月湖底泥疏浚后底栖动物群落的恢复及其与环境的关系

研究对月湖底泥疏浚后底栖动物群落动态进行逐月的周年调查,并分析了底栖动物密度、生物多样性与环境因子的关系,结果表明：疏浚导致大型底栖动物基本消失,现存量从疏浚前的（4387±885）ind·m-2降低至（80±21）ind·m-2。疏浚后,寡毛类成为受干扰系统恢复过程中的先锋种类,在春季（4月）和秋冬之际（11月）出现2个密度高峰,分别为（1010±230）ind·m-2和（1538±408）ind·m-2,而摇蚊幼虫在疏浚一年后的秋冬季密度达到高峰（2021±612）ind·m-2,二者均基本恢复到疏浚前的密度水平。种类组成与疏浚前相似,优势种类数较疏浚前多,7月份以前,以霍甫水丝蚓占绝对优势,7月份以后以长足摇蚊占绝对优势。生物多样性在秋冬季恢复到疏浚前水平。寡毛类、摇蚊幼虫的密度、生物多样性与湖水溶氧、透明度呈显著正相关,与水体营养水平（TN、TP、有机碎屑）呈显著负相关（P〈0.05）。分析认为疏浚后底栖动物群落的季节变化与动物的生命周期（繁殖和生长）密切相关,而营养水平不是限制动物种群密度分布的主要因子。从底栖动物群落的恢复情况来看,疏浚后的底质环境更有利于底栖动物群落的生存和底栖生态系统的重建。     

环渤海近岸海域表层沉积物及底栖生物中PBDEs的赋存特征及富集行为

多溴联苯醚(PBDEs)作为一种新型的持久性有机污染物,在海洋环境中广泛存在,研究PBDEs在不同介质中的赋存状态对于理解其环境行为及归趋具有重要的意义。通过采集不同区域沉积物及生物样品,考察了PBDEs在环渤海近岸海域表层沉积物及底栖生物中的含量及空间分布特征、污染模式及生物-沉积物富集因子。结果表明,环渤海沿岸表层沉积物中PBDEs总量(Σ10PBDEs)的浓度范围在0.446~26.8 ng·g-1(干重,dw)之间,中值为1.02 ng·g-1(dw),底栖生物中PBDEs(Σ9PBDEs)的浓度范围为0.053~9.90 ng·g-1(dw),中值为1.25 ng·g-1dw;沉积物中BDE-209为最主要的单体,平均丰度达到90.5%,生物体中主要以低溴代BDEs为主,其中单体BDE-47的含量最高,平均丰度范围为43.2%~49.7%;沉积物和生物中PBDEs的含量在空间上存在显著的差异,其中莱州湾和锦州附近区域的结果明显高于其他区域;5种不同的底栖生物对PBDEs均表现出一定的生物富集性,其中∑9PBDEs的BSAF值按从大到小的顺序为菲律宾蛤仔(0.43~4.06,mean=1.19)紫贻贝(0.34~2.86,1.03)四角蛤蜊(0.17~1.95,0.82)麻蛤(0.13~2.33,0.61)牡蛎(0.09~1.20,0.52)。辛醇水分配系数(log KOW)与不同物种BSAF值的相关性分析结果表明,除BDE-17单体外,其他单体的BSAF值表现出随log KOW的升高而下降的趋势。     

平原河网地区大型底栖动物群落结构及其与环境因子的关系

大型底栖无脊椎动物是河流生态系统的重要组成生物,具有活动范围相对固定、生命周期较长、生活习性相对稳定等特点,可有效指示河流水质和水生态系统健康状况。有关大型底栖生物群落结构特征及其与水环境之间的关系研究一直是河流生态系统的研究热点。底栖动物具有较强的地域性,其群落结构特征受当地的自然环境特征和社会经济发展程度的双重因素影响。为研究典型平原河网地区的底栖动物群落结构及对水环境状况的响应特征,在上海市选取了83个河道断面进行大型底栖动物采样分析,共获取底栖动物20个分类单位（种）,其中软体动物10种,环节动物6种,节肢动物4种。上海河道底栖动物群落结构总体呈现结构单一、物种丰富度低、高度耐污性等显著特征,环节动物的栖息密度和出现频率均最高。城市化水平的空间差异性直接影响底栖动物空间分布的异质性,由市区至近郊、远郊,物种数从11种逐渐上升至15种,而栖息密度则由8 776.3个/m2下降至690.3个/m2。底栖动物群落结构的空间分布特征与水质理化指标的空间分布特征具有良好的对应性,水质空间变化导致环节动物和软体动物、节肢动物的空间分布存在一定交错性,耐污性较强的环节动物主要分布在有机污染重、溶解氧低的市区河道断面,而喜清洁环境的软体动物和节肢动物主要分布在水质较好的郊区断面。寡毛纲物种的栖息密度与溶解氧质量浓度呈显著负相关性。     

