臺灣中部河川之水質及其對魚類之影響

Water Quality in Rivers of Central Taiwan and Its Effect on Fish

鄭森雄(Sen-Shyong Jeng) ； 王松賓(Sung-Bin Wang)

《臺灣水產學會刊》 5卷1期 (1976/12) Pp. 43-60

https://doi.org/10.29822/JFST.197612.0007

摘要

爲知臺灣中部河川之基本水質及其受污染情形，乃自1975年7月起，至1976年5月止，在大肚溪、洋厝溪、員林大排水、麥嶼溪及濁水溪等溪流，共進行了10次水質調查，由實驗結果得知下列事實：
1.臺灣中部溪流，因受降雨之影響，在每年十一月至次年四、五月，河水量寡；由四、五月至十一月，則河水量豐。
2.大肚溪已受臺中市、彰化市工業廢水及部分都市污水之嚴重影響，不論乾、雨季，水質均劣；河道下游，終年無魚，尤以乾季污染更重。臺灣化學纖維公司排水口以下河水，COD幾乎皆在1000ppm以上，pH在2~4之間，並有强烈毒性，卽使稀釋至25%，亦能使試魚在4日內死亡過半。
3.洋厝溪與員林大排水原係供農田水利灌溉用，已成眾多工廠之排水溝及彰化、員林等城鎮之下水道。在乾季，其溪水之溶氧甚低，污染較重之溪水，甚至含有急性毒物。其下游亦終年不見魚跡。
4.在臺灣中部，爲供乾季灌溉農田及工業用水，在河道上築有許多水閘，或以沙石圍堵河道；因此在乾季，工廠排出之廢水乃停留於河床。臺灣中部河川之中上游，在雨季雖然有魚，但在乾季期間，因河水之量日減，相對地廢水之濃度越來越高，至某一程度，卽使河魚大量死亡。
5.乾季累積於河床之污染物，在春夏之交，初次大雨來時，一次被冲至河口，此與雲、嘉地區水污染情形類似，但因中部地區，工廠離海岸較近，在乾季時，污染物之累積量可能較小，故一次冲至河口之量較少，但因廢水經常流出，其對沿岸貝類之慢性毒性可能較大。
6.臺灣中部多數河川，因污染情形嚴重，除令魚類直接死亡，絕滅之外，且因水中含有過多之SO4與Na，亦不適於農業灌溉，及工業冷却等用途，必須立刻積極防治。

並列摘要

Central Taiwan is one of the important fish culture and agricultrual centers on the Island. Several rivers flow from east to west entering the Taiwan Strait, supplying water for irrigation of paddy fields and carrying nutrients to the coastal areas for the cultivation of clam and oyster. As the result of recent rapid industrial development in Taiwan, the rivers and coastal areas suffered great damage from industrial wastes. In order to know the water quality in central Taiwan today and its effect on fish, a comprehensive study was made.
In the first report, the water quality of central Taiwan rivers, including the Ta-tu River, Yang-tz Brook, Yuan-lin Drainage Cannal, Mai-hsu Brook and Cho-shui River (Fig.1), was investigated from July, 1975 through May, 1976. After 10 surveys, detailed data were obtained, as shown in Appendix 1 to 7. Based on these data, it was found that the orginal river water in central Taiwan has the characteristics of higher Mg, SO4 concentrations. However, most of the rivers were heavily polluted in mid and down stream.
Just as in southwest Taiwan, the rivers in central Taiwan are full in the rainy season, May to October, and short of water in the dry season, November to April as shown in Figs. 2 and 3.In both the rainy and dry seasons, the Ta-tu River has been heavily polluted by industrial wastes and city sewage from Changhua and Taichung, more severe in the dry season, No fish is found down from St. T2 of the Ta-tu River the year round near the outlet of Taiwan Chemical Fiber Co. Water sampled from this station toxic shows chemical oxygen demand higher than 1,000ppm, pH of 2-4, besides other acute substances (Table 4). The Yang-tz Brook and Yuanlin Drainage Canal were originally built for irrigation, but have become the drainage ditch of various plants, and the sewer of Chunghua and Yuanlin. In the dry season, the dissolved oxygen concentration in midstream (St. Y2, L2, L3) is as low as 0 to 2ppm (Fig. 6), containing acute toxic substances.
In order to conserve water for irrigation, in the dry season many floodgates have been built along the rivers. Sand and stones were used to block river water for industrial use. As a consequence, the industrial wastes discharged from plants settle on the river beds in the dry season. With the decrease of river water, concentrations of waste become worse. Though fish survive in up and midstream of the rivers in the rainy season, they suffer high mortality when the concentration of the wastes reaches a certain level in the dry season. On February 13-14, 1976, large scale death of river fish occurred.
River pollution in central Taiwan is similar to that in south-west Taiwan, i.e., in the rainy season, pollution is less, but in the dry season the rivers are heavily polluted, and industrial wastes settle on the beds. With the first heavy rain at the beginning of the rainy season, the pollutants concentrated on the river beds are flushed into the estuaries.