Al. Bates et al., SPECIATION AND ISOTOPIC COMPOSITION OF SEDIMENTARY SULFUR IN THE EVERGLADES, FLORIDA, USA, Chemical geology, 146(3-4), 1998, pp. 155-170
We have studied the sulfur speciation and isotopic composition of two
peat cores from Water Conservation Area 2A (WCA 2A) in the Florida Eve
rglades. Core site El is affected by agricultural runoff from the Hill
sboro Canal which drains the Everglades Agricultural Area; Core site U
3 is distant from the canal and relatively unaffected by agricultural
runoff, Depth profiles of the total sulfur content of both cores show
fairly constant levels (similar to 0.7 wt.%) below about 25-30 cm dept
h in Core El and below 40-45 cm in Core U3. Above these depths, total
sulfur increases to as much as 1.52 wt.% in Core El and 1.74 wt.% in C
ore U3, suggesting that more sulfur has entered the sediments and/or t
hat more sulfur is being retained in recent times at both sampling sit
es. The changes in total sulfur content with depth in Core El correlat
e with changes in total phosphorus that have been observed in other st
udies at con sites near the Hillsboro Canal. This correlation of total
sulfur with phosphorus with depth is not seen in Core U3 located away
from the canal, possibly because phosphorus is more effectively retai
ned than sulfur in the organic sediment near the canal. Organic-sulfur
(OS) concentrations are at least twice as high as the disulfide-sulfu
r (DS) concentrations in the upper parts of both cores suggesting that
iron is presently limiting the amount of disulfide minerals formed in
these sediments. The degree of pyritization (DOP) in the upper parts
of the cores suggest that sulfide mineralization is limited by the ava
ilability of highly reactive iron during the earliest stages of diagen
esis. Positive delta(34)S values for reduced sulfur forms in both core
s indicate a relatively restricted sulfate reservoir, consistent with
nearly complete reduction of the sulfate available in the sediment at
any given time. Differences between the two cores appear in the delta(
34)S values for the near-surface sediments. The DS delta(34)S values i
n the upper 10.0 cm of sediment are more positive at site El, with a m
ean delta(34)S value of + 12.9 per mil, than at site U3, with a mean d
elta(34)S value of + 2.9 per mil. These results may indicate that incr
eased rates of organic deposition due to nutrient loading near the can
al have increased the rate of sulfate reduction at the El site in rece
nt times. Acid-volatile-sulfide (AVS) concentrations are lower than DS
and OS concentrations by at least a factor of 10. increasing delta(34
)S values for AVS with increasing depth in both cores suggests ongoing
reduction of a limited porewater sulfate reservoir after deposition.
The disulfide and organic-sulfur delta(34)S values diverge from the de
lta(34)S values for AVS with depth, suggesting that most of the transf
ormation of AVS into disulfide minerals or incorporation of sulfur int
o organic matter occurs in the near-surface sediments. A comparison of
organic-sulfur delta(34)S values in the dominant flora at the U3 site
(sawgrass leaves and periphyton) with organic-sulfur delta(34)S value
s at the top of the U3 core indicates that there was early incorporati
on of an isotopically light sulfide species into the organic matter. P
ublished by Elsevier Science B.V.