青岛汇泉湾排污口附近大型底栖动物的群落结构和多样性

为了解污水排海对大型底栖动物群落结构和多样性的影响,于2015年8月对青岛汇泉湾第一海水浴场中潮带一个排污口附近不同距离站位的大型底栖动物,通过野外采样调查、室内生物鉴定和环境因子测定以及多元数据统计分析,对其丰度、生物量、种类组成、多样性、群落结构及其与环境因子的关系进行了研究.结果表明,该区域大型底栖动物的平均丰度为(825.6±115.9)ind/m~2,随着与排污口的距离增加,丰度呈下降趋势.大型底栖动物的平均生物量为(77.7±46.2)g/m~2,随着与排污口的距离增加,呈现出先增加后减小的趋势.本次调查共鉴定出大型底栖动物34种,包括节肢动物门甲壳类动物12种,软体动物门动物10种,环节动物门多毛类动物10种,纽形动物门动物1种及鱼类1种.多元统计分析结果表明,随着与排污口的距离增加,大型底栖动物的群落结构和优势种组成呈现出了显著的变化.距离排污口最近的S1站位的优势种为双扇股窗蟹、宽身大眼蟹、菲律宾蛤仔和颗粒拟关公蟹,距离排污口20-80 m的S2-S3站位的优势种为双扇股窗蟹、日本外浪漂水虱、中阿曼吉虫、叉毛矛毛虫和日本拟背尾水虱,而距离排污口最远的S5站位的优势种为日本外浪漂水虱、中阿曼吉虫、叉毛矛毛虫和河蜾蠃蜚.各种多样性指数在空间分布上都呈现出了相同的格局,即随着与排污口的距离加大,先增加后减小.基于香农-威纳多样性指数和ABC曲线的结果表明,研究海域大部分沉积物环境处于轻度污染状态,部分区域处于清洁状态.相关性分析结果表明污水排海会导致沉积物有机质含量增加从而对大型底栖动物产生影响.本研究表明大型底栖动物数量和群落随与排污口距离增加而变化,在海洋环境监测中具有重要的应用价值.     

凋落物覆盖及掩埋对不同质量的藜蒴种子萌发和幼苗生长的影响

以南亚热带常见的先锋乡土树种藜蒴(Castanopsis fissa)为研究对象.通过室内萌发试验,分析了种子质量、凋落物覆盖和掩埋对种子萌发及幼苗早期生长的影响.结果表明,藜蒴种子能否成功萌发并形成幼苗的决定性因素是种子的掩埋深度.掩埋显著抑制了藜蒴种子萌发及形成幼苗的过程,随掩埋深度的增大,这种抑制作用越明显.掩埋对幼苗的存活和生物量没有显著影响,但可提高幼苗根部生物量的分配.深度掩埋时,质量大的种子在幼苗形成过程中具明显优势;而置于土壤表层或浅埋的种子成苗率与种子质量的相关性较低.大质量种子形成的幼苗更易于存活,在生物量的积累方面也表现H{一定的优势.凋落物覆盖未抑制幼苗的出土,且对幼苗的存活和生长具有明显的促进作用,表现在可提高幼苗的相对生长率以及生物量的积累.另外,凋落物的覆盖明显提高了幼苗生物量在其冠部的分配.因而,若利用直接播撒藜蒴种子的方式改造南亚热带退化草坡.理论上应尽可能选用大质量的种子直接播种于地表,并覆以原有的地表凋落物,以促进藜蒴幼苗成功建立.     

