Dietrich Borchardt

Modelling water quality, bioindication and population dynamics in lotic ecosystems using neural networks

The assessment of properties and processes of running waters is a major issue in aquatic environmental management. Because system analysis and prediction with deterministic and stochastic models is often limited by the complexity and dynamic nature of these ecosystems, supplementary or alternative methods have to be developed. We tested the suitability of various types of artificial neural networks for system analysis and impact assessment in different fields: (1) temporal dynamics of water quality based on weather, urban storm-water run-off and waste-water effluents; (2) bioindication of chemical and hydromorphological properties using benthic macroinvertebrates; and (3) long-term population dynamics of aquatic insects. Specific pre-processing methods and neural models were developed to assess relations among complex variables with high levels of significance. For example, the diurnal variation of oxygen concentration (modelled from precipitation and oxygen of the preceding day; R 2 0.79), population dynamics of emerging aquatic insects (modelled from discharge, water temperature and abundance of the parental generation; R 2 0.93), and water quality and habitat characteristics as indicated by selected sensitive benthic organisms (e.g. R 2 0.83 for pH and R 2 0.82 for diversity of substrate, using five out of 248 species). Our results demonstrate that neural networks and modelling techniques can conveniently be applied to the above mentioned fields because of their specific features compared with classical methods. Particularly, they can be used to reduce the complexity of data sets by identifying important (functional) inter-relationships and key variables. Thus, complex systems can be reasonably simplified in clear models with low measuring and computing effort. This allows new insights about functional relationships of ecosystems with the potential to improve the assessment of complex impact factors and ecological predictions.

Integrated Water Resources Management under different hydrological, climatic and socio-economic conditions

The International Water Research Alliance Saxony (IWAS) project (2009–2014) was dedicated to investigate global challenges concerning integrated water resources management (IWRM) in different model regions in Eastern Europe (region R1), Central and Southeast Asia (R2 and R3), the Middle East (R4) and Latin America (R5). This thematic issue compiles the most important scientific results of the second phase of the IWAS project which was introduced by Kalbus et al. (2012). The main results and lessons learned from the transdisciplinary IWRM project are presented in Seegert et al. (2014). The IWAS project was structured into the above-mentioned model regions (R1–5) and into cross-cutting topics: Q1—Model based scenario analysis, Q2—Technology development, Q3— Governance, and Q4—Capacity development (Fig. 1). The first cross-cutting topic Q1 was dedicated to modelbased scenario analysis of hydrological and climate related processes. Within the first project phase of IWAS a ToolBox for hydrological process simulation was developed and exemplary applied to the IWAS investigation regions (Kalbacher et al. 2012). The toolbox concept has been completed by invoking data integration as well as model visualization methods (Rink et al. 2014; Bilke et al. 2014). Within the second IWAS project phase, the toolbox has been extensively applied to several IWAS model regions: R1 (e.g. Fischer et al. 2014; Koerner et al. 2014; Pavlik et al. 2014), R2 (e.g. Karthe et al. 2014), R4 (e.g. Kloss et al. 2014; Graebe et al. 2013; Subagadis et al. 2014; Walther et al. 2014), R5 (e.g. Borges et al. 2014; Da Anunciacao et al. 2014; Goncalves et al. 2013) to address a variety of questions for surface water and groundwater management. More general works were Barfus and Bernhofer (2014) who applied global climate models (GCM) to different model regions and Pluntke et al. (2014) dealing with uncertainty in hydrological modeling due to data scarcity. The second cross-cutting topic Q2 was focused on technology development, implementation and transfer. Three work packages in Q2 were dealing with the Sewchar concept for sustainable sanitation systems (Fuehner et al. 2012), hydrothermal carbonization for treatment of domestic waste and sewage sludge (Poerschmann et al. 2014), and the development of multisensory systems for the detection of pathogens. The remaining transdisciplinary topics were dealing with aspects of governance (Q3) and capacity development (Q4). Dombrowsky et al. (2014) were discussing socioeconomic questions of water governance in transition countries as well as institutional and legal constraints for transboundary river basin management. Capacity development is an important method for the implementation of IWRM concepts (Leidel et al. 2014). As a result of the IWAS capacity development activities an E-learning platform has been established (Leidel et al. 2013, see http:// www.iwrm-education.de). IWAS Ukraine (R1) was dealing with a variety of IWRM aspects elaborating on socio-economic as well as natural science questions (Dombrowsky et al. 2014; Hagemann et al. 2014) discussing the role of water governance in transition countries as well as institutional and legal constraints on transboundary river basin management. A decision support concept was developed by Leidel et al. J. Seegert O. Kolditz (&) P. Krebs D. Borchardt Technische Universitat Dresden, Dresden, Germany e-mail: ees-editor@ufz.de

