C. Demas | USGS Science

USGS1994

Geochemistry and solid-phase association of chromium in sediment from the Calcasieu River and estuary, Louisiana, U.S.A.

Sediment samples were collected from the lower Calcasieu River and estuary, Louisiana, in a study of the release of metals from sediments to the overlying water column. Whole samples were characterized by analyses that included: (1) determination of total sediment ammonium concentrations; (2) determination of total sediment Cr, Mn and Fe concentrations; (3) extraction of sediment with hydrogen peroxide followed by dilute hydrochloric acid to obtain recoverable metals, including oxides; and (4) extraction of sediment with hydrogen peroxide plus pyrophosphate at a pH of 7-8 to recover organically-bound Cr but not metal oxides. Concentrations of Cr, Mn and Fe in sediment interstitial water were determined. The concentrations of Cr in interstitial water could not be predicted from total sediment concentrations of Cr. Degradation of organic matter appeared to be the mechanism that caused elevated Cr concentrations in the interstitial water. Concentrations of Cr in interstitial water were positively correlated with total concentrations of ammonium in sediment. Concentrations of Cr in interstitial water that exceeded water-column concentrations of Cr were found when the total concentrations of ammonium in sediment exceeded 1 ??mol per gram wet weight. Concentrations of metals in interstitial water that are larger than metal concentrations in the water column create a potential for diffusive flux and metal enrichment of the overlying water column. ?? 1994.

Chemical Geology↗

USGS1992

Comparison of methods for the removal of organic carbon and extraction of chromium, iron and manganese from an estuarine sediment standard and sediment from the Calcasieu River estuary, Louisiana, U.S.A.

U.S. National Bureau of Standards (NBS) estuarine sediment 1646 from the Chesapeake Bay, Maryland, and surface sediment collected at two sites in the Calcasieu River estuary, Louisiana, were used to evaluate the dilute hydrochloric acid extraction of Cr, Fe and Mn from air-dried and freeze-dried samples that had been treated by one of three methods to remove organic carbon. The three methods for the oxidation and removal of organic carbon were: (1) 30% hydrogen peroxide; (2) 30% hydrogen peroxide plus 0.25 mM pyrophosphate; and (3) plasma oxidation (low-temperature ashing). There was no statistically significant difference at the 95% confidence level between air- and freeze-dried samples with respect to the percent of organic carbon removed by the three methods. Generally, there was no statistically significant difference at the 95% confidence level between air- and freeze-dried samples with respect to the concentration of Cr, Fe and Mn that was extracted, regardless of the extraction technique that was used. Hydrogen peroxide plus pyrophosphate removed the most organic carbon from sediment collected at the site in the Calcasieu River that was upstream from industrial outfalls. Plasma oxidation removed the most organic carbon from the sediment collected at a site in the Calcasieu River close to industrial outfalls and from the NBS estuarine sediment sample. Plasma oxidation merits further study as a treatment for removal of organic carbon. Operational parameters can be chosen to limit the plasma oxidation of pyrite which, unlike other Fe species, will not be dissolved by dilute hydrochloric acid. Preservation of pyrite allows the positive identification of Fe present as pyrite in sediments.

Chemical Geology↗