截污后深圳河落马洲段大型底栖动物群落的恢复过程

2000年4月至2002年4月,对截污前后的深圳河落马洲段大型底栖动物进行两周年的季度监测.结果表明,截污前深圳河落马洲段没有发现大型底栖动物;截污后大型底栖动物种数、密度、生物量和种类多样性指数(H′)有随时间推移呈增加的趋势;截污后底泥中硫化物、总氮、总磷随时间推移呈下降趋势.由此可见,截污后深圳河落马洲段大型底栖动物从无到有,种数、密度和生物量从少到多,群落结构处于向多样性恢复的过程中.图6表2参11     

多金属矿区土壤重金属垂向污染特征及风险评估

重金属在土壤中向下迁移可能会对地下水造成污染,了解重金属在剖面上的迁移特征对污染控制与防范有重要意义。为深入了解多金属矿区尾矿库土壤重金属垂直迁移与生态风险问题,分层采集了某多金属矿区尾矿库坝下附近0~100 cm深度的土壤样品,分析检测了不同深度土壤中Cr、Cd、Pb、Cu、Zn、Ni总量及有效态含量。综合考虑多元素协同作用、毒性水平、污染浓度以及环境对重金属污染敏感性等因素,采用Hakanson潜在生态风险指数法对土壤污染状况及生态环境风险进行了评价,并对土壤中铅、锌重金属的形态垂向分布特征及其迁移能力进行了分析研究。结果表明,研究区域土壤重金属污染严重,垂向污染也达到了一定的深度,上层土壤、中层土壤综合污染指数均达到重度污染级别,下层土壤综合污染指数达到中度污染级别。供试土壤的污染程度最重的指标为Pb和Zn,污染最重的土层为0~30 cm上层土壤。从生态风险来看,单项潜在生态风险指数在3.07~77.1之间,上层土壤单项潜在生态风险CdCuPbNiAsZn,矿区场地土壤修复过程中应重点关注Cd、Cu的生态风险影响;此外,由于As在土壤中具有较强的垂向迁移能力,也应予以重点关注。     

水葫芦生态净化工程对竺山湖底栖动物群落结构变化的影响

在解决了机械化采收、资源化利用的终端处理后,利用适应性广、生物量大、净化能力强的漂浮植物净化污染水体,成为当前受污水体、尤其是富营养化水体生态治理的有效治理手段之一。在常规控养水生植物净化水体的工程实践中,主要是在风浪扰动小的岸边或内河里进行,在湖泊等多风浪扰动的较大水体中进行控养水生植物、净化水体的工程实践尚不多见。因此,根据江苏省通过种养水葫芦(Eichharnia crassipes)净化太湖受污水体的治理要求,江苏省农科院在太湖竺山湖中央水域连续进行了放养1000亩水面水葫芦的生态净化工程。本研究主要针对这种工程措施下,通过2011年控养水葫芦后研究其对水体环境的影响及底栖生物群落结构和多样性的变化。结果表明,软体动物(主要是铜锈环棱螺)的平均密度从远离到种养区内分别为15.13、15.63、22.63 ind·m-2,生物量从远离到种养区内分别为17.00、17.60、25.50 g·m-2,密度和生物量表现为种养区内要高于种养区外围;种养区内寡毛类(主要是霍甫水丝蚓)和摇蚊幼虫类的密度和生物量的变化表现为远种养区近种养区种养区内,表明以水葫芦为代表的漂浮植物规模化种养后,对底栖环境有一定的改善效果;然而,短期内的控养水葫芦进行水体生态治理,不能立即显现出明显的改善效果,尤其是对于太湖这样一个浅水、多风浪扰动的大水体,更需要长期、持久的多措施并举才能起到效果。利用Shannon-Weaver和Simpson指数来评价底栖环境,水体仍处于重度污染状态。因此,短期内规模化控养水葫芦生态净化工程措施未表现出对底栖生境及底栖生物的不良影响。     

