HYDROLOGICAL CONTROLS ON COPPER, CADMIUM, LEAD AND ZINC CONCENTRATIONS IN AN ANTHROPOGENICALLY POLLUTED MANGROVE ECOSYSTEM, WYNNUM, BRISBANE, AUSTRALIA
Mw. Clark et al., HYDROLOGICAL CONTROLS ON COPPER, CADMIUM, LEAD AND ZINC CONCENTRATIONS IN AN ANTHROPOGENICALLY POLLUTED MANGROVE ECOSYSTEM, WYNNUM, BRISBANE, AUSTRALIA, Journal of coastal research, 13(4), 1997, pp. 1150-1158
Biogenic sulphides, particularly pyrite and hydrated iron-monosulphide
s, are common in sediments in mangrove ecosystems where they may provi
de a geochemical trap for heavy metals. However, oxidation of the sulp
hides can lead to remobilisation of metallic species and the developme
nt of acid sulphate soil conditions. In this paper the effects of prol
onged dry conditions on the metal binding capacity of sediments in a m
angrove forest are investigated. Data from 1989 show that the mangrove
forest is acting as a buffer between a domestic garbage tip and the o
pen waters of Moreton Bay. However, prolonged dry conditions during 19
91 removed much of this buffering capacity and some metals were mobili
sed to deeper layers in the sediment or transported down the hydraulic
gradient until chemical conditions more favourable for metal trapping
were encountered This study shows that understanding the transient na
ture of geochemical conditions in natural environments is important in
environmental management because: (a) consideration needs to be given
to how environmental data collected at one time may be affected by na
tural changes (commonly cyclic) in geochemical conditions; (b) conside
ration needs to be given to how human activities may have affected nat
ural changes in geochemical conditions; and (c) planned development or
environmental remediation work will need to anticipate the consequenc
es of natural changes in geochemical conditions.