Transverse evolution of a plasma channel in air induced by a femtosecond laser

We investigate the evolution of filamentation in air by using a longitudinal diffraction method and a plasma fluorescence imaging technique. The diameter of a single filament in which the intensity is clamped increases as the energy of the pump light pulse increases, until multiple filaments appear. (c) 2006 Optical Society of America.

濒危植物疏花水柏枝种群生物学和回归引种的研究

　本文对三峡库区濒危植物疏花水柏枝的种子形成与传播、种子萌发与幼苗定居、植株生长动态等种群生物学特性及其与环境的关系，特别是对水淹胁迫的生理学与生态学响应进行了研究，并以此为基础结合疏花水柏枝抢救工程的实施，对疏花水柏枝回归引种的相关生态学问题进行了探讨。 　　疏花水柏枝植株的生殖分配极高，每株所形成的花枝、花序和种子数量都比较多，其种子传播的方式有风传播和水传播，种子直接传播是疏花水柏枝种群进行扩增的主要途径，自然分布疏花水柏枝种群因此而常常成群分布。种子通过江水的二次传播是沿长江呈星状分布的疏花水柏枝各种群间进行基因交流的主要途径。限制疏花水柏枝种子萌发的环境因素主要是土壤含水量，这也是导致该物种在自然条件下仅分布于消落带的关键因素。疏花水柏枝一年生幼苗的成活率以及衡量植株生长状况的生物量、枝条数和根系长度都随着密度的增加而显著下降，表明密度对疏花水柏枝一年生幼苗的定居与生长有明显的制约作用。疏花水柏枝每年夏天都要经历长时间的水淹，在该时期无论是否被水淹，其幼苗地上部的生长都处于停滞（休眠），水淹后植株生物量都有一定程度的减少，但在各种水淹程度处理与对照之间除根深有显著差异外，幼苗的存活率、生物量、一级枝数、一级枝长度、根冠比的差异都不显著，表明水淹对幼苗的定居和生长没有显著影响，疏花水柏枝是通过快速的生物量丧失和快速恢复来适应水淹阶段的环境胁迫的。夏季适当的水淹不仅不会影响植株的生长，反而有利于该物种躲避这个阶段河滩上的高温天气，提高幼苗的成活率。 　　疏花水柏枝对水淹的生理生态适应机制较复杂。夏季水淹过后，植株进入生长恢复阶段，恢复初期植株的日均蒸腾强度与日均光合速率随着其在夏季被淹没时间的增加而增加，说明夏季水淹有利于植株尽快恢复生长。生长季节的水淹胁迫会使疏花水柏枝植株最初的光合作用和蒸腾作用的能力有所下降，但是长期水淹后，植株会形成适应，其光合与水分生理又会恢复到正常状态。疏花水柏枝植株也会在生理生化上对水淹胁迫作出响应。在夏天洪水季节无论是否被水淹，植株的可溶性糖总糖与蔗糖的都含量上升，根系活力、丙二醛（MDA）含量、过氧化物酶(POD)活性、多酚氧化酶(PPO)活性在各种水淹处理与对照之间以及淹水后与淹水前之间没有显著差异，从生理上表明疏花水柏枝的生长在夏季处于生长停滞（休眠）状态，其生理生化变化是植株对休眠的响应。夏天洪水季节结束后，各处理植株的多酚氧化酶活性、过氧化物酶活性、蔗糖与总糖含量在生长恢复阶段显著下降，丙二醛含量、根系活力则分别有所增加，表明植株在生理生化上也得到恢复，且植株在夏季是否受水淹胁迫对生长恢复阶段植株的生理生化变化没有显著影响。生长阶段的水淹胁迫会导致丙二醛含量、多酚氧化酶、过氧化物酶活性上升，其中前两者的变化显著，而根系活力、可溶性总糖含量则在水淹后表现为下降。但是经长期水淹后，各种生理生化指标会逐渐恢复到正常水平，表明该物种对水淹的适应能力较强，水淹并不会对植株形成长期的生理压力。 　　疏花水柏枝被回归引种于长江三峡的几个主要支流上，形成几个相对隔离的重建种群。种群遗传多样性、年龄结构、分布格局、繁殖与扩展等生物学特性是种群持续发展的基础，疏花水柏枝种群的重建中必须予以考虑。各移栽点应分别从不同的地点采集移栽材料，且以生长旺盛、繁殖力强、遗传性状稳定的3-10年植株为主。在疏花水柏枝种群恢复与重建中目前所面临的主要问题是如何增强被隔离的种群间的基因交流、促进种群的种子扩散与萌发、协调新建种群与当地物种的关系、营造有利于新建种群定居与生长的生态环境。

