Annotated Bibliography of Scientific Literature on Water Quality from the Lake Tahoe Basin: 2008-2010
Produced for the Tahoe Science Consortium by researchers as the University of California - Davis, University of Nevada – Reno, Desert Research Institute, US Forest Service – Pacific Southwest Research Station and US Geological Survey – Carson City.
Juky 16, 2011
Table of Contents
Introduction………………………………………………………………………… ..1 Air Quality as Related to Atmospheric Deposition and Water Quality……………. .3 Aquatic Ecology…………………………………………………………………….11 Aquatic Invasive Species…………………………………………………………... 14 Fire, Biomass, and Forest Runoff Quality………………………………………... 19 Climate Change……………………………………………………………………..29 Groundwater………………………………………………………………………...34 Lake Tahoe TMDL………………………………………………………………….37 Land Use Mapping………………………………………………………………… 49 Nearshore Water Quality…………………………………………………………... 52 Optical Properties, Fine Particles and Plankton Ecology………………………….. 55 Restoration Monitoring…………………………………………………………….. 62 Soils and Sediment Erosion Processes……………………………………………... 70 Toxic Compounds and Biotoxicity………………………………………………… 78 Urban Stormwater and BMP Monitoring…………………………………………...81 Extra-Topical Issues……………………………………………………………….104
Introduction
The indigenous Washoe Tribe historically referred to Lake Tahoe as “big sky lake.” After an expedition to Lake Tahoe in 1861, Mark Twain wrote, "So singularly clear was the water, that where it was only 20 or 30 feet deep the bottom was so perfectly distinct that the boat seemed floating in the air! Yes, where it was even 80 feet deep. Every little pebble was distinct, every speckled trout, every hand's- breadth of sand ... the water was not merely transparent but dazzlingly, brilliantly so."
The clarity and color of Lake Tahoe’s water today are world renowned and taken as an example of a very clean lake. However, the lake’s watershed and air basin are part of a changing landscape, with substantial portions of this once pristine region now urbanized. Studies during the past 40-plus years have shown that many factors have interacted to degrade the Lake Tahoe basin’s water quality and aquatic ecology. Issues including: the significant loss of clarity; establishment of aquatic invasive species; change in biodiversity; loss of natural habitat; increased land disturbance and erosion; increase in urban stormwater runoff; degradation of stream environment zones; loss of natural landscapes capable of detaining and infiltrating stormwater and snowmelt runoff and loss of landscape that naturally remove pollutants from surface runoff; atmospheric deposition of pollutants directly to the lake surface are of concern at the local, state, and federal level. The progressive decline in lake water clarity has served as a key indicator of the decline in Lake Tahoe’s historical ultra-oligotrophic condition. Moreover, many consider lake water clarity a gauge of the watershed’s health as a whole.
Water resource agencies have adopted regulations to protect Lake Tahoe’s clarity and overall aquatic health. The State of California has declared Lake Tahoe as an Outstanding National Resource Water under the US Federal Clean Water Act. This designation affords Lake Tahoe the highest level of protection under the Act. Lake Tahoe and Mono Lake are the only California lakes to receive this title. The State of Nevada similarly recognizes the uniqueness of Lake Tahoe by designating it as a “water of extraordinary ecological or aesthetic value.” The mission of the TRPA is to “cooperatively lead the effort to preserve, restore, and enhance the unique natural and human environment of the Lake Tahoe Region now and in the future.”
Several decades of progressively greater disturbance in the Tahoe basin, along with increased pollutant loading, have been accompanied by a concerted effort on the part of the Basin’s science community to (1) understand the processes that control water quality, (2) provide technical knowledge to help guide water quality and aquatic habitat restoration, (3) monitor restoration effectiveness within an adaptive management framework, and (4) provide decision-makers, resource managers and the public with information regarding the implications of allowing current trends to continue unabated.
During the past quarter century, numerous institutions have made substantial efforts to control these impacts, reverse the decline in lake clarity, and reduce pollutant loading to Lake Tahoe, its tributaries and its ground-water aquifers (e.g. TMDL, Regional Plan). The watershed approach taken at Lake Tahoe recognizes that water quality is linked to upland watershed processes and air quality as well as to the legacy of adverse impacts to terrestrial and aquatic habitats.
1 Consequently, successful implementation of land, air, and water quality restoration projects is considered key to arresting further decline in lake clarity. This understanding precipitated the formulation of the Environmental Improvement Program (EIP) by the Tahoe Regional Planning Agency (TRPA) and its partners in the federal, state, and local governments, and the private sector. The EIP is a regional restoration plan that presents restoration projects, along with scientific guidance, considered necessary to achieve environmental goals in the Tahoe basin. The TMDL is a scientifically and technically informed program that lays out a ‘road map’ for how the EIP will stem the loss of clarity in Lake Tahoe.
Science has played a key role in decision making within the community of resource management agencies. Hundreds of scientific papers and reports have been written on many aspects of Lake Tahoe, its watershed, and its water quality since studies first began over 40 years ago.
The purpose of this document is to summarize the bulk of the scientific literature that has been published in 2008-2010 related to water quality at Lake Tahoe. References are given so the interested reader can delve more deeply into these scientific papers and reports. We also created an annotated bibliography for each reference wherein we summarize the key points in the document. This is intended to provide an overview of the material contained in each document.
We separated the scientific literature into 15 theme area related to water quality. The literature related to other important topics (e.g. forest health, fire, social economics, air quality and human health) are not part of this effort. Finally, within each theme we provide a brief overview, summarize papers from peer-reviewed scientific journals, present other scientific literature from Lake Tahoe studies on these theme, and close each theme with a brief discussion related to how this information is related to management actions.
2
Air Quality as Related to Atmospheric Deposition and Water Quality
Overview
Starting in the second half of the 20th century, decline in Lake Tahoe’s water clarity and degradation in the basin’s air quality have become major concerns due to its unique scenic features. Gaseous and particulate nitrogen (N) and particulate phosphorus (P) loading via direct atmospheric deposition and sediment transport to the lake have also been implicated as responsible for its eutrophication and decline in water clarity. Estimates suggest that atmospheric N deposition contributes 55% of the total N loading to the lake, while atmospheric P deposition contributes 15% of the total P loading. In order to improve both air quality and, as a consequence, water quality, it is necessary to develop an understanding of the sources of the atmospheric pollutants. Once this is accomplished, it is possible to implement cost-effective strategies to reduce this impact. Midlake meteorology station and deposition collector. Photo: TERC. Peer Reviewed Journal Publications Credit: Fugitive Dust Emissions from Paved Road Travel in the Lake Tahoe Basin. 2009. D. Zhu, H. Kuhns, S. Brown, J. Gillies, V. Etyemezian, A. Gertler. JA&WMA. 59: 1219-1229. A year-round monitoring study of road dust emissions around the lake was completed in 2007 using the Testing Re-entrained Aerosol Kinetic Emissions from Roads (TRAKER) system developed at the Desert Research Institute (DRI). Results of this study found that, compared with the summer season, road dust emissions increased by a factor of 5 in winter, on average, and about a factor of 10 when traction control material was applied to the roads after snow events. For winter and summer, road dust emission factors (grams coarse particulate matter [PM10] per vehicle kilometer traveled [g/vkt]) showed a decreasing trend with the travel speed of the road. The highest emission factors were observed on very low traffic volume roads on the west side of the lake. The principle factors influencing road dust emissions in the basin are season, vehicle speed (or road type), road condition, road grade, and proximity to other high-emitting roads. Combined with a traffic volume model, an analysis of the total emissions from the road sections surveyed indicated that urban areas (in particular South Lake Tahoe) had the highest emitting roads in the basin.
A Summary of the Lake Tahoe Atmospheric Deposition Study (LTADS). 2009. L. Dolislager, R. VanCuren, J. Pederson, A. Lashgari, E. McCauley. Atmospheric Environment. doi:10.1016/j.atmosenv.2009.09.020.
3 The Lake Tahoe Atmospheric Deposition Study (LTADS) was conducted by the California Air Resources Board (CARB) primarily to generate refined estimates of the atmospheric deposition of nitrogen (N), phosphorous (P), and particulate matter (PM) directly to Lake Tahoe. LTADS estimated that approximately 185, 3, and 755 metric tons respectively of N, P, and PM being directly deposited to the lake from the atmosphere. Various measurements of emissions, meteorology, and air quality were made within and west (typically upwind) of the Lake Tahoe Air Basin to better understand the pollutant sources contributing to the atmospheric deposition.
The data indicate that ammonia (NH3) contributes the bulk of the N loading. Aerosols with diameters greater than 2.5 μm contribute the bulk of the P and PM mass loadings. The emission sources of P and PM appear to be primarily local and associated with motor vehicles. However, construction, fires, and natural sources also contribute to the pollutant loadings.
Air pollution in the shore zone of a Large Alpine Lake – 1 – Road dust and urban aerosols at Lake Tahoe, California–Nevada. 2009. R. VanCuren, J. Pederson, A. Lashgari, L. Dolislager, E. McCauley. Atmospheric Environment. doi:10.1016/j.atmosenv.2009.12.001 Concentrated human activity and limited atmospheric mixing create a high potential for airborne pollutant impacts to alpine lakes developed as mountain resorts. The 2002–2004 Lake Tahoe Atmospheric Deposition Study (LTADS) was conducted as part of a multi-agency effort to develop a water quality management plan for the lake. Estimating aerosol deposition to the lake requires detailed knowledge of the spatial and temporal patterns of aerosol concentration, size distribution, and chemical composition over the entire basin – and developing a management plan requires also that the sources of the aerosols be known with considerable specificity. In lieu of the intensive measurement network implied by this level of detail, it was hypothesized that a set of measurements to characterized the temporal, spatial, and size distribution patterns of particles in ambient air and in local emissions in the vicinity of Lake Tahoe could be used to extrapolate long time series of simple measurements to an annual aerosol deposition computation. Authors report the results of our detailed aerosol measurement campaign. Results show that there are strong systematic and repeating gradients in aerosol loading that occur as functions of location, land use, traffic activity, and time of day, and that road dust is a major source of aerosols around the lake. In addition, there was observed a strong consistency of particle size distributions as a function of source type, largely independent of particle concentrations. Authors demonstrated the use of particle counters to directly observe downwind dispersion and deposition of particles. Together, these findings support the use of imputed location- and time-specific size distributions in annual aerosol deposition calculations, even though particle size distributions were not directly measured in the LTADS baseline monitoring program, and that program was conducted at only a limited set of sites in the Tahoe basin.
Aerosol generation and circulation in the shore zone of a large alpine lake - 2 - Aerosol distributions over Lake Tahoe, CA. 2009. R. VanCuren, J. Pederson, A. Lashgari, L. Dolislager, E. McCauley. Atmospheric Environment. doi:10.1016/j.atmosenv.2009.08.049. The temporal, spatial, and size-distribution patterns of particles in ambient air over the surface of Lake Tahoe (Nevada and California) were studied as part of the 2003-2004 Lake Tahoe atmospheric deposition study (LTADS). The concentration of population along the shoreline of Lake Tahoe makes accurate characterization of local aerosol generation and transport especially important in estimation of
4 annual particle flux to the surface of the lake. Measurements taken while cruising on the lake show that aerosol concentrations in near-shore areas are primarily controlled by a combination of diurnal cycling of land- and lake- breezes and particle emissions driven by cycles of human activity near the shore. These effects were observed to be highly localized. Highest concentrations were found just offshore from urbanized areas, especially shoreline centers of activity; lowest concentrations were found along undeveloped shoreline; low- to- intermediate concentrations were measured over the middle areas of the lake. The on-lake data reported here indicate that aerosols over the lake, and thus dry deposition to the lake, are dominated by the same processes that control on-shore emissions, and that the impact is strongest in the near shore areas of the lake.
Inferring Deposition Velocities From Changes in Aerosol Size Distributions Downwind of a Roadway. 2011. D. Zhu, H. Kuhns, J. Gillies, V. Etyemezian, A. Gertler, S. Brown. Atmospheric Environment 45(4): 957-966. Deposition velocities for particulate matter (PM) from road traffic in the Lake Tahoe basin were estimated using a mass-balance model and measurements from four size-specific PM profilers and meterological instruments located at 15m upwind and 5, 30 and 100 m downwind of major highway. Coarse PM (2.5 – 10 µm) concentration decreased exponentially with downwind distance from the highway. Particles with diameters between 0.3-0.5 µm show almost a homogeneous distribution across the road indicating the smallest particles are unrelated to a road source. Calculated deposition velocities generally increased with particle size and ranged from <0.1 cm s-1 for particles from 1-2.5 µm diameter to 1.6 cm s-1 for particles >15 µm diameter. Wind speed and direction play important roles in determining deposition velocities of particles induced by road traffic. Higher PM concentrations were observed when strong onshore winds dominated during the daytime and traffic counts were high. The highest impact to water quality came between late afternoon and early morning, when offshore winds blew traffic-induced PM towards the lake to be deposited.
Other Scientific Literature
Development of an Air Pollutant Emissions Inventory for the Lake Tahoe Basin that Incorporates Current and Future Land Use Scenarios. 2008. A. Gertler, E. Weinroth, M. Luria, J. Koracin. Prepared for USEPA Region 9, San Francisco, CA, July 31, 2008. CO: Mobile sources and residential fuel combustion. There is a strong seasonal dependence in the residential fuel combustion source.
PM10, PM2.5, P, and PO4: Area wide sources, particularly residential fuel combustion and road dust resuspension. Emissions are significantly higher during the winter period. Use of the DRI TRAKKER data (Kuhns, 2007) significantly reduced the estimated resuspended road dust contribution when compared with the CARB inventory.
NOx and NH3: Mobile sources are the dominant contributor. VOCs: Mobile sources, biogenic sources, and area wide sources all contribute to VOC emission. There is a strong seasonal dependence in the biogenic and area wide source contributions
Lake Tahoe Source Attribution Study (LTSAS): Receptor Modeling Study to Determine the Sources of Observed Ambient Particulate Matter in the Lake Tahoe Basin. 2009. J. Engelbrecht A. Gertler, T. VanCuren. Prepared for the USDA Forest Service Pacific Southwest Research Station, September 2, 2009.
5 Re-suspended paved road dust is the major source of PM10 in the basin. The results supported this hypothesis. This was best seen at the two high traffic sampling sites in the densely populated areas (South Lake Tahoe and Sandy Way) and the near-roadway site.
Wood burning is an important source of PM2.5 during the winter months. The results supported this hypothesis. The receptor models demonstrated that residential wood combustion, with possible contributions from wildfires and controlled burns are the major PM2.5 sources of pollution during the fall and winter months.
Motor vehicle tailpipe emissions is the major source of PM2.5 in the basin. The results do not support this hypothesis. This is an important source but as a percentage of PM2.5 mass the chemical mass balance (CMB) receptor model derived value varied from 23 to 33%.
Secondary pollutants from outside the basin are minor sources of PM2.5 and PM10. The results supported this hypothesis. The maximum predicted contributions from secondary sources to PM2.5 were found to vary from 8 to 12%. Emissions from controlled burns inside the basin, and wildfires outside the basin are minor sources of the observed PM. The results are inconclusive in supporting this hypothesis. Due to the smoke from residential wood burning during the fall and winter, the contributions from wildfires and controlled burns in or outside the basin could not be assessed. Emissions from restaurants can be an important source of PM at some locations. This could not be determined. In the absence of measured meat and other cooking markers in the ambient samples, or chemical source profiles, this source could not be identified or modeled. Overall, the most important sources to control are emissions from light-duty gasoline vehicles. The results did not support this hypothesis. As stated under 1, 2, and 3 above, the most important sources to control are road dust, followed by wood smoke and mobile sources. The major source of phosphorous is soils, while the contributions from wood burning are small. The results supported this hypothesis. Initial data analysis, including the calculation of correlation coefficients did not confirm any relationship of phosphorus with wood combustion. Phosphorus was highly correlated with all soil species in PM10. Phosphorous concentrations in the coarse fraction are elevated and are therefore indicative of mechanically re-suspended soil. The results supported this hypothesis. PCA and subsequent data analysis revealed that phosphorus occurs as individual mineral grains in the coarse geological fraction, as re-suspended road dust. Phosphorous from mobile source tailpipe emissions is small. The results supported this hypothesis. Phosphorus from motor vehicle emissions as measured in PM2.5 was very low for all cases. If phosphorus had been in motor vehicle emissions in measureable concentrations, it would have occurred evenly distributed in all the South Lake Tahoe, Sandy Way, and Lake Forest samples, which was not the case. Nitrogen is a minor component of the coarse PM fraction. Hence the PM contribution to the atmospheric deposition of N is small. The results supported this hypothesis. On average about 3 3 3 0.30 g/m nitrate occurs in the TSP fraction, with about 0.26 g/m in PM10 and 0.15 g/m in PM2.5. Deposition in the lake from aerosol nitrate will therefore be small. Soil is the major contributor to atmospheric sediment deposition in the lake. The results supported this hypothesis. The receptor modeling show that road dust in the PMCoarse size fraction, partly from de-icing procedures during winter months is an important source to control. Road dust accounted for as much as 60% of PM10 and, based on its size, has the potential to be deposited in Lake Tahoe.
An Integrated Science Plan for the Lake Tahoe Basin: Conceptual Framework and Research Strategies. 2009. A. Gertler, T.A. Cahill, T.M. Cahill, S. Cliff, C. Emmett, J. Koracin, H. Kuhns, J. Molenar, J. Quashnick, J. Reuter. In: Hymanson, Z.P.; Collopy, M.W., eds. An integrated
6 science plan for the Lake Tahoe basin: conceptual framework and research strategies. Gen. Tech Rep. PSW-GTR-226. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 37-81. Chapter 3. Air quality in the Lake Tahoe basin is known to affect lake water quality, forest health, and human health. To address the continuing concerns about air pollution impacts and develop a sound scientific approach for mitigating these impacts, this chapter updates the work of Cliff and Cahill (2000) and builds upon the Lake Tahoe Atmospheric Deposition Study (CARB 2006) by delineating remaining knowledge gaps and defining the research needs and strategies to close these gaps. To support this approach, a number of Tahoe-specific subthemes related to air quality were identified, including: Tahoe basin meteorology; atmospheric deposition of N, P, and particles; local versus regional transport of air pollutants; Tahoe basin air quality: the criteria pollutants; air pollution emission inventories; atmospheric modeling of the Lake Tahoe basin; and impacts of fire on air quality. Air quality monitoring in the Tahoe basin needs to be improved. The first step is to develop a comprehensive monitoring plan for the basin that addresses the criteria air pollutants (covered under the National Ambient Air Quality Standards) and species affecting human and ecosystem health (including water clarity), along with the required spatial and temporal distribution of the measurements. Once this plan is prepared, sampling locations can be chosen and appropriate air quality sensors can be deployed. Air quality and meteorological monitoring are best integrated to maximize efficiencies and information gain.
Lake Tahoe Water Quality Investigations – 2007 to 2010: Identification and Enumeration of Atmospheric Deposition. 2010. S. Hackley, B. Allen, D. Hunter and J. Reuter. Publication by University of California, Davis – Tahoe Environmental Research Center. Prepared for the California Lahontan Regional Water Quality Control Board. 21-38 pp. Precipitation amounts were relatively low in WY 2007 (27.92 in.) and 2008 (24.98 in.) at the TERC Lower Ward Valley station. Moderate levels of precipitation occurred in WY 2009 (37.34 in.) and WY 2010 (through mid-June 37.50 in. had fallen). Atmospheric deposition continues to be a significant source of nitrogen and phosphorus loading for the lake. DIN in wet precipitation at Lower Ward Valley was very low in WY 2007-2008. These low DIN loads (~500 g/ha) were the lowest since the record began in 1981. The DIN load increased in WY 2009 with increased precipitation, however it was still relatively low when compared with all data 1981-2009. Total loads of SRP were also low in WY 2007 and 2008. With increased precipitation in WY 2009 loads of SRP increased but were still relatively low when compared with the long-term data set.
DIN in Dry deposition at the Lower Ward station showed some fluctuation 2007-2009. NH4-N loading in dry deposition at Lower Ward was consistent for WY 07- WY08 and slightly higher in WY 09. Loading of NO3-N was somewhat variable between years. TKN loading in dry deposition was fairly consistent. Levels of SRP, DP and TP loading in Dry deposition at the Lower Ward Valley station were all significantly greater in WY 2008 compared with WY 2007 and WY 2009 values. The elevated levels of dry deposition of phosphorus at the Lower Ward station appears to have been the result of phosphorus contributions during the ash deposition event in July 2008.
For Dry-bulk deposition to the lake at buoys TB1 and TB4 loading rates for NO3-N and NH4-N and TKN were relatively consistent during WY 2007-2009. N and P deposition at the on-lake buoy buckets has remained relatively consistent since WY 05 even though there is some interannual variability. At buoy TB-4 SRP, DP, and TP loading was highest in WY 2008 and
7 low in WY 2009. At mid-lake buoy TB-1 SRP, DP and TP loading rates were the highest in WY 2008 and lowest in WY 2009. The deposition of phosphorus during the ash deposition event in July 2008, contributed to elevated annual P deposition at buoy stations TB4 and TB1 in WY 2008. During summer 2008 a prolonged period (> 3 weeks) of smoke occurred in the basin associated with a large number of lightning started wildfires to the west of Lake Tahoe in Northern California. During this period of elevated smoke an unusual ash deposition event occurred July 9 in the northwest portion of the basin. A significant spike in SRP concentrations and loads was observed at the Lower Ward Valley site and on the buoys on the lake associated with this event. The impact of deposition of this ash was also observable as moderate spikes in DIN at all three sites. This was an particularly interesting event that we were able to monitor during the atmospheric deposition monitoring program. Calculations specifically related to the WY 2008 fire/smoke/ash event should be viewed as preliminary until these additional analyses are complete. They are included to keep the Basin’s resource agencies up-to-date with our current ideas on this interesting event. These findings should not be used at this time to support policy decisions.
Examination of Dust and Air-Borne Sediment Control Demonstration Projects. 2010. H. Kuhns, D. Zhu, J. Gillies, A. Gertler, S. Cliff, Y. Zhao, S. Brown, D. Fellers, M. Pook. Prepared for the USDA Forest Service Pacific Southwest Research Station, November, 2010.
Within 5 m downwind of the road, PMlarge (Total suspendable material - PM10) accounts for ~half of the airborne mass emissions, PMcoarse (PM10 - PM2.5) account for the other half with PM2.5 representing less than 0.5%. Using the conservative Stokes deposition velocities, 99% of PMlarge, PMcoarse, and PM2.5 deposit within 300 m, 5.2 km and 40 km of the ground level emission point with wind speeds of 2 m/s. Using more realistic deposition velocities (relevant for forested areas) the 99% deposition points reduce to 70 m, 400 m, and 19 km, respectively. As a result the bulk of airborne emissions will deposit within a few km of the road. Phosphorous (a nutrient for algal growth in the lake) airborne concentrations in resuspended road dust were greatest in fine particles. Phosphorus did not appear to be associated with most of the road dust mass since 85% of roadside phosphorus was in PM2.5 size fraction compared to only 20% of the crustal species. Roadside fine PM phosphorus concentrations are greatest during peak travel times. A potential source of road side phosphorus is the burning of motor oil that contains the oil additive Zinc dialkyldithiophosphates (ZDDP). Conservative approximations suggest that the contribution of vehicle exhaust to lake phosphorus loading is very small with an upper limit of 0.02%, far below the major source stormwater runoff at 65%. Wintertime street sweeping when roads are dry after storms (ASAP sweeping) was the strongest predictor of Emissions Equilibrium (EE, a traffic speed independent measure of road emission strength). Many secondary and tertiary roads are only swept seasonally and serve as a reservoir of material that is suspended into the air when abrasives are tracked onto higher speed roads.
On an annual cost effectiveness basis, street sweeping costs $0.6 per kg PM10 emissions reduced. This estimate does not include capital costs of the sweeper valued at ~$250K each. These operational costs are less than 0.5% when compared with roads resurfacing of fair conditions roads ($300 per kg PM10 emission reduction) or resurfacing of poor condition roads ($700 per kg PM10 emission reduction). Road segments that employed anti-icing pretreatment on roadways had lower EE values by a factor of two. While being correlated with cleaner roads, anti-icing provides other benefits including reduced salt application, reduced abrasive application, and better utilization of resources since brine can be applied during routine shifts up to three days in advance of a storm.
8 Although not rigorously quantitative, cost benefits are estimated to be on the same order as sweeping (~$0.6 per kg PM10 emissions reduced). Reduced PM benefits of anti-icing need to be assessed in the context of road side vegetative health since the anti-icing material may be more toxic to plants than the traditional sand mixed with salt. Roads with paved shoulders or barriers that prevented entrainment of material from the sides of roads had 50% lower EE than did roads with narrow (less than 3 feet) or unpaved shoulders. Shoulder improvement costs 10%-20% of road resurfacing and may prove to reduce airborne emissions. In comparison, ASAP Sweeping and anti-icing are substantially less expensive and more likely to provide significant emission reduction benefits. Potential basin wide road dust PM10 emission reductions of ~67% of the present value may be achievable if the emission equilibrium reservoir can be reduced through regional street sweeping and anti-icing practices. To be most effective, emission control strategies should require that not only primary roads, but all roads, be swept after snow storms to recover applied abrasive material. Impacts of Vehicle Activity on Airborne Particle Deposition to Lake Tahoe. 2011. D. Zhu, H. Kuhns, J. Gillies, A. Gertler, J. Mason. Prepared for the USDA Forest Service Pacific Southwest Research Station, April, 2011. Proximity to the lake, prevailing wind directions, and traffic patterns play a dominant role in determining which roads have the greatest potential to deposit fine sediment into the lake. It appears that only roads close to the lake have a substantial impact on atmospheric deposition of fine particles. Moreover, most areas around the lake benefit from onshore wind directions during peak traffic times (i.e. daylight hours) that effectively push emissions away from the lake. However, this is not the case in El Dorado County (California) and Douglas County (Nevada), which are calculated to be responsible for 67% of the paved road dust deposited to the lake. More aggressive measures to reduce the reservoir of suspendable material on roads in these areas will be more cost-effective than applying a blanket policy to the entire road network. Emissions vary both by season and by location. Wintertime Total Suspended Particle (TSP) emissions are ~5 greater than summertime TSP emissions due to the application of traction control material to the roads during the winter. Vehicle kilometers traveled (VKT) are not evenly distributed in the basin’s urban area; in particular, the South Lake Tahoe area has the highest VKT values in the basin. Although South Lake Tahoe (in El Dorado County, CA) already employs an aggressive street sweeping program, its high VKT causes it to still be a major source of atmospheric deposition of particles into the lake. Approximately 98% of the vehicles in the basin are in the light-duty class. So, although the wakes from mid- and heavy-duty trucks can entrain dust particles from the sides of roadways, the number of such vehicles is insufficient to make a major impact.
Only ~2% of road emissions of PM10 (20 Mg/year) and ~1.5% of TSP (35 Mg/year) is estimated to reach the lake. The vast majority of PMlarge emitted into the air is deposited within minutes, especially in the presence of dense vegetation. An analysis of vegetative density coverage was overlaid on the spatially resolved emission inventory so that each road segment could be assessed based on the type of vegetation on the shortest path to the lake. Lake Tahoe Atmospheric Deposition Study (LTADS) referenced in the 2010 Total Maximum Daily Load report estimated that dry atmospheric depositions to the lake are 230 Mg/year of PM10 and 590 Mg/year TSP. Including wet deposition, the total atmospheric deposition to the lake are 375 Mg/year of PM10 and 755 Mg/year TSP. Our results indicate that PMlarge and PMcoarse are rapidly depleted near their source and thus the shoreline concentrations may only be representative of the first 1-to-3 kilometers offshore. The results support much lower estimates of dry deposition to the lake than calculated by LTADS. We estimate that from paved road travel,
9 the atmospheric dry deposition to the lake is approximately 6% of the total LTADS dry deposition. Other sources of fine sediment that are not included in our estimates include unpaved road travel that is relatively small (due to development around the lake and especially in the wintertime when a snow pack is present) and located at greater distances from the shore than paved roads. In addition, re-entrained windblown dust is not factored into our estimates.
Application to Management
Air quality management, for the purpose of water quality load reduction, has been conceptually established by science at Lake Tahoe. However, the direct application of this understanding to ‘on the ground’ management is still being established. Unlike point-source discharges, where the source is specifically known or even the out-fall pipes for urban stormwater where the pollutant source(s) is located in the localize catchment, atmospheric deposition of fine sediments, nutrients and other possible pollutants is very difficult to pin-point. Furthermore, science in general has little experience with linking the many, diffuse sources of materials that can enter a waterbody to specific restoration actions. Atmospheric deposition is difficult directly measure and its spatial patterns can be complex in a lake as large as Lake Tahoe. While water flows downhill in relatively confined channels that can be seen by the investigator, air currents are much more ephemeral. Currently, scientists and resource managers at Lake Tahoe are still in the process of defining how the airshed functions, identifying sources of pollutants that could affect water quality, and determining their transport to the Lake. Understanding, for example, how a road sweeping program will affect lake clarity is a complex issue that requires more fundamental knowledge.
10 Aquatic Ecology
Overview
The ecology of native species in Lake Tahoe is an important reflection on the health of the lake’s ecosystem. Shifts in community assemblages and trophic food web structures can indicate a variety of different causative mechanisms such as human development, invasive Conceptual model of the current Lake Tahoe aquatic food web. species impacts, climate Source: S. Chandra change and other environmental disturbances. The restoration of the native ecosystem is highly contingent upon the knowledge of how native species are changing over time, and how these are interacting with human induced pressures on Lake Tahoe. There have been some studies carried out on the native benthic and pelagic communities of Lake Tahoe, with the aim of understanding long-term changes to these populations.
Peer Reviewed Journal Publications
Evaluating the Reintroduction Potential of Lahontan Cutthroat Trout in Fallen Leaf Lake, California. 2009. R. Al-Chokhachy, M. Peacock, L. Heki, G. Thiede. North American Journal of Fisheries Management. 29: 1296-1313. doi: 10.1577/M08-087.1 The potential for reintroducing Lahontan cutthroat trout (Oncorhynchus clarkii henshawi), a species listed under the Endangered Species Act, into a lacustrine system where the biotic community has changed dramatically since the species' extirpation was evaluated. Since 2002, 76,547 Lahontan cutthroat trout have been reintroduced into Fallen Leaf Lake, California. Creel surveys, diet data, mark–recapture methods, bioenergetics modeling, and netting data across seasons were used to evaluate the habitat use, growth, and relative abundance of Lahontan cutthroat trout and the abundance, diet, habitat use, and predation by nonnative species. Sampling totals (n = 2) and survey observations (n = 3) indicate low survival and abundance of reintroduced fish and together with creel data indicate the importance of epilimnetic habitats across size-classes. Despite substantial growth, Lahontan cutthroat trout exhibited low condition factor values (average = 0.69). Substantial predation pressure was found from a large population of lake trout (Salvelinus
11 namaycush). An analysis of lake trout diets showed an increase in piscivory and in the percentage of stomachs containing Lahontan cutthroat trout anchor tags with increasing predator size. Overall, it was estimated that lake trout consumed over 38 percent of reintroduced Lahontan cutthroat trout. However, using bioenergetics modeling it was estimated that lake trout consumed considerable amounts of salmonid biomass during this period, which greatly exceeded the biomass of Lahontan cutthroat trout reintroduced in 2006. During the stratification period, there was little overlap in habitat use between lake trout and Lahontan cutthroat trout, but overlap was high during the spring and autumn. Together, the results suggest that Lahontan cutthroat trout have few refugia from direct and indirect negative interactions with nonnative species and that alternative approaches are needed.
Other Scientific Literature
Development of a Benthic Macroinvertebrate Index of Biological Integrity (IBI) for Stream Assessments in the Eastern Sierra Nevada of California. 2009. D. Herbst, E. Silldorff. Final Technical Report submitted to California State Water Resources Control Board. 87 p. www.swrcb.ca.gov/water_issues/programs/swamp/docs/.../east_sierra.pdf. The assessment of biological integrity of streams is mandated through the Clean Water Act as a component of water quality regulation and protection. While various types of aquatic organisms have been used as indicators of biological integrity, benthic (i.e., bottom-dwelling) macroinvertebrates have been used most extensively and have been shown to provide a reliable measure of stream health. While this is regional analysis that was not restricted to the Tahoe basin, some of the study sites were located in to immediately adjacent to the Tahoe basin. Furthermore, as the TRPA develops a monitoring program for status and trends, this report was considered highly relevant. Using collections of macroinvertebrates from streams of the eastern Sierra Nevada, this report details how data from these samples were used to develop a quantitative Index of Biological Integrity (IBI). The IBI is an index composed of multiple metrics (much like composite economic indicators) that can be used to accurately and cost-effectively assess stream health. Component metrics were selected for inclusion in the IBI based on performance indicators such as sensitivity in response to disturbance stressors, high signal-to-noise ratio (strong response to stress with low variation), and little redundancy with other metrics. Ten metrics were selected through this process and were compared to different combinations and numbers of metrics. Classification structure from the 10-Metric IBI was also compared to the performance of a multivariate (RIVPACS-type) predictive model, and to a 9-Metric IBI based on lower taxonomic resolution. A high degree of conformity was seen in the assessment results produced by the different approaches. Future refinements of these recommended biocriteria may include contrasts with independent validation data sets (i.e., stream surveys not used to develop the metrics), comparisons to periphyton (i.e., algae) indicators, use in conjunction with other data to develop biocriteria for the entire Sierra Nevada, combination with water chemistry and physical/habitat measures to permit integrated assessments of water quality, and development of additional options to apply these data for regulatory decision-making.
NICHES: Nearshore Indicators for Clarity, Habitat and Ecological Sustainability. 2010. S. Chandra, C. Williamson, J. Oris, G. Schladow. Prepared for the Pacific
12 Southwest Research Station. Lake Tahoe's fishery is among one of the least studied of all the large lakes in the world. Over time there have been a variety of stressors (e.g. introduction of species, eutrophication, nearshore habitat modification), which may have impacted the fishery and only a limited amount of snapshot investigations have been conducted to investigate these impacts or determine the status of a particular species. With little to no information on the status of fishery, in particular the nearshore components where most of the native, littoral fish reside, we have compiled information to determine the status of the nearshore native and non-native fish community and if there are quantifiable indicators and methodologies that can be created to determine the condition of the nearshore fishery. Furthermore, we conducted experiments to determine if ultraviolet radiation (UV) can be used to link nearshore and non-native fish ecology to the physical environment.
