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

Abstract

The proximal substrate source of planktonic bacteria is dissolved organic carbon (DOC), and the combined sources of DOC (bulk, phytoplankton production, and advected) set an upper limit on how much C is available for bacterial 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 extracellular 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 bacterial C was unaccounted for. Despite overestimating DOC and doubling bacterial growth efficiency (BGE), BR in the lakes was 1.25-2 times greater than our estimate of DOC supply. We hypothesize that a major source of organic C for planktonic bacteria in these lakes comes from drawdown of bulk DOC and/or decomposition of particulate material.