No abstract

Oxygen consumption is used to study the dynamics of dissolved organic carbon (DOC) utilization by bacteria. Preliminary incubation experiments examining oxygen consumption and bacterial growth demonstrated that a small labile fraction of the total DOC pool typically supports bacterial metabolism. Bacterial growth and respiration rates were frequently fastest within the first few hours of incubation experiments suggesting that the pool of organic matter used for growth was rapidly consumed. Comparisons of bacterial production and respiration with total DOC concentrations suggested that approxinlately 1 to 3 % of the pool supports bacterial growth. The presence of a small labile component of the DOC pool suggests a close coupl~ng between bacteria and sources of substrate. Bacterial coupling to phytoplankton was examined in mesocosm experiments in which phytoplankton were enriched with nutrients and bacterial production and oxygen consumption were followed over diel cycles. Bacterial production, oxygen consumption and the availability of organic matter were highest during daylight, when phytoplankton production was assumed to be greatest. The effect of a varying carbon supply over diel cycles on bacterial growth efficiency was examined. During the mesocosm experiment, growth efficiencies were greatest during daylight when substrate availability was greatest. At several estuarine sites, efficiencies varied markedly over daily and seasonal temporal scales. These results suggest that growth efficiency is an important consideration when estimating the bacterial role in aquatic carbon cycles.

ABSTRACT:The relationship between bacteria, phytoplankton and heterotrophlc microflagellates is examined over large spatial and seasonal scales in the Delaware Estuary, USA. The estuary was sampled along the main salinity axis (0 to 30 ppt), from near Philadelphia to the mouth, between February and Auqust 1985. Samples were analysed for bacterial abundance and production, for heterotrophic microflagellate abundance and rate on bacteria, and for phytoplankton production and biomass. Temperature was a major factor that requlated bacteria and microflaqellates. With the exception of cold peridds, bacterla and microflagellates appeared to respond to phytoplankton production During the spring and summer, bacterial production and microflagellate grazing were highest in the lower estuary, where phytoplankton production was also highest. Bacter~al production was on average 23 % of the phytoplankton carbon production. In this area of the estuary grazing on bacteria was h~ghest. Bacterivores grazed 95 % of the bacterial production. Estimates on the carbon flow from phytoplankton to bacteria and subsequently to microflagellates suggest that bacteria and microflagellates do not return lost phytoplankton production to the main phytoplankton-zooplankton food chain in the Delaware Estuary. Instead, it appears that the primary effect of heterotrophic microbes is the mineralization of organic compounds to their inorganic constituents.

The Essex, Parker and Ipswich River estuaries are salt marsh estuaries that empty into Ipswich Bay in northern Massachusetts, USA. The Essex estuary was the subject of a year-long study of planktonic bacteria numbers and heterotrophic activity, with monthly sampling of the entire range of water within the estuary. Both numbers and activity were fractionated into 4 sizes using Nuclepore filters. The Ipswich and Parker River estuaries were sampled along with the Essex on 5 occasions for comparison purposes. In winter, counts and activity were uniformly low throughout the Essex estuary. During spring, there gradually developed a peak of bacteria in mid-estuarine waters which was sustained through the summer and subsided in fall. The seasonal range in these waters was 10-fold (0.7 to 7.0 X lo6 m l l ) , while the range was lower in coastal waters (4-fold). This peak also occurred prominently in the Parker, but was modified in the Ipswich because of physical factors. Maximum numbers and activity were consistently found in the 0.4 to 0.6 pm fraction. Bacteria counts were strongly related to temperature, with the greatest dependence in mid-estuarine waters. Heterotrophic activity was logarithmically related to temperature and followed the same pattern as counts. The increment of bacteria with linear distance upriver to where the maximum is found was very similar in the 3 estuaries. It is suggested that this is a function of the availability of substrate as influenced by tidal mixing, and involves considering the bacteria as dynamic constituents of estuarine and coastal waters rather than conservative constituents reflecting only the mixing of water masses.

Standard Form 298 (Rev. 8-98)Prescribed by ANSI Std. Z39.18Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Approved for public release; distribution is unlimited. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) SPONSOR / MONITOR'S ACRONYM(S) 9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES)11 Unclassified Unclassified UnclassifiedUnlimited 42Michael T. Montgomery 202-404-6419Mineralization rates of 14C-TNT, -DNT, and -DAT were measured in surface sediments, with depth in sediment cores, and in the water column during 12 research cruises over the past 4 years in the San Francisco Bay, Chesapeake Bay, and Hawaii. Mineralization rates were also compared to uptake and incorporation rates of TNT, DNT, and DAT into the natural microbial assemblage. In general, the bacterial mineralizations rates were similar, or an order of magnitude faster, than those for organic hydrocarbons measured at the same time. Using seawater sampled from a historical UXO field, we found that while bacterial mineralization was rapid (>1 ug L-1 d-1, unfiltered water in dark), photodegradation was even faster (16 ug L-1 d-1, filtered water in light) and the combination of light and unfiltered water was greater than the sum of the two rates (103 ug L-1 d-1), suggesting either that the prescnce of active phytoplankton is important or photodegradation enhances bacterial mineralization.