SNPLMA Proposal for Theme 2c (Near-Shore Water Quality)
Project Title: Predicting and Managing Changes in Near-Shore Water Quality
I. Project Team and Contact Information
P.I.: S. Geoffrey Schladow
Tahoe Environmental Research Center
University of California
One Shields Ave, Davis, CA 95616
Phone:530-752-6932
Fax: 530-752-0589
E-mail: gschladow@ucdavis.edu
Co-P.I.: Rick Susfalk
Desert Research Institute
2215 Raggio Drive Parkway, Reno, NV 89512
Phone: 775-673-7453
Fax: 775-673-7363
E-mail: rick.susfalk@dri.edu
Co-P.I.: Alan Heyvaert
Desert Research Institute
2215 Raggio Drive Parkway, Reno, NV 89512
Phone: 775-673-7322
Fax: 775-673-7363
E-mail: alan.heyvaert@dri.edu
Co-P.I.: Sudeep Chandra
Department of Natural Resources & Environmental Sciences
University of Nevada, Reno, NV 89512
Phone: 775-784-6221
Fax: 775-784-4583
E-mail: sudeep@cabnr.unr.edu
Co-P.I.: Francisco Rueda
Instituto del Agua - Universidad de Granada
C/Ramón y Cajal, 4
18071-Granada, SPAIN
Phone: + 34 958 248018
Fax: + 34 958243094
E-mail: fjrueda@ugr.es
Co-P.I.: Fabian Bombardelli
Department of Civil & Environmental Engineering
University of California
One Shields Ave, Davis, CA 95616
Phone:530- 752-0949
Fax: 530-752-0589
E-mail: fabombardelli@ucdavis.edu
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II. Justification Statement
Most visitor and resident experiences at Lake Tahoe occur within or close to the near-shore environment,
and conditions there translate directly into public perception of lake conditions. Increased activity in the
near-shore zone is anticipated in the coming years, with more residents and visitors projected, including a
30% increase in boat traffic and up to 1000 more buoys (TRPA Shorezone EIS 2007).
Conditions in the near-shore zone have degraded over time. Elements of this degradation include elevated
turbidity (Taylor et al. 2004), the establishment and spread of invasive fish species (common carp,
largemouth bass, and bluegill) and aquatic plants (water milfoil and curly leaf pondweed) around
embayments in the lake (UC Davis Tahoe Environmental Research Center (TERC) and University of
Nevada Reno (UNR) unpublished data; Walter 2000; Anderson and Spencer 1996), and increasing
concentrations of periphyton (attached algae) on rocks, piers and other hard substrate (Hackley et al.
2004, 2005, 2006). The near-shore zone represents the region where direct anthropogenic inputs of
pollutants are largest – for example elevated gasoline components in marinas (Allen et al. 1998; Miller et
al. 2003) and accidental spills such as the 2005 raw sewage release at Kings Beach.
There is currently a lack of understanding of the processes that have contributed to this degradation, and
the types and magnitudes of the efforts needed to restore conditions to desirable levels. Much more
information is needed regarding the sources and impacts of nutrient and particle loads in the near-shore
zone. This proposal will contribute to an integrated understanding of the near-shore environment and will
fill important knowledge gaps by
1) identifying and describing the key processes impacting water quality,
2) prioritizing for management agencies the multiple sources having the greatest impact,
3) providing a predictive model that creates a framework for testing management strategies
4) testing this model against existing and new data sets for near-shore clarity, periphyton distribution
and invasive species distribution
5) utilizing the results from this study and existing long-term monitoring data to evaluate current
water quality standards/thresholds for the near-shore zone of Lake Tahoe.
III. Background/Problem Statement
Lake Tahoe’s near-shore zone has received less research attention than watershed and mid-lake processes.
Instead, mid-lake clarity has been the primary response variable for lake management. Implicit in this
approach was the assumption that if mid-lake conditions improved then a concomitant improvement in
near-shore conditions would follow. Recent optical modeling (Swift et al. 2006) suggests that mid-lake
clarity is predominantly controlled by the concentration and size distribution of fine, inorganic particles
(< 20 microns). The near-shore zone, by contrast, is more biologically productive suggesting that nutrient
fluxes and other factors may play a much larger role in that zone. It therefore cannot be assumed that the
same management strategies will work for both the near-shore and mid-lake. There is a need for both
appropriate near-shore data and understanding of near-shore processes to develop the decision-support
tools needed for scientifically sound management strategies and thresholds.
