The socio-economic costs and benefits of environmental groundwater threshold values in
the Scheldt basin in the Netherlands
Authors:
Roy Brouwer, Sebastiaan Hess, Maaike Bevaart, Kees Meinardi
Institute for Environmental Studies (IVM), Vrije Universiteit Amsterdam De Boelelaan 1087, 1081 HV, Amsterdam, the Netherlands
IVM Report Number R06-05
24 November 2006
Abstract
The main objective of Work Package 5 (Socio-economic analysis) in the EU funded project BRIDGE is to develop, apply and test economic methods for the identification of economically efficient groundwater threshold values. The objective is not to derive threshold values for specific groundwater pollutants for which no threshold values are available yet, but to demonstrate the use and usefulness of the applied economic methods in sustainable groundwater policy and management. This paper
presents the results for nitrate contamination from agriculture in the Dutch Scheldt basin as one of the case studies elaborated in WP5. The same methodology can be used for the economic underpinning of other relevant pollutants for which threshold values have to be established in the near future following the adoption and implementation of the European Groundwater Directive.
The work in WP5 differs from the other BRIDGE work packages in that it focuses explicitly on practical and feasible groundwater management to reach possible groundwater threshold values.
Corresponding with the way environmental objectives are set in the European Water Framework Directive (WFD), i.e. based on some ecological reference situation, the BRIDGE methodology to establish groundwater threshold values excludes any a priori economic considerations or criteria.
Economic criteria start playing a role after the threshold values have been set, namely in the design of practical groundwater management measures. For example, measures have to be cost-effective according to the WFD, meaning that the environmental threshold values have to be reached at their lowest cost. The socio-economic welfare implications of establishing different groundwater threshold values, including natural background levels, are addressed in this case study through (1) cost-
effectiveness analysis using an integrated groundwater-surface water model, (2) contingent valuation of the non-market benefits of groundwater protection, and (3) cost-benefit analysis of different groundwater threshold values.
Assessing the environmental impact of programs of measures on water quality with some degree of confidence is one of the most important problems in the implementation of the WFD, and will also be one of the most important challenges in the implementation of the new European Groundwater Directive. Given the fact that the groundwater threshold values are fixed in terms of pollutant concentration levels, the effect of policy measures has to be evaluated in terms of their impact on water quality basin-wide. This is currently the weakest link: the relationship between socio-economic activities (pressures) and the actual impact of these activities or changes in these activities on
groundwater quality. In the case study presented here, an integrated groundwater-surface water model is used to better understand these relationships in time and space. For this purpose an existing
groundwater model was adapted and modified to reflect the specific hydrological, geological and chemical groundwater processes and conditions in the case study area.
The model application does not solve all the problems surrounding the environmental impact assessment. The results are still surrounded by many uncertainties, but the modeling approach provides a more structured and systematic approach to deal with these uncertainties. Existing expert knowledge is captured and made explicit in formal linear and non-linear relationships. Presenting these relationships in a transparent and systematic way and formalizing them in a model opens up the opportunity to discuss and debate them in a more structured way than currently is the case, and modify these relationships based on scientific progress.
In the contingent valuation survey local residents in the case study area are asked for their knowledge, awareness, perception, attitudes, preferences and valuation of different groundwater threshold values.
For this purpose a ‘groundwater quality ladder’ is developed and tested, reflecting different use and non-use related economic values. The economic value of the non-market benefits of different
groundwater threshold values is measured in terms of public willingness to pay. This was done in such a way that the estimated costs related to different groundwater threshold values are comparable with the estimated economic values for the same groundwater threshold values in a cost-benefit analysis.
Although economic use values dominate the economic values found for different groundwater threshold values, we also find a substantial non-use or existence value for groundwater protection.
Taxpayers are willing to pay a substantial amount of money extra for groundwater quality that is close to its natural background level, providing support for the receptor based approach advocated in BRIDGE.
The economic impact assessment provides the basis for the evaluation of possible disproportionate costs, and consequently possible objective or time derogation as in the WFD, i.e. lowering
groundwater threshold values or delaying them in time. The economic analysis is merely one criterion in the decision-making procedure about disproportionate costs. The question whether a higher
threshold value of 25 milligrams nitrate per litre for the whole basin compared to the current threshold value of 50 milligrams results in disproportional costs depends on policy maker assessment of the presented economic information. Different policymakers may hold different views depending on the available policy alternatives and their perceived viability, that is, the political support they expect to receive for the implementation of these measures from the sector involved. Asking taxpayers as one of the sectors expected to be affected by future groundwater policy to inform policy makers about the importance and value they attach to groundwater protection, the cost of a more stringent groundwater threshold value up to 25 milligrams per litre for the whole basin should not exceed 30 euro per household per year over and above what they currently pay for water. In this way the taxpayer’s maximum willingness to pay is used as one of the possible economic threshold values for disproportional costs, accounting for the taxpayer’s ability to pay.
Acknowlegments
This report is part of Work Package 5 (‘Socio-Economic Analysis’) coordinated by the Institute for
Environmental Studies (IVM), Vrije Universiteit Amsterdam, in the EU funded Specific Targeted Research project (STREP) ‘Background cRiteria for the IDentification of Groundwater thresholds’ (BRIDGE), contract n° SSPI-2004-006538. We are grateful to the regional WFD Groundwater Working Group in Zeeland for their valuable contribution to this project in the form of the supplied data and information. In particular, we want to thank Eddie Lere, Lein Kaland and Arnold Keizer from the Province Zeeland for their continuous support and willingness to share their expert knowledge with us. Also the information about the agricultural cost indicators provided by Lennard Mokveld and Stijn Reinhard from the Agricultural-Economics Institute is gratefully acknowledged here, and the information provided by the agriculture and water experts Jos Goosen and Rien Klippel from the regional water board Zeeuwse Eilanden. A final word of thanks also goes to the Scheldt river basin coordinator Loes de Jong for her support and allowing us to collaborate so closely with all the experts involved in the implementation of the WFD in the basin.
