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Applications of nitrification and urease inhibitors (NUI) with nitrogen fertilisers on agricultural soils are intended to improve the efficiency of nitrogen fertilisers and also to prevent nitrogen emissions from the fertilisers. However, the deliberate release of chemicals into the environment carries a certain degree of risk due to spreading in the water systems. Both sensitive ecosystems and water supplies may be affected. Processes that need to be considered for a reliable assessment regarding the fate and distribution of these substances in the different compartments are manifold. So far, reliable predictions in literature are scarce and regulatory approaches are based on limited information on substance fate.Yet, two out of the ten NUIs currently approved in Germany, have been found in surface waters, prompting further investigation. In this context, no analytical method has been established so far for some of the other NUIs, thus there is no information available on the occurrence of these substances. In order to gain transparency on the actual environmental fate and implications for drinking water production of these NUI has been analyzed In addition to legal approval procedure different processes and scenarios relevant to their fate were investigated in the INHIBIT project.Following a comprehensive literature review, experimental investigations were carried out to further evaluate the environmental behaviour of these substances on an empirical basis. Initially, a multi-method was developed for the simultaneous determination of 1H-1,2,4-triazole (triazole), dicyandiamide (DCD), 3,4-Dimethylpyrazol-phosphate (DMPP), 3-Methylpyrazole (3-MP), N-(n-butyl)thiophosphoric triamide (NBPT) and N-(2-nitrophenyl)phosphoric triamide (2-NPT) in soil pore water. Experiments conducted in this research project provided essential empirical information on the hydrolysis stability, degradation behaviour and sorption tendency in soils for selected NUI. In addition, vessel, column, lysimeter and practical field application tests were carried out to obtain empirical information on the leaching risk of these substances via the transport pathway unsaturated zone-leachate-groundwater. Furthermore, the indirect input pathway via infiltrating surface waters (bank filtration) was investigated. Studies were carried out on different soils and using different parameters in order to depict different site conditions.Results indicated a high hydrolysis stability for the nitrification inhibitors (NI) DCD, DMPP, 3-MP and triazole. The hydrolysis stability of the urease inhibitors (UIs) NBPT and 2-NPT is strongly pH-dependent. While NBPT is particularly unstable in an acidic environment, 2-NPT shows the lowest stability in a more alkaline environment. Sorption tendency to soils of all compounds was low. Microbial degradation of NI in soils was lower compared to urease inhibitors (UIs). Overall, the NI triazole, DCD, 3-MP and DMPP were found to be potentially relevant substances for drinking water production. The NI active substances DCD and triazole were additionally monitored in several surface waters and were frequently detected, in some cases at very high concentrations of several µg/L. These findings underline the relevance of these substances for water resources.

Biogeochemical redox processes control the chemical behavior of many major and trace elements, making their comprehension crucial for predicting and protecting environmental health. Nitrogen (N) is especially susceptible to changes in soil redox conditions and affects the cycles of other redox-sensitive species. Elevated N concentrations, in nitrate form, in agricultural soils and associated freshwater ecosystems constitute a problem in many parts of the world. Although a wide variety of measures have been adopted, their assessment through concentration measurements in groundwater and surface water of the different monitoring networks has shortcomings. Nitrate, as a non-point pollutant, is subject to several processes (e.g., transformation and retardation) before it is detected, making it impossible to evaluate measurements' effectiveness reliably. Thus, we designed and constructed a monitoring station featuring commercially available products and self-manufactured components at an agricultural site for the in situ assessment of nitrate-related processes by high-resolution monitoring of hydraulic (soil water content, matric potential, groundwater head) and hydrogeochemical variables (oxidation-reduction potential and groundwater and pore water chemistry) within the vadose zone and the shallow aquifer. The monitoring station has proven to be a reliable tool. Changes over depth and time of measured variables have been identified, allowing the detection of the transient behavior of the redox reactive zone and the interpretation of ongoing denitrification processes and other redox nitrate-triggered phenomena, such as uranium roll-front and selenium accumulation at the redox interface. Measuring both geochemical and soil water variables allows for the calculation of in situ solute inputs into the groundwater and their reaction rates.

A possible adaptation pathway for water suppliers in Germany who face a climatically driven increase in water stress is the development of aquifers which are not used at their full potential. However, identifying suitable sites for aquifer development can go along with severe conflict potential due to the great variety of stakeholders who are involved in the decision-making process. We approach this multi-actor and multi-criteria decision-making problem by developing a geoinformation system-based analytic hierarchy process ensemble (GIS-AHP ensemble). As opposed to the classic GIS-AHP method that yields ratings of site suitability based on a single expert evaluation, the here proposed new GIS-AHP ensemble method respects multiple expert evaluations and allows for quantifying the robustness of yielded site ratings in multi-actor contexts, which helps to mitigate conflict potential. The respectively derived GIS-AHP ensemble site ratings for northwest Germany are successfully checked for plausibility in the framework of the study by using long-established groundwater abstraction areas as indicators for good site conditions. The GIS-AHP ensemble site ratings are further tested regarding their usability for long-term water supply planning by integrating a groundwater recharge scenario under climate change for the period 2020 to 2050. The proposed GIS-AHP ensemble methodology proves useful in the given case study for fostering integrated environmental decision-making and exhibits a high transferability to other, thematically differing site selection problems.

