Ruhr River Research Articles

Efficacy of point source legislation quantified for a 64-year river water quality trajectory of phosphorus loading

Changes in river water quality often follow typical trajectories characterized by sequential phases of degradation and recovery induced by management measures, typically achieved with combinations of legislative and technological interventions. However, the key question about the effectiveness of the different types of legal interventions – source control, use-related, and end-of-pipe – remains poorly understood. With the case of phosphorus (P), which is a valuable indicator of surface water quality and a widespread target of legislation at various governance levels in order to control eutrophication of water bodies, we quantified the relation between point source loading of P and resulting river water quality for a multidecadal trajectory of the river Ruhr (Germany). In particular, we analysed P-related legislation targeting point source pollution enforced at EU, national, state, and local level and linked their development with measured total phosphorus (TP) concentrations in the river Ruhr (Germany). To this end, we combined archival data with information in the literature and conducted interviews with contemporary witnesses to describe and quantify the efficacy of each legislative approach. Although not specifically targeted at P reduction, end-of-pipe measures (sewer systems and wastewater treatment plants (WWTP)) reduced TP inputs to surface waters already in the 1960s and 1970s, curbing TP inputs to the Ruhr by 38% in 1980. The first targeted source control legislation – the banning of phosphates in textile detergents in 1981 – effectively reduced TP concentrations in WWTP influents by 36% since 1990. In combination with stronger end-of-pipe legislation focusing on P elimination in WWTP since the 1990s, TP concentrations in WWTP effluents were reduced by 86% at the end of the 1990s and by 92% in 2021. Complete and successful source control for textile detergents made use-related legislation redundant. Our study demonstrates that source control measures should be prioritized, because they are the fastest way to curb emissions. These findings provide insights that can inform efficient decision-making regarding water quality in a trajectory perspective of hierarchical governance and technological needs, as well as effective policy-making and management for other pollutants requiring control from point sources.

Individual small in-stream barriers contribute little to strong local population genetic structure five strictly aquatic macroinvertebrate taxa.

Water flow in river networks is frequently regulated by man‐made in‐stream barriers. These obstacles can hinder dispersal of aquatic organisms and isolate populations leading to the loss of genetic diversity. Although millions of small in‐stream barriers exist worldwide, their impact on dispersal of macroinvertebrates remains unclear. Therefore, we, therefore, assessed the effects of such barriers on the population structure and effective dispersal of five macroinvertebrate species with strictly aquatic life cycles: the amphipod crustacean Gammarus fossarum (clade 11), three snail species of the Ancylus fluviatilis species complex and the flatworm Dugesia gonocephala. We studied populations at nine weirs and eight culverts (3 pipes, 5 tunnels), built 33–109 years ago, mainly in the heavily fragmented catchment of the river Ruhr (Sauerland, Germany). To assess fragmentation and barrier effects, we generated genome‐wide SNP data using ddRAD sequencing and evaluated clustering, differentiation between populations up‐ and downstream of each barrier and effective migration rates among sites and across barriers. Additionally, we applied population genomic simulations to assess expected differentiation patterns under different gene flow scenarios. Our data show that populations of all species are highly isolated at regional and local scales within few kilometers. While the regional population structure likely results from historical processes, the strong local differentiation suggests that contemporary dispersal barriers exist. However, we identified significant barrier effects only for pipes (for A. fluviatilis II and III) and few larger weirs (>1.3 m; for D. gonocephala). Therefore, our data suggest that most small in‐stream barriers can probably be overcome by all studied taxa frequently enough to prevent fragmentation. However, it remains to be tested if the strong local differentiation is a result of a cumulative effect of small barriers, or if larger in‐stream barriers, land use, chemical pollution, urbanization, or a combination of these factors impede gene flow.

