基于ENVISATASAR的长江口南汇潮滩土壤湿度定量研究

互花米草入侵对长江口湿地土壤碳动态的影响布乃顺;杨骁;黎光辉;马溪平;宋有涛;马放;李博;方长明;闫卓君【摘要】为了评价互花米草入侵对长江河口湿地土壤碳动态的影响,利用配对的试验设计在长江口崇明东滩湿地的高潮滩和低潮滩各设置1条入侵种互花米草与土著种的配对样线.结果表明,与土著植物相比,互花米草入侵显著增加了长江口湿地的植物碳库、土壤微生物碳、土壤总碳库和有机碳库,而对占土壤总碳库60％以上的无机碳库无显著影响,意味着互花米草入侵导致的土壤总碳库改变主要是通过增加土壤有机碳库来实现的.高潮滩互花米草和芦苇群落的年均土壤呼吸强度分别为(210.02±4.90),(157.79±6.39)mg/(m2·h);低潮滩互花米草和海三棱藨草群落年均土壤CO2排放速率分别为(157.41±5.27),(110.90±5.16)mg/(m2·h),表明互花米草入侵显著增加长江口湿地的土壤呼吸.上述结果意味着互花米草入侵同时增加土壤碳输入和碳输出,但入侵也显著增加了土壤碳库表明入侵增加的土壤碳输入显著高于增加的土壤碳输出.本研究表明互花米草入侵可能会增强了长江河口湿地的土壤碳汇强度和固碳能力.但仍然需要长期系统的监测研究,以便全面定量评估互花米草入侵我国滨海湿地的综合生态影响.【期刊名称】《中国环境科学》【年(卷),期】2018(038)007【总页数】9页(P2671-2679)【关键词】植物入侵;土壤呼吸;互花米草;土壤碳动态;长江河口湿地【作者】布乃顺;杨骁;黎光辉;马溪平;宋有涛;马放;李博;方长明;闫卓君【作者单位】辽宁大学环境学院,辽宁沈阳 110036;华东师范大学河口海岸学国家重点实验室,上海 200062;辽宁大学环境学院,辽宁沈阳 110036;辽宁大学环境学院,辽宁沈阳 110036;辽宁大学环境学院,辽宁沈阳 110036;辽宁大学环境学院,辽宁沈阳 110036;哈尔滨工业大学城市水资源与水环境国家重点实验室,黑龙江哈尔滨150090;复旦大学生命科学学院,上海 2004381;复旦大学生命科学学院,上海2004381;辽宁大学化学院,辽宁沈阳 110036【正文语种】中文【中图分类】X171植物入侵已成为最严重的生态环境问题之一[1-2],入侵会显著影响土著生态系统的物种组成、群落结构以及土壤性质等[3],进而改变局域或区域碳循环的关键过程和组分包括土壤碳动态[4-5].土壤碳库是大气碳库的3倍以上,是生物碳库的4倍以上[6].作为土壤碳输出的主要途径,土壤呼吸所释放CO2的量是人类活动释放CO2量的10倍以上[7-8].因此,植物入侵对土壤碳动态的微小改变可能会对大气组成和全球变化产生较大影响.当前研究主要关注植物入侵对土壤碳库特征和碳输入过程的影响,认为植物入侵通过增加净初级生产力,进而增加了土壤碳库[9].土壤碳动态是系统碳输入和输出过程平衡的结果[10].植物入侵也有可能通过影响碳输出过程来改变土壤碳动态,然而目前对植物入侵如何影响土壤碳输出过程(如土壤呼吸)还关注较少.已有的少量研究表明,植物入侵可能会对土壤呼吸产生复杂影响.牧豆树入侵德克萨斯州草原通过增加底物含量显著增加了土壤呼吸[11],北美圆柏入侵堪萨斯州东北部草原通过降低土壤温度显著减少了土壤CO2排放[12].Eldridge等[13]的综合分析表明,灌木入侵草原对土壤呼吸无显著影响.这些研究主要关注植物入侵对草原生态系统土壤呼吸的影响,而对其他生态系统尤其是湿地关注较少.湿地面积仅占陆地面积的 4%～6%,其土壤碳储量约占全球土壤碳储量的33%左右[14],且湿地是最易遭受入侵的生态系统之一[15].滨海湿地是湿地的重要类型,广泛分布于沿海海陆交界地带[16].近来研究表明,滨海湿地蓝碳生态系统具有高效的固碳能力,在应对全球变化中具有重要作用[17-18].在全球气候变化的背景下,亟需深入系统的探讨植物入侵对滨海湿地土壤呼吸及碳动态的影响及其可能的机制.互花米草(Spartina alterniflora)入侵中国滨海湿地为研究植物入侵对湿地土壤呼吸及碳动态的影响提供机会.互花米草原产于北美东海岸,于1979年被人为引进中国[19].此后,互花米草在中国滨海湿地(包括长江河口湿地)迅速扩散,逐步取代本地土著植物群落,形成单优势植物群落[20].长江河口湿地高潮滩主要土著植物群落为芦苇(Phragmites australis),低潮滩则为海三棱藨草(Scirpus mariqueter).互花米草被引入长江河口湿地后迅速扩散,取代了大面积芦苇和海三棱藨草群落,成为优势植物群落之一[21].互花米草入侵影响了土壤线虫群落结构[22],改变了土壤微生物群落结构[23].已有一些研究探讨互花米草入侵对碳循环关键过程和组分的影响,表明互花米草通过影响生理生态特征、植物净初级生产力等[20,24-27],改变了土壤碳输入过程,进而影响土壤碳动态[24,28-29],而对互花米草入侵是否能通过改变土壤碳输出过程(即土壤呼吸)进而影响土壤碳动态尚缺乏深入系统研究.同时,当前主要关注互花米草入侵对土壤总碳库[24]和有机碳库[29-31]的影响,而入侵对土壤无机碳库(土壤总碳库的重要组成部分)的影响还关注不够.此外,目前互花米草入侵对土壤碳库影响的研究主要关注对表层土壤碳库的影响[29-31],深层土壤碳库可占0至100cm土壤全剖面碳库的 60%以上[32],在全球气候变化的背景下,需理解互花米草入侵对深层土壤碳库的影响.本研究在长江口崇明东滩湿地的高潮滩和低潮滩各建立1条研究样线,每条样线上均采用配对试验设计,高潮滩为互花米草和芦苇群落的配对样线,低潮滩为互花米草和海三棱藨草群落的配对样线.通过比较互花米草群落和土著植物群落之间相应组分的差异,探讨互花米草入侵对长江河口湿地土壤呼吸的影响程度及可能的机制,并探索互花米草入侵对湿地植物碳库、土壤总碳库、土壤有机碳库和无机碳库的影响.以期为评价植物入侵的生态后果、湿地有效管理和合理利用以及应对全球变化提供理论依据和科技支撑.1 材料与方法1.1 研究区概况本研究在上海崇明东滩湿地(31°25′～31°38′N,121°50′～122°05′E)内进行,东滩湿地位于长江口崇明岛东部,于 2002年被湿地国际秘书处正式列入国际重要湿地名录.2005年7月,东滩湿地被国务院批准建立上海崇明东滩鸟类国家级自然保护区[33].东滩湿地处于亚热带季风区域,温和湿润,四季分明,年均降水量1022mm,主要集中在4～9月;年均温为15.3℃,最热月为7、8月间,月平均气温27.5℃,最冷月为1月,月平均气温2.9℃[33].东滩湿地植物群落结构相对简单,主要优势物种为土著种芦苇和海三棱藨草,以及入侵种互花米草,各自形成单优势群落[21].芦苇主要分布于高潮滩,海三棱藨草则主要分布于低潮滩,互花米草在从大堤至光滩的不同潮位均有分布.互花米草和芦苇均为禾本科维管植物,海三棱藨草为莎草科植物,为潮滩演替先锋种.互花米草于 2001年被人为引入东滩湿地,此后在潮间带迅速扩散,成为主要优势物种之一.1.2 试验设计2011年1月初,在东滩湿地的高潮滩和低潮滩各设置1条南北方向的样线,均平行于1998年修建的大堤(图 1).在每条样线上各选取 3个样点,每个样点采取配对的试验设计.高潮滩样线长约 1.2km,为互花米草和芦苇群落配对样线,低潮滩样线长约0.7km,为互花米草和海三棱藨草群落配对样线,在进行植物和土壤样品采集以及土壤呼吸测定时,每个样点的每种群落均设置3个重复.配对的试验设计尽可能使得同一样点相邻群落间土壤本底和受到潮水等外来因素干扰相一致.图1 研究样线和样点在崇明东滩湿地的分布示意Fig.1 Locations of sampling transects and sites in Dongtan wetland of Chongming Island, the Yangtze River estuary, China本研究样地均设置在互花米草、芦苇和海三棱藨草各自单优势群落内,互花米草群落植物生物量、植株密度和基径均显著高于芦苇群落,而植株高度低于芦苇群落[34].互花米草群落植物生物量、植株高度和基径均显著高于海三棱藨草群落,而植株密度低于海三棱藨草群落[24].1.3 植物和土壤样品采集及分析为了研究互花米草入侵对植物碳库的影响,于2011年 8月底收割地上部分生物量,样方面积为0.25m2,同时用内径为 10cm,长为 110cm 的不锈钢管采集地下生物量,将取出样品在清水中洗净.将地上和地下植物样品50℃烘干后研磨过100目不锈钢筛,用于测试植物碳含量,并计算植物碳库.为了探讨互花米草入侵对土壤碳库的影响,于2011 年8 月按深度依次采集0～20、20～40、40～60、60～80和80～100cm共 5层土壤样品,称取样品鲜重,取出少量样品105℃烘干测定土壤含水量,计算土壤容重.将剩余样品风干后研磨过100目不锈钢筛用于测试总碳和有机碳含量,结合土壤容重,计算土壤总碳库和有机碳库,土壤总碳库减去有机碳库即为土壤无机碳库.于2014年7月在相同的样线和样点上采集0～30cm 的土壤样品用于测定土壤有机碳库.为了探讨互花米草入侵对土壤微生物碳和理化性质的影响,于2011年8月采集0～20cm的土壤,取出部分新鲜土壤样品稍微风干后,过 20目不锈钢筛后用于测定微生物碳含量;其余样品自然风干后,过 20目不锈钢筛后用于测定 pH和盐度.土壤样品采集均用内径为3.5cm,长为110cm的不锈钢管进行.土壤盐度用电导法测定,采用水土比为5:1提取水溶液后用电导率仪(Seven Conductivity Meter S30,METTLER TOLEDO,Switzerland)测定.土壤 pH采用水土比为5:1提取水溶液后用PHBJ-260型便携式 pH计(上海仪电科学仪器股份有限公司,中国)测定.土壤总碳含量的测定用元素分析仪(FlashEA 1112Series CN Analyzer, Thermo Fisher Scientific,USA)进行.土壤有机碳含量使用有机碳分析仪(Multi N/C 3100with solid module HT1300, Analytik Jena AG, Germany)进行测定.土壤微生物碳含量的分析采用氯仿熏蒸提取法[35],使用有机碳分析仪(MultiN/C 3100Analytik Jena AG, Germany)测定提取液中碳含量.1.4 土壤呼吸的测定为了探讨互花米草入侵对土壤呼吸的影响,2011年1月初在每个样点每种植物群落内埋设3个内径为20cm的PVC圈,用于定点监测土壤呼吸速率.每半个月齐地刈割1次PVC圈内的植物,并在测量土壤呼吸的前一天再次齐地刈割 PVC圈内的植物,以便保持在整个测量周期内, PVC圈内无植物生长.东滩湿地是典型潮汐滩涂湿地,受半日周期和半月周期潮汐的影响,农历初一和十八潮汐的潮高最大,因此,在东滩湿地进行原位监测的难度较大.本研究于2011年1月、3月、5月、8月、10月、11月用LI-8100A土壤碳通量自动测量系统(Li-COR Corporate, USA)测定6次土壤呼吸速率.同时用便携式数字温度计(JM624,天津今明仪器有限公司)测量植物群落内土壤 5cm深度的温度,并采集0至 5cm深度的土壤带回实验室,105℃烘干后测定土壤含水量.于2014年4月、7月和9月在相同的样线和样点上用 LI-8100A土壤碳通量自动测量系统(Li-COR Corporate,USA)测定6次土壤呼吸速率.2015年以后,本研究的样地受到东滩湿地互花米草生态控制工程的强烈干扰.1.5 数据分析采用重复测量方差分析比较高潮滩互花米草和芦苇群落之间及低潮滩互花米草和海三棱藨草群落之间土壤呼吸、温度和含水量的差异.采用单因素方差分析比较高潮滩互花米草和芦苇群落之间及低潮滩互花米草和海三棱藨草群落之间植物碳库、土壤总碳库、土壤有机碳库、土壤无机碳库、微生物碳、盐度和 pH的差异.采用单因素方差分析比较高潮滩互花米草和低潮滩互花米草群落之间植物碳库、土壤总碳库、土壤有机碳库、土壤无机碳库和微生物碳的差异.所有统计分析均使用软件SPSS 13.0 (SPSS Inc., USA)完成.图3 2011年高潮滩和低潮滩不同植物群落的土壤温度与含水量的季节变化Fig.3 Temporal variations in soil temperature and moisture in different plant stands in the high and low tide zones in 20112 结果2.1 不同植物群落间植物碳库的差异高潮滩互花米草群落植物碳库为(3.35±0.08)(kg·C)/m2,显著高于芦苇群落植物碳库((2.05±0.07)(kg·C)/m2)(P＜0.01,图 2);低潮滩互花米草群落植物碳库同样显著高于海三棱藨草群落植物碳库,分别为:(3.78±0.14)和(0.66±0.04)(kg·C)/m2(P＜0.001,图 2).此外,低潮滩互花米草群落植物碳库显著高于高潮滩互花米草群落植物碳库(P＜0.05,图2).图2 高潮滩和低潮滩不同植物群落的植物碳库Fig.2 Plant carbon pool in different plant stands in the high and low tide zones2.2 不同植物群落间土壤理化性质的差异图4 高潮滩和低潮滩不同植物群落下土壤盐度和pHFig.4 Soil salinity and pH in different plant stands in the high and low tide zones互花米草芦苇海三棱藨草高潮滩和低潮滩土壤温度在互花米草群落与土著植物群落之间均无明显差异(图3a,b).而高潮滩和低潮滩土壤含水量均是互花米草群落显著高于土著植物群落(P＜0.05,图3c, d).高潮滩互花米草群落土壤盐度显著低于芦苇群落(P＜0.05,图 4a),低潮滩土壤盐度在互花米草群落与海三棱藨草群落之间无显著差异(图 4a).土壤 pH 在互花米草与土著植物群落之间没有显著差异,且均在8.0以上(图4b),表明入侵对土壤pH没有影响.2.3 不同植物群落间土壤碳库的差异高潮滩互花米草群落0至100cm深度土壤总碳库和有机碳库分别为(18.05±0.15)和(5.52±0.18)(kg·C)/m2,显著高于芦苇群落0至100cm深度土壤总碳库((17.21±0.30)(kg C)/m2)和有机碳库((4.74±0.24)(kg C)/m2)(P＜0.05,图 5a, b).低潮滩互花米草群落土壤总碳库((14.96±0.19)(kg C)/m2)和有机碳库((4.10±0.15) (kg C)/m2),同样显著高于海三棱藨草群落土壤总碳库((13.58±0.28)(kg C)/m2)和有机碳库((2.80±0.16)(kg C)/m2)(P＜0.05,图 5a, b).同时,2014 年7月测定的0～30cm的土壤有机碳库同样是互花米草群落显著高于土著植物群落(P＜0.05,图6).东滩湿地0～100cm深度土壤无机碳库显著高于有机碳库,占总碳库比例60%以上,且不同潮位和不同植物群落之间土壤无机碳库的大小无显著差异(图5c, d).从 0～100cm 的土壤剖面来看,高潮滩互花米草群落0至20、20至40、40至60cm土壤层的有机碳库均显著高于芦苇群落相应土壤层的有机碳库(P＜0.05,图5a).低潮滩互花米草群落0至20、20至40、40至60、60至80cm土壤层的有机碳库均显著高于海三棱藨草群落相应土壤层的有机碳库(P＜0.05,图5b).图5 高潮滩和低潮滩不同植物群落下土壤有机碳库和无机碳库Fig.5 Soil organic carbon pool and soil inorganic carbon pool in different plant stands in the high and low tide zones图6 2014年7月测定的高潮滩和低潮滩不同植物群落下0～30cm土壤有机碳库和无机碳库Fig.6 Soil organic carbon pool and soil inorganic carbonpool(0～30cm) in different plant stands in the high and low tide zones inJuly 2014高潮滩互花米草群落土壤微生物碳含量为(80.99±9.26)mg/g,显著高于芦苇群落土壤微生物碳含量((56.27±3.39)mg/g)(P＜0.05,图 7),低潮滩互花米草群落土壤微生物碳含量同样显著高于海三棱藨草群落土壤微生物碳含量,分别为:(45.65±2.51)和((31.63±2.59)mg/g)(P＜0.001,图 7).图7 2011年8月测定的高潮滩和低潮滩不同植物群落下土壤微生物碳Fig.7 Soil microbial biomass carbon in different plant stands in the high and low tide zones in august 20112.4 不同植物群落间土壤呼吸的差异图8 2011年(a,b)和2014年(c,d)高潮滩和低潮滩不同植物群落下土壤呼吸的季节变化Fig.8 Temporal variations in soil respiration in different plant stands in the high and low tide zones 2011 (a,b) and 2014 (c,d)高潮滩互花米草群落土壤呼吸显著高于芦苇群落(图 8a),年平均土壤呼吸强度分别为(210.02±4.90)和(157.79±6.39)mg/(m2·h).互花米草与芦苇群落之间的差异主要体现在生长季,非生长季土壤呼吸差异较低.低潮滩互花米草和海三棱藨草群落年均土壤 CO2排放量分别为(157.41±5.27)和(110.90±5.16)mg/(m2·h),前者显著高于后者(图 8b),差异同样主要体现在生长季.同时,2014年4月、7月和9月测定的土壤呼吸速率同样是互花米草群落显著高于土著植物群落(P＜0.05,图8c,d). 此外,高潮滩互花米草和芦苇群落间年均土壤呼吸的差异为(52.23±8.29)mg/(m2·h),与低潮滩互花米草和海三棱藨草群落年均土壤呼吸的差异((46.51±8.78))mg/(m2·h)无显著差异.3 讨论3.1 互花米草入侵对植物碳库的影响与土著植物群落相比,互花米草群落具有较高的植物碳库,这个研究结果与Liao等[24]和Peng等[36]的研究一致.与土著种相比,入侵种往往有比较优势的生理生态特征,进而显著增加生态系统的净初级生产力[37].与土著种芦苇和海三棱藨草相比,互花米草有更高的净光合速率、叶面积指数和较长的生长季[25,38].此外,潮滩湿地氮素含量是植物生长重要限制因子,植物净初级生产力会随着氮素水平的增加而显著增加[39].在与潮水的交互作用,互花米草群落比土著植物群落能获取更多的无机氮等营养盐[36].与土著植物相比,互花米草具有上述比较优势,其入侵长江河口湿地增加了植物碳库,从而显著增加了湿地生态系统的碳输入.东滩湿地低潮滩互花米草群落的植物碳库显著高于高潮滩互花米草群落,意味着互花米草入侵低潮滩对东滩湿地碳输入的增加更显著,互花米草入侵对植物碳库和碳输入影响的潮位效应在之前的研究中未受足够关注.形成这种碳库空间格局可能是由于(1)低潮滩比高潮滩受潮水淹没的频率高,时间长[40],使得低潮滩互花米草群落在于潮水交互作用中能获取更多的无机氮等营养盐[36];(2)互花米草站立凋落物会抑制其地上部分生长[41].低潮滩大部分凋落物会被潮水带走,使得凋落物对互花米草新生植株的抑制作用较小.高潮滩凋落物主要是原位分解,对互花米草新生植株的抑制作用较强.在低潮滩,互花米草取代海三棱藨草成为先锋种,并表现出良好的生长态势,有利于长江河口湿地生态系统碳的累积.3.2 互花米草入侵土壤碳库的影响植物的功能特征通过改变碳输入进而影响土壤动态[42].与土著植物相比,互花米草具有比较优势的生理生态特征[25,38],显著增加了净初级生产力,从而增加了东滩湿地的土壤有机碳库.植物净初级生产力和土壤有机碳的增加为微生物生长提供了更多可利用性底物,使得互花米草入侵显著增加土壤微生物碳含量.互花米草入侵对高潮滩土壤有机碳库的增加达到了 60cm 深度,对低潮滩土壤有机碳库的增加达到了 80cm 深度,表明互花米草入侵既增加表层土壤有机碳库,与之前的研究结果[29-31]相一致,同时表明互花米草入侵也会增加深层土壤的有机碳库.一方面,与土著种芦苇和海三棱藨草相比,互花米草在 0～100cm土壤剖面上均具有较高的根系生物量[24],意味着互花米草入侵同时增加了表层和深层土壤碳输入.另外一方面,互花米草比芦苇和海三棱藨草有更强的促淤效应[36],使原来表层土壤更快更深地埋入下层,使深层土壤有机碳库增加.此外,与高潮滩相比,低潮滩受潮水影响更频繁,时间更长,土壤淤积速率相对较高,低潮滩表层土壤更快更深地埋入下层,使得互花米草入侵低潮滩能增加较深土壤层次的有机碳库.总的来说,互花米草入侵不仅增加了表层土壤有机碳库,同时显著增加了深层土壤有机碳库,且在评价互花米草入侵对滨海湿地土壤有机碳库的作用时,应考虑其促淤作用导致的土壤层次位移的影响. 东滩湿地土壤无机碳库占总碳库的60%,显著高于土壤有机碳库.Liao等[24]和Peng等[36]仅比较了不同植物群落间土壤总碳库的差异,其他一些研究主要关注互花米草入侵对土壤有机碳库的影响[29-31],可能难以恰当反映互花米草入侵对土壤碳库特征的影响.土壤无机碳库受植物种类以及土壤理化性质如 pH等因素影响[43].互花米草根系会分泌小分子有机酸进入土壤[44],从而有降低土壤 pH和改变土壤无机碳库的潜在影响.然而,东滩为典型潮汐滩涂湿地,周期性潮汐淹没维持了东滩湿地稳定的碱性土壤环境(pH＞8.0)[45].本研究表明,目前东滩湿地土壤无机碳库并未受到互花米草入侵的影响,入侵导致的土壤总碳库变化主要是通过增加土壤有机碳库来实现的,但未来仍然需要长期监测研究来探讨互花米草入侵对土壤无机碳库的潜在影响.3.3 互花米草入侵对土壤呼吸的影响无论是与高潮滩芦苇群落相比,还是与低潮滩海三棱藨草群落相比,互花米草入侵均显著增加了土壤呼吸.土壤呼吸主要由微生物呼吸(异养呼吸)和根呼吸(自养呼吸)两部分组成[46].一方面,与土著植物相比,互花米草比土著植物有较为优势的生理生态特征如光合速率,叶面积指数和生长速率等,显著了增加净初级生产力.其入侵可为微生物提供更多容易利用的底物如根系分泌物、凋落物和有机质等,并且增加微生物生物量,使得微生物呼吸增加.另外一方面,互花米草根系生物量显著高于土著植物[24],导致其入侵会显著增加根系呼吸.此外,互花米草和芦苇为维管植物,可以通过植物体内的导管作用向土壤输送 O2,海三棱藨草不是维管植物,通过植物体向土壤输送 O2的功能相对较差.与芦苇相比,互花米草具有较高的植物生物量、植株密度和根系生物量[24],增强其向土壤输送O2能力,从而促进土壤CO2的产生和排放.值得注意的是,美国东海岸与长江河口湿地正好相反,芦苇作为外来种入侵互花米草群落,显著增加了植物净初级生产力[47],但是芦苇群落土壤有机碳含量或略低于互花米草群落[48],或与互花米草群落基本无差异[49].目前尚未见芦苇入侵美国东海岸湿地土壤呼吸影响原位监测研究.基于已有的研究,芦苇入侵增加了美国东海岸湿地的土壤碳输入,但并未增加土壤碳库,我们推测芦苇入侵可能会显著增加美国东海岸湿地土壤呼吸,进而显著增加湿地土壤碳输出.在全球变化的背景下,未来开展互花米草入侵对中国滨海湿地影响与芦苇入侵美国东海岸湿地影响异同的比较研究,对深入系统的理解植物入侵对湿地土壤碳动态的影响有重要意义.3.4 互花米草入侵对土壤动态的影响本研究表明互花米草入侵长江河口湿地显著增加了植物碳库和土壤呼吸,意味着互花米草入侵同时增加土壤碳输入和碳输出,其综合效应是互花米草入侵显著增加了长江河口湿地土壤碳库,表明入侵增加的土壤碳输入显著高于增加的土壤碳输出,入侵可能会增强了滨海湿地的碳汇强度和固碳能力.值得注意的是,由于互花米草入侵通过增加土壤呼吸增加了土壤碳输出,仅从互花米草入侵对碳输入过程的影响难以准确评价入侵对土壤碳动态的影响,需综合考虑互花米草入侵对土壤碳输入和碳输出过程的影响.已有研究表明,滨海湿地是“蓝色碳汇”的重要组成部分[17-18],互花米草入侵中国滨海湿地可能会有助于提升湿地固碳能力,在减缓全球变化方面可能会有一定的作用.然而,互花米草入侵显著改变了中国滨海湿地植物[25]、底栖动物[21]、土壤动。

