The Aquisafe project aims at mitigation of diffuse pollution from agricultural sources to protect surface water resources. The first project phase (2007-2009) focused on the review of available information and preliminary tests regarding (i) most relevant contaminants, (ii) system-analytical tools to assess sources and pathways of diffuse agricultural pollution, (iii) the potential of mitigation zones, such as wetlands or riparian buffers, to reduce diffuse agricultural pollution of surface waters and (iv) experimental setups to simulate mitigation zones under controlled conditions. The present report deals with (iii) and has the purpose to provide a brief overview of the current state of knowledge related to the role of riparian zones as best management practices for water quality improvement at the watershed scale. Research indicates that landscape hydrogeological characteristics such as topography and surficial geology influence both riparian zone hydrology and biogeochemistry. Topography, depth to a confining layer and soil hydraulic conductivity all affect groundwater input to riparian zones and the water table fluctuation regime throughout the year. Research also indicates that although most biologically mediated reactions in soil are redox dependant, landscape hydrogeology, by affecting riparian hydrology, affects the redox conditions in the soil profile. In turn, microbial processes and changes in element concentrations are predictable as a function of the redox state of the soil.Variations in biogeochemical conditions directly affect the fate of multiple contaminants in riparian systems. In particular, variations in soil redox potential in riparian zones can affect the evolution of numerous contaminants and solutes within riparian zones like pesticides, phosphorus, NO3-, N2O, NH4+, SO42-, CH4, Fe2+/Fe3+ or Dissolved Organic Carbon (DOC). Of all the solutes/contaminants mentioned above, nitrate is one of the most important concerning water quality in many areas of the US and Western Europe. Consequently, many studies have investigated nitrate removal in riparian systems. Depending on site conditions, nitrate retention generally varies between 60 and 90 %; however, there are situations where nitrate removal is less or even where a riparian zone becomes a source of N to the stream. Although the riparian literature is clearly dominated by nitrate removal studies, many studies also focus on phosphorus, sediments, pesticides, chloride, bromide and bacteria. Although there are situations where riparian zones have been shown to be sources of P, Atrazine, bromide, E. coli or E. streptococci bacteria, riparian zones generally contribute to the reduction of most contaminants in subsurface flow and overland flow. Nevertheless, although conditions favorable to the reduction or oxidation of a given contaminant at the microbial level are often known, more research needs to be conducted to determine the variables controlling the fate of contaminants other than nitrate in soil at the riparian zone scale.Finally, although many studies have investigated the hydrological and biogeochemical functioning of riparian zones in the past few decades, much research remains to be conducted in order to quantify and predict the impact of riparian zones on water quality at the watershed scale in a variety of climatic and hydrogeological settings. In particular, better strategies and/or tools to generalize riparian function at the watershed scale need to be developed. Particular areas where research is needed to achieve this goal include: 1) the development of strategies to quantify and model the cumulative impact of individual riparian zones on water quality at the watershed scale; 2) a better quantification of the importance of spatial and temporal variability in hydrologic and biogeochemical riparian functioning relative to annual nutrient transport; 3) a better understanding of the role of vegetation in terms of its impact on riparian biogeochemical processes and the response of these processes to manipulations of vegetative cover; 4) a better understanding of the impact of human activities and infrastructure on riparian zone function in both urban and rural landscapes; 5) a better understanding of the fate of emerging contaminants in riparian systems.

