View
216
Download
0
Tags:
Embed Size (px)
Citation preview
Sources of Ca to Sources of Ca to Watersheds: Explaining the Watersheds: Explaining the
ExcessExcess
Corey LawrenceCorey LawrenceNick RisingNick Rising
Christopher AndersenChristopher Andersen
Presentation OverviewPresentation Overview
The Issue:The Issue: Excess Calcium in Watersheds Excess Calcium in Watersheds Useful Tools:Useful Tools: Strontium Isotope System Strontium Isotope System
and Elemental Ratiosand Elemental Ratios Papers:Papers:
Clow et al., 1997 – Dust Clow et al., 1997 – Dust White et al., 1999 – Disseminated CalciteWhite et al., 1999 – Disseminated Calcite
------------------------------------------------------------------------------------ Interesting Tangent:Interesting Tangent:
Ley et al., 2004 – Extreme MicrobesLey et al., 2004 – Extreme Microbes
Calcium in WatershedsCalcium in Watersheds
Importance of Ca for forest productivity and watershed Importance of Ca for forest productivity and watershed alkalinityalkalinity
Silicate vs. Carbonate WeatheringSilicate vs. Carbonate Weathering Excess Ca relative to Mineral StoichiometryExcess Ca relative to Mineral Stoichiometry
Short Term Short Term • AcidificationAcidification• Biological LossesBiological Losses
Long Term Long Term • Accelerated Silicate Phase WeatheringAccelerated Silicate Phase Weathering• Selective Leaching of AnthrociteSelective Leaching of Anthrocite• Disseminated CalciteDisseminated Calcite• Eolian DustEolian Dust
Introduction to the Introduction to the Strontium Isotope System.Strontium Isotope System.
Corey LawrenceCorey Lawrence
Source: Capo et al., 1998
8787Rb decays to Rb decays to 8787Sr Sr through beta decaythrough beta decay
Rubidium and Strontium Rubidium and Strontium behave differently in behave differently in during melting during melting process leading to process leading to segregation during segregation during mantle melting.mantle melting.
Strontium Isotope SystemStrontium Isotope System
Indicator of both age and geochemical Indicator of both age and geochemical originorigin Older rocks with same initial Rb/Sr will have Older rocks with same initial Rb/Sr will have
higher higher 8787Sr/Sr/8686Sr than younger ones.Sr than younger ones. Rocks of a given age composed of different Rocks of a given age composed of different
minerals will show differentiation in strontium minerals will show differentiation in strontium ratiosratios
The combination of these factors allows The combination of these factors allows strontium to be used a tracer of cation sourcestrontium to be used a tracer of cation source
Source: Capo et al., 1998
Strontium vs. CalciumStrontium vs. Calcium
Both are alkaline earth elements with +2 Both are alkaline earth elements with +2 valence chargevalence charge
Strontium Strontium Atomic number = 38Atomic number = 38 Ionic Radius = 1.18 angstromsIonic Radius = 1.18 angstroms
CalciumCalcium Atomic number = 20Atomic number = 20 Ionic Radius = 1.00 angstromsIonic Radius = 1.00 angstroms
Source: Kennedy et al., 2002
Source: Capo et al., 1998
Source: Blum et al., 2002
Critical AssumptionsCritical Assumptions
Strontium is not fractionated by biological Strontium is not fractionated by biological or physical mechanismsor physical mechanisms
Strontium isotopic ratios are constant over Strontium isotopic ratios are constant over time and climatetime and climate
Congruent weatheringCongruent weathering Differences in isotope ratios between Differences in isotope ratios between
sources are large enough to solve mixing sources are large enough to solve mixing modelmodel
Source: Bullen et al., 1997
Source: White et al., 1999
Strontium 87/Strontium 86 as a Tracer of Strontium 87/Strontium 86 as a Tracer of Mineral Weathering Reactions and Calcium Mineral Weathering Reactions and Calcium
Sources in an Alpine/Subalpine Sources in an Alpine/Subalpine Watershed, Loch Vale, Colorado.Watershed, Loch Vale, Colorado.
(Clow et al., 1997)(Clow et al., 1997)
Nick RisingNick Rising
GoalsGoals
““Our specific objective was to use Our specific objective was to use Sr-87/Sr-86 as a tool to characterize the Sr-87/Sr-86 as a tool to characterize the dominant sources of dissolved calcium in dominant sources of dissolved calcium in surface waters in Loch Vale.”surface waters in Loch Vale.” Determine sources of excess Ca in Determine sources of excess Ca in
watershed. watershed.
