Some Coastal Environmental Problems in Taiwan ABSTRACT

Transcription

1 ACTA OCEANOGRAPHICA TAIWANICA (2001),39,1-10 Kuang-Lung Fan' ABSTRACT There are three major environmental problems along the coast of Taiwan : coastal water pollution, coastal erosion and land subsidence. The population is over 23 millions in Taiwan, with the area about 36,000 krrr', The main three sources which cause the coastal pollution are municipal, industrial and livestock wastewater. Lots of the wastewater are discharged directly to the ocean, harbours or rivers. The pollutants in harbours or rivers will eventually be delivered to coastal waters. The tidal current is the major force dispersing the pollutants nearshore. The polluted water extends to an area about 5 km on both sides from the discharge source, and within about 3~4 km off-shore. The long-shore current induced by breaking waves is the major force shaping the coastal morphology. Along the western coast of Taiwan, the long-shore current mainly flows northward along the southern section, and southward along the northern section. In the last one hundred years, in general, the coast has been eroded along the northern and southern sections of western coast, and some reclaimed lands were formed in the middle section. Recently, erosion in some coastal zones is quite serious because of excess groundwater extraction, especially along the southwestern coast. Groundwater extraction might also induce land subsidence. There are some areas near the coast which suffer serious land subsidence problems. Along the eastern coast of Taiwan, there are not many people and pollutant sources. However, the government plans to move some enterprises with high pollution, such as cement factories, to the eastern coast. We concern that the environmental problems will become serious there. (Keywords: coasts, pollution, erosion, subsidence) Introduction Most of the 21 major rivers and harbours in Taiwan are seriously polluted, especially on the western coast, where major pollutants come from harbours and rivers. The weather pattern in Taiwan also makes the situation worse; it is wet in the summer, and dry in the winter. Industrial effluents discharged from riverside factories into the almost dry river bed accumulate during the dry season. These pollutants are released to the coastal areas during the spring rainy season in large quantity, jeopardizing the mariculture environment. This paper cites conditions in Er-Jen River and Nan-Wan Bay to exemplify the tidal current process which transports pollutants along the coast. Er-Jen River is located on the southwestern coast of Taiwan (see Fig. 3), where green oysters were found (Hung and Han, 1991). Nan- Wan Bay is located in the southern tip of Taiwan (see Fig. 5), where bleaching corals were found (Fan, 1992). The long-shore current induced by the breaking waves is the major force shaping the coastal morphology. Recently, land subsidence induced by groundwater extraction also plays an important role in affecting the coastal environment in Taiwan. l.institute ofoceanography, National Taiwan University, Taipei, Taiwan, ROC.

2 Discussion There are three major factors affecting the coastal environment; they are the near-shore tidal current, long-shore current induced by breaking waves and land subsidence. The three major environmental problems along the coast of Taiwan are stated as follows: 1. Coastal Water Pollution The population is 23 millions in Taiwan, with the are about 36,000 knr'. And more than 90% ofthe population live along the western coast. In Taiwan, there are about 100,000 factories and 10 millions pigs. Most ofthe industrial areas are located on the southwestern coast. On the average the excrement of a pig is 6~8 times of a human being. The major sources of the pollutants in the coastal seas come from municipal, industrial and livestock wastewater. The above-mentioned three kinds of wastewater have almost same pollutant quantities. The tidal current is the main force dispersing the pollutants discharged from the coast. Along the western coast of Taiwan, the tidal current flows northward in the southern section, and southward in the northern section during flood tide. The current direction reverses during ebb tide (Fan, 1991) as shown in Fig. 1. The semi-diurnal tide dominates the current in the vicinity ofer-jen River (Chern, 1982). The current velocity ranges from 10 to 30 em / sec, with the current direction mainly parallel to the coastline (Su et al., 1986). The current flows in the NNW direction during flood tide, and in the SSE direction during ebb tide. Fig. 2 shows the tidal range along the western coast of Taiwan, which is highest in middle Taiwan Strait and low at both ends. Er-Jen River is located about 8 km south of Tainan. The tidal range is only about one meter. The quantity of sea water flowing in and out of Er-Jen River is small, and the discharge from the river is small except during the summer flood period. Most of the pollutants in the river flow to the ocean only during the ebb tide. N i _: ebb : flood Fig. I General tidal current patterns along the western coast of Taiwan. Since the semi-diurnal tide dominates the current in this area, the tidal current changes direction every 6 hours or so. With a tidal current velocity of 20 em / sec, 2