All nutrients, sediments and contaminants (except atmospheric deposition) must pass through the nearshore to ultimately affect mid-lake water quality and clarity. Similarly, introduction of nonnative species
occurs within the near-shore zone. However, the near-shore does not function simply as a conduit for the
transport of sediment and nutrient loads from streams and direct runoff to the mid-lake. Rather, it
functions as a complex and variable component of the whole-lake ecosystem that has its own unique
properties.
Perimeter surveys (Taylor et al., 2004) quantified turbidity on a basin-wide scale, finding a distinct
association between elevated near-shore turbidity and several developed areas. However, this program did
not identify mechanisms of near-shore turbidity, nor characterize the temporal duration or specific source
characteristics of high turbidity “events”.
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Measurement of the accumulation of periphyton at the shoreline during the spring and summer has been
ongoing since 2000 (Hackley et al. 2004, 2005, 2006); historic data are available from 1982-1985. The
data suggests the average annual maximum biomass measured as chlorophyll a concentration has been 36 times higher in areas of increased development.
In the last 18 years, nonnative species have established in the near-shore zone and are thought to play an
important role in mobilizing nutrients for near-shore periphyton and phytoplankton production (Walter
2000). In 1995 Eurasian watermilfoil was first detected in South Lake Tahoe and has since spread rapidly
to marinas along the West and Northeastern shores and in Emerald Bay. Recently curly leaf pondweed
has been found and has the potential to rapidly spread around the shorezone (Anderson, unpublished
data). Warmwater, nonnative fish species have also established in the near-shore environment (Reuter and
Miller 2000) in the same period. Largemouth bass are now common while redside shiner and speckled
dace populations declined or were virtually eliminated from the Tahoe Keys (DFG, unpublished data).
Preliminary studies conducted by UNR and TERC in 1999, 2003, and 2006 demonstrate that 50% of
marina sites contain nonnative, warmwater fish species.
Figures1a, 1b and 1c illustrate the variability of these water quality parameters in Lake Tahoe’s nearshore zone. The variability depends on the physical forcing (e.g. meteorology), lake currents, geographic
features (e.g. embayments), type of bottom substrate, seasonal fluctuations in the hydrologic cycle,
locations of streams and urban stormwater discharges, and near-shore storage and buffering capacities.
These processes and linkages, and their control over near-shore water quality and biology are poorly
understood and has led to the establishment of ambiguous and questionable near-shore thresholds, most
notably for near-shore water clarity and periphyton. The implementation of a coordinated and sustained
data collection effort directed toward development of predictive modeling tools will facilitate the
selection of appropriate metrics for best management of the near-shore environment, will guide efforts
toward appropriate mitigation practices in the watershed and on the lake, and will provide a rational basis
for the long term, affordable monitoring.
IV. Proposal Goals, Objectives and Hypotheses:
The goal of this proposal is to develop a process-based understanding of the controls on four primary
water-quality issues impacting the near-shore zone. These are:
• near-shore clarity
• periphyton (attached algae) growth
• distribution and factors facilitating the spread of nonnative plant and fish species
• fate of pollutants in the near-shore zones (from streams, storm drains, spills etc.
Achievement of this goal will result in a dataset that will be used to assess existing near-shore standards
and thresholds, and to provide rational management alternatives, if necessary.
To accomplish these goals, we will investigate the linkages between the physical and biological
components in the near-shore zone of the lake. The proposal objectives are to
• Develop and test a 3-D hydrodynamic, thermodynamic, particle tracking and scalar transport
model of the near-shore zone
• Conduct detailed experiments to refine linkages between nutrients and particles (inorganic,
detrital and algal)) to the near-shore zone, biological production (periphyton and planktonic
algae), and factors controlling the spread of nonnative plant and fish species,
• Conduct a spatial survey of near-shore conditions
• Quantify the distribution and production of fish, periphyton, algae and nonnative aquatic plants
• Interpret water quality data in terms of the model results
• Develop potential near shore management strategies and evaluate impacts on water quality issues
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The proposal hypotheses are:
• Water quality conditions in the near-shore are dominated by nutrient loads, rather than particle
loads
• Sediment resuspension from wind-wave action is an important source of nutrients and fine
particles in the near-shore zone
• South Lake Tahoe is a seeding source for nonnative species for the rest of the near-shore zone of
Lake Tahoe
• The dispersal and spread of invasive species is controlled by a combination of water temperature,
characteristics of the bottom substratum, and water currents
• Meaningful water quality standards/thresholds for near-shore water clarity and periphyton growth
can be developed based on knowledge of local sources of nutrients and fine particles and
modeling results
• The transport and spread of discharges (streams and accidental spills) in the near-shore zone can
be predicted using a 3-D hydrodynamic model.
