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The exchange of water and solutes between the stream and groundwater along a stream network affects the source composition of discharge and solute load in the stream. To date, this hydrologic turnover has only been analyzed with respect to the exchange of water. In this study, we extend the concept of hydrologic turnover to solutes and analyze the effects of different hydrologic conditions on the spatial patterns and magnitude of exchange fluxes. Based on a coupled stream‐groundwater model built in MODFLOW using the Streamflow‐routing package, we simulated stream‐groundwater exchange along a stream of 30 km in length and evaluated the evolution of stream water source composition under different precipitation and streamflow conditions. Results show that even for highly variable hydrologic conditions, the direction of stream‐groundwater exchange (loss/gain) remained unchanged in consistently gaining or losing reaches, but changed in interspersed transitional reaches. The comparison between the source composition of discharge and nitrate load in stream water revealed a decoupling of discharge and solute load contribution from groundwater to the stream, as zones of high water gains do not necessarily coincide with zones of high solute concentrations. Overall, nearly 80% of total groundwater contributions to the outflow of water from the catchment were generated over only 20% of the total stream length. Our research highlights the importance of distinguishing water and solute load contributions to streams. This in turn implies that to reduce groundwater‐borne nutrient loads to streams, measures need to focus on the specific reaches with highest load contributions. Plain Language Summary: Streams and groundwater are connected and continuously exchange water and solutes. For example, the inflow of groundwater into streams not only increases streamflow, but also influences the chemical composition of stream water if the groundwater contains different solutes than the stream. Therefore understanding the spatial patterns of water and solute contributions from groundwater to the stream is important for the management of stream water quality. Taking the lower Selke River in central Germany as an example, we investigated the influence of stream gains and losses on the source composition of discharge and solute loads along the stream network as well as the influence of different precipitation and streamflow conditions. We found that higher precipitation and the associated elevated groundwater recharge or lower stream flows can increase the total length of gaining reaches, decreasing the relative importance of the source water from the upper stream. Due to the heterogeneous distribution of groundwater and solute gains, the magnitude of solute contribution from groundwater to stream can be quite different from the associated discharge contribution. However, both water and solute contributions are typically dominated by focused groundwater gains along only a few key reaches. Key Points: Across a wide range of hydrologic scenarios, at least 37% of the stream length is characterized by losing conditionsHeterogeneous solute concentrations in groundwater induce a different solute source composition from stream water source compositionMost of the groundwater contributions to stream water are generated over only a small fraction of total stream length [ABSTRACT FROM AUTHOR]

Due to rapid economic development and population growth, China is facing severe water problems that include sea-level rise and increasing salinization, floods, water pollution, water shortage, soil erosion and ecosystem deterioration, as well as biodiversity loss. In recent decades, China is progressively more concerned with its water issues that are now at the center of social and political attention. Having to overcome similar challenges, Germany has taken a leading role in the field of water sciences and technology. In particular, China can benefit from the lessons learnt in Germany concerning the rehabilitation of water resources in areas heavily affected by chemical industry and mining after the reunification in 1989. German-Chinese cooperation in water sciences started over 25 years ago and dealt with increasing challenges in the 21st century. Following the open space workshop during the Water Research Horizon Conference in Berlin 2014, this article provides a view of some of the challenges and potential opportunities of German-Chinese cooperation in water science and technology. [ABSTRACT FROM AUTHOR]

We propose a framework for the 3D exploration of heterogeneous environmental data within a geographical region of interest. Based on Unity, the system can be built for a variety of platforms and works both on regular machines as well as in virtual reality environments, where it can be considered a basis for a virtual geographic environment. Focussing on the catchment of the Müglitz River in south-eastern Germany, a large collection of observation data acquired via a wide range of measurement devices has been integrated in a geographical reference frame for the region. Results of area-wide numerical simulations for both groundwater and soil moisture have been added to the scene and allow for the exploration of the delayed consequences of transient phenomena such as heavy rainfall events and their impact on the catchment scale. This study focusses on the concurrent visualisation and synchronised animation of multiple area wide datasets from different environmental compartments. The resulting application allows to explore the region of interest during specific hydrological events for an assessment of the interrelation of processes. As such, it offers the opportunity for knowledge transfer between researchers of different domains as well as for outreach to an interested public. [Display omitted] • Visualisation of a large heterogeneous data collection in a unified geographical context • Concurrent visualisation of time-dependent observation and simulation data • Visual demonstration of multi-compartment analysis from basic input data • Interactive framework for outreach activities and stakeholder information • General framework for creating similar applications for other regions of interest. [ABSTRACT FROM AUTHOR]