A Chamberless Method for Determining SOD

Sediment oxygen demand (SOD) may be a significant component of the dissolved oxygen budget in waterways, comprising up to 50% in some systems. Therefore, SOD has the potential to significantly impact proper respiratory function of aquatic ecological systems and contribute to water quality problems. An accurate and reliable determination of SOD is needed for both water quality studies and ecosystem management. Current chamber-based in situ measurement techniques are often difficult to implement, require expensive equipment, limit the number of data points that can be collected, and can produce inconsistent results. This study sought to develop an alternative to chamber-based measurement techniques that will allow easier collection of multiple measurements for more thorough quantification of a system, especially as SOD varies over space and time. This study developed a measure-plus-calculate technique to determine SOD at a particular site in a water body without using a chamber by first measuring values for water temperature, water DO, sediment oxygen uptake rate, sediment porosity, stream hydraulic diameter, and stream velocity. These values are entered into a spreadsheet containing the solution to oxygen consumption and transport equations to then determine SOD at the site. The required stream measurements can be completed using equipment available in a typical water quality laboratory. This article focuses on the development of the SOD determination model, and a companion article includes methods used to determine model parameters and validation of the model by comparing it to chamber-measured SOD. This model is available free-of-charge from the corresponding author or at www.baeg.uark.edu/730.php.