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Lake Tahoe is one of the three clearest lakes of its
size in the world. The water quality of the Lake, and
its tributaries, highly contributes to the scenic quality
of the Lake Tahoe Basin, yet water quality depends on
a fragile balance among soil, vegetation, and human impact.
The focus of water quality protection in the Basin is
to minimize human disturbance, and to reduce or eliminate
the addition of pollutants that result from development.
Seventy percent of the Earth´s surface is covered
with water, only three percent of that water is freshwater
that can be consumed by humans. Of that three percent,
99 percent, is frozen in polar ice caps. These facts aid
in the conclusion that water is an extremely valuable
resource that must be protected.
Lake Tahoe is experiencing a phenomenon known as cultural
eutrophication, which is the Lake´s response to accelerated
inputs of nutrients to the Lake due to development in the Basin.
Impervious land coverage, land disturbance, and atmospheric
deposition are typical products of development that impact the
Lake´s nutrient and sediment load.
 Since
Lake Tahoe does not benefit from the flushing action of
runoff like other water bodies such as Fallen Leaf Lake,
correcting Lake Tahoe´s imbalanced nutrient and
sediment load is a difficult task. A drop of water resides
in Fallen Leaf Lake approximately eight years, described
as “residence time.” The entire volume of
water in Fallen Leaf Lake exchanges, or is completely
flushed, approximately every eight years. In contrast,
Lake Tahoe has a remarkable residence time of 700 years,
making the Lake behave like a sink without a drain. Preventing
additional sediment from flowing into Lake Tahoe is a
complicated endeavor and controlling the sources of nutrients
is paramount to reversing the loss of water clarity.
Since the early 1970s, Congress has passed legislation
designed to protect and preserve the Earth´s supply
of freshwater. Lake Tahoe´s designation as an Outstanding
National Resource Water (ONRW) is a result of these legislations.
With this designation, Lake Tahoe is provided the highest
level of protection under the antidegradation policy and
no further degradation should be permitted. (Water
Quality Standards Handbook, Second Edition, 1993)
In 1972, Congress enacted the Clean Water Act (CWA)
to restore and maintain the chemical, physical, and biological
integrity of the Nation´s waters. At that time,
point source discharges from industrial and urban sources
were severely impairing lakes and streams throughout the
country. Now, much of the damage is from nonpoint sources
such as, urban development runoff, agriculture, silviculture,
and animal feeding operations. In 1987, Congress amended
the CWA to authorize programs and resources to address
nonpoint source pollution. (Lake Tahoe Source Water
Protection Program Project Report, TRPA, 2000)
The Safe Drinking Water Act (SDWA) of 1974 authorized
the EPA to set standards to protect users from any contamination
in public water systems that may have adverse heath effects.
In 1986, the EPA established or revised standards for
83 contaminants listed by Congress. The SDWA was amended
again in 1996 to include funding, prevention, regulatory
improvements, consumer information along with a requirement
that states prepare a source water assessment and implement
source water protection programs. (Lake Tahoe Source
Water Protection Program Project Report, TRPA, 2000).
Sources:
Draf TRPA EIP 2003 Update
Draft TRPA 2001 Threshold Evaluation
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WQ-1 Littoral Lake Tahoe
The shallow areas (and therefore the littoral
zone – out to 100 meters depth) are the first to receive nutrient
and sediment loads from tributary and groundwater sources.
Turbidity thresholds numerical standards were set to indicate
trends in loading of sediment, and are also affected by algal
productivity where the management standards are for phosphorus,
nitrogen, and iron loading. The basis for the recommendation
suggests that shallow areas of the lake should show trends
with respect to phytoplankton and periphyton (attached) algal
production that are similar to those in pelagic waters for
phytoplankton. The indicator unit for this threshold is turbidity.
WQ-2 Pelagic Lake Tahoe, Deep Water
Average Secchi depth, December-March, shall not
be less than 33.4 meters.
WQ-2A Capital Improvement Program
Clarity, winter, pelagic Lake Tahoe
WQ-2B Best Management Practices (BMPs)
Clarity, winter, pelagic Lake Tahoe
WQ-3 Pelagic Lake Tahoe, Phytoplankton
Primary Productivity
Phytoplankton primary productivity and transparency
standards were set to identify the desired “end state” so
that it could be determined when enough has been done to protect
the unique clarity of the Lake. Both pelagic and littoral
thresholds call for major reductions of nitrogen and phosphorus
loading measured during the early 1970s. Indicator units
include Secchi Depth, and phytoplankton primary productivity.
