Spatial Distribution of Microbial Communities in the Alluvial Aquifer along the Oyodo River, Miyakonojo Basin, Japan

Abstract

The hydrogeological properties of groundwater and behavior of nitrate attenuation in the nitrate-polluted alluvial aquifer, Miyakonojo Basin have been investigated in previous studies, but little knowledge is known about the spatially microbial communities especially associated with nitrate depletion. The objectives of the present study are to reveal the profile of microbial communities in the alluvial aquifer, Miyakonojo Basin, and the association with environmental variations based on cloning-library approach together with hydrogeochemical variables. The results showed that high bacterial diversity was characteristic of a large number of operational taxonomic units unique to the samples. The presence of some human-/livestock related bacteria was consistent with the distribution of high nitrate concentrations, which indicated an influence of hydrogeochemical variables on microbial composition. Methane-producing archaea and ammonia-oxidizing archaea were primarily found in the anoxic and oxic environments, respectively, reflected by the distribution of welded tuff. Additionally, heterotrophic and mixo-/autotrophic denitrifiers were ubiquitously distributed, but denitrification process only occurred under the anoxic environment. Microorganisms involved in the various metabolic processes were found to coexist in the same samples. Together, this study suggested that the description of microbial communities profile and associated putative metabolic processes could reflect the hydrogeochemical conditions of the alluvial aquifer, Miyakonojo Basin.