@article{MusolffSchmidtRodeetal.2016,
  author    = {Musolff, Andreas and Schmidt, Christian and Rode, Michael and Lischeid, Gunnar and Weise, Stephan M. and Fleckenstein, Jan H.},
  title     = {Groundwater head controls nitrate export from an agricultural lowland catchment},
  series = {Advances in water resources},
  volume    = {96},
  journal   = {Advances in water resources},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {0309-1708},
  doi       = {10.1016/j.advwatres.2016.07.003},
  pages     = {95 -- 107},
  year      = {2016},
  abstract  = {Solute concentration variability is of fundamental importance for the chemical and ecological state of streams. It is often closely related to discharge variability and can be characterized in terms of a solute export regime. Previous studies, especially in lowland catchments, report that nitrate is often exported with an accretion pattern of increasing concentrations with increasing discharge. Several modeling approaches exist to predict the export regime of solutes from the spatial relationship of discharge generating zones with solute availability in the catchment. For a small agriculturally managed lowland catchment in central Germany, we show that this relationship is controlled by the depth to groundwater table and its temporal dynamics. Principal component analysis of groundwater level time series from wells distributed throughout the catchment allowed derivation of a representative groundwater level time series that explained most of the discharge variability. Groundwater sampling revealed consistently decreasing nitrate concentrations with an increasing thickness of the unsaturated zone. The relationships of depth to groundwater table to discharge and to nitrate concentration were parameterized and integrated to successfully model catchment discharge and nitrate export on the basis of groundwater level variations alone. This study shows that intensive and uniform agricultural land use likely results in a clear and consistent concentration-depth relationship of nitrate, which can be utilized in simple approaches to predict stream nitrate export dynamics at the catchment scale. (C) 2016 Elsevier Ltd. All rights reserved.},
  language  = {en}
}
@article{MunzOswaldSchmidt2016,
  author    = {Munz, Matthias and Oswald, Sascha Eric and Schmidt, Christian},
  title     = {Analysis of riverbed temperatures to determine the geometry of subsurface water flow around in-stream geomorphological structures},
  series = {Journal of hydrology},
  volume    = {539},
  journal   = {Journal of hydrology},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0022-1694},
  doi       = {10.1016/j.jhydrol.2016.05.012},
  pages     = {74 -- 87},
  year      = {2016},
  abstract  = {The analytical evaluation of diurnal temperature variation in riverbed sediments provides detailed information on exchange fluxes between rivers and groundwater. The underlying assumption of the stationary, one-dimensional vertical flow field is frequently violated in natural systems where subsurface water flow often has a significant horizontal component. In this paper, we present a new methodology for identifying the geometry of the subsurface flow field using vertical temperature profiles. The statistical analyses are based on model optimisation and selection and are used to evaluate the shape of vertical amplitude ratio profiles. The method was applied to multiple profiles measured around in-stream geomorphological structures in a losing reach of a gravel bed river. The predominant subsurface flow field was systematically categorised in purely vertical and horizontal (hyporheic, parafluvial) components. The results highlight that river groundwater exchange flux at the head, crest and tail of geomorphological structures significantly deviated from the one-dimensional vertical flow, due to a significant horizontal component. The geometry of the subsurface water flow depended on the position around the geomorphological structures and on the river level. The methodology presented in this paper features great potential for characterising the spatial patterns and temporal dynamics of complex subsurface flow geometries by using measured temperature time series in vertical profiles. (C) 2016 Elsevier B.V. All rights reserved.},
  language  = {en}
}
@article{GruenebergerSchmidtJahnetal.2016,
  author    = {Gr{\"u}neberger, Anja Maria and Schmidt, Christian and Jahn, Sandro and Rhede, Dieter and Loges, Anselm and Wilke, Max},
  title     = {Interpretation of Raman spectra of the zircon-hafnon solid solution},
  series = {European journal of mineralogy},
  volume    = {28},
  journal   = {European journal of mineralogy},
  publisher = {Schweizerbart},
  address   = {Stuttgart},
  issn      = {0935-1221},
  doi       = {10.1127/ejm/2016/0028-2551},
  pages     = {721 -- 733},
  year      = {2016},
  abstract  = {Zircon (ZrSiO4), hafnon (HfSiO4) and five intermediate compositions were synthesized from a Pb silicate melt. The resulting crystals were 20-300 mu m in size and displayed sector and growth zoning. Raman spectra were acquired at locations in the sample for which preceding electron microprobe (EMP) analyses revealed sufficient compositional homogeneity. The dataset documents shifts of Raman bands with changing composition. In this study, bands that have previously not been reported were found for the intermediate compositions and for pure hafnon, in particular at wavenumbers less than 200 cm(-1). For these external modes, the dataset provides new insight into the compositional dependence of their frequencies. Density-functional theory calculations support the observations and are used for a detailed interpretation of the spectra. The pitfalls of the EMP analysis along the zircon-hafnon join are highlighted.},
  language  = {en}
}