The impact of bed disturbance on the growth of the nuisance diatom didymosphenia geminata in Boulder Creek, CO

Didymosphenia geminata, or “rock-snot”, is a nuisance diatom species that can form large amounts of stalk material that covers the streambed. These blooms impact the aesthetic value and biodiversity of mountain streams across many parts of North America and Europe and threaten both valuable fish species such as trout and the sustainability of water supply infrastructure. The objective of this study is to investigate the hydrologic factors affecting the growth of D. geminata, and in particular the impact of floods and bed disturbance. Developing a quantitative understanding of the impact of flood events on the growth of D. geminata is crucial in understanding the impact of flow regulation on the increasing risk of nuisance blooms and if environmental flood releases from reservoirs are to be considered as a possible mitigation option. This paper will present the initial results from the analysis of the impact of a flood event on the growth of D. geminata in Boulder Creek, CO during the summer of 2006. This flood event resulted in significant decrease in coverage of D. geminata. Analysis of the hydrologic properties of the flood event suggest that there is a critical level of shear stress that is possibility related to bed disturbance that is a significant factor in reducing the coverage of D. geminata. This has implications for the possible consideration of managed flood releases for the control of future growth of D. geminata in regulated mountain rivers.