Understanding dissolved oxygen concentrations in a discontinuously perennial stream within a managed forest

Abstract

The concentration of oxygen dissolved in water affects aquatic organisms. Unrestrained logging and site preparation can depress dissolved oxygen (DO) concentrations in adjacent streams by elevating temperatures (with removal of riparian shade), impounding channels (reduced reaeration rates), and introducing fresh, oxygen-depleting slash. One of the first paired watershed studies investigating the use of streamside management zones, the Alsea Watershed Study (AWS) in coastal Oregon (1958–1973), highlighted the potential to depress DO concentrations in streams adjacent to harvest units. This and other studies spurred development of Best Management Practices (BMPs) and forest practice rules to maintain, among other things, favorable DO concentrations in streams. A new study of the Alsea watersheds (2006–2015) found little signal of management effects on DO concentrations. It did find that a discontinuously perennial stream (where reaches go subsurface during low flows) can experience naturally low DO concentrations. Forest managers can avoid exacerbating low DO conditions using simple BMPs, but discontinuously perennial forest streams are predisposed to low DO concentrations.