环境科学研究  2020, Vol. 33 Issue (6): 1488-1496  DOI: 10.13198/j.issn.1001-6929.2020.05.24

引用本文  

齐月, 李俊生, 马艺文, 等. 黄河三角洲滨海滩涂湿地沉积物重金属空间分布及生态风险评价[J]. 环境科学研究, 2020, 33(6): 1488-1496.
QI Yue, LI Junsheng, MA Yiwen, et al. Distribution and Risk Assessment of Heavy Metals of Surface Sediments in Intertidal Flats of the Yellow River Delta, China[J]. Research of Environmental Sciences, 2020, 33(6): 1488-1496.

基金项目

科技部重点研发计划项目(No.2016YFC0503304, 2017YFC0506200)
National Key Research and Development Program of China (No.2016YFC0503304, 2017YFC0506200)

责任作者

李俊生(1968-), 男, 安徽巢湖人, 研究员, 博士, 博导, 主要从事生物多样性保护、自然保护区管理、生物安全评估以及气候变化影响评价研究, lijsh@craes.org.cn.

作者简介

齐月(1983-), 女, 黑龙江齐齐哈尔人, 博士, 主要从事污染生态学、生物多样性保护研究, qiyue8351572@163.com

文章历史

收稿日期:2020-03-10
修订日期:2020-05-06
黄河三角洲滨海滩涂湿地沉积物重金属空间分布及生态风险评价
齐月1,2, 李俊生1,2, 马艺文1,2, 贺婧1,2, 付刚1,2, 沈奇1,2, 赵彩云1,2, 曹明1,2    
1. 中国环境科学研究院生态研究所, 北京 100012;
2. 环境基准与风险评估国家重点实验室, 北京 100012
摘要:为了解黄河三角洲滨海滩涂湿地沉积物中重金属的污染程度,对黄河三角洲位于渤海湾、黄河口附近、莱州湾等滨海滩涂样地的表层沉积物中4种重金属(Cd、As、Cu、Pb)的含量及其空间分布进行研究,分析其含量与环境因子的相关性,并采用地累积指数和潜在生态风险指数评价其污染程度及生态风险.结果表明:表层沉积物中Cu、As、Cd、Pb的平均含量分别为14.36、7.92、0.20、16.24 mg/kg.不同样地间除Pb以外,其他3种重金属含量均差异显著,黄河口附近滩涂Cu含量高于非河口滨海滩涂,Cd含量呈南高北低的分布特征,As含量在渤海湾东侧滨海滩涂中较高.相关性分析显示,Cu、As、Pb来源相同或相近,Cd与Cu来源相同或相近,Cd与As来源不同;粒径 < 4 μm的沉积物含量与Cu、Pb、As含量均呈显著正相关,粒径为4~63 μm的沉积物含量与Cu、As含量均呈显著负相关.地累积指数评价表明,研究区Cd为轻度污染,其他重金属无污染;综合潜在生态风险指数分析表明,研究区重金属潜在生态风险指数(RI)介于59.21~158.63之间,平均值为107.71,属于低风险,黄河口附近及莱州湾滨海滩涂沉积物中重金属潜在生态风险高于渤海湾滨海滩涂.研究显示,黄河三角洲位于莱州湾及黄河口附近的滨海滩涂湿地沉积物中重金属的潜在生态风险需要重点防控.
关键词滩涂湿地    表层沉积物    重金属    空间分布    生态风险    
Distribution and Risk Assessment of Heavy Metals of Surface Sediments in Intertidal Flats of the Yellow River Delta, China
QI Yue1,2, LI Junsheng1,2, MA Yiwen1,2, HE Jing1,2, FU Gang1,2, SHEN Qi1,2, ZHAO Caiyun1,2, CAO Ming1,2    
1. The Institute of Ecology, Chinese Research Academy of Environmental Sciences, Beijing 100012, China;
2. State Key Laboratory of Environmental Criteria and Risk Assessment, Beijing 100012, China
Abstract: This study explored heavy metal pollutants in the intertidal flats of the Yellow River Delta. The contents and spatial distribution of four heavy metals (Cd, As, Cu and Pb) in the surface sediment samples collected from the coastal tidal flats in the Yellow River Delta were determined. The Pearson correlation for heavy metals and the environmental factors was analyzed. The geo-accumulation index and potential ecological risk index were used to estimate the degree of heavy metal contamination in the surface sediments. The results indicated that the average content of Cu, As, Cd and Pb in surface sediments was 14.36, 7.92, 0.20 and 16.24 mg/kg, respectively. There were significantly different in the content of Cu, As, and Cd between the different sample sites. There were no significantly different in the content of Pb between the different sample sites. The content of Cu in the tidal flats near the Yellow River Estuary was higher than that in Laizhou Bay and Bohai Bay, and the content of Cd in the tidal flats in Laizhou Bay was higher than that in Bohai Bay, and the content of As in the tidal flats in northeast of the Yellow River Delta was higher than that of the other sample sites. According to the correlation analysis, the sources of Cu, Pb and As were same or similar, and the sources of Cd and Cu were same or similar, while the sources of Cd and As were different. Clay particle content (< 4 μm) of the sediments were significantly positively correlated with the content of Cu, Pb and As. Silt particle content (4-63 μm) of the sediments were significantly negatively correlated with the content of Cu and As. The evaluation results of the geo-accumulation index showed that Cd pollution level was low and Cu, Pb and As were not polluted. The average potential ecological risk index (RI) of heavy metals was 107.71 (ranged from 59.21 to 158.63), indicating low ecological risk. The RI of heavy metals of surface sediments in the coastal tidal flats of the Yellow River Estuary and Laizhou Bay was higher than that of Bohai Bay. This study shows that the potential ecological risk of heavy metals in the sediments of the coastal tidal flats in the Yellow River Delta needs to be controlled, especially in Laizhou Bay and the Yellow River Estuary.
Keywords: tidal flats    surface sediments    heavy metals    spatial distribution    ecological risk    

