| dc.description.abstract | Grand Lake O� The Cherokees provides recreational activities, water supply, hydroelectric power and flood control to the residents of Oklahoma and beyond. Grand Lake has experienced high eutrophication levels resulting in hypoxia during summer stratification. A three-layer steady state vertical dissolved oxygen model for summer-stratified conditions was developed to investigate oxygen profiles above and below the thermocline. The model was used to determine the relative effect of source and loss terms for oxygen and sediment oxygen demand (SOD) on bottom water hypoxia under summer-stratified conditions. The source terms investigated were atmospheric reaeration and phytoplankton production in the surface layer, while the loss terms were phytoplankton respiration, decomposition of organic matter, nitrification, and SOD. Observed water quality data, kinetic coefficients, and physical data obtained on Grand Lake were used in pre-processing calculations to derive estimates to the model inputs. Spatial gradients along the length of Grand Lake for riverine, transition, lacustrine zones and a site close to the dam were analyzed using data collected in 2013 and 2015 under stratified conditions when the hypolimnion was depleted of oxygen in June, July, and August. Predictions from the four stations provided reasonable agreement to the observed dissolved oxygen profiles. Phytoplankton production, high light limitation, and phosphorus were identified as the most critical factors controlling the source for oxygen production in the surface layer, while nitrification and organic carbon decomposition were the largest dominant loss terms controlling oxygen consumption over the entire water column. Sediment oxygen demand was identified as the least critical factor for oxygen demand in the water column. | |