Application to Management
The restoration of important native species such as the Lahontan cutthroat trout (LCT) and the endemic blind amphipod (Stygobromus tahoensis) and Tahoe stonefly (Capnia lacustra) are highly dependent on the understanding of a whole lake ecosystem structure. Based on the studies above, there is an indication of a shift in the benthic macroinvertebrate as well as fishery assemblages of Lake Tahoe. Water resources managers have identified the need for the re-introduction of LCT as well as the conservation of the nearshore health of the lake, given the number of non-native species introductions to this zone. Futher studies concerning the interaction between native species and observed species declines and non-native species establishments are needed. In particular, the extent of native Chara beds (habitat for important native benthic macroinvertebrates as well as fish spawning) and other aquatic macrophytes, native fishes and native bivalves have few recent surveys or studies.
13 Aquatic Invasive Species
Overview
The dispersal and establishment of aquatic invasive species to inland freshwater bodies is more pervasive now than it ever has been in the past. Human mediated vectors such as recreational boating, angling, water conveyance structures and commercial shipping is the number one source of spread of aquatic invasive species (AIS) and has accelerated rates of AIS dispersal across landscapes. Increases in the numbers of lakes, rivers and reservoirs that contain harmful aquatic invasive species further contribute to the problem of AIS range expansion by providing more sources for other uninfested sites. Species such as the Asian clam (Corbicula fluminea), quagga and zebra mussel (Dreissena spp.), Eurasian watermilfoil (Myriophyllum spicatum), Hydrilla (Hydrilla verticillata), Spiny waterflea (Bythotrephes longimanus) and bighead carp (Hypophthalmichthys nobilis) have already caused significant ecological and economic damage to freshwater systems in North
America and continue to spread. Lake Tahoe is Boat inspection station on road entering the highly utilized by humans for recreational purposes, Tahoe Basin. Photo: Tahoe Daily Tribune. and with this comes the risk of introduction of AIS, either unintentionally through passive transfer on boats or boating equipment, or intentionally through fisheries introductions. Lake Tahoe has a number of AIS in various phases of invasion, namely Asian clam, Eurasian watermilfoil, curly leaf pondweed (Potamogeton crispus), signal crayfish (Pacifastacus leniusculus) and a number of warmwater fish invaders including largemouth bass (Micropterus salmoides) and bluegill sunfish (Lepomis spp). Research into the invasion of aquatic species in Lake Tahoe is rapidly expanding and considers the ecological requirements, spread and impacts to native species in the lake, and control.
Peer Reviewed Journal Publications
Distribution and Aundance of Warmwater, Vertebrate Invaders in Lake Tahoe. 2008. M. Kamerath, S. Chandra, B. Allen. Aquatic Invasions. 3: 35-41. This study showed that from the 1970’s to 1990’s, in the Tahoe Keys, a major rearing area of native fishes, warmwater fish species were rarely found, whereas native minnows remained abundant as evidenced by a snapshot sample obtained in 1999. By 2003, largemouth bass (Micropterus salmoides) were common, whereas redside shiner (Richardsonius balteatus) and speckled dace (Rhinichthys osculus) populations declined or were virtually eliminated from the Tahoe Keys.
14 First Documentation of Salmincola Californiensis in Lake Tahoe, CA-NV, USA. 2009. M. Kamerath, B. Allen, S. Chandra. Western North American Naturalist. 69(2): 257-259. Salmincola californiensis is a parasitic copepod in the Lernaeopodidae family that commonly parasitizes salmonid fishes (Oncorhynchus spp.) by attaching near the fins and on gill filaments. Historically their distribution was limited to streams that emptied into the Pacific Ocean. During the summer of 2006, several rainbow trout (Oncorhynchus mykiss) captured in Lake Tahoe were infested with S. californiensis. This is the first known record of S. californiensis in Lake Tahoe.
Ultraviolet Radiation Affects Invisibility of Lake Ecosystems by Warm-water Fish. 2010. A. Tucker, C. Williamson, K. Rose, J. Oris, S. Connelly, M. Olson, D. Mitchell. Ecology 91(3): 882-890. This study examined how water temperature and transparency to ultra-violet radiation (UVR) influence the suitability of nearshore habitats for invasive warm-water fish in Lake Tahoe, a sub-alpine oligotrophic lake. Larval bluegill and largemouth bass were exposed to solar UVR to establish a UVR dose- response relationship for each species. These results were combined with UVR transparency data from monthly profiles (May-October 2009) to predict fish survival in each nearshore site as a function of UVR exposure. Using data from the literature and from monthly temperature profiles this study also predicted larval fish survival at each nearshore site as a function of temperature. UVR and temperature dependent survival estimates were combined to produce a single estimate of potential survival at each nearshore site. Model results were corroborated by in situ incubation experiments. Results suggest that current UVR transparency and water temperature limit establishment of non-native fish in most, though not all, nearshore sites.
Other Scientific Literature
Determining Factors for Eurasian Watermilfoil (M. spicatum) Spread in and Around Lake Tahoe, CA-NV. 2008. B. Kendall, S. MacIntyre. UC Water Resources Center Technical Completion Report Project No. WR-1010. This study addressed the question of habitat and/or dispersal limitation for watermilfoil by assessing the movement of recreational boaters within Lake Tahoe, and between Lake Tahoe and other locations, as well as characterizing nearshore habitat locations in highly visited boating destinations. Additionally, this report examined the nature of recreational boater movement data, and the impacts of boater preference as well as the impact of the spatial aspect of data gathering from one versus many locations. This study included: 1) an examination of the use of transportation models known as gravity models to describe recreational boater traffic to inland waterways in California and Nevada, 2) an analysis of waterway access point habitat quality as it relates to Eurasian watermilfoil, and 3) the invasion of Eurasian watermilfoil within Lake Tahoe, and how that relates to within-lake boater movement and habitat variables associated with invaded and uninvaded sites within Lake Tahoe.
Asian Clam (Corbicula fluminea) of Lake Tahoe: Preliminary Scientific Findings in Support of a Management Plan. 2008. M. Wittmann, S. Chandra, J. Reuter, G.
15 Schladow, S. Hackley, B. Allen and A. Caires. http://terc.ucdavis.edu/research/AsianClam2009.pdf This study was the first to investigate Asian clam (Corbicula fluminea) establishment in Lake Tahoe and its apparent associated environmental impacts. Asian clam had been qualitatively observed in Lake Tahoe at very low densities (3- 212 individuals/m2) since 2002, but in 2008 populations were quantified using dredge sampling and found in much higher, but patchy densities in the southeastern portion of the lake (50-3000 individuals/ m2).\ Through field surveys, laboratory experimentation and literature reviews it was found that Asian clams 1) excrete elevated levels of nitrogen and phosphorus into the water at the lake-sediment interface where they reside, 2) filter high volumes of water, 3) are strongly correlated with algal growth, and 4) are an actively reproducing community in Lake Tahoe – producing at least two cohorts per season. Potential impacts of exponential increases of this species include degraded water quality - including increases in benthic algal blooms, the decline of phytoplankton and zooplankton communities, degradation of aesthetic and recreational beach use through excess shell material deposition, disruption to Lake Tahoe fishes, increased levels.
Quagga Mussel Risk Assessment - An Experiment Test of Quagga Mussel Survival and Reproductive Status Using Lake Tahoe Water with a Prediction of Invasion into Western Water Bodies. 2009. S. Chandra, M. Wittmann, A. Caires, A. Kolosovich, J. Reuter, G. Schladow, J. Moore, T. Thayer. Lake Tahoe Aquatic Invasive Species Integrated Management Strategy Report. This laboratory study tested the survival, growth, and reproductive potential for quagga mussels collected from Lake Mead, NV-AZ when exposed to the low calcium, oligotrophic waters of Lake Tahoe for a 51-day period. Quagga mussel showed 87 percent survival with a positive growth rate over the experimental period. Reproductive status was variable with 43 percent of individuals (male and female) showing sperm and oocyte production, 14 percent in a post-spawn phase, and 29 percent showing gonad resorption. Studies conducted to evaluate the short-term (≤48 h) effects from quagga establishment suggest reductions in algal biomass of up to 76 percent and increases in the nutrient pools of bioavailable phosphorus and nitrogen. This is the first study to address survivability and reproduction as it relates to water column characteristics for quagga mussel specifically, in reference to reservoirs, conveyance systems, and natural lakes in the Western US.
Lake Tahoe Region Aquatic Invasive Species Management Plan, California - Nevada. 2009. USACE. 84 pp + Appendices. Substantial changes to the Lake Tahoe Region’s economy, pristine water quality, aesthetic value, and recreational pursuits are occurring, partly due to the harmful impacts of non-native aquatic plants, fish, invertebrates, and other invaders. These non-native aquatic organisms are considered ‘invasive’ (or aquatic invasive species [AIS] in water) when they threaten the diversity or abundance of native species or the ecological stability of infested waters, or commercial, agricultural, aquacultural or recreational activities dependant upon such waters (NANPCA 1990). At least 20 non-native species are established in the Lake Tahoe Region, including aquatic plants, fishes, invertebrates, and an amphibian.
16 The potential economic impact to the Lake Tahoe Region caused by new AIS introductions such as quagga or zebra mussels (Dreissena bugensis and D. polymorpha, respectively) or expanding invasive aquatic plant populations would be substantial. The combined economic impacts to recreation value, tourism spending, property values, and increased boat/pier maintenance, when evaluated over a 50 year period, is estimated at $417.5 million (present value), with an average annual equivalent value of $22.4 million per year. Spending on prevention and early eradication produces a higher benefit to cost ratio than post-infestation control programs such that maximum benefits are realized through early and preemptive action. The purpose of the Lake Tahoe Region AIS Management Plan (the Plan) is to facilitate coordination of regional, bi-state, state, and federal programs and to guide implementation of AIS prevention, monitoring, control, education, and research in the Lake Tahoe Region. The goals of the Plan are to: prevent new introductions of AIS to the Lake Tahoe Region, limit the spread of existing AIS populations in the Lake Tahoe Region by employing strategies that minimize threats to native species, and extirpate existing AIS populations when possible, abate harmful ecological, economic, social and public health impacts resulting from AIS. The intent of the Plan is to provide more localized guidance for preventing and managing AIS in the Lake Tahoe Region and will not be in conflict with the California AIS Management Plan (CAISMP), administered by the California Department and Fish and Game (CDFG) or the anticipated plan from the state of Nevada.
Effectiveness of Aquatic Invasive Plant Control in Emerald Bay, Lake Tahoe, California. 2011. D. Shaw, Z. Hymanson, K. Boyd, T. Sasaki. Tahoe Science Newsletter. Vol 2. No 3. http://tahoescience.org/EventImage.aspx?sa=1&id=356. The establishment of invasive aquatic plant species in Emerald Bay is of great concern to a large variety of interests due to the adverse effects these plants can have on near shore ecology and visitor enjoyment. Potential impacts from invasive plant infestations include: localized degradation in water quality due to increased transfer of sediment-bound nutrients into the water column through plant root uptake and subsequent plant senescence; sediment accumulation and substrate alteration allowing further expansion of the infestation; changes in habitat conditions that favor non-native fish such as catfish and bass, and nuisance algae; adverse swimming conditions and negative impacts on recreational boating; increasing amounts of plant material washing up and fouling beaches; and the increased potential spread of invasive plants to other areas in Emerald Bay and Lake Tahoe (Eiswerth et al. 2000). The invasive aquatic plant, Eurasian watermilfoil (Miriopyllum spicatum; hereafter EWM), was first reported in the Tahoe Keys in the 1960’s (Donaldson and Johnson 2009). Surveys in 1995 documented EWM in Emerald Bay. A cooperative effort among management and regulatory agencies, scientists, and professional divers was initiated to combat the invasive aquatic plant infestation in Emerald Bay after the dramatic expansion was discovered in 2003. A series of small-scale treatments were deployed in Emerald Bay between 2005 and 2009, but the infestation continued to persist. By the end of 2009 three separate patches of EWM were established at the western end of Emerald Bay, covering a combined area of nearly 3 acres. In 2010, a combination of treatment methods over a larger proportion of one infestation site in a strategic attempt to attain control and eventually complete removal of a discrete infestation area was pursued. This paper describes the 2010 project and initial results. The 2010 strategic effort to remove all plants in a discrete infestation with multiple
17 treatment methods yielded promising initial success. By combining methods, a large continuous area was treated more efficiently, with benthic barriers treating the main area of the infestation, and diver-assisted suction removal specifically targeting hard to reach areas, margins and gaps in the barriers, and sparsely infested areas. This combination of treatment methods maximized the cost/benefit ratio, and one method reinforced the effectiveness of the other. Approximately one-third of the infested substrate in Emerald Bay was reduced to a level that can be maintained with small scale annual retreatments.
Application to Management
Findings of scientific reports related to AIS in Lake Tahoe have significantly contributed to management actions within the Tahoe basin. The TRPA and TRCD (Tahoe Resource Conservation District) have instigated a highly comprehensive trailered boat inspection program in Lake Tahoe that intercepts each vessel that enters the basin and examines them as a vector for AIS, in particular, dreissenid mussel species such as the quagga or zebra mussel. With the understanding that recreational boats that come to Lake Tahoe are potential vectors for AIS and also that dreissenid mussel species have the potential to survive in this lake, agencies have taken a pre- cautionary approach and have implemented a strong prevention program within the basin. In addition, multiple agencies are working in tandem with university researchers on management actions related to the Asian clam as well as Eurasian watermilfoil and curly leaf pondweed. These management programs are highly integrated with the ecological knowledge base for the optimal management of these species with regard to life history strategies, ecological needs, and seasonal variability in population structure and reproduction. Currently, the use of mild aquatic herbicides for the reduction of invasive aquatic plants in the Tahoe basin is under consideration. The knowledge of the recent spread of aquatic invasive species within Lake Tahoe has inspired the deliberation of a variety of treatment methods in the lake, both chemical and non-chemical for various types of aquatic invasive species. The partnership between science and management was highlighted by the recent (summer of 2010) experimental deployment of two one-half acre rubber bottom barriers to test the feasibility of reducing Asian clam populations on a larger spatial scale.
18
Fire, Biomass and Forest Runoff Quality
Overview
The Lake Tahoe basin represents a complex forested ecosystem consisting of numerous sub-watersheds and tributaries that discharge directly to Lake Tahoe. The following literature focuses on the implications of fire and biomass management strategies relative to their potential impacts on organic and soil nutrient (N, P, S) status and related discharge water quality. An accumulating forest floor as a result of fire suppression has resulted in the build-up of large nutrient pools that now provide a “natural” source of long term nutrient availability to surface waters. As a consequence, stand and forest floor replacing wildfire may cause a large magnitude nutrient mobilization impact on runoff water quality. Mechanical harvest and controlled burning have become popular mitigation management strategies. The most ecologically significant long-term effects of prescribed fire appear to be the loss of C and N from the forest floor. Although the application of prescribed fire may have some initial impact on overland flow nutrient loading, controlled burning in conjunction with mechanical harvest has the potential to improve runoff water quality by reducing long- term N and P discharge and improving the overall health of forest ecosystems without the danger of the nutrient mobilization “shock” typically associated with high intensity wildfires.
Peer Reviewed Journal Publications
Factors Affecting Mineral Nitrogen Transformations by Soil Heating: A Laboratory- Simulation Fire Study. 2008. D. Glass, D. Johnson, R. Blank, W. Miller. Soil Science. 173: 387-400. The purpose of this study was to investigate laboratory and field factors affecting the magnitude and direction of soil ammonium, nitrate, total carbon and total nitrogen changes in response to fire. Ammonium was generally found to increase with burn temperature and duration. Increasing the initial soil water content diminished this response in one soil studied, but not the other. Little or no change was seen in total N, total C, or C:N ratio. Low-severity fire can cause very large and highly variable changes in ammonium and nitrate, with little or no change in total C or N. In contrast, high-severity fire has varying effects on ammonium and nitrate but generally causes losses of total soil C and N.
Fire Effects on Carbon and Nitrogen Cycling in Forests of the Sierra Nevada
19 Mountains. 2008. D. Johnson, M. Fenn, W. Miller and C. Hunsaker. In: A. Bytnerowicz, M. Arbaugh, C. Anderson, A. Riebau (eds.), Wildland Fires and Air Pollution. Developments in Environmental Science, Elsevier. Fuels treatments proposed for National Forests are intended to reduce fuel accumulations, wildfire frequency and severity, and to protect property at the wild land-urban interface. If fuels treatment are not conducted, then wild land fires typically are more severe and frequent causing worse public health and welfare effects. A better understanding of air pollution and smoke interactions is needed in order to protect the public health and allow for socially and ecologically acceptable use of fire as a management tool. This text offers such an understanding and examines innovative wide-scale monitoring efforts (field and remotely sensed).
The Combined Effects of Thinning and Prescribed Fire on Carbon and Nutrient Budgets in a Jeffrey Pine Forest. 2008. D. Johnson, J. Murphy, R. Walker, W. Miller, D. Todd, Jr. Annals of Forest Science 65:601-612. Carbon and nutrient removals by two methods of thinning and subsequent prescribed fire (in both thinned and un-thinned plots) were estimated for Jeffery pine forest in the eastern Sierra Nevada mountains of California. Carbon and nutrient exports were greater in plots that had been thinned and burned than in plots that were burned only, but differences were statistically significant only in the cases of C, P, K, and not for N, S, or Ca. The combined effects of thinning and burning on C and N removals were approximately equal for the two harvesting methods even though harvesting dominated exports in the Whole Tree treatment and burning dominated exports in the Cut-to-Length treatment. Comparisons of nutrient removals with ecosystem capital and calculations of potential replenishment of nutrient losses by atmospheric deposition suggested that N is the nutrient likely to be most depleted by harvesting and burning treatments.
Biochemical Cycling in Forest Soils of the Eastern Sierra Nevada Mountains, USA. 2009. D. Johnson, W. Miller, R. Susfalk, R. Dalgren, J. Murphy, D. Glass. Forest Ecology and Management. 258: 2249-2260. This study reviews some of the unique features of biogeochemical cycling in forests of the eastern Sierra Nevada Mountains, USA. Islands of fertility” are common in these forests, a result of spatial variations in both litterfall and decomposition rates. Dry summer conditions greatly inhibit biological activity in the O horizon, and thus most annual litter decomposition takes place beneath the snowpack when moisture is available. Water and nutrient fluxes vary spatially because of snowdrift in winter and surface runoff over hydrophobic soils in summer and fall. Because of the very dry summers, rooting in the O horizons is absent in these forests, and thus competition between microbes and trees for nutrients in that horizon is non-existent. Nutrients mineralized from the O horizon and not taken up by plants enrich runoff through the O horizons over hydrophobic mineral soils, resulting in very high concentrations of inorganic N and P in runoff waters. The most significant temporal variation is due to periodic fire, which we estimate causes annualized N losses that are two orders of magnitude greater than those associated with leaching and runoff. We hypothesize that fire suppression during the 20th century may have contributed to the deterioration of nearby Lake Tahoe by allowing buildups of N
20 and P in O horizons which could subsequently leach from the terrestrial ecosystem to the Lake in runoff. In general, we conclude that biogeochemical cycling in these forests is characterized by greater spatial and temporal variability than in more mesic forest ecosystems.
Effects of Mechanical Harvest Plus Chipping and Prescribed Fire on Sierran Runoff Water Quality. 2009. T. Loupe, W. Miller, D. Johnson, J. Sedinger, E. Carroll, R. Walker, J. Murphy, C. Stein. Journal of Environmental Quality. 38: 537-547. The purpose of this study was to evaluate the effects of biomass reduction using mechanical harvest followed by chipping and/or controlled burning on surface runoff and associated water quality. Treatment effect was a strong predictor of discharge loads for nitrate nitrogen and sulfate, but a weak predictor for ortho-phosphate phosphorus loads. Discharge loads of nitrate N and sulfate in the surface runoff were greater for the unburned harvested and burned unharvested treatments than for the unburned unharvested control sites and the burned and harvested combined treatments. Nonetheless, the effects of mechanical harvest and/or controlled burning on runoff water quality were minimal compared to the potential for a large-magnitude nutrient mobilization as a result of wildfire.
Prescription Fire and Anion Retention in Tahoe Forest Soils. 2009. T. Caldwell, D. Johnson, W. Miller, R. Qualls, R. Blank. Soil Science 174: 594-600. Prescribed burning is a management option to reduce fire hazard in the Lake Tahoe Basin. However, subsequent nutrient loading to the lake is of major concern. The effect of prescribed burning and residual ash on soil chemical properties and anion concentrations was studied in both the field (Tahoe National Forest) and laboratory. Saw- tooth and Marlene field sites were chosen on the basis of the dominant parent materials found in the Tahoe Basin: andesite and decomposed granite, respectively. Field studies consisted of preburn, postburn, and post-snowmelt soil analyses. Laboratory experiments consisted of variable ash to soil mixtures followed by membrane extraction. Measured burn intensities varied within and between study sites with a mean soil temperature of 190C 168C at Sawtooth (andesite) and 402C 198C at Marlene (decomposed granite). Respective burn intensities were not correlated to any ion concentration at either site. Soil samples collected postburn and post-snowmelt indicated that burning tended to increase soil pH, extractable calcium (Ca2+), and water-soluble 2- sulfate (SO4 ), although not always statistically significant. No consistent trend was observed for orthophosphate. Laboratory additions of ash to both unburned soils resulted in a substantial increase in 2- both pH and SO4 ; conversely, extractable orthophosphate decreased. The increase in 2- SO4 far exceeded the content of the ash and thus is hypothesized to be caused by pH- induced desorption from the unburned soil. Results were similar for both parent materials, indicating that nutrient retention may be controlled by soil pH resulting from ash incorporation.
Snowbrush (Ceanothus velutinus Dougl) Effects on Nitrogen Availability in Soils and Solutions from a Sierran Ecosystem. 2010. C. Stein, D. Johnson, W. Miller, R. Powers, D. Young, D. Glass. Ecohydrology (In Press). This study investigated the effects of N-fixing vegetation on water quality and soil leaching by comparing mineral N concentrations in soil solution, runoff, O (organic)
21 horizon leachates, and resin lysimeters in adjacent snowbrush (Ceanothus velutinus Dougl.) and Jeffrey pine (Pinus jeffreyii Grev. & Balf) stands, and the effects of cutting and herbiciding snowbrush on mineral N leaching. - Soil solutions from snowbrush had slightly but not significantly elevated NO3 - + concentrations compared to those from Jeffrey pine. Leaching rates of NO3 and NH4 from O horizons as measured by resin lysimeters beneath snowbrush were lower than those beneath Jeffrey pine, and leaching rates in mineral soil (15 cm) were not significantly different. + Nitrate and NH4 concentrations in O horizon interflow from snowbrush was significantly elevated compared to Jeffrey pine and snowbrush litter was the primary source of this elevated mineral N. Cutting and herbiciding of snowbrush stands in a recently-burned (1994) site had no effect on mineral N leaching rates even when followed by mastication of biomass and incorporation into the soil. We conclude that snowbrush has little or no effect on mineral N leaching in soils despite elevated mineral N concentrations in O horizon interflow.
The Effects of Slash Pile Burning on Soil and Water Macronutrients. 2010. B. Johnson, D. Johnson, W. Miller, E. Carroll-Moore, D. Board. Soil Science. (in press). Significant effects of slash pile burning on soil chemistry and water quality were observed in forested sites in the eastern Sierra Nevada Mountains of Nevada. Slash piles in upland and meadow sites were instrumented postburn with ceramic cup lysimeters, runoff collectors, and resin stakes (Plant Root Simulatori probes) along transects from pile centers to unburned areas. Ash and soil samples also were collected along these transects. The pH and concentrations of most nutrients in the soil were highest in the centers of the piles. Larger piles had lower levels of total carbon and total nitrogen in the pile centers (indicative of high burn temperatures and volatilization) compared with smaller piles. There also were differences between meadow and non-meadow systems including higher - 2- soil NO3 and lower SO4 amounts in the meadow areas. Soil solution data indicated that - - peak concentrations exceeded EPA water quality standards for both NO2 N and NO3 N at all three sites and were 2.5 to 3 times the standards in two sites. Runoff solution peak concentrations also exceeded the standards but only in the meadow site.
A Review of Biomass Management Strategies and Effects on Sierran Forest Water Quality. 2010. W. Miller, D. Johnson, S. Karam, R. Walker, P. Weisberg. Forests. 1(3): 131-153. doi:10.3390/f1030131). This synthesis focuses on historical and current nutrient pools and the effects of biomass management in watersheds of the basin relative to their potential impacts on nutrient (N, P) related discharge water quality. An accumulating forest floor as a result of fire suppression has resulted in the build-up of large nutrient pools that now provide a “natural” source of long term nutrient availability to surface waters. As a consequence, stand and forest floor replacing wildfire may cause a large magnitude nutrient mobilization impact on runoff water quality. Mechanical harvest and controlled burning have become popular management strategies. The most ecologically significant long-term effects of controlled fire appear to be the loss of C and N from the forest floor. Although the application of controlled fire may have some initial impact on overland/litter interflow nutrient loading, controlled burning in conjunction with mechanical harvest has the potential to improve runoff water quality by reducing N and P discharge and improving the overall health of forest ecosystems without the danger of a high intensity wildfire.
22
Moisture Effects on Carbon and Nitrogen Emission from Burning Wildland Biomass. 2010. W. Chen, P. Verburg, A. Shackelford, D. Zhu, R. Susfalk, J. Chow, J. Watson. Atmos. Chem. Phys. 10:1-9. Carbon (C) and nitrogen (N) released frombiomass burning have multiple effects on the Earth’s biogeochemical cycle, climate change, and ecosystem. These effects depend on the relative abundances of C and N species emitted, which vary with fuel type and combustion conditions. This study systematically investigates the emission characteristics of biomass burning under different fuel moisture contents, through controlled burning experiments with biomass and soil samples collected from a typical alpine forest in North America. Fuel moisture in general lowers combustion efficiency, shortens flaming phase, and introduces prolonged smoldering before ignition. It increases emission factors of incompletely oxidized C and N species, such as carbon monoxide (CO) and ammonia (NH3). Substantial particulate carbon and nitrogen (up to 4 times C in CO and 75% of N in NH3) were also generated from high-moisture fuels, maily associated with the pre-flame smoldering. This smoldering process emits particles that are larger and contain lower elemental carbon fractions than soot agglomerates commonly observed in flaming smoke. Hydrogen (H)/C ratio and optical properties of particulate matter from the highmoisture fuels show their resemblance to plant cellulous and brown carbon, respectively. These findings have implications for modeling biomass burning emissions and impacts.
Other Scientific Literature
Leachate Geochemical Results for Ash Samples from the June 2007 Angora Wildfire Near Lake Tahoe in Northern California. 2008. P. Hageman, G. Plumlee, D. Martin, T. Hoefen, M. Adams, P. Lamothe, T. Todorov, M. Anthony. U.S. Department of the Interior, U.S. Geological Survey. Open-File Report 2008–1170. 14 p. This report releases leachate geochemical data for ash samples produced by the Angora wildfire that burned from June 24 to July 2, 2007, at Lake Tahoe. The leaching studies are part of a larger interdisciplinary study whose goal is to identify geochemical characteristics and properties of the ash that may adversely affect human health, water quality, air quality, animal habitat, endangered species, debris flows, and flooding hazards. The leaching study helps characterize and understand the interactions that occur when the ash comes in contact with rain or snowmelt, and helps identify the constituents that may be mobilized as run-off from these materials. Similar leaching studies were conducted on ash and burned soils from the October 2007 southern California.
Monitoring of Slash Piles Burned in Stream Environment Zones: 2003 and 2008. 2008. D. Downie. US Forest Service, Lake Tahoe Basin Management Unit. 18 p. Although this is qualitative monitoring based on a small sample size, the results suggest that burning piles in SEZs may have relatively slight impacts on soil, vegetation, and water quality, especially if pile size is controlled in order to limit soil temperature. However, the photos from Pioneer Unit 15 suggest that even large, hot pile burns may revegetate well in SEZs. Erosion would likely be a concern on steeper slopes than those observed in this analysis.
23 Soil and Water Quality Response to Fuels Management in the Lake Tahoe Basin. 2009. P. Verburg, W. Miller, M. Busse, E. Rice, M. Grismer. In: Effects of Fuels Management in the Tahoe Basin: A Scientific Literature Review. Stine, P.A, and Long, J.W. (Eds.). Final Report. Nov 29th, 2009. USDA Forest Service, Pacific Southwest Station (Davis, CA) and the Tahoe Science Consortium (Incline Village, NV), pp. 115- 182. Fire suppression has caused a large accumulation of biomass in the Lake Tahoe Basin increasing the risk of catastrophic wildfires and dictating the need for a comprehensive fuel management program. However, fuel reduction treatments should be designed to minimize nutrient and sediment releases from soils into streams, groundwater, and ultimately, Lake Tahoe. Current fuel-reduction treatments include hand thinning, mechanical thinning (including cut-to-length, whole-tree harvesting, end lining, over the snow treatment, or mastication) for the initial treatment of standing vegetation. This is typically followed by treatment of residual ground fuels through either pile burning in hand thin units, or mastication within mechanical treatment units. Underburning is utilized as a maintenance treatment once initial fuels have been treated, and occurs approximately 5 to 7 years after the initial fuels treatment. Adequate knowledge of potential risks posed by treatments and Best Management Practices (BMPs) designed to mitigate, or avoid such impacts is essential for managers prior to developing fuel reduction strategies. This paper reviews the potential impacts of prescribed fire and mechanical thinning on soil chemical, physical, and biological properties in semi-arid forest ecosystems. The main effect of prescribed fire on soil nutrients is a loss of N contained in the forest floor and possibly a transformation of P forms. Soil N and P concentrations may change but these changes are often short-lived and do not always impact stream water chemistry. Prescribed fire can affect soils through the formation of water repellent layers especially when soils are dry and soil litter cover is continuous, thereby decreasing water infiltration and increasing runoff and erosion. Prescribed fire can affect soil biota, especially in wet soils, but it is unclear how these effects impact ecosystem functioning. Burning of slash piles can cause localized, high severity burn areas that can significantly impact soils but the effects on a watershed scale have not been quantified. Mechanical thinning can affect soil physical properties such as bulk density and porosity, but these impacts are likely to be small since soils in the Lake Tahoe Basin are typically coarse-textured. The presence of slash on the soil surface can further minimize the impacts of mechanical thinning on soil compaction, but can also increase the intensity of subsequent fires and formation of water repellent layers. Within the Lake Tahoe Basin, there is considerable concern regarding the management of Stream Environment Zones (SEZs). The wetter soils in SEZs most likely would limit the impacts of prescribed fire on soils but may increase the impacts of mechanical thinning. Pile burning in SEZs in the Tahoe Basin has not been permitted/implemented in the past in the Tahoe Basin, but the first projects to be permitted to include this activity are expected to occur in late 2009. Although the literature review indicated some general trends, impacts depend on climate conditions, antecedent soil conditions, and soil type. Consequently, management decisions at the site-specific level require further quantitative assessment and follow-up evaluation, preferably using a set of standard measurement techniques and protocols. In addition, many of the studies address small-scale and short-term response to management. It is often unclear if localized impacts can be scaled up to the watershed level. In addition, if studies show adverse management impacts on soil characteristics, the
24 short duration of many studies often limits the possibility to determine if these effects will persist over the long-term.
Water Quality Conditions Following the 2007 Angora Wildfire in the Lake Tahoe Basin. 2010. J. Reuter, A. Heyvaert, A. Oliver, A. Parr, R. Susfalk. Joint report by University of California, Davis – Tahoe Environmental Research Center and Desert Research Institute, Reno, NV. 101 p. This investigation reports on a monitoring program during Water Years 2008 and 2009 to evaluate the impact of the Angora wildfire on water quality in surface runoff from urban areas, Angora Creek and downstream in the Upper Truckee River. The USGS – Carson City and the USFS – LTBMU also partnered on this project to provide data. The monitoring design was intended to address the following: (1) water quality impacts to Angora Creek within the burned watershed, (2) comparison to post-fire conditions, (3) influence of urban runoff on downstream water quality, (4) effect of passage through the Washoe Meadows (natural grass) ecosystem on downstream water quality, (5) time needed for burned area to return to pre-fire conditions, vis-à-vis, pollutant loading on water quality conditions, and (6) change in pollutant loading characteristics to Lake Tahoe, via the Upper Truckee River. Water quality data collected at a monitoring site on Angora Creek, just upstream from an urban subdivision, allowed for an evaluation of pre-fire and post-fire sediment and nutrients concentrations. This site represents the cumulative effects of the burned undeveloped upland forest where both the erosion hazard and the severity of the fire were high. An historic dataset from this site, collected by the USFS – LTBMU between 1991- 2001 proved invaluable for this comparison. All the measured nutrient and sediment constituents showed a post-fire increase – especially nitrate (a form of nitrogen available to algae). A decline in nitrate, was seen in 2009 which is typically reported in the literature. All the other constituents, save soluble reactive phosphorus (SRP), showed an increase in concentration in Year 2 (2009), presumably due to increased precipitation and flow. Other studies in the western US suggest a period of 3-10 years is needed for a recovery to near baseline conditions. There was no evidence of massive sediment or nutrient inputs from the burned area into Angora Creek. Along the downstream transect of Angora Creek, total-P load increased as flowed moved through the urban landscape. This difference was most significant in WY 2009 when precipitation and flow was higher. In WY 2008, phosphorus load declined by approximately 35 percent before reaching the Upper Truckee River while in WY 2009 this reduction was 75 percent. Load reduction was most probably related to groundwater infiltration, which is characteristic of the wet meadow. In years of higher flow the wet meadow vegetation should act to also reduce downstream transport. Since Angora Creek is tributary to the Upper Truckee River (UTR), the historic LTIMP data for the UTR was used to evaluate impacts from the fire on downstream water quality. Flow and load of suspended sediments, total nitrogen dissolved nitrogen, total phosphorus and soluble phosphorus from Angora Creek in Water Years 2008 and 2008 had no statistically significant effect on the UTR. Both years fit within the excepted flow versus nutrient load relationship seen historically for the Upper Truckee River.
2009 Addendum to 2007 Angora Wildfire Hydrophobicity Field Monitoring Report. 2010. T. Tolley, S. Norman. Lake Tahoe Basin Management Unit. The third year of data collection for hydrophobicity in the Angora Burn area is presented in this addendum. Six transects were measured for hydrophobicity, three slopes with a SE aspect were characterized as hydrophobic, three slopes with a NE aspect were not.
25 Hydrophobicity of the SE facing slopes did not change significantly over the three years. Visual observations across the entire burn area indicated that vegetation is returning vigorously, especially in areas of high burn severity. Areas covered with either vegetation, pine needles, or hydromulching showed less rilling following high runoff events. Overall, increased erosion resulting from the fire has not manifested as a serious problem, and the ground cover continues to increase.
