EPA New England Regional Laboratory (Office of Environmental Measurement and Evaluation)
Sediment Oxygen Demand Studies
Sediment Oxygen Demand (SOD) is the sum of all biological and chemical processes in sediment that utilize (take up) oxygen. SOD studies are used in mathematical models that aid in determining waste load allocations, which in turn are used in determining Total Maximum Daily Loads and in NPDES permits. They are also useful in measuring the depletion of oxygen in waters that have been stratified. In these waters, the sediment and the bottom layer of water are somewhat "trapped" and the oxygen is depleted as a result of decay of organic matter and lack of exchange of oxygenated water from upper layers.
SOD studies involve collecting a sediment core sample, which is a vertical column of a measurable volume of sediment and overlying water. The core samples are brought to EPA New England's mobile laboratory for analysis. The depletion of dissolved oxygen in the water column is measured over a three hour time period, and from this the Sediment Oxygen Demand is calculated.
SOD studies are conducted in selected New England rivers each year. Recent studies have included the Royal, Penobscot and St. Croix rivers in Maine, and the Contoocook River in New Hampshire.