Using simple pseudo-3D hydrogeological modelling and a simplified agronomical representation to build a pertinent decision-making tool for local stakeholders: the Vivier karstic spring (France) case study

International audienceThe Syndicat des Eaux du Vivier (Vivier Water Agency-SEV) is a public agency monitoring the production, treatment, distribution and quality control of drinking water in Niort town in western France. The municipal drinking water supply mainly comes from a karstic resurgence, the Vivier spring, which is registered as a " Grenelle " priority water supply since 2013. There is a strong pressure from agriculture, which is illustrated since the 90' by nitrate concentration that exceed the European drinking water standards. There is also an increasing pressure on water quantity, mainly due to irrigation and drinking water demand, particularly in low water periods when the karst can be subject to collapses due to the low pressure in the karstic galleries. Modelling the hydrogeology of the area will help to optimize the effective quantitative and qualitative water resource management. Hydrogeological and agronomical modelling is done using the BICHE-MARTHE software chain, developed at the BRGM. Comparing observed and simulated groundwater levels, stream flows, springs flows and overflow at the Vivier spring gives satisfactory results considering the limited knowledge on the area. This part of the modelling has been strengthened by a comparison with a sensibility approach with GARDENIA regarding irrigation and with an approach using neural networks. The model integrates Agricultural practices observed in the catchments area to simulate nitrate transfers. The resulting nitrate concentrations are correct for the Vivier spring and its associated catchments (Gachet I and III) and stays within a reasonable range for other observation points on the catchments area. Modelling, together with the learnings of the measurements campaign analyses, allows us to better understand how the Vivier hydrosystem works. The spring has two supply methods: a short one-year-cycle, during which meteoric waters get through the karstic system and join the Vivier spring, and a multi-year cycle during which the effective rainfall slowly percolates through non-karstic rocks. Basic simulations are conducted to better identify the impact of agricultural and quantitative pressures on the water supply. They outline the karstic system sensibility to any * Intervenan

Application d'une approche risque pour l'évaluation des pressions significatives en nitrate d'origine agricole diffuse sur les eaux souterraines des aquifères crayeux du bassin de Paris.

International audienceL'évaluation des pressions significatives sur les eaux souterraines est une étape importante de l'état des lieux réalisé tous les 6 ans en lien avec la directive cadre sur l'eau et les SDAGE. Ce travail permet de localiser les secteurs du territoire où les pressions peuvent entrainer une dégradation de la qualité des eaux et donc où des actions doivent être mises en place pour réduire les pressions et assurer la qualité de la ressource en eau dans le futur

Estimating nitrate and pesticide transfer mode within the unsaturated zone of a fluvioglacial aquifer and its implication on spatial and temporal concentration variability

International audienceThe Meyzieu fluvioglacial aquifer of 113 km 2 located at the eastern part of Lyon is intensively exploited and subject to multiple pressures (urban, industrial, agriculture). Nitrate concentrations are quite high while pesticides contamination is low considering the past and today's pressure. A project was initiated in 2011 with the objective of determining the role of the unsaturated zone in the transfer of NO 3 and pesticides from soil to groundwater. Monthly monitoring of major elements, some pesticides, and stable water isotopes is carried out at three sampling points located along the flow lines. Additional information such as hydrogeological functioning, pressure inventory was gathered and additional data from three water sampling campaigns was collected. The temporal variation of NO 3 , metolachlor and metabolites and atrazine and metabolites is quite different at the three monitoring points. At the sampling point located upstream, where the unsaturated zone has a thickness around 40m, the nitrate concentrations are comprised between 20 and 40 mg.l-1 from 2004 to mid-2013. From mid-2013 nitrate concentrations are increasing regularly and are now reaching 70 mg.l-1. This point presents the highest level in atrazine metabolites (DEA) of the area but with concentrations lower than 0.05 µg.l-1 and very low detection of metolachlor or its metabolites. In the centre of the basin, where agriculture pressure is the highest and unsaturated zone of up to 30m in depth, nitrate concentrations are above 50 mg.l-1 with low seasonal variations. Metolachlor is lower than 0.03 µg.l-1 but values of 0,39 µg.l-1 max. of ESA metolachlor (MESA) were reached. Downstream, just before the discharge area, the sampling point shows the lowest and more stable nitrate concentrations (around 40 mg.l-1). The water level in this sector is at less than 20 m deep. Metolachlor have been detected only once while MESA is nearly always detected and can reach 0.24 µg.l-1