Nutrient Emissions from Prescribed Fire in the Lake Tahoe Basin: Implications from Field and Laboratory Observations. 2010. P. Verburg, A. Shackelford, W. Chen, D. Zhu, R. Susfalk, B. Fitzgerald. Prepared by the Desert Research Institute, Reno, NV. 81 p. Prescribed fire is a common management practice for reducing excessive forest fuel loading to minimize the risk of wildfire. Prescribed fire may however adversely impact air and water quality by releasing nutrients from soils and vegetation upon combustion. The quantity and quality of nutrients released is dependent on fuel characteristics and environmental conditions. Fuel moisture is an important variable that can impact nutrient release since it affects combustion conditions. This study assesses the carbon (C) and nitrogen (N) release as affected by fuel moisture during a prescribed fire near Incline Village (NV) following mechanical thinning. The field component of this study involved a pre- and post-fire fuel inventory to estimate C and N losses under fall fuel moisture conditions. The laboratory component of the study further investigated effects of moisture on nutrient release and speciation. The laboratory study focused on the main gaseous and particulate C and N species that can affect air quality. Different fuel types were wetted followed by combustion in a custom designed combustion chamber that allowed for direct measurement of amounts and composition of nutrients released into the air. The moisture levels for soil, litter and duff ranged from 3 (air-dry) to 25% while moisture contents for vegetative materials ranged from 5 (air-dry) to 85%. Results from the field study showed that total fuel reductions were close to 90% and C and N losses closely followed patterns in fuel mass reductions. Soil extractable ammonium (NH4+) increased immediately following fire, but we no clear trends were observed for extractable nitrate (NO3-). The laboratory combustion experiment showed that increasing fuel moisture caused increases in total particulates, including PM2.5 and C and N species, and gaseous ammonia (NH3) emissions for several fuel types. Nutrient emission factors were highest for litter and leaves. The results from our study have potentially important management implications. Conducting fuel treatments when fuel moisture is low will likely maximize fuel consumption while minimizing air quality impacts. However, dry burns not only increase fuel consumption which will reduce C sequestration, they also favor conversion of fuels to CO2 which is an important greenhouse gas.
Rapid Response to a Wildfire in the Tahoe Basin. 2011. A. Getler, A. Heyvaert, Z. Hymanson, J. Long, W. Miller, J. Reuter, P. Stine. Prepared for the USDA Forest Service Pacific Southwest Research Station. 31 p. Several kinds of catastrophes could have significant immediate and persistent effects on the natural resources and habitats of the Lake Tahoe Basin. Tahoe Science efforts funded through the Southern Nevada Public Lands Management Act called upon the Tahoe
26 Science Consortium to “build a reserve to fund rapid response science efforts (e.g., focused research or short-term monitoring) deemed necessary to obtain information about the effects of catastrophes (e.g., wildfires, sewage spills, or earthquakes), or provide critical baseline information to understand the effects of restoration and remediation efforts undertaken in response to a catastrophe.” This provision was established to ensure that the science community would be prepared to mobilize an immediate response to a catastrophic event in the Basin, with the aim of developing information to understand the near-term effects of the catastrophe. The purpose of this plan is to describe the specific scientific activities that will address the most immediate information needs of government agencies, regional stakeholders, and scientists about the effects of a wildfire in the Tahoe Basin. This plan describes a strategy for focused, short-term assessments to quantify the level of impacts on air quality, soil resources, water quality, and aquatic resources. There are immediate and long term ramifications of a wildfire to a variety of natural resources, and this plan addresses only the scientific efforts associated with assessing the immediate ramifications and appropriate remedial actions.
Application to Management
Pre-settlement ecosystems in the upper watersheds of the Lake Tahoe Basin are estimated to have been typified by much smaller N and P nutrient pools in the biomass compared to their present day counterparts. Historical discharge/recharge water quality was thus likely to be more nutrient depleted, helping to facilitate the ultra-oligotrophic status of Lake Tahoe. However, fire suppression has resulted in the decline of forest health, accumulation of extremely high fuel loads, thickened O (organic) horizons, and the increased risk of catastrophic wildfires. An accumulating forest floor similar to that present in the eastern Sierra Nevada today sequesters nutrients and leads to the build-up of large nutrient pools in the biomass that provides for long-term nutrient availability to surface waters through either leaching or by way of surface runoff or litter interflow.
As an additional consequence, stand and forest floor replacing wildfire causes a large magnitude nutrient mobilization, resulting in a substantial “nutrient shock” to discharge water quality. For this reason, mechanical harvest and controlled burning have become popular management strategies in the Sierra Nevada; albeit little was previously known about how they impact discharge water quality. The most ecologically significant long- term effects of prescribed fire appear to be the loss of C and N from the forest floor. While the application of prescribed fire may have some initial impact on overland flow nutrient loading (and therefore degrading surface water quality), the effects thus far appear to be minimal (with the possible exception of S) and temporary. Over the longer term, controlled burning in conjunction with mechanical harvest has the potential to improve runoff water quality by reducing N and P discharge and improving the overall health of forest ecosystems without the danger of the nutrient mobilization shock typically associated with high intensity wildfires.
Restoration strategies are generally implemented to mitigate known adverse impacts from either natural events or anthropogenic activities. Choosing the most effective strategy requires a thorough knowledge of the mitigation objective, process mechanics, both short and long-term functionality, and whether or not these components differ depending on
27 location within a given watershed or the Tahoe basin in general. Research on soils and nutrient cycles in pristine forests should be conducted whenever possible, and sites should be established to measure nutrient cycling, including inputs, such as plant-soil fluxes through litterfall, crownwash, and root turnover as well as losses from erosion, leaching, runoff, wind, or fire. A high priority should be given to sites where a suitable control portion is available, especially if pre-event or pre-treatment data is available or can be obtained.
Finally, the fate of these forest ecosystems in a changing climate will have a direct impact on forest health, fire hazard, biomass mitigation strategies, and water quality. It is therefore important to increase our understanding of nutrient cycling in eastern Sierra Nevada watersheds in order to better understand the factors affecting the well- documented, long-term deterioration of water quality in Lake Tahoe. Future efforts focused on measuring the effectiveness of restoration and mitigation strategies should be more mechanistic, and treated as separate entities rather than as a combined program. Similar slope stabilization, infiltration, and/or re-vegetation programs should be monitored in similar and divergent environments as a means of ascertaining why some work better on improving discharge water quality than others in one locale verses another.
28 Climate Change
Overview
The 21st Century global climate is expected to experience long-term human-induced changes in response to greenhouse gases that have been added to the atmosphere by human activities. Several decades of warming and a variety of hydrologic and landscape responses have already occurred and are expected to accelerate this century until greenhouse- gas emissions are brought under control. How these Radiative forcing based on IPCC emission scenarios. A2- less global-scale climate and optimistic GHG emission scenario. B1 more optimistic GHG landscape changes will play out emission scenario. Taken from M. Dettinger. at Lake Tahoe is highly uncertain, but researchers in the Basin has begun to address this issue by (1) looking at the historic records to identify changes that can already be seen and (2) by employing state-of-the-art numerical models of the global climate system that provide a number of plausible scenarios that can be investigated and evaluated to determine likely points of particular vulnerability in the Basin’s hydrologic characteristics, nutrient and sediment loading and lake response. Since the first published paper reporting that both air temperature in the Tahoe basin and the water temperature of Lake Tahoe had measurably risen since the early 1970s (Coats et al. 2006), a number of research papers/reports have been written on the potential impact of climate change to water resources in the Tahoe basin. In particular, questions related to how climate change may affect water quality planning and the Lake Tahoe TMDL (Total Maximum Daily Load) have been investigated.
Peer Reviewed Journal Publications
Impacts of Climate Change on Lakes and Reservoirs Dynamics and Restoration Policies. 2008. G. Sahoo, G. Schladow. Sustainability Science. 3(2): 189-199. This study provided the first model results investigating climate change effects on physical processes in Lake Tahoe. A 40-year simulation showed that Lake Tahoe should continue to become warmer and more thermally stable, resulting in a reduced frequency and depth of deep mixing. Reduced mixing could have significant adverse impacts on the lake ecosystem (e.g. dissolved oxygen, bottom sediment nutrient release).
What do Lakes and Reservoirs Tell Us About Climate Changes? 2008. C. Williamson, J. Saros. Eos. 89(52): 546.
29 A total of 92 scientists and 17 students from 18 countries gathered on the shores of Lake Tahoe at a Chapman Conference (Chapman Conference on Lakes as Sentinels, Integrators, and Regulators of Climate Change; Incline Village, Nevada, 8–10 September 2008). Four working groups examined the role of lakes and reservoirs as sentinels, integrators, and regulators of climate change. They also discussed how to incorporate inland waters into global climate models. The sentinel value of lakes comes from their clear responses to changes in air temperature, precipitation, snowpack, and glacial meltwater, conference speakers reported. Signals include decreases in the duration of winter ice cover by 12 days in the past 100 years. Impoundment of water by humans accounts for a 0.55 millimeter per decade underestimate of sea level rise. Climate is also modifying the phenology of aquatic organisms, leading to a temporal mismatch between consumers and their food resources. Lakes and reservoirs are also important regulators of climate change. Although they represent only about 3 percent of the land surface area of the Earth, they play an important role in the global carbon cycle as processors of the organic carbon from terrestrial ecosystems. For more information related to this Chapman Conference on lakes and climate change held at the Tahoe Center for Environmental Science and co-hosted by the UC Davis – Tahoe Environmental Research Center see the following publications: Williamson, C., J. Saros and D. Schindler. 2009. Sentinels of Change. Science 323: 887-888 I and Williamson, C., J. Saros, W. Vincent and J. Smol. 2009. Lakes and reservoirs as sentinels, integrators, and regulators of climate change. Limnology and Oceanography 54(6): 2273-2282.
Lacustrine Turbidites as Indicators of Holocene Storminess and Climate: Lake Tahoe, California and Nevada. 2008. D. Osleger, A. Heyvaert, J. Stoner, K. Verosub. Journal of Paleolimnology. 42(1): 103-122. Sediment cores taken from Lake Tahoe permit the discrimination of turbidities (material contained in turbidity currents) initiated by seismic-inducted debris flows from those generated by severe storms over the past 7000 years. Based on multiple geochemical signatures taken from deep-water cores, the turbidites appear to show the rapid influx of terrigenous sediments within runoff from the water triggered by high intensity storms. A reasonable degree of temporal overlap suggested that turbidite clusters could provide a measure of long-term regional historic precipitation. Between ~3000 and ~900 B.P. there appeared to be an extended period of dryness in the Tahoe basin.
Lake Warming Favours Small-sized Planktonic Diatoms. 2009. M. Winder, J. Reuter, G. Schladow. Proceedings of the Royal Society. 276: 427-435. The diatoms are a very abundant group in the Lake Tahoe phytoplankton community. Since the early 1980s the strength of thermal stratification in Lake Tahoe has intensified significantly. Simultaneously, there was shift in the size-distribution of diatoms toward smaller cells (4-14 µm) over the past 25-30 years. Vertical mixing controls the annual transport of nutrients from the enriched bottom waters to the surface. As thermal stratification in Lake Tahoe became more pronounced with climate change and lake warming, mixing was reduced. This lead to a more nutrient- depleted chemical environment in the upper waters which favored small diatom species with a high surface are to volume ratio.
30 The slower sinking rate of small cells strongly influences energy transfer through the food web and carbon cycling. As stratification continues to intensify over time, the further reduction in deep mixing may select for even better-adapted species.
Satellite Observations Indicate Rapid Warming Trend for Lake in California and Nevada. 2009. P. Scheider, S. Hook, R. Radocinski, G. Corlett, G. Hulley, G. Schladow, T. Steissberg. Geophysical Research Letters. Vol. 36. DOI:10.1029/2009GL040846. Lake larges are excellent indicators of climate change; however, their usefulness is limited by the lack of in situ measurements and the paucity of long-term data records. Thermal infrared satellite imagery was shown in this study to provide frequent and accurate retrievals of lake surface temperatures spanning several decades on a global scale. The results of this data analysis showed that for six California and Nevada lakes (Lake Tahoe, Lake Almanor, Clear Lake, Pyramid Lake, Walker Lake and Mono Lake), average summer nighttime lake temperature in the near surface water have warmed at a rate of 0.11±0.02 °C per year since 1992. This independently confirmed the warming trend for Lake Tahoe published by Coats et al. in 2006. For the six lakes, the lake surface temperature is warming approximately twice as fast as the average minimum air temperature, as measured from a buoy near the lake surface.
Space Observations of Inland Water Bodies Show Rapid Surface Warming Since 1985. 2010. P. Schneider, S. Hook. Geophysical Research Letters. (37), L22405, DOI 10.1029/2010GL045059. Surface temperatures were extracted from nighttime thermal infrared imagery of 167 large inland water bodies distributed worldwide beginning in 1985 for the months July through September and January through March. Results indicate that the mean nighttime surface water temperature has been rapidly warming for the period 1985–2009 with an average rate of 0.045 ± 0.011°C yr−1 and rates as high as 0.10 ± 0.01°C yr−1. Worldwide, the data show far greater warming in the mid‐ and high latitudes of the northern hemisphere than in low latitudes and the southern hemisphere. The analysis provides a new independent data source for assessing the impact of climate change throughout the world and indicates that water bodies in some regions warm faster than regional air temperature. The data have not been homogenized into a single unified inland water surface temperature dataset, instead the data from each satellite instrument have been treated separately and cross compared. Future work will focus on developing a single unified dataset which may improve uncertainties from any inter‐ satellite biases.
Climate Change in the Tahoe Basin: Regional Trends, Impacts and Drivers. 2010. R. Coats. Climatic Change. DOI 10.1007/s10584-010-9828-3. Decadal-scale time trends in historic air temperature, precipitation and intensity, spring snowmelt timing, and lake temperature at Lake Tahoe were quantified and related to large-scale climatic trends in the western USA. The results for the Tahoe basin contrast somewhat with the surround region. The air temperature and precipitation data for Lake Tahoe show a shift from snow to rain, a decline in the number of winter days below freezing, and an increase in both the frequency and the extremes of intense rainfall over the period 1910-2007. Total annual
31 precipitation at Tahoe City seemed to trend slightly upward but this was not statistically significant. Streamflow records in the Tahoe basin show a shift towards earlier dates in the peak of snowmelt runoff for the period 1961-2005. A similar trend was not necessarily seen outside of the Tahoe basin. The volume of Lake Tahoe has warmed at an average rate of 0.013 °C per year between 1970-2007, and the large heat budget of the lake itself may be enhancing the affect of anthropogenic greenhouse gases.
Other Scientific Literature
The Effects of Climate Change on Lake Tahoe in the 21st Century: Meteorology, Hydrology, Loading and Lake Response. 2010. R. Coats, J. Reuter, M. Dettinger, J. Riverson, G. Sahoo, G. Schladow, B. Wolfe, M. Costa-Cabral. Prepared for SNPLMA Science Round 8. 200 p. Details of expected meteorologic conditions over the next 100 years, based on various emission scenarios for greenhouse gases, were modeled for the Tahoe basin using a sophisticated downscaling methodology. This information was used in a series of water resource models to investigate possible changes hydrology, sediment and nutrient loading to Lake Tahoe, BMP design and effectiveness and lake response during the 21st Century. Highlights of this research suggest: (a) upward trend for air temperature, (b) o strong trends in the amount of annual precipitation, (c) a continuing shift from snowfall to rain along with an earlier timing of snowmelt and runoff, (d) some increase in drought severity, (e) dramatic increases in flood magnitude in the middle third of the century, (f) sediment and nutrient loading to Lake Tahoe should not increase to any meaningful level, and water yield may decline, (g) climate change will result in a modest decline in BMP performance for fine sediment particle load may decline modestly, however, load reduction should still be significant, (h) by the middle of the 21st Century Lake Tahoe could cease to mix to the bottom, resulting in complete oxygen depletion in the deep waters and an increase in sediment release of nitrogen and phosphorus – effect on Lake Tahoe’s nutrient budget would be dramatic with a probable dramatic and long-lasting impact on the food web and trophic status of Lake Tahoe, (i) the resulting annual Secchi depth in the later portion of the 21st Century could be in the range of 15-20 m as compared measured values of 21-22 m since 2000 and, (j) climate change could drive the lake surface level down below the natural rim towards the end of the Century.
Application to Management
The 21st Century global climate is expected to experience long-term changes in response to anthropogenic greenhouse gas emissions. Discussions on the potential impacts of climate change on water resources in the Tahoe basin have only recently begun and our scientific understanding to date has focused on identifying existing impacts and trends in the historic data. Based on the studies above, lake physical processes (mixing), nutrient loading from the bottom sediments, hydrology and biodiversity are all likely to be further impacted by continued climate change. An important topic not yet investigated is the possible impact of a warmer lake on the ability of aquatic invasive species to colonize and flourish. While water resource managers need to take all the into consideration
32 discussions are needed on how to best develop a management strategy (1) under conditions of high uncertainty (i.e. predicting conditions out over 100 years not assured) and (2) over a period of perhaps 100 years into the future (i.e. management time-scales cannot be assured past a period of 1-2 decades).
33 Groundwater Overview
Groundwater in the Lake Tahoe basin is the primary source of domestic and municipal water supply and an important source of inflow to Lake Tahoe. The most extensive and productive aquifers in the Lake Tahoe basin are composed of younger alluvium, glacial till and outwash deposits, and at depth, older alluvium. There are five major aquifers areas around the lake; South Lake Tahoe/Stateline, Tahoe City West Shore, Kings Beach/Tahoe Vista, Incline Conceptual model of groundwater and hydrologic cycle Village, and East Shore (includes Sand in Lake Tahoe. Source: US ACOE, Sacramento District. Harbor, Glenbrook, and Zephyr Cove). Each aquifer is bounded by the shore of Lake Tahoe and by the contact between basin fill and bedrock. The maximum thickness of the aquifers probably is at the shoreline at a depth of about 1,000 ft to bedrock. Water levels below land surface ranged from 1-260 feet with a median of 8 feet and ranged 6,230 to 7,260 feet altitude of land surface for 188 wells in the database. Over the past 30–40 years, Federal, State, and local agencies, and research institutions have collected hydrologic data to quantify the groundwater resources in the Lake Tahoe basin. In 1990, USGS and Tahoe Regional Planning Agency (TRPA) established a groundwater monitoring network with 32 sampling sites to provide a long-term database on groundwater. Previous groundwater studies found concentrations of nitrogen, phosphorus, and iron to be greater in ground water than in the lake. As part of the Lake Tahoe TMDL, it was identified that groundwater accounted for 13 and 15 percent of the basin-wide nitrogen and phosphorus loading, respectively.
Peer Reviewed Journal Publications
Other Scientific Literature
Hydrologic and Water-Quality Responses in Shallow Ground Water Receiving Stormwater Runoff and Potential Transport of Contaminants to Lake Tahoe, California and Nevada, 2005-07. 2008. J. Green, C. Thodal, T. Welborn. U.S. Geological Survey Scientific Information Report 2008-5162, 65 p. Detention basins are considered effective best management practices for mitigation of suspended sediment and nutrients associated with runoff, but effects of infiltrated stormwater on shallow ground water are not known. The results of the groundwater flow model indicate mean groundwater discharge of 256 acre feet per year, contributing 27 pounds of phosphorus and 765 pounds of nitrogen to Lake Tahoe within the modeled area; however, only 0.24 percent of
34 this volume and nutrient load was attributed to stormwater infiltration from the associated detention basin. Settling of suspended nutrients and sediment, biological assimilation of dissolved nutrients, and sorption and detention of chemicals of potential concern in bottom sediment are the primary stormwater treatments achieved by the detention basins. Mean concentrations of unfiltered nitrogen and phosphorus in inflow stormwater samples compared to outflow samples show that 55 percent of nitrogen and 47 percent of phosphorus are trapped by the detention basin. Organic carbon, cadmium, copper, lead, mercury, nickel, phosphorus, and zinc in the uppermost 0.2 foot of bottom sediment from the detention basin were all at least twice as concentrated compared to sediment collected from 1.5 feet deeper.
Hydrogeology of the Lake Tahoe Basin, California and Nevada. 2009. R. Plume, M. Tumbusch, T. Welborn. U.S. Geological Survey Scientific Investigations Map 3063, 1 sheet. To successfully and efficiently manage the ground-water resources throughout the Lake Tahoe basin, the U.S. Geological Survey (USGS) in cooperation with the U.S. Forest Service (USFS) compiled and evaluated the pertinent geologic, geophysical, and hydrologic data, and built a geodatabase incorporating the consolidated and standardized data for the Lake Tahoe basin that is relevant for examining the extent and characteristics of the hydrogeologic units that comprise the aquifers.
Investigation of Groundwater Flow in Foothill and Mountain Regions Using Heat Flow Measurements. 2009. J. Trask, G. Fogg. UC Water Resources Center Technical Completion Report Project No. WR-1006. 74 p. A field and model investigation was performed to assess the potential of subsurface temperature measurements for tracing groundwater flow in montane areas. Modeling investigations include development of a novel, conceptually simple ‘black box’ subsurface thermal energy balance approach. This robust model approach can be used together with T-profile data to bracket the rate of mountain-front groundwater recharge. Temperature profiles measured in the Tahoe basin region indicate that there are substantial areal differences in the rate of high elevation deep bedrock groundwater recharge, and in valley bedrock discharge. Surface T and T-profile measurements together are shown to be useful in defining valley basin-fill aquifer recharge sources. Subsurface heat flow patterns are altered in distinct ways, as reflected in T-profiles, by recharge into the top (soil percolation down to water table), sides (mountain-front recharge) and bottom (mountain- block recharge) of montane valley basin-fill aquifers.
Application to Management
To successfully and efficiently manage the groundwater resources throughout the Lake Tahoe basin, the U.S. Geological Survey (USGS) in cooperation with the U.S. Forest Service (USFS) compiled and evaluated the pertinent geologic, geophysical, and hydrologic data. A geodatabase was built incorporating the consolidated and standardized data for the Lake Tahoe basin that is relevant for examining the extent and characteristics of the hydrogeologic units that comprise the aquifers. Managers are concerned with groundwater because of use as a drinking water supply and because it is a pathway for pollutant loading to Lake Tahoe. The pollutants of concern extend beyond
35 those considered important for lake clarity, and include toxic compounds. The relationship between infiltration/percolation basins used for urban stormwater treatment is a growing topic of inquiry at Lake Tahoe that needs further research. Water quality treatment basins at Lake Tahoe are designed to capture stormwater runoff and allow sediments, nutrients and other pollutants to filter out before reaching a surface water body. The ultimate impact of these BMPs on groundwater quality and drinking water supplies will benefit from continued research.
36 Lake Tahoe TMDL
Overview
The California water quality target for Secchi depth is 29.7 m (97 feet). Since values are now 10 m (33 feet) worse, the U.S. Clean Water Act requires the establishment of a TMDL or total maximum daily load.” A TMDL is a water quality protection program to restore lake clarity and achieve the intended water quality target. The Lake Tahoe TMDL for clarity consists of three phases: (1) Existing inputs and pollutant load capacity, (2) Pollutant reduction analysis and planning, and (3) Implementation and operation. Protection of Lake Tahoe’s famed clarity is goal of the TMDL. Phase 1 focused on: Source: Charting the Course to Clarity. What pollutants are causing Lake Tahoe’s clarity loss? How much of each pollutant is reaching the Lake? How much of each pollutant can Lake Tahoe accept and still achieve the clarity goal?
Phase 2 addressed: What are the options for reducing pollutant inputs? What is the best strategy for implementing load reduction? Phase 3 considers: Are the expected reductions being met? Is clarity improving in response to load reductions? Can innovation and new information improve success?
A 20-year interim goal, known as the Clarity Challenge has been established. It requires basin-wide pollutant load reductions be achieved within 15 years, followed by five years of monitoring to confirm that 24 m (79 feet) of Secchi depth transparency has been reached. The 24 m value represents and actual improvement of clarity.
Peer Reviewed Journal Publications
Effect of Sediment and Nutrient Loading on Lake Tahoe Optical Conditions and Restoration Opportunities Using a Newly Developed Lake Clarity Model. 2010. G. Sahoo, G. Schladow, J. Reuter. Water Resources Research, 46. W10505,
37 doi:10.1029/2009WR008447. A quasi two dimensional lake clarity model (LCM) has developed for the Lake Tahoe TMDL to better understand the impacts of pollutant load on lake/reservoir water quality and to provide guidelines for lake/reservoir management and restoration. Though the LCM can be applied to any lake, the model was calibrated and validated using the available detailed data set of Lake Tahoe. The estimated and measured annual average Secchi depths demonstrate a very high degree of agreement with relative error of less than 6 percent. The sensitivity analysis was performed on those parameter(s)/load(s) found to have a large effect on lake clarity. Loading and settling rates of fine inorganic particles (<16 mm in diameter) were found to have the largest effect on lake clarity. Atmospheric load adds inorganic particles and nutrients to the surface layer, thus directly affecting lake clarity. Since maximum chlorophyll a concentration is observed in deep water (approximately 50 m below surface) during spring and summer, the Secchi depth (approximately 20–22 m) was found to be relatively insensitive to the change in chlorophyll a concentration in this deep layer. The model was used to simulate different load reduction scenarios to help answer questions such as how much load reduction is needed to restore Lake Tahoe’s historic clarity of approximately 30 m and how quickly this change can be achieved? The LCM provides a firsthand scientific solution to managers that the historic clarity can be achieved if total reduction of nutrients and inorganic particles loads will be reduced to approximately 55% from all sources or approximately 75% from urban sources.
Other Scientific Literature
Understanding the role of stormwater management activities in the Lake Tahoe clarity TMDL: Application of a meta-heuristic optimization technique for cost-benefit evaluation among pollutant sources. 2008. J. Riverson, J. Zhen, K. Alvi, J. Sokulsky, C. Praul, J. Reuter. Proceedings of the Water Environment Federation, WEFTEC 2008: Session 71 through Session 80, pp. 5617-5635(19). The primary stressors associated with Lake Tahoe’s decline in clarity have been identified as nutrient driven algae production and an increase in ultra-fine sediment. Sources of nutrients and sediments are primarily urban runoff and forest upland erosion, atmospheric deposition, and stream channel erosion. $1.5 billion is the estimated cost of restoring lake clarity, and therefore a premium has been placed on developing informative decision support analyses. A meta-heuristic optimization technique was applied to evaluate cost-benefits and selection trade-offs among various pollutant control methods. Three strategies were examined to better recommend a management strategy: (1) extension of current practice, (2) focus on innovation, (3) an all out push. The recommended strategy focused on maximizing control of fine sediment particles because this pollutant is responsible for approximately 66% of clarity loss. Controlling urban storm water sources made the greatest impact to improving clarity. The next step in the process is to translate the recommended strategy into a TMDL implementation strategy.
Lake Tahoe TMDL Pollutant Reduction Opportunity Report v2.0 (PRO Report v2.0). 2008. Prepared by the California Regional Water Quality Control Board, Lahontan Region, Nevada Division of Environmental Protection. 279 p.
38 This report outlines the pollutant control options available for the following sources of pollutants: atmospheric deposition, urban uplands, groundwater, forested uplands, and stream channel erosion, including treatment tiers and analysis methodology for each. It outlines the potential pollutant load reductions associated with each based on different levels of effort, as well as anticipated costs of implementation on a basin-wide scale.
Integrated Water Quality Management Strategy Project Report v1.0. 2008. Prepared by the California Regional Water Quality Control Board, Lahontan Region, Nevada Division of Environmental Protection. 108 p. The Integrated Water Quality Management Strategy Project is part of the Lake Tahoe TMDL development process and aims to answer the following questions: a. What are the options for reducing pollutant inputs to Lake Tahoe? b. What strategy should we implement to reduce pollutant inputs to Lake Tahoe? The answers to question (a) were developed by technical experts and are outlined in PRO Report v2.0. Question (b) requires an integrated strategy that employs pollutant controls in each of the four primary sources of fine sediments and nutrients to Lake Tahoe: urban uplands, forested uplands, atmospheric deposition, and stream channel erosion. The Recommended Strategy uses the best available science and extensive stakeholder input to describe a strategy to inform the Lake Tahoe TMDL implementation plan so that the Clarity Challenge may be achieved. It is also intended to guide implementing agencies in their efforts to reduce pollutant loading. However, site specific implementation strategies will need to be developed for each geographically different project location. The Recommended Strategy focuses on urban runoff and includes three treatment tiers with the following source controls: a. Best Current Practices (Tier 1) – detention and retention basins, stormwater vaults, road shoulder stabilization, vacuum sweeping on heavily sanded roads, limited impervious coverage b. Advanced, Intensive Practices (Tier 2) – Wetland and passive filtration basins, media filters in stormwater vaults, deicing compounds or advanced abrasive (sand) recovery, intensive maintenance of stormwater infrastructure, 100% completion of private property BMPs c. Innovative Technology (Tier 3) – Active pumping and filtration systems for stormwater applied to urban areas with concentrated impervious coverage (such as downtown areas) and Tier 2 treatment applied to urban areas with dispersed impervious coverage (such as many residential areas). The Recommended Strategy focuses on stationary sources dust resulting in atmospheric deposition, such as vacuuming, paving dirt roads, enacting speed limits in dirt roads, laying gravel on dirt roads, using dust suppressing moisture during construction projects, reducing residential wood burning emissions. It is recommended that stream channel erosion be tackled by restoring the Upper Truckee River, Blackwood Creek, and Ward Creek first because of their high contribution of sediment and nutrient loading. This will be accomplished through bank protection, bank strengthening, toe stabilization, bank lowering or angle reduction. Forested upland erosion may be controlled by waterbars, armored ditches, and rut stablization on unpaved roads, hydro-seeding and tackifier for ski runs, mulching and revegetation on ski runs, road re-contouring, tilling, soil amending, and urban sediment capture to name a few.
39 This report also describes how the Recommended Strategy was developed and the analyses used to determine how pollutant loads were allocated.
Charting the Course to Clarity 2008-2009: The Lake Tahoe Total Maximum Daily Load. 2009. Prepared by the Lahontan Regional Water Quality Control Board and the Nevada Division of Environmental Protection. 32 p. Lake Tahoe’s clarity can be restored. Scientific research tells us that it is possible for people to once again be able to see to depths of close to 100 feet in Lake Tahoe. The California Regional Water Board, Lahontan Region (Lahontan Water Board) and Nevada Division of Environmental Protection (NDEP) are committed to the Lake Tahoe TMDL, a strategy to return Lake Tahoe to a clarity depth of nearly 100 feet, the clarity standard. Although Lake Tahoe clarity has been in decline for decades, recent science indicates the rate of decline has slowed. This good news is likely in response to the water quality improvement projects that are part of the Environmental Improvement Program (EIP). Science shows that an increase in the number and efficacy of these and other types of water quality improvement projects is key to achieving the clarity standard. Charting the Course to Clarity 2008-2009 presents highlights of the strategy for restoring Lake Tahoe’s clarity. If citizens and their government agencies support an effective course of action based in scientific understanding of Lake Tahoe, the clarity standard can be achieved. The strategy presented in this document is the result of decades of data collection, the work of hundreds of scientists and engineers, and the involvement of citizens. The key questions regarding Lake Tahoe clarity are: a. What pollutants are causing Lake Tahoe’s clarity loss? b. How much of each pollutant is reaching Lake Tahoe? c. How much of each pollutant can Lake Tahoe accept and still achieve the clarity standard? d. What should be the strategy for reducing pollutant inputs to Lake Tahoe? e. How will the strategy be implemented? f. How will progress be assessed? The Lahontan Water Board and NDEP propose the Clarity Challenge; a call to reverse the clarity decline and to achieve and sustain clarity nearing 80 feet by 2025. Realizing the Clarity Challenge is an essential first step toward ultimately achieving the historic clarity of nearly 100 feet. Slowing the clarity decline is an important step. Reversing the decline will be even bigger. The Clarity Challenge is a call to action—successful restoration of the Lake will require the sustained daily, coordinated participation of people and their governments. Achievement of the Clarity Challenge is estimated to require 1.5 billion dollars (in 2008 dollars) in capital improvement costs over the next 20 years. Financial and participatory commitment by the people vested in the ecological, social and economic vitality of Lake Tahoe is essential to success. Coordinated commitments and resources at the private, local, state and federal level, contributing to the overall objectives of the EIP, will make the return to clarity possible.
Charting the Course to Clarity Video. 2009. Prepared by the Nevada Tahoe Conservation District. Lake Tahoe's famed clarity is being impacted by fine sediment particles and nutrient pollutants. The Tahoe Total Maximum Daily Load (TMDL) was a science-based effort designed to determine pollutant reductions needed to restore historic clarity within the
40 Lake and craft a cost-effective, workable strategy to reduce them. This video describes the TMDL analysis and provides information on what you can do to help.
Lake Tahoe Advanced Stormwater Treatment Feasibility Analysis (Phase II). 2009. Prepared for the Army Corps of Engineers. Prepared by 2NDNATURE. The reduction of fine sediment particle loading to Lake Tahoe is the main focus of the Lake Tahoe Total Maximum Daily Load (TMDL). Stormwater generated from urban areas has been identified as the major contributor of fine particles to the lake. The two most effective means of reducing this load have been identified as source control and/or stormwater treatment. Advanced stormwater collection and treatment may be the best way to meet TMDL targets. Phase I of this study identified microfiltration as the technology with greatest potential for treating fine particles in urban stormwater. The Phase II study narrows the uncertainties associated with the lack of stormwater implementation experience regarding microfiltration performance, and the feasibility of applying it to stormwater using Placer County as an example. Implementation appears to be most feasible in more densely developed urban drainages because necessary stormwater collection and storage systems would be more expensive in less densely developed areas. This suggests that microfiltration may not be a cost- effective solution for many of the urban drainages in the Tahoe Basin and therefore unlikely to meet the future TMDL goals alone. It is estimated that a reduction of 80% of fine sediment loading could be achieved if microfiltration was implemented in three candidate catchments (Kings Beach, Tahoe City and Lake Forest). However, these three catchments are estimated to constitute less than 10% of the total Placer County fine sediment load. Source control can realistically be applied to a much greater urban area in the Tahoe Basin than the collection and storage systems necessary for the application of microfiltration.
