Nitrates in upper groundwater under agricultural land, 1992-2010

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The average nitrate concentration in groundwater in the sandy region of the Netherlands has decreased so much that the target of 50 mg/l is within reach. This is however not yet the case in the loess region, but the target has already been achieved in the clay and peat regions.

Nitrate concentration in groundwater in sandy region near target

One of the objectives of Dutch fertilizer policy is to reduce nitrate concentrations in the upper groundwater under agricultural land to a maximum of 50mg/l. The area-weighted average nitrate concentration in the upper groundwater in the sandy, loess and clay regions decreased during the monitoring period (see figure). On average, the target was also achieved in the clay region. In the peat region, the target was already much lower than 25 mg/l at the start of the monitoring period. The target is within reach in the sandy region, but not yet in the loess region. When the measured concentrations are corrected for meteorological effects and sampling effects (only available for sand and clay), a different picture is seen in the sandy region, where the corrected average shows a downwards trend. The higher concentration in 2008 can be accounted for by the lower precipitation surplus that year.

Spread in nitrate concentrations between farms, farm types and regions

There is a spread in nitrate concentrations between farms, farm types and regions. Concentrations are higher under arable and horticultural land than under farmland used for dairy cattle (Hooijboer & de Klijne, 2012). The nitrate concentration under dairy farms with a derogation was already below 50 mg/l on average in 2008, 2009 and 2010, and the percentage of farms with concentrations above 50 mg/l decreased from 46% in 2007 to 41% in 2010 (Zwart et al., 2011). Nitrate concentrations were higher in the southern sandy region than in other areas of the sandy region, due to the presence of more crops and ground sensitive to leaching combined with the greater number of intensive farms included in the random selection.

There is as yet no exact definition of when the Netherlands will have met the targets of the Nitrates Directive as, in the case of groundwater, it is still unclear to what extent spatial averaging may be applied to meet the nitrate objectives of the EU Nitrates Directive (PBL, 2012).

Nitrogen surplus important factor in groundwater and ditch water quality

An important factor in groundwater and ditch water quality is the nitrogen surplus in the soil surface balance of farms. The nitrogen surpluses of dairy farms on sandy ground decreased after 2006, whereas almost no decline was seen on arable farms on sandy ground (LEI, 2012).

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Reference of this webpage

CBS, PBL, RIVM, WUR (2024). Nitrates in upper groundwater under agricultural land, 1992-2010 (indicator 0271, version 09,

) www.clo.nl. Statistics Netherlands (CBS), The Hague; PBL Netherlands Environmental Assessment Agency, The Hague; RIVM National Institute for Public Health and the Environment, Bilthoven; and Wageningen University and Research, Wageningen.