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Fig. 6. Flow-weighted average annual NO3–N concentration as a function of the natural logarithm of the April through September water yield (mm yr-1). The open circles are the observed values for the 1982–2001 water years, with error bars representing the 95% confidence limits for individual observations based on regression analysis that incorporates autocorrelation of model residuals (r = model residual from previous year); the curved line is the expected mean value estimated from the regression analysis; the solid triangle is the expected mean value at the 1945 water yield with 95% confidence limits; and the solid square is the 1945 value with an error bar representing the maximum estimated effect (+19%) of compositing samples over approximately 10 d.
