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Gullies and ravines affect human lives and the environment in many countries worldwide, however, few studies have assessed the impacts of the damage caused by these large linear erosions and clarified their influencing parameters. This work systematizes available information about the variables relevant to analyze the impacts of ravines and gullies on socioeconomic conditions and ecosystem services. Based on keyword searches performed in the Scopus, Web of Science and Dimensions databases, more than 120 articles from 27 countries were identified that addressed and valuated these different types of impacts. Although many studies discuss the impacts of ravines and gullies, few studies have performed valuations of these impacts. We compiled the impacts in urban and rural areas, considering the changes caused by ravines and gullies throughout a hydrographic basin. The results allowed for the elaboration of a theoretical model of the possible impacts of gullies and ravines and how they can be valued. The results demonstrate that the most significant impacts, according to the literature, are in South America, Africa, China and India, which are related to disordered land occupation. In some cases, the lack of capacity to respond to environmental and social problems aggravates the scenario and leads to significant losses. Implementing the evaluation is challenging due to the high number of different forms of possible impacts, in the short, medium and long term, related to environmental, economic and social changes.

Polycyclic aromatic hydrocarbons (PAHs) are emitted to the atmosphere by various anthropogenic activities as well as natural sources, they undergo long-range transport, are degraded (e.g., by photolysis) and finally they are deposited onto the surface and potentially accumulate in topsoil. The dry deposition of particle-bound PAHs dominates the accumulation of PAHs in soil and their further fate in soil is governed by sorption/desorption from these airborne particles. This paper offers an overview on concentrations of particle-bound PAHs, the dry deposition fluxes and finally concentrations of PAHs in soil. In addition, spatial and temporal variations of PAHs are considered. The results show that concentrations of particle-bound PAHs typically range from 1 mg g

Nitrate reduction constitutes an important natural mechanism to mitigate the widespread and persistent nitrate contamination of groundwater resources. In fractured aquifers, however, the abundance and accessibility of electron donors and their spatial correlation with groundwater flow paths are often poorly understood. In this study, the nitrate reduction potential of a fractured carbonate aquifer in the Upper Muschelkalk of SW Germany was investigated, where denitrification is due to the oxidation of ferrous iron and reduced sulfur. Petrographical analyses of rock samples revealed concentrations of syn-sedimentary and diagenetically formed pyrite ranging from 1 to 4 wt.% with only small differences between different facies types. Additional ferrous iron is available in saddle dolomites (up to 2.6 wt.%), which probably were formed by tectonically induced percolation of low-temperature hydrothermal fluids. Borehole logging at groundwater wells (flowmeter, video, gamma) indicates that most groundwater flow occurs along karstified bedding planes partly located within dolomites of the shoal and backshoal facies. The high porosity (15–30%) of these facies facilitates molecular diffusive exchange of solutes between flow paths in the fractures and the reactive minerals in the pore matrix. The high-porosity facies together with hydraulically active fractures featuring pyrite or saddle dolomite precipitates constitute the zones of highest nitrate reduction potential within the aquifer. Model-based estimates of electron acceptor/donor balances indicate that the nitrate reduction potential protecting water supply wells increases with increasing porosity of the rock matrix and decreases with increasing hydraulic conductivity (or effective fracture aperture) and spacing of the fracture network.

Over the past decades, fractured and karst groundwater systems have been studied intensively due to their high vulnerability to nitrate (NO3−) contamination, yet nitrogen (N) turnover processes within the recharge area are still poorly understood. This study investigated the role of the karstified recharge area in NO3− transfer and turnover by combining isotopic analysis of NO3− and nitrite (NO2−) with time series data of hydraulic heads and specific electrical conductivity from groundwater monitoring wells and a karstic spring in Germany. A large spatial variability of groundwater NO3− concentrations (0.1–0.8 mM) was observed, which cannot be explained solely by agricultural land use. Natural-abundance N and O isotope measurements of NO3− (δ15N and δ18O) confirm that NO3− derives mainly from manure or fertilizer applications. Fractional N elimination by denitrification is indicated by relatively high δ15N- and δ18O-NO3− values, elevated NO2− concentrations (0.05–0.14 mM), and δ15N-NO2− values that were systematically lower than the corresponding values of δ15N-NO3−. Hydraulic and chemical response patterns of groundwater wells suggest that rain events result in the displacement of water from transient storage compartments such as the epikarst or the fissure network of the phreatic zone. Although O2 levels of the investigated groundwaters were close to saturation, local denitrification might be promoted in microoxic or anoxic niches formed in the ferrous iron-bearing carbonate rock formations. The results revealed that (temporarily) saturated fissure networks in the phreatic zone and the epikarst may play an important role in N turnover during the recharge of fractured aquifers.

Although passive sampling has been applied to determine concentrations of semi-volatile organic chemicals such as polycyclic aromatic hydrocarbons (PAHs) in air and water for about two decades and is well established, several uncertainties and challenges remain. This study presents a comprehensive validation of polyethylene thin sheets as passive air samplers (PE-PAS), detailing alternative approaches to calibration and analysis. Besides measuring the uptake kinetics in the field using time series deployments of PE-PAS at 3 field sites under varying seasonal conditions (temperature, wind) with a performance reference compound (PRC), we implement a numerical model to fit uptake kinetics based on partition and diffusion coefficients adapted to hourly changes of temperature. This model follows similar approaches as reported in earlier studies, but we use loss curves of a spiked PRC (anthracene-D10) to fit the air-side boundary layer (δg), which is limiting mass transfer between air and PE, instead of calibrating the PAS sampling rate. Surprisingly, air side boundary layers, and thus inherent sampling rates, were almost equal at the different locations but varied for the different sampling campaigns by about a factor of two. This variation is probably due to short term effects, but a robust average over all seasons and locations could be obtained (1 mm ± 0.5 mm) which is characteristic for our sampling design. A well-known δg allows concentrations in air of compounds with very different uptake kinetics onto the PE-PAS to be estimated. Additionally, as in previous studies, our results indicate stable distribution patterns of PAHs in the environment of the study region in Germany. Given a practical chosen PE-PAS deployment time, representative compounds may be selected that integrate over the desired monitoring time period (e.g. fluorene for days, phenanthrene for weeks and pyrene or fluoranthene for many months to years). Measurement of one PAH applied with specific ratios derived from stable distribution patterns of PAHs, in the absence of influential local point sources, can then be used to estimate air concentrations of PAHs that are more difficult to quantify during the monitoring period.

In this study, levels and sources of aliphatic hydrocarbons and hopanes in surface sediments collected from rivers and estuaries of Peninsular Malaysia were assessed. The concentrations of total n-...

