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Variations of iron flux and organic carbon remineralization in a subterranean estuary caused by interannual variations in recharge

Geochimica et Cosmochimica Acta

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, , , and
DOI: 10.1016/j.gca.2012.10.055

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Abstract

We determine the inter-annual variations in diagenetic reaction rates of sedimentary iron (Fe ) in an east Florida subterranean estuary and evaluate the connection between metal fluxes and recharge to the coastal aquifer. Over the three-year study period (from 2004 to 2007), the amount of Fe-oxides reduced at the study site decreased from 192 g/yr to 153 g/yr and associated organic carbon (OC) remineralization decreased from 48 g/yr to 38 g/yr. These reductions occurred although the Fe-oxide reduction rates remained constant around 1 mg/cm2/yr. These results suggest that changes in flow rates of submarine groundwater discharge (SGD) related to changes in precipitation may be important to fluxes of the diagenetic reaction products. Rainfall at a weather station approximately 5 km from the field area decreased from 12.6 cm/month to 8.4 cm/month from 2004 to 2007. Monthly potential evapotranspiration (PET) calculated from Thornthwaite’s method indicated potential evapotranspiration cycled from about 3 cm/month in the winter to about 15 cm/month in the summer so that net annual recharge to the aquifer decreased from 40 cm in 2004 to -10 cm in 2007. Simultaneously, with the decrease in recharge of groundwater, freshwater SGD decreased by around 20% and caused the originally 25 m wide freshwater seepage face to decrease in width by about 5 m. The smaller seepage face reduced the area under which Fe-oxides were undergoing reductive dissolution. Consequently, the observed decrease in Fe flux is controlled by hydrology of the subterranean estuary. These results point out the need to better understand linkages between temporal variations in diagenetic reactions and changes in flow within subterranean estuaries in order to accurately constrain their contribution to oceanic fluxes of solutes from subterranean estuaries.

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Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Variations of iron flux and organic carbon remineralization in a subterranean estuary caused by interannual variations in recharge
Series title:
Geochimica et Cosmochimica Acta
DOI:
10.1016/j.gca.2012.10.055
Volume
103
Year Published:
2013
Language:
English
Publisher:
Elsevier
Contributing office(s):
St. Petersburg Coastal and Marine Science Center
Description:
15 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Geochimica et Cosmochimica Acta
First page:
301
Last page:
315
Country:
United States
State:
Florida
Other Geospatial:
Indian River Lagoon