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河道疏浚底泥分类处置方案概述河道疏浚工作是河道治理中的一个重要环节。
疏浚除了要清除河道内堵塞物外，还需要清理河床泥沙和底泥，以保证河道的畅通和增加储存水量。
但这些底泥中通常含有大量有机物和重金属等污染物质，处理不当会对环境造成严重影响，因此需要对河道底泥进行分类处置。
底泥分类底泥根据不同的污染程度和特性可以分为以下几类：无害底泥这种底泥的污染程度比较轻，可以安全地用于填埋、坑场覆盖等一些低风险的场合。
农田利用底泥这种底泥中含有丰富的养分，可以用于农田土地改良和农田肥料补充。
填埋底泥这种底泥是不能用于农业和生态环境远离的区域。
但是处理后可用于填埋场等场所。
建筑材料底泥经过处理，这种底泥可以反复利用，制作水泥、砖块等建筑材料，避免资源浪费。
沉积池泥沙这种沉积池底泥/泥沙污染程度比较严重，可通过焚烧等方式进行处理。
底泥处置技术底泥的处理技术主要包括化学法、物理法和生物法。
化学法化学法主要指的是化学沉淀法和氧化还原法。
化学沉淀法能有效地去除重金属等有害物质，氧化还原法则对有机污染物的去除效果较好。
但是，化学法处理底泥的成本较高，还可能对环境造成二次污染。
物理法物理法主要指的是固液分离和筛分法。
固液分离是将底泥中的固态物质和水分离开来，筛分法是将底泥中的大颗粒物料与小颗粒物料进行分离。
物理法处理底泥的成本较低，效果一般。
生物法生物法主要指的是菌类等微生物对底泥中有机污染物质进行分解、去除的方法。
生物法处理底泥的成本相对较低，而且能够达到较好的处理效果。
但是，处理周期较长，效果难以保证。
总结对于不同污染程度和特性的河道底泥，有不同的分类和处理方法。
在选择底泥处理技术时，应该综合考虑处理效果、成本、周期等因素，以达到经济、环保、可持续的处理方案。
淤泥清理施工方案生物修复技术在水体淤泥处理中的应用淤泥清理施工方案：生物修复技术在水体淤泥处理中的应用随着工业化进程的加快，水体污染问题日益严重。
其中，水体淤泥的堆积是一大隐患，给水生态系统和人类健康带来威胁。
因此，寻找有效的淤泥处理方法显得尤为重要。
本文将介绍一种被广泛应用的淤泥清理施工方案——生物修复技术。
一、淤泥的形成及其问题首先，我们需要了解淤泥的形成过程。
淤泥即水体底部沉积的悬浮颗粒物和有机物的沉积物。
在水体中，淤泥的形成主要受水流速度、悬浮物质浓度和水体深度等因素的影响。
然而，淤泥的堆积可能导致以下问题：1. 水体富营养化：淤泥中富含营养物质，如氮、磷等，当堆积过多时，会导致水体富营养化，引发藻类暴发生长，破坏生态平衡。
2. 水体自净能力下降：淤泥会降低水体的透明度，阻碍光线和氧气的进入。
同时，淤泥中的有机物和细菌会消耗水中的氧气，导致水体自净能力下降。
3. 水质污染：淤泥中的重金属、有机物和细菌等有害物质会对水体造成污染，危害人类健康。
二、生物修复技术的原理生物修复技术是利用生物体对淤泥中有机物和重金属等污染物进行分解、降解和吸附的过程，从而减少或消除水体淤泥的方法。
其原理主要包括以下几个方面：1. 微生物降解：通过添加一定数量的微生物，如细菌、藻类等，利用它们的生物吸附、分解和转化作用，降解淤泥中的有机物质。
2. 纤维植物吸附：一些纤维植物，如芦苇、莲藕等，具有良好的吸附能力，可以吸附淤泥中的重金属物质。
3. 水生植物生长：通过种植水生植物，如菖蒲、香蒲等，利用它们的根系吸附和吸收作用，减少淤泥中的营养物质。
三、生物修复技术的应用实例生物修复技术已在水体淤泥处理中广泛应用，并取得了显著的效果。
以下是几个成功的应用实例：1. 微生物菌剂降解淤泥：通过添加特定的微生物菌剂，如好氧生物菌剂、厌氧生物菌剂等，可以有效地分解淤泥中的有机物，提高水体的自净能力。
2. 生态沉淀池的建设：通过修建生态沉淀池，种植纤维植物和水生植物，利用植物吸附、降解和分解的作用，提高水体淤泥的处理效果。
淤泥沉积的植物和动物生态系统淤泥沉积是指河流、湖泊、海洋等水体中，由于颗粒物的悬浮和沉积而形成的一种岩石。
在自然界中，淤泥沉积属于重要的地质过程之一，同时也是形成生态系统的重要基础。
淤泥沉积物里含有大量的有机物，这些有机物可以为许多植物和动物提供生存和繁殖的条件。
本文将着重探讨淤泥沉积的植物和动物生态系统，从而更好地了解这一生态系统的生态价值和影响。
1、淤泥沉积对植物生态系统的影响淤泥沉积是许多植物生长的必要条件。
淤泥中含有许多有机质，这些有机质能够为植物生长提供必要的养分。
此外，淤泥沉积物中含有的水分是许多植物生长的重要前提。
这些有机质和水分，能够为植物提供良好的生长环境，让许多植物在淤泥环境中找到自己的生存之路。
淤泥沉积物还对植物的分布和生态系统的结构有着重要的影响。
例如，深入沉积的淤泥可以起到稳定土层的作用，从而让多种植物在淤泥环境中安居乐业。
此外，淤泥沉积物中蕴含着丰富的营养物质，可以为不同的植物提供不同的生存条件。
因此，在淤泥沉积环境中，植物生态系统的种类和分布格局十分多样化。
2、淤泥沉积对动物生态系统的影响淤泥沉积物同样对动物生态系统的建立有着重要的作用。
淤泥沉积环境中，许多小型生物（如浮游生物和蠕虫等）在其表面上寻找食物和庇护所，从而形成了一些小型生态系统。
这些生态系统为生态环境中的宏观动物提供了许多必要的生存条件。
例如，淤泥环境中栖息有刺鳟、鲶鱼等物种，可以吞噬淤泥中的小型生物从而生存。
同时，这些生态系统还为淤泥环境中的植物和其它生物提供了一个"自我保护"的机制，防止该环境的生物群落被外部因素所破坏。
除了小型生态系统外，淤泥沉积还对动物的物种个体生长有着至关重要的作用。
淤泥环境中，动物可以在稳固的河床或海底中找到栖息地，而淤泥沉积物中所含有的有机成分也能提供足够的营养和充分的生长空间。
同时，淤泥中的气泡和细微的间隙，也可以为动物提供极好的呼吸条件和庇护所。
3、淤泥沉积的生态价值和需引起人们的关注淤泥沉积物在自然界中扮演了十分重要的角色，还为人类提供了极高的生态保护价值。
2024年浅析疏浚工程对环境的影响一、疏浚工程概述疏浚工程是指对水体底部进行挖掘、清理和拓宽等作业，以改善水流条件、增加航道深度、扩大港口规模或满足其他水利工程建设需求的一种工程活动。
疏浚工程广泛应用于河流、湖泊、港口、航道等水域，对于促进水上交通、提高水体利用效率和改善生态环境具有重要意义。
二、环境影响分析疏浚工程对环境的影响是多方面的，主要包括以下几个方面：1. 水体生态环境的影响疏浚工程会改变水体的自然形态和流动状态，影响水体中的生物群落结构和生态平衡。
挖掘作业会破坏底栖生物的栖息地，导致生物种类和数量的减少。
同时，水流速度的改变也可能导致水体中的营养盐分布不均，影响水生植物的生长和繁殖。
2. 地质环境的影响疏浚工程会破坏河底或海底的地质结构，可能引发地质灾害，如河床侵蚀、海岸侵蚀等。
此外，挖掘产生的弃土和废弃物可能堆积在河道或海岸线上，对周边环境造成污染和安全隐患。
3. 水质的影响疏浚工程可能导致水体中的悬浮物、重金属和有毒有害物质含量增加，对水质造成污染。
同时，疏浚作业产生的噪音和振动也可能对周边水体中的生物造成不利影响。
三、环境保护措施为了减轻疏浚工程对环境的影响，需要采取一系列环境保护措施，包括：1. 优化疏浚工艺选择科学合理的疏浚工艺和设备，减少挖掘对底栖生物和水体环境的破坏。
同时，优化施工时间，避开生物繁殖季节和敏感时段，以减少对生物的影响。
2. 强化施工现场管理加强施工现场的环境管理，规范作业流程，防止弃土和废弃物对周边环境的污染。
同时，加强施工现场的安全管理，防止事故发生。
3. 生态保护与修复在疏浚工程前进行生态评估，预测工程对生态环境的影响。
在疏浚过程中采取生态保护措施，如设置生态保护区、生态补偿等。
工程完成后进行生态修复，如种植水生植物、放养生物等，促进生态环境的恢复。
4. 水质监测与治理加强水质监测，及时发现和处理疏浚工程对水质的影响。
对于产生的污染问题，采取有效的治理措施，如增加沉淀池、过滤设备等，确保水质达标排放。
湖泊底泥疏浚环境效应湖泊底泥疏浚是指通过人工干预来清理湖泊底部积聚的沉积物，以改善湖泊的环境质量和生态系统的健康状况。
底泥疏浚对湖泊的环境效应是多方面的，本文将从水质改善、生物多样性维护和环境保护等方面展开论述。
首先，湖泊底泥疏浚可以明显改善水质。
底泥中富集了大量的有机质和营养物质，如果不及时清除，会导致湖泊富营养化的问题。
过多的有机质和营养物质会引发水体中藻类大量繁殖，形成蓝藻水华。
蓝藻水华不仅会消耗水体中的氧气，导致水体缺氧，还会产生有害的毒素，对水生生物和人类健康造成危害。
底泥疏浚的主要目的之一就是清除底泥中的有机物和营养物质，减少水体中养分的负荷，从而有效控制湖泊富营养化现象的发生，改善水质。
其次，底泥疏浚对湖泊生物多样性的维护具有重要意义。
底泥是湖泊生态系统中的重要组成部分，其中存有丰富的生物资源。
然而，过多的底泥沉积会导致湖底氧气供应不足，导致湖底缺氧，使底栖生物的生存状况变差。
清除底泥可以改善湖底的氧气供应状况，提供更好的生存环境，从而促进底栖生物的繁殖和生长。
底泥疏浚还可以改善湖泊的水动力条件，减少湖底沉积物对水动力的抑制作用，提高水的透明度和透光度，促进水生植被和浮游生物的生长。
这些都有助于保护湖泊的生物多样性，维持湖泊生态系统的平衡。
此外，底泥疏浚还有助于环境保护。
底泥中常含有重金属、有机污染物和农药等有害物质，如果不及时清除，这些有害物质可能会被再次释放到水体中，对水质造成污染。
湖泊水质污染不仅会危害水生生物的健康，还会影响人类对湖泊水资源的利用。
底泥疏浚通过清除底泥中的有害物质，可以减少这些物质对水质的污染风险，保障水环境的健康与稳定。
然而，湖泊底泥疏浚并非没有负面效应。
首先，底泥疏浚可能会造成悬浊物的再次悬浮，降低水质透明度，对水生植物和浮游生物造成一定影响。
此外，疏浚过程可能会引发氧气消耗，导致湖水缺氧。
疏浚作业所用的机械设备和人工操作也会产生一定程度的噪音和振动，对湖泊周边的生态环境和动植物造成一定干扰。
湖泊治理解决方案河道污染是区域人口、经济、社会发展到一定阶段后造成的，污染治理的根本性措施是污染源的治理。
因此，世界各国均把污水截流、废水达标排放和控制排污总量作为河道整治的首要措施。
然而，由于难以根除的面源污染及内源污染，即使在污水排放得到有效控制的情况下，河道污染及其富营养化问题仍然十分突出.为此，各地在河道治理中，把污染源治理和强化水体的自净能力同时作为河道修复的重要目标。
纵观国内外河道治理现状，以下几种方法较为引人关注：1、引流冲污和综合调水引流冲污实质上是对水体污染物和浮游藻类的稀释扩散,就局部而言常被视为解决水体富营养化相对简单、易行和代价较低的办法。
如杭州西湖自钱塘江引水后对延缓水体富营养化发挥了一定的作用。
