Distribution dynamics of the inorganic nitrogen and assessment of ambient water quality at the estuary seawaters in North Yellow Sea

Monitoring of the inorganic nitrogen levels was carried out at the estuary in North Yellow Sea from 1999 to 2000. The results showed that the inorganic nitrogen to the estuary seawater primarily derived from riverine discharges, terrestrial sources, which were peak on May or on July per year, and decreased in autumn. Rainfall can delay the occurrence of the decrease in the inorganic nitrogen to the estuary seawater. The inorganic nitrogen levels in the estuaries of Yalujiang river, near Yiquan, Dayang river, and Zhuanghe river were 0.561, 0.476, 0.410 mg/L and 0.494 mg/L, respectively, which were higher than the criterion of fourth-class seawater. The highest content of the nitrites in the seawaters near Yiquan and the estuaries of Biliu river were 0.108 mg/L and 0.265 mg/L, over the threshold values of healthy fisheries.