编者按：“龙计划”（Dragon Programme）是中国科技部与欧洲空间局（European Space Agency，ESA）在对地观测领域的重大国际科技合作计划，目的是联合中欧知名遥感专家开展合作研究，促进遥感技术应用水平的提高。

“龙计划1”于2004年启动，2008年4月结束，资助了16个项目。

2008—2012年为“龙计划2”阶段，资助25个项目，涉及陆地资源与环境、海洋学与海岸带、灾害、地形制图、大气、定标与检验6个领域，主要研究ESA、TPM和中国EO数据在中国陆地、海洋和大气科学领域中的应用发展。

“龙计划”二期项目介绍欧洲空间局（ESA）和中国科技部国家遥感中心在对地观测应用开发领域的合作已经超过15年。

2004年，双方合作启动“龙计划1”，在16个优先领域利用欧空局地球遥感卫星（ESA ERS）和欧洲环境卫星（Envisat）数据在中国开展科学与应用研究。

2008年开始“龙计划2”，继续扩大合作领域，主要利用ESA、第三方卫星（TPM）和中国的对地观测（EO）数据（详情见表1-2）在中国陆地、海洋和大气领域开展科学应用研究，为期4年，将于2012年完成。

“龙计划2”的预期成果包括：促进ESA、TPM和中国的EO数据的科学应用发展；通过联合中欧科学家，促进对地观测科学与应用的学术交流；在项目中期和结束时，发表合作撰写的研究与应用成果；提供ESA、TPM和中国EO数据在陆地、海洋和大气应用领域的处理、算法和产品的培训。

二期项目涉及陆地资源与环境、海洋学与海岸带、灾害、地形制图、大气、定标与检验6个领域，共25个项目，各项目执行摘要如下。

1 陆地资源与环境（Land Resources and Environment）1.1Forest Ecosystems：森林生态系统观测技术研究研究内容：①进一步推动、改善“龙计划1”森林项目取得的成果，制作1995—2005—2010阶段森林变化图，并加强与德国航天局TerraSAR-X项目、联合国粮农组织的森林资源评价项目的合作；②为“欧洲生命行星计划”中地表和生态结构观测提供优先服务，对生态系统大小、物理结构、模式、物候、生物群落型、土地覆盖与土地利用特征，以及火灾、病虫害、干旱等自然和人为干扰的鉴别和监测提供服务；③开拓对多参数雷达数据（多频率、多极化及多角度）、新型高光谱数据、光学和雷达合成分析的应用研究。