V. Approach, Methodology, and Geographic Location of Research
The proposal has 5 components: (1) 3-D modeling, (2) enhanced on-shore and in-situ monitoring, (3)
detailed experimental periods (includes current and wave measurements, tracer experiments, boat surveys,
sediment sampling), (4) lakeshore surveys of outfalls and linkages to near-shore conditions, and (5)
synthesis. The geographic focus of the research is the South Lake Tahoe near-shore zone. This is where
the effects from urbanization are expected to be most evident and where measurements have
demonstrated impaired water quality (Taylor et al. 2004). However, the measurements will be integrated
with lakewide monitoring efforts, and the findings will be applicable to the near-shore zone of the entire
lake.
1. Modeling:
A model of mid-lake conditions has been developed to predict lake response to changes in loading rates
(Schladow et al. 2006a) and is currently a primary management tool for the TMDL program. This model
is one-dimensional (in the vertical direction), which is appropriate for the pelagic zone where horizontal
gradients are generally small compared with vertical gradients. In the near-shore zone, this assumption
does not hold and a full three-dimensional (3-D) modeling approach is necessary. It is proposed to use the
public domain, 3-D model, Si3D (Smith 1997) to calculate the time varying, three-dimensional water
circulation of the near-shore zone in Lake Tahoe. This model has provided excellent results in large lakes
such as Lake Tahoe, CA-NV (Rueda et al. 2003), Clear Lake, CA (Rueda and Schladow, 2003; Rueda et
al. 2005) and the Salton Sea, CA (Schladow et al. 2006b). Details of the model formulation are provided
in these citations.
The model will be run using spatially interpolated meteorological data from a network of 10 real-time
meteorological stations on and around Lake Tahoe, thereby incorporating the known spatial heterogeneity
of the wind forcing. Bathymetric data will be based on USGS data. Initial conditions and subsequent
calibration data will be provided from the routine monitoring profiles (every 10 days) conducted by
TERC and the measurements proposed herein.
A two step approach will be used to provide the high resolution needed for the near-shore zone.. First, an
initial coarse grid (200 m x 200 m x 4 m) will estimate flows over the entire lake. Second, in a sub-region
in the near-shore zone a highly refined grid (20 m x 20 m x 1 m) will be used, with the coarse grid model
result providing the necessary boundary conditions for this sub-region. While this does not allow for the
highly resolved near-shore dynamics to impact the whole-lake circulation (i.e. information is only fed
from the coarse grid to the fine grid), this is considered a minor shortcoming given the enormous size of
the lake.
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The 3-D model will yield velocity and temperature distributions along the entire near-shore zone of South
Lake Tahoe (Fig. 2). Using these distributions, the transport of scalar quantities (such as nutrients)
inserted at stream mouths, storm-water drains and by groundwater can be assessed. The distribution of
fine particles (< 20 microns) from these same sources can be tracked. An existing sediment resuspension
model based on wind/wave interactions (Chung et al. 2007) will be coupled to Si3D to assess the
importance of sediment resuspension for particle and nutrient input in the near-shore zone. Coupling the
resulting particle distribution with the previously developed optical model (Swift et al. 2006) will allow
spatially distributed estimates of light attenuation to be made.
2. Enhanced On-Shore and In-Situ Monitoring for Model Calibration
The precise measurement locations and parameters monitored will depend upon the model results. At
present, there are two in-situ sensor arrays mounted in the near-shore zone of South Lake Tahoe
(Timbercove pier and Tahoe Keys). These are managed by TERC, and include continuous measurements
of turbidity, chlorophyll, conductivity and temperature. To expand spatial coverage DRI will install one
additional array at a location determined by model results and consistent with the regional water clarity
surveys presented below.
A complete shoreline survey of the intensive study area will be conducted to determine GPS locations and
site characteristics of all stormwater and stream outfall points. These locations will be compared to sites
existing in the TRPA outfall map. Five of these sites will be instrumented for continuous flow,
temperature and turbidity measurements. Suspended sediment loads entering the near-shore will be
estimated by establishing site-specific relationships with turbidity. Water quality samples will be
collected at each site during three events bracketing the experimental periods described below, and
analyzed for water quality characterization and particle size distribution, as well as for particle
fingerprinting characteristics (by ICP-MS and XRD). Measurements will be coordinated with on-going
USGS monitoring of the Upper Truckee River and Edgewood Creek.
Periphyton growth in the intensive area will be monitored at piers and other hard surfaces for algal
biomass using methods currently employed in the lake-wide periphyton monitoring program (Hackley et
al. 2004, 2005, 2006). Biomass will be measured as mg chlorophyll a/m2 and monitored at 2-4 weekly
intervals during the spring-summer growth period. Biomass will also be analyzed for total nitrogen and
phosphorus content to relate to nutrient availability.
