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For the first time, the AGRUM model consortium—consisting of the agro-economic model RAUMIS, the water balance model mGROWA, the hydrological nutrient transport models DENUZ, WeKu and MEPhos, and the urban emission model MONERIS—was jointly set up throughout Germany (357,000 km2). This provided a nationwide consistent nutrient model to capture the current status of N and P inputs to surface waters from diffuse sources and urban areas. Diffuse nutrient emissions were quantified in high spatial resolution for the input pathways' groundwater, drainage runoff, and natural interflow (100 m × 100 m), as well as for water erosion and wash-off (25 m × 25 m). The sum of diffuse nutrient inputs to surface waters is about 385,000 metric tons N/yr and ca. 11,530 metric tons P/yr. Urban emissions were quantified either as point source inputs (wastewater treatment plants, industrial direct dischargers) or at municipality scale for different collection and treatment systems, e.g., rainwater sewers or decentralized treatment plants, and sum up to ca. 95,000 t N/yr and 7500 t P/yr. As modelled, total N and P inputs into surface waters correspond well with observed N and P loads in rivers. The model results represent valuable information for water managers, being responsible for the preparation of management plans for the third management cycle of the EC Water Framework Directive spanning from 2021 to 2027. [ABSTRACT FROM AUTHOR]

A growing literature indicates that untreated wastewater from leaky sewers stands among major sources of pollution to water resources of urban systems. Despite that, the quantification and allocation of sewer exfiltration are often restricted to major pipe areas where inspection data are available. In large-scale urban models, the emission from sewer exfiltration is either neglected (particularly from private sewers) or represented by simplified fixed values, and as such its contribution to the overall urban emission remains questionable. This study proposes an extended model framework which incorporates sewer exfiltration pathway in the catchment model for a better justified pollution control and management of urban systems at a nationwide scale. Nutrient emission from urban areas is quantified by means of the Modelling of Nutrient Emissions in River Systems (MONERIS) model. Exfiltration is estimated for public and private sewers of different age groups in Germany using the verified methods at local to city scales, upscaling techniques, and expert knowledge. Results of this study suggest that the average exfiltration rate is likely to be less than 0.01 L/s per km, corresponding to approximately 1 mm/m/year of wastewater discharge to groundwater. Considering the source and age factors, the highest rate of exfiltration is defined in regions with significant proportions of public sewers older than 40 years. In regions where public sewers are mostly built after 1981, the leakage from private sewers can be up two times higher than such from public sewers. Overall, sewer exfiltration accounts for 9.8% and 17.2% of nitrate and phosphate loads from urban systems emitted to the environment, which increases to 11.2% and 19.5% in the case of no remediation scenario of projected defective sewer increases due to ageing effects. Our results provide a first harmonized quantification of potential leakage losses in urban wastewater systems at the nationwide scale and reveal the importance of rehabilitation planning of ageing sewer pipes in public and private sewer systems. The proposed model framework, which incorporates important factors for urban sewer managers, will allow further targeting the important data need for validating the approach at the regional and local scales in order to support better strategies for the long-term nutrient pollution control of large urban wastewater systems. [ABSTRACT FROM AUTHOR]

The European Water Framework Directive demands to assess and report the chemical and ecological status of water bodies (WB). Linking their status to drivers and pressures and deriving suitable mitigation measures require knowledge of the shape and area of WB catchments. We derived a network of 26 570 WB catchments in Germany using the hydrologically‐defined drainage basins of the German federal states. We established a network of 338 149 drainage basins. This network underwent plausibility checks and a validation with the catchment areas of 348 monitoring stations across Germany. To this network, we assigned the longest intersecting or the next downstream WB code. To account for geometric inaccuracies we revised spurious intersections resulting in splittings and cycles in the WB network. As WB may be ecologically but not hydrologically well defined, we split them at confluences and intersections. The network of drainage basins matched the monitoring stations with a Nash‐Sutcliffe efficiency of 1.00. The final WB network contained 11 005 out of the 11 586 original WBs longer than 1 m. The corresponding local catchment areas range from <<0.0001 to 446 km2, with a median of 10 km2. The dataset combines the requirements of hydrological and ecological modelling applications at basin or national scales with the needs of the EU reporting which can foster their acceptance by state authorities and river‐basin management. [ABSTRACT FROM AUTHOR]