第54卷 第4期 2024年4月中国海洋大学学报P E R I O D I C A L O F O C E A N U N I V E R S I T Y O F C H I N A54(4):106~115A pr .,2024泥质潮滩水盐运移过程电阻率探针高精度监测效果分析❋李明波1,2,张宇丰3,郭秀军3,4❋❋,吴 振1,2,武 斌1,2,马 健1,2,聂佩孝1,2(1.山东省第四地质矿产勘查院,山东潍坊261021;2.山东省地矿局海岸带地质环境保护重点实验室,山东潍坊261021;3.中国海洋大学环境科学与工程学院,山东青岛266100;4.山东省海洋环境地质工程重点实验室,山东青岛266100)摘 要: 本研究在莱州湾泥质潮滩开展测试,量化分析了环状电阻率探针监测沉积物电阻率与孔隙水盐度变化的能力,并使用该技术初步刻画了细粒沉积层中水盐运移过程㊂结果表明,环状电阻率探针监测结果可精细描述沉积物电阻率的分布及变化规律;基于监测结果换算的孔隙水盐度变化比与实际孔隙水盐度变化比存在ʃ10%的误差,环状电阻率探针具有粗略定量分析泥质潮滩水盐运移过程的能力;潮汐循环中泥质潮滩地下水水盐运移过程在涨潮时期,高盐度水体主要补给细粒沉积层的顶部与底部㊂高潮时期间,细粒沉积层顶部与底部的盐分逐步丧失,中部水体盐分累积速率加快㊂退潮时期,细粒沉积层盐分整体丧失,高盐度水体通过渗出面向外释放㊂关键词:环状电极电阻率探针;泥质海岸;水盐运移过程;监测效果;盐度变化比中图法分类号: P 345 文献标志码: A 文章编号: 1672-5174(2024)04-106-10D O I : 10.16441/j.c n k i .h d x b .20230008引用格式: 李明波,张宇丰,郭秀军,等.泥质潮滩水盐运移过程电阻率探针高精度监测效果分析[J ].中国海洋大学学报(自然科学版),2024,54(4):106-115.L i M i n g b o ,Z h a n g Y u f e n g ,G u o X i u j u n ,e t a l .H i g h -p r e c i s i o n m o n i t o r i n g e f f e c t a n a l y s i s o f r e s i s t i v i t y pr o b e i n t h e w a t e r a n d s a l t t r a n s p o r t p r o c e s s i n m u d d y t i d a l f l a t [J ].P e r i o d i c a l o f O c e a n U n i v e r s i t y of C h i n a ,2024,54(4):106-115. ❋ 基金项目:山东省第四地质矿产勘查院科技创新项目(K J 2106);山东省地矿局科技公关项目(K Y 202206);潍坊市财政基金项目(S D G P 370700202102000413);山东省地下水环境保护与修复工程技术研究中心(筹)开放基金项目(201703075-57)资助S u p p o r t e d b y t h e S c i e n c e a n d T e c h n o l o g y I n n o v a t i o n P r o j e c t o f N o .4E x p l o r a t i o n I n s t i t u t e o f G e o l o g ya n d M i n e r a l R e s o u r c e s o f S h a n -d o n g P r o v i n c e (K J 2106);t h e K e y S c i e n t i f i c a n d T e c h n o l o g i c a l R e s e a r c h P r o j e c t ,S h a n d o n g P r o v i n c i a l B u r e a u o f G e o l o g y &Mi n e r a l R e s o u r c e s (K Y 202206);t h e W e i f a n g F i n a n c i a l F u n d P r o j e c t (S D G P 370700202102000413);t h e O p e n F u n d P r o j e c t o f S h a n d o n g Pr o v -i n c e G r o u n d w a t e r E n v i r o n m e n t P r o t e c t i o n a n d R e s t o r a t i o n E n g i n e e r i n g T e c h n o l o g y Re s e a r c h C e n t e r (201703075-57)收稿日期:2023-01-10;修订日期:2023-03-04作者简介:李明波(1986 ),男,高级工程师,研究方向为区域地质调查与矿产勘查㊂E -m a i l :l i m i n g b o @s d d k s y.c o m ❋❋ 通信作者:郭秀军(1972 ),男,教授㊂E -m a i l :g u o j u n qd @o u c .e d u .c n 泥质海岸是世界重要的海岸类型之一,广泛分布于海湾及河流入海区域㊂当前泥质海岸的关注问题集中在滨海湿地土壤盐渍化以及滨海卤水资源可持续开发上㊂厘清泥质海岸表层细粒沉积层中水体与溶质的分布㊁迁移规律,是解决以上环境及资源问题的基础㊂泥质海岸地下水水文过程模型的建立始于21世纪初,至今仍在修改㊁完善㊂当前研究该问题的主要方法包括地球化学分析㊁数值模拟及原位地球物理调查㊂传统研究主要基于地下水常规离子分析㊁氢氧同位素测试等地球化学分析结果,确定泥质海岸多层含水层系统中水㊁盐的来源,以此为基础建立地下水与溶质的补给模型[1-2];随着算法优化,数值模拟与原位水文观测结合的方法开始用于泥质海岸多层含水层中流场㊁溶质分布及变化规律的研究[3-9]㊂马倩㊁常雅雯与郭雪倩将多层含水层系统中各地层视为均质,初步模拟分析了多层含水层系统中流场与溶质的分布演化过程,评价了弱透水层中天窗区对越流补给的影响,量化了海底地下水排泄通量[5-7]㊂X i n 等[8]与X i a o 等[9]模拟了受生物活动影响更为复杂的地下水循环过程㊂证明了生物通道能够显著促进表层沉积物中海水的循环速率;地球物理电学观测是一类新兴的地下水文过程观测方法,S u 等[10]应用此方法分析了潮汐对泥质海岸沉积物电性的影响,并划分了莱州湾滨海含水层系统中的海水入侵通道㊂F u 等[11]基于电阻率层析成像(E l e c -t r i c a l r e s i s i t i v i t y t o m o g r a p h y,E R T )监测结果,建立了泥质海岸多层滨海含水层系统中的水盐运移模型;张宇丰等[12]基于E R T 与水文参数监测结果,讨论了表层细粒沉积层的渗透性差异对海水-潜水卤水交换过程的影响,初步量化了潮汐循环中多层滨海含水层内发生的盐分通量㊂综上可知,当前已有研究更多关注泥质海岸多层滨海含水层系统,并以此建立大尺度的水盐运移模型㊂事实上,潮间带生卤㊁土壤盐渍化及生物活动的区域多集中在表层细粒沉积层中[9,13-15]㊂在蒸发与潮汐循环4期李明波,等:泥质潮滩水盐运移过程电阻率探针高精度监测效果分析作用下,潮间带细粒沉积层中孔隙水盐度维持在较高水平的动态平衡中,每年每平方千米的表层细粒沉积层可为地下卤水资源补给16万m 3大于10波美度的卤水[15]㊂活跃的生物活动产生的通道能够增大表层细粒沉积物的渗透性与异质性,显著加快海水-地下水的交换速率,不仅为潮间带生卤补给浅层卤水资源提供优先路径,还促进了基质中孔隙水与海水等其他水体间的溶质交换,改变基质中孔隙水盐度,影响土壤盐渍化进程[8-9,11-13]㊂准确㊁细致认识细粒沉积层中水盐运移规律是揭示潮滩生卤补给潜水卤水机制与通量的基础,可为滨海地下卤水资源以及生态环境管理提供理论支持,但目前未有研究能够精细描述潮汐循环中细粒沉积层中水盐的运移过程㊂为精细刻画以上过程,要求监测技术对地下介质变化的反应有较高灵敏度,同时具有较高的空间分辨能力㊂由于不同含盐量沉积物存在明显电性差异,电学监测可基于此物理前提对水盐运移过程进行刻画[16-18]㊂电阻率探针技术在垂直方向上具有较高的分辨能力,其还能避免E R T 监测随探测深度增加探测灵敏度下降的缺点㊂目前电阻率探针技术主要应用于海底水土界面划分[19]㊁海洋土蚀积过程监测[20-21]㊁海底浅层气迁移过程监测[22-23]以及土壤盐渍化监测[24],但目前尚未对电阻率探针监测泥质潮滩水盐运移过程的能力进行分析㊂本研究选取莱州湾南岸泥质潮滩为研究区开展工作,分析环状电阻率探针(R i n g e l e c t r o d e r e s i s t i v i t ypr o b e ,R E P )监测潮汐过程表层细粒沉积物中水盐运过程的灵敏度,评价依据孔隙水盐度变化比量化分析孔隙水盐分累积与释放过程的误差,并基于R E P 监测结果初步描述潮汐过程中泥质海岸表层细粒沉积层中的水盐运移过程㊂1 研究区概况研究区位于中国山东省莱州湾南岸的淤泥质海岸㊂该区域地形平缓,平均坡度小于千分之三(<3ɢ),宽阔的潮滩向莱州湾内延伸5~20k m ,平均水平水力梯度1.64%,地下潜水位高程约为-0.8m [25-26]㊂该区域地层自上而下可分为表层细粒沉积层㊁潜水卤水层㊁弱透水层及承压卤水层四层,分别为厚约4~5m 的粘质粉土层;厚约6~8m 的中细砂层;厚5~7m 的粘质粉土层;中砂层与细砂层[26-28]㊂图1 研究区位置㊁工作布设位置及地质钻孔柱状图F i g .1 L o c a t i o n ,w o r k i n g p o i n t a n d g e o l o g i c a l c o l u m n s o f s t u d y ar e a 研究区潮汐属于不规则半日潮,平均潮差约为0.9m ,平均涨潮时间382m i n ,平均落潮时间366m i n㊂莱州湾南岸属暖温带大陆性季风气候,年均降雨量和蒸发量分别为559.5和1936.7m m [26],蒸发作用强烈㊂莱州湾海域自上更新世以来经历了三次海侵与海退,在滨海含水层系统内形成了水平带状分布的三至五层卤水㊂位于顶部的潜水卤水T D S 值在50~140g /L 之间[26,29]㊂2 工作布设与方法2.1R E P 参数设置及电阻率计算方法本研究中使用的环状电极探针总长4m ,数据采集段长3.45m ,24个不锈钢电极环(C 1 C 24)等间距分布,电极极距a 为0.15m ,电极环半径b 为0.03m ,装置示意图与实物图见图2㊂电学测量选用W e n n e r 排列,数据采集时两个供电电极发射电流,形成电场,电701中 国 海 洋 大 学 学 报2024年场大小正相关于供电电极间的距离,环电极探针所测电阻率数据为电场范围内介质整体的电阻率,根据W e n n e r 排列测量原理,有效测量半径为1.5倍的极距,即0.225m ㊂测量仪器为G e o pe n 公司生产的E 60D N 分布式电图2 R E P 监测系统示意图(a )及R E P 探杆实物图(b)F i g .2 S c h e m a t i c d i a g r a m o f R E P m o n i t o r i n gs y s t e m (a )a n d R E P p h y s i c a l ph o t o (b )法仪及多电极智能电缆㊂使用12V 直流电源对测量仪器及主机供电㊂测量供电时长为1s ,电流大小为1A ㊂每次测量分别以C i 与C i +3为供电电极A ㊁B ,以C i +1与C i +2为测量电极M ㊁N (i 为测量次数)㊂测量时记录电位差ΔV i 与电流I i ,基于公式(1)可计算得到细粒沉积层不同深度位置的沉积物电阻率ρi[23]㊂ρi =π2b ΔV iI il n 4a +2πb 4a +πb-1㊂(1)2.2R E P 测量精度验证分别在淡水及海水环境下测试R E P 测量精度㊂使用自来水与自配高盐度水(盐度为30)分别模拟淡水环境与海水环境㊂淡水及海水电阻率分别为23.64与0.251Ω㊃m ㊂使用R E P 测量不同环境中介质电阻率,每类环境中重复试验3组,取三组试验的均值与介质电阻率实测值对比,分析R E P 装置自身的测量误差㊂图3显示了两个R E P (R 1与R 2)在淡水及海水环境中的测量误差㊂在淡水环境中,R E P 的测量误差区间在ʃ1%之内;在盐度较高的海水环境中,电极受极化影响程度升高,R E P 测量误差区间虽有增大但未超过ʃ3%,约1/2的数据点落在误差区间ʃ1%之内㊂因此R E P 基本能够满足在不同类型地下水环境中开展监测工作的测量精度要求㊂图3 不同环境中两个R E P (R 1与R 2)测量误差图F i g .3 E r r o r d i a gr a m o f t w o R E P m e a s u r e m e n t s (R 1&R 2)i n d i f f e r e n t e n v i r o n m e n t s 8014期李明波,等:泥质潮滩水盐运移过程电阻率探针高精度监测效果分析2.3R E P 原位布设及数据采集方法在距离G 1点80及110m 位置分别布设电阻率探针R 1和R 2,具体点位如图1所示㊂采用旋转贯入的方式将电阻率探针置入沉积物中㊂装置布设完成后需稳定1周再进行测量㊂在单个潮汐循环内的不同潮时(a ㊁b ㊁c 与d 时刻)开展测量工作(测量时刻见图4)㊂a 与d 时刻海水未覆盖潮滩;b 与c 时刻,海水覆盖潮滩㊂每组测量工作总时长约为70s㊂图4 R E P 测量时刻及潮位信息F i g.4 R E P m e a s u r e m e n t