| Summary: | 碩士 === 國立臺灣大學 === 海洋研究所 === 93 === The propose of this research is to study on the temporal-spatial variation of chlorophyll
a concentrations in the Fei-Tsui Reservoir and the mechanism of how typhoons impact on
it. The surface water temperature (ST), chlorophyll a (Chl a), phaeopigments a (Phae a)
ratio (PhR= Phae a/(Phae a+Chl a)), total suspended matters (TSM) and soluble reactive
phosphorus (SRP) have been measured in the Fei-Tsui Reservior from 2004 Feb to 2005
Apr, especially made high frequent sampling after typhoons. The result during the
researching period told that the vertical distribution of Chl a concentrations was higher at
the surface but lower at the bottom. The highest Chl a concentrations often located at 5m
depth of water. The horizontal distribution of the Chl a concentrations was higher in the
upstream but lower in the downstream. About the temporal distribution, the average of
integrated Chl a concentrations above 10m (IChl a10m) had the highest value in autumn (5.2
mg L-1) and the lowest in winter (0.24 mg L-1). For its annual average value was 2.3 ± 1.2 mg
L-1. The multiple regression analysis shows that the change of IChl a10m during research is
related with ST and PhR (indicated the grazing of the zooplankton or the descending of the
phytoplankton). The term TSM is considered with IChl a10m during typhoon season from
Aug to Dec. The term SRP reveals related with IChl a10m only during cold season from Dec
to next Mar. After typhoon or heavy rain, high TSM turbidity current was presented in the
middle and bottom water (about 20~80m water depth) of the reservoir; the Chl a
concentrations rose at the upper water body of the turbidity current, which the depth of
subsurface chlorophyll maxima appeared deeper. The data analysis shows that TSM is
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positive related with SRP. That indicates the turbidity current can be a source of phosphate.
It could be one reason of why the high Chl a concentrations presents during the typhoon
season. The numerical model analysis shows that the strong breeze of typhoon can’t draw
the material of deep water up because the water temperture stratification is so strong in
summer. But the stratification is weaker in the late autumn that typhoon can make the
mixing layer deeper efficaciously and causes the material of deep water is brought into
upper water body. As these results point out, if the SRP or Chl a concentrations reveal high
value in summer, the input should come from upstream. If the high TSM and SRP water
induced by summer typhoon accumulates in the reservoir, it will mix with surface water
causing by the typhoon in autumn or surge in winter and will affect the magnitude of the
bloom in this autumn or next spring.
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