The concentration of trifluoroacetic acid in surface and groundwaters and drinking water is subject of increasing concern. Since there is no standardised procedure available, German standardisation body DIN has initiated the first draft standard using liquid chromatography with tandem mass spectrometry (LC–MS/MS) after direct injection for the concentration range between ≥ 0.1 and 3 µg/L. Herein, the interlaboratory comparison as final validation step involving 12 expert laboratories from Germany and Switzerland is described. Two groundwaters, two surface waters, a drinking water, a rainwater, and two fortified groundwater samples displayed relative repeatability standard deviations between 3 and 7% and relative reproducibility standard deviation between 6 and 20% and were included in the draft standard DIN 38407-53.
Drinking water enters buildings with a given microbiological community composition. Within premise plumbing systems, the drinking water is subject to very different conditions and temperatures. Whereas part of the water stays cold, another part is heated to provide hot water. In this study, drinking water samples were taken at different locations in four buildings that had central heating circles and that were equipped with ultrafiltration modules. The latter were intended to keep bacterial numbers low. When studying the increase in bacterial concentrations in these water samples using regrowth tests at different incubation temperatures, a temperature-dependence could be observed. Bacteria in cold water samples propagated best when incubated at 22°C, but often poorly at 36°C and not at all at 50°C. Bacteria in hot water samples showed the reverse behavior and grew best when incubated at 50°C, whereas growth at 22°C was poor or associated with a long growth lag. Water samples from distal taps in periphery locations used for retrieving both cold and hot water showed intermediate growth behaviors. Results suggest the existence of different temperature-adapted bacterial populations within domestic drinking water systems. The finding was supported by sequence data revealing distinct differences in the microbiomes between cold and hot water samples. Abundant bacterial groups in hot water included Deinococci, Kryptonia, Ignavibacteria, Nitrospiria, Gemmatimonadetes and different genera of Gammaproteobacteria. Stagnation of hot water at 50°C, 55°C, or 60°C furthermore shaped the microbiome in different ways indicating that small temperature differences can have a substantial impact on the bacterial communities.
The fraction of precipitation that infiltrates soils and subsequently becomes recharge is one of the principle components of an unconfined aquifer's water budget (this fraction is here termed recharge efficiency). Here we tested how recharge efficiency will respond to climate change including a possible plant physiological response to climate change (e.g., stomatal closure; increasing leaf area) in a catchment used for drinking water production in western Germany. To this end we used a soil water model (HYDRUS‐1D) forced with climate data spanning the time period from 1971 to 2099. Three different vegetation types were considered: turf grass representing the primary infiltration sites within residential areas; maize representing the main crop on agriculturally used land; and beech representing the forested parts of the catchment. We found that, the positive effects of climate change on recharge efficiency (more rain during the main recharge season in winter, less crop water demand due to faster plant ripening in spring and summer, increased plant water use efficiency, reduced global radiation as cloud density increases) were not completely compensated by the negative effects (less precipitation, higher leaf area index and increasing vapour pressure deficit in summer season) at our study site. Because total annual precipitation increased slightly until the end of the 21th century, changes in the amount of total annual recharge were also positive, though moderate (up to +20% change in the period 2071–2099 as compared to 1970–2000). The results of this study will be helpful for water authorities managing water rights under the perspective of a changing climate. In the future, our study site is expected to receive sufficient recharge from precipitation to maintain current rates of groundwater withdrawal for public water supply and irrigation. Thus, the region's agriculture sector may become a ‘global warming winner,’ when cropping in other regions in Europe may increasingly suffer from drying conditions during the growing season.
Denitrification in soils and aquifers sustains low nitrate concentrations in many anaerobic groundwaters despite massive inputs of N from agriculture. However, this ecosystem service sometimes comes at the cost of trace metal mobilization and concerns have been raised that denitrification in anaerobic groundwater may lead to trace metal contamination. But it remains unclear, if denitrification must necessarily result in trace metal concentrations that are potentially harmful for humans. For example, formation of iron(oxy)hydroxides after the reaction of nitrate with pyrite may reduce rather than increase the mobility of certain trace metals in aquifers. We quantified the potential health risk resulting from denitrification-associated trace metal pollution (Mn, Ni, As, Cd, U) in anaerobic groundwater with different degrees of nitrate pollution in >800 wells located in Northern Germany. Overall, observed rates of violations of legal quality standards for U, As and Cd are moderate in the study area (<10% of all wells) but elevated for Mn (>50%), which is a common contaminant under the often anaerobic conditions in the study area. However, in groundwater where denitrification had partially proceeded, the risk for drinking water standard violations was higher for Ni, Cd and U (up to a factor of 4 for Ni) as compared to anaerobic groundwater without denitrification, but lower for Mn and As. Especially poorly buffered groundwaters with pH < 5.5 are at risk of Ni and Cd contamination resulting from denitrification, while the opposite is true for Mn and U. Thus, we establish a clear linkage between nitrogen biogeochemistry and trace metal mobility and show how perturbations of groundwater redox and pH conditions by nitrate can further deteriorate groundwater quality. In addition, we find that the combination of oxygen concentrations of lower than 1 mg L−1, and nitrate concentrations above 1 mg L−1 allows for identification of denitrification (as evidenced by excess N2 in groundwater) with 90% accuracy. The methodology developed herein can be used to inform water treatment planning about potential trace metal contamination when drinking water should be produced from anaerobic aquifers beneath agricultural landscapes.
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.
