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Natural dissolved organic matter (DOM) can serve as an additional substrate for organic micropollutant (OMP) degrading bacteria, thus influencing OMP biodegradation in aquatic systems. DOM biodegradation depends on the OMP degrader's ability to grow on different DOM constituents, and on its capability to compete for DOM constituents against the rest of the resident aquatic microbial community. This study aimed to investigate the growth of a model OMP degrader strain, Novosphingobium sp. KN65.2 (assumed specialist), isolated for its ability to mineralize carbofuran, on thirteen DOM constituents; compare its metabolic capabilities to those of a common freshwater strain (Pseudomonas fluorescens sp. P17) (generalist); and to evaluate competition for specific compounds. Growth experiments were carried out in pure- and mixed culture batch experiments. The DOM constituents tested included aromatic amino acids and a range of phenolic acids (lignin derivatives). The OMP degrader could biodegrade approximately half of the tested compounds. It showed a high specialization for substrates containing a hydroxyl-group in the para-position of the primary aromatic ring substituent. However, its broad substrate range enabled the strain to grow on the same number of auxiliary substrates as the generalist. Moreover, the OMP degrader was able to successfully compete against the generalist for the biodegradation of one (4-hydroxybenzaldehyde) out of three substrates (4-hydroxybenzoic acid, 4-hydroxybenzaldehyde, L-tyrosine), which were biodegraded by both strains. The study results provide insight on the substrate specificity of a model OMP degrader, which can inform development of modeling frameworks investigating the influence of DOM on OMP biodegradation.

We congratulate Heal et al. for initiating an important discussion on how to broaden the scope of the water–energy–food nexus. We agree that more explicit inclusion of water quality into the nexus is an important step forward. At the same time, water quality is itself an indicator of e.g. ecosystem services and biodiversity, and improvement of water quality comes with a cost in terms of resource consumption that is typically not included in models studying the water–energy–food nexus. We already see hesitation in using the nexus for policy development, and further complexity may be an additional barrier to its practical implementation. So, while the consideration of water quality is indeed important for the nexus, it also suggests that perhaps it is necessary to consider more local contexts than striving for one global framing for analysis of the water–energy–food nexus.

Climate change and intensifying agricultural production and urbanization are central factors driving the global freshwater biodiversity decline. To design sustainable green transition schemes and support urban planning, a deeper understanding of the numerous interacting physicochemical and biogeochemical processes and their relation to ecological quality becomes essential. This study thus aims to explore links between hydrological regimes and patterns evident for key water quality parameters and benthic invertebrate indicators in a peri-urban catchment that has undergone several stream restoration projects. Results indicate significant seasonal variability in discharge and physico-chemical parameters confounding the identification of sources behind detrimental impacts on ecological quality, which may lead to the implementation of inappropriate mitigation strategies. Notably, sampling at the sub-catchment level underlined the dynamic contributions of both agricultural and urban-like areas for nitrogen and phosphorus, while non-volatile carbon was mainly exported from agricultural lands. Multivariate statistical methods were used to classify benthic macro- and meioinvertebrate (specifically nematode) taxa showing poor-to-moderate and poor-to-good ecological quality, respectively. Poor ecological quality was mostly found in the upstream part of the catchment, driven by a combination of low habitat quality and periodically impaired physico-chemical conditions (e.g. dissolved oxygen, temperature, and suspended solids). In addition, the nematode-based stress index NemaSPEAR[%] (expressing the proportion of species-at-risk within a sample and specifically sensitive to the chemical contamination), indicated a TSS-related transport of contaminants to the sediment. It could also reveal both the negative impacts of different urban features (low ecological quality just downstream of combined sewer overflows), as well as the potential benefits of wastewater effluents (i.e