WQ-4 Tributaries
Streams receive nutrient and
sediment loads from overland flows and deliver these loads
to the littoral and pelagic zones of the Lake. Indicators
include annual average concentrations per California and Nevada
standards for nitrogen, phosphorus, and iron, and 60 mg/l
at 90th percentile for suspended sediment.
WQ-5 Stormwater Runoff, Surface Water
Surface runoff from urban areas carries chemical
loads in addition to nutrients and sediment. Indicators include
TRPA surface water discharge standards.
WQ-6 Stormwater Runoff, Groundwater
Infiltrated surface runoff that does not enter
tributaries or the Lake directly
eventually discharges to streams or the Lake
over time through groundwater
discharge. The indicator units, which include
TRPA discharge standards to
groundwater, take into consideration the filtering
effect of the soil profile.
WQ-7 Other Lakes
Since the quality of other lakes
of the Region affect the quality of Lake Tahoe,
standards for “Other Lakes´ have been established.
Indicators include water quality standards established by
California and Nevada.
Click
here for more information about water quality indicators from
the TRPA 2001 Threshold Update
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A goal of TIIMS is housing documents about the past, present and future environmental
research conducted in the Lake Tahoe Basin. Scientific research
conducted by organizations, agencies, and universities aims
to detect, for example, water clarity and discover ways to
monitor and ultimately improve environmental conditions.
Ongoing research efforts collecting baseline data will help
regulatory agencies establish regulations and develop limits
and indicators designed to improve environmental health.
Ongoing water quality studies include: the Total Maximum Daily Load (TMDL)
development research that will link the Lake Tahoe Clarity
Model with an interacting watershed model to reduce loads
into Lake Tahoe; Impacts of Motorized Watercraft; and Urban
Runoff Characterization and Treatment as part of TMDL development
and other monitoring programs. The Science Advisory Group
(SAG) continues discussing the objectives and prioritization
of these and other studies based on Key Management Questions
for Lake Tahoe. SAG advises the Tahoe Regional Planning Agency
(TRPA) on expenditures for Threshold Update research that
potentially relates to all nine TRPA environmental thresholds
and economic models for the Basin.
As SAG reviews the Research Agenda, the Lake Tahoe Interagency Monitoring
Program (LTIMP) committee has identified water quality issues
which drive identification for further research needed to
meet water quality objectives of TRPA, and the other LTIMP
members such as the California Regional Water Quality Control
Board - Lahontan Region, and the Lake Tahoe Basin Management
Unit - USDA Forest Service. In addition, the Water Quality
Working Group (WQWG), which strives to increase and maintain
communication and collaboration among water quality interests
in the Lake Tahoe Region, also assists TRPA in identification
of the current major issues confronting water quality agencies,
including research needs.
With assistance from the SAG, LTIMP, and WQWG, TRPA is able to identify and
direct limited funding to priority studies that will provide
critical information to managers and policy makers.
Participants in water quality research in the Lake Tahoe Basin include: USDA
Forest Service, USDA Air Resource Specialists, USDA Natural
Resource Conservation Service, US Army Corps of Engineers,
US Geological Survey, EPA, University of Nevada, Reno, Desert
Research Institute, University of California, Davis, Lahontan
Regional Water Quality Control Board, California Tahoe Conservancy,
Tahoe Regional Planning Agency, Various consultants under
contract to Basin agencies and the federal agencies.
TIIMS is always searching for more documents to include in this section so
please contact tiims@trpa.org
with possible links to other water quality research.
Source:
2003 EIP Update
Documents
Volume I of the 208 plan: Water Quality Management Plan for the Lake Tahoe Region (24.3 MB Zip File)
Water
Quality Monitoring Protocols and Sampling Guidelines (3.05
MB Zip File)
TRPA
Watershed Map
Lake
Tahoe Water Quality and Shore Erosion Study
Lake
Tahoe: Reservoir of History, Body of Hope
Carpenter, S.R., and Cottingham, K.L. 1997. Resilience
and Restoration of Lakes. Conservation Ecology [online]
1(1): 2.
Forney, W., Richards, L., Adams, K.D., Minor, T.B., Rowe, T.G., LaRue Smith,
J., and Raumann, C.G., 2001. Land Use Change and Effects
on Water Quality and Ecosystem Health in the Lake Tahoe Basin,
Nevada and California. OFR_01_418, USGS, 29 p.
Forney, W., Raumann, C., Minor, T.B., LaRue Smith, J., Vogel, J., and Vitales,
R. 2002. Land Use Change and Effects on Water Quality and
Ecosystem Health in the Lake Tahoe Basin, Nevada and California:
Year-1 Progress. OFR_02_014. USGS, 19 p.
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