Variation and Environmental Association of Ecosystem Metabolism in the Lower Klamath River: 2007-2014

The Klamath River and some of its tributaries are designated on the Clean Water Act (CWA) Section 303(d) list as impaired water bodies. Water quality is a concern in the Klamath River because it affects culturally and economically important salmon fisheries as well as public health. During the summer months, photosynthesis by aquatic plants and algae attached to the streambed elevate dissolved oxygen (O2) concentrations during the day, creating a 24-hour cycle in dissolved O2 concentrations. Respiration at night by those same organisms and bacteria has the reverse effect, depressing dissolved O2 levels. Resulting low nighttime dissolved O2 concentrations can exceed water quality standards and be stressful to fish (NCRWQCB 2010).

Ecosystem metabolism describes the fixation of organic carbon (gross primary production, GPP) and the mineralization of organic carbon (ecosystem respiration, ER). GPP and ER are integrative measures of river ecosystem health, and are complementary to more commonly used structural metrics that are regularly monitored on the Klamath River, such as dissolved O2 concentration, water temperature, and periphyton biomass. Ecosystem metabolism directly controls dissolved O2 concentrations in aquatic ecosystems and algal biomass, in part, forms the base of animal productivity in river food-webs (Thorp and Delong 2002, Cross et al. 2013).
Time series of daily metabolism estimates across many years allows examination of controls on metabolism at multiple time scales. Knowing what drives metabolism in the Klamath River will allow us to predict how rates of GPP and ER, and in turn, dissolved O2 concentrations will respond to changes in environmental conditions and management actions. Additionally, rates and patterns in ecosystem metabolism may be useful explanatory variables in other studies conducted in the Klamath River.