贵州贞丰洞穴大型底栖动物群落结构及水质生物评价

了解洞穴大型底栖动物的群落结构是研究洞穴生态系统的重要内容,也是对生态学领域研究的重要补充.于2019年10月（平水期）及2020年8月（丰水期）对贵州省贞丰县5个洞穴内大型底栖动物进行采样调查,分析大型底栖动物组成、优势种、多样性、功能摄食群的分布特征,并基于大型底栖动物生物学指数对洞穴水质进行评价.结果得出：两个水期共获大型底栖动物63种,隶属4门7纲19目46科,其中水生昆虫41种,占65.07%,闪蚬Corbicula nitens、四节蜉Baetis sp.、蚋Simulium sp.是两个水期的共有优势种.在时间上,大型底栖动物的密度、生物量和多样性指数（ShannonWiener、Pielou和Margalef指数）均表现为平水期>丰水期.在空间上,密度和Margalef指数表现为有光带>弱光带>黑暗带,生物量、Shannon-Wiener指数和Pielou指数表现为弱光带>有光带>黑暗带. Jaccard相似性系数和聚类分析结果表明,同一洞穴相邻光带之间的相似性较高,不同洞穴相同光带或不同光带之间的相似性偏低.洞穴大型底栖动物由5个功能摄食...     

铅锌矿区不同程度尾矿砂重金属污染土壤的纵向微生物群落结构分析

为研究受铅锌矿区不同程度尾矿砂重金属污染土壤的纵向微生物群落结构及其与重金属含量之间的关系,在尾矿砂坝坍塌冲刷形成的河谷岸边、距离河谷800 m的柑橘园以及距离河谷2 000 m的水稻田3个采样点对垂直深度为0—20、20—40、40—60、60—80 cm处的土壤进行取样,测定土样中的重金属含量、理化性质以及土壤的微生物群落结构。结果表明:重金属在该地区土壤中存在明显的纵向迁移,重金属污染越严重的土壤中的纵向迁移就越明显;Cd污染为该地区土壤最主要的重金属污染,潜在生态危害达中等程度以上。各采样点土壤的含水率(MC)、pH在不同采样深度处无明显差异,而TC、TN与TS在不同采样深度处差别较大;通过土样重金属含量与理化性质的冗余分析发现,TN、TC以及pH与各类重金属含量呈正相关关系,而MC以及TS和各类重金属含量表现出负相关关系。受植物根系的影响,柑橘园的20—40 cm深度与水稻田的0—20 cm深度处土壤微生物群落的多样性比其他土样高。属分类水平上,各采样点纵向微生物群落差异很大,分布极其不均匀。土壤纵向微生物优势菌属与重金属含量的冗余分析表明,纵向微生物优势菌属与重金属含量关系紧密,其中Luteibacter、Effusibacillus、Solibacter、Stenotrophomonas、Tumebacillus和Paucimonas 6个菌属与土样重金属含量呈现较强的正相关关系,而Paraburkholderia、Ramlibacter、Bacillus、Pseudarthrobacter、Pseudoduganella、H16和Nitrososphaera7个菌属与土样重金属含量相关关系接近于0,这些菌属均可能具有一定的重金属耐受能力,具有被开发为土壤重金属污染微生物原位修复菌剂的潜力。     

水稻秸秆沟埋还田对麦田土壤环境的影响

通过大田试验,采用秸秆沟埋还田方式,设置沟埋深度分别为20、30、40、50 cm及对照5个处理,将上季作物秸秆进行全量还田(秸秆沟埋量为2 kg.m-1),研究水稻秸秆沟埋还田对麦田土壤含水量、温度、容重和孔隙度等的影响。结果表明,降水结束后12 d内,沟埋深度20和30 cm处理土壤含水量(与埋草沟边水平距离10 cm处)显著下降(P<0.05);而沟埋深度40和50 cm处理土壤含水量(与埋草沟边水平距离10 cm处)与对照差异未达显著水平。埋草沟秸秆下层土壤温度变化较小,秸秆对下层土壤具有保温作用;除沟埋深度20 cm处理外,其他不同沟埋深度处理均能明显降低秸秆上层土壤容重,增加土壤总孔隙度,使耕层土壤疏松。     

