projects > geochemistry of wetland sediments > abstract
Nutrient Geochemistry of the South Florida Wetlands Ecosystem: Sources, Accumulation and Biogeochemical CyclingW.H. Orem, H.E. Lerch, R.A. Zielinski, A.L. Bates, A. Boylan, and M. Corum The south Florida wetlands ecosystem (the Everglades and Florida Bay) has historically been an
oligotrophic environment. Anthropogenic activities (especially agriculture) during the past century,
however, have delivered excess phosphorus (P) to some areas of the northern Everglades, contributing
to changes in water quality and ecology. The fate of this excess P and its long-term effects on biological
resources are unclear. South of the Everglades, changes in nutrient loads to Florida Bay are
hypothesized to be linked to recent events of seagrass die-off and microalgal blooms. Restoration of
the Everglades and Florida Bay to a more natural nutrient balance will require crucial baseline
information on the ecosystem's recent nutrient history, the sources of nutrients to the ecosystem, and
the biogeochemical cycling of nutrients within the ecosystem. This project 3 has focused on
establishing: (1) the source(s) of nutrients to contaminated areas of the northern Everglades and to
Florida Bay, (2) the spatial and temporal variation of nutrients within the ecosystem, and (3) the rates
of accumulation and recycling of nutrients in sediments (including the flux of nutrients from sediment
porewater to surface water).
Our results show that concentrations of P at pristine sites in the freshwater Everglades range
from 1-20 µg/L in surface water, 10-100 µg/L in sediment porewater, and 300-500 µg/g (dry wt) in
sediments. At contaminated marsh sites, however, P concentrations often exceed 100 (g/L in surface
water, 3,000 µg/L in porewater, and 2,000 µg/g in surface sediment. Profiles of total P in dated ( We have used the concentration and alpha activity ratio ( In preliminary work, we have determined that tree islands represent another zone of P
enrichment in the Everglades. Studies of sediments from the heads of two tree islands in WCA-3B
showed concentrations of up to 3,000 µg/g on one island and up to 1,500 µg/g on the second. These
concentrations are far in excess of those observed in the surrounding pristine marsh (values of around
200-300 µg/g), and approach or exceed P concentrations in contaminated areas of WCA-2A. The
source of the high levels of P on tree islands is uncertain, but we hypothesize that it originates from the
guano of nesting birds. The P concentrations of sediments in the tail and edge of the tree island are also
in excess of concentrations in the surrounding marsh, but less than values found on the head. Runoff
of P from the head may explain the distribution of P in the tail, and P-enrichment may play a role in
the development of tree island tails.
In the southern Everglades, we have conducted extensive sediment and water sampling in Taylor
Slough and the C-111 basin. In addition, water sampling and sediment coring have been undertaken at
sites in Florida Bay and the mangrove fringe zone surrounding Florida Bay. The objective of this work
was to examine source(s) of nutrients and nutrient cycling in the southeastern Everglades and
northeastern Florida Bay. Analysis of samples and data from this study is still underway; some
preliminary conclusions, however, have been developed. Concentrations of total P in sediments at the
head of Taylor Slough approach values of 1,000 µg/g, in excess of concentrations for pristine areas of
the Everglades. This suggests P contamination at the head of Taylor Slough from canals discharging
at the head of the Slough. Total P concentrations in sediments diminish to the south to nearly
background levels (< 500 µg/g) by the center of the Slough. Accumulation rates for P range from
1.4 gP/m 3This work was conducted in close collaboration with scientists from the U.S. Geological Survey, the South Florida Water Management District, the Florida Game and Fresh Water Fish Commission, the U.S. Department of Agriculture, and the University of Florida.
(This abstract was taken from the Proceedings of the South Florida Restoration Science Forum Open File Report)
|
|
U.S. Department of the Interior, U.S. Geological Survey, Center for Coastal Geology This page is: http://sofia.usgs.gov /projects/wetland_seds/wetlandabsfrsf.html Comments and suggestions? Contact: Heather Henkel - Webmaster Last updated: 11 October, 2002 @ 09:30 PM (KP) |