Denitrification in salt marsh sediments: Evidence for seasonal temperature selection among populations of denitrifiers.

Direct measurements of bacterial denitrification in salt marsh sediments near Woods Hole, Massachusetts were made over a 10-month period using a simple and precise gas-chromatographic technique. Based on laboratory experiments at 5°, 10°, and 20°C, it is shown that seasonal temperature variations select for at least two distinct populations of denitrifiers.In situ incubations suggest that resident populations of denitrifying bacteria are cold-sensitive. Salt marsh denitrifying bacteria are not optimally adapted to their thermal environment, but to temperatures 5°-10°C higher. In these water-logged muds, rates of bacterial denitrification (0.3-1.5μg N2/gm sediment-hr) are up to three orders of magnitude greater than maximum potential rates of insitu bacterial and algal nitrogen fixation.