In aquatic fresh ecosystems, prokaryotes are responsible for the bulk of aerobic respiration. They generate most of the CO2 from freshwater, yet rarely are their rates of respiration estimated in situ. Here, direct measurements were made of the rate at which freshwater bacteria and Archaea used dissolved oxygen in the tropical waters of the Panama Canal, Central America. Respiration rates were estimated from measurements of oxygen uptake rates in a dark chamber attached to a sonde in situ in bays, coves and the Panama Canal around Barro Colorado Island. The rate at which oxygen was taken up was then converted to the rate at which carbon dioxide was respired; rates ranged from 1 to 20 g C m−3 d−1. Results showed aquatic bacterial respiration in these tropical freshwaters can return large amounts of dissolved organic carbon to the atmosphere as CO2. Hence, CO2 outgassing from these tropical freshwaters respiration should be considered as a significant source of carbon to the atmospheric global carbon budget.

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