Food abundance and energetic carrying capacity for wintering waterfowl in the Great Salt Lake wetlands Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/x633f300x

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  • Great Salt Lake (GSL), Utah, is surrounded by 191,884 hectares of wetlands. These wetlands provide critical habitat for hundreds of thousands of breeding, migrating and wintering waterfowl each year. As the human population around GSL increases, government officials have proposed to divert more water from the Jordan, Ogden, and Bear Rivers to meet municipal demands. Freshwater diversions from the rivers that supply the wetlands will likely decrease the amount of wetland habitat available to waterfowl. To justify current and future water allocation for wetlands around the GSL, managers must quantify the value of these habitats to migratory wetland birds, and one measure of habitat quality is food abundance. However, food abundance in the GSL wetlands is unknown. In this study, I quantified food abundance in managed and unmanaged wetland areas along the east side of the GSL. Managed wetlands included state, federal, and private lands contained within levees and actively managed as waterfowl habitat. I defined unmanaged wetlands as those shallow water areas outside levees impacted by freshwater flows from the Jordan, Bear, and Ogden Rivers and from managed wetlands. Unmanaged wetlands are under no specific management regime and are under the greatest threat by proposed water diversions because they are currently not protected under Utah water laws. I used multi-stage and simple random sampling to quantify food abundance in managed and unmanaged wetland. Sampling in managed wetlands occurred during September 2005-2006 (n = 12) and unmanaged wetlands during 2006 (n = 3) before the majority of waterfowl arrive on fall migration. I estimated the biomass of seeds, tubers, invertebrates, and submerged aquatic vegetation (SAV). Mean tuber and invertebrate biomass was similar between managed and unmanaged wetlands in 2006 (ps > 0.09); however, leafy biomass was 37% higher in unmanaged wetlands (t = 2.47, p = 0.015) and seed biomass was 65% higher in managed wetlands (t = 5.06, p <0.001). I then used biomass estimates to calculate energetic carrying capacity of both managed and unmanaged wetland habitats and determine the effects of possible water diversions from unmanaged wetlands on migratory waterfowl. I used information on daily bird energy needs, biomass estimates, and true metabolizable energy of each food type to estimate duck carrying capacity in habitats dominated by submerged aquatic vegetation. I separated ducks into three guilds based on food habits and feeding methods (dabblers, divers and grazers). The unit of comparison for energetic carrying capacity was Duck Use Day (DUD), defined as the amount of energy needed to support one duck for one day. Carrying capacity was higher in managed vs. unmanaged habitats for all three duck foraging guilds. If unmanaged wetlands decline by 80%, I estimated that duck carrying capacity would decrease 34% for grazers, 20% for divers, and 14% for dabblers. Results from this research provide a quantitative value to both managed and unmanaged wetlands surrounding the GSL to wintering waterfowl and provide guidance for the future conservation, restoration and maintenance of hundreds of thousands of hectares of critical wetland habitat.
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