@article{sprenger_llorens_gallart_benettin_allen_latron_2022, title={A multi-objective parameterization of StorAge Selection functions based on stable isotopes sampled at the catchment outlet and in trees to constrain water age estimations for runoff and evapotranspiration fluxes}, url={https://doi.org/10.5194/iahs2022-356}, DOI={10.5194/iahs2022-356}, abstractNote={<p>It is important to understand how precipitation is stored in catchments, released via evapotranspiration (ET), or recharges aquifers and streams. We investigated this partitioning of precipitation using stable isotopes of water (<sup>2</sup>H and <sup>18</sup>O) at the Can Vila catchment in the Spanish Pyrenees mountains. The isotope data covered four years, comprising >550 rainfall and >980 stream water samples. They were complemented by fortnightly plant-water-isotope data sampled over eight months. The isotope data were used to quantify how long it takes for water to become evapotranspiration or discharged as streamflow, using StorAge Selection (SAS) functions. We calibrated the SAS functions using a conventional approach, fitting the model solely to stream water isotope data, as well as a multi-objective calibration approach, in which the model was simultaneously fitted to tree-xylem-water isotope data.</p><p>Our results showed that the conventional calibration approach was not able to adequately simulate the observed xylem isotope ratios. However, the SAS model was capable of adequately simulating both observed streamwater and xylem water isotope ratios, if those xylem water isotope observations were used in calibration. This multi-objective-calibration approach led to a more constrained parameter space, facilitating parameter value identification. The model was tested on a segment of data reserved for validation, showing a Kling-Gupta Efficiency of 0.72, compared to the 0.83 observed during in the calibration period.</p><p>The water age dynamics inferred from the model calibrated using the conventional approach differed substantially from those inferred from the multi-objective-calibration model. The latter suggested that the water supplying evapotranspiration is much older (median age 150-300 days) than what was suggested by the former (median age 50-200 days). Regardless, the modeling results support recent findings in ecohydrological field studies that highlighted both subsurface heterogeneity of water storage and fluxes and the use of relatively old water by trees. We contextualized the SAS-derived water ages by also using young-water-fraction and endmember-splitting approaches, which respectively also showed the contribution of young water to streamflow was variable but sensitive to runoff rates, and that ET was largely sourced by winter precipitation, that must have resided in the subsurface across seasons. &#160;</p>}, author={Sprenger, Matthias and Llorens, Pilar and Gallart, Francesc and Benettin, Paolo and Allen, Scott and Latron, Jérôme}, year={2022}, month={Sep} }
 @article{carroll_deems_sprenger_maxwell_brown_newman_beutler_williams_2022, title={Modeling Snow Dynamics and Stable Water Isotopes Across Mountain Landscapes}, volume={3}, url={https://doi.org/10.1002/essoar.10510911.1}, DOI={10.1002/essoar.10510911.1}, abstractNote={Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Geophysical Research Letters. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing the latest version by default [v1]Modeling Snow Dynamics and Stable Water Isotopes Across Mountain LandscapesAuthorsRosemary W.H.CarrolliDJeffrey SDeemsiDMatthiasSprengeriDReed M.MaxwellWendy SBrownAlexanderNewmaniDCurtis ABeutlerKenneth HurstWilliamsiDSee all authors Rosemary W.H. CarrolliDCorresponding Author• Submitting AuthorDesert Research InstituteiDhttps://orcid.org/0000-0002-9302-8074view email addressThe email was not providedcopy email addressJeffrey S DeemsiDUniversity of Colorado BoulderiDhttps://orcid.org/0000-0002-3265-8670view email addressThe email was not providedcopy email addressMatthias SprengeriDLawrence Berkeley National LaboratoryiDhttps://orcid.org/0000-0003-1221-2767view email addressThe email was not providedcopy email addressReed M. MaxwellPrinceton Universityview email addressThe email was not providedcopy email addressWendy S BrownRocky Mountain Biological Laboratoryview email addressThe email was not providedcopy email addressAlexander NewmaniDRocky Mountain Biological LaboratoryiDhttps://orcid.org/0000-0002-1574-8754view email addressThe email was not providedcopy email addressCurtis A BeutlerRocky Mountain Biological Laboratoryview email addressThe email was not providedcopy email addressKenneth Hurst WilliamsiDLawrence Berkeley National Laboratory (DOE)iDhttps://orcid.org/0000-0002-3568-1155view email addressThe email was not providedcopy email address}, publisher={Wiley}, author={Carroll, Rosemary W.H. and Deems, Jeffrey S and Sprenger, Matthias and Maxwell, Reed M. and Brown, Wendy S and Newman, Alexander and Beutler, Curtis A and Williams, Kenneth Hurst}, year={2022}, month={Mar} }
 @article{carroll_deems_sprenger_maxwell_brown_newman_beutler_williams_2022, title={Modeling Snow Dynamics and Stable Water Isotopes Across Mountain Landscapes}, url={https://doi.org/10.1029/2022GL098780}, DOI={10.1029/2022GL098780}, abstractNote={Abstract}, journal={Geophysical Research Letters}, author={Carroll, Rosemary W. H. and Deems, Jeffrey and Sprenger, Matthias and Maxwell, Reed and Brown, Wendy and Newman, Alexander and Beutler, Curtis and Williams, Kenneth H.}, year={2022}, month={Oct} }
 @article{sprenger_llorens_gallart_benettin_allen_latron_2022, title={Precipitation fate and transport in a Mediterranean catchment through models calibrated on plant and stream water isotope data}, url={https://doi.org/10.5194/hess-2022-93}, DOI={10.5194/hess-2022-93}, abstractNote={Abstract. To predict hydrologic responses to inputs and perturbations, it is important to understand how precipitation is stored in catchments, released back to the atmosphere via evapotranspiration (ET), or transported to aquifers and streams. We investigated this partitioning of precipitation using stable isotopes of water (2H and 18O) at the Can Vila catchment in the Spanish Pyrenees mountains. The isotope data covered four years of measurements, comprising > 550 rainfall and > 980 stream water samples, capturing intra-event variations. They were complemented by fortnightly plant-water-isotope data sampled over eight months. The isotope data were used to quantify how long it takes for water to become evapotranspiration or discharged as streamflow, using StorAge Selection (SAS) functions. We calibrated the SAS functions using a conventional approach, fitting the model solely to stream water isotope data, as well as a multi-objective calibration approach, in which the model was simultaneously fitted to tree xylem-water isotope data. Our results showed that the conventional model-fitting approach was not able to constrain the model parameters that represented the age of water supplying ET. Consequently, the ET isotope ratios simulated by the conventionally calibrated model failed to adequately simulate the observed xylem isotope ratios. However, the SAS model was capable of adequately simulating both observed stream water and xylem water isotope ratios, if those xylem water isotope observations were used in calibration (i.e., the multi-objective approach). The multi-objective-calibration approach led to a more constrained parameter space, facilitating parameter value identification. The model was tested on a segment of data reserved for validation, showing a Kling-Gupta Efficiency of 0.72, compared to the 0.83 observed during in the calibration period. The water-age dynamics inferred from the model calibrated using the conventional approach differed substantially from those inferred from the multi-objective-calibration model. The latter suggested that the median ages of water supplying evapotranspiration is much older (150–300 days) than what was suggested by the former (50–200 days). Regardless, the modeling results support recent findings in ecohydrological field studies that highlighted both subsurface heterogeneity of water storage and fluxes and the use of relatively old water by trees. We contextualized the SAS-derived water ages by also using young-water-fraction and endmember-splitting approaches, which respectively also showed the contribution of young water to streamflow was variable but sensitive to runoff rates, and that ET was largely sourced by winter precipitation, that must have resided in the subsurface across seasons.
