Water Quality and Trophic State of Kaw Lake

This study measures the concentration of nitrogen, phosphorous and chlorophyll a levels in Kaw Lake, Oklahoma using the Carlson Trophic State Index (TSI). Kaw Lake is 16 km east of Ponca City and about 5 km from Kaw Nation headquarter in Kaw City, OK. The Lake was constructed in 1976 by the Army Corps of Engineers (ACE) for the purpose of water supply, recreation, electricity and wildlife conservation services. Since the early 20th century, lakes have been classified according to the trophic state into oligotrophic, mesotrophic and eutrophic based on secchi disk depth transparency, chlorophyll a, and total phosphorous and total nitrogen concentrations. The purpose of this study was to evaluate the productivity of Kaw Lake and algal biomass production through the interaction of nutrient concentration mainly total phosphorous, chlorophyll a and secchi disk transparency as defined in Carlson Trophic State Index. In order to determine the trophic state index, water samples were collected from the surface of the lake to 6 meters depth at 1.2 meters vertical interval of the lake profile. The samples were analyzed for the concentration of nitrogen and phosphorous along with chlorophyll a at a certified commercial laboratory in Stillwater, OK from January to December, 2013-2015. The three years of TSI data analysis indicates that the average TSI of secchi disk transparency was in the range of 61-70, chlorophyll a 42-55, total phosphorous 99-104 and total nitrogen 164-166. The overall result of the study showed that the Carlson TSI of Kaw Lake excluding nitrogen ranged between 67-74 indicating that the lake is eutrophic to hypereutrophic requiring measures to control runoff, sedimentation and algal biomass. Based on the nitrogen and phosphorous ratio examined Kaw Lake is predominately nitrogen limited lake. This study suggests that managers and policy makers should take actions to slow down or halt eutrophication by applying best management practices of the soil and water conservation measures. A measure that minimizes fertilizer use, storm water runoff, septic system effluents and dredging of sediment deposition should be incorporated in the short and long term lake management practices of the watershed program.