生物操控法對湖庫營養鹽通量的影響 -以金門陽明湖為例

The effects of biomanipulation on the nutrient flux in a subtropical reservoir

吳柏勳(Bo-shiun Wu)

指導教授 ： 吳先琪

國立臺灣大學/工學院/環境工程學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.01360

摘要

隨著國人永續發展意識的提升，環保永續的工程方法成為了目前開發與整治計畫所必須考慮的方法。生態工程即是結合維護自然環境與符合人類社會需求所設計的永續工程。生物鏈法為生態工程的一種，主要係利用自異營性微生物、水生植物以及浮游動物等生物系統之控制，進行水中有機物與無機物的移除及水質改善。中研院之研究團隊以位於金門縣地區之陽明湖水庫為研究對象，自民國97年7月開始，以改變生物鏈結構的方式，放養圓蚌於湖庫中，進行水質的淨化。本研究配合該生物鏈工法，佐以沉降筒放置、底泥採集以及模式模擬等方法，更深入地了解圓蚌對於淨化水質以及相關的污染物移除的成效。
研究結果顯示，水質項目中葉綠素a、總磷以及溶解總磷，在時間的分佈上均有下降的趨勢，然而在空間分佈上，A、B兩點則幾乎相同。表示陽明湖受到水平混和作用的影響極大。陽明湖底泥分析結果顯示，因陽明湖地處於半封閉的環境條件，外部的污染負荷幾乎只在降雨沖刷兩岸才會發生，使得底泥總磷濃度主要是受到水庫內部污染的循環，亦即與藻類死亡沉降與底棲生物礦化分解釋出磷的作用有關。沉降物通量4次測定之結果顯示，A、B兩點並無明顯之趨勢。然而分析沉降物之總磷、有機碳以及凱氏氮含量，發現均高出底泥甚多，表示陽明湖之沉降物多為上層水體藻類、動植物死亡屍體與有機性顆粒之沉降造成。
底泥磷釋出測定之結果，厭氧狀況下的平均底泥磷釋出率為3.36 mg/m2/d，好氧狀況下的平均底泥磷釋出率為1.66 mg/m2/d。比較磷沉降通量與底泥磷釋出通量，發現9月與10月之磷沉降通量，均大於底泥磷釋出通量，故此時底泥為污染物的匯；11月至3月之磷沉降通量與底泥磷的釋出通量大致相當，故推測此時陽明湖之營養鹽上下通量係維持平衡。另外，以A、B兩點之磷沉降通量平均值計算水庫磷質量平衡時，幾乎能夠準確地預測磷的變化量。
測定圓蚌濾水率的實驗中發現，在早上10點至下午2兩點時，圓蚌之濾水率僅0.07與0.08 l/hr；下午2點至5點與5點至6點的濾水率分別可達0.37與0.18 l/hr；下午6點至隔天早上10點的濾水率，下降至0.06與0.018 l/hr。表示圓蚌濾食行為與生理時間及水中葉綠素a濃度相關。

模式模擬陽明湖水庫7、8兩月放入圓蚌後之總磷濃度變化，上、下層磷濃度分別為146.1 μg/L及79.1 μg/L。與現地觀測值相較，模式模擬之上、下層水磷濃度均低估現地觀測值許多。

關鍵字

生態工程 ； 生物鏈法 ； 沉降物通量 ； 底泥磷釋出率 ； 濾水率

並列摘要

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.

並列關鍵字

Ecological engineering ； Food chain manipulation ； settling flux ； releasing flux of the phosphorus ； filtering rate

參考文獻

Appan, A., Wang, H., 2000. Sorption isotherms and kinetics of sediment phosphorus in a tropical reservoir. Journal of Environmental Engineering. 126, 993-998.

Boström, B., Anderson, Jens M., Fleischer, S., Jansson, M., 1988. Exchange of phosphorus across the sediment interface. Hydrobiologia. 170, 229-244.

Bergen, S.D., Bolton, S.M., Fridley, J.L., 2001. Design principles for ecological engineering. Ecological engineering. 18, 201-210.

Coughlan, J., 1969. The estimation of filtering rate from the clearance of suspensions.Marine Biol. 2, 356-358

Conover R.J., 1962. Assimilation of organic matter by zooplankton. Limnology and Oceanography. 11, 338–354.