                        }, author={Sprenger, Matthias and Llorens, Pilar and Gallart, Francesc and Benettin, Paolo and Allen, Scott T. and Latron, Jérôme}, year={2022}, month={Mar} }
 @article{sprenger_llorens_gallart_benettin_allen_latron_2022, title={Precipitation fate and transport in a Mediterranean catchment through models calibrated on plant and stream water isotope data}, volume={26}, ISSN={["1607-7938"]}, url={https://doi.org/10.5194/hess-26-4093-2022}, DOI={10.5194/hess-26-4093-2022}, abstractNote={Abstract. To predict hydrologic responses to inputs and perturbations, it is important to understand how precipitation is stored in catchments, released back to the atmosphere via evapotranspiration (ET), or transported to aquifers and streams. We investigated this partitioning of precipitation using stable isotopes of water (18O) at the Can Vila catchment in the Spanish Pyrenees mountains. The isotope data covered four years of measurements, comprising >550 rainfall and >980 stream water
samples, capturing intra-event variations. They were complemented by
fortnightly plant water isotope data sampled over eight months. The isotope
data were used to quantify how long it takes for water to become
evapotranspiration or to be discharged as streamflow using StorAge
Selection (SAS) functions. We calibrated the SAS functions using a
conventional approach fitting the model solely to stream water isotope
data and a multi-objective calibration approach in which the model
was simultaneously fitted to tree xylem water isotope data. Our results showed that the conventional model-fitting approach was not able to constrain the model parameters that represented the age of water
supplying ET. Consequently, the ET isotope ratios simulated by the
conventionally calibrated model failed to adequately simulate the observed
xylem isotope ratios. However, the SAS model was capable of adequately
simulating both observed stream water and xylem water isotope ratios, if
those xylem water isotope observations were used in calibration (i.e., the
multi-objective approach). The multi-objective calibration approach led to a more constrained parameter space facilitating parameter value
identification. The model was tested on a segment of data reserved for
validation showing a Kling–Gupta Efficiency of 0.72 compared to the 0.83
observed during in the calibration period. The water-age dynamics inferred from the model calibrated using the
conventional approach differed substantially from those inferred from the
multi-objective calibration model. The latter suggested that the median ages of water supplying evapotranspiration is much older (150–300 d) than what was suggested by the former (50–200 d). Regardless, the modeling results support recent findings in ecohydrological field studies that highlighted both subsurface heterogeneity of water storage and fluxes and the use of relatively old water by trees. We contextualized the SAS-derived water ages by also using young-water-fraction and endmember-splitting approaches, which respectively also showed the contribution of young water to streamflow was variable but sensitive to runoff rates and that ET was largely sourced by winter precipitation that must have resided in the subsurface across seasons.
                    }, number={15}, journal={HYDROLOGY AND EARTH SYSTEM SCIENCES}, author={Sprenger, Matthias and Llorens, Pilar and Gallart, Francesc and Benettin, Paolo and Allen, Scott T. and Latron, Jerome}, year={2022}, month={Aug}, pages={4093–4107} }
 @article{sprenger_llorens_gallart_benettin_allen_latron_2022, title={Supplementary material to &quot;Precipitation fate and transport in a Mediterranean catchment through models calibrated on plant and stream water isotope data&quot;}, url={https://doi.org/10.5194/hess-2022-93-supplement}, DOI={10.5194/hess-2022-93-supplement}, abstractNote={Fig. 1 Median water age in stream runoff (Q, blue), the catchment's storage (S, grey), and the evapotranspiration flux (ET, orange).Age estimates shown for the best simulation (dark color) and the top 100 simulations (light color) for the conventional calibration approach, KGEQ.Compared to the results of the multi-objective calibration (Figure 5), the median ages of Q, S and ET are more uncertain and tend to overlap.}, author={Sprenger, Matthias and Llorens, Pilar and Gallart, Francesc and Benettin, Paolo and Allen, Scott T. and Latron, Jérôme}, year={2022}, month={Mar} }
 @article{benettin_rodriguez_sprenger_kim_klaus_harman_velde_hrachowitz_botter_mcguire_et al._2022, title={Transit Time Estimation in Catchments: Recent Developments and Future Directions}, url={https://doi.org/10.1029/2022WR033096}, DOI={10.1029/2022WR033096}, abstractNote={Abstract}, journal={Water Resources Research}, author={Benettin, Paolo and Rodriguez, Nicolas B. and Sprenger, Matthias and Kim, Minseok and Klaus, Julian and Harman, Ciaran J. and Velde, Ype and Hrachowitz, Markus and Botter, Gianluca and McGuire, Kevin J. and et al.}, year={2022}, month={Nov} }
 @article{carroll_deems_maxwell_sprenger_brown_newman_beutler_bill_hubbard_williams_2022, title={Variability in observed stable water isotopes in snowpack across a mountainous watershed in Colorado}, volume={36}, url={https://doi.org/10.1002/hyp.14653}, DOI={10.1002/hyp.14653}, abstractNote={Abstract}, number={8}, journal={Hydrological Processes}, publisher={Wiley}, author={Carroll, Rosemary W. H. and Deems, Jeffery and Maxwell, Reed and Sprenger, Matthias and Brown, Wendy and Newman, Alexander and Beutler, Curtis and Bill, Markus and Hubbard, Susan S. and Williams, Kenneth H.}, year={2022}, month={Aug} }
 @article{sprenger_carroll_dennedy‐frank_siirila‐woodburn_newcomer_brown_newman_beutler_bill_hubbard_et al._2022, title={Variability of Snow and Rainfall Partitioning Into Evapotranspiration and Summer Runoff Across Nine Mountainous Catchments}, volume={49}, url={https://doi.org/10.1029/2022GL099324}, DOI={10.1029/2022GL099324}, abstractNote={Abstract}, number={13}, journal={Geophysical Research Letters}, publisher={American Geophysical Union (AGU)}, author={Sprenger, Matthias and Carroll, Rosemary W. H. and Dennedy‐Frank, James and Siirila‐Woodburn, Erica R. and Newcomer, Michelle E. and Brown, Wendy and Newman, Alexander and Beutler, Curtis and Bill, Markus and Hubbard, Susan S. and et al.}, year={2022}, month={Jul} }
 @article{sprenger_carroll_dennedy-frank_siirila-woodburn_newcomer_brown_newman_beutler_bill_hubbard_et al._2022, title={Variability of snow and rainfall partitioning into evapotranspiration and summer runoff across nine mountainous catchments}, url={https://doi.org/10.1002/essoar.10511257.1}, DOI={10.1002/essoar.10511257.1}, abstractNote={Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Geophysical Research Letters. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing the latest version by default [v1]Variability of snow and rainfall partitioning into evapotranspiration and summer runoff across nine mountainous catchmentsAuthorsMatthiasSprengeriDRosemary W.H.CarrolliDP. James JDennedy-FrankErica R.Siirila-WoodburniDMichelle E.NewcomeriDWendy SBrownAlexanderNewmaniDCurtis ABeutlerMarkusBilliDSusan S.HubbardKenneth H.WillamsiDSee all authors Matthias SprengeriDCorresponding Author• Submitting AuthorLawrence Berkeley National LaboratoryiDhttps://orcid.org/0000-0003-1221-2767view email addressThe email was not providedcopy email addressRosemary W.H. CarrolliDDesert Research InstituteiDhttps://orcid.org/0000-0002-9302-8074view email addressThe email was not providedcopy email addressP. James J Dennedy-FrankStanford Universityview email addressThe email was not providedcopy email addressErica R. Siirila-WoodburniDLawrence Berkeley National Laboratory (DOE)iDhttps://orcid.org/0000-0001-9406-124Xview email addressThe email was not providedcopy email addressMichelle E. NewcomeriDLawrence Berkeley National Laboratory (DOE)iDhttps://orcid.org/0000-0001-5138-9026view email addressThe email was not providedcopy email addressWendy S BrownRocky Mountain Biological Laboratoryview email addressThe email was not providedcopy email addressAlexander NewmaniDRocky Mountain Biological LaboratoryiDhttps://orcid.org/0000-0002-1574-8754view email addressThe email was not providedcopy email addressCurtis A BeutlerRocky Mountain Biological Laboratoryview email addressThe email was not providedcopy email addressMarkus BilliDLawrence Berkeley National LaboratoryiDhttps://orcid.org/0000-0001-7002-2174view email addressThe email was not providedcopy email addressSusan S. HubbardLawrence Berkeley National Laboratory (DOE)view email addressThe email was not providedcopy email addressKenneth H. WillamsiDLawrence Berkeley National LabiDhttps://orcid.org/0000-0002-3568-1155view email addressThe email was not providedcopy email address}, author={Sprenger, Matthias and Carroll, Rosemary W.H. and Dennedy-Frank, P. James J and Siirila-Woodburn, Erica R. and Newcomer, Michelle E. and Brown, Wendy S and Newman, Alexander and Beutler, Curtis A and Bill, Markus and Hubbard, Susan S. and et al.}, year={2022}, month={May} }