淹水对三峡库区几种植物的生理生态影响

自然界木本植物在某些情况下可能面对淹水带来的胁迫伤害，木本植物对淹水的生理生态响应及适应机制的研究，不仅可以从机理上解释河岸带和消落区树种分布的规律，对于大型水库消落区的治理也能起到理论依据的作用，因此，木本植物对淹水的生理生态响应及适应机制历来是植物生理生态研究领域的热点问题之一。 三峡水库蓄水造成库区部分陆地岛屿化，这将对岛屿优势植物带来深远影响。短柄枹栎(Quercus glandulifera)、栓皮栎(Quercus variabilis)、马尾松(Pinus massoniana)是这些岛屿上的三种优势树种。在岛屿形成初期，应用生理生态学手段，在7月和9月分别对其水势和叶绿素荧光进行了野外测定，从而为岛屿化对植物生理生态影响的研究和监测提供重要的本底数据。研究结果表明马尾松较其它两种植物更耐旱。水势和Fv/Fm在清晨高中午低，经过一个晚上可以基本恢复，因此就目前状况看岛上的三种优势植物均生长健康。但是库区蓄水后，在淹水胁迫下植物的生理生态过程将如何变化，还需要后期的连续观测。 枫杨（Pterocarya stenoptera）、池杉（Taxodium ascendens）和栓皮栎（Quercus variabilis）是三峡库区河岸带和库塘消落区常见的植物，对于河岸带和库塘消落区的水土保持和水源涵养具有十分重要的作用。通过设计模拟淹水实验，研究了这三种植物对淹水的生理生态响应及适应机制。淹水对枫杨和栓皮栎生理生态过程的早期影响是快速降低了二者的最大净光合速率、气孔导度、最大光化学量子效率（Fv/Fm）。但经过最初的下降后，枫杨的最大净光合速率、气孔导度和最大光化学量子效率逐渐恢复，而栓皮栎的则持续下降。在试验过程中，枫杨和池杉均产生了有利于吸收氧气的不定根和肥大的皮孔，而栓皮栎没有产生不定根。随淹水时间的增加枫杨的叶绿素含量与对照没有显著差异;而栓皮栎的叶绿素含量在第33天后大幅降低，Chla/Chlb的比值下降。淹水后第10天和70天测定的清晨水势，受淹栓皮栎比对照高，而受淹枫杨比对照低。淹水导致池杉和栓皮栎的根/茎/叶膜质过氧化状态均呈现动态变化。淹水处理的栓皮栎根的MDA含量低于对照而池杉的高于对照，比如：淹水24天后，栓皮栎根的丙二醛含量是对照的73％;而池杉是对照的111.5％。淹水处理第10天和第24天两个种的叶和茎MDA含量均高于对照但第50天则略低于对照。淹水导致池杉和栓皮栎两个种的根/茎/叶可溶性糖含量呈现动态变化。持续淹水导致栓皮栎叶片可溶性糖含量相比于对照先略下降后上升，茎可溶性糖含量显著上升而根可溶性含量先下降后上升。而池杉根/茎/叶可溶性糖含量对照和处理之间差异不显著。淹水导致栓皮栎的比叶重（Leaf dry mass per area）持续升高，池杉的与对照没有显著差异。淹水导致栓皮栎的根系活力持续下降，池杉则开始时下降后又升高，这可能与池杉在淹水过程中产生了有利于吸收氧气的不定根，而栓皮栎没有产生不定根有关。 以上生理生态的实验结果说明相对枫杨和池杉，栓皮栎应属于对淹水较敏感的树种。并得到以下一些结论：1）间接支持了“长期淹水导致不耐淹种（如栓皮栎）库量减小，进而导致光合速率下降的负反馈效应”假说;2）淹水对不耐淹种光合速率下降的影响至少包括气孔开度降低、光化学量子效率降低和库尺寸下降导致的光合速率下调的负反馈效应（长期）三个生理生态原因;3）淹水对水势的影响与树种相关;4）淹水并未导致不耐淹种（如栓皮栎）根膜质过氧化状态上升，而是导致其下降。导致其下降的主要原因是根系缺氧造成的;5）淹水胁迫初期耐淹种（如枫杨和池杉）和不耐淹种（栓皮栎）均出现部分生理生态过程的下调，持续时间大概在1－10天内。随后耐淹种生理过程逐渐恢复而不耐淹种在略为恢复1－2天后逐渐下降到较低水平。耐淹种恢复的关键原因可能是不定根和肥大的皮孔的出现。 令人意外的是70天的淹水过程并没有导致栓皮栎的死亡，这说明该树种对淹水具有一定的忍耐能力。因此，栓皮栎分布于河岸带和消落区较高海拔处并很少受到季节性淹水影响的生理生态原因可能还包括其他方面。淹水后可能要面对土壤透气性恢复带来的生理干旱胁迫可能对栓皮栎的生理过程造成影响。因此进一步研究淹水后恢复过程中三个种的生理生态过程对于深刻理解河岸带和消落区树种分布的生理生态原因无疑具有十分重要的理论意义。

