中文摘要：

分别于2014年3月（枯水期）和7月（丰水期）对钦州湾海区Chl a浓度分布及其粒级组成进行了分析。结果表明,研究区域两个时期都具有较高氮浓度和氮磷比,枯水期磷酸盐浓度高于丰水期,Chl a浓度及其粒径结构差异显著。枯水期Chl a浓度（1.70±0.74μg/L）显著低于丰水期浓度（7.81±3.63μg/L）（p〈0.01）。优势粒级从枯水期Nano级Chl a（51.8±14.0%）向丰水期Pico级（50.4±17.4%）演变。Pico级与Micro级共同构成了丰水期的Chl a浓度高值,两个时期Nano级Chl a浓度无明显差别。Nano级Chl a对总Chl a浓度的贡献存在着自枯水期优势（51.8±14.0%）至丰水期降低（15.5±9.2%）的动态变化。通过与营养盐和盐度等因子的相关分析,可知浮游植物粒级组成的差异与钦州湾陆地径流的输入、营养盐浓度变动及高密度牡蛎养殖密切相关。

英文摘要：

The distribution and size-fractional Chl a concentration（ 20 μm,2 - 20 μm, 2 μm） in Qinzhou bay were studied in March（ dry season） and July（ wet season）,2014. Dissolved inorganic nitrogen concentration and N/P ratio were both high in the two seasons,whereas soluble reactive phosphorus concentration in dry season was higher than wet season. Chl a concentration and size structure were significantly different between two seasons. The Chl a concentration in dry season（ 1. 70 ± 0. 74 μg/L） was significantly lower than in wet season（ 7. 81 ± 3. 63 μg/L）（ p 0. 01）. The dominant size fraction was transformed from nano-phytoplankton（ 51. 8 ± 14. 0 %） in dry season to pico-phytoplankton（ 50. 4 ± 17. 4 %） in wet season. The high concentration of Chl a in wet season was contributed by pico-and micro-phytoplankton. Concentration of Chl a which contributed by nano-phytoplankton was not differ significantly between two seasons,however,their contributions to total Chl a concentration was declined from51. 8 ± 14. 0 % in dry season to 15. 5 ± 9. 2 % in wet season. According to the results,runoff input,the change of nutrient concentrations and high density of oyster cultivation were considered to be the major factors leading to the change of phytoplankton size structure in Qinzhou bay.