NUTRIENTS LOADING AND ITS IMPACT ON THE COASTAL ENVIRONMENT: KYEONGGI BAY, KOREA

초록

To investigate controlling factors determining water quality in the Kyeonggi Bay, we measured nutrients, COD and heavy metals of seawater, and applied data to a mass balance model. Inorganic total nitrogen (NH4++NO2-+NO3-) ranged from 9.1 to 16.3 M with an annual average of 12.3 M and phosphate ranged from 0.37 to 2.29 M with an annual average of 1.03 M in the outer bay showing a typical N/P ratio. However, inorganic nitrogen was very high in the Han River estuary ranging from 20.0 to 124.5 M during one tidal cycle (12.5-30.0 ‰). N/P ratio in the estuary was 160 and rapidly decreased to 20 in the outer bay. The present result showed that nutrient environment of the study area can be characterized as a conservative estuary with high nutrient loading. Patterns of pollutant distribution showed that the metropolitan area was most responsible for high nutrients and organic loading in the form of domestic sewage and coastal industrial complex was responsible for the elevated heavy metal concentration in the bay. Result of mass balance box model revealed that metropolitan area discharged 50 tons N d-1 and 135 tons COD d-1 through Han River and coastal city and industrial complex discharged 33 tons N d-1 and 69 tons COD d-1 into the Incheon Harbor channel, respectively. The other minor sources such as the maritime activity and islands residence were negligible. Since the metropolitan area is in charge of more than 60% of total overloading from 6 major nutrient sources, reducing domestic sewage and increasing efficiency of wastewater treatment facilities of metropolitan area seem to be the most important factor controlling water quality in the Kyeonggi Bay.