BMP RAM Technical Document: Tool Prepared For Use By The Lake Tahoe Stormwater Community and Environmental Improvement Program (EIP). 2009. Prepared for the Lake Tahoe Stormwater Community and Environmental Improvement Program. Prepared by 2NDNATURE. 55 p. The Best Management Practices Rapid Assessment Methodology (BMP RAM) is a tool that can assist Lake Tahoe natural resource managers in assessing the relative condition of urban stormwater Treatment BMP’s. It uses simple and repeatable field observations to determine the maintenance urgency for a particular Treatment BMP. Four distinct treatment processes have been identified to target fine sediment particles and nutrients in stormwater runoff known to impair Lake Tahoe water quality: infiltration, particle settling, media filtration and nutrient cycling. These four processes have been used to define twelve unique Treatment BMP types, each one having one or more specific rapid field observations to evaluate the functional condition of the Treatment BMP. Field observations are analyzed and expressed as a BMP RAM score from 0 (worst) to 5 (best). This tool can be used to track conditions over time, and will inform future improvements in design and maintenance strategies of Treatment BMPs.
BMP RAM User Manual V.1: Tool Prepared For Use By The Lake Tahoe Stormwater Community and Environmental Improvement Program (EIP). 2009. Prepared for the
41 Lake Tahoe Stormwater Community and Environmental Improvement Program. Prepared by 2NDNATURE. 110 p. Assessment Methodology (BMP RAM) evaluations provide a practical, consistent and reliable tool to track the condition of a particular urban stormwater Treatment BMP. The primary purpose of the BMP RAM is to inform resource managers of the relative urgency of maintenance for a particular Treatment BMP based on an assessment of its condition relative to its condition at time of installation or immediately following complete maintenance. The BMP RAM is comprised of six STEPs: (1) define urban catchment of interest, (2) create inventory of Treatment BMPs, (3) set benchmark and threshold values for fine sediment, total suspended sediment, phosphorus and nitrogen loading, (4) conduct field observations, (5) calculate BMP RAM score using BMP RAM database, (6) analyze results.
Pollutant Load Reduction Model (PLRM) – Model Development Document. 2009. Prepared for California Regional Water Quality Control Board, Lahontan Region, US Army, Corps of Engineers and Southern Nevada Public Lands Management Act. Prepared by Northwest Hydraulic Consultants Inc., Geosyntec Consultants, Inc. and 2NDNATURE. 95 p. plus appendices. Three documents are available to Pollutant Load Reduction Model (PLRM) users to assist in applying and understanding the PLRM: a. User’s Manual b. Applications Guide c. Model Development Document The User’s Manual and Applications Guide provide information that is directly applicable to setting up and performing basic PLRM simulations. The information in this Model Development Document supplements these documents to provide the interested reader with more background on the PLRM program structure; development of data sets supporting the PLRM; and technical algorithms used to develop data sets as well as inform computational methods. Although the information in this document will not generally be needed to perform basic simulations, it provides important background on the fundamental model structure and supports a more in-depth understanding of model computations and a baseline for future model development. This document is organized into the following sections and topics. a. Section 2 – PLRM Technical Overview: Provides an overview of the program structure, the file structure, and the supporting database. b. Section 3 – Precipitation and Meteorological Extrapolation: Describes the methods used to generate location specific precipitation and temperature data to run long-term continuous simulations of hydrology. Appendix A supplements this section. c. Section 4 – Hydrologic Properties and Methods: Describes the methods and data sets used to simulate infiltration using the Green-Ampt method; tracks volumes infiltrated to groundwater; accounts for evapotranspiration; and simulates snowmelt. d. Section 5 – Land Use Conditions and Pollutant Source Controls: Describes the methods and data sets used to represent pollutant source controls (PSCs). Two separate methods are used to represent the implementation of PSCs on 1) public right-of-ways (Road Methodology), and on 2) predominantly private land uses (Parcel Methodology). Appendix B and C provide additional information:
42 Appendix B describes the effort undertaken to apply available Tahoe storm water quality monitoring data and qualitative observations to identify key urban road conditions influencing water quality and estimate associated characteristic runoff concentrations (CRCs). Appendix C describes the assumptions used to create a default primary and secondary urban road risk GIS layer to categorize and prioritize relative risk of all urban roads with respect to potential water quality degradation. e. Section 6 – Hydrology and Hydrologic Source Controls: Describes the methods used to represent hydrologic source controls (HSC), including the representation of private property BMPs. f. Section 7– Storm Water Treatment: Describes the methods and data sets used to represent storm water treatment (SWT). Describes the types of SWT facilities than can be represented, and their representation using SWMM5 objects. Reference information and assumptions are provided for the development of characteristic effluent concentrations (CECs) for each SWT type. Sections 3 through 7 of this document provide summaries of key data sets and technical algorithms developed for the PLRM. Each individual summary is organized into the following sub-topics: a. Background – where applicable to the topic, a brief description of SWMM5 computational methods applied or other applicable information to the data set or technical algorithm b. Capabilities – function of the data set or technical algorithm as implemented in the PLRM c. Approach – a summary of the approach developed d. Confidence – the overall confidence in results that will be generated by the model in a range of applications is generally described in terms of 1) uncertainty, 2) sensitivity, and 3) user flexibility e. Associated Database Tables – where applicable to the topic, the relevant tables or queries associated with the data set or technical algorithm f. Future Supporting Efforts – recommendations for future development g. References – references consulted to develop the data set or technical algorithm
This technical report is supplemented by the following documentation/software packages. The reader is requested to visit the TRPA TIIMS website (http://tiims.org/TIIMS-Sub- Sites/PLRM/docs-downloads.aspx) to download these section. Further, instructions on the application of PLRM is also found on TIIMS (http://tiims.org/TIIMS-Sub- Sites/PLRM.aspx).
PLRM Software Installation Package (24.9 MB EXE File) (January 2010) - Downloading the PLRM software to your computer requires saving the EXE file and following the installation instructions found in the User's Manual in Section 1.5.
Microsoft Access Runtime Installation Package (57.6 MB EXE File) - Microsoft Access Runtime 2007 is a free program that needs to be installed to run the PLRM if you do not have Microsoft Access 2007 installed on your computer. If you do have Microsoft Access 2007 installed, you do not need to download or install Runtime 2007.
User's Manual (December 2009) - The manual is the primary document describing how to use the PLRM. The manual provides information that is directly applicable for setting up and performing basic PLRM simulations.
43 Applications Guide (October 2010) - The guide provides simple example applications of the PLRM. The example applications walk the user through the basic concepts for developing a PLRM simulation.
Model Development Document (October 2009) - The document supplements the User's Manual by providing the interested reader with more background on the PLRM program structure; development of data sets supporting the PLRM; and technical algorithms used to develop data sets as well as inform computational methods.
Road Risk GIS Layer (March 2011) - The GIS shapefile provides default Road Risk Categories for Primary and Secondary Roads in the Tahoe Basin. This information is a necessary input for the PLRM in the Road Methodology. The March 2011 version includes updates to Washoe County, Douglas County, and the City of South Lake Tahoe.
Road Shoulder Condition GIS Layer (March 2011) - The GIS shapefile provides estimated PLRM attributes for road shoulder condition and impervious area connectivity for all Tahoe Basin roads. Attributes were estimated in 2010. A document summarizing the methods used to develop the GIS layer, as well as guidance on how to interpret the attribute table is provided in the Zip file download.
PLRM Met Grid (March 2011) - The GIS shapefile provides the PLRM Meteorological Grid. Also included in the download are two Google Earth KML files. One KML file provides the ID for each Met Grid that is entered in PLRM. The other KML file provides the estimated average annual precipitation for each Met Grid.
PLRM Input Template (October 2010) - Microsoft Excel file that can be used to document all PLRM inputs in an easily reviewable format.
PLRM Update History (October 2010) - The text file describes updates to the PLRM software and supporting documentation.
Lake Clarity Crediting Program Handbook: for Lake Tahoe TMDL Implementation v0.99. 2009. Prepared for Lahontan Water Quality Control Board and Nevada Division of Environmental Protection. Prepared by Environmental Incentives, LLC. South Lake Tahoe, CA. 173 p. The Lake Clarity Crediting Program (Crediting Program) establishes the framework that connects on-the-ground actions to the goal of restoring Lake Tahoe clarity. It defines a comprehensive and consistent accounting system administered by the Lahontan Regional Water Quality Control Board (Water Board) and the Nevada Division of Environmental Protection (NDEP) to track pollutant load reductions from urban stormwater using Lake Clarity Credits. The Crediting Program aligns policies with ongoing implementation in order to drive accountability and motivate effective action to improve Lake Tahoe clarity. Urban stormwater contributes more than 70 percent of fine sediment particles and a significant portion of the nitrogen and phosphorus loads to the lake. The Clarity Challenge defines an interim clarity milestone of 24 meters. Meeting this milestone requires a 34 percent basin-wide reduction of fine sediment particles from urban stormwater. The Lake Clarity Credit is defined on the basis of a relationship among pollutant load reductions (load reductions) of fine sediment particles, total nitrogen and total phosphorus. The current credit definition focuses on load reductions of the primary pollutant of concern: fine sediment particles. 1 Lake Clarity Credit = 1.0 x 1016 fine sediment particles with a diameter smaller than 16 m Pollutant load reduction is defined as the difference between the estimated average annual amount of pollutants entering Lake Tahoe under standard baseline conditions5
44 and the estimated average annual amount of pollutants entering the lake under expected conditions. All pollutant loading reaching a surface waterbody that flows to Lake Tahoe is assumed to enter the lake. Credits are awarded annually for effective, ongoing implementation of pollutant controls in urban catchments.
Load Reduction Planning Tool (LRPT): A Tool to Estimate the Water Quality Benefits of Parcel Scale Retrofit Projects in the Tahoe Basin. 2010. Prepared for the Army Corps of Engineers. Prepared by 2NDNATURE. 35 p. The LRPT is used to estimate the potential water quality pollutant load reductions associated with implementing proposed Best Management Practices (BMPs) on the scale of individual parcels. These include redevelopment projects, private parcel retrofits and single family BMP implementation in the Tahoe Basin. This report presents a Microsoft Excel application that uses site specific data input by the user to represent the spatial heterogeneity of surfaces and a simple mathematical model that routes runoff across a parcel to estimate average annual runoff from the site. It also includes a function to estimate performance decay of BMPs over time as a function of commitment to maintenance. The document provides a description of the calculations used, a user guide, and recommendations for future improvements to the estimation tool.
PLRM, Focused Stormwater Monitoring to Validate Water Quality Source Control and Treatment Assumptions. 2010. Prepared for the US Army, Corps of Engineers. Prepared by 2NDNATURE. 118 p. The Pollutant Load Reduction Model (PLRM) is a tool used to quantify the pollution generated from a catchment based on land uses. It allows resource managers to estimate pollutant load reductions resulting from proposed urban stormwater quality improvement options and compare alternatives. The objective of this Phase I database refinement monitoring is to develop a more comprehensive understanding of the generation, transport and fate of fine particles, particularly from urban roads, as well as the treatment efficiency of stormwater treatment BMPs. Datasets are also intended to inform two rapid assessment methods (RAMs), the BMP RAM and the Road RAM. A stormwater data collection strategy was implemented to address current water quality data gaps for urban roads. Thirty-two urban roads and two impervious commercial land use areas were selected within the Tahoe Basin to represent six road risk categories as defined by the PLRM Road Methodology. Various data were collected to characterize the conditions of the road with regard to fine particles and total suspended sediment. Sweeping, source control may change sediment loads, but it was found that a number of visual and rapid proxies appear to be promising predictors of TSS and FSP concentrations measured on urban road surfaces.
Lake Tahoe Total Maximum Daily Load Technical Report. June 2010. Prepared by the California Regional Water Quality Control Board, Lahontan Region, Nevada Division of Environmental Protection. 350 p. This report provides the scientific justification for the Final Lake Tahoe TMDL for fine sediment, nitrogen and phosphorus, the pollutants responsible for reducing deep water transparency in Lake Tahoe. It focuses on identifying pollutant sources and the amount of pollutant load reduction necessary for achieving water quality objectives. It is intended
45 to provide the framework for evaluating various pollutant control opportunities to inform an Integrated Water Quality Management Strategy (IWQMS; see below), a single Recommended Strategy that will describe how the restoration of lake transparency will be accomplished. A source analysis lists groundwater input, shoreline erosion, upland inputs (forest and urban), stream channel erosion, and atmospheric deposition as the major sources of pollutants to the lake, with fine sediments being the most detrimental to lake optical properties. The Lake Clarity Model is presented that simulates lake response (Secchi depth) to changes in pollutant loading.
Final Lake Tahoe Total Maximum Daily Load Report. October 2010. Prepared by the California Regional Water Quality Control Board, Lahontan Region, South Lake Tahoe, CA and Nevada Division of Environmental Protection, Carson City, NV. 380 p. The Clean Water Act requires states to establish total maximum daily loads (TMDLs) for water bodies that do not meet water quality standards. Lake Tahoe has not met its deep water transparency standard since its adoption due to the increase in fine sediment particles that scatter light, and increased phytoplankton growth from nutrient inputs that absorb light. The goal of the Lake Tahoe TMDL is to restore Lake Tahoe’s deep water transparency with a 29.7 meter annual average Secchi depth. This document summarizes the Numeric Target, Pollutant Source Analysis, Load Allocations, Implementation Plan, Adaptive Management Process, and required Regulatory Analysis for achieving this goal. Achieving the goal is expected to take 65 years. However, a 20-year interim goal, known as the Clarity Challenge, has been set that requires basin-wide load reductions of nitrogen, phosphorus and fine sediment particles to occur in 15 years, with a five-year post reduction monitoring period to confirm that a 24 meter Secchi depth has been reached. The Integrated Water Quality Management Strategy Report (see below) outlines one Recommended Strategy for meeting the Clarity Challenge goal. The Recommended Strategy focuses on reducing fine sediment input to the lake from the four largest pollutant sources (source categories): urban upland runoff, atmospheric deposition, forested upland runoff, and stream channel erosion. The Lake Tahoe TMDL implementation plan described in this document emphasizes ongoing implementation of known technologies for reducing fine sediment loading, as well as encouraging new and innovative ways to treat stormwater, manage forested lands, restore streams, and reduce dust to name a few. This document also describes the necessity for monitoring, adaptive management, public participation, and regulatory analysis to ensure the success of the meeting the Clarity Challenge over the next 15 years.
Adaptive Management and Effective Implementation of Sediment TMDLs in the Lake Tahoe Basin. 2010. M. Grismer, K. Drake, M. Hogan. Watershed Science Bulletin. October 2010. In the Lake Tahoe basin, reaching the TMDL targets for fine sediment particles (<16 m) is especially important as part of efforts to improve declining Lake clarity as well as to protect and restore other beneficial uses. The study objectives include: 1) to demonstrate use of a modeling approach that is based on several years of data collection to predict daily sediment loads and possible reductions from the Boulder Bay (BB) urban redevelopment area on the Lake’s north shore and the Homewood Creek (HMR) watershed on the Lake’s west shore, and 2) illustrate how
46 adaptive management can be applied on a site- or program-scale to measure, track and support more effective implementation of sediment TMDLs. Treating model predictions as hypotheses to be tested is a critical step towards developing an accurate understanding of actual treatment outcomes. It is suggested that this approach supports the premise that the most cost-effective approach to TMDL implementation is based on developing an accurate understanding of treatment/BMP effectiveness through field measurements at the project scale rather than relying solely on modeled predictions. Further, that those field measurements be used to further calibrate and/or parameterize the models employed so that their predictive power is increased and load reduction technologies improved. This monitoring, or field measurement effort would be included as part of the project permitting such that future costs are considered in the original planning.
Assessment of Tahoe Basin Roads: Road Shoulder Condition, Connectivity, Compaction, and Pollutant Generation Risk. 2011. Prepared by Northwest Hydraulic Consultants. 12 p. The work described in this document was initiated based on the findings in the report: Analysis of Differences in Pollutant Load Estimates Generated by LSPC and PLRM (NHC and Tetra Tech, 2010), prepared for the Water Quality Modeling Toolbox Project (SNPLMA Grant PO23). The previous report investigated functional differences between the Lake Tahoe Watershed Model (LSPC) and the Pollutant Load Reduction Model (PLRM), and concluded that differences in output generated by the two models can be reasonably explained based on differences associated with a few key functions and data inputs. The report noted that while reconciliation of some of the differences between the models is possible, absolute alignment of the two models is not a realistic strategy because the models are intended to be applied on different spatial scales. The representation of road land uses in LSPC and PLRM was found to cause the most significant variation in pollutant load estimates between the two models (NHC and Tetra Tech, 2010). As a step towards model integration and consistency in model application, road conditions relevant to PLRM inputs were assessed in this study for all Lake Tahoe Basin roads. The products developed from this work are Geographic Information System (GIS) shapefiles that characterize attributes of Tahoe Basin roads important to water quality and which are directly applicable to load estimation in PLRM. Section 2 describes the parameters defined and the procedures used for data collection and compilation. Section 3 of this document discusses potential uses of the products developed.
Application to Management The results of science investigations related to the TMDL have shown that the restoration of Lake Tahoe is possible. Load reductions are needed in all source categories but the science indicates that efforts must focus on urban stormwater because it is both the greatest source and largest opportunity for load reductions. Implementation of current practices may not be sufficient to reach established water clarity goals, i.e. business as usual. Rather, advanced and innovative controls will be needed. Examples include enhanced roadway operations and maintenance practices such as removing particles from roadways using high-efficiency vacuum sweepers and/or using alternatives to roadway abrasives application as well as conveying stormwater to local or regional facilities that feature enhanced treatment through chemical or biological processes. While the focus to
47 restore pelagic clarity relies on fine sediment particle reductions, simultaneous reductions in nutrients are also an important part of improving pelagic and nearshore water quality conditions. Future science priorities include monitoring the effectiveness of existing and new load reduction technologies and management practices; improving and enhancing tools and protocols to track and estimate progress toward achieving restoration goals; and monitoring the status and trends associated with both pelagic and nearshore conditions in order to discern if restoration strategies are working as expected.
48 Land Use Mapping
Overview
Mapping in the Tahoe basin has a long history dating back to the very early expeditions in the mid-late 1800s. The Basin has been subject to significant landscape-altering human activity since the mid-1850s; in particular widespread timber harvest from the 1850s to 1920s and urban development from the 1950s to the present. The former was well captured in the 1920s and 1930s through the Wieslander Vegetation Type Mapping project of the USFS California (now Pacific Southwest) Forest and Range Experiment Station. The US Geological Survey has been particularly active in mapping endeavors producing high quality maps of both the lake bottom and the surrounding drainage basin. These types of maps are particularly GIS mapping of land use conditions. critical in support of hydrology studies and Source: Lake Tahoe TMDL runoff modeling. With the advent of the Lake . Tahoe TMDL, the importance of developing land-use maps became evident since runoff and pollutant load is highly dependent on land type and proximity to the lake or one of its tributaries. In addition, land use mapping provides a unique opportunity to chronicle spatial and temporal changes in the forest and developed landscape. Historic and current aerial photographs taken from an airplane, as well as more recent satellite imagery provides a unique opportunity to reconstruct these changes with a good degree of certainty. An inventory of land uses by area, along with the rate change with time can also serve as a useful indicator to measure progress towards achieving goals set forth in regional planning documents.
Peer Reviewed Journal Publications
Change in the Forested and Developed Landscape of the Lake Tahoe Basin, California and Nevada, USA, 1940-2002. 2008. C. Raumann, M. Cablk. Forest and Ecology Management. 255: 3424-3439. Spatial and temporal distribution and variability of historical changes in land use and land cover in the southern Lake Tahoe basin was mapped, quantified, and described to establish a baseline and document subsequent changes. The assessment relied on post- classification change detection of multi-temporal land-use/cover and impervious-surface- area data that were obtained in images from 1940, 1969, 1987, and 2002. The most significant changes during the 62-year study period were an increase in developed lands with a corresponding decrease in natural land cover, changes in forest density within the forested areas, forest loss, forest expansion, and tree mortality. The highest rates of change occurred from 1940 to 1969. Causes of these changes included regional population growth, tourism demands, timber harvest for local use, fire suppression, bark beetle attack, and fuels reduction activities.
49
Other Scientific Literature
Historical Orthoimagery of the Lake Tahoe Basin. 2008. C. Soulard, C. Raumann. U.S. Geological Survey Data Series 376. 7 p. A series of historical digital orthoimagery datasets were developed for 1940, 1969 and 1989 from aerial photography. These datasets have a 1-meter resolution. Precision- corrected Ikonos satellite imagery was used for 2002. This reports discusses the methodology (and accuracy) employed to be able to distinguish between alnd uses such as water, wetland, mechanical disturbed, transportation, grass/shrubland, forest/woodland, recreational, commercial and residential. This project demonstrates the significant value of the distinctive data record of historical aerial photographs when processed in a manner that can be used within geographic information systems (GIS).
Lidar Remote Sensing, Lake Tahoe Watershed, California/Nevada. 2011. Watershed Sciences, Inc., www.opentopography.org Lidar point cloud data for the whole Lake Tahoe Basin (941 km2) on the California/Nevada border are now available. This 12+ billion point dataset was collected by Watershed Sciences, Inc. through a contract administered by Tahoe Regional Planning Agency (TRPA) and the U.S. Geological Survey. The Tahoe LiDAR project was funded through a Southern Nevada Public Land Management Act grant program that is administered by the US Bureau of Land Management to support a range of environmental and ecological science and planning activities. At greater than 11 shots per square meter, these data provide an amazing representation of the landscape within the Tahoe Basin, and we anticipate them being one of the more heavily utilized datasets hosted by OpenTopography. OpenTopography has signed a memorandum of understanding with TRPA to leverage the OpenTopography system to provide public access to these valuable data. This initial release provides access to the raw lidar point cloud data, but later releases will include Google Earth image overlays (e.g. image below), as well as pre-computed digital elevation model (DEM) data. We’ve also set up a Lake Tahoe Lidar User Group discussion forum for users who wish to interact with others working with these data.
Application to Management
Land use mapping has already had a large influence for land use planning, water quality planning and forest management in the Tahoe basin. Accurate and detailed maps of land use, when converted for use within geographic information systems (GIS) and resource management models are vital. Prior to the advent of GIS, maps primarily depicted geology, geography and other features of the landscape. GIS-modeling provides researchers and resource managers with a very powerful tool that allows for the understanding of landscape based/driven processes (e.g. influence of slope and soils on distribution of vegetation, influence of distance or a road from a watercourse on nutrient and sediment load). For urban stormwater management and water quality restoration the degree of connectivity between impervious land surfaces is vital when developing an urban stormwater master plan. A fixed-wing aircraft survey of the Tahoe basin using LiDAR (LIght Detection And Ranging) is currently planned. LiDAR includes the use of
50 lasers and GPS which allows very accurate production of digital elevation models (DEMs), canopy height and density estimation, fault zones, etc. A concurrent, satellite- based hyperspectral survey is also planned, allowing for further discrimination of forest type, health etc. With regard to forest condition and management, technologies such as LiDAR and hyperspectral imaging will support processes-oriented research and allow for evaluation and trend detection on a basin-wide scale.
51 Nearshore Water Quality
Overview
The nearshore region in lakes plays a vital ecological role with respect to (1) habitat and spawning grounds for fish and benthic macroinvertebrates, (2) lake productivity, foodweb dynamics and carbon cycling, and (3) as the region where materials associated with runoff and streamflow first enter the Lake. Most visitor and resident experiences at Lake Tahoe occur within or close to the nearshore environment, and conditions there translate directly into public perception of lake conditions. Environmental conditions in the nearshore have changed over Luxuriant growth of attached algae in the time in response to natural and anthropogenic shallow nearshore region. Source: TERC. factors. These changes have included heavy growth of periphyton (attached algae) on rocks, piers, and other hard substrate; regions of turbid water resulting from the discharge of urban stormwater runoff directly into the nearshore; elevated concentrations of gasoline components in and near marinas; the accidental release of raw sewage such as the 2005 Kings Beach spill; and the establishment and spread of invasive fish species such as the common carp, largemouth bass, and bluegill, invasive aquatic plants such as Eurasian water milfoil and curly leaf pondweed, and most recently benthic invertebrates such as the Asian clam. Increased activity in the nearshore zone is anticipated in the coming years, with more residents and visitors projected, including a 30 percent increase in boat traffic and up to 1000 more buoys.
Peer Reviewed Journal Publications
Spatial and Temporal Patterns of Nearshore Clarity in Lake Tahoe from Fine Resolution Turbidity Measurements. 2010. M. Shanafield, R. Susfalk, K. Taylor. Lake and Reservoir Management. 26(3): 178-184. The nearshore areas of lakes respond quickly to watershed runoff, increases in tributary inflows from annual snowmelt and increased anthropogenic activity in the drainage basin. This area of the lake serves both as an early warning system for water quality degradation and as an indicator of the effectiveness of land management practices or sediment control projects. This study evaluated the usefulness of combining fine-scale water quality measurements and discrete particle sample analysis to gain a better understanding of seasonal and spatial trends in the nearshore area of Lake Tahoe. Turbidity and mineral composition at 0.5 m depth were measured in nearshore waters near the City of South Lake Tahoe at a spatial resolution of 5–30 m.
52 Particles filtered from discrete samples collected 200 m from shore were analyzed by scanning electron microscopy and chemical analysis using quantum electron dispersive spectrometry. Baseline turbidity levels were extremely low (0.15 NTU) during calm periods in the fall, but rose to levels above 4.0 NTU in response to winter and spring precipitation events and spring snowmelt runoff. Discrete samples collected 200 m from shore contained over 80% organic material during the dry part of the year and at least 50% mineral particles during the winter and spring. The effectiveness of this method for detecting variability in nearshore conditions at Lake Tahoe is promising for monitoring the littoral areas of other pristine lakes facing increased anthropogenic pressure and other watershed disturbances. Other Scientific Literature
Linking On-Shore and Near-Shore Processes: Near-Shore Water Quality Monitoring Buoy at Lake Tahoe. 2009. R. Susfalk, A. Heyvaert, T. Mihevc, B. Fitzgeral, K. Taylor. Publication by the Desert Research Institute, Reno, NV. 48 p. Snapshot surveys have historically been used at Lake Tahoe to assess near-shore water clarity. Although they can provide data along the entire lake perimeter, they are not well suited for quantifying longer-term trends because of the lack of data between individual surveys. The objective of this study was to address several practical questions pertaining to the construction, operation, and maintenance of an autonomously deployed near-shore buoy capable of providing continuous water clarity measurements. A buoy was deployed 40 m off of Third Creek between April and October of 2008. Sensors included two turbidimeters, a light transmissometer, a water temperature sensor, a wind speed and direction sensor, and associated supporting electronics. Biofouling of the sensor’s optics was the greatest concern in limiting the length of autonomous deployment. Approaches for cleaning were discussed. Turbidity measured within the adjacent creeks was diluted by a factor of three-to-one, or more, compared to that measured at the buoy. The Third Creek watershed exceeded current near-shore thresholds (3 NTU) during four percent of the 3451 hours that the buoy was deployed. Based on their poor performance at ultra-low turbidity levels, it was concluded that turbidimeters should only be used to assess obvious clarity-degrading events (e.g. >1 NTU), such as for compliance monitoring. The light transmissometer was more suitable for long-term monitoring of near-shore conditions as it measured both scattering and absorption processes and was sensitive to small clarity changes under background conditions. A cost-effective near-shore monitoring plan was suggested, comprised of shorter-term compliance monitoring using turbidimeter-based systems and longer-term threshold monitoring using transmissometer-based systems. This report includes a discussion of a mechanism to support compliance and the implementation of more realistic thresholds that permit threshold exceedance during unusual or infrequent events.
Lake Tahoe Water Quality Investigations – 2007 to 2010: Periphyton. 2010. S. Hackley, B. Allen, D. Hunter and J. Reuter. Publication by University of California, Davis – Tahoe Environmental Research Center. Submitted to the California Lahontan Regional Water Quality Control Board. 39-78 pp. Peak periphyton biomass is consistently high in the urbanized northwest portion of the lake. Biomass along the east shore is typically low. The observed patterns are likely a combination of several interacting factors nutrient inputs (e.g. surface runoff, enhanced inputs from urban/disturbed areas, groundwater, lake mixing/upwelling/ currents), lake
53 level, substrate availability and perhaps even wind and wave action as they act to dislodge biomass from their bottom substrates. In Water Year 2008 very significant peaks in periphyton growth were measured at five sites. Four of the sites along the west and northwest shore had chlorophyll levels well over 100 mg chl/m2 (Rubicon Point, Pineland/Sunnyside, Tahoe City and Dollar Point. One site along the southeast shore (Zephyr Point) also had a significant spring peak ~75 mg chl/m2. The spring peaks for biomass at all these sites appeared to be largely the result of increased growth of the stalked diatom Gomphoneis herculeana. The spatial distribution of periphyton was similar in Water Year 2009, except biomass was somewhat lower. Lake level fluctuation appears to play a role in amount of periphyton biomass observed in the shallow eulittoral zone (0.5 m deep). During years when lake surface elevation is very low, biomass associated with the stable deeper blue-green algal communities is located close to the surface. This heavy biomass is not necessarily a consequence of high nutrient availability but rather is a consequence of the lowering lake level. Bright green filamentous green algae (typically Zygnema sp.) were often found associated with blue-green algae near the surface under conditions of lowered lake levels, particularly along the east shore. The bright green filamentous algae growth can be quite striking. In low water years, this algae growth is apparent to boaters, kayakers and others using the east shore. This is in contrast to high water years, when rocks along the east shore may have relatively little algae growth near the surface, due to the rocks recently being submerged. While the concentration of fine sediment particles appears to be very important in affecting lake visibility (Secchi depth), these particles have virtually no impact on periphyton growth. This biomass accumulation is very dependent on nutrient availability.
Application to Management
Despite its economic importance for tourism and significance to the overall biodiversity and function of the lake, the nearshore environment at Lake Tahoe has not received the same level of attention as has the lake’s open waters and its surrounding watershed. The Lake Tahoe TMDL has recently provided a blueprint for managing the open-water environment of Lake Tahoe where the decline in transparency has been well documented. Water quality agencies are now turning their attention to understanding nearshore processes in order to obtain science-based recommendations for the development of a long-term management and monitoring program for Lake Tahoe’s nearshore environment. In particular, managers are now beginning to focus on the evaluation of environmental indicators that can be used to assess if nearshore desired conditions are being attained.
54 Optical Properties, Fine Particles and Plankton Ecology
Overview Limnological research at Lake Tahoe focused on phytoplankton growth (primary productivity), plankton ecology and lake optical properties (especially Secchi depth transparency) for many decades as this ultra- oligotrophic waterbody Lake Tahoe’s changing water clarity. Source: TERC. experienced the onset of cultural eutrophication. Indeed, the observation that Lake Tahoe was losing its famed clarity at the rate of approximately 0.3 m per year (nearly 1 foot per year) since 1968 continues to set the stage for policy decisions related to water quality management and restoration actions. The League to Save Lake Tahoe’s slogan of Keep Tahoe Blue succinctly sums up a longstanding conservation effort to protect this unique natural resource. In the late 1990s and early 2000s researchers found that very fine sediment particles significantly contribute to Lake Tahoe’s current optical characteristics. Prior to this, all the attention was focused on connection between nutrients, algae and clarity. Research conducted in support of the Lake Tahoe TMDL was able to define the relationship(s) between algae, fine sediment and lake clarity to a point where we have now predicted targets of load reduction for these pollutants. Despite this significant progress, research on the topic of lake optical properties, fine particles and plankton ecology is still relevant as (1) new issues are recognized (e.g. invasive species, ultraviolet light, climate change), (2) long-term monitoring results focus our attention on the changes that are occurring in Lake Tahoe and (3) the response of Lake Tahoe to pollutant load reduction programs is evaluated.
Peer Reviewed Journal Publications
Temporal Organization of Phytoplankton Communities Linked to Physical Forcing. 2008. M. Winder, D. Hunter. Oecologia, 156: 179–192. This study documented shifts in phytoplankton structure and vertical positioning that have accompanied intensified long-term stratification in a natural ecosystem. Ordination analysis was used to extract gradients in phytoplankton composition in Lake Tahoe over a 23-year period of record. Community structure in the 1980s was associated most strongly with resource availability (low nitrogen to phosphorus ratios, deeper euphotic zone depth), while intensified stratification dominated the phytoplankton structure since the late 1990s. Within the diatom community, small-sized cells increased with reduced mixing, suggesting that suppressed turbulence provides them with a competitive advantage over large-sized cells. Among the morphologically diverse chlorophytes, filamentous and coenobial forms (colony of cells usually within a mucilaginous matrix) were favored under intensified stratification. The selection for small-sized diatoms is accompanied by
55 a shoaling trend in their vertical position in the water column. In contrast, the motile flagellates displayed a deeper vertical positioning in recent years, indicating that optimal growth conditions shifted likely due to reduced upwelling of nutrients.
Lake Tahoe vs. Lake Kinneret Phytoplankton: Comparison of Long-term Taxonomic Size Structure Consistency. 2008. Y. Kamenir, M. Winder, Z. Dubinsky, T. Zohary, G. Schladow. Aquatic Sciences, 70: 195-203. Both theoretical ecology and lake management practices acutely need quantitative assessment tools for the analysis of structural changes taking place in the plankton community. Traditional Taxonomic Size Spectrum (TTSS), a tool allowing such assessment, is usually based on size distributions of organisms irrespective of their taxonomy. This study examined whether consistent TTSS patterns prevail across ecosystems using subtropical and eutrophic Lake Kinneret, Israel, and temperate and oligotrophic Lake Tahoe, USA in a case study. A typical annual TTSS pattern was revealed. The Lake Tahoe TTSS similarity level during four years (Pearson r = 0.92 to 0.99) is comparable to that of the Lake Kinneret during its stable period even for pairs divided by >20 years, r > 0.8. While the Lake Tahoe TTSS general pattern resembles that of Lake Kinneret, the two lakes are distinguishable by means of cluster analysis. A high similarity (r = 0.91) was found between the eight-year averaged TTSSs of the two lakes. The above results suggest that the long-term consistency of the aquatic assemblage taxonomic size structure pattern is a general phenomenon. This pattern deserves special attention at times of accelerated global climate change, compounded by ever increasing anthropogenic impacts.
