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Hunkeler, Daniel
Nom
Hunkeler, Daniel
Affiliation principale
Fonction
Professeur ordinaire
Email
daniel.hunkeler@unine.ch
Identifiants
Résultat de la recherche
Voici les éléments 1 - 10 sur 181
- PublicationAccès libre
- PublicationAccès libreCross-sphere modelling to evaluate impacts of climate and land management changes on groundwater resources(2021-8)
; ; ; - PublicationAccès libreA Framework for Untangling Transient Groundwater Mixing and Travel Times(2021-2)
; ; ; ; Kipfer, RolfUnderstanding the mixing between surface water and groundwater as well as groundwater travel times in vulnerable aquifers is crucial to sustaining a safe water supply. Age dating tracers used to infer apparent travel times typically refer to the entire groundwater sample. A groundwater sample, however, consists of a mixture of waters with a distribution of travel times. Age dating tracers only reflect the proportion of the water that is under the dating range of the used tracer, thus their interpretation is typically biased. Additionally, end-member mixing models are subject to various sources of uncertainties, which are typically neglected. In this study, we introduce a new framework that untangles groundwater mixing ratios and travel times using a novel combination of in-situ noble gas analyses. We applied this approach during a groundwater pumping test carried out in a pre-alpine Swiss valley. First, we calculated transient mixing ratios between recently infiltrated river water and regional groundwater present in a wellfield, using helium-4 concentrations combined with a Bayesian end-member mixing model. Having identified the groundwater fraction of recently infiltrated river water (Frw) consequently allowed us to infer the travel times from the river to the wellfield, estimated based on radon-222 activities of Frw. Furthermore, we compared tracer-based estimates of Frw with results from a calibrated numerical model. We demonstrate (i) that partitioning of major water sources enables a meaningful interpretation of an age dating tracer of the water fraction of interest and (ii) that the streambed has a major control on the estimated travel times. - PublicationAccès libreLow-flow behavior of alpine catchments with varying quaternary cover under current and future climatic conditions(2020-10)
; ; Alpine environments are particularly vulnerable to climatic warming, and long term observations suggest a shift of snow-influenced river discharge towards earlier periods of the year. For water resources management, the seasonal patterns of discharge in alpine areas are particularly relevant, as the shift to lower flows in summer and autumn combined with increased water demand could lead to water shortage in downstream catchments. The storage of groundwater in alpine catchments could significantly modulate how changing climatic conditions influence the annual streamflow regime. However, groundwater storage and its buffering capacity in alpine areas remain poorly understood. Moreover, studies on how climate change will impact water resources in alpine areas rarely consider the influence of geology. In this paper, catchment geology is used as a basis for the classification of future summer low flows behavior of several alpine catchments in Switzerland. Based on the analysis of the relationship between low-flow indicators and geology, the role of unconsolidated quaternary deposits is explored. We show that quaternary deposits play a critical role in the seasonal storage of groundwater, which can contribute to rivers during lowflow periods. Three climate change simulations based on extreme RCP 8.5 scenarios are fed into a conceptual hydrological model to illustrate the buffering role of groundwater. Past and future low flows normalized by mean past and future streamflows appear correlated with the percentage of unconsolidated quaternary deposits. These results highlight that catchments with high groundwater contribution to streamflow relative to precipitation will have a slower decrease in future summer discharge. Therefore, we propose two indicators that can be used to anticipate the response of future summers low flows in alpine areas to climate change: the current winter low flows and the percentage of unconsolidated quaternary deposits of the catchments. - PublicationAccès libreSnow cover monitoring by remote sensing and evaluating melting water efects on karstic springs discharges (a case study from Lasem area)(2020-5)
- PublicationAccès libreInfluence of surface water – groundwater interactions on the spatial distribution of pesticide metabolites in groundwater(2020-4)
; ; In groundwater, pesticidemetabolites tend to occurmore frequently and at higher concentrations than their parent pesticides, due to their highermobility and persistence. These properties might also favor their transfer across surface water – groundwater interfaces. However, the effect of surface water – groundwater interactions on the metabolite occurrence in groundwater and pumpingwells has so far received little attention.Weinvestigated the spatial distribution of metabolites in an unconsolidated aquifer, which interacts with two surface water bodies originating from catchments with contrasting land use. We focused onmetabolites of the herbicide chloridazon, namely desphenyl-chloridazon (DPC) and methyl-desphenyl-chloridazon (MDPC) and characterized surface water – groundwater interactions with various environmental tracers (e.g. electrical conductivity, stable water isotopes,wastewater tracers). In zones influenced by a river fromamountainous area,metabolite concentrations were low(median values ≤0.50 μg L−1 for DPC, ≤0.19 μg L−1 forMDPC). In contrast, high concentrations occurred in areas dominated by recharge fromagricultural fields and/or influenced by a streamfroman adjacent intensely farmed catchment (median values up to 1.9 μg L−1 for DPC and up to 0.75 μg L−1 forMDPC). An endmember analysis using hydro-chemical data suggested that about 20% of the DPC mass in a pumping well originated from the neighboring catchment and on its own would cause a concentration above 0.1 μg L−1 for DPC. Our findings highlight that the mobile metabolites can be imported from zones with intense agriculture outside of the exploited aquifer via surface-water groundwater interactions influencing the metabolite concentration level and longterm dynamics in the aquifer. - PublicationAccès libreDual-Element Isotope Analysis of Desphenylchloridazon to Investigate Its Environmental Fate in a Systematic Field Study:A Long-Term Lysimeter Experiment(2020-3)