Table of content
Abstract
1. Introduction
2. Methodological framework
2.1. The role of economics in the Water Framework Directive 2.2. Practical steps
3. General case study description
4. Identification of groundwater priority substances and pollution sources
5. Future trends and driving forces underlying groundwater use until 2015
6. Risk of non-compliance: expected pressures and impacts until 2015
7. Current groundwater policy measures
8. Additional groundwater protection measures 8.1. Individual groundwater protection measures 8.2. Groundwater protection policy scenarios
9. Integrated modelling of the environmental impacts of groundwater protection measures on groundwater bodies and connected surface water bodies
9.1. Introduction 9.2. Model structure
9.2.1. Precipitation module
9.2.2. Nutrient concentrations and transport 9.2.3. Hydrological module
9.2.4. Nitrate module
9.2.5. Regional specification and calibration
9.3. Model results
9.3.1. Baseline scenario
9.3.2. Policy scenario A: Livestock extensification 9.3.3. Policy scenario B: Manure free zones 9.3.4. Policy scenario C: After crop
9.3.5. Policy scenario D: Optimization manure application practices 9.3.6. Policy scenario E: Nature development
10. Cost-effectiveness analysis: identification of the least cost way to reach groundwater threshold values in 2015
10.1. Introduction
10.2. Cost assessment and cost-effectiveness of policy scenarios 10.3. Uncertainty and sensitivity analysis
11. Public perception and valuation of the non-market benefits of groundwater protection related to different threshold values
11.1. Introduction
11.2. Sample and questionnaire design
11.3. Respondent demographic and socio-economic characteristics 11.4. Public tap water use and price awareness
11.5. Public knowledge and perception of groundwater quality
11.6. Public preferences and willingness to pay for different groundwater threshold values 11.7. Factors determining public willingness to pay for different groundwater threshold values 11.8. Total economic value of different groundwater threshold values
12. Cost-benefit analysis: identification of the economic efficiency of different groundwater threshold values
12.1. Introduction
12.2. Costs and benefits of reaching ‘good’ groundwater quality in 2015 12.3. Costs and benefits of reaching ‘very good’ groundwater quality in 2015 12.4. Uncertainty and sensitivity analysis
13. Conclusions and recommendations
References
1. Introduction
Aquatic ecosystems are adaptive, but ecologically sensitive systems, which provide many important services to human society. This explains why in recent years much attention has been directed towards the formulation and operation of sustainable management strategies, the recent adoption of the European Water Framework Directive (2000/60/EC) being a good case in point. Both natural and social sciences can contribute to an increased understanding of relevant processes and problems associated with such strategies. The key to a better
understanding of aquatic ecosystem problems and their mitigation through more sustainable management lies in the recognition of the importance of the diversity of functions and values supplied to society at different spatial and time scales. This includes a better scientific understanding of aquatic ecosystem structure and processes and the significance of the associated socio-economic and cultural values (Brouwer et al., 2003).
The Water Framework Directive (WFD) is the first European Directive to explicitly recognize the importance of this interdependency between aquatic ecosystems and their socio-economic values and provides a much more integrated catchment approach to water policy. Investments and water resource allocations in river basin management plans will be guided by cost
recovery, cost-effectiveness criteria and the polluter pays principle. The plan formulation and assessment process must furthermore include a meaningful consultative dialogue with
relevant stakeholders. Such a dialogue will inevitably raise socio-political equity issues across the range of interest groups and therefore affect the management strategies.
Although groundwater resources are an integral part of catchment wide aquatic ecosystems, their position and role are not well defined in the WFD. No new quality standards were listed that apply uniformly to all groundwater bodies throughout Europe to define good groundwater chemical status, because of the natural variability of groundwater chemical composition and the present lack of monitoring data and knowledge. Article 17 stipulates that the European Parliament and the Council shall adopt specific measures to prevent and control groundwater pollution on the basis of a proposal for a new Groundwater Directive. The new Groundwater Directive (GWD) complements the provisions already in place in the WFD and in the existing Groundwater Directive 80/68/EEC, which will be repealed in 2013 under the WFD.
In its communication COM(2003)550, the European Commission states that groundwater bodies shall be considered as having good groundwater chemical status when the measured or predicted concentration of nitrates, pesticides and biocides do not exceed standards laid down in existing legislation (Directives 91/676/EEC, 91/414/EEC and 98/8/EC respectively). For other pollutants good groundwater chemical status is reached when it can be demonstrated that the concentrations of substances do not undermine the achievement of the environmental objectives (good ecological and chemical status) for associated surface waters or result in any significant deterioration of the ecological or chemical status of these surface water bodies, nor should concentrations result in any significant damage to terrestrial ecosystems which depend directly on the groundwater body. For these other pollutants, groundwater quality threshold values have to be established by Member States in all bodies of groundwater that were characterized in the recent first WFD reporting obligations as being at risk.
In order to support this process of determining future groundwater quality threshold values for European groundwater bodies, the Environment Directorate-General of the European
Commission commissioned a 2-year project to develop a general methodology for establishing groundwater threshold values called BRIDGE (Background cRiteria for the IDentification of Groundwater thresholds, contract n° SSPI-2004-006538). The methodology has to apply to substances from both natural and anthropogenic sources and threshold values defined at the level of national river basin districts or groundwater body levels should be representative for the groundwater bodies at risk in accordance with the analysis of pressures and impacts carried out under the WFD. In the proposal for the new GWD these threshold values will be used for defining good groundwater chemical status.
As part of BRIDGE, a socio-economic assessment is carried out in support of setting threshold values for specific groundwater pollutants and the evaluation of the social and economic consequences of specific threshold values. The assessment procedure follows the economic analysis outlined in the Water Framework Directive (WFD) and more specifically in the WATECO guidance for the economic analysis. Based on a common methodology (Brouwer, 2005a), the socio-economic assessment procedure is tested and illustrated in a number of practical case studies in France, Finland, Latvia, the Netherlands and Portugal. The main objective of this report is to present the results of the socio-economic assessment
procedure applied in one of these case studies: the Scheldt basin in the Netherlands.
The remainder of this report is organized as follows. Chapter 2 briefly reviews the methodological steps in the socio-economic assessment procedure. These steps are subsequently elaborated in separate chapters (chapters 3-12). Chapter 13 concludes and discusses the implications of the outcomes of the socio-economic assessment procedure for future groundwater threshold values.
2. Methodological framework
2.1. The role of economics in the Water Framework Directive
The WFD is one of the first European Directives in the domain of water, which explicitly recognizes the role of economics in reaching environmental and ecological objectives. The Directive calls for the application of economic principles (e.g. polluter pays principle), approaches and tools (e.g. cost-effectiveness analysis) and for the consideration of economic instruments (e.g. water pricing methods) for achieving good water status for water bodies in the most effective manner. The Guidance Document on the Economic Analysis prepared in 2002 by the European Water and Economics Working Group (WATECO) advises that the various elements of the economic analysis should be integrated in the policy and management cycle in order to aid decision-making when preparing the river basin management plans. The integration of economics throughout the WFD policy and decision-making cycle is presented in Figure 1.