三峡库区岸边植物水分利用研究

随着三峡大坝建设，在2003年6月三峡库区蓄水到135 m水位，之后人为调节使其在137-139 m范围内波动变化。从2003年7月开始，我们对库区植物的水分关系及其对三峡水位上升的可能反应进行了系统研究。 在库区中残存的次生松栎混交林，我们从江边沿海拔梯度设置了3块样地：Riparian，Mid-hill和Top-hill样地，垂直高度相差约20 m。从2003年7月到2004年7月，我们比较了岸边样地内与高处两样地内植物的木质部水分稳定同位素D和18O值，植物清晨和中午水势，叶片碳稳定同位素值13C，以及2004年7月测定的气体交换。岸边 植物木质部水分同位素值显著高于江水的同位素值，而与高处两样地内植物木质部水分同位素相近。岸边植物与高 处植物具有相近的清晨水势和中午水势，也表明对岸边植物来说，江水并不是它们重要的水分来源。同样，岸边植 物叶片 13C值与高处同种植物的值也不存在显著差异。我们研究的3种植物清晨水势都与土壤含水量正相关，尤 其浅层土壤更为显著。研究结果表明岸边植物几乎没有利用江水，而同高处两样地内植物一样，都是以利用渗入到土壤中的降雨为主。 松栎混交林中，马尾松与槲栎相比，净光合速率和气孔导度，叶片含N量，以及清晨水势低于槲栎，而中午水势，叶片13C值高于槲栎。两种树木叶片13C值与含N量都成正相关关系。槲栎叶片13C值与清晨水势成负相关，而马尾松针叶13C值与清晨水势相关性并不显著。 在岸边的松栎混交幼林与成年林相比，幼树的清晨水势略高于对应的成年树，叶片13C值低于成年树;幼树的光合速率和气孔导度略高于成年树，而瞬时水分利用效率低于成年树，但差异均不显著。马尾松幼苗为实生苗，与成年树相比，更偏向于利用浅层土壤水;而槲栎幼树多为从原来被砍伐的树上萌生的，木质部水分同位素与成年树相近。 从2004年5月到10月，我们又对大坝下游江段岸边植物（马尾松，枫杨和柑桔）的水分关系进行了研究。木质部水分同位素比率表明，岸边植物木质部水分同位素比率与高处植物具相近的值，且显著高于江水同位素值。研究表明岸岸边和高处植物以降雨或靠降雨补充的浅层地下水为主要水分来源，即便岸边植物也几乎不利用江水。岸边植物与高处植物具有相近的清晨水势和中午水势，光合速率和气孔导度，以及叶片C值等，也进一步说明岸边植物与高处植物具有相近的水分生理特征。 叶片13C可以指示植物的一些生理过程，我们对松栎混交林中不同生活型植物的13C值进行了分析，乔木层叶片 13C值比较高，其中常绿针叶的值又高于落叶阔叶树木的值;林下灌木，非禾本科草本，及藤本植物的13C值都明显低于乔木层。 三峡大坝改变河水对植物生理生态过程的影响是一个长期的过程，库区水位上涨是否影响到岸边植物的生理过程及生长等，需要进一步作长期、定位和连续的观测研究。