滨海滩涂湿地是陆海生态过渡带,包括潮间带泥滩、沙滩和海岸其他咸水沼泽,受海洋和陆地的双重影响,具有特殊的气候、水文、土壤和生物特征,是十分脆弱的生态系统[1-3].同时,滨海滩涂湿地具有生物多样性维持、水质净化、旅游文化等多种生态系统服务[4-5].然而,我国滨海滩涂湿地生态系统服务功能日益退化,环境污染是重要的影响因素之一[3].其中,重金属作为典型的累积性污染物,对人类健康和生态环境具有显著的生物毒性和持久性威胁[6-7],将会改变滨海滩涂湿地生态系统的关键生态过程[3].湿地沉积物作为重金属污染物的主要载体和宿体,其重金属含量也可以反映水环境的污染状况[1, 8].因此,滨海滩涂湿地沉积物中重金属污染状况受到国内外关注.邻近河口区的滨海滩涂沉积物中重金属污染状况常是大家关注的重点,学者们在坦桑尼亚Msimbazi河、马兰西亚巴生河、阿根廷布兰卡河[1, 9-10]以及我国的黄河[11-12]、长江[13-16]、钱塘江[17]、珠江[18]的河口区滨海滩涂湿地均开展了大量研究.非河口区如日本东南沿海[19]、我国莱州湾[20]及江苏沿海[21-22]分布的滨海滩涂湿地沉积物中重金属污染状况也越发受到关注.为深入揭示滨海滩涂湿地污染特征,河口区及非河口区的研究均不局限于在相同的地貌单元内开展[23-24],这对科学保护和修复滨海滩涂湿地具有重要意义.

