Diffuse nitrate (NO3-) contamination from intense agriculture adversely impacts freshwater ecosystems, and can also pose a risk to human health if receiving surface waters are used for drinking water production. Implementation of near-natural mitigation zones such as reactive swales or wetlands have been proven to be promising measures to reduce nitrate loads in agricultural drainage waters. However, the behaviour of these systems at low temperatures and its dependence on system design is not well known until now. In this part of the Aquisafe project, the behaviour of a full scale (length: 45 m) infiltration ditch and two parallel wetlands (surface flow wetland and infiltration wetland) treating drainage water of two agricultural watersheds in Brittany (France) with high nitrate concentrations in the receiving river, were constructed and monitored for 3 flow seasons in 2011, 2012 and 2013 to evaluate field scale performance of these systems. As the flow in both sites is usually restricted to winter and spring months (December – May), systems usually operate at low water temperatures of 5°C - 10°C. Tracer tests revealed shorter than designed retention times (average values for whole flow season 2013: 1.1 h for infiltration ditch, 4.3 h for infiltration wetland and 8.4 h for surface wetland) due to high inflows and preferential flow. This likely is the main reason for observed low average retention of nitrate loads of 1.5-3% during the whole flow season. However, increase of relative nitrate retention to up to 80% during low flow conditions at the end of flow season in May with higher HRT and increasing temperatures show that investigated systems generally work. Results show a stronger correlation between residence time and nitrate reduction for all three systems compared to correlation with temperature. Retention times necessary in existing systems to achieve nitrate retention >30% were 1 day for infiltration ditch and 3 days for wetlands. Performance was compared to results of two technical scale reactive swales (length: 8 m) operated for 1.5 years at two different residence times (0.4 and 2.5 days), situated at a test site of the German Federal Environmental Agency (UBA) in Berlin (Germany). Similar nitrate reduction was observed for comparable temperature and HRT values (during low flow conditions at end of flow season 2013), showing that up-scaling is a suitable approach to transfer knowledge gathered from technical scale experiments to field conditions. For the design of new mitigation systems, expected inflow volumes have to be investigated carefully in advance to ensure a sufficient residence time for effective nitrate reduction at low temperatures.

Diffuse nitrate (NO3) contamination from intense agriculture adversely impacts freshwater ecosystems, and can also result in nitrate concentrations exceeding limits set in drinking water regulation, when receiving surface waters are used for drinking water production. Implementation of near-natural mitigation zones such as reactive swales or wetlands have been proven to be promising measures to reduce nitrate loads in agricultural drainage waters. However, the behavior of these systems at low temperatures and its dependence on system design is not well known until now. In this study, the behavior of a full scale (length: 45 m) reactive swale treating drainage water of an agricultural watershed in Brittany (France) with high nitrate concentrations in the receiving river, was monitored for one season (6 months). As flow in this field scale system is usually restricted to winter and spring months (December – May), it usually operates at low water temperatures of 5°C - 10°C. Tracer tests revealed shorter than designed retention times due to high inflows and preferential flow in the swale. Results show a correlation between residence time and nitrate reduction with low removal (<10%) at short residence times (<0.1 d), increasing to >25% at residence times >10h (0.4 d). Performance was compared to results of two technical scale reactive swales (length: 8 m) operated for 1.5 years at two different residence times (0.4 and 2.5 days), situated at a test site of the German Federal Environmental Agency (UBA) in Berlin (Germany). Similar nitrate reduction was observed for comparable temperature and residence time, showing that up-scaling is a suitable approach to transfer knowledge gathered from technical scale experiments to field conditions. For the design of new mitigation systems, one recommendation is to investigate carefully expected inflow volumes in advance to ensure a sufficient residence time for effective nitrate reduction at low temperatures.

In recent years, organic micropollutants have been detected in urban storm runoff in several European studies. As rain water runoff in Berlin and other German and European cities is often discharged untreated in separated sewer systems, urban stormwater is a large potential source of micropollutants affecting receiving surface waters. As a consequence, it is important to know the local extent of the issue to be able to evaluate potential measures. In this study, a one year monitoring programme is conducted in the city of Berlin to estimate yearly loads of micropollutants from urban stormwater entering Berlin surface waters. Five different catchment types typical for Berlin were determined after analysis of GIS data (old building areas <1930, newer building areas >1950, single houses with gardens, roads and commercial areas) and monitoring points were selected fulfilling a number of criteria (including representativeness of catchment type, accessibility, sufficient flow, manhole size). Samples are taken using automatic samplers and a sampling strategy was developed to obtain best possible representative composite samples representing the average concentration of the sampled storm event. Results will then be used with measured flow data to calculate micropollutant loads of individual catchment types. A runoff model for Berlin applied to the individual catchment types and coupled with pollutant concentration relationships will be used to extrapolate results to city scale.

