Saturday, 15 July 2006

Space-time Trajectories of Soil Total Phosphorus in a Large Subtropical Wetland.

Gregory L. Bruland, Univ of Florida, IFAS, Soil and Water Science Dept, 2169 McCarty Hall / PO Box 110290, Gainesville, FL 32611-0290, Todd Z. Osborne, Univ of Flo rida, IFAS, Soil and Water Science Dept, 106 Newell Hall / Box 110510, Gainesville, FL 32611, K. Ramesh Reddy, Univ of Florida, Soil and Water Science Dept, 106 Newell Hall, P. O. Box 110510, Gainesville, FL 32611-0510, Sabine Grunwald, Soil & Water Science Dept, Univ of Florida, 2169 McCarty Hall, PO Box 110290, Gainesville, FL 32611, Susan Newman, South Florida Water Management District, Everglades Div, P.O. Box 24680, West Palm Beach, FL 33416-4680, and William F. DeBusk, Escambia County Engineering Dept, Water Quality Section, 1190 W. Leonard Street, Pensacola, FL 32501.

The assessment of spatial and temporal changes in the distribution of soil nutrients can be used as a method to quantify long-term impacts to an ecosystem. In this study, we assessed space-time trajectories of soil total phosphorus (TP) in a large subtropical wetland, Water Conservation Area 3 (WCA-3) of the Everglades. Soil cores were collected in 1992 and 2003 from two depths (0-10 cm and 10-20 cm) at 176 sites. To reflect hydrologic boundaries within the system, WCA-3 was divided into three zones (3AN, 3AS, and 3B). Total P was mapped on both a mass (TPm) and a volumetric basis (TPv) to determine if spatial distributions varied depending on the choice of units. Interpolated maps for both years showed that the highest levels of TPm were located in 3AN and in boundary areas of all zones that received surface water inputs from canals. Increases in TPm were greatest in central 3AN in an area adjacent to the Miami Canal that received inputs from a water control structure. Interpolated maps for TPv, illustrated that a TPv hotspot present in 1992 had disappeared by 2003. The highest levels of TPv in 2003 were located in northwestern 3AN, a region of WCA-3 that has been chronically overdrained and burned in 1999. From 1992 to 2003, increases in TPm were observed for 53 % of the area of WCA-3, while only 16 % of WCA-3 exhibited increases in TPv. In 1992, approximately 21 % of WCA-3 had TPm concentrations in the 0-10 cm layer > 500 mg kg-1, indicating P enrichment beyond historic levels. Eleven years later, 30 % of the area of WCA-3 had TPm > 500 mg kg-1. This indicated that during this period, the area of WCA-3 with enriched TPm concentrations increased about one % year-1. The combination of geostatistical and GIS techniques used in this study may provide a model for future research designed to quantify space-time trajectories of soil properties across various ecosystems.

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