Macrosystems: Temperature, water travel time, and dissolved organic matter structure river microbial communities in the Connecticut River watershed: water samples

Microbes are central players in biogeochemical cycles globally, and yet in river ecosystems we know little about the fundamental forces that govern microbial community composition. We hypothesized that composition is controlled by factors that affect growth rate and the time available for growth to occur, estimated as flow-weighted network travel time of water. This metric combines geography and river discharge to estimate the time that organisms and materials are in a river. This contrasts with hydrologic metrics that are static (order, area) or do not include network geography (discharge). We show that water travel time, temperature, and DOM are drivers of stream microbial communities, suggesting that growth rate and time to grow sets the pace of river bacterioplankton succession and associated biogeochemical transformations along the river continuum. These results suggest that bacterioplankton, like DOM, are controlled by the hydrologic forcing postulated in the Pulse-Shunt Concept.