Metal Deposition in Baldcypress Tree Rings: Nickel, Copper, Chromium, Manganese and Iron Margaret S. Devall1, Leonard B. Thien2, and George C. Flowers2 1USDA Forest Service, Center for Bottomland Hardwoods Research, P.O. Box 227, Stoneville, MS 2Tulane University, New Orleans, LA
Methods • Cypress trees cored along bayou and reference area and chronology developed • 5-year increments ground and pressed into pellets • X-ray fluorescent spectrometer used to analyze samples • Concentrations presented in spatial and temporal dimensions
Results • First, levels of metals presented with respect to proximity to point source • Second, history of pollution documented
Mean level of Ni is 6.6 at Stations 0-60 and 4.5 atStations80-160.
Mean level of Mn is 20.2 at Stations 0-60 and 29.1 at Stations 80-160.
Conclusions • Metal mobility and availability are different in wetland soils. • Sulfate in the brackish water is reduced to sulfide and reacts with metals to form precipitates. • The sediments are highly polluted but precipitates are stable as long as reducing conditions are maintained. • Fe and Mn are more soluble and available to plants in the reduced state. This may account for their higher concentration in the tree rings.
Conclusions • Waterlogged soil, circumneutral to basic pH, and acid volatile sulfides from brackish lake water are the cause of relatively low levels of metals in tree rings in spite of heavily polluted soil. • Recently the levels of all metals in Stinking Bayou and levels of Cr, Mg and Fe in Bayou Trepagnier, likely due to urbanization.