The Aquisafe project assesses the effectiveness of natural mitigation zones in reducing diffuse pollution to surface waters. In one case study on a constructed wetland in agriculturally dominated Western France, nitrate concentrations from drainage inflows to a small river decreased up to tenfold on the way through an intermediary constructed wetland. However, only ~30 % of the total N-load is retained in the wetland, whereas ~70 % enters the river directly during high flow events as a result of low soil permeability. The study underlines the importance of flow paths and infiltration for nitrate removal in natural or constructed wetlands, which is often neglected in practice.

In the rural and semi-rural environment many sources of contamination may impact surface water quality. In addition to nutrients from agricultural activities, contaminants occurring at low concentration so-called trace contaminants are a growing issue for water quality. To address this issue and investigate mitigation measures, the Berlin Centre of Competence for Water (KompetenzZentrum Wasser Berlin) developed a collaborative research project called Aquisafe, in association with the Indiana University – Perdue University Indianapolis (IUPUI), the German Federal Agency for the Environment “Umweltbundesamt” (UBA) and Veolia Water. The project aims at investigating mitigation zones such as constructed wetlands or riparian zones to improve the quality of surface water with respect to diffuse pollution. Before using models and conducting field experiments, the first part of the project is an extensive analysis of the nature, occurrence, and risks of source water contamination in rural and semi-rural areas. This is the subject of the poster. The objectives of this first part of the project are (i) to provide background information on surface water and its use in Europe, particularly regarding drinking water supply, (ii) to investigate the characteristics of the families of pollutants that are potentially of interest, and finally (iii) to select the most relevant trace contaminants to be investigated in future field experiments. To reach these objectives, an extensive literature review was carried out, using different criteria to select the relevant families of pollutants and then the individual substances. The screening process is currently in progress and includes a collection of substance characteristics that will be used for subsequent selection, such as toxicity or persistence in the environment. Key figures and information were collected concerning the nature, use and vulnerability of surface water in Europe that provides 70% of total water abstraction (drinking water, industry and agriculture) in Europe. The main pollutant families of interest for the screening process were the following: pesticides used in agriculture (e.g. glyphosate or isoproturon), pollutants coming from the spreading of animal waste on land (e.g. veterinary pharmaceuticals or hormones), pollutants coming from the spreading of sludge from wastewater treatment plants (e.g. heavy metals or hormones), pollutants from natural areas (e.g. flame retardants in forests), and pollutants from transportation networks (e.g. heavy metals from vehicles). Consequently in a rural or semi-rural area, the land use in the watershed plays a key role in the selection and assessment of priority pollutants coming from diffuse sources and entering surface waters. The work is still in progress concerning the review of pollutant families, and will lead to the final screening at substance level, providing a list of key contaminants for the other work packages within the Aquisafe project. Eventually, corresponding data for the same issues in the United States will be added and provide a comparison between the two continents.

Major reservoirs are a key element for public water supply in many countries. In Europe over 800 major reservoirs serve primarily this purpose. Eutrophication affects significant numbers of lakes and reservoirs, and is the well-known issue currently impacting drinking water supply reservoirs. In most cases, phosphorus is the principal cause of eutrophication, and therefore has been studied intensively. The presence of micro pollutants (e.g. pesticides, pharmaceutically active compounds - PhaCs) is not systematically monitored but some substances are very mobile and tend to resist degradation. Such contaminants have been detected in numerous surface water bodies (lakes, reservoirs and rivers). As agriculture is intensifying and land use is changing in many areas, the impact of diffuse pollution on water quality is expected to be more pervasive in the future. The project Aquisafe proposes to investigate the topic in a multi-step approach which will include: i) an analysis of the nature, occurrence and risk of surface water contamination, ii) a modelling approach to quantify the contaminants origin, load and repartition to assess the effects of adapted controlled measures, and iii) the development, adaptation or optimisation of the design and operation of mitigation zones (riparian corridors and small scale wetlands) to reduce downstream loads of pollutants. Thus, Aquisafe is a first step to establish the state-of-the-knowledge on current existing solutions, identify emerging issues and assess the feasibility of using models for the evaluation of mitigation zones for contaminants removal. Within the Aquisafe project it will expected: i) a recommendation on potential key substances to be targeted, also for further investigations, ii) an identification of drinking water source vulnerability to emerging contaminants using a coupled modelling approaches, and iii) an analysis of existing mitigation methods and scientific background for the construction of riparian corridors and/or constructed wetlands in order to mitigate trace contaminants entering the surface water.

The KompetenzZentrum Wasser Berlin (KWB) is a private research and development center, created in 2000, with a status of public interest, and mainly supported by Veolia Water and Berliner Wasser Betriebe. This is where I did a six month-training period as part of my studies at the French AgroParisTech ENGREF engineering school. Within the department “Point and non-point source pollution control”, the KWB initiated a program called Aquisafe. The aim is to investigate the mitigation of trace contaminants from diffuse sources in rural and semi-rural areas to improve water quality of surface water bodies. The sustainable way of addressing pollution control is that the selected mitigation metods are natural or nature-based: namely constructed wetlands and riparian1 corridors. To develop knowledge and tools about these mitigation zones, an innovative approach was chosen when conducting the project: - The first part aims at a background study about surface water and pollutions from diffuse sources, leading to a progressive focus on key pollutants for the future of the project. The second part investigates modelling tools as diagnosis tools for the repartition and load of contaminants in a watershed. The third part contains field experiments and uses results from previous parts. The final purpose is to assess the mitigation efficiency of the systems and to optimize their design in the perspective of improving surface water quality. In charge of the first part, I did set the context of the project by reviewing background information on surface waters in Europe and associated pollutions, that move to water via soil surface run-off or subsurface run-off. After using criteria related to the Aquisafe context, the main pollutant families of interest for the rest of the screening process are pesticides used in agriculture, pollutants coming from the spreading of animal waste on land, pollutants coming from the spreading of sludge from wastewater treatment plants, pollutants from natural and extensive areas, and pollutants from transportation networks. During the study it appeared that in a rural or semi-rural area, the land use of the watershed plays a key role in the selection and assessment of priority pollutants coming from diffuse sources and entering surface waters. The importance of this factor should always be kept in mind as the project goes on. The work is still in progress concerning the review of pollutant families, and will lead to the final screening at the molecule level, providing a list of key contaminants for the other parts of the Aquisafe project. Finally the results of Aquisafe will tell if such sustainable mitigation zones can be used as a real innovative management tool of diffuse pollution in a watershed.