Quantification of the travel time distribution and transport parameters in fractured aquifers is crucial for understanding contaminant transport in fractured systems. Although knowledge about the travel time distribution is a helpful tool to assess the solute transport, it can’t be measured directly. Travel time is typically back-computed from different tracers in groundwater by applying well established analytical methods. However, in fractured aquifers diffusive exchange with the rock matrix, intersection of streamtubes and associated mixing, as well as other processes can cause deviation of the estimated travel time from the mean advective travel time. Direct numerical modelling of the tracer’s reactive behavior with the travel time as one of the calibrated parameters can lead to non-uniqueness of the result. These non-unique solutions typically lead to a high level of parametric uncertainty especially on catchment scale. In this work, we address the reduction of uncertainty in mean travel time, shape parameter of travel time distribution, fracture aperture, and porosity by means of multiobjective optimization enhanced by surrogate modelling. For pre-selection of potentially plausible model runs Gaussian Processes Emulation (GPE) was applied within four-parametric space. We use the GPE with multitracer conditioning for pre-selection of plausible parameter combinations. Posterior distributions were employed to estimate the mean groundwater travel times at sampling locations, to distinguish between different rock facies of captured streamlines, and to get an estimate of fracture apertures. We confirm the hypothesis that using tritium and helium isotopes together with radiogenic helium measurements helps to achieve a unimodal posterior distribution and reduces uncertainty significantly.

The recycling of mineral materials is a sustainable and economical approach for reducing solid waste and saving primary resources. However, their reuse may pose potential risks of groundwater contamination, which may result from the leaching of organic and inorganic substances into water that percolates the solid waste. In this study, column leaching tests were used to investigate the short- and long-term leaching behavior of “salts”, “metals”, and organic pollutants such as PAHs and herbicides from different grain size fractions of construction & demolition waste (CDW) and railway ballast (RB) after a novel treatment process. Specifically, silt, sand and gravel fractions obtained after a sequential crushing, sieving, and washing process (“wet-processing”) of very heterogeneous input materials are compared with respect to residual contamination, potentially limiting their recycling. Concentrations in solid fractions and aqueous leachate were evaluated according to threshold values for groundwater protection to identify relevant substances and to classify materials obtained for recycling purposes according to limit values. For that, the upcoming German recycling degree was applied for the first time. Very good agreement was observed between short and extensive column tests, demonstrating that concentrations at L/S 2 ratios are suitable for quality control of recycling materials. Different solutes showed a characteristic leaching behavior such as the rapid decrease in “salts”, e.g., SO42− and Cl−, from all solid fractions, and a slower decrease in metals and PAHs in the sand and silt fractions. Only the gravel fraction, however, showed concentrations of potential pollutants low enough for an unlimited re-use as recycling material in open technical applications. Sand fractions may only be re-used as recycling material in isolated or semi-isolated scenarios. Leaching from heterogeneous input materials proved harder to predict for all compounds. Overall, column leaching tests proved useful for (i) initial characterization of the mineral recycling materials, and (ii) continuous internal (factory control) and external quality control within the upcoming German recycling decree. Results from such studies may be used to optimize the treatment of mixed solid waste since they provide rapid insight in residual pollution of material fractions and their leaching behavior.

A simple first order approximation was derived to model sorption/desorption kinetics of hazardous compounds in batch experiments based on a coupled film and intraparticle diffusion model. The solution is accurate enough to replace infinite series expansions needed in analytical solution for intraparticle diffusion and it accounts for the mass transfer shift from diffusion in the external aqueous boundary layer to the intraparticle pore space. With increasing distribution coefficient (K

Atmospheric deposition of polycyclic aromatic hydrocarbons (PAHs) onto soil threatens terrestrial ecosystem. To locate potential source areas geographically, a total of 139 atmospheric bulk deposition samples were collected during 2012-2019 at eight sites in Shanghai and its surrounding areas. A multisite joint location method was developed for the first time to locate potential source areas of atmospheric PAHs based on an enhanced three dimensional concentration weighted trajectory model. The method considered spatial and temporal variations of atmospheric boundary layer height and homogenized all results over the eight sites via geometric mean. Regional transport was an important contributor of PAH atmospheric deposition while massive local emissions may disturb the identification of potential source areas. Northwesterly winds were associated with elevated deposition fluxes. Potential source areas were identified by the multisite joint location method and included Hebei, Tianjin, Shandong and Jiangsu to the north, and Anhui to the west of Shanghai. PM and SO

Initial conditions (pre-equilibrium or after the first flooding of the column), mass transfer mechanisms and sample composition (heterogeneity) have a strong impact on leaching of less and strongly sorbing compounds in column percolation tests. Mechanistic models as used in this study provide the necessary insight to understand the complexity of column leaching tests especially when heterogeneous samples are concerned. By means of numerical experiments, we illustrate the initial concentration distribution inside the column after the first flooding and how this impacts leaching concentrations. Steep concentration gradients close to the outlet of the column have to be expected for small distribution coefficients (Kd<1 L kg−1) and longitudinal dispersion leads to smaller initial concentrations than expected under equilibrium conditions. In order to elucidate the impact of different mass transfer mechanisms, film diffusion across an external aqueous boundary layer (first order kinetics, FD) and intraparticle pore diffusion (IPD) are considered. The results show that IPD results in slow desorption kinetics due to retarded transport within the tortuous intragranular pores. Non-linear sorption has not much of an effect if compared to Kd values calculated for the appropriate concentration range (e.g., the initial equilibrium concentration). Sample heterogeneity in terms of grain size and different fractions of sorptive particles in the sample have a strong impact on leaching curves. A small fraction (Kd) carrying the contaminant may lead to very slow desorption rates (because of less surface area)—especially if mass release is limited by IPD—and thus non-equilibrium. In contrast, mixtures of less sorbing fine material (“labile” contamination with low Kd), with a small fraction of coarse particles carrying the contaminant leads to leaching close to or at equilibrium showing a step-wise concentration decline in the column effluent.

Nitrate removal in oligotrophic environments is often limited by the availability of suitable organic electron donors. Chemolithoautotrophic bacteria may play a key role in denitrification in aquifers depleted in organic carbon. Under anoxic and circumneutral pH conditions, iron(II) was hypothesized to serve as an electron donor for microbially mediated nitrate reduction by Fe(II)-oxidizing (NRFeOx) microorganisms. However, lithoautotrophic NRFeOx cultures have never been enriched from any aquifer, and as such, there are no model cultures available to study the physiology and geochemistry of this potentially environmentally relevant process. Using iron(II) as an electron donor, we enriched a lithoautotrophic NRFeOx culture from nitrate-containing groundwater of a pyrite-rich limestone aquifer. In the enriched NRFeOx culture that does not require additional organic cosubstrates for growth, within 7 to 11 days, 0.3 to 0.5 mM nitrate was reduced and 1.3 to 2 mM iron(II) was oxidized, leading to a stoichiometric NO(3)(−)/Fe(II) ratio of 0.2, with N(2) and N(2)O identified as the main nitrate reduction products. Short-range ordered Fe(III) (oxyhydr)oxides were the product of iron(II) oxidation. Microorganisms were observed to be closely associated with formed minerals, but only few cells were encrusted, suggesting that most of the bacteria were able to avoid mineral precipitation at their surface. Analysis of the microbial community by long-read 16S rRNA gene sequencing revealed that the culture is dominated by members of the Gallionellaceae family that are known as autotrophic, neutrophilic, and microaerophilic iron(II) oxidizers. In summary, our study suggests that NRFeOx mediated by lithoautotrophic bacteria can lead to nitrate removal in anthropogenically affected aquifers. IMPORTANCE Removal of nitrate by microbial denitrification in groundwater is often limited by low concentrations of organic carbon. In these carbon-poor ecosystems, nitrate-reducing bacteria that can use inorganic compounds such as Fe(II) (NRFeOx) as electron donors could play a major role in nitrate removal. However, no lithoautotrophic NRFeOx culture has been successfully isolated or enriched from this type of environment, and as such, there are no model cultures available to study the rate-limiting factors of this potentially important process. Here, we present the physiology and microbial community composition of a novel lithoautotrophic NRFeOx culture enriched from a fractured aquifer in southern Germany. The culture is dominated by a putative Fe(II) oxidizer affiliated with the Gallionellaceae family and performs nitrate reduction coupled to Fe(II) oxidation leading to N(2)O and N(2) formation without the addition of organic substrates. Our analyses demonstrate that lithoautotrophic NRFeOx can potentially lead to nitrate removal in nitrate-contaminated aquifers.

