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Since 1960's (Squaw Valley Olympics) Lake Tahoe has been undergoing eutrophication1 at a fairly rapid rate.
In the 1970's and 1970's it was loosing about 1 foot per year in clarity due to development.
Conservations efforts reduced that to about 1/2 foot per year in the 90's
See Why is it so blue? at Tahoe Info.
Turbidity increases / Limnology:
Early rcds 130' 1968 102' 1992 78' late 1990's 65' 2002 78' 2004 72'See Clarity at TERC
Clairty is best in Feb. and Mar. (85-103') and worse in May (62-82') after rains and snow melt.
The flood of 1997 and heavy snows in 2010 produced a dramatic reduction in clarity.
Settling basins and wetlands capture and treat soil particles down in the 50 to 60 micron size range, while the particles of interest, those with attached, bio-available Phosphorus are in the 5 micron size range.
Sources of particulate matter:
Fine sediment, much of it resulting from land disturbance in the basin, affects each clarity measurement about twice as much as the effect from floating algae.
The Lake Tahoe Atmospheric Deposition Study (LTADS) conducted by the California Air Resources Board in 2002-2003 found that airborne input of nutrients and fine sediment to Lake Tahoe's surface is significant. Most of the airborne input affecting the Lake is generated within the Basin, not from outside as previously thought. The main sources of airborne pollutants are motor vehicles, wood burning, and road dust. 2
A study by Taylor et al. (2003) explored near shore clarity by collecting field measurements of turbidity in (NTU - nephelometric turbidity units) between September 2001 and August 2003. The study showed moderate to extremely elevated near-shore turbidity in the south shore area. Specifically, the mouth of the Upper Truckee River was characterized as having extremely elevated turbidity, while the Al Tahoe intervening zone, Bijou Creek, Tahoe Keys Marina and Ski Run Marina showed moderate levels of turbidity. 2
Water Flow Data: (Inflow - Outflow)|
One reason for the clarity is that 36-40 % of the precipitation falling into the Lake Tahoe Basin falls directly upon the Lake (It has a watershed-to-lake ratio of only 1.6:1, much smaller than the 10:1 value found for a typical watershed.)
Flows of ten streams (e.g., Upper Truckee River, Ward
Creek, Trout Creek, Third Creek, Logan House Creek, Incline Creek, Glenbrook Creek,
General Creek, Edgewood Creek and Blackwood Creek) are estimated to account for up
to 50-55 percent of the total stream input.
Source: Marjanovic, Lake Tahoe Basin Characterization & Assessment of Exemplary Programs for Water Quality Crediting and Trading Feasibility Analysis, 1989 |
Also: Truckee River Chronology at nv.gov, Oct, 2011
and Rush, F. Eugene, "Water Resources-Information Series Report 17: Bathymetric Reconnaissance of Lake Tahoe, Nevada and California," Prepared cooperatively by the Geological Survey, U.S. Department of the Interior and the Division of Water Resources, Department of Conservation and Natural Resources, State of Nevada, Carson City, Nevada, 1973.
Mean annual precipitation is 31 in. The middle quartile values are from 21 - 43 in/year.
The capacity of Lake Tahoe id 39 trillion gallons.
The 1935 Truckee River
Agreement, limited the operating range of Lake
Tahoe's surface elevation to between 6,223.0 feet (its
natural rim) and 6,229.1 feet. The dam at Tahoe City is 6 ft high.
Because the volume of the lake is so large (156 km3) and its hydraulic residence time so long (about 650 years), its eutrophication may be essentially irreversible.
Can be restored to 100' by cutting pollution from runoff, chimney soot, dust and vehicle emissions by 35%
High turbidity areas Emerald Bay and off Tahoe City and South Shore and Incline
Temperature has increased 1/3° from 1969-2006 from global warming.
WHY ARE SHORELINE SCENIC RATINGS DECLINING?
TRPA has divided the land area in the Lake Tahoe Basin into three priority watersheds. Priorities are based on many characteristics including topography, soil erodibility, and soil type, proximity to streams, etc.
They have established a schedule for implementing Best Management Practices or BMPs for property owners in each of these watersheds.
The Lahontan Regional Water Quality Control Board is develop a program, TMDL (Total Maximum Daily Load) (mandated by the Clean Water Act) to limit the flux of nutrients and fine sediment to the Lake. is a water quality restoration plan, mandated by the federal Clean Water Act, designed to reduce the amount of pollution contributing to the decline of Lake Tahoe's clarity.