As more regions in the world look to replenish depleted aquifers, treated wastewater (TWW) is increasingly infiltrated in managed aquifer recharge (MAR) schemes. While MAR is a promising emerging technology, it also has the potential to generate pollutants along the infiltration flow path. In this study, we infiltrated treated wastewater through an organic-rich soil in column experiments operated with wetting and drying cycles. Ammonium, which was present only in trace concentrations in the TWW, increased in concentration with depth and exceeded the EU Water Framework Directive limit of 0.5 mg/L for up to a year, depending on the sampling depth. Pore water samples collected at the end of drying periods showed very high nitrate concentrations, indicating nitrification of some of the ammonium. Oxidation reduction potential often exceeded 200 mV during drying periods, showing conditions for nitrification, but dropped below −100 mV during wetting periods, creating several possible pathways for ammonium production. Potential sources of ammonium are (1) dissolved organic nitrogen in the TWW, (2) nitrate in the TWW, and (3) organic nitrogen in the soil. δ15N in ammonium in pore water samples (mean 4.7‰) was slightly higher than δ15N in the soil (2.4‰), indicating that the soil was likely the major source but also that nitrate (mean 17.2‰) may have been the source of some of the ammonium. Fractionation of 15N in nitrate as well as high concentrations of acetate (a labile organic carbon source) also indicate that dissimilatory nitrate reduction to ammonium may have formed some of the NH4+.

Most of the knowledge on the occurrence of Uranium (U) in groundwater comes from in-situ manipulation experiments in the field, computational modelling studies or from laboratory analyses where individual processes of U mobilization were studied in isolation. Because of Uranium's vital redox chemistry it interacts, often simultaneously, with many other element cycles (e.g., sulfur, carbon, iron, and manganese) making it difficult to predict U concentrations in natural environments. For the present study a large data set was analyzed to predict the occurrence of U in groundwater from basic hydrochemistry. The data set consists of more than 8000 chemical groundwater analyses (including Uranium concentrations) from more than 2000 sampling locations. A strong relation between U concentrations and electric conductivity as well as alkalinity was observed, suggesting that weathering of geogenic source material and desorption from mineral surfaces is the principle mechanism of U release. Except for aquifers with strongly reducing conditions this process leads to a slow but continuous accumulation of U in groundwater in most cases. Importantly, the occurrence of U is modulated by the prevailing redox conditions in an aquifer. Uranium concentrations were moderate under oxic conditions and highest under manganese and nitrate-reducing conditions (heterotrophic as wells as autotrophic nitrate reduction). Only in iron- and sulfate-reducing groundwater the probability of U concentrations above 1 μg l−1 was virtually zero, as these ground waters act as U sinks. The combination of mineral weathering (especially carbonates) with mobilization of U under manganese and nitrate reducing conditions results in the highest risk of detecting U. In contrast, a low risk is associated with low pH (

Uranium (U) concentrations in groundwater extracted for drinking water usage from a Quaternary fluvial aquifer partly exceed the German drinking water guideline of 10μgL-1. Responsible sources and mobilization processes were unknown and gave rise to this study. Land use of the watershed is mainly agricultural leading to groundwater nitrate concentrations >50mgL-1 and a need for water treatment prior to utilization as drinking water. This is successfully accomplished by addition of nutrients triggering bacterial nitrate reduction, followed by the addition of NaOH for water softening and CO2 for pH adjustment, with subsequent reinfiltration into the aquifer. Three boreholes were drilled to obtain a total of 127 solid samples from Quaternary and underlying Tertiary sediments. Geochemistry and mineralogy were assessed using elemental analysis (CS, ICP-MS), X-ray diffraction and scanning electron microscopy to complement hydrochemical data and unravel U occurrence in the subsurface. Solid phase U fractionation was characterized by a sequential extraction procedure, U remobilization potential by a 137days column experiment. Shallow Quaternary sediments yielded low U contents 10μgL-1 almost exclusively appear in this same depth range, and only in wells influenced by water treatment runoff. Results suggest that the applied water treatment approach triggers U remobilization from geogenic sources in the aquifer. The most probable mechanism is dissolution of U bearing calcite induced by CO2 application; redox reactions and pH-driven desorption appear to play a minor role in mobilization. We conclude that groundwater treatment should carefully account for unwanted hydrogeochemical side effects triggering the mobilization of geogenic trace elements such as uranium.