 @article{zhao_sprenger_barzegar_tang_adamowski_2022, title={Withdrawn: Similar Isotopic Biases of Plant Stem Bulk Water From Different Water Sources by Cryogenic Vacuum Distillation Demonstrated Through Rehydration Experiments}, volume={49}, url={https://doi.org/10.1029/2021GL096474}, DOI={10.1029/2021GL096474}, abstractNote={Abstract}, number={13}, journal={Geophysical Research Letters}, publisher={American Geophysical Union (AGU)}, author={Zhao, Pei and Sprenger, Matthias and Barzegar, Rahim and Tang, Xiangyu and Adamowski, Jan}, year={2022}, month={Jul} }
 @article{carroll_deems_maxwell_sprenger_brown_newman_beutler_bill_hubbard_williams_2021, title={Stable Water Isotope Inputs Across Mountain Landscapes}, url={https://doi.org/10.1002/essoar.10507500.1}, DOI={10.1002/essoar.10507500.1}, abstractNote={Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Water Resources Research. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing the latest version by default [v1]Stable Water Isotope Inputs Across Mountain LandscapesAuthorsRosemary W.H.CarrolliDJeffrey SDeemsiDReed M.MaxwellMatthiasSprengerWendy SBrownAlexanderNewmaniDCurtisBeutlerMarkusBilliDSusan S.HubbardKenneth HurstWilliamsiDSee all authors Rosemary W.H. CarrolliDCorresponding Author• Submitting AuthorDesert Research InstituteiDhttps://orcid.org/0000-0002-9302-8074view email addressThe email was not providedcopy email addressJeffrey S DeemsiDUniversity of Colorado BoulderiDhttps://orcid.org/0000-0002-3265-8670view email addressThe email was not providedcopy email addressReed M. MaxwellPrinceton Universityview email addressThe email was not providedcopy email addressMatthias SprengerNCSUview email addressThe email was not providedcopy email addressWendy S BrownRocky Mountain Biological Laboratoryview email addressThe email was not providedcopy email addressAlexander NewmaniDRocky Mountain Biological LaboratoryiDhttps://orcid.org/0000-0002-1574-8754view email addressThe email was not providedcopy email addressCurtis BeutlerRocky Mountain Biological Laboratoryview email addressThe email was not providedcopy email addressMarkus BilliDLawrence Berkeley National LaboratoryiDhttps://orcid.org/0000-0001-7002-2174view email addressThe email was not providedcopy email addressSusan S. HubbardLawrence Berkeley National Laboratory (DOE)view email addressThe email was not providedcopy email addressKenneth Hurst WilliamsiDLawrence Berkeley National Laboratory (DOE)iDhttps://orcid.org/0000-0002-3568-1155view email addressThe email was not providedcopy email address}, author={Carroll, Rosemary W.H. and Deems, Jeffrey S and Maxwell, Reed M. and Sprenger, Matthias and Brown, Wendy S and Newman, Alexander and Beutler, Curtis and Bill, Markus and Hubbard, Susan S. and Williams, Kenneth Hurst}, year={2021}, month={Jul} }
 @article{gallart_valiente_llorens_cayuela_sprenger_latron_2020, title={Investigating young water fractions in a small Mediterranean mountain catchment: Both precipitation forcing and sampling frequency matter}, volume={6}, url={https://doi.org/10.1002/hyp.13806}, DOI={10.1002/hyp.13806}, abstractNote={Abstract}, journal={Hydrological Processes}, publisher={Wiley}, author={Gallart, Francesc and Valiente, María and Llorens, Pilar and Cayuela, Carles and Sprenger, Matthias and Latron, Jérôme}, year={2020}, month={Aug} }
 @article{knighton_kuppel_smith_soulsby_sprenger_tetzlaff_2020, title={Using isotopes to incorporate tree water storage and mixing dynamics into a distributed ecohydrologic modelling framework}, volume={2}, url={https://doi.org/10.1002/eco.2201}, DOI={10.1002/eco.2201}, abstractNote={Abstract}, journal={Ecohydrology}, publisher={Wiley}, author={Knighton, James and Kuppel, Sylvain and Smith, Aaron and Soulsby, Chris and Sprenger, Matthias and Tetzlaff, Doerthe}, year={2020}, month={Apr} }
 @article{sprenger_allen_2020, title={What Ecohydrologic Separation Is and Where We Can Go With It}, volume={56}, url={https://doi.org/10.1029/2020WR027238}, DOI={10.1029/2020WR027238}, abstractNote={Abstract}, number={7}, journal={Water Resources Research}, publisher={American Geophysical Union (AGU)}, author={Sprenger, Matthias and Allen, Scott T.}, year={2020}, month={Jul} }
 @article{zhu_wang_kong_zheng_feng_zhang_yuan_song_sprenger_2019, title={Interaction of Surface Water and Groundwater Influenced by Groundwater Over-Extraction, Waste Water Discharge and Water Transfer in Xiong'an New Area, China}, volume={11}, ISSN={["2073-4441"]}, url={https://doi.org/10.3390/w11030539}, DOI={10.3390/w11030539}, abstractNote={Understanding the interaction of surface water and groundwater affected by anthropogenic activities is of great importance for water resource and water quality management. The Xiong’an New Area, located in the North China Plain, has been designated a new building area by China’s government. Groundwater has been over pumped and artificial water was transferred to meet the water supply in this region. Therefore, the natural interaction of surface water and groundwater has been greatly changed and there has been a complex impact of the groundwater from anthropogenic activities. In this study, we used water chemical ions and stable isotopes of δ2H and δ18O to assess the interaction of surface water and groundwater in the Xiong’an New Area. We carried out field surveys and water sampling of the Fu River (domestic waste water discharge), Lake Baiyangdian (artificial water transfer), and the underlying groundwater along the water bodies. Results show that the artificial surface water (discharged and transferred) became the major recharge source for the local groundwater due to the decline of groundwater table. We used groundwater table observations, end-member mixing analysis of the stable isotopic composition and chloride tracers to estimate the contributions of different recharge sources to the local groundwater. Due to the over pumping of groundwater, the lateral groundwater recharge was dominant with a contribution ratio ranging from 12% to 78% in the upper reach of the river (Sections 1–3). However, the contribution of lateral groundwater recharge was estimated to be negligible with respect to the artificial water recharge from Lake Baiyangdian. Seepage from the Fu River contributed a significant amount of water to the connecting aquifer, with a contribution ranging from 14% to 75% along the river. The extent of the river influence into the aquifer ranges as far as 1400 m to the south and 400 m to the north of the Fu River. Estimations based on isotopic fractionation shows that about 25% of Lake Baiyangdian water was lost by evaporation. By using the stable isotopes of oxygen and hydrogen in the lake water, an influencing range of 16 km west of the lake was determined. The interaction of the surface water and groundwater is completely changed by anthropogenic activities, such as groundwater over pumping, waste water discharge and water transfer. The switched interaction of surface water and groundwater has a significant implication on water resources management.}, number={3}, journal={WATER}, author={Zhu, Meijia and Wang, Shiqin and Kong, Xiaole and Zheng, Wenbo and Feng, Wenzhao and Zhang, Xianfu and Yuan, Ruiqiang and Song, Xianfang and Sprenger, Matthias}, year={2019}, month={Mar} }
 @article{sprenger_llorens_cayuela_gallart_latron_2019, title={Mechanisms of consistently disjunct soil water pools over (pore) space and time}, volume={23}, ISSN={["1607-7938"]}, url={https://doi.org/10.5194/hess-23-2751-2019}, DOI={10.5194/hess-23-2751-2019}, abstractNote={Abstract. The storage and release of water in soils is critical for
sustaining plant transpiration and groundwater recharge. However, how much
subsurface mixing of water occurs, and how much of the water is available for plants or otherwise percolates to streams and the groundwater is not yet
understood. Based on stable isotope (2H and
18O) data, some studies have found that water infiltrating into soils can bypass older pore
water. However, the mechanisms leading to the separation of water routed
to the streams and water held tightly in smaller pores are still unclear.
