The no-project alternative analysis: An early product of The Tahoe Decision Support System

David L. Halsing, Mark L. Hessenflow, Anne Wein

ABSTRACT
The report on the development of a No-project alternative analysis (NPAA) or “business as usual” scenario with respect to a 20-year projection of 21 indicators of environmental and socioeconomic conditions in the Lake Tahoe Basin for the Tahoe Regional Planning Agency (TRPA). Our effort was inspired by earlier work that investigated the tradeoffs between an environmental and an economic objective. The NPAA study has implications for a longer term goal of building a Tahoe Decision Support System (TDSS) to assist the TRPA and other Basin agencies in assessing the outcomes of management strategies. The NPAA assumes no major deviations from current management practices or from recent environmental or societal trends and planned Environmental Improvement Program (EIP) projects. Quantitative “scenario generation” tools were constructed to simulate site-specific land uses, various population categories, and associated vehicle miles traveled. Projections of each indicator’s attainment status were made by building visual conceptual models of the relevant natural and social processes, extrapolating trends, and using available models, research, and expert opinion.
We present results of the NPAA, projected indicator status, key factors affecting the indicators, indicator functionality, and knowledge gaps. One important result is that current management practices may slow the loss or degradation of environmental qualities but not halt or reverse it. Our analysis also predicts an increase in recreation and commuting into and within the basin, primarily in private vehicles. Private vehicles, which are a critical mechanism by which the Basin population affects the surrounding environment, are a key determinant of air-quality indicators, a source of particulate matter affecting Secchi depth, a source of noise, and a factor in recreational and scenic quality, largely owing to congestion. Key uncertainties in the NPAA include climate change, EIP project effectiveness, and external population, economic activity, and air pollution.

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A study of ancient trees rooted 36.5 m (120') below the surface level of Fallen Leaf Lake, California

John A. Kleppe

ABSTRACT
The author of this paper has discovered large trees rooted at a depth of 36.5 m (120’) below existing surface level of Fallen Leaf Lake. Fallen Leaf is one of the major watershed areas for Lake Tahoe. Some of these trees measure over 30 m (98’) tall with a circumference of over 4.5 m (15’), which is an indication that they were over two hundred years in age when they died. The significance of this discovery is the fact that for these trees to be rooted below the surface of the lake, the lake must have been down at least 36.5 m for over two hundred years. This would indicate that a “mega drought” had occurred, since several of these trees have been carbon dated to have “drowned” in 1215 A.D. ± 40 years. This would indicate that the drought persisted during the medieval period 850-1150 A.D., and was followed by an extremely wet period that brought the lake level back up high enough to drown the trees. There are also signs on these trees that another severe drought occurred sometime later, but did not persist for as long as the first one.
The author obtained a small grant to help in the study of these submerged rooted trees. He has been operating a Remotely Operated Vehicle (ROV) that can obtain high resolution color video and retrieve small wood samples down to a depth of about 152 m (500’) below the lake surface. The trees are invisible to sonar since they have become completely water logged from being underwater for approximately 800 years. Visual searching has been required to locate them.
This paper reports on the progress being made to study what may be the only known full size trees that grew during the Medieval drought period in the Sierras. The tree ring data from these trees are providing a valuable climate history of the Lake Tahoe Basin.

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Pilot filtration studies for turbidity and nutrient removal at Lake Tahoe

Dipen M. Patel, Jeffrey R. Hauser, John Johnston, Jeffry G. Curtis

ABSTRACT
The California Department of Transportation (Caltrans), which is responsible for more than 500 storm water discharge points in the Tahoe Basin, has constructed a small-scale test facility for developing new treatment technologies to meet numeric effluent discharge limits due in 2008. The primary constituents of concern are turbidity, phosphorus and nitrogen. Of particular interest are settling and gravity filtration treatment systems because of their relatively low maintenance requirements and potential for deployment within the Caltrans right-of-way.