The Aquisafe project aims at mitigation of diffuse pollution from agricultural sources to protect surface water resources. The first project phase (2007-2009) focused on the review of available information and preliminary tests regarding (i) most relevant contaminants, (ii) system-analytical tools to assess sources and pathways of diffuse agricultural pollution, (iii) the potential of mitigation zones, such as wetlands or riparian buffers, to reduce diffuse agricultural pollution of surface waters and (iv) experimental setups to simulate mitigation zones under controlled conditions. The present report deals with (iii), providing a review of the potential of constructed wetlands to protect surface waters from diffuse agricultural pollution. Population growth and industrialization have lead to the demise of large majorities of natural wetland systems. Recent research continues to suggest the importance of these often saturated areas in the natural remediation of pollutants in water, as well as being aesthetically pleasing and acting as potential habitat for declining species. The drastic losses in wetland areas, combined with the realization of their importance, have stimulated recent attempts at wetland restoration and even construction of wetlands where they would not have naturally occurred. In terms of substance remediation, constructed wetlands were traditionally used for the treatment of point sources, such as urban or industrial waste water. Recently they have also become increasingly popular for the treatment of diffuse pollution from agriculture and urban storm runoff. Constructed wetlands have been shown to be efficient in the treatment of nutrients, organic matter and heavy metals. Few studies also show their potential against trace organics, such as pesticides and pharmaceutical residues and against pathogens. Retention efficiencies vary significantly among case studies. In agricultural settings the following design criteria should be considered: (i) Water residence time in wetlands is critical. Some studies concerning nutrient removal suggest that a constructed wetland should be about 5 % of the watershed area and assure water residence time of 7 days. (ii) Vegetation is important to slow down flow and increase sedimentation. Regular cutting and removal of plants is controversially discussed, since it may reduce their beneficial effect on wetland hydrology. (iii) Constant redox conditions are important to avoid release of sedimented or adsorbed pollutants. (iv) A combination of constructed wetlands with buffer strips showed very positive results.

An international review of the market, current practices and R&D projects on the topic of rainwater harvesting management was performed. The review highlighted leading countries in different regions of the world, but also the variety of practices and acceptance. Current R&D issues and further research needs are identified and discussed. The application of RWHM techniques at household level seems to be mature, but sanitary risks exist when rainwater is used inside homes and also reserve on economical an environmental aspects can be drawn when drinking water supply is available. Promising concepts are being developed and demonstrated at larger scale such as industrial or commercial buildings or even urban catchments where the use of rainwater and the operation of the systems are under full control. For schemes of this scale, the integration and optimization of several beneficial aspects such as –traditionally- additional water supply and stormwater management, but also urban planning with water and green spaces, energy compensation in buildings and in the cities or ecological enhancement seems to be promising. Specific expertise will be required to best plan these schemes according to the local conditions and targets and to operate, maintain and upgrade them over their entire life time.

The Soil and Water Assessment Tool (SWAT) has been applied to the Ic watershed, Brittany, France, to evaluate scenarios for reduction of nitrate in stream water. For the simulated period the model showed fair results with a mean index of agreement of 0.64 at the watershed outlet for discharge and nitrate loads. The management goal for the watershed is the meeting of drinking water threshold at the watershed outlet. An analysis of observed data revealed that nitrate loads would have to be reduced by at least 17% on average to reach that goal. Scenarios investigated cover fertilizer reduction and the introduction of wetland buffer zones. Decreased nitrogen inputs were realized on a) selected subbasins and b) all agricultural fields; wetlands were placed at three model subbasins. Most effective measures were a 50% fertilizer decrease on selected subbasins resulting in a range of 13 22 % reduction of nitrate loads with a high uncertainty. Consequently, none of the tested measures is likely to achieve a sufficient reduction. Combined measures such as enhanced fertilizer management and concurrent introduction of wetlands seem to be the most promising way to approach the drinking water threshold.

The Aquisafe project aims at mitigation of diffuse pollution from agricultural sources to protect surface water resources. The first project phase (2007-2009) focused on the review of available information and preliminary tests regarding (i) most relevant contaminants, (ii) system-analytical tools to assess sources and pathways of diffuse agricultural pollution, (iii) the potential of mitigation zones, such as wetlands or riparian buffers, to reduce diffuse agricultural pollution of surface waters and (iv) experimental setups to simulate mitigation zones under controlled conditions.

