Pollutant Loading from Airshed

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Pollutant Loading from Airshed Watershed
Sources to Lake Tahoe Influence on Declining
Lake Clarity
John E. Reuter - University of California, Davis
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Presentation Topics

• Lake Tahoe and overview of impacts
• Transport of toxics to lake
• Atmospheric deposition, nutrient budget
  nutrient limitation
• Current research on nutrient and particle sources
• Linkage to Tahoe TMDL

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Introduction to Lake Tahoe and Key Environmental
Impacts
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Air Pollution - Just One of Multiple Ecosystem
Stressors
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Features of Lake Tahoe
Subalpine, oligotrophic, low nutrients in
soils 800 km2 drainage 500 km2 lake
surface 499 m max. depth 650 yr hydraulic
residence 80 land managed by USFS
Urban-wildland interface
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Lake Tahoe A Changing Ecosystem

• Significant portions are urbanized
• Increased resident population
• Millions of tourists
• Peak VMT gt1,000,000 miles/day
• Loss of wetland and runoff infiltration
• Extensive road network
• Land disturbance - soil erosion
• Air pollution

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Changing Landscape has Lead to Following Lake
Issues

• Loss in transparency
• Increased algal growth
• Changes in biodiversity
• Higher load of nutrients and fine-sediment
• Wetland/riparian habitat loss
• Invasion of non-native biota
• Air quality impacts
• Appearance of toxics (e.g. PCB, Hg, MTBE)
• Significant effort on part of state and federal
  agencies, local government, universities and
  environmental consultants to address these and
  other issues

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Transport of Toxics to Lake and Incorporation
into Biota

• Air Pollution is Just Not a Local Issue

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Regional Transport of Mercury
Alan C. Heyvaert et al. (2000)
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Transport of Organic Toxics
S. Datta, F. Matsumura et al. (1998)

• Air, water, snow fish samples taken at Tahoe
  and nearby lake showed measurable levels of PCBs
• Low levels of contamination but mass balance
  suggests
• a) atmospheric sources dominate
• b) out-of-basin transport

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Atmospheric Deposition, Nutrient Budget
Nutrient Limitation

• Influence on Long-term Decline of
• Lake Clarity

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Unraveling Cause(s) for Declining Water Clarity

• Nutrients stimulate algae
• Fine-sediments directly reduces clarity (1-20 µm)
• Progressive accumulation leads to long-term
  decline
• Management strategy - P, N, sediment control
• Evidence for possible recovery
• TMDL, EIP other plans are addressing load
  reduction

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Initial Lake Tahoe Nutrient Budget
Jassby et al. (1994), Reuter et al. (2000)

• Total-N Total-P
• Atmospheric Deposition 234 (59) 12.4 (28)
• Stream loading 82 (20) 13.3 (31)
• Direct runoff 23 (6) 12.3 (28)
• Groundwater 60 (15) 4 (9)
• Shore erosion 1 (lt1) 1.6 (4)
• Total 400 43.6

• Strongly suggests importance of AD for nutrients
• Little data on inorganic particle deposition
  (soils)
• Size and low nutrient condition of Tahoe
  increases its importance
• More work underway to improve initial estimate
  (ARB, DRI, UCD)

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Change in Algal Response to Nutrients
Goldman et al. (1993), Jassby et al. (1994)

• Long-term shift from NP co-limitation to
  consistent P limitation
• Data strongly suggests that AD, with high NP
  ratio is associated with this shift
• Fundamental change in lake ecosystem function
• AD-N very important in coastal oceans
• Another example of airshed-watershed interaction

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Current Research on Nutrient and Particle Sources

• Not So Elementary My Dear Watson

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Current Research is a Work in Progress

• Sources of N, P and fine-sediment - local,
  regional and global
• In-basin or out-of-basin a key management
  question
• The Lake Tahoe Air Quality Research Scoping
  Document (Cliff et al. 2000) identified need to
  look at
• Fires (controlled/wild)
• Road dust
• Vehicle exhaust
• Residential heating
• Upwind emissions
• LTADS -gt CARB and universities are addressing
  source

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LTAM Predicts Smoke PM2.5 forWildfire
Prescribed Burns
S. Cliff T. Cahill (2002)

• PM2.5 (µg/m3) based on 3 fire scenarios
• a) Historical wildfire (12-16 ha)
• b) Hypothetical prescribed burn, 50-ha, Ward
  Valley
• c) Same as b, with 100-ha prescribed burn
• Significant implications for visibility and
  source for direct deposition

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Aircraft Measurements of N P in Forest Fire
Smoke in and Around Tahoe Basin
Q. Zhang et al. (2002)

• TN - 5-6 x higher in forest fire smoke than clean
  Tahoe air, with a greater contribution by ON
• P - 10 x higher in smoke plume much less P in
  slightly smokey air
• Bulk deposition measured at Tahoe 5-10 times
  during smoke period
• Smoke can be nutrient source, but depends on
  transport and deposition

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Aerosols at South Lake TahoeEvidence for the
Role of Road Dust
Cahill et al. (2003)

• Continuous monitoring of 8 size modes (0.09-35
  µm) in summer and winter with Drum Sampler at
  site downwind of Highway 50. Analysis for 32
  elements done at 3 hr intervals.
• Conclusions
• Hwy 50 major source of coarse particles
  (2.5-35 µm)
• Particles gtPM10 contain most P
• Previous AQ studies did not focus on larger
  cuts
• Hwy 50 also source of fine particles
  (0.09-0.26 µm) from
• diesels, smoking cars and fine ground road
  soil
• Transport out over lake occurs each night
• Data suggest that winter P is strong
  associated with road
• sanding/drying conditions while in summer
  values are more consistent day-to-day
  suggesting road dust from highway and
  near-highway soils
• Contribution to whole-lake P budget now being
  evaluated

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Linkage to Tahoe TMDL

• Total Daily Maximum Load
• Best Understood as Water Clarity Restoration Plan

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Elements of a TMDL
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Conceptual Load Reduction Model
Informed by Clarity model Multiple
potential solutions
Parameters are for illusrative purposes only
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Load Reduction Matrix
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Example Load Reduction Alternatives
A Urban (34) U-2, U-6, U-14, U-26, U-56,
U-78 Atmospheric (12 ) A-3, A-7, A19,
A43 Stream Channels (20) ST-10, ST-34,
ST-43 Ground Water (12) GW-2, GW-4,
GW-18 Forested Areas (22) FA-11, FA-23,
FA-25 TOTAL REDUCTION 15,000 kg tbd/yr
C Urban (20) Atmospheric (15) Stream Channels
(30) Ground Water (25) Forested Area
(15) TOTAL REDUCTION 15,000 kg tbd/yr
B Urban (20) Atmospheric (25) Stream Channels
(25) Ground Water (15) Forested Areas
(15) TOTAL REDUCTION 15,000 kg tbd/yr
Parameters are for illustrative purposes only
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Conclusion

• Science-Based Decision Making
• Stakeholder Driven