Here, we address the current limitations of the understanding of subsurface
mixing and their consequences regarding the application of stable isotopes in
ecohydrological studies. We present an extensive data set, for which we
sampled the isotopic composition of mobile and bulk soil water
in parallel with groundwater at a fortnightly temporal resolution and stream water and rainfall at a much higher resolution in a Mediterranean
long-term research catchment, in Vallcebre, Spain. The data reveal that the
mobile and tightly bound water of a silty loam soil in a Scots pine forest
do not mix well; however, they constitute two disjunct subsurface water pools
with little exchange, despite intense rainfall events leading to high soil
wetness. We show that the isotopic compartmentalization results from the rewetting
of small soil pores by isotopically depleted winter/spring rain. Thus,
stable isotopes, and, in turn, water residence times, do not only vary
across soil depth, but also across soil pores. Our findings have important
implications for stable isotope applications in ecohydrological studies
assessing the water uptake by plants or the process realism of hydrological models,
as the observed processes are currently rarely implemented in the simulation
of water partitioning into evapotranspiration and recharge in the critical
zone.
                    }, number={6}, journal={HYDROLOGY AND EARTH SYSTEM SCIENCES}, publisher={Copernicus GmbH}, author={Sprenger, Matthias and Llorens, Pilar and Cayuela, Carles and Gallart, Francesc and Latron, Jerome}, year={2019}, month={Jun}, pages={2751–2762} }
 @article{zheng_wang_sprenger_liu_cao_2019, title={Response of soil water movement and groundwater recharge to extreme precipitation in a headwater catchment in the North China Plain}, volume={576}, ISSN={["1879-2707"]}, url={https://doi.org/10.1016/j.jhydrol.2019.06.071}, DOI={10.1016/j.jhydrol.2019.06.071}, abstractNote={Soil water storage and movement are highly heterogeneous across landscapes and their response to spatiotemporal variations in meteorological forcing is complex. While different pools of soil water (including bound and mobile water) are observed, the mechanisms of soil water movement in semi-arid and sub-humid regions are not well understood due to high variation in soil water storage conditions. The Taihang Mountain is a headwater region that recharges both groundwater and surface water systems of the North China Plain, where groundwater levels have been declining and water storage loss is serious. Increasing land cultivation in the Taihang Mountain areas has increased evapotranspiration and reduced both surface runoff and groundwater recharge. Although extreme precipitation is critical for groundwater recharge in the headwater regions, the response mechanism of soil water movement and groundwater recharge remains unclear. In this study, soil water movement and groundwater recharge mechanisms in a cultivated farmland (FL) and land under natural vegetation (NV) were determined for a normal and an extreme precipitation year through the combined use of soil water content and stable isotopes of water (18O and 2H). Soil water got enriched in δ18O and δ2H (δ18O changed from −11.2 to −7.0‰ at NV and from −11.1 to −4.4‰ at FL; δ2H changed from −71 to −49‰ at NV and from −73 to −30% at FL) with increasing soil depth during the growing season suggesting that winter precipitation was generally transported via advection dispersion flow mechanism. However, this process was accompanied by the mixing of previously enriched soil water after large rain events (20–50 mm/day) during the rainy season in a normal precipitation year. Water movement changed from translatory flow to preferential flow after extreme precipitation in a wet precipitation year. Cultivation intensified water evaporation in the top soil layer (upper 10–20 cm), and induced preferential flow down to 50 cm soil depth under FL relative to land under NV. Thus, cropping significantly reduced groundwater recharge. Excessive storm during a wet year produced bypass flow after the first rainstorm, which rapidly recharged deep soil layers (50–100 cm depth). Bypass flow induced by excessive precipitation and contributed the most to groundwater in FL. The observed rapid response of soil water and groundwater to extreme precipitation events is critical for soil and water management to mitigate problems such as nitrate leaching and groundwater contamination in headwater regions of semi-arid and sub-humid areas.}, journal={JOURNAL OF HYDROLOGY}, publisher={Elsevier BV}, author={Zheng, Wenbo and Wang, Shiqin and Sprenger, Matthias and Liu, Bingxia and Cao, Jiansheng}, year={2019}, month={Sep}, pages={466–477} }
 @misc{sprenger_stumpp_weiler_aeschbach_allen_benettin_dubbert_hartmann_hrachowitz_kirchner_et al._2019, title={The Demographics of Water: A Review of Water Ages in the Critical Zone}, volume={57}, ISSN={["1944-9208"]}, url={https://doi.org/10.1029/2018RG000633}, DOI={10.1029/2018RG000633}, abstractNote={Abstract}, number={3}, journal={REVIEWS OF GEOPHYSICS}, publisher={American Geophysical Union (AGU)}, author={Sprenger, Matthias and Stumpp, Christine and Weiler, Markus and Aeschbach, Werner and Allen, Scott T. and Benettin, Paolo and Dubbert, Maren and Hartmann, Andreas and Hrachowitz, Markus and Kirchner, James W. and et al.}, year={2019}, month={Sep}, pages={800–834} }
 @article{sprenger_tetzlaff_buttle_laudon_leistert_mitchell_snelgrove_weiler_soulsby_2018, title={Measuring and Modeling Stable Isotopes of Mobile and Bulk Soil Water}, volume={17}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85045392401&partnerID=MN8TOARS}, DOI={10.2136/vzj2017.08.0149}, abstractNote={Core Ideas
Bulk soil water isotopes have an evaporation signal, but mobile water isotopes do not.
These differences are time variant and linked to the volume and age of the mobile water.
Two pore domains (fast and slow) improve simulations of soil water isotope dynamics.
A new model accounts for isotopic exchange via water vapor between two pore domains.
This exchange is relevant for proper simulation of the evaporation signal in bulk soil water.