GeologyGeology
80% Precambrian Gneiss.80% Precambrian Gneiss. 20% Precambrian Silver Plume Granite.20% Precambrian Silver Plume Granite. Mineralogy: Mineralogy:
Quartz (28-41%)Quartz (28-41%) Plagioclase* (25-30%)Plagioclase* (25-30%) Biotite (6-16%)Biotite (6-16%) Microcline (9-34%)Microcline (9-34%) Sillimanite (0-6%)Sillimanite (0-6%)
MethodsMethods
Stream gaging stations on Andrews Creek Stream gaging stations on Andrews Creek and Icy Brook used to take water samples.and Icy Brook used to take water samples.
Eolian Dust samples collected at weather Eolian Dust samples collected at weather station.station.
Bedrock, soil and dry deposition samples Bedrock, soil and dry deposition samples were also taken from the catchment. were also taken from the catchment.
Calcium SourcesCalcium Sources
Weathering of plagioclase was thought to Weathering of plagioclase was thought to be the dominant source of dissolved Ca.be the dominant source of dissolved Ca. Stream water has higher amounts of Ca than Stream water has higher amounts of Ca than
plagioclase.plagioclase. Previous studies have shown that Previous studies have shown that
weathering of calcite in bedrock is also a weathering of calcite in bedrock is also a source of Ca.source of Ca.
Dry deposition (dust) may also be a major Dry deposition (dust) may also be a major source.source.
Sr-87/Sr-86 VariabilitySr-87/Sr-86 Variability
Stream water samples have highest Sr-Stream water samples have highest Sr-87/Sr-86 ratios.87/Sr-86 ratios.
Springs have the largest range of ratios.Springs have the largest range of ratios. Represent shallow subsurface flow (highly Represent shallow subsurface flow (highly
variable).variable). Soils have lower ratios, but higher than Soils have lower ratios, but higher than
precipitation.precipitation. Soil Sr-87/Sr-86 ratios are derived from Soil Sr-87/Sr-86 ratios are derived from
mixing atmospheric and bedrock sources. mixing atmospheric and bedrock sources.
Effects of DustEffects of Dust
Eolian dust increases Ca/Na ratios while Eolian dust increases Ca/Na ratios while keeping Sr ratios steady.keeping Sr ratios steady.
Dust, when combined with precipitation, Dust, when combined with precipitation, yield higher Ca/Na ratios with lower Sr-yield higher Ca/Na ratios with lower Sr-87/Sr-86 ratios.87/Sr-86 ratios. More important in rain than snow.More important in rain than snow.
Mass Balance equation was used to determine the weathering rates which account for flux into the Andrews Creek subbasin.
42% Plagioclase
38% Calcite
18% Biotite
2% Microcline
ResultsResults
Using Sr-isotope mixing equation, 1/5 Using Sr-isotope mixing equation, 1/5 to 1/3 of annual inputs into streams are to 1/3 of annual inputs into streams are the result of dry deposition (dust). the result of dry deposition (dust). 26% (+/- 7%) from dust.26% (+/- 7%) from dust. 23% (+/- 1%) from weathering of 23% (+/- 1%) from weathering of
plagioclase.plagioclase. 41 to 59% from the dissolution of calcite in 41 to 59% from the dissolution of calcite in
bedrock.bedrock.
The role of disseminated calcite in the The role of disseminated calcite in the chemical weathering of granitoid rocks chemical weathering of granitoid rocks
(White et al., 1999)(White et al., 1999)
Goals:Goals: Investigate sources for the release of excess Investigate sources for the release of excess
Ca by detailing the content and distribution of Ca by detailing the content and distribution of disseminated calcite in granitoid rocksdisseminated calcite in granitoid rocks
Long term experimental weathering studies on Long term experimental weathering studies on both fresh and naturally weathered granitoids.both fresh and naturally weathered granitoids.
Use results to interpret observed solute Use results to interpret observed solute concentrations and weathering fluxesconcentrations and weathering fluxes
The ApproachThe Approach Compare minerology using XRD ,cathode luminescence, Compare minerology using XRD ,cathode luminescence,
and SEM.and SEM. Measure solute concentration from laboratory sequential Measure solute concentration from laboratory sequential
weathering experiment using ICP-MS.weathering experiment using ICP-MS. Contrast weathering experiment with observed stream Contrast weathering experiment with observed stream
chemistry in sampled watersheds.chemistry in sampled watersheds.
