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Cows grazing in improved pasture

Seasonal wetland in improved pasture

Water Quality Impacts of Cattle Ranching.  Lake Okeechobee is the largest lake in the southeastern United States and is a critical water body in south-central Florida, serving the multiple purposes of water supply, recreation and flood control.  It has experienced a variety of human-induced impacts over the past half  century, including excessive nutrient inputs from agricultural activities in the watershed, unnatural variations in the lake water levels, and the invasion and expansion of exotic species.  Beef cattle ranches are the dominant land use in the watershed north of Lake Okeechobee, which serves as the headwaters for the Florida Everglades.  The coverage of wetlands in the region has declined from 25% to 15% during the past few decades, due to an imposed drainage network for flood control and the conversion of more land to improved beef cattle pasture.  As a result of these land use changes, nutrient loading has increased into Lake Okeechobee, a major component of the Greater Everglades Ecosystem.  Phosphorus concentrations and loads in this critical water body have doubled within the past two decades, resulting in increased frequency of algal blooms, and prompting regulatory agencies to establish the first Total Maximum Daily Load (TMDL) in the State of Florida.  Although substantial reductions have been achieved in the amount of phosphorus loads to Lake Okeechobee, the loads still are above the target specified by legislative and regulatory agencies.  Since the dairy industry had achieved significant reductions in the amount of phosphorus leaving dairy farms, beef cattle operations have become a more important source of phosphorus to Lake Okeechobee, on a relative scale.

Nutrient Cycling in Subtropical Rangelands. Cattle grazing has been shown to increase the mineralization of nutrients in some grassland ecosystems. Grazing induces changes in nutrient transformations by removing aboveground biomass and stimulating microbial activity and the forms and availability of soil nutrients. These changes can lead to changes in plant species composition, which, in the long-term, may affect litter quality, mass and seasonal dynamics of litter inputs. Cycling of nutrients through grazers may increase the readily-mineralizable pool of nutrients at the soil surface where they are more accessible for uptake by plants and microorganisms. Grazing can increase N mineralization at the landscape scale, overriding influences of local topography. Consequently shoots of plant from grazed areas can have greater nutrient concentration than shoots from non-grazed areas. Grazing can also alter the allocation of energy to the belowground foodweb. These interactions are extremely important to overall system function. There is a lack of general principles concerning grazing influences on belowground processes, due to the complexity of interactions and the variety of mechanisms that mediate grazing influences. Furthermore, there is a general lack of information on these complex interactions, indicating a need for more research in this area under a variety of experimental settings.

Wetland Ecology and Nutrient Cycling.   Top  Wetlands are valuable as sources, sinks and  increasing attention because of their role as habitat for threatened wildlife and their capacity to assimilate nutrients. There is considerable interest in the ability of these wetlands to act as buffers or nutrient sinks in agricultural landscapes. Although natural wetlands have the short-term capacity to remove nutrients, it is unclear how they will function in the long-term, because of the possibility that they may become nutrient saturated and serve as net sources rather than sinks of nutrients. Furthermore, non-point sources of nutrient pollution can threaten the natural structure and function of wetlands. To obtain a better understanding of the function of wetlands in agricultural landscapes, it is necessary to investigate key nutrient cycling processes in these wetlands and to evaluate their response to different management practices. Grazing of livestock is a major land use surrounding many critical wetland habitats, but the impact of grazing livestock on wetland ecosystem has not been well studied.

Wetland Restoration. Top  Our goal is this project is to assess the effectiveness of ecological restoration of ~750 acres of degraded wetlands at two locations at the MacArthur Agro-ecology Research Center on Buck Island Ranch.  The wetlands are being restored as part of the USDA Wetland Reserve Program (WRP) and our restoration goals will be guided by the overall goals of the WRP program.  Final design plans for the sites have not been developed but we have a good idea of what the restoration design will entail and expect that the restoration activities will start early in 2004.  The overall goals for our WRP project, which correspond to USDA goals for the WRP Program, are: 

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