但从整体出发，这种办法实为污染转移，有以邻为壑之嫌；综合调水不同于引流冲污，主要解决水资源的再分配，利用一定的水利设施合理调活河网水系，达到“以动制静、以清稀污、以丰补枯、改善水质”的目的，尤其对提高水体的自净能力能发挥较好的作用.2、曝气复氧曝气复氧对消除水体黑臭的良好效果已被国内一些实验室试验及河流曝气中试所证实.其原理是进入水体的溶解氧与黑臭物质（H2S，FeS等还原物质）之间发生了氧化还原反应。
对于长期处于缺氧状态的黑臭河流,要使水生态系统恢复到正常状态一般需要一个长期的过程，水体曝气复氧有助于加快这一过程。
由于河道曝气复氧具有效果好、投资与运行费用相对较低的特点，已成为一些发达国家如美国、德国、法国、英国及中等发达国家与地区如韩国、香港等在中小型污染河流污染治理经常采用的方法.3、底泥疏浚在污染源控制达到一定程度以后,底泥则成为水体污染的主要来源.因此清淤疏浚通常被认为是消除内源污染的重要措施.然而，疏浚技术通常是决定疏浚效果好坏的关键.从最早的人工挖泥到现在的精确水下吸泥，疏浚过程对环境的影响正在变得越来越小。
疏浚作为水利工程和航道工程措施有重要效用，但作为水质治理目前还存在一些难于克服的问题,如一定程度上引起上覆水污染物浓度增加，疏浚后淤泥以其量大、污染物成分复杂、含水量高而难以处理等等.4、化学絮凝处理化学絮凝处理技术是一种通过投加化学药剂去除水层污染物以达到改善水质的污水处理技术。
航道疏浚对水域生态的影响在人类社会的发展进程中，为了满足日益增长的航运需求，航道疏浚成为了一项重要的工程活动。
然而，这一活动在改善航道条件的同时，也不可避免地对水域生态产生了诸多影响。
航道疏浚，简单来说，就是通过挖掘、清淤等手段，加深、拓宽航道，以提高通航能力。
但在这个过程中，大量的底泥被搅动、挖掘和搬运，这对水域的生态环境造成了直接和间接的干扰。
首先，航道疏浚会对水生生物的栖息地造成破坏。
水域底部的底泥通常是许多底栖生物的生活场所，如贝类、虾蟹等。
疏浚作业会直接破坏这些生物的栖息环境，导致它们失去家园。
一些底栖生物可能会在这个过程中死亡，而那些幸存下来的生物则需要重新寻找合适的栖息地。
这对于底栖生物的种群数量和多样性都会产生不利影响。
其次，疏浚过程中产生的悬浮泥沙会使水体变得浑浊。
悬浮在水中的泥沙会降低水体的透明度，影响光线的穿透，从而对水生植物的光合作用产生抑制作用。
光合作用的减弱会导致水生植物生长缓慢，甚至死亡。
而水生植物作为水域生态系统中的生产者，对于维持整个生态系统的平衡和稳定至关重要。
它们的减少会连锁影响到以它们为食的草食性动物，进而影响整个食物链。
再者，疏浚作业还可能会带来污染物的释放和扩散。
底泥中往往积累了一定量的污染物，如重金属、有机物等。
在疏浚过程中，这些污染物可能会被重新释放到水体中，加剧水质的恶化。
这不仅对水生生物的生存造成威胁，还可能影响到周边地区的用水安全。
另外，航道疏浚会改变水流的速度和流向。
水流是水域生态系统中物质和能量传递的重要载体。
水流的改变可能会影响到鱼类等水生动物的洄游路线，干扰它们的繁殖和生长。
同时，水流的变化也可能会影响到营养物质的分布，进而对水域生态系统的结构和功能产生深远影响。
然而，我们也不能因噎废食，完全否定航道疏浚的积极作用。
在合理规划和科学管理的前提下，航道疏浚可以带来显著的经济和社会效益。
例如，它可以提高航运效率，促进贸易发展，为地区经济增长做出贡献。
M.SchratzbergeráH.L.ReesáS.E.BoydEffects of simulated deposition of dredged material on structure of nematode assemblages±the role of burialReceived:29July1999/Accepted:17January2000Abstract A microcosm experiment was designed to evaluate the e ects of the simulated deposition of uncontaminated dredged material on nematode assem-blages from estuarine intertidal mud.The main objective was to assess the ability of nematodes to migrate verti-cally into native muddy and non-native sandy sediment deposited in di erent amounts and frequencies.Results from univariate and graphical methods of data-evalua-tion revealed that nematodes were capable of migrating over a wide depth range from the bottom mud layer into the top layer of deposited sand and mud.A diverse mud assemblage of nematodes was able to survive in non-native®ne sand for the experimental period of2mo. Multivariate analyses showed that the amount of deposit and the frequency of deposition were interactive factors.A high amount of sediment deposited once at the beginning of the experiment caused more severe changes in assemblage structure than the same amount deposited in more frequent but smaller doses.The response of most species to the experimental treatments appeared to be an integrated response to the enhancing e ect of food input accompanying the deposit and the negative e ect of burial.Upward migration of nema-todes is a process which has often been underestimated in its importance for recolonisation of areas where uncontaminated dredged material is deposited.Active migration of nematodes can signi®cantly a ect the recovery of a dredgings disposal site.IntroductionDredging is essential for the construction of water-based infrastructure and to maintain navigation in ports, harbours,and inland waters.In the United Kingdom, much of the material removed is disposed of at sea (Group Coordinating Sea Disposal Monitoring1996; International Navigation Association1998).In1996,46 million wet tonnes of dredgings were disposed of at sea around the England and Wales coastlines(Centre for Environment,Fisheries and Aquaculture Science1998). The predominant e ects of dredgings disposal on the benthic fauna are related to changes in the concentra-tions of suspended solids and in sedimentation rates. Direct burial by dredged material,often discharged in large quantities during a dredging operation,is often the most obvious impact on benthic organisms.The fate of buried organisms is important in terms of survivorship and possible recolonisation of a dredging material disposal-site.The survival potential of individual species depends on their ability to migrate upwards through the deposited sediment and thus restore the normal contact between the animal and water(Maurer et al.1980; Essink1993).A number of®eld studies have dealt with the e ects of dredgings disposal on macrofauna(Poiner and Kennedy1984;Lopez-Jamar and Mejuto1988;Essink 1999),and meiofauna(Somer®eld et al.1995).The ef-fects of burial on single macrofauna species(Maurer et al.1980,1981,1982,1986and references therein; Chandrasekara and Frid1998)and on nematode