1861-1901 Clear-cut logging of an estimated 60 percent of the Basin during the Comstock-era to supply lumber for silver mines in Nevada. 1899 Lake Tahoe Reserve established to address the treatment of the land 1905 became Tahoe National Forest 1910's Effort to make it a National Park failed 1960-1974 Congressional acts passed to resolve controversies over uses of public lands. Clean Air (1963) and Clean Water Acts (1972), the National Environmental Policy Act (1969). 1969, Tahoe Regional Planning Agency (TRPA) created by the United States Congress was the first bi-state regional environmental planning agency in the country. 1985 California Attorney General, John Van de Kamp, filed suit in 1985 to prevent TRPA from granting any further permits for development. Developers were outraged but lost all of their court appeals. 1950's UC Davis starts studying the basin's ecological problems and their causes. 1990 Tahoe National Forest Plan sets stringent environmental standards 1997 President Clinton and Vice President Gore attend the first annual Lake Tahoe Summit They announced the Tahoe Restoration Act which authorized $300 million over 10 years for restoration of the Tahoe Basin. 1997 Environmental Improvement Program (EIP) - a coordinated effort designed to protect and restore Lake Tahoe's natural resources. The program includes a list of erosion control, land acquisition, watershed, and forest ecosystem restoration projects. 2000 Congress authorizes $300 million towards restoration of water quality in Lake Tahoe over a period of 10 years. 2005 The Tahoe Center for Environmental Sciences (TCES) building at Sierra Nevada College in Incline Village started. Fundraising started in 1994 $13 million in donations, including $2.6 million from the David and Lucile Packard. UC Davis and Sierra Nevada College.
PPr - Primary Productivity - The numeric criterion for algal productivity (mg C/m2/yr.
Source: Tech Report 3-15 2
Groups Solving Problems:
Current TRPA regulations require all homes in the Tahoe Basin to be retrofit with Best Management Practices or BMPs.
Backyard Conservation Program at Lake Tahoe is part of a cooperative national program
with the Natural Resources Conservation Service, the National Association of Conservation Districts
and the Wildlife Habitat Council.
University of California, Davis, Tahoe Environmental Research Center (TERC)
League to Save Lake Tahoe (The "Keep Tahoe Blue" people) formed in 1957 is a privately funded, non-profit, public benefit membership organization. Through our Advocacy and Monitoring program, the League acts as the primary watchdog for Lake Tahoe's environment. One of our fundamental goals is to ensure that laws and plans intended to protect the Lake Tahoe Basin are adequate and effectively enforced. To this end, the League closely monitors the work of the Tahoe Regional Planning Agency.
John Muir Institute of the Environment at the University of California at Davis.
UNR Academy for the Environment
NASA's Jet Propulsion Lab with UC Davis have installed a network of research and monitoring buoys on Lake Tahoe.
Tahoe Integrated Information Management System (TIIMS) is a bi-state, multi-agency information management system developed to house and disseminate wide-ranging information about Lake Tahoe Basin planning and restoration efforts via the Internet.
Tahoe Resource Conservation District (TRCD) and the Natural Resources Conservation Service (USDA/NRCS), working with their many partners, will protect and enhance the water quality of Lake Tahoe through reduction of impacts associated with the development and management of private residences in the Basin.
California Tahoe Conservancy - The Conservancy is an independent State agency within the Resources Agency of the State of California. It was established to develop and implement programs through acquisitions and site improvements to improve water quality in Lake Tahoe, preserve the scenic beauty and recreational opportunities of the region, provide public access, preserve wildlife habitat areas, and manage and restore lands to protect the natural environment.
Tahoe Interagency Monitoring Program (LTIMP) created to acquire and disseminate the water quality information necessary to support science-based environmental planning and decision making in the basin. The LTIMP is a cooperative program with support from 12 federal and state agencies with interests in the Tahoe Basin.
Lahontan Regional Water Quality Control Board - The mission of the RWQCBs is to develop and enforce water quality objectives and implementation plans which will best protect the beneficial uses of the State's waters, recognizing local differences in climate, topography, geology and hydrology. Lahontan works to preserve and enhance the quality of California's water resources and ensure their proper allocation and efficient use for the benefit of present and future generations.
1. Eutrophication is the enrichment of an ecosystem with chemical nutrients, typically compounds containing nitrogen or phosphorus. Eutrophication is considered a form of pollution because it promotes plant growth, favoring certain species over others and forcing a change in species composition.
The Natural Resources Conservation Service (NRCS) has several national programs to provide technical and financial assistance for conservation and restoration projects on private lands. These programs include the Environmental Quality Incentives Program (EQIP), the Wetland Reserve Program (WRP), and the Wildlife Habitat Incentives Program (WHIP).
Truckee River Chronology at nv.gov, Oct, 2011