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Rama Kotra Larry P. Gough, 2000, Geochemical Processes in Organic-rich Sediments of South Florida - Mercury and Metals.
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An understanding of the relationship between diagenesis, concentration, speciation, and historical variation of elements of environmental significance is essential for planners in developing long-term remediation and management strategies for wetlands of south Florida. A better understanding of the controls on the cycling of these elements is critical for making informed decisions regarding the regulation of water levels and anticipating the effect of water regulation.
Water - Surface water samples, analyzed for major and trace elements (except Hg), were collected in field-rinsed 1 L polyethylene bottles and transferred via filtration in the field (by passing through pre-rinsed cellulose acetate 0.45 micron membranes) to acid-washed and field-rinsed 250 ml bottles. Element stability was assured by the addition of 10 drops of concentrated, ultra-pure nitric acid. Samples collected for Hg analyses were taken from the same 1 L bottle. The samples were filtered as above and 30 ml was added to glass, oven-baked bottles with teflon-coated lids. Mercury stability was assured by the addition of 1.5 ml of sodium dichromate/nitric acid.
Vegetation - The vegetation component of the biogeochemical cycling of trace elements was investigated using sawgrass (Cladium jamaicensis Crantz), the dominant species in the Everglades marsh. In addition, bromeliads (Tillandsia spp, also known as air plants) were collected when available because of their ability to concentrate airborne metals and therefore act as air quality monitors. Data for the air plant samples are reported in Gough and others, 1996, OFR 96-91.
Sawgrass leaves (about 200 g, dry weight) were clipped using stainless steel shears at about 10 cm above the high water level. Flowering structures, if present, were removed. Samples consisted of a composite of four individual plants collected within three meters of the site where the core material was taken. The material was double sealed in plastic bags and chilled using "wet ice". Sawgrass roots consisted of the material below the sediment level for each sawgrass clump. This usually consisted of the basal protion below the meristem that contains the major rhizomes (but not the fibrous "feeder" roots). The material was field rinsed, double sealed in plastic bags, and chilled using "wet ice".
Organic-rich sediments - Sediment cores were obtained by pushing a piston-sealed, 10.2 cm diameter, acrylic butyrate core liner into the sediment using the method described in Orem and others, 1997, OFR 97-454. Usually greater than 60 cm of sediment were collected in the core liner at the sites. The cores were maintained in an upright position until they were extruded and sectioned, usually within 8 hours of collection. All sediment samples were placed in plastic bags, chilled, and shipped to the laboratory where they were frozen.
Detailed discussions of sample preparation and analyses for water, plant, and sediment samples can be found in Arbogast, 1996, Gough and Crock, 1997, Holmes, 1998, Lichte and others, 1986, and Orem and others, 1999.
In the laboratory, sawgrass was removed from the sample bags, placed in Teflon beakers, submerged and rinsed in deionized water, and drained. This process was repeated at least three times. Plant material was then placed in plastic colanders, rinsed briefly with deionized water, and allowed to drip drain. Colanders were then placed directly into ovens and the material was dried for 24 hr. at about 40 deg. C. This temperature is near the maximum summer ambient field temperature and should not result in any important loss of Hg through volatilization. Samples were then ground in a Wiley mill to pass a 2-mm (10-mesh) sieve. Splits of the ground plant material were ashed at 450-500 deg. C over an 18 hr. period and ash yield was determined.
In order to insure adequate material and sample type for the various analyses conducted, replicate cores were commonly extracted from each study site. The cores used for the geochronology studies (210Pb analyses) and pore water chemistry were sectioned (extracted) at 2 cm intervals whereas the cores used in the trace metal geochemical studies were sectioned at 5 cm intervals. Because most core material below about 40 cm was several hundred years old, the interval for sectioning commonly increased to 5 or 10 cm for all cores. This was performed in order to economize on the total number of samples being analyzed. For element analyses, subsets of the sediment core sections were dried, ground, and ashed in a manner similar to the plant samples (Arbogast, 1990; Balistrieri and others, 1995). For details on the 210Pb sediment dating method see Holmes (1998).
