Trace Metals in the Sediments of Water Conservation Area–2A of the Everglades, Florida.

Sediment contamination by inorganic compounds presents a major challenge for the restoration of degraded aquatic systems.  Several water conservation areas are built in the south Florida to collect polluted runoff from the 283,280 ha of Everglades Agricultural Area (major crop is sugarcane) to reduce the delivery of polluted runoff water to environmentally sensitive ecosystem of Everglades.  Our objective in this study was to determine the levels of trace metals contamination in sediments of 43,281 ha of Water Conservation Area–2A (WCA–2A).  We collected 117 sediment samples from 0–10 cm depth in WCA–2A using a helicopter and air boat during Nov–Dec 2008.  Samples were grouped into three dominant ecotypes of ridge, slough, and typha present in the WCA–2A.  Sediments were analyzed for physico-chemical properties and trace metals.  The mean pH in three ecotype sediments was 6.75–6.82, while EC was slightly greater in ridge (0.69 dS/m) than typha (0.58 dS/m) and slough (0.40 dS/m).  Mean oxidation-reduction potential was greatest in typha (–113 mV) than ridge (–85.3 mV) and slough (–48.3 mV) sediments.  Among 11 trace metals (As, B, Co, Cr, Cu, Mn, Mo, Na, Ni, Pb, Zn) detected in sediment samples, Na had the greatest contents of 2070 mg/kg in typha, followed by 1735 mg/kg in ridge, and 1297mg/kg in slough.  Contents of Cd and Se were below the method detection limits (Cd: 0.01 mg/L; Se: 0.2 mg/L) and are not reported.  Contents of four trace metals were significantly greater in typha (B: 48.7; Cu: 10.3; Mo: 3.7; Ni: 6.5 mg/kg) than ridge and slough (B: 37.3–37.6; Cu: 7.0–7.3; Mo: 2.2–2.8; Ni: 5.1–5.5 mg/kg).  Interestingly, contents of Mn were significant lower in typha (31 mg/kg) than both ridge (84 mg/kg) and slough (51 mg/kg).  In the ridge sediments, contents of Cr (2.5 mg/kg) and Pb (20.8 mg/kg) were significantly greater than typha (Cr: 1.97 mg/kg; Pb: 10 mg/kg).  While the contents of As (5.9–6.9 mg/kg), Co (1.1–1.3 mg/kg), and Zn (15.1–17.2 mg/kg) were not significantly different among ridge, slough, and typha sediments.  In summary, none of the trace metals contents in the sediments exceeded the sediment toxicity thresholds.  Our results can aid in setting the baseline concentrations of trace metals in sediments of WCA–2A and measuring the success of Comprehensive Everglades Restoration Plan (CERP) in reducing the trace metals runoff to Everglades.