Recent findings from stable isotope studies have opened up new questions about differences in the isotopic composition (δ2H and δ18O) of mobile (MW) and bulk water (BW) in soils. We sampled the isotopic compositions of MW using suction lysimeters and BW with the direct‐equilibration method. The study was conducted at two landscape units in each of three catchments: the Bruntland Burn (Scotland), Dorset (Canada), and Krycklan (Sweden). We further used the numerical one‐dimensional flow model SWIS (Soil Water Isotope Simulator) to simulate the hydrometric and isotopic dynamics. The model included evaporation fractionation, allowed differentiation between a fast and a slow flow domain, and included isotopic exchange via water vapor. Our measurements showed that MW plots along the local meteoric water lines, whereas BW plots below, which is indicative of evaporation fractionation. We suggest that the relative volume of MW to BW is relevant for explaining these isotopic differences because MW volumes are usually relatively low during periods of high evaporation. Under this condition, differences between MW and plant water isotopes are not paradoxical but rather related to the water that cannot be sampled with suction lysimeters but is still available for plant water uptake. The simulations accounting for fast and slow flow supported the conceptualization of the two soil pore domains with isotopic exchange via vapor exchange because this model setup resulted in the best model performance. Overall, these findings are of high relevance for current understanding related to the source and isotopic composition of water taken up by plants.}, number={1}, journal={Vadose Zone Journal}, publisher={Soil Science Society of America}, author={Sprenger, Matthias and Tetzlaff, Doerthe and Buttle, Jim and Laudon, Hjalmar and Leistert, Hannes and Mitchell, Carl P.J. and Snelgrove, Jenna and Weiler, Markus and Soulsby, Chris}, year={2018}, pages={0} }
 @article{sprenger_tetzlaff_buttle_carey_mcnamara_laudon_shatilla_soulsby_2018, title={Storage, mixing, and fluxes of water in the critical zone across northern environments inferred by stable isotopes of soil water}, volume={6}, url={https://doi.org/10.1002/hyp.13135}, DOI={10.1002/hyp.13135}, abstractNote={Abstract}, number={12}, journal={Hydrological Processes}, publisher={Wiley}, author={Sprenger, Matthias and Tetzlaff, Doerthe and Buttle, Jim and Carey, Sean K. and McNamara, James P. and Laudon, Hjalmar and Shatilla, Nadine J. and Soulsby, Chris}, year={2018}, month={Jun}, pages={1720–1737} }
 @article{sprenger_tetzlaff_buttle_laudon_soulsby_2018, title={Water ages in the critical zone of long-term experimental sites in northern latitudes}, volume={22}, url={https://doi.org/10.5194/hess-22-3965-2018}, DOI={10.5194/hess-22-3965-2018}, abstractNote={Abstract. As northern environments undergo intense changes due to a
warming climate and altered land use practices, there is an urgent need for
improved understanding of the impact of atmospheric forcing and vegetation on
water storage and flux dynamics in the critical zone. We therefore assess the
age dynamics of water stored in the upper 50 cm of soil, and in evaporation,
transpiration, or recharge fluxes at four soil–vegetation units of podzolic
soils in the northern latitudes with either heather or tree vegetation
(Bruntland Burn in Scotland, Dorset in Canada, and Krycklan in Sweden). We
derived the age dynamics with the physically based SWIS (Soil Water Isotope
Simulator) model, which has been successfully used to simulate the
hydrometric and isotopic dynamics in the upper 50 cm of soils at the study
sites. The modelled subsurface was divided into interacting fast and slow
flow domains. We tracked each day's infiltrated water through the critical
zone and derived forward median travel times (which show how long the water
takes to leave the soil via evaporation, transpiration, or recharge), and
median water ages (to estimate the median age of water in soil storage or the
evaporation, transpiration, and recharge fluxes). Resulting median travel
times were time-variant, mainly governed by major recharge events during
snowmelt in Dorset and Krycklan or during the wetter winter conditions in
Bruntland Burn. Transpiration travel times were driven by the vegetation
growth period with the longest travel times (200 days) for waters infiltrated
in early dormancy and the shortest travel times during the vegetation period.
However, long tails of the travel time distributions in evaporation and
transpiration revealed that these fluxes comprised waters older than
100 days. At each study site, water ages of soil storage, evaporation,
transpiration, and recharge were all inversely related to the storage volume
of the critical zone: water ages generally decreased exponentially with
increasing soil water storage. During wet periods, young soil waters were
more likely to be evapotranspired and recharged than during drier periods.
While the water in the slow flow domain showed long-term seasonal dynamics
and generally old water ages, the water ages of the fast flow domain were
generally younger and much flashier. Our results provide new insights into
the mixing and transport processes of soil water in the upper layer of the
critical zone, which is relevant for hydrological modelling at the plot to
catchment scales as the common assumption of a well-mixed system in the
subsurface holds for neither the evaporation, transpiration, or recharge.
                    }, number={7}, journal={Hydrology and Earth System Sciences}, publisher={Copernicus GmbH}, author={Sprenger, Matthias and Tetzlaff, Doerthe and Buttle, Jim and Laudon, Hjalmar and Soulsby, Chris}, year={2018}, month={Jul}, pages={3965–3981} }
 @article{sprenger_tetzlaff_buttle_laudon_soulsby_2018, title={Water ages in the critical zone of long-term experimental sites in northern latitudes}, volume={3}, url={https://doi.org/10.5194/hess-2018-144}, DOI={10.5194/hess-2018-144}, abstractNote={Abstract. As northern environments undergo intense respond due to a warming climate and altered land use practices, there is an urgent need for improved understanding of the impact of atmospheric forcing and vegetation on water storage and flux dynamics in the critical zone. We therefore assess the age dynamics of water stored in the upper 50 cm of soil, and in evaporation, transpiration or recharge fluxes at four soil-vegetation units of podzolic soils in the northern latitudes with either heather or tree vegetation (Bruntland Burn in Scotland, Dorset in Canada, and Krycklan in Sweden). We derived the age dynamics with the physically based SWIS (Soil Water Isotope Simulator) model, which has been successfully used to simulate the hydrometric and isotopic dynamics in the upper 50 cm of soils at the study sites. The modelled subsurface was divided into interacting fast and slow flow domains. We tracked each day's infiltrated water through the critical zone and derived forward median travel times (which show how long the water takes to leave the soil via evaporation, transpiration or recharge), and median water ages (to estimate the median age of water in soil storage or the evaporation, transpiration and recharge fluxes). Resulting median travel times were time-variant, mainly governed by major recharge events during snow melt in Dorset and Krycklan or during the wetter winter conditions in Bruntland Burn. Transpiration travel times were driven by the vegetation growth period with longest travel times (200 days) for waters infiltrated in early dormancy and shortest travel times during the vegetation period. However, long tails of the travel time distributions in evaporation and transpiration revealed that these fluxes comprised waters older than 100 days. At each study site, water ages of soil storage, evaporation, transpiration and recharge were all inversely related to the storage volume of the critical zone: water ages generally decreased exponentially with increasing soil water storage. During wet periods, young soil waters were more likely to be evapotranspired and recharged than during drier periods. While the water in the slow flow domain showed long-term seasonal dynamics and generally old water ages, the water ages of the fast flow domain were generally younger and much flashier. Our results provide new insights into the mixing and transport processes of soil water in the upper layer of the critical zone, which is relevant for hydrological modelling at the plot to catchment scales as the common assumption of a well-mixed system in the subsurface neither holds for the evaporation, transpiration nor recharge.
