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

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

Introduction to Lake Tahoe and Key Environmental Impacts

Air Pollution - Just One of Multiple Ecosystem Stressors

Features of Lake Tahoe Subalpine, oligotrophic, low nutrients in soils 800 km^2 drainage 500 km^2 lake surface 499 m max. depth 650 yr hydraulic residence 80% land managed by USFS Urban-wildland interface

Lake Tahoe: A Changing Ecosystem  Significant portions are urbanized  Increased resident population  Millions of tourists  Peak VMT >1,000,000 miles/day  Loss of wetland and runoff infiltration  Extensive road network  Land disturbance - soil erosion  Air pollution

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

Transport of Toxics to Lake and Incorporation into Biota Air Pollution is Just Not a Local Issue

Regional Transport of Mercury Alan C. Heyvaert et al. (2000)

Transport of Organic Toxics  Air, water, snow & fish samples taken at Tahoe and nearby lake showed measurable levels of PCBs Air, water, snow & fish samples taken at Tahoe and nearby lake showed measurable levels of PCBs Air, water, snow & fish samples taken at Tahoe and nearby lake showed measurable levels of PCBs  Low levels of contamination but mass balance suggests: Low levels of contamination but mass balance suggests: Low levels of contamination but mass balance suggests: a) atmospheric sources dominate a) atmospheric sources dominate b) out-of-basin transport b) out-of-basin transport S. Datta, F. Matsumura et al. (1998)

Atmospheric Deposition, Nutrient Budget & Nutrient Limitation Influence on Long-term Decline of Lake Clarity

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

“Initial” Lake Tahoe Nutrient Budget  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) 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 (<1%) 1.6 (4%) Total Jassby et al. (1994), Reuter et al. (2000)

Change in Algal Response to Nutrients  Long-term shift from N&P co-limitation to consistent P limitation  Data strongly suggests that AD, with high N:P 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 Goldman et al. (1993), Jassby et al. (1994)

Current Research on Nutrient and Particle Sources ‘Not So Elementary My Dear Watson’

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) Fires (controlled/wild) Road dust Road dust Vehicle exhaust Vehicle exhaust Residential heating Residential heating Upwind emissions Upwind emissions  LTADS -> CARB and universities are addressing source

LTAM Predicts Smoke PM2.5 for Wildfire & Prescribed Burns  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 S. Cliff & T. Cahill (2002)

Aircraft Measurements of N & P in Forest Fire Smoke in and Around Tahoe Basin  TN 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 Q. Zhang et al. (2002) Top of bar = Particulate N Bottom of bar = Gaseous N

Aerosols at South Lake Tahoe: Evidence for the Role of Road Dust  Continuous monitoring of 8 size modes ( 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 ( µm) Particles >PM10 contain most P Previous AQ studies did not focus on larger cuts Hwy 50 also source of fine particles ( 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 Cahill et al. (2003)

Linkage to Tahoe TMDL Total Daily Maximum Load Best Understood as Water Clarity Restoration Plan

Elements of a TMDL  Problem Statement  Numeric Target  Source Analysis  Linkage Analysis  Load Allocations  Margin of Safety  Implementation Plan

% Nitrogen Reduction % Phosphorus Reduction % Sediment Reduction ………Red …….Yellow …..Blue 33 & above..Purple ………Red …….Yellow …..Blue 33 & above..Purple Final Secchi Depth (m) Conceptual Load Reduction Model Parameters are for illusrative purposes only Informed by Clarity model Multiple potential solutions

Load Reduction Matrix

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 B Urban (20%) Atmospheric (25%) Stream Channels (25%) Ground Water (15%) Forested Areas (15%) 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 Parameters are for illustrative purposes only Example Load Reduction Alternatives

Conclusion Science-Based Decision Making Stakeholder Driven