| Summary: | 碩士 === 國立臺灣大學 === 環境工程學研究所 === 97 === With the increasing concern of sustainable development, sustainable engineering has become the approach for the development or remediation projects. Ecological engineering is one of the sustainable engineering approachs which integrates the needs of conserving with natural environment and the needs of human society.
Food chain manipulation is one kind of ecological engineering, it mainly uses autotrophic and heterotrophic microorganisms, aquatic plants, planktons and so on to improve the water quality and remove organic and inorganic matters in water. A research team has been investigating a biomanipulation approach in Yangming Reservoir in Kinmen County. To change the food chain structure, clams (Anodonta woodiana) were put into the reservoir to purify water since July of 2008. Trapping the settling materials, collection of sediment, model simulation as well as water quality monitoring were applied, to find the effectiveness of water purification and removing contaminants with calms.
The results showed that chlorophyll a, total phosphorus and total dissolved phosphorus were decreasing with time; however, they were almost homogeneous spatially by the strong horizontal mixing. Sediment analysis showed that variation of the concentrations of total phosphorus, organic carbon and Kjeldahl nitrogen were mainly due to the internal cycle of materials in the reservoir, that is, related to the death and settlement of algae and zooplanktons, and the mineralization and decomposition of benthic organisms. The results of four settling fluxes measured showed that no obvious difference at A and B points. However, the concentrations of total phosphorus, organic carbon and Kjeldahl nitrogen of settling matter were much higher than those in the sediment, it means that settling matter in Yangming Reservoir are mainly composed of the death and settlement of algae, zooplanktons and organic particulates.
The releasing flux of the phosphorus(P) through the boundaries of bottom sediment in an aquarium in the laboratory were 3.36 and 1.66 mg m-2day-1 in anoxic and oxic conditions, respectively, in Yangming Reservoir. With the comparison between the settling flux of P and the releasing flux of P, it was found that the settling flux of P were all higher than the releasing flux of P in September and October, so sediment was a sink of the pollutant at that time. The settling flux of P was roughly equal to the releasing flux of P from November to March. The settling and releasing flux of nutrient was in balance at that time. Furthermore, when using the settling fiux of P at point A to calculate the mass balance of P, it is able to accurately predict the variation in the amount of P.
This study found that the filtering rate of clams were only 0.07 and 0.08 L/hr from 10:00 am to 2:00 pm; it could attain to 0.37 and 0.18 L/hr in 2:00 pm to 5:00 pm and 5:00 pm to 6:00 pm, respectively. It also descended to 0.06 and 0.08 l/hr from 6:00 pm to 10 am. It indicates that the filtering rate of clams is related to the physiological time.
After adding clams in July and August, the predicted concentration of total P is 126.5 μg/l and 79.1 μg/l in upper and lower water body, respectively. Comparison of the concentrations in the field and model simulated, the simulated concentration of total P in upper water is much underestimated comparing to the the measured concentrations in the field. The simulated concentration of total P in lower water is much overestimated comparing to the the measured concentrations in the field.
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