Special attention is being given to media to remove the dissolved fraction of phosphorus in the runoff, which can cause violation of the effluent limit even after the particulate fraction is removed. Three grades of sand, activated alumina, and aluminum oxide were tested during the 2001/02 wet season. Fine sand, activated alumina, expanded shale, and limestone were tested during the 2002/03 wet season. During the 2001/02 season, none of the media filters tested were able to meet the surface discharge limits for the primary constituents of concern. Hydraulic application rates were reduced in the 2002/03 season. In some filters, dosing was controlled at the inlet; in others, dosing was controlled at the outlet, leading to submerged conditions. In the 2002/03 results, filtration through activated alumina or expanded shale following sedimentation almost always met the surface water discharge limits for turbidity (20 NTU) and total phosphorus (0.1 mg/L). Both media, however, increased pH and contributed dissolved aluminum to the effluent

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Relation between urbanization and relative toxicity of semipermeable membrane device extracts in the Lake Tahoe Basin and Truckee River watershed, Nevada and California

Timothy G. Rowe, Michael R. Rosen, Steven L. Goodbred, Douglas O. Shipley

ABSTRACT
Rapid growth in urban areas of the United States has caused concern about the effects on water quality of streams and aquatic ecosystems. One way to assess the effects of urbanization on stream-water quality is through deployment of passive samplers that accumulate many of the organic environmental contaminants associated with urban landscapes. Semipermeable membrane devices (SPMDs) use a lipid (triolein) to mimic contaminant accumulation in fatty tissue of aquatic organisms. These devices concentrate many organic compounds in the water column including polycyclic-aromatic hydrocarbons (PAHs), certain pesticides and urban compounds and many other hydrophobic-organic contaminants (HOCs).
Possible effects of urbanization on stream-water quality in the Truckee River and Lake Tahoe Basins of Nevada and California were examined using toxicity tests on organic compounds extracted from SPMDs deployed during the summer baseflow period August-September 2002. Sampling sites included six in the Lake Tahoe Basin, a Truckee River tributary and main-stem site in the upper reaches and two main-stem and two tributary sites in and near the Reno/Sparks urban area.
SPMD toxicity tests resulted in higher relative toxicity and higher PAH concentrations in urban areas within Reno compared to less urbanized areas in the Lake Tahoe Basin; however, low levels of ‘relative toxicity’ were found at all sites in the Lake Tahoe Basin. A second relative toxicity value (EC50) was generally associated with more urbanized sites, but there was no statistical difference between Lake Tahoe Basin and Truckee River sites and no correlation with land use, indicating that the EC50 test does not discriminate well for urbanization in these watersheds. The Pyrene Index (PI) showed the best correlation between PAH concentration and urbanization, suggesting that it could be used as an indicator of urbanization in the Lake Tahoe and Truckee River watersheds.

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Modeled inputs of atmospheric nitrogen to the Lake Tahoe Basin due to gaseous pollutant deposition

Leland W. Tarnay, Dale W. Johnson and Alan W. Gertler

ABSTRACT
Causes of the decline in water quality in Lake Tahoe have been attributed to nutrient additions stemming from various watershed-related changes such as urban development on the one hand to atmospheric nutrient deposition on the other. Several independent estimates exist that quantify the magnitude of these atmospheric sources at the scale of the entire Lake Tahoe Basin (LTB), but there are no estimates of deposition at the scales appropriate for mass balance (i.e., comparison of nutrient inputs vs. outputs for a given watershed). This study leverages ambient measurements of pollutant concentrations and Geographic Information System (GIS) maps of forest canopy characteristics to estimate the variation of gaseous nitrogen (N) pollutant deposition at watershed scales in the LTB. We find that (1) modeled inputs, when integrated over the entire area of the LTB, match those produced by other methods, (2) modeled N deposition to drier east-side watersheds can be twice that of wet deposition, and (3) daytime fluxes of gaseous N are responsible for most modeled dry deposition during the three month summer period of this study. Although uncertainties created by local mountain topography and meteorology prevent definitive deposition measurements, we conclude that dry N deposition likely provides substantial N (average of 1.4 kg-N ha-1 or about 1/3 of annual deposition) to some parts of the LTB, especially in areas near the sources of gaseous N pollution (up to 2.1 kg-N ha-1, or 1/2 of annual deposition). The potential effects of this localized N deposition (including possible linkages with aquatic and terrestrial eutrophication) warrant further study.

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