When people care problems can be solved
LAKE TAHOE: A CASE STUDY FOR ADDRESSING THE DECLINE OF CLARITY IN A SUB-ALPINE LAKE JOHN REUTER and GEOFF SCHLADOW
Lake Tahoe UC Davis San Francisco Los Angeles
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
11000 sq ft labs, offices 1500 sq ft outreach 3000 sq ft class rooms
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
Cause for Concern 30 m (100 ft target)
CONTRIBUTORS TO CLARITY DECLINE AT LAKE TAHOE
POLLUTANTS OF CONCERN Ultra-fine soil particles Nutrients and algal growth
Land disturbance - soil erosion
Wetlands Removal Before
After
Traffic Congestion Photo – Larry Prosor
Road Construction
Atmospheric Deposition
Angora Fire acres burned homes lost
Stream Runoff
Urban Runoff
ORIGINALLY
NOW
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?
TMDL Overview Total Maximum Daily Load TMDL = science based water quality restoration plan
Nutrient & Fine Sediment Budget
Nitrogen
Phosphorus
Particle Number <20 µm
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
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
75% Reduction from Urban Runoff to Meet WQS of 30 m for Secchi Depth
Application to Grand Lake
Science should be part of decision-making
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?)
Solutions require: Shared responsibility Multi-year commitment Stakeholder participation