Source: WATECO Guidance Document
Figure 1: The role of economics throughout the WFD implementation process
The main elements of the economic analysis are found in Articles 5 and 9 and Annex III in the WFD. Economic arguments also play an important role in the political decision-making process surrounding the preparation of river basin management plans in Article 4 where derogation can be supported by the strength of economic arguments when setting environmental objectives. The economic analysis can be summarised as follows:
1) Economic characterisation of the river basin (Article 5)
• Assessment of the economic significance of water use in the river basin.
• Forecast of supply and demand of water in the river basin up to 2015.
• Assessment of current cost recovery by estimating the volume, prices, investments and costs associated with water services in order to be able to assess cost recovery of these water services, including environmental and resource costs.
2) Cost-effectiveness analysis (Article 11 and Annex III)
• Evaluation of the costs and effectiveness of the proposed programme of measures to reach the environmental objectives.
3) Disproportional costs (Article 4)
• Evaluation whether costs are disproportionate.
4) Cost recovery and incentive pricing (Article 9)
• Assessment of the distribution of costs and benefits and the potential impact on cost recovery and incentive pricing.
The three main steps in the economic analysis identified by Wateco (2002) and the associated time path are illustrated in Figure 2. The first step, the economic characterisation of river basins, has recently been completed. In the next two years (2005-2006) the preliminary risk analysis carried out so far for the different European river basins will be further elaborated (including the more detailed definition of environmental objectives) and a start will be made with the identification of additional measures needed to reach good water status in a second step.
By the end of 2007 each EU Member State has to produce an overview of its basic and additional measures according to Article 11, from which the most cost-effective programme of measures will be selected in step 3 by the end of 2008. Based on a cost-effectiveness analysis of programmes of measures, the question whether the total costs of additional measures to reach good water status are disproportionate will be addressed by the end of
2009. Finally, the financial implications of the basic and additional measures for different groups in society has to be evaluated by 2010, including the level cost recovery, changes in the use and level of economic instruments (e.g. levies, taxes, water prices) and their role in achieving a more efficient and sustainable water use.
Source: modified from the WATECO Guidance Document
Figure 2: Steps in the economic analysis in the WFD and corresponding time path
2.2. Practical steps
In the common methodological framework for the socio-economic assessment procedure in BRIDGE, the steps in the economic analysis in the WFD presented in the previous section have been translated in the following practical steps:
1) Socio-economic analysis of current and future groundwater use and corresponding pressures and impacts
2) Risk and uncertainty analysis of non-compliance (‘gap analysis’)
3) Estimation of costs and effectiveness of possible compliance measures to bridge gap in cost-effectiveness analysis (least cost way to achieve threshold values)
4) Assessment and estimation of benefits of meeting groundwater threshold values 5) Cost-benefit analysis supporting decision-making regarding groundwater threshold
levels
These steps are taken iteratively but usually include various feedbacks to previous levels of analysis and evaluation. The main objective of the first step is to describe and analyze current groundwater use patterns and the pressures exerted by key socio-economic sectors, possibly resulting in non-compliance with existing or new threshold values. This analysis, based on existing data and information, will be done for a number of selected substances and for key sectors exerting significant pressure on groundwater bodies. Related to this is the prediction of expected future pressures and impacts on groundwater chemical status from socio- economic driving forces, i.e. the identified key sectors. Based on current relationships between socio-economic groundwater use and corresponding pressures and impacts on groundwater quality, socioeconomic trends are estimated and translated in terms of expected future pressures and impacts on groundwater systems.
In the second step, current and future pressures from socio-economic driving forces and their expected impact on groundwater chemical status are compared with possible groundwater quality threshold values. The main objectives of the second step are to identify (i) the gap between expected groundwater quality and these thresholds values in the future (2015) and (ii) the key factors determining this gap and the uncertainty surrounding these factors. The uncertainty analysis is introduced here explicitly in view of the often complex source- pathway-risk relationships in the context of groundwater contamination.
Once the gap has been assessed (in a qualitative or quantitative way depending on available data and information) for specific key pollutants and clusters of groundwater bodies, possible measures to meet the groundwater quality thresholds can be identified in step 3. A list of possible measures or strategies in order to prevent and abate groundwater contamination and meet the established threshold values for a selection of groundwater pollutants will be compiled. A distinction will be made between preventive and remediation measures. For each measure in the list, the direct financial costs will be estimated and, where possible, the indirect economic costs. Besides costs, also the direct and indirect effects on groundwater
chemical status will be assessed. Based on this information, the least cost way to reach proposed groundwater threshold values will be estimated.
Besides costs, the proposed measures to reach groundwater threshold values may also result in significant and substantial socio-economic benefits, such as clean drinking water or ecological benefits. Preventive measures may result in significantly different types of benefits than remediation measures, depending on the pollution source. Besides market valuation techniques, also specific non-market valuation methods will be used in this fourth step to assess the non-priced socio-economic and environmental benefits involved of meeting groundwater threshold values in the case studies, such as contingent valuation. As in previous European funded research projects, a standard valuation format will be developed and applied in the case studies. On the basis of a subsequent cross-country comparison the validity and reliability of benefits transfer will be tested, i.e. using benefit estimates for groundwater threshold values in different, case study specific policy contexts.
Finally, based on the results from the previous steps, a cost-benefit analysis (CBA) will be carried out in the fifth step to assess the economic efficiency of proposed groundwater threshold value(s) for specific pollutants. The outcome of the CBA provides information about the extent to which costs exceed benefits or vice versa. Besides economic efficiency, also other criteria that are expected to play an important role in the real life decision-making process will be investigated in a qualitative and where possible quantitative way. These include the distribution of costs and benefits across the various relevant stakeholder groups involved (in time also across generations in view of the important temporal aspect of groundwater contamination and protection), the possible interaction effects between different pollutants and the expected ecological benefits of improved groundwater quality. Multi- criteria techniques can in that case be applied if sufficient information is available, resulting in a ranking of threshold value options using top-down ranking methods (assigning weights to different criteria) or interactive and participative bottom-up methods, involving the various stakeholders involved.