assemblages(Romeyn and Leiseboer1989)have been assessed in short-term laboratory experiments.Howev-er,there is still a lack of experimental studies assessing the e ects of di erent quantities and frequencies of dredgings disposal on benthic assemblages and,inMarine Biology(2000)136:519±530ÓCrown Copyright2000Communicated by J.P.Thorpe,Port ErinM.SchratzbergerUniversity of Wales Bangor,School of Ocean Sciences,Menai Bridge LL595EY,Gwynedd,North Wales,Great BritainM.Schratzberger(&)áH.L.ReesáS.E.BoydThe Centre for Environment,Fisheries and Aquaculture Science,Burnham Laboratory,Remembrance Avenue,Burnham-on-Crouch CM08HA,Essex,EnglandFax:0044(0)1621784989e-mail:m.schratzberger@particular the role of active migration of buried fauna in the recolonisation process.A microcosm experiment was designed to assess the ability of nematodes derived from a muddy estuary to migrate vertically into native muddy and non-native sandy sediment deposited in di erent amounts and frequencies.The objective of the study was to test three null hypotheses:(1)The response of nematode assem-blages does not depend on the sediment characteristics of the deposited material;similar migration and survival rates are expected regardless of whether native or non-native sediment is deposited.(2)The response of nem-atode assemblages does not depend on the quantity disposed of;within certain limits,migration and survival rates are similar for di erent depths of deposited sedi-ment layers.(3)The response of nematode assemblages does not depend on the frequency of disposal;rates of upward migration and survival do not di er when the same amount of sediment is deposited in more frequent but smaller doses.The e ects of contaminants which are often present in dredged harbour sediments were not considered in this study.Materials and methodsCollection sitesIntertidal estuarine sediments with their natural meiofaunal com-munities were collected from two sites in south east England (Es-sex)at low tide.Sand was collected from Shoebury at low water on 14October 1998.A spade was used to a depth of 5cm in order to transfer sand into a bucket.The poorly sorted sediment (s =1.3F )had a median particle diameter of 108l m and consisted of 91%sand (63l m to 2mm)and 9%mud (<63l m).The sediment contained 2.1%total organic carbon.Mud was collected from Creeksea on 15and 23October 1998.Mud from mean low-water level was scraped into a bucket from the top 2cm using a spade.The very poorly sorted sediment (s =2.8F )had a median particle diameter of 63l m and consisted of 6%gravel (>2mm),36%sand and 58%mud.The sediment contained 1.2%total organic carbon.Sand and mud collected on 14and 15October 1998was used as deposit for the experimental treatments (Table 1).Prior to setting up the experiment,these sediments were defaunated.They were repeatedly frozen to a temperature of )20°C for 12h and thawed at room temperature for 48h.Defaunation was achieved after this process had been repeated three times.Weighed amounts of sand and mud were then frozen until used for experimental treatments.Additional samples of 70g of homogenised mud and 100g of homogenised sand (four replicates for each type)were ®xed in 4%formalin before defaunation to obtain samples of natural nematode assemblages in these sediments.On return to the laboratory,mud collected on 23October 1998was homogenised by gentle stirring before subsamples for the mi-crocosms were taken (Table 1).Seventy grams of homogenised mud (four replicates)were ®xed in 4%formalin to obtain samples of natural nematode assemblages used to initiate the experiment.Heavy metal concentrations of all sediments used in the experiment were low (Table 1).Experimental set-upIndividual microcosms consisted of glass cylinders (i.d.4.5cm,height 45cm)closed with a rubber bung at the bottom end.The cylinders were ®lled with 70g of homogenised Creeksea mud,collected on 23October 1998,and topped up with ®ltered seawater of natural salinity (33&S).A 3mm-thick glass disc on top of the bung prevented direct contact of the sediment with the rubber material.The microcosms were run as closed systems with aeration.As the homogenisation of ®eld-collected sediment destroyed the nat-ural strati®cation,all microcosms were left unmanipulated for one week until suspended sediment particles in the water column had settled.Small enclosures such as these microcosms are characterised by a larger surface area-to-volume ratio compared to natural sediment in the ®eld.This can result in altered chemical and biological conditions in the water column from surface growth