Nature-Based Solutions (NBS) can be defined as solutions based on natural processes that meet societal challenges and simultaneously provide human well-being and biodiversity benefits. These solutions are envisioned to contribute to operationalizing sustainable development strategies, especially in the context of adaptation to climate change (e.g. flood risk reduction). In order to quantify NBS performance, ease their uptake and advocate for them as alternatives to “business-as-usual” infrastructures, a comprehensive, holistic valuation of their multiple benefits (multiple advantages and disadvantages) is needed. This entails quantifying non-market benefits for people and nature in addition to determining the (direct) cost-benefit of the risk-reduction measure. Despite the importance given to the assessment of non-tangible benefits for people and nature in the literature, systematic data collection on these dimensions seems to be missing. This study reviews publications that used stated preference methods to assess non-market human benefits of NBS and NBS-like strategies. Its aim is to highlight any biases or knowledge gaps in this kind of evaluation. Our results show that the valuation of non-tangible benefits of NBS (e.g. increased recreation and well-being, enhanced biodiversity) still suffers from a lack of common framing. Despite some steps being taken on enabling interconnected benefit assessments, unexploited opportunities concerning the integrated assessment of non-market human and nature benefits predominate. Moreover, the research to-date appears based on a case-to-case approach, and thus a shared holistic method does not emerge from the present literature, potentially delaying the uptake of NBS. We argue that future research could minimize missed opportunities by focusing on and systematically applying holistic benefits assessments. Methods based on stated preference surveys may help to ensure holistic approaches are taken, as well as contributing to thei

When assessing strategies for implementation of Nature-Based Solutions (NBS) it is fundamental to quantify all benefits for securing better, informed decision making. Particularly relevant is the quantification of their multiple co-benefits for communities and the environment. One of the most widespread techniques to quantify these values is to use contingent valuation (CV) methods, such as the Willingness-To-Pay (WTP) approach. Within the CV method, questionnaires are the main tool used to elicit the value attributed to a specific good by the respondents. However, many studies focus on site-specific economic valuation, whereby transferability to other locations is jeopardized. We therefore created a survey to explore how the valuation of an NBS is shaped by its relationship with the users (e.g. frequency and length of visits), and how these responses are linked to both the respondents and the sites’ characteristics (e.g. socio-economic status, size of the NBS, etc.). We applied this method to a case study comprised of two distinct areas located in Aarhus, Denmark, asking users to explore their perception of the two NBS sites with different features. Both NBS sites have as overarching goals to (i) prevent flooding from cloudburst or water bodies, (ii) improve the biodiversity in the area, and (iii) benefit the local population, e.g. by providing more recreational areas. Despite these common goals, the two sites differ by a number of characteristics, i.e. size, location, and time passed since construction. One NBS involves a large artificial lake in a peri-urban setting, while the other is a small urban park. Respondents were allowed the option of either expressing a value for only one, or for both of the sites. We analyzed both responses that stated a WTP and protest votes, that is, responses that rejected the valuation scenario altogether. We found that older citizens are more likely to protest, as well as those not visiting the sites. For the r

Tracer tests represent a well-established method for delineating key environmental processes in various media and engineered systems. Tracers like Rhodamine B and WT are frequently applied due to their strong fluorescence even at low concentrations. However, due to a lack of ecotoxicological data, limit values for these tracers cannot be determined. This study fills this critical data gap by providing ecotoxicity data for Rhodamine B and WT using a battery of short-term standardized tests, including growth rate inhibition tests with algae (Raphidocelis subcapitata) and lethality tests using crustaceans (Daphnia magna) and zebrafish (Danio rerio) embryos, and estimating EQS for surface water. For Rhodamine B, the effective and lethal concentration (EC50 and LC50) –causing 50% toxicity were in the range of 14–24 mg/L. For Rhodamine WT, no statistically significant effects were observed (p<0.05) at the tsted concentrations (up to 91, 100 and 200 mg/L for algae, crustaceans and fish embryos, respectively). Thus for all tested organisms, Rhodamine B was more toxic than Rhodamine WT (more than 14 times more toxic for R. subcapitata, 5.6 times for D. magna, 15 times for D. rerio embryos,based on EC10 and LC10 values). These results signify that read-across assessments using ecotoxicity data obtained with Rhodamine B is not advisable for estimating the ecotoxicity of Rhodamine WT. The annual-average quality standard (AA-QS) and maximum allowable concentration quality standard (MAC-QS) for Rhodamine B were found to be 14 and 140 µg/L, respectively. For Rhodamine WT, the corresponding values were estimated to >91 µg/L (AA-QS) and >910 µg/L (MAC-QS). Hence, concentrations below 140 µg/L or 910 µg/L for Rhodamine B and WT, respectively, are not expected to pose a risk to aquatic freshwater life in the case of intermittent discharges, e.g. tracer experiments released in streams.

