Abstract from the 2002 AGU Spring Meeting.

A rising delivery rate of phosphorus to the northern Everglades, beginning in the late 1950's, is considered to be the primary cause of increased biomass production due to plant evasion of non-indigenous cattails (Typha) over native sawgrass (Cladium). One notably impacted area is along the northern boundary of Water Conservation Area 2 (WCA2) and the Hillsboro Canal. Along this boundary phosphorus-rich canal waters from upland agricultural regions enter and flow southward across WCA2. The biochemical effect of these waters extends approximately 6 km south of the canal, with cattails dominating the plant community for the first 2.5 km, followed by a mixed cattail-sawgrass community from about 2.5-6.0 km, and essentially pure sawgrass beyond about 6 km. In 1997, we collected soil cores from six sites along the transect to examine systematic changes in total phosphorus (TP) along a well-defined succession gradient and, if possible, to establish a sediment chronology using Pb-210--Ra-226as verified by the 1963-1964 fallout Cs-137 peak marker. Along transect, mean concentrations of phosphorus in surface waters and in soils (peats) decline markedly with distance from the canal. To test the assumption that phosphorous was the major parameter affecting the growth of cattail and to link accumulation rates to phosphorous levels, a model was developed that links the short-lived isotopes and phosphorous concentrations. This model is based on three assumptions: 1. Plants derive most of their phosphorous for growth from surface waters and soils; 2.The amount of phosphorus recruited by plants each year is proportional to soil total phosphorous concentrations that year; 3.Net soil accretion rates are linearly related to soil phosphorous concentrations. This model successfully predicts many details in the observed, highly irregular and largely non-exponential Pb-210 profiles. Temporal changes in the rate of accumulation of phosphorus (flux of phosphorous (FTP) in total phosphorous gm-2yr-1) and in soil accumulation was consistent among all sites. Between 1900 and 1960 phosphorous fluxes and soil accretion increase slightly and more-or-less linearly. After 1960, with the exponential rise in phosphorous, the soil accretion rate was determined to increase, also, at exponential rate, doubling each 30 ñ 6 years. At flux of total phosphorous (FTP) above 0.5 gm-2yr-1 in near surface soils, cattails have replaced sawgrass, below about 0.2, sawgrass populations are apparently not impacted. It remains to be seen if surface FTP values in the range of 0.2-0.5, indicate possibly undetected succession in progress at sites other than those examined in this study.

¹cholmes@usgs.gov, U.S. Geological Surevy, 600 Fourth Street South, St. Petersburg, FL 33701 United States

²John.A.Robbin@noaa.glerl.gov, Great Lake environmental Reserach laboratory, 2205 Commonwealth Blvd., Ann Arbor, MI 48105 United States

³krr@ufl.edu, Dept. of soil and water Science, University of Florida, Gainsville, Fl 32611 United States

⁴snewman@sfwmd.gov, South FLorida Water Management District, 3301 Gun Club Rd, West Palm Beach, FL 33416 United States ⁵mmarot@usgs.gov, 600 Fourth St.South, St. Petersburg, FL 22701 United States

Back to Project Homepage