The dynamic hyporheic microbiome: a flume investigation into hyporheic microbial community response to surface channel flow perturbations

The hyporheic zone (HZ) is widely recognized as a locus of important biologically mediated chemical reactions. Additionally, a growing body of research indicates that the highly dynamic nature of surface hydrologic processes drives similarly dynamic conditions within the HZ. Prior flume experiments have shown that even short-lived surface channel flow perturbations can have lasting impacts on the distribution of dissolved oxygen, an important biogeochemical actor, in the HZ. This distribution of dissolved oxygen is driven by the interaction between the delivery of oxygenated surface water into the HZ via hyporheic exchange, and the oxygen-consuming processes that occur in the HZ itself. Surface channel flow dynamism combined with the condition that the quantity of dissolved oxygen present in any given HZ location is both a function of, as well as a driver for, the microbial metabolic processes available and active at that location raises the questions: "Does flow-perturbation-induced dissolved oxygen dynamism translate into changes in local hyporheic microbial community structure? And if so, over what time scales do these microbial community structure shifts occur?"

We explore these questions through the integration of large-scale time-series flume experiments with 16S rRNA gene sequencing for microbial community structure paired with FTICR-MS characterization of environmental metabolites and associated biochemical transformations. This novel combination of tools allows us to observe hyporheic microbiome dynamics under tightly controlled experimental conditions. We show indications of a dynamic hyporheic microbiome driven at least in part by dissolved oxygen dynamics, but we also show evidence that other processes are likely at play. These results drive further questions into the complex nature of hyporheic microbiome dynamics.