One great advantage of optical hyperspectral remote sensing from unmanned aerial systems (UAS) compared to satellite missions is the possibility to fly and collect data below clouds. The most typical scenario is flying below intermittent clouds and under turbulent conditions, which causes tilting of the platform. This study aims to advance hyperspectral imaging from UAS in most weather conditions by addressing two challenges: (i) the radiometric and spectral calibrations of miniaturized hyperspectral sensors; and (ii) tilting effects on measured downwelling irradiance. We developed a novel method to correct the downwelling irradiance data for tilting effects. It uses a hybrid approach of minimizing measured irradiance variations for constant irradiance periods and spectral unmixing, to calculate the spectral diffuse irradiance fraction for all irradiance measurements within a flight. It only requires the platform's attitude data and a standard incoming light sensor. We demonstrated the method at the Palo Verde National Park wetlands in Costa Rica, a highly biodiverse area. Our results showed that the downwelling irradiance correction method reduced systematic shifts caused by a change in flight direction of the UAS, by 87% and achieving a deviation of 2.78% relative to a on ground reference in terms of broadband irradiance. High frequency (< 3 s) irradiance variations caused by high-frequency tilting movements of the UAS were reduced by up to 71%. Our complete spectral and radiometric calibration and irradiance correction can significantly remove typical striped illumination artifacts in the surface reflectance-factor map product. The possibility of collecting precise hyperspectral reflectance-factor data from UAS under varying cloud cover makes it more operational for environmental monitoring or precision agriculture applications, being an important step in advancing hyperspectral imaging from UAS.

Current sustainability assessment (SA) tools to help deal with contaminated groundwater sites are inherently subjective and hardly applied. One reason may be lack of proper tools for addressing contaminant spread which are basically objective. To fill this gap, there is a need for contaminant transport models that provide site managers with needed room for applying their judgments and considerations about the efficiency of each remediation method based on their experiences in similar cases. INSIDE-T uses trend analysis and inverse modeling to estimate transport parameters. It then simulates contaminant transport both with and without the inclusion of remedial actions in a transparent way. The sustainability of each remedy measure can then be quantified based on the underlying SA tool (INSIDE). INSIDE-T was applied to a site in south Sweden, contaminated with pentachlorophenol. Simulation scenarios were developed to enable comparison between various remediation strategies and combinations of these. The application indicated that natural attenuation was not a viable option within the timeframe of interest. Although pump-and-treat combined with a permeable reactive barrier was found to be just as effective as bioremediation after five years, it received a much lower sustainability score overall. INSIDE-T outcomes enable site managers to test and evaluate different scenarios, a necessity in participatory decision-making practices such as remediation projects.

The need for innovative systemic approaches for managing water resources that integrate natural and human dimensions is well established. Although systemic, participatory modelling has been shown to support stakeholder involvement and integrated analysis, the uptake within acrimonious, data-scarce contexts – especially in the developing world – is limited. This study details a process designed to address challenges facing the lower Olifants River Catchment in South Africa, including deteriorating water quality, data paucity and stakeholder conflict. Narratives and quantitative data were used to build a system dynamics (SD) model, ResiMod, within a participatory process. The paper demonstrates how narratives can inform, and be informed by, iterative model development whilst integrating scientific data. The approach facilitated an exploration of perceptions of causality, connections between stakeholder sectors, and mitigatory actions for responding to climate-change impacts on biodiversity. This offers a promising approach to support improved communication and learning in disputed, data-scarce contexts.