黄河三角洲滨海滩涂湿地是环渤海滨海湿地的重要组成部分[25],是渤海湾与莱州湾近岸海水水质净化的潜在天然场所[26-27];同时也是黄河三角洲湿地最主要的一类天然湿地[28],为东北亚内陆和环西太平洋鸟类迁徙提供了重要的中转站和越冬栖息地,对于全球生物多样性保护具有重要意义[29].然而,近年来随着黄河三角洲地区城市和港口的发展,工农业建设、石油开采等人类活动不断威胁着区域内滨海滩涂湿地的环境质量.以往关于黄河三角洲湿地重金属污染状况的研究,主要集中在黄河口湿地和黄河三角洲内陆水域[11, 30-33],也有研究关注黄河口以北位于渤海湾的滨海滩涂湿地[34-35].然而,滨海滩涂湿地沿黄河三角洲海岸线分布于渤海湾、黄河口、莱州湾不同的地貌单元下,却鲜有研究全面关注黄河三角洲不同地貌单元下滨海滩涂湿地沉积物中重金属的分布特征.鉴于此,该研究探讨黄河三角洲分布于渤海湾、黄河口及莱州湾的滨海滩涂湿地沉积物中重金属(Cd、Cu、Pb、As)的含量及其空间分布特征,并对其生态风险进行评估,以期为黄河三角洲滨海滩涂湿地的生态保护及污染治理提供基础支撑.

1 材料与方法 1.1 研究区概况

黄河三角洲位于山东省北部,渤海湾与莱州湾之间,占地面积约6 000 km2,海岸线全长约350 km.黄河三角洲向海突出的沙嘴形成的海岸,其演变特征类型为淤进型;沙嘴以北海岸位于渤海湾南部,以侵蚀型海岸为主,而沙嘴以南海岸位于莱州湾西侧,则主要属于稳定型海岸[36].黄河三角洲属温带半湿润大陆性季风气候,年均气温11.7~12.6 ℃.年均降水量530~630 mm,其中70%的降水集中在夏季,年均潜在蒸发量2 049 mm[37].

1.2 样品采集

2017年9月在黄河三角洲沿着海岸从滨州市徒骇河河口至东营市支脉沟口共选取7个潮滩采样地(见图 1),分别位于渤海湾、黄河口附近及莱州湾海岸.根据实际调研,东营港以南至黄河口以北的海岸线,由于堤坝等人工设施的修建,滨海滩涂已被破坏,未能布设样地,选取的样地相对均匀地分布于黄河三角洲海岸线,且均为光滩和碱蓬单一植物种群滩涂.在每个样地内分别垂直于海岸线布设3条样线,各样线间距为200~400 m;每条样线从低潮潮位线向岸上分别设定6个采样点,其中样地2和样地4因修筑堤坝分别仅完成5个采样点布设,采样点间距为200 m,共计120个采样点.对于每个采样点采用五点梅花取样法取0~5 cm表层沉积物,混合四分法取样.将每个采样点的土样放入塑封袋中运回实验室,室内自然风干,待测.在有地表植被的采样点设1 m×1 m的植物样方,记录植株密度.

图 1 采样点分布示意 Fig.1 The locations of the sampling sites
1.3 样品分析

沉积物粒径采用Mastersizer 2000粒径分析仪测定,按黏土(< 4 μm)、壤土(4~63 μm)和砂土(> 63 μm)分级.沉积物样品经过风干、研磨、过0.149 mm筛,采用MultiN/C3100固体模块HT1300(Analytikjena,德国)分析总氮(TN)含量;采用HClO4-H2SO4消煮[38],钼锑抗分光光度法测定总磷(TP)含量;采用10%(V / V)的盐酸溶液酸化去除沉积物中碳酸盐,在100 ℃下焙烧3~12 h,采用Multi N/C3100固体模块HT1300分析总有机碳(TOC)含量;采用HCl-HNO3-HF-HClO4消解,石墨炉原子吸收分光光度法测定沉积物中Pb和Cd含量,火焰原子吸收分光光度法测定沉积物中Cu含量,二乙基二硫代氨基甲酸银分光光度法测定沉积物中As含量. Pb、Cd、Cu、As的标准物质为GBW07423洪泽湖积物(GSS-9),标样回收率分别为89%±4%、90%±4%、89%±4%、86%±4%.取过2 mm筛的沉积物,土水比为1 :2.5下悬浮30 min,用pH计(FE20-FiveEasyTM pH, Mettler Toledo,德国)测定pH.