t i m e a n d t i d e l e v e l 本研究利用重复测量与互异性测量的方法评估电阻率测量误差[30]㊂在不同潮时的测量工作包含2次顺序测量(重复测量)及1次逆序测量(互异性测量)㊂理论上,供电电极次序互换以及测量电极次序互换不会使某一位置处R E P 测量电阻率数值发生改变㊂在本次原位监测中,重复测量㊁互异性测量结果与三次测量结果均值的误差均在ʃ2.5%之内㊂本次研究最终采用三次测量结果的均值㊂2.4沉积物物理关系泥质潮滩沉积物中黏粒含量较高,表面电导率与孔液电导率会同时影响沉积物电阻率ρ[31]㊂N g u ye n 等人和S h a o 等人提出的阿尔奇公式的变形可分离表面电导率及ρw 对ρ影响,从而建立孔隙水电阻率(ρw )与ρ的关系[32-33]:1ρ=1F 'ρw+b ㊂(2)式中:F '为有效地层因子;b 为表面电导率对ρ的贡献,与流体电导率无关㊂莱州湾南岸泥质潮滩表层沉积物F '为2.5,b 为0.335[12]㊂代入公式(2)可建立ρ与ρw 的关系㊂2.5孔隙水盐度变化换算方法孔隙水盐度S 可依据M a n h e i m 公式(3)[34]由ρw换算得到,ρw 则是基于R E P 测量得到的ρ与沉积物物理关系换算得到:S =k ˑρ-1.0233w㊂(3)孔隙水盐度变化情况由相邻观测时刻的孔隙水盐度变化比(δS )体现,计算公式如下:δS =S t -S 0S 0㊂(4)式中:S 0为前一时刻孔隙水盐度;S t 为后一时刻孔隙水盐度㊂结合公式(3),(4),可将R E P 探测的ρ转化为孔隙水盐度变化比δS R E P :δS R E P =ρ-1.0233w t -ρ-1.0233w 0ρ-1.0233w 0㊂(5)式中:ρw 0为前一时刻ρ换算所得的ρw ;ρw t 为后一时刻ρ换算所得的ρw ㊂3 结果与讨论3.1R E P 探测细粒沉积物电阻率能力评价图5(a )显示了涨潮过程表层细粒沉积物ρ的变化情况㊂距离岸线不同位置的测量结果呈现出相近的分布及变化规律㊂a 时刻,自滩面向深部ρ逐渐降低,在高程-0.825~-2.475m 之间ρ稳定在0.68Ω㊃m 左右㊂在-2.475m 以深区域,由于接近潜水卤水层的顶界,ρ逐步降低;b 时刻,海水淹没潮滩,在高程-0.825m 以浅区域ρ显著降低(由0.82Ω㊃m 降低至0.63Ω㊃m ),在高程-0.825~-2.475m 之间ρ降低幅度较小,但在-2.475m 以深区域ρ降低幅度再次升高㊂图5(b)显示了退潮过程表层细粒沉积物ρ的变化情况㊂退潮过程中ρ整体升高(由0.63Ω㊃m 升高至0.7Ω㊃m ),在细粒沉积层顶部与底部ρ升高趋势显著㊂此外,在R 1测点高程-1.425m 处与R 2测点高程-1.725m 处,分别存在局部ρ显著升高区域㊂R E P 监测结果显示,表层细粒沉积物电阻率随深度加深发生复杂的变化㊂细粒沉积层的浅部与深部易受到海水以及深层卤水的影响,在潮汐循环中ρ出现了更大的波动㊂由于该区域沉积物渗透性普遍较低(10-7~10-6m s -1)[12],细粒沉积层中部的ρ波动幅度较小㊂在相同研究区㊁相同季节中,F u 等人使用E R T 技术观测到表层细粒沉积物ρ的波动范围为0.47~0.91Ω㊃m [11]㊂本次研究中R E P 测量ρ的波动范围(0.54~0.83Ω㊃m )与F u 等人基本一致㊂但R E P 监测结果与E R T 监测数据反演结果相比,前者数据点数量在垂向上更密集(21个v s 4个),垂向分辨率更高,ρ在垂直方向上具有更复杂的分布规律(见图5)㊂这说明虽然E R T 技术在水平方向上具有较高分辨能力,且E R T 与R E P 监测技术均能够准确㊁灵敏的捕捉到介质性质的改变,但在垂直方向上E R T 技术难以捕捉更细致的规901中 国 海 洋 大 学 学 报2024年图5 涨潮过程(a )及退潮过程中表层细粒沉积物电阻率变化规律(b)F i g .5 R e s i s t i v i t y v a r i a t i o n o f s h a l l o w f i n e -g r a i n e d s e d i m e n t s d u r i n g ri s e t i d e (a )a n d e b b t i d e (b )律㊂因此单纯采用E R T 数据对地下水水文过程进行分析时,可能由于数据垂向分辨率较低,难以对水盐运移过程做出精确解释㊂在未来分析泥质潮滩水盐运移过程时,可以采用E R T 与R E P 综合调查的方法,并依据研究尺度以及数据采集所需时长综合确定R E P 电极间距等其他测量参数,以达到调查㊁研究所需的期望分辨率㊂3.2δS R E P 准确度分析将不同潮时R E P 测量的ρ依次代入公式(2)建立的ρ与ρw 关系式中,计算得ρw (见图6)㊂再将相邻时刻的ρw 代入公式(5),计算得到涨潮过程㊁高潮时与退潮过程中的δS R E P (见图7)㊂随后将相邻潮时,各监测点位不同高程处(高程-0.14,-1.14及-2.14m )孔隙水样品实测盐度(S )代入公式(4),计算得到涨潮过程与退潮过程中实测孔隙水盐度变化比δS P (见图7)㊂最后将涨潮过程与退潮过程中的δS P 与相近高程范围内的三个δS R E P 数据均值δ S R E P 做对比(见图7,9),分析δS R E P 的准确度㊂图7显示,在不同高程位置处,δS P 与δS R E P 的数值大小基本一致㊂图8显示了δS P 与δ S R E P 数据关于δ S R E P =δS P 的拟合情况㊂其中R 2为0.9297,因此δ S RE P 能够基本准确反映孔隙水盐度的实际变化情况㊂图6 涨潮过程(a )及退潮过程(b )中沉积物电阻率ρ换算孔隙水电阻率ρw 的结果F i g .6 R e s u l t s o f c o n v e r t i n g ρi n t o ρw d u r i n g r i s e t i d e (a )a n d e b b t i d e (b )0114期李明波,等:泥质潮滩水盐运移过程电阻率探针高精度监测效果分析图7 潮汐过程δS R E P ㊁δS P 的对比结果F i g .7 ρw c a l c u l a t i o n r e s u l t s a n d δS R E P ㊁δS P c o m p a r i s o n r e s u l t s d u r i n g t i d a l c y c l e R E P 探测所得ρ经过拟合式与公式(5)转换的δS R E P 与实际的孔隙水盐度变化比(δS P )存在ʃ10%的误差㊂涨潮过程,孔隙水盐度升高,δS R E P 与真实值相比普遍偏小,约为0.9~1倍的δS P ;退潮过程,孔隙水盐度降低,δS R E P 与真实值相比普遍偏大,约为1~1.1倍的δS P ㊂依据以上R E P 探测方法及数据处理方法所得孔隙水盐度变化比,在定量分析孔隙水盐分释放与累积过程方面具有较高的可信程度㊂结合装置测量精度验证结果可知,造成这种误差的因素有多种,包括装置自身误差(ʃ3%),测量误差(ʃ2.5%)以及依据沉积物物理关系将ρ换算为ρw 所产生的误差㊂当进行区域孔隙水盐通量计算,特别是涉及大范围区域盐通量量化分析时(例如潮滩生卤产生盐分总量评价㊁滨海卤水111中 国 海 洋 大 学 学 报2024年资源盐分开采总量评价等),为避免产生较大误差,可结合原位实测孔隙水盐度变化,修正基于R E P 测量值计算的δS R E P㊂图8 δS P 与δ S R E P 的关系及误差区间F i g .8 R e l a t i o n s h i p b e t w e e n δS P a n d δ S R E P an d e r r o r i n t e r v a l 3.3基于R E P 探测结果的泥质潮滩细粒沉积层中水盐运移过程评价当前研究认为,泥质潮滩中分别存在细粒沉积层的盐分累积区和盐分释放区,各区域分布范围在短期内不会随潮位升降发生明显改变㊂潮汐过程中,潮滩大部分区域细粒沉积层深部的等效水头高于浅部,这意味着泥质潮滩大部分区域以地下水排泄释放盐分为主[6-7];在泥质潮滩局部存在高渗透性区域(10-4~10-5m /s),例如生物活动产生的洞穴集群分布区,在该区域主要发生高盐度海水与地下卤水的交换,当海水淹没滩面后,细粒沉积层将接受大量盐分补给[8-9,11-12]㊂周期性发生的风暴潮作用与旱季强烈的蒸发作用是细粒沉积层中孔隙水盐分再分配的重要因素[12,26]㊂然而本次调查研究结果显示(见图7),在细粒沉积物垂向渗透系数(10-6~10-7m /s)较低的区域内,高盐度海水与地下卤水仍能够在涨潮阶段补给细粒沉积层,补给的盐分会在退潮过程中释放㊂这意味着潮汐即为调控细粒沉积层中水盐再分配的重要因素,泥质潮滩中各区域均会随潮汐涨落发生盐分的累积与释放,其水盐运移过程如下㊂涨潮过程中(见图7(a )㊁(a ')),细粒沉积层累积盐分,其顶㊁底部盐分累积量较高㊂由滩面向细粒沉积层顶部补给的盐分主要来自蒸发盐的溶解下渗㊂上涨的海水携带滩面蒸发浓缩的盐分,通过表层沉积物中密集分布的生物通道向细粒沉积层中运移[9,12-13,26];从细粒沉积层底部向其内部补给的盐分主要来自越流的地下卤水㊂该区域浅层卤水水位高程高于细粒沉积层底面,具有微承压水性质㊂随潮位升高,浅层地下水水位随之升高,进一步促进了卤水自细粒沉积层底部向其内部补给[7]㊂对比细粒沉积层顶部与底部区域的ρw与δS R E P 可知,涨潮期间细粒沉积层中的盐分更多来自滩面的高盐度水体㊂高潮时期间(见图7(b )㊁(b ')),细粒沉积层顶㊁底部从累积盐分转变为释放盐分,沉积层中部区域开始快速累积盐分㊂在本阶段内,在滩面累积的蒸发盐被海水溶解稀释,海水盐度逐步降低㊂受此影响,细粒沉积层顶部孔隙水盐分通过滩面向海水中释放,另一部分盐分向细粒沉积层中部运移;地下卤水水位在本阶段持续升高但盐度降低,受此影响,细粒沉积层底部的盐分开始向卤水层中释放,另有一部分盐分在竖直向上的流场驱动下向细粒沉积层中部运移[6-7]㊂退潮过程中(见图7(c )㊁(c ')),细粒沉积层整体丧失盐分,其顶㊁底部的盐分释放速率小幅度升高,而中部区域盐分释放速率显著提升㊂随着潮位下降,海水从滩面快速退去,渗出面在潮滩范围内大面积发育,同样在竖直向上的流场驱动下,大量高盐度孔隙水通过潮滩渗出面向外排泄[5,12]㊂与已建立的水盐运移过程模型相比[6-9,11-12],本研究刻画的潮汐作用下泥质潮滩细粒沉积层水盐运移模型更符合实际情况㊂其体现在泥质潮滩各个区域中的孔隙水盐度不会随时间变化而无限制升高或降低,而在本研究刻画的水盐运移模型中,不同深度细粒沉积层中孔隙水普遍经历了盐分累积与丧失过程(见图7)㊂这主要得益于R E P 监测技术较高的时空分辨率㊂4 结论本研究基于原位测试结果,分析了R E P 监测技术对泥质潮滩细粒沉积物中孔隙水盐度变化的分辨能力,初步细致刻画了泥质潮滩细粒沉积层中水盐运移过程,所得主要结论如下:(1)R E P 监测结果能够准确反映泥质潮滩沉积物电阻率随潮汐涨落的变化㊂R E P 技术比E R T 技术拥有更高的垂向分辨能力,可捕捉到更细致的垂向电阻率分布及变化规律㊂将E R T 与R E P 监测技术结合可实现区域水盐运移过程精细刻画㊂(2)δS R E P 与δS P 存在ʃ10%的误差㊂造成该误差的原因包括系统自身误差,测量误差以及依据沉积物物理关系将R E P 测量的ρ换算为ρw 所产生的误差㊂虽然以上误差的存在对粗略定量分析细粒沉积层中水2114期李明波,等:泥质潮滩水盐运移过程电阻率探针高精度监测效果分析盐运移过程的影响不大㊂但应用该方法量化分析大范围区域的地下水盐通量时,需结合实测孔隙水盐度变化,修正基于R E P测量值计算所得δS R E P㊂(3)潮汐循环中细粒沉积层内水盐运移过程如下:涨潮时期为细粒沉积层顶㊁底部累积盐分的主要阶段㊂高盐度水体分别通过滩面入渗及浅层卤水越流的途径向细粒沉积层中补给;在高潮时期间,受盐度降低的海水与卤水影响,细粒沉积层顶㊁底部的盐分开始逐步丧失,但沉积层中部孔隙水盐分累积速率加快;退潮时期为细粒沉积层盐分丧失阶段,在竖直向上的地下水流场驱动下,高盐度水体通过潮滩渗出面向外释放㊂参考文献:[1] W o o d W W,S a n f o r d W E,H a b s h i A R S A.S o u r c e o f s o l u t e s t o t h e c o a s t a l s a b k h a o f A b u D h a b i[J].G e o l o g i c a l S o c i e t y o f A m e r i c aB u l l e t i n,2002,114(3):259-268.[2] H u s s a i n M,A l-S h a i b a n i A,A l-R a m a d a n K,e t a l.G e o c h e m i s t r ya n d i s o t o p i c a n a l y s i s o fb r i n e s i n t h ec o a s t a l s a b k h a s,E a s t e r n r e-g i o n,K i n gd o m o f S a u d i A r a b i a[J].J o u r n a l o f A r i d E n v i r o n me n t s, 2020,178:104142.[3] M a Q,L i H,W a n g 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长江河口泥沙混合和交换过程研究【摘要】：本文通过全面分析进入二十一世纪初期(2003-2007年)长江口及其临近海域大面积同步观测的悬沙粒度、表层沉积物粒度、流速、含沙量和盐度系列资料,探讨了在河口混合环境下泥沙的交换过程和规律,从河口-陆架系统的角度研究悬浮泥沙在河口和陆架的输移和归宿问题。

