Person: Gräff, Thomas
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Veröffentlichung Impact of river reconstruction on groundwater flow during bank filtration assessed by transient three-dimensional modelling of flow and heat transport(2019) Wang, Wei-shi; Gräff, Thomas; Oswald, Sascha E.Bank filtration (BF) is an established indirect water-treatment technology. The quality of water gained via BF depends on the subsurface capture zone, the mixing ratio (river water versus ambient groundwater), spatial and temporal distribution of subsurface travel times, and subsurface temperature patterns. Surface-water infiltration into the adjacent aquifer is determined by the local hydraulic gradient and riverbed permeability, which could be altered by natural clogging, scouring and artificial decolmation processes. The seasonal behaviour of a BF system in Germany, and its development during and about 6 months after decolmation (canal reconstruction), was observed with a long-term monitoring programme. To quantify the spatial and temporal variation in the BF system, a transient flow and heat transport model was implemented and two model scenarios, 'with' and 'without' canal reconstruction, were generated. Overall, the simulated water heads and temperatures matched those observed. Increased hydraulic connection between the canal and aquifer caused by the canal reconstruction led to an increase of ~23% in the already high share of BF water abstracted by the nearby waterworks. Subsurface travel-time distribution substantially shifted towards shorter travel times. Flow paths with travel times <200 days increased by ~10% and those with <300 days by 15%. Generally, the periodic temperature signal, and the summer and winter temperature extrema, increased and penetrated deeper into the aquifer. The joint hydrological and thermal effects caused by the canal reconstruction might increase the potential of biodegradable compounds to further penetrate into the aquifer, also by potentially affecting the redox zonation in the aquifer. © 2019 Springer Nature Switzerland AGVeröffentlichung Heart rate as an early warning parameter and proxy for subsequent mortality in Danio rerio embryos exposed to ionisable substances(2022) Schweizer, Mona; Gräff, Thomas; Kühnen, Ute; von der Ohe, Peter C.Environmental risk assessments of organic chemicals usually do not consider pH as a key factor. Hence, most substances are tested at a single pH only, which may underestimate the toxicity of ionisable substances with a pKa in the range of 4-10. Thus, the ability to consider the pH-dependent toxicity would be crucial for a more realistic assessment. Moreover, there is a tendency in acute toxicity tests to focus on mortality only, while little attention is paid to sublethal endpoints. We used Danio rerio embryos exposed to ten ionisable substances (the acids diclofenac, ibuprofen, naproxen and triclosan and the bases citalopram, fluoxetine, metoprolol, propranolol, tramadol and tetracaine) at four external pH levels, investigating the endpoints mortality (LC50) and heart rate (EC20). Dose-response curves were fitted with an ensemble-model to determine the true uncertainty and variation around the mean endpoints. The ensemble considers eight (heart rate) or twelve (mortality) individual models for binominal and Poisson distributed data, respectively, selected based on the Akaike Information Criterion (AIC). In case of equally good models, the mean endpoint of all models in the ensemble was calculated, resulting in more robust ECx estimates with lower 'standard errors' as compared to randomly selected individual models. We detected a high correlation between mortality (LC50) at 96 hpf and reduced heart rate (EC20) at 48 hpf for all compounds and all external pH levels (r = 0.98). Moreover, the observed pH-dependent effects were strongly associated with log D and thus, likely driven by differences in uptake (toxicokinetic) rather than internal (toxicodynamic) processes. Prospectively, the a priori consideration of pH-dependent effects of ionisable substances might make testing at different pH levels redundant, while the endpoint of mortality might even be replaced by a reliable sublethal proxy that would reduce the exposure, accelerating the evaluation process. © 2021 The AuthorsVeröffentlichung An assessment of mercury and its dietary drivers in fur of Arctic wolves from Greenland and High Arctic Canada(2022) Sinding, Mikkel-Holger S.; Gräff, Thomas; Czirják, Gábor Á.; Treu, GabrieleMercury has become a ubiquitous hazardous element even ending up in pristine areas such as the Arctic, where it biomagnifies and leaves especially top predators vulnerable to potential health effects. Here we investigate total mercury (THg) concentrations and dietary proxies for trophic position and habitat foraging ((delta)15N and (delta)13C, respectively) in fur of 30 Arctic wolves collected during 1869-1998 in the Canadian High Arctic and Greenland. Fur THg concentrations (mean +/- SD) of 1.46 +/- 1.39 (micro)g g -1 dry weight are within the range of earlier reported values for other Arctic terrestrial species. Based on putative thresholds for Hg-mediated toxic health effects, the studied Arctic wolves have most likely not been at compromised health. Dietary proxies show high dietary plasticity among Arctic wolves deriving nutrition from both marine and terrestrial food sources at various trophic positions. Variability in THg concentrations seem to be related to the wolves' trophic position rather than to different carbon sources or regional differences (East Greenland, the Foxe Basin and Baffin Bay area, respectively). Although the present study remains limited due to the scarce, yet unique historic study material and small sample size, it provides novel information on temporal and spatial variation in Hg pollution of remote Arctic species. © 2022 The AuthorsVeröffentlichung Water budget and the role of land-sea interactions of a coastal wetland at the German Baltic Coast(2017) Gräff, Thomas; Bronstert, Axel; Oswald, Sascha E.; Alroggen, NiklasVeröffentlichung How can we model subsurface stormflow at the catchment scale if we cannot measure it?