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Larry P. Gough
Kotra, R. K.; Holmes, C. W.; Orem, W. H.; Hageman, P. L.; Briggs, P. H.; Meier, A. L.; Borwn, Z. A.
Gough, L. P.; Severson, R. C.; Montour, M. R.; Briggs, P. H.; Adrian, B. M.; Curry, K. J.; Fey, D. L.; Hageman, P. L.; Papp, C. S.
Engleman, E. E.; Peard, J. L.
Crock, J. G.
Meier, A. L.; Crock, J. G.
Grimes, D. J.; Ficklin,. W. H.
carter, L. M. H.; Toth, M. I.; and Day, W. C., editors
Crock, J. G.
Dumoulin, J. A. And Gray, J. E., editors
Lerch, H. E.; Rawlik, P.
Bates, A. L.; Lerch, H. E.; Corum, M.; Boylan, A.
Golightly, D. W.; Lamother, P. J.
Kotra, R. K.; Holmes, C. W.; Briggs. P. H.; Crock, J. G.; Fey, D. L.; Hageman, P. L.; Meier, A. L.
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").
U.S. Department of the Interior, U.S. Geological Survey, Center for
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