香溪河消落带狗牙根附生生物膜的形成及其重金属富集特征

Formation and Heavy Metal Enrichment of Epiphytic Biofilm in Cynodon dactylon in the Water Level Fluctuation Zone of the Xiangxi River

通过挂瓶实验模拟消落带淹水期不同水深(水面下0.2、5、10 m)狗牙根附生生物膜的形成过程,通过野外采集消落带淹水期不同水位(175、165、155 m)狗牙根附生生物膜,研究了三峡库区香溪河消落带狗牙根附生生物膜的组成、特征及其对4种重金属(Cr、Cu、Pb和Cd)的富集特征。结果显示,0.2~10 m淹水深度下,狗牙根表面在淹水后7 d内附着生物膜,在28 d内形成,不同淹水深度导致的光照差异是影响生物膜形成的关键因素;淹水期狗牙根生物膜相对生物量(RB)、叶绿素(Chl)和胞外聚合物(EPS)平均含量分别为1112.05±651.02、0.81±0.45、22.47±9.35 mg/g,最终在狗牙根表面形成约1.1倍湿质量的生物膜。狗牙根生物膜中Cr、Cu、Pb和Cd平均含量分别为74.94±17.18、20.46±2.61、14.25±3.08、0.57±0.10 mg/kg,为香溪河水体同类重金属含量的18000倍以上;单位面积狗牙根生物膜对Cr、Cu、Pb和Cd的富集量分别达到23.08、5.78、4.02、0.16 mg/m^(2),与全国同类重金属平均大气沉降通量相比,Cr含量相近,Cu、Pb和Cd含量约是1/4。香溪河消落带淹水期间,狗牙根表面形成了与其生物量相当的生物膜,并富集了水体中的重金属,而消落带落干后,生物膜脱落进入土壤,可能成为消落带重金属污染的一个重要来源。

A hanging bottle experiment was conducted to simulate the formation process of Cynodon dactylon biofilm at different water depths(0.2,5,and 10 m below the water surface)in the flooding stage of the water level fluctuation zone(WLFZ).Field samples of Cynodon dactylon epiphytic biofilms were collected at different water levels(175,165,and 155 m)in the flooding stage of the WLFZ.The composition and characteristics of the epiphytic biofilms and the enrichment characteristics of four heavy metals(Cr,Cu,Pb,and Cd)in Cynodon dactylon in the Xiangxi River WLFZ of the Three Gorges Reservoir Area were exam⁃ined.The results demonstrated that Cynodon dactylon attached to the biofilm within 7 days and fully formed within 28 days after being flooded at water depths ranging from 0.2 m to 10 m.The variation in illumination due to different water depths was identified as the key factor influencing biofilm growth.During the flooding period,the average relative biomass(RB),chlorophyll(Chl),and extracellular polymeric substance(EPS)of the Cynodon dactylon biofilm were 1112.05±651.02,0.81±0.45,and 22.47±9.35 mg/g,respectively.The biofilm formed on the surface accounted for approximately 1.1 times the wet weight of Cynodon dactylon.The average content of Cr,Cu,Pb,and Cd in the Cynodon dactylon biofilm was 74.94±17.18,20.46±2.61,14.25±3.08,and 0.57±0.10 mg/kg,respectively.which was more than 10,000 times higher than the corresponding concentrations in the Xiangxi River water.The enrichment of Cr,Cu,Pb,and Cd by the Cynodon dactylon biofilm per unit area was 23.08,5.78,4.02,and 0.16 mg/m^(2),respectively.In comparison to the national average atmospheric deposition flux of the same heavy metals,the content of Cr was found to be similar,whereas the content of Cu,Pb,and Cd was approximately one-fourth.During the flood⁃ing stage of the WLFZ,a biofilm of comparable biomass was formed on the surface of Cynodon dactylon,which accumulated heavy metals from the water.However,after the WLFZ dried up,the biofilm would detach and enter the soil,potentially becom⁃ing an important source of heavy metal pollution in the WLFZ.