                        }, publisher={Copernicus GmbH}, author={Sprenger, Matthias and Tetzlaff, Doerthe and Buttle, Jim and Laudon, Hjalmar and Soulsby, Chris}, year={2018}, month={Mar} }
 @article{sprenger_tetzlaff_tunaley_dick_soulsby_2017, title={Evaporation fractionation in a peatland drainage network affects stream water isotope composition}, volume={53}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85011063373&partnerID=MN8TOARS}, DOI={10.1002/2016WR019258}, abstractNote={Abstract}, number={1}, journal={Water Resources Research}, publisher={Wiley-Blackwell}, author={Sprenger, Matthias and Tetzlaff, Doerthe and Tunaley, Claire and Dick, Jonathan and Soulsby, Chris}, year={2017}, month={Jan}, pages={851–866} }
 @article{angermann_jackisch_allroggen_sprenger_zehe_tronicke_weiler_blume_2017, title={Form and function in hillslope hydrology: characterization of subsurface flow based on response observations}, volume={21}, url={https://doi.org/10.5194/hess-21-3727-2017}, DOI={10.5194/hess-21-3727-2017}, abstractNote={Abstract. The phrase form and function was established in architecture and biology and refers to the idea that form and functionality are closely correlated, influence each other, and co-evolve. We suggest transferring this idea to hydrological systems to separate and analyze their two main characteristics: their form, which is equivalent to the spatial structure and static properties, and their function, equivalent to internal responses and hydrological behavior. While this approach is not particularly new to hydrological field research, we want to employ this concept to explicitly pursue the question of what information is most advantageous to understand a hydrological system. We applied this concept to subsurface flow within a hillslope, with a methodological focus on function: we conducted observations during a natural storm event and followed this with a hillslope-scale irrigation experiment. The results are used to infer hydrological processes of the monitored system. Based on these findings, the explanatory power and conclusiveness of the data are discussed. The measurements included basic hydrological monitoring methods, like piezometers, soil moisture, and discharge measurements. These were accompanied by isotope sampling and a novel application of 2-D time-lapse GPR (ground-penetrating radar). The main finding regarding the processes in the hillslope was that preferential flow paths were established quickly, despite unsaturated conditions. These flow paths also caused a detectable signal in the catchment response following a natural rainfall event, showing that these processes are relevant also at the catchment scale. Thus, we conclude that response observations (dynamics and patterns, i.e., indicators of function) were well suited to describing processes at the observational scale. Especially the use of 2-D time-lapse GPR measurements, providing detailed subsurface response patterns, as well as the combination of stream-centered and hillslope-centered approaches, allowed us to link processes and put them in a larger context. Transfer to other scales beyond observational scale and generalizations, however, rely on the knowledge of structures (form) and remain speculative. The complementary approach with a methodological focus on form (i.e., structure exploration) is presented and discussed in the companion paper by Jackisch et al.(2017).
                    }, number={7}, journal={Hydrology and Earth System Sciences}, publisher={Copernicus GmbH}, author={Angermann, Lisa and Jackisch, Conrad and Allroggen, Niklas and Sprenger, Matthias and Zehe, Erwin and Tronicke, Jens and Weiler, Markus and Blume, Theresa}, year={2017}, month={Jul}, pages={3727–3748} }
 @article{jackisch_angermann_allroggen_sprenger_blume_tronicke_zehe_2017, title={Form and function in hillslope hydrology: in situ imaging and characterization of flow-relevant structures}, volume={21}, url={https://doi.org/10.5194/hess-21-3749-2017}, DOI={10.5194/hess-21-3749-2017}, abstractNote={Abstract. The study deals with the identification and characterization of rapid subsurface flow structures through pedo- and geo-physical measurements and irrigation experiments at the point, plot and hillslope scale. Our investigation of flow-relevant structures and hydrological responses refers to the general interplay of form and function, respectively. To obtain a holistic picture of the subsurface, a large set of different laboratory, exploratory and experimental methods was used at the different scales. For exploration these methods included drilled soil core profiles, in situ measurements of infiltration capacity and saturated hydraulic conductivity, and laboratory analyses of soil water retention and saturated hydraulic conductivity. The irrigation experiments at the plot scale were monitored through a combination of dye tracer, salt tracer, soil moisture dynamics, and 3-D time-lapse ground penetrating radar (GPR) methods. At the hillslope scale the subsurface was explored by a 3-D GPR survey. A natural storm event and an irrigation experiment were monitored by a dense network of soil moisture observations and a cascade of 2-D time-lapse GPR trenches. We show that the shift between activated and non-activated state of the flow paths is needed to distinguish structures from overall heterogeneity. Pedo-physical analyses of point-scale samples are the basis for sub-scale structure inference. At the plot and hillslope scale 3-D and 2-D time-lapse GPR applications are successfully employed as non-invasive means to image subsurface response patterns and to identify flow-relevant paths. Tracer recovery and soil water responses from irrigation experiments deliver a consistent estimate of response velocities. The combined observation of form and function under active conditions provides the means to localize and characterize the structures (this study) and the hydrological processes (companion study Angermann et al., 2017, this issue).
                    }, number={7}, journal={Hydrology and Earth System Sciences}, publisher={Copernicus GmbH}, author={Jackisch, Conrad and Angermann, Lisa and Allroggen, Niklas and Sprenger, Matthias and Blume, Theresa and Tronicke, Jens and Zehe, Erwin}, year={2017}, month={Jul}, pages={3749–3775} }
 @article{soulsby_braun_sprenger_weiler_tetzlaff_2017, title={Influence of forest and shrub canopies on precipitation partitioning and isotopic signatures}, volume={31}, url={https://doi.org/10.1002/hyp.11351}, DOI={10.1002/hyp.11351}, abstractNote={Abstract}, number={24}, journal={Hydrological Processes}, publisher={Wiley-Blackwell}, author={Soulsby, Chris and Braun, Hannah and Sprenger, Matthias and Weiler, Markus and Tetzlaff, Doerthe}, year={2017}, month={Nov}, pages={4282–4296} }
 @article{sprenger_tetzlaff_soulsby_2017, title={No influence of CO2 on stable isotope analyses of soil waters with off-axis integrated cavity output spectroscopy (OA-ICOS)}, volume={31}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85011665212&partnerID=MN8TOARS}, DOI={10.1002/rcm.7815}, abstractNote={RationaleIt was recently shown that the presence of CO2 affects the stable isotope (δ2H and δ18O values) analysis of water vapor via Wavelength‐Scanned Cavity Ring‐Down Spectroscopy. Here, we test how much CO2 is emitted from soil samples and if the CO2 in the headspace influences the isotope analysis with the direct equilibration method by Off‐Axis Integrated Cavity Output Spectroscopy (OA‐ICOS).}, number={5}, journal={Rapid Communications in Mass Spectrometry}, publisher={Wiley-Blackwell}, author={Sprenger, Matthias and Tetzlaff, Doerthe and Soulsby, Chris}, year={2017}, month={Mar}, pages={430–436} }
 @article{sprenger_tetzlaff_soulsby_2017, title={Soil water stable isotopes reveal evaporation dynamics at the soil–plant–atmosphere interface of the critical zone}, volume={21}, url={https://doi.org/10.5194/hess-21-3839-2017}, DOI={10.5194/hess-21-3839-2017}, abstractNote={Abstract. Understanding the influence of vegetation on water storage and flux in the upper soil is crucial in assessing the consequences of climate and land use change. We sampled the upper 20 cm of podzolic soils at 5 cm intervals in four sites differing in their vegetation (Scots Pine (Pinus sylvestris) and heather (Calluna sp. and Erica Sp)) and aspect. The sites were located within the Bruntland Burn long-term experimental catchment in the Scottish Highlands, a low energy, wet environment. Sampling took place on 11 occasions between September 2015 and September 2016 to capture seasonal variability in isotope dynamics. The pore waters of soil samples were analyzed for their isotopic composition (δ2H and δ18O) with the direct-equilibration method. Our results show that the soil waters in the top soil are, despite the low potential evaporation rates in such northern latitudes, kinetically fractionated compared to the precipitation input throughout the year. This fractionation signal decreases within the upper 15 cm resulting in the top 5 cm being isotopically differentiated to the soil at 15–20 cm soil depth. There are significant differences in the fractionation signal between soils beneath heather and soils beneath Scots pine, with the latter being more pronounced. But again, this difference diminishes within the upper 15 cm of soil. The enrichment in heavy isotopes in the topsoil follows a seasonal hysteresis pattern, indicating a lag time between the fractionation signal in the soil and the increase/decrease of soil evaporation in spring/autumn. Based on the kinetic enrichment of the soil water isotopes, we estimated the soil evaporation losses to be about 5 and 10 % of the infiltrating water for soils beneath heather and Scots pine, respectively. The high sampling frequency in time (monthly) and depth (5 cm intervals) revealed high temporal and spatial variability of the isotopic composition of soil waters, which can be critical, when using stable isotopes as tracers to assess plant water uptake patterns within the critical zone or applying them to calibrate tracer-aided hydrological models either at the plot to the catchment scale.
