基于水生动物评价持续高余氯尾水排放对湿地水体的影响

Evaluation of impact of continuous discharge of high residual chlorine tailwater on wetland water ecosystem based on aquatic animals

尾水补充河涌既能在一定程度上解决废水带来的污染问题,也能缓解城市缺水、水动力不足的情况,具有显著的社会效应、生态效应和经济效应。新冠疫情爆发以来,各污水处理厂尾水中含氯消毒剂投加量显著增加,含有过量余氯的尾水排入河涌可能对水生生物存在潜在的影响。海珠湿地属于三角洲城市湖泊与河流湿地,与40条河涌交织联通,是广州市规模最大、保存最完整的湿地生态系统。选择海珠湿地典型河涌进行了长时间的跟踪观测,在尾水暂停排放期(2021年8月5日至10日),尾水排放1个月(2021年9月10日至13日)及3个月(2021年11月15日至18日)后分别测定了尾水主要流经河涌的水体理化指标、鱼类和底栖动物物种数量和密度,同时选择与尾水不直接连通的水体作为参考点。通过相对重要性指数、物种数量和密度以及冗余分析等研究尾水排放前后鱼类和底栖动物的群落结构特征,使用鱼类和底栖动物生物完整性指数综合评价尾水排放前后受纳水体水生态健康状况。研究表明:1、尾水排放后,排放口附近水体余氯、总氮以及盐度显著上升;2、随着尾水的持续排放,适应性强的耐污鱼类成为优势种,鱼类群落结构朝着耐污类群方向发展,而底栖动物中耐污优势类群寡毛纲颤蚓科和多毛纲疣吻沙蚕物种数量有所降低,其密度则呈大幅下降趋势,尤其是在尾水排放口附近水体;3、通过鱼类生物完整性指数评价受纳水体水环境健康质量,尾水排放前后评价结果无显著差别,主要为亚健康和一般,而通过底栖动物生物完整性指数评价则发现在排放口附近评价结果由排水前的亚健康为主变为持续排水后的亚健康和一般为主,其它点位在尾水排放前后则无明显差别,主要以健康为主;4、随着尾水的持续排放,底栖动物受到余氯的影响越来越明显,鱼类则没有受到明显影响。总体而言,高余氯尾水持续排放明显改变了水质并影响了水生动物的生存,后续还需进一步探讨尾水排放对其它水生生物的影响及具体的影响机制。对尾水排放前后鱼类和底栖动物群落结构特征及生物完整性做了详细探讨,为水环境健康评价以及尾水的合理利用提供理论和数据支持。

Tailwater replenishment of urban river can not only solve the pollution problem caused by waste water to a certain extent,but also alleviate the shortage of water and hydrodynamic power in cities,which has significantly social,ecological and economic effects.Since the outbreak of COVID⁃19,the dosage of chlorine⁃containing disinfectant in tailwater has increased significantly,and the excessively residual chlorine had a potential impact on aquatic organisms.Haizhu Wetland belongs to the urban lake and river wetland of the delta,which contains 40 rivers and is the largest and best⁃preserved wetland ecosystem in Guangzhou.In this study,we selected typical streams in the Haizhu wetland for a long period of tracking observation.The physical and chemical index,the number and density of fish and benthic animals in the streams were measured during three periods:the suspension of tailwater discharge period(5—10,Aug,2021),one month(10—13,Sep,2021),and three months(15—18,Nov,2021)after the tailwater was discharged,respectively.The stream that was not directly connected with the tailwater was selected as the reference point.Index of biologic integrity,redundancy analysis and other methods were used to explore the impact of continuous discharge of high residual chlorine tailwater on aquatic animals,and to evaluate the water ecological health status.The results showed that:(1)after the discharge of tailwater,the residual chlorine,total nitrogen and salinity in the water near the discharge outlet increased significantly.(2)With the continuous discharge of tailwater,adaptable and pollution⁃tolerant fish became the dominant species,while the number of dominant pollution⁃tolerant species in benthic animals decreased,and their density decreased significantly,especially in the streams near the discharge outlet.(3)According to the fish biologic integrity index,the water environmental quality were mainly sub⁃healthy and general in health,and had no significant difference among the measured sites.While by the benthic biologic integrity index,the water environmental quality near the discharge outlet changed from sub⁃health before discharge to sub⁃health and general in health after continuous discharge.There was no significant difference at other sites before and after tailwater discharge,mainly for health.(4)With the continuous discharge of tailwater,the effect of residual chlorine on benthic animals was more and more significant,but the effect on fish did not change obviously.In general,the continuous discharge of tailwater with high residual chlorine significantly changed the water quality and affected the survival of aquatic animals.Further studies are needed to explore the impact of tailwater discharge on other aquatic organisms and the specific influencing mechanism.In this study,the characteristics of community structure and biological integrity of fish and benthic animals before and after discharge of tailwater were discussed in detail.The study provided the theoretical and data support for water environmental health assessment and rational utilization of tailwater.