of algae.Therefore,the experiment was run in the dark for 2mo at a tem-perature of 15°C.Experimental treatmentsDeposition of dredged material was simulated by adding defau-nated sand or mud in di erent quantities and frequencies to the treatments.There were four replicate control microcosms which remained unmanipulated and eight treatments with four replicates each (Table 2,Fig.1).Throughout the text the treatment codes in Table 2are used to identify microcosms.Final sediment depths of 3and 6cm were chosen as they represent situations at typical disposal sites (Poiner and Kennedy 1984).The high-frequency Treatments S1,S2,M1and M2,simu-lated situations of frequent deposition of dredged material at a disposal site or transport of dredged material to adjacent areas.The low-frequency Treatments S3,S4,M3and M4,simulated a single deposit of dredged material at a speci®c disposal site.On Days 8,13,18,22,27,32,36,41,46and 50,sediment colour,conductivity,pH and water temperature were recorded before the water was changed in all microcosms.Two-thirds of the water was siphoned out,and defaunated sediment which had been defrosted the previous day was washed into the treatments with ®ltered seawater.All microcosms were then ®lled up with fresh ®ltered seawater.After the last sediment deposition,the micro-cosms were maintained for 1wk to allow the nematode assem-blages time to respond to the ®nal addition of defaunated sediment.At the end of the experiment after 57d,the supernatant water in the microcosms was siphoned out carefully and a rubber bung was placed at the top end of the cylinder.The bung at the bottom end was removed,and the cylinder was placed above the rubber disc of a plunger.The cylinder was pushed upwards slowly,extruding the sediment which was sectioned into slices of 3cmTable 1Types of and heavy-metal concentrations [ppm]in sediment used in experiment Type Date (1998)Used asSediment layer in microcosms Cu Cd Pb Hg Sand 14Oct Defaunated deposit Top,middle 30<0.27490.24Mud 15Oct Defaunated deposit Top,middle 22<0.24330.11Mud23OctHomogenised sediment containing meiofaunaBottom23<0.25330.12520depth (top,middle,bottom layer:Fig.1).All samples were ®xed in 4%formalin.Sample-processingAfter washing the samples onto a 63l m sieve,the meiofauna was extracted with Ludox (McIntyre and Warwick 1984;Somer®eld and Warwick 1996).The extraction was repeated three times.As nematode abundances in both sediments were high subs-amples were taken,applying a method described by Pfannkuche and Thiel (1988)and Somer®eld and Warwick (1996).Subsamples of 10%were evaporated slowly in anhydrous glycerol,mounted,and evenly spread on slides for identi®cation and counting.Nematodes were identi®ed to genus or species using the picto-rial keys of Platt and Warwick (1983,1988)and Warwick et al.(1998).Data-processingThe total number of individuals,total number of species,Shannon±Wiener index (H ¢),species richness (Margalef's d )and evenness (Pielou's J ¢)were calculated to describe nematode assemblage structure.Bartlett's and Cochran's tests were used to test for homogeneity of variance.One-way ANOVA was applied to test the null hypothesis that there were no signi®cant di erences between treatments.The Tukey HSD multiple-comparisons test was used in pairwise comparisons of controls and treatments.Univariate ana-lyses were performed using the software package STATGRAPH-ICS Plus,Version 3.3.Sets of species counts for single samples were also summarised in k -dominance curves (Lambshead et al.1983;Platt et al.1984).Diversity can be assessed unambiguously when the k -dominance curves from the assemblages to be compared do not overlap.In this situation the lowest curve represents the most diverse assemblage.A procedure described by Clarke (1990)was applied to test the null hypothesis that the k -dominance curves were not signi®cantly dif-ferent from each other at p <0.05.Non-parametric multi-dimensional scaling (MDS)ordination using the Bray±Curtis similarity measure was applied to species abundance data followed by analysis of similarities (ANOSIM,Clarke 1993)to test the null hypothesis that there were no signi®-cant di erences in nematode assemblage composition between di erent samples.In order to determine the contribution of individual species to the average Bray±Curtis dissimilarity between samples,the simi-larity percentages program (SIMPER,Clarke and Warwick 1994)was applied.These analyses were performed using the software package PRIMER,developed at the Plymouth Marine Laboratory (Clarke and Warwick 1994).Table 2Code used to