Temporal and spatial distributions of phytoplankton and various forms of inorganic nitrogen in Lake Taihu

Abstract

为研究太湖浮游植物和各形态无机氮的时空分布特征及其相互关系,于2010年3月至2011年2月在太湖全湖范围内选取9个采样点进行每月采样分析,结果表明:太湖无机氮主要以硝态氮和铵氮形式存在,前者占76%,后者占22%;太湖北部靠近西北沿岸的湖区以及竺山湾的铵氮和亚硝态氮浓度通常要明显高于其他点位.太湖各采样点TIN(总溶解性无机氮)的季节变化趋势很相似,都表现为春季最高,夏秋季降低,冬季又有所升高;夏季北部湖区TIN降幅明显大于南部,使得前者TIN/TSP(总溶解性磷)远小于后者.春季太湖南部的微囊藻复苏量大于北部,但夏秋季微囊藻的暴发主要发生在太湖北部,此时微囊藻大暴发的点位(如梅梁湾)通常都伴随着很低的硝态氮浓度和TIN/TSP,使得这些点位比其他地方更容易发生N限制;Chl.a/浮游植物的比值与浮游植物总数呈极显著负相关,而与TIN/TSP的比值呈极显著正相关,这说明当藻类大量暴发而TIN/TSP下降时,浮游植物单个细胞内的平均Chl.a含量会有所下降,这种现象的原因有待进一步研究;绿藻、硅藻、裸藻和隐藻在时空分布上有一定相似性,而这四种藻与微囊藻则有较大差异.;Monthly whole-lake samplings (9 selected sites) were conducted from March 2010 to February 2011 to study the temporal and spatial distributions of phytoplankton and various forms of inorganic nitrogen and their relationships in Lake Taihu. Nitrate and ammonium were the major forms of inorganic nitrogen in the lake, which accounted for 76% and 22%, respectively. Concentrations of ammonium and nitrite in the northwest coastal belt and Zhushan Bay in the northern lake were usually significantly higher than other sampling sites. Seasonal variations of total soluble inorganic nitrogen (TIN) were very similar, in various sampling sites, which had generally a highest concentration in the spring, declined during summer-fall seasons, and then recovered in the winter. The summer TIN variations declined in the northern lake and was larger than these in the southern lake, which made the ratio of TIN:TSP in the northern lake much lower than that in the southern lake. Spring Microcystis spp. recruitment in the southern lake was more than that in the northern, but summer-fall blooms of Microcystis spp. mainly occurred in the northern lake, and the sites where Microcystis spp. greatly bloomed (e. g. Meiliang Bay) were usually accompanied with low levels of nitrite concentration and TIN:TSP ratio. The ratio of Chl.a:phytoplankton was significantly negative-correlated with phytoplankton number and positivecorrelated with the ratio of TIN:TSP, which indicated that the average content of Chl.a per phytoplankton cell declined with algae bloom and the ratio of TIN:TSP declines. The cause of this phenomenon needs further investigation. Temporal and spatial distributions of bacillariophyta, chlorophyta, euglenophyta and cryptophyta were similar to each other, but differed from that of Microcystis spp..