Using environmental tracers to determine the relative importance of travel times in the unsaturated and saturated zones for the delay of nitrate reduction measures

Gerber, Christoph; Purtschert, Roland; Hunkeler, Daniel; Hug, Rainer; Sültenfuss, Jürgen (2018). Using environmental tracers to determine the relative importance of travel times in the unsaturated and saturated zones for the delay of nitrate reduction measures. Journal of hydrology, 561, pp. 250-266. Elsevier 10.1016/j.jhydrol.2018.03.043

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Groundwater quality in many regions with intense agriculture has deteriorated due to the leaching of nitrate and other agricultural pollutants. Modified agricultural practices can reduce the input of nitrate to groundwater bodies, but it is crucial to determine the time span over which these measures become effective at reducing nitrate levels in pumping wells. Such estimates can be obtained from hydrogeological modeling or lumped-parameter models (LPM) in combination with environmental tracer data. Two challenges in such tracer-based estimates are (i) accounting for the different modes of transport in the unsaturated zone (USZ), and (ii) assessing uncertainties. Here we extend a recently published Bayesian inference scheme for simple LPMs to include an explicit USZ model and apply it to the Dünnerngäu aquifer, Switzerland. Compared to a previous estimate of travel times in the aquifer based on a 2D hydrogeological model, our approach provides a more accurate assessment of the dynamics of nitrate concentrations in the aquifer. We find that including tracer measurements (³H/³He, ⁸⁵Kr, ³⁹Ar, ⁴He) reduces uncertainty in nitrate predictions if nitrate time series at wells are not available or short, but does not necessarily lead to better predictions if long nitrate time series are available. Additionally, the combination of tracer data with nitrate time series allows for a separation of the travel times in the unsaturated and saturated zone.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute > Climate and Environmental Physics

UniBE Contributor:

Gerber, Christoph and Purtschert, Roland

Subjects:

500 Science > 530 Physics

ISSN:

0022-1694

Publisher:

Elsevier

Language:

English

Submitter:

Doris Rätz

Date Deposited:

24 May 2018 10:39

Last Modified:

24 Oct 2019 21:38

Publisher DOI:

10.1016/j.jhydrol.2018.03.043

BORIS DOI:

10.7892/boris.116543

URI:

https://boris.unibe.ch/id/eprint/116543

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