Storm Events Restructured Bacterial Community and Their Biogeochemical Potentials

Key Points:1. The Hurricane Irene and Tropical Storm Lee significantly restructured the microbial communities in headwater streams;2. Shifts of bacterial populations, functional genes and diversity indices indicated the inputs from terrestrial and re-suspended sediments;3. “Mass effects” and “species sorting” are the major mechanisms in re-assembly of the microbial community after big storm events.ABSTRACTLarge 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, we characterized the bacterial population structure from White Clay Creek (Chester Co., PA, USA) 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 population structure based on analyses of 3,004,072 sequences indicated an increase of bacterial diversity during peak discharge of the storm. Successional changes of bacterial community structure during the events were observed: Betaproteobacteria and Thermi decreased in relative abundance, while members of Alphaproteobacteria, 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) indicated 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 inoculated microbes from terrestrial and streambeds to headwaters, and downslope dispersal (“mass-effect”) and “species-sorting” likely restructure the microbial community structure as well as the potentials for nutrient cycling.