得到的认识不仅是河口泥沙研究从定性研究向定量研究的进展,而且粒度谱计算方法还为泥沙交换研究提出了适用于其他潮汐环境的沉积动力分析的新思路。

从悬沙粒度的角度分析泥沙在河口-陆架的混合和交换过程,丰富了河口泥沙运动和沉积动力学的理论和方法,对其他河口的相关研究具有借鉴意义。

对长江河口悬沙粒度的组成、时空分布特征,特别是对流域来水来沙改变包括流域大型水利工程的响应做了分析。

系统探讨了高浊度河口混合环境下泥沙的交换过程和规律。

研究表明长江口悬浮泥沙与表层沉积物高交换区(交换率＞0.6)主要分布在南槽口外的泥质区和杭州湾附近海域,悬浮泥沙大量参与造床,其中长江口外泥质区的交换率高达0.9以上;低交换区(交换率＜0.1)分布在长兴岛以上的河口上段和陆架残留砂区,悬浮泥沙基本不参与造床。

而浑浊带区域的交换率在0.4-0.6之间,说明河流输入的悬沙在浑浊带区域直接沉积的比例并不是最高,其高沉积区的泥沙部分来自泥质区内随涨潮流再次输入河口的泥沙。

粒度谱计算的结果表明,大约有47%的悬浮泥沙沉积在拦门沙海域及水下三角洲前缘,超过50%的悬浮泥沙摆脱河口的“束缚”进入杭州湾以及向南输运,这与其他方法得到的结果相近。

