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Seasonal enhancement of submarine groundwater discharge (SGD)-derived nitrate loading into the Ria Formosa coastal lagoon assessed by 1-D modeling of benthic NO3 profiles
Ibánhez, J.S.P.; Leote, C.; Rocha, C. (2013). Seasonal enhancement of submarine groundwater discharge (SGD)-derived nitrate loading into the Ria Formosa coastal lagoon assessed by 1-D modeling of benthic NO3 profiles. Est., Coast. and Shelf Sci. 132: 56-64. hdl.handle.net/10.1016/j.ecss.2012.04.015
In: Estuarine, Coastal and Shelf Science. Academic Press: London; New York. ISSN 0272-7714, more
Peer reviewed article  

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Author keywords
    beach; diagenesis; groundwater; nitrate; sand; SGD; Ria Formosa; Portugal

Authors  Top 
  • Ibánhez, J.S.P.
  • Leote, C.
  • Rocha, C.

Abstract
    The role of benthic sandy ecosystems in mitigating View the MathML sourceNO3- loads carried by Submarine Groundwater Discharge (SGD) to coastal marine ecosystems is uncertain. Benthic biogeochemical mediation of View the MathML sourceNO3--rich submarine groundwater discharge was studied at the seepage face of a barrier island site in the Ria Formosa coastal lagoon (Southern Portugal). Preliminary analysis of View the MathML sourceNO3- porewater distributions at the seepage face during discharge indicated that benthic biogeochemical processes could significantly affect the fluxes of groundwater-borne View the MathML sourceNO3- into the lagoon. In order to discriminate between the relative contribution of transport and reaction processes to shape and concentration range evidenced by in-situ porewater View the MathML sourceNO3- gradients, an advection-dispersion-reaction (ADR) model of View the MathML sourceNO3- diagenesis was applied to describe View the MathML sourceNO3- porewater profiles obtained in March, June, September and December 2006. Good agreement between modeled and measured profiles was obtained. Model-derived apparent benthic nitrification and View the MathML sourceNO3- reduction rates ranged from 0.01 to 5.2 mmol m-2 h-1, sufficient to explain gross observed changes in View the MathML sourceNO3- fluxes arriving at the seepage face (up to 70% within the surficial 20 cm depth layer). Results of the analysis indicated that the upper limit of the seepage face promoted mitigation of View the MathML sourceNO3- fluxes to the lagoon throughout the year. In contrast, the lower limit of the seepage area promoted net amplification of the View the MathML sourceNO3- fluxes into the lagoon in June and September. These results will help constrain further work aiming to clarify the role of permeable sediments in mitigating nitrogen loading of coastal ecosystems.

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