We investigated the effects of climate variability on the thermal structure of Lake Tahoe, California-Nevada, 1970, and with principal components analysis and step-wise multiple regression, related the volume-weighed average lake temperature to trends in climate. We then used a 1-dimensional hydrodynamic model to show that the observed trends in the climatic forcing variables can reasonably explain the observed changes in the lake. Between 1970 and 2002, the volume-weighted mean temperature of the lake increased at an average rate of 0.015 • C yr −1 . Trends in the climatic drivers include 1) upward trends in maximum and minimum daily air temperature at Tahoe City; and 2) a slight upward trend in downward long-wave radiation. Changes in the thermal structure of the lake include 1) a long-term warming trend, with the highest rates near the surface and at 400 m; 2) an increase in the resistance of the lake to mixing and stratification, as measured by the Schmidt Stability and Birge Work; 3) a trend toward decreasing depth of the October thermocline. The long-term changes in the thermal structure of Lake Tahoe may interact with and exacerbate the well-documented trends in the lake's clarity and primary productivity.

Secchi depth has been measured in Lake Tahoe an average of every 12 d since July 1967. Because of the unusual clarity of the lake, Secchi depth measurement is responsive to small changes in light-attenuating particles, and the record exhibits strong variability at the seasonal, interannual, and decadal scales. Using recently developed methods of applied time-series analysis, the mechanisms of change were delineated at each scale. The seasonal pattern is a bimodal one, with two minima at approximately June and December. The June minimum is due mostly to cumulative discharge of suspended sediments following melting of the snowpack. The December minimum is probably a result of mixed-layer deepening as the thermocline passes through layers of phytoplankton and other light-attenuating particles that reach a maximum below the summer mixed layer. The interannual scale exhibits two modes of variability, one during the weakly stratified autumn-winter period and the other during the more stratified springsummer period. The first mode is a result of variable depth of mixing in this unusually deep lake, while the second results from year-to-year changes in spring runoff. A decadal trend also exists (Ϫ0.25 m yr Ϫ1 ), resulting from accumulation of materials in the water column. It is not yet understood, however, how much of this change is due to phytoplankton or recent phytoplankton-derived materials and how much is due to other materials such as mineral suspensoids. Based on the available measurements and physical considerations, both categories may play a significant role.

Chlorophyll‐temperature profiles were measured across Lake Tahoe about every 10 days from April through July 1980. Analysis of the 123 profiles and associated productivity and nutrient data identified three important processes in the formation and dynamics of the deep chlorophyll maximum (DCM): turbulent diffusion, nutrient supply rate, and light availability. Seasonal variation in these three processes resulted in three regimes: a diffusion‐dominated regime with a weak DCM, a variable‐mixing regime with a pronounced, nutrient supply‐dominated DCM, and a stable regime with a deep, moderate light availability‐dominated DCM. The transition between the first two regimes occurred in about 10 days, the transition between the last two more gradually over about 3 weeks. The degree of spatial variability of the DCM was highest in the second regime and lowest in the third. These data indicate that the DCM in Lake Tahoe is constant in neither time nor space.

Direct-democratic processes have won popular support but fall far short of the standards of deliberative democracy. Initiative and referendum processes furnish citizens with insufficient information about policy problems, inadequate choices among policy solutions, flawed criteria for choosing among such solutions, and few opportunities for reflection on those choices prior to decision making. We suggest a way to make direct democracy more deliberative by grafting randomly selected citizen assemblies onto existing institutions and practices. After reviewing the problems that beset modern direct-democratic elections and the long history of randomly selected citizen assemblies, we propose five different varieties of randomly constituted citizen bodies—Priority Conferences, Design Panels, Citizens’ Assemblies, Citizens’ Initiative Reviews, and Policy Juries. After selecting members through stratified random sampling of citizens, each of these assemblies would operate at a different stage of the legislative process, from initial problem identification through approval of a finished ballot measure. Highly structured procedures guided by professional moderators and featuring expert testimony on policy and legal matters would help to ensure deliberative quality, and careful institutional designs would make each body politically powerful. In the end, these citizen bodies would be likely to address the deliberative deficit of direct democracy and better achieve the public’s desired policy objectives.

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Discovery of the fuel additive methyl tert-butyl ether (MTBE) in drinking water supplies is of concern to public health officials, water suppliers, and the public. Despite recent policy decisions, few published studies exist on the concentrations, sources, and fate of MTBE in surface waters. The purpose of this study was to determine (1) the relative contribution of motorized watercraft as a source of MTBE, (2) its seasonal distribution, (3) loss from the water column, (4) the extent of vertical transport, and (5) its persistence between years; this work was done in Donner Lake, California, a multiple-use lake in the Sierra Nevada Mountains. MTBE measurements were made at 9 individual depths from surface to bottom on 16 dates. Recreational boating was the most important source of MTBE. Statistically, 86% of the change in MTBE was explained by variation in motorized watercraft use. Neither highway runoff nor precipitation contributed significantly. MTBE concentration ranged from <0.1 µg‚L -1 to a high of 12 µg‚L -1 . Between July 1 and 7, 1997, MTBE content rose dramatically from 115 to 365 kg. By January, levels had declined to a minimum of 15 kg, suggesting little interannual persistence. The major loss of MTBE appeared to be volatilization at the air-water interface characterized by two distinct periods. During the boating season, MTBE decline was 1.2 kg‚day -1 (193 day half-life). At the end of the boating season, MTBE loss increased to 8.1 kg‚day -1 (14 day halflife). Thermal stratification acted to retard MTBE transport to deeper depths.

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