部分菊科入侵种种子(瘦果)的萌发能力和幼苗建群特性

对入侵种种子生物学各方面的了解有助于更好地预测入侵趋势和评估可持续管理的策略.研究通过对部分菊科入侵种种子(瘦果)进行的室内萌发实验和土壤埋藏实验,通过与相关研究的对比和分析,对这些入侵种的萌发能力和幼苗建群特性进行了研究.10个入侵种种子室内萌发实验的结果表明,在25℃、12h光照的情况下,除钻形紫菀和一年蓬以外,被研究的其它8个种的终萌发率超过了50%,而且都显示出早期快速萌发的特点.用SPSS的曲线拟合工具对10个种的累积萌发趋势进行了曲线回归分析,对应的最佳模型均为三次曲线方程.不同土壤埋藏深度下幼苗出苗实验的结果表明,菊科8个入侵种的种子在表土的出苗率均最高,随着覆土厚度的增加,种子的出苗率逐渐降低,当覆土厚度超过3 cm以上时,所有种子均不能出苗.种子在不同的埋藏深度的出苗情况与种子的大小有关,较大种子破土能力相对较强;种子在不同的埋藏深度的出苗情况与种子本身的萌发能力也相关.土壤埋藏期限的实验结果表明,随埋藏时期的增加,小蓬草、苏门白酒草和一年蓬3个人侵种种子的活力逐步降低,在土壤中埋藏12个月后,其活力分别为21.34%、18.15%和27.38%.这些入侵种较广的种子萌发温度适应范围和高萌发率为防除工作带来了困难.在生产上,可通过不同时期的翻耕、将种子深埋等措施减少这些入侵种的危害.     

文蛤养殖水体中重金属Cu的安全限量值研究

通过引入沉积物因子,构建海水-底泥-生物体体系,应用半静态双箱动力学模型在室内模拟了沉积物暴露条件下文蛤(Meretrix meretrix)对重金属Cu的生物富集实验。通过对富集与排出过程中文蛤体内重金属Cu的动态监测和监测结果的非线性拟合,得到了文蛤富集Cu的动力学参数:吸收速率常数k1为71.18、排出速率常数k2为0.03,生物富集系数(bioconcen-tration factors,BCF)平均值为4283.86。对模型的拟合优度检验结果显示,沉积物暴露条件下文蛤对重金属Cu的生物富集数据符合双箱模型。根据双箱动力学模型推算出来的文蛤养殖水体中Cu的安全限量值为0.017mg·L-1。实验结果表明,沉积物暴露条件下双箱动力学模型在一定条件下是可以应用于文蛤富集动力学研究的。通过对比室内模拟实验与实地调查所得BCF发现本研究得出的Cu的安全限量值略高于现有标准。     

The effects of burial by sand on survival and growth of Pitcher’s thistle (Cirsium pitcheri) along lake huron

Greenhouse experiments were conducted to determine the effects of sand burial on survival and growth of seedlings ofCirsium pitcheri. In 1992–1993, seedlings were buried to depths of 0, 25, 50, 75, and 100% of their height while in 1993–1994, the seedlings were buried to depths of 0, 4 cm (single burial), 4 cm (repeated burial of 1 cm every 8 days), 8 cm (single burial) and 8 cm (repeated burial of 2 cm every 8 days). Several physiological traits, net photosynthetic rate, chlorophyll a∶b ratio, leaf area, number and length of leaves, number of internodes, amount of tillering, and biomass, were measured. The results showed that all seedlings died in the complete (100%) burial, 20% died in the 75% burial and none died in the 0, 25 and 50% burial treatments. Burial of seedlings to a depth of 25% stimulated their growth but 75% burial significantly decreased the total dry weight. Repeated burial treatments exhibited significantly greater stimulation of growth than single burial. Surviving seedlings grew through the sand deposit by elongating the stem and leaf petioles, increasing the number of nodes and the length of internodes. This elongation occurred at the expense of development of the root system indicating that available energy was re-allocated to above-ground parts.     