; - PublicationAccès libreControls on the persistence of aqueous-phase groundwater contaminants in the presence of reactive back-diffusion(2020-3)
; The persistence of groundwater contaminants is influenced by several interacting processes. Physical, physico-chemical, and (bio-)chemical processes all influence the transport of contaminants in the subsurface. However,for a given hydrogeologicalsystem, itisgenerally unclear to whichdegree each of these phenomena acts as a con-trol on plume behaviour. Here, we present a comprehensive investigation of these processes and their influenceson plume behaviour and persistence in layered sedimentary systems. We investigate different scenarios that rep-resentfundamental configurationsof common contaminantsituations. A confined aquifer over- and underlain byaquitard layers is investigated in a source-removal scenario and a constant-source equilibrium scenario. Addi-tionally, an aquitard overlain and underlain by high permeability units is investigated in a source-removal sce-nario. In these investigations, we vary layer thickness, as well as parameters governing advection, (back-)diffusion, sorption, and degradation. Extensive analysis of these results enables quantification of the influenceof these parameters on maximum down-gradient concentration, plume persistence duration, and plume spatialextent. Finally, parameterspace dimensionality reductionisused to establishtrends and regimes inwhichcertainprocesses dominate as controls. A lower limit to plume extent as a function of a novel constructed parameter isalso determined. These results provide valuable quantitative information for the assessment of the fate ofgroundwater contaminants and are applicable to a wide range of aqueous-phase solutes. - PublicationAccès libreLithological and tectonic control on groundwater contribution to stream discharge during low-flow conditions(2020-3-1)
; ; ; ; Knowing how stream discharge in an ungauged catchment reacts to dry spells is a major challenge for managing water resources. The role of geology on these dynamics is poorly understood. For the Swiss Molasse basin, we therefore explored how the geology influences the groundwater contribution to stream flow during low-flow conditions. Using existing data from geological reports and maps as well as from deep boreholes, we constructed a basin-wide overview of the hydrogeological quality of the bedrock and investigated five catchments in 3D. We found that catchments with the most permeable sedimentary bedrock are least sensitive to low flows (marine sandstone, K = 10−4 to 10−5 m/s, Peff = 5–10%). In contrast, if bedrock K is low (K < 10−6 m/s), the presence of a productive Quaternary volume becomes decisive for groundwater contribution to stream flow. Limitations exist due to a restricted database for K and Peff values of the Molasse and limited information on continuation of lithologies with depth. This emphasizes the need for more hydrogeologically relevant data for the future management of water resources. Our results highlighting what lithotypes favor groundwater contribution to stream flow are valid also in other regions for the assessment of a catchment’s sensitivity to low flows - PublicationAccès libreCompound-specific chlorine isotope fractionation in biodegradation of atrazin(2020-2)
; Elsner, MartinAtrazine is a frequently detected groundwater contaminant. It can be microbially degraded by oxidative dealkylation or by hydrolytic dechlorination. Compound-specific isotope analysis is a powerful tool to assess its transformation. In previous work, carbon and nitrogen isotope effects were found to reflect these different transformation pathways. However, chlorine isotope fractionation could be a particularly sensitive indicator of natural transformation since chlorine isotope effects are fully represented in the molecular average while carbon and nitrogen isotope effects are diluted by non-reacting atoms. Therefore, this study explored chlorine isotope effects during atrazine hydrolysis with Arthrobacter aurescens TC1 and oxidative dealkylation with Rhodococcus sp. NI86/21. Dual element isotope slopes of chlorine vs. carbon isotope fractionation (ΛArthroCl/C = 1.7 ± 0.9 vs. ΛRhodoCl/C = 0.6 ± 0.1) and chlorine vs. nitrogen isotope fractionation (ΛArthroCl/N = −1.2 ± 0.7 vs. ΛRhodoCl/N = 0.4 ± 0.2) provided reliable indicators of different pathways. Observed chlorine isotope effects in oxidative dealkylation (εCl = −4.3 ± 1.8‰) were surprisingly large, whereas in hydrolysis (εCl = −1.4 ± 0.6‰) they were small, indicating that C–Cl bond cleavage was not the rate-determining step. This demonstrates the importance of constraining expected isotope effects of new elements before using the approach in the field. Overall, the triple element isotope information brought forward here enables a more reliable identification of atrazine sources and degradation pathways.