Holistic water quality models to support decision‐making in lowland catchments with competing stakeholder perspectives are still limited. To address this gap, an integrated system dynamics model for water quantity and quality (including stream temperature, dissolved oxygen, and macronutrients) was developed. Adaptable plug‐n‐play modules handle the complexity (sources, pathways) related to both urban and agricultural/natural land‐use features. The model was applied in a data‐rich catchment to uncover key insights into the dynamics governing water quality in a peri‐urban stream. Performance indicators demonstrate the model successfully captured key water quantity/quality variations and interactions (with, e.g., Nash‐Sutcliff Efficiency ranging from very good to satisfactory). Model simulation and sensitivity results could then highlight the influence of stream temperature variations and enhanced heterotrophic respiration in summer, causing low dissolved oxygen levels and potentially affecting ecological quality. Probabilistic uncertainty results combined with a rich dataset show high potential for ammonium uptake in the macrophyte‐domi-nated reach. The results further suggest phosphorus remobilization from streambed sediment could become an important diffuse nutrient source should other sources (e.g., urban effluents) be mitigated. These findings are especially important for the design of green transition solutions, where single‐objective management strategies may negatively impact aquatic ecosystems.

Attenuation processes of chlorinated ethenes in complex near-stream systems result in site-specific outcomes of great importance for risk assessment of contaminated sites. Additional interdisciplinary and comprehensive field research is required to enhance process understanding in these systems. In this study, several methods were combined in a multi-scale interdisciplinary in-situ approach to assess and quantify the near-stream attenuation of a chlorinated ethene plume, mainly consisting of cis-dichloroethene (cis-DCE) and vinyl chloride (VC), discharging to a lowland stream (Grindsted stream, Denmark) over a monitoring period of seven years. The approach included: hydrogeological characterisation, reach scale contaminant mass balance analysis, quantification of contaminant mass discharge, streambed fluxes of chlorinated ethenes quantified using Sediment Bed Passive Flux Meters (SBPFMs), assessment of redox conditions, temporal assessment of contaminant concentrations, microbial analysis, and compound-specific isotope analysis (CSIA). This study site exhibits a special attenuation behaviour not commonly encountered in field studies: the conversion from an initially limited degradation case (2012-16), despite seemingly optimal conditions, to one presenting notable levels of degradation (2019). Hence, this study site provides a new piece to the puzzle, as sites with different attenuation behaviours are required in order to acquire the full picture of the role groundwater‐surface water interfaces have in risk mitigation. In spite of the increased degradation in the near-stream plume core, the contaminant attenuation was still incomplete in the discharging plume. A conceptualization of flow, transport and processes clarified that hydrogeology was the main control on the natural attenuation, as short residence times of 0.5-37 days restricted the time in which dechlorination could occur. This study reveals the importance of: taking an integrated approach to understand th

A comparison of tools for measuring discharge rates in a sandy streambed was conducted along a transect near the north bank of the Grindsted å (stream). Four tools were evaluated at six locations spaced 3 m apart in the stream: mini‐piezometers, streambed point velocity probes (SBPVPs), temperature profilers, and seepage meters. Comparison of the methods showed that all identified a similar trend of low to high groundwater discharges moving westward along the transect. Furthermore, it was found that the differences between discharges estimated from Darcy calculations (using the mini‐pizometers), and SBPVPs were not statistically different from zero, at the 90% confidence level. Seepage meter estimates were consistently lower than those of the other two methods, but compared more reasonably with the application of a correction factor of 1.7, taken from the literature. In contrast, discharges estimated from temperature profiling (to a depth of 40 cm) were found to be about an order of magnitude less than those determined with the other methods, possibly due to interferences from horizontal hyporheic flow. Where the various methods produced statistically different discharge estimations at the same location, it is hypothesized that the differences arose from method‐specific sources of bias, including installation depths. On the basis of this work, practitioners interested in measuring flow across the GWSWI (groundwater‐surface water interface) achieve the least variability with seepage meters and the SBPVP. However the accuracy of the seepage meter depended on a calibrated correction factor while that of the SBPVP did not.

