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General Session 2: Marine & estuarine biogeochemistry |
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Spatiotemporal variability of physical-biological process in Hong Kong waters: Observational study
GS2-45-S
Dujun Wei* , Environment Science Programs, Hong Kong University of Science and Technology
Jianping Gan, Division of Environment and Department of Mathematics, Hong Kong University of Science and Technology
Presenter Email: dweiaa@connect.ust.hk
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| Hong Kong (HK) waters, located at the mouth of Pearl River Estuary (PRE), are physically driven by multi-forcing of the buoyancy of river discharge, winds and tides, and biologically regulated by nutrient loading from Pearl River. In this study, we use biophysical data collected from Hong Kong Environmental Protection Department (EPD), from 2000 to 2015 to investigate the spatiotemporal variability of physical-biological process in HK waters. During summer, salinity/temperature increased/decreased from the northwest to the southeast in the entire stratified water column. The river water tended to be trapped in the shallower waters and temperature increased/decreased near sewage sites in the western/eastern part of HK waters. During winter, HK was less influenced by the river discharge and wind stirring greatly weakened the water stratification. There was still an ascending trend of salinity from the northwest to the southeast, while the spatial variation of temperature was very weak with relatively warm temperature in sewage discharge sites. River discharge was the main source of nutrients. Nitrate concentration in summer was double or even triple of that in winter, especially at the surface. Distribution of nitrate/phosphate resembled to the salinity distribution, as a result of influence of river discharge. Eutrophication occurred mainly in the western part of HK. Local point-sources greatly elevated the local nutrient concentration in the northwestern part of HK and phosphate concentration in Victoria Harbor. Biological bloom was correlated to nutrient concentration from river discharge in the western waters, to sea temperature near sewage discharge site in the central waters, and to nutrient of cross-shelf transport in the eastern waters. The dissolved oxygen (DO) distribution in the water column was quite consistent with the distribution of biological bloom at most areas during summer, and surface DO was much higher than bottom DO. In contrast, the vertical DO gradient was very small during winter. The long-term trend shows a continuous increase of nutrient and decrease of bottom DO in summer. Ascending nutrient concentration could be due to descending river discharge with changeless nutrient amount, and it led to rising phytoplankton. This demonstrates a close linkage between the surface eutrophication and bottom DO. On the other hand, wind stress increased and enhanced upwelling during the observed period, which could also contribute to the decrease of bottom DO. This study characterizes linkage of physical and biological process in HK water spatiotemporally. |
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