Integration of self-organizing maps, statistical analysis, and hydrogeochemical modeling methods to identify spatio-seasonal variations in mine water quality

Monitoring the quality of mine drainage is an important task in the Ruhr coalfield in western Germany, especially after decommissioning all mining activities in 2018. In this study, seasonal and spatial variations in mine water quality of abandoned coal mines around the lower Ruhr river area were investigated. Statistical analysis, self-organizing maps (SOMs), and hydrogeochemical modeling were used to reveal changes in the water quality of 103 water samples collected between January 2018 and November 2019. An analysis of physical and chemical properties using SOM subdivided mine water samples into five groups: freshwater (groups 1, 2, 3, and 4) and brackish water (group 5) with different physical and chemical characteristics. Freshwater samples were mostly distributed in the southern and central parts, whereas brackish water samples were mostly distributed in the northeastern part of the study area. Approximately 18% of the sampling locations experienced significant seasonal changes during the study period, while 82% of the remaining locations showed only slight variations. Across all groups, seasonal variations in the water quality were less pronounced than differences between southern and northeastern sampling locations. A significant increase was observed in major ion concentrations, TDS, and EC values from southern to northern and northeastern sampling points during the monitoring period. A general trend of approaching saturation state from studied mineral phases was detected with increasing TDS concentrations from groups 1, 2, 3, and 4 to group 5. Trace element concentrations were relatively low, except for several streams with higher Fe and Mn concentrations, and varied between seasons. The SOM approach helped to identify the seasonal changes in mine water properties in the area. The evaluation of changes in mine water quality is useful for the management and protection of water resources, especially drinking water resources, in the densely populated Ruhr area.

Effects of conventionally-treated and ozonated wastewater on mortality, physiology, body length, and behavior of embryonic and larval zebrafish (Danio rerio)

To date, micropollutants from anthropogenic sources cannot be completely removed from effluents of wastewater treatment plants and therefore enter freshwater systems, where they may impose adverse effects on aquatic organisms, for example, on fish. Advanced treatment such as ozonation aims to reduce micropollutants in wastewater effluents and, thus, to mitigate adverse effects on the environment. To investigate the impact and efficiency of ozonation, four different water types were tested: ozonated wastewater (before and after biological treatment), conventionally-treated wastewater, and water from a river (River Ruhr, Germany) upstream of the wastewater treatment plant effluent. Zebrafish (Danio rerio) embryos were used to study lethal and sublethal effects in a modified fish early life-stage test. Mortality occurred during exposure in the water samples from the wastewater treatment plant and the river in the first 24 h post-fertilization, ranging from 12% (conventional wastewater) to 40% (river water). Regarding sublethal endpoints, effects compared to the negative control resulted in significantly higher heart rates (ozonated wastewater), and significantly reduced swimming activity (highly significant in ozonated wastewater and ozone reactor water, significant in only the last time interval in river water). Moreover, the respiration rates were highly increased in both ozonated wastewater samples in comparison to the negative control. Significant differences between the ozonated wastewater samples occurred in the embryonic behavior and heart rates, emphasizing the importance of subsequent biological treatment of the ozonated wastewater. Only the conventionally-treated wastewater sample did not elicit negative responses in zebrafish, indicating that the discharge of conventional wastewater poses no greater risk to embryonic and larval zebrafish than water from the river Ruhr itself. The sublethal endpoints embryonic- and larval behavior, heart rates, and respiration were found to be the most sensitive endpoints in this fish early life-stage test and can add valuable information on the toxicity of environmental samples.

«СТАРЫЙ ГОРОД» – «БЕЗЫМЯНКА» – КРЕАТИВНЫЙ ГОРОД

«Bezymyanka» is the name of the largest industrial district of the city of Kuibyshev, now Samara. The expressive name can also be interpreted as a metaphor for many industrial cities of the Soviet era. In the XXI century various projects for the transformation of industrial cities are known. The cultural capital of Europe in 2007 was the oldest mining city in Germany, Essen, together with nearby industrial ancient mining towns in the Ruhr River Valley. The project was won by solving environmental problems and creative reformatting of the industrial city. It should be noted that the problems of Soviet industrial cities are presented in numerous Russian and foreign studies. So, the article refers to modern works on the search for justified transformations of «Soviet Magnitka»; Uralmash in Ekaterinburg and other problematic industrial cities. The purpose of this article is to draw attention to various interpretations of such cities. In Samara, there is also «bifurcation»: the old city and industrial Bezymyanka. To expose the sociocultural contradiction between the «old» and the «industrial city», the article reveals discrepancies that inhibit development. The author draws attention to the unique and overtaken by its time Grushinsky festival, in particular, its leaders. Conclusion: the lack of the balance of «old», «Soviet» and «post-Soviet» territories inside of one city is a problem of lack of personalities.

