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IV. Scientific Information Required for Lake and Watershed Management Integrated Lake Water Clarity Model The Tahoe Regional Planning Agency currently has water quality thresholds designed to protect the beneficial uses of Lake Tahoe. Their intended purpose is to set goals for desired water quality. Combined, the Thresholds express the desire for lake clarity to return to the period 1967-1971 when quality was significantly better. However, by themselves, they are not an adequate framework for assessment of lake and watershed management alternatives. For this we need to know (1) What are the sources of sediment and nutrients to the lake and what are their respective contributions, (2) How much of a reduction in loading is necessary to achieve the desired Thresholds, and (3) How will this reduction be achieved? A science-based link between watershed and atmospheric processes, loading, and lake response which can be used to guide management is lacking. A critical component for long-term planning at Lake Tahoe is a water quality model, based on the lake's assimilative capacity to receive and process sediment and nutrients. By knowing the level of loading required to achieve the Thresholds, responsible agencies will be better able to plan in a more quantitative and progressive manner. The TRG has been developing such a model and now has much of the data needed to begin construction and calibration of this model. The model will consist of a series of sub-components which are intended to define the relationships between (1) land-use in the surrounding watershed(s) and sediment/nutrient loading to the tributaries, (2) sediment/nutrient loading and algal growth, and (3) algal growth and sediment (silt) loading and clarity. By mathematically linking these variables, water clarity will be described in terms of nutrient loading from both the watershed and atmosphere. Water quality models are used in both diagnosing lake problems and in evaluating alternative solutions. For Lake Tahoe, we have the rare opportunity to incorporate an existing long-term data base with studies of processes and responses in this lake. The overall model consists of the following components (Figure 18):
These components represent focused models on their own. When combined into a larger, more-comprehensive product, they will provide new insight on predicted lake response based on various management and loading scenarios. This overarching model, referred to as the TRG Clarity Model, will be used in a predictive fashion. This is a very important consideration since actual changes in Tahoe's clarity are expected to lag behind instantaneous loading reductions because of the long hydraulic and nutrient residence times. With a Threshold value of 33.4 m for Secchi depth, the question that has yet to be addressed at Lake Tahoe is what is the magnitude of sediment and nutrient loading which will allow for this Threshold to be achieved, and how is this level of loading achieved? Unless these and other related questions can be answered management will continue to be based on a conceptual rather than a quantitative approach. |
Figure 18. TRG Clarity Model for prediction of watershed management alternative on Secchi depth. | |
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Focal Point for UC Davis Research in the Sierra Nevada While many university and governmental research programs have been active in the Sierra Nevada ecoregion for decades, the Sierra Summit held in the early 1990's galvanized agency and public support for a more visionary approach to the problems that beset this biome. Since then interest in the Sierra Nevada has continued to grow, and at the request of the U.S. Congress and the State of California, the University directed the Sierra Nevada Ecosystem Project and the Sierra Nevada Research Program, respectively. These projects have succeeded in furthering our understanding of critical management issues. Lake Tahoe serves as the focal point for the Sierra Nevada watershed research conducted under the auspices of the Center for Ecological Health Research (CEHR). The CEHR is one of four Centers for Research Excellence established nationally by the US EPA over five years ago. A five-year grant renewal was just recently awarded by the EPA to continue the CEHR's research on assessment of multiple stress in ecosystems. Building on research of the Center's principal investigators and on the management / policy needs of agency and elected decisionmakers, the objectives of the Sierra Nevada Watershed research program are to (1) define important groups of environmental stresses and determine how they interact with natural and anthropogenic features of the watershed landscape, (2) determine the interactive effect of multiple stress on watershed structure and function, (3) develop new and innovative chemical, biological and modeling tools to assess multiple stress at the population and watershed levels, (4) conduct studies at the larger and integrative ecosystem level, and (5) use the results of investigations to provide watershed managers and decisionmakers with science-based tools for a more effective ecological and socioeconomic approach to environmental policy and protection. A total of nearly 20 UC Davis faculty work with the TRG on issues pertaining to Lake Tahoe and the Sierra Nevada. | ||
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Future Program Needs Much of the anticipated work of the Tahoe Research Group will focus on continued research and monitoring to protect water quality, with specific attention to applied research in the areas of watershed management, airshed management, lake management, water quality protection and land use policy. Significant emphasis will be placed on collaborative scientific efforts and the ultimate goal of much of this work is to incorporate findings into regulatory processes within the Tahoe basin. The TRG has presented a comprehensive outline for future research at Tahoe which also has broad applicability in the entire Sierra Nevada ecoregion - this outline is referred to as Lake Tahoe Agenda 2000: Programmatic Goals. Major topics included in the TRG's Agenda 2000 are:
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I. Introduction II. The Cause for Concern III.The Role of Research and Monitoring at Lake Tahoe IV. Scientific Information Required for Lake and Watershed Management V. Proposed New UC Davis Research & Educational Facility at Lake Tahoe VI. Concluding Thoughts | ||