大沽排污河生态修复河道水质综合评价及生物毒性影响

为了改善城市河道水质,实现排污河污染控制与修复,在天津市大沽排污河的上游代表性河段开展了河道原位生态修复工程示范。对植物修复后河道的污染状况进行了监测和分析,与清洁河道做了比较,并对水质修复效果和生物毒性影响状况进行综合分析和评价,研究生态修复示范工程对排污河水质的修复效果和生态效应。结果表明:经种植水葱等水生植物进行生态修复后,河道污染一定程度上降低,水质得到改善。大沽河主要污染是营养元素N、P污染和有机物污染,重金属污染不严重。植物修复对电导率、溶解性总固体(TDS)、盐度、氯化物有一定影响,但影响不显著;对COD等有机污染的修复效果较好,最高去除效率可达54%,但相比清洁水域值依然较高,有机污染依然较严重;对营养元素N、P没有修复效果,反而修复区有升高的趋势,相对清洁水域污染严重。主成分分析表明水质参数主要是氨氮、总氮、总磷代表的营养元素及pH值、DO、电导率、TDS、盐度和氯化物,综合评定结果显示修复区域芦苇根部水质最好;聚类分析将17个水质指标分成5类,并与主成分分析结果显示出一致性。植物根际周边的微生物数量多,群落多样性高。植物修复对水样植物毒性影响明显,能降低其毒性;水样对发光菌均具有毒性作用,存在潜在的急性生物毒性;修复区水样对水生动物大型蚤不存在急性生物毒性。

Evaluation of the effects of ecological remediation on the water quality and biological toxicity of Dagu Drainage River in Tianjin

An ecological restoration project was conducted in the upstream portion of the Dagu River to improve the urban river water quality as well as to achieve pollution control and remediation of a sewage drainage river. Plant species for phytoremediation were screened and different species were used in the field project. The growth occurred in the following order: macrophytes > slope plants > submerged plants; among different microphytes, Sagittaria sagittifolia > Phragmites australis > Scirpus tabernaemontani > Typha angustata > Iris pseudacorus; among floating plants, Water lily > Lotus. The pollution status of the water body in the phytoremediation area was monitored and compared with that of a clean water area in Mati Lake at Nankai University and the Outer Ring River of Tianjin. In addition, the effects of remediation on the water quality and ecological toxicity of the drainage water were analyzed and assessed comprehensively to show the effects of the ecological remediation project. The results showed that the water quality was improved by the cultivation of aquatic plants such as Scirpus tabernaemontani. N and P were found to be the main pollutants in the Dagu Drainage River, and heavy metal contamination was not serious. Phytoremediation affected conductivity, total dissolved solids (TDS), salinity and chloride content to some extent. Good remediation results were observed for organic pollutants such as COD, with a degradation rate of 54% around the plants. Water samples in the plant growth area showed much lower COD values than those from areas with no plant growth. The N and P values were also highly relative to clean water, which was assumed to be a result of the bottom sludge with low dissolved oxygen (DO) and pH conditions. Principal component analysis showed that the water quality parameters were mainly nutrient related substances such as ammonia, total nitrogen, total phosphorus, and other items such as pH, DO, conductivity, TDS, salinity and chloride. Comprehensive assessment showed that water quality in the reed root zone was the best. The 17 water quality parameters were grouped into five categories based on cluster analysis, which showed good consistency with the results of principal component analysis. The plate counting method result showed that the microbial numbers surrounding the rhizosphere were high and had higher species diversity. The number of bacteria was lower than that of fungi. Phytoremediation reduced the toxicity of water samples on root elongation of wheat. The water sample was toxic to luminescent bacteria, which indicated potential acute toxicity, but the difference was not significant. The water in the remediation area did not show acute toxicity against daphnia. Further screening of remediation plants should be conducted to identify plants species with higher nitrogen and phosphorus absorption ability to enable the removal of pollutants from contaminated river systems. Additionally, microbial consortium can be added to the water system to increase the decomposition of organic pollutants and transformation of toxic substances, which can improve the efficiency of remediation projects and realize ecological restoration of rivers.