Bob J. Presley

Anoxic, Hypersaline Basin in the Northern Gulf of Mexico

A 400-square-kilometer depression in the continental slope of the northern Gulf of Mexico (approximately 27�N, 91�W) has been found to contain anoxic, hypersaline (∼250 grams per kilogram) water in the bottom 200 meters. The interface between the brine and overlying seawater acts as a midwater seismic reflector similar to those seen in the Red Sea. The bulk chemical composition of the brine is similar to that from the Red Sea, but differences between the two in both heat content and geomorphological setting indicate different modes of origin.

Manganese fluxes from Mississippi Delta sediments

Abstract Massive sediment deposition on the Mississippi River Delta establishes reducing conditions sufficient to bring about Mn dissolution in the top millimeters of sediment. As a result, significant fluxes of dissolved Mn pass from the Delta sediments to the overlying water column. This process is examined by study of chemical partitioning of Mn in river particulates and Delta sediments and from interstitial water chemistry. Remobilized Mn is actively transported away from the Delta area with aluminosilicate detritus thereby providing “excess” Mn to the deep Gulf of Mexico at the expense of the Delta sediments.

Trace metal chemistry of Galveston Bay: water, sediments and biota

Abstract Galveston Bay is the second largest estuary in Texas. It receives major urban runoff from the Houston area, its major river drains the Dallas-Ft Worth Metroplex, and the area surrounding the Bay is intensely industrialized, with chemical and petroleum production being especially prominent. Consequently, there are serious concerns about the possible contamination of the Bay and previous studies have indicated toxic metals at elevated concentrations (e.g. NOAA, 1989a). We have conducted an extensive investigation of Galveston Bay trace metals, in which their distribution in the water column, oysters and sediments were determined. Results of the water column and oyster analyses indicate that metal levels in open areas of Galveston Bay are currently similar to those in more pristine bays elsewhere. Industrial metal inputs to the Bay have not led to greatly increased concentrations in water, sediments and biota. However, the sediment analyses indicated that such inputs may have been significant in the past. Total Cu, Zn, Pb, and Ag concentrations in the waters, determined by state-of-the-art clean

Heavy metals in sediments from San Antonio Bay and the northwest Gulf of Mexico

Sediments from San Antonio Bay, the northwest Gulf of Mexico, and the Mississippi River Delta were acid leached and analyzed for Fe, Mn, Pb, Zn, Cd, Cu and Ni by atomic absorption spectrophotometry. In order to account for differences in sediment clay, carbonate, and organic matter content, metal concentrations were normalized to Fe. Significant linear correlations of metals to Fe were obtained for unpolluted sediments and deviations from these “natural” statistical populations were found for areas thought to have metal input caused by man.San Antonio Bay sediments show little evidence of metal pollution despite 70 years of shell dredging in the bay. However, the San Antonio-Guadalupe River system, the bays prime sediment source, has 10% to 50% higher than natural levels of Pb, Cd and Cu.Sediments from a 1500 km2 area of the Mississippi River Delta have Pb and Cd concentrations 10% to 100% higher than expected levels. The vertical distribution of Pb and Cd in these sediments suggests that inputs have occurred during the past 30 to 40 years. We find no indication of metal pollution in other areas of the Delta or along the continental shelf of the northwest Gulf of Mexico.

Trace metals in gulf on Mexico oysters

Oysters (Crassostrea virginica) from 50 to 69 locations (sites) along the Gulf of Mexico coastline, collected annually in 1986, 1987 and 1988, have been analyzed for 13 trace metals, including most of the metals of concern from an environmental quality perspective. Essentially the entire U.S. Gulf coastline was sampled, from far south Texas to far south Florida. Pooled samples of 20 oysters from three different stations at each site were analyzed by atomic absorption spectrophotometry. The concentrations found were generally less than or equal to literature values from other parts of the world thought to be uncontaminated by anthropogenic trace metal inputs. A few sites did, however, show apparent trace metal pollution and other sites gave anomalous values that cannot readily be explained by either known anthropogenic or natural causes. The range of values for the overall data set (maximum/minimum) varied from 15-fold for Mn to 624-fold for Pb, whereas the coefficient of variation (standard deviation/mean) was generally in the 50-60% range for most metals. Variations were much greater between stations than between years at a given station. Enrichments usually occurred in suites of three to four elements with Ag, Cd, Cu and Zn being the most common suite, thus several strong inter-element correlations were found. There was, however, little correlation between metal levels in oysters and in sediments from the collection sites even when sediment data were rationed to Al (sediment data are not given here). There was likewise little correlation between oyster metal levels and size, sex or reproductive stage of the oysters (data given elsewhere). Geographically, appreciably elevated (greater than 3 times average) metal levels were generally restricted to single sites within bays or estuaries, implying local control. On the other hand, regionally, Ag, Cd and Se levels were somewhat higher in Texas oysters than in those from Florida, whereas the reverse was true for As and Hg. Concentrations were lower than average for several metals in oysters from central Louisiana, especially Ag, Cd and Cu. Thus, the Mississippi River outflow and extensive offshore oil development do not seem to enrich oysters in trace metals.

