Oxidative precipitation of groundwater‐derived ferrous iron in the subterranean estuary of a coastal bay

Sediment cores from the intertidal zone of Waquoit Bay (Cape Cod, Massachusetts) yielded iron oxide‐coated sands in the subterranean estuary, which underlies the head of the bay. The oxides were dark red, yellow and orange colors and are formed by the oxidation of ferrous iron‐rich groundwater near the groundwater‐seawater interface. Within these iron oxide‐rich sediments, the concentration of the combined amorphous and crystalline forms of iron oxides ranged between 2500 and 4100 ppm of Fe. These concentrations were 4–6 times greater than the surface sands, and 10–15 times more Fe rich than sands collected from an off‐site location. The precipitation of iron oxides in subterranean estuaries could act as a geochemical barrier by retaining and accumulating certain dissolved chemical species carried to the coast by groundwater. Indeed, phosphorus concentrations in the iron oxide‐rich sands of Waquoit Bay were 5–7 times greater than the overlying surface sands.

[1]  L. Stookey.  Ferrozine---a new spectrophotometric reagent for iron , 1970 .

[2]  E. Sholkovitz,et al.  Flocculation of dissolved organic and inorganic matter during the mixing of river water and seawater , 1976 .

[3]  O. Borggaard,et al.  The influence of iron oxides on phosphate adsorption by soil , 1983 .

[4]  R. Parfitt.  Phosphate reactions with natural allophane, ferrihydrite and goethite , 1989 .

[5]  Brian L. Howes,et al.  Transport of groundwater-borne nutrients from watersheds and their effects on coastal waters , 1990 .

[6]  G. Simmons,et al.  Importance of submarine groundwater discharge (SGWD) and seawater cycling to material flux across sediment/water interfaces in marine environments , 1992 .

[7]  U. Schwertmann,et al.  Fast and Slow Phosphate Sorption by Goethite-Rich Natural Materials , 1992 .

[8]  H. T. Kloosterhuis,et al.  Phosphate sorption in superficial intertidal sediments , 1994 .

[9]  J. Griffioen.  Uptake of Phosphate by Iron Hydroxides during Seepage in Relation to Development of Groundwater Composition in Coastal Areas. , 1994, Environmental science & technology.

[10]  W. Moore.  Large groundwater inputs to coastal waters revealed by 226Ra enrichments , 1996, Nature.

[11]  W. Jarrell,et al.  Formation and stability of iron(II) oxidation products under natural concentrations of dissolved silica , 1996 .

[12]  C. Slomp,et al.  Phosphorus binding by poorly crystalline iron oxides in North Sea sediments , 1996 .

[13]  G. Hall,et al.  Selective leaches revisited, with emphasis on the amorphous Fe oxyhydroxide phase extraction , 1996 .

[14]  Thomas C. Cambareri,et al.  Watershed Delineation and Ground Water Discharge to a Coastal Embayment , 1998 .

[15]  G. Luther,et al.  Advective Transport Affecting Metal and Nutrient Distributions and Interfacial Fluxes in Permeable Sediments , 1998 .

[16]  W. Moore.  The subterranean estuary: a reaction zone of ground water and sea water , 1999 .

[17]  W. Moore,et al.  Marsh nutrient export supplied by groundwater discharge: Evidence from radium measurements , 2000 .

[18]  M. Charette,et al.  Utility of radium isotopes for evaluating the input and transport of groundwater‐derived nitrogen to a Cape Cod estuary , 2001 .

[19]  M. Charette,et al.  Assessing Rates and Mechanisms of Submarine Groundwater Discharge: A Combined Approach Using Seepage Meters and Radium Isotopes , 2001 .

[20]  S. Sañudo-Wilhelmy,et al.  Influence of net groundwater discharge on the chemical composition of a coastal environment: Flanders Bay, Long Island, New York. , 2001, Environmental science & technology.

[21]  U. Schwertmann,et al.  Iron Oxides , 2003, SSSA Book Series.