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.