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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2007–5117

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Data Caveats and Future Directions

The major limitation of the Klamath Tribes dataset is the two-week sampling interval. The sampling program was designed to assess long-term trends in water quality and to provide a yearly status of the lake ecosystem by sampling at a consistent set of sites representing conditions all around the lake, and doing so on a consistent and sustainable interval over a long period of time. It was not designed to address the relation between water quality in the lake in any given year and various forcing functions, both of which vary significantly on time scales as short as a few days. Therefore this dataset lends itself to the types of empirical approaches to the data analysis that are presented in this report. If a particular variable was of overwhelming importance, and particularly if the predominant time scale were a month or more, then this empirical approach could be counted on to demonstrate this strong relation. In reality, it seems that many variables are of nearly equal importance, and that water quality is a result of the complex interaction of a number of processes at once.

This limitation was suspected after the first attempt was made to correlate water-quality variables with lake level and climatic factors (Wood and others, 1996). Since that time, new data-collection efforts have begun. Specific conductance, pH, water temperature, and dissolved oxygen have been measured in-situ around the lake with continuous water-quality data sondes since 2002. Nutrients and chlorophyll‑a have been collected at a small subset of representative sites on a weekly time interval. The availability of these datasets has confirmed that water quality varies significantly on time scales as short as a few days. In addition, a hydrodynamic model of the lake has been developed that shows that wind-driven currents play a large role in determining the water quality in the lake, particularly in the northern third of the lake, and that these currents respond to changes in the wind forcing in a matter of hours. The model (Wood and Cheng, 2006), as well as supporting light/dark bottle experiments (Mary Lindenberg, U.S. Geological Survey, unpub. data, 2005, 2006), also indicates that the deep trench along the western shoreline is important because it is an area of net consumption of dissolved oxygen. The datasets currently being collected and the modeling effort are providing the opportunity to explore relationships among variables using a process-based, rather than empirical, approach. In the long term, this approach will likely provide more insight into the complex interaction of processes that determine water quality at a particular place in the lake at a specific point in time.

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