西湖引水前后氮 , 磷 , 叶绿素 A 含量的年周期变化

研究了杭州西湖引水前后主要湖区水体中的氮、磷、叶绿素a的年周期动态变化。结果表明:外湖等五个湖区的总氮含量在春季和秋季有两个高峰值,与引水前相比变化不大。硝酸盐氮各湖区均在1～4月呈现高峰。各湖区的总磷含量5月开始急剧上升,9月后降至最低;氮、磷在各湖区的年平均含量也略有差异,一般以岳湖和北里湖湖区的含量较高,而三潭内湖和小南湖湖区相对较低。对各湖区水样检测的相关分析表明:总磷和叶绿素a的年周期动态变化密切相关,而可溶性磷与各湖区的叶绿素a含量相关不显著,但其动态变化一致。从西湖水质改善的程度来看,引水工程只是治理西湖的一项重要措施,但不是根本措施,还需进一步加强截污、科学疏挖、控制游船数量等综合治理。

ANNUAL CYCLICAL CHANGES OF NITROGEN, PHOSPHORUS AND CHLOROPHYLL A CONCENTRATIONS IN WEST LAKE BEFORE/AFTER THE WATER DIVERSION

With the aim of improvement in water quality and the rise in sightseeing value of West Lake, about 11. 690 millions yuan RMB was invested in the construction of the water diversion project by national government. After 3-year feasibility studies and over 2-year water diversion experiments, the project from the Qiantang River to West Lake was launched in February, 1985 and completed in September, 1986. The article studied the annual cyclical changes of nitrogen, phosphorus and chlorophylLa concentrations in main parts of West Lake before/after the water diversion. As a result, the seasonal course of total nitrogen concentration which consisted of two peaks occurring in spring and autumn differed from that of pre-diversion project. The concentrations of nitrate in various lake districts all had their peaks in spring (from January to April), while those of total phosphours appeared in autumn from August to November.An interrelated analysis of samples from various lake districts indicated that the annual cyclical changes of total phosphorus and that of chlorophyll a were closely correlated, but no distinct correlation found between those of dissolved phosphorus and chlorophyll a.As an important but not a fundamental step, the water diversion project did improve the water quality of West Lake in some way, but not so effective as expected. The problem concerning West Lake should be tackled in a comprehensive way, such as pollutants interception, deposit dredging, and pleasure-boat control.