河川中懸浮固體的流布對水體與底泥中重金屬銅傳輸的影響

Influence of Suspended Solids on the Distribution of Copper Metals in Riverine Environment

闕亦吟(Yi-Yin Chueh)

指導教授 ： 范致豪

國立臺灣大學/生物資源暨農學院/生物環境系統工程學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201802817

摘要

重金屬在河川中的污染分佈受地表水傳輸和沈積作用所控制，污染物質除了於水體環境中進行傳遞和擴散外，溶解態重金屬和水體中的懸浮固體結合形成吸附態重金屬沉積於底泥，底泥重金屬受到擾動再次懸浮於河川水體中，此為河川二次污染的重要原因。爰此，本研究結合土壤水文評估模式與水質模式，探討河川中懸浮固體的濃度對水層和底泥層的重金屬濃度分布的影響；河川懸浮固體輸出推估乃運用水土評估工具SWAT建立二仁溪集水區土砂推估模式，將集水區內氣候條件、土壤性質資料、土地利用以及農地作物種類納入考慮，模擬集水區內流量與泥沙的傳輸情形，並藉由SWAT-CUP校正SWAT的模擬流量；重金屬流布方面，蒐集環保署針對二仁溪流域內的事業放流水檢測濃度值和重金屬排放總量管制制度，選用重金屬銅做為模擬對象，計算各子流域的污染排放量，建置二仁溪WASP水質模式。依據環保署對二仁溪重金屬污染整治策略以及未來氣候推估情境，設計枯水時期懸浮固體產出變化、加嚴工廠重金屬放流水總量管制標準和氣候變遷RCP4.5情境，分析集水區內重金屬分布差異的影響。
從水質模擬結果分析顯示，水中懸浮固體濃度高容易使水中溶解態重金屬銅附著於懸浮固體上形成吸附態重金屬銅；而重金屬主要是以吸附態形式存在於水層和底泥層，而高濃度的水中吸附態重金屬銅也使得底泥層重金屬銅濃度更為顯著。在枯水時期降雨量減少，二仁溪整體的泥沙產量降低，在水中懸浮固體降低的情況下，水中重金屬濃度相較於基期最高濃度高出2.15倍，底泥層約減少0.8倍的重金屬濃度。氣候變遷對於二仁溪河川銅濃度有顯著之影響，高流量稀釋水體的重金屬濃度，也降低水中吸附態重金屬沉積於底泥，使得中上游區域水體與底泥重金屬較低。事業放流水加嚴標準策略對於河川和底泥重金屬濃度都有明顯改善，距離出海口25公里至出海口間，水體和底泥重金屬濃度最多削減效果達66%，顯示水體重金屬濃度削減能改善底泥重金屬濃度。以上結果得知透過懸浮固體能促進水體與底泥間的重金屬傳輸，地表水的污染控制也能降低底泥表層的污染濃度。本研究藉由重金屬在水相與固相濃度之差異，對於未來探討底泥重金屬污染改善策略提供另一層面的參考依據。

關鍵字

SWAT模式 ； 懸浮固體 ； WASP模式 ； 底泥重金屬 ； 重金屬移動途徑

並列摘要

The distribution of heavy metal depends on the transport phenomenon between surface water and sediment. Due to the transfer and diffusion of pollutants within water bodies, the dissolved heavy metals are adsorbed to suspended solids in aqueous phase thus to form the sorbed heavy metals which might deposit in the sediment subsequently. Resuspension of heavy metals from sediment might easily cause secondary pollution of rivers. Therefore, this study combines the soil hydrological assessment model and water quality model to estimate the distribution of heavy metals in the investigated river system. The Soil and Water Assessment Tool (SWAT) was employed to estimate the soil flux using climatic and topographical data, soil properties, soil utilization categories and vegetation types. The SWAT-CUP was used to calibrate all the required parameters. Furthermore, the copper is selected to be the indicator of concern to represent the heavy metal distribution using Water Quality Analysis Simulation Program Model (WASP). By considering the government heavy metal emission control measures and the factories’ locations, the heavy metal yields and their distribution within aqueous and sediment phases were calculated. Different scenarios were designed, including suspended solids yield in the dry period, more-stringent heavy metal discharge control measures and climate change impacts. These scenarios were used to estimate the heavy metals distribution in this watershed.
The water quality simulation result demonstrated that the dissolved copper in the water phase is adsorbed to suspended solids easily, resulting in the high concentration of sobbed copper in in water phase. The adsorbed form of the heavy metal is the main type of heavy metals present in water and sediment phases; moreover, the high concentration of adsorbed heavy metals in water phase might result in high heavy metal concentration in sediment phase. In dry period, less sediment and suspended solids yielded in Erren River watershed because of the less rainfall. Therefore, the heavy metal concentration in water phase increased by 215% compared with baseline concentration; however, there is a 20% decrease in heavy metal concentration in the sediment phase in comparison with baseline concentration. Heavy metal concentration in aqueous phase is diluted by high flow and high flow also reduces the adsorption of heavy metals from water to sediment, which causes the concentration of Cu lower than the baseline in upper and middle part of Erren River. More-stringent heavy metal discharge control measures may significantly improve the quality of aqueous and sediment phases. In the mid-downstream river section, the concentration of heavy metals in water body and sediment decreased by 66%. Based on the results from the present study, suspended solids can be the key role of heavy metals transportation between water and sediment phases. The heavy metal pollution in sediment phase might be alleviated by reducing the heavy metal concentration in the surface water phase. In this study, the transportation of heavy metals in water and sediment should provide a reference for the heavy metal pollution management and water quality assurance standard achievement in the future watershed management strategy.

並列關鍵字

SWAT model ； suspended solid ； WASP model ； heavy metals in river sediments ； heavy metal transportation

參考文獻

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