The steps above are part of (1) the economic analysis in the WFD as outlined in Article 5 and Annex III (economic characterization of water use, projection of future water demand and cost-effectiveness analysis) (2) the risk analysis carried out in the WFD to assess the extent to which the objectives of the WFD are expected to be met in 2015 (also Article 5), (3) the
identification of strategies to prevent and control groundwater pollution in order to reach good chemical groundwater status (Article 11 and 17), and (4) the socio-economic underpinning of possible time or objective derogation (Article 4). The various steps when evaluating groundwater threshold values have been visualized in Figure 3.
Figure 3: Contribution of the socio-economic analysis to the process of setting groundwater threshold values and achieving good chemical groundwater status (related to the relevant articles in the WFD)
The socio-economic characterization of groundwater bodies in a river basin provides the basis for the estimation of expected future socio-economic trends and their impact on chemical groundwater status. The risk analysis in the WFD consists of comparing the expected future development of pressures and impacts on groundwater bodies as a result of socio-economic driving forces and the WFD objectives related to groundwater chemical status, which need to be made operational. In this way, the socio-economic analysis can also provide input in the process of setting groundwater threshold values, based on the assessment of the least cost way to reach groundwater threshold values compared to their expected social and economic benefits.
3. General case study description
The Dutch case study in WP5 is located in the south-west of the Netherlands and is part of the international Scheldt river basin district (SRBD), one of the fifteen international Pilot River Basins (PRB) under the WFD Common Implementation Strategy (CIS). The Scheldt
originates in the north-west of France, flows through Belgium and ends in the Scheldt estuary in Zeeland in the Netherlands (Figure 4). Besides being part of the international SRBD, the Dutch part of the SRBD is also one of the four official WFD river basins in the Netherlands.
We will refer to this Dutch part of the international SRBD interchangeably as either ‘Dutch Scheldt basin’ or ‘Zeeland’.
Figure 4: The international Scheldt river basin district
Agriculture is the main form of land use in the Dutch Scheldt basin, especially arable farming, followed by grassland for livestock (Table 1). Almost 80 percent of the predominantly peat clay area is used for agriculture and 30 percent of the sandy soils. Fifty-five percent of the sandy soil area consists of surface water, while 5% of the peat-clay area is water. About 10 percent of the whole sand soil and peat-clay area is urban area. The remainder is natural area.
Agricultural land use
Absolute area size (ha)
Relative area size (%)
Arabale land 108,007 80.6
Horticulture 4,773 3.6
Glasshouse horticulture 163 0.1
Grassland 16,378 12.2
Fruit farming 4,635 3.5
Total 133,956 100.0
Table 1: Agricultural land use in the Dutch Scheldt basin in 2000
The dunes in the western coastal zone and the far eastern sand soil areas are protected areas under the Habitat and Bird Directive (Figure 5). Only a few small peat-clay areas also fall under these Directives. All groundwater bodies in the basin are related to groundwater dependent aquatic and terrestrial ecosystems (Meinardi et al., 2005).
Source: Meinardi et al. (2005).
Figure 5: Protected natural areas in the Dutch Scheldt basin
The 2005 national WFD article 5 report considered three different regions in the Dutch Scheldt basin as groundwater bodies: (i) the relatively high sandy areas with Pleistocene soils along the border in Zeeuws-Vlaanderen and in the western part of Brabant, (ii) the dune areas
Habitat Directive
Bird Directive
along the coast, and (iii) the Holocene soils in the rest of the basin. However, more detailed information led to a further distinction of regions in the Holocene area, where creek and gully areas are present with soils of fine sand, clay sand and sandy clay and adjacent areas are covered with relatively thick clay and peat layers. Considering the depth of their hydrological base, the creek areas are further divided into shallow groundwater bodies in Zeeuws-
Vlaanderen (m.s.l. -5m), deeper groundwater bodies in Zuid-Beveland and Walcheren (m.s.l.
-10m), and deep groundwater bodies in Noord-Beveland, Schouwen-Duiveland and Tholen (m.s.l. -25m). The creek areas are underlain by fresh or brackish groundwater volumes to the indicated depth at maximum. The Holocene clay and peat deposits need no further distinction, because all water discharge occurs in the topsoil. The distinguished groundwater bodies and regions are represented in Figure 6.
Source: Province Zeeland (2006).
Figure 6: Fresh groundwater bodies identified in the Dutch Scheldt basin
The sandy soil groundwater volumes originate from different processes and periods. The fluviatile creek systems, the aeolian dunes and the aeolian sand bodies in Zeeuws-Vlaanderen and the Brabantse Wal are described hereafter.
Brabantse Wal
The ‘Brabantse Wal’ forms part of a much larger sandy plateau situated in the province Brabant and in adjacent Belgium. The soil consists of mainly sandy deposits with local clay- layers from Pleistocene origin, in the former Rhine-Meuse delta. In the higher parts of the plateau sand-drifts are present. The sharp edge is formed by the river Scheldt that eroded the western fringe of the plateau. The higher parts are mainly forested. A particular feature is that in certain parts of the area an upper saturated groundwater layer (perched groundwater) rests upon an unsaturated zone and below that on a thicker saturated groundwater mass. Land surface of the Brabantse Wal is m.s.l. plus 20 meters at maximum. The total area size is approximately 1,200 ha.
Zeeuws Vlaanderen
In Zeeuws Vlaanderen (the southern part of Zeeland) another Pleistocene sandy soil is found.
The difference with the Brabantse Wal is its height, at maximum m.s.l. plus 4 meter. The aquifer thickness is much less than underneath the Brabantse Wal. The total area size is approximately 400 ha.
Creek and gully systems
Creek systems are sandy soils situated in a peat-clay environment. In some cases sandy layers are present under the creek systems. The sandy bodies allow rainwater to easily infiltrate, reducing in this way surface runoff. Local monitoring suggest that about half of net
precipitation infiltrates towards deeper sand layers and the other half is surficially discharged (Van den Eertwegh and Meinardi, 1997). Fresh groundwater is present in lenses of limited dimensions under the creek system. This groundwater becomes generally more brackish at increasing depth. In other words, creek systems can function as recharge areas for aquifers.
The groundwater under the creek system is relatively fresh and originates from rainwater directly infiltrated in the system. Water under creek systems is vulnerable to changes in the hydrological situation.
In the Dutch Scheldt basin several creek systems are present. The total area size is about 51,000 ha. The largest creek system (39,175 ha) is situated in Zeeuws-Vlaanderen, the most southern part of Zeeland. In that part of the area the impervious clay layer of Boom is found near the surface. The thickness of the aquifer is relatively small. The clay layer of Boom is dipping to the North. The size of the creek systems also decreases in northern direction. The
layer is tilted (dipping towards north-easterly direction) and found close to the surface in the Scheldt basin. In the Dutch Scheldt basin the depth of the top of the clay layer of Boom varies between less than 3 meters in the south-western part to 100 meters in the north-eastern part.
