Environmental Engineering Reference
In-Depth Information
abundance.of.pasture.seed..To.maximize.its.value.as.a.medium.to.support.
growth.of.eucalypts.and.preferred.native.grasses,.it.is.essential.to.minimize.
the. establishment. of. the. highly. competitive. exotic. pasture. species.. As. the.
majority.of.the.species.present.in.this.weed.seed.bank.are.exotic.grasses,.it.
is.possible.to.apply.selective.grass.herbicides.to.eliminate.germinating.seed-
lings.(pre-emergent.herbicides).or.foliar.herbicides.to.eliminate.established.
grasses..Such.use.of.selective.herbicides,.especially.pre-emergent.herbicides,.
to.control.monocot.weeds,.has.been.effective.in.regeneration.of.weed-infested.
Australian.bushland.(Buchanan.1989)..Adequate.weed.control.and.leaching.
of.salts.from.the.biosolids.by.rainfall.prior.to.planting.could.provide.a.cover.
more.suitable.to.eucalypt.survival.and.establishment.
Applying.a.thin.layer.of.crushed.oxide.waste.rock.over.tailings.was.effec-
tive.in.reducing.initial.exposure.of.plant.roots.to.excessive.salinity.and.arse-
nic.in.the.tailings..The.physical.structure,.however,.of.this.substrate.was.not.
favorable.for.good.root.development.because.of.the.poor.hydraulic.conduc-
tivity.and.the.increased.resistance.due.to.its.tendency.to.indurate.during.the.
dry.months..Biosolids.amendments.created.a.substrate.which.was.beneicial.
for.the.establishment.of.both.pasture.and.eucalypts.because.amended.oxide.
covers. and. tailings. had. lower. bulk. density. as. well. as. increased. hydraulic.
conductivity. and. moisture-holding. capacity.. These. indings. are. consistent.
with.the.ever-increasing.number.of.reports.of.the.improvements.in.soil.phys-
ical.properties.from.incorporation.of.biosolids.into.mine.wastes.
Pasture. species. and. eucalypts. did. not. accumulate. signiicant. amounts.
of. arsenic. in. their. leaves.. While. uptake. of. As. was. greater. than. from.
non-mining.soils.with.negligible.As,.the.concentration.of.the.metalloid.in.
leaves.of.plants.from.the.experimental.covers.was.similar.to.values.recorded.
from.other.mine.sites.which.had.stabilized.arsenic.tailings.(Costello.et.al..
2004).. It. is. possible. however. for. eucalypts. (Ashley. and. Lottermoser. 1999).
and. pasture. species. (DeKoe. 1994). to. take. up. more. As. from. highly. acidic.
soils..The.low.uptake.of.As.by.the.suite.of.species.in.the.experiments.relects.
the. low. bioavailability. of. the. toxic. metalloid. in. the. sulidic. tailings. cov-
ers,. where. it. appears. that. the. geochemistry. of. the. system. attenuates. the.
release. of. more. mobile. forms. of. arsenic.. In. the. most. recent. assessment. of.
the.research.plots.it.was.showed.that.after.5.year's.growth.all.four.tree.spe-
cies.accumulated.low.As.concentrations.(King.et.al..2008),.the.highest.being.
recorded.in.mature.leaves,.ranging.from.0.3.to.5.1.μg/g.As.. E. polybractea .had.
signiicantly.higher.foliar.As.than.the.other.three.species.but.there.was.also.
great.variation.within.the.species..Between.5.and.10.times.lower.concentra-
tions.were.recorded.in.stem.samples.and.no.As.was.detected.in.young.leaf.
tips.. There. was. also. signiicant. variation. in. the. growth. of. trees. upon. the.
site.. E. cladocalyx .grew.taller.than.the.other.species.although.greater.varia-
tion.was.detected.within.the.species.than.between..Variation.in.tree.heights.
was.not.correlated.with.As.concentrations.in.either.stems.or.leaves..Arsenic.
bioavailability.was.determined.to.depths.of.2.2.m.and.found.to.be.low.when.
compared.with.total.As.in.the.tailings.
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