here estimated to 5-7 €/ha/year plus implementation costs at the farm. At the society level, the N-retention maps allow authorities to point out opportunities for a more targeted implementation of field measures to efficiently reduce the delivered N-load to surface waters.

Cost effectiveness, nitrogen, and phosphorus removal in field-based woodchip bioreactors treating agricultural drainage water.

Nitrogen (N) and phosphorus (P) losses to surface and coastal waters are still critically high across Europe and globally. Measures to mitigate and reduce these losses are being implemented both at the cultivated land surface and at the edge-of-fields. Woodchip bioreactors represent a new alternative in Denmark for treating agricultural drainage water, and the present study-based on two years of data from five Danish field-based bioreactors-determined N removal rates varying from 1.49 to 5.37 g N m-3 d-1 and a mean across all bioreactors and years of 2.90 g N m-3 d-1. The loss of phosphorus was relatively high the first year after bioreactor establishment with rates varying from 298.4 to 890.8 mg P m-3 d-1, but in the second year, the rates ranged from 12.2 to 77.2 mg P m-3 d-1. The investments and the costs of the bioreactors were larger than expected based on Danish standard investments. The cost efficiency analysis found the key issues to be the need for larger investments in the bioreactor itself combined with higher advisory costs. For the four woodchip bioreactors considered in the cost efficiency analysis, the N removal cost was around DKK 350 per kg N ($50 per kg N), which is ca. 50% higher than the standard costs defined by the Danish authorities. Based on the estimated costs of the four bioreactor facilities included in this analysis, a bioreactor is one of the most expensive nitrogen reduction measures compared to other mitigation tools.

Establishing long-term nitrogen response of global cereals to assess sustainable fertilizer rates.

Insight into the response of cereal yields to nitrogen fertilizer is fundamental to improving nutrient management and policies to sustain economic crop benefits and food sufficiency with minimum nitrogen pollution. Here we propose a new method to assess long-term (LT) regional sustainable nitrogen inputs. The core is a novel scaled response function between normalized yield and total net nitrogen input. The function was derived from 25 LT field trials for wheat, maize and barley in Europe, Asia and North America and is fitted by a second-order polynomial (R2 = 0.82). Using response functions derived from common short-term field trials, with soil nitrogen not in steady state, gives the risks of soil nitrogen depletion or nitrogen pollution. The scaled LT curve implies that the total nitrogen input required to attain the maximum yield is independent of this maximum yield as postulated by Mitscherlich in 1924. This unique curve was incorporated into a simple economic model with valuation of externalities of nitrogen surplus as a function of regional per-capita gross domestic product. The resulting LT sustainable nitrogen inputs range from 150 to 200 kgN ha-1 and this interval narrows with increasing yield potential and decreasing gross domestic product. The adoption of LT response curves and external costs in cereals may have important implications for policies and application ceilings for nitrogen use in regional and global agriculture and ultimately the global distribution of cereal production.

Costs of regulating ammonia emissions from livestock farms near Natura 2000 areas - analyses of case farms from Germany, Netherlands and Denmark.

Natura 2000 areas are designated according to the EU's Birds and Habitats Directives in order to protect particular habitats and species. A variety of these habitats and species are particularly sensitive to deposition of nitrogen caused by ammonia emissions. Livestock farming is the primary source of this pollution. The purpose of this paper is to compare the costs of reaching the ammonia emission targets for different livestock farms near Natura 2000 sites in the Netherlands, Germany (Schleswig-Holstein), and Denmark. These countries have some of the highest NH3 deposition rates in Europe, and Germany in particular will have to implement new measures to reach the NEC requirements for 2030. This will also benefit nature sites in Denmark as a large share of the ammonia emissions is dispersed over long distances. The general regulation includes implementation of BAT technologies and emission ceilings. The analysis looks at regulatory aspects, the emission requirements and the cost of implementing the technologies to reduce emissions further. The selected case farms are a finisher farm and a dairy farm, and the distance to a Natura 2000 site is 400 and 2000 m. In all three countries, relatively few livestock farms are situated near or inside Natura 2000 areas. The regulatory approach is very different in the three countries and key issues are: additional deposition from projects, neighbouring livestock farms (cumulation), the inclusion of background deposition and the use of the critical loads concept. The Dutch PAS system is interesting as projected reductions in emissions are distributed as additional "room for development" today. The costs for the case farm with finishers in Schleswig-Holstein are the highest as the Filter Decree requires the use of air scrubbers. The findings suggest that farms 400 m from a Natura 2000 site in the Netherlands face lower and less costly constraints than in the other countries, whereas the opposite is the case for farms 2000 m from Natura 2000 sites. The requirements near Natura 2000, where strict requirements apply, are so high that farms will expand at a different site instead.

