United States
Environmental Protection
Agency
Environmental Monitoring Systems
Laboratory
Las Vegas NV 89114
Research and Development
EPA-600/S4-81-026 Apr. 1981
Project Summary
Meadowland Natural
Treatment Processes in the
Lake Tahoe Basin: A Field
Investigation
F. A. Morris, M. K. Morris, T. S. Michaud, and L. R. Williams
An area planning agency for Lake
Tahoe suggested that natural
treatment processes in stream envi-
ronment zones could be used to
control nutrients and sediment flow-
ing toward the lake. The purpose of
the study was to measure the amount
of constituents filtered from runoff
water by natural processes; the study
was a survey of existing conditions
only, and no attempt was made to
alter those conditions.
Samples were collected from seven
tributary systems in the South Lake
Tahoe area and analyzed to determine
nutrient and sediment load before,
during, and after storm episodes, and
during seasonal weather changes.
All sheet-flow systems demon-
strated filtration of pollutants and
sediments to some extent; however,
variables such as beaver dams and
livestock grazing together with storm
episodes yielded inconsistent results.
It was concluded that sheet flow can
be an effective way of treating runoff
waters, and that ponding of runoff
waters can also reduce chemical and
sediment loads.
It was recommended that further
study of the tributary systems be
undertaken to determine impact of
several untested variables, and that a
test be initiated to determine the feasi-
bility of diverting stream flow to sheet
flow to enhance natural filtration
processes.
This Project Summary was develop-
ed by EPA's Environmental Monitor-
ing Sysjtems Laboratory. Las Vegas,
NV, to announce key findings of the
research report that is fully docu-
mented in a separate report of the
same title (see Project Report ordering
information at back}.
Introduction
The clear water of Lake Tahoe in
Northern California is currently in
danger of being clouded and muddied by
surface water runoff from land develop-
ment and construction activities in foot-
hills surrounding the lake. Only two
other lakes in the world have water as
clear and clean as Lake Tahoe: Crater
Lake in Oregon and Lake Baikal in the
Soviet Union. Maintaining the clarity of
Lake Tahoe for future generations of
Americans to enjoy is currently a top
priority of regional, state, and federal
interests and the subject of continuing
attention by the representatives of
those interests. Regional planning
agencies are charged with responsibil-
ity for making decisions about the future
handling of surface waters entering the
lake, as the nutrients and sediments
they carry are the greatest current
danger to the purity of the lake water.
Background of the study. The study
was conducted at the request of the U.S.
Environmental Protection Agency in
San Francisco (Region IX). The results
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are to be used by the responsible
agencies to develop a n Areawide Waste
Treatment Management Program for
Lake Tahoe. The management program
was mandated by passage of the 1972
Federal Water Pollution Control Act,
Section 208 (Public Law 92-500).
The Problem. The great volume of
water in Lake Tahoe could effectively
dilute large amounts of nutrients and
sediment if the lake waters were totally
mixed. However, increased algal growth
in waters near the shore had been
observed.
An area planning agency had sug-
gested that natural treatment processes
in stream environment zones (e.g.,
marshes, meadowlands, watercourses,
drainageways, and floodplains) could be
used to control nutrients and sediment
flowing toward the lake. A field investi-
gation was needed to evaluate changes
in the quality of runoff waters as they
passed through meadowlands.
Purpose of the study. The purpose of
the study was to measure the a mount of
nutrients and sediments in water
(1) entering and leaving natural
meadowlands around Lake Tahoe, (2) at
the outlet of streams draining into the
lake, and (3) at sites along those
streams. In addition, stream depth,
width, and water velocity were
measured, and air and water
temperatures at each study site were
recorded. Special studies were under-
taken to obtain additional information
from the area. The runoff from roads in
the winter was studied to determine the
nutrients being washed from roadways.
Volcanic cinder, used as a road abrasive
in winter, was studied for its nutrient
contribution. In a special study for the
U.S. Forest Service, the amount of pol-
lutants in Tallac Lagoon and its main
tributary were measured. Finally, a
special study of a specific site on the
Trout-Cold Creek stream system was
undertaken in an attempt to pinpoint the
source of severely elevated levels of
nitrogen compounds discovered during
the course of the study.
Description of the Study Area
The Tahoe Basin is located on the
California-Nevada border. Two-thirds of
the Basin is in California, and one-third
is in Nevada.
