臺灣西南部河川水質污染與養殖貝類之大量死亡

Effect of River Water Pollution on the Mass Mortalities of Cultured Shellfishes along the Southwest Coast of Taiwan

鄭森雄(Sen-Shyong Jeng)

《臺灣水產學會刊》 4卷1期 (1975/06) Pp. 51-71

https://doi.org/10.29822/JFST.197506.0006

摘要

爲研討臺灣淺海養殖貝類在每年四、五月大量死亡原因，乃詳細分析朴子溪及其附近河川之水質化學。從1974年3月至1975年4月，以朴子溪及其河口爲主，共進行了八次水質化學調查。由調查及實驗結果得知下列事實：
1.在雲林、嘉義、臺南地區，每年從十一月左右，以迄次年四、五月，俱屬乾季，在此期間，溪流之河床乾涸，水流幾乎停止；從四、五月至十月底爲雨季，河水豐富，水流亦快。在河川之兩旁，有許多工廠排出大量廢水，然而廢水對河川之污染程度受河水之流量，流速密切的影響。
2.在雨季之六月至十月，因工業廢水得到河水之稀釋，所以河川水之化學需氧量較低，溶氧較高，水質污濁程度較微。
3.在乾季之十一月至次年四、五月，則工廠排出之廢水得不到河水之稀釋，因此不易流至河口，而大量沉積於河床上。是故工廠附近之河川水質極爲污濁；但河口附近之水域則因流來之廢水量少，污染程度不重。
4.在乾季與雨季交接之四、五月，初次大雨卽將乾季中長期累積於河床之污染物，一次冲至河口，使溶解氧大降，化學需氧量增高，水色變爲紅褐，因此對河口生物造成嚴重傷害。
5.臺灣淺海養殖貝類大量斃死之主因，乃因河川水質污染所致，使貝類致死者乃爲污染物中之有毒物質，詳見另文報告。
6.朴子溪及其附近許多河川水質之污染程度已相當嚴重，非但不能做爲飲水來源，亦不能做爲水產用水。

並列摘要

Culture of oyster and clam along the southwest coast of Taiwan is one of the important fisheries of this Island. Those shellfishes have suffered high mortalities each year in April-May since 1969. The Average death rate was about 40%, sometimes reaching as high as 70 to 80%. The loss was estimated to be NT$ 100 million anually. Several things have been suspected to be the causes of the mass mortalities, such as: (1) water pollution from rivers; (2) disease of the shellfishes; (3) sudden change of environmental factors, e. g., temperature or salinity; (4) overcrowding on the culture beds; (5) red tide (6) pesticide pollution, etc. In order to determine the cause of these mass mortalities, the possible effects from water qualities and toxic substances were studied. It was found that water pollution of the streams was the major cause of the large scale death of the shellfishes. In Taiwan, oyster and clam are cultured in the estuaries of many streams, because there are very few bays along the coast of this Island. There are many industrial plants, mostly paper mills, located upstream near the railroad (Fig.2). Most of these plants discharge their wastes without prior treatment. Theoretically, the oyster and clam should be affected by the pollutants from the plants. But many people do not believe water pollution to be the cause of the mass mortalities of oyster and clam, because the plants discharge their wastes all year around, but the oyster and clam die only in April or May.
However, if we are familiar with the climate and river condition of Taiwan, we shall understand that water pollution is the most probable cause of the mass mortalities of oyster and clam. In southwest Taiwan, the rainy season is from May to October and the dry season is from November to April (Fig.3). In the rainy season, the river is full of water. Therefore, the discharged industrial waste may be diluted by river water, and the shellfishes cultured in the estuaries will not be harmed. In the dry season, the quantity of the river water is small and the flow is very sluggish. Hence, most of the pollutants will not reach the estuaries, but settle on the river bed. At the beginning of the rainy season, i. e., April or May, the first heavy rain may bring the pollutants concentrated on the river bed down the coastal areas and cause the oyster and clam to die.
Po-Tzu River was selected as a model to study whether this postulation is true. Six sampling stations along the river, and 4 stations around the estuaries were set up (Fig.2). From April 1974 through April 1975, 8 samplings were made to study the water qualities of the river: flow rate (Fig.4). COD content (Fig.6), dissolved oxygen (Fig.7), pH (Fig.8), color of water (Fig.9), ammonia nitrogen (Fig.10), basic anion and cation groups (Fig.5 and Appendixs 1 to 8), and the dissolved oxygen in the pathway of the plant wastes (Fig.11). In addition, the dissolved oxygen in the rivers of the southwest area of Taiwan were also studied (Fig.12). Base on these data, it was concluded that these rivers were heavily polluted by industrial wastes in the dry season i.e., from October through April. Although the estuaries where the oyster and clam were also polluted by industrial wastes in the dry season, the heaviest pollution occurred at the beginning of the rainy season.