| Summary: | 博士 === 國立中興大學 === 水土保持學系所 === 97 === Fazih River which located in west side of Taichung basin, while Tou-Bian-Keng Creek at southern-east side, and Mu-Dan Creek which located at Swan-Shi, Taipei county were chose as study areas in this study. By using SPOT satellite image analysis to explore landscape structure changes during different periods, and select record stations among basins to conducting water quality and fish survey, in order to exploring vicissitude and causes of environmental transformation. The study results are extracted as follow:
According to SPOT satellite images(2000-2008)analysis, the developed land is the most major land use(49% of the whole watershed areas), and the expansion of developed land is higher than other land use, while Tou-Bian-Kang(2003-2007) and Mu-Dan(2004-2007) Creeks are mainly occupied by woodland, yet developed land use shows increase trends according with urban expansion. Mu-Dan Creek has increase in farm land while Tou-Bian-Kang Creek shows opposite trend due to bloom of tourism industry(substituted by building land). The changes of indicators such as NP、MPS、MSI、MPFD and MPI of landscape structure index indicated that scatter distributed landscape of Fazih River and Tou-Bian-Kang Creek watersheds were effected by the change of developed land and farm land, and the shape of patches are gradually transform to regular and fracture. The NP and MPI of Mu-Dan Creek show decline while MPS shows increase trends.
According to water quality analysis of three streams, Fazih River located at plain urban area has poorer water quality and higher change then the other two Creeks due to pollutant influx. While Tou-Bian-Kang and Mu-Dan Creeks are located at higher elevation has result in lower human impacts, the water quality influence are mainly from temperature difference and rainfall caused by seasonal changes. Further, the analysis of water quality assessment index of Fazih River has show that the changes of RPI(river pollution index) and WQI8(water quality index) at F2(Tung-Hai Bridge)and F5(Chi-Chen Bridge)were influenced by operation of Central Taiwan Science Park in Taichung(with 1.5km in distance from F2 station) and neighbor building land development since latter half of 2004, the water pollution of F2 began severer than F5, the most turning point occurred at March 2005, but after that, compare to F5, the RPI shows higher increases rate, on the other hand, the WQI8 shows higher decrease rate, both indicated the deteriorate in water quality.
Base on fish survey in Fazih River, tilapia(exotic species) is the superiority specie because of higher pollutant endurance, and show opposite trend with Rhinogobius candidianus(endemic species). Owing to limitation of carrying capacity of ecological habitat, when exotic species invade severely, it will threaten the population of endemic species. The amount and distribution of endemic species both in Tou-Bian-Kang and Mu-Dan Creeks are superiority, and has lower pollutant endurance fish. This study also figure out that torrential rain will cause negative effect to fish richness, lower segments(with higher flood peak) are higher than upper ones. precipitation more than 200mm/day(torrential rain level) will obviously decrease fish amount, however, water pollution will cause decrease both in richness and diversity of fish.
By using IBI(index of biotic integrity) to evaluate quality of aqua-habitat environment of three streams has indicated that IBI value of Fazih River are between very poor to fair, which shows human activity interference, exotic species invade, water pollution and torrential rain effects are main factors which deteriorate environmental quality of Fazih River. Tou-Bian-Kang Creek, due to less of human activity interference and environmental diversity of watershed(including higher elevation and slope variation of stream bed), the IBI values are between good to poor, while Mu-Dan Creek possess poor to good in IBI values, yet poor values are obviously higher than good values. The results has illustrated that Mu-Dan Creek is much worse than Tou-Bian-Kang Creek in habitat quality, although two Creeks are both lacated at suburbs. The main reason is that Mu-Dan Creek suffer from typhoon and northern-east monsoon, and leading to torrential rain impacts. In addition, Mu-Dan Creek is rife with concrete works, which cause unstable situation more severely than Tou-Bian-Kang Creek.
By following the interrelation analysis results of landscape, water quality and fish amount, those indicated that aqua-habitat environment of Fazih River is affected by the increase of developed lands, yet the decrease of forestry area will also reduce both of endemic and exotic species in Fazih River. In addition, because of lacking of forest to preserve and filtrate water, small scale change in land use will cause relatively higher impact. Although Tou-Bian-Keng Creek and Mu-Dan Creek are located at suburbs, due to expansion of land use, woodland were reclaim to residential or economical crops uses, has also injure nature environment and aqua-habitat.
In general, satellite images are available for monitoring landscape transformation of watershed, thus to reflecting aquatic environment change of streams indirectly. The analytic results are useful for soil conservation management works. Further, maximum rainfall intensity of 200mm/day can be used as critical value of fish persistence. To mitigate man-made interferences on the rehabilitation of fish, the protection tasks such as temporary close stream usage are necessary as if fish resilience can not reach original conditions before torrential disturbance. The IBI assessment standards which are developed in this study are available for conducting field survey and analysis in winter to judgment of fish resilience, and used to evaluating the necessity of protection strategies.
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