本文提供了一种研究泥沙输运和沉积量的新的计算方法。

率先对长江河口悬沙粒度的组成、时空分布特征,特别是对流域来水来沙改变包括流域大型水利工程的响应做了分析。

认识包括:河口-陆架的悬沙整体呈现“细-粗-细”的变化规律。

拦门沙海域最粗,江阴-南支上段其次,陆架区最细,认为河口拦门沙区悬沙中值粒径的增加主要受到滩槽泥沙交换和床面泥沙再悬浮的影响。

中国环境科学 2019,39(4)：1744~1752 China Environmental Science 长江口潮滩沉积物古菌群落结构与多样性李小飞1,侯立军2,刘敏3* (1.福建师范大学,湿润亚热带生态地理过程教育部重点实验室,福建福州 350007；2.华东师范大学,河口海岸学国家重点实验室,上海 200241；3.华东师范大学地理科学学院,地理信息科学教育部重点实验室,上海200241)摘要：以长江口潮滩为研究对象,采用高通量测序技术,研究了潮滩沉积物古菌群落结构与多样性及其影响因素.结果表明,沉积物中古菌群落OTUs数量为900~1417,Shannon指数为7.02~8.02,均表现出从低盐度向高盐度样点降低的变化特征.各采样点古菌群落特异性OTUs占各采样点总OTUs的24.2%~57.3%,而共有的OTUs仅占1.2%,说明各样点沉积物中古菌群落特异性较高.沉积物中古菌主要隶属于广古菌门(Euryarchaeota)和奇古菌门(Thaumarchaeota),而深古菌门(Bathyarchaeota)也是古菌群落的重要组成部分,其相对丰度占到17.7%~25.9%.主成分和聚类分析表明芦潮港和东海农场沉积物中古菌群落结构相似,白龙港和浏河口群落组成相近,而浒浦与其他采样点的古菌群落组成差别较大.通过典范对应分析,研究区沉积物中古菌群落结构与沉积物盐度水平有着非常密切的关系.上述研究结果表明长江口潮滩沉积物中古菌群落结构组成和多样性具有高度的空间差异性,且沉积物盐度是群落差异的决定性影响因素.关键词：高通量测序；古菌群落；多样性；潮滩沉积物中图分类号：X172 文献标识码：A 文章编号：1000-6923(2019)04-1744-09Archaeal community structure and diversity in intertidal sediments of the Yangtze River Estuary. LI Xiao-fei1, HOU Li-jun2, LIU Min3* (1.Key Laboratory for Humid Subtropical Eco-geographical P rocesses of the Ministry of Education, Fujian Normal University, Fuzhou 350007, China；2.State Key Laboratory of Estuarine and Costal Research, East China Normal University, Shanghai 200241, China；3.Key Laboratory of Geographic Information Science of the Ministry of Education, School of Geographic Sciences, East China Normal University, Shanghai 200241, China). China Environmental Science, 2019,39(4)：1744~1752 Abstract：High-throughput sequencing was used to investigate the archaeal community structure and diversity, and associated influencing factors in the intertidal sediments of the Yangtze Estuary. The results indicated that the OTUs and Shannon index of archaeal community in the intertidal sediments were 900~1417 and 7.02~8.02, respectively, which both decreased from low to high salinity sampling sites. The specific OTUs of archaeal community structure accounted for 24.2%~57.3% of total OTUs in each sampling site, and identical OTUs only occupied for 1.2%, indicating that archaeal community structure varied highly along the sampling sites. The archaeal community was dominated by the Euryarchaeota and Thaumarchaeota. The Bathyarchaeota contributed a great parts of archaeal community, accounting for 17.7%~25.9% of total community. The principal component and cluster analysis suggested that the archaeal community structure in sites LCG and DHNC was similar, and archaeal community structure in BLG showed a similarity with LHK, while archaeal community structure showed a great difference in XP compared to others sampling sites. Canonical correlation analysis suggested that distribution of archaeal community structure in the intertidal sediments was tightly correlated with the sediment salinity. These results indicated that archaeal community structure and diversity were highly variable in the intertidal sediments of the Yangtze Estuary. In addition, sediment salinity was the crucial factor affecting the variabilities in archaeal community structure and diversity in the Yangtze Estuary.Key words：high-throughput sequencing；archaeal community；diversity；intertidal sediment河口潮滩是重要的生态系统,其生物地球化学循环过程受到人们的广泛重视[1-2].生物地球化学循环过程主要以微生物介导作用完成,微生物在物质循环与能量流动方面起着非常的重要作用[3].微生物种类丰富,数量庞大,适应性强,并且能够对环境变化做出快速而又敏感的反应,因而微生物成为了评价河口环境状况和功能变化的重要指标之一[4].近年来,大量的人为污染物进入到河口环境,对河口生态环境造成了严重威胁[5].此外,由全球变化导致的海平面上升、盐水入侵和植被入侵等环境问题也影响着河口生态服务功能和生物地球化学循环[1-2,6-7].在这些环境变化下,河口潮滩微生物群落结构和多样性也势必发生明显的变化,进而影响其生物地球收稿日期：2018-09-25基金项目：国家自然科学基金资助项目(41701548,41761144062)* 责任作者, 教授, mliu@4期李小飞等：长江口潮滩沉积物古菌群落结构与多样性 1745化学循环过程.因此,深入研究河口潮滩微生物群落的动态变化及其影响因素具有重要的意义.近年来,河口环境微生物多样性及其功能成为了热点研究内容[4-5,8-9].有研究发现Chesapeake河湾爆发的季节性蓝藻会对细菌群落产生重要的影响,这种影响主要通过细菌厌氧呼吸所导致[10].然而,也有研究发现,浮游植物不是影响细菌群落的因素,而是受制于营养盐水平作用影响[4].此外,滨海地区由陆向海的空间距离是沉积物中微生物群落变化的最主要因素,并且微生物Deltaproteobacteria和Gammaproteobacteria是氮污染变化的敏感微生物群落[8].此外,有研究表明长江口崇明东滩,中潮滩和低潮滩沉积物优势细菌为变形菌(Proteobacteria),高潮滩的优势菌为拟杆菌(Bacteroidetes);并且细菌多样性表现为中潮滩最高,而高低潮滩较低,由此说明潮滩环境能够显著影响微生物群落结构和多样性[11].迄今为止,有关河口潮滩及近海沉积物中微生物的研究主要集中于细菌或氮循环微生物群落及影响因素,而古菌的群落结构与多样性及其对环境变化的响应研究鲜见报道.在微生物群落中,古菌是一类有别于细菌的原核微生物[12-13],具有分布广泛、资源潜力大,在生物地球化学循环中起着重要作用[14].此外,古菌具有独特的基因类型和代谢特征,对环境变化具有适应甚至改变能力[13,15-16].因此,研究河口潮滩古菌群落结构与多样性对于了解河口生态服务功能具有重要的现实意义和科学价值.近年来,受人类活动高强度的影响,长江口地区生态环境发生了显著变化[17],不仅影响生物地球化学循环过程,而且对微生物的群落结构与多样性产生重要的影响[5,9].此外,由于咸淡水的交互作用以及人为污染物排放,长江口环境因子具有明显的时空差异特征[5].为此,本研究以长江口潮滩为典型研究对象,采用高通量测序技术,开展沉积物古菌群落结构、多样性及其影响因素研究,不仅可深化河口潮滩微生物对环境变化的认识,同时也可为评价河口生态环境提供重要的参考依据.1材料与方法1.1研究区概况与样品采集长江口是长江的入海口,位于我国东部滨海岸(21º5~122º30´E,30º52~31º46´N).因河流携带的泥沙和潮周期作用的影响,长江口发育着广阔的潮滩湿地[18].长江口气候类型为亚热带季风气候,夏季年平均温度为28.9℃,冬季年平均温度为5.6℃,且年平均降水量为1100mm[19].近年来,由于人类活动的影响,长江口活性氮的浓度升高了约10倍,成为了富营养化发生和加剧的主要因素之一[20].于2017年6月,在长江口的浒浦(XP)、浏河口(LHK)、白龙港(BLG)、东海农场(DHNC)和芦潮港(LCG)的5个潮滩落潮后露出的表层沉积物(0~5cm)进行采集,采样点空间分布如图1.在样品采集的过程中,现场记录采样点的经纬度和潮滩环境整体特征.在每个样点进行多点沉积物采集,相同质量的鲜重沉积物混合,并保存于已灭菌的离心管中,放置于带有冰块的保温箱中立即带回实验室.在实验室里,将沉积物样品充分混匀,并分成2份.一份沉积物保存于4℃冰箱中,立即分析其理化性质;另一份保存于–80℃超低温冰箱中用于微生物分析.图1 长江口采样点地理位置Fig.1 Locations of the sampling sites in the Yangtze Estuary 1.2样品理化性质分析沉积物pH值和盐度用1:2.5(沉积物:水)混匀后,分别采用pH计(S210,梅特勒-托利多,瑞士)和盐度计(YSI M odel 30,美国)测定.沉积物粒径组成采用马尔文激光粒度仪测定(M astersizer 2000,英国).经过烘干研磨的沉积物用1mol/L盐酸除去无机碳后,有机碳采用元素分析仪测定(MaxCNOHS,德国).沉积物中NH4+-N,NO3–-N和NO2–-N用2mol/L氯化钾溶液浸提后,采用连续流动仪测定(SAN+++, Skalar,荷兰).沉积物二价铁和三价铁用1mol/L盐酸浸提,采用邻菲罗啉比色法测定[21].在样品分析1746 中国环境科学 39卷过程中,每个理化性质进行3个重复测定,结果取平均值.1.3沉积物DNA提取与PCR扩增及高通量测序沉积物DNA采用强力土壤DNA试剂盒,并按照说明书的步骤进行提取(M oBio, USA).采用微量紫外分光光度计测定提取后的DNA的浓度和纯度(Thermo, USA),随后用1%的琼脂糖进行电泳.沉积物古菌群落以古菌16S rRNA的V4~V5区域作为目标DNA序列进行PCR 扩增[22].PCR 扩增采用的引物为上游524F (5'–TGYCAGCCGCCGCGGTAA–3')和下游958R (5'–YCCGGCGTTGA VTCCAATT–3'),并各自添加不同的Barcode序列进行V4~V5区域扩增.PCR扩增均采用Takara试剂公司提供的试剂进行,且反应条件为95℃预变性3min;95℃变性30s,55℃退火30s,72℃延伸45s,45个循环;最后72℃延伸10min.PCR扩增结束后,产物使用1%琼脂糖进行凝胶电泳,将其进行纯化,并将纯化后的产物送至北京诺禾致源科技有限公司Illumina-Hiseq平台上进行高通量测序(2×300bp).1.4数据处理与分析将测定的扩增子采用QIIME软件进行分析.对原始序列数据进行质量控制,去除低质量以及嵌合体序列,以获得高精确和高质量的DNA序列信息.采用邻近算法,以97%的相似水平进行古菌操作分类单元(OTU)进行分类.采用MOTHUR计算每个样本古菌的Shannon指数、Simpson指数、Chao 1指数以及ACE指数.群落结构空间差异采用主成分和聚类方法分析.此外,采用典范对应分析进行沉积物理化因子与群落的相关性(Canoco, 4.5). 2结果2.1沉积物理化性质从表1中可看出,沉积物盐度在空间分布上具有明显的差异,其值为0.2‰~5.5‰,最小值为浒浦,最大值为芦潮港.沉积物pH值在空间差异变化较小,其值为7.6~8.2.白龙港沉积物TOC的含量最高(1.82%),而浏河口沉积物TOC含量最低(1.31%).从沉积物中各形态无机氮的含量来看,NH4+-N含量最高,其值为34.8~73.2µg/g; NO3–含量为11.4~18.3µg/g,其中芦潮港含量最低,浏河口含量最高.各采样点沉积物的NO2–-N含量差别较小,其值为0.05~0.08µg/g.沉积物中Fe(II)和Fe(III)含量分别是9.1~17.1mg/g 和4.5~11.4mg/g.沉积物粒径组成主要以粉粒为主,占58.7%~71.3%;其次是黏粒和砂粒,分别占13.2%~ 24.3%和4.4%~28.1%.2.2沉积物古菌群落丰富度和多样性经古菌16S rRNA高通量测序,并将原始序列去除低质量与嵌合体序列后,得到各潮滩沉积物古菌有效序列数量分别为58959,33918,44319,78839和36208.对这些有效序列进行分析,分别得到1417,1082,1320,1087和900个古菌OTUs(表2).样品测序文库覆盖率为97.2%~98.7%,说明文库达到饱和,所获得的OTUs能够代表样品的所有古菌总量.古菌OTUs数量和Chao 1指数从低盐度向高盐度逐渐降低,即说明低盐度沉积物具有较高的古菌丰富度,而高盐度沉积物具有较低的古菌丰富度.白龙港沉积物古菌OTUs数量最高,而浒浦沉积物中古菌Chao 1指数最高;芦潮港沉积物OTUs数量和Chao 1指数最低.表1潮滩沉积物理化性质Table 1 Physicochemical properties of intertidal sediments样品名采样点盐度(‰)pH值TOC(%)NH4+-N(µg/g)NO3–-N(µg/g)NO2–-N(µg/g)Fe(II)(mg/g)Fe(III)(mg/g)黏粒(%)粉粒(%)砂粒(%)XP 浒浦 0.2±0.01e 7.8±0.3a 1.56±0.11b 64.1±6.2a14.6±2.2b0.08±0.01a9.1±0.6c 6.8±0.6b 16.2±1.7b 65.1±4.1a18.7±1.2b LHK 浏河口 0.4±0.02d 7.6±0.5a 1.31±0.16c 73.2±7.1a18.3±1.6a0.07±0.008a12.6±0.7b 4.5±0.3c 13.2±1.4c 58.7±5.3b28.1±3.5a BLG 白龙港 0.6±0.02c 8.0±0.4a 1.82±0.09a 51.3±4.2b15.7±1.4b0.06±0.002a17.1±1.4a 6.2±0.8b 18.1±1.2b 62.5±8.2a19.4±2.4b DHNC 东海农场 2.4±0.12b 8.2±0.3a 1.41±0.12c 61.2±3.9a14.2±2.0b0.05±0.003a12.3±0.9b11.4±0.7a 24.3±3.4a 71.3±4.2a 4.4±0.3d LCG 芦潮港 5.5±0.26a 8.1±0.4a 1.36±0.06c 34.8±5.3c11.4±0.9bc0.06±0.004a11.7±1.1b10.3±1.0a 21.9±2.5a 67.2±6.1a10.9±1.6c 注:不同小写字母表示样点之间的显著性差异(P<0.05).此外,ACE指数也代表古菌物种数量,其值为1012~1866,表现出低盐度沉积物高,高盐度沉积物低.Shannon指数和Simpson指数表示群落多样性.4期 李小飞等：长江口潮滩沉积物古菌群落结构与多样性 1747发现浒浦样点古菌的Shannon 指数最高,白龙港样点古菌的Simpson 指数最高.从古菌丰富度和多样性来看,两者都表现出随盐度升高而降低,特别是盐度最高的芦潮港的古菌丰富度和多样性最低,由此说明盐度对古菌群落的丰富度和多样性产生重要影响.表2 潮滩沉积物古菌群落高通量测序文库质量汇总Table 2 Information of high -throughput DNA sequencing library of archaeal community in the intertidal sediments样品名有效序列数 OTUsChao 1ACE Shannon Simpson 覆盖率(%)XP 58959 1417 1744 1866 8.02 0.980 97.2 LHK 33918 1082 1154 1154 7.86 0.986 98.3 BLG 44319 1320 1760 1803 7.99 0.988 98.7 DHNC 78839 1087 1341 1398 7.02 0.963 98.1 LCG 36208 900 1033 1012 7.06 0.969 99.4 注:XP 为浒浦,LHK 为浏河口,BLG 为白龙港,DHNC 为东海农场,LCG 为芦潮港,下同.72516BLGLCG DHNCLHKXP7952625773761610 31 516 10 1 217 6427616 19471711122223115295 62 252图2 采样点潮滩沉积物古菌群落高通量测序OTUs 维恩图 Fig.2 Venn diagram of archaeal community in the intertidalsediments of sampling sites采用维恩图分析了古菌群落OTUs 在不同采样点之间的相似性和特异性特征,结果见图2.从图中可看出,5个采样点潮滩沉积物中共有的古菌OTUs 数量为72,仅占到总OTUs 数量的1.2%,且主要属于广古菌门(Euryarchaeota)和奇古菌门(Thaumarchaeota).研究区浒浦、浏河口、白龙港、东海农场和芦潮港样点沉积物中特有的古菌OTUs 数量分别为795,262,376,577和516,其中浒浦样点沉积物古菌特有的OTUs 最多,是浏河口样点沉积物古菌特异性OTUs 最小的3倍.各样点沉积物特有的古菌群落OTUs 占到各总OTUs 的24.2%~57.3%,其中芦潮港所在比例最高,而浏河口最低.通过对古菌群落结构PCoA 分析,表明古菌群落结构表现出较大的差异.主成分1和2分别贡献了48.2%和29.9%,其中白龙港和浏河口相似性距离较近,与芦潮港、东海农场和浒浦分离较远.潮滩沉积物古菌群落空间差异与沉积物盐度分布极为相似,由此说明盐度是古菌群落差异的主要因素.-0.4-0.20.0 0.2 0.4-0.6-0.4-0.20.00.20.4P C 2 (29.9%)PC 1 (48.2%)图3 采样点潮滩沉积物古菌群落结构PCoA 分析 Fig.3 P rincipal co -ordinates analysis of archaeal communityin the intertidal sediments of sampling sites2.3 沉积物古菌群落组成特征采样点沉积物古菌群落在门水平的相对丰度如图4所示.沉积物古菌主要隶属于广古菌门(Euryarchaeota)、奇古菌门(Thaumarchaeota)和深古菌门(Bathyarchaeota).广古菌门在样点芦潮港、白龙港和浏河口样点沉积物占绝对优势,相对丰度占47.0%、50.9%和52.9%.东海农场和浒浦样点沉积物中奇古菌门占主要优势,相对丰度为47.3%和37.8%.此外,沉积物中深古菌门也占到很大一部分,特别是浏河口、白龙港和芦潮港样点的深古菌门1748 中国环境科学 39卷相对丰度达到25.23%、24.85%和25.91%.0.00 0.25 0.50 0.75 1.00图4 采样点潮滩沉积物古菌在门分类水平的相对丰度Fig.4 Relative abundance of archaeal communitycomposition at phylum level in intertidalsediments of sampling sites根据群落相对丰度以及古菌群落top10进行主要优势群落分析[13].各采样点沉积物中古菌群落结构组成和主要优势菌属(Top 10)所占比例差异较大(图5).芦潮港沉积物中占优势的古菌菌属为Methanosarcina(甲烷八叠球菌属)、Methanococcoides(拟甲烷球菌属)以及Candidatus_ Nitrosopumilus(氨氧化古菌),相对丰度分别占到21.3%、5.3%和2.9%.东海农场沉积物中占优势的古菌菌属分别为Candidatus_Nitrosopumilus(氨氧化古菌属,17.1%)、Methanocorpusculum(甲烷粒菌属, 4.8%)和Methanosarcina(甲烷八叠球菌属,1.1%).白龙港沉积物中占优势的古菌菌属分别为Methanosaeta(甲烷鬃菌属,16.1%)、Methanobacterium(甲烷杆菌属,9.2%)、Methanoregula(甲烷微菌属,5.2%)、Methanolinea(甲烷绳菌属,4.2%).浏河口沉积物中古菌菌属主要为Methanosaeta(甲烷鬃菌属,18.7%)、Methanoregula(甲烷微菌属,6.2%)、Methanobacterium(甲烷杆菌属,5.6%)和Methanolinea(甲烷绳菌属,5.5%).浒浦沉积物中占优势的古菌菌属为Methanosaeta(甲烷鬃菌属,5.7%)、Methanobacterium(甲烷杆菌属,5.7%)、uncultured_ crenarchaeote(泉古菌属,2.9%)和Candidatus_ Methanoperedens(甲烷氧化古菌属,2.1%).采用Unifrac法将沉积物古菌菌属进行加权聚类分析,并考虑古菌菌属的数量特征和进化关系,以此计算出样品之间的聚类关系与热图(图6).从图中可看出,芦潮港和东海农场的古菌群落组成相似性较近,白龙港和浏河口古菌物种组成相近,而浒浦与其他采样点的古菌物种组成差异较大,由此说明沉积物环境影响着古菌群落的空间差异.各样点沉积物中古菌菌属存在较大的差异,均有特异性的古菌群落.白龙港沉积物主要分布的古菌菌属为Methanomassiliicoccus、Methanomethylovorans、Methanosphaera、Methanosaeta、Methanospirillum 和Methanothermococcus 6个属群落. Methanosphaerula、Candidatus_Aenigmarchaeum、Methanosaeta、Mthanoregula、Methanolinea、Methanothermococcus、Methanosphaera、Methanospirillum 等8个古菌菌属主要分布于浏河口.而浒浦沉积物优势古菌菌属与其他采样点沉积物中的古菌菌属完全不同,主要是Methanofollis、Candidatus_Korarchaeum、Candidatus_ Nitrososphaera、Dechloromonas、Methanohalophilus、Methanoculleus、Methanocella、Candidatus_ Nitrosoarchaeum、Candidatus_Methanoperedens、unidentified_archaeon、Methanothermobacter 11个菌属.Methanomicrobium、Methanolobus、Methanimicrococcus、Methanosarcina、Methanococcoides、Methanogenium和ANME-3等6个古菌菌属主要分布于芦潮港.Candidatus_ Nitrosopumilus、Candidatus_Caldiarchaeum、Cadldithrix、Methanocorpusculum、Algoriphagus、Candidatus_lainarchaeum、Candidatus_ Nitrosopelagicus 7个古菌属分布于东海农场.LCG DHNC BLG LHK XP0.00.20.40.60.81.0OthersCandidatus_MethanoperedensMethanocorpusculumMethanococcoidesuncultured_crenarchaeoteMethanolineaMethanoregulaCandidatus_NitrosopumilusMethanobacteriumMethanosarcinaMethanosaeta图5 采样点潮滩沉积物古菌的Top 10菌属相对丰度Fig.5 Relative abundance of the Top 10 archaeal at genus level in the intertidal sediments of sampling sites4期 李小飞等：长江口潮滩沉积物古菌群落结构与多样性 1749图6 采样点潮滩沉积物古菌属相水平聚类分布Fig.6 Heatmap of archaeal genus in the intertidal sediments of sampling sites2.4 古菌群落组成与理化因子关系C C A 2图7 潮滩沉积物中古菌Top10菌属群落组成与环境因子的典型相关分析Fig.7 Canonical correlation analysis between the archaealcommunity and sediment properties in the intertidalsediments数字1、2、3、4、5、6、7、8、9、10分别代表古菌群落菌属Methanosaeta 、Methanosarcina 、Methanobacterium 、Candidatus_Nitrosopumilus 、Methanoregula 、Methanolinea 、uncultured_crenarchaeote 、Methanococcoides 、Methanocorpusculum 、Candidatus_Methanoperedens通过典范对应分析(CCA)了古菌群落组成与环境因子的关系.CCA1 和CCA2 的特征值分别是54.5%和41.4%(图7),共解释了总变异的95.6%,说明这些环境因子能够很好地解释沉积物中古菌群落结构的变化.从图7可知,古菌优势菌属Methanosaeta 、Methanobacterium 、Methanoregula 、Methanolinea、uncultured _crenarchaeote和Candidatus_Methanoperedens 与盐度具有明显的相关性,说明盐度对这几种优势菌属具有显著的影响.沉积物中Fe(II)是影响产甲烷菌属Methanobacterium 、Methanoregula 和Methanolinea的因素.此外,NO 3–-N 与NO 2–-N 对古菌菌属Methanosarcina、Methanococcoides、Methanocorpusculum 和Candidatus_Nitrosopumilus 也有一定的影响.因此,从以上分析的结果看,长江口潮滩沉积物中古菌群落的分布与盐度具有非常密切的关系,表明盐度是古菌群落差异的决定性因素. 3 讨论自然环境中微生物群落组成与分布是多种环境因子综合作用的结果,既具有普遍性,也具有特异性[23].微生物对外部环境变化具有很强的敏感性,因1750 中国环境科学 39卷此,微生物的群落组成与动态变化在很大程度上能够指示环境因子的变化.古菌是一类分布广泛的微生物群落,具有环境来源特异和功能作用突出的特征,且参与碳氮生物地球化学循环过程[24-25].不同的自然环境中,其水热组合与环境因子存在很大的差异,从而显著地影响古菌群落的组成和多样性.有研究报道我国不同地区盐碱土古细菌群落组成差异较大,主要以广古菌门(Euryarchaeota)和奇古菌门(Thaumarchaeota)为主,分别占总群落的3.0%~67.8%和 2.8%~72.7%,此外还有少量的泉古菌门(Crenarchaeota)[13].然而,有研究发现黄河口不同盐生植被类型土壤古菌主要属于泉古菌门(Crenarchaeota)和广古菌门(Euryarchaeota),广古菌门为优势菌群,相对丰度占4.63%(白茅土壤)~ 97.15%(光板地);泉古菌门的相对丰度比广古菌门小得多,仅为0.05%(翅碱蓬土壤)~1.61%(白茅土壤)[26].本研究对长江口潮滩沉积物中古菌群落分析,发现各采样点沉积物中古菌群落组成结构一致,不仅包括了分布广泛的广古菌门(Euryarchaeota)和奇古菌门(Thaumarchaeota),还有深古菌门(Bathyarchaeota)这类特异性较高的古菌群落,特别是浏河口、白龙港和芦潮港沉积物中的深古菌门占到很大一部分,相对丰度分别为25.23%、24.85%和25.91%.深古菌门(Bathyarchaeota)能够降解芳香族化合物,具有生物降解的能力,在自然环境中参与污染物降解等生态活动[27].本研究中浏河口、白龙港和芦潮港均为船舶港口,柴油泄漏和燃烧等烷烃有机污染严重,从而导致沉积物中具有较丰富的深古菌门群落.此外,潮滩沉积物中还发现丰度较高的一类古菌菌门Lokiarchaeota(洛基古菌),相对丰度0.2%~ 3.2%,该群落一般生活在深海热泉,而陆地环境分布较少[14].因此,河口潮滩中的古菌群落比其他环境更具有丰富和特异的古菌群落组成,这可能是由于河口潮滩复杂的环境差异所导致的.然而,河口潮滩环境的物理、化学和生物因子时空变化剧烈,古菌群落组成、丰度和多样性很可能具有很大的空间差异性.长江口潮滩沉积物中优势古菌菌属主要为产甲烷古菌属、氨氧化古菌属以及甲烷氧化古菌.然而,采样点沉积物中的古菌优势菌属既具有相似性又存在着一定的差别,其中盐度较高的芦潮港和东海农场存在相同的菌属有Methanosarcina(甲烷八叠球菌属)、以及Candidatus_Nitrosopumilus(氨氧化古菌属);盐度较低的白龙港和浏河口相同的菌属为Methanosaeta(甲烷鬃菌属)、Methanobacterium(甲烷杆菌属)、Methanoregula(甲烷微菌属)和Methanolinea(甲烷绳菌属);而盐度最低的浒浦为Methanosaeta(甲烷鬃菌属)、Methanobacterium(甲烷杆菌属)、uncultured_crenarchaeote(泉古菌属)和Candidatus_Methanoperedens(甲烷氧化古菌属).有研究表明闽江口潮汐淡水沼泽湿地土壤中优势产甲烷菌为Methanoregula(甲烷微菌属)和Methanosarcina(甲烷八叠球菌属)[28].此外,渤海沉积物中产甲烷菌的优势菌属为Methanobacterium(甲烷杆菌属)和Methanosarcina(甲烷八叠球菌属)[29].与前人研究结果相比,长江口潮滩沉积物的产甲烷菌菌属种类较多,有Methanosarcina(甲烷八叠球菌属)、Methanosaeta (甲烷鬃菌属)、Methanobacterium (甲烷杆菌属)、Methanoregula(甲烷微菌属)和Methanolinea(甲烷绳菌属).有研究揭示产甲烷菌较适宜在具有一定盐性的环境中生长[30],长江口潮滩环境有着较广的盐度梯度差异,且环境因子组合多样,这也可能导致不同类型的产甲烷菌群的分布.