Microbial Communities in Sierra Nevada Streams

Sierra Nevada streams are important sources of water for travelers, agriculture, and cities but are contaminated with pathogens. Thus, identifying factors that increase pathogens in surface waters is a public health priority. Exotic trout may be one such factor if they increase pathogen loads in the Sierra Nevada.

Trout introductions have reduced foraging behavior of native invertebrate herbivores, thereby increasing algal density (a trophic cascade). Because bacteria live on the surfaces of algae, we hypothesize that trout presence increases total bacterial counts—potentially including bacteria pathogenic to humans—in the water column of headwater streams. The results of this study could be used by managers to inform cost-benefit analyses regarding trout stocking and removal.