Sulphate reduction in the root zone of the seagrass Zostera noltii on the intertidal flats of a coastal lagoon (Arcachon, France)

Abstract

Rates of sulphate reduction were determined in sediments from the eutrophic Bay of Arcachon, France. A comparison was made between sediment overgrown with the eelgrass Zostera noltii and unvegetated sediment. Rates of sulphate reduction were about twice as high in the root zone from 1 to 4 cm depth in the Z. noltii sediments (about 600 nmol cm-3 d-1) as compared to the activity in the equivalent layer of the unvegetated sediment. The sulphate reduction in the root zone was not stimulated by light, which in other studies with other submersed macrophytes has been shown to promote sulphate reduction due to heightened excretion of organic molecules. Furthermore, in a field experiment, we were not able to detect any diurnal variation in the activity within the root zone. The stimulation of sulphate reduction by the presence of the Z. noltii was most likely due to degradation of leaf and root fragments which were found mixed into the sediment. Incubation times with radioactive sulphate had to be kept very short (preferably 15 min) to avoid a substantial reoxidation of sulphide and hence an underestimation of the rate of sulphate reduction.