Chris Berger

Impact of Phosphorus Loading from the Watershed on Water Quality Dynamics in Lake Tenkiller, Oklahoma, USA”

Tenkiller Lake is a Corps of Engineers reservoir operated by the Tulsa District located in Oklahoma. Because of concern over possible impacts to the reservoir of poultry waste applied to agricultural lands in the basin, a hydrodynamic and water quality model of Tenkiller Lake was constructed to evaluate how the reservoir would respond to changes in nutrient loading from the watershed. The CE-QUAL-W2 model was calibrated to field data over the period of January 1, 2005 through September 2007. Comparisons of field data to model predictions were made for water level, temperature, NH4-N, NO3-N, PO4-P, total N, Total P, chlorophyll a, and dissolved oxygen at multiple reservoir sites at various depths. The model was used to predict the response of the reservoir to changes in Total P loading in the watershed over a 50-year period. Several scenarios were run with the model including no changes in nutrient loading from the watershed, natural conditions, and cessation of further land application of poultry waste in the watershed. Results and recommendations for achieving water quality targets in Lake Tenkiller were outlined. The cessation scenario showed that even after 50 years, the reservoir would still not have recovered to a natural pristine state. High residual Total P loading in the basin from past agricultural practices would continue to degrade water quality.

Modeling the Response of Dissolved Oxygen to Phosphorus Loading in LakeSpokane

ABSTRACT Wells SA, Berger CJ. 2016. Modeling the response of dissolved oxygen to phosphorus loading in Lake Spokane. Lake Reserv Manage. 32:270–279. Mathematical models of hydrodynamics and water quality are often used to determine the assimilative capacity of a waterbody when waterbodies violate state water quality standards. A model of the Spokane River and Lake Spokane in eastern Washington was developed to evaluate the assimilative capacity of the waterbody by setting a total maximum daily load (TMDL). A CE-QUAL-W2 model of this system was developed to establish the TMDL limits for the critical low-flow year of 2001. A recent paper evaluated this model and raised several issues about the validity of this model application as a regulatory tool related to its ability to predict total phosphorus, dissolved oxygen, and chlorophyll a relationships. This paper analyzes the validity of their critiques. For example, the critique used an incorrect formula to calculate total phosphorus inflows into Lake Spokane and used a volume-weighted minimum hypolimnetic dissolved oxygen (DOmin) that was not representative of hypolimnetic conditions. They also assumed incorrectly that the hydrologic, meteorological, operational, and sediment conditions of the 2001 TMDL model would be representative of conditions in other years. Although the water quality model of Lake Spokane can be improved, the critique does not invalidate the model as a tool to evaluate how the lake responds to nutrient environmental controls.

Prediction of GHG Emissions from a New Reservoir

Not until the 1990s was the significance of carbon emissions from reservoirs to greenhouse gas (GHG) accumulation in the atmosphere realized. Currently, hydroelectric projects proposed for World Bank funding must estimate their net GHG footprint, which in most cases has been estimated based on field measurements from similar reservoirs. Here we describe the development and application of CE-QUAL-W2 for prediction of future water quality and net GHG emissions from the proposed Amaila reservoir and downstream Kuribrong River in Guyana, South America. Sediment diagenesis was simulated, and the model enhanced to include the decomposition of a submerged tropical forest. The project site is located upstream of Amaila Falls in the remote highlands of the Guiana Shield. The water quality of the upper Kuribrong River exhibits low pH, low alkalinity, and somewhat high organic carbon concentrations, which is very different from reservoirs in the lowlands of French Guiana and Brazil where GHG fluxes have been measured. High CO 2 concentrations in the reservoir were caused primarily by the low pH and high CO 2 concentrations in the river inflows. Much of this CO 2 was emitted to the atmosphere within the reservoir, and most of the rest was passed through the dam. Net CO 2 emissions for the average flow year with vegetation harvested or burned were 30,799 T/yr. Net emissions for the no removal of vegetation were 71,824 T/yr. Methane concentrations in the dam outflow were less than 0.8 mg/L after the first year and 0.4 mg/l after 5 years.

Modeling of Water Quality and Greenhouse Emissions of Proposed South American Reservoirs

Water quality and hydrodynamic models of proposed hydroelectric projects in Guyana and in Peru were developed to help evaluate the environmental impacts on water quality and greenhouse emissions of these new reservoirs. The public domain 2-dimensional (longitudinal-vertical) hydrodynamic and water quality model, CE-QUAL-W2, was chosen for these projects. Modeled state variables included water surface elevation, velocities, temperature, dissolved oxygen, labile/refractory dissolved organic matter, labile/refractory particulate organic matter, CBOD, algae, PO4-P, NH3-N, NO3-N+NO2-N, suspended solids, pH, alkalinity, Total inorganic C, dissolved CO2, and sediments. CO2 fluxes from the reservoirs were also estimated. New state variables, methane (CH4) and hydrogen sulfide (H2S) constituents were added to the model including the processes of anaerobic release from the sediments and reaeration. Water quality model simulations were conducted for low, average, and high flow years and included the river systems downstream of the proposed reservoirs. The impacts of reservoir upon dissolved oxygen, carbon dioxide, methane, hydrogen sulfide, temperature, algae, and carbon loads were evaluated. Atmospheric emissions of carbon dioxide were predicted for the reservoir and river