洱海南部近岸微囊藻原位增殖的季节变化及影响因子

Seasonal variations and the influencing factors of the in-situ proliferation of Microcystis in the nearshore water of southern Lake Erhai,Southwest China

2017年7月—2018年4月在洱海南部近岸开展了4个季度的野外调查,利用细胞分裂频率法研究微囊藻原位增殖的季节变化及影响因子,结果显示:微囊藻细胞分裂频率的变化范围为6.13%~29.23%,白天显著大于夜间,但两个点位间和表中底3层间的差异均不显著;经计算,微囊藻原位生长速率的均值为(0.36±0.06)d^(-1),总体高于其它有相关研究的湖泊。同时,微囊藻细胞分裂频率和原位生长速率具有显著的季节变化,表现为冬季最大(1月,19.65%±4.10%、(0.39±0.01)d^(-1)),秋季(10月,14.48%±4.73%、(0.36±0.02)d^(-1))和夏季(7月,12.77%±3.81%、(0.37±0.07)d^(-1))次之,春季(4月,10.37%±2.64%、(0.30±0.06)d^(-1))最小,其中营养盐浓度的作用不明显,而地表太阳辐射和水温等影响较大。进一步分析发现,除地表太阳辐射外,影响细胞分裂频率昼夜变化的其它因子具有一定的季节异质性。研究结果可为深入研究洱海微囊藻水华发生机制及预测预警提供参考。

Based on the seasonal field investigations from July 2017 to April 2018,seasonal variations in the in-situ proliferation(growth)of Microcystis using frequency of dividing cells(FDC)technique and their influencing factors were studied in the nearshore water of southern Lake Erhai,Southwest China.Our results showed that the FDC of Microcystis ranged from 6.13%to 29.23%,which was significantly greater during the day than at night,while the differences both between the two sampling sites and among the three sampling depths(i.e.,surface,0.5 m;middle,1.0 m;bottom,1.5 m)were not significant.The mean in-situ growth rate of Microcystis was calculated to be(0.36±0.06)d^(-1),which was generally higher than that of other lakes that had been studied.Meanwhile,both the FDC and the in-situ growth rate showed significant seasonal variations,i.e.,the largest in winter(January,19.65%±4.10%,(0.39±0.01)d^(-1)),followed by autumn(October,14.48%±4.73%,(0.36±0.02)d^(-1))and summer(July,12.77%±3.81%,(0.37±0.07)d^(-1)),and the smallest in spring(April,10.37%±2.64%,(0.30±0.06)d^(-1)),which was mostly due to the important influences of surface solar radiation downwards,and water temperature,etc.,whereas the nutrient concentrations did not play significant roles.Furthermore,except the key factor surface solar radiation downwards,other major environmental factors affecting the diurnal changes of FDC had seasonal heterogeneities to some extent.Our results can provide a useful information for further studying the occurrence mechanism of cyanobacterial(Microcystis)bloom as well as its prediction and early warning in Lake Erhai.