                    }, number={7}, journal={Hydrology and Earth System Sciences}, publisher={Copernicus GmbH}, author={Sprenger, Matthias and Tetzlaff, Doerthe and Soulsby, Chris}, year={2017}, month={Jul}, pages={3839–3858} }
 @article{sprenger_tetzlaff_soulsby_2017, title={Stable isotopes reveal evaporation dynamics at the soil-plant-atmosphere interface of the critical zone}, volume={2}, url={https://doi.org/10.5194/hess-2017-87}, DOI={10.5194/hess-2017-87}, abstractNote={Abstract. Understanding the influence of vegetation on water storage and flux in the upper soil is crucial in assessing the consequences of climate and land use change. We sampled the upper 20 cm of podzolic soils at 5 cm intervals in four sites differing in their vegetation (Scots Pine (Pinus sylvestris) and heather (Calluna sp. and Erica Sp)) and aspect. The sites were located within the Bruntland Burn long-term experimental catchment in the Scottish Highlands; a low energy, wet environment. Sampling took place on 11 occasions between September 2015 and September 2016 to capture seasonal variability in isotope dynamics. The pore waters of soil samples were analysed for their isotopic composition (δ2H and δ18H) with the direct equilibration method. Our results show that the soil waters in the top soil are, despite the low potential evaporation rates in such northern latitudes, kinetically fractionated compared to the precipitation input throughout the year. This fractionation signal decreases within the upper 15 cm resulting in the top 5 cm being isotopically differentiated to the soil at 15–20 cm soil depth. There are significant differences in the fractionation signal between soils beneath heather and soils beneath Scots pine, with the latter being more pronounced. But again, this difference diminishes within the upper 15 cm of soil. The enrichment in heavy isotopes in the topsoil follows a seasonal hysteresis pattern, indicating a lag time between the fractionation signal in the soil and the increase/decrease of soil evaporation in spring/autumn. Based on the kinetic enrichment of the soil water isotopes, we estimated the soil evaporation losses to be about 5 and 10 % of the infiltrating water for soils beneath heather and Scots pine, respectively. The high sampling frequency in time (monthly) and depth (5 cm intervals) revealed high temporal and spatial variability of the isotopic composition of soil waters, which can be critical, when using stable isotopes as tracers to assess plant water uptake patterns within the critical zone or applying them to calibrate tracer-aided hydrological models either at the plot to the catchment scale.
                        }, publisher={Copernicus GmbH}, author={Sprenger, Matthias and Tetzlaff, Doerthe and Soulsby, Chris}, year={2017}, month={Feb} }
 @article{sprenger_weiler_2017, title={Tracing Water Through the Critical Zone}, volume={98}, DOI={10.1029/2018eo074313}, abstractNote={The authors of a recent paper in Reviews of Geophysics describe how isotope hydrology offers new insights into interactions at the interface between soil, vegetation, and the atmosphere.}, journal={Eos}, publisher={American Geophysical Union (AGU)}, author={Sprenger, Matthias and Weiler, Markus}, year={2017}, month={Jun} }
 @article{sprenger_erhardt_riedel_weiler_2016, title={Historical tracking of nitrate in contrasting vineyards using water isotopes and nitrate depth profiles}, volume={222}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84958984676&partnerID=MN8TOARS}, DOI={10.1016/j.agee.2016.02.014}, abstractNote={The European Water Framework Directive (EWFD) aims to achieve a good chemical status for the groundwater bodies in Europe by the year 2015. Despite the effort to reduce the nitrate pollution from agriculture within the last two decades, there are still many groundwater aquifers that exceed nitrate concentrations above the EWFD threshold of 50 mg L⿿1. Viticulture is seen as a major contributor of nitrate leaching and sowing of a green cover was shown to have a positive effect on lowering the nitrate loads in the upper 90 cm of the soil. However, the consequences for nitrate leaching into the subsoil were not yet tested. We analyzed the nitrate concentrations and pore water stable isotope composition (δ 2H) to a depth of 380 cm in soil profiles under an old vineyard and a young vineyard with either soil tillage or permanent green cover in between the grapevines. The pore water δ 2H data was used to calibrate a soil physical model, which was then used to infer the age of the soil water at different depths. This way, we could relate elevated nitrate concentrations below an old vineyard to tillage processes that took place during the winter two years before the sampling. We further showed that the elevated nitrate concentration in the subsoil of a young vineyard can be related to the soil tillage prior to the planting of the new vineyard. If the soil was kept bare due to tillage, a nitrate concentration of 200 kg NO3⿿-N ha⿿1 was found in 290⿿380 cm depth 2.5 years after the set-up of the vineyard. The amount of nitrate leaching was considerably reduced due to a seeded green cover between the grapevines that took up a high share of the mineralized nitrate reducing a potential contamination of the groundwater.}, journal={Agriculture, Ecosystems & Environment}, publisher={Elsevier BV}, author={Sprenger, Matthias and Erhardt, Martin and Riedel, Monika and Weiler, Markus}, year={2016}, month={Apr}, pages={185–192} }
 @article{sprenger_leistert_gimbel_weiler_2016, title={Illuminating hydrological processes at the soil-vegetation-atmosphere interface with water stable isotopes}, volume={54}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84988028235&partnerID=MN8TOARS}, DOI={10.1002/2015rg000515}, abstractNote={Abstract}, number={3}, journal={Rev. Geophys.}, publisher={Wiley-Blackwell}, author={Sprenger, Matthias and Leistert, Hannes and Gimbel, Katharina and Weiler, Markus}, year={2016}, pages={674–704} }
 @article{jackisch_angermann_allroggen_sprenger_blume_weiler_tronicke_zehe_2016, title={In situ investigation of rapid subsurface flow: Identification of relevant spatial structures beyond heterogeneity}, volume={5}, url={https://doi.org/10.5194/hess-2016-190}, DOI={10.5194/hess-2016-190}, abstractNote={Abstract. Rapid subsurface flow in structured soils facilitates fast vertical and lateral redistribution of event water. Despite their significance and omnipresence the related processes are challenging hydrological exploration, monitoring, modeling and theory. One reason for this is that flow processes at high velocities are difficult to observe in the subsurface. Another reason is that advective flow is channeled in distinct connected structures several orders of magnitude smaller than commonly resolved observation volumes. This is the second part of a companion paper with a focus on \\textit{in situ} experimental exploration of rapid subsurface flow. Complementary to the temporal dynamics, this study looks into the identification of spatially organized structures. We present a bottom-up approach with point-scale measurements, plot-scale multi-tracer experiments and a hillslope-scale irrigation experiment. Special emphasis is given to the employed 2D and 3D time-lapse ground penetrating radar monitoring under field conditions on forested, young soils on periglacial slope deposits. The study highlights the difficulty to draw conclusions beyond overall heterogeneity from point observations in a basically unknown and structured domain. We also spotlight the challenge to identify relevant structures based on a single quasi-static exploration. A coherent combination of different hydrological and geophysical methods to monitor the system under driven conditions was key to reduce ambiguity in the identification of hydrologically relevant structures and the overall process understanding.
