太湖蓝藻死亡腐烂产物对狐尾藻和水质的影响

为揭示富营养化造成淡水生态系统中沉水植物消亡的机制，本文就太湖蓝藻大规模死亡腐烂后的产物对水体水质以及沉水植物造成的影响进行了研究。本文以沉水植物穗花狐尾藻为研究对象，测定了水质参数（pH值，浊度（NTU），温度，溶解氧（DO），电导率（Ec），盐度，磷酸根（PO43-））以及狐尾藻Fv/Fm指标。将采自太湖梅梁湾的蓝藻水华，降解一个星期左右。随后在处理组中加入该蓝藻降解物，对照组中不加入。结果表明，加入蓝藻死亡腐解液后，水体的溶解氧、pH值均比对照组显著降低，浊度则显著升高。对照组中穗花狐尾藻生长良好，其Fv/Fm约为0.8，而经蓝藻腐烂液处理的实验组，穗花狐尾藻在两天之内便接近死亡状态，其Fv/Fm值降至0.3左右。以上结果表明蓝藻死亡腐烂后形成的腐解液确实能在很短时间内给沉水植被带来灭顶之灾。而在短时间内并不能形成大量附着生物，故本实验可排除其对水生植物的影响。本文证实了蓝藻死亡腐烂后的降解液极有可能是导致沉水植物消亡的主要原因。至于是由于蓝藻腐解液引起的哪种因素起主导作用，还有待进一步研究。

Effect of decomposition products of cyanobacteria on Myriophyllum spicatum and water quality in Lake Taihu,China

In order to reveal the mechanism on degradation of submerged macrophytes in the eutrophying freshwater ecosystems in shallow lakes, the effects of the decomposition products of cyanobacteria on the growth of submerged macrophyte and water quality were studied by laboratory experiment in this paper. In order to simulate the environment of Lake Taihu, the cyanobacterial bloom dominated by microcystis was collected from the surface water of Meiliang Bay in Lake Taihu, and the submerged macrophyte Myphyllum spicatum with the same vigor and the same size were collected from the aquatic planting areas near the Meiliang Bay. After one week degradation of algae bloom under dark and anaerobic condition, the bloom scum with the concentration about 0.47 g/mL was applied to Myphylum spicatum incubation system. The system contained about 8-10 Myphyllum spicatum which was growing in 12 L water in the tank. Then we planted the macrophyte on ca. 8 cm-thick sediment on the bottom of the tank. The water quality index including pH value, turbidity (NTU), temperature, dissolved oxygen (DO), electrical conductivity (Ec), salinity, phosphate radical (PO43-) in the system and the index Fv/Fm of M.spicatum spicatum were measured to monitor the water quality and physiological activity of Myphyllum spicatum in the system. The results showed that DO value and pH value in water of Myphyllum spicatum incubation system drop significantly after the application of bloom decompostion residuals, and the turbidity increased markedly, which possibly resulted from both the large amounts of reducing substances and suspended substances in the decomposition products of cyanobacteria. The phosphate(PO43-) concentration in water almost keep stable during the experiment and showed no dinstinct trends of change in the groups, which indicated that phosphorus nutrient did not significantly affect the growth of M. spiatum. The temperature and salinity in experimental groups also insignificantly differed from the control group from the results. After two days cultivation, the values of Fv/Fm always maintained nearly 0.8 in the control group, but it decreased sharply to 0.3 in treatment groups. It meant that the growtn of M. spicatum in the control group was much better than the growth in experimental groups which was on the margin of death. In other words, M. spicatum was strongly affected by the decomposition products of cyanobacteria in Lake Taihu. Interestingly and importantly, the submerged macrophyte M. spicatum was dead in merely two days after the application of decomposition products of cyanobacteria. Being the time so short, periphyte is hard to develop and become the key reason for the dead of M. spicatum. And the incubation system is a glass side tank, so the overshadow of bloom is not the real reason for the dead of the macrophyte. So the chemical products from the dead cyanobacteria might be the major factor causing the degradation of submerged macrophytes in the freshwater systems. In this way, besides the living cyanobacteria, the dead ones could also affect the submerged macrophytes at an even greater extent. Additionally, the importance of various factors from the decomposition products is still worthy to have a further study.