Characterization of the Spatial and Parameter Variability in a Subtropical Wetland

S. Grunwald, K.R. Reddy and J.P. Prenger  
Soil and Water Science Department
University of Florida
2169 McCarty Hall, P.O. Box 110290
Gainesville, FL 32611-0290
Phone: 352-392-1951 ext. 204 ; Fax: 352-392-3902

The eutrophication of subtropical wetland ecosystems has profound effects on biogeochemical patterns, pedo- and biodiversity, and ecological function. We investigated  a nutrient-enriched subtropical wetland, which is undergoing natural succession. We collected 20 biogeochemical soil properties at 267 sites to characterize the current ecological status. This exhaustive dataset served as a reference. Our goal was to identify properties which accounted for much of the spatial and the parameter  variability. We used Conditional Sequential Gaussian Simulation (CSGS) to generate realizations of biogeochemical properties to characterize spatial patterns and to assess explicitly the uncertainty of predictions. We used Principal Component (PC) Analysis to transform a number of possibly correlated variables into a smaller number of uncorrelated variables. CSGS was used to generate realizations of PCs. Each biogeochemical property was mapped into a PC indicating its significance to explain variability in  the dataset. A spatial sensitivity analysis using subsets drawn randomly from the exhaustive dataset suggested that dynamic biogeochemical properties grouped into PC1 require sampling densities of > 3.75 sites/100 ha whereas properties grouped into PC2 require a sample density of > 2.52 sites/100 ha to reproduce the spatial patterns and variability across the wetland.  Our results are valuable to document the current ecological spatial patterns in this wetland and  optimize future sampling designs in subtropi cal wetlands explicitly considering parameter and spatial variability.

Keywords: stochastic simulation, realizations, biogeochemical soil properties, principal component analysis, spatial patterns, spatial variability

In: McRoberts, R. et al. (eds).  Proceedings of the joint meeting of The 6th International Symposium On Spatial Accuracy Assessment In Natural Resources and Environmental Sciences and The 15th Annual Conference of The International Environmetrics Society, June 28 – July 1 2004, Portland, Maine, USA.


Grunwald2004accuracy.pdf140.01 KB