To determine if South Lake Tahoe, the area with the greatest abundance and diversity of nonnative
species, is a seeding source for the rest of the near-shore-zone of Lake Tahoe, we will tag fish and plants
within the Tahoe Keys and determine the factors controlling their spread. Acoustic telemetry will be used
to track migration patterns, habitat utilization, and the daily movement in association with physical and
chemical information collected during the experiment. Largemouth bass (n=20) and bluegill (n=20) will
be marked and monitored during the Spring- Summer seasons. Stationary acoustic receivers will
determine their depth and movement across the habitat. Every two weeks through the summer and fall, a
portable acoustic receiver will be used to locate tagged fish. Tags will be recovered and downloaded
quarterly. Monthly surveys will be conducted through the winter and spring when warm water species are
expected to be less active. When possible, fish collections from the area will be done to determine the
diets of each species present and used to analyze competition for available resources and predation.
3. Detailed Experimental Periods for Model Development
Two detailed experiment periods (30 day) will be conducted to assess temporal response of the model to
changes in near-shore conditions, including currents and wave patterns, runoff volumes and water
temperatures, meteorology, etc. These experimental periods will be timed to coincide with an ASTER
satellite overflight midway during each experiment. Fig. 3 shows a schematic of the types of
measurements to be made.
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Direct measurement of near shore currents and wave height and direction spectra will be made using a
bottom mounted Nortek AWAC. The AWAC is an acoustic Doppler profiler, that combines dynamic
measurement of wave height and direction. A similar study by Schladow et al. (2006c) was conducted at
the Salton Sea, and the measurement and analysis techniques have been largely developed. The AWAC
will be co-located with a YSI multi-parameter probe that will simultaneously measure turbidity, dissolved
oxygen, temperature and conductivity, and a thermistor chain to continuously record thermal
stratification. Weekly water column profiles of temperature, particle size distribution, PAR radiation, UV
radiation, chlorophyll (species-discriminated) concentration and oxygen concentration at the AWAC site
will also be made.
Contiguous spatial sampling will be conducted within the study area’s near-shore environment utilizing
boat-mounted instruments and methods developed by Taylor et al. (2004). Briefly, a bow-mounted probe
delivers a stream of lake water through on-board instruments measuring turbidity, light transmissivity,
relative chlorophyll, temperature, and particle size distribution. Under normal operation, water is
collected from within 50 cm of the surface along a prescribed, continuous transect comprised of multiple
passes at varying distances from the lakeshore. These near-shore synoptics will be conducted at least
twice during each 30-day experimental period, with two occurring during the ASTER overflights, if
feasible. Tracer experiments, using either introduced or natural tracers will be conducted at the times of
the boat surveys and will focus on the fate and spatial distribution of individual streams or stormwater
drains.
Sediment peepers (dialysis samplers) will be deployed within the study area during detailed experiments
to measure porewater concentrations and calculate potential nutrient flux between sediments and
overlying water. Similar methods could be used to assess urban contaminant concentrations in the nearshore, if deemed relevant to this study.
Relative periphyton growth will be measured at selected points within the study area during experimental
periods by deployment of artificial substrate racks. The results will be calibrated to corresponding
measurements on natural substrate at existing long-term sites.
4. Lakeshore Surveys of Stormwater Outfalls and Near-Shore Conditions
While intensive process-based experiments will focus on the South Lake Tahoe area for calibration and
testing of the model, as described above, it remains important to assess current water quality conditions in
the entire lake’s near-shore zone. Lakeshore surveys provide the opportunity to extend the same on-shore
to near-shore linkages that will be concurrently explored in the intensive area. Two whole-lake near-shore
surveys will be conducted, corresponding in time to the periods of intensive monitoring at South Lake
Tahoe. Lakeshore surveys will collect the same data as the South Lake Tahoe regional surveys, except
that only one pass is routinely made along the lakeshore. Additional passes at varying distances from
shore will be conducted in areas of impaired water clarity to assess spatial extent. Background samples
will also be collected at five to seven sites for periphyton growth, substrate characterization, substrate
sediment particle size distribution, nutrient and chemical characterization of particles for relative source
fingerprinting, and standard water quality assessments. The on-shore runoff from these sites will be resampled for nutrient and source fingerprinting analyses during a characteristic runoff event, as identified
from the existing Tahoe Basin Stormwater Monitoring Network (TERC/DRI), to inform on-shore to nearshore linkages. The location of these sites will be determined from previous data and the observation of
current conditions at stormwater outfall points.
