Microbial respiration and production in the Delaware Estuary

The paucity of data on respiration has hampered efforts to understand the relationships between respiration and microbial biomass production and the impact of respiration on oxygen concentrations and net community production. The goal of this study was to estimate total and bacterial respiration in the water column of the Delaware Estuary where primary and bacterial production has been examined extensively in the past. We found that respiration often exceeded in situ primary production at several sites in the estuary and in different seasons, and that net oxygen production consequently was negative, especially at an upstream station in the Delaware River where oxygen concentrations are often below saturation. Respiration by heterotrophic bacteria accounted for about 50% of total respiration and correlated significantly with C-14 primary production, but there was no significant correlation between bacterial production (thymidine and leucine incorporation) and primary production. A simple budget was used to explore relationships among production, respiration and input of terrestrial carbon. These calculations revealed that some values, e.g. high bacterial production relative to primary production along with low bacterial respiration relative to total respiration, were not consistent with common estimates of bacterial growth efficiency, although nonsteady-state conditions should not be ignored. However, other values of bacterial respiration (50% of total) and production (bacterial production: primary production ratio equal to about 0.8) in the Delaware River were consistent with high growth efficiencies (30%) of bacteria using a large input of terrestrial organic material. This input may explain why heterotrophic bacteria appear to have a larger impact than primary production on net oxygen saturation in the Delaware Estuary.