Watershed Processes Laboratory  

Relationship between stream sediment transport and primary production

The effects of channel bed disturbance on benthic chlorophyll a accrual were examined in three reaches of the Williams Fork River, CO (2004-2007) and at Oak Creek, OR (2015-2016). A field-calibrated multidimensional hydraulic model was used for estimation of shear-stress distributions. Sediment grain size was used to determine the critical shear stress for bed movement. Disturbance mapping showed that the common concept of bed disturbance as a byproduct of high-flow events is overly simplistic. In the Williams Fork, bed movement occurs constantly over certain portions of the bed, even at low flows. Periphyton biomass accumulated exponentially in the Colorado sites but accumulation rates were inversely proportional to local disturbance. Periphyton biomass increased by approximately three orders of magnitude across the three reaches, but failed to reach a plateau. A combination of moderate grazing rates, low-nutrient concentrations, moderately impaired solar irradiance, and, most importantly, low temperatures explains the failure of periphyton biomass to reach a plateau.

In Oak Creek mean shear stress in the channel bed across all sampling dates explained 49% of the variance in Chl-a. Over the 18 sampling dates — encompassing post-disturbance impacts and subsequent recovery — Chl-a differed between disturbance level categories defined based on the relative movement of the median grain size on 14 occasions. However, low disturbance locations were not always associated with higher Chl-a. The algal Chl-a biomass at any given time was a function of the stage of algal recovery following a high flow event and the magnitude of the disturbance itself — impacting algal loss during the event. Resistance of the algal communities to bed disturbance and resilience to recovery following a flow event varied spatially. Areas with low shear stress were less susceptible to scour during moderate disturbance events but were slower to recover when scour occurred. In contrast, high shear stress areas responded rapidly to flood events with rapid declines, but also recovered more quickly and appeared to have high potential for maximum accrual within our study reach. Ultimately, timing along with the inverse relationship between resiliency and disturbance frequency highlights the complexity of these processes and the importance of studying the interactions between geomorphic and ecological processes with high resolution across spatial and temporal scales.

Relationship between shear stress and Chl-a during 18 sampling events in Oak Creek, OR. (A) All measurements and (B) mean values of shear stress and Chl-a per sampling date.                                                                                                   

Shear stress distributions for six of the modeled flows between 0.4 and 3.4 m3/s in Oak Creek OR.

Funded by

Award # 1619700

Publications

33. *Cargill, S., Segura, C., *Villamizar, S., and Warren., D. 2021. The influence of lithology on stream metabolism in headwater systems, Ecohydrology;e2284. https://doi.org/10.1002/eco.2284

32. Heaston, E.D., Segura, C. and Warren, D.R. 2020, Do electrofishing activities impact stream biofilm standing stocks? An assessment from two headwater streams in western Oregon. North American Journal of Fisheries Management. Accepted Author Manuscript. https://doi.org/10.1002/nafm.10549

17. *Katz S, Segura C, Warren DR.  2018.  The influence of channel bed disturbance on benthic Chlorophyll a: A high resolution perspective. Geomorphology 305 141-153.

4.  Segura C, McCutchan JH, Lewis Jr WM, Pitlick J.  2011.  The influence of channel bed disturbance on algal biomass in a Colorado mountain stream. Ecohydrology. 4, 411-421.