The distribution of aquatic ecosystems along Zhonggang River is affected by mainly water quality, salinity, water temperature, bed material, and river patterns. The distribution of terrestrial animals along Zhonggang River is most affected by mainly land utilization and the degree of naturalness of vegetation, while land utilization and the degree of naturalness of vegetation are affected by altitude, landform, geology, climate, traffic, and other factors.
The composition of bird species at the estuary area is greatly affected by the season, and usually the bird composition is more abundant at the end of fall and during the beginning of winter to spring, which is the duration for migration, including many kinds of sandpipers, charadriidae, heron, anatidae, and other kinds of migratory birds and birds of passage.
Due to the high development, the mammals at the midstream and downstream areas are mostly bats, small Insectivora, and rodents, and sometimes Formosan hares can be found on grass-covered lands that are less bothered by people. Because the degree of naturalness of vegetation is higher at the midstream area and human interference is relatively lower, it is more possible to find some mid-sized mammals.
The reptiles at the developed areas of the midstream and downstream are mostly small lizards, japaluras, and skinks that prefer an open environment with sunshine and geckos that adapt to artificial buildings, and snakes and terrapins can sometimes be seen at rivers and in barren grasslands. The investigating range of amphibians is mainly the frogs of anura, and the number of species of frogs at the midstream and downstream is usually less because they are affected by the development and most of the species are those adapting to farmland. The composition of the frogs is more abundant in the midstream area.
Opsariichthys pachycephalusOpsariichthys pachycephalus
Butterflies are affected by agriculture more at the midstream and downstream environment usually because the kinds of crops or green manure are unvaried. Therefore, the butterfly species are few but the amount of butterflies is large. Moreover, part of the composition of butterflies is the butterflies that use the grass growing naturally along the farmland and road as food plants and the butterflies that have better migration and larger population because they are less limited by the distribution of food plants in areas. Due to the higher diversity of vegetation in the midstream, the diversity of the butterfly species also is increasing. Large numbers of wandering gliders of dragonflies usually emerge at the estuary of the downstream to midstream and upstream at the end of summer to fall.
On investigating migratory species in this project, the longitudinal river habitats are blocked by transverse artificial structures (such as ground sills, check dams, and dams) consecutively, so some small fish and shrimp might belong to land-locked species. Moreover, the released group of Japanese mitten crab is also found when visiting the investigated sites. Seeing from the investigation results, we can find that the distribution of the current migratory species in the drainage of Zhonggang River might be limited by the transverse structure at the river.
On water quality analysis, the pollution level of rivers is lower (such as Nanpu Bridge, Shouchang Bridge, Beipu Cold Spring, Tong-an Bridge, Penglai River Natural Ecological Conservation Zone, the junction of Nanhe River and Donghe River, Donghe suspension bridge, and so on) at the part closer to the upstream and the surrounding area with a lower development level, while the pollution level of the water level is slightly higher (such as Wufu Bridge, Toufen Bridge, Ping’an Bridge, the junction of Nangang River and Zhonggang River, Shiliaokeng Bridge, and so on) at the sampling stations with higher development level at midstream and downstream.
As for fish, the Taiwan shoveljaw carp representing the environment with unpolluted water quality is mainly distributed at the Nanzhuang River branch (Tianmei weir), Daping River branch (Beipu Cold Spring), and Nanhe River branch (Penglai River Natural Ecological Conservation Zone). The distribution of Taiwan torrent carp representing light polluted water quality is wider than that of the Taiwan shoveljaw carp, so besides Wufu Bridge, Toufen Bridge, the junction of Nangang River and Zhonggang River, and Shiliaokeng Bridge, the fish are also found in other sampling stations.
The emerging of part of terrestrial animals is related to the quality of the river. Seeing from the current investigation results, the index species described above are found more easily at the sites closer to the upstream, such as Beipu Cold Spring, Shouchang Bridge, Penglai River Natural Ecological Conservation Zone, Tong-an Bridge, and so on. Furthermore, the better the environment, the more the group number is, and the abundant estuary wetland ecology is still kept around Wufu Bridge at the estuary of the downstream.