Bacterial dissolved organic carbon demand in McMurdo Dry Valley lakes, Antarctica

The proximal substrate source of planktonic bacteria is dissolved organic c arbon (DOC). and the combined sources of DOC (bulk, phytoplankton productio n, and advect ed) set an upper limit on how much C is available for bacteri al respiration (BR). We compared measurements of bacterial production (BP) and estimates of BR to measurements of what we assumed to be the major DOC inputs for three permanently ice-covered lakes in Antarctica: Lakes Fryxell , Hoare, and Bonney. These measured inputs, which included phytoplankton ex tracellular release (ECR), stream input, and upward diffusion of DOC across the chemocline, sediments, and benthic microbial mats. were three to eight times smaller than planktonic BR, suggesting that a major source of bacter ial C was unaccounted for. Despite overestimating DOC and doubling bacteria l growth efficiency (BGE), BR in the lakes was 1.25-2 times greater than ou r estimate of DOC supply. We hypothesize that a major source of organic C f or planktonic bacteria in these lakes comes from drawdown of bulk DOC and/o r decomposition of particulate material.