美工圖片   Investigation of Current Status in Dong-gang River System (The 7th River Management Office, WRA, MOEA. April, 2006)

The regulations of our investigation is based on the River Planning Section formulated by Water Resources Planning Institute, WRA, MOEA, The phase of the investigate plan are two years and focus on the entire environment on main stream and branch of Donggang River. The investigations are including the fundamental data of physical environment, fauna and flora of the river, and use Geographic Information System to make an ecological database and website search system. To provide water conservancy engineers the reference materials to manage, plan and design to Donggang River. The achievements of the investigation are above.

Donggang River basin

Donggang River is located in Taiwan’s Pingtung County. It is the most populated and culturally diverse region on the Pingtung plains. Officially the river system covers around 767.07km2, with agriculture being the most common industry. There are a total of 25 branches to the Donggang River system that are currently crossed by 16 bridging structures. Most of the structures on its branches are made from reinforced concrete, though the main river itself still retains much of the original ecology and characteristics. Due to the concreting of river branches, their ecology and characteristics have become less developed. The river flood plains are usually used for agriculture and fisheries. The upper reaches of the Donggang River system are of the mountain river type, with many picturesque waterfalls and giant boulders. The middle and lower reaches used to be part of the Yiliao River, which in ancient times created a network of crisscrossing waterways. During wet periods, the Donggang River system has an annual runoff volume of around 956.98 million m3.

The spatial usages of rivers around sampling stations of the Donggang River basin are mainly for the works of agricultural and fishery industries. In the aspect of agriculture, the majority of cultivations are fruit farms and areca palms. The establishments of fishponds are the major usages of river spaces for the fishery

industry. Therefore, the types of leisure activities around these areas are extremely multiple, mainly for fishing, jogging, and bicycle riding, and the periods of engaging leisure activities chiefly take place during daytime and evening.

In the 2 year investigation, the animal survey have recorded 26 species from 15 families of fish were found in main stream, of which 10 species were estuarine species, 5 were endemic species, and 6 exotic species. Survey in the tributaries in the branch yielded 21 species from 11 families were found, of which 3 were estuarine species, 6 were endemic species and 4 were exotic species. Crustaceans have recorded 15 species from 6 families in main stream, of which 10 species were estuarine species, 3 were endemic species, 1 was exotic species, and 5 species were totally freshwater species. Survey in the tributaries yielded 8 species from 4 families, of which 3 were estuarine species, 4 were endemic species, 1 was exotic species, and 5 were totally freshwater. Furthermore, 11 species from 8 families of mollusks were found in the main stream, and 8 species from 5 families were found in the tributaries. Physa acuta, an exotic species, was the most abundant species and was discovered mostly in polluted areas.

Macrobrachium asperulum

 

Phytoplankton and periphyton were abundant in the main stream of Donggang River. Fixed stations such as Donggang bridge and shingshe bridge were extremely eutrophic year long, whereas Lungdung bridge was less eutrophic. Most of the phytoplankton found here were can usually be found in polluted waters, species such as Microcystis and Trichodesmium were indicators of polluted waters. In the tributaries, fixed stations such as Rende bridge and Jiaping bridge were highly eutrophic, whereas Jhide bridge, Wanan bridge and Chingshuei park were cleaner. Similar to the main stream stations, species found at the tributaries were those that can survive in polluted waters.

There were 33 species of aquatic insects found at the main stream of Donggang River, with a total abundance of 557 individuals. Order Odonata was the most diverse group, with 5 families and 13 species found, with a total of 87 individuals. Order Diptera were found with 3 families, 5 species and 321 individuals, followed by orders Ephemeroptera (4 families, 4 species, 49 individuals) and Hemiptera (3 families, 4 species, 63 individuals). Eight orders, 26 families, 35 species and 833 individuals of aquatic insects were found at the tributaries. Diptera was the most diverse order, with 6 families, 8species and 301 individuals. Ephemeroptera was the second with 4 families, 6 species and 157 individuals, followed by Hemiptera with 4 families, 5 species and 321 individuals. On the Ground we have recorded 103 species of Insects, 105 species of Birds and 11 of them were listed as protected species, 13 species of Mammals and 2 of them were listed as protected species. Amphibians and reptiles have recorded 14 and 30 species, and 6 and 5 species were listed as protected species, respectively.

The vegetation around the Donggang River basin, after the searcher finished the survey, can be divided into four types: the plant society of cultivable lands, the shade and gardening trees, the graze lands, and the secondary forests. Through statistic analysis, there are 189 species in the first year, and 167 in the second year. Most of these plants are attributed as familiar species around the low altitude, and their populations are usually large and stable, no species is rare and need to be protected in nowadays.

In this project, to support the decision making process for stream habitat restoration and management, an analysis model was introduced to integrate stream spatial, chronological, physical, chemical and biological information, so-called 5S model. Based on the investigation results, five S-indexes (System conditions, Stream hydrology, Structures, Substances and Species) for selected specie, Macrobrachium asperulum, were evaluated to describe the overall status for their living conditions. Thus, the suggestions of habitat restoration in Donggang River have been accomplished from this two years project. The suggestions such as to improve water quality in the midstream reach, to connect the stream corridor and bed material continuity were immediate applications in the practices of river environment management.