Journal
ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH
Volume 25, Issue 11, Pages 10654-10667Publisher
SPRINGER HEIDELBERG
DOI: 10.1007/s11356-018-1302-1
Keywords
Submarine groundwater discharge; Subterranean estuaries; Nitrate removal; Organic matter; Seepage faces; Remineralisation
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Funding
- Portuguese Foundation for Science and Technology (FCT)
- EU (FEDER)
- Portuguese Government [PTDC/MAR/70247/2006]
- Fundação para a Ciência e a Tecnologia [PTDC/MAR/70247/2006] Funding Source: FCT
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Seepage faces, the outer rim of subterranean estuaries, are an important reaction node for SGD-borne nitrate (NO3-) on a global scale. Labile dissolved organic matter (DOM) has been suggested to be a key factor constraining the NO3- removal rate in aquifer systems. To determine whether and to what extent the availability of labile DOM affects benthic NO3- reduction in seepage faces, a series of flow-through reactor (FTR) experiments with sandy sediment collected from a seepage face was conducted under oxic conditions. Experimental results revealed that the addition of labile DOM (glucose) to porewater did not trigger a significant enhancement in NO3- reduction rate. In contrast, the aerobic respiration was boosted from ca. 50 to 90 mu mol dm(-3) sediment h(-1) by glucose amendments, accounting for approximately 70% consumption of the labile DOM pool. This rapid consumption may increase the NO3- reducing capability within the sediment, but only indirectly. Together with fluorescent DOM (FDOM) analyses, it can be inferred that NO3- reducers tend to choose sediment organic matter the prime electron donor under the experimental conditions. As a result, enrichment of DOM in seepage faces, depending on composition, might only stimulate aerobic respiration and nitrification, thus promoting the increase of ensuing NO3- fluxes to adjacent coastal waters.
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