1.4 潜在生态风险评价 1.4.1 地累积指数评价法

地累积指数法(Igeo)是依据沉积物中重金属的背景值定量分析其污染程度的方法[24, 39],计算公式:

$ {I_{{\rm{geo}}}} = {\rm{lo}}{{\rm{g}}_2}\frac{{{c^i}}}{{1.5 \times {c_{\rm{b}}}^i}} $ (1)

式中:ci为样本中重金属i含量的测定值,mg/kg;cbi为重金属i的背景值,该研究中分别为山东省土壤元素背景值(Cu、Cd、Pb、As含量背景值分别为24.0、0.084、25.8、9.3 mg/kg)[40]和中国浅海沉积物元素背景值(Cu、Cd、Pb、As含量背景值分别为15.0、0.065、20.0、7.7 mg/kg)[41];修正系数1.5用来消除沉积或成岩作用引起的背景值变动的误差.地累积指数法评价分级见表 1.

表 1 地累积指数法评价分级描述 Table 1 The classification of Igeo
1.4.2 潜在生态风险指数评价法

潜在生态风险指数(RI)考虑了重金属的污染程度、生物毒性和综合生态风险,体现了生物有效性和相对贡献比例及地理空间差异等特点[24, 39],用于定量评价单一重金属风险等级和多个重金属的总体风险等级,计算公式:

$ {\rm{RI}} = \sum\limits_{i = 1}^n {{E_{\rm{r}}}^i} = \sum\limits_{i = 1}^n {({T^i} \times {C_{\rm{f}}}^i)} = \sum\limits_{i = 1}^n {\left( {{T^i} \times \frac{{{c^i}}}{{{c_{\rm{b}}}^i}}} \right)} $ (2)

式中:RI为多金属潜在生态风险指数;Eri为金属i的潜在生态风险因子;Cfi为金属i的污染因子;Ti为金属i的毒性响应因子;cbi为沉积物和土壤背景参考值,依据中国浅海沉积物元素背景值[41]Ti反映了金属在水相、固相和生物相之间的响应关系,Hakanson[42]给出了重金属的毒性响应系数(Cd为30,As为10,Pb、Cu均为5). Eri和RI的风险分级标准见表 2.

表 2 潜在生态风险因子(Eri)和生态风险指数(RI)等级划分 Table 2 Classification of potential ecological risk (Eri) and hazard quotient (RI)
1.5 数据分析

采用双因素方差分析法(Two-way ANOVA)研究样地间、距低潮潮位线不同距离间以及二者间相互作用对沉积物中重金属含量的影响.对差异显著的主要影响因素先用单因素方差分析(ANOVA),再用Fisher′s Protected LSD检验各处理间的显著性差异(P < 0.05).若转换数据不满足方差齐性,则采用非参数Kruskal-Wallis检验后进行所有成对的多重比较.采用Pearson相关分析研究重金属含量的自相关性,及其与沉积物理化性质、植株密度间的相关性.数据以均数±标准差表示.采用Excel 2010软件整理数据,采用SPSS 20.0软件进行数据分析,使用Origin 8.5软件作图.

2 结果与讨论 2.1 沉积物中重金属含量

黄河三角洲滨海滩涂湿地沉积物中重金属的平均含量见表 3,其中,Cu含量为11.49~16.74 mg/kg,As含量为6.34~10.66 mg/kg,Cd含量为0.10~0.30 mg/kg,Pb含量为13.57~19.04 mg/kg.工业和城市活动增加了海洋环境中的重金属含量,也直接影响着海岸生态系统[19],这或许是该研究结果低于天津滨海湿地中重金属含量(见表 3)的影响因素之一.较莱州湾海域而言,渤海湾对滨海滩涂湿地的环境压力并不相同[43],这是影响该研究中重金属含量高于莱州湾滨海滩涂湿地沉积物中相应数值(见表 3)的潜在因素.此外,除承受当地人类活动和海洋的双重压力外,黄河三角洲还要承接流域沿线各城市沿黄河传导的人类活动压力.这与长江口滨海滩涂湿地所承受的压力相似,但是该研究中Cu、Cd和Pb的含量均低于长江口滩涂湿地沉积物中相应数值[15, 24],或许与近年来长江经济带的快速发展有关.