Patterns of Spatial and Temporal Variability of UV Transparency in Lake Tahoe, California-Nevada. 2009. K. Rose, C. Williamson, S. Schladow, M. Winder, J. Oris. Journal of Geophysical Research-Biogeosciences, 114: G00D03, doi:10.1029/2008JG000816. Lake Tahoe is an oligotrophic subalpine lake that is renowned for its clarity. The region experiences little cloud cover and is one of the most UV transparent lakes in the world. As such, it is an ideal environment to study the role of UV radiation in aquatic ecosystems. Long-term trends in Secchi depths showed that water transparency to visible light has decreased in recent decades, but limited data are available on the UV transparency of the lake. This work examined how ultraviolet radiation varies relative to longer-wavelength photosynthetically active radiation (PAR, 400–700 nm, visible wavelengths) along inshore-offshore transects in the lake and down a vertical profile in the water column throughout 2007. UV transparency was more variable than PAR transparency horizontally across the lake and throughout the year. Seasonal patterns of Secchi transparency differed from both UV and PAR, indicating that different substances may be responsible for controlling transparency to UV, PAR, and Secchi. In Lake Tahoe’s surface waters, UVA (380 nm) often attenuated more slowly than PAR, a pattern visible in only exceptionally transparent waters with very low dissolved organic carbon. On many sampling dates, UV transparency decreased progressively with depth suggesting surface photobleaching, reductions in particulate matter, increasing chlorophyll a, or some combination of these increased during summer months.
56 Combining these patterns of UV transparency with data on visible light provides a more comprehensive understanding of ecosystem structure, function, and effects of environmental change in highly transparent alpine and subalpine lakes such as Tahoe.
Photosynthetic Picoplankton Dynamics in Lake Tahoe: Temporal and Spatial Niche Partioning Among Prokaryotic and Eukaryotic Cells. 2009. M. Winder. Journal of Plankton Research, 31: 1307-1320. Dynamics of prokaryotic and eukaryotic picophytoplankton were investigated over a 2- year time period using flow cytometry and combined with an in situ experiment. Pronounced seasonal patterns and clear temporal and spatial partitioning were observed between picocyanobacteria and picoeukaryotes. Picocyanobacteria dominated in the nutrient deficient upper water column during the stratified season, while picoeukaryotes reached maximum abundance during isothermal conditions and maintained high numbers in deep-water layers during the stratified season. Picocyanobacteria were more sensitive to high solar and UV radiation compared with picoeukaryotes, which were not affected by high solar radiation and nutrient enrichment stimulated their growth. The opposing response of these two populations is consistent with their vertical distribution: picocyanobacteria dominate below the 30 perent isolume (depths having the same light intensity) and above the nitrocline depth, whereas picoeukaryotes increase in the vicinity of the nitrocline and thus increased nutrient concentration. This spatial separation of picophytoplankton groups along environmental gradients in Lake Tahoe is consistent with other deep-oligotrophic lakes and the marine environment, suggesting that these marine and freshwater organisms have similar ecophysiological requirements. These results highlight that the smallest photosynthetic communities show taxon-specific responses to mixing and resource availability, which affect the structure and dynamics of picophytoplankton.
Long-term Changes of the Chrysophyte Population in Lake Tahoe. 2009. M. Winder, D. Hunter. Verh. Internat. Verein. Limnol, 30(7): 1051–1055. The analysis of long-term data collections provides insight into the structure and function of ecosystems because it allows the identification of trends over background noise from inter-annual variation. This becomes particularly important for phytoplankton populations since they exhibit high seasonal and interannual variability. Between 1982 and 2006 some phytoplankton groups were able to adapt to the changing environment and maintain or increase their abundance; however, the chrysophytes, significantly decreased over time. Chrysophytes are flagellated cells that are extremely good competitors for phosphorus in nutrient-poor environments with low water temperatures and high transparency. The timing of the spring peak of the entire chrysophyte community was consistent throughout the sampling period. However, the peak biovolume for many of the dominant genera shifted to an earlier point in the calendar year during the 25-year observation period, particularly Kephrion spp., flagellates, Chrysolykos spp., and Epipyxis spp., while the peak in S. petersenii biovolume shifted to later in the season. This indicates that individual species show different sensitivity to environmental changes. By observing trends of the entire group, important species-specific responses may be overlooked.
Using Laser Diffraction Data to Obtain Accurate Particle Size Distributions: The Role
57 of Particle Composition. 2010. S. Andrews, D. Nover, G. Schladow. Limnology and Oceanography Methods 8:507-526. Inorganic particles and organic phytoplankton cells, both common in natural waters, have very different indices of refraction. This can affect results from laser diffraction particle size analyzers, which measure light scattering and assume an index of refraction in order to calculate the particle size distribution. This investigation examined the effect of the assumed index of refraction on laser diffraction data. A Laser In-situ Scattering and Transmissometry (LISST)~100X instrument was used to record scattered light distributions from glass microspheres, phytoplankton monocultures, and natural particle samples of mixed composition. The scattering distributions were processed with kernel matrices, derived using Mie theory, assuming either organic or inorganic compositions. Processing with an assumed inorganic index of refraction was found to produce the most accurate results over the majority of the samples tested. The effect of scattering by particles having diameters outside of the instrument inversion range was also assessed. The presence of significant concentrations of particles exceeding the LISST range (>250 microns) produced little effect; however, particles smaller than the lower limit (<1.25 microns) influenced concentrations over the entire LISST size range and produced counterintuitive effects, such as increased concentrations in the largest size bins.
When UV Meets Fresh Water. 2010. C.E. Williamson, K.C. Rose. Science, 329: 637- 639. Ultraviolet radiation (UV) has the highest energy and shortest wavelength of all radiation to pass into the earth’s atmosphere. Many of it’s damaging effects have been well studied in light of the discovery that the protective ozone shield was being depleted, such as its ability to damage DNA and affect an organisms ability to reproduce. Recently it has become clear that UV has beneficial effects on individuals and thus natural ecosystems as well. Many organisms, including a wide variety of fish, birds, spiders, zooplankton, use UV in orientation, communication, navigation, foraging and mate selection. In clear, cold-water lakes like Lake Tahoe, high levels of UV transparency may maintain native fish communities from invasive freshwater fish. For example, the invasive warm- water Bluegill reproduces only in the nearshore where water temperatures will support spawning. In areas of the lake where the water is very clear however, levels of UV radiation that penetrate the water column are lethal to spawning due to DNA damage. Thus the Bluegill are restricted to areas with reduced transparency due to human or natural disturbance.
Limitations of Laser Diffraction for Measuring Fine Particles in Oligotrophic Systems: Pitfalls and Potential Solutions. 2011. S. Andrews, D. Nover, J. Reuter, G. Schladow. Water Resources Research., 47, W05523, doi:10.1029/2010WR009837. Sampling of suspended particulates in oligotrophic environments is inherently difficult because of low ambient concentrations. The performance of a Laser In Situ Scattering and Transmissometry (LISST) series particle size analyzer is evaluated for use in such low concentration environments. Five issues were studied for their effect on recorded particle size distributions: the instrument limits of detection, the kernel matrix used in the inversion of the scattered light distribution, the effect of particles sized outside the instrument inversion limits
58 (1.25–250 µm), the effect of ambient light conditions, and the effect of sampling in density stratified conditions. The LISST was evaluated using a series of small-scale lab experiments and concentrate mainly on fine particles (<20 µm). Kernel matrix processing effects were shown to have large impacts on fine particle measurements, but accurate results can be obtained with the correct matrix choice. Concentration detection limits may be sufficient for the clearest fresh water environments, but may be too high for accurate sampling in the oligotrophic open ocean. Large out of range particles (>250 µm) show little effects on the size distribution, but small particles (<1.25 µm) have large impacts. High ambient light conditions, typical in clear oligotrophic systems, create erroneously high concentrations of fine particles, and profiling in density stratified conditions was found to create incorrectly low concentrations. Recommendations are provided for the next generation of in situ laser diffractometers, and advice is provided for current use of this instrument in oligotrophic environments.
The Influence of Ambient Light Intensity on In-Situ Laser Diffractometers. 2011. S. Andrews, D. Nover, K. Reardon, J. Reuter, G. Schladow. Water Resources Research. 47, W06509, doi:10.1029/2010WR009841 This study evaluated the effect of the ambient light-field intensity on measurements made with a Laser In Situ Scattering and Transmissometry (LISST) series instrument. Paired light–dark scattering distribution were recorded over a range of underwater light intensities in high turbidity and low turbidity water. Light measurements displayed large erroneous concentrations of particles in the smallest size bin (1.25–1.48 µm) and showed effects over the full range of the PSD. Ambient light was found to exhibit the same constant distribution over the instrument photodetectors in both water samples, although the magnitude of the response, in laser counts per unit ambient light intensity, was PSD dependent. A technique for post processing data to remove the influence of light is presented for moored deployment and vertical profile data collected at Lake Tahoe, California–Nevada, USA. While measurements removed of the light effect were successfully reconstructed, the technique may not be applicable to data where the PSD or the LISST orientation relative to the sun direction change rapidly, or when light intensities are high enough to quench the instrument photodetectors.
Other Scientific Literature
Sources, Distribution and Dynamics of Fine Particles in Lake Tahoe: Linkage to Restoration of Lake Clarity. 2009. G. Schladow, D. Nover. Final report submitted to the US EPA Region IX and funded under the Southern Nevada Public Lands Management Act, Round 5. Fine particles have been measured in Lake Tahoe water regularly over the past ten years in order to identify long term trends in particle loads and particle dynamics as well as the impact of these particles on clarity and the effectiveness of pollution reduction strategies. Clear seasonal and intra-annual trends in particle concentration are evident in the data. Spikes in fine particle concentration can be seen during the spring/summer and likely correspond to the spring snowmelt period. Particle concentrations reach a distinct low in winter, when flow to the lake is at a minimum and productivity is reduced. In addition to seasonal variations in particle concentration, intra-annual variations have a pronounced impact on the particle concentrations. During extremely wet years particle concentrations
59 peak, while they tend to decline during extremely dry years. These macro-climatic impacts appear to dominate seasonal trends in particle concentrations. Despite limitations in the temporal resolution of these data, these data highlight important annual and seasonal trends in fine particle dynamics and underscores important drivers of fine particles in the Lake Tahoe Basin. Fine particles have also been measured in Tahoe streams over approximately the same period of time. In addition to elucidating long term trends in stream particle loads, this data has been used to develop relationships between stream flow and particle flux that are useful management tools for predicting particle delivery to the lake. In addition to fine particle data, Fluoroprobe and Seabird measurements have been collected at Tahoe and long term data for a variety of physical, chemical and biological water quality constituents are presented. ICP-MS data was collected for both stream and lake samples from the Tahoe Basin in order to identify the chemical characteristics of particles coming from the various streams surrounding the lake and the particles in the lake water itself. A series of experiments are presented which show the dynamics of fine particles on much smaller temporal scales than can be seen in the long term monitoring data.
Lake Tahoe Water Quality Investigations – 2007 to 2010: Algal Bioassay Experiments. 2010. S. Hackley, B. Allen, D. Hunter, J. Reuter. Publication by University of California, Davis – Tahoe Environmental Research Center. Submitted to the California Lahontan Regional Water Quality Control Board. 6-13 pp. The response of Lake Tahoe water to nitrogen (N) and phosphorus (P) enrichment has been tested using algal growth bioassays since the 1960’s. In a typical bioassay, lake water is collected from 0-20 m, pre-filtered to remove the larger zooplankton and returned to the lab. The water is distributed among flasks to which small amounts of nitrogen (20 µg N/L) or phosphorus (at two different levels: 2 µg P/L and 10 µg P/L) or the combination of both N and P are added. One set is left as a control. During the period 9/07 to 4/10 there was a significant growth response to the combination of N+P in nearly all bioassays (11 of 12 bioassays). This reinforces the fact that Tahoe phytoplankton are still N and P co-deficient and that nutrient reduction is important for the management of excessive algal growth. Nitrogen limitation was prevalent during the summer to fall (into November) period during 2007- 2009 with 5 of 6 bioassays showing N stimulation. This was a change from summer to fall bioassays 2004-2007 when no summer N limitation was observed and either P or N+P co-limitation was prevalent. P limitation remained prevalent during January-April. Nitrate availability from deep mixing is likely a potential contributing factor to this apparent P limitation.
Lake Tahoe Water Quality Investigations – 2007 to 2010: Identification and Enumeration of Phytoplankton/Zooplankton. 2010. S. Hackley, B. Allen, D. Hunter, J. Reuter. Publication by University of California, Davis – Tahoe Environmental Research Center. Submitted to the California Lahontan Regional Water Quality Control Board. 13-20 pp. Highest bio-volume and abundance of phytoplankton is found in the summer, and is lowest in the winter. Diatoms are the dominant group during most of the annual cycle. They are responsible for much of the variability throughout the year. In the summer of 2008 and 2009, total cell bio-volume was near 200 mm3/m3 with the small centric diatoms, Cyclotella glomerata and Cyclotella gordonensis (~5 µm) the dominant species.
60 Chlorophytes, chrysophytes, and cryptophytes are ever-present with more consistent bio- volume and abundance. Dinoflagellates are usually large cells and therefore contribute significantly to the total bio-volume even though the population abundance (in terms of cell number) is low. Cyanophytes are most abundant during the late summer and tend to have a more opportunistic niche within the community. The zooplankton community of Lake Tahoe has been relatively consistent since the 1980s, dominated by the copepod species Diaptomus tyrelli and Epischura nevadensis, and the rotifers Kellicottia spp, Keratella spp. and Polyarthra spp.
Application to Management
The Lake Tahoe TMDL recognizes the role played by both fine sediment particles and algae as drivers of lake clarity and trophic state. While the influence of fine sediment particles on Secchi disk transparency is helping the guide urban stormwater management in the Tahoe basin, it has been long understood that primary productivity and phytoplankton biomass are critical with respect to aquatic ecology, food webs, dissolved oxygen levels, carbon cycling and the vertical penetration of light to zones below the Secchi depth. The trophic status of a waterbody refers to position along a continuum from ultra-oligotrophic (pristine, highly oxygenated water) to hyper-eutrophic (algal scums and prohibitively low levels of oxygen that exclude desired biota). Not only is Lake Tahoe moving away from its ultra-oligotrophic status as cultural eutrophication has altered lake conditions, but the overlay of other stressors such as climate change and the establishment of aquatic invasive species can add significantly to this change. State and federal regulatory requirements recognize the unique nature of Lake Tahoe and acknowledge that the observed shift in trophic status is undesirable. Research in the areas of optical properties, plankton ecology and fine particles helps agencies to better anticipate the magnitude and timing of Lake Tahoe’s response to watershed restoration and pollutant reduction actions and to evaluate new environmental threats to its unique status as one of the world’s deepest, clearest lakes.
61 Restoration Monitoring
Overview
Restoration projects are an important focus of many land management agencies in the Tahoe basin. Restoration monitoring is an important tool used to track the success of these restoration efforts. By tracking key indicators, such as sediment delivery, water temperature, fish spawning success, or growth of desired species, managers can answer important questions about Cove East restoration project. Source: TRPA. restoration progress. Monitoring also helps local watershed managers fine-tune their restoration strategies based on what techniques prove to be effective. Monitoring is a key component to a successful adaptive management program. Adaptive management is a structured, iterative process of decision making when faced with the uncertainty that is associated with natural ecosystems. Data collected from restoration monitoring is used to reduce this uncertainty. In this way, managers accrue information needed to improve future management and scientists improve their understanding of ecosystem function. Best Management Practices or BMPs for stormwater treatment can be considered a special category of restoration monitoring. This is an important theme for Tahoe basin water quality managers and therefore, they are considered in their own section.
Peer Reviewed Journal Publications
Quantifying Reductions of Mass-Failure Frequency and Sediment Loadings from Streambanks Using Toe Protection and Other Means: Lake Tahoe, United States. 2009. A. Simon, N. Pollen-Bankhead, V. Mahacek, E. Langendoen. Journal of the American Water Resources Association. 45(1): 170-186. Streambank erosion by mass-failure processes represents an important form of channel adjustment and a significant source of sediment in disturbed streams. Mass failures regularly occur by a combination of hydraulic processes that undercut bank toes and geotechnical processes that cause bank collapse by gravity. Little if any quantitative information is available on the effectiveness of bank treatments on reducing erosion. To evaluate potential reduction in sediment loadings emanating from streambanks, the hydraulic and geotechnical processes responsible for mass failure were simulated under existing and mitigated conditions using a Bank-Stability and Toe- Erosion Model (BSTEM). Two critical erosion sites were selected from each of the three watersheds known to contribute the greatest amounts of fine sediment by streambank processes in the Lake Tahoe Basin. A typical high-flow annual hydrograph was selected for analysis.
62 Bank-material strength data were collected for each layer as were species-specific root- reinforcement values. The effects of the first flow event on bank-toe erosion were simulated using an excess shear-stress approach. The resulting geometry was then exported into the bank-stability submodel to test for the relative stability of the bank under peak flow and draw- down conditions. In this way, BSTEM was used iteratively for all flow events for both existing and mitigated conditions. On average, 13.6% of the material was eroded by hydraulic shear, the remainder by mass failures, which occurred about five times over the simulation period. Simulations with 1.0 m-high rock-toe protection showed a dramatic reduction in streambank erosion (69- 100%). Failure frequency for the simulation period was reduced in most cases to a single episode. Thus, an almost 90% reduction in streambank loadings was achieved by virtually eliminating the erosion of only 14% of the material that was entrained by hydraulic forces.
Other Scientific Literature
Lonely Gulch Watershed Restoration - Monitoring Report, 2002-2006. 2008. N. Brill, C. Oehrli, T. Tolley, S. Norman. US Forest Service, Lake Tahoe Basin Management Unit. 23 p. The purpose of monitoring was to evaluate the effectiveness of a restoration project to restore bank stability along a 350-foot section of Lonely Gulch Creek, located on the west shore of Lake Tahoe. Prior to this restoration in 2003, the site was deemed vulnerable to large-scale stream bank erosion as stream banks caved-in from excessive tree fall of dead and dying conifer lining the banks of the creek. The Forest Service utilized four metrics to track the performance of the treatments employed: 1) stream flow turbidity and suspended sediment samples, 2) photo points with pictures taken annually as a qualitative measure of streambed and bank stability, 3) stream cross-section monitoring as a quantitative measure of streambed and bank stability and 4) macroinvertebrate inventory as a quantitative measure of stream system health (compared against other Tahoe basin streams). Conclusions from the monitoring data were: 1) turbidity and SSC data stayed well within state water quality standards and did not indicate significant differences between above and below project sampling locations, 2) photo documentation indicates that the streambed and banks are recovering and vegetation appears to be on a positive trajectory in terms of developing a riparian corridor, 3). repeat cross-section measurements indicate some isolated lateral erosion of banks, but not considered excessive. Vertical adjustments are minor and appear to be a reflection of expected natural flux, 4) macroinvertebrate sampling indicates that the site is biologically healthy when compared to other Basin streams and 5) there was no visible indications that the streambed, banks, or riparian vegetation at the site responded negatively to a large mid winter flood occurring on December 31, 2005.
Interim Monitoring Report for Blackwood Creek Restoration Phase I and II: Fish Ladder Removal and Barker Pass Road Crossing Replacement, Period of Record 2003- 2008. 2009. C. Oehrli, S. Norman. US Forest Service, Lake Tahoe Basin Management Unit. 19 p. In September of 2003, the U.S. Forest Service removed a concrete fish ladder in Blackwood Creek, and in 2006 replaced the stream crossing on Barker Pass Road. The stream channel was reconstructed at both of these sites as these structures were removed.
63 A monitoring approach consisting of visual observations documented by photo points and physical measurements of channel morphology was used to address the following project goals: (1) remove in-channel structures, and create stable channel geomorphology, with improved aquatic habitat and (2) promote recovery of stream bank and floodplain riparian vegetation, through channel design, including restoring connectivity of stream channel to the adjacent floodplain. Longitudinal profile surveys and photos at the fish ladder showed that after early adjustments, the channel was vertically stable, but will likely continue to experience minor adjustments. Sediment deposition from upstream transport suggests that the trend from step/pool toward riffle/pool channel forms may have started. At the bridge, thalweg profile and cross section stability are trending similar to what is occurring at the fish ladder. While the photos and thalweg surveys do show that the step/pool design is maintaining grade and form, it was concluded that the current configuration did not adequately promote depositional or hydro-geologic conditions to meet project goals. The Phase IIIB redesign will increase functional floodplain area, promoting better conditions for riparian vegetation colonization and increasing the rate at which this channel reach will evolve to the desired riffle/pool channel form.
Final Monitoring Report for Marlette Creek Dam Removal and Restoration Project, Period of Record 2002 to 2008. 2009. T. Tolley, T. Loupe, S. Norman. US Forest Service, Lake Tahoe Basin Management Unit. 30 p. A small earthen dam on the South Fork of Marlette Creek was removed in August 2003, and restoration efforts were implemented to reconstruct the stream through this area and restore the former dam and reservoir site. When the dam was in place, it trapped sediment in a reservoir formed behind the dam, depriving downstream areas of sediment and causing severe stream bank erosion in downstream channel reaches. A monitoring program was implemented to (1) evaluate project effectiveness in riparian vegetation establishment, and geomorphic changes in the stream channel and floodplain and (2) determine whether water quality in terms of sediment and turbidity, improved as a result of the project. Cross sections indicated that significant stream bank erosion and down cutting continued to occur after project completion. Additional stabilization measures were implemented one year following the restoration project along a channel reach of approximately 200 feet in length where the most severe erosion occurred. These efforts were largely unsuccessful, as the erosion continued to cause boulders that were embedded in the stream banks for stabilization to become dislodged and fall into the stream, bringing large quantities of soil with them. Stream bank erosion and channel widening is most severe in the reach that flows through the upstream end of the former reservoir site, where the stream entered the reservoir. The primary causes of the post-project erosion are thought to include; (1) a stream channel design that was too straight and steep for the loose, unconsolidated material through which it flows, (2) not removing enough of the sediment that had accumulated in the upstream end of the reservoir, and (3) inadequate bank stabilization measures that incorporated only boulder-size rocks in the banks without mid-size rocks to secure the boulders.
64 Cookhouse Meadow Restoration Monitoring Report. 2009. U.S. Department of Agriculture, Forest Service. South Lake Tahoe, CA: Lake Tahoe Basin Management Unit. 52 p. In 2005 and 2006, the USFS implemented a stream channel/floodplain restoration project in Big Meadow Creek through Cookhouse Meadow, located adjacent Highway 89 just below Luther Pass. Restoration activities included the construction of 2,400 feet of new stream channel (designed as a Rosgen C stream channel type) to replace 1400 feet of existing deeply incised and eroding stream channel (classified as a Rosgen G channel). This restoration effectively raised the elevation of the stream channel by approximately 6 to 10 feet, and reduced the relative channel bed to bank height so that the riffle elevation is 1 to 1.5 feet from the top of bank. This conversion in channel type is expected to achieve the following two objectives. 1) Restore stream channel geomorphic function in terms of channel stability, and aquatic habitat features. 2) Restore floodplain connectivity which will; (a) Increase meadow surface flooding frequency, so that the surface floods two out of every three years on average, (b) Restore seasonal ground water levels and associated capillary rise in the central meadow to support growth of moist and wet meadow vegetation through August 15 under average hydrologic conditions, and reverse the trend of dry meadow grasses and conifer invasion. This report provides an interim analysis of data collected to answer monitoring questions related to project goals/objectives. Replacement of the old channel with a new channel successfully converted the channel type from an incised channel, experiencing accelerated bank erosion and effectively dewatering the meadow (“G” Rosgen channel type), to a stable channel form (“C” Rosgen channel type) that is now connected to the adjacent floodplain. In addition, the restoration project has resulted in dramatic increases in groundwater levels, increasing the duration of available water for meadow vegetation substantially. Channel survey measurements (cross sections and longitudinal profiles) as well as visual observations indicate that the channel is maintaining both horizontal and vertical stability, and is maintaining the desired channel stability and habitat characteristics of a “C” Rosgen stream channel type. Visual observations note that lateral and point bar formation, as well as the development of scour and corner pools are occurring. The desired gravel dominant channel substrate is also being maintained (Rosgen class “4”).
Forest Road Monitoring - 2006-2008. 2009. N. Brill, J. Harris, S. Norman. US Forest Service, Lake Tahoe Basin Management Unit. 9 p. This report summarizes a three-year monitoring program (2006 thru 2008) which evaluated the effectiveness of the LTBMU’s Forest Road BMP Retrofit Program. This report evaluated the effectiveness of 4.21 miles of upgrades that occurred during this period. Relatively few upgrades have occurred in this period, compared to the 154 mile of upgrades evaluated in the 2007 report. All four road surface, drainage and slope protection evaluations for implemented BMP upgrades were rated effective. Stream crossing evaluations determined that all sites with a stream crossing were rated effective at preventing plugging and reducing diversion potential. Sidecast Material evaluations were also rated effective at all sites. A total of 4.21 miles of road were evaluated of which 2.08 miles were located outside an SEZ, had no risk of sediment delivery to a water body and therefore were not rated. The remaining 2.13 miles consisted of 0.54 miles of low risk and 1.59 miles of moderate risk road. All 1.59 miles of moderate risk road segments were located on Slaughterhouse Canyon road. Monitoring results indicate that BMP retrofits overall have been effective at reducing the
65 risk of road-borne sediment migration to water bodies in the Lake Tahoe basin. WQRAP (Water Quality Risk Assessment Protocols) scores were low with the exception of road 18E22.5, Slaughterhouse Canyon Road (a trail to road conversion), which received predominately moderate ratings due to the surface type and gradient.
Lower Rosewood Creek Restoration Project: Suspended Sediment Loads and Particle Size, 2002-2007. 2009. R. Susfalk, B. Fitzgerald. Division of Hydrologic Sciences, Desert Research Institute, Nevada System of Higher Education. Publication No. 41248 The purpose of the Rosewood Creek Restoration Project was to improve the SEZ and mitigate suspended sediment into Third Creek and ultimately Lake Tahoe. Pre-construction monitoring was used to assess the effectiveness of restoring poorly stabilized, deeply incised banks in reducing erosion and changing the particle size distribution of suspended sediment after construction. Monitoring in the first few post-construction years did not show much improvement, but years three and four showed reduced sediment loading in a little less than half of the precipitation events that were monitored.
Trout Creek Restoration Monitoring: Changing Benthic Invertebrate Indicators in a Reconstructed Channel. 2009. D. Herbst. Final Technical Report submitted to the City of South Lake Tahoe. 22 p. www.waterboards.ca.gov/lahontan/water_issues/programs/swamp/docs/herbst_troutcreek 092009.pdf. Benthic macroinvertebrate (BMI) communities are important bioindicators of ecosystem structure and function, and instream BMI assemblages can be used to assess the extent to which restoration efforts have benefitted aquatic life. Trout Creek (a tributary to the Upper Truckee River) had been straightened and channelized to facilitate historic land uses. A project to reconfigure and reconstruct the channel of Trout Creek was completed during 2000-01. BMI communities and instream habitat features were monitored before and after the project, to gauge the effects of channel reconstruction. The bioassessment results showed rapid and robust improvements in BMI communities during the first two years after construction of the new channel. However, bioassessment results collected six and seven years after channel reconstruction showed that the improvements in biological integrity were not sustained, and that some reconstructed sections of the creek could still be considered to be biologically “impaired.” The author discusses potential reasons why biological integrity in the reconstructed channel continues to exhibit signs of degradation, and recommends further long-term monitoring. The author also recommends that future channel reconstruction projects include long-term monitoring, because initial improvements may be short-lived.
Burke Creek Restoration Project Alternatives Analysis Report, Burke Creek at Highway 50, Stateline, Nevada. 2009. Winzler and Kelly, Michael Love and Associates, McBain and Trush, Inc. Prepared for the Tahoe Regional Planning Agency. 324 p. The Burke Creek restoration project area includes the region immediately upstream and downstream of Highway 50, north of the Kahle and Highway intersection, and near the town of Stateline, NV (Figure ). The Tahoe Regional Planning Agency (TRPA) along with Douglas County, Nevada Department of Transportation (NDOT), U.S. Fish and Wildlife (USFS), Nevada Department of State Lands (NDSL), and private property owners formed the Technical
66 Advisory Committee (TAC) for the restoration project, which provided guidance and feedback to the project design team. Several project objectives were discussed including the following: a. Improving fish passage conditions b. Improving flood flow conveyance c. Improving sediment transport d. Improving riparian corridor The above objectives were recognized as being interrelated and the project is intended to explore restoration alternatives that have multiple ecological benefits. The following tasks were established and discussed in the document: a. Existing Conditions and Data Analysis b. Topographic and Bathymetric Surveying c. Geomorphic Setting and Reach Designations d. Sediment Supply, Transport, and Deposition Analysis e. Channel Stability Evaluation f. Selection of Reference Reaches g. Hydrologic Conditions and Design Flow h. Existing Fish Passage Conditions i. Vegetation Analysis j. Alternatives Analysis k. Alternative Comparison l. Outstanding Issues and Assumptions
Riparian Ecosystem Restoration Effectiveness Framework. 2010. Prepared for SNPLMA Round 8. Prepared by 2NDNATURE. 130 p. The Framework was developed to focus the process and improve communication when stream restoration practitioners are implementing specific restoration goals. It is expected to simplify the summary of existing conditions, the development of testable restoration objectives, improve the quality of restoration project monitoring and engage the adaptive management process. The final products of The Framework will improve reporting consistency for future projects, and thus the availability and quality of data and information available to make long-term adaptive management decisions.
Quantification and Characterization of Trout Creek Restoration Effectiveness; Focused Development of a Stream Load Reduction Methodology (SLRT), Final Characterization Plan. 2010. Prepared for SNPLMA Round 9. Prepared by 2NDNATURE. 52 p. The restored reach of Trout Creek became the case study for testing the utility of the Stream Load Reduction Tool (SLRT) Methodology. Goals: (1) provide detailed guidance on the recommended methods to quantify the water quality benefit of stream restoration in the Lake Tahoe Basin, (2) characterize the “desired condition” analog of a restored stream morphology and condition in the Lake Tahoe Basin (Trout Creek) by directly applying techniques developed by 2NDNATURE and others for Lake Tahoe streams. Objectives: (1) create and assess a range of methods to quantify the total and fine sediment load reduction of stream restoration efforts, (2) compile and apply available data to inform the inputs and validate the outputs of the SLRT estimates, (3) design and implement a detailed data collection effort from the case study site to increase existing data and inform SLRT assumptions, input parameters and validate results, (4) if funding
67 allows, apply the version of the California Rapid Assessment Methodology (CRAM) meant for rivers to the case study site and other sites to test the applicability of CRAM to discern pre and post restoration effects and detect differences in SEZ conditions in the Tahoe Basin.
North Canyon Creek Restoration Project: Phase I. 2010. Prepared for the US Army Corps of Engineers. Prepared by 2NDNATURE. 103 p. 2NDNATURE teamed up with Huffman and Carpenter to assist the Nevada Tahoe Resource Team (NTRT) with assessing and documenting existing conditions and identifying priority restoration strategies for the North Canyon Creek Restoration Project located near Spooner Summit. The project area includes Spooner Meadow and the upper portions of North Canyon Creek. The project area has been significantly impacted by historic human activities including logging operations in the late 1800’s and cattle grazing in the early 1900’s. Numerous hydrologic control devices changed flowpaths and contributed to higher stream flows and subsequent increased channel erosion and flow. Grazing compacted soils and changed ecosystem diversity. Unpaved roads contribute to higher sediment loads entering the creek, and are a potential source of fine sediment particles. Wildlife data for a range of animals was compiled, and archeological sites of major importance were identified. All these impacts were quantitatively assessed and can be used to compare the effectiveness of any restoration efforts in the future.
Riparian Ecosystem Restoration Effectiveness Framework: Tracking the Benefits of Stream and Floodplain Restoration in the Lake Tahoe Basin. 2010. Prepared for the Pacific Southwest Research Station. Prepared by 2NDNATURE, River Run Consulting, Environmental Incentives. 130 p. 2NDNATURE, River Run Consulting and Environmental Incentives collaborated on the completion of a SNPLMA Round 8 research grant (original proposal attached as Appendix A) to focus and improve the quality of stream restoration effectiveness evaluations in the Lake Tahoe Basin. The research team coordinated and solicited feedback from a Technical Advisory Committee (TAC) consisting of Lake Tahoe stream restoration practitioners from California State Parks, California Tahoe Conservancy, US Forest Service Lake Tahoe Basin Management Unit, Lahontan Regional Water Quality Control Board (LRWQCB), Tahoe Regional Planning Agency (TRPA) and a design engineer consultant. The 2NDNATURE team developed a recommended Riparian Ecosystem Restoration broad goal statement and conceptual model to focus the Lake Tahoe Basin‐wide discussions. The Riparian Ecosystem Restoration and Effectiveness Framework (Framework) was developed to focus the process and improve the communications when stream restoration practitioners are implementing specific restoration projects. The Framework process is expected to simplify the summary of existing (impaired conditions), the development of testable restoration project objectives, improve the quality of restoration project monitoring strategies and actualize the adaptive management process. This document contains a number of specific recommendations and guidelines on how to improve the quality of protocol and metric selection, analysis and reporting to increase the confidence in effectiveness monitoring results. The final products of the Framework will increase consistency of the documentation of the restoration team intentions to interested parties many years following the completion
68 of the restoration actions, thereby directly improving the availability and quality of the data and information available to make long‐term adaptive management decisions.
A Symposium on SEZ Restoration Monitoring in the Tahoe Basin. 2010. Proceedings from the February 9-10, 2010 Symposium, Tahoe Center for Environmental Sciences, Incline Village, NV. The specific objectives of this symposium were to: Consider past and current Tahoe Basin SEZ restoration programs and examine the approaches developed to assess the effectiveness of stream channel and flood plain restoration projects. Learn about monitoring and assessment techniques from outside the Tahoe Bain, to understand their strengths and possible weaknesses. Consider proposed frameworks for planning and monitoring the effectiveness of stream and flood plain restoration projects. Consider tools to quanify stream and flood plain project-level water quality benefits and inform basin-wide progress in meeting Lake Tahoe TMDL targets. Identify research needed to develop new tools and address uncertainties. Abstracts can be found at www.tahoescience.org/tsc_products/Products.aspx
Application to Management
Restoration monitoring is now a fairly well established component of environmental improvement projects nation-wide. If designed well and implemented effectively, they provide both the land use manager and scientist with very helpful information. If the design is weak, not only are economic resources wasted, but, by necessity managers have to operate “in the dark” with respect to future actions. It is important to clearly define the objectives of restoration monitoring and create specific questions or hypotheses that need to be answered. If not restoration monitoring can devolve into an unjustified effort to collect as much data as possible without a clear vision of why the data is being collected. When establishing restoration monitoring it must be recognized that not all projects require a “Cadillac” monitoring plan, depending on the relevant questions. Sometimes monitoring can be photo-point information or other variations on visual monitoring. Other times, sophisticated scientific techniques and instrumentation is required. Since longer periods of time are required for projects to restore or significantly improve an area of degraded environmental condition, restoration monitoring may take years to show an effect.
