密云水库环境的现状和变化趋势

Status and tendency of environment in Miyun Reservoir

根据１９９６年对密云水库调查的部分结果，分析了该水库生物理化环境的现状和变化趋势，并进行了营养程度评价。结果表明：水温有明显的４季变化，溶解氧和ｐＨ适中；无机氮含量丰富，无机磷很缺乏，Ｎ／Ｐ大大超过１６／１，浮游植物数量和生物量年平均值分别为４０５５５×１０５Ｌ－１和３０１３５ｍｇ／Ｌ，浮游动物数量和生物量年平均值分别为６５２６６１Ｌ－１和２４７１２ｍｇ／Ｌ。与历史同期相比，无机氮略有下降，无机磷下降很显著，但浮游植物量却有很大提高。密云水库为中营养型水库，但有富营养化趋势。

The water temperature of Miyun Reservoir changes perceivably with seasons,and the DO and pH of the water are moderate. The environment of the reservoir is favorable for the growth of freshwater organisms.The inorganic nitrogen is very abundant,but the phosphate is very scarce ,and N/P ratio is much higher than 16/1. The yearly average numbers of phytoplankon and annual mean biomass are 405 55×10 5 L -1 and 3 013 5 mg/L respectively, while those of zooplankton are 65 266 1 L -1 and 2 471 2 mg/L. Compared with historical data, the content of inorganic nitrogen decreases slightly,and that of phosphate decreases considerably, but the numbers of phytoplankton increases greatly.Although Miyun Reservoir is a kind of mesotrophic waters, it tends to be eutrophic.