Restoring groundwater quality at the drinking water catchment scale: A multidisciplinary and participatory approach.

Preserving or restoring the quality of groundwater resources with regard to nitrate is a major challenge. To date, useful and easily applicable tools to identify the best measures to implement at local scale are lacking. An innovative methodology is proposed to identify cost-effective restoration measures at the drinking water catchment scale. The methodology is based on the articulation of two tools: a model simulating nitrate groundwater contamination time series and an economic evaluation, within a participatory approach. It was applied to a representative drinking water catchment in Northwest France that has been affected by nitrate contamination for decades. Five scenarios of measures (changes in fertilization and intercropping practices, or in cropping patterns) were co-constructed with stakeholders, evaluated in terms of cost and impact on groundwater nitrate concentration, and discussed with stakeholders. Overall, two scenarios stand out. Introducing hemp in crop rotations is the only scenario generating an economic benefit, but for a very low impact on nitrate concentration (decrease of 4 mg/l by 2050 for 10% of hemp in crop rotations). Introducing alfalfa in crop rotations is the most effective measure to decrease nitrate concentration (decrease of 23 mg/l by 2050 for 20% of alfalfa in crop rotations), and for a moderate cost compared to the other scenarios (25-51 €/ha/year). Results show that substantial changes in cropping patterns - more important than those imagined initially by stakeholders (e.g. converting 40% of cropland to alfalfa) are needed to restore groundwater quality targets in the medium-long term. Measures deemed promising and achievable by the stakeholders proved to be insufficiently effective. The approach developed has been shown to provide valued and trusted information to stakeholders and to objectify debates. Stakeholders have shown interest in the evaluation of costs and further socio-economic information, in addition to the evaluation of the effectiveness of measures on groundwater quality, validating the multidisciplinary dimension of the approach. The approach has the advantage of being easy to implement, and is therefore applicable to other study sites where needed.

Is it worth protecting groundwater from diffuse pollution with agri-environmental schemes? A hydro-economic modeling approach.

In Europe, 30% of groundwater bodies are considered to be at risk of not achieving the Water Framework Directive (WFD) 'good status' objective by 2015, and 45% are in doubt of doing so. Diffuse agricultural pollution is one of the main pressures affecting groundwater bodies. To tackle this problem, the WFD requires Member States to design and implement cost-effective programs of measures to achieve the 'good status' objective by 2027 at the latest. Hitherto, action plans have mainly consisted of promoting the adoption of Agri-Environmental Schemes (AES). This raises a number of questions concerning the effectiveness of such schemes for improving groundwater status, and the economic implications of their implementation. We propose a hydro-economic model that combines a hydrogeological model to simulate groundwater quality evolution with agronomic and economic components to assess the expected costs, effectiveness, and benefits of AES implementation. This hydro-economic model can be used to identify cost-effective AES combinations at groundwater-body scale and to show the benefits to be expected from the resulting improvement in groundwater quality. The model is applied here to a rural area encompassing the Hesbaye aquifer, a large chalk aquifer which supplies about 230,000 inhabitants in the city of Liege (Belgium) and is severely contaminated by agricultural nitrates. We show that the time frame within which improvements in the Hesbaye groundwater quality can be expected may be much longer than that required by the WFD. Current WFD programs based on AES may be inappropriate for achieving the 'good status' objective in the most productive agricultural areas, in particular because these schemes are insufficiently attractive. Achieving 'good status' by 2027 would demand a substantial change in the design of AES, involving costs that may not be offset by benefits in the case of chalk aquifers with long renewal times.