Neutrophilic microbial pyrite (FeS2) oxidation coupled to denitrification is thought to be an important natural nitrate attenuation pathway in nitrate-contaminated aquifers. However, the poor solubility of pyrite raises questions about its bioavailability and the mechanisms underlying its oxidation. Here, we investigated direct microbial pyrite oxidation by a neutrophilic chemolithoautotrophic nitrate-reducing Fe(II)-oxidizing culture enriched from a pyrite-rich aquifer. We used pyrite with natural abundance (NA) of Fe isotopes (NAFe-pyrite) and 57Fe-labeled siderite to evaluate whether the oxidation of the more soluble Fe(II)-carbonate (FeCO3) can indirectly drive abiotic pyrite oxidation. Our results showed that in setups where only pyrite was incubated with bacteria, direct microbial pyrite oxidation contributed ca. 26% to overall nitrate reduction. The rest was attributed to the oxidation of elemental sulfur (S0), present as a residue from pyrite synthesis. Pyrite oxidation was evidenced in the NAFe-pyrite/57Fe-siderite setups by maps of 56FeO and 32S obtained using a combination of SEM with nanoscale secondary ion MS (NanoSIMS), which showed the presence of 56Fe(III) (oxyhydr)oxides that could solely originate from 56FeS2. Based on the fit of a reaction model to the geochemical data and the Fe-isotope distributions from NanoSIMS, we conclude that anaerobic oxidation of pyrite by our neutrophilic enrichment culture was mainly driven by direct enzymatic activity of the cells. The contribution of abiotic pyrite oxidation by Fe3+ appeared to be negligible in our experimental setup.

Compared with dry and wet deposition rates, air-soil exchange fluxes cannot be directly measured experimentally. Polyethylene passive sampling was applied to assess transport directions and to measure concentration gradients in order to calculate diffusive fluxes of polycyclic aromatic hydrocarbons (PAHs) across the air-soil interface in an urban park of Shanghai, China. Seven campaigns with high spatial resolution sampling at 18 heights between 0 and 200 cm above the ground were conducted in 2017–2018. Air-to-soil deposition was observed, e.g. for phenanthrene, and soil-to-air volatilization for high molecular weight compounds, such as benzo[b]fluoranthene. Significant linear correlations between gaseous PAH concentration and log-transformed height were observed. Influence of vegetation on vertical concentration gradients of gaseous PAHs was insignificant in most cases except during the growing season. Local micrometeorological conditions resulted in a directional eddy diffusion in air and then influenced vertical diffusion of gaseous PAHs. Furthermore, the vertical eddy diffusivity was estimated as a function of distance to the air-soil surface. Air-soil exchange fluxes based on the Mackay's fugacity approach were calculated and confirmed by diffusive fluxes within air layer based on vertical concentration gradient of PAHs and eddy/molecular diffusion. Polyethylene passive sampling technology provides a useful tool to investigate air-soil exchange process.

Microplastic particles are ubiquitously detected in the environment. Despite intensive public and scientific discussions, their potential to transport contaminants in rivers and oceans under environmental conditions is still under assessment. In the present study we measured sorption isotherms and kinetics in batch experiments using phenanthrene (as a typical hydrophobic wastewater contaminant) and microplastic particles of different sizes and materials. We observed a linear sorption isotherm for polyethylene, in contrast to nonlinear sorption of polyamide and polystyrene, which could be best described by the Freundlich and the Polanyi-Dubinin-Manes isotherms, respectively. We modeled sorption kinetics as a combination of external mass transfer governed by diffusion through an aqueous boundary layer and intraparticle diffusion within the plastic. Which of these processes controls the kinetics depends on the sorption strength, particle size, diffusion coefficients, and time. We used semi-analytical and numerical methods to simulate the coupled mass transfer for both linear and nonlinear sorption. We successfully applied the semi-analytical model to polyethylene and the numerical code to polyamide and polystyrene, reproducing the measured kinetics and obtaining reasonable values for mass transfer and intraparticle diffusion coefficients. Subsequently, we used these coefficients to estimate the transport potential and relevant time scales for microplastic-bound contaminants under environmental conditions. Environ Toxicol Chem 2019;38:1635-1644. © 2019 SETAC.

Column leaching tests are frequently used and accepted for investigation of release of hazardous substances from solid materials. Independent of differences due to the field of application or national regulations, column tests assume that local equilibrium is established in the experiment which facilitates transfer of results to field conditions. In the process of harmonization and standardization within Europe the question on the influence of flow rate and grain size distribution on the local equilibrium was raised. Thus, a set of experiments using two different masonry materials with varying grain size distribution and flow rate were conducted including stop/flow experiments. Results are compared to a numerical model which takes intraparticle pore diffusion-controlled release of Mo and V into the percolating water into account. Due to the relatively high intraparticle porosity of the materials (24–29%) data and model indicate that initially equilibrium-state conditions prevail followed by rapidly decreasing concentrations. The model fits data for Mo and V reasonably well; however, after the initial decline of concentrations (at L/S > 2) extended tailing is observed especially of elements occurring as oxides, which is not captured by the model.

Transport of hydrophobic pollutants in rivers such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and heavy metals is often facilitated by suspended sediment particles, which are typically mobilized during high discharge events. Suspended sediments thus represent a means of transport for particle related pollutants within river reaches and may represent a suitable proxy for average pollutant concentrations estimation in a river reach or catchment. In this study, multiple high discharge/turbidity events were sampled at high temporal resolution in the Globaqua River Basins Sava (Slovenia, Serbia), Adige (Italy), and Evrotas (Greece) and analysed for persistent organic pollutants such as PAHs (polycyclic aromatic hydrocarbons) or PCBs (polychlorinated biphenyls) and heavy metals. For comparison, river bed sediment samples were analysed as well. Further, results are compared to previous studies in contrasting catchments in Germany, Iran, Spain, and beyond. Overall results show that loadings of suspended sediments with pollutants are catchment-specific and relatively stable over time at a given location. For PAHs, loadings on suspended particles mainly correlate to urban pressures (potentially diluted by sediment mass fluxes) in the rivers, whereas metal concentrations mainly display a geogenic origin. By cross-comparison with known urban pressure/sediment yield relationships (e.g. for PAHs) or soil background values (for metals) anthropogenic impact – e.g. caused by industrial activities – may be identified. Sampling of suspended sediments gives much more reliable results compared to sediment grab samples which typically show a more heterogeneous contaminant distribution. Based on mean annual suspended sediment concentrations and distribution coefficients of pollutants the fraction of particle facilitated transport versus dissolved fluxes can be calculated. © 2018 The Authors, This work was supported by the 7th Framework Programme of the European Commission under Grant Agreement no 603629-ENV-2013-6.2.1-GLOBAQUA