Xenobiotic organic compounds can be discharged from contaminated groundwater inflow and may seep into streams from multiple pathways with very different dynamics, some not fully understood. In this study, we investigated the spatio‐temporal variation of chlorinated ethenes discharging from a former industrial site (with two main contaminant sources, A and B) into a stream system in a heterogeneous clay till setting in eastern Denmark. The investigated reach and near‐stream surroundings are representative of peri‐urban settings, with a mix of high channel alteration and more natural stream environment. We therefore propose an approach for risk assessing impacts arising from such complex contamination patterns, accounting for potential spatio‐temporal fluctuations and presence of multiple pathways. Our study revealed substantial variations in pathway contributions and overall contaminant mass discharge to the stream. Variable contaminant contributions arising from both groundwater seepage and urban drains were identified in the channelized part of the north stream, primarily from source A. Furthermore, variations in the hyporheic and shallow groundwater flows were found to enhance contaminant transport from source B. These processes result in an increase of the overall mass of contaminant discharged, correlating with the channels' flow. Thus, an in‐stream control plane approach was found to be an effective method for integrating multiple and variable discharge contributions quantitatively, although information on specific contaminant sources is lost. This study highlights the complexity and variability of contaminant fluxes occurring at the interface between groundwater and peri‐urban streams, and calls for the consideration of these variations when designing monitoring programmes and remedial actions for contaminated sites with the potential to impact streams.

A groundwater plume containing high concentrations of pharmaceutical compounds, mainly sulfonamides, barbiturates and ethyl urethane, in addition to chlorinated ethenes and benzene was investigated. The contamination originating from a former pharmaceutical industry discharges into a multilayered aquifer system and a downgradient stream. In this study, geological and hydrogeological data were integrated into a numerical flow model to examine identified trends using statistical approaches, including principle component analysis and hierarchal cluster analysis. A joint interpretation of the groundwater flow paths and contaminant concentrations in the different compartments (i.e. groundwater and hyporheic zone) provided insight on the transport processes of the different contaminant plumes to the stream. The analysis of historical groundwater concentrations of pharmaceutical compounds at the site suggested these compounds are slowly degrading The pharmaceutical compounds migrate in both a deep semi-confined aquifer, as well as in the shallow unconfined aquifer, and enter the stream along a 2 km stretch. This contrasted with the chlorinated ethenes, which mainly discharge to the stream as a focused plume from the unconfined aquifer. The integrated approach developed here, combining groundwater flow modelling and statistical analyses of the contaminant concentration data collected in groundwater and the hyporheic zone, lead to an improved understanding of the observed distribution of contaminants in the unconfined and semi-confined aquifers, and thus to their discharge to the stream. This approach is particularly relevant for large and long-lasting contaminant sources and plumes, such as abandoned landfills and industrial production sites, where field investigations may be very expensive.

The water sector needs to increase its resource efficiency; failure to do so may have negative effects on economic development and growth. Achieving a higher level of innovative capacity within the water sector may govern a country's capacity to meet specific water challenges while becoming still more important for ensuring sustainable economic development. Traditional water technologies are reaching their stagnation point; in a transition to more sustainable technologies, eco-innovation is the core driver. Based on the national innovative capacity (NIC) as an analytical framework, - indicators that govern the innovative capacity of the water sector were tested in a comparative analysis of Europe versus China, representing respectively, an early mover and a late mover in the green economy agenda. Additionally, an analysis of the evolution of the water technological development is provided. The innovative capacity in the water sector was found to be strongly related to the national innovative strategy. Environmental regulations, research and development and international collaboration were all found to be determinants for both Europe's and China's NIC in the water sector. The level of direct investments and private research and development, on the other hand, were found to be a determinant for China only. However, the evolution of the NIC determinants could not provide any insight as to whether China may reach the same level of NIC in the water sector as Europe. This analysis contributes nonetheless to increasing the level of understanding in the field of water innovation dynamics - providing insights - as to why Europe and China present different innovative capacities in the water sector.

