Eutrophication, Nutrient Enrichment and Water Quality of Kaw Lake

This article discusses the water quality of Kaw Lake using the Carlson Trophic State Index (TSI), which involves measuring Secchi disk transparency, chlorophyll-a, total nitrogen, and total phosphorus levels. Since the early 20th century, lakes have been classified based on their trophic state into three categories: oligotrophic, mesotrophic, and eutrophic. This classification relies on measuring Secchi disk depth transparency, chlorophyll-a levels, and total phosphorus and nitrogen concentrations. The primary goal of this study was to assess the productivity of Kaw Lake and algal biomass production by evaluating the interaction between nutrient concentrations—primarily total phosphorus and chlorophyll-a—and Secchi disk transparency as defined by the Carlson Trophic State Index. Excessive nutrients, such as nitrogen and phosphorus from agricultural runoff and wastewater, can reduce the water transparency, and decrease oxygen levels of the Kaw Lake ecosystem.

To determine the trophic state index, water samples were collected from the top of the lake to a depth of 6 meters, at vertical intervals of 1.2 meters. These samples were analyzed for nitrogen, phosphorus concentrations, and chlorophyll-a, at a certified commercial laboratory in Stillwater, Oklahoma, from January to December 2013 to 2015. The analysis of three years of TSI data revealed that the average TSI for Secchi disk transparency ranged from 61 to 70, chlorophyll-a from 42 to 55, total phosphorus from 99 to 104, and total nitrogen from 164 to 166. The study found that the Carlson TSI of Kaw Lake, excluding nitrogen, ranged between 67 and 74, indicating that the lake is classified as eutrophic to hypereutrophic. This condition necessitates measures to control runoff, sedimentation, and algal biomass. Furthermore, the nitrogen-to-phosphorus ratio indicates that Kaw Lake is predominantly nitrogen-limited. Understanding this nitrogen limitation is crucial for effective management interventions. This study suggests that managers and policymakers actively address eutrophication by implementing the best management practices (BMP) of the nonpoint source pollution (NPS) programs.