One hundred milligrams of plant and sediment sample ash was digested with mixed acids. After complete digestion of the ash, 40 major and trace elements were determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) (Lichte and others, 1987). Mercury was determined directly on a subset of the dried, ground, unashed plant and sediment material by cold vapor atomic absorption spectrometry (AAS)(Kennedy and Crock, 1987). Total sulfur was determined in plant samples only on 250 mg of the ground material by combustion at 1370 deg. C in an oxygen atmosphere with infrared detection of evolved SO2 (Jackson and other, 1985). Water samples were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS) (Meier and others, 1994; Arbogast, 1996).
The element analyses (except for Hg) for the sediment material were all performed in a non-government contract laboratory. Analyses for plant material and water were performed by the Denver Laboratories of the USGS.
Blind standard reference materials were submitted to the laboratories as part of each suite of samples. This included material from the National Institute of Standards and Technology (NIST), the National Bureau of Standards (NBS), and from internal USGS prepared materials. In addition, some of the material was sampled twice in the field (identified by a "Y"), and split in the laboratory for duplicate analysis (identified by an "X").
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Gough, L. P. Kotra, R. K.; Holmes, C. W., 2000, Regional Geochemistry of Metals in Organic-Rich Sediments, Sawgrass and Surface Water, from Taylor Slough, Florida: USGS Open-File Report OFR 00-327, Reston, VA, U.S. Geological Survey.
Arbogast, B. F., editor, 1996, Analytical methods manual for the Mineral Resource Surveys Program, U.S. Geological Survey: USGS Open-File Report 86-525, U.S. Geological Survey, Reston, VA.
Balistrieri, L. S. Gough, L. P.; Severson, R. , 1995, The effect of acidic, metal-enriched drainage from the Wightman Fork and Alamosa River i=on the composition of selected wetlands in San Luis Valley, Colorado: USGS Open-File Report 95-568, U.S. Geological Survey, Denver, CO.
Holmes, Charles W. , 1998, Short-Lived Isotopic Chronometers: USGS Fact Sheet 73-98, U.S. Geological Survey, St. Petersburg, Florida.
Jackson, L. L. Engleman, E. E.; Peard, J. , 1985, Determination of total sulfur in lichens and plants by combustion-infrared analysis: Environmental Science & Technology v. 19, issue 5, American Chemical Society, Washington, DC.
Kennedy, K. R. Crock, J. G., 1987, Determination of mercury in geological materials by continuous-flow, cold-vapor, atomic absorption spectrophotometry: Analytical Letters v. 20, Taylor & Francis Inc., Philadelphia, PA.
Arbogast, B. F., editor, 1990, Quality Assurance manual for the Branch of Geochemistry, U.S. Geological Survey: USGS Open-File Report 90-668, U.S. Geological Survey, unknown.
Lichte, F. E. Meier, A. L.; Crock, J. G., 1986, Determination of the rare earth elements in geologic materials by inductively coupled plasma mass spectrometry: Analytical Chemistry v. 59, no. 8, American Chemical Society, Washington, DC.
Meier, A. Grimes, D. J.; Ficklin,. W. H., 1994, Inductively coupled plasma mass spectrometry - a powerful tool for mineral resource and environmental suudies: USGS Circular 1103A, U.S. Geological Survey, unknown.
carter, L. M. H.; Toth, M. I.; and Day, W. C., editors
Gough, L. P. Crock, J. G., 1997, Distinguishing between natural geologic and anthropogenic trace element sources, Denali National Park and Preserve: USGS Professional Paper 1574, U.S. Geological Survey, unknown.
Dumoulin, J. A. And Gray, J. E., editors
Orem, W. H. Lerch, H. E.; Rawlik, P., 1997, Geochemistry of surface and pore water at USGS coring sites in wetlands of South Florida, 1994 and 1995: USGS Open-File Report 97-454, U.S. Geological Survey, Reston, VA.
Orem, W. H. Bates, A. L.; Lerch, H. E.;, 1999, Sulfur contamination in the Everglades and its relation to mercury methylation: USGS Open-File Report 99-181, U.S. Geological Survey, Reston, VA.
Lichte, F. E. Golightly, D. W.; Lamother,, 1987, Inductively coupled plasma-atomic emission spectrometry: USGS Bulletin 1770, U.S. Geological Survey, Reston, VA.
Gough, L. P. Kotra, R. K.; Holmes, C. W., 1996, Chemical analysis results for mercury and trace elements in vegetation, water, and organic-rich sediments, south Florida: USGS Open-File Report 96-91, U.S. Geological Survey, unknown.
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geochemistry of metals in organic-rich sediments
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