The large number of micropollutants (pharmaceuticals, chlorinated solvents) and their transformation products makes it challenging to quantify their occurrence and ecological risk. Conventionally, chemical impacts to ecosystems and source types are assessed individually, and groundwater contamination is often neglected. This may lead to critical underestimations of the combined impact caused by interactions occurring between stressors not typically evaluated together, e.g. organic groundwater pollutants and metals, and prevent the linkage of chemical and ecological impacts in peri-urban catchments. Contaminated sites represent a major environmental problem for Denmark, potentially polluting soil, groundwater and surface water. Determination of flow paths and groundwater fluxes are essential for evaluating the transport and fate of contaminant plumes discharging to streams. Here, the application of novel approaches is presented for evaluating the governing parameters, including an appreciation of the scale of variability, in order to resolve ecological status under conditions of multiple stress and develop the scientific basis for assessing the risk potential of contaminated sites to impact streams. The overall aims of the field investigations were to (i) test the applicability of different methods for mapping groundwater contamination impacting streams, (ii) perform a risk assessment using the contaminant mass discharge approach, and (iii) assess the stream’s chemical and ecological status. We identified sources and levels of chemical stressors along a 16-km groundwater-fed stream corridor (Grindsted, Denmark). Potential pollution sources included two contaminated sites, aquaculture, wastewater/industrial discharges, and diffuse sources from agriculture/urban areas. The results indicate a substantial impact on Grindsted stream from multiple sources of many origins. Impaired ecological conditions, represented by a lower abundance of meiobenthic individuals

Freshwaters are among the most endangered ecosystems worldwide, due predominantly to excessive anthropogenic practices compromising the future provisioning of ecosystem services. Despite increased awareness of the role of multiple stressors in accounting for ecological degradation in mixed land-use stream systems, risk assessment approaches applicable in field settings are still required. This study provides a first indication for ecological consequences of the interaction of organic and inorganic chemical stressors, not typically evaluated together, which may provide a missing link enabling the reconnection of chemical and ecological findings. Specifically, impaired ecological conditions – represented by lower abundance of meiobenthic individuals – were observed in the hyporheic zone where a contaminant groundwater plume discharged to the stream. These zones were characterized by high xenobiotic organic concentrations, and strongly reduced groundwater (e.g. elevated dissolved iron and arsenic) linked to the dissolution of iron hydroxides (iron reduction) caused by the degradation of xenobiotic compounds in the plume. Further research is still needed to separate whether impact is driven by a combined effect of organic and inorganic stressors impacting the ecological communities, or whether the conditions – when present simultaneously – are responsible for enabling a specific chemical stressor's availability (e.g. trace metals), and thus toxicity, along the study stream. Regardless, these findings suggest that benthic meioinvertebrates are promising indicators for supporting biological assessments of stream systems to sufficiently represent impacts resulting from the co-occurrence of stressors in different stream compartments. Importantly, identification of the governing circumstances is crucial for revealing key patterns and impact drivers that may be needed in correctly prioritizing stressor impacts in these systems. This study further highlights the importance of

The Streambed Point Velocity Probe (SBPVP) measures in situ groundwater velocities at the groundwater-surface water interface without reliance on hydraulic conductivity, porosity, or hydraulic gradient information. The tool operates on the basis of a mini-tracer test that occurs on the probe surface. The SBPVP was used in a meander of the Grindsted Å (stream), Denmark, to determine the distribution of flow through the streambed. These data were used to calculate the contaminant mass discharge of chlorinated ethenes into the stream. SBPVP data were compared with velocities estimated from hydraulic head and temperature gradient data collected at similar scales. Spatial relationships of water flow through the streambed were found to be similar by all three methods, and indicated a heterogeneous pattern of groundwater-surface water exchange. The magnitudes of estimated flow varied to a greater degree. It was found that pollutants enter the stream in localized regions of high flow which do not always correspond to the locations of highest pollutant concentration. The results show the combined influence of flow and concentration on contaminant discharge and illustrate the advantages of adopting a flux-based approach to risk assessment at the groundwater-surface water interface. Chlorinated ethene mass discharges, expressed in PCE equivalents, were determined to be up to 444 kg/yr (with SBPVP data) which compared well with independent estimates of mass discharge up to 438 kg/yr (with mini-piezometer data from the streambed) and up to 372 kg/yr crossing a control plane on the streambank (as determined in a previous, independent study).

