Glucose exchanges in a salt marsh‐estuary: Biological activity and chemical measurements1

Abstract

Spatial changes in concentrations and uptake rates of glucose in a Spartina alterniflora salt marsh estuary (Duplin River, Sapelo Island, Georgia) were determined to assess the source and fate of glucose in the system. Concentrations were highly variable along the length of the river and over several tidal periods, with high values (5–20 µg·liter −1) in March and low values (1–10 µg·liter −1) in August. Glucose was rapidly cycled in the headwaters as indicated by uptake rates and turnover times. Respiration of added [14C]glucose was relatively constant within the system and temporally.Two striking features of this system were a glucose gradient from Doboy Sound (high glucose) water toward the transitional zone (low glucose) and another one from the headwaters (high glucose) toward the transitional zone, and a decrease in activity in the 3‐µm size fraction from Doboy Sound toward the transitional zone and an increase in activity from this zone toward the headwaters. Conclusions based on various hydrological and biological time scales indicate that glucose exchange associated with the tides (i.e. glucose mixing between zones) is small compared to recycling within the system.