3 Kuang-Lung Fan we can observe that, during 6 hours' ebb tide, the polluted river water may flow to about 5 Ian south of the river. During the next 6 hours' flood tide, the polluted river water in the ocean, together with any newly discharged river water, flows to about 5 Ian north of the river as shown in Fig. 3. So, the polluted water, in general, extends to an area of about 5 Ian on both sides from the discharge source, and within about 3-4 km offshore. In fact, the water discharged from Er-Jen River is seriously polluted and it is easy to distinguish the river water from the clean sea water. Sometimes, the boundary between river water and sea water can be recognized easily even five or six hours after the river water has discharged to the ocean. Tan-Sbui Kee-Lung Hsin-Chu Tai-Chung _ Tai-Nan Kao-Hsiung Fig, 2 The average tidal ranges along the western coast of Taiwan. 120'lO'E Km I r \.'\ \ \ I I ~ 22'SD'Nf ---, Ebb tide Flood tide Fig. 3 The major area affected by the polluted water discharged from Er-Jen River during ebb tide (A), and during flood tide (B). In Taiwan, the sea water along the western coast are polluted, especially on the southwestern coast, and there are many pollutant sources along the coast. Sometimes, in one area, the sea water contains many different pollutants discharged from a variety of sources. Along the western coast of Taiwan, there are four main pollutant sources: harbours, ocean outfalls, rivers and industrial districts. In ad- 3

4 dition, there are also many other pollutant sources, such as power plants and trash dumpsites. The sea water along the southwestern coast is heavily contaminated. It has already jeopardized coastal mariculture. Han (1989) measured the copper concentration in oysters in 12 major culture areas along the western coast of Taiwan, finding concentrations as shown in Fig. 4. In general, the oyster becomes green when it contains over 500 ppm copper dry weight (Zamuda, 1984). Fig. 4 shows that in the No.10 district, located in Er-Jen River estuary, the copper content was over 4,000 ppm (also see Fig. 3) Cl QE Copper ppm-dry w.t, N t > e---' '. :it,:? TAIWAN 23' Fig. 4 The average values of copper (ppm, dry wt.) in oysters (Crassostrea gigas) collected from different culture areas (after Han, 1989). Date: July 3, 1987 Time 08:10-08:30 Air temp. ; 30'C TIDE o SCALE 1000M NAN-WAN BAY *little BAY t.t : Temp. rise with respect to background station at the same depth Fig. 5 Surface water temperature increments near the outlet of the third nuclear power plant in the morning of July 3, 1987 (after Fan, 1988). 4

5 Kuang-Lung Fan The weather type in Taiwan also makes the situation worse. On average, 76% ofthe rainfall in Taiwan is in the six-month season from May to October. The other six-month period, from November to April, is considered the dry season. The contrast of being dry in winter and wet in summer is even more evident in southern Taiwan, with even 90% of the rainfall in the wet season (Hsu and Ching, 1978). In the dry season, the river water is dirty. When the spring rainy season begins, the pollutants accumulated in the river bed are released to the coastal areas endangering the cultured oysters, clams and fishes. The third nuclear power plant is located on the ocean coast near Nan-Wan Bay in southern Taiwan (see Fig. 5). There are 179 coral species found in Nan-Wan Bay (Yang et al.,1982). Corals are abundant along the coastline near the third nuclear power plant. The No.1 and No.2 units there began operating in July 1984 and May 1985, respectively. The current near the outlet area flows towards the SW for most of the time during the flood. During the ebb, it flows sometimes to the SW, and sometimes to the NE, but with a predominantly SW direction (Liang et ai., 1978). There is also some evidence to indicate that sea water near the outlet might recirculate to the intake area (Su et ai., 1980). For this reason TAIPOWER located the intake to the northeast of the outlet (see Fig. 5). TAIPOWER also constructed a 120 ill offshore surface discharge to avoid recirculation. The second unit of the third unclear power plant began operating in May Unfortunately, the first unit caught fire in July 1985 and stopped operation until January Two units operated simultaneously again since January In early July 1987, almost all the coral living in a water depth less than 3 m in Little Bay was bleached. Fig. 5 shows the temperature increment near the outlet of the third nuclear power plant on July 3, The data, supplied by the Radioactive Laboratory, TAIPOWER, were collected from 8:10 to 8:30, during the flood tide. The surface water temperature at a background station near the intake is 27.9 C, the area oftemperature increment >4DC extends from the outlet to m offshore in the southern and western directions. In this case, the surface water temperature in Little Bay, on the western side of the outlet, exceeds 31.9 C. In some areas, the temperature exceeds 34 C. The thermal discharge water, for the most part, lies in the surface 3 m layer and will damage or kill corals in shallow waters near the shoreline. This first serious incident was found in early July 1987 occurred during the first summer when both nuclear reactors ofthe third nuclear power plant were operating simultaneously (Fan,1988). In the summer of 1988, the thermal plume from the third nuclear power plant damaged corals in a more extended area. In May 1989, TAIPOWER installed more pumps to increase cooling water by 10% in volume. Since then, most of the bleached corals began to recover (Huang et ai., 1991; Fan,1992). 2. Coastal Erosion When waves come close to the coastline, where the water depth becomes shallow, then waves break. If the propagating direction is not perpendicular to the coastline, then there will be a long-shore movement generated as the wave breaks. This long-shore current is strong enough to displace sand near the shoreline. The 5

