Effects of Land Use on Soil Phosphorus Fractions in the Florida Everglades

The Florida Everglades is the largest ecosystem in the United States, and it is vulnerable to a multitude of threats including nutrient loading. Approximately 50% of the Everglades wetland has been drained for agricultural and urban development, which has altered water flow patterns. To better understand the sources of phosphorus (P) that could potentially enter the Everglades, this project investigated differences in soil P pools among four distinct land use types (farmland, forest, residential, and natural preserve areas). Twenty-six soil samples collected from these land uses were extracted for four P pools (H2O-P, NaHCO3-P, NaOH-P, and HNO3-P) and the concentrations of inorganic P (Pi) was quantified using UV-Vis spectroscopy. Among these pools, the H2O-Pi pool is the most bioavailable fraction, while the HNO3-Pi pool is the least bioavailable. Our preliminary data show the general order of Pi concentrations among different soil types is: HNO3-Pi>NaHCO3-Pi>NaOH-Pi>H2O-Pi. Soils from natural preserves and within the Everglades National Park exhibit lowest total P, representative of natural P content in the originally oligotrophic ecosystem. Soils with high P content in farmland and adjoining areas likely originated from use of chemical fertilizers or other sources of supplemental P. These P pools are being analyzed for phosphate-oxygen isotopes and elemental fingerprinting to identify specific sources. Collective results will then be used to identify land uses that contribute to high P loading to the Everglades. This information is expected to be useful in developing better management strategies to reduce nutrient load in the Everglades.