聚积蓝藻不同打捞强度下藻源污染物释放特征研究

The release characteristics of algae-derived pollutants in different salvage intensities after cyanobacteria accumulation

通过室内培养(35℃、6000 lx)模拟夏季环境条件下湖湾带高密度(~1.3×10^(11)cells·L^(-1))蓝藻聚积.实验设置了未打捞组及3种打捞强度组,分别为低、中和高强度组,其对藻密度的去除率可分别达到60.57%±0.09%、88.49%±0.52%和94.23%±0.00%,并以湖水组(Lw)作对照,研究了聚积蓝藻在不同打捞强度下的藻源污染物释放特征.结果表明:蓝藻聚积36 h内是打捞的"窗口期",在此期间打捞效果最佳,而后蓝藻死亡、叶绿素a(chl.a)下降.蓝藻聚积过程中,氨氮(NH_4^+)和磷酸盐(PO_4^(3-))分别为溶解性氮磷(DTN、DTP)的主要形态.氮磷营养盐和藻源有机物(AOM)均在窗口期后5 d或8 d内快速释放,而后降低并进入内源循环.因此,窗口期后5 d内为打捞的"有效期",在此期间应增加打捞频率及强度确保对污染物的控制效果.不同打捞强度下藻源污染物的释放特征差异显著,低强度打捞未能遏制蓝藻死亡降解,而中、高强度打捞解除了蓝藻生长密度制约,延缓藻细胞死亡,减缓藻源污染物的释放.打捞强度越大,藻源污染物释放速率越低,对污染物的控制效果越明显.当达到中强度打捞时,AOM的释放得到基本控制,因此,中强度打捞是控制水体AOM的必要强度.

An culture enrichment experiment（ 35 ℃,6000 lx） was carried out in lab to simulate the pollution process of high density of cyanobacteria aggregation（ about 1. 3 ×10^（11）cells·L^（-1）） in summer. Three salvage strength,with low-,moderate-and high-intensity were set up and removed 60. 57% ±0. 09%,88. 49% ± 0. 52%,and 94. 23% ± 0. 00% of algal cells,respectively,with non-salvage as control and lake water without cyanobacteria as blank. The releasing characteristics of algae-derived pollutants in different salvage strength was studied. The results show that 36 h was the optimal＂window period＂for salvaging,and then cyanobacteria decayed and chlorophyll a（ chl. a） declined gradually. During cyanobacteria accumulation,ammonia nitrogen（ NH_4~＋） and phosphate（ PO_4^（3-）） were the main forms of dissolved nitrogen（ DTN） and phosphorus（ DTP）,respectively. Algae-derived nitrogen and phosphorus,and algogenic organic matter（ AOM） released fast during the first 5 d or 8 d,and then the concentrations of pollutants caused byaccumulative cyanobacteria decreased and entered into endogenous circulation. Therefore the fifth day after the window period was the ＂valid period＂during which it is necessary to increase salvage frequency and intensity to ensure effectiveness. Salvage strength had significantly effects on the release of algae-derived pollutants. The low-intensity group could not restrain cyanobacteria to decay,nevertheless the moderate and high intensities of salvage strength avoid cyanobacterial growth dependence which deferred the death of algal cells and slowed down the release of algae-derived pollutants. In general,the higher the salvage strength,the slower the algae-derived pollutants release and the more effective treatment obtained. However the moderate intensity salvage is required in order to control the release of AOM.