Integrated Wetland System
Rachel Carson, Dell Farris, Karl Garbrecht, Taber Midgley, Mattie Nutley, Kevin Stunkel
Environmental engineering is a sector that is experiencing increasing growth. Water quality research has experienced considerable growth since the passage of the Clean Water Act in the 1970s. A growing level of environmental awareness is leading to an increase in regulations to control and improve present conditions. The degree of surface water degradation is becoming increasingly apparent and the motivation to fix these problems is becoming stronger. Increasing population and strain on rivers and lakes is also bringing this issue to the forefront. Even in times of economic downturn, environmental laws are still in effect and the population should continue to be concerned with clean water supplies. The main motivation for this project is the condition of the water in the Illinois River and Lake Tenkiller Ferry. Increased nutrient concentrations, including phosphorus, have caused habitat degradation in the river. This is indicated by the loss of macro-invertebrates in the water. Increases in algal production are expected due to loss of riparian buffers and nutrient enrichment. At some sites on the river, the dissolved oxygen demand exceeds the EPA criterion. There are other motivations for this project and the following section describes three court cases concerning the Illinois River Watershed. The first resulted in Arkansas being forced to follow Oklahoma’s water quality criterions, and the last two specifically target the poultry industry.
Flowing from northwestern Arkansas into northeastern Oklahoma, the Illinois River is a source for recreation and drinking water in both states. The Illinois River Basin covers 1,645 square miles between Oklahoma and Arkansas and is dammed south of Tahlequah, Oklahoma to form Lake Tenkiller Ferry.The river and lake are used for recreational activities such as fishing, water skiing, swimming, diving, noodling and floating. Communities which rely on the river and lake for drinking water include Siloam Springs, Arkansas and Tahlequah, Oklahoma. The river and lake also support a diverse habitat which is heavily used for hunting and other recreational activities. Lake Tenkiller Ferry is becoming increasingly eutrophic because of excess nutrients, primarily phosphorus, conveyed by the river. Eutrophication causes algal blooms, limiting the oxygen availability for fish and other aquatic wildlife. Phosphorus in the river comes from point and non-point sources originating mostly from municipal wastewater treatment plants and runoff from agricultural fields respectively. Point sources can be easily identified, given they come from a single point and are essentially constant. Efforts have been made, and are still ongoing, to reduce the amount of phosphorus being discharged from the six major wastewater plants in Arkansas within the Illinois Basin. These plants account for about 32% of the phosphorus load and are the main source of phosphorus during base flow in the Illinois River2. Non-point sources are more difficult to quantify. Due to the commanding presence of the poultry industry in northwestern Arkansas, 210 million kilograms of poultry litter is produced each year, most of which is used to fertilize agricultural fields in the region. The litter contains 2.9 million kilograms of phosphorus, and during storm events much of this phosphorus is washed off the fields and into streams, which eventually drain into the Illinois River. The non-point source pollution, which accounts for about 66 percent of the total phosphorus load, has the greatest effect during high flow and storm events. The Illinois River has been a source of legal disputes for over a decade. The river has been declared a “Wild and Scenic River” by the state of Oklahoma, and with that designation comes a numerical criterion of 0.037 mg/l phosphorus. This criterion is not currently being met. The U.S. Supreme Court has ruled the state of Arkansas must comply with Oklahoma’s water quality standards. The Environmental Protection Agency has recently commenced a two-year study investigating the entire Illinois River watershed to provide a “Total Maximum Daily Loads” study for Lake Tenkiller Ferry. This study would provide a further limit on the amount of nutrients flowing through the river to the lake.
Scope of Work
Initial activities included jar tests to compare alum injection concentrations to flocculent settling times and dissolved phosphorus and sediment removal efficiencies in water samples from the Illinois River. Due to time restrictions, seasonality was not addressed in this study and water was only acquired in late February for the jar tests at a location just downstream of the proposed site for the constructed wetland. The results from the jar tests were used to determine the optimal alum injection concentration which was incorporated into a subsequent mesocosm study. Following the development and evaluation of potential design alternatives for the wetland system, testing of the selected design was conducted. These tests provided phosphorus removal efficiencies of the design. Results from the mesocosm study were used to evaluate applicability and effectiveness of the proposed wetland system design to make recommendations for in situ phosphorus attenuation in the Illinois River. The public good of recreational uses has been evaluated through the travel cost and total willingness to pay equations and estimates. A cost effective analysis has been conducted which compares alternatives for reducing phosphorus in the Illinois River. Communication materials produced include a billboard design, public service announcement, team website, educational website, wetlands educational factsheet, YouTube video, and an educational video