(2018) Chifflard, Peter; Blume, Theresa; Märker, Katja; Gräff, ThomasVeröffentlichung LogD-based modelling and "Delta"logD as a proxy for pH-dependent action of ionizable chemicals reveal the relevance of both neutral and ionic species for fish embryotoxicity and possess great potential for practical application in the regulation of chemicals(2023) Köhler, Heinz R.; Gräff, Thomas; Schweizer, Mona; Maletzki, Dirk; Kühnen, Ute; von der Ohe, Peter C.Depending on the ambient pH, ionizable substances are present in varying proportions in their neutral or charged form. The extent to which these two chemical species contribute to the pH-dependant toxicity of ionizable chemicals and whether intracellular ion trapping has a decisive influence in this context is controversially discussed. Against this background, we determined the acute toxicity of 24 ionizable substances at up to 4 different pH values on the embryonic development of the zebrafish, Danio rerio, and supplemented this dataset with additional data from the literature. The LC50 for some substances (diclofenac, propranolol, fluoxetine) differed by a factor of even >103 between pH5 and pH9. To simulate the toxicity of 12 acids and 12 bases, six models to calculate a pH-dependant logD value as a proxy for the uptake of potentially toxic molecules were created based on different premises for the trans-membrane passage and toxic action of neutral and ionic species, and their abilities to explain the real LC50 data set were assessed. Using this approach, we were able to show that both neutral and charged species are almost certainly taken up into cells according to their logD-based distribution, and that both species exert toxicity. Since two of the models that assume all intracellular molecules to be neutral overestimated the real toxicity, it must be concluded, that the toxic effect of a single charged intracellularly present molecule is, on the average, lower than that of a single neutral molecule. Furthermore, it was possible to attribute differences in toxicity at different pH values for these 24 ionizable substances to the respective deltas in logD at these pH levels with high accuracy, enabling particularly a full logD-based model on the basis of logPow as a membrane passage descriptor to be used for predicting potential toxicities in worst-case scenarios from existing experimental studies, as stipulated in the process of registration of chemicals and the definition of Environmental Quality Standards (EQS). © 2023 The Author(s).Veröffentlichung Soil moisture and matric potential - an open field comparison of sensor systems(2020) Jackisch, Conrad; Germer, Kai; Gräff, ThomasSoil water content and matric potential are central hydrological state variables. A large variety of automated probes and sensor systems for state monitoring exist and are frequently applied. Most applications solely rely on the calibration by the manufacturers. Until now, there has been no commonly agreed-upon calibration procedure. Moreover, several opinions about the capabilities and reliabilities of specific sensing methods or sensor systems exist and compete. A consortium of several institutions conducted a comparison study of currently available sensor systems for soil water content and matric potential under field conditions. All probes were installed at 0.2†m†b.s. (metres below surface), following best-practice procedures. We present the set-up and the recorded data of 58 probes of 15 different systems measuring soil moisture and 50 further probes of 14 different systems for matric potential. We briefly discuss the limited coherence of the measurements in a cross-correlation analysis. The measuring campaign was conducted during the growing period of 2016. The monitoring data, results from pedophysical analyses of the soil and laboratory reference measurements for calibration are published in Jackisch et al. © Author(s) 2020Veröffentlichung Simulating future salinity dynamics in a coastal marshland under different climate scenarios(2018) Eberhard, Julius; Van Schaik, N. Loes M. B.; Gräff, Thomas; Schibalski, AnettSalinization is a well-known problem in agricultural areas worldwide. For the last 20-30 years, rising salinity in the upper, unconfined aquifer has been observed in the Freepsumer Meer, a deep grassland area near the German North Sea coast. In order to investigate long-term development of soil salinity and water balance, the one-dimensional SWAP model was set up and calibrated for a soil column in the area, simulating water and salt balance at discrete depths for 1961-2099. The model setup involved a deep aquifer as the only source of salt through upward seepage since other sources were negligible. In the vertical salt transport equation, only dispersion and advection were included. Six different regional outputs of statistical downscaling methods (WETTREG, XDS), based on simulations of different GCMs (ECHAM5, ECHAM6, IPSL-CM5) driven by greenhouse gas emission scenarios (SRES-A2, SRES-B1) and concentration pathways (RCP45, RCP85), were used as scenarios. These comprised different rates of increasing surface temperature and essentially different trends in seasonal rainfall. The results of the model runs exhibit opposing salinity trends for topsoil and deeper layers: While the projections of some scenarios entail decreasing salinities near the soil surface, most of them project a rise in subsoil salinity with strongest trends of up to +0.9 mg cm-3 (100a)-1 at -65 cm. The results suggest that topsoil salinity trends are affected by the magnitude of winter rainfall trends while high subsoil salinity trends correspond to low winter rainfall and high summer temperature. Absolute salinity is high in scenarios of high-temperature and low-rainfall summers. How these projected trends affect the vegetation and thereby future land use will depend on the future management of groundwater levels in the area. © Author(s) 2019Veröffentlichung Auswirkungen des Sturmhochwassers der Ostsee am 4./5. Januar 2017 auf das renaturierte Niedermoor "Hütelmoor und Heiligensee" an der deutschen Ostseeküste(2017) Miegel, Konrad; Gräff, Thomas; Franck, Christian; Salzmann, ThomasVeröffentlichung Cluster analysis and self-organizing maps to understand congener patterns of PCB and dioxins/furans(2019) Gräff, Thomas; Fiedler, Heidelore; Höllrigl-Rosta, Andreas; Knetsch, Gerlinde