6 sands then drift along the coast area. On some coasts, the sands accumulate to form reclaimed land, while elsewhere the beaches are eroded. The major waves, mainly induced by wind, approach northern Taiwan from the N-NNE direction, and in southern Taiwan from the SSW-SW direction. These major wave directions in Taiwan Strait will induce the long-shore current to flow southward in northern Taiwan, and northward in southern Taiwan (Lee and Hou, 1979). The major wind and sand drift directions are shown in Fig. 6. This current can not only transport the pollutants in sea water near the shore, but also move the coastal sand to change the coastline morphology. Generally, the coasts have been eroded in the northern and southern sections of the western coast, while in the middle section, the drift sands, either from the littoral zone or suspended particles in the river discharges, are deposited, reducing water depth, or even forming new land. In the past two decades, coastal erosion has become serious, especially along the western coast (see Fig. 7). Most areas have coastal dykes to protect the land. Fig. 7 also shows six districts with serious erosion problems, where even the coastal dykes are destroyed frequently (Chang, 1993; Fan, 1995). Among the six districts, only the No.1 district along the SE coast of Taiwan has long been an erosion coast because it gets large wave energy, frequently from the SE direction especially during the summer typhoon season. The main reasons for recent serious coastal erosion for the other five districts can be attributed to: (1) construction of many dams upstream in the rivers in the past 20 years, reducing the transfer of some sand to the littoral zones; (2) over-extraction of groundwater by fishermen for mariculture making the coastal zones unstable and inducing erosion (to be described below). The government already began to move some enterprises to the eastern coast, and broaden some coastal roads. At some sections of the coastal roads, we have to put cement blocks to protect them from erosion. We expect the environmental problems will become serious there in the near future. N I N i ~pa-li ' I TOil-Cheng ;/3 TAIWAN STRAIT I TAIWAN TAIWAN sci Ma-Sha-Kou 6' Ko-Tsai-Liao South T.i-T"" Il 'j1 : Erosion Coast ~ Serious Erosion Fig. 6 The major wave directions (--~ ) in Taiwan Strait and the long-shore current directions( --? ) along western Taiwan coast. Fig. 7 Coasts with erosion problems in Taiwan (after Chang, 1993). 6

