Environmental Engineering Reference
In-Depth Information
which.is.necessary.to.allow.satisfactory.growth.of.tree.species..The.presence.
of.deep.cracks.is.also.important.for.the.structural.stability.of.trees.whereby.
deep. roots. are. required. for. anchorage. to. minimize. the. risk. of. windthrow.
(Bengough.2003),.particularly.in.the.windy.conditions.frequently.present.on.
the.exposed.surface.of.the.TSF..It.has.been.shown.that.deep.ripping.of.recon-
structed.soil.proiles.after.bauxite.mining.was.a.major.factor.in.the.survival.
of.the.main.tree.species.(Rokich.et.al..2001)..This.work.showed.that.signii-
cant.differences.in.the.root.architecture.occurred.in.deep-ripped.substrates..
Root.proliferation.at.depth.would.also.improve.downward.transfer.of.water.
when.the.surface.layers.of.soils.with.low.permeability.are.wetted.after.rain-
fall.(Burgess.et.al..2001)..Another.effect.of.root.proliferation.at.depth.would.
be.further.oxidation.in.the.tailings..Through.the.release.of.oxygen.and.other.
oxidants.plant.roots.can.cause.oxidation.of.iron.sulides.in.soils.to.precipi-
tate. Fe. oxides. or. iron. plaques. on. plant. roots. (Armstrong. 1967,. Batty. et. al..
2000,. Armstrong. and. Drew. 2002).. Further. research. is. necessary. to. under-
stand. this. important. root. property. particularly. of. the. tree. species. used. in.
this.study..This.mechanism.may.be.important.in.the.natural.attenuation.of.
As.in.this.mine.substrate..This.is.particularly.relevant.as.it.has.been.shown.
recently.that.formation.of.the.amorphous.colloids.on.the.surface.of.rice.roots.
enhanced. arsenite. and. decreased. arsenate. uptake. (Chen. et. al.. 2005).. They.
showed.that.the.presence.of.iron.plaque.diminished.the.effect.of.phosphate.
on.arsenate.uptake,.possibly.through.a.combined.effect.of.arsenate.desorp-
tion.from.iron.plaque.
The.value. of.using.drought-tolerant.eucalypts,.which.do.not.take.up.As,.
as.part.of.the.phytoremediation.prescription.has.been.clearly.demonstrated..
The. study. has. shown. that. growing. high. value. species. such. as. the. ones.
selected.for.the.trials.can.deinitely.enhance.the.value.of.the.TSF.as.a.land.
resource.for.agro-forestry..This.is.in.contrast.to.a.pasture.only.cover.which.
would.be.far.less.productive.and.would.have.to.be.continually.maintained.
to. minimize. the. establishment. of. tree. species.. The. fact. that. the. trees. have.
successfully.penetrated.deep.into.the.tailings.indicate.that.there.is.little.risk.
of. windthrow.. As. a. result,. there. is. minimal. risk. of. elevated. arsenic. levels.
appearing. on. the. surface. after. phytostabilization.. The.downward. progres-
sion.of.oxidation.within.the.tailings.proile.beneath.the.vegetated.thin.covers.
indicates. that. this. method. of. rehabilitation. is. sustainable. when. applied. to.
sulidic.tailings.with.excess.acid.neutralizing.capacity,.such.as.occur.widely.
in.the.Victorian.Goldields.
Acknowledgments
The.authors.are.indebted.to.Graham.Brock.without.whose.vision.and.appre-
ciation.of.the.value,.rather.than.the.cost,.of.environmental.research.at.Stawell.
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