The Aquisafe project aims at mitigation of diffuse pollution from agricultural sources to protect surface water resources. The first project phase (2007-2009) focused on the review of available information and preliminary tests regarding (i) most relevant contaminants, (ii) system-analytical tools to assess sources and pathways of diffuse agricultural pollution, (iii) the potential of mitigation zones, such as wetlands or riparian buffers, to reduce diffuse agricultural pollution of surface waters and (iv) experimental setups to simulate mitigation zones under controlled conditions. The present report deals with (ii), presenting existing diagnostic methods for agricultural diffuse pollution on a river basin scale. The report focuses on methods with low to moderate data requirements and analytical effort. Generally no numerical models but mostly GIS based approaches have been considered. The described methods were distinguished along two questions: 1. Does diffuse agricultural pollution play an important role in a given catchment? 2. Which areas within the catchment contribute highly to diffuse pollution of the receiving river, i.e. which areas are critical source areas (CSAs)? Question 1 can be answered by using nutrient measurements, mass balance approaches or land use based methods. For most catchments some nutrient measurements and land use data are available, which allow a first assessment whether diffuse pollution could play a role. For question 2, the identification of CSAs, a number of GIS-based methods was found in scientific literature. Since most available methods focus on nutrients and since spatial data on other contaminants, such as pesticides, are typically not available, the report outlines methods for the two critical nutrients nitrogen and phosphorus. Each method can be looked up separately, as they are summarized in a similar structure. Moreover Table 8 in Appendix G provides a quick overview of all the presented methods. All the described approaches focus on nutrients, as they are a major concern and often in the focus of research projects. In general the presented methods consider three aspects to assess the risk of pollution from an area within a river basin: 1. The source of nutrients on agricultural land is included through fertilizer application, livestock numbers or indirectly via land use. 2. Transport to the river is mainly assessed via soil type, land cover, elevation and distance to the river 3. In addition several methods take retention processes into account during transport to or within the river It is important that different contaminants show different behaviour. For instance, phosphorus is pre-dominantly particle-bound, enters rivers via soil erosion and can be retained by adsorption or plant export. Nitrate, the dominant form of nitrogen, is very well soluble, is lost mostly through leaching and most efficiently retained by denitrification. Consequently, methodologies for the assessment of CSAs for phosphorus and nitrogen were looked at separately. While many promising methods with limited data requirements and analytical efforts were identified in the report, few concepts (such as the Universal Soil Loss Equation for phosphorus) seem to be well established. Most literature concerns specific local or regional case studies. As a result, transferability to other catchments is questionable. The highest potential is seen in qualitative, multi-criteria methods (such as the scoring approach by Trepel and Palmeri, 2002), which can be adapted by the user depending on the diagnostic aim as well as local data availability. In summary, it is recommended to test several of the presented GIS methods on one or two catchments to gain experience in their handling and their transferability.

The Aquisafe project is a cooperation of the Indiana University Purdue University Indianapolis (IUPUI, USA), the German Federal Environment Agency (UBA, Germany) and the Berlin Centre of Competence for Water (KWB, Germany). The aim of the project is the development of a scheme for natural mitigation zones to protect surface waters from diffuse pollution in rural and semi-rural environments. In particular, key contaminants, applicable management and modelling tools and potential substance removal by constructed wetlands or riparian zones are being studied. Within these frameworks, two case studies are carried out in Brittany, the number one agricultural region in France. A hydrological model is currently being applied on the Ic catchment (92 km2) to test its capability of (i) understanding hydrological, basin-scale regimes, (ii) predicting the effect of mitigation measures and (iii) distinguishing diffusion pathways for different types of contaminants. In the second case study, a constructed wetland in Iffendic on the River Meu is monitored as an example of a natural and inexpensive mitigation option. On the way through the wetland nitrate concentrations from drainage inflows to the river decreased more than tenfold. In the ongoing monitoring, knowledge on hydrological flowpaths is improved to be able to quantify the retention potential of constructed wetlands in Brittany for nitrate and other agriculturally-based pollutants, such as pesticides.