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publications > open file report > ofr 01-007 > results and discussion
Geochemistry of Sulfur in the Florida Everglades:
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| Solid Phase Sulfur Geochemistry | Dissolved Sulfate Concentrations and Isotopic Compositions |
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Solid phase cores were collected in the EAA, WCA 2A, WCA 1A (Loxahatchee National Wildlife Refuge), Taylor Slough, and Lake Okeechobee (see Figures 1 & 2).
WCA 1A is a "pristine" area protected from canal discharge. Two sediment cores were obtained from this area in April 1995, one near the Hillsboro Canal at site 1, and one away from the canal at site 7 (Fig. 1). Sulfur species contents for these sampling sites were obtained only on a percent by wet weight basis (Table 1 , Fig. 3). These data shows that sulfur contents are about the same at both sites except that organic sulfur is much higher at site 1. The 
34S values are positive at both sites (Table1, Fig. 3), indicating freshwater levels of sulfate.
Total sulfur content (percent dry weight) is similar in sediment collected in 1994 at two sites: one near the Hillsboro Canal (E1) and another far from the canal (U3) (Table 2, Fig. 4). At each site, total sulfur shows a significant increase in the upper part of the core, probably indicating an increase in sulfur loading in the marsh in recent times. Sulfur speciation analyses (Table 2 , Fig. 5) indicate that most of the sulfur is in the form of organic sulfur, probably due to iron limitation of sulfide fixation. Positive 34S values for the sulfur species (Table 2 , Fig. 5) show that there is a relatively restricted supply of sulfate for reduction to sulfide, although one negative 34S value for disufide sulfur (pyrite) at U3 could indicate an increase in sulfate availability at the time of fixation (Bates et al., 1998).
Sediment collected in 1996 from site F1 (near the Hillsboro Canal) and from site ("new" U3--not the same as the site from 1994, see Fig. 1) has total sulfur content slightly lower than in the sediment collected in 1994 (Table 2 , Fig. 6). Because the core lengths were shorter in 1996 (only the top 15 cm of sediment), it is not possible to tell if there is a decrease with depth as there was in the sediment collected in 1994. Organic sulfur is the dominant species (Table 2 , Fig. 7) near the top of the sediment at F1 and U3, however, disulfides increase with depth. As in the sediment samples collected in 1994, the 34S values are positive (Table 2 , Fig. 7), indicating a limited supply of sulfate.
April 1996
April 1996
Percent Dry Weight
Organic sulfur is the dominant sulfur species in another short core (top 15 cm) collected in WCA 2A in 1995 (Table 2 , Fig. 8), however the results are available only on a percentage wet weight basis. More positive 34S values for disulfide sulfur and organic sulfur are found in the near-surface sediment (top 3 cm) (Table 1 , Fig. 8) near the canal (F1) than far from the canal (U3new). This may be the result of higher rates of sulfate reduction near the canal.
Agricultural soil at the U.S. Department of Agriculture (USDA) Research Center at Canal Point and at the University of Florida Agricultural Research Center was analyzed for total sulfur 34S values. These values fall in a range from 12.63 to 19.37, with higher values in the top 5 cm of the three cores sampled (Table 3 , Fig. 9). Total sulfur was determined only on a dry weight basis, and appears to increase with depth in the two meter core (Table 3 ).
Total sulfur as a percent of dry weight was obtained for two cores from Lake Okeechobee, one from the center of the lake and the other from South Bay at the southern tip of the lake (Table 4 , Fig. 10). Total sulfur content is higher at the periphery of the lake than at the center, and both cores show a general decrease in sulfur content with depth.
Total sulfur contents (Table 5 , Fig. 11) are higher in the upper part of sediment collected at the head of Taylor Slough (Fig. 1) than in sediment collected in the middle part of the Slough (Fig. 1). This could be the result of the proximity of the head of the slough to agricultural fields and canal drainage (the head of the Slough also has higher total phosphorus levels in the sediment (Orem et al., 1999), possibly from agricultural runoff. Organic sulfur is the dominant sulfur species at both sites (Table 5 , Fig. 12). Sulfur species 34S values are positive at both sites (Table 5 , Fig. 12), indicating freshwater levels of sulfate. The 34S values of sulfate sulfur are quite high (approaching 30 per mil) near the top of the core at the head of the slough. This could be the result of a very restricted source of sulfate (not likely considering that the sulfur content is relatively high near the top of the core) or to high 34S values in the source sulfate.
Percent Dry Weight
Percent Dry Weight
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U.S. Department of the Interior, U.S. Geological Survey
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Last updated: 29 November, 2004 @ 01:45 PM (KP)
