Bacterial production in the Delaware Bay estuary estimated from thymidine and leucine incorporation rates

Abstract

The thymidine and leucine methods were examined and used to estimate bacterial production in the Delaware Estuary. During growth experiments that minimized grazing on bacteria, conversion factors for both thymidine and leucine were initially high and then rapidly decreased to values lower than commonly-used factors (2.0 X 10" cells mol-' for thymidine). The low thymidine conversion factors may have been due to l3~]thymidine incorporation into protein, which was 72 % of total incorporation in untreated samples from the estuary. Addition of glucose reduced the leucine conversion factor from 7.4 to 3.6 X 1016 cells mol-' and the thymidine conversion factor from 1.53 to 0.68 X 10'' cells mol-'. Ammonium additions had no effect. The thymidine and leucine approaches gave similar estimates of bacterial production in the Delaware Bay (20 to 70 X 106 cells I-' h-'). Both methods confirmed that bacterial production was highest at about 40 to 50 km upstream of the mouth, which coincides with the peak in primary production. Bacterial production was about 30 % of primary production in most regions of the estuary, but increased to over 100 O/ O in the turbidity maximum where primary production was low. Bacterial production in the Delaware Estuary is apparently controlled by phytoplankton production in spite of large allochthonous sources of dissolved organic matter.