Fig. 5. Water year arithmetic average NO₃–N concentrations as a function of the natural logarithm of April through September water yield (mm yr^-1). The open circles are the 1982–2001 observed annual values, 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 at the 1945 water yield with 95% confidence limits; and the solid square is the observed 1945 value with an error bar representing the maximum estimated influence (+19%) of compositing samples over approximately 10 d.