We investigate denitrification in a ferric iron-containing fractured micritic limestone aquifer (Triassic Upper Muschelkalk) in south-west Germany by numerical simulations. Low porosity values (average value of 1%), partly small pore sizes of the rock matrix (~ 0.1 μm), and thus potential absence of microbial activity in the rock matrix suggest that denitrification is taking place solely in the fracture. A key question is whether the nitrate reduction derived from groundwater observations at 25 locations in the study area can be explained by a model that restricts microbial denitrification to the fractures. A travel time-based reactive transport model is developed to efficiently simulate long-term nitrate reduction on the catchment scale. The model employs a 2-D numerical reaction model describing the fracture-rock matrix system and parametric travel time distributions. The role of (i) biotic and abiotic iron oxidation, (ii) the type and amount of iron bearing minerals, and (iii) mass transfer between matrix and fracture are investigated. The simulations show that pyrite and siderite (used as surrogate for iron carbonates) together as a source of electron donors provide enough reduction potential to decrease the nitrate concentrations as observed in the field. This confirms the hypothesis that diffusion-controlled mass transfer of electron donors from the matrix to the fracture is sufficient to establish considerable denitrification in the fracture. Uncertainty in modelled concentrations is demonstrated as a result of both the geochemical aquifer properties and the unknown shape of travel time distributions.

PFAS contaminated compost materials have been applied over the last few decades to agricultural fields in Germany, resulting in large-scale diffuse PFAS plumes. The leaching behavior of PFAS from the first two identified contaminated agricultural sites in Germany were investigated, one at Brilon-Scharfenberg, North Rhine-Westphalia Site (BS-NRW), and the other at Rastatt/Mannheim, Baden-Wurttemberg. The specific objectives of this study were to assess the longevity of the PFAS agricultural sources and compare standardized column percolation tests to long-term leaching of PFAS from contaminated sites. The advection-dispersion model (ADM) was used to compare the leaching behavior of PFOA and PFOS from standardized column percolation tests and long-term field leaching data from the BS-NRW site. Column leaching tests conducted with PFOS and PFOA contaminated soil simulated the initial rapid decline but did not predict the long-term behavior (tailing) observed at the field site over 12 years. Trend analyses of the PFAS field data from the BS-NRW showed that concentrations had stabilized and that individual PFAS exhibited distinct seasonal fluctuations; the latter is likely due to the ongoing transformation of precursors and a seasonal influence on production rates of mobile PFAS. Mass balances conducted at both sites indicate that complete removal of these compounds will likely take years to decades to occur, which is expected from the results of the column leaching tests.

Fractured and karstified aquifers are often vulnerable to pollution by nitrate or other anthropogenic compounds. Therefore, a better understanding of the flow and transport processes in these aquifers is imperative for effective drinking water management. In this study, we used the analysis of tritium and tritiogenic helium-3 concentrations to estimate the residence and exposure time of nitrate transported in a fractured groundwater system of the Upper Muschelkalk in southwest Germany.The recharge area is characterised by elevated nitrate concentrations of up to 60 mg/L which are in accordance with dominating agricultural landuse in the catchment. Further along the groundwater flow direction a significant decrease in dissolved oxygen as well as nitrate concentrations to values close to the detection limit is observed.Tritium/3He ages were found to be in the range of zero to forty years. However, in the fractured aquifer the age tracers were most probably affected by mixing and exchange processes that might change the concentration as well as the ratio of tritium and helium-3 in addition to radioactive decay. Therefore, we investigated the impact of different transport processes such as mixing of water parcels at fracture joints or exchange between mobile water on fractures and the pore matrix using forward convolution approaches for both isotopes separately.In combination with hydrochemical, multi-isotopic, petrographical, and molecular biological data, the groundwater residence time data was intended to gain crucial insight into the processes and limiting factors of autotrophic denitrification found within the Muschelkalk aquifer.

Fractured or karstified carbonate rocks constitute major drinking water resources all over the world. Nitrate is one of the major threads for drinking water suppliers in regions with intensive agrucultural use. Field scale observations in the Upper Muschelkalk aquifer in the area “Oberes Gäu”, SW-Germany, suggest that denitrification due to oxidation of Fe(II) or sulfide-bearing minerals might be a relevant attentuation process at least in cases of extended mean residence times (> 5-40 years).To identify reactive minerals within the rock matrix rock samples have been taken from major facies types within the Upper Muschelkalk from outcrops, drillings and carbonate quarries. Samples have been analysed in polished thin sections using transmitted & reflected light microscopy as well as electron microscopy including energy-dispersive elemental analysis.Reactive Fe(II) and sulfide-bearing minearls are pyrite and marcasite as well as saddle dolomites (Fe-bearing dolomites). Concentrations of these minerals depend on facies types and amount to several weight percent iron. Porosities range from very low values (In combination with a hydrogeological characterization, these investigations allowed to delineate reactive zones within the fractured aquifer. Denitrification within these reactive zones depends on the amount and dissolution of these minerals as well as effective diffusion in the pore space.

Hydrophobic pollutants in rivers are transported to varying degrees either in the dissolved or particle-bound phase. For either very turbid rivers or very strongly sorbing compounds, transport dynamics are closely coupled to the cascading sediment movement throught the stream network. Hence, an understanding of sediment storage and mobilisation/movement, including the interaction of suspended and bed sediment phases is the basis for properly discribing contaminant transport.Suspened sediments from the Ammer River in southwestern Germany show a gradual decrease of polycyclic aromatic hydrocarbons (PAH) loadings in a downstream direction, reflecting urban sources in the headwaters. The decrease of PAH loading is, however, only weak which we attribute to only moderate inputs of more or less clean sediments along the river profile, capable of diluting the contaminant signal. The bed sediments of the river comprise a large fraction of grain sizes < 250 µm and constitute an important storage compartment for hydrophobic contaminants. Transformation or leaching into the water phase may reduce the stored amounts. Furthermore, the particle-bound mobility of the stored contaminants clearly depends on the distribution among grain size fractions. We have, therefore, also sampled the bed sediments < 250 µm along the river profile and separated into four grain size fractions (< 19 µm, 19-54 µm, 54-100 µm, 100-250 µm) using vacuum filtration and fine stainless steel meshes. The fractions have been analyzed for urban pollutants of different origins (PAH, heavy metals and the musk fragrance galaxolide) and particulate organic carbon (POC) content. First results show that POC is enriched in the 19-54 µm fraction and that metal contents are neither correlated with POC nor with grain size. This contradicts the common assumption that compounds typically sorbing to surfaces acumulate in the finest fractions due to the large specific surface area. Final results for PAH and galaxolide concentrations as a function of POC contents and particle sizes will also be presented (analysis still pending). At least for PAH a strong affinity to organic carbon is anticipated, while not much is known to date about the sorption and storage behaviour of galoxolide.The results will give further insights into the environmental behaviour of the investigated compound groups. Comparison with data from suspended sediment sampling will enhance our understanding of mobile and immobile phase interactions and, hence, the transport dynamics of these sediment-associated pollutants.