表 3 莱州湾、渤海湾及其滨海湿地表层沉积物重金属平均含量比较 Table 3 Comparison of the mean contents of heavy metals in surface sediments of Laizhou Bay, Bohai bayand thiercoastal wetlands

通过双因素方差分析可知,黄河三角洲滨海滩涂湿地不同样地间沉积物中Cu、Cd和As的含量均差异显著,但Pb含量差异不显著(见表 4).由于黄河三角洲海岸地貌凹凸相间较为复杂,其不同的地貌单元具有不同的动力沉积环境[44-45],这对重金属沉积会有一定影响.距低潮潮位线不同距离的沉积物中Cu、Cd、Pb和As的含量均无显著差异,样地与距低潮潮位线距离间对4种重金属含量的影响无交互作用(见表 4).这表明在距低潮潮位线1 000~1 200 m的范围内,潮汐过程或许不是影响该滨海滩涂湿地沉积物中重金属分布的因素,且不同样地间潮汐作用相似.

表 4 双因素方差分析(F值)不同影响因素对表层沉积物中重金属含量的影响 Table 4 Two-way ANOVA results (F values) for testing for different factors with heavy metals in the surface sediments
2.2 沉积物重金属的空间分布特征

图 2所示,黄河三角洲滨海滩涂湿地沉积物中不同重金属含量具有不同的空间分布特征.黄河口附近样地5的Cu含量略高于渤海湾及莱州湾样地〔见图 2(A)〕.沉积物中Cd含量呈现南高北低的空间分布特征,黄河口附近样地5及莱州湾样地6、样地7的Cd含量均高于渤海湾样地1~样地4〔见图 2(B)〕.沉积物中Pb含量呈现出渤海湾西侧和黄河口附近样地较低的分布特征,即样地4和样地7的Pb含量均较高,而样地1、样地3、样地5的Pb含量均较低〔见图 2(C)〕.沉积物中As含量的空间分布特征与Cd含量相反,呈现渤海湾东侧样地偏高的分布趋势,即样地2、样地3和样地4的Cd含量均较高〔见图 2(D)〕.

注:不同小写字母表示差异显著性(P < 0.05). 图 2 不同样地间表层沉积物中4种重金属的平均含量 Fig.2 The average concentrations of 4 heavy metals in the surface sediments at different sample sites
2.3 重金属含量与环境因子的关系

相关性分析显示,Cu含量与As、Cd、Pb含量均呈显著正相关,As含量与Cu、Pb含量均呈显著正相关,而Cd含量与As含量呈显著负相关(见表 5).相关性分析结果可用于判断重金属污染来源是否相同,根据相关性显著的重金属具有相同来源[47-48]的原则来判断,Cu、As、Pb来源相同或相近,Cd与Cu来源相同或相近,而Cd与As的来源不同.

表 5 沉积物中4种重金属与环境因子的Pearson相关性分析 Table 5 The Pearson correlation coefficients for 4 heavy metals and the environmental factors of the sediments

相关性分析结果(见表 5)表明,黏土(< 4 μm)含量与Cu、Pb、As含量均呈显著正相关,表明粒径 < 4 μm的黏土对Cu、Pb、As的吸附效果更强;壤土(4~63 μm)含量与Cu、As含量呈显著负相关,表明随着沉积物中壤土含量的增加,Cu、As含量会有所减少;砂土(> 63 μm)含量与各重金属含量均无显著相关性.沉积物粒径大小及其组分可以影响潮间带重金属含量,因为粒径小的沉积物具有更大的比表面积利于吸附[20].

