ecological modelling 201 ( 2 0 0 7 ) 521–535 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/ecolmodel Modeling of the spatial variability of biogeochemical soil properties in a freshwater ecosystem  S. Grunwald a,* , K.R. Reddy a , J.P. Prenger a , M.M. Fisher b a Soil and Water Science Department, University of Florida, 2169 McCarty Hall, PO Box 110290, Gainesville, FL 32611-0290, United States b St. Johns Water Management District, Palatka, FL, United States article info Article history: Received 29 June 2005 Received in revised form 9 October 2006 Accepted 26 October 2006 Published on line 4 January 2007 Keywords: Spatial patterns Spatial variability Wetland Soil phosphorus Stochastic simulation Principal component analysis abstract Ecosystem services are dependent on the geospatial composition, structure, and function of an ecosystem. Our goal was to gain a better understanding of the variability of biogeochem- ical soil properties along gradients of impacted and unimpacted zones within a subtropical wetland in Florida. Our objectives were to (i) characterize the spatial variability and distri- bution of soil total phosphorus (TP), (ii) identify the magnitude and scale at which multiple biogeochemical soil properties account for variability within the ecosystem, and (iii) map the distribution of this variability. We collected soil samples (0–10cm) at 266 sites within the Blue Cypress Marsh Conservation Area (4900 ha) in Florida that were analyzed for 18 different biogeochemical properties. Conditional sequential Gaussian simulation and prin- cipal component analysis was used to identify three major groups of behavior: (i) labile, fast response properties with fine-scale spatial autocorrelation; (ii) stable, slow response prop- erties with regional spatial autocorrelation; (iii) properties showing intermediate response. The uncertainty of the spatial variability measures was described using small and large realizations as well as standard deviation maps. The first principal component (PC) [group (i)] contributed with 33.91%, the second PC [group (ii)] with 15.93%, and the third PC [group (iii)] with 11.32% to the total variance. Properties that explain much of the underlying vari- ability in a wetland are expected to be more sensitive to change than others that show more homogeneous patterns. More research is needed to reveal geospatial interrelationships of biogeochemical properties and their underlying spatial structure in aquatic ecosystems. © 2006 Elsevier B.V. All rights reserved. 1. Introduction Anthropogenic activities has led to rapid alterations in the composition, structure and function of ecosystems (Vitousek et al., 1997) so that in many cases their capacity to provide necessary services has been either overwhelmed or eroded (Palmer et al., 2004). Ecosystem services are the set of ecosys- tem functions that are useful to humans. Many of these are  This research was supported by the Florida Agricultural Experiment Station and approved for publication as Journal Series No. R-09967 (Institute of Food and Agricultural Sciences, University of Florida). ∗ Corresponding author. Tel.: +1 352 392 1951x204; fax: +1 352 392 3902. E-mail address: SGrunwald@ifas.ufl.edu (S. Grunwald). critical to our survival (e.g. climate regulation, filtering of pol- lutants) while others enhance it (e.g. aesthetics) (Kremen, 2005). Management of ecosystem services is complex and requires assessing the key environmental factors and their spatio-temporal scale over which they operate among others (Kremen, 2005). Wetland ecosystems are often endpoints of transport flow paths accumulating matter and nutrients from upland areas. While many site-specific wetland studies have 0304-3800/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ecolmodel.2006.10.026