PAHs (polycyclic aromatic hydrocarbons) in urban areas are usually bound to particles. Concentrations are different in different compartments (airborne particles, street dust, suspended sediments in rivers and channels). This study follows concentrations of PAHs from particles in air to street dust and finally suspended sediments in the city of Tehran, Iran compared to Tubingen, Germany. Data sets are based on own investigations (PAHs on suspended sediments), or taken from literature studies (PAHs in street dust and airborne particles). Based on a cross-comparison of concentrations of PAHs on particles, and their congener distribution patterns, the occurrence, interrelation (exchange and mixing processes), as well as possible dilution processes among PAHs in the different particle classes are disentangled. Results show that for Tehran and Tubingen PAHs in airborne particles are very high (in the range of 500 mg kg−1). However, in street dust and suspended sediments PAHs concentrations on particles are around 100 times lower. Surprisingly concentrations in street dust and suspended sediments are 5 to 10 times lower in Tehran (average 0.5 mg kg−1) than in Tubingen (average 5 mg kg−1). Since it is unlikely that PAHs emissions are lower in the Tehran megacity, an effective dilution of the atmospheric signal by uncontaminated (background) particles is hypothesized. Uncontaminated particles may stem from wind erosion of bare surfaces, construction and sand mining sites or even dust from the desert areas, which are frequent in arid climate in Tehran.

Background The contamination of aquatic ecosystems with both anthropogenic pollutants and particles in particular (microscopic) plastic debris items is of emerging concern. Since plastic particles can accumulate contaminants and potentially facilitate their transport, it is important to properly investigate sorption mechanisms. This is especially required for a large variety of chemicals that can be charged under environmental conditions and for which interactions with particles may hence go beyond mere partitioning. Results In this study, sorption experiments with two types of microplastic particles (polyethylene and polystyrene) and 19 different contaminants (pesticides, pharmaceuticals, and personal care products) were performed at three different pH values. We could show that sorption to plastic particles is stronger for hydrophobic compounds and that neutral species usually contribute more to the overall sorption. Bulk partitioning coefficients were in the same order of magnitude for polyethylene and polystyrene. Furthermore, our results confirm that partition coefficients for polar compounds can only be accurately determined if the solid-to-liquid ratio in batch experiments is more than 6–7 orders of magnitude higher than any plastic concentration detected in the environment. Consequently, only a minor fraction of pollutants in water bodies is associated with microplastics. Conclusions Although neutral species primarily dominate the overall sorption, hydrophobic entities of ionic species cannot be neglected for some compounds. Notwithstanding, our results show that since microplastic concentrations as currently observed in the environment are very low, they are only a relevant sorbent for strongly hydrophobic but not for polar compounds. Electronic supplementary material The online version of this article (10.1186/s12302-018-0155-z) contains supplementary material, which is available to authorized users.

Chemical weathering of sedimentary rocks is of great importance in determining seepage water chemistry, carbon, iron, calcium and sulfur turnover, as well as mineral transformation. In this study, we used the numerical code MIN3P to investigate controls on seepage water chemistry during chemical weathering of marine mudrocks. In particular, we focused on the pyrite- and kerogen-bearing formation, Opalinus Clay (with outcrops in the area of the Swabian and Franconian Alb in Southern Germany), a typical fine-grained sedimentary mudrock that had been deposited during the Middle Jurassic in a shallow marine environment. In the geochemical model we considered four reactive minerals, i.e. , pyrite, kerogen, calcite and siderite (assuming silicate minerals to be stable), and ran model scenarios over a time period of 10 kyrs (since the last ice age). Our numerical results show that chemical weathering of Opalinus Clay is driven by oxygen ingress (which depends on effective gas diffusion, and thus on water saturation). Due to oxidation of pyrite and kerogen seepage water acidifies, which leads to dissolution of carbonate minerals, i.e. , calcite and siderite. As a consequence, porosity and groundwater alkalinity increase, and CO 2 is released into the atmosphere at early decades. Following the consumption of primary reactive minerals, iron oxides precipitate in the oxic zone. We compared our model results with field data of water saturation, porosity, and water chemistry. The overall reasonable fit between model results and field data demonstrates the applicability of the numerical code MIN3P to quantify chemical weathering of pyrite-bearing sedimentary mudrocks and to predict seepage water chemistry that is impacted by geochemical water-rock interactions.

Column leaching tests have become a standard method for assessing leaching of pollutants from materials used, e.g., for road and railway constructions and in landscaping measures. Column tests showed to be practical in laboratories yielding robust and reproducible results. However, considerable uncertainty still exists related particularly to the degree of equilibration of the pore water with the solids during preparation (pre-equilibration) and percolation of the column. We analyse equilibration time scales and sensitivity of concentrations in column leachate with respect to initial conditions in a series of numerical experiments covering a broad spectrum of material and solute properties. Slow release of pollutants from solid materials is described by a spherical diffusion model of kinetic sorption accounting for multiple grain size fractions and sorption capacities. Results show that the cumulative concentrations are rather independent of the pre-equilibration level for a broad spectrum of parameter settings, e.g. if intra-particle porosity is high, grain size is small, or if the sorption coefficient is large. Sensitivity increases with decreasing liquid solid ratios and contact time during percolation. Significant variations with initial column conditions are to be expected for material and compound properties leading to slow release kinetics. In these cases, sensitivity to initial conditions may have to be considered.

The distribution and bioconcentration of polycyclic aromatic hydrocarbons (PAHs) in water, suspended particulate material (SPM), algae, and zooplankton samples from the Pearl River Delta (PRD), South China, were investigated. The PAHs in the water and SPM samples is significantly associated with chlorophyll a (Chl a), implying the important role of the aquatic productivity on PAH distribution. PAHs in the water or SPM samples were strongly correlated to dissolved organic carbon (DOC) or algal particulate organic carbon (A-POC). Moreover, the log bioconcentration factor (BCF) values (mL g−1) of PAHs in both the algae and zooplankton samples were linearly related to their log octanol-water coefficient (Kow) values. However, the slopes of these relationships were negatively correlated with Chl a, attributing to the difference in the dominant plankton species or the non-equilibrium exchange between air-water-biota. The above results indicate the important role of trophic levels on the distribution and bioaccumulation of PAHs.