Distribution and Chemistry of Manganese, Iron, and Suspended Particulates in Orca Basin

The intense halocline and redoxcline in the Orca Basin, northwest Gulf of Mexico, induce dramatic water column profiles for manganese, iron, and suspended particulates. Within a 17 m interval, the salinity of the basin water increases from 66 to ≈260 & permil and dissolved oxygen decreases to zero. Midway through this transition zone, concentrations of suspended matter peak at ≈900 μg/liter. Dissolved iron and manganese concentrations in the anoxic brine increase from oceanic values to maxima of 1.6 and 22 mg/liter, respectively. Upward migration of dissolved manganese from the brine leads to production of manganese-rich particles in the slightly oxygenated overlying water.

Distribution of sedimentary phosphorus in Gulf of Mexico estuaries

Sediment samples were collected from all the major bays and estuaries along the US Gulf of Mexico Coastline in 1986–1988 by the NOAA NS & T Program (NOAA (1989), The National Status and Trends Program for marine environmental quality; NOAA/OMA, Rockville, MD, USA). These have been analyzed for total phosphorus as well as leachable Al-P, Ca-P and Fe-P. Total phosphorus concentration ranges from 1·8 to 45·9 μmol/g and averages 11·3 μmol/g. Higher values were found in Louisiana estuaries than in those in Texas but the highest values occur in the phosphate rock mining region of southern Florida. Ca-P is the most abundant leachable species and is higher in samples from higher salinity sites. n nPrevious unpublished data by one of the authors (D.A.) on solid phase and pore water phosphate from 18 cores collected on the Mississippi River Delta, are reported for the first time here. Low dissolved phosphate (< 5 μM/liter) was found at the surface of several cores but values at 1 m depth were mostly much higher (up to 145 μM/liter). Pore water phosphate gave a significant positive correlation with solid phase inorganic phosphorus, but a poor correlation with solid organic phosphorus, showing the importance of inorganic reactions in controlling dissolved PO4 in pore water.

The geochemistry of trace metals in the Brazos River estuary

Abstract A seasonal study of trace metal behavior and transport in the Brazos River estuary was conducted in the winter, spring and fall of 1981. Surface water was analyzed for total dissolved Pb, Cu, Mn and Fe, and particulate Cd, Pb, Cu, Mn and Fe. Ancillary data included river discharge, total suspended matter, pH, major ions, nutrients, dissolved and particulate organic carbon and humic acid. The major ions were generally conservative across the river water-seawater mixing zone; however, a significant input of alkalinity and Ca was measured in the spring, attributable to cation exchange on clays and sediment diagenetic processes. Distinct concentration maxima were found in the 3–10‰ chlorinity range for dissolved Pb (0·06–0·9 n m ), Cu (6–42 n m ), Mn (2–290 n m ) and Fe (5–80 n m ). Particulate metal concentrations showed significant seasonal and spatial variations: Cd, 0·09–0·57 ppm; Pb, 15–43 ppm; Cu, 12–32 ppm; Mn, 250–1990 ppm and Fe 0·5–5·4%. Reducing conditions leading to diagenetic remobilization in estuarine sediments are proposed to be an important source of dissolved metals for estuarine water. Calculations of dissolved riverine metal transport to the ocean that include estuarine metal input are as much as 40 times greater than when estuarine processes are ignored.

Waste Material Behavior and Inorganic Geochemistry at the Puerto Rico Waste Dumpsite

Samples of a pharmaceutical waste were taken prior to dumping at a site over the Puerto Rico Trench and analyzed for the cations Ag, Al, As, Ca, Cd, Co, Cu, Fe, Hg, K, Li, Mg, Mn, Mo, Na, Ni, Pb, Sb, Sr and Zn. Iron and Mn were found at concentrations of 170 ppm and 5.2 ppm respectively with the other heavy metals present at below 1 ppm. of the remaining cations, the most abundant were: Ca at 290 ppm, K at 340 ppm, Mg at 33 ppm, and Na at 9,900 ppm.