Harmonizing agriculture and vulnerable drinking water abstractions in Overijssel, the Netherlands: a collaborative approach
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Since the seventies, in the Netherlands, the agricultural emissions of nutrients and chemicals used for crop protection to water systems have strongly increased. Since the early nineties, these emissions have been reduced by policy measures. In spite of these efforts, water abstraction sites in the sandy areas of the province of Overijssel, the Netherlands, are still experiencing an increasing impact of agricultural emissions on the quality of abstracted groundwater. To meet the requirements of article 7.3 of the WFD, the province of Overijssel assessed the risks on water quality for drinking water abstraction sites in the province. Emissions from dairy farms were indentified as significant sources for which measures were necessary in groundwater protection areas (GWPA). In 2011, a project was formulated based on voluntariness and mutual gains aiming at reducing nitrate leaching and N surpluses and increasing the financial benefits of the farmers at the same time. Farmers were invited to join the project and were supported by agricultural consultants. Measures were selected that would contribute to maintenance of the production intensity without violating values for nitrate leaching to groundwater. These values were transposed into operational boundary conditions, i.e. maximum acceptable N surplus (kg ha-1) on farm and on soil scale. The effect of the measures was monitored by the indicators of the agricultural management and the nitrate concentration of the shallow groundwater. The economic impact was established for each farmer based on the measures agreed upon and the characteristics of the farm. As result of this management, N-surpluses of the soil balance decreased from 165 to 83 kg ha-1 in the period 2012 to 2014. The nitrate concentration in the shallow groundwater fluctuated in 2011, 2012 and 2013 between 93 and 104 but tended to decline to 84 and 75 mg NO3l-1 in 2014 and 2015 respectively. The potential increase in financial benefits of measures implemented in 2015 ranges from € 80 – 135 /ha and € 3,200 - 6,850 / farm for soil measures only and up to € 290 /ha and € 14,500 / farm including all measures. These results were considered as a proof of concept for the approach. To meet the WFD-objectives, it is required to extend this approach from farm level to a regional level, i.e. the entire GWPA. The initial group of farmers shared this dilemma, contributed to develop a strategy for extending the approach and participated in extension activities to commit and inform besides new farmers also contractors and consultants working with the farmers in the GWPA. Extending the proof of concept required a collaborative approach in which new ways of knowledge exchange were implemented.