identify microcosms Code TreatmentS13cm defaunated sand added in 10doses of 0.3cm S26cm defaunated sand added in 10doses of 0.6cm S33cm defaunated sand added in 1dose at beginning of experimentS46cm defaunated sand added in 1dose at beginning of experimentM13cm defaunated mud added in 10doses of 0.3cm M26cm defaunated mud added in 10doses of 0.6cm M33cm defaunated mud added in 1dose at beginning of experimentM46cm defaunated mud added in 1dose at beginning ofexperimentFig.1Schematic diagram of sand and mud treatments (Treatment codes and descriptions in Table 2)521ResultsVisual observationsRecords of the sediment colour in the microcosms provided important information on the degree of aera-tion in the di erent layers.Measurements of the redox-potential were not made,as this would have resulted in physical disturbance of the sediment.The addition of defaunated sand and mud had a visible impact on the microcosms.After the®rst treat-ment,added sediment overlaid a bottom layer of brown Creeksea mud containing the nematode assemblages. This bottom layer showed anoxic patches in the low-Frequency Mud Treatments M3and M4after18d and in the respective Sand Treatments S3and S4after27d. By Day50,the bottom sediment layer had turned grey in all treatments.The added sediment portions in the high-frequency treatments were visible as distinct layers,suggesting that physical impact on the existing sediment structure arising from the addition of sediment was minimal.E ects of laboratory conditions on natural nematode assemblagesConductivity(49.6 2.9l s cm)1),pH(8.2 0.1)and temperature of the water(13.0°C 1.0C°)in the microcosms remained constant throughout the duration of the experiment.There were no signi®cant di erences between treatments.The response of nematode assemblages to laboratory conditions was re¯ected in a signi®cant decline of total nematode abundances in the control microcosms com-pared to the respective®eld samples collected on23 October1998(F-ratio=7.46,p=0.03).Changes of other univariate measures were not signi®cant at p<0.05.ANOSIM detected a signi®cant di erence between nematode assemblages from the®eld samples and those which were extracted from the controls at the end of the experiment.However,their level of dissimilarity(29%) was lower than between controls and the di erent sedi-ment layers of the treatments(dissimilarity to top layer 34%,middle layer of low-frequency treatments 35%, bottom layer 63%).The natural mud samples used to initiate the experi-ment were dominated by Sabatieria breviseta,Aponema torosa,Terschellingia communis,T.longicaudata, Daptonema normandicum,D.furcatum and the chroma-dorids Ptycholaimellus ponticus and Chromadora mac-rolaima.Signi®cant di erences between nematode assemblag-es derived from the®eld sampling site and those from control microcosms at the end of the experiment were mainly due to decreasing abundances of Sabatieria breviseta,the chromadorids Ptycholaimellus ponticus and Chromadora macrolaima,and the Daptonema spe-cies D.normandicum,D.furcatum and D.hirsutum in the controls.E ects of simulated deposition of dredged materialon nematode assemblagesA graphical summary of means and95%pooled con®-dence intervals of univariate indices is presented in Fig.2.One-way ANOVA detected signi®cant di erences between treatments for all univariate measures except evenness,J¢(Table3).In the top sediment layer,signi®cant changes occurred only in response to the high amount(6cm)of mud that was deposited once at the beginning of the experiment(Treatment M4).Nematode assemblages responded with a signi®cant decrease in total abundance (log),number of species and species richness compared both to controls and to treatments where the same amount of mud was administered in ten doses throughout the experiment(Treatment M2).Species richness was signi®cantly higher in Sand Treatment S4 than in the respective Mud Treatment M4.In the middle and bottom sediment layers,signi®cant reductions in univariate measures(other than evenness) occurred for most treatments compared with control microcosms.Univariate measures were lower in the treatments than in the controls.The k-dominance curves for nematode assemblages from the controls and treatments are shown in Fig.3. For the top sediment layer,signi®cant di erences between controls and treatments were not detected except for Mud Treatment M4.The deposition of the large amount of defaunated mud in one single dose resulted in a signi®cant decrease of diversity,whereas dominance increased.In accordance with the results from the univariate