Dissolved organic matter (DOM) is linked to the heterogeneous distribution of elevated arsenic (As) in groundwater used for drinking and irrigation purposes, but the relationship between DOM characteristics and arsenic mobility has yet to be fully understood. Here, DOM from groundwater sampled in the Bengal Basin region was characterized using both conventional bulk emission-excitation (EEM) spectroscopy and high-performance size exclusion chromatography coupled to spectroscopy (HPSEC-EEM). Notably, application of the novel HPSEC-EEM approach permitted the total fluorescence of individual samples to be independently resolved into its underlying components. This allowed the external validation of the bulk-sample fluorescence decomposition and offered insight into the molecular size distribution of fluorescent DOM. Molecular size distributions were similar for the UVA fluorescent (C310, C340) as well as the three visible fluorescent (C390, C440 C500) components. There was a greater visible fluorescence in shallow aquifer samples (10-33 m) with high As (SH, up to 418µg/L) than in samples from the same depth with lower As (up to 40µg/L). This indicated a link between DOM quality and As mobility within the shallow aquifer. The deep aquifer samples (170-200 m) revealed DOM characteristics similar to SH samples but had low As concentrations (

Investigating stream water quality under conditions of multiple stress Contaminated sites are among one of the major environmental problems in Denmark, contaminating soil, groundwater and surface water bodies located nearby. Recently, screening tools and risk assessment methods have been developed to support the Danish Regions in evaluating the impact contaminated groundwater originating from these sites may have on Danish streams (Miljøprojekt nr. 1846, Miljøprojekt nr. 1604 ). However, investigations related to stream water affected by contaminated sites have to-date only covered single sources of contaminants. This report provides a decision support tool for assessing the importance of contaminated sites in relation to other potential sources impacting the streams, with the aim of identifying the impact drivers in a multiple stressor context.

Det danske samfund bruger hvert år mange midler på at undersøge, risikovurdere og oprense forurenede grunde. Det er derfor vigtigt, at vi konstant forbedrer de undersøgelser, der ligger til grund for, hvorledes vi risikovurderer og prioriterer de mange forurenede grunde til oprensning.

Traditionally, the monitoring of streams for chemical and ecological status has been limited to surface water concentrations, where the dominant focus has been on general water quality and the risk for eutrophication. Mixed land use stream systems, comprising urban areas and agricultural production, are challenging to assess with multiple chemical stressors impacting stream corridors. New approaches are urgently needed for identifying relevant sources, pathways and potential impacts for implementation of suitable source management and remedial measures. We developed a method for risk assessing chemical stressors in these systems and applied the approach to a 16-km groundwater-fed stream corridor (Grindsted, Denmark). Three methods were combined: (i) in-stream contaminant mass discharge for source quantification, (ii) Toxic Units and (iii) environmental standards. An evaluation of the chemical quality of all three stream compartments – stream water, hyporheic zone, streambed sediment – made it possible to link chemical stressors to their respective sources and obtain new knowledge about source composition and origin. Moreover, toxic unit estimation and comparison to environmental standards revealed the stream water quality was substantially impaired by both geogenic and diffuse anthropogenic sources of metals along the entire corridor, while the streambed was less impacted. Quantification of the contaminant mass discharge originating from a former pharmaceutical factory revealed that several 100 kgs of chlorinated ethenes and pharmaceutical compounds discharge into the stream every year. The strongly reduced redox conditions in the plume result in high concentrations of dissolved iron and additionally release arsenic, generating the complex contaminant mixture found in the narrow discharge zone. The fingerprint of the plume was observed in the stream several km downgradient, while nutrients, inorganics and pesticides played a minor role for the stream health. The res