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Steven S. Cliff, Tony VanCuren, John E. Reuter and Thomas A. Cahill DELTA Group, Department of Applied Science University of California, Davis Data collected in recent years suggest that deposition of bio-available airborne nitrogen, phosphorous, and insoluble fine particles contribute much of the clarity degradation at Lake Tahoe, with the remainder being due to pollutants transported to the lake via surface and ground water (Figure 1). The air at Tahoe is implicated as a source of about one quarter of all and a third of soluble reactive phosphorous, more than half of the nitrogen, and a significant, but not fully quantified, portion of the insoluble fine particles. All three components add to the reduced clarity of the lake. We believe it is fair to state that the air is one of the, if not the, most important components of overall lake clarity reduction. Certainly, the linkage between the air and lake is one of the least understood of the ecological system. Therefore, we have proposed research that is needed to progress from the present qualitative understanding of the effects of air pollutants on Lake Tahoe to a quantitative assessment of the contributions of individual sources and calculations of the potential benefits of various regulatory alternatives (TRPA Scoping Document, 2000). Figure 1: Input of nutrients to Lake Tahoe
The federally chartered Bi-state Compact mandates that Tahoe Regional Planning Agency (TRPA) protect Lake TahoeÕs environment, especially the lakeÕs famed water clarity, by adopting planning standards and setting environmental carrying capacity thresholds. The current standards and thresholds as adopted in the 1987 Regional Plan, have reduced environmental degradation in the Lake Tahoe Basin, but have not fully halted the progressive loss of lake clarity. If current lake water quality trends are not reversed in the near future permanent degradation of water quality will result. TRPA is required to adopt a new 20-year Regional Plan in 2007. In order to aid this new Regional Plan, the air quality research program builds on the foundation of past research with a focused program of water and air quality measurement leading to development of predictive tools suitable to evaluate potential strategies to reverse the air deposition effects on lake clarity. Air pollutant sources that are being studied include fires, road dust, vehicle exhaust, and residential heating emissions originating in the Basin, and the whole spectrum of emissions from upwind population centers. The past year has focused on installation of a new sampling site at Thunderbird Lodge, transplanting of the South Lake Tahoe site (Figure 2), and groundwork for installation of a new site at the Coast Guard station in Lake Forest. Further, preparations for increased research equipment at the D.L. Bliss State Park and South Lake sites have been made. It is anticipated that sampling for N, P, and fine particles deriving from all atmospheric sources will occur at these 4 sites over the next year. In addition, two new sites will be installed, one mid-lake and one ridgeline. The ridgeline site will help further quantify the out-of-basin derived pollutants, and flux to the lake will result from mid-lake sampling. We have faced numerous challenges during installation and sampling thus far, but anticipate generous headway for the future of this program. Results from previous studies are summarized in the Watershed Assessment (Chapter 3, 2000) and the Scoping Document (2000). Figure 2: Air quality site at South Lake Tahoe. Measurements for PM2.5, PM10 (mass and composition), meteorology, ammonia, nitric acid, total P and bio-available P are taken roughly weekly. This is one of 6 existing or proposed sites around the Tahoe basin.  Cliff, S.S. and T.A. Cahill, "Air Quality in the Lake Tahoe Basin", In The Lake Tahoe Watershed Assessment, D. D. Murphy and C.M. Knopp, eds. pp. 129-211, U.S.F.S. PSW-GTR 175 (May 2000). Reuter et al., The Lake Tahoe Air Quality Research Scoping Document: Determining the Linkage Between Air Quality, Water Quality and Transportation, July 2000. |