The striking beauty of the Basin
resulted from earthquake faulting activ-
ity which dropped the floor of the Basin
and raised the surrounding mountains.
The steep-sided depression formed by
the earth movements filled with water,
resulting in Lake Tahoe.
The surface area of Lake Tahoe is
122,000 acres; the surface area of the
surrounding land is 202,000 acres.
About one-half of the land surrounding
the lake has a slope steeper than 20
percent. Most of the 45,000 acres of
land with a slope of 10 percent or less is
located at the south end of the lake.
The natural level of the outlet of the
lake at Tahoe City is 6,223 feet above
sea level. A low dam provides regulation
of the lake level for water storage. The
total amount of water in the lake subject
to regulation is about 745,000 acre-
feet.
Runoff from rainfall and snowmelt
travels into Lake Tahoe through 64
separate watersheds of varying types.
These tributary streams provide the link
between land and soils, and the water
quality of the lake. Stability of the soils
over which the water courses vary, with
very unstable granitic soils susceptible
to erosion on the south and east, and
more stable volcanic and metamorphic
solid soils in the north and west. Be-
cause the soils surrounding the lake
tend to be sterile, and the growing
season short, vegetation is difficult to
reestablish if it is disturbed by land
development.
Theoretical Assumptions
Underlying the Study
Studies of the effect of water flowing
over meadowlands have shown that
stream environment zones can provide
a natural barrier to sediment. Other
studies show that nearly all phosphorus
and most nitrogen in surface runoff is
attached to sediment. Therefore, by
removing the sediment, most of the
nutrients should also be removed.
Research Questions
Data were collected to provide
answers to the following questions:
1. Does runoff water in Lake Tahoe
Basin show decreased amounts of
sediments and plant nutrients
after crossing natural meadow-
lands?
2. How does change in loading and
flow rate affect the natural treat-
ment?
3. Does algal growth in nearshore
waters reflect nutrient contribu-
tions from tributary streams?
4. Is runoff from roads a major 4
source of nutrients for the Lake "
Tahoe tributary system, and does
volcanic cinder contribute further
to nutrient loading?
5. Does the quality of water change
as it flows through Tallac Lagoon
and its major tributary?
6. What is the source of elevated
levels of nitrogen in Trout Creek?
Procedure
Sample sites and collection of data.
Sites for collection of water samples
were established as shown on the
Figures 1 and 2. Key to the location
symbols on the maps is as follows:
Site A - Trout Creek
Site B - Upper Truckee River (less
than 1 year of data)
Site C - Angora Creek and Sawmill
Road Drainage
Site D - Tallac Creek
Site E & F - Blackwood Road
Drainage and Chonokis-Glen
Road
Site G - Tallac Lagoon (less than 1
year of data)
Sites LL1 and LL2 - Lake Tahoe
Nearshore (unimpacted control
area)
Site DL1 - (Nearshore, Off Tallac
Creek)
Site BL1 - (Nearshore, Off Upper
Truckee)
Site EL1 - (Nearshore, Blackwood
. Drainage)
Sites for collection of water samples
were established along seven stream
tributary systems (A through G above),
consisting of four streams and three
meadowland drainage areas. Stakes
were placed at the sampling sites to
ensure that measurements were taken
in the same location during the samp-
ling period. Data collection sites were
established in five locations along the
shore of Lake Tahoe, three in impacted
areas affected by tributary streams and
two in unimpacted areas.
Samples were taken from September
1977 through August 1978; however,
some sample sites were added after the
study began and less than a full year of
data were collected at those sites.
Samples were taken at biweekly inter-
vals during the winter and weekly inter-
vals during the rest of the year. Winter
lasts approximately 6 months in the
Tahoe region.
Methods of analysis. Water samples
were analyzed to determine levels of
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PlacerCa,
El Dorado Co
0 Miles 5
0 Kilometers 8
ww
I-Z-I Sampling Areas
£*•"
^ /#
V v
1. Lake Tahoe meadowland sampling system locations.
(1) nitrogen, phosphorus, and carbon
nutrients; (2) chlorophyll a and fecal
coliform; (3) pH, alkalinity, conductivity,
residue, dissolved oxygen, and turbidity.
The techniques used for analysis of
water samples followed procedures
from Standard Methods for the Exami-
nation of Water and Waste Water
(APHA, 1975) and Methods for Chemi-
cal Analysis of Water and Wastes (EPA,
1974). Where comparison was desired,
results were tested for significance
using a standard one-way analysis of
variance. Significance was determined
at the .05 level of confidence. The data
were entered in STORET, a computer-
ized water quality data base.
