Research Questions and General Approach
More than 50 % of a landscape are drained by first and second order streams. These small streams are typically well connected to groundwater and consequently are primary receptors for diffuse contaminant inputs from sub-catchments. Hence the initial chemical signature of stream water as well as the overall water quality in rivers is largely governed by processes in these lower order headwater streams. Here, the transition zone between groundwater and surface water is commonly rich in organic material and often characterized by steep redox gradients and high biogeochemical activity, providing potentially highly reactive conditions for the turnover of redox-sensitive species such as pesticides and nutrients. This project will evaluate the importance of this transition zone for pollutant transformation and subsequent effects on stream water quality. Specific goals are to
- identify integral indicators to evaluate and quantify reaction potentials in the transition zone
- assess locations in the transition zone showing high reactivity and mass flux for NH4+, NO3–, and pesticides
- determine the variability of concentrations and fluxes of the lead substances over time and at integrating locations
- unravel key microbial populations involved in oxidative and reductive nitrogen cycling in groundwater-stream transition zones, elucidate the controls of their activity as impacted by seasonal dynamics and differential land-use
- derive effective turnover rates in the transition zone compared to turnover in other compartments of a sub-catchment based on process-based reactive transport modeling at local scales
Spatially highly resolved monitoring of water and solute fluxes using novel online field probes are coupled to a new method for sensitive 15N/14N isotope analysis and molecular biological tools to address the above mentioned research objectives. Field investigations are complemented by spatially explicit numerical models as depicted in the interdisciplinary toolbox above. This unique combination of approaches helps:
- To characterize the spatial and temporal patterns of groundwater infiltration and exfiltration in two contrasting first-order streams.
- To unravel spatio-temporal patterns of reactivity and nitrogen turnover for different land uses and hydraulic conditions.
- To evaluate the microbiology and transformation potential of the transition zone along highly instrumented stream transects.
- To evaluated the importance of the streambed and the near-stream aquifer for solute turnover.
Jakus, N., Blackwell, N., Osenbrueck, K., Straub, D., Byrne, J.M., Wang, Z., Lueders, T., Grathwohl, P., Kleindienst, S., Kappler, A. (submitted). Nitrate removal by a novel autotrophic nitrate-reducing iron(II)-oxidizing culture isolated from a pyrite-rich limestone aquifer.
Yang, J.,Heidbüchel, I., Xie, Y., Musolff, A., Fleckenstein, J.H. (in review) Exploring Solute Export in Catchments with Strong Seasonality Using StorAge Selection Functions, Water Resources Research.
Zhu, B., Friedrich, B., Wang, Z., Táncsics, A., Lueders, T. (2020). Availability of nitrite and nitrate as electron acceptors modulates anaerobic toluene-degrading communities in aquifer sediments. Front Microbiol, in press.
Lihl C., Heckel B., Grzybkowska A., Dybala-Defratyka A., Ponsin V., Torrentó C., Hunkeler D., Elsner M. (2020): Compound-Specific Chlorine Isotope Fractionation in Biodegradation of Atrazine, Environmental Science: Processes & Impacts (2020), DOI: 10.1039/C9EM00503J.
Lutz, S. R., Trauth, N., Musolff, A., Van Breukelen, B. M., Knöller, K., & Fleckenstein, J. H. (2020): How important is denitriﬁcation in riparian zones? Combining end‐member mixing and isotope modeling to quantify nitrate removal from riparian groundwater. Water Resources Research, 56, e2019WR025528. doi.org/10.1029/2019WR025528.
Melsbach A., Torrentó C., Ponsin V., Bolotin J., Lachat L., Prasuhn V., Hofstetter T., Hunkeler D., Elsner M. (2020): Dual-Element Isotope Analysis of Desphenylchloridazon to Investigate its Environmental Fate in a Systematic Field Study - A Long-Term Lysimeter Experiment, Environ. Sci. Technol. 54. DOI: 10.1021/acs.est.9b04606.
Zhu, B., Wang, Z., Kanaparthi, D., Kublik, S., Ge, T., Casper, P., Schloter, M., Lueders, T. (2020): Long-read amplicon sequencing of nitric oxide dismutase (Nod) genes reveal diverse oxygenic denitrifiers in agricultural soils and lake sediments. Microbial Ecology 2020. https://doi.org/10.1007/s00248-020-01482-0.
Knapp J.L.A., Osenbrück K., Brennwald M.S., Cirpka O.A. (2019) In-situ mass spectrometry improves the estimation of stream reaeration from gas-tracer tests, Sci. Total Environ., 655: 1062-1070.
Marozava, S., Meyer, A., Perez-de-Mora, A., Gharasoo, M., Zhuo, L., Wang, H., Cirpka, O., Meckenstock, R., Elsner, M. (2019). Mass Transfer Limitation During Slow Anaerobic Biodegradation of 2-Methylnaphthalene, Environ. Sci. Technol. 53 (2019) pp. 9481-9490, DOI:10.1021/acs.est.9b01152.
Jan-Micha Zarbock (2020): The influence of fast circulating groundwater components on the Mühlbach drainage system near Unterjesingen.
Fabian Kiemel (2020): Experimental investigation to quantify hydrologic turnover.
Alisa Finkbeiner (2020): Biogeochemistry and reactive processes in the riparian zone and aquifer of an agricultural first-order catchment.
Florian Faltermeier (2018): Experimental investigation of stream-groundwater interaction using salt tracer tests.
Judith Abele (2017): Zeitliche und räumliche Variabilität der Stickstoffspezies im Ammertalaquifer, Unterjesingen (Mühlbach).
Kim Schwarz (2016): Beispielhafte Anwendung des USGS MINIPOINT samplers: tiefenaufgelöste Erfassung gelöster Substanzen in der hyporheischen Zone.
Sara E. Anthony (2019): Travel Times of Infiltrating Surface Water determined via Electrical Conductivity Monitoring, Stable Water Isotope, and 222Radon Studies.