ResultsResults
There is a range of calcite and COThere is a range of calcite and CO22 between between
granitoidsgranitoids Weathered material contains much less Ca and Weathered material contains much less Ca and
COCO22 than fresh material than fresh material
ResultsResults
Ca, Na, and Si decrease with time during the Ca, Na, and Si decrease with time during the simulated weathering of fresh materialsimulated weathering of fresh material
Na typically lower than Ca in all sites except Rio Na typically lower than Ca in all sites except Rio Icacos.Icacos.
Comparing Ca/Na ratios suggests stream Comparing Ca/Na ratios suggests stream solutes are a mixture of fresh and weathered solutes are a mixture of fresh and weathered material in Loch Vale and Yosemitematerial in Loch Vale and Yosemite
Contrasting Ca/Na results in other watersheds Contrasting Ca/Na results in other watersheds suggest must reflect differences in weathering suggest must reflect differences in weathering conditionsconditions
ResultsResults
Decreasing calcium concentrations Decreasing calcium concentrations correlates with decreasing pHcorrelates with decreasing pH
Effluent alkalinities are elevated relative to Effluent alkalinities are elevated relative to calcium in Yosemite and Rio Icacos calcium in Yosemite and Rio Icacos granitiodsgranitiods Indicates alkalinity is derived from both calcite Indicates alkalinity is derived from both calcite
dissolution and silicate hydrolysis in these dissolution and silicate hydrolysis in these systems.systems.
Sr/Ca ratios are higher in Sr/Ca ratios are higher in the plagioclase than in the plagioclase than in disseminated calcite.disseminated calcite.
Effluent Sr/Ca ratio Effluent Sr/Ca ratio should reflect a mixture should reflect a mixture of the two sources of the two sources Elevated Sr/Ca in Rio Elevated Sr/Ca in Rio Icacos suggests Icacos suggests nonstoichiometric nonstoichiometric weatheringweathering
94-80% Ca contribution 94-80% Ca contribution in Yosemitein Yosemite
65% Ca contribution in 65% Ca contribution in Rio IcacosRio Icacos
Initial effluent from Initial effluent from fresh rock is close to fresh rock is close to Ca saturationCa saturation
Both fresh and Both fresh and weathered effluent weathered effluent calcite saturation calcite saturation decreases with timedecreases with time
Lack of correlation Lack of correlation between the calcite between the calcite content of the fresh content of the fresh granitoid and the granitoid and the extent of calcium extent of calcium excess in streams excess in streams reflects differences in reflects differences in natural weathering natural weathering conditions.conditions.
ConclusionsConclusions
Calcite occurs in granitoid microfractures Calcite occurs in granitoid microfractures as disseminated calciteas disseminated calcite
Calcite is preferentially removed during Calcite is preferentially removed during natural weathering conditionsnatural weathering conditions
Calcium excess is related to age of Calcium excess is related to age of bedrock and weathering conditionsbedrock and weathering conditions
Accessory calcite can contribute to Accessory calcite can contribute to significant proportion of stream Ca in significant proportion of stream Ca in younger basinsyounger basins
Microbial population dynamics in an Microbial population dynamics in an extreme environment: controlling extreme environment: controlling
factors in talus soil at 3750 m in the factors in talus soil at 3750 m in the Colorado Rocky MountainsColorado Rocky Mountains
(Ley et al., 2004)(Ley et al., 2004)
Chris AndersenChris Andersen
IntroductionIntroduction High elevation talus slopes are extreme High elevation talus slopes are extreme
environments for life. They contain oligotrophic environments for life. They contain oligotrophic cold soils, with very little microbial biomass, that cold soils, with very little microbial biomass, that are key components of water catchment areas are key components of water catchment areas that supply drinking water.that supply drinking water.
Purpose: Purpose: Evaluate the seasonality of Carbon (C) inputs to talus Evaluate the seasonality of Carbon (C) inputs to talus
and microclimate characterized by soil moisture and and microclimate characterized by soil moisture and temp. temp.
Determine how these factors correlated with microbial Determine how these factors correlated with microbial biomass dynamics in vegetated and unvegetated biomass dynamics in vegetated and unvegetated soils.soils.
