Publication Date:
2016-11-28
Description:
Fluxes of submarine groundwater discharge (SGD) were investigated into two tidal rivers on the north and south shore of Long Island, NY, during July 2015. Ground-based handheld thermal infrared (TIR) imagery, combined with direct push-point piezometer sampling, documented spatially heterogeneous small-scale intertidal seepage zones. Pore waters were relatively fresh and enriched in nitrogen (N) within these small-scale seeps. Pore waters sampled just 20 cm away, outside the boundary of the ground-based TIR-located seepage zone, were more saline and lower in N. These ground-based TIR-identified seeps geochemically represented the terrestrial fresh groundwater endmember, whereas N in pore waters sampled outside of the TIR-identified seeps was derived from the remineralization of organic matter introduced into the sediment by tidal seawater infiltration. A 222Rn (radon-222) time-series was used to quantify fresh SGD-associated N fluxes using the N endmembers sampled from the ground-based TIR pore water profiles. N fluxes were up-scaled to groundwater seepage zones identified from high-resolution airborne TIR imagery using the two-dimensional size of the airborne TIR surface water anomalies, relative to the N flux from the time-series sampling location. Results suggest that the N load from the north-shore tidal river to Long Island Sound is underrepresented by at least 1.6–3.6%, whereas the N load from SGD to a south-shore tidal river may be up to 9% higher than previous estimates. These results demonstrate the importance of SGD in supplying nutrients to the lower reaches of tidal rivers and suggest that N loads in other tidal river environments may be underestimated if SGD is not accounted for. Copyright © 2016 John Wiley & Sons, Ltd.
Print ISSN:
0885-6087
Electronic ISSN:
1099-1085
Topics:
Architecture, Civil Engineering, Surveying
,
Geography
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