本研究中,潮滩沉积物古菌菌属分布较多的还有Candidatus_Nitrosopumilus,属于氨氧化古菌,其中盐度较高的东海农场和芦潮港分布最多,相对丰度分别为17.1%和3.0%,其他采样点的相对丰度均低于0.2%,说明Candidatus_ Nitrosopumilus菌属适宜在高盐度环境生长. Candidatus_Nitrosopumilus能够把NH4+-N氧化成NO2–-N,利用NH4+-N作为唯一能源正常生长[31].有研究表明在潮滩环境硝化速率与氨氧化古菌具有显著的相关性,而与氨氧化细菌不相关,氨氧化古菌对硝化过程的贡献比氨氧化细菌更大,说明氨氧化古菌对硝化作用起到主导作用[30].此外,在大多数陆地与水生态环境中,氨氧化古菌的丰度和表达量一般高于氨氧化细菌,表明氨氧化古菌在氮素循环中的生态功能更加重要[31].受人为活动的影响,河口环境氮污染日益严重,氨氧化古菌在河口环境的生态作用更加明显.近年来,自然环境中Candidatus_ Methanoperedens菌群因其参与氮和甲烷耦合过程,且能够氧化甲烷和去除硝酸盐,该群落因而引起了人们的广泛关注.本研究中,所有采样点均发现了Candidatus_Methanoperedens菌群的4期李小飞等：长江口潮滩沉积物古菌群落结构与多样性 1751存在,盐度最低的浒浦沉积物中相对丰度最高(2.1%),而盐度高的芦潮港和东海农场相对丰度最低(3.1~9.3),表明Candidatus_Methanoperedens菌群不适宜在高盐度环境.然而,由于PCR扩增引物特异性的限制,沉积物中还可能会有一些尚未检测到的古菌群落,需要采用多种方法与手段进行分析,以此得到更加全面的群落信息.有学者对淡水湿地研究发现,随着添加盐度的增加,土壤中产甲烷菌群落多样性降低[32].同样,本研究发现河口潮滩沉积物古菌群落丰富度和多样性随着盐度增加而降低(表2),表明盐度能够显著地影响古菌群落.然而,也有研究报道渤海沉积物盐度不是影响古菌群落结构的因素,这可能是因为该研究区的盐度梯度变化较小[29].此外,从群落进化亲缘距离来看,盐度对古菌群落进化具有非常重要的影响.本研究发现,相同的盐度环境具有较相似的进化关系(图3、6),亲缘关系较近,说明具有高度相似的古菌群落结构组成.因此,在河口潮滩环境中,盐度是影响沉积物中古菌群落结构和多样性的关键性因素.此外,也有研究表明沉积物中Fe(II)离子也是影响产甲烷菌属Methanobacterium、Methanoregula和Methanolinea的因子,这是因为高浓度的Fe(II)能够促进产甲烷菌的生长[30].同样,本研究也发现潮滩沉积物中Fe(II)对古菌群落Methanobacterium、Methanoregula和Methanolinea也有一定的影响.有研究证实,在淹水环境下,氨氧化古菌丰度比细菌要高,这是因为在低氧或缺氧环境更有利于古菌微生物的生长;同时古菌也能够在较低营养盐环境中得到生长[33].此外,植被也会通过营养盐和电子供体有效性来对微生物的群落结构和多样性产生重要的影响,因而在今后的研究中也应引起重视[37].本研究中各样点之间存在较少的共有OTUs数量(图2),进一步说明潮滩沉积物古菌群落的空间差异较大,且复杂多变的环境条件是影响沉积物古菌群落结构差异的重要因素.4结论4.1长江口潮滩沉积物中古菌物种丰富度和多样性空间变化明显,表现出从低盐度向高盐度环境降低的特征.4.2潮滩沉积物中古菌以广古菌门(Euryarchaeota)、奇古菌门(Thaumarchaeota)和深古菌门(Bathyarchaeota)为主;样点芦潮港、东海农场、白龙港、浏河口和浒浦沉积物中的最优势古菌菌属分别为Methanosarcina (21.3%),Candidatus_ Nitrosopumilus (17.1%),Methanosaeta (16.1%),Methanosaeta (18.7%)和Methanosaeta (5.7%).4.3特有古菌群落占到各采样点总古菌群落的24.2%~57.3%,且特异性程度随采样点沉积物盐度升高而增加.4.4盐度是潮滩沉积物中古菌丰富度、多样性和群落结构空间差异的主要决定性因子.参考文献：[1] Zhou M, Butterbach-Bahl K, Vereecken H, et al. 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The environmental changes and mitigation actions in the Three Gorges Reservoir region,ChinaQuanfa Zhang a,*,Zhiping Lou b,1a Key Laboratory of Aquatic Botany and Watershed Ecology,Wuhan Botanical Garden,Chinese Academy of Sciences,Wuhan430074,PR Chinab Bureau of Life Sciences and Biotechnology,Chinese Academy of Sciences,Beijing100864,PR China1.IntroductionSun Yat-Senfirst proposed that a series of large dams be builtin the Yangtze River in his1919article‘‘The InternationalDevelopment of China’’,and it remained an aspiration forChina over the20th century.Since the1930s,a number offeasibility studies were undertaken for constructing a largedam in the upper reach of the Yangtze River even after theChina’s revolutionary governmental transition in1949.From1958to1984,China built the Lushui Dam in Chibi City,about110km south of Wuhan City of Hubei Province,and conducteda variety of small-scale experiments and technical tests for abig dam in the Yangtze River.The Gezhouba Dam,built38kmdownstream of the current Three Gorges Dam(TGD)sitebetween1970and1988,essentially concluded thefinal testsbefore commencing building the TGD.The TGD,begun to be built in1993and completed in2009,isby far the world’s largest hydroelectric scheme.It is designedto help controlfloods and improve navigation on the YangtzeRiver,and perhaps more importantly increases China’s energysupply for its rapid economic development.The dam is aconcrete gravity type with a height of185m and total waterstorage capacity of39.3billion m3.Itsflood control capacity ise n v i r o n m e n t a l s c i e n c e&p o l i c y14(2011)1132–1138a r t i c l e i n f oPublished on line17August2011Keywords:Three Gorges DamBiodiversity conservationWater environmentUplandsDrawdown zonea b s t r a c tThe Three Gorges Dam(TGD)is by far the world’s largest hydroelectric scheme.Due to itsunprecedented magnitude,the TGD has been controversial ever since it was proposed in theearly20th century and building commenced in1993.Recent problems,including geologicaldisasters(e.g.,landslides)in the uplands and algal blooms in the aquatic environment sincethe reservoir’s partialfilling to156m in2006,suggest that the environmental challenge hasnever been greater than now.The environmental deterioration might be further intensifiedwhen the reservoir reaches itsfinal water level of175m.Solving the environmentalchallenges will be essential for the sustainable development of the Three Gorges Reservoirregion(TGRR),and environmental sustainability in the TGRR is a high priority for the nationconsidering its critical location in the Yangtze Basin,which contributes40%of China’s GDP.This article reviews primary environmental assessments for biodiversity conservation,thewater environment,water levelfluctuation zone,and the uplands after the partialfilling inthe reservoir region.It also discusses the success of mitigation efforts to date.Although thereare successes in mitigation particularly in conservation of endangered plants andfishes,itseems likely that environmental conditions in the TGRR could only get worse in the shortterm.Building a partnership among the TGD stakeholders,including local residents,gov-ernments,and international communities is necessary to meet the mounting environmentalchallenge in the TGRR and beyond.#2011Elsevier Ltd.All rights reserved.*Corresponding author.Tel.:+862787510702;fax:+862787510251.E-mail addresses:qzhang@(Q.Zhang),zplou@(Z.Lou).1Tel.:+861068597503;fax:+861068597518.a v a i l ab l e a t w w w.sc i e nc ed i re c t.c o mjournal homepage:/locate/envsci1462-9011/$–see front matter#2011Elsevier Ltd.All rights reserved.doi:10.1016/j.envsci.2011.07.00822.1billion m 3,increasing the flood control ability from the present 10-year to a 100-year frequency flood.It has installed a total generating capacity of 22,400MW (100billion kWh),equivalent to consumption of more than 60million tonnes of raw coal annually,dramatically increasing energy supply for China’s economic development.Meanwhile,the dam increases water depth by more than 100m,effectively improving the navigability in the 600km section of the Yangtze River between Yichang and Chongqing (Fig.1A).The TGD will form a reservoir with a total water surface area of 1080km 2in the Yangtze River between Chongqing and Yichang.The region surrounding the reservoir,with a total area of approximately 58,000km 2,has now become known as the Three Gorges Reservoir Region (TGRR)(Fig.1).Due to its unprecedented magnitude,the TGD has been controversialever since its implementation.A comprehensive environmen-tal impact assessment was conducted in the 1980s (RCEETG,1987),and many of the predicted environmental problems have been realized recently by the partial filling of the reservoir in the past 5years (RCEETG,1987;Shen and Xie,2004;Wu et al.,2004;Liu et al.,2006a,b;Xu et al.,2006;Zhang et al.,2006).Systematic monitoring since 1997have also provided the evidence of environmental changes in the TGRR and downstream of the Yangtze Basin (/).Solving the environmental challenges surrounding the TGD will be essential for the sustainable development of the TGRR and remains a high priority for the country as well.However,any efforts will have to rely on the determination of the environmental changes in the region that are due totheFig.1–The Location of the Three Gorges Dam,the Gezhouba Dam and the Three Gorges Reservoir Region (TGRR),China.(A)DEM and roads and (B)land use and land cover and locations for biodiversity conservation networks.e n v i r o n m e n t a l s c i e n c e &p o l i c y 14(2011)1132–11381133construction of the TGD.The challenge has never been greater than now,indicated by the geological disasters(e.g.,land-slides)in the uplands and algal blooms in the aquatic environment that have occurred since the reservoirfilled to 156m in2006(Hu and Cai,2006;Liu et al.,2006a,b;Ye et al., 2007;Fu et al.,2010),and the situation may be intensified when the reservoir reaches thefinal water level of175m in the next few years.This article categorically summarizes the current status of the region based on environmental and ecological research, particularly those studies published in Chinese scientific literature.It presents the changes in biodiversity and associated conservation efforts,and it reassesses the envi-ronmental implications in the water environment,the water-level-fluctuation-zone,and the uplands after partial reservoir filling.In particular,mitigation strategies and conservation efforts are discussed.The ultimate objective is to help formulate strategies for the TGD management and environ-mental sustainability in the TGRR.2.Biodiversity conservationOne of the most immediate consequences of the dam building is the loss and fragmentation of habitats due to both the inundation and the subsequent resettlement of the human population in new areas(Wu et al.,2004;Wang et al.,2006; Yang et al.,2006;New and Xie,2008).As one of the biodiversity hot spots of China,the TGRR has nearly6400plant species (including cultivated varieties;19.3%of the total number of species found in China),more than3400insect species(8.5%of the China’s total),and about500terrestrial vertebrate species (22%of the China’s total)(Huang,2001).Because of its distinctive geographic location,complex topography and climatology,there are a number of endemic and ancient species in the terrestrial and aquatic environments of the TGRR(Chen et al.,1994,2004;Xie,2003).Ironically many unique species persisted during the Quaternary glaciations, yet the inundation and dam construction will be disastrous for many of these species and communities.The inundation and the resettlement will affect at least36 vegetation types,Fortunately most of them are considered to have low conservation or economic values,because they are mostly secondary shrub and grass communities that are widely distributed in other areas(Huang,2001;Tian et al., 2007).Thus,conservation efforts have been primarily concen-trating at the species level,with transplantation and conser-vation of more than200plant species including37threatened species in the TGRR.The conservation strategy has been following a strategy of‘‘introduction–propagation–reintroduc-tion’’.For instance,Adiantum reniforme var.sinense and Myricaria laxiflora are2species which are primarily distributed in the altitude of80–480m and70–155m in the Three Gorges valley from Yichang to Chongqing,respectively,areas which are largely impounded by the reservoirfilling(Shi et al.,2005; Wang et al.,2003).Species like Securinega wuxiensis and Neyraudia wushanica will also lose their critical habitat(Huang, 2001;New and Xie,2008).Without other viable options,those species were introduced into botanical gardens for ex situ preservation in early1980s.A recent study has indicated that more than85%of the species’genetic diversity has been preserved(Li et al.,2003).With the successful development of their propagation capacity including the sexual and asexual reproduction of individual plants(Lin,1989;Xu et al.,1998), they have been reintroduced to their natural habitat with the objective of restoring the original communities that occurred before inundation in the TGRR(Chen et al.,1994).The Yangtze River is also one of the richest areas in freshwaterfish species diversity with361species,of which177 are endemic.Up to40fish species have been affected due to interruption of their migratory paths and the loss of spawning grounds by the construction of the Gezhouba Dam(38km downstream from the TGD)(Dudgeon,2000;Fu et al.,2003). Sharp declines in the populations of three endemic ancient fish species namely the Chinese sturgeon(Acipenser sinensis), river sturgeon(Acipenser dabryanus),and Chinese paddlefish (Psephurus gladius)has been observed(Fu et al.,2003).Aquatic mammals,such as the Yangtzefinless porpoise(Neophocaena phocaenoides asiaeorientalis)and the Chinese river dolphin (Lipotes vexillifer),which has nee recently categorized as ‘‘functionally extinct’’,are also seriously threatened(Wang et al.,2006;Turvey et al.,2007;Zhao et al.,2008).The TGD has further affected the survival of mammals due to the increased use of the river by shipping vessels,leading to physical injuries due to collision,and noise disturbance,as well as the changes in hydrological regime(Fu et al.,2003;Wu et al.,2004).The impacts of dam construction onfish species and aquatic mammals seem inevitable(Rosenberg et al.,1997). Without adequate conservation measures to allow uninter-rupted migration in the dam infrastructure(e.g.,fish pas-sages),conservation efforts have been focusing on identifying and establishing reserves for the endemic species in the tributaries of the upper Yangtze(Park et al.,2003).A program of artificial reproduction of endemicfish species has been performed for more than a decade.For plant species conservation,a program has been initiated recently to conserve three more endangered species,Rhamnus tzekweien-sis,Buxus ichangensis,and Plantago erosa var.fengdouensis following the same strategy that has successfully preserved A.reniforme var.sinense and xiflora(i.e.,‘‘introduction–propagation–reintroduction’’).Consequently,the efforts have also been shifted to the preservation of regional ecosystems with consideration of typical vegetation types(e.g.,evergreen forests)and rare and endangered species in the region.An ecosystem conservation network has been developed in the TGRR including Dalaoling(Yichuang City,Hubei Province), Longmuhe(Xinshan County,Hubei Province),Shiping(Fengdu County,Chongqing),and Wushan(Wushan County,Chongq-ing)(Fig.1).The three former sites are intended for evergreen forest preservation and Wushan is specifically for the conservation of vegetation on Karst.3.The water environmentPollutants of the Three Gorges Reservoir(TGR)primarily result from(1)runoff from the upper steams of the Yangtze,(2) industrial and domestic wastewater and agricultural runoffs in the TGRR,(3)waste materials from shipping,and(4)internal sources of pollutant from toxic industrial sediments lefte n v i r o n m e n t a l s c i e n c e&p o l i c y14(2011)1132–1138 1134behind as the TGDfilled(Liu et al.,2006a,b;Zhu et al.,2006).In 2006,the industrial and domestic wastewater released into the TGR from the TGRR was1.124billion tonnes,and fertilizer and pesticide application for agriculture(a total area of977,700ha) in the region was154,000and655.47tonnes,respectively. After the reservoirfilled,increased