Regenwasserabfluss ist die größte unbehandelte Quelle von potentiell hohen Spuren-stofffrachten in urbane Oberflächengewässer. In Berlin werden ca. 74% oder jährlich 44 Millionen m³ des Regenwasserabflusses weitgehend unbehandelt eingeleitet. Dies ent-spricht etwa 5% des jährlichen Abflusses der Stadtspree an der Mündung in die Havel. Erste Studien aus der Schweiz und Frankreich zu ausgewählten organischen Spurenstoffen (z.B. Biozide, Kunststoffinhaltsstoffe, Verbrennungsprodukte) im Regenwasserabfluss und Oberflächengewässern zeigen zum Teil hohe Konzentrationen von Substanzen mit möglicher Relevanz für aquatische Organismen oder die mensch-liche Nutzung.

This report summarizes relevant available knowledge on the removal of micropollutants from WWTP effluent in natural treatment systems such as constructed wetlands (polishing). Five studies were found investigating removal of various micropollutants in eight different full scale systems located in Spain, southern France, Korea and Sweden (all being different configurations of free water surface wetlands), demonstrating good removal (>80%) for more than 15 micropollutants compounds under summer conditions, e.g. diclofenac, ketoprofen, naproxen, ibuprofen, galaxolide, atenolol, ciprofloxacin, triclosan, glyphosate, ofloxacin and metoprolol. Hydraulic retention times (HRT) ranged from 0.25 to 30d. At HRT of 0.25d, only naproxen and atenolol were removed by >80% in summer, highlighting the importance of HRT for system performance. Another important factor influencing the removal is temperature and season with lower removal in winter. However, in warm climates (e.g. two studies in northern Spain and one study in southern France), reduction of removal efficiencies in winter is less pronounced with values for removal of the majority of investigated pharmaceuticals in winter still being >60%. In 4 FWS wetlands sampled during winter at sub-zero temperatures in Sweden, though, removal was mostly below 50%. A variety of removal mechanisms simultaneously occur in natural treatment systems and are relevant to varying extent for each compound and system type. Important removal mechanisms are biodegradation (e.g. for naproxen, ibuprofen), photodegradation (e.g. for diclofenac, ketoprofen, sulfamethoxazole) and adsorption (e.g. for galaxolide, tonalide). The relevance of plant uptake and phytodegradation as removal mechanisms is not fully understood; however, a few studies demonstrate the translocation of pharmaceuticals (e.g. carbamazepine) to plant tissue. For biodegradation, redox conditions are an important parameter influencing microbial degradation pathways. Design guidelines for eco-engineered treatment systems targeting the removal of micropollutants are not available to date. In addition, data necessary to dimension ecoengineered treatment systems that target the reduction of micropollutants in WWTP effluent (e.g. kinetic data such as removal rates and its dependence on temperature) is lacking. For the development of design guidelines for eco-engineered systems targeting the removal of micropollutants, removal rates for each system type and compound and their dependence from temperatures needs to be determined for all compounds of interest. Furthermore, more research is necessary for a deeper understanding of processes in eco-engineered systems, especially the relevance of the different removal mechanisms and conditions for removal for each individual micropollutant of interest. Nevertheless, eco-engineered treatment systems are a promising technology for polishing of WWTP effluent, including further removal of micropollutants.

In agricultural watersheds affected by diffuse pollution, limitation of fertilizer and pesticide application may not be sufficient to achieve good river water quality. After waterworks had to be closed in Brittany due to elevated nitrate concentrations in the river Ic (> 50 mg-NO3 L-1), the project Aquisafe has been initiated. The objective of Aquisafe is to reduce pollutant loads (nitrate and pesticides) from agricultural fields by implementation of near-natural mitigation zones at diffuse pollution hotspots at the head of watersheds. Simple and small solutions have to be designed in order to more efficiently reduce nitrate and pesticide concentrations in receiving rivers. In addition, a planning tool has to be developed to determine optimal locations to construct these systems. Finally, a tool to assess the effectiveness of these reactive zones on watershed water quality will be implemented. In order to reach the first objective, design features are tested on three scales: 1) laboratory scale, 2) technical scale and 3) field scale. 1) In the laboratory, column experiments were conducted with different organic substrates at short hydraulic residence times (HRT). The efficiency for parallel reduction of nitrate and two common herbicides in Europe, Bentazon and Isoproturon, was explored (Krause Camilo, 2012). 2) In technical scale, two parallel swales were filled with the most suitable material determined in (1) for a one year test. The influence of HRT and temperature was investigated. For nitrate, high reduction could be achieved at short HRT; results for herbicides still have to be confirmed. 3) One infiltration ditch and two simple wetlands were constructed in Brittany (France), taking into account experiences from other scales. These systems are now monitored to investigate the effects of upscaling. Site locations were chosen based on a validated and repeatable GIS-based overlay method that prioritises zones of potential contribution to nitrate pollution (Orlikowski et al, 2011). Additionally, a new wetland module is being developed for the Soil and Water Assessment Tool (SWAT). It allows to predict impacts of wetland constructions on nitrate concentrations in receiving rivers; the module is now implemented but still has to be calibrated with in situ monitoring results. The presentation will focus on results of the up-scaling approach, and will show how the tools of Aquisafe can be used for supporting the development of strategies at catchment scale.