@article{KrauseTecklenburgMunzetal.2013,
  author    = {Krause, Stefan and Tecklenburg, Christina and Munz, Matthias and Naden, Emma},
  title     = {Streambed nitrogen cycling beyond the hyporheic zone: Flow controls on horizontal patterns and depth distribution of nitrate and dissolved oxygen in the upwelling groundwater of a lowland river},
  series = {Journal of geophysical research : Biogeosciences},
  volume    = {118},
  journal   = {Journal of geophysical research : Biogeosciences},
  number    = {1},
  publisher = {American Geophysical Union},
  address   = {Washington},
  issn      = {0148-0227},
  doi       = {10.1029/2012JG002122},
  pages     = {54 -- 67},
  year      = {2013},
  abstract  = {Biogeochemical turnover in hyporheic zones is known to have the potential to affect the chemical signature of surface water cycling through shallow streambed sediments. This study investigates the impact of streambed physical properties on the fate of nitrate and dissolved oxygen in groundwater upwelling through the streambed of a lowland river. For analyzing depth-dependent patterns and zonation of nitrogen concentrations, diffuse gel probes in shallow (top 15 cm) streambed sediments have been deployed in a nested setup together with multilevel minipiezometers for streambed sediments of 15-150 cm. Spatial heterogeneity of groundwater upwelling was controlled by patterns of low-conductivity peat and clay strata that caused locally confined conditions, suggesting increased streambed residence times. Nitrate concentrations in the upwelling groundwater changed by up to 68.06 mg L-1 within the top 15 cm of streambed sediments and by up to 107.47 mg L-1 at depths of 15-150 cm, indicating that significant nitrogen turnover was not restricted to shallow streambed sediments. Intensive reduction of nitrate concentrations was found, in particular, in vicinity of low-conductivity streambed strata. The coincidence of confined groundwater upwelling and reduced oxygen concentrations at these locations suggests that increased residence times and associated depletion of dissolved oxygen create conditions favorable for nitrate reduction. Our results highlight that increased nitrogen turnover at aquifer-river interfaces is not necessarily limited to shallow streambed zones, where surface water is mixing with groundwater, but can affect upwelling groundwater in reactive hot spots that extend to greater streambed depths and beyond hyporheic mixing zones. Citation: Krause, S., C. Tecklenburg, M. Munz, and E. Naden (2013), Streambed nitrogen cycling beyond the hyporheic zone: Flow controls on horizontal patterns and depth distribution of nitrate and dissolved oxygen in the upwelling groundwater of a lowland river,},
  language  = {en}
}
@article{MunzKrauseTecklenburgetal.2011,
  author    = {Munz, Matthias and Krause, Stefan and Tecklenburg, Christina and Binley, Andrew},
  title     = {Reducing monitoring gaps at the aquifer-river interface by modelling groundwater-surface water exchange flow patterns},
  series = {Hydrological processes},
  volume    = {25},
  journal   = {Hydrological processes},
  number    = {23},
  publisher = {Wiley-Blackwell},
  address   = {Malden},
  issn      = {0885-6087},
  doi       = {10.1002/hyp.8080},
  pages     = {3547 -- 3562},
  year      = {2011},
  abstract  = {This study investigates spatial patterns and temporal dynamics of aquifer-river exchange flow at a reach of the River Leith, UK. Observations of sub-channel vertical hydraulic gradients at the field site indicate the dominance of groundwater up-welling into the river and the absence of groundwater recharge from surface water. However, observed hydraulic heads do not provide information on potential surface water infiltration into the top 0-15 cm of the streambed as these depths are not covered by the existing experimental infrastructure. In order to evaluate whether surface water infiltration is likely to occur outside the 'window of detection', i.e. the shallow streambed, a numerical groundwater model is used to simulate hydrological exchanges between the aquifer and the river. Transient simulations of the successfully validated model (Nash and Sutcliff efficiency of 0.91) suggest that surface water infiltration is marginal and that the possibility of significant volumes of surface water infiltrating into non-monitored shallow streambed sediments can be excluded for the simulation period. Furthermore, the simulation results show that with increasing head differences between river and aquifer towards the end of the simulation period, the impact of streambed topography and hydraulic conductivity on spatial patterns of exchange flow rates decreases. A set of peak flow scenarios with altered groundwater-surface water head gradients is simulated in order to quantify the potential for surface water infiltration during characteristic winter flow conditions following the observation period. The results indicate that, particularly at the beginning of peak flow conditions, head gradients are likely to cause substantial increase in surface water infiltration into the streambed. The study highlights the potential for the improvement of process understanding of hyporheic exchange flow patterns at the stream reach scale by simulating aquifer-river exchange fluxes with a standard numerical groundwater model and a simple but robust model structure and parameterization. Copyright},
  language  = {en}
}
@article{KrauseBronstert2004,
  author    = {Krause, Stefan and Bronstert, Axel},
  title     = {Approximation of Groundwater - Surface Water - Interactions in a Mesoscale Lowland River Catchment},
  year      = {2004},
  language  = {en}
}