Evaluation of Limiting Nutrients and Trophic State For Selected Ponds in the National Elk Refuge

Abstract

Executive Summary: During the years 2000 and 2001 several water samples were taken and observations were made in order to assess the limiting nutrients and the trophic state of the water at five locations in the National Elk Refuge near Jackson, Wyoming. These five locations were: Pond by Hay Barn, Pond by Gravel Pit, Pond by Miller House, Flat Creek (at bridge) in Elk Refuge, and Elk Refuge Outlet (Flat Creek at City Bridge). Nitrogen and phosphorus measurements were taken and the nitrogen-phosphorus (N:P) ratio was determined for each sample. The N:P ratios for the ponds were high which indicates that phosphorus was generally the limiting nutrient and the N:P ratios for Flat Creek were low which indicates that nitrogen was limiting. Along with phosphorus, chlorophyll-a measurements were also taken, and these data were used in the Carlson Model in order to determine the trophic state. The Carlson results indicate that the ponds are classified as oligotrophic to slightly mesotrophic (good water quality) and Flat Creek is classified as mesotrophic. However, based on the phosphorus measurements only, without the chlorophyll-a, the ponds are classified as mesotrophic and the Creek is classified as eutrophic (poor water quality). With the exception of the Elk Refuge Outlet (Flat Creek), which is eutrophic, there are no serious identified areas of water quality concern with regards to eutrophication in the Elk Refuge. These results should be useful in comparing with past and future studies in order to determine the effects of animal and human interaction on these waters.