Storm Events Restructured Microbial Community and Their Biogeochemical Potentials

Abstract:

Climate change is altering intensity, frequency, and duration of hurricanes and tropical storms nationwide. Since 1980s, increased heavy downpours (up to 71%) have been observed for the Northeast and Mid-Atlantic region of the United States. Large storm events have the potential to deliver significant upland and distal materials to headwaters. More importantly, “seeding and mixing” from terrestrial sources may result in “new” microbial consortia that facilitates nutrient transformation and export to receiving waters. Thus, there is an urgent need to investigate how storm events affect the microbial community structures and their potential functions.

From Aug. 26 to Sep. 8 2011, within days of each other, Hurricane Irene and Tropical Storm Lee passed through southeastern Pennsylvania and resulted in increased discharge in White Clay Creek. Bacterial population composition during the events was assessed by high-throughput sequencing of the 16S rRNA genes from collected water samples. Detailed bacterial community structure based on analysis of 3.3 million sequences indicated that a significant increase of bacterial diversity in samples during peak discharge of the storm. Successional changes of bacterial community before, during and after the events were observed: Betaproteobacteria, Actinobacteria, and Spirochaetes decreased in relative abundance, while the relative abundance of members of Acidobacteria, Alphaproteobacteria, Nitrospirae, Planctomycetes, and Verrucomicrobia increased during peak discharge, suggesting impacts from terrestrial inputs. At the same time, isotope hydrograph separation also indicated watershed runoff comprised the majority of water in the stream during peak flow. Cyanobacteria bloomed after the storm events, indicating that photosynthesis was one of the primary recovering processes. Real-time PCR (qPCR) analyses on functional genes (e.g., nitrification amoA, and denitrification nirS/nirK) suggested that storm events also changed the functional perspectives of the microbial communities, and therefore altered the subsequent biogeochemical transformation processes at headwater streams.