東京湾2定点における栄養塩類濃度の経年変動

抄録

Vertical profiles of nutrients were obtained at two monitoring stations (F3 and F6) near the center of Tokyo Bay from 1989 to 2004. During this 16-year period, ammonium concentration decreased consistently at all depths of both stations. Nitrate and nitrite concentrations also decreased significantly at most depths of the inner-side station (F3), whereas only nitrite concentration decreased significantly in surface layers at the mouth-side station (F6). Phosphate and silicate concentrations decreased significantly in the surface waters of both stations. The water-column integrated ammonium concentrations decreased significantly at both F3 and F6, and so did the integrated nitrate and nitrite concentrations at F3. Since the water-column integrated chlorophyll a concentration decreased as well, enhanced nutrient consumption due to an increase in primary production is not the reason for the decrease in nutrient concentrations. The decrease likely reflects the reduced load of nutrients in the bay.