Including aesthetic and recreational values in cost-effectiveness analyses of land use change based nitrogen abatement measures in Denmark.

In recent years there has been an increased focus on including aspects such as greenhouse gas emissions and biodiversity in cost-effectiveness analyses of nitrogen (N) abatement measures. Side-effects such as aesthetic and recreational benefits generated by the land use changes implied by some N abatement measures, such as afforestation and constructed wetlands, are included in ecosystem service approaches, but seldom explicitly in cost-effectiveness analyses. While several studies have estimated these values for e.g. forests and wetlands, per se, few have studied how these effects are valued by the general population when generated through the implementation of land use changes driven by measures aimed at reducing the loss of nitrogen from agriculture. The land use changes implied by the N abatement measures have different characteristics to that of the evaluations of forests for recreation or larger wetlands created or maintained for biodiversity, mainly because the area affected varies considerably in size and shape. In this paper, we estimate the welfare economic impacts of some of the potential side-effects, such as recreational and aesthetic effects, of three N abatement measures related to agricultural land use change: afforestation, constructed wetlands or energy crops. We incorporate the value of these side-effects in a standard cost-effectiveness analysis and discuss the policy implications. This allows us to evaluate to what extent the inclusion of these side-effects change the ranking of the measures and the cost levels used. We thereby provide a more holistic approach to the cost-effectiveness analysis of land use change based N abatement measures, and discuss the challenges relating to the spatial aspects that arise when accounting for the value of the analyzed side-effects. The analysis shows that public access to the area largely determine whether the selected measures are perceived as positive or negative. The impact of the analyzed side-effects on the cost-effectiveness analysis critically depends on the size of the affected population, as the value of the side-effects are measured per household.

Economic gains from targeted measures related to non-point pollution in agriculture based on detailed nitrate reduction maps.

From 1990 to 2003, Denmark reduced N-leaching from the root zone by 50%. However, more measures are required, and in recent years, the focus has been on how to differentiate measures in order to ensure that they are implemented where the effect on N-loss reductions per ha is the greatest. The purpose of the NiCA project has been to estimate the natural nitrate reduction in the groundwater more precisely than before using a plot size down to 1ha. This article builds on these findings and presents the possible economic gains for the farmer when using this information to reach a given N-loss level. Targeted measures are especially relevant where the subsurface N-reduction varies significantly within the same farm and national analyses have shown that a cost reduction of around 20-25% using targeted measures is likely. The analyses show an increasing potential with increasing variation in N-reduction in the catchment. In this analysis, the knowledge of spatial variation in N-reduction potential is used to place measures like catch crops or set-a-side at locations with the greatest effect on 10 case farms in the Norsminde Catchment, Denmark. The findings suggest that the gains are from 0 to 32€/ha and the average farm would gain approximately 14-21€/ha/year from the targeted measures approach. The analysis indicates that the economic gain is greater than the costs of providing the detailed maps of 5-10€/ha/year. When N-loss reduction requirements are increased, the economic gains are greater. When combined with new measures like mini-wetlands and early sowing the economic advantage is increased further. The paper also shows that not all farms can use the detailed information on N-reduction and there is not a clear link between spatial variation in N-reduction at the farm level and possible economic gains for all these 10 farms.

Nitrate reduction in geologically heterogeneous catchments--a framework for assessing the scale of predictive capability of hydrological models.