Implementation of agronomical and geochemical modules into a 3D groundwater code for assessing nitrate storage and transport through unconfined Chalk aquifer

International audienceChalk aquifer is the main water resource for domestic water supply in many parts in northern France. In same basin, groundwater is frequently affected by quality problems concerning nitrates. Often close to or above the drinking water standards, nitrate concentration in groundwater is mainly due to historical agriculture practices, combined with leakage and aquifer recharge through the vadose zone. The complexity of processes occurring into such an environment leads to take into account a lot of knowledge on agronomy, geochemistry and hydrogeology in order to understand, model and predict the spatiotemporal evolution of nitrate content and provide a decision support tool for the water producers and stakeholders. To succeed in this challenge, conceptual and numerical models representing accurately the Chalk aquifer specificity need to be developed. A multidisciplinary approach is developed to simulate storage and transport from the ground surface until groundwater. This involves a new agronomic module " NITRATE " (NItrogen TRansfer for Arable soil to groundwaTEr), a soil-crop model allowing to calculate nitrogen mass balance in arable soil, and the " PHREEQC " numerical code for geochemical calculations, both coupled with the 3D transient groundwater numerical code " MARTHE ". Otherwise, new development achieved on MARTHE code allows the use of dual porosity and permeability calculations needed in the fissured Chalk aquifer context. This method concerning the integration of existing multidisciplinary tools is a real challenge to reduce the number of parameters by selecting the relevant equations and simplifying the equations without altering the signal. The robustness and the validity of these numerical developments are tested step by step with several simulations constrained by climate forcing, land use and nitrogen inputs over several decades. In the first time, simulations are performed in a 1D vertical unsaturated soil column for representing experimental nitrates vertical soil profiles (0-30m depth experimental measurements in Somme region). In the second time, this approach is used to simulate with a 3D model a drinking water catchment area in order to compared nitrate contents time series calculated and measured in the domestic water pumping well since 1995 (field in northern France – Avre Basin region). This numerical tool will help the decision-making in all activities in relation with water uses

Nitrogen surplus : a unified indicator for water pollution in Europe?

Pollution of ground-and surface waters with nitrates from agricultural sources poses a risk to drinking water quality and has negative impacts on the environment. At the national scale, the gross nitrogen budget (GNB) is accepted as an indicator of pollution caused by nitrates. There is, however, little common EU-wide knowledge on the budget application and its comparability at the farm level for the detection of ground-and surface water pollution caused by nitrates and the monitoring of mitigation measures. Therefore, a survey was carried out among experts of various European countries in order to assess the practice and application of fertilization planning and nitrogen budgeting at the farm level and the differences between countries within Europe. While fertilization planning is practiced in all of the fourteen countries analyzed in this paper, according to current legislation, nitrogen budgets have to be calculated only in Switzerland, Germany and Romania. The survey revealed that methods of fertilization planning and nitrogen budgeting at the farm level are not unified throughout Europe. In most of the cases where budgets are used regularly (Germany, Romania, Switzerland), standard values for the chemical composition of feed, organic fertilizers, animal and plant products are used. The example of the Dutch Annual Nutrient Cycling Assessment (ANCA) tool (and partly of the Suisse Balance) shows that it is only by using farm-specific "real" data that budgeting can be successfully applied to optimize nutrient flows and increase N efficiencies at the farm level. However, this approach is more elaborate and requires centralized data processing under consideration of data protection concerns. This paper concludes that there is no unified indicator for nutrient management and water quality at the farm level. A comparison of regionally calculated nitrogen budgets across European countries needs to be interpreted carefully, as methods as well as data and emission factors vary across countries. For the implementation of EU nitrogen-related policies notably, the Nitrates Directive-nutrient budgeting is currently ruled out as an entry point for legal requirements. In contrast, nutrient budgets are highlighted as an environment indicator by the OECD and EU institutions

Improving the consideration of hydrogeological characteristics to assess the contamination groundwater by pesticides at national scale (France).

