SUMMARY:

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The results of analysis of solid phase sediment samples from the Everglades indicate that there has been an increase in sulfur input to the Everglades in recent times. This is particularly evident in sediment from WCA 2A that receives direct runoff from the Hillsboro Canal. Concentrations of sulfur species show that organic sulfur is usually the dominant species in the core sediments, probably because sulfide fixation is limited by reactive iron availability. The organic sulfur is likely produced by reaction of sulfide with the organic matter-rich sediment. Positive ³⁴S values for almost all sulfur species in all sediment samples indicate that there is a relatively restricted supply of sulfate. Variations in the ³⁴S values with depth in the sediment are the result of changes in the amount of sulfate available, variations in the rate of reduction of sulfate to sulfide, and/or to changes in the ³⁴S values of the source sulfate.

We conclude from our data that much of the dissolved sulfate in the northern Everglades is coming from the EAA by way of the canals that drain the agricultural lands. The origin of this sulfate could be sulfur from fertilizer used in the EAA, rainwater, Lake Okeechobee water, groundwater, or a combination of these sources. The sulfate concentration in rainwater is far too low to account for the concentration of sulfate found in the canals in the EAA. Lake Okeechobee is certainly the origin of much of the water in the EAA canals (Bottcher and Izuno, 1994). During seasons of normal rainfall, the sulfate concentration was low in surface water collected from Lake Okeechobee and from the Kissimmee River as it enters the lake (Fig. 1; Fig. 2a) in comparison to the sulfate concentrations in water collected from the canals in the EAA (Fig. 2a). In contrast, during the Spring-Summer 1998 drought season, sulfate concentrations in canal water in the EAA plummeted to values only a little higher than in the Lake. It is likely that during a dry season the water in the canals is dominated by discharge from the lake with limited contributions from rainfall runoff from EAA fields (Bottcher and Izuno, 1994). Sulfate concentrations during periods of drought therefore largely reflect Lake Okeechobee discharge. Three separate batches of elemental sulfur fertilizer (98% S^o), usually referred to as agricultural sulfur, were purchased in the EAA and analyzed for total sulfur ³⁴S values. The values obtained were 15.7 (purchased in 1996), 20.3 (purchased in 1997), and 15.9 per mil (purchased in 1999). We found that sulfate extracted from agricultural soil had a ³⁴S value of 15.6 per mil. These values are at least consistent with agricultural sulfur being a major contributor to sulfate content in the agricultural lands and the adjacent canals. However, concentrations of sulfate from groundwater (9 m) beneath the ENR are as high as sulfate in the canals in the EAA, and some of the ³⁴S values for sulfate in groundwater in the ENR are close to the values for sulfate in the EAA canals (15 to 22 per mil). If groundwater beneath the ENR (formerly a part of the EAA) is representative of groundwater beneath the EAA, then pumping or natural discharge of groundwater to the EAA canals cannot be excluded as contributors of sulfate to the canals that drain the EAA. An analysis of groundwater from within the EAA is planned for in the future.