河川高流量期磷負荷推估方法之研究

Estimation of Phosphorus Loading in Rivers during High Flow Periods

劉紀宏(Jih-Hung Liu)

指導教授 ： 林正芳

國立臺灣大學/工學院/土木工程學研究所/博士(2013年)

https://doi.org/10.6342/NTU.2013.01026

摘要

臺灣的水庫均有承受到營養鹽過盛引發藻類生長，而導致水庫優養化之隱憂，對於磷負荷量之控制成為了維持水庫水質的最重要課題，許多在濱水從事茶園或果園等的農業活動在水庫的上游集水區進行，其所產生的營養物包含磷都是典型會在高流量時期會沖刷進入河川的污染物，每年大有約70∼90%以上的磷在這個時期藉由河川流入水庫。暴雨對地面的沖擊常會造成土壤沖蝕而引發河川中之懸浮固體物濃度之暴增，而顆粒態磷也是在這個期間被沖刷進入河川，使得顆粒態磷的含量成了高流量期間河川中總磷之主要成份。
本研究於2006年在翡翠水庫上游魚逮魚堀溪集水區上之大林橋為主要研究採樣地點，本研究對於水樣之吸脫附動力研究中，發現水質樣品在保存16個小時以後，其泥砂對於磷之吸、脫附作用可以達到平衡，而在高流量時期以拉格密爾等溫吸附模式可以得到較佳顆粒態磷之模擬成效，另外相關資料也用於推估0609暴雨及碧利斯颱風期間之高流量期間所產生之總磷負荷量佔了2006年全年總磷負荷量之0.7%及28.8%，可見高流量期間之總磷負荷量著實佔了全年總磷負荷量中很重要的一部分，另就整場暴雨期間之若以河川中之採樣資料做為採樣時河川全斷面之相關污染物濃度值時，需另外考量採樣點之選址，需可使污染物濃度在河川斷面中達到完全混合之狀態，否則推估方式將產生相當之誤差。
本研究另外於桑美颱風及珊珊颱風之高流量期間，在河川橫斷面以固定間距定出若干垂線進行污染物濃度之全斷面採樣以瞭解高流量期間河川全斷面污染物濃度之分佈情形，期研擬以更有效率的方式採樣，採得較具代表性之採樣資料，泥砂部分採用邱氏泥砂濃度分佈公式可獲得不錯之成果，而在溶解態磷部分，從擴散理論為基礎求得之無因次濃度剖線，依研究成果可知若假設河川中之主要污染源發生之機率落在全水深之機率均相等，則在水深之0.4∼0.6D之範圍進行採樣，可以較易採得平均濃度之水質濃度資料；另外，在顆粒態磷濃度剖線部分，發現高流量時期河川中之懸浮固體物之泥砂顆粒粒徑多屬粉土或黏土質為主，其相較於一般之泥砂對於磷有更大的吸附量，在桑美及珊珊颱風中所採得之水質樣品，其比吸附量 (=X/m)的範圍分別為79∼3,065 mg P/kg SS及67∼13,329 mg P/kg SS，此因高流量期間泥砂多屬於脫附狀態，而在實際應用時，若透過最小基礎濃度 與吸附係數 及 之相關性，則未來在應用上可減化許多為求取係數值之多餘採樣，可使磷之採樣更為有效率及經濟，綜合本研究之研究成果，可以高流量時期採樣及對於河川負荷量之推估，間接瞭解集水區之土地使用管理成效，相關成果也可以做為未來集水區土地使用管理之參考。

關鍵字

高流量期 ； 總磷 ； 磷負荷量 ； 吸附 ； 脫附 ； 等溫吸附模式

並列摘要

The reservoir in Taiwan almost subjected to the problem of eutrophication because of the surplus of nutrient result in the uncontrollable growth of algae. It is the most important topic to control the loading of phosphorus, in order to retain the good water quality of reservoir. Numerous agricultural activities, especially the production of tea or fruit in riparian areas, are conducted in watersheds in the upstream of reservoir. Nutrients from such activities, including phosphorus, are typically flushed into rivers during high flow period, when over 70 to 90 % of the yearly total amount of phosphorous enters reservoirs. Excessive or enhanced soil erosion from rainstorms can dramatically increase the river sediment load and the amount of particulate phosphorus flushed into rivers, at this time, the particulate phosphorus is the dominant form of phosphorus.
The study area Da-Lin bridge is located at the Daiyujay Creek watershed, which feeding the Feitsui Reservoir in Taiwan. First, the kinetic of adsorption/ desorption is found that after the water samples preserved over 16 hours the adsorption and desorption of the system approached equilibrium. During the high flow rate periods the Langmuir isotherm performed the best results of the others in the specific adsorption of phosphorus, furthermore, the amounts of TP transported through the river cross section during the June 9 rainstorm and Typhoon Bilis during duration T were accounted for roughly 0.7% and 28.8% of total TP loading during 2006, respectively. It shows that during the high flow rate periods which contributed the most amount of TP loading in a year. During high flow rates periods, the sampling data the of the river always regarded as the average concentration of the river section, which must be confirm first that the nutrient concentration is completely mixed at the sampling section or the estimation of the method may make some error.
Besides, river section are classified into several subsections during typhoon Saomai and typhoon Shanshan and the sampling and simulation are excuting by each subsection to identified a more efficiency method for more representative data. The Chiu’s sediment concentration distribution formula performs the suspended solid concentration well. As mention to the dissolved phosphorus, the method is developed by the diffusion theory and then dimensionless concentration profile formula is obtained. According to the result, assume that the major source of the nutrient occurred at the depth of the river with the same opportunities. The results show that as the average concentration could easily pump at the depth between 0.4-0.6D. In addition, as mention to the particulate phosphorus concentration profile, the results found that the most part of the suspended solid could classified as silt or clay, which used to adsorbed more particulate phosphorus than any others. The specific adsorption (=X/m) ranges of water samples in the typhoon Saomai and Shanshan are observed as 79-3,065 mg P/kg SS and 67-13,329 mg P/kg SS, respectively, which almost at the state of desorption. The usage of relation between basic concentration with adsorption coefficients and , whicn simplified the amount of sampling. So that the cost of sampling should be save and further makes the sampling of phosphorus becomes more efficiency and economic. To summarized the results of the research, which could found out the effect of management of land use in watershed by estimation of phosphorus loading during high flow periods and could also used as the references for the management of land use in watershed in future.

並列關鍵字

high flow periods ； total phosphorus ； phosphorus loading ； adsorption ； desorption ； adsorption isotherm

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