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
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
Atmospheric Deposition,
Nutrient Budget & Nutrient
Limitation
Influence on Long-term Decline of
Lake Clarity
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
“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 (<1%) 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)
Change in Algal Response to Nutrients
Goldman et al. (1993), Jassby et al. (1994)

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 airshedwatershed interaction
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)
• Road dust
• Vehicle exhaust
• Residential heating
• Upwind emissions

LTADS -> CARB and universities are addressing source
LTAM Predicts Smoke PM2.5 for
Wildfire & 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
Aircraft Measurements of N & P in Forest
Fire Smoke in and Around Tahoe Basin
Q. Zhang et al. (2002)
Concentrations of Gaseous and Fine Particulate N
800
600
400
Forest fire
Tahoe (Slightly smoky)
Tahoe (Clear)
Medium Sierra
Low Sierra
Concentration (nmol N m-3-air)
1000
Top of bar = Particulate N
Bottom of bar = Gaseous N
200
0
HNO3(g)+NO3(p)
NH3(g)+NH4(p)
ON(g)+ON(p)
TN(g)+TN(p)

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
Aerosols at South Lake Tahoe:
Evidence 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 >PM10 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
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
Conceptual Load Reduction Model
40
90100
% Sediment Reduction
20 30
0 10
80
50 60 70
0
10
20
30
40
50
60
70
80
90
100
• Informed by
Clarity model
• Multiple potential
solutions
0 10
20 30
40 50
Final Secchi
Depth (m)
60 70
80 90
100
Parameters are for
illusrative purposes only
20- 25………Red
25.5-28…….Yellow
28.5-32.5…..Blue
33 & above..Purple
Load Reduction Matrix
Load Reduction Opportunities
URBAN
U-1
Infiltration
U-2
Wetland Treatment
U-3
Source Control
U-4
Chemical Enhancement
ATMOSPHERIC
A-1
Vehicle Emission Control
A-2
Wood Stove Management
A-3
Out-of-Basin Source Control
A-4
Dust Management
STREAM CHANNELS
ST-1 Stream Restoration
ST-2 Bank Stabilization
ST-3 Hydrological Controls
GROUND WATER
GW-1 Fertilizer Management
GW-2 Source Control
FORESTED AREAS
FA-1 Road Management
FA-2 Trail Management
FA-3 Fire Restoration
Estimated
Load
Reduction
Effectiveness
Cost
Contstraints
Etc.
4
7
6
9
$
$$
$
$$$
2
7
1
8
tbd
tbd
tbd
tbd
xx
xx
xx
xx
kg/yr
kg/yr
kg/yr
kg/yr
4
5
2
7
$$
$$
$$$
$
4
3
9
2
tbd
tbd
tbd
tbd
xx
xx
xx
xx
kg/yr
kg/yr
kg/yr
kg/yr
7
7
5
$$$
$$
$
5
3
2
tbd
tbd
tbd
xx kg/yr
xx kg/yr
xx kg/yr
3
8
$$
$
7
2
tbd
tbd
xx kg/yr
xx kg/yr
6
5
7
$$$
6
tbd
$$
5
tbd
$$
4
tbd
Total Possible Load Reduction
xx kg/yr
xx kg/yr
xx kg/yr
xx kg/yr
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
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
Conclusion
Science-Based Decision Making
Stakeholder Driven