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

Floating photovoltaic (FPV) arrays alter the methane (CH₄) cycling dynamics of waterbodies on which they are deployed. Here, we investigated dissolved CH₄ dynamics and associated CH₄ cycling microbial communities (methanogens and methanotrophs) in the second year of FPV deployment (70% aerial coverage) in experimental ponds. We found that bottom-water CH₄ concentrations were twice as high in ponds with FPV compared to those without, while surface water CH₄ concentrations were orders of magnitude lower than bottom-waters, but did not differ between treatments. There was no change in the relative abundances of putative sediment methanogens or methanotrophs, but FPV restructured methanogen communities. FPV promoted late-summer methanotroph blooms in the water column, with abundances surpassing 1,000,000 cells mL^-1. We conclude that prolonged periods of CH₄ production in low oxygen FPV ponds favored blooms of methanotrophs, that may mitigate diffusive CH₄ emissions to the atmosphere by consuming dissolved CH₄.