Analysis of Human Impacts on the Deterioration of an Aquatic Ecosystem in Korea and Development of a Computer-Aided System for Basin-Wide Management

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The Nakdong River Basin is one of the largest river basin in Korea. The rapid economic growth in the basin, however, brought the shortage of water resources and water pollution in the river. One of the largest project to develop water resources is the construction of a reservoir in the mouth of the Nakdong River. It is clear that the reservoir would supply large amount of water and support rapid growth of various activities in the lower basin. However, little efforts have been made to control quality of river water and reservoir, and it is probable that aquatic ecosystem along the river and reservoir will be damaged.It is urgent need, therefore, to change the system of water use and wastewater discharge not only in the area around the reservoir but also in the upper basin such as Daegu to protect water environment of the reservoir. The purpose of this cooperative study is to develop a computer-aided system for the comprehensive management of aquatic environment based on water use, wast … More ewater management, agricultural and industrial activities in the Nakdong River basin.Sampling stations are selected to cover the whole range of basin area of the Nakdong River. Sampling were carried out times per year. The maximum flow rate in Waegwan was 99.71m3/sec in August and the minimum was 39.22m3/sec in April. In Hyeunpung, flow rate ranged from 134.05 (Jun) to 61.41 (April)m3/sec, while it was 609.26m3/sec in October and 49.53m3/sec in Jun in Namji. The distribution of BOD5 in the river of Nakdong and Kumho was 1.6-37.9 and 0.9-74.4mg/l, respectively. The BOD5 at Hyeunpung ranged from 14.8(Dec.) to 37.9(Apr.) mg/l, indicating that the water quality at Hyeunpung is significantly influenced by the heavily polluted Kumho river. The ranges of major nutrient concentrations in the Nakdong river upper stream were 1.9-22.6mg/l for TKN, 0.8-21.9mg/l for NH3-N, 2.2-32.9mg/l for DT-N, 0.037-0.10mg/l for PO4-P and 0.52-1.2mg/l for DT-P. The nutrient concentrations in the Kumho river were 0.062-0.8mg/l for NH3-N and 0.007-0.56mg/l for PO4-P.The highest value of BOD5 among the in the lower stream was 55.2mg/l at sampling station MN-11. The calculated mean value of BOD concentration was 7.3mg/l. The concentration of ortho-phosphate (PO4-P) ranged from 0.03 to 0.25mg/l and its mean value was 0.089mg/l (Fig.5). NH4-N concentration was in the range of 0.09 and 3.28mg/l and its mean value was 1.37mg/l.Trihalomethanes Formation Potential (THMFP) was 176.3ug/l at the station K5. Sewage treatment plant seemed to discharge a large amount of precursor in their wastewater to public water bodies. A strong correlation between the TOC and THMFP was noted. In Naedang water purification plant, raw water is taken from the Nakdong River. In Achang water purification plant, raw water is taken from the Gachang dam, which is located upper basin of the Nakdong River. It was found that THM were formed during prechlorination rapidly, and increase in water distribution system.The characterization and distribution of dissolved stream humic substances (HA plus FA) in the Nakdong River was studied. The concentration of the humic substances in waters of the river varied considerably with locality, ranging from 91.8mg/3l in water from Kangchang to 4.3mg/3l in water from Samnangjin. The amount of the stream HA was markedly higher in the Kangchang water than in the Hyunpung water and in the Samnangjin water. Most of the stream humic substances, especially of the stream HA, found in the Kangchang water should have originated from these external sources.Per capita or unit areal loading for domestic water, livestock, and farm land and forest were summarized from published information. Also, unit loading of industrial wastewater per employee and production were summarized. An easy of access software to help water authorities for setting basin-wide comprehensive management program on water quality control was developed.. The system enables to estimate pollution loads from the basin including both point and non-point sources and to predict quality of the water bodies based on the present load and expected loads after alternative management plans are implemented. The major functions incorporated into the system to fulfill the system performance are as follows ;1) Definition of geological and administrative mapping of pollution sources,2) Inputs of socioeconomic information supported by an advisory system,3) Calculation and summation of pollutant loads,4) Water quality in rivers and tributaries,5) Water quality in lakes and reservoirs, and6) Supporting functions for check and correction.The system developed proved the effectiveness of the concept of system development and will be expanded to the Nak-Dong River Basin successfully. Less