The second creek system is situated on the (former) islands Noord- en Zuid-Beveland and Walcheren in the central part of Zeeland. The total area size of this system is 10,425 ha. The last and most northern creek system is situated on the northern island Beveland. This is just a small system (1,175 ha), but the aquifer is deeper than the two other creek systems (25m on average).
Dune areas
The area size of the dunes in the Scheldt basin is limited (4,050 hectare). Two dune systems exist, one in Schouwen and a smaller one in Walcheren. Also Zeeuws –Vlaanderen is
protected by a dune area in the west, but that ridge only consists of one row of dunes and this small area is neglected in the present study. The Holocene dunes are from aeolian origin.
Dune areas are sandy areas, which were scarcely vegetated in the past, but became more densely vegetated in present times largely due to an increased atmospheric deposition of nutrients. Net precipitation infiltrates in the sandy soils and forms a separate groundwater volume floating on higher density salt groundwater. Groundwater abstraction represents a significant change in the hydrological situation, but nowadays almost none of the existing drinking water wells in the dunes are used anymore. Extraction is downscaled to incidental individual use.
Clay-Peat areas
Cycles of transgressions and regressions occurred in the Holocene period. Clay was deposited during transgressions and during regressions peat layers were formed by vegetation trying to keep up with sea level rise. As a result, a clay-peat landscape is left. Both the clay layers and peat layers contain salt due to the presence of seawater during flooding. Shallow peat layers diminish due to oxidation (after land reclamation), resulting in land subsidence and additional nutrients in groundwater. The total area size is 98,000 ha.
4. Identification of groundwater priority substances and pollution sources
Atmospheric deposition and agriculture are the main sources of groundwater pollution in the Dutch Scheldt basin. Fresh groundwater extraction for drinking water and irrigation purposes takes place well within the boundaries of the groundwater bodies’ regeneration capacity.
Groundwater extraction was just over ten million cubic metres in 2000 (Figure 7). Drinking water companies have extracted approximately between 5 and 6 million cubic metres annually over the past 5 years, of which most (4 million m3) through infiltrated surface water. The 425 groundwater extraction installations for agriculture are under strict control by the Province Zeeland, the responsible groundwater management authority in the basin, in order to avoid salinization. Groundwater use by industry shows a decreasing trend, totalling no more than 3 million cubic metres annually, and consists mainly of salt groundwater.
Source: Province Zeeland (2002).
Figure 7: Groundwater extraction by different sectors in the Dutch Scheldt basin in 2000
Nitrates and pesticides from agriculture exert significant pressures on the fresh groundwater stocks in the basin and are the only groundwater polluting substances for which the Province has developed policy (related to the European Nitrates Directive) and takes measures.
However, atmospheric deposition of nitrates (from agriculture and industry within and outside the basin) is at least equally important. The extent of the nitrate problem is shown in Figure 8.
Mainly based upon current and expected nitrate problems, the sand soil and clay-peat groundwater bodies have been characterized as ‘at risk’. The dune and deep groundwater bodies are not at risk.
56%
23%
10%
2% 6% 3%
Drinking water Industry Drainage
Irrigation Nature conservation Groundwater sanitation
Source: Meinardi et al. (2005).
Source: Meinardi et al. (2005).
Figure 8: Nitrate concentrations in the upper groundwater bodies
Information about pesticides is almost not available. There are numerous types of pesticides and their use is usually limited to a number of years after which they are replaced by other, more environmentally friendly types. Monitoring and analysis of pesticides is furthermore complicated and expensive (Meinardi et al., 2005). Their concentration levels are currently not systematically measured through any of the existing monitoring networks. Existing national policy is such that current pesticides used are broken down in soils before entering groundwater bodies where they are not allowed to exceed a threshold value of 0.1 µg/l.
Pesticides are mainly used in arable farming (potato cultivation), but sometimes also in livestock farming when part of the land is used for maize cultivation as a fodder for livestock.
Although the pressure exerted by pesticide use is not negligible because of intensive arable farming in the Scheldt basin, the limited available monitoring evidence and model simulations of pesticide behaviour in soils and groundwater suggest that average concentration values are probably lower than the threshold values.
Other important pollutants found in the groundwater aquifers include chloride and arsenic.
However, the presence of chloride and arsenic concentrations in groundwater in the Scheldt basin are the results of high concentrations of natural background levels and natural
processes. Chloride enters the area from the sea (long-term sea level rise is expected to result ultimately in the disappearance of the fresh groundwater stocks) and as an outpouring spring behind embankments and dike enclosures (the entire estuary is embanked after the flood
>100 mg NO3/l 0
0-37.5 37.5-50 50-100
disaster in 1953 killing more than 1,000 people). Furthermore, phosphate is released from the peat-clay soils (where agriculture is the main form of land use) when in contact with salt groundwater. This too is a natural process although agriculture adds phosphate too.
The presence of outpouring saltwater springs in the area also has an important positive effect, especially in the agricultural peat-clay areas. Through its upward pressure, outpouring springs prevent other polluting substances to enter deeper (> 3 metres) groundwater layers. As most agricultural land is drained, a substantial amount of polluting substances (nitrates and pesticides) therefore enters the surface waters through the drainage system. Given these groundwater quality problems in the Dutch part of the international SRBD, the case study presented here will focus on the reduction of nitrates from agriculture. This is considered the main management problem in the area by the province Zeeland (personal communication regional Groundwater Working group, 2005). It is also the only problem for which concrete policy and management measures can be identified, related to a specific source of pollution, and associated costs and benefits can be estimated.
5. Future trends and driving forces underlying groundwater use until 2015
Expected developments in agriculture are based on a regional study carried out by the Agricultural-Economics Institute (LEI) and compared to the extrapolation of trends from the past. The future development of the agricultural sector in the Scheldt basin is measured in terms of changes in area size. The regional predictions clearly show a different picture compared to the extrapolation of trends from the past (Figure 9). Based on the regional study, the area used for arable farming is expected to decrease, whereas the area used for dairy farming (grassland), horticulture and fruit cultivation is expected to increase.