Water resources and their management in central Asia in the early twenty first century: status, challenges and future prospects

Large parts of Central Asia are characterized by a semiarid to arid climate. Therefore, areas close to shallow groundwater, rivers and lakes are characterized by unique water-dependent ecosystems and human societies which have developed over millennia in close interaction with the naturally limited water resources. In the early 21st century, global climate change, population growth, river damming, large-scale water abstractions and rising levels of pollution exert multiple pressures on the region’s water resources, aquatic and terrestrial ecosystems at historically high levels. Water scarcity threatens the livelihood of populations locally and in transboundary settings by a growing competition over a limited resource. This context is of particular importance since all major rivers of the region cross at least one international border. The complexity and character of water-related challenges in the region mean that management approaches need to be integrative, taking into account the natural resource basis, environmental limits and the socio-cultural and geopolitical dimension. This paper frames the thematic issue of Environmental Earth Sciences and provides a comprehensive overview about the current state of knowledge about water resources and their management in Central Asia. There is a focus on case studies looking at the Selenga–Baikal–Angara Basin, the Lake Aral Basin including the Syr Darya and Amu Darya river systems, the Tarim and the Illi River Basins. Aiming to be an up-to-date interdisciplinary scientific reference on the region’s water-related challenges, this thematic issue gives theoretical and practical insights into solutions and best practice examples of water management.

The IWAS-ToolBox: Software coupling for an integrated water resources management

Numerical modeling of interacting flow and transport processes between different hydrological compartments, such as the atmosphere/land surface/vegetation/soil/groundwater systems, is essential for understanding the comprehensive processes, especially if quantity and quality of water resources are in acute danger, like e.g. in semi-arid areas and regions with environmental contaminations. The computational models used for system and scenario analysis in the framework of an integrated water resources management are rapidly developing instruments. In particular, advances in computational mathematics have revolutionized the variety and the nature of the problems that can be addressed by environmental scientists and engineers. It is certainly true that for each hydro-compartment, there exists many excellent simulation codes, but traditionally their development has been isolated within the different disciplines. A new generation of coupled tools based on the profound scientific background is needed for integrated modeling of hydrosystems. The objective of the IWAS-ToolBox is to develop innovative methods to combine and extend existing modeling software to address coupled processes in the hydrosphere, especially for the analysis of hydrological systems in sensitive regions. This involves, e.g. the provision of models for the prediction of water availability, water quality and/or the ecological situation under changing natural and socio-economic boundary conditions such as climate change, land use or population growth in the future.

Ecological impact of urban stormwater runoff studied in experimental flumes: Population loss by drift and availability of refugial space