The distribution and abundance of nonnative plant and fish species will occur at biweekly intervals across
the near-shore zone of the entire lake and in the focus area of South Lake Tahoe. All embayments and
marinas (n=18) evaluated in 2006 will be combined with additional sites measured by the USDA Aquatic
Weeds Laboratory at UC Davis. Plant abundance and distribution will be coordinated with ongoing
surveys conducted by the USDA laboratory. Species identification, above ground biomass, stand
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structure (height) and density will be measured at each location. Point-transects will be used to
characterize the abundance and presence/ absence of nonnative fish species at each location. Minnow
traps will be used to characterize minnow abundance. Diets of fish species and growth rates determined
by scale analysis will occur for each habitat/ embayment. We will determine if there are correlations
between habitat structure, thermal regime, water quality and the presence of nonnative fish species.
5. Synthesis
The results from each task shall be integrated into a summary report that discusses the factors important
to near-shore clarity, periphyton, nonnative species distribution and water quality. The near-shore model
will be described in detail, with results presented as a series of management scenario assessments. Data
supporting linkages to on-shore processes will be presented and discussed, as well as the interactive
effects from clarity, periphyton growth, invasive species distribution and hydrodynamic factors. These
results shall be used to inform recommendations for management options to improve and sustain the nearshore environment of Lake Tahoe. In addition, the results will permit an informed analysis of the existing
near-shore water quality standards (for both periphyton and clarity) and if warranted recommendations on
revisions.
VI. Deliverables and Products
• A calibrated 3-D hydrodynamic, thermodynamic, particle tracking and scalar transport model
(with documentation) of the near-shore zone of South Lake Tahoe, that can be extended to other
near-shore areas.
• Report on the detailed experiments, with specific reference to determinants of water clarity,
periphyton growth, spread of nonnative species and the relative importance of sediment
resuspension, streamloads and intervening zone loads of fine particles and nutrients. This will
form the basis of a conceptual model of the near-shore zone that will address the coupling of
processes and outcomes within this zone
• Report on spatial survey of near-shore conditions for entire lake
• Report on the distribution of fish, periphyton and nonnative aquatic plants in the near-shore
• Report on effectiveness of potential near shore management strategies and evaluation of impacts
on individual water quality issues
• Report on current and improved water quality standards
VII. Schedule of Events, Reporting and Deliverables
DATE
Jun-07
Jan-08
Apr-08
Apr-08
May-08
Jun-08
Aug-08
Aug-08
TASK
Commence project
Complete hydrodynamic/thermal model
First lakewide perimeter survey
First Intensive Experiment
Complete first year monitoring
Annual Report
Second lakewide perimeter survey
Second Intensive Experiment
Complete inclusion of particle tracking, scalar transport, sediment
Sep-08
resuspension, optical sub-models
Dec-08 Complete analysis of intensive experiments and lakewide surveys
Apr-09 Draft Final Report
May-09 Final Report and submission of manuscript(s) to peer-reviewed journals
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XI. Figures
Fig. 1 a Turbidity distribution 2000-2002 (Courtesy R. Susfalk)
Distribution of Periphyton Biomass (Chl. a)
at 0.5m depth Spring 2006
Concentration of
Chl. a (mg/sq. m.)
Kings Beach
Incline Village
0 - 10
Carnelian Bay
11 - 25
´
26 - 50
51 - 100
101 - 500
Tahoe City
Glenbrook
Homewood
Meeks Bay
Rubicon Bay
Zephyr Cove
South Lake Tahoe
Note: Width of band out from shore
does not represent extent of coverage;
only growth at 0.5m depth contour
Fig 1b Periphyton distribution in Spring 2006 (courtesy J. Reuter)
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Fig 1c Water milfoil and nonnative, warmwater fish species distribution and monitoring sites
(courtesy S. Chandra)
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Fine model grid and
intensive field
experiment area
Fig.2 Lake Tahoe with 50 m depth contours indicated. Red box shows schematically location of
the highly refine 3-D model grid. Intensive field experiment area is located within this box. Blue
squares indicate meteorological stations. Red stars are long-term mid-lake sampling stations.
Existing water quality measurements are also taken at Timbercove.
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ASTER satellite
data
Met. station
WIND
Boat-mounted turbidity,
particle size distribution,
chlorophyll, DO etc.
sampling
Thermistor
chain
pier
YSI multi-parameter
probe
Submerged
Storm-water
plume
Tagged fish
And plants
Sediment resuspension
plume
YSI multi-parameter
probe
AWAC – current profile
and wave height and direction
Fig. 3. Schematic of range of sampling during the two intensive experiments.
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