Arable farming
20 40 60 80 100 120 140
1980 1985 1990 1995 2000 2005 2010 2015 Regional prediction Trend from the past
Grassland
20 40 60 80 100 120 140
1980 1985 1990 1995 2000 2005 2010 2015 Regional prediction Trend from the past
Horticulture
20 40 60 80 100 120 140
1980 1985 1990 1995 2000 2005 2010 2015 Regional prediction Trend from the past
Fruit cultivation
20 40 60 80 100 120 140
1980 1985 1990 1995 2000 2005 2010 2015 Regional prediction Trend from the past
Figure 9: Prediction of changes in arable farming, grassland, horticulture and fruit cultivation in the Dutch Scheldt basin until 2015 (1980=100)
The regional study about future agricultural developments is largely based upon national and regional trends where shifts can be observed away from arable farming, and regional policy laid down in the area’s regional plans (the 1997 regional ‘Streekplan Zeeland’ and the 2003 provincial strategic vision ‘Strategische Visie Provincie Zeeland’), which aims to encourage diversification and high value added production systems.
The value added of arable farming, currently the predominant form of land use, is much lower than dairy farming or horticulture. Hence, a future trend away from low value added arable farming seems to be likely. To what extent a shift will take place to higher value added activities such as dairy farming, horticulture or fruit cultivation is uncertain. This depends among others upon European Common Agricultural Policy (CAP), future restrictions on the limited fresh groundwater reserves in the basin, in the long run possibly also on climate change and the associated saltwater intrusion in the area, and local nature development plans and associated claims on the limited fresh groundwater reserves.
The Province Zeeland has recently started implementation of nature development plans where arable land is converted into nature on 4,400 ha agricultural land. This is shown in Figure 10.
The little yellow spots are the places where this new nature development is to take place. The purple and green areas refer to existing nature areas owned by different organizations
(Province or nature protection organizations).
Source: Province Zeeland (2006).
Figure 10: Location of newly planned nature development areas (yellow) in the Dutch Scheldt basin
The developments described above will be used later on in this study in the construction of the baseline scenario.
6. Risk of non-compliance: expected pressures and impacts until 2015
As part of the Article 5 reporting requirements (finished in December 2004), a risk analysis was carried out for the surface and groundwater bodies in the Dutch SRBD. The assessment of the status of the four main groundwater bodies in the SRBD (clay-peat, sand soils, dunes and deep groundwater) is based on groundwater quantity and quality considerations.
Currently, groundwater extraction in all these groundwater bodies is in balance with natural replenishment rates (rainfall). However, drainage and water level management practices to keep the area dry and accessible for the multitude of use functions like agriculture, housing, industry and recreation result in drying up of natural areas. Insufficient knowledge and information exists to assess the corresponding damage to aquatic and terrestrial ecosystems in the area (Projectgroep IKS, 2004). The same applies for the impact of groundwater quality on terrestrial ecosystems. Current threshold values in the river basin are based on national policy, where:
- for the whole groundwater body a maximum tolerable concentration level applies of 50 milligrams nitrate (NO3-) per litre;
- drainage water from the upper peat-clay layer to surface water cannot exceed 2.2 milligram nitrogen (N-total) and 0.15 milligram phosphorous (P-total) per litre.
In addition, for those groundwater bodies, which are used for human consumption, total concentration of pesticides cannot exceed 0.5 µg/l and chloride 150 mg/l. In order to assess the expected status of groundwater bodies in 2015, current nitrate levels of groundwater bodies were analyzed and expected trends in sources and pollutants. If average nitrate levels are higher than 75 percent of the norm, the groundwater body is classified as ‘at risk’
(Projectgroep IKS, 2004).
The results from the risk analysis for the expected agricultural pressures in the SRBD are presented in Table 2 where expected future emission levels are expressed in an index. The subsequent impact on water quality is qualitative based on expert judgment. The risk analysis was originally carried out for surface water. However, the results for surface water are
assumed to equally apply to groundwater. Overall, nutrients are expected to remain a problem in 2015, whereas for most pesticides it is expected that they will not exceed the imposed threshold value of 0.1 µg/l.
Although the emissions from fertilizers are expected to decrease as a result of a significant reduction in arable farming and a more stringent interpretation of the Nitrates Directive (ending the derogation of 250 kg N/ha for grassland in the Netherlands), subsequent delivery from the accumulated stock of nutrients in the soils is not expected to result in a noticeable improvement of groundwater quality in the next 10-15 years. Moreover, the increase in horticulture (open land and greenhouse) may result in an increase of both pesticides and fertilizer. Whether there will be an increase in pesticide use largely depends on the success of the existing voluntary agreement in Zeeland regarding more sustainable pesticide use, which aims to reduce environmental pressures from pesticide use by 95 percent in 2010. However, whether this reduction is feasible is questionable in view of the fact that the agreement is voluntarily.
Substance Source
Emission loads in 2015 compared to 2000 (index where 2000=100)
Will threshold be reached in 2015?
(expert judgment)
Nutrients
P Arable farming
Horticulture Glasshouse horticulture Grassland Fruit cultivation
83 255 255 130 114
No
N Arable farming
Horticulture Glasshouse horticulture Grassland Fruit cultivation
83 255 255 130 114
No
Pesticides
Alachloride Arable farming Horticulture Glasshouse horticulture Grassland Fruit cultivation
83 255
255 130 114
Yes
Substance Source
Emission loads in 2015 compared to 2000 (index where 2000=100)
Will threshold be reached in 2015?
(expert judgment)
Atrazine Arable farming 83 Yes
Chloride- fenvinfos
Arable farming 83 Yes
Chloride- pyrifos
Arable farming Horticulture
83 255
Unknown
Diuron Arable farming Horticulture Glasshouse horticulture Grassland Fruit cultivation
83 255 255 130 114
Yes
Isoproturon Arable farming 83 Probably not
Simazine Arable farming Horticulture Glasshouse horticulture Grassland Fruit cultivation
83 255 255 130 114
Yes if substance is considered a dangerous
priority substance
Trifluralin Arable farming Horticulture Glasshouse horticulture Grassland Fruit cultivation
83 255 255 130 114
Main waterways do not exceed threshold values;
smaller water bodies unknown
Source: Nieuwkamer et al. (2003).
Table 2: Summary results risk analysis main polluting substances from agriculture in the Dutch Scheldt basin
7. Current groundwater policy measures
At European level the implementation of the Nitrates Directive (91/676/EEC) is the most important current policy, indicating under which circumstances and during which time periods it is possible to apply fertilizer on agricultural land. The two most important measures from this Directive are
- User norm of 170 kg N/ha from animal fertilizer for arable land. The Netherlands uses a derogation of 250 kg N/ha for grassland. However, this exemption was recently overruled by the European court.
