Using soil profiles of seeds and molecular markers as proxies for sawgrass and wet prairie slough vegetation in Shark Slough, Everglades National Park

We measured the abundance of Cladium jamaicense (Crantz) seeds and three biomarkers in freshwater marsh soils in Shark River Slough (SRS), Everglades National Park (ENP) to determine the degree to which these paleoecological proxies reflect spatial and temporal variation in vegetation. We found that C. jamaicense seeds and the biomarkers Paq, total lignin phenols (TLP) and kaurenes analyzed from surface soils were all significantly correlated with extant aboveground C. jamaicense biomass quantified along a vegetation gradient from a C. jamaicense to a wet prairie/slough (WPS) community. Our results also suggest that these individual proxies may reflect vegetation over different spatial scales: Paq and kaurenes correlated most strongly (R 2 = 0.88 and 0.99, respectively) with vegetation within 1 m of a soil sample, while seeds and TLP reflected vegetation 0–20 m upstream of soil samples. These differences in the spatial scale depicted by the different proxies may be complementary in understanding aspects of historic landscape patterning. Soil profiles of short (25 cm) cores showed that downcore variation in C. jamaicense seeds was highly correlated with two of the three biomarkers (Paq, R 2 = 0.84, p<0.005; TLP, R 2 = 0.97, p<0.0001), and all four of the proxies indicated a recent increase in C. jamaicense biomass at the site. Using a preliminary depth-to-age relationship based on matching charcoal peaks with available ENP fire records (1980-present) specific to our coring site, we found that peak-depths in C. jamaicense seed concentration appeared to correspond to recent minimum water levels (e.g., 1989 and 2001), and low seed abundance corresponded to high water levels (e.g., 1995), consistent with the known autecology of C. jamaicense. In summary, the combination of C. jamaicense seeds and biomarkers may be useful for paleoecological reconstruction of vegetation change and ultimately in guaging the success of ongoing efforts to restore historic hydrologic conditions in the South Florida Everglades.

Areal and vertical distribution of total soil mercury and total phosphorusin the southern half of water conservation area 3-A, Everglades, Southern Florida

Total soil-mercury and phosphorus concentrations were determined in 64 sites in the southern half of Water Conservation Area 3A, an area of approximately 500 km2 . Surface soil-Hg concentrations ranged from 117 to 300 ng-g-1;total phosphorus concentrations range from 350 to 850 pg~g-1. No consistent north-south or east-west trends are found in the mercury or phosphorus surface concentrations when they are normalized to soil bulk density. Nine sites were used for the determination of the vertical distribution of soilmercury. Vertical profiles of soil-Hg revealed decreasing concentrations with depth and correlated well with phosphorus in soil profiles. Mercury concentrations in soil profiles may be interpreted as an increase in the rate of deposition of mercury in the region in recent decades and/or as postdepositionalmobilization of mercury to surface layers.

Carbon and nutrient storage in subtropical seagrass meadows: examples from Florida Bay and Shark Bay

Seagrass meadows in Florida Bay and Shark Bay, contain substantial stores of both organic carbon and nutrients. Soils from both systems are predominantly calcium carbonate, with an average of 82.1% CaCO3 in Florida Bay compared to 71.3% in Shark Bay. Soils from Shark Bay had, on average, 21% higher organic carbon content and 35% higher phosphorus content than Florida Bay. Further, soils from Shark Bay had lower mean dry bulk density (0.78 ± 0.01 g mL-1) than those from Florida Bay (0.84 ± 0.02 mg mL-1). The most hypersaline regions of both bays had higher organic carbon content in surficial soils. Profiles of organic carbon and phosphorus from Florida Bay indicate that this system has experienced an increase in P delivery and primary productivity over the last century; in contrast, decreasing organic carbon and phosphorus with depth in the soil profiles in Shark Bay point to a decrease in phosphorus delivery and primary productivity over the last 1000 y. The total ecosystem stocks of stored organic C in Florida Bay averages 163.5 MgCorg ha-1, lower than the average of 243.0 MgCorg ha-1 for Shark Bay; but these values place Shark and Florida Bays among the global hotspots for organic C storage in coastal ecosystems.

Phosphorus Biogeochemistry and the Impact of Phosphorus Enrichment: Why Is the Everglades so Unique?

The Florida Everglades is extremely oligotrophic and sensitive to small increases in phosphorus (P) concentrations. P enrichment is one of the dominant anthropogenic impacts on the ecosystem and is therefore a main focus of restoration efforts. In this review, we synthesize research on P biogeochemistry and the impact of P enrichment on ecosystem structure and function in the Florida Everglades. There are clear patterns of increased P concentrations and altered structure and processes along nutrient-enrichment gradients in the water, periphyton, soils, macrophytes, and consumers. Periphyton, an assemblage of algae, bacteria, and associated microfauna, is abundant and has a large influence on phosphorus cycling in the Everglades. The oligotrophic Everglades is P-starved, has lower P concentrations and higher nitrogen–phosphorus (N:P) ratios, and has oxidized to only slightly reduced soil profiles compared to other freshwater wetland ecosystems. Possible general causes and indications of P limitation in the Everglades and other wetlands include geology, hydrology, and dominance of oxidative microbial nutrient cycling. The Everglades may be unique with respect to P biogeochemistry because of the multiple causes of P limitation and the resulting high degree of limitation.

A model of the hydrothermal system at Casa Diablo in Long Valley, California, based on resistivity profiles and soil mercury analyses

A description and model of the near-surface hydrothermal system at Casa Diablo, with its implications for the larger-scale hydrothermal system of Long Valley, California, is presented. The data include resistivity profiles with penetrations to three different depth ranges, and analyses of inorganic mercury concentrations in 144 soil samples taken over a 1.3 by 1.7 km area. Analyses of the data together with the mapping of active surface hydrothermal features (fumaroles, mudpots, etc.), has revealed that the relationship between the hydrothermal system, surface hydrothermal activity, and mercury anomalies is strongly controlled by faults and topography. There are, however, more subtle factors responsible for the location of many active and anomalous zones such as fractures, zones of high permeability, and interactions between hydrothermal and cooler groundwater. In addition, the near-surface location of the upwelling from the deep hydrothermal reservoir, which supplies the geothermal power plants at Casa Diablo and the numerous hot pools in the caldera with hydrothermal water, has been detected. The data indicate that after upwelling the hydrothermal water flows eastward at shallow depth for at least 2 km and probably continues another 10 km to the east, all the way to Lake Crowley.