点源污染对三峡库区陆生植物群落的影响

三峡库区一些污染严重的工业企业是当地主要的点源污染源，对周围植物群落产生了巨大危害，而植物是生态系统赖以存在的基础，它的生长发育直接影响到生态系统的结构及其正常功能的实现。本研究按照与点源污染源的距离为梯度，通过在三峡库区兴山县白沙河磷化工厂周围布设了32个植物群落固定样地，并以点源污染无法影响到的植物群落为对照，进行样地的野外群落学调查;在每个样地取不同种植物叶片100克左右和样地0~20cm土壤500克，以石灰滤纸法同步进行大气氟化物的取样。样品带回室内应用氟离子选择电极法，测定大气氟化物含量、植物叶片氟的累积量和土壤水溶性氟的含量。同时在野外调查时使用PAM2100叶绿素荧光仪测定植物最大光化学效率即Fv/Fm的值。通过野外调查试验和相关的室内分析，研究了（1）：点源污染对三峡库区陆生植物群落组成和物种多样性的影响;（2）：点源污染中的主要污染物对植物及土壤环境的影响;（3）：不同物种叶片最大光化学效率Fv/Fm对污染胁迫响应的差异。结果如下： 点源污染对植物群落物种丰富度以及Pielou均匀度指数均有不同程度的影响，对于群落结构相对简单的马尾松林和柏木林的不利影响更为显著。相对于污染区来说，对照区中物种重要值的集中程度有所下降。许多物种的重要值在污染区与对照区有明显的变化。马尾松（Pinus massoniana）、檵木（Loropetalum chinense ）、铁仔（Myrsine africana）、卷柏（Selaginella tamariscina ）等对照区重要值较污染区为高，黄檀（Dalbergia hupeana ）、菱叶海桐（Pittosporum truncatum）、君迁子（Diospyros lotus）等污染区的重要值较对照区为高。群落中有些物种比如柏木（Cupressus funebris）的天然更新也受到污染的影响。 污染区土壤pH值大多低于对照区，但是与离污染源距离的相关性不强。污染区有些物种比如马尾松、柏木等叶片中的全氟含量与大气中氟化物的含量和土壤水溶性氟含量明显正相关。但是另外有些物种氟的累积量受点源污染的影响不显著，比如菱叶海桐、翅柃（Eurya alata）等在污染严重的样地内生存状况仍然很好。 在距离点源污染近的样地内，大多数物种的最大光化学效率Fv/Fm的值显著下降。栓皮栎（Quercus variabilis）、马尾松和柏木等的Fv/Fm值与距污染源的距离呈明显的正相关，都是随着离污染源越来越近而逐渐降低。根据污染区相对对照区Fv/Fm值下降幅度的不同，把植物划分为三种类型：对污染敏感型如柏木、铁仔、檵木等，中等敏感型如油桐（Vernicia fordii）、香叶树（Lindera communis）和不敏感型如山胡椒（Lindera glauca）和 蝴蝶花（Iris japonica）等。

