How Much Does Stream-Groundwater Exchange Influence Whole-Stream Metabolism in a Small Mountain Stream?
Journal Article
Overview
abstract
To estimate whole-stream metabolism, the open-channel oxygen method has; traditionally provided underlying assumptions for modeled estimates of; gross primary productivity (GPP) and ecosystem respiration (ER). The; open-channel oxygen method employs the diel dissolved oxygen (DO) curve,; which attributes stream metabolism to four processes: photosynthesis by; primary producers, oxidative respiration, reaeration, and groundwater; flux. Of these processes, groundwater flux is often assumed to be; negligible when modeling whole-stream metabolism, which may introduce; bias in estimates of GPP and ER. For example, if net groundwater flux is; into the main channel, we may expect an overestimation of modeled ER due; to dissolved oxygen dilution effects from influent groundwater. Although; this error is recognized, there is a lack of continuous and spatial data; that quantifies the extent of bias that is introduced by not including; groundwater flux in model parameters. To investigate this bias, we; measured whole-stream metabolism and groundwater flux in Como Creek, a; headwater catchment 26 km west of Boulder, CO. DO sensors were deployed; in the stream and groundwater wells in June 2018 at 3 sites along 500 m; of the reach. BASE (Bayesian Single-station Estimation), a package; available through R, was used for modeling whole-stream metabolism; between peak streamflow and baseflow. BASE also optimizes the reaeration; coefficient, which was estimated both including and neglecting; groundwater discharge and DO concentration. Preliminary results indicate; that Como Creek has a net groundwater flux out of the stream, resulting; in higher rates of GPP in the groundwater-corrected model output, and; indicating the potential for bias in uncorrected models.
