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William H. Orem, Debra A. Willard, Harry E. Lerch, Anne L. Bates, Ann Boylan, and Margo Comm
Sediment cores from two tree islands (Nuthouse and Gumbo Limbo) located in Water Conservation Area 3B of the Everglades, Florida were examined for preliminary studies of their nutrient geochemistry and paleoecology. Cores were collected from sites on the head, tail, and surrounding slough/marsh at each of the islands, and sediments from these cores were analyzed for various chemical constituents. Porewater in cores collected from the head and surrounding slough/marsh was also analyzed for its chemical composition for the purpose of evaluating nutrient recycling from tree island heads. Intervals in selected cores from both tree islands were dated using 14C analysis. The major objectives of the study were to: 1) determine the concentrations and accumulation rates of nutrients (carbon, nitrogen, and phosphorus) in sediments of tree islands, 2) examine the role of nutrients (if any) in the development of tree island tails and 3) examine downcore trends in nutrient element concentrations for evidence of ecological changes through time.
Organic carbon data suggest different histories for the two tree islands, with the head of Gumbo Limbo being dry and the head of Nuthouse submerged for most of the last 2,000 years. The sediments from the heads of both tree islands have very high concentrations of total phosphorus (TP): up to 1,500 µg/g at Nuthouse and up to 3,000 µg/g at Gumbo Limbo. These concentrations are 6 to 12 fold higher than the concentrations of TP found in the surrounding pristine slough/marsh sediments, and approach concentrations observed in phosphorus-contaminated areas of Water Conservation Area 2A. The source of the excess TP on the tree island heads is uncertain, but may be from guano deposited by birds nesting in the canopy of the tree islands. Concentrations of TP in sediments of the tree island/marsh/slough complex decrease in the order:
head > near tail = head edge > far tail > slough/marsh.
This indicates the possibility of transport of phosphorus in runoff from the head to the surrounding slough/marsh. On Nuthouse head, peaks in TP concentration were observed at 0.31-0.28 ka (thousands of years ago) and 1.85-1.50 ka, based on
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U.S. Department of the Interior, U.S. Geological Survey, Center for Coastal Geology This page is: http://sofia.usgs.gov/sfrsf/rooms/wild_wet_eco/tree_islands/ch5.html Comments and suggestions? Contact: Heather Henkel - Webmaster Last updated: 08 April, 2003 @ 11:13 AM (KP) |