International audienceAccording to the European Water Framework Directive, Member States have to conduct study of anthropogenic pressure and its impact on the status of water bodies, and to implement programs of measures in order to reverse any significant and sustained upward trend in the concentration of any pollutant. Focused on pesticides in groundwater, the aim of this work is to propose new tools to the stakeholders to identifying groundwater bodies presenting a risk of not achieving « good chemical status ». Several parameters control the transfer of a pesticide from the soil to the groundwater: climate conditions (i.e. recharge), soil and hydrogeological characteristics, pesticides physico-chemical properties. The issues of this study are (1) to take account of hydrogeology context, besides soil and pesticide physico-chemical properties relatively well studied as in registration procedure; (2) to work at national scale which involve to consider variability of land uses and practices, (hydro)geology and climate conditions. To overcome difficulties, this study proposes to identify, when data make it possible, the main driver (hydrogeology or pesticides properties) which explains transfer of pesticides into groundwater at the water body scale. This aspect is particularly innovative as, to date, hydrogeology contexts are usually not considered. Thus, for instance, timeframe of transfer in the unsaturated zone is also considered.Despite work being performed for several substances with contrasted physico-chemical properties, the outcome will be a classification of substances in different groups according to their chemical properties and their potential occurrence in groundwater.The work is based on existing data only. From French databases, BNVD (French national database of the sales of pesticides) and ADES (national French data base on groundwater resources gathering), we are able to link pesticides use and groundwater impact. As a first step, several specific pesticides were selected as study case and lead to distinguish groundwater bodies as: -Groundwater bodies where pressure cannot be evaluated ;-Groundwater bodies with no pressure (sale) ; -Groundwater bodies where pressure (sale) lead to an impact (quantification of the specific substance) ;-Groundwater bodies where there is a pressure (sale) but no impact which means (1) geological conditions offer a natural protection of groundwater quality or (2) the transfer time into groundwater is longer than the observation period or (3) the fate of pesticides lead to a limited transfer.From the different maps and the pesticides studied, final results would be to classify groundwater bodies as: -The main driver is hydrogeology: whatever the substance i.e. whatever the pesticide properties, impacts on groundwater quality are similar. Either, geological conditions protect the groundwater resources, pesticides do not transfer to groundwater or, there is no natural protection, whatever the substance, it transfers to groundwater. -Geological conditions are not the main driver but the pesticide properties do. Therefore, depending on pesticides physico-chemical properties, substances will transfer to groundwater or not. A classification of substances in several groups according there properties (DT50 and Koc) will be performed. The main expected outcome of this project is the establishment of methodology of characterization of the link between pressure and impact, at national scale. Final results would provide operational tools to the stakeholders to go further in the pressure and impact analysis of the pesticide in groundwater to improve the risk evaluation and adapt program of measures to reach the “good chemical status” of groundwater bodies

Challenges for linking (agricultural) pressure indicators with (water quality) state indicators - Examples from Fairway project

International audienceTo effectively reduce the agricultural impact on the aquatic environments, the cause-effect relations between agricultural practices and water quality should be well understood. In that conditions, environmental Indicators are often used since they can display in rather simple terms some complex environmental phenomenon variation. Yet, the selection or the creation of the best indicator to explain a phenomenon could be challenging. In the FAIRWAY (Farm systems management and governance for producing good water quality for drinking water supplies) project, we focused on the identification of indicators in order to quantitatively and conceptually show the relationship between agricultural practices (driving forces and pressure indicators) and drinking water quality (state indicators) that could be used in the European Member States. Hence, our main objective was not to create new indicators but to assess the link between indicators. The objective of this study is to determine how indicators of pressure and of state i.e. water quality can be linked to assess the efficiency of mitigation measures using common European indicators. First, we conducted a survey among the FAIRWAY case studies to identify indicators, then statistical tests were performed between selected indicators of pressure and state for both nitrate and pesticide. We examined 1) the link between indicators, and 2) the relevance of some indicators, as statistical calculations give the mathematical expression for the link that exists between them. The tests reveal two assessments. -Firstly, the lag time between contaminant emission and environmental impacts should be assessed. Cross-correlation appears to be a promising method to tackle it, but this method is not applicable on every site generally because of the lack of appropriate data. -Secondly, the determination of European indicators is not trivial. Despite common regulatory drivers at the European scale, the calculation of indicators is highly flexible across Europe. This flexibility appears during collect, storage or dissemination of input data from the Member states. Harmonized practices in term of data collection is needed and once information is acquired it is essential that it is made available using FAIR (Findable, Accessible, Interoperable, Reusable) principles to all the potential users. Today, as implementation of regulations have been country-specific, the uniform application of datadriven indicators of pressure and status indicators across Europe remains challenging

