Bacterial secondary production in oxic and anoxic freshwaters

Abstract

Across a series of nine lakes that ranged from ultraoligotrophic to eutrophic, bacterial production was greatest in anoxic hypolimnetic water despite lower hypolimnetic temperatures. Mean (by lake) aerobic bacterial production ranged from 2.6 to 17 mg C m−3d−1 while mean anaerobic bacterial production ranged from 1.1 to 47 C mg C m−3d−1. Overall mean anaerobic bacterial production was 1.6 times greater than mean aerobic bacterial production. The relatively high rates of bacterial production in anoxic waters are due to larger bacterial populations growing slightly more slowly than their aerobic counterparts. Our data suggest that bacterial production in cold, anoxic water is as large or larger than that in warm, oxic surface waters and bacterial production in anoxic water is much greater than aerobic bacterial production at comparable temperatures.We measured hypolimnetic accumulation of dissolved inorganic C to estimate the minimum possible growth efficiency for hypolimnetic bacteria. Growth efficiency, bacterial production/(bacterial production+bacterial respiration), ranged from 6 to 40% and averaged from 16 to 30% in anoxic water, depending on how it was calculated. The growth efficiency of anaerobic bacteria is about equal to that reported for aerobic bacteria.