Karstsysteme mit einem allogenen Zufluss uber Schwinden zeigen oft komplexe Netzwerke interagierender Karstwegsamkeiten. Zur Analyse der hydrodynamischen Funktionsweise solcher Karstaquifere wurde am Beispiel des Tanneben-Massivs ein Strukturmodell entwickelt, welches die Karstantwort auf hydraulische und hydrochemische Signale als Mischung unterschiedlicher Abflusskomponenten berechnet. Strukturparameter, wie die Anzahl der Flieswege und die Aktivierungssequenz, wurden anhand von Tracerexperimenten abgeleitet. Dazu wurden Tracerdurchbruchskurven hinsichtlich der zeitlichen Auspragung von Multipeaks in Abhangigkeit von den wahrend der Experimente vorherrschenden Stromungsbedingungen analysiert. Mittels Modellrechnungen konnte fur das Tanneben-Massiv gezeigt werden, dass die Stoffausbreitung im Karstnetzwerk sowie die Stoffkonzentrationen an der Karstquelle durch die Stromungsbedingungen in einem Zeitraum vor und nach der Injektion beeinflusst werden. Grund hierfur ist die durch den strukturellen Aufbau solcher Karstsysteme bedingte Aufteilung des Grundwasserstroms auf Fliespassagen unterschiedlicher hydraulischer Eigenschaften. So werden bei einem hohen Zufluss Karstwegsamkeiten aktiviert, welche das Lurbach-Hammerbach-Abflusssystem mit dem weiter nordlich gelegenen Schmelzbach-System verbinden. Beim Uberschreiten der Durchflusskapazitat des Karstsystems infolge von Starkregenereignissen oder durch die Blockade von Fliespassagen kommt es zu einem Ruckstau im Bereich der Schwinde und damit einer Verlangerung der Abflussphase an der Karstquelle.

A structure model was used to analyse solute-transport parameter estimates based on tracer breakthrough curves. In the model system, groundwater flow is envisioned to be organised in a complex conduit network providing a variety of short circuits with relative small carrying capacities along different erosion levels. The discharge through the fully filled conduits is limited owing to void geometries and turbulent flow; thus, a hierarchic overflow system evolves where conduits are (re-)activated or dried up depending on the flow condition. Exemplified on the Lurbach–Tanneben karst aquifer, the applicability of the model approach was tested. Information derived from multi-tracer experiments performed at different volumetric flow rates enabled to develop a structural model of the karst network, under constraint of the geomorphological and hydrological evolution of the site. Depending on the flow rate, groundwater is divided into up to eight flow paths. The spatial hierarchy of flow paths controls the sequence of flow path activation. Conduits of the topmost level are strongly influenced by reversible alteration processes. Sedimentation or blocking causes an overflow of water to the next higher conduit. Flow path specific dissolutional denudation rates were estimated using the temporal development of the partial discharge. Copyright © 2012 John Wiley & Sons, Ltd.

In vielen Wassergewinnungsgebieten wird die chemische Beschaffenheit der Grund- und Rohwasser entscheidend durch die Reaktion von organisch gebundenem Kohlenstoff (OC) mit den im Grundwasser gelosten Oxidationsmitteln O2(aq), Nitrat und Sulfat beeinflusst. Die Redoxreaktionen zwischen dem Reduktionsmittel OC und den Oxidationsmitteln folgen zwar thermodynamischen Gesetzmasigkeiten, sind aber kinetisch gehemmt. Um die Entwicklung der Grund- und Rohwasserqualitat mithilfe eines reaktiven Stofftransportmodells berechnen zu konnen, muss die Reaktionskinetik des organisch gebundenen Kohlenstoffs berucksichtigt werden. Am Beispiel des Wassergewinnungsgebietes Forstwald (Krefeld) wird praxisnah gezeigt, wie die Reaktionskinetik von OC aus routinemasig durch den Wasserversorger erhobenen Daten zur Grundwasserbeschaffenheit abgeleitet und in ein reaktives Stofftransportmodell (PhreeqC) implementiert werden kann. Die chemisch-thermodynamisch basierte Berechnung der Verteilung aquatischer Spezies im Gleichgewicht mit Mineral- und Gasphasen wird mit einer doppelten Michaelis-Menten-Kinetik fur den oxidativen Abbau feststoffgebundener organischer Kohlenstoffverbindungen gekoppelt. Anhand von Messwerten zur raumlich-zeitlichen Entwicklung der Grundwasserbeschaffenheit wird der Ansatz auf Plausibilitat gepruft.

In many countries bank filtration is used as the first step of drinking water treatment. River water percolates the riverbed and aquifer sediments which serve as a natural filter removing substances like nitrate, particular and dissolved organic matter and trace elements. Raw water quality, therefore, depends on both river water quality as well as hydrogeochemical processes within the sediment. Exemplified by the case study of Auf dem Grind, Well II (Dusseldorf, Germany), the geohydraulic and hydrogeochemical processes of a catchment area that is strongly influenced by bank filtration were investigated. Raw water extracted from Well II showed significantly elevated manganese concentrations compared to river water and to raw water from other wells in the catchment area. A reactive transport model was developed for retracing the measured raw water quality. Retrospective modeling revealed the principles of long and midterm changes in raw water quality, especially fluctuations in manganese concentrations. Based on the model-scenario, the effects of varying river water qualities and/or agricultural fertilization practices can be predicted. The quantitative understanding of coupled hydrogeochemical and hydraulic processes enables the development of sustainable strategies optimizing raw water quality, e. g. with regard to a cost effective water treatment.