• Impervious surface is a key indicator of urbanization impacts. • Major imperviousness development recorded in low-density population regions. • Steeper run-off and nutrient increases came from non-urban rather than urban areas. • Urbanization reduced sensitive species in favor of tolerant and non-native species. Urbanization is a key factor driving water quality and biological communities in freshwater systems. While urbanization impacts on water resources were well-studied in urban areas, few studies have examined the growing impacts in non-urban areas. Here we investigate the spatiotemporal trends of urbanization using high-resolution impervious surface data of both urban and non-urban areas across Germany, and evaluate the urbanization impacts on changes of run-off, nutrient emissions, and macroinvertebrate communities. The emission changes were modelled using the MONERIS-PCRaster tool, while the macroinvertebrate community responses to urbanization were determined using Generalized Least Square models. We find that urbanization expanded by 3.2% from 2006 to 2015 nationwide, and primarily occurred in less-populated regions. The non-urban areas contributed 19.3–19.6% of the imperviousness expansion nationwide, which were equivalent to the 'unaccounted' increases of 15.5–15.9% of run-off, 10.6–11.0% of total nitrogen, and 12.5–12.9% of total phosphorus when only emissions from urban areas were modelled. Incorporating the emissions from both urban and non-urban areas revealed significant impacts of urbanization on macroinvertebrate community composition changes, with increases in more pollution-resistant and non-native species (particularly in large rivers), and reductions of more sensitive taxa. The community responses were jointly determined by local catchment characteristics and urbanization stressors. Our results suggest neglected effects of non-urban impervious surfaces and the importance of using impervious surface data instead of urban land classes to better represent urbanization processes and impacts in long-term planning and management of freshwater systems. [ABSTRACT FROM AUTHOR]

Climate change is one of the main drivers of river warming worldwide. However, the response of river temperature to climate change differs with the hydrology and landscape properties, making it difficult to generalize the strength and the direction, of river temperature trends across large spatial scales and various river types. Additionally, there is a lack of long-term and large-scale trend studies in Europe as well as globally. In this study, we investigated the long-term (25 years; 132 sites) and the short-term (10 years; 475 sites) river temperature trends, patterns and underlying drivers within the period 1985-2010 in seven river basins of Germany. The majority of the sites underwent significant river warming during 1985-2010 (mean warming trend: 0.03 °C year−1, SE = 0.003), with a faster warming observed during individual decades (1985-1995 and 2000-2010) within this period. Seasonal analyses showed that, while rivers warmed in all seasons, the fastest warming had occurred during summer. Among all the considered hydro-climatological variables, air temperature change, which is a response to climate forcing, was the main driver of river temperature change because it had the strongest correlation with river temperature, irrespective of the period. Hydrological variables, such as average flow and baseflow, had a considerable influence on river temperature variability rather than on the overall trend direction. However, decreasing flow probably assisted in a faster river temperature increase in summer and in rivers in NE basins (such as the Elbe basin). The North Atlantic Oscillation Index had a greater significant influence on the winter river temperature variability than on the overall variability. Landscape and basin variables, such as altitude, ecoregion and catchment area, induced spatially variable river temperature trends via affecting the thermal sensitivity of rivers, with the rivers in large catchments and in lowland areas being most sensitive. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We introduce an approach for establishing reference conditions (RC) for rivers of the German Baltic Sea catchment, based on predictive modelling. An extensive data set of statistics from the year 1880 was coupled with literature data, providing a comprehensive basis for the calculation of regional historical nutrient emissions into rivers, river nutrient concentrations, and nutrient loading into the sea. Four different scenarios were calculated: scenario 1 assumed RC following previously established criteria for lakes (Poikane et al. in Environ Manag 45(6):1286-1298, ), scenario 4 applied the nutrient emission conditions of 1880 (considering non-intensive land usage, the presence of tile drainage systems, sewer systems, and the human population from 1880), and scenarios 2 and 3 considered intermediate conditions. Our results showed that nutrient emissions from scenario 1 accounted for approximately one-tenth of the currently observed total nitrogen (TN) and total phosphorus (TP) emissions. The nutrient emissions calculated for 1880 (scenario 4) were found to be 47 % (TN) and 55 % (TP) higher than those calculated considering reference lake conditions (scenario 1). Our results suggest that RC nutrient concentrations in rivers in the German Baltic Sea catchment were clearly below 0.05 mg/l for TP and 1 mg/l for TN. This range is in accordance with historical and calculated pristine nutrient concentrations from other rivers in similar catchments. [ABSTRACT FROM AUTHOR]

