Sources of Atmospheric Pollutants Leading to Declining Water Clarity in aHigh Altitude LakeAlan Gertler Jülide Kahyaoğlu-KoračinDesert Research Institute, Reno, NV

Leland TarnayU.S. National Park Service, Washington, DC

AcknowledgementsDesert Research Institute:

John LewisHebrew University:

Menachem LuriaUniversity of California, Davis

Geoffrey SchladowCalifornia Air Resources Board

Paul AllenVernon Hughes

Funding:Nevada NSF- EPSCoRNSF Advanced Computing in Environmental Sciences (ACES)DRI – Center for Watersheds and Environmental Sustainability

Presentation Overview

MotivationMonitoring Results

MethodologyFlux estimatesIn basin vs. out of basin sources

Modeling ResultsBack trajectory analysesMeteorological and dispersion simulations

Nature of the Problem

Since 1968, lake clarity has been decreasing at 0.25 m/yr.Possible causes of this include hydrologic and atmospheric input of:

Nitrogen (N)Phosphorous (P)Sediment

Sources of Nitrogen

Surface Runoff10%

Stream Loading20%

Groundwater Discharge

15%

Atmospheric Deposition

55%

Sources of Phosphorous

Surface Runoff35%

Stream Loading29%

Groundwater Discharge

9%

Atmospheric Deposition

27%

Monitoring Objectives

Measure ambient concentrations of N pollutants at sites located around the LTB.Perform measurements during periods when dry deposition is expected to dominate.Couple the ambient data with available air quality and meteorological data to provide an estimate of the contributions from in-basin and out-of-basin sources.

Lake Tahoe - Location

Prevailing Westerlies

Lake Tahoe - Location Reno

Central ValleyS. Lake Tahoe

NASA Photo

Lake Tahoe

Sampling Locations

Thunderbird LodgeThunderbird LodgeEcho SummitEcho Summit

BlissBlissBarkerBarker

South Lake TahoeSouth Lake Tahoe

(View from above Incline Village, at the north end of the Lake Tahoe Basin)

Methods: Measuring Pollutant Concentrations

HNO3NH3NH4NO3

Methods: Integrating Bigleaf with a GIS

Estimated Flux

Nitrogen species Lower limit(106 g)

Upper limit(106 g)

Estimate(106 g)

HNO3 26.7 33.7 30.2

NH3 2.9 22.1 14.6

NH4NO3 0.1 4.9 4.6

TOTAL 29.7 60.8 49.4

Comparison With Other Studies

In Basin vs. Out of Basin?

Spatial distributionsInter-site correlationsDevelopment of isoplethsAir mass age

2000 Results – HNO3

0

5

10

15

20

25

30

35

40

45

7/26 8/2 8/10 8/16 8/22 8/28 9/3 9/9 9/15

Date

HN

O3

(nm

ol/m

3)

BARKECHO BLISSOLATBRDBACKGROUND

Most sites similar, with So Lake higher → Regional + local source

2000 Results – NH3

0

20

40

60

80

100

120

140

7/26 8/2 8/10 8/16 8/22 8/28 9/3 9/9 9/15

Date

NH

3 (n

mol

/m3)

BARKECHOBLISSOLATBRDBACKGROUND

Major differences → Local source

2000 Results – All Sites

HNO3 (nmol m-3)

NH3 (nmol m-3)

24 hr median (± 1 S.E.) 14 (1.2) 14 (3.9) Day median (± 1 S.E.) 17 (1.8) 20 (5.0) Night median (± 1 S.E.) 13 (1.2) 10 (6.2) Background 5, 6 6.6-7.1 0.0-40 Stat. Sig. day/night difference (p = 0.05)? yes no

HNO3 – Inter-site Correlations

HNO3 South Lake

Tahoe Thunderbird

Lodge Echo

Summit Barker Pass

Bliss State Park

South Lake Tahoe 1 Thunderbird Lodge 0.65 1 Echo Summit 0.57 0.91 1 Barker Pass 0.72 0.87 0.88 1 Bliss State Park 0.70 0.84 0.85 0.90 1