Urban stormwater runoff discharged through sewer systems into streams causes flush spills of water and pollutants in the receiving water. To make the right decisions in future plannings of the very costly rehabilitation of sewer systems, a solid ecological data base on the critical parameters of sewer overflows is badly needed. Therefore, we designed a laboratory flume which was operated in circular flow mode (to ensure adaptation of the test organisms) and in flow-through mode during the simulation of sewer overflows (to allow a proper evaluation of population loss by drift). Examples on the behaviour during the adaptation phase and the population loss during the exposure to flush spills of water and/or a mixture of sewage and clean water of a benthic invertebrate (Gammarus pulex) demonstrate the potential of the flume to identify critical parameters of sewer overflows at “quasireal-world-conditions”. We found clear evidence for synergetic effects since the exposure to high flow and sewage caused higher population loss ofGammarus than the sum of population loss at exposure to only high flow or only sewage. Population loss considerably depended on the availability of refugial space: if the interstices of the gravel in the flume were silted, this loss was higher than at open interstices. Only ten minutes of movement of the material forming the flume bottom reduced the population ofGammarus to about 60 or 50% of its initial size. Hence, our data strongly suggest that the characteristics of the receiving stream (refugial space, bed stability) play an important role for the potential ecological impact of a sewer overflow. Changes of stream morphology and/or creation of refugial space plus an appropriate technical solution for overflow treatment may be less costly and more effective than a large-scale technical project. Thus, the stream itself should be a major element in future management decisions.

Disentangling the influence of hydroclimatic patterns and agricultural management on river nitrate dynamics from sub-hourly to decadal time scales

Despite extensive efforts to reduce nitrate transfer in agricultural areas, limited response is often observed in the nitrate concentration in rivers. To investigate the reasons for this limited response, nitrate dynamics in a 100km(2) agricultural catchment in eastern Germany was analysed from sub-hourly to decadal time-scales. Sub-hourly analysis of storm event dynamics during a typical hydrological year (2005-2006) was performed to identify periods of the year with high leaching risk and to link the latter to agricultural management practices in the catchment. Dynamic Harmonic Regression analysis of a 32-year (1982-2014) record of nitrate and discharge revealed that i) the long-term trend in nitrate concentration was closely related to that in discharge, suggesting that large-scale weather and climate patterns were masking the effect of improved nitrogen management on nitrate trends; ii) a persistent seasonal pattern with winter concentration maxima and summer minima could be observed, which was interpreted in terms of a dynamic nitrate concentration profile in the soil and subsoil; and iii) the catchment progressively changed from chemodynamic to more chemostatic behaviour over the three decades of study, which is a sign of long-term homogenisation of nitrate concentrations distribution over depth. This study shows that detailed physical understanding of nitrate dynamics across time scales can be obtained only through combined analysis of long-term records and high-resolution sensor data. Hence, a joint effort is advocated between environmental authorities, who usually perform long-term monitoring, and scientific programmes, which usually perform high-resolution monitoring.

Suspended sediments in the Kharaa River catchment (Mongolia) and its impact on hyporheic zone functions

A previous study investigating the ecological status of the Kharaa River in Northern Mongolia reported fine-grained sediments as being a major stress factor causing adverse impacts on the benthic ecology. However, the source of these sediments within the catchment as well as the specific impact on hyporheic zone functions in the Kharaa River remained unclear. Therefore, the objective of the current study was to investigate the underlying source–receptor system and implement an integrated monitoring approach. Suspended sediment sources within the Kharaa catchment were identified by using extensive spatially distributed sediment sampling and geochemical and isotope fingerprinting methods. On the receptor side, the ecological implications across a gradient of fine-grained sediment influx were analyzed using a distinct hyporheic zone monitoring scheme at three representative river reaches along the Kharaa River. Results of suspended sediment source monitoring show that during snowmelt runoff, riverbank and gully erosion were the dominant sources. During the summer period, upland erosion contributed a substantial share of suspended sediment. Fine-grained sediment influx proved to be the cause of habitat loss in the hyporheic zone and benthic oxygen production limitation. This combined catchment and in-stream monitoring approach will allow for a better understanding and spatially explicit analysis of the interactions of suspended sediment transport and hyporheic zone functioning. This information has built the basis for a coupled modeling framework that will help to develop efficient management measures within the Kharaa River basin with special emphasis on rapidly changing land-use and climatic conditions.

