1. When people care problems can be solved

2. LAKE TAHOE: A CASE STUDY FOR ADDRESSING THE DECLINE OF CLARITY IN A SUB-ALPINE LAKE JOHN REUTER and GEOFF SCHLADOW

3. Lake Tahoe UC Davis San Francisco Los Angeles

4. TAHOE ENVIRONMENTAL RESEARCH CENTER TERC conducts research, education and public outreach on lakes and their surrounding watersheds and airsheds. TERC provides objective scientific information for restoration and sustainable use of the Lake Tahoe Basin and inland waters in general. terc.ucdavis.edu

5. 11000 sq ft labs, offices 1500 sq ft outreach 3000 sq ft class rooms

6. LAKE TAHOE BASIC FACTS 11 th deepest lake in the world Maximum Depth = 501 m Mean Depth = 330 m Lake Surface Area = 500 sq. km Watershed Area = 800 sq. km Shoreline length = 115 km Ultra-oligotrophic Monomictic 63 Inflowing streams 1 Outflowing stream Mean residence time ~ 600 yrs Altitude = 1895 m Latitude = 39 °N

7. Cause for Concern 30 m (100 ft target)

8. CONTRIBUTORS TO CLARITY DECLINE AT LAKE TAHOE

9. POLLUTANTS OF CONCERN Ultra-fine soil particles Nutrients and algal growth

10. Land disturbance - soil erosion

11. Wetlands Removal Before

12. After

13. Traffic Congestion Photo – Larry Prosor

14. Road Construction

15. Atmospheric Deposition

16. Angora Fire - 3100 acres burned - 253 homes lost

17. Stream Runoff

18. Urban Runoff

19. ORIGINALLY

20. NOW

21. Lake Tahoe Water Quality Management Approach l What is the problem and what causes it? l What are sources and relative contributions of nutrients and fine-sediments? l How much of a reduction is needed to achieve the desired conditions? l How will this reduction be achieved?

22. TMDL Overview Total Maximum Daily Load TMDL = science based water quality restoration plan

23. Nutrient & Fine Sediment Budget

24. Nitrogen

25. Phosphorus

26. Particle Number <20 µm

27. Lake Tahoe Clarity Model DLM Hydrodynamic/Thermodynamic Model Tributaries Climate, Precipitation Land Use Atmospheric Deposition Algal Growth Lake N, P, Si Inorganic Particles Loss Secchi Depth Light Scattering & Absorption Groundwater Tributaries Climate, Precipitation Land Use Atmospheric Deposition

28. WATER QUALITY INPUTS STREAMS [DO, BOD, CHLa, P (PP, THP, POP, RP), N (NO3, NH4, DON, PN, PON), # PART] G/WATER [P (THP, RP), N (NO3, NH4, DON), # PART] ATMOS [P ( THP, POP, RP ), N ( NO3, NH4, DON) ] PHYSICAL FORCING INPUTS MET [U, SW, LW, RH, T, PRECIP] STREAMS [Q, T] GROUNDWATER [Q] LAKE MODEL PHYSICS BIOLOGY

29. 75% Reduction from Urban Runoff to Meet WQS of 30 m for Secchi Depth

30. Application to Grand Lake

31. Science should be part of decision-making

32. Importance of Data Knowledge Nice existing data base Future collection to answer specific questions to guide solutions (e.g. what is an appropriate target for water clarity?)

33. Solutions require: Shared responsibility Multi-year commitment Stakeholder participation