Regional Modeling of Carbon, Nitrogen and Phosphorus Geospatial Patterns. Chapter 9, Pp. 293-310. in Hanrahan G. (ed.) Modeling of Pollutants in Complex Environmental Systems

Quantifying spatial distributions and spatially-explicit relationships of soil carbon (C), nitrogen (N) and phosphorus (P) and environmental factors allows us to derive functional relationships and assess anthropogenic induced nutrient imbalances. The objectives of this study were to: (i) characterize geospatial patterns of C, N, and P across a large subtropical region in the southeastern U.S., (ii) assess the spatial variability of C:N and N:P ratios, and (iii) explain C, N, and P spatial patterns in soils using inferential, spatially-explicit models that relate environmental soil-forming (SCORPAN) factors to soil properties. A comprehensive landscapescale study was conducted in the subtropical Santa Fe River Watershed (SFRW) in north-central Florida. Samples at 143 sites in four soil layers (L1, L2, L3, and L4) were collected and analyzed for soil C, N, and P, and numerous environmental soil-forming factors were derived for the watershed to characterize climate, topography, soils, land use, vegetation, and geology. We used Log-Normal Kriging to characterize spatial patterns of C, N, and P and derive C:N and N:P ratios. Regression Committee and Classification Trees were used to quantify relationships between soil C:N, N:P, and CNP classes and environmental factors. Carbon, N, and P showed distinct spatial long-range patterns (> 9,247 m) within the watershed in different layers. The median ratios of C:N were 21.3 (L1), 23.8 (L2), 16.1 (L3), and 9.4 (L4), whereas median N:P ratios were 70.5 (L1), 51.9 (L2), 59.3 (L3), and 49.6 (L4). The C:N:P were 1,726:81:1 (L1), 1,195:51:1 (L2), 1,064:70:1 (L3), and 572:60:1 (L4) based on soil property medians. Net mineralization of N was pronounced across the watershed on 39.5% (L1), 8.4 % (L2), 57.0 % (L3), and 96.6 % (L4) of the area with C:N < 20. In contrast, net immobilization, characterized by areas with C:N > 30, were minor with 2.1 % (L1), 20.1 % (L2), 3.1 % (L3), and 0.0 % (L4). Although spatial coverage of low N:P (< 8) predominated across the watershed with 35.9 % (L1),