氮磷的不同供应比例和频度对藻类水华形成的影响

为了探讨氮磷的不同供应比例和频度对藻类水华形成的影响,本研究设计了7种氮磷添加比例（质量比）：只添加氮（以＋N表示）、50：1、20：1、7：1,1：1、1：7和只添加磷（以＋P表示）;2种添加频度：频度较大的L系列（实验前期每日均进行添加）,频度较小的S系列（只在实验过程中添加1次）。两种添加频度下,相同添加比例的处理的营养盐添加量相近。在处理＋N、50：1、20：1、7：1和1：1中以N浓度为基准进行相应比例的P添加,在处理1：1、1：7和＋P中以P浓度为基准进行相应比例的N添加。在1：1处理缸中N、P净增加均约为2.4mg·L-1。实验水体来自一个浮游植物丰富但没有微囊藻水华的天然富营养池塘。实验于2007年8月1日—8月13日在室外采用玻璃缸进行。结果表明,两种添加频度以及不同氮磷添加比例下,实验过程中出现的水华种类均为微囊藻（Microcysti sspp.）水华,没有固氮藻类水华出现。在两种不同添加频度下,微囊藻水华在处理＋N、50：1、20：1、7：1和1：1中明显形成,而处理＋P和1：7中,微囊藻水华的出现会晚几天或者水华现象不明显,这表明本实验中单独添加氮比单独添加磷对微囊藻水华形成的促进作用要明显些。水体中微囊藻水华的出现与适宜的氮磷比例添加有关,氮磷添加比例适宜时,两种不同的添加频度下均可出现微囊藻水华,但氮磷营养盐的不同添加比例和频度均没有导致固氮藻类水华的出现。

Effect of Different Ratios and Frequencies of Nitrogen and Phosphorus Addition on Algal Bloom Formation

To determine the effects of different ratios and frequencies of nitrogen（N） and phosphorus（P） addition on algal bloom formation,an experiment was carried out with glass jars from 1 August 2007 to 13 August 2007 outdoors,which included 7 kinds of N to P ratios（mass ratio）：N addition alone（＋N）,50：1,20：1,7：1,1：1,1：7 and P addition alone（＋P）;and 2 kinds of frequencies：high frequency（L）,addition was conducted every day in the first few days,and low frequency（S）,addition was only once in the middle of the experiment.The addition amount for the treatments with the same ratio from the 2 kinds of frequencies was close to each other.In treatments ＋N,50：1,20：1,7：1 and 1：1,P addition were based on N mass,and in treatments 1：1,1：7 and ＋P,N addition were based on P mass.And in treatment 1：1,the net addition of N and P was about 2.4 mg·L-1 each for both the 2 kinds of frequencies.The experimental water was from a natural eutrophic pond rich of phytoplankton but without Microcystis bloom.The results showed the algal blooms appeared in this experiment were all Microcystis blooms regardless of what addition ratios or frequencies,and no nitrogen-fixing algae bloom appeared.Microcystis blooms obviously formed in treatments ＋N,50：1,20：1,7：1 and 1：1 in both the 2 kinds of addition frequencies,while in treatments 1：7 and ＋P of the 2 kinds of frequencies,Microcystis bloom formation would be a few days later or not obvious.It showed the N addition alone for promoting Microcystis bloom formation was relatively evident than that of P addition alone.Our experiment here showed that Microcystis bloom formation was related to nutrients addition of appropriate N：P ratios,and when the added N：P ratios were appropriate,Microcystis bloom appeared in both the 2 addition frequencies.However,the different addition ratios and frequencies here did not lead to nitrogen-fixing algae bloom formation.