data analyses,k-dominance plots illustrate that assem-blages from the middle and bottom layer of the treat-ments were less diverse and more dominated by lower numbers of species than those from the controls.Most di erences were signi®cant at p<0.05.Diversity was signi®cantly higher in the middle layers of the high-fre-quency Treatments S2and M2than in their respective low-frequency Treatments S4and M4.The MDS ordinations for the di erent sediment layers based on square-root transformed data are pre-sented in Fig.4.In the plot for the top sediment layer, samples are scattered over the plot area,with Treat-ments S4and M4located furthest away from the con-trols.In the plots for the middle and bottom sediment layers,there is clear separation between controls and treatments.ANOSIM results in Tables4to6indicate that for all sediment layers undisturbed nematode assemblages were signi®cantly di erent from those exposed to the depo-sition of defaunated sand and mud(only exception is top layer of S1).For the top and middle sediment layers522F i g .2N e m a t o d e a s s e m b l a g e s .G r a p h i c a l s u m m a r y o f m e a n s a n d 95%p o o l e d c o n ®d e n c e i n t e r v a l s o f u n i v a r i a t e i n d i c e s f o r c o m m u n i t i e s f r o m s a n d a n d m u d (C i r c l e d b a r s v a l u e s s i g n i ®c a n t l y d i e r e n t f r o m c o n t r o l s a t p <0.05;t r e a t m e n t c o d e s a s i n T a b l e 2)523(Tables4and5),signi®cant di erences also occurred between most treatments,but this was not the case for the bottom sediment layer(Table6). Assemblages from the top and middle sediment layers were more similar to the controls than those from the bottom layer.The level of similarity between treatments was highest for assemblages extracted from the top sediment layer and lowest for those from the middle layer of the high-amount treatments(Treatments S2,S4, M2,M4).Results from univariate and graphical methods of data evaluation con®rm that nematodes migrated from the bottom mud layer into the top layer of the defau-nated deposits.In addition,results from multivariate analyses show that for both sand and mud the high amount of sediment deposited once at the beginning of the experiment had a more severe e ect on the assem-blages than the same amount deposited in more frequent but smaller doses.Species-speci®c responses to simulated depositionof dredged materialTwo-thirds of all nematodes in the control microcosms belonged to the species Sabatieria breviseta,Aponema torosa,Metachromadora vivipara,Terschellingia com-munis and T.longicaudata,S.breviseta and A.torosa were also dominant in all sediment layers of the sand and mud treatments.Viscosia viscosa reached high numbers in the top sediment layer of the high-frequency Sand Treatments S1and S2,whereas Daptonema tenuispicu-lum showed high abundances in this layer of the low-frequency Treatments S3and munis and D. tenuispiculum were common in the top sediment layer of all mud treatments with the exception of Treatment M4. Results from the SIMPER analyses reveal that signi®cant di erences between undisturbed nematode assemblages from the control microcosms and those from the top sediment layer of the treatments resulted from changes in the abundances of dominant species, including Sabatieria breviseta,Aponema torosa,Ter-schellingia communis and T.longicaudata and the low-abundance species Daptonema normandicum and D.tenuispiculum.All these species occurred in markedly di erent numbers in the sand and mud deposits before defaunation(Table7).Compared to control micro-cosms,abundances of S.breviseta and A.torosa were signi®cantly lower in most low-frequency treatments (Treatments S3,S4,M3,M4;Fig.5)munis and T.longicaudata were signi®cantly less abundant in the sand treatments(Fig.5).Despite their di erent re-sponses to laboratory conditions,species belonging to the genus Daptonema proved to be good discriminators between treatments and controls(Fig.5).D.normandi-cum was signi®cantly more abundant in most high-frequency treatments than in the controls,whereas D.tenuispiculum reached high numbers in the low-frequency sand treatments(Treatments S3and S4). Assemblages extracted from the bottom sediment layer of all treatments and the middle sediment layer of the high-amount treatments(Treatments S2,S4,M2, M4)were characterised by signi®cantly lower abun-dances of Sabatieria breviseta,Aponema torosa,Meta-chromadora vivipara,Viscosia viscosa,Terschellingia communis and Daptonema tenuispiculum than those ex-tracted from the controls.Discussion and