环境因素是影响重金属沉积的重要因素之一[20].相关性分析表明,不同重金属含量与沉积物pH、TOC含量、TN含量、TP含量的相关性各不相同(见表 5).结果显示,Cu含量与TOC含量呈显著正相关,表明沉积物中TOC含量增加则会增强沉积物对Cu的吸附;Cu含量与沉积物pH呈显著负相关,与天津滨海土壤的研究结果[49]相同,也有研究表明马来西亚巴生河口滨海滩涂湿地中Cu含量与沉积物pH呈负相关但不显著[1],这与试验条件下沉积物pH升高会增加沉积物对Cu的吸附[50]有所不同,在自然环境中是否有其他环境因素影响了不同pH沉积物对Cu的吸附值得深入思考. As、Pb含量均与沉积物中TOC含量呈显著正相关,但与TN含量呈显著负相关,As含量还与沉积物中TP含量呈显著正相关,表明沉积物中有机质含量越高,As和Pb含量也越高,而沉积物中TN含量越高则As和Pb的含量会降低. Cd含量与沉积物中TP含量呈显著负相关,表明沉积物中TP含量越高,Cd含量就越低.碱蓬为研究区域中的单一植物群落,其密度与Cu、As、Cd、Pb含量均无显著相关性,表明其密度对滩涂沉积物中重金属含量的影响不大.

2.4 重金属污染评价 2.4.1 地累积指数评价法

根据地累积指数法分析,不同样地间各重金属Igeo的平均值排序为Cd>As>Cu>Pb,且相对于山东省土壤元素背景值分析结果〔见图 3(a)〕而言,依据中国浅海沉积物元素背景值分析各重金属的污染水平更高〔见图 3(b)〕.依据中国浅海沉积物元素背景值分析〔见图 3(b)〕来看:Cd的Igeo平均值为0.664,属于轻度污染,位于渤海湾的样地1~样地4属于轻度污染和无污染,位于黄河口附近的样地5属于偏中度污染,位于莱州湾的样地6和样地7属于偏中度污染;As的Igeo平均值为-0.710,属于无污染,位于渤海湾的样地2~样地4中有少量采样点处于轻度污染,其他样地均处于无污染但接近轻度污染的临界值;Cu和Pb的Igeo平均值分别为-0.722、-0.975,各样地均属于无污染但接近轻度污染临界值,其中Cu在样地2中有少量采样点处于轻度污染.

图 3 黄河三角洲滨海滩涂湿地7个样地表层沉积物中重金属的地累积指数(Igeo) Fig.3 Geo-accumulation index (Igeo) assessment of heavy metals in surface sediments at 7 sample sites of the Yellow River Delta
2.4.2 潜在生态风险指数分析法

潜在生态风险评价结果(见表 6)表明,沉积物中Cu、Pb、As的Eri均低于40,属于低风险;黄河三角洲北部位于渤海湾的样地1~样地4中Cd的Eri∈(40,80],属于中等风险,而黄河口附近样地5及其以南位于莱州湾的样地6和样地7中Cd的Eri∈(80,160],属于高风险.各重金属风险顺序为Cd>As>Cu>Pb,与2.4.1节中结果相同,且与渤海沉积物中重金属的Eri(Cd、As、Cu、Pb的Eri分别为92.53、11.92、6.66、6.01)排序结果[43]一致,与环渤海地区土壤重金属的Eri(Cd、As、Cu、Pb的Eri分别为78.53、9.51、6.97、6.46)排序结果[51]相似.由此得知,海陆双重压力可能共同增加了该区域滨海滩涂湿地沉积物Cu和Pb的潜在生态风险,而由海洋传导到其他滨海地区的人类活动压力或许增加了Cd和As的潜在生态风险.值得关注的是,该区域重金属的潜在生态风险主要是Cd引起,与刘志杰等[12]的研究结果一致.由于渤海沉积物及环渤海土壤中Cd的潜在生态风险均较高,因此,黄河三角洲滨海滩涂湿地沉积物中Cd的污染防治工作需联合渤海与环渤海区域环境治理共同开展.

