富营养化水体生态修复技术中凤眼莲与磷素的互作机制

Mechanism of Interaction between Eichhornia crassipes and Phosphorus in Ecological-remediation Technology of Eutrophic Water

为进一步完善富营养水体生态修复技术体系,提升除磷效能,从磷素对水体富营养化进程的贡献展开分析,指出磷素是制约浮游藻类生长的关键因素,并分析了凤眼莲Eichhornia crassipes与磷素的互相作用机制,即磷素对凤眼莲植株生理性状具有影响,而凤眼莲对磷的吸收同化作用又促成了除磷目标。研究显示:随着水中可获取磷浓度的升高,凤眼莲吸收的磷素更多地分配在茎叶部分。水体磷浓度过高,将激发凤眼莲对磷素的超累积性;水环境中磷素缺乏,凸显出凤眼莲的根部形态可塑性。水体氮磷浓度比(N/P)为2.5~5时凤眼莲可获得最大生物产量。凤眼莲对可溶性反应磷具有极优的净化效果;在藻华爆发期间,凤眼莲能通过密集根系捕获飘移的蓝藻,并吸收利用藻细胞衰亡所释放的磷素。在工程实践中,需统筹考量磷去除效果与去除速率,在高污染负荷的情况下,应优先考虑去除速率;当水再生作为饮用水源时,应优先考虑去除效果。凤眼莲生态修复工程设计须遵循先后次序:(1)最终水质目标;(2)生物产量;(3)植株品质。最终水质目标及营养去除与营养负荷水平密切相关。在大型湖泊和水库实践应用中,须先控制外源磷负荷,再逐步削减内源磷负荷。利用凤眼莲深度净化污水处理厂尾水,或在高负荷的入河、湖口处种养凤眼莲,可减轻外源磷负荷;在蓝藻积累和衰亡的背风区域种养凤眼莲,以吸收蓝藻释放的营养,从而减轻内源磷负荷。

The aims of the article are to optimize the ecological-remediation technology for eutrophic water utilizing Eichhornia crassipes and to improve the removal capacity of phosphorus （P） by the macrophyte. According to the contribution of phosphorus to eutrophication, it was pointed out in this study that phosphorus was the key factor limiting growth of floating algae. The mechanism of interaction between Eichhornia crassipes and phosphorus was discussed in the article, that was, the physiological character of the macrophyte was affected by phosphorus, and phosphorus, on the other hand, was removed from the water by assimilation of the macrophyte. Our results showed that Eichhornia crassipes accumulated more phosphorus in organs of leaf and stem with increasing available phosphorus concentration in water. Excessive phosphorus in water stimulated the hyperaccumulation of water hyacinth to phosphorus, while scarce of phosphorus in water increased root length and biomass of Eichhornia crassipes and enhanced nutrient acquisition. The ratio of N/P concentrations was 2.5~5, which fell in the range required for maximum biomass yield of the macrophyte. Eichhornia crassipes exhibited excellent capacity for removal of soluble reactive phosphorus （SRP）. During the outbreak of algal blooms, water hyacinth could capture cyanobacteria through dense roots and absorb the phosphorus released by dead cells of algal. The efficiency and effectiveness of phosphorus removal should be comprehensively considered in the practice of engineering. In the situation of high pollution loads, the criterion of effectiveness might be the priority. However, when water reclamation was aimed for drinking water resources, the criterion of efficiency would be the priority. In practice of bioremediation by water hyacinth, project design should follow the order of： （1） final water quality, （2） biological yield, and （3） quality of biomass. The final water quality and nutrient removal are closely linked with nutrient loading level. In the practical application in large lakes and reservoirs, exogenous phosphorus loading should be controlled first, and endogenous phosphorus source should then be reduced gradually. Removal of water hyacinth at or near river estuaries with high nutrient loading. Removal of endogenous phosphorus could be achieved by cultivating Eichhornia crassipes at lee site where algae accumulated and died, with released nutrients being absorbed by the macrophyte.