69 Soils and Sediment Erosion Processes
Overview
Watershed runoff and erosion are complex processes. Progress is currently being made to model sediment erosion and quantitatively evaluate total and fine loading to Lake Tahoe; however, these simulations depend on a good understanding of the mechanisms at play. How soil disturbance (e.g. ski runs, road- cuts), subsequent restoration, and Hillslope erosion adjacent to Lake Tahoe. Source: Int. Erosion forest management effects water Control Assoc. quality is a principle concern as resource management and regulatory agencies endeavor to determine how land practices are associated with changing watershed sediment loads. Recent studies in the Tahoe basin have begun to examine some of these processes at scales ranging from soil microbial communities as affected by disturbance to watershed sediment loading associated with changes in land management. Between these micro and macro scales, the factors controlling soil aggregation, breakdown, repellency and sediment transport at the plot scale are considered. Many of these individual efforts are being integrated in more detailed watershed models to begin to address some of the issues faced by the agencies charged with land management across the Basin.
Peer Reviewed Journal Publications
Soil Restoration and Erosion Control: Quantitative Assessment and Direction. 2007. M. Grismer. Transactions of the American Society of Agricultural and Biological Engineers. 50(5): 1619-1626. Available predictions of erosion rates from partially rehabilitated or treated soils (e.g. grass covers, tillage, compost/mulch incorporation) are poor, due in part to limited data on the factors affecting infiltration/runoff rates associated with these treatments. This is especially true for mountainous, subalpine landscapes. A new erosion control paradigm should be directed at restoring soil ecologic functioning. Such information is important with respect to water quality modeling/monitoring for TMDLs and other nonpoint source control programs. Erosion-related research on soil detachment processes have focused on bare soils in laboratory or flume-based conditions. Field studies of sediment erosion processes are needed considering the actual litter/duff surface layers common in range and forest settings (e.g. information on runoff particle-size distributions, restoration method and fine sediment control, soil shear strengths of “native” and rehabilitated soils, indicators for soil rehabilitation, soil treatments of hydrologic conditions).
70 Runoff Sediment Particle Sizes Associated with Soil Erosion in the Lake Tahoe Basin, USA. 2008. M. Grismer, A. Ellis, A. Fristensky. Land Degradation & Development. 19: 331-350. This work investigated the dependence and significance of runoff sediment particle-size distribution and sediment yield (i.e. erodibility) on mountainous slopes and compared these relationships between erosion control treatments (e.g. mulch covers, compost, woodchip amendment, plantings) with bare and undisturbed forest soils. Granitic soils had larger particle sizes than volcanic soils in bulk soil and runoff samples. Consequently, runoff rates, sediment concentrations and sediment yields were greater from bare volcanic soil as compared to bare granitic soil at similar slopes. Sediment yield was 3-4 times larger from volcanic soils compared to granitic soils. Overall, results suggest that woodchips and fine organic cover were the two treatments that are the most suitable for erosion control on Tahoe basin soils in terms of runoff rates, sediment loads and generation of fine particles.
A Modeling Approach for Ultrasonic Soil Aggregate Stability Assessment. 2008. A. Fristensky, M. Grismer. Catena. 74: 153-164. A method is presented to investigate the stability of soil aggregates by simultaneously modeling the redistribution of particles throughout any desired set of soil particle-size intervals as ultrasonic energy is applied to a soil-water suspension. Application of the method was demonstrated for five particle-size subgroups (0.04-2000 μm) subject to 12 levels of ultrasonic energy. Two groups of aggregates were detected with significantly different (p<0.05) ultrasonic stability: (1) macro-aggregates ranging 250-2000 μm in size and (2) a finer, relatively stable group ranging 20-1000 μm. The coarser, less-stable group liberated 13 percent clay (0.04-2 μm), 53 percent fine silt (2-20 μm), and 34 percent coarse silt and sand (20-250 μm); while the finer, more-stable group liberated 26 percent clay and 74 percent fine silt.
Fine-Sediment Loadings to Lake Tahoe. 2008. A. Simon. Journal of the American Water Resources Association. 44(3): 618-639. The objective of this study was to determine the amount of fine sediment delivered to Lake Tahoe from each of the 63 channelize tributaries. This research used combinations of field-based observations of channel and bank stability with measured and simulated data on fine-sediment loadings to estimate fine-sediment loadings from unmonitored basins throughout the Lake Tahoe basin. Loadings were expressed in the conventional format of mass per unit time but also in the number of particles finer than 20 μm, the latter for future use in a lake-clarity model. The greatest contributors of fine sediment happened to be those with measured data, not requiring extrapolation. In descending order, they are as follows: Upper Truckee River [1,010 tonnes per year (T/year)], Blackwood Creek (846 T/year), Trout Creek (462 T/year), and Ward Creek (412 T/year). Summing estimated values from the contributing watersheds provided an average, annual estimate of fine-sediment (<0.063 mm) loadings to the lake of 5,206 T/year. A total of 7.79 x 1019 particles in the 5-20 μm fraction were calculated to enter Lake Tahoe in an average year with the Upper Truckee River accounting for almost 25% of the total. Contributions from Blackwood, Ward, Trout, and Third creeks account for another 23% of these very fine particles. Thus, these five streams making up about 40% of the basin area, account for almost 50 percent. [Note from editor - these estimates are not accounting for the urban stormwater runoff that flows directly into the lake and which are characterized by very high concentrations of fine sediment particles].
71 Contribution of fine sediment from streambank erosion were estimated as about 25% of the average, annual fine-sediment load delivered via stream flow.
Evaluation of Ultrasonic aggregate Stability and Rainfall Erosion Resistance of Disturbed and Amended Soils in the Lake Tahoe Basin, USA. 2009. A. Fristensky, M. Grismer. Catena. 79: 93-102. Application of organic soil amendments to disturbed soil improves aggregate stability and reduces soil susceptibility to erosion. This study assessed the effect of two experimental amendments - compost and a woodchip mulch - at a series of highly disturbed sites in the Tahoe basin. Soil treatments were observed to significantly (p<0.05) increase both aggregation (300 percent average increase) and aggregate stability (600 percent increase) relative to untreated soil at some sites. Results varied based on treatment and condition. Results suggest that ultrasonic aggregate stability values may be useful indicators of soil susceptibility to runoff and erosion under rainfall.
Integrated Monitoring and Assessment of Soil Restoration Treatments in the Lake Tahoe Basin. 2009. M. Grismer, C. Shnurrenberger, R. Arst, H. Hogan. Environmental Monitoring and Assessment. 150: 365-383. Revegetation and soil restoration efforts associated erosion control are rarely monitored for hydrologic function, much less, ecologic function and long-term sustainability. Authors present a comprehensive, integrated field-based evaluation and assessment of the hydrologic function, with the hypothesis that restoration of sustainable function will result in longer term erosion control benefits than temporary actions. Recommended monitoring includes cover-point and ocular assessment of plant cover, species type and diversity, soil sampling for nutrient status, rainfall simulation measurement of infiltration and runoff, cone penetrometer measurements of soil compaction and thickness of mulch layer.
Sediment Budget for Subalpine Watersheds, Lake Tahoe, California, USA. 2009. A. Stubblefield, J. Reuter, C. Goldman. Catena. 76: 163-172. Pinpointing erosional ‘hot spots’ or sediment source areas within a watershed can be difficult because of the highly non-linear and episodic nature of effective runoff and sediment transport. Continuous monitoring of stream networks can provide insight into sediment source areas not possible from routine sampling by capturing episodic events and integrating entire storm events. This study presents the results of a three-year study of spring snowmelt runoff in watersheds of Lake Tahoe, California, USA, using a network of nine nephelometric turbidometers. It was estimate that montane badlands, comprising 1.2% of the Ward Creek watershed (25 km2), contributed 10–39 percent of snowmelt-derived suspended sediment load. The larger (29.5 km2) Blackwood Creek watershed also showed high relative erosion rates from volcanic terrain. Tributaries draining forested granitic and metasedimentary headwater regions had minimal sediment loads. Monitoring networks indicated that temporary main channel storage regulated release of fine sediment eroded from steep headwater slopes. This lag between erosion and delivery may lead to underestimation of gully erosion contribution to sediment budgets.
72 Evaluating the Efficacy of Wood Shreds for Mitigating Erosion. 2009. R. Foltz, N. Copeland. Journal of Environmental Management. 90: 779-785. An erosion control product made by shredding on-site woody materials was evaluated for mitigating erosion through a series of rainfall simulations. Tests were conducted on bare soil and soil with 30, 50, and 70% cover on a coarse and a fine-grained soil. Results indicated that the wood product known as wood shreds reduced runoff and soil loss from both soil types. Erosion mitigation ranged from 60 to nearly 100% depending on the soil type and amount of concentrated flow and wood shred cover. Wood shreds appear to be a viable alternative to agricultural straw. A wood shred cover of 50% appears optimal, but the appropriate coverage rate will depend on the amount of expected concentrated flow and soil type.
Dry-Season Soil Water Repellency Effects on Infiltration Rates in the Tahoe Basin. 2010. E. Rice, M. Grismer. California Agricultur. 64(3): 141-148. Soil-water repellency may be an important factor in watershed runoff and erosion post wildfire and under late-season dry conditions, however its quantification for comparison and modeling purposes has been lacking. This study used a rainfall simulator and mini-disc infiltrometer with and without inclusion of a surfactant solution to determine levels of repellency in terms of infiltration rates for undisturbed forest soils (slopes at 10-15 %). For volcanic soils, infiltration rates using the surfactant exceeded those without by 20 % when there was little litter cover; but by a factor of three with substantial litter cover. For granitic soils the surfactant enhanced infiltration 4-fold with little litter and 8-fold with substantial litter. Dry season hydrophobicity appears to have substantial effects on plot-scale infiltration and erosion rates at several Tahoe basin sites.
Other Scientific Literature
Vegetation Management in Sensitive Areas of the Lake Tahoe Basin: A Workshop to Evaluate Risks and Advance Existing Strategies and Practices. Independent review panel report. 2008. Elliot, W. J., W. Miller (Chair), B. Hartsough, S. Stephens. 20-22 February, 2008, Incline Village, NV. Tahoe Science Consortium. 30 p. The invited review panel spent two days listening to presentations related to different points of view on the impacts of forest management on water quality and fire risk. The peer-reviewed report from the review panel concluded that using current practices, watershed damage would be minimal from activities to reduce fire risk in or near developed areas. The panel also recommended that a simplified system be established to obtain permission to carry out fuel treatment activities, rather than the method in place at that time that required multi agency approval, often requiring similar application information.
Assessing the Sources and Transport of Fine Sediment in Response to Management Practices in the Tahoe Basin using the WEPP Model. 2009. E. Brooks, W. Elliot, J. Wu, S. Dun, J. Boll. SNPLMA Round 7 Project #2A11 Quarterly Report submitted to the LTBMU. 24 p.
73 This technical report provided an evaluation of the WEPP-UI watershed model using observed stream flow, sediment load, and snow water equivalent data collected in the General creek, Blackwood creek, Upper Truckee, Logan House, and Glenbrook creek watersheds. Model agreement to predicted sediment load was very good in all watersheds. Stream flow was over-predicted in the watersheds located on the drier- eastern side of the lake. The model identified shallow volcanic soils as primary contributors of upland sediment load in undisturbed watersheds.
Improving Erosion Modeling on Forest Roads in the Lake Tahoe Basin: Small Plot Rainfall Simulations to Determine Saturated Hydraulic Conductivity and Interrill Erodibility. 2009. N. Copeland, R. Foltz. Written for presentation at the 2009 ASABE Annual International Meeting, June 21 – June 24, 2009. 12 p. The Tahoe basin economy is dependent upon the protection of the beauty of Lake Tahoe and the continued availability of recreational opportunities in the area; however, scientists estimate that the continued increase in fine sediment and nutrient transport to the lake threatens to diminish this clarity in as little as 30 years. The LTBMU plans to employ WEPP: Road as a predictive tool for land planning in the basin. WEPP: Road was developed by the Rocky Mountain Research Station as an interface to the Water Erosion Prediction Project (WEPP) model. WEPP: Road allows users to quantify sediment production from road surfaces and to assess the effectiveness of best management practices on those surfaces. Model accuracy may be improved through use of site-specific parameters. The purpose of this study was to obtain estimates of hydrologic parameters for native surface roads comprised of soils derived from the two predominant parent materials in the Lake Tahoe basin. Rainfall simulations were conducted on four unpaved roads to determine the saturated hydraulic conductivity and interrill erodibility. The average measured saturated hydraulic conductivity was 16 mm hr-1 and the average measured interrill erodibility was 1.0 x 106 kg s-1 m-4. The roads measured in this study typically produced sustained and relatively high sediment concentrations throughout the simulation period. Sustained sediment concentrations may have been due to soil water repellency.
Improving Road Erosion Modeling for the Lake Tahoe Basin and Evaluating BMP Strategies for Fine Sediment Reduction at Watershed Scales Final Report. 2010. R. Foltz, W. Elliot, N. Wagenbrenner. Prepared for Pacific Southwest Research Station. 25 p. Roads, especially with native surfaces, can be the greatest single source of sediment delivered to stream systems (Megahan, 1972; King and Gonsior, 1980). The Forest Service Lake Tahoe Basin Management Unit (LTBMU) evaluated 134 miles of road decommissioning and BMP upgrades between 2003 and 2005 (USDA Forest Service LTBMU, 2006), focusing on the road segments that were hydrologically connected to streams (USDA Forest Service LTBMU, 2005). Their road BMP upgrades were to protect soil and water resources and included upgrades of surfacing (e.g., pavement), drainage (e.g., rocked ditch), and slope stabilization (e.g., rocked fillslope and revegetation). One of the evaluation methods used by LTBMU was WEPP: Road, an interface developed by the USDA Forest Service Rocky Mountain Research Station (RMRS) using the Water Erosion Prediction Project (WEPP) model (Elliot et. al, 1999). WEPP: Road
74 allows the users to quantify the sediment load and assess the effectiveness of BMPs on soil erosion. In order for WEPP: Road to produce more accurate results, the model parameters need to be refined for a specific region. We proposed to fill this critical need by 1) parameterizing the WEPP model specifically for the Lake Tahoe Basin, 2) improving the current WEPP: Road interface, 3) validating the WEPP model for the Lake Tahoe Basin and 4) developing a quantitative approach to identify erosional “hot spots” and the adequate BMPs to efficiently reduce the sediment transport to stream channels.
Integrated Science Plan for the Lake Tahoe Basin: Conceptual Framework and Research Strategies: Chapter 5 - Soil Conservation Research Strategy. 2010. W. Miller, E. Carroll-Moore, H. Tretten, D. Johnson (Z. Hymanson and M. Collopy, eds.). US Forest Service General Technical Report, PSW-GTR-226, pp. 183-236. This presentation provides a brief introduction of various sub-themes important to Soil Conservation in the Lake Tahoe Basin that includes a description of what the sub-theme is, what we know about it, and its overall relevance (perceived or real) as a research issue important to management strategies in the Lake Tahoe basin. The following sub-themes were adopted as the primary categories or conditions of interest to agencies and the public: Key Soil Properties and Conditions; Development and Application of Predictive Models as Related to Soil Conservation; Effects of Climate Change as Related to Soil Conservation; and Policy Implications and Adaptive Management Strategies as Related to Soil Conservation. A prioritized listing of the three most immediate near-term soil conservation research needs within each sub-theme category is presented. This approach was taken because different agencies may be more focused on the components of a given sub-theme rather than the broader category of Soil Conservation as a whole.
Road Cut and Fill Slope Sediment Loading Assessment Tool: Project Report. 2010. Prepared for the Pacific Southwest Research Station. Prepared by K. Drake, R. McCullough, Integrated Environmental Restoration Services, M. Grismer, UC Davis. 22 p. Achieving the fine sediment load reduction targets set forth in the Lake Tahoe TMDL depends on an accurate understanding and characterization of sediment source areas. An estimated 72% of the fine sediment particle (FSP, <16 microns) load entering Lake Tahoe is believed to originate from urban areas. Road cut and fill slopes represent a persistent and readily treatable source of FSP loading and are widespread along most roadways in the Lake Tahoe Basin, particularly within urban areas. Roads cut and fill slopes tend to be characterized by steep slopes, compacted soils, and low levels of soil cover. Such areas represent a “perfect storm” for detachment and transport of FSPs. The overall purpose of this project was to develop the data and tools necessary to improve estimates of pollutant loading and load reductions from road cut and fill slopes. The end product of this effort is the Road Cut and Fill Slope Sediment Loading Assessment Tool (RCAT), a simple and repeatable field assessment methodology and spreadsheet tool designed to assist the Lake Tahoe erosion control and stormwater community in characterizing the functional condition of road cut and fill slopes and estimating the associated sediment and FSP loading from these areas.
75 Microbial Community Composition and Stability of Disturbed Soils in the Lake Tahoe Basin, USA: 1. Assessment. In press. A. Collins and M. Grismer. Environmental Monitoring and Assessment. The influence of the microbial community on soil stability/erodibility was studied at Lake Tahoe using rainfall simulation and phospholipid fatty acid analysis (PLFA). Experiments were conducted on disturbed soils of volcanic and granitic origin and treatments included soil loosening and erosion control amendments. Increased infiltration rates on ski-run and road-cut soils were associated with increased total microbial biomass, and road-cut soils were specifically associated with fungal biomass. It appears that to increase soil infiltration rates, especially on severely degraded soils (e.g. road-cuts), high-carbon content amendments that appear to select for fungi are better than nitrogen rich materials.
Microbial Community Composition and Stability of Disturbed Soils in the Lake Tahoe Basin, USA: 2. Restoration Trajectory. In press. A. Collins and M. Grismer. Environmental Monitoring and Assessment. Guidance is required to determine if soil treatments are actually moving the soils towards restored, or pre-disturbance functional conditions. This work considers the relative success of restoration treatments, not only in terms of hydrologic parameters, but also as a function of microbial community structure and stress indicators. Test plots included disturbed volcanic and granitic soils, with treatments ranging from bare, to tilled and amended soils. The PLFA results showed that fingerprints differed from location to location, but at all locations native plots were significantly different than treated plots, and furthermore, that all treated plots were more similar to one another than to native plots. Stress indicator biomarkers varied as a function of the occurrence of runoff.
Rainfall Simulation Studies – A Review of Designs, Performance and Erosion Measurement Variability. 2011. M. Grismer. Draft final report written in support of the Rainfall Simulations Methods workshop (March 4, 2011). Workshop convened by the Tahoe Science Consortium (http://www.tahoescience.org/). 101 p. The unpredictability, infrequent and random nature of natural rainfall makes difficult the study of its effects on soils while rainfall is occurring. The use of rainfall simulators (RSs) and perhaps runoff simulators for rill erosion can overcome some of these difficulties, enabling a precise, defined storm centrally located over runoff measurement “frames”. RSs are often used to study the effects of various soil factors on rates of infiltration and erosion in the field. That no standardized methodology has been proposed or can be identified in the literature, making comparisons between study results difficult has long been recognized. Concerns such as these have also arisen in the Tahoe Basin, because a variety of methods for measurement of infiltration and erosion rates have been deployed, but comparisons between results of different studies are uncertain. The objective of this paper is to review the more recent literature of the past two decades concerning application of RS techniques in the field and how they might apply to forested, rangeland, ski-run conditions to that found in the Tahoe Basin. As many of the RS-derived erosion measurement efforts are, at least in part, motivated by the historical conceptual view of erosion processes, first, the prevailing descriptions of the erosion processes as they developed from the classic USLE-based interpretation to
76 sediment transport and WEPP-based analyses are considered. Next, as a primary concern of the past has been the ability of RSs to replicate “natural” rainfall characteristics, available studies of these characteristics are reviewed and compared with laboratory analyses of rain drop-sizes, their distributions and kinetic energies (KEs). These reviews set the stage for consideration of RS designs and field methodologies as they may have been affected by attempted definitions of erodibility and “natural” rain characteristics. Following review of RS designs and issues associated with field plot conditions, some of the key issues associated with RS-based erosion measurements; the processes involved in forested landscapes, their interpretation, sources of error or uncertainty and up-scaling plot results to hillslope and catchments are considered. Here, the focus is largely on “portable” RS usable in field studies of these various processes on a range of slopes.
Application to Management
Tools to better simulate sediment erosion – including the fine sediment fraction – are important to the Lake Tahoe TMDL and restoration projects designed to abate this load. Researchers are very actively engaged in this effort and they have taken a two-pronged approach, (1) understanding the mechanistic details of erosion and sediment transport in the complex topography afforded by the Tahoe basin and (2) incorporate this knowledge into the development of management models.
Field-based monitoring of hydrologic processes is crucial towards developing effective means of containing and reducing sediment and fines loading to the Lake. To effectively implement and accurately assess the progress and outcomes of TMDL efforts, it is necessary to base initial hydrologic modeling efforts on directly measured runoff, water quality and climate data and to link modeling assumptions to a clearly articulated Adaptive Management implementation process supported by this quantitative performance monitoring.
Treating distributed hydrologic model predictions as hypotheses to be tested is a critical step towards developing an accurate understanding of actual restoration or treatment outcomes. The most cost-effective approach to TMDL implementation is likely based on developing an accurate understanding of treatment/BMP effectiveness through field measurements at the project scale rather than relying solely on modeled predictions – this is exactly the approach being taken for urban stormwater through the Lake Tahoe Regional Stormwater Monitoring Program (RSWMP), but needs to also be applied to non-urban uplands. Further, it is expected that those field measurements will be used to further calibrate and/or parameterize the models employed so that their predictive power is increased and load reduction technologies improved.
77 Toxic Compounds and Biotoxicity
Overview
Even though there are no major industrial/commercial sources of toxic pollutants at Lake Tahoe, as there are in large urban areas, understanding the biogeochemistry and biotoxicity of potentially toxic compounds is of concern. Previous investigations have shown that toxics can be transported in the Tahoe basin and the Sierra Nevada by atmospheric winds as part of continental or global transport. The work done at Lake Tahoe on the gasoline additive MTBE (methyl tertiary butyl ether) in the late 1990s reinforced that local sources (in that case direct exhaust of watercraft emissions to the lake) can also be important. While biotoxicity at Lake Tahoe has not been the problem it is in more industrialized waterbodies, researchers remain active in this field because of the important, Runoff of highway pollutants. Source: Jim potential consequences to human health and aquatic Markle life should this become a more significant issue.
Peer Reviewed Journal Publications
Potential Toxicity Conerns from Chemical Coagulation Treatment of Stormwater in the Tahoe Basin, California, USA. 2009. S. Lopus, P. Bachand, A. Heyvaert, I. Werner, S. Teh, J. Reuter. Journal of Ecotoxicology and Environmental Safety. 72(7): 1933-1941. Coagulant dosing of stormwater runoff with polyaluminum chlorides (PACs) is used in numerous waterbodies to improve water clarity, but the potential risks of PACs to aquatic organisms in Lake Tahoe, California are not fully understood. To assess these risks, the USEPA 3-species toxicity test and a non-standard fish test using Japanese medaka (Oryzias latipes) were used to determine the toxicity of PAC-treated and non-treated stormwater samples to aquatic species. Samples received coagulant dosing using three different coagulants (JC1720, PAX-XL9, Sumalchlor50) at levels optimized with jar testing. Raw stormwater was toxic to algae and fathead minnows (mortality). Treatment with coagulants increased toxicity to zooplankton (reproduction) and had no consistent effects on other toxicity metrics.
Treatment with Chemical Coagulants at Different Dosing Levels Changes Ecotoxicity of Stormwater from the Tahoe Basin, California, USA. 2010. P. Bachand, S. Bachand, S. Lopus, A. Heyvaert and I. Werner. Journal of Environmental Science and Health, Part A: Toxic/Hazardous Substances and Environmental Engineering, 45(2): 137-154. doi:10.1080/10934520903425459. Polyaluminum chloride coagulants (PACs) have shown great promise in removing fine particles and phosphorus from stormwater before it enters the Lake Tahoe. This study investigated stormwater and coagulant toxicity under non-dosed, optimally-dosed, and
78 over-dosed conditions using the US EPA 3-species test through growth of green algae (Selenastrum capricornutum), zooplankton (Ceriodaphnia dubia) mortality and reproduction, and larval fish (fathead minnow, Pimephales promelas) mortality and biomass. A series of stormwater samples collected during a spring snowmelt runoff event were dosed with two different coagulants (a chitosan and a PAC) at levels optimized with a streaming current detector. Non-treated highway runoff was toxic to zooplankton and fish. Optimal coagulant dosing increased algal growth and reduced zooplankton toxicity. Overdosing at two and three times the optimal level of a PAC decreased zooplankton reproduction and increased fish mortality. PAC-related toxicity was correlated with increasing total unfiltered aluminum and decreasing alkalinity, pH, and DOC. Because of toxicity risks, the recommendation was to keep PAC coagulant dosing at or below optimal levels in practice.
Mercury Flux to Sediments of Lake Tahoe, California-Nevada. 2010. P. Drevnick, A. Shinnehan, C. Lamborg, D. Engstrom, M. Bothner, J. Oris. Water Air Soil Pollution. doi10.1007/s11270-009-0262-y. Mercury (Hg) flux to the sediments of Lake Tahoe, California–Nevada were estimated as 2 and 15–20 µg/m2/year in preindustrial and modern sediments, respectively. These values result in a modern to preindustrial flux ratio of 7.5–10, which is similar to flux ratios recently reported for other alpine lakes in California, and greater than the value of 3 typically seen worldwide. Possible hypotheses to explain the high flux ratios, include (1) proportionally less photoreduction and evasion of Hg with the onset of cultural eutrophication and (2) a combination of enhanced regional oxidation of gaseous elemental Hg and transport of the resulting reactive gaseous Hg to the surface with nightly downslope flows of air.
Whole-Watershed Mercury Balance in a Sierra Nevada Ecosystem. 2011. X. Faïn, D. Obrist, A. Pierce, C. Barth, M. Gustin, D. Boyle.. Geochimica et Cosmochimica Acta. 75(9): 2379-2392. Little data is available on mercury (Hg) dynamics at high-elevation mountain sites. In this project, a whole-watershed approach was used to quantify major fluxes and pools of Hg in Sagehen basin, a closed basin in the Sierra Nevada mountains in California and just north of Lake Tahoe. Over a period spanning 9 months (January-September 2009), the estimated wet deposition input to the watershed was 3.8 µg m-2. Dry deposition added additional Hg in the range of 0.30-2.45 µg m-2 and was the dominant deposition process during the dry summer. Seasonal snowpack accounted for only half of the Hg deposited by wet deposition. We suggest that photo-induced reduction of Hg(II) in snow and subsequent volatilization was responsible for this loss. Thus, snowpack in the Sierra Nevada mountains likely reduce the effective atmospheric mercury flux via wet deposition due to significant re-emission fluxes prior to snowmelt. Stream runoff collected at the outlet of the watershed could account for only 6 percent of total Hg wet deposition suggesting that a large fraction of mercury deposition was sequestered in the ecosystems, specifically in the soils.
Other Scientific Literature
Application to Management
79
Continued research on toxic compounds and potential biotoxicity at Lake Tahoe is important to resource managers in that it allows them to stay abreast of this topic before significant problems arise. Protection of human health and aquatic life is of concern to all water quality managers regardless of location. The MTBE example cited above was an ideal example of how research lead directly to policy decisions and the solution of a problem. While Lake Tahoe is not known for issues of toxicity, it is nevertheless critical that researchers are supported to conduct investigations whenever an issue of possible toxicity arises.
80 Urban Stormwater and BMP Monitoring
Overview
Estimates from the Lake Tahoe TMDL for water transparency show that urban stormwater makes important contributions to the loading of fine sediment particles (72 percent), total phosphorus (39 percent) and total nitrogen (17 percent). While urban stormwater and BMP effectiveness is not new at Lake Tahoe, in 2000 the Lake Tahoe Watershed Assessment highlighted the fact that that pervious work was spotty, new well organized, lacked a developed set of Stormwater inflow on. Source:laketahoenews.net.jpg. monitoring questions, was done with inconsistent techniques and overall did not provide the level of information needed for water quality planning and restoration. This changed with the advent of the TMDL program in the early 2000s and since then urban stormwater and BMP monitoring has become much more sophisticated and drive by key management questions.
Peer Reviewed Journal Publications
Nutrient and Sediment Production, Watershed Characteristics and Land Use in the Tahoe Basin, California-Nevada. 2008. R. Coats, M. Larsen, A. Heyvaert, J. Thomas, M. Luck, J. Reuter. Journal American Water Resources Association. 44(3): 754-770. Data from both the Lake Tahoe Interagency Monitoring program (stream water quality) and the TMDL Stormwater Monitoring project were used to address the following questions: (1) what are the fluxes and concentrations of nitrogen and phosphorus entering the lake from surface runoff; (2) how do the fluxes and concentrations vary in space and time; and (3) how are they related to land use and watershed characteristics. Flow-weighted average concentrations and annual fluxes and used within a multiple regression format to relate those variable to a suite of GIS-derived explanatory variables. The final selected regression models explained 47-62 percent of the variance in constituent concentrations in the stormwater monitoring catchments, and 45-72 percent of the variance in mean annual yields in the larger watersheds. The results emphasize the importance of impervious surface and residential density as factors in water quality degradation, and well-developed soil as a factor in water quality maintenance.
Feasibility Study and Conceptual Design for Using Coagulants to Treat Runoff in the Tahoe Basin. 2010. P. Bachand, A. Heyvaert, S. Prentice, T. Delaney. Journal of Environmental Engineering. 136(11): 1218-1230. This study used settling columns to show the feasibility of coagulant dosing to target fine particle removal from stormwater. Coagulation reduced mean turbidity and phosphorus by 85–95% within 10 hours of dosing. To achieve equivalent treatment levels, an order of magnitude increase in time
81 was required for the non-treated stormwater. This work presents a conceptual model for applying this coagulant dosing technology to stormwater treatment basins and wetlands to increase their efficiency and effectiveness by an order of magnitude in targeting fines. This would also optimize the performance of acreage used for stormwater treatment. Given the paucity of available acreage in the Tahoe basin for implementing stormwater BMPs, this technology could be used to retrofit existing basins and thereby greatly increase effective total fine particle and phosphorus removals.
BMP- SA: A Forest Road BMP Planning Decision Support Tool Combining WEPP: Road Erosion Modeling with Simulated Annealing Optimization. 2010. J. Efta and W. Chung. Environmental Modelling & Software. Submitted. To minimize erosion from forest roads, managers install and maintain physical Best Management Practices (BMPs). BMP installation on a watershed scale is a difficult task because of the need to prioritize locations while accounting for multiple constraints, such as available budget, BMP maintenance, and equipment scheduling. BMP-SA, a decision support tool which uses simulated annealing as its heuristic solver, addresses this challenge. BMP-SA accounts for sediment leaving the forest buffer through incorporation of modeled road erosion predictions and alternative BMP options for problematic road segments. WEPP: Road, a physically-based road erosion prediction tool, provides a user- friendly platform for assessing erosion risk. This paper presents a methodology for predicting road segment erosion risk, identifying applicable BMP treatments, and applying BMP-SA to an area of interest. Field surveys of forest roads at Glenbrook Creek, NV provided inputs for WEPP: Road and subsequent identification of erosion risk potential. Appropriate BMPs were identified for segments posing an erosion risk. These BMPs, associated sediment, costs, and maintenance frequencies were input into BMP-SA. The model minimized sediment leaving the buffer over the course of the planning horizon at a given budget. Sediment was minimized by comparing potential BMP installation and maintenance scenarios. Preexisting BMP maintenance costs, new BMP installation costs and maintenance regimens, and equipment scheduling considerations were accounted for within the model. Three scenarios at multiple initial budget levels were modeled to demonstrate the utility of this methodology. Of the 173 surveyed segments, 38 segments were available to have BMPs installed. The best possible solution yielded a reduction in estimated sediment leaving the buffer over the course of the planning horizon by 72%. BMP-SA can be applied to any watershed, but relies heavily on the perceived accuracy of road erosion predictions.
Stormwater and Fire Inputs of Black Carbon to Lake Tahoe. 2011. M. Bisiaux, R. Edwards, A. Heyvaert, J. Thomas, B. Fitzgerald, R. Susfalk, G. Schladow, M. Thaw. Submitted to Environmental Science and Technology. 45(6): 2065-71. Although recognized as a part of the global carbon cycle and as a critical component of modern climate forcing, little is known about black carbon in terrestrial waters. This study presents results on the measurement of black carbon nanoparticles (BCn) for waters of the Lake Tahoe watershed. Black carbon was measured with a Single Particle Soot Photometer (SP2) coupled with a flow injection system. BCn concentrations in storm water runoff, streams, nearshore and mid-lake samples were compared for different periods of the years from 2007 to 2009, and under different weather conditions.
82 BCn concentrations in the lake were < 0.5µg/L. These concentrations more than doubled during a local wildfire event, suggesting a significant input of black carbon by dry deposition to the lake surface. Low BCn concentrations in stream water from the fire area (0.1 to 16 µg/L) suggest low mobility of BCn in the soils of the fire site. Black carbon in storm water runoff from urbanized areas and highways surrounding Lake Tahoe was 100 to 1000 times more concentrated than from the mid-lake, with most concentrations in the range of 40 to 100 µg/L and a maximum concentration of 600 µg/L.
Other Scientific Papers
Upper Cutthroat Infiltration Testing and Stormwater Runoff Study. 2008. A. Heyvaert, A. Parra, R. Townsend, C. Strasenburgh. Report produced by the Desert Research Institute, Reno, NV. 67 p. Infiltration is an important strategy for Tahoe basin stormwater management. Yet, is only limited data available to determine the effectiveness of different infiltration practices. The Upper Cutthroat Erosion Control Project (Placer County) was designed to implement a series of infiltration components. This project was constructed within a largely residential area of Kings Beach, California, in a neighborhood characterized by steep slopes with poor drainage control. The main objectives of this study were to quantitatively assess, under natural and simulated conditions, whether various infiltration components were effective at reducing runoff volumes within the project area, and to provide empirical data that could be used for model development and calibrations that would improve future project designs. Data were obtained by monitoring flows through selected infiltration components, as well as by monitoring total outflow from the project area on a continual basis throughout the year. In addition, simulated runoff experiments introduced water into each project component in series, and then monitored the steady-state infiltration rates during both seasonally moist and seasonally dry soil conditions. Overall, the steady-state infiltration rates for components tested during runoff simulations averaged about 0.0006 ± 0.0002 cfs/m2. Calculated infiltration efficiencies were more variable and dependent upon experimental flow rates. The cumulative test results at point of discharge from the Upper Cutthroat project area ranged from 59–86 percent infiltration efficiency. The annual runoff coefficient for the entire Upper Cutthroat project drainage during WY2006 was 0.29 for an efficiency of 71 percent. Selected periods of runoff from seasonal snowmelt and discrete rain events yielded infiltration efficiencies that ranged from 60–100% for a monitored drainage swale.