7 Kuang-Lung Fan N Taip~i basinr area =252 square km drnax =2.24 rn '-...~-... \ " ị --c,>i.--..// i- /.---( =-----,;;--...".-..,.----=-I'.~..:>: ( '(-..,> / j i ':::, TAIWAN ( i......j.~.j 1. /J -: r.>,.r\, /i,,/ i \'"-../ i ( J) I. i.'.. subsidence area...~-./ coun ty boundary Fig. 8 The map of land subsidence districts in Taiwan (after Tseng and Yen, 1993). 3. Land Subsidence Since 1983, the impact of groundwater extraction for mariculture has caused a serious land subsidence problem along the littoral zone in Taiwan (Tseng and Yen, 1993)_ There are eight districts which suffer from serious land subsidence problems. Among these, only the Taipei basin is located inland. The other seven are located along the littoral zone in seven counties (see Fig. 8). Fig. 8 shows that the biggest subsidence area covering three counties, Chang-Hua, Yun-Lin and Chia-Yih, is located in the middle part of the western coast, an area reclaimed in the last one hundred year. Two districts with a subsidence depth of over 2 metres are the No.8 Ping- Tung district in southern Taiwan, where the maximum subsidence depth is 2.54m, and No.2 Taipei basin, and located in northern Taiwan where the maximum subsidence depth is 2.24 m. The Government has restricted pumping of groundwater in the Taipei basin in 1978, since then the land has subsided no more than 1 em a year (Chang, 1993). Groundwater extraction has not only caused land subsidence, but also resulted in a progressive deterioration of groundwater quality. Sea water intrusion was first detected in the Yun-Lin destrict, now the largest land subsidence area in Taiwan (see Fig. 8). The county has more than 6,000 deep wells for pumping groundwater, most for fishery business (Tsao, 1983). Once the land subsidence occurs, even if the groundwater level recovers in the future, the ground-layer will not be able to recover, and will lead to the loss of national land resources, the exhaustion of groundwater resources and problems of sea water intrusion and flooding of coastal villages. 7

8 Almost every year in the summer typhoon season, storm surges often destroy the coastal dykes, and sea water floods the coastal villages, especially along the western and southwestern coasts (Fan, 1993). In some villages, the flood water rises to 2 meters deep or more during flood tide. Some villages even have to evacuate people to other safe places. These phenomena have happened almost every year during the summer typhoon season, especially in the No.4, 5, 6 and 7 districts. The total land subsidence area is about 1,164 km"; the area of Taiwan is about 36,000 knr'. This means that 3.23% of Taiwan suffers from land subsidence. In fact, most oftaiwan is mountainous. Plains have a total area ofonly 11,000 krrr', so that land subsidence covers 11 % of the productive plains in Taiwan. In the No.8 district (see Fig 8), the land subsidence phenomena are even more peculiar; some old houses and tombs subsided into the ground, while some newly-built houses were lifted 1 to 3 meters above ground. Concluding remarks When pollutants are discharged or dumped near coastal areas around Taiwan, they usually wander alongshore back and forth. Marine pollution has already jeopardized the mariculture environment along the western coast. It is highly undesirable that industrial wastes be discharged to the ocean or rivers on the western coast. It has been suggested that the mariculture beds be moved to eastern Taiwan where most coastal areas are still not polluted. However, Taiwan is a small island. If we continue to pollute the land, rivers and ocean or over-use the coastal lands, sooner or later, we will find no other places in Taiwan for mariculture or for a good living environment and our natural land and groundwater resources will be lost. The marine pollution not only lowered our living standard, but also threatened our health. In order to improve our environment, we should reduce the quantity of all kinds of wastewater, and handle them well before they are discharged to the rivers, habors or ocean. Besides, we should also manage our coastal development better to avoid any bad results. References Chang, S.c. (1993) Land-subsidence-Water resources problem in Taiwan. Proceedings ofsymposium on Sustainable Development of Water Resources, Taipei, volume 3: pp (in Chinese). Chern, C.S. (1982) Current and wave measurement in the vicinity of Hsien-Da-Kang and Tung-Kang (continued). National Taiwan Univ. Special Publ. No. 39, 77 pp (in Chinese). Fan, K.L. (1988) The thermal effluent incident of the third nuclear power plant in southern Taiwan. Acta. Oceanographica Taiwanica, 20, Fan, K.L. (1991) Current affecting the marine environment along the Taiwan southwestern coast. Proceedings of International Marine Pollutions Symposium, Tainan, Taiwan, pp Fan, K.L. (1992) The thermal discharges from nuclear power plants in Taiwan. Chemistry and Ecology, Vol. 6: Fan, K.L. (1993) The coastal environmental status and problems in Taiwan. Engineering Environment 5:1-27 (in Chinese). Fan, K.L. (1995) The coastal environment characteristics of Taiwan. Chemistry and 8

