Evaluating agri-drinking water quality indicators in three case studies
|Main authors:||Birgitte Hansen, Hyojin Kim, Ingelise Møller, Abel Henriot, Marc Laurencelle, Tommy Dalgaard, Morten Graversgaard, Susanne Klages, Claudia Heidecke and Nicolas Surdyk|
|FAIRWAYiS Editor:||Jane Brandt|
|Source document:||»Birgitte Hansen, Hyojin Kim, Ingelise Møller, Abel Henriot, Marc Laurencelle, Tommy Dalgaard, Morten Graversgaard, Susanne Klages, Claudia Heidecke and Nicolas Surdyk 2021. Evaluation of ADWIs: agri-drinking water quality indicators in three case studies (FAIRWAY Project Deliverable 3.2)
Results from this research task have also been published
- as a scientific paper: »Kim, H.; Surdyk, N.; Møller, I.; Graversgaard, M.; Blicher-Mathiesen, G.; Henriot, A.; Dalgaard, T.; Hansen, B. Lag Time as an Indicator of the Link between Agricultural Pressure and Drinking Water Quality State. Water 2020, 12, 2385
- and for a more general readership in an article in The Conversation: »Moins de nitrates dans l’eau, une vraie course de fond (English summary »Reducing nitrates in water, a real long-distance race)
In this section of FAIRWAYiS we build on the literature review, expert and database consultation that was used to develop a preliminary selection of indicators that is described in »Agri-drinking water quality indicators and IT/sensor techniques. Here we take the next step in the development of agri-drinking water indicators (ADWIs), based on statistical analyses of available data from 3 of the 13 FAIRWAY case studies. This information is used in the »Harmonised indicator database.
Take home messages
ADWIs are defined within the DPLSIR-framework including a new 'link' type of indicator. The link indicator is developed to better explain the relationship between pressure from agriculture and state of water quality. At the time of writing this report, three of the FAIRWAY case studies, two in Denmark (Aalborg and Tunø) and one in France (La Voulzie) had sufficient data (i.e. long-term series of water quality in groundwater in combination with nitrogen (N) pressure indicators) for the required analysis of a shortlist of nitrogen, pesticide and link indicators.
»Framework, case studies and indicators
Analysis reveals the relative significance of the nitrogen and pesticide indicators
»Analyses and results
Of the nitrogen indicators the agricultural N surplus pressure indicator is identified and reconfirmed as a suitable indicator and as a significant, prevalent, effective, and easy to use indicator regarding nitrate contamination of water. The nitrate leaching below the soil zone would be the most appropriate state indicator but is seldom collected because sampling equipment to measure leaching is very costly to install and to maintain for monitoring, and the results can be difficult to upscale. However, in this study, nitrate leaching from pore water data were available from Tunø, Denmark. This is an exceptional case and here we show how they can be used in combination with the N surplus and groundwater nitrate data. In general, the more abundant state indicator such as nitrate concentrations in groundwater is recommended as this is the standard state quality indicator.
Selecting directly appropriate pesticide indicators are much more difficult than for nitrogen due to the lack of long time series of both pesticide application pressure and pesticide concentration state data. In the specific case of La Voulzie, the analyses of the two other pressure indicators (area of main crop type and amount of application of pesticides) regarding pesticide contamination of groundwater were appropriate choices of indicators. These indicators are transparent and easy to use and to communicate to stakeholders. However, they cannot be abundant indicators because it is rare that a single pesticide product is used on all the agricultural fields having the same crop type in a catchment. Therefore at specific moments, when some pesticides are intrinsically linked to the growth of crops, these two pressure indicators (area of main crop type and amount of application of pesticides) could be usable indicators of potential pesticide contamination. An attempt can be made by using N surplus as the pressure indicator of intensive agriculture and probable use of pesticides. It is suggested that the use of nitrogen fertilizers and pesticides is positively correlated when long time series of data are available. This link shows the joint increase of nitrate and pesticide during the rise of modern agriculture.
Lag times may provide a valuable insight into the mode of contaminant transport because they represent the shortest travel time that delivers the agricultural signal to the water sample collection point. In contrast, the groundwater age represents the mean residence time of the existing groundwater at the collection point. Therefore, knowledge of both groundwater age and lag time are important for protection of the aquatic environment.
»Conclusions and recommendations
A leaflet has been prepared to disseminate the importance of linking agricultural impact and drinking water quality response using examples from the 3 case studies. Workshops and presentations have highlighted the importance of coherency and consistency in agri-environmental measures since, in some hydrological context, only long-term coherent policies will produce sufficient effects. Passive samplers have been used to both involve local stakeholders in monitoring and improve water quality monitoring itself by adding an integrative sampling to point sampling.
»Dissemination to stakeholders