Environmental Engineering Reference
In-Depth Information
increase.in.the.usage.of.resources..They.have.long.been.used.as.convenient.
sites. for. waste. disposal. and. discharge. of. untreated. sewage. and. livestock.
wastewater. (Clough. et. al.. 1983).. As. a. transit. zone. between. terrestrial. and.
marine. environments,. mangrove. wetlands. also. inevitably. receive. contami-
nants.from.tidal. water,.rivers,.and. storm.runoff.(Tam.and. Wong. 1993,.1995,.
2000,.Ke.et.al..2002)..Mangrove.sediments.have.been.reported.to.serve.as.reser-
voirs.of.contaminants,.including.nitrogen.and.phosphorus.(e.g.,.Corredor.and.
Morell.1994,.Tam.and.Wong.1996b,.Rivera-Monroy.et.al..1999),.heavy.metals.
(e.g.,.Harbison.1986,.Silva.et.al..1990,.Tam.and.Wong.1993,.1995,.1996a,.1999a),.
and.organic.pollutants.(e.g.,.Tam.et.al..2001,.Maskaoui.et.al..2002).
Scientiic. evidence. of. mangrove. wetlands. thriving. in. a. relatively. harsh.
intertidal. environment. (e.g.,. periodic. changes. in. temperature,. water.
and. salt. exposure,. and. varying. degrees. of. oxygen. depletion). over. long.
geological. time. scales. suggests. their. high. tolerance. to. extreme. envi-
ronmental. conditions. (Alongi. 2008).. Mangrove. plants. have. developed.
physiological,.morphological,.and.anatomical.adaptations,.such.as.salt.reg-
ulation,. well-developed.aerenchyma,. and. highly. specialized.root. systems.
(e.g.,.knee.joints,.pneumatophores.or.aerial.roots,.cable.roots,.and.buttress/
prop. roots),. to. cope. with. anoxic. and. saline. environments. (Lugo. 1980,. Pi.
et.al..2009)..These.adaptive.changes.in.mangrove.plants,.together.with.the.
harsh.growth.conditions.(environmental.extremes.and.pollution),.suggest.
the.possibility.of.using.mangrove.plants.in.phytoremediation.of.contami-
nated.water.and.sediments.
Heavy. metals. (e.g.,. copper,. zinc,. and. lead). and. petroleum. hydrocar-
bons.(e.g.,.aliphatic.and.aromatic.hydrocarbons).are.ubiquitous.pollutants.
causing. serious. environmental. problems.. Due. to. the. close. proximity. of.
mangrove. wetlands. to. human. activities. and. along. the. route. of. oil. trans-
portation,. elevated. concentrations. of. heavy. metals. and. hydrocarbons. in.
mangrove.sediments.have.been.reported.(Tam.and.Wong.1993,.1995,.1996a,.
1999a,. Tam. et. al.. 2001,. Ke. et. al.. 2005).. Accidental. oil. spills. have. also. been.
reported. in. Hong. Kong. mangrove. wetlands. from. time. to. time. (Ke. et. al..
2002,.Wong.et.al..2002,.Tam.et.al..2005).
We.are.one.of.the.irst.groups.to.employ.mangrove.wetlands.in.the.phy-
toremediation. of. wastewater. and. contaminated. sediments. (e.g.,. Yim. and.
Tam.1999,.Ke.et.al..2003a,b,.Wu.et.al..2008,.Yang.et.al..2008)..A.prerequisite.
for.the.success.of.phytoremediation.of.these.pollutants.is.to.screen.tolerant.
plants..Our.research.group.has.been.working.on.the.toxicity.of.heavy.metals.
and.hydrocarbons.present.in.the.mangrove.plants.since.the.1990s,.and.most.
of.the.early.studies.focused.on.growth.response.and.accumulation.in.plants.
(e.g.,.Yim.and.Tam.1999,.Ke.et.al..2003a,b)..The.toxic.effects.of.these.pollut-
ants.on.mangrove.plants,.in.particular.at.the.morphological.(e.g.,.structural.
changes.in.roots),.physiological,.and.biochemical.levels,.have.received.little.
attention.until.the.past.5.years..This.chapter,.therefore,.reviews.our.research.
on. the. structural,. physiological,. and. biochemical. changes. of. mangrove.
plants,. including. root. anatomy,. radial. oxygen. loss. (ROL),. iron. (Fe). plaque.
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