Abstract:
Recent advances in water quality monitoring have facilitated the acquisition of temporally rich datasets that allow comprehensive
analysis of patterns and underlying processes and drivers at multiple scales. We analyzed data from a
continuous water quality monitor on the tidal Occoquan River, a tributary of the tidal Potomac River and Chesapeake
Bay. Temperature, conductivity, dissolved oxygen (DO), and pH were collected at 15 minute intervals from April
through early November of 2010. Results of time series analysis indicate that, on a short-term basis, conductivity
manifested an underlying semidiel pattern, presumably driven by tidal excursion. In comparison, DO, pH, and
temperature exhibited a diel pattern correlated with the daily light and temperature cycle. Longer-term patterns were
related to longer-term climatic factors such as a dry summer with low freshwater inputs, seasonal progressions of light
and temperature, and a river discharge spike in early October. Examination of multiday patterns in DO and pH using 15
minute data during a climatically stable period illustrated both diel and semidiel patterns. Patterns in a period of strong
hydrological forcing revealed a disruption of diel and semidiel patterns for several days with a general restoration of
patterns thereafter. Both diel and seasonal data suggest that abundant submerged aquatic vegetation in the study area
was the main primary producer component driving diel and seasonal DO and pH patterns.
