Acknowledgements. We would like to thank members of the Northern Rivers Institute, Aberdeen University, for helpful discussions of data. We also thank Lars Rasmussen, Jolanta Kazmierczak and Charlotte Ditlevsen for help in the field. This study is part of the Hydrology Observatory, HOBE (http://www.hobe.dk), funded by the Villum Foundation and was as well funded by the Aarhus University Research Foundation.Peer reviewedPublisher PD

Duque, C.

Engesgaard, P. K.

Poulsen, J. R.

Sebok, E.

Tetzlaff, D.

English

Sebök, Éva

Engesgaard, Peter Knudegaard

Copenhagen University Research Information System

Detecting groundwater discharge dynamics from point-to-catchment scale in a lowland stream:combining hydraulic and tracer methods

Detecting, quantifying and understanding groundwater discharge to streams
are crucial for the assessment of water, nutrient and contaminant
exchange at the groundwater–surface water interface. In lowland agricultural
catchments with significant groundwater discharge this is of particular
importance because of the risk of excess leaching of nutrients to streams.
Here we aim to combine hydraulic and tracer methods from point-to-catchment
scale to assess the temporal and spatial variability of groundwater
discharge in a lowland, groundwater gaining stream in Denmark. At the point-scale, groundwater fluxes to the stream were quantified based on vertical
streambed temperature profiles (VTPs). At the reach scale (0.15–2 km), the
spatial distribution of zones of focused groundwater discharge was
investigated by the use of distributed temperature sensing (DTS).
Groundwater discharge to the stream was quantified using differential
gauging with an acoustic Doppler current profiler (ADCP). At the catchment
scale (26–114 km2), runoff sources during main rain events were
investigated by hydrograph separations based on electrical conductivity (EC)
and stable isotopes 2H/1H. Clear differences in runoff sources
between catchments were detected, ranging from approximately 65% event
water for the most responsive sub-catchment to less than 10% event water
for the least responsive sub-catchment. This was supported by the
groundwater head gradients, where the location of weaker gradients
correlated with a stronger response to precipitation events. This shows a
large variability in groundwater discharge to the stream, despite the
similar lowland characteristics of sub-catchments indicating the usefulness
of environmental tracers for obtaining information about integrated
catchment functioning during precipitation events. There were also clear
spatial patterns of focused groundwater discharge detected by the DTS and
ADCP measurements at the reach scale indicating high spatial variability,
where a significant part of groundwater discharge was concentrated in few
zones indicating the possibility of concentrated nutrient or pollutant
transport zones from nearby agricultural fields. VTP measurements confirmed
high groundwater fluxes in discharge areas indicated by DTS and ADCP, and
this coupling of ADCP, DTS and VTP proposes a novel field methodology to
detect areas of concentrated groundwater discharge with higher resolution

J. R. Poulsen

E. Sebok

C. Duque

D. Tetzlaff

P. K. Engesgaard

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Detecting groundwater discharge dynamics from point-to-catchment scale in a lowland stream: combining hydraulic and tracer methods

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Detecting groundwater discharge dynamics from point-to-catchment scale in a lowland stream : Combining hydraulic and tracer methods

Detecting groundwater discharge dynamics from point-to-catchment scale in a lowland stream : Combining hydraulic and tracer methods

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