A model analysis of the tidal engine that drives nitrogen cycling in coastal riparian aquifers

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Created: Mar 26, 2019 at 2:46 p.m.
Last updated: Mar 23, 2020 at 12:45 p.m.
DOI: 10.4211/hs.39abb2d1a3614b88afc02b22b77021a2
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In coastal rivers, tides facilitate surface water-groundwater exchange and strongly coupled nitrification-denitrification near the fluctuating water table. We used numerical fluid flow and reactive transport models to explore hydrogeologic and biogeochemical controls on nitrogen transport along an idealized tidal freshwater zone based on field observations from White Clay Creek, Delaware, USA. The capacity of the riparian aquifer to remove nitrate depends largely on nitrate transport rates, which initially increase with increasing tidal range but then decline as sediments become muddier and permeability decreases. Over the entire model reach, local nitrification provides a similar amount of nitrate as surface and groundwater contributions combined. More than half (~66%) of nitrate removed via denitrification is produced in-situ, while the vast majority of remaining nitrate removed comes from groundwater sources. In contrast, average nitrate removal from surface water due to tidal pumping amounts to only ~1% of the average daily in-channel riverine nitrate load or 1.77 kg of nitrate along the reach each day. As a result, tidal bank storage zones may not be major sinks for nitrate in coastal rivers but can act as effective sinks for groundwater nitrate. By extension, tidal bank storage zones provide a critical ecosystem service, reducing contributions of groundwater nitrate, which is often derived from septic tanks and fertilizers, to coastal rivers.

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Coordinate System/Geographic Projection:
WGS 84 EPSG:4326
Coordinate Units:
Decimal degrees
Place/Area Name:
White Clay Creek



Funding Agencies

This resource was created using funding from the following sources:
Agency Name Award Title Award Number
National Science Foundation EAR-1446724
Geologic Society of America
National Science Foundation EAR-1446763
National Science Foundation EAR-1752995

How to Cite

Wallace, C. D., A. H. Sawyer, R. T. Barnes, M. R. Soltanian, R. S. Gabor, M. J. Wilkins, M. T. Moore (2020). A model analysis of the tidal engine that drives nitrogen cycling in coastal riparian aquifers, HydroShare, https://doi.org/10.4211/hs.39abb2d1a3614b88afc02b22b77021a2

This resource is shared under the Creative Commons Attribution CC BY.



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