香港近岸海域营养盐结构特征及其对浮游植物生长的影响

TEMPORAL AND SPATIAL DISTRIBUTION OF NUTRIENTS AND CHL A IN THE COASTAL AREA OF HONG KONG

本文利用2000年3月至2001年5月在香港近岸牛尾海海域(Porter Shelter,Hong Kong)14个航次的现场调查数据,对水体中营养盐组成结构和叶绿素a含量进行了分析研究。结果表明,该海域表层和底层水体中溶解无机氮(DIN,包括NO3-N+NO2-N,NH4+-N)平均浓度范围分别为1.24—9.72 mol/L及1.30—7.49 mol/L,均表现为冬季最高、秋季最低。不同季节表层水体中PO43-P浓度范围为0.14—0.46 mol/L,夏季平均浓度最底;底层PO43-P浓度变化不大,但夏季仍低于其他季节。不同季节表层和底层水体中SiO32-Si的变化趋势基本相似,平均浓度范围分别为7.80—18.47 mol/L和8.13—16.87 mol/L,均在冬季最高,其它季节差别不大。叶绿素a分析结果显示,表层水体高生物量大多出现在夏末秋初季节(如8月份),春季(4月份)次之;底层水体叶绿素a秋季最高,夏季次之。进一步分析了该海域营养盐对浮游植物生长的可能限制因子,结果表明表层水体春季呈现氮–磷协同限制的可能性、夏季磷限制较明显,秋季表现为显著的氮限制。底层水体春、夏季呈现氮–磷协同限制的趋势,秋季也表现为明显的氮限制。冬季磷酸盐浓度相对氮、硅的含量较低,但各种营养盐相对于浮游植物生长的最低阈值都比较丰富,所以,冬季表、底层水体中营养盐对浮游植物的生长均不形成限制因素。另外,除了夏季表层水体外,其它季节该水域浮游植物生长受溶解无机硅限制的可能性较少。

Regular cruise from March 2000 to May 2001 was conducted monthly （or twice in one month） to investigate the nutrients and chl a in the coastal area of Hong Kong （Porter Shelter, HK）. Both of the surface and bottom water were selected to determine the nutrient concentrations and chl a distribution in different seasons. The results show that the annual average concentration of total dissolved inorganic nitrogen （DIN including NO3？-N＋NO2？-N, NH4＋-N） were 1.24—9.72mol/L and 1.30—7.49mol/L in surface and bottom water, respectively. The highest value of DIN was in winter and the lowest was in autumn during the investigation period. PO43？-P concentration in surface water changed from 0.14 to 0.46mol/L in different seasons （minimum in summer）. The bottom PO43？-P concentration was more steadily than in the surface water. However, it still showed a decrease tendency in summer days. As for SiO32？-Si, the average concentrations changed in same characteristics in both the surface and bottom waters in range of 7.80—18.47 and 8.13—16.87mol/L, respectively. The highest SiO32？-Si concentration was in winter, and in other season there was no obvious difference. The results of chl a in different seasons revealed that in surface water the highest biomass was in summer （August） and the second peak value was in spring. Chl a concentration in bottom water was the highest in autumn and summer was following. Further analysis of the nutrients limitation for phytoplankton growth showed that in surface water there was a possibility of N and P cooperation limiting in spring. Similarly, it showed P-limitation in summer and N-limitation in autumn obviously. However, in bottom water it revealed that there was a trend of N and P cooperative limitation during spring and summer. And it also showed N-limitation in autumn obviously. Although PO43？-P concentration was lower than those of nitrogen and silicate concentrations in winter, all nutrient concentrations were higher than the minimal value of phytoplankton requirement. This means there was no limiting nutrient in winter to restrict the growth of organism in both the surface and bottom waters. In addition, there was less opportunity for Si-limitation in surface and bottom water during the year except the surface water in summer.