Groundwater flooding: Ecosystem structure following an extreme recharge event

Julia Reiss, Anne Robertson, Daniel Perkins, Cristina Canhoto, Stefan Krause, Paul Romeijn, Katarina Elisabeth Fussmann

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1) Aquifers are recharged by surface water percolating through soil and rock and by connections with surface streams and rivers. Extreme rainfall can cause extensive flooding of surface waters and, eventually, of groundwaters. However, how the resultant changes in nutrients impact groundwater organisms and the structure of groundwater food webs is largely unknown.
2) We monitored abiotic (nutrients, temperature and more) and biotic (all organismal groups except viruses) conditions in eight groundwater boreholes in two locations in a chalk aquifer over the course of 25 weeks (ten sampling occasions), following an extreme rainfall- and groundwater-flooding event in the UK.
3) We show that groundwater flooding can cause substantial nutrient fertilisation of aquifers – nutrient concentrations (especially dissolved organic carbon) in the groundwater were highest when we started the sampling campaign, directly following the flood event, and then decreased over time while groundwater levels also declined back to their baseline.
4) Bacteria in the open water (i.e. bacteria not associated with sediment) became more abundant as the water table and DOC concentrations decreased. Importantly their functional richness tracked the DOC patterns, illustrating that bacteria were responsible for respiring DOC. Microbial metabolic activity and bacterial respiration, measured using smart tracers, supported this finding; DOC and microbial respiration showed a positive correlation.
5) The other biota (protists, micro- and macro-metazoans) showed different abundance patterns over time, but importantly, the entire sediment community, ranging from bacteria to macrofaunal species, showed a strong community size structure (mean size spectra slope: 1.12). Size spectra changed gradually through time towards steeper slopes, except in the very deep aquifer.

© 2018, Elsevier. The attached document (embargoed until 16/10/2020) is an author produced version of a paper published in SCIENCE OF THE TOTAL ENVIRONMENT uploaded in accordance with the publisher’s self- archiving policy. The final published version (version of record) is available online at the link below. Some minor differences between this version and the final published version may remain. We suggest you refer to the final published version should you wish to cite from it.
Original languageEnglish
Pages (from-to)1252–1260
JournalScience of the Total Environment
Early online date16 Oct 2018
Publication statusPublished - 20 Feb 2019

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