Linking photochemical carbon transformations and microbial responses in the Amazon River plume
Green, Joanna Louise
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This work focuses on the interplay between sunlight-driven and microbe-driven transformation of dissolved organic matter (DOM) from a dynamic system, the Amazon River plume. To mimic the mixing of river water with the ocean, organic matter was collected from river and low-salinity plume water, filter-sterilized, irradiated, and then inoculated with microbial communities from down-plume along the salinity gradient. Bacterial production and respiration were measured by 3H-leucine incorporation and oxygen consumption rates. The DOM was characterized spectrally via excitation-emission matrix fluorescence (EEMs) and analyzed with parallel factor (PARAFAC) analysis; generating three unique components that aligned with previous studies. Those identified as terrestrial in origin diminished with irradiation. Additions of low-salinity organic matter stimulate bacterial activity in the saltier plume, sub-plume, and oceanic water. Short-term solar exposure to this organic matter enhances the stimulatory effect further. The DOM starting material and the microbial community selected determine the rates of the carbon transformations.