Wednesday, November 18, 2020, 12:00PM - 2:00PM
Dissolved oxygen (DO) concentrations in rivers are critical for aquatic habitat and controlled by biological generation and uptake, and physical factors. One important physical factor is hydrology: not only streamflow dynamics (changing amounts of water), but also changes in surface-groundwater exchanges. Over a period of 15 months in East River, Colorado from August 2017 (a somewhat ‘average’ flow year) to October 2018 (a low flow year), high frequency (5 minute) DO and temperature data were collected in the water column of the river and directly in the streambed at depths of 10 cm, 20 cm, and 35 cm. Using the VFLUX2 model, temperature data were used to estimate vertical upwelling and downwelling vertical fluxes of water. We find that there was downwelling throughout both years, and increased fluxes into the bed during peak flows. From relating vertical flux to steam discharge and groundwater tables we find that stream discharge is a control of streambed DO during low flow. We calculated DO removal from the channel to the bed, finding enhanced removal rates in 2018. We observed an extended hyporheic anoxic period throughout the summer and fall of 2018 due to increased DO removal rates. The three subsurface locations were found to not all be on the same flow path, which may account for some of the DO differences in 2017 while increased removal due to low flow conditions are the primary factor in 2018. This research has advanced our understanding of the dependence of DO in both the streambed and open channel on stream-groundwater exchanges by showing periods of stream discharge control on DO dynamics.