shipping added an additional 3.8million tonnes of waste materials into the reservoir(SEPA,2009).The dam itself does not necessarily contribute to an increase in pollutants in the reservoir,but related activities including resident relocations,reservoir filling and mitigation strategies may have affected the water environment of the reservoir.The authorities have been implementing an ambitious plan to build a total of20waste treatment plants in the TGRR to control the point-source pollution into the reservoir.The treatment facilities have the potential to treat at least85%of sewage and garbage by2010,dramatically reducing inputs of industrial and domestic pollutants from the TGRR into the Reservoir.Low treatment rates persist,despite the new capacity,due to inadequatefinancial support for facility operation and lack of wastewater collection pipelines,so untreated wastewater is still going directly into the river and finally to the reservoir.A huge amount of toxic sediment from factories,mines,and garbage dumping sites remained on site after relocation of some 1.4million people.There will be increasing internal source of pollution with toxics including arsenic,sulfides,cyanides and mercury from these sources remaining in the reservoir after it fills(Yu et al.,2006;Zhang et al.,2006;Ye et al.,2010).Although the government had campaigned to clean up the banks and the waste sites of the reservoir before the reservoirfilling,the efforts have not completely decontaminated toxic wastes.Meanwhile, contaminated sedimentations from upstream will accumulate in the reservoir as the water level rises(Zhou et al.,2006).The water chemistry of the reservoir has generally been stable since the reservoir beganfilling in2003(SEPA,2009; Zhang et al.,2005;/).Yet,algae blooms,an indicator of water quality,have frequently occurred since this time.Intensive studies have been carried out on the reason for these blooms in the Xiangxi River(Hubei)and Daning River(Chongqing)(Ye et al.,2007).It has been concluded that the occurrence is largely attributable to the accumulation of nutrients triggered by the change in the hydrological regime (Hu and Cai,2006;Zeng et al.,2007).The waterflow in the TGRR has been dramatically slowed down by the reservoirfilling. Thus,the pollution could not be diluted andflushed to the sea as such has occurred for thousands of years before damming. Wastes,especially nutrients from the upper streams of the tributaries in the TGRR,have accumulated in the bays.Thus, algal blooming would be inevitable without substantial reduc-tion of nutrients from the upper streams of the tributaries(Hu and Cai,2006;Bi et al.,2010).Currently,there is any effective measure to control algae bloom and developing new prevention techniques are in high demand.4.The water levelfluctuation zone(Wlfz)Perhaps the most visible change due to the reservoirfilling would be the formation of a Yellow Belt along the riverbanks of the mainstream and tributaries in the TGRR.The full functional Reservoir would have a water levelfluctuating between145m and175m,i.e.,145m in summer(May–October)forflood control and175m in winter(November–April)for energy generation.The area between the high(i.e., 175m)and low(i.e.,145m)water level is called the water level fluctuation zone(WLFZ).A recent study has estimated the total area of the WLFZ in the reservoir is ca.350km2primarily composing of agricultural lands(30%),bare lands(40%)and urban areas(10%)before inundation(Zhang,2008).For such a large area in the terrestrial-aquatic ecotone of the TGRR,its environmental implications should not be underestimated (New and Xie,2008).In this newly formed ecotone,the previous habitat is terrestrial,and the hydrological regime is the opposite of the natural one,with post-damflooding occurring in winter rather than summer.Plant species adapted to previously terrestrial habitats would disappear and few species are expected to survive in the novel habitats,leading to potential invasion by exotic species,soil erosion and sedimentation,and the loss of amenity value for tourism in the TGRR(Zhao et al.,2007;New and Xie,2008).Geological disasters including soil erosion and land sliding are likely to be intensified,threatening the safety of human life and property(Xu et al.,2006;Wang et al.,2008). Intensified agricultural activities due to relocation of the human population will certainly increase the pollutants into the reservoir(Xu et al.,2005).Wastes accumulating from the uplands and upstream in summer will be exposed in the WLFZ and subject to high temperature,becoming an ideal place for the propagation of bacteria,virus,and other pathogens;the occurrence of epidemic diseases is a great possibility(Su et al., 2003).The alteration of ecosystem construction and function will have significant consequences for human well-being (Kittinger et al.,2010).There are few options available for meeting the challenges and demands for ecosystem restoration in the WLFZ. Currently,civil engineering approach,i.e.,using concrete surface for slope protection and soil erosion control,has been widely applied in particular for slope stabilization in urban areas along the mainstream of the Yangtze River.However, building of concrete surface is costly and its resultant landscape is incompatible with the natural scene in the Three Gorges.Thus,civil engineering approach is not desirable in terms of cost,tourism and the environment.Revegetation of the WLFZ is an environmentally friendly alternative but would be challenging.The greatest challenge is that few species are expected to survive in an annual cycle of the aquatic–terrestrial environment with half a year under inundation as deep as30m(Zeng et al.,2007;Fan et al.,2006;Tan et al., 2010).Since2000,research has been conducted to determine the suitability of potential plant species for the novel habitat in the WLFZ.A number of species including Cynodon dactylon and Salix variegata have showed their potential(Tan et al.,2010). Recently,revegetation demonstration projects have been carried out with success in Zhong County,Wanzhou District of Chongqing Municipality and Zigui County of Hubei Province.Because of the waterfluctuation level of30m and enormous demands of land for economic development in the TGRR,new approaches including integration of ecologicale n v i r o n m e n t a l s c i e n c e&p o l i c y14(2011)1132–11381135and engineering procedures have been proposed and imple-mented in Kai County and Fengjie County of Chongqing.These options may be an applicable option particularly in the urban areas and tributaries for environmental restoration in the WLFZ.These proposals include building small dams to stabilize the water level to 170m in the tributaries,reducing the waterfluctuation level to5m in the WLFZ and maintaining a minimum water level for wetland formation.The environ-mental restoration will therefore focus on a rather easier task of wetland restoration.However,water quality in the small reservoir is still of great concern and these projects will reduce the water storage capacity forflood control,one of the primary objectives of the dam construction.5.The uplandsGeographically,the TGRR is located in the transitional zone from the Tibetan Plateau in the west to the east rolling hills and plains of China.96%of the total landscape areas(i.e., approximately85,000km2)are mountains and hills,and about half of them are forested lands,shrubs,and meadow(Zhang et al.,2009).Most of the vegetated lands are intensively degraded(Zhang et al.,2007).Agricultural lands,with only 0.07ha/person,are often located in the mountainous region. Due to the low soil quality and extensive soil erosion,the massive use of fertilizers causes releases of large quantity of nitrates and phosphates,increasing their concentrations in the reservoir and consequently leading to eutrophication(Li et al.,2005;Liu et al.,2006a,b).Non-point source pollutants are increasingly becoming the primary pollutants of the reservoir (SEPA,2009).There are close to1.4million migrants who have been resettled due to the dam construction,and most of them have been moved to the steep hills of the TGRR.Relocation of towns, manufacturers,and temporary land usage for construction has cleared large areas of previously vegetated and agricul-tural nd reclamation to compensate for the losses of productive agricultural lands to the impoundment has led the intensification of the human–land conflict,also compromising the reforestation efforts in the TGRR(Jackson and Sleigh,2000; Heming et al.,2001;Zhang et al.,2007).Moreover,these activities will profoundly increase non-point source pollution into the reservoir(SEPA,2009),and cause rampant soil erosion, riverbank collapses and landslides along the shores of the Yangtze’s mainstreams and tributaries,leading further deterioration of the environment.The TGRR has been one of the primary regions for national ecological restoration projects.The‘‘Natural Forest Conserva-tion Program’’,‘‘Protective Afforestation along the Upper and Middle Reaches of the Yangtze River’’,and‘‘Conversion of Cropland to Forest Program’’have been implemented,and arable lands of1810km2have been transformed into forests between1992and2002(Zhang et al.,2007).Additionally,in partnership with local authorities and NGO’s an experimental project in Yunyang County of Chongqing Municipality has been implemented as a demonstration of the‘‘Green Belt’’establishment in the TGRR since2004and that has success-fully transformed over400ha of bare land into forest plantations.The effort has taken a traditional approach in terms of technology but the partnership with participation of various stakeholders has shown the model for the ecological restoration applicable for the entire TGRR.Reforestation of large land areas has many obstacles,in particular resistance from local residents because of competi-tion for land in the TGRR.Thus,a new concept known as ‘‘Ecological Shelter’’has been developed for environmental restoration in the TGRR(Liu,2007).While reforestation remains the primary objective,the effort will demonstrate sound practices both economically and environmentally for ecological restoration by planting native species with imme-diate economic values or/and abilities to absorb large quantity of nutrients and reduce soil erosion(Ng et al.,2008).It will also consider all the elements including vegetative lands,agricul-tural lands,townships in the landscape matrix and economic activities such as forestry and poultry for the ultimate objective of non-point pollution control.Additionally,integra-tive watershed management has implemented in the TGRR aiming at reducing nutrients into the reservoir from the upper streams into the reservoir.6.ImplicationsLarge-scale hydroelectric development has far-reaching so-cial,economic and environmental implications(Rosenberg et al.,1997).As the TGRR is located in a rather ecologically fragile region and China’s society and economy in a rapid transitional motion,the environmental changes in the TGRR would be dramatic.Due to the scale of the TGD,many changes are unprecedented such as formation of‘‘Yellow Belt’’with a total area of ca.350km2along the riverbanks in the TGRR. Thus,systematic monitoring on all aspects of the environ-ment has been carried out since1997(/).Conservation of endangered and rare species in particular plants,aquatic mammals andfishes are of great concern surrounding the TGD.Known endangered plant species have been successfully preserved through ex situ programs and ongoing projects on the artificial breeding forfishes continu-ously increase their population in the Yangtze River.Yet,great challenge remains for the conservation of aquatic mammals. Establishment of nature reserve seems not quite effective, participation of international community with new approaches,ideas and technologies is urgently demanded.In order to improve the water environment,there are great needs to reduce waste inputs from all sources into the reservoir.Yet,there lacks operational fund for sewerage treatment which can reduce industrial and domestic waste-water,and the reservoirfilling will destabilize the river banks and increase the internal sources of pollutants due to sedimentation.Reduction of agricultural runoffs requires economic structure adjustment,such as transforming from land-based to knowledge-based economy,which will take decades,and waste materials from shipping and internal sources of pollutants from toxic industrial sediments will only increase by the improved navigation condition and periodic flooding in the reservoir,respectively.All those challenges will remain for the time being until more resources are allocated into the water conservation in the region.e n v i r o n m e n t a l s c i e n c e&p o l i c y14(2011)1132–1138 1136Never a water-level-fluctuation-zone of a reservoir is as large as the one in the Three Gorges Reservoir.To restore the riparian ecosystem,revegetation is quite successful and the technology is capable of establishing vegetation in the novel habitat.Yet, unregulated agricultural activities and possible accumulation of wastes will degrade the environment in the WLFZ.Periodic flooding will destabilize the structure of soil and rocks,causing soil erosion and land sliding.It may take decades for the geological structure to reach a new stable state.Due to all the constraints and challenges,the environment in the TGRR could only get worse in short term.Knowledge and new technology outside of China on the hydroelectric projects may provide reference to the TGD and help develop strategy for environmental conservation in the TGRR.Thus,building a partnership among TGD stakeholders,including local resi-dents,Chinese government,and international communities is necessary to meet the mounting environmental challenge in the TGRR andfinally demonstrate the capacity of humanity to reach sustainable development solutions.AcknowledgementsWe wish to acknowledge the constructive comments and suggestions from Dr.Martin Beniston and two anonymous reviewers.The research is supported by the Executive Office of the State Council Three Gorges Construction Committee of China(SX2008-005and SX2010-014)and the‘‘Hundred-Talent Project’’of the Chinese Academy of Sciences(O629221C01). 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