Figure 7

Nutrient concentrations. (a) Seasonal variations (left) and climatological averages (right) of DIN concentrations observed at the mouths of the eight major rivers. Error bars on the averages indicate errors estimated by assuming the nutrient concentration for the missing data period lies between zero and the maximum values. Black dots with each river color indicate values calculated by observational datasets. (b) DIN concentrations of groundwater measured at observation wells. Shaded areas indicate each watershed along the bay. Black lines denote the paths of eight major rivers. (c) The average concentrations of NH₄ (red), NO₂ + NO₃ (blue), and DIN (red + blue) for groundwater and stream waters. Error bars indicate the standard errors of the concentrations for NH₄ and NO₂ + NO₃ (downward bars) and DIN (upward bars).