It is a great challenge to accurately estimate chemical activity of hydrophobic organic contaminants in field soils. Ex-situ and in-situ determinations were developed for this purpose based on low-density polyethylene (LDPE) passive sampling and non-equilibrium correction by release of performance reference compounds (PRCs) previously spiked to the samplers. This work investigated kinetic processes of target contaminants’ uptake into and PRCs’ release from the sampler in an ex-situ soil suspension incubated for 100 days. A close agreement of kinetic parameters for pyrene’s (target) uptake into and deuterated pyrene’s (PRC) release from LDPE indicated their similar exchange kinetics. Three kinetic models were developed to correct uptake of target compounds in non-equilibrium conditions via release processes of PRCs. The second-order kinetic model was recommended for ex-situ measurements. The PRC-based non-equilibrium corrections were further applied to in-situ static passive sampling from several weeks to months in a PAH-contaminated field site. Two-weeks’ deployments were sufficient for quantifying lighter PAHs (logKOA 9.0), even if over four months. Concentration estimates from the in-situ and ex-situ passive samplings were comparable in order of magnitude with traditional estimation from equilibrium partitioning models considering both organic and black carbon fractions.

We present a semi-analytical model for the transport of solutes being subject to sorption in porous aquifers. We couple a travel-time based model of advective transport with a spherical diffusion model of kinetic sorption in non-uniform material mixtures. The model is formulated in the Laplace domain and transformed to the time domain by numerical inversion. By this, three-dimensional transport of solutes undergoing mass transfer between aqueous and solid phases can be simulated very efficiently. The model addresses both hydraulic and reactive heterogeneity of porous aquifers by means of hydrofacies, which function as homogeneous but non-uniform subunits. The total exposure time to each of these subunits controls the magnitude of sorption effects, whereas the particular sequence of facies through which the solute passes is irrelevant. We apply the model to simulate the transport of phenanthrene in a fluvio-glacial aquifer, for which the hydrofacies distribution is known at high resolution, the lithological composition of each facies has been analyzed, and sorption properties of the lithological components are available. Taking the fully resolved hydrofacies-model as reference, we evaluate different approximations referring to lower information levels, reflecting shortcomings in typical modeling projects. The most important feature for a good description of both the main breakthrough and tailing of phenanthrene is the non-uniformity of the porous medium. While spatial heterogeneity of chemical properties might be neglected without introducing a large error, an approximation of the facies' composition in terms of a uniform substitute material considerably compromises the quality of the modeling result. This article is protected by copyright. All rights reserved.

Temperature changes can drive cycling of semi-volatile pollutants between different environmental compartments (e.g. atmosphere, soil, plants). To evaluate the impact of daily temperature changes on atmospheric concentration fluctuations we employed a physically based model coupling soil, plants and the atmosphere, which accounts for heat transport, effective gas diffusion, sorption and biodegradation in the soil as well as eddy diffusion and photochemical oxidation in the atmospheric boundary layer of varying heights. The model results suggest that temperature-driven re-volatilization and uptake in soils cannot fully explain significant diurnal concentration fluctuations of atmospheric pollutants as for example observed for polychlorinated biphenyls (PCBs). This holds even for relatively low water contents (high gas diffusivity) and high sorption capacity of the topsoil (high organic carbon content and high pollutant concentration in the topsoil). Observed concentration fluctuations, however, can be easily matched if a rapidly-exchanging environmental compartment, such as a plant layer, is introduced. At elevated temperatures, plants release organic pollutants, which are rapidly distributed in the atmosphere by eddy diffusion. For photosensitive compounds, e.g. some polycyclic aromatic hydrocarbons (PAHs), decreasing atmospheric concentrations would be expected during daytime for the bare soil scenario. This decline is buffered by a plant layer, which acts as a ground-level reservoir. The modeling results emphasize the importance of a rapidly-exchanging compartment above ground to explain short-term atmospheric concentration fluctuations.

The present study was carried out in Haraz basin (Iran) that is located in south of the Caspian Sea. The goal of this study was to establish correlations amongst total suspended solids concentration (TSS) and turbidity with total pollutant concentrations to evaluate the dissolved and particle-bound concentrations of major toxic metals. It also aimed to validate TSS and/or turbidity measurements as proxies to monitor pollutant fluxes. Eight metals, namely nickel, lead, cadmium, copper, zinc, cobalt, arsenic and strontium were analyzed for dissolved and total concentrations in water at ten locations within the catchment. TSS and turbidity were also measured. Sampling campaigns were designed to cover both the rainy (December) and the dry (May) season within the basin. The robust relationship between TSS (202–1212 mg/l) and turbidity (63–501 NTUs) in both seasons warranted their interchangeable potential as proxies within the observed ranges. Total element concentrations were plotted in separate attempts versus TSS and turbidity for all locations and both events. Very good linear correlations were attained where the slopes represent the metals concentration on suspended solids and the intercept the dissolved concentration in water. The results achieved by these linear regressions were in very good agreement with independently measured values for dissolved concentration and concentrations on river bed sediments taken at the same locations. This demonstrates that turbidity and/or TSS measurements may be used for monitoring of metal loads if once calibrated against total concentration of metals. The results also revealed that in the lower Haraz catchment metal concentrations on suspended and river bed sediment were homogeneously distributed along the investigated river stretch. This is assumed to be due to intensive gravel and sand mining activities in the upper and middle part of the catchment.

Leaching behavior of organic contaminants such as polycyclic aromatic hydrocarbons (PAHs) can be altered in the presence of organic amendments through enhanced sorption of PAHs to the amended soil. The aim of the present study was to investigate the influence of biochar in two forms (i.e., crushed and pulverized), and granular activated carbon on immobilization and leaching behavior of selected PAHs from contaminated soil into water using the column leaching test. The influence of biochar particle size on leaching behavior of PAHs in biochar-amended soil was also evaluated for the first time in this study. Results showed relatively high initial concentrations of naphthalene, fluorene, and pyrene for unamended column (B1). Strong sorption of all PAHs to soil was observed in this study. At the end of the experiment less than one percent of the solid phase content of the sum of PAHs was released into water in columns B3 and B4. Change in pH due to the application of organic amendments did not affect PAH leaching results. The addition of pulverized biochar and granular activated carbon to soil remarkably reduced mobilization and leaching of the studied PAHs in most cases; however, higher molecular weight PAHs (i.e., pyrene, benzo(b)fluoranthene, and indeno(1,2,3cd)) were mobilized in the presence of crushed biochar in soil. The controlling role of biochar particle size on mobilization and release of PAHs in soil was observed. The application of pulverized biochar and activated carbon increased colloid content of the column effluents while reducing their dissolved organic carbon (DOC) content, suggesting a more significant role of colloid-facilitated transport than DOC-associated transport of PAHs in their leaching from carbon-amended soils, particularly for higher molecular weight PAHs. Based on the obtained results, pulverized biochar and granular activated carbon demonstrated promising and comparable performance in immobilizing PAHs in soil and reducing their leaching from soil into water through enhanced sorption of PAH compounds, which is markedly favorable in terms of soil remediation.

One of the best-known and largest karst areas in Germany, the Blautopf Catchment, offers unique access to waters of the unsaturated zone through a large cave system. It was investigated with stable isotopes (18O/16O and D/H ratios expressed in permille = ‰) in precipitation, seepage- and groundwater as tracers for water flow, mixing, and storage. The precipitation showed a distinct seasonality with δ18O values between −2.9 and −24.6‰ during summer and winter, respectively. However, the isotope signals in seepage water in the caves as well as the discharge were almost completely buffered and ranged around an average δ18O value of −10‰. This value was also close to the long-term average value of local precipitation, −9.3‰. The homogeneous isotopic composition of the Blautopf Spring was unexpected, as its highly variable discharge (0.3 to 32 m3 s−1) is typical for a fast responsive karst system. These isotopic similarities could be explained by nearly complete mixing of the water already in the vadose zone. The data set therefore presents a case study to narrow down zones of mixing in karst catchments. It also confirms the minor role of the fast conduit system in the water balance of the Blautopf Catchment.

