Spatial variability, distribution and uncertainty assessment of soil phosphorus in a south Florida wetland

Phosphorus enrichment has been of major concern in the Greater Everglades (GE) ecosystem since the early 1980s. Our objectives were to estimate spatio–temporal patterns of soil total phosphorus (TP) in Water Conservation Area 2A (WCA-2A) in the GE ecosystem and to compare two different geostatistical methods: ordinary kriging (OK) and conditional sequential Gaussian simulation (CSGS), addressing spatial variability, continuity and uncertainty of TP estimations. Overall, TP estimated with OK and CSGS were higher in 1998 than in 1990. Both methods generated spatial patterns of TP in 1998 which showed a spatial expansion of the phosphorus enrichment identified in the 1990 dataset. Cross-validation using OK produced a mean prediction error of 10.71 (1990) and 6.07 (1998). CSGS modeled the spatial uncertainty of TP estimations explicitly with 50 generated realizations. Uncertainty was modeled using the E-type mean of TP, which ranged from 216 to 2100mg kg 1 in 1990 and 325.2 to 3660mg kg 1 in 1998. Standard deviations ranged from 0 to 550mg kg 1 maximum. To evaluate TP exceeding a threshold of 450TPmg kg , which represents natural historic wetland conditions, we produced probability maps. Results suggested a distinctly higher retention of TP using CSGS when compared to the OK generated probability maps. Spatial probability patterns are valuable to guide the restoration process of this wetland. Jackknifing was used to estimate the bias of the descriptive statistics and semivariance. The total number of samples was robust enough to produce stable variograms; however, jackknifing suggested that more samples at closer distances from each other should be collected to reduce the uncertainty of the semivariance and to address short-range spatial variability. Copyright # 2004 John Wiley & Sons, Ltd.