- Balancing crop demand and supply of N (animal and chemical).
The Nitrates Directive is implemented in the Netherlands at national level through the
‘Fertilizer Law’ (Meststoffenwet). Dutch national manure policy consists of a minerals registration system for fertilizer use introduced in 1998, called MINAS (‘Mineralenaangiftesysteem’), and a manure market trade system based on regionally allocated quota. Recently, the Dutch Fertilizer Law has been revised in order to better meet the Nitrates Directive: the MINAS system has been modified to include the fertilizer user norms and the grassland derogation of 250 kg N/ha has been repealed and fertilizer user norms changed to 170 kg N/ha.
Two other important national policies are the decision taken on the 1st of March 2000 about emissions from open cultivation and livestock (‘Lozingenbesluit Open teelt en Veehouderij’) and the voluntary agreement for sustainable pesticide use signed by the branche organizations of water boards, water companies, agricultural organizations and the pesticides trade organization. The former contains a number of obligatory measures to reduce peak concentrations of pesticides and fertilizers in surface water (not necessarily total emissions) such as careful application of pesticides and fertilizer near watercourses (including buffer zones) and a ban on the discharge of untreated wastewater from agriculture. The latter aims to reduce pesticide use by 95 percent in 2010, but depends largely on farmers volunary participation. The government’s admittance policy for pesticides has a significant impact on their presence in the water environment. If a specific pesticide is prohibited, it will rapidly (within a number of years) disappear in the water column. However, often new pesticides are then introduced again and their presence in the water environment increases.
At regional level, a number of information and education initiatives exist to encourage farmers to modify and optimize their pesticide and fertilizer use. A special regional team including all regional government and interest groups has been set up to coordinate knowledge and information transfer (‘Regioteam Zuiver Zeeuws Water’). Projects coordinated by this team include issuing cultivation certificates (start in 2001), where cultivation patterns by farmers are monitored and analyzed in order to optimize pesticide and fertilizer use and the program ‘Met minder mineralen meer mans’ (start in 2004), where farmers are informed about the availability of more optimal alternative fertilizer application schemes.
The existing institutional context of groundwater protection and corresponding measures and instruments in the case study area is summarized in Table 3. Besides a number of preventive measures to protect groundwater quality (e.g. buffer zones), the institutional arrangements surrounding groundwater protection in the Netherlands and in the SRBD more specifically are mainly focused on groundwater extraction, less directly on groundwater quality, although groundwater quantity (and extraction levels) and quality are obviously closely related.
Existing institutional embedding
groundwater protection Associated measures and instruments National
Water Law (Wet op de Waterhuishouding) Obligatory groundwater abstraction registration
Groundwater Law Groundwater abstraction permits
Soil Protection Law (Wet Bodembescherming) Groundwater levy Regional
Provincial Environmental Policy Plan (Provinciaal Milieubeleidsplan)
Monitoring network
Provincial Environmental Resolution (Provinciale Milieuverordening Zeeland)
Buffer zones
Provincial Infiltration Decision Soil Protection (Infiltratiebesluit Bodembescherming)
Abstraction and infiltration facility control
Table 3: Overview existing national and regional institutional context groundwater protection
8. Additional groundwater protection measures
8.1. Individual groundwater protection measures
Based on the existing groundwater policy measures, possible additional measures in the agricultural sector in the Dutch Scheldt basin were identified to reach existing groundwater threshold values in 2015. This was done through the organization of a workshop in May 2005, in which national and regional agriculture experts participated. Where possible, the costs of the identified measures were estimated based on available information at the Agricultural- Economics Institute (LEI). Initially, the effectiveness of the measures was assessed by the experts in terms of their relative nutrient emission load reduction to surface water (i.e. as a percentage of the current total load). The workshop results were subsequently also evaluated separately by the WFD groundwater expert working group in Zeeland.
Box: Possible groundwater protection measures identified by the regional WFD groundwater expert working group
• Creation of manure free buffer zones
• Creation of wetlands to absorb drainage water
• Flexible watershore management where water levels are allowed to fluctuate
• Subsidy arrangement for the extensification of agricultural practices near edges of arable land
• Advise farmers about more optimal manure practices
• Application of ‘green’ manure to reduce nitrogen runoff from animal manure
• Testing manure machines
• Introduction of a manure license, incl. farmer examination to optimize manure application practices
• Information, education and publicity
• Growing after-crops for nutrient intake
• Manure separation in autumn and applying separated manure in other time period
• Transformation to organic farming
• Extensification of dairy farming
• Manure fermentation in combination with manure separation
• Higher milk production by improved breeding hence allowing more extensive dairy farming
• Not allowing dairy cattle to leave cowsheds during certain time periods
• Reducing drainage
First, measures relevant for groundwater protection were identified. Secondly, the
effectiveness of the relevant measures was evaluated in reducing nutrient emission loads to groundwater bodies1. The identified measures specifically related to the reduction of nutrient loads to groundwater are listed below. These individual measures were subsequently
combined and translated into a number of regional policy scenarios presented in the next section.
8.2. Groundwater protection policy scenarios
The following five regional policy scenarios were subsequently developed and elaborated for the six different groundwater bodies (dunes, creeks (north, south and central), sand and clay- peat) based on the identified individual groundwater protection measures:
• Scenario A: livestock extensification
• Scenario B: manure free zones
• Scenario C: after-crop
• Scenario D: optimization of nutrient application
• Scenario E: nature development.
Scenario A: livestock extensification
In this scenario the total number and intensity of livestock (cows per hectare) are assumed to decrease in the future, reducing the nutrient load on grassland. As a result, also a decrease in nitrate concentrations in groundwater and surface water around grassland areas is expected.
Currently, in Zeeland 72 cows are found on average on every 100 hectares (LEI, 2006). Under this policy scenario we assume that the number of cows per hectare will be reduced by 10 percent.
Scenario B: manure free zones
Another way to actively influence nitrate concentrations is through the introduction of manure free zones. In large parts of the Netherlands the agricultural fields are surrounded by ditches.
The ditches transport the water discharged from the agricultural fields to low lying areas. If
1 The costs of the measures identified at the original workshop are the same irrespective of the question whether they protect surface or groundwater. In some cases they protect both surface and groundwater at the same cost price.
manure is added or spread close to those ditches, part of it will end up in the surface water by overland flow. Manure free zones are zones of approximately 5 meters at all edges of the land. If along those strips of land no manure is added, less manure will directly flow to the surface water and nitrate concentrations are expected to decrease. On grassland manure free zones can be introduced by placing a (extra) fence to prevent cattle to get close to the ditches.
