| 英文摘要 |
This project was a continuity of ‘‘Eutrophication control for reservoir water quality by ecological engineering”, focusing on the topic of improving the water quality by means of food chain technology. Following a review of the literatures, various methodologies, results, limitations and conditions for employment the food chain technology were summarized. For practicing, the Hsin-shan water reservoir was chosen as the experimental site. Over this year, sampling in three seasons, were done to collect the data including physico-chemical variables of water quality, compositions and structures of planktons, benthos, invertebrates and fishes in the water reservoir. The results showed that this reservoir was in meso- to eutrophic state of -mesosaprobity indicated by phytoplankton as well as zooplankton. Various forms of pollutants originated from Keeling River were the main factors resulting in the eutrophication of this water reservoir. Phosphate was identified as the key nutrient related to the growth of the primary producer. In zooplankton assemblages, Cladocera such as Daphania, Bosmin, and Diaphaosoma were the most dominant genus over others. Of Crustacea, both the Cladocera and Copepoda dominated, up to 2002, 1940, and 123 at three different localities. There was little change in the amount and composition of insects and benthos, suggesting that a low density and low seasonal succession of them. The fish assemblages were composed by some common species such as Sinibrama macrops, Hemiculter leucisculus, Oreochromis sp., Gambusia affinis, and Rhiogobius spp. Of shellfish, Sinotaia quadrata dominated. The feeding of fishes was investigated from the kind of ingested food in stomach. All of the data suggested that this reservoir was a mature ecosystem.
In late summer, from August to October, thermo-stratification occurred. This has resulted in oxygen deficiency with dissolved oxygen lower than 2 mg/L in hypolimnic layer. The Microcystis-blooming in spring was considered to be a result of increase in nutrients owing to the upwelling from the anaerobic hypolimnion occurred in late-winter, March to April. In addition, the anaerobic environment was disadvantageous for survival of zooplankton as well as benthos.
Some strategies of bio-manipulation, such as wet land, submerged macrophytes, control of herbivorous fish, and shellfish-culturing, were suggested as the applicable technologies to this water reservoir. Particularly, fishes such as Ctenopharyngodon idellus and shellfish such as Anodonta woodiana, were recommended as the potential culturing organisms for removal of algae with pearl as by-product in the future. The wetland was suggested as the potential methods to remove both the phosphorus- and nitrogen- containing pollutants originated from Keelung river. The runoff from the surrounding of the reservoir can be lowered by floating island vegetated with water plants and culturing of shellfish. Furthermore, moderate hypolimnic aeration without destroying the thermo-stratification was suggested to enhance the dissolved oxygen of hypolimnion and to inhibit the release of nutrients, particularly phosphate.
The simulation of the variables of water quality by Vollenweider and WASP water quality models gave the similar tendency for both the measured and simulated data, suggesting that either model was applicable to this aquatic environment. The simulation by Ecopath model indicated that the aquatic ecosystem in this water reservoir was in mature status. Basing on the combined model of WASP-Ecopath, it was attempted to estimate the amount of mussels required for improving the water quality of this water reservoir.
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