Aspects Of Microbial Heterotrophic Production In A Highly Turbid Estuary

The uptake of 14C glucose by natural microbial populations has been studied in the Severn Estuary and Bristol Channel, U.K.; the turbidity (suspended solids) in the estuary varied between < 5 mg · 1−1 at the seaward extremity to >800 mg · 1−1 in the estuary proper. The heterotrophic potential, Vm, was found to correlate with turbidity and particulate organic carbon but there was no correlation between microbial biomass, as assessed by plate counts, and turbidity or Vm; measurement of Vm ranged from 0.9 × 10−4 to 288 × 10−4μgC·1−1·h−1 and turnover time from <2 to >100 h. In 17 out of 42 experiments, the uptake of 14C glucose did not conform to Michaelis kinetics and in five of these experiments the data suggested that there may be a threshold of glucose concentration below which there is no uptake.

Primary Production In A Turbid Estuary

The primary production in the Bristol Channel, U.K., was studied from 1973 to 1977: in this estuary, the euphotic zone extends from less than 0.5 m to greater than 10m and there is a large riverine input of inorganic nutrients. The standing stock of phytoplankton chlorophyll a was measured in 1973 and 1974 and was similar throughout the Bristol Channel but the rate of primary production was much greater where the water was less turbid. The estimated primary production was 6.8g C m−2 for the most turbid region and 164.9g C m−2 for the Outer Bristol Channel. A larger proportion of the annual primary production occurred in the spring in the Outer Channel than in the most turbid regions. Phaeocystis developed into blooms in some, but not all, years and exhibited a different light saturation curve to other phytoplankton populations. Serial incubations of short duration gave higher fixation rates than day-long incubations and it is argued that photoinhibition is probably insignificant in a mixed water column. Excretion rates of dissolved organic carbon by phytoplankton were always low.

Primary Production In An Estuarine Environment - Comparison Of Insitu And Simulated Insitu C-14 Techniques

A simulated in situ incubation box has been compared with in situ exposure for 14C production measurements in an estuarine environment. Measurements were made over the course of 14 months, mainly in the Tamar estuary; production rates ranged from less than 1 mg C m−2h−1 to 350 mg C m−2h−1 and there was no significant difference between results from the two methods. In the estuarine waters investigated, the simulated in situ incubator with neutral density filters, used with a Secchi disc to determine sampling depths, gives a satisfactory estimate of in situ primary production.