Improving the Water Quality of Lake Tahoe One Development at a Time: Watershed LID Retrofits in the Tahoe Basin. 2008. S. L. Schuster, P.E., CPESC, CPSWQ. Watershed Retrofit with LID. pp 1607-1616. doi 10.1061/41099(367)138. American Society of Civil Engineers. http://cedb.asce.org/cgi/WWWdisplay.cgi?262857 Low-impact design (LID) based retrofit projects in developed areas of the Lake Tahoe basin have been shown to be effective in improving water quality. The projects aim to reduce the amount of nutrients and very fine sediments entering the lake via stormwater runoff. Such projects include extensive erosion and sediment control, and stormwater management to reduce the volume and improve the quality of stormwater eventually discharged to the lake. The administration of a large number of similar projects precipitated the development of
83 standardized planning and design guidelines to better focus funding on projects know to be effective. Designs consider source control as a top priority, followed by hydrologic controls and treatment controls. Soils and water are considered valuable resources to be retained on site. Three examples of LID based retrofit projects (Tahoe Estates Erosion Control Project, Lake Forest Area A Erosion Control Project, and Sierra Tract Phase 2 Erosion Control Project) are presented to illustrate the application of the design guidelines and the lessons learned in the process.
NDOT Lake Tahoe Basin Stormwater Monitoring Program: Monitoring Seasons 2005- 06, 2006-07, 2007-08. 2008. Prepared for the Nevada Department of Transportation. Prepared by CDM/Will Rogers, Reno. NV. This report presents results of the Lake Tahoe Basin Stormwater Monitoring Program conducted by the Nevada Department of Transportation in the Tahoe basin, Nevada. Includes monitoring that was conducted from December 2005 through April 2008. The goals of this program were (1) characterize stormwater and the treatment effectiveness of various BMPs used by NDOT at Lake Tahoe and (2) collect data in support of the Lake Tahoe TMDL. Ten monitoring stations were installed in the fall of 2005, and monitored during the 2005-2006 winter season (October-April), the summer of 2006 (May-September), the 2006-2007 winter season (October-April) and the 2007-2008 winter season (December- April). In addition to flow, analytes included conductivity, pH, TP, ortho-P, TKN, nitrate, TSS, turbidity total iron and dissolved zinc. Concentrations and loads are reported. Data was used to create summary statistics, influent to effluent comparisons by analyte and by BMP, load reduction and BMP effectiveness, discharge limit comparison, runoff characterization from improved and unimproved highways, comparison with Caltrans and other available data, elevation impacts, impacts of traffic, particle size analysis of sediment, and sediment accumulation in BMPs.
Brockway Project Area Stormwater Runoff and Characterization Study. 2008. A. Heyvaert, A. Parra, C. Strasenburgh, R. Townsend. Report produced by the Desert Research Institute, Reno, NV. 56 p. The Brockway Erosion Control Project is currently in the planning and development phase. Placer County has implemented an alternatives formulation process to explore a set of designs that will include erosion control and hydrologic control features to treat runoff from a commercial area in the westernmost portion of Crystal Bay. The purpose of the Brockway stormwater monitoring effort is to provide better information for improved project design and assessment. It will also provide pre-project water quality information that can later be compared to post-project monitoring. Five sites were monitored for continuous flow, and nutrient and sediment concentrations during precipitation events to establish pre-project water quality conditions discharged from the area.
Lake Tahoe Basin Regional Stormwater Monitoring Program - Conceptual Development Plan (Phase 1). 2008. A. Heyvaert, J. Reuter, J. Thomas, W. Miller, Z. Hymanson. Prepared in partnership with the Tahoe Science Consortium (www.tahoescience.org/). 45 pp.
84 Regarding the control of pollutant loading from urban stirmwater, there has to be a system of quality assurance and quality control to assure that management objectives are adequately addressed with available resources, and that actions are taken proactively when specified objectives are not achieved. Such is the purpose of the regional stormwater monitoring program. At its inception this program will provide a process by which to collectively formulate goals and objectives, to evaluate progress, and to adjust our actions and funding to best achieve articulated resource management goals in the present and for the future. Despite progress made to better manage stormwater and BMP effectiveness monitoring, there is general consensus that critical opportunities to increase our understanding of these topics have been missed in the past because of the lack of a coordinated monitoring program. With the advent of the Lake Tahoe TMDL, the Pathway 2007 Regional Plan, and discussions of adaptive management, it is understood that a well-designed and integrated monitoring plan is needed to meet the needs of all involved parties. This document discusses the programmatic objectives of a regional stormwater monitoring plan for Lake Tahoe. They include: develop a stormwater monitoring program that is directly responsive to the needs of both regulatory and land management agencies and project implementers; provide consistency in sampling design, data reporting and quality assurance; develop data management and communication tools for efficient and effective reporting on current conditions and trends; assure cost-effective high benefit from regional stormwater monitoring through a coordinated program that informs priority management decisions; and implement a sustainable RSWMP organizational structure with stable funding, dedicated personnel and adequate resources. This document also discusses monitoring goals, including: pollutant source monitoring, pollutant reduction monitoring, BMP design, operation and maintenance monitoring, load reduction model calibration and validation; and data management, analysis and dissemination.
Water Quality Performance Evaluation of Park Avenue Detention Basins; South Lake Tahoe, CA. 2008. Prepared by 2NDNATURE. 117 p. Very large reductions in fine particle and nutrient loading from urbanized areas need to be achieved in order to reach the Lake Tahoe TMDL goal of restoring lake clarity to 100 ft. in the next 20-30 years. Stormwater detention basins are designed to treat stormwater for nutrients and sediments before discharge to the lake. The main objective of this project was to monitor the two detention basins on Park Avenue to quantify the hydrologic and water quality benefits of basin construction. The upper basin was inundated 100% of the time, while the lower basin was inundated only 0.85% of the time. Up to 50% of the water routed toward the Park Avenue basins entered the bypass pipe and was routed around both basins suggesting that operational changes could be made to maximize treatment capacity. The upper basin has a lower infiltration rate than the lower basin assumed to be due to trapping of sediment and fine particles delivered to the basin and the extensive establishment of vegetation. The infiltration rate could be increased through regular maintenance thus increasing the annual volumes able to be treated in the upper basin. Surface water load reductions were observed for both nutrients and fine particles through nine discreet storm events over two years. The observations and results of this study were used to inform and improve design, operation and maintenance of stormwater improvement projects in Lake Tahoe.
85 Truckee River Water Quality Monitoring Plan. 2008. Prepared for Placer County and the Town of Truckee. Prepared by 2NDNATURE. The Truckee River Water Quality Monitoring Plan (TRWQMP) was created in response to an order issued by the Lahontan Regional Water Quality Control Board (LRWQCB) to Placer County and the Town of Truckee requiring the creation of a comprehensive monitoring program for the middle Truckee River. It is part of a much larger stormwater program in the Truckee River Watershed. Both the town and the county have developed and are implementing Stormwater Management Programs (SWMPs), and the purpose of the TRWQMP is to design a strategy allowing them to assess the effectiveness of the ongoing SWMPs in protecting downstream water resources. The TRWQMP provides a framework and strategy to develop a consistent, reliable and cost-effective means of tracking stormwater quality and the condition of the surface water resources. The results of the TRWQMP inform the adaptive management process of the SWMPs so that local agencies can continue to effectively implement actions to protect surface water quality. The goals of the TRWQMP are: (1) Ensure regulatory compliance for Placer County and the Town of Truckee with the NPDES permit, Lahontan Board Orders, Middle Truckee River Sediment TMDL, Squaw Creek Sediment TMDL, and the Martis Valley Community Plan, (2) Develop water quality monitoring datasets that will be scientifically defensible and provide accurate data to evaluate the effectiveness of SWMPs in protecting surface water resources, (3) Develop a TRWQMP that is economically feasible to implement and maintain over time, (4) Ensure that the TRWQMP allows collaboration, effort-sharing and integration of multiple independent private and public monitoring efforts.
Stormwater Characterization from the Lake Forest Project Area. 2008. D. Rios, A. Heyvaert, S. Brown. Prepared for the Placer County Department of Public Works. 47 p. Placer County Design Division contracted with the Nevada Tahoe Conservation District (NTCD) to monitor hydrology and water quality at seven stormwater and stream sites at Lake Forest in preparation to construct a comprehensive urban stormwater management project. This report summarizes the data from June 2007 through July 2008. During this period, precipitation was well below normal limiting the number of events sampled. Continuous data recording sites were established at the downstream end of the project area on Lake Forest Creek and Polaris Creek (LF6 and LF7, respectively). These two sites were equipped with automated water quality samplers, and also recorded continuous temperature, conductivity, and stage. One site was established at an ephemeral stream channel above the project area (LF2) and equipped with continuous stage and temperature recording equipment. Four additional monitoring sites were established at which discrete measurements were collected. At all sites discrete temperature, conductivity, and dissolved oxygen measurements were made during runoff events. In addition, discrete water quality grab samples were collected at sites not equipped with automated samplers. Eleven events were analyzed for this report consisting of 3 thunderstorms, 3 snowmelt, 3 baseflow, and 2 rain runoff events. Baseflow stream monitoring generated event mean concentrations (EMCs) for samples collected hourly for 24 hours. The EMCs for all baseflow water quality constituents were generally at least an order of magnitude less than event concentrations. Average total suspended solids (TSS) concentrations indicate approximately 2,000 pounds of sediment is discharged to the lake from each creek annually during baseflow conditions.
86 Thunderstorm events generated the highest turbidity and pollutant concentrations. For example, TSS was 2.7, 36, and 115 times greater than rain, snowmelt, and baseflow events, respectively. LF2 only flowed once during peak snowmelt, but is known to flow more frequently during years with normal precipitation. Of all the sites, LF4 and LF5 mean concentrations were consistently several times higher than all other sites. LF4 concentrations represent runoff from a commercial corridor conveyed along road side ditches. LF5 is water discharged from the surrounding residential area as well as seasonal natural flow from forested uplands at LF2 that travel through a culvert under the community served by Glen Brae Circle. Pollutant loads at LF7 were approximately double the loads at LF6 (the volume of water was approximately the same). Despite this, the pollutant concentrations at LF7 were well below TRPA’s surface water quality discharge limits.
Heavenly Creek SEZ Demonstration Project - 2007 Soil Monitoring Report. 2008. S. Norman, T. Loupe, J. Keely. US Forest Service, Lake Tahoe Basin Management Unit. 56 p. The 21-acre Heavenly Creek SEZ Fuels Reduction Project, completed in late summer of 2007, represented the first use of low-ground-pressure CTL forwarder/harvester technology to treat overstocked fuels within lands classified in the Tahoe Basin as stream environment zone (SEZ). Project impacts were evaluated through a monitoring program designed to measure changes in soil quality (hydraulic conductivity, bulk density/soil porosity, and soil cover) that affect the capacity of the land to maintain healthy vegetation communities and resistance to erosion. Erosion and runoff model simulations, utilizing the measured changes in soil quality parameters, predict no real erosion or sediment delivery response as a result of project activities (<.03 ton/acre).
The post-project hydraulic conductivity (Ksat, a measure of the rate water flows through the soil) was 2.4 in/hr, well above the WEPP model predicted erosion response trigger level of 1.0 in/hr. Although Ksat was reduced by over 50%, the overall post-project conditions proved sufficiently favorable to prevent an erosive runoff response. This resiliency is due to a combination of low gradient slopes (<15%), high level of post- project soil cover (89%), robust vegetation cover, dry soil moistures (<11%), and the relatively high baseline Ksat values represented by the soils at the site (which are typical of Tahoe Basin SEZs).
Post-project Ksat measurements also detected no significant difference between areas where equipment operated over a slash mat, versus visible equipment tracks with out a slash mat. These results indicate that the high cost associated with creating and removing slash mats may be avoidable in SEZs with low soil moisture and other appropriate settings.
What is the Water Quality Benefit of the Boren Way Channel? 2008. El Dorado County, Department of Transportation. White Paper 08-01. On September 25, 2008, the El Dorado County Department of Transportation tested the transmission loss and infiltration treatment capacity using simulated runoff in an attempt to understand the benefit from an infiltration conveyance channel for fine particle treatment.
87 What is the Water Quality Benefit and TSS / PSD Removal Efficiency of the Sandfilter Located at the Apalachee Phase 1, Nottaway Basin? 2008. El Dorado County, Department of Transportation. White Paper 08-02. The sandfilter located at the end of Nottaway Street in the Apalachee Phase 1 project area is one of the few advanced filtration systems in the Tahoe basin for active stormwater treatment. The El Dorado County Engineering Division researched new specifications for the sand filter media for use in the sand filter by conducting in house tests to ensure proper drainage and treatment to maximize BMP efficiency and decrease the maintenance requirements of the system. By refining the media specifications, the Department intended to maximize pollutant load removal while decreasing the maintenance of the system that is currently required. After reconstruction of the sandfilter system it was then monitored for a single controlled event to measure the turbidity and fine sediment concentration of both the inflow and the outflow for pollutant load reduction analysis.
What is the Water Quality Benefit of the Boren Way Basin? 2008. El Dorado County, Department of Transportation. White Paper 08-04. On September 25, 2008, the El Dorado County Department of Transportation tested the transmission loss, storage volume and infiltration treatment capacity using simulated runoff in an attempt to understand the benefit from a treatment basin for fine particle treatment.
A Review of Particle Size Distribution in Sediment Sources from Water Quality and Erosion Control Project Areas in El Dorado County. 2008. El Dorado County, Department of Transportation. White Paper 08-05. A review of sediment sources within various Water Quality and Erosion Control Project Areas in El Dorado County is necessary in order to establish the source of suspended sediment in stormwater runoff which is potentially contributing to the decline in clarity of Lake Tahoe. This investigation attempts to establish whether there is a correlation between suspended sediment in runoff from Project areas in El Dorado County and the following potential sediment sources: a. Sediment available for washoff from the road surfaces, b. Sediment available for erosion along the EDOT paved roads, and c. Road cinders applied to roads during the winter by the EDOT Maintenance Department. The basis for this comparison will be Particle Size Distribution (PSD) with particular emphasis on sediment particles which are equal to or smaller than 20 microns in diameter.
Lake Village Stormwater Investigation Draft Final Report - A Study of Pre- and Post- CIP and BMP Implementation. 2009. Prepared by Nevada Tahoe Conservation District. Prepared for SNPLMA Round 6, Grant No. 06-DG-11051900-028. 93 p. Final study objectives were as follows: (1) summarize stormwater water quality and quantity from three catchments in and near the Lake Village HOA and (2) quantify the change in water quality from roof drip line runoff before and after installation of private BMPs. Catchment A runoff came from common areas with the Lake Village EIP project before a BMP capital improvement project (CIP). In Catchment B, stormwater improvements was dominated by flow from residential BMPs. Catchment C was
88 monitored as an untreated reference site. Ten pre-CIP events and 12 post-CIP events were sampled in Catchment A. The variability in the data made it difficult to identify trends in either event type or in the pre/post-CIP analysis. Overall, after the public BMPs were installed in Catchment A, concentrations of many constituents declined. The average particle size was relatively unchanged for pre- vs. post- events. The overall average particle size for TSS at Catchment A (plus Site B3 with similar site treatment), the sample sites dominated by road runoff in the HOA, was 61 µm. But the overall average particle size for the drip line sites was 130 µm. In addition, 25% of TSS from road runoff was smaller than 14 µm compared to 27 µm for the drip lines. These data support the Lake Tahoe TMDL findings that fine sediment primarily originates from road runoff. There were occasional spikes in ammonia concentrations (above 1 mg/l) at B1, B3, and Catchment C. Fertilizer does not appear to be the source of these spikes, but perhaps pet waste and/or first flush might be partial explanations. Compared to bio-available bioavailable nitrogen the runoff in this study was rich in bioavailable phosphorus. The traction control material used in Catchment C, was red cinders. Cinders are often considered a more significant source of phosphorus compared to other traction control material (e.g., sand). However, Catchment C phosphorus concentrations (i.e., SRP, DP, and TP) were consistent with the concentrations at the other sites. Thunderstorm events were generally brief with a relatively small volume, but they generally produced the highest concentration of particulate pollutants for each catchment. The drip line data clearly indicates armoring of drip line areas significantly reduces TSS concentration. However, the decrease in TSS concentration at the control sit) suggests this armoring could be in the form of pine needles. Results suggested that neither the length of the drip line, drip fall eight, drip line slope, nor armoring affect the size of particles transported during runoff events. The particle distribution is likely controlled by the soil type.
Forest Road Monitoring 2006-2008. 2009. US Department of Agriculture, Forest Service. South Lake Tahoe, CA: Lake Tahoe Basin Management Unit. 10 p. This report summarizes a three-year monitoring program (2006 thru 2008) which evaluated the effectiveness of the LTBMU’s Forest Road BMP Retrofit Program and up- dates the previous roads report covering the period between 2003 and 2005 (Breibart, 2007). This report evaluated the effectiveness of 4.21 miles of upgrades that occurred during this period. Relatively few upgrades have occurred in this period, compared to the 154 mile of upgrades evaluated in the 2007 report. The monitoring program goals include: evaluating BMP effectiveness at stream crossings utilizing Forest Service Region-5’s Best Management Practices Evaluation Program (BMPEP) protocols, assessing the change in risk of sediment transport as a result of BMP implementation using Water Quality Risk Assessment Protocols (WQRAP). Monitoring results indicate that BMP retrofits overall have been effective at reducing the risk of road-borne sediment migration to water bodies in the Lake Tahoe Basin. WQRAP scores are low with the exception of road 18E22.5, Slaughterhouse Canyon Road (a trail to road conversion), which received predominately moderate ratings due to the surface type and gradient. This road was upgraded because logging vehicles will use this road during proposed vegetation management activities. After vegetation management activities are completed the Forest plans to maintain this road as a level II road, closed to the public, but available for administrative use by the USFS.
89 It is recommended to increase the coverage of gravel surfacing of the road from currently covering the area of the stream crossings, to include the length of the road segments (with gradients >5%) connected to the stream crossing. This would increase the total length of gravel surfacing from 44 feet to 364 feet, and would result in reducing the rating from moderate to low risk for this road.
2007/2008 Annual Forest Monitoring Report. 2009. US Department of Agriculture, Forest Service. South Lake Tahoe, CA: Lake Tahoe Basin Management Unit. 47 p. This report contains a summary and analysis of monitoring activities implemented on the Lake Tahoe Basin Management Unit during the field season of 2007 into early 2008. The Lake Tahoe Basin Management Unit (LTBMU) Monitoring Program provides information to decision makers about the outcome of forest management activities on desired conditions for LTBMU resources. The goal of the Monitoring Program is to provide direction needed for the Forest Plan Revision, the Forest Environmental Management System (EMS), and NEPA Decision documents. The LTBMU Monitoring Program addresses four main categories of information needs: Implementation monitoring: Determines the degree and extent to which application of standards and guidelines met management direction and intent (what, when, where, and how management direction has been followed). Status-and-change monitoring of ecosystem conditions and management activities: Assesses important biophysical and socio-cultural conditions, to gauge if desired conditions are being achieved and to describe correlative relationship between management activities and conditions to identify potential causal factors for observed changes. Effectiveness monitoring: Provides a better understanding of how ecosystem components, structures, and processes respond to management activities, and how ecosystem components interrelate. Research: Designed to support land management by generating new information to address key information gaps related to the fundamental workings of ecosystem processes, interrelationships between processes, development and testing of different management approaches, and development and validation of habitat relationships, ecological indicators, and thresholds. This report is organized by key resource issue areas which include some of those identified in the Region 5 AMS, as well as resource issue areas unique to the Lake Tahoe Basin. The issue areas are (1) Lake Tahoe Clarity, (2) Aquatic, Riparian and Meadow Ecosystems, (3) Old Forest Ecosystems /General Forest Ecosystems (includes WUIs), (4) Fire and Fuels, (5) Noxious Weeds, (6) Recreation/Social Resources.
LTBMU 2008 BMPEP Monitoring Report. 2009. US Department of Agriculture, Forest Service. South Lake Tahoe, CA: Lake Tahoe Basin Management Unit. 14 p. In 2008, the Lake Tahoe Basin Management Unit (LTBMU) completed 39 Best Management Practices Evaluation Program (BMPEP) evaluations, as part of the Pacific Southwest Region’s effort to evaluate the implementation and effectiveness of BMPs designed to protect soil and water resources associated with Timber, Engineering, Recreation, Grazing, and Revegetation activities. Of the 43 Regional targets, only 39 evaluations were conducted due to a lack of qualifying projects for the E13- In-channel Construction Practices (5 targets / 3 qualifying projects) and F25-Prescribed Fire (2 targets / 0 qualifying projects). In 2008, 97% of the evaluations were rated as effective, which is above the average of 84%, for the previous two years. Only one BMP evaluation (3%), for the Ward Creek
90 Trail Bridge reconstruction project, was rated not effective due to the transportation of eroded sediments into Ward Creek. Although the current volume of sediment delivered to Ward Creek is estimated to be less than 1 cubic yard, there is the potential for more erosion during a wet year. It is recommended that slope stabilizing BMPs, such as matting and/or geotextile fabric, be installed in this area which will reduce likelihood of sediment transport and facilitate the establishment of natural revegetation. This site will be scheduled for follow up evaluation in the 2009 field season to determine if erosion has increased, and subsequently to evaluate the success of bank stabilization BMPs when implemented.
Deicer Report. 2009. Caltrans District 3. Office of Environmental Engineering, South 703 B Street, Marysville, CA. 26 p. The California Department of Transportation evaluates the effectiveness of Best Management Practices (BMPs) used to recover abrasive and deicing materials, and evaluates the impacts of abrasive and deicing materials on surface waters within the Lake Tahoe Hydrologic Unit (HU). This report describes the use of abrasive and deicing materials within the Lake Tahoe HU. Also contained in this report are the results of abrasive and deicing materials chemical and physical analyses, and annual results of the abrasive recovery program activities within the Lake Tahoe HU. To minimize impacts on Lake Tahoe and its tributaries, Caltrans has established a modified practice of applying traction sand at 600 lbs. per lane mile within the Tahoe basin. Areas that have heavy traffic, super elevations, or steep grades may receive up to 1,000 lbs. per lane mile as required to maintain a safe roadway. The practice has resulted in a decrease in the amount of sand applied over the past 16 snow seasons. Once sand is applied to highways, Caltrans incorporates BMPs to recapture this traction sand. These BMPs include (1) immediate sweeping of the traveled way and shoulders and (2) annual cleaning of sand traps and catch basins including vactor operations at drainage facilities. Based on their field data, it was reported that a total of 3,423 ton of sand was applied during the 2008/2009 snow season. During this season, 4,788 tons of sand and sediment were recovered.
Evaluating an Approach for Cost-Benefit Analysis of Project Alternatives. 2009. A. Heyvaert, T. Mihevc, J. Thomas, W. Miller, J. Reuter. Report produced by the Desert Research Institute, Reno, NV. 45 p. A variety of alternative restoration and stormwater management options are typically available to project designers. Each combination of alternative project features can yield different pollutant reduction efficiencies at different implementation costs. To date it has been difficult to develop an understanding of the relationship between alternative design options and their anticipated pollutant load reductions, along with an evaluation of cost estimates for these options. The purpose of this study was to examine the utility of a matrix evaluation approach initially developed by the Nevada Department of Transportation (NDOT) for investigating cost-benefit relationships available from alternative BMP implementations on a highway environmental improvement project. This matrix approach was then examined in relation to the Pollutant Load Reduction Model (PLRM). Toward that objective the EPA Storm Water Management Model, which is the underlying water quality model for the PLRM, was applied on a demonstration basis to a rainfall-runoff event in the north Tahoe state line drainage and resulting output was linked to an alternatives evaluation matrix, based on the NDOT prototype.
91 Results from that demonstration example showed that developing and linking an alternatives cost-benefit analysis module to the PLRM is feasible and would provide useful benefits for developing environmental improvement projects in the Tahoe Basin, along with better load reduction estimates compared to the spreadsheet approach initially developed for the highway projects.
2008 Best Management Practices Evaluation Program Report. 2009. N. Brill, J. Harris, S. Norman. US Forest Service, Lake Tahoe Basin Management Unit. 12 p. In 2008, the LTBMU completed 39 Best Management Practices Evaluation Program (BMPEP) evaluations, as part of the Pacific Southwest Region’s effort to evaluate the implementation and effectiveness of BMPs designed to protect soil and water resources. In 2008, 97 percent of the evaluations were rated as effective, which was above the average of 84 percent, for the previous two years. Only one BMP evaluation (3 percent), for the Ward Creek Trail Bridge reconstruction project, was rated not effective due to the transportation of eroded sediments into Ward Creek. Although the current volume of sediment delivered to Ward Creek is estimated to be less than 1 cubic yard, there is the potential for more erosion during a wet year. It was recommended that slope stabilizing BMPs, such as matting and/or geotextile fabric, be installed in this area which will reduce likelihood of sediment transport and facilitate the establishment of natural revegetation.
Is Sweeping an Effective Water Quality BMP During a Snow-Melt Condition in the Lake Tahoe Basin? 2009. El Dorado County, Department of Transportation. White Paper 09-01. In order to evaluate sweeping as a water quality Best Management Practice (BMP) during the snowmelt condition, turbidity of snowmelt was measured at various roads within El Dorado County during a warming trend in January 2009. The water quality samples were collected along Pioneer Trail, North Upper Truckee (NUT), Montgomery Estates, Tahoe Hills and Woodland Subdivisions. This study attempts to add to the understanding of the water quality benefit of changing the sediment characteristics of road and impervious shoulder surface by sweeping during the snowmelt condition.
Is Sweeping an Effective Water Quality BMP During a Winter Rainstorm Condition in the Lake Tahoe Basin? 2009. El Dorado County, Department of Transportation. White Paper 09-02. In order to evaluate sweeping as a water quality Best Management Practice (BMP) during the winter rainstorm condition, turbidity of runoff was measured at various roads within El Dorado County during a rainstorm in January 2009. The water quality samples were collected along Pioneer Trail, North Upper Truckee (NUT), Montgomery Estates, Tahoe Hills and Woodland Subdivisions. This study attempts to add to the understanding of the water quality benefit of changing the sediment characteristics of road and impervious shoulder surface by sweeping during the winter rainstorm condition.
Turbidity as a Surrogate for Total Suspended Sediment (TSS) in Urban Stormwater. 2009. El Dorado County, Department of Transportation. White Paper 09-03. The El Dorado County Department of Transportation has collected and analyzed stormwater samples from various Project areas for many years. In the past several years there has been an increasing emphasis regarding the concentration of fine sediment in urban stormwater. The laboratory techniques to measure the concentration of fine
92 sediment are expensive and time consuming and for this reason a field estimation technique is proposed using field turbidity.
How Does Street Sweeping Change the Turbidity and Sediment Concentration of Urban Stormwater in the Lake Tahoe Basin? 2009. El Dorado County, Department of Transportation. White Paper 09-04. The El Dorado County Department of Transportation (EDOT) regularly sweeps the County roads within the Lake Tahoe basin for a variety of reasons. One assumed benefit of the street sweeping program is the improvement in urban storm water quality exiting the EDOT right-of-way. The Center for Watershed Protection conducted a literature review in order to evaluate the benefits of sweeping and found that street sweeping does not guarantee water quality improvements (CPW, 2006). In order to establish the water quality benefits of the EDOT street sweeping program, a series of water quality sampling experiments were conducted during the fall of 2008 for storm water generated under real meteorological conditions. The premise for the experiments include sweeping portions of the Montgomery Estates subdivision within El Dorado County and comparing the characteristics of storm water within the swept regions and unswept regions. The hypothesis of these experiments was that the turbidity and the concentration of fine sediment would be higher in the control samples from unswept regions compared with the samples collected in the swept regions. A variety of measurement techniques were proposed to measure the benefit of sweeping. For these experiments it was assumed that sweeping did not change the volume of runoff, therefore the benefit of sweeping could be established simply by comparing the water quality of samples from swept and unswept regions.
South Lake Tahoe Average Annual Rainfall Intensities and Recurrence Intervals Based on Measured Meteorological Condition. 2009. El Dorado County, Department of Transportation. White Paper 09-05. The effectiveness of planning and design activities for water quality improvement projects within urban watersheds in the Lake Tahoe basin is dependent on the accuracy of estimating hydrological conditions for the erosion and water quality conditions. The hydrological cycle in this urban watershed is primarily driven by meteorological conditions and for this reason El Dorado County has maintained and operated several meteorological stations throughout the South Lake Tahoe region since 1997. In January 2008 a tabulation of this meteorological record was prepared in order to establish the measured rainfall intensities and recurrence intervals at two locations within the South Lake Tahoe region for average annual conditions. The results were then compared to the El Dorado County and NOAA precipitation design criteria. The continuous simulation of the hydrological cycle using measured meteorological data most accurately simulates the runoff and can be accomplished using the tabulation from these stations. Even without continuous simulation of runoff, these measurements will allow for a comparison between rainfall design criteria and the average annual rainfall at these two stations for the infrequent erosion condition and more common water quality condition.
What is the Water Quality Benefit of the Black Bart Ave./Martin Ave. Basin During a Winter Rainstorm? 2009. El Dorado County, Department of Transportation. White Paper 09-06.
93 The Black Bart Ave./Martin Ave. basin was constructed in order to mitigate the urban water quality impacts to Trout Creek from stormwater runoff from Black Bart Ave. On January 22nd and February 23, 2009, the El Dorado County Department of Transportation observed conditions at the basin and measured the rainfall intensity and turbidity of stormwater entering and exiting the basin.
Different Regional Road Management Approaches and Their Range in Stormwater Turbidity During a Winter Rainstorm. 2009. El Dorado County, Department of Transportation. White Paper 09-07. In order to evaluate the impact of different regional road management approaches on the water quality of stormwater during a winter rainstorm, turbidity of runoff was measured at a variety of El Dorado County and Washoe County roads. An understanding of the water quality benefits of these two different approaches is critical in achieving the water quality effluent limits that include turbidity of less than 20 NTUs (SWQIC, 2004). The Washoe County road network was selected to represent a road management approach to water quality with a relatively high emphasis on road sweeping and the El Dorado County road network was selected to represent a lower emphasis on road sweeping. It is assumed that road sweeping does not change the volume of runoff from a road system. Therefore the measure of the water quality effectiveness of these different road management approaches is in the comparison of the concentration of fine sediment in runoff. For this study, the measurement of field turbidity of the stormwater was used as a surrogate for the concentration of fine sediment. On January 22nd and 23rd 2009, a rainstorm occurred in the Lake Tahoe basin allowing for the comparison of the water quality for these two approaches to road management.
Development and Analysis of a Pre / Post Project Hydrologic Model in the Evaluation and Efficacy of an Urban Erosion Control Project. 2009. El Dorado County, Department of Transportation. White Paper 09-08. In order to estimate the effectiveness of the Apalachee Phase 1A project during rainfall for reducing the fine sediment transport to Lake Tahoe for the average annual hydrological condition, a hydrologic model was used to simulate runoff from the Project area. The model was developed for watershed E based on pre-project and post-project flow and meteorological measurements as well as the characteristics of the pre-project and post-project conditions.
The Influence of Rainfall Intensity and Duration on Lake Tahoe Fine Sediment Concentration in Urban Stormwater. 2009. El Dorado County, Department of Transportation. White Paper 09-09. The concentration of fine sediment in urban stormwater is often estimated based on event mean concentration (emc) and is generally estimated from the physical characteristics of the watershed. In urban stormwater there is a strong correlation between fine sediment emc and the maximum rainfall intensity (Gnecco et al, 2004). In addition, Sansalone et al. (1998) found a higher concentration of sediment in the first flush of urban stormwater and that the 2 to 8 micron particles were rapidly washed from the pavement. In order to improve the estimates of the concentration of fine sediment in Lake Tahoe urban runoff for typical rain fall conditions, El Dorado County compared the concentrations of fine sediment and rainfall intensity records for existing stormwater samples.
94 Lake Tahoe Clarity and Hydrologic Connectivity of Urban Stormwater Outfall. 2009. El Dorado County, Department of Transportation. White Paper 09-10. Soil moisture is an important control for the hydrologic connectivity for a semi-arid snowmelt-driven catchment (McNamara et al, 2005) and in order for fine sediment suspended in urban stormwater to be a detriment to the clarity of Lake Tahoe there must be hydrologic connectivity between the stormwater outfall and Lake Tahoe. Hydrologic connectivity can include outfall discharge directly to Lake Tahoe, discharge to a perennial tributary to Lake Tahoe, discharge to an ephemeral tributary to Lake Tahoe, discharge to an intervening area, or stormwater infiltration into the soil thereby recharging groundwater. For this analysis infiltration of stormwater into the soil is assumed to eliminate the transport of fine sediment to Lake Tahoe since pollutant concentrations generally decrease rapidly beneath stormwater infiltration basins (Deshesne et al, 2005). This study is focused on measuring the maximum connectivity of urban stormwater for regions within El Dorado County with the greatest connectivity between the County right of way (ROW) and stormwater discharge outfall pipes. This study documents the relationship between the area of impervious surface within the County ROW, the rainfall intensity and the separation distance from the stormwater outfall to surface water for relatively high average annual rainfall intensity conditions. The direct hydrologic connectivity of urban stormwater outfalls to Lake Tahoe is a certain lake clarity problem as are stormwater discharges to perennial streams since suspended fine sediment is likely to remain in suspension in streams long enough to reach Lake Tahoe. Stormwater outfalls directly connected to ephemeral streams have a reduced impact on lake clarity since ephemeral streams are only connected to Lake Tahoe seasonally. However, the fraction of stormwater volume from outfalls that discharge to intervening areas or subwatersheds are only a detriment to lake clarity if the stormwater eventually reaches Lake Tahoe. Therefore, in order for water quality improvement projects to benefit the quality of water within Lake Tahoe, the pollutant load estimates must address stormwater connectivity.