Interpreting the fate of wastewater contaminants in streams is difficult because their inputs vary in time and several processes synchronously affect reactive transport. We present a method to disentangle the various influences by performing a conservative-tracer test while sampling a stream section at various locations for chemical analysis of micropollutants. By comparing the outflow concentrations of contaminants with the tracer signal convoluted by the inflow time series, we estimated reaction rate coefficients and calculated the contaminant removal along a river section. The method was tested at River Steinlach, Germany, where 38 contaminants were monitored. Comparing day-time and night-time experiments allowed distinguishing photo-dependent degradation from other elimination processes. While photo-dependent degradation showed to be highly efficient for the removal of metroprolol, bisoprolol, and venlafaxine, its impact on contaminant removal was on a similar scale to the photo-independent processes when averaged over 24 h. For a selection of compounds analyzed in the present study, bio- and photodegradation were higher than in previous field studies. In the Steinlach study, we observed extraordinarily effective removal processes that may be due to the higher proportion of treated wastewater, temperature, DOC and nitrate concentrations, but also a higher surface to volume ratio from low flow conditions that favorizes photodegradation through the shallow water column and a larger transient storage than observed in comparable studies. ISSN:0048-9697 ISSN:1879-1026

Water scarcity is a serious environmental problem in many European regions, and will likely increase in the near future as a consequence of increased abstraction and climate change. Water scarcity exacerbates the effects of multiple stressors, and thus results in decreased water quality. It impacts river ecosystems, threatens the services they provide, and it will force managers and policy-makers to change their current practices. The EU-FP7 project GLOBAQUA aims at identifying the prevalence, interaction and linkages between stressors, and to assess their effects on the chemical and ecological status of freshwater ecosystems in order to improve water management practice and policies. GLOBAQUA assembles a multidisciplinary team of 21 European plus 2 non-European scientific institutions, as well as water authorities and river basin managers. The project includes experts in hydrology, chemistry, biology, geomorphology, modelling, socio-economics, governance science, knowledge brokerage, and policy advocacy. GLOBAQUA studies six river basins (Ebro, Adige, Sava, Evrotas, Anglian and Souss Massa) affected by water scarcity, and aims to answer the following questions: how does water scarcity interact with other existing stressors in the study river basins? How will these interactions change according to the different scenarios of future global change? Which will be the foreseeable consequences for river ecosystems? How will these in turn affect the services the ecosystems provide? How should management and policies be adapted to minimise the ecological, economic and societal consequences? These questions will be approached by combining data-mining, field- and laboratory-based research, and modelling. Here, we outline the general structure of the project and the activities to be conducted within the fourteen work-packages of GLOBAQUA., This work has been supported by the European Communities 7th Framework Programme Funding under Grant agreement no. 603629- ENV-2013-6.2.1-Globaqua and by the Generalitat de Catalunya (Consolidated Research Groups “2014 SGR 418 - Water and Soil Quality Unit” and 2014 SGR 291 - ICRA). Damià Barceló acknowledges support from the Visiting Professor Program of King Saud University. Special thanks are due to all partners of the GLOBAQUA consortium and the peer review panel for ensuring quality results and fruitful collaboration within the project.

Significance It has remained an unresolved question whether microorganisms recovered from the most arid environments on Earth are thriving under such extreme conditions or are just dead or dying vestiges of viable cells fortuitously deposited by atmospheric processes. Based on multiple lines of evidence, we show that indigenous microbial communities are present and temporally active even in the hyperarid soils of the Atacama Desert (Chile). Following extremely rare precipitation events in the driest parts of this desert, where rainfall often occurs only once per decade, we were able to detect episodic incidences of biological activity. Our findings expand the range of hyperarid environments temporarily habitable for terrestrial life, which by extension also applies to other planetary bodies like Mars., Traces of life are nearly ubiquitous on Earth. However, a central unresolved question is whether these traces always indicate an active microbial community or whether, in extreme environments, such as hyperarid deserts, they instead reflect just dormant or dead cells. Although microbial biomass and diversity decrease with increasing aridity in the Atacama Desert, we provide multiple lines of evidence for the presence of an at times metabolically active, microbial community in one of the driest places on Earth. We base this observation on four major lines of evidence: (i) a physico-chemical characterization of the soil habitability after an exceptional rain event, (ii) identified biomolecules indicative of potentially active cells [e.g., presence of ATP, phospholipid fatty acids (PLFAs), metabolites, and enzymatic activity], (iii) measurements of in situ replication rates of genomes of uncultivated bacteria reconstructed from selected samples, and (iv) microbial community patterns specific to soil parameters and depths. We infer that the microbial populations have undergone selection and adaptation in response to their specific soil microenvironment and in particular to the degree of aridity. Collectively, our results highlight that even the hyperarid Atacama Desert can provide a habitable environment for microorganisms that allows them to become metabolically active following an episodic increase in moisture and that once it decreases, so does the activity of the microbiota. These results have implications for the prospect of life on other planets such as Mars, which has transitioned from an earlier wetter environment to today’s extreme hyperaridity.

Flow-through experiments were performed in a newly designed experimental setup to study the water–rock interactions caused by CO 2 injection in sandstones obtained from the Altmark natural gas reservoir under the simulated reservoir conditions of 125 °C and 50 bar CO 2 partial pressure. Two different sets of experiments were conducted using CO 2 -saturated millipore water and CO 2 -saturated brine (41.62 g L −1 NaCl and 31.98 g L −1 CaCl 2 ·2H 2 O), mimicking the chemical composition of the reservoir formation water. The major components in the sandstone were quartz (clasts + cement), feldspars, clay minerals (illite and chlorite), and cements of carbonates and anhydrite. Fluid analysis suggested the predominant dissolution of anhydrite causing increased concentrations of calcium and sulfate at early time periods at non-equilibrium geochemical conditions. The Ca/SO 4 molar ratio (>1) indicated the concurrent dissolution of both calcite and anhydrite. Dissolution of feldspar and minor amounts of clay (chlorite) was also evident during the flow-through experiments. The permeability of the sample increased by a factor of two mostly due to the dissolution of rock cements during brine injection. Geochemical modeling suggests calcite dissolution as the major buffering process in the system. The results may in future studies be used for numerical simulations predicting CO 2 storage during injection in sandstone reservoirs.

