Geoscience Reference
In-Depth Information
An.analysis.for.the.northern.Rocky.Mountains.shows.that.since.1969.maximum.
snow-water.equivalent.(SWE).has.declined.and.peaked.earlier.(14.days).in.the.water-
year,. with. minimal. temporal. change. between. peak. and. 0. SWE.. The. number. of.
snow-free. days. and. ablation. days. indicates. temperature-driven. loss. of. snow. cover.
or. increasing. loss. of. snow. through. sublimation.. Although. accumulation. and. abla-
tion. days. did. not. change. signiicantly,. the. annual. number. of. snow-free. days. has.
increased,.resulting.in.an.average.loss.of.14.days.of.snow.cover.between.1969.and.
2007. due. to. higher. temperatures.. Minimum. temperatures. have. increased. more. at.
higher.elevations.than.in.valleys,.suggesting.that.altered.lapse.rates.may.have.a.dis-
proportionate.warming.effect.on.snowpack.retention.at.higher.elevations..This.effect.
on. snowpack. ablation. is. compounded. by. spring. nighttime. minimums. with. fewer.
freeze.events.since.the.1980s,.leading.to.more.rapid.melting.of.snow..These.results.
suggest.that.spring.runoff,.peak.discharge,.and.other.metrics.of.streamlow.would.be.
expected.to.change,.although.our.analysis.found.no.signiicant.changes.in.these.fac-
tors..Increased.summer.precipitation.in.the.northern.Rockies.appears.to.have.com-
pensated.for.earlier.snowmelt,.although.it.has.also.contributed.more.variability.and.
a.“lashier”.low.regime.
Monitoring.in.Rocky.Mountain.NP.since.1982.shows.that.there.was.a.period.of.
below-average.precipitation.during.2000-2006.and.a.steady.increase.in.summer.and.
fall.temperatures.of.0.12°C.per.year.since.1991..This.is.causing.increased.melting.of.
rock.glaciers.and.possibly.other.cryic.features,.with.a.consequent.increase.in.sum-
mer. stream. discharge.. Nitrate. concentrations,. as. well. as. the. weathering. products.
calcium.and.sulfate,.were.higher.in.rock.glacier.meltwater.for.the.period.2000-2006.
(Baron.et.al..2000b,.2009)..Melting.ice.in.glaciers.and.rock.glaciers.is.exposing.sedi-
ments.from.which.nitrogen.produced.by.nitriication.can.be.lushed..It.appears.that.
a.water.quality.threshold.was.crossed.in.Rocky.Mountain.NP.around.2000,.and.that.
nitrogen. release. from. ice. features. such. as. rock. glaciers. may. occur. throughout. the.
West.as.mountain.glaciers.retreat.
In.cold-water.isheries,.regulation.of.stream.temperature,.as.inluenced.by.snow-
pack.and.glaciers,.controls.the.distribution.and.abundance.of.invertebrates.(Hauer.
et.al..1997).and.ish.(Keleher.and.Rahel.1996;.Dunham.et.al..2003)..The.body.tem-
perature.of.salmonids.depends.on.the.temperature.of.their.surroundings,.with.a.char-
acteristically.narrow.range.of.thermal.tolerance..Bull.trout.(
Salvelinus conluentus
).
is.a.native.char.to.northwestern.North.America.that.requires.cold,.connected,.and.
complex.habitats..However,.populations.have.declined.over.the.past.century.due.to.
habitat.degradation,.nonnative.species.introductions,.and.elevated.water.temperature.
(Rieman. et. al.. 1997).. A. warming. climate. and. higher. daily. temperature. extremes.
during.summer.may.negatively.impact.existing.trout.populations.by.increasing.water.
temperatures. beyond. critical. physiological. thresholds. (Selong. et. al.. 2001). in. natal.
habitat.area.and.habitat.patches.(Rieman.et.al..1997).
In.conjunction.with.losing.the.cooling.effect.of.glaciers.and.perennial.snow.and.
ice,. stream. temperature. will. be. affected. by. changes. in. maximum. summer. tem-
peratures. and. minimum. winter. temperatures. (Keleher. and. Rahel. 1996).. Using. an.
upper.temperature.threshold.of.22°C.as.a.constraining.variable.for.cold-water.ish,.
Keleher.and.Rahel.(1996).predicted.that.the.length.of.streams.occupied.in.Wyoming.
would. decrease. 8-43%. for. increases. in. temperature. from. 1°C. to. 5°C.. Changes.
