Environmental Engineering Reference
In-Depth Information
Pasture. vegetation. can. regress. once. their. roots. penetrate. into. toxic. sub-
strates.beneath.benign.inert.covering.materials..This.scenario.may.occur.in.
direct.application.of.biosolids.on.tailings.which.created.a.thin.organic.layer.
of.either.5.or.10.cm.depth..The.mixture.was.suficient.to.attenuate.the.nega-
tive.effects.of.salinity..Exotic.pasture.immediately.established,.successfully.
seeding.and.regenerating.for.two.growing.seasons.for.both.application.rates.
of.biosolids..Furthermore,.roots.had.proliferated.down.to.a.depth.of.30.cm.
into.the.tailings.without.toxicity.effects.apparent.in.the.leaf.tissues..Most.of.
the. pasture. species. present. were. annuals. which. completed. their. life. cycle.
during.the.wetter.months..It.is.likely.that.salinity.is.not.a.major.limiting.fac-
tor.to.growth.during.this.period..Stabilization.of.the.tailings.in.these.treat-
ments.by.exotic.pasture.species.was.demonstrated..Further.work.is.required.
to.replace.exotic.species.with.native.species..Extensive.root.growth.was.also.
observed. in. the. biosolids-amended. oxide. cover.. Proliferation. of. ine. roots.
through.the.oxide.would.improve.its.physical.properties.
Formation. of. a. well-deined. oxidation. layer. did. not. result. in. release. of.
acidic. water. because. of. the. high. acid. neutralizing. capacity. of. the. tailings.
material.. Tree. species. have. been. able. to. persist. and. grow. successfully. over.
three.growing.seasons..Plant.growth.has.also.encouraged.weathering.of.the.
upper. proile. and. also. created. conditions. which. reduce. release. of. arsenic..
Biosolids. amendments. have. enhanced. the. biological. activity. of. soil. micro-
lora.as.well.as.the.improved.soil.structure.which.has.encouraged.weather-
ing..The.proliferation.of.eucalypt.roots.was.shown.to.be.associated.with.the.
presence.of.shrinkage.cracks.within.the.tailings..Some.roots.were.observed.to.
penetrate.to.the.base.of.the.tailings.layer.in.ProtoTERF.(>1.5.m)..It.is.possible.
that.the.largest.examples.of.
E. cladocalyx
.and.
E. polybractea
,.in.the.low-rate.of.
biosolids-amended.tailings.had.a.greater.reservoir.of.available.moisture.from.
extensive. fracturing. underneath. the. trees.. Assessment. of. crack. frequency.
was.performed.only.on.a.two-dimensional.scale.but.nonetheless.it.was.pos-
sible.to.show.the.importance.of.these.voids.in.root.distribution..It.is.evident.
that.these.fractures.are.the.preferential.avenues.for.root.growth.and.exten-
sion..Some.roots.were.observed.to.penetrate.to.the.base.of.the.tailings.layer.
(>1.5.m).. Through. the. release. of. oxygen. and. other. oxidants. plant. roots. can.
cause.oxidation.of.iron.sulides.in.soils.to.precipitate.Fe.oxides.or.iron.plaques.
on.plant.roots.(Armstrong.1967,.Batty.et.al..2000,.Armstrong.and.Drew.2002)..
Moreover,.it.appears.that.the.passage.of.oxygen.into.these.narrow.voids.can.
create.thin.oxide.skins.which.may.form.a.seal.to.the.release.of.saline.waters.
from.the.tailings..As.a.result,.water.which.accumulates.in.the.cracks.may.not.
be. as. saline. as. that. initially. present. in. the. upper. layers. of. the. ameliorative.
covers..Further.research.is.necessary.to.understand.this.important.root.prop-
erty.particularly.of.the.tree.species.used.in.this.study..This.mechanism.may.
be.important.in.the.natural.attenuation.of.As.toxicity.in.this.mine.substrate.
Quantiication.of.the.plant-available.water.is.necessary.to.predict.the.opti-
mum. density. of. vegetation. which. the. tailings. covers. can. support.. Further.
work. should. investigate. the. effect. of. deep. ploughing. on. water. harvesting.
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