                        }, publisher={Copernicus GmbH}, author={Jackisch, Conrad and Angermann, Lisa and Allroggen, Niklas and Sprenger, Matthias and Blume, Theresa and Weiler, Markus and Tronicke, Jens and Zehe, Erwin}, year={2016}, month={May} }
 @article{angermann_jackisch_allroggen_sprenger_zehe_tronicke_weiler_blume_2016, title={In situ investigation of rapid subsurface flow: Temporal dynamics and catchment-scale implication}, volume={5}, url={https://doi.org/10.5194/hess-2016-189}, DOI={10.5194/hess-2016-189}, abstractNote={Abstract. Preferential flow is omnipresent in natural systems. It links multiple scales from single pores to entire hillslopes and potentially influences the discharge dynamics of a catchment. However, there is still a lack of appropriate monitoring techniques and thus, process understanding. In this study, a promising combination of 2D time-lapse ground-penetrating radar (GPR) and soil moisture monitoring was used to observe preferential flow processes in highly structured soils during a hillslope-scale irrigation experiment. The 2D time-lapse GPR data were interpreted using structural similarity attributes, highlighting changes between individual time-lapse measurements. These changes are related to soil moisture variations in the subsurface. In combination with direct measurements of soil moisture, the spatial and temporal characteristics of the resulting patterns can give evidence about subsurface flow processes. The response dynamics at the hillslope were compared to the runoff response behavior of the headwater catchment. The experiment revealed a fast establishment of hillslope-scale connectivity despite unsaturated conditions, with high response velocities of up to 10−3 m s−1 or faster, and a high portion of mobile water. These processes substantially impact the overall catchment response behavior. While the presented approach is a good way to observe the temporal dynamics and general patterns, the spatial characteristics of small-scale preferential flow path could not be fully resolved.
                        }, publisher={Copernicus GmbH}, author={Angermann, Lisa and Jackisch, Conrad and Allroggen, Niklas and Sprenger, Matthias and Zehe, Erwin and Tronicke, Jens and Weiler, Markus and Blume, Theresa}, year={2016}, month={May} }
 @article{sprenger_seeger_blume_weiler_2016, title={Travel times in the vadose zone: Variability in space and time}, volume={6}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84980337504&partnerID=MN8TOARS}, DOI={10.1002/2015wr018077}, abstractNote={Abstract}, number={8}, journal={Water Resour. Res.}, publisher={Wiley-Blackwell}, author={Sprenger, Matthias and Seeger, Stefan and Blume, Theresa and Weiler, Markus}, year={2016}, month={Jun}, pages={5727–5754} }
 @article{sprenger_herbstritt_weiler_2015, title={Established methods and new opportunities for pore water stable isotope analysis}, volume={29}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84956594756&partnerID=MN8TOARS}, DOI={10.1002/hyp.10643}, abstractNote={Abstract}, number={25}, journal={Hydrol. Process.}, publisher={Wiley-Blackwell}, author={Sprenger, Matthias and Herbstritt, Barbara and Weiler, Markus}, year={2015}, month={Sep}, pages={5174–5192} }
 @article{sprenger_volkmann_blume_weiler_2015, title={Estimating flow and transport parameters in the unsaturated zone with pore water stable isotopes}, volume={19}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84930960378&partnerID=MN8TOARS}, DOI={10.5194/hess-19-2617-2015}, abstractNote={Abstract. Determining the soil hydraulic properties is a prerequisite to physically model transient water flow and solute transport in the vadose zone. Estimating these properties by inverse modelling techniques has become more common within the last 2 decades. While these inverse approaches usually fit simulations to hydrometric data, we expanded the methodology by using independent information about the stable isotope composition of the soil pore water depth profile as a single or additional optimization target. To demonstrate the potential and limits of this approach, we compared the results of three inverse modelling strategies where the fitting targets were (a) pore water isotope concentrations, (b) a combination of pore water isotope concentrations and soil moisture time series, and (c) a two-step approach using first soil moisture data to determine water flow parameters and then the pore water stable isotope concentrations to estimate the solute transport parameters. The analyses were conducted at three study sites with different soil properties and vegetation. The transient unsaturated water flow was simulated by solving the Richards equation numerically with the finite-element code of HYDRUS-1D. The transport of deuterium was simulated with the advection-dispersion equation, and a modified version of HYDRUS was used, allowing deuterium loss during evaporation. The Mualem–van Genuchten and the longitudinal dispersivity parameters were determined for two major soil horizons at each site. The results show that approach (a), using only the pore water isotope content, cannot substitute hydrometric information to derive parameter sets that reflect the observed soil moisture dynamics but gives comparable results when the parameter space is constrained by pedotransfer functions. Approaches (b) and (c), using both the isotope profiles and the soil moisture time series, resulted in good simulation results with regard to the Kling–Gupta efficiency and good parameter identifiability. However, approach (b) has the advantage that it considers the isotope data not only for the solute transport parameters but also for water flow and root water uptake, and thus increases parameter realism. Approaches (b) and (c) both outcompeted simulations run with parameters derived from pedotransfer functions, which did not result in an acceptable representation of the soil moisture dynamics and pore water stable isotope composition. Overall, parameters based on this new approach that includes isotope data lead to similar model performances regarding the water balance and soil moisture dynamics and better parameter identifiability than the conventional inverse model approaches limited to hydrometric fitting targets. If only data from isotope profiles in combination with textural information is available, the results are still satisfactory. This method has the additional advantage that it will not only allow us to estimate water balance and response times but also site-specific time variant transit times or solute breakthrough within the soil profile.
                    }, number={6}, journal={Hydrol. Earth Syst. Sci.}, publisher={Copernicus GmbH}, author={Sprenger, M. and Volkmann, T. H. M. and Blume, T. and Weiler, M.}, year={2015}, pages={2617–2635} }
 @article{sprenger_oelmann_weihermüller_wolf_wilcke_potvin_2013, title={Tree species and diversity effects on soil water seepage in a tropical plantation}, volume={309}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84884816813&partnerID=MN8TOARS}, DOI={10.1016/j.foreco.2013.03.022}, abstractNote={Plant diversity has been shown to influence the water cycle of forest ecosystems by differences in water consumption and the associated effects on groundwater recharge. However, the effects of biodiversity on soil water fluxes remain poorly understood for native tree species plantations in the tropics. Therefore, we estimated soil water fluxes and assessed the effects of tree species and diversity on these fluxes in an experimental native tree species plantation in Sardinilla (Panama). The study was conducted during the wet season 2008 on plots of monocultures and mixtures of three or six tree species. Rainfall and soil water content were measured and evapotranspiration was estimated with the Penman-Monteith equation. Soil water fluxes were estimated using a simple soil water budget model considering water input, output, and soil water and groundwater storage changes and in addition, were simulated using the physically based one-dimensional water flow model Hydrus-1D.

In general, the Hydrus simulation did not reflect the observed pressure heads, in that modeled pressure heads were higher compared to measured ones. On the other hand, the results of the water balance equation (WBE) reproduced observed water use patterns well. In monocultures, the downward fluxes through the 200 cm-depth plane were highest below Hura crepitans (6.13 mm day−1) and lowest below Luehea seemannii (5.18 mm day−1). The average seepage rate in monocultures (±SE) was 5.66 ± 0.18 mm day−1, and therefore, significantly higher than below six-species mixtures (5.49 ± 0.04 mm day−1) according to overyielding analyses. The three-species mixtures had an average seepage rate of 5.63 ± 0.12 mm day−1 and their values did not differ significantly from the average values of the corresponding species in monocultures. Seepage rates were driven by the transpiration of the varying biomass among the plots (r = 0.61, p = 0.017). Thus, a mixture of trees with different growth rates resulted in moderate seepage rates compared to monocultures of either fast growing or slow growing tree species. Our results demonstrate that tree-species specific biomass production and tree diversity are important controls of seepage rates in the Sardinilla plantation during the wet season.}, journal={Forest Ecology and Management}, publisher={Elsevier BV}, author={Sprenger, Matthias and Oelmann, Yvonne and Weihermüller, Lutz and Wolf, Sebastian and Wilcke, Wolfgang and Potvin, Catherine}, year={2013}, pages={76–86} }