Acid-volatile sulphide (,4VS) was measured at regular positions along eight transects through a mangrove forest in the Brisbane River, Queensland, ,4ustralia. Concentrations ranged from 0.33 to 22.61 wnol S g-t sediment dry weight. There was no correlation between A VS concentration
and the proportion of clay-sand in the sediment, but sediments with high ,4 VS concentrations tended to contain more water (r, = 0.42; p = 0.01). A VS concentrations were used to assess the potential bioavailability of the sediment heavy metal burden. The spatial variability of
potential bioavailability was high and depended to a great extent on which metals were considered as part of the 4 VS complexing system. It is suggested seasonal variations would further increase the observed variability in bioavailability. This variation should be taken into account when monitoring and assessing long-term trends in sediment toxicity. Copyright © 1996 Elsevier Science Ltd