珠江口及毗邻海域营养盐对浮游植物生长的影响

基于2006年7月(夏季),10月(秋季)和2007年3月(春季)的现场调查数据,对珠江口及毗邻海域中的营养盐和叶绿素a等环境生态因子的时空分布特性进行了对比分析,研究了氮磷比与叶绿素a含量和种群多样性之间的联系,探讨了该海域营养盐对于浮游植物生长的影响。结果表明:(1)研究海域营养盐表现出较强的季节和空间差异性,总氮(TN)和总磷(TP)浓度均值春季(1.545 mg/L、0.056 mg/L)和夏季(1.570 mg/L、0.058 mg/L)均大于秋季(1.442 mg/L、0.034 mg/L),且春夏季浓度空间差异更明显。(2)调查期间海域营养盐含量超标现象突出,夏季尤为明显。无机氮(DIN)总体均值0.99 mg/L,超四类海水标准限值1倍,活性磷酸盐(PO4-P)总体均值0.021 mg/L,DIN∶PO4-P平均值为130;叶绿素a浓度与营养盐、p H、温度有较显著的相关性。(3)叶绿素a浓度较高的站位,具有较高的DIN∶PO4-P值,但浮游植物多样性指数偏低,优势种明显,主要为中肋骨条藻。氮磷比的改变会影响不同生长特性的浮游植物间的竞争和种群结构的改变;今后海洋污染治理中,在控制氮、磷污染时要注意氮磷比的改变可能造成的浮游生态影响。

Seasonal and spatial variations of nutrient and the response of phytoplankton in PRE and Adjacent Sea Areas

The seasonal-spatial variations of nutrient and Chlorophyll-a around the Pearl River Estuary (PRE) and adjacent coastal waters were investigated based on the survey data collected at 25 stations in July, October 2006 and March 2007. The relationship were examined between the ratio of nitrogen to phosphorus (DIN:PO₄-P and TN:TP), the Chlorophyll-a concentration and the diversity of phytoplankton species, and the effects of nutrient limitation on the phytoplankton growth were taken into account. The results indicated that: 1) the concentrations of nutrients and Chlorophyll-a had a strong seasonal and spatial variation. Seasonally, the mean concentrations of TN and TP in March (spring) and July (summer) were higher than those in October (autumn), and an obvious special variation of nutrient concentrations had been found in summer and spring, while it were more even in autumn. Spatially, much lower nutrient concentrations in Daya Bay and Guanghai Bay were found in comparison with the high nutrient concentrations in Pearl River Estuary. 2) The nutrient concentrations in the study area were rather high, and exceed the China national seawater water quality standards remarkably, especially in summer. The mean DIN concentration was about 0.99 mg/L, which was more than twice of the water quality standard Category 4, the mean PO₄-P concentration was about 0.021 mg/L, and the mean ratio of DIN:PO₄-P was about 130 far above the Redfield ratio (16:1), which is the optimum value of phytoplankton nutrient requirements. With a significant enrichment of nitrogen relative to P, there was excess of N and potentially P limitation in coastal waters of PRE and nearby seas. Chlorophyll-a concentration showed a better correlation with nutrients, pH, and temperature in this region. 3) During the investigation in spring and summer, phytoplankton density distribution was variable, with major dominant species (Skeletonema costatum). The phytoplankton biomass were high at the stations where the N:P ratio was high while the diversity index was usually low. Thus, the growth of phytoplankton wasn''t inhibited in the high N:P ratio area. In that area, the phytoplankton biomass distinctly increased due to the emergence and growth of dominant species. It was shown that the demand for nitrogen and phosphorus nutrient might vary greatly with the different types of phytoplankton; as a result, the variation of the ratio of nitrogen to phosphorus might cause the differential responses between growth rates of various phytoplankton species, resulting in a change in phytoplankton community structure. The effect of N:P ratio on phytoplankton should be taken into account in the further water management.