Abstract
Aquifers are typically perceived as rather stable habitats, characterized by low biogeochemical and microbial community dynamics. Upon contamination, aquifers shift to a perturbed ecological status, in which specialized populations of contaminant degraders establish and mediate aquifer restoration. However, the ecological controls of such degrader populations, and possible feedbacks between hydraulic and microbial habitat components, remain poorly understood. Here, we provide evidence of such couplings, via 4 years of annual sampling of groundwater and sediments across a high-resolution depth-transect of a hydrocarbon plume. Specialized anaerobic degrader populations are known to be established at the reactive fringes of the plume. Here, we show that fluctuations of the groundwater table were paralleled by pronounced dynamics of biogeochemical processes, pollutant degradation, and plume microbiota. Importantly, a switching in maximal relative abundance between dominant degrader populations within the Desulfobulbaceae and Desulfosporosinus spp. was observed after hydraulic dynamics. Thus, functional redundancy amongst anaerobic hydrocarbon degraders could have been relevant in sustaining biodegradation processes after hydraulic fluctuations. These findings contribute to an improved ecological perspective of contaminant plumes as a dynamic microbial habitat, with implications for both monitoring and remediation strategies in situ.
Highlights
Over 97% of global non-glacial freshwater resources are retained in groundwater [1], which constitutes the main source of drinking water in many areas of the world
Hydraulic Dynamics and Plume Fluctuation Considerable dynamics of the groundwater table (GWT) were observed at the site during four yeaCrsoonfsisdaemrapblilnegdy(Fniagmuriecs1o).f AthedrgorpouonfdtwheatGerWtaTboleft w40ercemobbseetrwveeednaJtutlhye2s0it0e6daunrdinJganfouuary ye2a0r0s7owf saasmfopllionwge(dFibgyurae c1o).nAstadnrtoprisoef othfe~6G0WcmT oufnatliml Mosatr4c0hc2m00b9e.tAwfetenr tJhuilsy, 2a0n0e6qaunidvaJlaennutabruyt2m00o7re wraaspfiodlldoewcleidnebyofathcoenwstaatnert traisbeleofw~a6s0ocbmseurvnetdil uMnatrilchw2in0t0e9r. 2A0f0t9e.r this, an equivalent but more rapid decline of the water table was observed until winter 2009
BhetawveebeenenthperesvaiomuspllyinregpsoritnedF[e1b2r]u. ary 2006 and February 2007, the drop of the water table was reflected in a downshift of the toluene plume core from ~6.6 to 6.8 m depth, while maximal concenBteratwtioenens rtehme asianmedplaitn~gs40inmFge·Lbr−u1a(rFyig2u0r0e62aan).dTFheebrreuaacrtiyve20lo0w7,etrhferidnrgoepofofthteheplwumateerretmabaleinwedas reflected in a downshift of the toluene plume core from ~6.6 to 6.8 m depth, while maximal localized at ~7.1 m depth and concentrations remained at reactive, as suggested by an
Summary
Over 97% of global non-glacial freshwater resources are retained in groundwater [1], which constitutes the main source of drinking water in many areas of the world Despite this key relevance for our society, aquifers are still poorly understood as ecosystems, especially regarding the ecology of their primary populace, the microbes [2]. At a tar-oil contaminated aquifer in Düsseldorf-Flingern in Germany, we have previously shown that a locally enriched population of specialized anaerobic degraders had established at the sulfidogenic lower fringe of a toluene plume, indicative of a “hot-spot” of biodegradation in situ [12,13,14,15]. Possible feedbacks between abiotic habitat dynamics, such as fluctuating groundwater tables and degrader populations, have been rarely addressed to date
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