Spatial and temporal analyses of perfluorooctanoic acid in drinking water for external exposure assessment in the Ruhr metropolitan area, Germany

Perfluorooctanoic acid (PFOA) and related chemicals among the per- and polyfluoroalkyl substances are widely distributed in the environment. Adverse health effects may occur even at low exposure levels. A large-scale contamination of drinking water resources, especially the rivers Möhne and Ruhr, was detected in North Rhine-Westphalia, Germany, in summer 2006. As a result, concentration data are available from the water supply stations along these rivers and partly from the water network of areas supplied by them. Measurements started after the contamination’s discovery. In addition, there are sparse data from stations in other regions. Further information on the supply structure (river system, station-to-area relations) and expert statements on contamination risks are available. Within the first state-wide environmental-epidemiological study on the general population, these data are temporally and spatially modelled to assign estimated exposure values to the resident population. A generalized linear model with an inverse link offers consistent temporal approaches to model each station’s PFOA data along the river Ruhr and copes with a steeply decreasing temporal data pattern at mainly affected locations. The river’s segments between the main junctions are the most important factor to explain the spatial structure, besides local effects. Deductions from supply stations to areas and, therefore, to the residents’ risk are possible via estimated supply proportions. The resulting potential correlation structure of the supply areas is dominated by the common water supply from the Ruhr. Other areas are often isolated and, therefore, need to be modelled separately. The contamination is homogeneous within most of the areas.

Peter H. Huy

Peter H. Huy

Controls of point and diffuse sources lowered riverine nutrient concentrations asynchronously, thereby warping molar N:P ratios

The input of nitrogen (N) and phosphorus (P) into rivers has been reduced in recent decades in many regions of the world to mitigate adverse eutrophication effects. However, legislation focused first on the reduction of nutrient loads from point sources and only later on diffuse sources. These reduction strategies have implications on riverine N:P stoichiometry, which potentially alter patterns of algal nutrient limitation and the functions or community structure of aquatic ecosystems. Here, we use a dataset spanning four decades of water quality for the Ruhr River (Germany) to show that the asynchronous implementation of point and diffuse source mitigation measures combined with time lags of catchment transport processes caused a temporally asynchronous reduction in dissolved inorganic nitrogen and total phosphorus concentrations. This asynchronous reduction increased the molar N:P ratios from around 30 to 100 in the river sections dominated by point sources, reducing the probability of N limitation of algae in favor of P limitation.The Ruhr River catchment and the environmental policies implemented here illustrate the unintended effects of nutrient control strategies on the ecological stoichiometry at the catchment scale. We urge to assess systematically, whether unintentionally warped macronutrient ratios are observable in other managed river systems and to evaluate their environmental impacts.

Per- and polyfluoroalkyl substances in Chinese and German river water – Point source- and country-specific fingerprints including unknown precursors

