Abstract
Grand Lake O’The Cherokees, the third largest reservoir located in northeastern Oklahoma, provides recreational services, water supply, hydroelectric power, and flood control to residents of Oklahoma and neighboring states. Grand Lake has experienced major problems with eutrophication, harmful algal blooms, and dissolved oxygen (DO) depletion during summer. To better understand the dynamics of DO depletion in the hypolimnion of Grand Lake, a three-layer steady state vertical DO model for summer-stratified conditions was used to investigate dissolved oxygen profiles both above and below the thermocline. The DO model was used to determine the relative effects of atmospheric reaeration and phytoplankton production as a source of DO and phytoplankton respiration, decomposition of organic matter, and nitrification as loss terms for DO. Additionally, the importance of sediment oxygen demand (SOD) for hypolimnetic oxygen depletion was investigated at the sediment water-interface under stratified conditions. Observed water quality data, kinetic coefficients from the literature, and physical, biological, and chemical data collected throughout 2013 and 2015 along the spatial gradient of riverine, transition, lacustrine zones and a site close to the Grand Lake Pensacola Dam were used in the pre-processing calculations to derive estimates of kinetic rates as input parameters to the model. The estimated predictions from the model showed reasonable agreement with the observed vertical profiles of DO. Conclusions from this study indicate that phytoplankton production, high light limitation, and phosphorus were the major terms that controlled DO production in the surface layer, while nitrification and organic carbon decomposition were the major sinks of DO consumption in the bottom layer. Interestingly, SOD did not play a significant role in DO depletion in the water column.
Highlights
Nutrient Enrichment, Eutrophication and Oxygen Depletion in Lakes and ReservoirsIn the process of retaining minimal level of nutrients in lakes, rivers, and streams to support lakes productivity, the nutrients accumulate overtime causing eutrophication within the water column [1]
In 2013, the Trophic State Index (TSI) results show that Grand Lake was eutrophic in all the zones except for the riverine zone which was classified as hypereutrophic
The TSI results for 2015 indicate that Grand Lake was hypereutrophic in the riverine and transition zone, while the lacustrine zone and the site close to the dam were classified as eutrophic
Summary
In the process of retaining minimal level of nutrients in lakes, rivers, and streams to support lakes productivity, the nutrients accumulate overtime causing eutrophication within the water column [1]. Some major effects of eutrophication include nuisance levels of algae, taste and odor problems with water supply, occurrence of harmful algae blooms, increased bacterial production, and depletion of DO within the hypolimnion of lakes and reservoirs [3] [4] [5]. Costs related to harmful algae blooms in eutrophic lakes and reservoirs that provide drinking water services and other recreational activities have risen for water treatment costs to over a million United States (US) dollars per algal bloom event, while assessment and monitoring costs in impaired waterbodies have exceeded $50 million US dollars annually [3]
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