We introduce the German multi-metric assessment method PhytoFluss for large rivers, based on phytoplankton, which can be used to implement the European Water Framework Directive (WFD). First, we examined the response of chlorophyll a concentration to total phosphorus (TP) at 220 German river sites. Rivers could be assigned to one of four groups, based on the response curves: a) streams with high specific run-off (Rhine, Danube) had the lowest yield of chlorophyll a per unit of TP, followed by b) low yield in small lowland rivers (Trave, Stepenitz), c) medium-sized lowland rivers (Spree) and large central mountain rivers (Main) had intermediate yields of chlorophyll a, and d) streams with low specific run-off (Elbe, Weser) and Baltic tributaries (Penne, Warnow) had the highest yield of chlorophyll a per unit of TP. To define the five trophic status classes of phytoplankton biomass according the WFD, the chlorophyll a boundaries were derived from these response curves at the 75% percentile level. All selected sites were pre-classified with the combined trophic boundaries for TP and chlorophyll a to create the new four taxa composition metrics: The proportions of Chlorophytes, Cyanobacteria, or Pennales and of indicator taxa were selected as indicative parameters. When applying the final PhytoFluss method to 418 years of investigation from 150 German river sites, the percentages in each status according to the bio- component phytoplankton were: high 3%, good 19%, moderate 42%, poor 30%, and bad 5%. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

To implement the European Water Framework Directive (WFD) into German law, measures have to be taken to reduce the unacceptably high nutrient input into rivers. To identify the most effective measures, the sources and pathways of nutrient emissions into rivers have to be quantified. Therefore, the MONERIS model is applied, which quantifies nutrients emissions into river basins, via various point and diffuse pathways, as well as nutrient load in rivers. Most nitrogen emissions come from groundwater flow (43%), tile drainages (30%), and point sources (12%), whereas most phosphorus emissions come from groundwater flow (31%), point sources (23%), erosion (13%) and overland flow (12%). Because of their great distance from the river basin outlet, the southern sub-basins Werra and Fulda-Diemel have an 8% reduction in their nitrogen loads and a 15% and 16% reduction in their phosphorus loads, respectively. This reduction is due to retention in the main part of the river Weser. For the choice of the most effective measures, the different retention in the river is relevant. [ABSTRACT FROM AUTHOR]

Differences in quality, form and bioavailability of P originating from different sources are well known. Though, there is still a gap between different research disciplines addressing bioavailability of P in emissions, in surface waters and their resulting impact on aquatic primary producers and water quality. On river basin scale, longitudinal transport and transformation, time lags, changing hydrological conditions and the continuous mixing of upstream loads with laterally added emissions make the identification of links between DP emissions and ecological impacts a demanding task.In spite of extensive measures to reduce anthropogenic P emissions from agricultural areas, waste water and urban systems, excess Phosphorus is still a major threat to aquatic ecosystems. Recent studies even revealed that implemented measures partly showed unexpected or even unwanted effects. Consequently, the effect of measures to reduce emissions and the procedure in selecting the best measure is suggested subject to re-evaluation. Rather than discussing the general effect of measures to reduce total P emissions, we contemplated the potential effects of reducing readily bioavailable P forms to increase the effect of management measures.By applying the nutrient flux model MONERIS to Germany we identified the spatial distribution of total and dissolved P emissions and the share of the contributing sources and pathways. Subsequently, internal transport and retention processes have been modelled and the resulting concentrations compared to the observed concentrations as well as the change of relative shares of PO4 on TP (DP-TP-ratio).Our studies revealed the importance of P stored in agricultural soils and a clear spatial pattern in the DP-TP-ratio in emissions. However, this pattern showed clear, often contradictory, divergences from the observed DP-TP-ratio in surface waters. By using boosted regression tree approaches we identified slope, specific run-off and catchment size as main drivers explaining the observed DP-TP-ratio. Though, a correlation between the observed DP-TP-ratio in emission and such observed in surface waters could only be found for alpine and some hilly regions. Our results further indicate that major shares of P entering surface waters in particulate forms are easily transformed into bioavailable forms. As a consequence reduction needs shall not only be derived from the amount of emitted P (eutrophication potential) or the sole concentration in surface waters, but by the eutrophication effect, which is predominately dependent on the hydro-morphological characteristics. [ABSTRACT FROM AUTHOR]