This study aimed at comparing source-specific fingerprints of per- and polyfluoroalkyl substances (PFASs) in river water from China and Germany, selected as countries with different histories of PFAS production. Samples were collected from up- and downstream of seven suspected point sources in autumn 2018. Amongst the 29 analyzed legacy and emerging PFASs, 24 were detected, with a sum ranging from 2.7 ng/L (Alz River) to 420,000 ng/L (Xiaoqing River). While mass flow estimates for the Xiaoqing River and Yangtze River (mean: 20 and 43 t/y, respectively) indicated ongoing high emissions of the legacy compound PFOA in China, its ether-based replacements HFPO-DA and DONA showed the highest contribution downstream of a German fluoropolymer manufacturing site (50% and 40% of ΣPFASs measured, respectively). In river water impacted by manufacturing sites for pharmaceutical and pesticide intermediates, the short-chain compound PFBS was the most prevalent substance in both countries. The German Ruhr River, receiving discharges from the electroplating industry, was characterized by the PFOS replacement 6:2 FTSA. Isomer profiling revealed a higher proportion of branched isomers in the Chinese Xi River and Xiaoqing River than in other rivers. This points to different synthesis routes and underlines the importance of differentiating between linear and branched isomers in risks assessments. Upon oxidative conversion in the total oxidizable precursor (TOP) assay, the increase of the short-chain compound PFBA was higher in German samples than in Chinese samples (88 ± 30% versus 12 ± 14%), suggesting the presence of a higher proportion of unknown precursors to PFBA in the German environment. Amongst the ether-based replacements, DONA and 6:2 Cl-PFESA were fully or partially degraded to non-targeted oxidation products, whereas HFPO-DA showed no degradation. This indicates that the inclusion of ether-based PFASs and their oxidation products in the TOP assay can help in capturing a larger amount of the unknown PFAS fraction.

Impact of seasonality, redox conditions, travel distances and initial concentrations on micropollutant removal during riverbank filtration at four sites

Riverbank filtration (RBF) is a reliable water purification technique that has proven to be suitable for the removal of organic micropollutants. Its removal efficiency and dependency on a variety of factors such as redox conditions, temperatures, geology, travel times, level of initial micropollutant concentrations and seasonality were investigated during three seasonal sampling campaigns. Two anoxic (silty sand, Ems river) and two oxic (gravel, Ruhr river) RBF sites in Germany with different travel distances (42–633 m) were studied. Micropollutant concentrations were examined using a large-volume direct injection liquid chromatography method coupled to high-resolution mass spectrometry. Seasonal differences in micropollutant concentrations in the rivers were observed for chlorotolurone, diclofenac, terbuthylazine, mecoprop-P, MCPA (2-methyl-4-chlorophenoxyacetic acid) and propyphenazone. Redox dependencies in RBF were only found for sulfamethoxazole, propyphenazone, terbuthylazine and carbamazepine. Data for oxazepam, tramadol, N-desmethyl-tramadol, tilidin-desmethyl, carbamazepine and carbendazim indicate a required minimum travel distance of e.g. 100–200 m for the complete removal. Notably, travel time did not seem to be a substantial factor for their removal. High conductivity aquifers are also well suited for micropollutant removal. Seasonal initial concentration level variations showed no impact on the resulting abstraction well concentrations. Although the calculated removal efficiencies varied, they proved to be improper for seasonal raw water quality comparison. Knowledge of micropollutant behavior in riverbank filtration was broadened and RBF proved to be well suited for effective micropollutant reduction throughout the year, yet for a complete removal long travel distances or further technical purification steps are required.

ルール河(西ドイツ)の水管理

ルール河(西ドイツ)の水管理

Hidden parasite diversity in a European freshwater system

Parasites comprise a huge part of the biodiversity on earth. However, on a local scale, not much is known about their diversity and community structure. Here, we assess the diversity of larval trematode communities in an interconnected freshwater system of the River Ruhr in Germany and analyse how the parasites are spatially and temporally distributed in the ecosystem. A total of 5347 snail hosts belonging to six species revealed a highly diverse parasite fauna with 36 trematode species. More abundant snail species harboured more species-rich trematode faunas and communities, with the two dominant snail species, Radix auricularia and Gyraulus albus, accounting for almost 90% of the trematode diversity and harbouring spatially and temporally stable parasite communities. The results highlight the important role of stable keystone host populations for trematode transmission, structure and diversity. This local trematode diversity reveals information on definitive host occurrence and trophic interactions within ecosystems.