Alternative Road Traction Techniques as a Source Control Base Management Practice, 2009, El Dorado County, Department of Transportation. White Paper 09-13. In the Lake Tahoe basin, road traction sand improves vehicular traction in snow and ice- covered roads at all temperatures and is especially valuable if it is too cold for chemical de-icers to work (Road Management Journal, 1997). However road abrasives such as sand can end up in the environment in runoff to streams and rivers (EPA, 2002) and during the winter, one way that road maintenance activities can threaten water quality in the Lake Tahoe basin is the application of great quantities of traction sand (Lahontan, 1995). The most dominant pollutant of concern for Lake Tahoe clarity is sediment particles less than 16-microns (Swift, 2005) and Roberts (2007) estimated that 72% of the less than 20-micron sediment load to Lake Tahoe originates from the urban upland source category. According to the California Stormwater Quality Association Stormwater BMP Handbook (2003), the selection of best management practices (BMPs) should focus first on source control including activities intended to reduce the pollutants to the maximum extent practicable. This paper explores preventative measures, or source control considerations relative to fine sediment originating from road traction abrasives as a cost effective means of controlling fine sediment pollution at its source.
Impacts to Trout Creek Turbidity During a Late Winter Rainstorm. 2009. El Dorado County, Department of Transportation. White Paper 09-16.
95 On March 1st and 2nd the largest rainstorm since 2002 (EDOT 09-17) generated urban runoff which entered Trout Creek within portions of El Dorado County. Turbidity of surface water was measured along Trout Creek and at several El Dorado County stormwater outfalls between Columbine Trail and the Martin Avenue Bridge. In addition, observations of hydrologic connectivity were recorded to assess impacts of various stormwater outfalls on Trout Creek water quality.
2009 Best Management Practices Evaluation Program Report. 2010. N. Brill, J. Harris, S. Norman. USDA Forest Service, Lake Tahoe Basin Management Unit, Ecosystem Conservation Department. In an effort to evaluate the effectiveness of BMP’s designed to protect soil and water resources, the Lake Tahoe Basin Management Unit (LTBMU) completed 30 Best Management Practices Evaluation Program evaluations. The evaluations were conducted on randomly selected sites after a significant rain on snow event in May of 2010, which created conditions well suited to determining BMP effectiveness. 73% of the evaluations were deemed effective, and 27% were deemed not implemented and not effective. In 2009 90% of the randomly selected sites were deemed effective and 7% were deemed not implemented but still effective, and 3% were implemented but not effective.
2009 Temporary Best Management Practices Evaluation, Program Report. 2010. N. Brill, J. Harris. USDA Forest Service, Lake Tahoe Basin Management Unit, Ecosystem Conservation Department. The purpose of the Lake Tahoe Basin Management Unit’s (LTBMU) Temporary Best Management Practices (TBMP) is to monitor TBMPs applied to forest construction and restoration projects that may have short term adverse impacts to soil and water quality during implementation. TBMPs are required for all construction projects and designed to remain in place only until project completion when permanent BMPs may be applied. Six projects were evaluated in 2009. Minor deficiencies were documented at four sites, but were quickly resolved. Major deficiencies allowing sediment to be transported to an SEZ during a large storm event were reported at two sites. The difference between major and minor deficiencies refers only to whether sediment actually reaches an SEZ or not, and does not imply anything about the quantity of sediment reaching the SEZ.
2009 Trails BMP Retrofit Monitoring Report. 2010. N. Brill, J. Harris, S. Norman. USDA Forest Service, Lake Tahoe Basin Management Unit, Ecosystem Conservation Department. Pre-project monitoring of the 61 miles of bike trails in the North Shore transportationshed indicated a relatively low risk to water quality overall. A 1.7 mile stretch of trails originally deemed a moderate risk to water quality received post-project monitoring that indicated a drop to low risk. WEPP modeling indicates that even in the worst case scenarios, the potential for sediment impacts to water quality were quite low, and post-project evaluations indicate that impacts will be reduced further with planned trail upgrades. Decreasing trail slope is estimated to reduce sediment yields by 90%. The evaluations will continue in order to inform LTBMU staff of trail maintenance needs.
96 Tahoe Regional Stormwater Monitoring Program - Quality Assurance Project Plan (Phase 2). 2010. A. Heyvaert, J. Reuter, J. Thomas. Prepared for the USFS – Lake Tahoe Basin Management Unit. 98 p. This report represents one of the Phase 2 documents for the Tahoe Regional Stormwater Program (RSWMP). Since the specific TMDL requirements for monitoring were not yet developed, this work was not able to provide the final locations for monitoring sites. The primary questions that need to be addressed by an RSWMP include: (1) are the stormwater Characteristic Runoff Concentrations (CRC) developed for identified land use types in the Tahoe basin suitable for use in deriving model estimates of pollutant loading, (2) are the stormwater Characteristic Effluent Concentrations (CEC) developed for different treatment and source control practices appropriate for the PLRM estimates of loading reductions, (3) are drainage area load reduction estimates from PLRM (or other model) projections verified by field data collected from the projects under consideration and, (4) are pollutant loads from urban stormwater runoff in the Tahoe basin decreasing in response to EIP and TMDL implementation, and what are the long- term trends, vis-à-vis, TMDL load reduction targets. Topics addressed in this quality assurance project plan (QAPP) included but were not limited to: program design and organization; data quality objectives; monitoring and sampling design/methods; programmatic documentation and records; sample handling and custody procedures; analytical methods; quality control requirements, equipment inspection, calibration and maintenance requirements; inspection and acceptance of supplies and consumables; non-direct measurements; documentation and data management; assessment and response actions; programmatic reporting; review data, verification and validation; and Programmatic Verification and Validation Methods In-basin stormwater data from north shore and south shore locations were used to statistically determine the number of samples needed per year to provide a range of “allowable errors” for the annual mean concentration data. As expected (1) the lower the ‘allowable error’ value, the more samples are required; (2) concentrations of the dissolved nutrients ([NO3+NO2]-N) and SRP) are more variable and thus require a greater sampling frequency than the constituents associated with particulate matter; (3) the relationship between sample frequency and rain runoff/snowmelt versus summer thunderstorms was not always consistent across constituents; and (5) the results from north shore and south shore sites were typically similar, with exception of [NO3+NO2]-N during the rain runoff/snowmelt events and TN during the thunderstorm season. For an “allowable error” associated with the mean of 10 percent, a sampling frequency in the range of 10-15 samples per year during the rain runoff/snowmelt season for total or particulate-bound constituents may be sufficient. However, the sampling frequency for dissolved nutrients must be higher to achieve an equivalent “allowable error” of 10 percent. Given that most of the annual loading is associated with the largest storms, any sampling design must include these storms, i.e. a monitoring frequency of 10-15 storm events will not be adequate if the associated runoff is low.
Sampling and Analysis Plan - Tahoe Regional Stormwater Monitoring Program (Phase 2). 2010. A. Heyvaert, J. Reuter, J. Thomas. Final draft report submitted to the USFS – Lake Tahoe Basin Management Unit. 40 p. This is a companion document to the QAPP and DQO that provides a more detailed presentation of the sampling and analysis expected from the RSWMP program.
97 NEAT Report (Natural Environment As Treatment). 2010. Wood Rogers. California Department of Transportation District 3 (Contract: 03A1295). 74 p. The Natural Environment As Treatment (NEAT) Report is intended to serve as the basis for Lahontan Regional Water Quality Control Board and Caltrans - District 3 to develop a consensus approach for the prioritization and selection of water quality improvements within the Tahoe basin. It is intended that recommended water quality improvements in the NEAT Report will facilitate compliance with Caltrans Statewide National Pollutant Discharge Elimination System (NPDES) Permit. The NEAT Report includes a summary of Caltrans’ project specific design recommendations for existing water quality improvement projects located within the Basin and step-by-step processes for use during project scoping, approval and design. Water quality treatment recommendations provided herein are consistent with the current Project Planning and Design Guide (PPDG) and the Permit, as well as the Regional Board’s region-specific requirements. Thirty-eight miles of Caltrans’ highway within the Tahoe basin in El Dorado and Placer Counties were evaluated, using the methodologies and criterion developed by project partners (Caltrans and Lahontan). The NEAT evaluation categorized segments of the State’s highways within the project area into three distinct categories: (1) NEAT (Natural Environment as Treatment) - a segment of roadway where pollutants that would be transported by storm water runoff are adequately addressed by the natural environment, (2) MEAT (Modified Environment as Treatment) - a segment of roadway where minor modifications, similar to low impact type improvements, could be implemented in order to treat highway runoff and (3) TREAT (Treated Environment as Treatment) - a segment of highway where factors such as proximity to a receiving water, lack of vegetation, visible erosion, and/or significant amounts of impervious surface would indicate that storm water runoff should be collected and treated prior to discharge. It was determined by the partners that a qualitative approach (visual signs of erosion, lack of vegetation, amount of vegetation present, downstream topography, et al.) was preferred over a quantitative approach. Upon completion of the field analysis, data was processed to develop visual summaries (NEAT maps) of project results and recommendations. The NEAT maps are contained in this report.
Cultured Ecology Generation 2: Demonstrating Nutrient and Fine Particle Removal in Tahoe Basin Stormwater. 2010. A. Heyvaert, S. Patterson, S. Brown, J. Reuter, C. Strasenburgh. Prepared for Nevada Division of State Lands and Nevada Division of Environmental Protection. 68 p. A demonstration project utilizing cultured periphyton to treat stormwater runoff was constructed, operated, and monitored for approximately nine months (mid-February to early November) in 2008. The goal of this project was to demonstrate the applicability and effectiveness of periphyton-based cultured ecologies as a biologically-based advanced treatment system to reduce fine sediment particles and nutrient loads entering Lake Tahoe. A three-tank system was constructed and seeded with locally occurring periphyton species. Once established, periphyton growth was harvested approximately every two to four weeks. Samples for water chemistry analysis were collected approximately every two weeks. Treatment of stormwater from two larger runoff events was also evaluated. Two experiments were conducted to simulate stormwater runoff events, and a nitrogen fertilization experiment examined the enhancement of soluble phosphorus removal with
98 biological uptake. Combined results from the two natural runoff events and from the two simulated runoff experiments allowed calculation of realistic load reductions for SRP (39% ±23%), total phosphorus (34% ±12%), nitrate (41% ± 30%), total Kjeldahl nitrogen (30% ±23%), suspended sediment (29% ±29%) and fine sediment particles (16% ±13%). The site selection process demonstrated potential for application of this cultured periphyton technology to a wide range of places and situations in the Tahoe basin. As a polishing system for a detention basin or a wetland, the cultured periphyton system can remove dissolved nutrients and fine sediments to levels not achieved by basins or wetlands alone. Initial estimates indicate that runoff from a small neighborhood catchment with a design storm volume of 5,000 cubic feet could be treated over a period of three days with a setup around 3.5 times the size of this demonstration system.
Tahoe Stormwater and BMP Performance Database Monitoring and Reporting Guidance Document. 2010. A. Heyvaert, M. Leisenring, N. Beck, B. Wolfe. Prepared for the USDA Forest Service Pacific Southwest Research Station. 53 p. The Lake Tahoe TMDL has identified urban stormwater runoff as one of the main sources for pollutant loading of clarity‐degrading nutrients and fine sediment particles into Lake Tahoe (LRWQCB and NDEP 2010). Therefore, implementation of best management practices (BMPs) to reduce pollutant sources and treat urban stormwater is seen as one of the best options for mitigating the effects of landscape development and restoring lake clarity. The Lake Clarity Crediting Program (Crediting Program) defines a comprehensive and consistent accounting system for tracking pollutant load reductions with restoration and BMP implementation (LRWQCB and NDEP 2009). In concert with application of the Pollutant Load Reduction Model (PLRM) (nhc et al. 2009), the Crediting Program will allow project implementers and regulatory agencies to estimate the pollutant load reductions of various urban pollutant source control and treatment strategies on an urban catchment scale. Ultimately, however, these estimates must continue to be validated and improved by measurements of pollutant reductions linked to specific practices. The purpose of the Tahoe Stormwater and BMP Database (Database) is to guide the collection of consistent and reliable information on stormwater runoff characteristics and Treatment BMP performance around the Tahoe Basin. This Database has been developed in support of the Tahoe Regional Stormwater Monitoring Program (RSWMP) to provide a centralized, internet‐accessible, reliable source of stormwater data collected by different groups associated with the TMDL and RSWMP efforts. In its current form the Database accepts information from monitoring at stormwater runoff sites and on a subset of Treatment BMP types identified by the PLRM and the Best Management Practice Maintenance Rapid Assessment Methodology.
Best Management Practices Evaluation Program Annual Report. 2010. US Department of Agriculture, Forest Service. South Lake Tahoe, CA: Lake Tahoe Basin Management Unit. 30 p. In 2010, the Lake Tahoe Basin Management Unit (LTBMU) completed 39 Best Management Practices Evaluation Program (BMPEP) evaluations as part of the Pacific Southwest Region’s effort to evaluate the implementation and effectiveness of BMPs designed to protect soil and water resources associated with Timber, Engineering, Recreation, Revegetation and Prescribed Fire activities. All 39 Regional target evaluations were conducted in 2010; of these, 37 (95%) of the evaluations rated the BMPs effective and two (5%) evaluations rated the BMPs not effective.
99 Monitoring in 2010 also included two follow-up evaluations at sites which had reported BMP deficiencies in 2009; Regency Road 16N93 and Bliss Creek Road. The Regency Road deficiency of road use during wet periods was corrected by installation of a gate in 2010, and the fence repair needed to prevent unauthorized use of the Bliss Creek Road is planned for 2011. Improvements have been made to the BMPEP evaluation and reporting process, as a result of an interagency training exercise hosted by the LTBMU. These include efforts to decrease inter-evaluator variability, and develop, obtain, organize and review the relevant implementation documents more effectively.
Development and Understanding of Current Abrasive Practices, Their Water Quality Impacts and Alternatives for Improved Source Control / Recover. 2010. El Dorado County, Department of Transportation. White Paper 10-01. Sweeping is known throughout the nation to be effective at removing mass of material; however it is not well understood as far as impacts to water quality or improvements. The cost implications of these practices are not well understood and may not meet objectives; therefore source control is needed to curtail the increased mass of material being applied to the road surface each year. This paper will identify potential benefits that can be attained by simple source control measures such as abrasive screening, washing and cleaning to prevent the bulk of mass fine material being applied to the road surface each year. Alternative native abrasive media will also be discussed with results of preliminary investigations into the feasibility and practicality of utilizing native materials for traction. These methods of source control may yet be another option to improve maintenance practices for public safety used by all jurisdictions lake wide, while keeping current sweeping practices at maintainable levels of operations and within available budgets.
Small Scale Evaluation and Testing of the Tenant Sentinel Heavy Duty Outdoor Sweeper and its Effects on Urban Road Water Quality and Surface Characteristic. 2010. El Dorado County, Department of Transportation. White Paper 10-03. In order to evaluate sweeping as an urban water quality Best Management Practice (BMP) tool, washoff simulation was conducted along with corresponding Rapid Assessment Methodology (RAM) estimates before and after sweeping. The goal of this test was to measure turbidity of runoff at high, moderate and low accumulation areas of a road segment before and after sweeping to determine water quality benefits in a simulated condition. The water quality samples were collected on a section of 14th Green Drive in Incline Village, CA (Figure 1). This study attempts to add to the understanding of the water quality benefit of changing the sediment characteristics of road and impervious shoulder surfaces via sweeping.
Small Scale Evaluation and Testing of the Schwarze A8000 Regenerative Air Sweeper and its Effects on Urban Road Water Quality and Surface Characteristic. 2010. El Dorado County, Department of Transportation. White Paper 10-04. In order to evaluate sweeping as an urban water quality Best Management Practice (BMP) tool, washoff simulation was conducted along with corresponding Rapid Assessment Methodology (RAM) estimates before and after sweeping. The goal of this test was to measure turbidity of runoff at high, moderate and low accumulation areas of a road segment before and after sweeping to determine water quality benefits in a simulated condition. The water quality samples were collected in the Montgomery
100 Estates subdivision on Sierra House Trail and Bonanza st., El Dorado County, CA (Figure 1). This study attempts to add to the understanding of the water quality benefit of changing the sediment characteristics of road and impervious shoulder surfaces via sweeping.
Small Scale Evaluation and Testing of the Tymco DST-6 Regenerative Air Sweeper and its Effects on Urban Road Water Quality and Surface Characteristic. 2010. El Dorado County, Department of Transportation. White Paper 10-05. In order to evaluate sweeping as an urban water quality Best Management Practice (BMP) tool, washoff simulation was conducted along with corresponding Rapid Assessment Methodology (RAM) estimates before and after sweeping. The goal of this test was to measure turbidity of runoff at high, moderate and low accumulation areas of a road segment before and after sweeping to determine water quality benefits in a simulated condition. The water quality samples were collected in the Glorene and 8th subdivision on Clement st., El Dorado County, CA (Figure 1). This study attempts to add to the understanding of the water quality benefit of changing the sediment characteristics of road and impervious shoulder surfaces via sweeping.
Assessment of Particle Size Analysis in the Lake Tahoe Basin. 2011. A. Heyvaert, D. Nover, T. Caldwell, W. Trowbridge, G. Schladow, J. Reuter. Prepared for the USDA Forest Service Pacific Southwest Research Station. 164 p. Water clarity in Lake Tahoe has been declining for several decades. Much of this clarity loss has been caused by increased input and accumulation of fine particulates (<16 μm in diameter) in the lake. Therefore, accurate methods for analysis of fine particle concentrations and particle size distributions in water samples from the lake, from streams, and from urban runoff are of major importance. A variety of methods are currently in use at Tahoe for conducting laboratory analyses of suspended fine sediment particles (FSP), but there is not an existing set of protocols to assure consistency of results and data reporting. The main goal of this project was to assemble and analyze available data on particle size characterization reported for samples taken from Lake Tahoe, from Tahoe Basin streams, and from Tahoe area urban runoff. Additional objectives included 1) conducting a set of comparative tests on the methods currently in use for PSD analysis; 2) preliminary investigation on the use of surrogate measurements to complement or replace the explicit measurement of PSD; and 3) developing guidance for standardized analysis and reporting of new data by various groups. Available particle size data from lake, stream, and urban runoff samples that had been collected from 1999 to 2010 were assembled and analyzed. Lake concentrations tended to be highest in the upper water column above the Secchi depth and declined below the deep chlorophyll maximum. Annual average stream concentrations showed variable relative differences between sites and years, although relative ranks based on annual average flux were more consistent. FSP concentrations in stormwater samples were generally several orders of magnitude greater than the fine particle concentrations in lake and steam samples. Changes in PSD associated with holding times for stormwater samples were evident within a single day, tending toward increasing particle size, a process that continued with increased holding times. Sonication was generally effective at restoring characteristics of the PSD. A robust linear relationship was demonstrated between turbidity and FSP concentration in stormwater samples collected over an eight-year period from various urban locations
101 around the Tahoe Basin. A standard operating procedure for laser particle size analysis of Tahoe stormwater samples was developed, as well as specific operating parameters for both the LS-13320 and the DigiSizer instruments, and recommended reporting criteria.
NDOT Lake Tahoe Basin Stormwater Monitoring Program: Monitoring Seasons 2005- 06, 2006-07, 2007-08, 2008-09, 2009-10. 2011. Nevada Department of Transportation. Prepared by CDM/Will Rogers, Reno. NV. This report presents results of the Lake Tahoe Basin Stormwater Monitoring Program conducted by the Nevada Department of Transportation in the Tahoe basin, Nevada. Includes monitoring that was conducted from December 2005 through April 2010. The goals of this program were (1) characterize stormwater and the treatment effectiveness of various BMPs used by NDOT at Lake Tahoe and (2) collect data in support of the Lake Tahoe TMDL. Ten monitoring stations were installed in the fall of 2005, and monitored during the 2005-2006 winter season (October-April), the summer of 2006 (May-September), the 2006-2007 winter season (October-April) and the 2007-2008 winter season (December- April). A total of seven sites with ten monitoring stations were installed in the fall of 2005. These sites were monitored from the fall of 2005 through the 2008-09 winter season. For the 2009 – 2010 season the program was modified as follows: a. Particle size distribution analyses were added to characterize the distribution of fine sediment particles (FSP). FSP data was not previously collected. b. Monitoring of one site (NDOT 8) with two stations was discontinued because four years of data showed minimal treatment and the site was not optimal for collecting representative samples. c. Monitoring at one characterization site (NDOT 9) with one station was discontinued to allow for a new site to be added. Four years of urban, improved characterization data was collected. d. Monitoring at a new site (NDOT 11) with one station was added to perform pre-construction characterization at a cut slope section of roadway. e. Selected water quality constituents were removed from the analytical suite. In addition to flow, analytes included conductivity, pH, TP, ortho-P, TKN, nitrate, TSS, turbidity total iron and dissolved zinc. Concentrations and loads are reported. For the 2009-10 season the analytes were modified as follows: a. Fine sediment particle distribution analysis was added. b. Statistical analysis of the four years worth of data indicated continued monitoring for nutrients and metals would not yield statistically significant conclusions and these analytes were dropped. The reduced list included electrical conductivity (EC), pH, TSS, turbidity, and fine sediment particles. Data was used to create summary statistics, influent to effluent comparisons by analyte and by BMP, load reduction and BMP effectiveness, discharge limit comparison, runoff characterization from improved and unimproved highways, comparison with Caltrans and other available data, elevation impacts, impacts of traffic, particle size analysis of sediment, and sediment accumulation in BMPs.
102 Application to Management
Considerable financial and human resources have gone into urban stormwater control since the early 2000s. The intent of these efforts is to reduce fine sediment and nutrient loading to Lake Tahoe. Research and monitoring on this topic have played a fundamental part in the development of the Lake Tahoe TMDL, and continue to do so. To estimate whole-lake load reductions and develop water quality improvement strategies, scientists and engineers have had to develop water quality models and implement better monitoring programs. While the models have been very useful so far, there are identified levels of uncertainty that can be improved through continued and focused research and monitoring. Agencies, implementers and researchers must continue to work hand-in-hand in refining the key management questions, developing effective approaches to answer these questions, update existing models based on new knowledge, and tracking load reductions through integrated monitoring approaches.
103 Extra-Topical Issues
Overview
The only criteria used to place this scientific literature in a section was that it did not expressly fit under the other identified categories. This literature is equally important to the body of knowledge for water at Lake Tahoe; however, they did not appear to neatly fit under the identified categories. Those categories were selected with regard to management issues. Degraded nearshore water quality. Source: TERC. Credit: Peer Reviewed Journal Publications
Water Potential Changes in Fecal Matter & E. coli Survival. 2008. L. Garfield, M. Walker. Journal of Applied Microbiology, 105: 1009-1016. Examined the effects of temperature and osmotic stress on survival of commonly used indicator organisms in a fecal matrix at temperatures and evaporation rates typical of Lake Tahoe Found that 60 hrs of exposure to 2.0 mm/day evaporation rates and 15 hrs at 7.4 mm/day was sufficient to reduce E. coli populations to below the detection limit Significance: this suggests that potential for pollution from areas where pet feces accumulate near the lake pose a risk to water quality that is dependent upon environmental conditions, including important seasonal variables such as temperature.
Microbial Water Quality and Influences of Fecal Accumulation from a Dog Exercise Area. 2008. L. Garfield, M. Walker. Journal of Environmental Health. 71(4): 24-29. Examined spatial and temporal patterns in accumulation of feces in a popular pet exercise area near South Lake Tahoe and microbial water quality in a small stream. Estimated the total amount of fecal accumulation over the course of 15 months, using extrapolation techniques based on point measurements. Found that approximately 100 lbs (dry mass) of dog feces accumulated during the 15 month period. No significant relationship between accumulation of dog feces and bacterial water quality Results can be used to plan and carry out management approaches to prevent accumulation of fecal material in popular pet exercise areas.
A Report from Lake Tahoe: Observations from an Ideal Platform for Adaptive Management. 2009. D. Murphy, P. Manley. American Water Resources Association. Water Resources Impact. 11(3): 15-17. Though Lake Tahoe is still one of the world’s clearest lakes, it has lost half of its clarity since its discovery a century and a half ago due to various human induced impacts. However, the Lake Tahoe basin appears to be an ideal candidate for the implementation of adaptive management for many reasons. Its watershed area is clearly defined and relatively small, the ecosystems are well studied, many management goals that would
104 reduce further environmental degradation have been identified, and there is governmental commitment to financial support for projects that would improve environmental quality. The management and restoration goals have been unambiguous for more than 50 years, and an interagency collaboration produced the Environmental Improvement Program nearly 20 years ago toward those goals. In addition, A Lake Tahoe Watershed Assessment Report was prompted by the presidential visit in 1997, compiling available information in one document and used to develop a comprehensive conservation plan for the basin and calling for adaptive management. The Lake Tahoe basin has all the ingredients necessary for the success of adaptive management; availability of information, management actions achievable at a reasonable cost, and jurisdictional parties unified in meeting challenges of improving the environment, to name a few. The only thing that could hinder Tahoe from being “as good as it gets” with regard to implementing adaptive management is a lack of institutional collaboration, but hitherto that has not been the case.
Estimation of stream water temperature using regression analysis, artificial neural network, and chaotic nonlinear dynamic models. 2009. G. Sahoo, G. Schladow, J. Reuter. Journal of Hydrology, 378: 325-342. An empirical model (artificial neural networks (ANN)), a statistical model (multiple regression analysis (MRA)), and the chaotic non-linear dynamic algorithms (CNDA) were used to predict stream water temperature from solar radiation and air temperature data. Stream water temperature determines longitudinal distribution of biota, is a metabolic indicator for the water body, and determines to what depth stream water plunges in a lake ecosystem, bringing with it associated pollutants and therefore ecological impacts. Observed time series data were non-linear and non-Gaussian, thus a new data set was constructed with a time delay to closely resemble the inherent system dynamics. Several analyses were conducted to conclude that the temperature prediction performance of the models was best when the data presented to the model had a time lag of 1 to 3 days. Air temperature was found to be the most important variable influencing stream water temperature, however prediction efficiency increased slightly when solar radiation was included.
Environmental Temperature Sensing using Raman Spectra DTS Fiber-Optic Methods. 2009. S. Tyler, J. Selker, M. Hausner, C. Hatch, T. Torgersen, C. Thodal, G. Schladow. Water Resources Research, 45. W00D23, doi:10.1029/2008WR007052. Distributed temperature sensing (DTS) by fiber-optic cables provides the opportunity to monitor water, air, and media temperatures in a variety of systems at much higher spatial and temporal frequencies than any previous measurement method. This work focuses on providing the hydrologic user with sufficient knowledge and specifications to allow sound decisions on the application and deployment of DTS systems. In a series of field trials conducted in Lake Tahoe, both spatial repeatability and temporal resolution matched or exceeded many traditional field hydrologic instruments.
How Much Influence Does Landscape-Scale Physiography Have on Air Temperature in a Mountain Environment? 2009. S. Dobrowski, J. Abatzoglou, J. Greenberg, G. Schladow. Agricultural and Forest Meteorology. 149: 1751-1758.
105 Spatio-temporal patterns of temperature in mountain environments are complex due to both regional synoptic-scale and landscape-scale physiographic controls in these systems. Understanding the nature and magnitude of these physiographic effects has practical and theoretical implications for the development of temperature datasets used in ecosystem assessment and climate change impact studies in regions of complex terrain. This study attempts to quantify the absolute and relative influence of landscape-scale physiographic factors in mediating regional temperatures and assess how these influences vary in time. The approach was to decompose the variance in in situ temperature measurements into components associated with regional free-air temperature estimates and local physiographic effects. Near-surface air temperature data, collected between 1995 and 2006 from 16 meteorological stations in the Lake Tahoe region of California, USA were regressed against free-air temperature (North American Regional Reanalysis dataset) for the same period. Residuals from this fit represent spatial deviations from the regional mean and were modeled as a function of physiographic position on the landscape using variables derived from terrain analysis techniques. Linear models relating temperature residuals to physiographic variables explained roughly 10–90% of the variance in temperature residuals and had root mean squared error of 1.2–2.0 8C, depending upon the type of measurement and time of year. Results demonstrate that: (1) regional temperature patterns were the principle driver of surface temperatures explaining roughly 70–80% of the variance in in situ measurements; (2) the remaining variance was largely explained by spatial variability in landscape- scale physiographic variables; (3) the influence of physiographic drivers varied seasonally and was influenced by regional conditions. Periods of well-mixed atmospheric conditions lend themselves to the use of simple elevation-based lapse rate models for temperature estimation whereas other physiographic effects become more prominent during periods of enhanced atmospheric stability; and lastly (4) small differences in temperature due to landscape position, when integrated over time, can have a prominent effect on water balance and thus hydrologic and ecologic processes.
Other Scientific Literature
4th Biennial Lake Tahoe Science Conference. March 17-19, 2008. Tahoe Center for Environmental Sciences, Incline Village, NV. The 2008 Science Conference provided a forum where individuals involved in the science and management of the Lake Tahoe Basin could learn about and discuss the latest relevant scientific information and results. This conference brought together agency, academic, and stakeholder representatives, and provided the opportunity for networking, education, and the exchange of new ideas and information. The conference featured presentations covering a variety of topic areas. Contact the Tahoe Science Consortium, 291 Country Club Dr., Incline Village, NV for abstracts.
An Integrated Science Plan for the Lake Tahoe Basin: Conceptual Framework and Research Strategies. 2009. Reuter, J.E., J.M. Thomas and A.C. Heyvaert. In: Hymanson, Z.P.; Collopy, M.W., eds. An integrated science plan for the Lake Tahoe basin: conceptual framework and research strategies. Gen. Tech Rep. PSW-GTR-226.
106 Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 82-182. Chapter 4. Many of the current key management questions for water quality focus on the “pollutant pathway.” Topics include source identification, transport within the watershed, control and abatement, defining loads to the tributaries and the Lake, fate of fine sediments and nutrients in the Lake, and assessment of water quality response. Water quality research priorities were classified into the following larger categories: pollutant loading and treatment within the urban landscape; near-shore water quality and aquatic ecology; erosion and pollutant transport/reduction within the vegetated landscape; water quality modeling; and climate change.
Lake Tahoe Non-Motorized Boating Survey 2008. 2009. Prepared for Lake Tahoe Non- Motorized Boat Working Group. Prepared by Chuck Nozicka Consulting, University of Nevada Reno, Department of Resource Economics. 72 p. The Lake Tahoe Non-Motorized Boating Survey was conducted for the Lake Tahoe Non- Motorized Boat Working Group (NMBWG) and investigated non-motorized boating patterns in the Lake Tahoe Basin. The reported findings represent data collected during the summer and early fall 2008 travel season with the research focused on the peak th portion of that season – principally the 4 of July through Labor Day. The study was conducted by the team of Chuck Nozicka Consulting and the University of Nevada, Reno, Department of Resource Economics (UNR). The research project was designed to provide an accurate profile of non-motorized boat use patterns on Lake Tahoe. The boating pattern analysis specifically addressed use by boat type, years of participation in the activity, participating persons per household party, day versus overnight paddle trips, and time spent during each portion of the trip. The report also gathered boater facility ratings, motivations for boating Lake Tahoe and provided a respondent demographic profile and visitation characteristics. The findings present all results by resident and visitor respondents, a respondent demographic profile, boating patterns, travel characteristics, and reported non-motorized boater visitor expenditures.
Tahoe: State of the Lake Report. 2008, 2009 and 2010. Tahoe Environmental Research Center, University of California, Davis. One Shield Ave., Davis, CA 95616. http://terc.ucdavis.edu/ Water quality data for Lake Tahoe has been collected continuously since 1968. In these annual reports, scientists summarize how natural variability and human activity have affected the lake’s clarity, physics, chemistry and biology over that period. The data reveal a unique record of trends and patterns – the result of natural forces and human actions that operate over time scales ranging from days to decades. Each annual report also presents data for the pervious year. These patterns tell us that Lake Tahoe is a complex ecosystem, and it behaves in ways we don’t always expect. While Lake Tahoe itself is unique, the forces and processes that shape it are the same as those that apply in all natural ecosystems. Consequently, Lake Tahoe provides an analog for many other systems both in the western US and worldwide. This report is intended to inform scientists and non-scientists about the most important variables that affect lake health. Until recently, only one indicator of Lake Tahoe’s health status was widely used: the annual clarity In the Tahoe: State of the Lake Report, the UC Davis Tahoe Environmental Research Center (TERC) publishes many other environmental and water quality parameters that all provide indicators of the lake’s
107 condition. This report is not intended to be a scorecard for Lake Tahoe. Rather, it sets the context for understanding the changes that are seen from year to year and those that are observed over a time scale of decades. Categories for which data is presented include; meteorology, physical properties, nutrients and particles, biology, clarity and education and outreach. Each year, this report presents an overview of research studies on selected topics of interest, e.g. Asian clams, Angora Fire, etc.
Monitoring Past, Present, and Future Water Quality Using Remote Sensing. 2010. T. Steissberg, G. Schladow, S. Hook. Prepared for the Pacific Southwest Research Station. 111 p. A system was developed to semi-automatically acquire, store, and process satellite imagery to quantify water clarity and near-surface chlorophyll a concentration measurements over the entire lake as measures of nearshore and offshore water quality at Lake Tahoe. An automated atmospheric correction procedure and processing code were developed to produce high quality maps and time series of water quality at Lake Tahoe. These lakewide maps show significant variations in Secchi depth and chlorophyll a. The largest variations occur closer to shore, and the lowest Secchi depth and highest chlorophyll a are frequently seen to be associated with stream mouths and to occur at times of spring runoff. An unexpected finding of comparing the 8-year, monthly averaged Secchi depth around the lake periphery is that Secchi depth is consistently lower on the east side of the lake (from Stateline Point to Tahoe Keys) than on the west side of the lake. This appears to hold true at all times of year, and is most pronounced closest to shore (at the nearshore sampling stations). Consistently the lowest clarity region is between Glenbrook and Marla Bay. Chlorophyll a on the other hand, did not show as clear a pattern from east to west. The images in the report showed clearly that the distribution of clarity and chlorophyll a in the nearshore is very often controlled by the transport processes within the lake. In addition to the maps and time series, a web-accessible repository was created to store and distribute these and other satellite data products acquired or developed at Lake Tahoe on a near-real-time basis. The methodology developed for this study can be used to study historical or future changes in nearshore and offshore water clarity for any region of concern around Lake Tahoe and help guide management decisions and monitoring efforts related to water quality.
5th Biennial Lake Tahoe Science Conference. March 16-17, 2010. Tahoe Center for Environmental Sciences, Incline Village, NV. The 2010 Science Conference provided a forum where individuals involved in the science and management of the Lake Tahoe Basin could learn about and discuss the latest relevant scientific information and results. This conference brought together agency, academic, and stakeholder representatives, and provided the opportunity for networking, education, and the exchange of new ideas and information. The conference featured over 100 presentations covering a variety of topic areas. Contact the Tahoe Science Consortium, 291 Country Club Dr., Incline Village, NV for abstracts.
108
109