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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 - Water Quality
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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.
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 File)
Water
Quality Monitoring Protocols and Sampling Guidelines
(3.05 MB 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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