西太湖秋季蓝藻水华过后细胞裂解对溶解性有机碳影响

从2009年7月~2010年3月每月采集西太湖表层水样,分析叶绿素含量﹑蓝藻细胞裂解速率﹑磷酸盐浓度的变化,并通过切向流超滤系统分离得到的高分子量(1kDa~0.5μm)溶解性有机物的碳氮比值和高分子量溶解性有机碳浓度的变化.结果表明,西太湖蓝藻细胞裂解速率在11月达到最大值(0.43d-1),而磷酸盐和高分子量溶解性有机碳浓度分别在12月与9月达到最大值.细胞裂解速率与磷酸盐﹑高分子量溶解性有机碳浓度之间没有相关性,说明水华过后影响磷酸盐浓度﹑高分子量溶解性有机碳的因素很多,蓝藻细胞裂解只是其中重要因素之一.藻类水华的出现可能导致水体中其它磷形态(如有机磷)与磷酸盐之间的迁移转化,而大型浅水湖泊扰动导致的沉积物再悬浮和水华过后频繁的细菌活动都可能是影响高分子量溶解性有机碳的因素.秋季水华过后蓝藻细胞裂解释放的有机碳进入微食物网循环,引起细菌活动频繁,而溶解性有机物中含碳化合物比含氮化合物容易降解,所以碳氮比值逐渐减少.此外细菌通过硝酸盐合成溶解性有机氮也可能是碳氮比值减少的一个重要原因.

The effect of cyanobacteria on dissolved organic carbon post the bloom in autumn in Western Lake Taihu

Surface water sample from western Lake Taihu was collected monthly from July 2009 to March 2010. Chlorophyll a, cyanobacterial cell lysis rate, phosphate concentration were analyzed. Meanwhile high molecular weight (1kDa~0.5μm) dissolved organic carbon was separated by cross-flow ultrafiltration, and its concentration as well as the carbon to nitrogen ratio were measured. The highest cyanobacterial cell lysis rate (0.43d-1) was observed in November, while the maximum phosphate and high molecular weight dissolved organic carbon concentration was observed in December and September, respectively. No significant relationships were concluded between cell lysis rate and phosphate concentration, as well as high molecular weight dissolved organic carbon concentration. Cyanobacterial cell lysis rate was one of the factors that affect the levels of phosphate and high molecular weight dissolved organic carbon. The surrounding phosphate level was contributed to the phosphorus fractions transformation between organic phosphorus and phosphate. High molecular weight dissolved organic carbon in lake could be associated with other factors such as wind-induced resuspension of sediments and the frequent activity of bacteria through the microbial carbon loop. Compared to the nitrogen compounds, the carbon compounds were easily degraded, which resulted the decrease of carbon to nitrogen ratio after the bloom. Furthermore, the decrease of carbon to nitrogen ratio could have also been due to an increase in dissolved organic nitrogen produced from nitrate by heterotrophic bacteria.