conclusionsMethodological considerationsOne of the principal di culties associated with the outcome of small-scale laboratory experiments is the limited capacity to generalise about environmental e ects in the®eld,as it is impossible to replicate the complex environmental conditions that prevail over time and at di erent localities(Hall and Harding1997). Nevertheless,the responses of nematode species ob-served in our experiment were similar to those reported from®eld studies(Somer®eld et al.1995).Additionally, this microcosm experiment provided a means of assess-ing the response of nematodes to a variety of experi-mental treatments under replicated,controlled,and repeatable conditions.The most consistent response of mud nematodes to laboratory conditions was a decline in total nematode abundances in the control microcosms compared to the ®eld samples used to initiate the experiment.Abun-dances of some chromadorids decreased signi®cantly.A decline of chromadorids is a common response of nematode assemblages to laboratory conditions(Schr-atzberger and Warwick1999).Chromadorids are clas-si®ed as epigrowth feeders(Wieser1953),and their low survival rates in the controls may have been due to the lack of appropriate food sources in the microcosms since there was no addition of organic matter,and no primary production could take place in the dark.The enclosure of assemblages in microcosms did not allow the immigration of nematodes from surrounding sediment and the water column above,although these factors play an important role in natural recolonisation processes(Palmer and Gust1985;Walters and Bell 1986;review by Palmer1988and references therein;Table3F-ratios and signi®cance levels from one-way ANOVA tests for di erences in univariate indices between treatments Parameter Top layer Middle layer Bottom layerF-ratio p F-ratio p F-ratio p Abundance(log)3.91<0.0517.19<0.0511.60<0.05 No.of species9.20<0.0532.72<0.0516.07<0.05 Diversity(H¢) 3.02<0.059.90<0.05 5.23<0.05 Richness(d)8.28<0.0525.10<0.059.85<0.05 Evenness(J¢) 1.610.17 2.030.14 1.750.13 524F i g .3N e m a t o d e a s s e m b l a g e s .k -d o m i n a n c e c u r v e s o f a s s e m b l a g e s f r o m c o n t r o l m i c r o c o s m s a n d d i e r e n t s e d i m e n t l a y e r s o f s a n d a n d m u d t r e a t m e n t s (c o d e d a s i n T a b l e 2)525Le Guellec 1988;Colangelo and Ceccherelli 1994;Sun and Fleeger 1994).Immigration of nematodes was in-tentionally excluded from this experiment in order to focus on the role of active upward migration of nem-atodes.The addition of defaunated sediment to the treat-ments resulted in decreased oxygenation of the bottom mud layer.Changes in the sediment colour indicated that the experimental treatments represented situations at disposal sites where the benthic fauna is exposed to decreased ambient oxygen concentrations and to increased sulphide concentrations when covered by dredged material (Essink 1993).When sectioning the sediment from the microcosms using a plunger,it was impossible to avoid smearingofFig.4Nematode assemblages.Non-parametric multi-dimensional scaling ordination based on square-root transformed abundances of species from individual sand and mud microcosm samples,coded by treatment (as in Table 2)Table 4Dissimilarities (%)between nematode assemblages from top sediment layer of microcosms based on square-root trans-formed data (*signi®cantly di erent at p <0.05)ControlS1S2S3S4M1M2M3S131S230*26S338*31*33*S438*39*37*37*M133*3031*33*38M232*33*3138*4134M331*3130*35*363034*M440*41*40*44*3939*46*34*Table 5Dissimilarities (%)between nematode assemblages from middle sediment layer of microcosms based on square-root trans-formed data (*signi®cantly di erent at p <0.05)ControlS2S4M2S230*S438*60M232*4955M440*61*51*47Table 6Dissimilarities (%)between nematode assemblages from bottom sediment layer of microcosms based on square-root transformed data (*signi®cantly di erent at p <0.05)ControlS1S2S3S4M1M2M3S168*S266*39S368*4344S461*403846M155*44414743*M259*42*454945*43M364*444147414445M464*39394738414339526surface sediment into deeper sediment layers.As the same method was used for all microcosms,and abun-dances in the top sediment layer were always much higher than in deeper layers,this error is not considered to be of major importance.E ects of simulated deposition of dredged materialon structure of nematode assemblagesResults from univariate and graphical data analyses showed that mud nematodes are capable of migrating over a wide depth range into®ne sand as well as into mud. Results from