PARENT SESSION
Oral Session #17: Wetland Ecology. Presiding: E. Weiher.
Monday, August 6, 2001. 1:00 PM to 4:15 PM. Hall of Ideas H.
Influence of cattle ranching on nutrient dynamics in seasonal wetlands.
Gathumbi, Stanley1, Bohlen, Patrick2, Graetz, Don1, Steinman, Alan3, 1 2 3
ABSTRACT- Many wetland ecosystems are exposed to grazing livestock but few studies have addressed interactions between cattle ranching and nutrient dynamics in wetlands. We are examining the influence of cattle ranching on nitrogen and phosphorus cycling, productivity, and organic matter storage and quality in seasonal wetlands of subtropical rangelands in the Lake Okeechobee Basin of south-central Florida. We are studying these characteristics in a large-scale experiment involving pastures stocked at four different cattle densities (control, low medium and high) in two different land use types (improved and semi-native pastures). Phosphorus concentrations in wetland sediments were greater in improved pastures than semi-native pastures. Wetland sediment N:P and C:P ratios were lower in the improved than in the semi-native pastures, and these differences between the two pasture types were reflected in nutrient ratios of wetland vegetation. The nutrient ratios of sediments fell within the range of values for the Everglades Water Conservation Area's nutrient impacted and reference sites, suggesting a broad regional relevance for those values. Carbon storage was greater and C mineralization rates lower in sediments from wetlands in semi-native pastures than in those from improved pastures. These results indicate that land use changes associated with beef cattle ranching alter nutrient concentrations and the quality of organic matter in wetland sediments and may alter the capacity of these systems to act as sinks for nutrients and organic matter.
KEY WORDS: wetlands, phosphorus, nitrogen, grazing