水庫底泥磷通量之研究--以新山水庫、石門水庫為例

Abstract

磷（Phosphorus）是許多水生生物之營養鹽限制因子，當水中磷濃度過高時會造成藻類大量生長使水體優養化，因此研究水庫中之內、外部磷負荷是維持良好水質之重要方法。許多研究證實，底泥是水庫內部磷之源（Source）與匯（Sink），故本論文以新山及石門水庫為研究對象，探討底泥磷釋出通量及其影響因子。 以磷之序列分選技術對上層10公分底泥及沈降物進行分析得知，新山水庫底泥磷組成主要為有機磷，約佔總磷量之96%以上。石門水庫底泥磷組成以鈣結合磷為大宗，約佔總磷量之78%。由於新山水庫底泥含多量之鐵金屬，溶氧之程度會影響鐵之氧化還原狀態，進而控制底泥磷之釋出。石門水庫底泥含鈣、鋁金屬，因此底泥磷之釋出不受溶氧之影響。新山水庫由沈降物捕集器所收集之總磷沈降通量約為1.36至1.68 mg/m2/day，石門水庫約為6.04 mg/m2/day，石門水庫支沈降量顯然受到外來來源之影響甚鉅。 透過好氧與厭氧之磷釋出通量試驗得知，新山水庫底泥在好氧時磷釋出通量約為0.10 mg/m2/day，厭氧約為3.57 mg/m2/day。石門水庫底泥好氧釋出通量約為0.13 mg/m2/day，厭氧約為0.10 mg/m2/day。經水庫磷質量平衡計算，新山水庫之底泥磷釋出於2006年超越水庫水體外部磷負荷量，石門水庫僅佔外部負荷之1.7%。因此可推測底泥磷對新山水庫具有相當程度之影響，相對而言，石門水庫之底泥磷釋出量對水體水質影響程度甚微。

It has been demonstrated that phosphorus concentration is a limiting factor for the growth of planktons in reservoirs and lakes. High phosphorus concentration results in high rate of algae growth and eutrophic state of reservoirs. Bottom sediments have been identified as potential sink and source of phosphorus to the overlaying water. As a result, the understanding of the mechanisms and factors controlling phosphorus release flux from benthic sediment is needed. In the thesis, Hsin-shan Reservoir and Shih-men Reservoir were taken as our study sites for the investigation of sediment-water column interaction. The results of fractional extraction analysis of bottom sediments and settling matters show that organic-P and calcium-P dominate in Hsin-shan Reservoir and Shih-men Reservoir, respectively. Therefore, in Hsin-shan Reservoir, dissolved oxygen has great influence on the release of phosphorus from sediments because of its rich of ferric content in sediment. In contrast, in Shih-men Reservoir, dissolved oxygen may not affect the release of phosphorus since aluminum and calcium minerals dominate in sediment. Flux of total settling phosphorus collected by sediment traps ranged from 1.36 to 1.68 mg/m2/day in Hsin-shan Reservoir and 6.04 mg/m2/day in Shih-men Reservoir. For the reason above, settling flux in Shih-men Reservoir is influenced by external input significantly. Through the investigation of the phosphorus release flux under oxic or anoxic condition, the following results were observed: The release flux in oxic condition was about 0.10 and 0.13 mg/m2/day in Hsin-shan Reservoir and Shih-men Reservoir, respectively. Under anoxic condition, it was about 3.57 and 0.10 mg/m2/day in Hsin-shan Reservoir and Shih-men Reservoir, respectively. Mass balance for the annual external and internal phosphorus loading shows that released internal loading from bottom sediment has exceeded external loading in Hsin-shan Reservoir in 2006. However, internal phosphorus loading only accounts for 1.7% of the external loading in Shih-men Reservoir in the same year. So it is concluded that internal loading from sediments may have considerable impact on water quality in Hsin-shan Reservoir but minor impact in Shih-men Reservoir.