三峡水库蓄水对消落带土壤理化性状的影响

三峡水利枢纽工程的调度运行导致水库水位的涨落，从而在三峡水库周边水陆交错带形成周期性淹没与出露于水面的一段特殊区域，被称为三峡水库消落带。三峡水库消落带生态系统的健康是库岸稳定和水库安全运行的重要保障。土壤养分是三峡库区消落带土壤生态系统的重要组成部分。三峡水库蓄水以来，土壤理化性状发生改变，水土流失日益加剧。土壤是植物的基础，因此，对三峡水库消落带土壤性状的研究对消落带植被恢复有一定的指导意义，也为研究水库消落带水土流失提供依据，为研究水库消落带土壤污染与水体污染提供基础。 本文首先通过对重庆忠县石宝寨水库消落带不同水位、不同时期的表层土壤分析，研究了消落带不同水位土壤容重、酸碱度、有机质、全氮、全磷、全钾、硝态氮、氨态氮、速效磷、速效钾的含量变化。实验结果表明：（1）消落带土壤淹水前各测定指标在不同海拔高程之间的差异均不显著（P>0.05）；（2）三峡水库淹水后消落带土壤由微碱性变为碱性，养分平均含量普遍下降，土壤养分缺乏，淹水易造成养分流失；（3）不同淹水强度下，土壤pH 值、有机质、全氮、全磷、氨态氮、速效钾平均含量差异显著（P＜0.001），经过淹水土壤有机质、全氮、速效钾含量进一步降低；（4）不同淹水时期，土壤全钾、硝态氮、氨态氮平均含量差异显著（P＜0.001），速效氮含量随季节变化较大，与土壤水分有密切关系；（5）干湿交替更容易造成氮、磷解吸释放入水体，从而增加富营养化的风险。 其次，通过对石宝寨消落带5 个时间段6个水位的表层土壤分析，研究了消落带不同时期、不同淹水强度土壤酸碱度及Cu、Zn、Pb、Cr 的含量变化。结果表明（1）淹水土壤pH 显著高于未淹水土壤，长期淹水土壤重金属含量显著高于短期淹水土壤与未淹水土壤，146m 土壤重金属含量最高；（2）经过淹水土壤，pH 先升高后下降，铜含量、锌含量都下降，铬含量先上升后下降，铅含量随着土壤暴露先稍微上升，后又下降，但在08 年9 月达到最大值；（3）各土壤重金属之间均存在显著相关关系，表明三峡消落带土壤存在重金属复合污染隐患；（ 4 ） 以三峡水库土壤背景值为评价标准， 消落带土壤污染程度具有Cu>Pb>Zn>Cr 的特征，其中，铜污染相对最为严重，消落带土壤随着淹水强度的加大与淹水时间的延长，污染程度加重，消落带综合污染指数达到1.24，属于轻度污染级。

Variation in Reproductive Traits between Populations of Neosalanx taihuensis above and below the Three-Gorges Dam

Reproductive characteristics of the spring spawning stock of Neosalanx taihuensis varied significantly between the populations in the Three-Gorges Reservoir (TGR) and in the Tian-e-zhou Oxbow (TEO, below the dam). Larger body size, higher condition, higher fecundity, and larger oocyte diameter of the spawning stock in the TGR indicated faster individual growth and higher reproductive investment of the TGR population than the TEO population. With higher population abundance associated with higher reproductive investment of N. taihuensis in the TGR than in the TEO population, we suggest that reproductive investment is an important factor regulating resource fluctuation of N. taihuensis populations.

Construction of habitat suitability models (HSMs) for benthic macroinvertebrate and their applications to instream environmental flows: A case study in Xiangxi River of Three Gorges Reservior region, China

