Interfaces in urban surface waters
- © UWI
Urban surface waters are heavily modified systems that face various challenges caused by interactions between technical and natural compartments. The morphological degradation of surface waters due to water management can cause a disruption between water systems and their riparian area, floodplains, the hyporheic zone and aquifers. Further, high loads of pollutants, nutrients and organic carbon are discharged into the recipients from various sources like wastewater treatment plants (WWTP), industry, road runoffs, paved surfaces and atmospheric deposition. Eventually, this can result in the eutrophication of urban surface waters. In comparison to low affected surface waters, the water quality and quantity of urban ones are altered on microscale to macroscale spatial and temporal levels when flows across different interfaces appear. These deep gradients occur between (1) aquifers and surface waters, (2) atmosphere and surface waters, and (3) sediments and surface waters. In addition all these interfaces are also affected by urban technical systems. The main focus of the research in this common topic group is the semi-closed water cycle and management in the city of Berlin, Germany. The urban water management aims to manage a secure water supply for domestic and industrial consumption, an adequate sanitation, the protection of humans and infrastructure as well as urban ecosystems and the conservation of biodiversity. Such a system is vulnerable to changing meteorological conditions as well as pollutant loads. We are aiming to increase the understanding of urban flow dynamics, interactions between surface waters and their surrounding interfaces as well as the metabolism of surface waters to improve urban water management.
To assess water management measures paleolimnological methods are used to investigate sediments of urban surface waters in Berlin. These natural archives give information about past pollutant loadings and can act as possible internal sources. Further, with the help of coupled numerical models for hydrodynamics, water chemistry and diagenesis it is possible to optimize current and future lake water management as well as to find weaknesses and potential threats. This will be done by formulating different management scenarios using 1D as well as 2D lake models incorporating modelling systems like General Lake Model and ‘TELEMAC-MASCARET’(Project T4 ).
Further research activities include the investigation of the groundwater-surface water interface by extensive monitoring of a river field site (Project N6 ) and formulating a transport reaction model (Project N7 ). Here, a three-dimensional, integral single-domain model is applied and extended using the Navier-Stokes equation for surface water and groundwater. The simulations comprise flow, transport and reaction processes in the transitional area of surface water and groundwater. For the calculations, the computational fluid dynamics software 'OpenFOAM' is used.
Laboratory and modelling studies are used to explore the effects of bank filtration on lake ecosystems (Project N5 ) as well as drinking water purification regarding micropollutants. A particular focus is placed on the degradation processes of iodinated contrast media during bank filtration (Project T6 ). These diagnostic agents show decreasing concentrations during bank filtration although they are known to be very stable and persistent to conventional wastewater treatment. Further, the investigation of the effects of bank filtration on lake water ecosystems will result in a new research field which is approached in a number of different ways: (i) with field work, (ii) with experiments, both in a laboratory as well as a field setting and also (iii) by computer simulation using the ecosystem model ‘PCLake’.
A major field campaign intends to monitor the ecosystem metabolism (Project N4 – Clara Romero). This is motivated by two equally important aspects: (i) the need to estimate the total CO2 emissions from metropolitan areas to improve knowledge on the role of inland water in the global carbon cycle and (ii) the need to obtain a better mechanistic understanding of urban water networks as meta-ecosystems with ecosystem metabolism as a central integrative element of ecosystem functioning. Further, greenhouse gas emissions are aimed to be quantified, understanding the specific drivers in aquatic urban ecosystems. Different processes will be studied from production in the sediments to different flux pathways (Project N3 ).
Robert Ladwig (corresponding doctoral student)
Fatima El-Athman 
surface water – sediment (T4 - Robert Ladwig )
surface water – groundwater (N5 – Mikael Gillefalk , N6 – Jonas Schaper , N7 - Tabea Broecker , T6 - Fatima El-Athman )
surface water – atmosphere (N3 - Sonia Herrero , N4 - Clara Romero )
surface water - sediment (N3 - Sonia Herrero) 
- BWB –
Berliner Wasserbetriebe (BWB)
- Senatsverwaltung für Stadtentwicklung und Umwelt, Berlin 
- Netherlands Institute of Ecology (NIOO), Wageningen 
- Helmholtz Centre for Environmental Research (UFZ), Leipzig 
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