Mine water hydrogeochemistry of abandoned coal mines in the outcropped Carboniferous formations, Ruhr Area, Germany

A hydrogeochemical study was conducted in the outcropped part of the coal-bearing Upper Carboniferous formations in the Ruhr area to investigate the characteristics of regional mine water and understand the hydrogeochemical conditions. Twenty-eight mine water samples from the adits of different abandoned coal mines were collected and analyzed for major ions, iron (Fe2+, Fetotal) and sulfide (H2S). The water samples had a pH of 6.39–7.65. Total dissolved solids (TDS) ranged from 157 to 1806 mg L−1. Mine water samples were dominated by HCO3− > Ca2+ > SO42− > Mg2+ > Na+ > Cl− > K+ > NO3− > (F−, Li+). Several water samples had elevated SO42−, Fetotal, and H2S concentrations up to 354 mg L−1, 4.2 mg L−1, and 10 µg L−1, respectively. The water types (Ca–Mg–HCO3–SO4, Na–Ca–HCO3–SO4, Ca–Mg–Na–HCO3–SO4, and Na–Ca–Mg–HCO3–SO4) were the dominant hydrogeochemical facies. Gypsum and halite were always undersaturated, while calcite and dolomite were undersaturated in about 82% of water samples. The chemical weathering processes of pyrite, calcite, dolomite, gypsum, and halite, as well as ion exchange, appear to be the dominant hydrogeochemical processes controlling adit mine water chemistry. In general, there was an increasing trend of TDS and major ion concentrations from south to northeast in the study area. This study may aid in the improvement of water management in the Ruhr area since the adits discharge into the river Ruhr which is strongly used for the drinking water supply of a large metropolitan region in western Germany.

The role of spatial units in modelling freshwater fish distributions: Comparing a subcatchment and river network approach using MaxEnt

Species Distribution Models (SDM) are frequently used in ecological research, but the effects of model extent and granularity on model outcomes are rarely addressed. In freshwater SDMs, two different approaches are commonly used to define the granularity of the models, i.e. to subdivide entire river systems into appropriate spatial modelling units: river reaches on the actual river network or subcatchments. We built maximum entropy (MaxEnt) SDMs for barbel (Barbus barbus) and grayling (Thymallus thymallus) in the River Ruhr catchment in Germany with identical environmental predictor data and analysed the difference between these two approaches. All models performed well (AUC > 0.9) and geographic predictors (e.g. distance to the river source) dominated over hydromorphological predictors in explaining species distributions. There was high agreement between the two model setups in river parts of low and high habitat suitability but considerably lower agreement in river parts of medium habitat suitability. In these medium suitable river parts, model results were spatially very heterogeneous and alternated at fine spatial scales especially in models based on river reaches. Increasing model regularization, a setting to control overfitting, had a smoothing effect on the environmental variables in the river reach models similar to the coarser subcatchment granularity. A restriction of the spatial extent led to a shift in predictor contributions to the model and an increase of the importance of hydromorphologic predictors by ca. 45 %. Restricting the model extend to the natural core distributional area of a given fish species might therefore be considered beneficial for the application of SDMs in a management context. By decreasing the weight of fixed geographic predictors in the model, predictors relating to hydromorphological river structures (i.e. which are accessible for restoration projects) gain importance. We conclude that SDM setups based on river reaches and subcatchments can both give valuable complementary information about the distribution of species. The high-resolution model based on river reaches might better discover individual local habitat features, whereas the subcatchment model might better account for the minimum spatial requirements of a fish population.

Spatio-Temporal Data Modelling and Prediction of PFOA Drinking Water Contamination