Based on a long-term ecological monitoring, the present study chose the most dominant benthic macroinvertebrate (Baetis spp.) as target organisms in Xiangxi River, built the habitat suitability models (HSMs) for water depth, current velocity and substrate, respectively, which is the first aquatic organisms model for habitat suitability in the Chinese Mainland with a long-term consecutive in situ measurement. In order to protect the biointegrity and function of the river ecosystem, the theory system of instream environmental flow should be categorized into three hierarchies, namely minimum required instream flow (hydrological level), minimum instream environmental flow (biospecies level), and optimum instream environmental flow (ecosystem level). These three hierarchies of instream environmental flow models were then constructed with the hydrological and weighted usable area (WUA) method. The results show that the minimum required instream flow of Xiangxi River calculated by the Tennant method (10% of the mean annual flow) was 0.615 m(3) s(-1); the minimum instream environmental flow accounted for 19.22% of the mean annual flow (namely 1.182 m(3) s(-1)), which was the damaged river channel. ow in the dry season; and 42.91% of the mean annual flow (namely 2.639 m(3) s(-1)) should be viewed as the optimum instream environmental flow in order to protect the health of the river ecosystem, maintain the instream biodiversity, and reduce the impact of small hydropower stations nearby the Xiangxi River. We recommend that the hydrological and biological methods can help establish better instream environmental. ow models and design best management practices for use in the small hydropower station project. (C) 2008 National Natural Science Foundation of China and Chinese Academy of Sciences. Published by Elsevier Limited and Science in China Press. All rights reserved.

Peridiniopsis niei sp nov (Dinophyceae), a new species of freshwater red tide dinoflagellates from China

A new freshwater phototrophic species of the dinoflagellate genus Peridiniopsis, P. niei sp. nov., is described based on morphology. The new species appeared during spring with densities up to 1.48 x 10(7) cells L-1 in some tributaries and gullies of Three Gorge Reservoir and Lake Donghu, China, forming red tides. Peridiniopsis niei is a cyst-producing freshwater dinoflagellate that belongs to the group Penardii. The plate tabulation is po+x+4 '+0a+6 ''+5c+5s+5 '''+2 '''' and the plate pattern is symmetric. The cells of P. niei are pentagonal in ventral view, the epitheca is larger than the hypotheca, making up about 2/3 the length of the cell. Plate 3 ' is hexangular. The closest species to P. niei is P. penardii (Lemmermann) Bourrelly, but cells of the former are pentagonal, very compressed dorsoventrally, and the hypotheca is truncated with one transparent, robust spine on each antapical plate.

The role of cell-surface-bound phosphatases in species competition within natural phytoplankton assemblage: an in situ experiment

Despite it is widely acknowledged that the ability to hydrolyze dissolved organic matter using extracellular phosphatases is diverse in fresh water phytoplankton, the competition within single species related to presence and quantity of cell-surface-bound phosphatases has not been examined in natural conditions yet. Here, we studied phytoplankton species competition in a freshwater reservoir during an in situ experiment. A natural plankton community, with the exclusion of large zooplankton, was enclosed in permeable dialysis bags inside two large containers of different bioavailable phosphate concentrations. Phytoplankton species biomass and the abundance of bacteria were determined in purpose to compare the development of enclosed microbial communities. Total and cell-surface-bound phosphatase activities in the phytoplankton were investigated using the Fluorescently Labelled Enzyme Activity (FLEA) technique that allows for direct microscopic detection of phosphatase-positive cells and, with image cytometry, enables quantification of phosphatase hydrolytic capacity. Production of extracellular phosphatases was not completely inhibited or stopped in the phosphate-enriched environment, phytoplankton cells only showed the activity less often. Under the phosphate-nonenriched conditions, the production of phosphatases was enhanced, but active species did not proliferate amongst phytoplankton assemblage. Further, specific growth rates of the phosphatase-positive species in the non-enriched environment were lower than the same phosphatase-positive species in phosphate-enriched environment. Interestingly, the phosphatase-positive cells of Ankyra ancora increased their size in both treatments equally, although the population in phosphate-enriched environment grew much faster and the cell-specific phosphatase activity was lower. We hypothesize that brand new daughter cells had sufficient phosphorus reserves and therefore did not employ extracellular phosphatases until they matured and needed extra bioavailable phosphorus to support their metabolism before cell division. Based on presented in situ experiment, we propose that the ability to hydrolyze organic polymers and particles with cell-surface-hound phosphatases is advantageous for longer persistence of given population in a phosphate-scarce environment; although phosphatase-positive species cannot dominate the reservoir phytoplankton solely because of specific phosphorus-scavenging strategy.