Estimating pressure and impact of nitrates on groundwater at national level: New methodological developments

International audienceWithin the water framework directive the assessment of the impact on groundwater of the pressure from nitrate from agriculture origin is requested. At basin and national levels other methods should be developed in order to provide a uniform view of the pressure/impact issue.This presentation is based on a project which was initiated with the objective of proposing national maps of pressure and impact based on the combination of various thematic layers using a geographical information system.The first step was the development of a national approach for the calculation of the nitrogen pressure note for agricultural sources. To attribute the cultural pressure note, several notes have been attributed according to an expert judgment before attributing the final note ("previous crop" N surplus; "following crop" capacity of absorption). Using the existing map of the French plots (about 6 millions plots have been treated), it was thus possible to obtain a national map for the nitrogen pressure from agriculture. To validate the approach the pressure map has been compared with the nitrate concentration measured at monitoring points. Median of concentrations from the French Groundwater database was used. A quite good matching appears between cultural notes (today’s pressure) and median of NO3 concentration in groundwater (today’s impact)Due to different and sometimes long transfer and residence time of water and associated solutes it is necessary to take into account “delays” when comparing pressure and impact. Nitrates transfer estimation depends mainly on lithology. For sedimentary basin, unsaturated zone depth and existing data on nitrate transfer velocity were coupled in order to obtain information on NO3 delay in the unsaturated zone. For other lithologies, only data on “chemical and isotope tracer” ages were used to get an estimation of the residence time of the contaminant in the saturated zone. The various information layers will be combined in order to obtain a spatial distribution of the nitrate recharge ages (Wang et al., 2012) and link the today’s impact to the pressure at the origin of the impact (without the time delay). The proposed approach will give an homogeneous national view of the pressure / impact approach for nitrate and will permit highlighting the sectors where today’s pressure may lead to a degradation of groundwater quality and that will need local studies in order for the Water Manager to propose adequate program of measure

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

International audiencePreserving 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

MétéEAU Nappes: a real time water resource management tool and its application to a sandy aquifer in a high demand irrigation

International audienceThe MétéEAU Nappes water-resource-management tool is presented. It is usable on the aquifer or part-of-aquifer scale for real-time observation of the state of the groundwater resource, and it is already operating in France. This online decision support tool is also able to predict the state of the resource in the short- and mid-terms. The paper explains the use of the tool in a case study in the Authion Valley, in the north-west of France, chosen for its context of tension surrounding the groundwater resource resulting from high volumes of abstraction for irrigation. The results of the simulation highlight the advantages of MétéEAU Nappes as a tool for prediction and simulation of the state of the groundwater resource. The results also show the advantages of this type of tool for water resource management, such as supplying local actors with reliable and real-time observations of the aquifer and providing forecasts to anticipate possible water shortage.L’outil de gestion de la ressource en eau MétéEAU Nappes est présenté. Il est utilisable à l’échelle d’un aquifère, ou d’une portion d’aquifère, pour observer en temps réel l’état quantitatif de la ressource en eau souterraine, et il est déjà opérationnel en France. Cet outil web d’aide à la décision permet également de prédire l’état de la ressource en eau à court et moyen termes. L’article présente l’utilisation de l’outil sur un cas d’étude situé dans la vallée de l’Authion, dans le Nord-Ouest de la France, choisi pour son contexte de tension sur les ressources en eau du fait d’importants prélèvements souterrains pour l’irrigation agricole. L’application met en valeur les avantages de MétéEAU Nappes en tant qu’outil de prédiction et de simulation de l’état quantitatif de la ressource en eau souterraine. Les résultats obtenus permettent aussi d’illustrer l’intérêt de ce type d’outil pour la gestion des ressources en eau, par exemple pour fournir aux acteurs locaux des observations fiables et en temps réel de l’état de l’aquifère et fournir des prévisions pour anticiper d’éventuelles pénuries d’eau