帽峰山森林土壤碳氮随雨季月及土壤深度的时空变化特征

采用森林生态系统定位观测及对比试验方法,对广州帽峰山常绿阔叶林和杉木人工林（16年）土壤（0~90 cm）有机碳、无机碳、总氮及有机氮的雨季月（5—10月）含量动态、垂直梯度变化特征及土壤湿度影响进行了对比观测研究。结果表明：常绿阔叶林及杉木林土壤有机碳、无机碳雨季月的剖面权均含量变化趋势均为倒S型,常绿阔叶林土壤有机碳剖面权均质量分数较相应杉木林大0.14%、土壤无机碳则小0.12%。常绿阔叶林土壤表层0~10、10~30 cm有机碳雨季月含量变差较杉木林分别高出1.83%、0.61%,土壤30~90 cm雨季月含量变差相对较小;常绿阔叶林土壤70~90 cm无机碳含量在5—8月份较高、杉木林则以土壤30~50 cm在5、6及10月含量较高;常绿阔叶林群落土壤0~20 cm的总氮雨季月含量均大于相应杉木林,植被吸收作用影响使土壤20 cm以下层的雨季各月总氮相对较低;常绿阔叶林土壤剖面雨季月无机氮含量随土层深度递减变化显著,即表层0~30 cm受矿化作用影响较大、深层30~90 cm则受植被吸收作用影响较大;而杉木林土壤剖面层无机氮含量则随雨季的月变化显著,5—7月份含量相对较小、8—10月份含量相对较大。常绿阔叶林土壤有机碳、总氮含量随土壤深度的增加均呈幂函数规律的递减,而杉木人工林土壤有机碳随土壤深度的增加呈对数函数规律的递减、土壤总氮含量则随土壤深度的增加呈二次函数规律的递减。在0~10 cm处,土壤有机碳和有机氮含量与土壤湿度呈负相关。     

Seagrass mortality due to oversedimentation: an experimental approach

Mortality due to oversedimentation of the Mediterranean seagrassPosidonia oceanica was experimentally evaluated by field manipulations of the sediment level. Increased levels of sediment placed over plant shoots and rhizomes induced significant shoot mortality, even at moderate burial levels (ca. 5 cm). When sediment was added to reach levels 15 cm higher than the initial one, a 100 % mortality was observed after 200–300 days. The response of the plant was independent of site and depth. These results can be used in ecological risk assessment of coastal activities which potentially affect sediment deposition.     

Behavioural responses of the marine bivalve Macomona liliana exposed to copper- and chlordane-dosed sediments

Sublethal behavioural responses including avoidance and burial rate were compared with 10 d acute morbidity and mortality in bioassays using juvenile Macomona liliana 1 to 3 mm long. The bivalves showed significant movement away from all copper-dosed sediments, with maximal movement after 96 h at 25 mg Cu kg (dry wt)^-1. Increasing copper concentrations slowed the rate of burial, and above 15 mg Cu kg (dry wt)^-1, most shellfish failed to bury after 90 min. After 10 d exposure, morbidity (defined as inability to rebury) occurred at 15 mg Cu kg (dry wt)^-1 and mortality at 30 mg Cu kg (dry wt)^-1. In avoidance trials, chlordane had a significant effect on overall movement from 20 g kg (dry wt)^-1, but increasing concentrations reduced movement away from dosed sediment. Chlordance appeared to have no effect on burial rate. Survival was affected by 10 d exposure to 400 g chlordane kg (dry wt)^-1, with increased morbidity and death. The relative sensitivities of the responses shown by M. liliana to copper were avoidance > burial/morbidity > mortality, with a 6-fold difference in the response threshold between avoidance and mortality. With chlordance, an avoidance response was detected at a concentration 20-fold lower than that causing morbidity. Behavioural responses of M. liliana have the potential to provide a sensitive bioassay.     

