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WETLAND SOILS

Soil Total Mercury Concentrations across the Greater Everglades

^a School of Forest Resources and Conservation, Univ. of Florida, 328 Newins-Ziegler Hall, PO Box 110410, Gainesville FL 32611-0410
^b Wetland Biogeochemistry Lab., Soil and Water Science Dep., Univ. of Florida, 106 Newell Hall, PO Box 110510, Gainesville, FL 32611-0510
^c Environmental Engineering Sciences, Univ. of Florida, 320 Black Hall, PO Box 1106450, Gainesville, FL 32611-6450
^d Everglades Dep., South Florida Water Management District, PO Box 24680, West Palm Beach FL 33416

^* Corresponding author (mjc{at}ufl.edu).

Elevated Hg concentrations in the Everglades pose ecological and human health risks. We mapped soil total Hg concentrations per mass (THg_M) and area (THg_A) across the Everglades, and investigated relationships with soil properties (total P [TP] and organic matter content), community type, and hydrologic compartmentalization. Samples (n = 600) from surface soils (0–10 cm) were selected from a population of 1405 sites spanning the Everglades. Overall, 168 sites had THg_M levels >0.2 mg kg^–1; interpolation suggests that 23% of the Greater Everglades exceeds this threshold. Hot spots (>0.4 mg kg^–1) were observed in eastern Water Conservation Area (WCA) 1 and west-central WCA3A; parts of WCA2A, WCA3AN, and WCA3B were locally high. Despite significant global differences in THg_M among plant communities, differences evaluated using paired proximate sites were not significant, suggesting that large spatial scale depositional gradients govern ecosystem storage. Median THg_A was 1.89 mg m^–2 (range 0.07–12.05 mg m^–2), representing approximately 100 yr of atmospheric deposition at contemporary rates (19 µg m^–2 yr^–1). Correlation between TP and THg_M was positive in unimpacted areas (TP < 500 mg kg^–1, r = 0.69), but negative in impacted areas (TP > 500 mg kg^–1, r = -0.47), probably due to accelerated peat accretion rates in P-enriched areas. Moreover, while reverse correlation with distance from a canal for THg_M (0.70) and TP (–0.77) supports Hg enrichment via atmospheric deposition, THg_M hotspots in WCA3AS, WCA1, and the Holeyland and Rotenberger tracts are suggestive of local enrichment mechanisms. Finally, despite dramatic regional emissions declines, the estimated mass of Hg in surface soils across the Everglades has increased 20% (11,000 vs. 13,100 kg) since 1996; while the statistical significance of this change is unknown, it provides a useful benchmark for future surveys.

Abbreviations: BCNP, Big Cypress National Preserve • BD, bulk density • EAA, Everglades Agricultural Area • ENP, Everglades National Park • HLRB, Holeyland and Rotenberger tracts • LOI, loss-on-ignition • MeHg, methyl-mercury • OK, ordinary kriging • THg, total mercury • THg_A, total mercury per area • THg_M, total mercury per mass • TP, total phosphorus • WCA, water conservation area