Sources of Atmospheric Pollutants Leading to Declining Water Clarity in a High Altitude Lake

Transcription

1 Sources of Atmospheric Pollutants Leading to Declining Water Clarity in a High Altitude Lake Alan Gertler Jülide Kahyaoğlu-Koračin Desert Research Institute, Reno, NV Leland Tarnay U.S. National Park Service, Washington, DC

2 Acknowledgements Desert Research Institute: John Lewis Hebrew University: Menachem Luria University of California, Davis Geoffrey Schladow California Air Resources Board Paul Allen Vernon Hughes Funding: Nevada NSF- EPSCoR NSF Advanced Computing in Environmental Sciences (ACES) DRI Center for Watersheds and Environmental Sustainability

3 Presentation Overview Motivation Monitoring Results Methodology Flux estimates In basin vs. out of basin sources Modeling Results Back trajectory analyses Meteorological and dispersion simulations

4 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

5 Sources of Nitrogen Groundwater Discharge 15% Stream Loading 20% Surface Runoff 10% Atmospheric Deposition 55%

6 Sources of Phosphorous Stream Loading 29% Groundwater Discharge 9% Atmospheric Deposition 27% Surface Runoff 35%

7 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.

8 Lake Tahoe - Location

9 Lake Tahoe - Location Lake Tahoe Reno Central Valley Prevailing Westerlies S. Lake Tahoe NASA Photo

10 Sampling Locations Thunderbird Lodge South Lake Tahoe Echo Summit Bliss Barker (View from above Incline Village, at the north end of the Lake Tahoe Basin)

11 Methods: Measuring Pollutant Concentrations HNO 3 NH 3 NH 4 NO 3

12 Methods: Integrating Bigleaf with a GIS

13 Estimated Flux Nitrogen species Lower limit (10 6 g) Upper limit (10 6 g) Estimate (10 6 g) HNO NH NH 4 NO TOTAL

14 Comparison With Other Studies

15 In Basin vs. Out of Basin? Spatial distributions Inter-site correlations Development of isopleths Air mass age

16 2000 Results HNO 3 45 HNO3 (nmol/m3) BARK ECHO BLIS SOLA TBRD BACKGROUND 0 7/26 8/2 8/10 8/16 8/22 8/28 9/3 9/9 9/15 Date Most sites similar, with So Lake higher Regional + local source

17 2000 Results NH BARK ECHO BLIS SOLA TBRD BACKGROUND NH3 (nmol/m3) /26 8/2 8/10 8/16 8/22 8/28 9/3 9/9 9/15 Date Major differences Local source

18 2000 Results All Sites HNO 3 (nmol m -3 ) NH 3 (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, Stat. Sig. day/night difference (p = 0.05)? yes no

19 HNO 3 Inter-site Correlations HNO3 South Lake Tahoe Thunderbird Lodge Echo Summit Barker Pass Bliss State Park South Lake Tahoe 1 Thunderbird Lodge Echo Summit Barker Pass Bliss State Park

20 NH 3 Inter-site Correlations NH3 South Lake Tahoe Thunderbird Lodge Bliss State Park Echo Summit South Lake Tahoe 1 Thunderbird Lodge Bliss State Park Echo Summit Barker Pass Barker Pass

21 Spatial and Temporal HNO 3 Variation

22 Spatial and Temporal NH 3 Variation Day Night

23 Air Mass Age /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 Average Echo Day S. Lake Day Echo NT S. Lake NT Date HNO3/NOx

24 Summary Measurement Results HNO 3 accounts for 20% of direct Lake N deposition (wet and dry) and 50% or more of terrestrial N deposition (wet and dry). HNO 3 is regional with a significant local component. The sources of NH 3 are local.

25 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 HNO 3 using advanced atmospheric modeling systems.

26 Ensemble Analysis of Backward Air Mass Trajectories (day) June-Sep/00 5 PM (24-hr) P > 0.027, 25% < P < 0.027, 50% < P < 0.015, 75%

27 Modeling System (1) MM5 73xx73x km 193x169x35 5 km Two case studies coinciding with the field study by Tarnay (2001). Cases on August 22 and September 3, x117x35 15 km 85 hours forecast for each simulation.

28 Modeling System (2) San Francisco Sacramento Lake Tahoe CALMET/CALPUFF system using MM5 predicted fields as the first guess. Volume sources in California. 72 hours simulation for each case

29 Emissions (1) Point sources Meteorological sites Chemical sites TBLG 65 km BARK USCG BLIS SOLA Developed emissions estimates for the Tahoe basin: 7.3 NO x (tn/day). ECHO Data from 42 surface, 2 upper air, and 49 ozone stations. 45 km

30 Emissions (2) CALMET/CALPUFF CALPUFF 250x265x8 1 km Sources

31 CALMET Predicted Winds: August Y direction (km) 150 Y direction (km) X direction (km) X direction (km) Night Day

32 Regional background ~0.4 µg/m 3 Accounted for 81 to 98% of the observed HNO 3 Local sources responsible for 70% of the observations

33 HNO 3 Bytnerowicz et al.

34 Summary of Modeling Results The amount of transported HNO 3 was low (~0.4 µg/m 3). 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.

35 Summary and Conclusions Measurement Component: HNO 3 is the most important N species in terms of overall deposition. HNO 3 is regional with a significant local component. The sources of NH 3 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.

36 Much Nicer Than Most of the Places I Work

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