Removal of Benthic Algae in Swift-Flowing Streams: the Significance of Spatial and Temporal Variation in Shear Stress and Bed Disturbance

• Main Author: Cullis, James Duncan Sydney
• Format: Text
• Language: unknown
• Published: CU Scholar 2011
• Subjects: benthic algae; flushing flows; hydrodynamics; organic matter transport; stream ecosystems; Ecology and Evolutionary Biology; Geomorphology; Water Resource Management; McMurdo Dry Valleys; Antarc*; Antarctica
• Online Access: https://scholar.colorado.edu/cven_gradetds/225; https://scholar.colorado.edu/cgi/viewcontent.cgi?article=1231&context=cven_gradetds

In this thesis I investigate the role of spatial and temporal dynamics of flow, bed shear stress, and bed disturbance on the removal of benthic algal and the consequences for our understanding of the dynamics of stream ecosystems and the transport of organic matter in fluvial systems. I use data obtained from two specific case studies where benthic algal mats are key components in the overall system dynamics. The first case study investigates spatial and temporal variations in particular organic matter transport derived from the removal of benthic algae in a stream in the McMurdo Dry Valleys of Antarctica. The second case study uses a combination of field observations and analysis, one and two dimensional hydraulic modeling, and laboratory flume studies to investigate the controls on the removal of the stalk forming diatom Didymosphenia geminata. The results show that benthic algae growing in swift-flowing streams are well adapted to this environment. Hence the removal of organic material due to elevated shear stress alone is limited and effective control of nuisance blooms of benthic algae such as D. geminata requires flood events sufficiently high enough to result in wide spread disturbance of the stream substrate. These flow requirements are similar to the requirements for channel maintenance flows and could therefore be considered for inclusion in the operating rules for dams in order to maintain the diversity of stream ecosystems and functioning water supply infrastructure.