Limitations of the study. Variables not
tested include: (1) percent vegetation
cover; (2) beaver dams; (3) ground frost;
(4) snow cover; (5) sheet flow; (6) pollu-
tant sources; (7) soil type; and (8) effect
of livestock grazing. The study was de-
limited to marshlands or meadowlands
in the South Lake Tahoe area through
which water is impacted by a variety of
land-use sources. The study was a
survey of existing conditions, and no
attempt was made to alter those condi-
tions.
Results
All sheet-flow systems demonstrated
filtration of pollutants and sediments to
some extent; however, variables such
as beaver dams and livestock grazing
together with storm episodes yielded
inconsistent results.
Site A - Trout Creek. Substantial re-
ductions in concentrations of pollutants
and sediment occurred in that portion of
the stream and its tributary. Cold Creek,
which entered sheet flow. The upper
portion of both creeks is channelized.
After the two streams converge, the
flow toward the lake is impeded by
beaver dams that cause about 50
percent of the water to leave the
channel boundaries and flow across
meadowland. Seasonal trends indica-
ted fair to excellent reductions of all
constituents except ammonia-nitrogen.
The greatest reductions were noted
during fall and winter when the beaver
dams were intact. The percent of
change in the levels of sediment and
nutrients in Trout Creek during storms
provides evidence of its capacity to
absorb large, sudden loads of pollutants.
Site B - Upper TruckeeRiver. This sys-
tem contributes 23 percent of the
annual runoff into the lake. This site
was added to the study in June of 1978
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Placer Co.
El Dorado Co.
;-' Hotise Cr.
Cascade
Lake
Scale in Miles
0 1 2
Sampling Areas
Figure 2. Lake Tahoe nearshore sampling sites location map.
to determine if the large meadow asso-
ciated with it was responsible for any
filtering action. The stream remained
channelized through the data collection
period A slight reduction in participate
organic carbon was noted. All other
parameter values increased during all
observations.
Site C - Angora Creek and Sawmill
Road Drainage. Substantial contribu-
tions of surface water runoff entered
Angora Creek meadowland system be-
tween the two sample sites, doubling
the flow. Sediment and nutrient loading
increased up to four times at the second
downmeadow sample site. All constitu-
ents showed mean seasonal increases
or no change in concentration between
sample sites. The streams remained
channelized except during storm epi-
sodes, when reductions in nutrients and
sediment were observed.
The Sawmill Road Drainage is com-
prised entirely of snowmelt runoff from
a small, isolated area, and flowed only
from March 1978 to May 1978. Con-
centrations at the inlet to the meadow-
land system were usually below the
detection limits of the analyses.
Site D - Tallac Creek. The upper reach
of Tallac Creek flowed the entire year.
Groundwater contributions from num-
erous springs increased the annual flow
by 88 percent, which was not monitored.
Filtering efficiency of the channelized
portion of the stream was at least par-
tially due to the result of this dilution by
spring water. That portion of the Creek
which traveled in sheet flow across a
meadowland showed large net in-
creases in nutrient and sediment
concentrations. This meadowland is
used for grazing during the snow-free
period of the year and animals have
caused extensive disruption of the
ground surface and vegetation cover.
However, this meadowland system
consistently removed all nitrate and
nitrite-nitrogen overloads during
episodic flows.
Sites E andF - B/ackwood Road Drain- t
age and Chonokis-Glen Road Drainage.
Blackwood Road Drainage system con-
sistently showed substantial reductions
of sediment and nutrients after passing
as sheet flow over meadowlands. In all
measurements, even during episodes of
high runoff, this system consistently
filtered between 70 and 97 percent of
sediment alone from the water. In addi-
tion, all nutrients tested showed a
considerable reduction in concentration
after sheet flow.
The Chonokis-Glen Road Drainage
system had limited flow during the
study. Some pollutants were below the
limits of analytic detection as water
entered the sample site; however,
organic carbon, suspended solids, and
specific conductance were reduced
within the meadowland.
Site G - Tallac Lagoon. Tallac Lagoon
is located south of a residential develop-
ment and was included late in the study
to provide information to the U.S. Forest
Service about the treatment capabilities
of the lagoon. The lagoon is lined by
vegetation and water ponds within its
boundaries. Results from the limited
sampling showed reductions of sedi-
ment, nutrients, and turbidity.
