METHODS

Sampling Sites

Fieldwork was conducted from May 17-24, 1996 (table 1). May is the end of the dry period and usually allows for ready access to sediment sampling sites because of generally low water levels; however, during May 1996 relatively deep standing water was encountered. Proper collection permits were obtained from managers of all public lands visited.

Field Collections

Water--Surface water samples, to be analyzed for major and trace elements (except Hg), were collected as detailed in Gough and others (1996). Water samples 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 µ membranes), to acid-washed and field-rinsed 250 ml polyethylene 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 is being 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 biomonitors. Data for the air plant samples are reported elsewhere (Gough and others, 1996).

Sawgrass is a coarse, rhizomatous perennial sedge that can dominate both the wet (inundated for months at a time) and dry (seldom inundated) prairies across the Everglades peat lands (McPherson, 1973). This is particularly true east of Big Cypress National Preserve in the Water Conservation Areas and in Everglades National Park. Although locally dominant in marly or rocky areas with shallow sediments, it can be found growing in peaty material that is several meters deep (Duever and others, 1986). 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 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 portion below the meristem that contains the major rhizomes (but without the fibrous "feeder" roots). The material was field rinsed, doubled 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 of Orem and others (1997). 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.

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