multivariate data analyses revealed that a diverse mud assemblage is able to survive in native muddy and non-native sandy sediment for a duration of2mo. Nematode assemblages from the top sediment layer of most sand treatments were not signi®cantly di erent from those of the respective mud treatments.Similar migration and survival rates are expected,regardless of whether native or non-native sediment is deposited.Therefore,the ®rst null hypothesis,stating that the response of nema-tode assemblages does not depend on the sediment char-acteristics of the deposited material has to be accepted. In a laboratory experiment lasting for30d,Romeyn and Leiseboer(1989)showed that nematodes migrated through a layer of up to10cm only when both original and deposited sediment consisted of®ne sand.However, migration of nematodes into the deposit was limited to 1±2cm when mud was deposited onto sand.Results from other®eld studies and laboratory experiments have also demonstrated that migration and survival rates of benthic organisms are generally higher in sandy than in silty sediment(Maurer et al.1986;Essink1993; Somer®eld et al.1995).Wul et al.(1997)treated cores of natural sandy sediment with2.5mm autoclaved silt in order to assess the e ect of an increased load of®ne sediment on benthic microalgae,bacteria and meiofauna.After30d, they found no signi®cant di erences in the relative proportions of meiofaunal groups in the top sediment layer of the controls and the layer of added sediment. The authors suggested that the initial composition can be re-established in the treatments when the deposited silt layer does not exceed a critical depth.Although di erent from their native muddy sediment in terms of median,sorting coe cient,total organic content,and nematode assemblage structure before defaunation,the sand deposit used in this experiment provided an environment in which most nematode species were able to survive and reproduce successfully. It is likely that the di erences in sediment characteristics were too minimal to in¯uence most species.Results from our microcosm experiment showed that the frequency of deposition and the amount of deposited material are interactive factors which can play an im-portant role in the response of nematode assemblages. Our second and third null-hypotheses stated that the response of nematode assemblages does not depend on the quantity disposed of or the frequency of disposal. These null hypotheses can only be rejected for certain treatments.The high-frequency sand treatments were more similar to controls than the low-frequency treatments,indicating that for the deposition of non-native sandy sediment,the frequency of deposition and dose size were more impor-tant for successful upward migration and survival in the deposited sediment than the total amount deposited. The response of nematode assemblages to the depo-sition of their native muddy sediment was una ected by the frequency in the low-amount Treatments M1and M3.However,the frequency of deposition was an important factor in the high-amount Treatments M2 and M4,with most intense changes in assemblage structure occurring when the sediment was deposited in one large dose.Species-speci®c responses to simulated depositionof dredged materialMultivariate analyses of changes in assemblage structure indicated that species were a ected by the disposal of defaunated sediment in di erent ways.Low abundances of some nematode species in the top sediment layer of the experimental treatments might be due to their in-ability to migrate and/or to low survival rates in the deposited sediment.Results of the SIMPER analyses revealed that the response of nematodes to the deposition of uncontami-nated sediment is an integrated response to(a)the enhancing e ect of food input with the deposit,and(b) the negative e ect of burial.Impacts of burial depend on the ability of a species to withstand sedimentation andTable7General distribution of discriminating nematode species(Platt and Warwick1988;Warwick et al.1998)and their abundances ( SD)in sand and mud deposits before defaunationSpecies General distribution Abundance in sand depositbefore defaunation Abundance in mud deposit before defaunationSabatieria breviseta Muddy intertidal and subtidal sediments342 100950 450Aponema torosa Intertidal mud5 6317 137 Daptonema normandicum Mainly intertidal and shallow subtidal sand10 1436 112 Daptonema tenuispiculum Intertidal and subtidal mud and muddy sand8 591 37 Terschellingia communis Intertidal mud3 5380 86 Terschellingia longicaudata Intertidal mud0 0284 108527。
