Heterogeneity in hyporheic flow, porewater chemistry, and microbial community composition in an alpine

Groundwater and surface water mixing in streambeds (hyporheic exchange) is important for nutrient and carbon cycling, and acts as a control on the overall quality of surface water. Seasonal changes in river flow influence hyporheic exchange, which in turn controls chemical and microbial processes that dictate water quality. In this study, we aim to map relationships between hyporheic exchange, pore water chemistry, and microbial communities in the streambed of an alpine river during low flow conditions. We found that regions of the streambed with greater surface water influence had larger concentrations of oxygen and microbially-available carbon compounds. The composition of streambed microbial communities also shifted with changes in pore water chemistry, though communities were all similarly diverse. As climate change progresses, earlier snowmelt onset and reduced snowpack alter the timing and length of low streamflow periods. Our findings can help constrain how climate change may alter nutrient and carbon cycling in alpine watersheds.