TPS 931: Water and foodborne chemicals, Exhibition Hall, Ground floor, August 28, 2019, 3:00 PM - 4:30 PM Perfluorooctanoic Acid (PFOA) is suspected to have various adverse effects on human health. For the general population of large parts of North Rhine-Westphalia (NRW), Germany, contaminated drinking water can be regarded as an important pathway for exposure to PFOA. We model its state-wide concentrations in the course of time, thereby handling missing data. Following a PFOA contamination incident near the city of Arnsberg prior to 2006, concentrations in drinking water have been derived from a monitoring programme of the NRW state environmental agency (LANUV) and by further acquisition from water supply companies. Samples have been drawn from both the water supply stations and the network of water supply areas. Apart from such comprehensive data, there are regions with no or few measurements, usually non-detects. In order to estimate and to predict PFOA concentration means and standard deviations, we formulate spatio-temporal models based on these data, some information about (non-)contamination and spatial correlations via rivers. The water proportions in the complex relationship of 417 stations supplying 451 areas are estimated based on their supplied and demanded amounts. These weights are used to mediate between station and area level modelling. The correlation of spatio-temporally adjacent measurements are handled by a Markov-random-field (MRF) representing the neighbourhood structure and by smoothing approaches. We define spatial distances based on the stations’ connectivity via rivers. Spatio-temporal distances from polluted sites, particularly from the Arnsberg contamination, are included as covariates. Monthly predictions from 2006 to 2016 are accomplishable, whereby a MRF turns out to be computationally demanding. Restriction to stations with higher water amounts is a practicable option. Regional conditions have to be respected, as smoothing is not appropriate in regions or periods with sparse data. For the mainly affected region, a contamination decline along the river Ruhr and over time is reflected in the models.

Cost-effective reduction of micro pollutants in the water cycle – Case study on iodinated contrast media

Surface waters, especially in densely populated areas, are facing multiple anthropogenic pressures. Micro pollutants are of growing concern. Improved analytical methods are used to focus on substances like ICM with a (high) potential of hazardous effects against water organisms or the water quality in general ICM are essential for instance in computer tomographic examinations in medical facilities. Discharge of ICM to the sewer system occurs via human urine excretions. Common waste water treatment plants do not eliminate these substances completely. Therefore, increasing concentrations are found in the rivers worldwide. The project MERK'MAL explored a potentially cost-effective measure to reduce ICM in the River Ruhr, located in Germany, North Rhine-Westphalia. The results from this pilot study show that urine bags are an effective measure to reduce ICM concentrations. During the urine collection with bags measurements of ICM concentrations have shown a reduction, compared to the baseline concentration that was measured at the same sampling point in the effluent of the corresponding waste water treatment plant. The ICM reduction ranged between 20 and 34% for the mean values and between 7 and 33% for the median value. Additional payment equivalent costs per examination with ICM are approx. 3.36 €, full costs including imputed costs are expected in a cost range of 5.38 € to 6.09 € per examination. The extension of the study is envisioned, helping to sustainably enhance water quality in the River Ruhr in terms of ICM concentrations.

Multi-decadal trajectories of phosphorus loading, export, and instream retention along a catchment gradient

Phosphorus inputs to many rivers have been reduced in recent decades to mitigate the damaging effects of eutrophication. However, reductions in total phosphorus (TP) inputs rarely correspond with ecological improvements of the river ecosystem. We analyzed a unique weekly long-term data set ranging from 1966 to 2013, covering seven monitoring sites in the Ruhr River in Germany. We identified the relative importance of different TP sources, quantified long-term trajectories of degradation and recovery, including the dynamics of TP retention, and assessed the response of chlorophyll-a (Chl-a) to increasing and decreasing TP concentrations along the whole river gradient.We found that the decline of TP loads at the beginning of the 1980s was dominantly triggered by a reduction of point sources. The cumulative TP retention capacity increased along the river gradient, increasing from effectively zero in the upstream section, to 26% and 36% of TP input in the upper midstream and lower downstream section. This pattern is consistent with higher prevalence of impoundments and weirs downstream, indicating that TP retention is likely associated with sedimentation posing a potential risk due to remobilization of legacy phosphorus.Degradation and recovery pathways differ from upstream to downstream. Along the river continuum we found three distinct types of reversible trajectories: 1. instream storage only during the recovery phase (upstream only); 2. instream storage in both degradation and recovery phases, but with significantly different characteristics depending on TP input load (midstream only); 3. higher instream storage during the recovery phase (downstream only).While in-stream TP loads may recover rapidly, the ecological response to altered nutrient inputs can be associated with considerable time-lags and decouplings between Chl-a and TP concentrations. Therefore, river systems may not return to historically good ecological status solely from massive nutrient reduction, but may also require other management activities.