9 Kuang-Lung Fan Ecology, Vol. 10: Han, B.C. (1989) A study of copper species, distribution, bio-accumulation and complexing capacity in the marine environment. Ph.D. Thesis, Institute of Oceanography, National Taiwan University, 216 pp (in Chinese). Hsu, H.H. and S.H. Ching (1978) A discussion on the river characteristics and conservation of water resources in Taiwan. Proceedings ofthe Management of Watersheds and Rivers Workshop, Taipei, Taiwan, pp (in Chinese). Huang, C.C., TC. Hung, and K.L. Fan (1991) Nonbilolgical factors associating with coral bleaching events in the shallow water near the outlet of the third nuclear power plant. Acta. Oceanographica Taiwanica, 26, Hung, T'C. and B.C. Han (1991) Green oysters: Bioavailable copper and copper assimilative capacity in sea water. In Environmental Protection of Coastal Ecosystem (Eds. Hwang, D.F., Yoshida, T, Chen, C.C., Wu, M.Y and Jeng, S.S.) Council ofagriculture, Taipei, pp Lee, J.P. and H.S. Hou (1979) The study of littoral drift vs wave energy along the Taichung coast from Ta-Chia River to Ta-Tu River. Proceedings of the 3rd Ocean Engineering Workshop, Su-Ao, Taiwan, pp (in Chinese). Liang, N.K., S.L. Lien, W.e. Chen and H.T. Chang (1978) Oceanographic investigation in the vicinity of Ma-an-san---Nan-wan Bay. Inst. of Oceanogr., Nat 'I Taiwan Univ. Special pub!. No. 18, 207pp (in Chinese). Su, J.e., TC. Hung, YM. Chiang, TH. Tan, K.H. Chang, R.T Yang, LM. Jeng, K.L. Fan and H.T Chang (1980) An ecological and environmental survey on the waters adjacent to the nuclear power plant in southern Taiwan: The progress report ofthe first year study. SCOPE/ROC, Academia Sinica, Special Publ. 7, 115 pp (in Chinese). Su, r.c., TC. Hung, YM. Chiang, TH. Tan, C.C. Chen, K.L. Fan and YY Ting (1986) An ecological and environmental survey on the waters adjacent to Yung-An L.N.G. Station. SCOPE/ROC, Academia Sinica 46, 116 pp (in Chinese). Tsao, YS. (1983) Change of groundwater quality in the Yun-Lin basin due to over-pumping. Relation of Groundwater Quantity and Quality (Proceedings of the Hamburg Symposium, August 1983) IAHS Publ. no.146, pp Tseng, R.H. and C.P. Yen (1993) The study of regional land subsidence problems in Taiwan. Proc. 6th Conf. on Environmental Planning and Management in R.0. C. Taiwan. pp (in Chinese). Zamuda, e.d. (1984) The bioavailability of copper to the American oyster, Crassostrea virginica. Ph.D. Thesis, University ofmaryland, 213 pp. Yang, R.T, C.F. Dai, S.Z. Yeh, C.L. Sun, F.Y. Su, S.Y Liao, YK. Hsu, C.L. Chang and TY Chou (1982) Ecology and distribution of coral communities in Nan-Wan Bay, Taiwan. Inst. of Oceanogr., Nat'l Taiwan Univ. Special pub!. No. 40, 74pp (in Chinese). 9

10 台灣沿海環境的一些問題 范光龍 l 摘要 台灣治海環境有三個主要的問題 : 海水污染 海岸侵蝕與地層下陷 o 台灣面積詣, 000 平方公里, 但人口超過 2 千 3 百萬, 沿海污染物主要來自都市 工業及畜牧三種廢水, 很多廢水末經妥善處理就直接排入治海 海港或河川, 而海港或河川的污水最終還是會流到沿海 潮流是擴散治海污染物的主要力量, 污水一般涵蓋排放口左 右各 5 公里, 離岸 3~4 公里內的海域 波浪破碎後引起的治岸流是改變海岸地形的主要力量, 在台灣西海岸, 北半部的治岸流往南, 在南半部則往北, 一般而言, 近百年來, 西岸南 北兩段屬侵蝕海岸, 中間段則屬堆積海岸而形成海埔新生地, 近年來由於沿海超抽地下水, 有些海岸受嚴重侵蝕, 在西南治岸尤其嚴重, 超抽地下水還在有些沿海地方造成地層下陷的嚴重問題 在台灣東岸, 人口 污染源都較少, 然而政府計畫把西岸的水泥等高污染產業移往東岸, 我們擔心台灣東岸的沿海環境問題會變得更嚴重 ( 關鍵詞 : 海岸 污染 侵蝕 地層下陷 ) I. 國立台灣大學海洋研究所 l nυ