Compound-specific isotope analysis (CSIA) of organic pollutants has become a well-established tool for assessing the occurrence and extent of biodegradation processes in contaminated aquifers. However, the precision of CSIA is influenced by the degree to which assumptions underlying CSIA data interpretation hold under realistic field-scale conditions. For the first time this study demonstrates how aquifer analogs combined with reactive transport models offer an underexplored way to develop generic process understanding, evaluate monitoring and quantification strategies in highly heterogeneous subsurface settings. Data from high-resolution aquifer analogs were used in numerical experiments to track the propagation of a representative oxidizable organic compound (toluene) within a variety of realistic heterogeneous aquifers and to investigate its detailed fate. The simulations were used to analyze (1) the effects of physical aquifer heterogeneities on spatiotemporal patterns of contaminant concentrations and isotope signatures, (2) the performance of the commonly applied Rayleigh equation and (3) the applicability of an extension of the Rayleigh equation for complex hydrogeological conditions. The results indicate that if field-derived enrichment factors are applied without corrections for dilution, the conventional Rayleigh equation is inaccurate and estimates for biodegradation are typically overestimated and unreliable in heterogeneous aquifers. Underestimations can occur due to the partial source zone depletion. In contrast, if dilution can be accurately accounted for, field-derived enrichment factors comprise a suitable alternative to laboratory-derived and redox-specific enrichment factors. The study also examines to what extent variations in monitoring/sampling strategies influence the obtained results. Especially measurements from long-screened wells (> 1 m) reveal to be inappropriate for the application of the Rayleigh equation in the investigated aquifer analogs, as low resolution data sampled from the simulated scenarios only enable a qualitative assessment of biodegradation. Measurements from both long- and short-screened wells employing the Rayleigh equation streamline approach are only partly viable for in situ biodegradation measurements in heterogeneous systems.

In aqueous environments, hydrophobic organic contaminants are often associated with particles. Besides natural particles, microplastics have raised public concern. The release of pollutants from such particles depends on mass transfer, either in an aqueous boundary layer or by intraparticle diffusion. Which of these mechanisms controls the mass-transfer kinetics depends on partition coefficients, particle size, boundary conditions, and time. We have developed a semianalytical model accounting for both processes and performed batch experiments on the desorption kinetics of typical wastewater pollutants (phenanthrene, tonalide, and benzophenone) at different dissolved-organic-matter concentrations, which change the overall partitioning between microplastics and water. Initially, mass transfer is externally dominated, while finally, intraparticle diffusion controls release kinetics. Under boundary conditions typical for batch experiments (finite bath), desorption accelerates with increasing partition coefficients for intraparticle diffusion, while it becomes independent of partition coefficients if film diffusion prevails. On the contrary, under field conditions (infinite bath), the pollutant release controlled by intraparticle diffusion is not affected by partitioning of the compound while external mass transfer slows down with increasing sorption. Our results clearly demonstrate that sorption/desorption time scales observed in batch experiments may not be transferred to field conditions without an appropriate model accounting for both the mass-transfer mechanisms and the specific boundary conditions at hand.

Suspended particles in rivers can act as carriers of potentially bioavailable metal species and are thus an emerging area of interest in river system monitoring. The delineation of bulk metals concentrations in river water into dissolved and particulate components is also important for risk assessment. Linear relationships between bulk metal concentrations in water (CW,tot) and total suspended solids (TSS) in water can be used to easily evaluate dissolved (CW, intercept) and particle-bound metal fluxes (CSUS, slope) in streams (CW,tot = CW + CSUS TSS). In this study, we apply this principle to catchments in Iran (Haraz) and Germany (Ammer, Goldersbach, and Steinlach) that show differences in geology, geochemistry, land use and hydrological characteristics. For each catchment, particle-bound and dissolved concentrations for a suite of metals in water were calculated based on linear regressions of total suspended solids and total metal concentrations. Results were replicable across sampling campaigns in different years and seasons (between 2013 and 2016) and could be reproduced in a laboratory sedimentation experiment. CSUS values generally showed little variability in different catchments and agree well with soil background values for some metals (e.g. lead and nickel) while other metals (e.g. copper) indicate anthropogenic influences. CW was elevated in the Haraz (Iran) catchment, indicating higher bioavailability and potential human and ecological health concerns (where higher values of CSUS/CW are considered as a risk indicator).

Atmospheric deposition leads to accumulation of atmospheric polycyclic aromatic hydrocarbons (PAHs) on urban surfaces and topsoils. To capture the inherent variability of atmospheric deposition of PAHs in Shanghai's urban agglomeration, 85 atmospheric bulk deposition samples and 7 surface soil samples were collected from seven sampling locations during 2012–2014. Total fluxes of 17 PAHs were 587-32,300 ng m −2 day −1 , with a geometric mean of 2600 ng m −2 day −1 . The deposition fluxes were categorized as moderate to high on a global scale. Phenanthrene, fluoranthene and pyrene were major contributors. The spatial distribution of deposition fluxes revealed the influence of urbanization/industrialization and the relevance of local emissions. Meteorological conditions and more heating demand in cold season lead to a significant increase of deposition rates. Atmospheric deposition is the principal pathway of PAHs input to topsoils and the annual deposition load in Shanghai amounts to ∼4.5 tons (0.7 kg km −2 ) with a range of 2.5–10 tons (0.4–1.6 kg km −2 ).

The contamination of riverine sediments and suspended matter with hydrophobic pollutants is typically associated with urban land use. However, it is rarely related to the sediment supply of the watershed, because sediment yield data are often missing. We show for a suite of watersheds in two regions of Germany with contrasting land use and geology that the contamination of suspended particles with polycyclic aromatic hydrocarbons (PAH) can be explained by the ratio of inhabitants residing within the watershed and the watershed's sediment yield. The modeling of sediment yields is based on the Revised Universal Soil Loss Equation (RUSLE2015, Panagos et al., 2015) and the sediment delivery ratio (SDR). The applicability of this approach is demonstrated for watersheds ranging in size from 1.4 to 3000km2. The approach implies that the loading of particles with PAH can be assumed as time invariant. This is indicated by additional long-term measurements from sub-watersheds of the upper River Neckar basin, Germany. The parsimonious conceptual approach allows for reasonable predictions of the PAH loading of suspended sediments especially at larger scales. Our findings may easily be used to estimate the vulnerability of river systems to particle-associated urban pollutants with similar input pathways as the PAH or to indicate if contaminant point sources such as sites of legacy pollution exist in a river basin.

Lateral mass exchange at the fringe of solute plumes is a fundamental process leading to plume dilution and reactive mixing. Mass transfer between the plume and ambient water can be considerably enhanced by helical flow occurring in three-dimensional heterogeneous anisotropic porous media [1-3]. We performed steady-state conservative tracer experiments in a fully three-dimensional flow-through chamber to investigate the effects of helical flow on plume spiraling and deformation, as well as on its dilution [4]. Helical flow was created by packing the porous medium in angled stripes of materials with different grain sizes to create blocks with macroscopically anisotropic hydraulic conductivity. The hydraulic conductivity of the blocks was varied in different experiments. Solute concentrations and flow rates were measured at high spatial resolution for samples collected at 49 outlet ports. This allowed us to quantify spreading and dilution of the solute plumes at the outlet cross section. Moreover, we collected direct evidence of plume spiraling and visual proof of helical flow by freezing and slicing the porous medium at different cross sections and observing the dye-tracer distribution. Model-based interpretation of the results allowed substantiating the effect of the helical flow field on plume dilution and on mixing-controlled reactive transport. The simulation results were evaluated using metrics of reactive mixing such as the critical dilution index and the length of continuously injected steady-state plumes.