Field Survey and Analysis of Water Quality and Suspended Sediment in Houlong River Estuary

• Main Authors: Wei-ying Wang, 王惟盈
• Other Authors: Wen-cheng Liu
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/95440979148087505543

碩士 === 國立聯合大學 === 防災科技研究所 === 95 === Monthly Measurements in the Houlong River estuary were conducted from July 2006 to June 2007. The Measurement includes flood and ebb water surveys and two intensive surveys. Six sampling stations from downstream to upstream reach were measured during flood and ebb water surveys. The purpose of this study is to investigate the spatial and temporal variations of water quality and suspended sediment in the Houlong River estuary. The analyzing results reveal that the hydro-physical characteristics in the Houlong estuary were affected by the tide, freshwater discharge, and salt intrusion. The salinity distributions during flood and ebb tides present quit different patterns. As high freshwater discharge, the limit of salt intrusion pushes to downriver reach. It shows that the limit of salt intrusion is subject to freshwater discharge coming from upriver. The seasonal variations in air temperature and rainfall significantly influence the temperature in water column. Dissolved oxygen in the estuary are higher and more than 5 mg/L. Dissolved oxygen at the surface layer is higher than that at the bottom layers and is subject to the influence by rainfall and freshwater discharge. Suspended sediment concentration at the bottom layer is higher than that at the surface layer. Through the laser particle size distribution analyses, the particle size exhibits non-uniform distribution in water column. It results in the poor relationship between suspended sediment concentration and turbidity (R2=0.434). The analyses of bottom sediment in the Houlong estuary reveal that the sediment mostly belonged to the sand classification. The penetration of sunlight into the water column plays a critical role in the aquatic ecosystem. The measurement of phytosynthetically active radiation (PAR) indicates that the conventional exponential attenuation of light with depth is a very good model. A light attenuation coefficient (Ke) may be derived from the PAR measurements at each station. The linear regression between Ke and suspended sediment concentration presents a poor correlation (R2=0.434). The regression with salinity yields a fair correlation (R2=0.522). The simple measurements of Secchi depth (SD) provide an approximate estimate of the attenuation coefficient through an inverse linear relationship (R2= 0.607). The regression between Ke and chlorophyll a yields a good correlation, indicating that the chlorophyll a might be a good parameter for estimating light attenuation coefficient for practical application in the Holoung estuary. The multiple regression between Ke and both suspended sediment concentration and chlorophyll a was also performed. It results in the regression equation Ke=–0.603+0.0543*SS+0.0160*Chl-a (R2=0.286), indicating the poor correlation and does not to improve the predictability of Ke. The measurements at the Beshih Bridge show that no salt intrusion exhibits there. The regression between turbidity and suspended sediment concentration presents a poor correlation. However the freshwater discharge and suspended sediment concentration have a fair exponential relationship, indicating the equation as SS=3.71*Q0.806，R2=0.591. It reveals that the high freshwater discharges (Q) result in high concentration in suspended sediment.