表 6 黄河三角洲滨海滩涂湿地7个样地沉积物中各重金属的生态风险指数 Table 6 Individual and general indices of the ecological risk of heavy metals in surface sediments at 7 sample sites of the Yellow River Delta

黄河三角洲滨海滩涂湿地沉积物中重金属的RI平均值为107.71,属于低风险,各样地中仅样地7属于中度风险(见表 6).对各样地所有采样点沉积物中重金属的RI(见图 4)分析表明,黄河三角洲北部位于渤海湾的样地1、样地3和样地4所有采样点均属于低风险,处于相同地貌单元的样地2有7%的采样点属于中等风险;黄河口附近样地5有5%的采样点属于高风险、33%的采样点属于中等风险;黄河三角洲南部位于莱州湾的样地6有50%的采样点属于中等风险,样地7中有22%的采样点属于高风险,另有22%属于中等风险.莱州湾海域重金属污染程度低于渤海湾(见表 3),这与黄河三角洲位于莱州湾和渤海湾的滨海滩涂湿地沉积物中重金属的生态风险水平相反,且与其他样地相比,东营市区及广利港离样地7更近,由此得知,位于莱州湾的滨海滩涂湿地重金属的生态风险来源以陆源为主,甚至包括黄河传导的陆源风险.因此,需要重点防控位于莱州湾的滨海滩涂湿地沉积物中重金属的潜在生态风险.此外,山东黄河三角洲国家级自然保护区位于黄河口区域的管理站,相比位于黄河三角洲北部的管理站而言,更应重视沉积物中重金属潜在生态风险防控,以减少重金属污染对生物多样性的威胁.

图 4 黄河三角洲滨海滩涂湿地7个样地所有样点表层沉积物中重金属的综合潜在生态风险指数(RI) Fig.4 Potential ecological risk index (RI) of heavy metals in surface sediments at 7 sample sites of the Yellow River Delta
3 结论

a) 黄河三角洲滨海滩涂湿地沉积物中Cu、As、Cd、Pb的平均含量分别为14.36、7.92、0.20、16.24 mg/kg.不同样地间Cu、Cd、As含量均差异显著,但Pb含量差异不显著;在距低潮潮位线1 000~1 200 m范围内,距低潮潮位线不同距离间4种重金属的含量均无显著差异,且不同样地间与距低潮潮位线不同距离间对重金属含量的影响无交互作用.

b) 黄河三角洲滨海滩涂湿地沉积物中4种重金属空间分布特征不同.黄河口附近滩涂中Cu含量高于非河口滨海滩涂,Cd含量呈现出南高北低的空间分布特征,Pb含量在黄河口附近及位于黄河三角洲渤海湾西侧的滨海滩涂中较低,As含量在黄河三角洲渤海湾东侧的滨海滩涂中较高.

c) 相关性分析表明,Cu、Pb、As来源相同或相近,Cd与Cu来源相同或相近,Cd与As来源不同.黏土(< 4 μm)含量与Cu、Pb、As含量均呈显著正相关,壤土(4~63 μm)含量与Cu、As含量均呈显著负相关.沉积物中pH、TOC含量、TN含量、TP含量是影响重金属沉积的因素,而砂土(>63 μm)含量、碱蓬植株密度对重金属沉积无影响.

d) Cd、As、Cu、Pb的Igeo平均值分别为0.664、-0.710、-0.722、-0.975,Cd属于轻度污染,其他重金属无污染.依据EriIgeo分析各重金属风险顺序均为Cd>As>Cu>Pb,沉积物中重金属的潜在生态风险主要由Cd引起. 4种重金属的RI介于59.21~158.63之间,平均值为107.71,黄河三角洲滨海滩涂湿地属于低风险,仅位于莱州湾的样地7为中度风险.

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