Kan, J. 2018. Journal of Geophysical Research: Biogeosciences 123(7):2257–2269.
Large rainstorms deliver significant amounts of upland materials to headwater streams, thereby introducing the particle‐associated microorganisms from complex soil environments into stream networks. “Seeding and mixing” from terrestrial sources may generate “new” in‐stream microbial consortia and facilitate nutrient transformations and export to receiving waters. In order to investigate how large storm events influence the microbial community, bacterial community structure from White Clay Creek (Chester Co., PA, USA) were characterized following the Hurricane Irene and the Tropical Storm Lee. High‐throughput sequencing of the 16S rRNA genes was used to track changes of bacterial community before, during and after the events. Detailed bacterial community structures based on analyses of 3,004,072 sequences indicated an increase of bacterial diversity during peak discharge of the storm. Significant successional changes of bacterial community structure during the events were observed: Betaproteobacteria decreased in relative abundance, while members of Deltaproteobacteria, Acidobacteria, Chloroflexi, Nitrospirae, Planctomycetes, and Verrucomicrobia increased with the discharge suggesting potential impacts from terrestrial inputs and re‐suspended sediments. Cyanobacteria bloomed after the storm events, indicating that photosynthesis was one of the primary recovering processes. Real‐time PCR (qPCR) analyses on functional genes (amoA for nitrification, and nirS/nirK for denitrification) suggested that storm events also changed the functional perspectives of the microbial communities, with the potential for alteration of subsequent biogeochemical transformations. Thus, large storm events inoculate microbes from terrestrial and streambeds to headwaters, and downslope dispersal (“mass‐effect”) and “species‐sorting” likely restructure the microbial community structure as well as potential nutrient cycling.