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Understanding the hydrochemical evolution of a coastal dune system in SW England using a multiple tracer technique

Allen, Debbie; Darling, W. George; Williams, Peter J.; Stratford, Charlie J.; Robins, Nick S.. 2014 Understanding the hydrochemical evolution of a coastal dune system in SW England using a multiple tracer technique. Applied Geochemistry, 45. 94-104. 10.1016/j.apgeochem.2013.12.014

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Abstract/Summary

An improved knowledge of the hydrology of coastal dune systems is desirable for successful management of their diverse ecology under a changing climate. As a near-pristine coastal dune spit system, Braunton Burrows (SW England) is an ideal location for the study of the natural processes governing recharge to the dune groundwater system and the evolution of its water quality. Whereas previous investigations have tended to focus on inter-dune slacks, this study has also given attention to infiltration through the high dunes. Cores were taken through dunes and the resulting sand samples processed to provide information on grain size distribution and porewater chemistry. Groundwater samples were obtained from beneath dunes and slacks. A variety of geochemical techniques were applied including hydrochemistry, stable isotopes and residence time indicators. The unsaturated zone profiles indicate the existence of piston flow recharge with an infiltration rate of 0.75–1 m/yr, although faster rates probably also occur locally. Groundwater beneath the high dunes gave ages in the range 13–16 yr, compared to the dune slack groundwater ages of 5–7 yr, and an age of 22 yr for groundwater from the underlying mudstone aquifer. The chemistry of waters in both unsaturated and saturated zones is dominated by Ca and HCO3, supplemented by variable amounts of other ions derived from marine aerosols and limited reaction with sand grains and their coatings. The main chemical evolution of the porewaters occurs rapidly through the mobilisation of surface salt crusts and dissolution of shell carbonate. This situation changes little in the underlying groundwater, though an evolution towards reducing conditions increases the concentrations of redox-sensitive species such as Fe and Mn. The rapid chemical evolution of the infiltrating water means that its composition will respond quickly to changes in the supply of shell material and/or marine salts, which are possible consequences of climate change. However, the residence time measurements suggest the dune aquifer has a relatively long turnover time which will to some extent buffer such changes. The results of the present study should be transferable to natural dune systems in similar coastal situations.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1016/j.apgeochem.2013.12.014
CEH Sections: Acreman
ISSN: 0883-2927
Additional Keywords: GroundwaterBGS, Groundwater, Aquifer characterisation, Environmental tracers
Date made live: 29 Jan 2014 14:51 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/504676

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