River rehabilitation in urban areas – restrictions, possibilities and positive results

Abstract Reaching the goal of good ecological status stipulated by the European Water Framework Directive (WFD) is generally difficult in German rivers. Appropriate habitat conditions for multiple and abundant incidence of flora and fauna are still missing. Existing water bodies, particularly in urban areas, are extremely affected by anthropogenic-induced pressures, resulting in reinforced river bottoms and river banks. In such regions, river rehabilitation is a challenging task and often requires a step by step approach to alter the given conditions. Nevertheless, work must be done and may create successful results as in the case of the Sprockhoevel creek. Over recent years this 11-km-long river in the western and industrialised part of the Ruhr River basin has partly been changed in shape to better resemble nature. Such change implies the widening of the river bed, the improvement of the river bottom by inserting natural gravel substrate, the removal of drop structures and the construction of a new river bed. Presently, this part of the river has again become a valuable habitat for aquatic life. Moreover, the area surrounding the rehabilitated Sprockhoevel creek is now also attractive for the neighbourhood community. Rehabilitation projects have the additional effects of reconnecting people to nature, encouraging public interest in near-natural aquatic systems, and catalysing further investments in similar projects.

Regional analysis of parameter sensitivity for simulation of streamflow and hydrological fingerprints

Abstract. Diagnostics of hydrological models are pivotal for a better understanding of catchment functioning, and the analysis of dominating model parameters plays a key role for region-specific calibration or parameter transfer. A major challenge in the analysis of parameter sensitivity is the assessment of both temporal and spatial differences of parameter influences on simulated streamflow response. We present a methodological approach for global sensitivity analysis of hydrological models. The multilevel approach is geared towards complementary forms of streamflow response targets, and combines sensitivity analysis directed to hydrological fingerprints, i.e. temporally independent and temporally aggregated characteristics of streamflow (INDPAS), with the conventional analysis of the temporal dynamics of parameter sensitivity (TEDPAS). The approach was tested in 14 mesoscale headwater catchments of the Ruhr River in western Germany using simulations with the spatially distributed hydrological model mHM. The multilevel analysis with diverse response characteristics allowed us to pinpoint parameter sensitivity patterns much more clearly as compared to using TEDPAS alone. It was not only possible to identify two dominating parameters, for soil moisture dynamics and evapotranspiration, but we could also disentangle the role of these and other parameters with reference to different streamflow characteristics. The combination of TEDPAS and INDPAS further allowed us to detect regional differences in parameter sensitivity and in simulated hydrological functioning, despite the rather small differences in the hydroclimatic and topographic setting of the Ruhr headwaters.

Small but diverse: larval trematode communities in the small freshwater planorbids Gyraulus albus and Segmentina nitida (Gastropoda: Pulmonata) from the Ruhr River, Germany.

In contrast to the well-studied trematode fauna of lymnaeid snails, only little is known about the role of small planorbid snails as first intermediate hosts for trematodes in temperate freshwater systems. This study aims at closing this gap by assessing the diversity and composition of larval trematode communities in Gyraulus albus and Segmentina nitida in a Central European reservoir system, and by providing an updated comprehensive review of the published trematode records of these snail hosts. A total of 3691 planorbid snails (3270 G. albus; 421 S. nitida) was collected in three consecutive years from four reservoirs of the River Ruhr catchment area in Germany. Gyraulus albus showed a higher overall trematode prevalence (11.7%) and more diverse trematode fauna (12 species) compared to S. nitida, which harboured three species and showed a lower trematode prevalence (1.7%). Altogether, 13 trematode species belonging to four families were identified in both hosts. Seven trematode species encountered in this study represent novel records for these hosts, and/or constitute first records of these larval stages from Germany. Trematode component communities in G. albus were stable across seasons and years, indicating excellent conditions for trematodes in this snail host and the continuous presence of the final hosts of the most dominant trematode species. Overall, this study reveals the importance of small planorbid snails, in particular G. albus, as first intermediate hosts for a species-rich trematode fauna in European freshwater systems, and highlights the parasites' contribution to the ecosystem's biodiversity.