Annual variations of biotic integrity in the upper Yangtze River using an adapted index of biotic integrity (IBI)

Adaptive modification and use of Karr's index of biotic integrity (IBI) for the upper Yangtze River, including 12 metrics in five categories, have typically occurred in line with the data collected by 6-year commercial fisheries investigation. These investigations were undertaken annually in four sections of the Upper Yangtze main channel between 1997 and 2002. These four monitoring sections (Yibin - YB, Hejiang - HJ, Mudong - MD, and Yichang - YC) were selected because they represent the part of the river that will be covering a 1000 kin stretch that includes the future Three Gorges Reservoir (TGR), upstream of the Three Gorges Dam (TGD), an area influenced by the construction of TGD. in addition, historical data were used to show changes in the watershed by comparison with field investigations recently. The biotic integrity of the four sections were calculated and classified into different levels annually for recognizing its spatial and temporal variations. It was observed that IBI scores were becoming lower diminishingly since 1997 in all the four sections. Because all the data were collected before the impoundment of the Three Gorges Reservoir, it is obvious that human activities, especially over-fishing, must be crucial factor instead of damming in the upper Yangtze River in that period. (C) 2008 Published by Elsevier Ltd.

Post-impoundment biomass and composition of phytoplankton in the Yangtze River

Damming, and thus alteration of stream flow, promotes higher phytoplankton populations and encourages algal blooms (density > 10(6) cells L-1) in the Three Gorges Reservoir (TGR). Phytoplankton composition and biomass were studied in the Yangtze River from March 2004 to May 2005. 107 taxa were identified. Diatoms were the dominant group, followed by Chlorophyta and Cyanobacteria. In the Yangtze River, algal abundance varied from 3.13 x 10(3) to 3.83 x 10(6) cells L-1, and algal biomass was in the range of 0.06 to 659 mg C m(-3). Levels of nitrogen, phosphorus and silica did not show consistent longitudinal changes along the river and were not correlated with phytoplankton parameters. Phytoplankton abundance was negatively correlated with main channel discharge (Spearman r = -1.000, P < 0.01). Phytoplankton abundance and biomass in the Yangtze River are mainly determined by the hydrological conditions rather than by nutrient concentrations.

The impact of planktivorous fishes on microcystin concentrations in Meiliang Bay, Lake Taihu, China

In an eight-month enclosure experiment in Meiliang Bay of Lake Taihu, a shallow subtropical lake in China, silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) collectively reduced cyanobacterial biomass. Microcystin concentration was six times higher in the 0.35 km(2) control enclosure (without fish) than in two similar-sized enclosures that had been stocked with both carp species. Furthermore, toxic Microcystis spp. increased microcystin production when exposed to silver carp and bighead carp.

The research of phosphorus of Xiangxi River nearby the Three Gorges, China

The Xiangxi River is the first middling tributary of the Changjiang River near the Three Gorges Dam. The River is subject to phosphorus pollution mainly from industrial wastewater. As the water quality of the Xiangxi River could directly influence the water quality of the Three Gorges Reservoir, the research on phosphorus levels and its change in the sediment profile of the Xiangxi River could provide useful information in the dynamic changes in the system, thereby offering options for mitigative measures. Water and sediment samples from lower reaches of Xiangxi River were collected and the different forms of phosphorus in sediments of the Xiangxi River were studied. The concentrations of total phosphorus in sediment ranged from 757.67 to 1438.54 mg/kg. Inorganic phosphorus concentrations ranged from 684.63 to 1055.58 mg/kg. Phosphorus contamination was serious in some parts of the Xiangxi River. With an average concentration of 635.17 mg/kg, calcium-bound phosphorus is the main form among different inorganic phosphorus forms. Labile phosphorus and iron/aluminum-bound phosphorus measured 3.40, 0.05and 35.28 mg/kg, respectively. The mobilization potential of phosphorus of sediments was studied through adsorption and release experiments. The equilibrium concentration of phosphorus adsorption and release was around 0.1 mg/L. The initial concentrations of phosphorus in the overlying water and the sediments have obvious effect on phosphorus mobilization potential. In addition, the release rate of phosphorus in sediment increased with water depth.