Although biogeochemical processes are often studied at the watershed scale, watershed-scale microbial distributions are poorly understood. Global-scale studies have shown that edaphic factors (e.g. pH, carbon to nitrogen ratios (C:N)) can drive microbial community diversity, composition, and structure, but it is not clear if these are also influential at smaller scales. Here we examined the distributions of Bacteria and Archaea and how they related to slope aspect, vegetation type, and edaphic factors within a watershed near Boulder, CO. Bacterial diversity was correlated with pH and negatively correlated with C:N. Microbial community composition varied with slope aspect, and vegetation type, correlating with pH and C:N. Archaeal relative abundance was inversely correlated with C:N. Similar to global-scale observations, watershed-scale microbial distributions are predictable by edaphic factors, thereby providing clues to uncultivated organisms\u27 ecology. Where organisms\u27 ecology is known, this study demonstrated the potential to use microbial distributions to identify biogeochemical hotspots