ApproachApproach
Characterize unvegetated vs. vegetated soilsCharacterize unvegetated vs. vegetated soils Measure C inputs to soils from eolian dust and Measure C inputs to soils from eolian dust and
measure photosynthetically active radiation measure photosynthetically active radiation (PAR) as a proxy for Photosynthesis(PAR) as a proxy for Photosynthesis
Estimate miomass of two microbial functional Estimate miomass of two microbial functional using substrate induced respiration methodusing substrate induced respiration method Glutamate Mineralizers (GM) Glutamate Mineralizers (GM)
• General heterotrophs General heterotrophs • Largest functional group in tundra soilLargest functional group in tundra soil
Salicylate Mineralizers (SM)Salicylate Mineralizers (SM)• Specialized group of fungi in unvegetated soilsSpecialized group of fungi in unvegetated soils
DescriptionDescription
Unvegetated soil Unvegetated soil coarse textured, coarse textured, very little organic very little organic
mattermatter low water retention low water retention
capacitycapacity low level of nutrientslow level of nutrients low levels of microbial low levels of microbial
biomass.biomass.
Vegetated soil Vegetated soil loamy Textureloamy Texture 8-16% organic matter8-16% organic matter higher water retention higher water retention higher microbial higher microbial
biomassbiomass
DescriptionDescription
The microclimate, in both vegetated and The microclimate, in both vegetated and unvegetated soils, of the high elevation talus unvegetated soils, of the high elevation talus slopes were divided into three distinct periods:slopes were divided into three distinct periods: WinterWinter- soil temps. remained below zero and covered - soil temps. remained below zero and covered
by thick snow. Period lasted from beginning of by thick snow. Period lasted from beginning of permanent snow to the start of snowmelt in May.permanent snow to the start of snowmelt in May.
SpringSpring- period where snowpack still covered the soils - period where snowpack still covered the soils and melt water influenced the talus slopes. Lasted (at and melt water influenced the talus slopes. Lasted (at most) late May to early August.most) late May to early August.
SummerSummer- period of desiccation, high temp, relieved - period of desiccation, high temp, relieved by rare rain events. Lasted from late July or early by rare rain events. Lasted from late July or early August to early October.August to early October.
Eolian DustEolian Dust
Total amount trapped over winter/spring Total amount trapped over winter/spring 1997-1998 = 43 kg ha1997-1998 = 43 kg ha-1-1
Accounts for 2.1 ug OM gAccounts for 2.1 ug OM g-1-1
Summer dust deposition 1997-1998 = 7.7 Summer dust deposition 1997-1998 = 7.7 kg hakg ha-1-1
Accounts for 0.38 ug OM gAccounts for 0.38 ug OM g-1-1
Figure 5Figure 5 Fig. 5A & B shows the Fig. 5A & B shows the
differences in the amount of differences in the amount of warm-adapted and cold-warm-adapted and cold-adapted GM biomass in adapted GM biomass in vegetated and unvegetated vegetated and unvegetated soils. soils.
Fig. 5C & D shows the Fig. 5C & D shows the differences in the amount of differences in the amount of warm-adapted and cold-warm-adapted and cold-adapted SM biomass in adapted SM biomass in vegetated and unvegetated vegetated and unvegetated soils.soils.
ResultsResults Soils temps. never dropped below -2.9C.Soils temps. never dropped below -2.9C.
Temp. wasn’t low enough to freeze soils in the winterTemp. wasn’t low enough to freeze soils in the winter Temp. was high enough to desiccate soils in the Temp. was high enough to desiccate soils in the
summer.summer.
The dominant C input in the unvegetated soils The dominant C input in the unvegetated soils was due to the deposition of eolian dust particles was due to the deposition of eolian dust particles during the snowmelt of the spring. during the snowmelt of the spring.
The main C input in vegetated soils occurred The main C input in vegetated soils occurred during the spring snowmelt when the dust during the spring snowmelt when the dust particles were released. particles were released.
Results ContinuedResults Continued
The GM biomass reached its peak when the The GM biomass reached its peak when the dust particles were released with the snowmelt dust particles were released with the snowmelt in both the vegetated and unvegetated soils.in both the vegetated and unvegetated soils.
The SM biomass fluctuated with temperature. The SM biomass fluctuated with temperature. The warm-adapted SM peaked in the summer The warm-adapted SM peaked in the summer
while the cold-adapted peaked in the winter.while the cold-adapted peaked in the winter.