NH3 – Inter-site Correlations

NH3 South Lake

Tahoe Thunderbird

Lodge Bliss State

Park Echo

Summit Barker Pass

South Lake Tahoe 1 Thunderbird Lodge -0.62 1 Bliss State Park -0.27 0.41 1 Echo Summit 0.01 0.41 0.61 1 Barker Pass -0.01 0.85 0.92 0.92 1

Spatial and Temporal HNO3Variation

Spatial and Temporal NH3Variation

Day Night

Air Mass Age

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

7/25

/00

8/1/

00

8/9/

00

8/15

/00

8/21

/00

8/27

/00

9/2/

00

9/8/

00

9/14

/00

Ave

rage

Date

HN

O3/

NO

x

Echo DayS. Lake DayEcho NTS. Lake NT

Summary Measurement Results

HNO3 accounts for 20% of direct Lake N deposition (wet and dry) and 50% or more of terrestrial N deposition (wet and dry).HNO3 is regional with a significant local component. The sources of NH3 are local.

Objectives of Modeling Component

To determine the characteristics of summertime transport of N to the Lake Tahoe Basin.To determine in-basin vs. out-of-basin sources of HNO3 using advanced atmospheric modeling systems.

Ensemble Analysis of Backward Air Mass Trajectories (day)

June-Sep/00 5 PM (24-hr)

P > 0.027, 25%P > 0.027, 25%0.015 < P < 0.027, 50%

0.0048 < P < 0.015, 75%

Modeling System (1)

MM5MM5

117x117x35117x117x3515 km15 km

193x169x35193x169x355 km5 km

73xx73x3573xx73x351.6 km1.6 km

• Two case studies coinciding with the field study by Tarnay (2001).

•Cases on August 22 and September 3, 2000.

•85 hours forecast for each simulation.

Modeling System (2)

CALMET/CALPUFF system using MM5 predicted fields as the first guess.Volume sources in California.72 hours simulation for each case.

50 100 150 200

50

100

150

200

250

Lake

Tah

oe

San Francisco

Sacramento

Point sourcesMeteorological sitesChemical sites

SOLA

ECHO

BLIS

TBLG

BARK

USCG

45 km

65 km

Emissions (1)

• Developed emissions estimates for the Tahoe basin: 7.3 NOx(tn/day).

•Data from 42 surface, 2 upper air, and 49 ozone stations.

Emissions (2)CALMETCALMET/CALPUFFCALPUFF250x265x8250x265x81 km1 km

SourcesSources

CALMET Predicted Winds: August 22

50 100 150 200X direction (km)

50

100

150

200

250

Y di

rect

ion

(km

)

50 100 150 200X direction (km)

50

100

150

200

250

Y di

rect

ion

(km

)

DayNight

•Regional background ~0.4 µg/m3

•Accounted for 81 to 98% of the observed HNO3

•Local sources responsible for 70% of the observations

HNO3 – Bytnerowicz et al.

Summary of Modeling ResultsThe amount of transported HNO3 was low (~0.4 µg/m3).

For the high concentration period, predicted concentrations accounted for 81% of the observations and local sources comprised approximately 70% of the predictions.

For the low concentration period, predicted concentrations accounted for 98% of the observations, and out- of-basin sources comprised approximately 70% of the predictions.

Summary and ConclusionsMeasurement Component:

HNO3 is the most important N species in terms of overall deposition.HNO3 is regional with a significant local component. The sources of NH3 are local.

Modeling Component:Backward trajectory analysis showed a transport potential from the California valley; however, the possibility of significant pollutant transport was weak. For the high concentration day, local sources dominated.

Bottom line: To reduce the atmospheric contribution of N to the lake, local sources must be controlled.

Something else to consider:Transport may be a significant source of N flux in remote watersheds.

Much Nicer Than Most of the Places I Work