Background/Question/Methods Lakes provide an excellent opportunity to investigate spatial influences on community assembly processes. With easily delineated boundaries, lakes represent physically, chemically, and biologically heterogeneous patches distributed throughout the landscape. Previous aquatic microbial ecological research has focused on within lake drivers of community dynamics. Although strong relationships between environmental, chemical, and biological characteristics and bacterial community change have been made, the potential influence of immigration has largely been ignored. Many microbial ecologists assume that the majority of microbial species are consistently distributed around the globe at a significant rate, but the influence of this dispersal on recipient ecosystems has rarely been considered. Our study sought to quantify rates of bacterial immigration into seepage lakes via atmospheric deposition and characterize the influence of bacterial immigration on the dynamics of seepage lake bacterial community dynamics. Deposition rates and composition of bacterial cells, as well as composition of two north temperate lakes were sampled three times weekly from May 28th 2007 to July 27th 2007. Both ribosomal RNA gene fingerprinting and sequences were used to assess the overlap of composition between the atmosphere and the lakes. The influence of immigrating bacterial taxa on lake bacterial community dynamics was also assessed.

Results/Conclusions Our results suggest that deposition rates of bacterial cells are surprisingly large, but lake biotic and abiotic characteristics act as strong environmental filters. The weak influence of immigrating bacterial taxa suggests that a species sorting concept best describes aquatic bacterial metacommunity dynamics. These findings agree well with previous findings for passively dispersed, planktonic taxa, such as zooplankton.