Higher methanotroph abundance and bottom-water methane in ponds with floating photovoltaic arrays

Floating photovoltaic (FPV) arrays alter the biogeochemistry of waterbodies on which they are deployed. Here, we investigated dissolved methane (CH ₄ ) dynamics and associated CH ₄ cycling microbial communities in the second-year of FPV deployment (70% aerial coverage) in experimental ponds. We found that bottom-water CH ₄ concentrations were twice as high in ponds with FPV compared to those without. Surface water CH ₄ concentrations were orders of magnitude lower than bottom-waters, but were similar between ponds with and without FPV. There were no differences in potential sediment CH ₄ production or CH ₄ associated microbes. Instead, dissolved CH ₄ patterns could be explained by elevated abundance of methanotrophic bacteria in the water column of FPV ponds, where late-summer abundances exceeded 1,000,000 cells mL ^-1 . Prolonged periods of CH ₄ production in low oxygen FPV ponds likely favored blooms of methanotrophs in surface waters where some oxygen is available, mitigating diffusive CH ₄ emissions to the atmosphere following FPV deployment.