In order to fulfil the requirements of the EU Water Framework Directive nitrate load from agricultural areas to surface water in Denmark needs to be reduced by about 40%. The regulations imposed until now have been uniform, i.e. the same restrictions for all areas independent of the subsurface conditions. Studies have shown that on a national basis about 2/3 of the nitrate leaching from the root zone is reduced naturally, through denitrification, in the subsurface before reaching the streams. Therefore, it is more cost-effective to identify robust areas, where nitrate leaching through the root zone is reduced in the saturated zone before reaching the streams, and vulnerable areas, where no subsurface reduction takes place, and then only impose regulations/restrictions on the vulnerable areas. Distributed hydrological models can make predictions at grid scale, i.e. at much smaller scale than the entire catchment. However, as distributed models often do not include local scale hydrogeological heterogeneities, they are typically not able to make accurate predictions at scales smaller than they are calibrated. We present a framework for assessing nitrate reduction in the subsurface and for assessing at which spatial scales modelling tools have predictive capabilities. A new instrument has been developed for airborne geophysical measurements, Mini-SkyTEM, dedicated to identifying geological structures and heterogeneities with horizontal and lateral resolutions of 30-50 m and 2m, respectively, in the upper 30 m. The geological heterogeneity and uncertainty are further analysed by use of the geostatistical software TProGS by generating stochastic geological realisations that are soft conditioned against the geophysical data. Finally, the flow paths within the catchment are simulated by use of the MIKE SHE hydrological modelling system for each of the geological models generated by TProGS and the prediction uncertainty is characterised by the variance between the predictions of the different models.

Costs and benefits of nitrogen for Europe and implications for mitigation.

Cost-benefit analysis can be used to provide guidance for emerging policy priorities in reducing nitrogen (N) pollution. This paper provides a critical and comprehensive assessment of costs and benefits of the various flows of N on human health, ecosystems and climate stability in order to identify major options for mitigation. The social cost of impacts of N in the EU27 in 2008 was estimated between €75-485 billion per year. A cost share of around 60% is related to emissions to air. The share of total impacts on human health is about 45% and may reflect the higher willingness to pay for human health than for ecosystems or climate stability. Air pollution by nitrogen also generates social benefits for climate by present cooling effects of N containing aerosol and C-sequestration driven by N deposition, amounting to an estimated net benefit of about €5 billion/yr. The economic benefit of N in primary agricultural production ranges between €20-80 billion/yr and is lower than the annual cost of pollution by agricultural N which is in the range of €35-230 billion/yr. Internalizing these environmental costs would lower the optimum annual N-fertilization rate in Northwestern Europe by about 50 kg/ha. Acknowledging the large uncertainties and conceptual issues of our cost-benefit estimates, the results support the priority for further reduction of NH3 and NOx emissions from transport and agriculture beyond commitments recently agreed in revision of the Gothenburg Protocol.

Combining active farmer involvement with detailed farm data in Denmark: a promising method for achieving water framework directive targets?

The Water Framework Directive (WFD) encourages active involvement during its implementation, although no specific participatory methods are suggested, whilst implementing the target-oriented Directive will require detailed agri-environmental data at catchment and farm level. The paper is a case study of the Danish AGWAplan project, which actively involved farmers in the selection of measures to reduce diffuse nutrient pollution at farm and catchment level, thereby providing an example of how active involvement might be operationalised. Active involvement has been identified as being of central importance to the success of the WFD. The project also entailed the accumulation of extensive agri-environmental data. The aim of the paper is to evaluate AGWAplan to establish the extent to which its expected objectives have been achieved and how, and to determine whether the project approach might facilitate WFD goals if implemented in forthcoming river basin management plans (RBMPs). AGWAplan resulted in advantageous outcomes, including win-win solutions to reduce nutrient leaching and greater acceptance of policy, although the original reduction targets where not fully reached. The paper concludes that actively involving farmers in a similar manner in RBMPs may make an important contribution to the implementation of the WFD, although caveats regarding its potential for transfer to other areas are identified.