Water quality in the Santa Fe River Watershed, located in north central Florida, has been decreasing. Changing land use and off-site movement of nitrogen have been implicated in this change. Study objectives were (1) to evaluate the effect of land use on total amounts of carbon, nitrogen, and phosphorus in the surface 10 cm of soil and (2) contrast by land use the distribution of carbon, nitrogen, and phosphorus among soil particle fractions to better understand which fractions are most influenced by these changes. Land use in the watershed is approximately 68 percent forested, 14 percent improved pasture, 7 percent residential area, 5 percent crop, and 3 percent rangeland. Total organic carbon, total nitrogen, and extractable phosphorus were measured in four soil size fractions (2mm to 250 micron, 250 to 150 microns, 150 to 53 microns, and less than 53 microns) from the 0-10 cm soil depth at 140 locations in the watershed. Forested areas were compared to the other land uses. Non-wetland forested areas had the lowest nitrogen and carbon concentrations while forested wetlands had more within all land uses. The largest size fraction in forested areas was richer in nitrogen and carbon than in other land uses. The smallest size fraction contained the highest amount of nitrogen and carbon across all land uses. Forested areas were generally lower in phosphorus than other land uses. These results, along with a companion abstract on soil solution nitrate, indicate that while forested land use dominates the landscape, it has the lowest probability of adding additional pollutants to the Santa Fe River. Crop land, which is only 5 percent of the total watershed area, has some of the highest nitrogen and phosphorus impacts and is located at sites that pose the greatest impact on surface and ground water resources.
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