The assumption under this scenario is the compulsory establishment of manure free buffer zones on both grassland and arable land. The total size of these buffer zones along existing watercourses in the Dutch Scheldt basin is 4,290 ha (i.e. along 8580 km of ditches, channels and other watercourses in the Dutch Scheldt basin).
Scenario C: after-crop
After harvesting crops, the land often remains idle and unused until new seeds are planted.
Nutrients present on the land are absorbed by water and transported down or runoff to the ditches. Another option is to introduce after-crops that are able to take up (large amounts of) nitrogen. An after-crop is harvested before the arable crops are seeded. In that way nitrogen concentrations in soil and water are expected to decrease. In this scenario we assume that this measure is implemented on half of the arable land. This measure cannot be applied to all agricultural activities, because of for example differences in harvesting time, soil and crop types etc.
Scenario D: optimization of nutrient application
Other possibilities to reduce nitrate concentrations include an increase of agricultural extension services (information and education), soil analysis and other nutrient optimizing services. Farmers can be informed about the consequences of their current agricultural
activities and new techniques. Soil analysis increases farmer knowledge about nutrients and is a good monitoring tool necessary to determine relationships and consequences of nutrient uptake processes. Optimization of nutrient addition processes is only possible through regularly checks of the used materials and timing of the spreading of manure. The effect of this scenario is hard to translate into a concrete concentration decrease. We assume here that the effect of manure optimization is smaller on grassland than on arable land. For the assessment of the impact of these pressure reductions, we furthermore assume that gains in nitrate load reductions can be up to 5% for grassland and 10% for arable land.
Scenario E: nature development
In addition to the existing nature development plans in Zeeland, covering 4,000 ha of arable land that will be converted into nature, further nature development can take place to reduce the emission of nitrogen to groundwater bodies. We assume here that on top of the existing nature development plans another 10 percent of the total arable area will be converted. This means that no fertilizer will be used on this land anymore and groundwater levels will go up on average with 50 centimetres.
These scenarios have been calculated through with an existing, but specifically for the Dutch Scheldt basin modified groundwater model. The model and model results are presented in the next section.
9. Integrated modelling of the environmental impacts of groundwater protection measures on groundwater bodies and connected surface water bodies
9.1. Introduction
A first preliminary assessment of the effectiveness of the identified individual measures presented in section 8.1 was made by the regional WFD groundwater working group in Zeeland. The results of this expert judgment based assessment are presented in Table 4.
Measure
Effectiveness
(% reduction of total emission load)
Creation of manure free buffer zones 1-5
Creation of wetlands to absorb drainage water 1-5
Fluctuating watershore levels 5
Subsidy arrangement for edges arable land 1-5
Advise farmers about more optimal manure practices 10
Application of ‘green’ manure 10
Testing manure machines 1-5
Introduction of a manure license 5
Information, education, publicity 1-5
Growing after-crops for nutrient intake 1-5
Manure separation 1-5
Transformation to organic farming 20
Extensification dairy farming 1-5
Manure fermentation 10
Higher milk production by improved breeding 1-5
Not allowing dairy cattle to leave cowsheds 10
Reducing drainage 0
Table 4: Expected effectiveness of individual groundwater protection measures in terms of groundwater pressure reduction
The groundwater experts felt uneasy giving these numbers explicitly, claiming that the effect of a specific measure depends on a variety of factors, including soil and geo-hydrological cycle characteristics, and that the expected uncertainty surrounding the impact assessment presented in Table 4 is therefore high. The assessment presented in Table 4 is based on a
reduction of the pressure only, not the corresponding impact on groundwater quality. It is especially this complex relationship between the pressure of an economic activity and the subsequent impact on groundwater quality that is highly dependent on existing hydro- ecological conditions and surrounded by a lot of uncertainty (see Figure 11). Therefore, a more formal groundwater model, called NPKRUN, is used for the environmental impact assessment regarding groundwater quality and connected surface water quality.
Figure 11: Visualization of the complexity of groundwater processes captured in NPKRUN
9.2. Model structure
The model NPKRUN (NPK refers to Nitrogen, Phosphor and Potassium in Dutch) was originally developed at the National Institute for Public Health and the Environment (RIVM) in the Netherlands as a tool to predict nutrient concentrations in groundwater and connected surface water. The model was developed to generate: (1) national and regional overviews of groundwater flows and their travel times; (2) national and regional images of nutrient transport in the soil including deep layers; (3) national and regional assessments of the presence of nutrients and nutrient transport in different parts of the soil and in draining
overland flow interflow
drain discharge ditch level phreatic level
temporary phreatic level compacted layer
flow directly through the soil
groundwater seepage (net) precipitation
chemicals
tile drain
groundwater recharge
surface water flows. The model determines values of precipitation surplus, groundwater recharge and travel times of groundwater in grid cells of 500 by 500 meters. The results are aggregated across grid cells to determine transport of water and nutrients to draining surface water. The model is built to establish long year averages of these parameters, but it is also possible to run the model for one specific year2.
In this case study, we adapt and use the model relationships to better understand and underpin the environmental impact assessment of reduced nitrate leaching due to the implementation of the developed policy scenarios for the Dutch Scheldt basin presented in section 8.2. The model consists of three parts or calculation modules (Figure 12): a precipitation module, a nutrient module and a hydrological module. Combined they feed into the nitrate module, which estimates and predicts nitrate concentrations in groundwater and connected small surface waters such as ditches and channels. The nitrate concentration calculations are basically performed in a series of database calculations. The calculations are put into a tree structure and for every branch separate calculations are carried out. This makes it possible to proceed stepwise through the calculations.
Figure 12: NPKRUN model chain
2 The model NPKRUN has been applied for practical policy use, but only limited. A more frequently used model is STONE, which also models nitrogen and phosphorous leaching to groundwater and surface waters.
Like NPKRUN, STONE also consists of a chain of models or modules. The output of the STONE model consists for each scenario of maps of, for example, N and P immobilisation in soils, N and P concentrations in groundwater, and N and P leaching to surface waters. The grid cells used differ among modules and range from 25 to 22.000 ha.
PRECIPITATION MODULE
NITRATE MODULE NUTRIENT MODULE
HYDROLOGICAL MODULE