Sites LL 1 and LL2 - Lake Tahoe Near- J
shore (unimpacted); and Sites DL 1, BL 1, "
and EL1 (impacted). Nearshore samp-
ling yielded variable data within and
between stations; however, there were
no significant differences in the con-
stituents in the water between
impacted and unimpacted lake areas.
Street runoff. Results of the study of
street runoff indicate that roadways
contribute high levels of nitrogen, and
volcanic cinder adds high levels of
phosphorus to the runoff waters.
Air and water temperature, storm
incidence, and stream flow. These
results can be found in the study from
which this summary was written.
Discussion
Of the systems that exhibited sheet
flow, only Blackwood Road Drainage
and, to a lesser extent. Trout Creek and
the Chonokis-Glen Road Drainage
system demonstrated reductions in
sediments and pollutants after
meadowland sheet flow. Tallac Lagoon
demonstrated reductions primarily due
to the ponding of water. Since nearly all
phosphorus and most nitrogen in
surface runoff is attached to sediments,
the removal of suspended solids results
in the removal of these constituents
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from the water. Adsorption to clays and
other substances can also contribute to
organic carbon losses.
The reduction of the constituents in
the water flowing across meadowlands
in the Tahoe Basin can be credited both
to sedimentation and to the interaction
of the soil-water complex. The oxidized
layer of submerged soils in the
meadowland acts as a chemical trap for
phosphorus, iron, and silicon. Other
researchers note that the oxidized and
reduced layers together cause a loss of
nitrogen in its usable forms and suggest
that in the case of orthophosphorus, the
rate of sorption by the sediments
decreases with decreasing concentra-
tion of overlying water; therefore, the
efficiency of the meadowlands in con-
stituent removal would be greatest
when the concentrations of the constit-
uents are highest.
All meadowlands with sheet flow that
had measurable amounts of nitrate and
nitrite-nitrogen exhibited significant
reductions of this constituent; however,
the filtering efficiency dropped off
dramatically during the high flows
accompanying rainstorms. Since nitrate
and nitrite-nitrogen is a dissolved
fraction and is not readily adsorbed to
the soil surface a biological mechanism
for reduction is suggested.
The nearshore lake sampling resulted
in a limited data base. A one-way
analysis of variance was not significant
between stations when tested at the .05
level of confidence. The results suggest
that nearshore lake stations are
homogeneous with relation to most
parameters. Goldman has stressed the
importance of continuous monitorinc of
tributary and nearshore waters utilizing
measures of primary productivity and
heterotrophic activity. Data suggest that
within the littoral zone of Lake Tahoe
the impacts due to tributary inputs are
dispersed over short periods of time and
short distances to create a relatively
homogeneous nearshore environment.
Conclusions
Because consistent reduction in
nutrients and sediment was not demon-
strated during all seasons, the results of
the study are inconclusive. Instances of
sheet flow enhancing the reduction of
sediments and nutrients occurred,
showing the probability that sheet flow
can be an effective way of treating
runoff waters. Ponding of runoff waters
was also effective in reducing chemical
and sediment loads.
Recommendations
It is recommended that further study
of the tributary systems to Lake Tahoe
be undertaken to determine the impact
of the untested variables on the reduc-
tion of constituents in the water enter-
ing Lake Tahoe. In addition, the feasibil-
ity of converting channelized streams
through meadowlands to sheet flow
should be determined, and overload
capacities and functional longevity of
meadowland treatment systems should
be tested. The nature of treatment
processes within basin meadowlands
should be^ studied.
For purposes of determining subtle
differences in the littoral zones of Lake
Tahoe nearshore waters, an extensive
network of sampling stations consisting
of several transect sites to address
littoral drift patterns should be included
in future studies.
F. A. Morris and M. K. Morris are with the Department of Biolgoical Sciences,
University of Nevada. Las Vegas. NV 89154 and T. S. Michaud and L. R.
Williams are EPA authors with the Environmental Monitoring Systems
Laboratory. Las Vegas, NV 89114.
L. R. Williams is the EPA Project Officer (see below).
The complete report, entitled "Meadowland Natural Treatment Processes in the
Lake Tahoe Basin: A Field Investigation," (Order No. PB 81-185 639; Cost:
$15.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
P.O. Box 15027
Las Vegas. NV89114
i US GOVERNMENT PRINTING OFFICE: 1061 -757-012/7089
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