Siphon size and burying depth in deposit- and suspension-feeding benthic bivalves

This paper analyses the significance of siphon investment in the life strategy of benthic bivalves. It describes the relationships between siphon weight, burying depth and shell size in Mya arenaria, Cerastoderma edule. Scrobicularia plana and Macoma balthica. All data were collected on an intertidal flat in the Dutch Wadden Sea during seven successive winter and summer periods. The four species have in common that (1) the increase of depth in relation to size can be described with an S-curve; (2) there is a linear relationship between log siphon weight and log shell size; (3) siphon investment is maximal for the size classes with the greatest increase in their depth; (4) siphon weight, in proportion to total body weight, decreases gradually for the larger size classes whose depth does not increase; (5) burying depth increases with siphon weight if individuals within a same size class are compared, but burying depth levels off above a certain siphon weight. Macoma balthica and Scrobicularia plana live twice as deep in winter as in summer, although siphon weight for both seasons is about the same. In summer both species use a part of the siphon to graze the surface around the burrow, whereas deposit feeding does not occur in winter. This might explain the seasonal variation in burying depth. On the other hand Cerastoderma edule and Mya arenaria, which are both suspension feeders, show hardly any increase of depth in winter as compared to summer. For benthic bivalves the risk of being taken by a predator decreases with depth. The burying depth levels off where individuals reach the depth refuge (though in winter Scrobicularia plana live at greater depth). The conclusion is that siphon size is one of the main factors determining the burying depth of benthic bivalves and thus plays a critical role in their survival.     

An experimental study on recolonization and succession of marine macrobenthos in defaunated sediment

Hypoxia/anoxia in coastal waters is a world wide problem which often results in mass mortality and defaunation of benthos. In this study, field experiments were carried out to examine recolonization and succession of macrobenthic infauna in defaunated sediments, and the time required for recovery from complete defaunation to a stable community. Trays (33 cm length × 25.5 cm width × 11 cm depth) of defaunated sediment were exposed at the subtidal of a pristine site in subtropical Hong Kong. Temporal changes of macrobenthic communities in defaunated sediment were analyzed by univariate and multivariate statistics, and compared with those in undisturbed natural sediment at the same site. Initial colonization of macrobenthos occurred rapidly. A total of 42 species was found, with an average of 258 animals per tray and 24 species per tray recorded in the first month. Abundance showed a small peak (496 animals per tray) after 3 months, reached a sharp peak (1154 animals per tray) after 6 months, and declined thereafter. Species number increased gradually, reached a maximum (68 species per tray) after 9 months, and then decreased. Recolonization was predominantly contributed by larval settlement rather than adult migration. Temporal changes in abundance, species number and diversity of the macrobenthic community in defaunated sediment resemble the spatial changes along a decreasing pollution gradient previously defined by other authors. Results of this experiment suggest that newly available sediment may allow more species to colonize (or coexist) than sediment pre-occupied by an established community. This is probably due to less interspecific competition in the former habitat. No significant difference in abundance or species richness was observed between defaunated and natural sediments after 15 months, suggesting that a stable community had been achieved, although minor variations in species composition were still discernible between defaunated and natural sediments. Received: 24 May 1999 / Accepted: 20 October 1999     

Ecological effects of dumping of dredged sediments; options for management

Dredging and dumping of dredged sediments in estuarine and coastal waters may lead to increased turbidity and enhanced sediment deposition at dump sites. This mainly affects primary production by phytoplankton, performance of visual predators (e.g. fish, birds), and growth and survival of benthic organisms. This paper combines a compilation of literature information and results of additional experimental studies on the effect of enhanced concentrations of suspended matter (SPM) on growth of bivalve molluscs, and on survival of macro- and meiozoobenthos after dumping of dredged sediments. Furthermore, it focuses on non-toxic dredged sediments only. Release of nutrients from dredged sediments did, so far, hardly influence estuarine phytoplankton production. Increased turbidity may affect dab as well as prey location by sandwich terns. Enhanced SPM-concentrations are unfavourable for young herring and smelt. Growth of filter-feeding bivalves may be impaired, especially at SPM-concentrations >250 mg/l. Estuarine nematodes can survive burial by 10 cm of dumped dredged sediment provided that its physical characteristics are similar to those of the original sediment. Sessile benthos organisms such as mussels and oysters can cope with sediment deposition of only 1–2 cm. Other macrozoobenthos can survive sediment deposition of 20–30 cm. Recovery of benthos at a dump site will occur if the interval between successive dumpings is sufficiently long. Options for management of dumping of dredged sediments are described, relating to different locations of dump sites in estuarine and coastal waters, to different seasons, and to the actual use (area and frequency) of dump sites.