The project Aquisafe assesses the potential of selected near-natural mitigation systems, such as constructed wetlands or infiltration zones, to reduce diffuse pollution from agricultural sources and consequently protect surface water resources. A particular aim is the attenuation of nutrients and pesticides. Based on the review of available information and preliminary tests within Aquisafe 1 (2007-2009), the second project phase Aquisafe 2 (2009-2012) is structured along the following main components: (i) Development and evaluation of GIS-based methods for the identification of diffuse pollution hotspots, as well as model-based tools for the simulation of nutrient reduction from mitigation zones. (ii) Assessment of nutrient retention capacity of different types of mitigation zones in international case studies in the Ic watershed in France and the Upper White River watershed in the USA under natural conditions, such as variable flow. (iii) Identification of efficient mitigation zone designs for the retention of relevant pesticides in laboratory and technical scale experiments at UBA in Berlin. The following report focuses on (ii), providing an overview of existing mitigation systems that may reduce transport of agricultural pollutants to surface waters, with a particular focus on nitrate. The report is based on an extensive review of scientific literature as well as practical guidelines. The review emphasizes on systems, which can treat pollutant loads from agricultural fields with surface or tile drainage. Such mitigation systems could play an important role in intensely used agricultural areas, where existing efforts in farm or crop management are not sufficient to reach water quality goals in receiving rivers. This is typically the case for agricultural catchments with high ratio of artificial drainage, which allows an almost complete transfer of water and contaminants, particularly during high flow events. For each identified mitigation system, its general approach, performance against nitrates and other contaminants, boundary conditions as well as expected cost are given. The systems are structured according to their place on the pathway between field and surface water into 1. systems which attempt to reduce contaminant loads in the drainage pipes and ditches (section 2), 2. systems, which can be placed between drainage system and surface water (section 3), 3. systems, which can be placed in the receiving surface water (section 4). The review shows that there are a number of feasible options with the potential to mitigate NO3 - pollution from drained agricultural land. The most promising approaches with high removal potential were found to be: - controlled drainage (section 2.2), - bioreactors at the tile level (section 2.3.2), - reactive swales (section 2.4.2), - constructed wetlands (section 3.2) and - river-diversion wetlands (section 4.2.2). Most practical experience exists for constructed wetlands with surface flow (globally) and for controlled drainage (mainly in the USA), whereas the other systems are currently at an experimental state. v For a model agricultural area, the above systems resulted in expected nitrate reduction between 14 and 82 % and cost efficiencies between 23 and 246 € kg-N-1. In terms of absolute nitrate removal, (i) wood chip walls parallel to tile drains and (ii) constructed wetlands with straw as carbon source were found to be most effective. However, for both systems there are relatively few experiences so further testing will be necessary. Regarding cost efficiency, (iii) constructed surface flow wetland with low construction cost (dam) and (iv) controlled drainage are most efficient. Whereas constructed surface flow wetlands can be implemented independently, drainage control structures need to be managed by farmers, which requires their active cooperation and proper training.