Continuous In-Stream Assimilatory Nitrate Uptake from High-Frequency Sensor Measurements

Recently developed in situ NO3– sensors provide new opportunities to measure changes in stream concentration at high temporal frequencies that historically have not been feasible. In this study, we used multiparameter sensor measurements to relate assimilatory NO3– uptake to metabolic rates and calculate continuous uptake rates for two stream reaches and a whole stream network. Two years of continuous 15 min data from a forest and agricultural reach of the Selke river (456 km2) revealed a strong correlation between assimilatory NO3– uptake and growth primary production (GPP) for the forest (r2 = 0.72) and agricultural (r2 = 0.56) stream reach. The slopes of these regressions were in agreement with predicted assimilatory N-uptake based on additional metabolic data. Mean yearly assimilatory NO3– uptake rates (Ua) were 7.4 times higher in the agricultural stream reach (mean 78.3 mg N m–2 d–1, max 270 mg N m–2 d–1) than in the forest stream reach (mean 10.7 mg N m–2 d–1, max 97.5 mg N m–2 d–1). Nitrate uptake velocities (Vf,a) tended to decrease with increasing nitrate concentrations for periods with high light availability. Percentage daily assimilatory NO3– uptake peaked at 47.4% of the daily NO3– loading input to the stream network across the entire watershed, whereas the percentage yearly assimilatory NO3– uptake was 9.0% of nitrogen loading to the stream network. This is a maximum because uptake can be revered by mineralization processes. The percentage yearly assimilatory NO3– uptake was lower in the forest-dominated upstream subwatershed (4.8%) than in the lower agriculture dominated subwatershed (13.4%).

Bioindication of chemical and hydromorphological habitat characteristics with benthic macro-invertebrates based on Artificial Neural Networks

This study aims to enhance the discussion about the usefulness of Artificial Neural Networks and specific input relevance detection for water quality assessment. The focus is on the development of neural modelling techniques initiating further research on predictor selection for bioindication. We tested the predictability of abiotic variables and quality indices BOD5, conductivity, NH3-N, NH4-N, NO2-N, NO3-N, Ntotal, oxygen, pH-value, Ptotal, water temperature, chemical and morphological water quality class and saprobic index by means of benthic macro-invertebrates on 51 sampling sites of nine small streams in Central Germany. The results show that General Regression Neural Networks and modified Multi-Layer-Perceptrons can successfully be applied for modelling and predicting ecological and environmental data because of their ability to solve non-linear and multidimensional problems. Nevertheless, Linear Neural Networks have been proved suitable in some cases. Particularly, stepwise method, genetic algorithms and sensitivity analysis can be used to reduce the complexity of data sets in a reasonable way by detecting important predictors. In many cases the prediction accuracy even increases. In addition, using only the presence of species instead of their abundance provides mostly better results, simpler models and an easier collection of data. Thus, complex systems can be illustrated in easily surveyed models with low measuring and computing effort. We claim that the identification of indicator species and the assessment of complex anthropogenic impacts can be improved substantially and managed more efficiently using the neural-based approach. It is predestinated for bioindication, particularly with regard to aquatic ecosystems.

The Bode hydrological observatory: a platform for integrated, interdisciplinary hydro-ecological research within the TERENO Harz/Central German Lowland Observatory

This article provides an overview about the Bode River catchment that was selected as the hydrological observatory and main region for hydro-ecological research within the TERrestrial ENvironmental Observatories Harz/Central German Lowland Observatory. It first provides information about the general characteristics of the catchment including climate, geology, soils, land use, water quality and aquatic ecology, followed by the description of the interdisciplinary research framework and the monitoring concept with the main components of the multi-scale and multi-temporal monitoring infrastructure. It also shows examples of interdisciplinary research projects aiming to advance the understanding of complex hydrological processes under natural and anthropogenic forcings and their interactions in a catchment context. The overview is complemented with research work conducted at a number of intensive research sites, each focusing on a particular functional zone or specific components and processes of the hydro-ecological system.