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1.
2012年5月—10月,大庆库里泡浮游植物的种类组成、丰度、优势种及多样性调查研究结果表明,库里泡共鉴定浮游植物380个分类单位(349种29变种2变型),隶属于8门11纲22目41科104属。库里泡浮游植物群落组成主要是绿藻—硅藻型,浮游植物种类数随季节的变化顺序为:8月6月7月5月9月10月。浮游植物丰度季节性变化明显,变化范围为5.94×10~5—119×10~5 ind·L~(-1)。浮游植物优势种不同季节间既有交叉又有演替,优势种类大多为中营养型和中—富营养型指示种。多样性评价结果表明,浮游动物被长期高强度捕捞后,库里泡的浮游植物群落种类组成比较丰富,群落结构复杂且稳定性较好,水体处于β—中污染至轻污染水平。  相似文献   

2.
为了解三峡库区的忠县甘井河段水域牧场生态渔业对水环境的影响,于2013年3、6、9及12月按季度对该河段4个站点进行了浮游植物群落结构及水体理化因子的监测,并采用生物多样性指数法和综合营养状态指数法对水体营养状况进行了评价。结果表明,该河段浮游植物有7门93个属种,其中绿藻门的物种数最多,有37种,占浮游植物群落总数的39.79%,其次为硅藻门和蓝藻门,物种数分别为26种和13种,分别占浮游植物群落总数的27.96%和13.98%;浮游植物的年均丰度为757.67×104 ind./L,变化范围(3.06—5743.99)×104 ind./L,年均生物量为4.40 mg/L,变化范围0.03—17.67 mg/L;水体的年平均透明度为1.18 m,叶绿素a、总磷、总氮含量分别为8.54μg/L、0.13 mg/L、1.95 mg/L;浮游植物香农多样性指数(H′)、均匀度指数(J)年均值分别为2.90和0.88,全年综合营养状态指数值为37.59—71.86,由此推断,甘井河水质属于中污染—轻污染状态、中营养型—富营养型。在鱼类生长旺季的6月,甘井河段养殖区内的水质优于非养殖区,这可能与养殖区内放养滤食性鱼类有关,证实了水域牧场没有带来水环境的污染,反而能提高生物多样性,在一定程度上改善了水体。  相似文献   

3.
博斯腾湖浮游植物群落结构特征及其影响因子分析   总被引:1,自引:0,他引:1  
2011年对博斯腾湖大湖区17个采样站位的浮游植物及水体主要理化因子进行了4次系统调查。结果表明,在17个站位共鉴定出浮游植物127种(属),其中优势种(属)9种。浮游植物群落全年均以硅藻为主导,冬、春季节,浮游植物组成呈硅藻-甲藻型,优势类群主要为贫-中营养型浮游藻类,到夏、秋季节逐渐形成硅藻-绿藻型,以富营养型的浮游藻类为优势类群。浮游植物总平均生物量为(2.51±2.95)mg/L,生物量季节变动显著,峰值出现在夏季,冬季最低。基于Canoco的多变量分析表明:环境变量共解释了浮游植物群落总变异的54.5%,水温是影响浮游植物分布最重要的环境因子,其次为枝角类丰度。水中氮含量是影响浮游植物丰度的主要因子,同时浮游植物对水体有机物含量也有较大的影响。  相似文献   

4.
南海北部浮游植物生长对营养盐的响应   总被引:18,自引:0,他引:18  
彭欣  宁修仁  孙军  乐凤凤 《生态学报》2006,26(12):3959-3968
2004年夏季作者在南海北部海域研究了浮游植物生长的营养动力学,结合物理-化学过程对浮游植物生物量分布的影响与机制进行了研究,阐明了水平对流和中尺度涡对营养盐分布的影响及浮游植物生长和现存生物量对其的响应。受西南季风和东向沿岸流作用所形成的Ekman输送的影响,南海北部海岸带表层海水作离岸运动,使深层富含营养盐的冷水爬坡涌升到表层来补充,激发浮游植物生物量迅速增长。海区反气旋涡使海水辐聚下沉,造成水体具高温、低盐、高溶解氧浓度、低营养盐浓度和低浮游植物生物量。同时通过现场营养盐加富试验,发现该海域营养盐是浮游植物生长的主要限制因子,而且是多种营养元素共同限制了浮游植物的生长,添加单一的营养盐并不能促进浮游植物的生长。在生物量出现增长的试验组中,营养盐添加不仅促使浮游植物生物量的增长,而且也改变了浮游植物的粒级结构和群落结构。例如,在站S1008,培养前叶绿素a浓度为0.28 mg.m-3,加富培养60 h后浮游植物生物量在NP和NPSi的试验组中有显著的增加,叶绿素a浓度分别达1.07 mg.m-3和1.19 mg.m-3;培养前粒度分级叶绿素a主要以Pico级份占优势,而加富试验结束后,在NP和NPSi的试验组以Nano级份占优势,其它试验组仍以Pico级份占优势;同时,在培养后生物量出现增长的试验组,浮游植物群落的优势类群从甲藻向硅藻演替。  相似文献   

5.
为探讨在克氏原螯虾(Procambarus clarkii)稻田养殖水体中施用不同肥料对浮游植物群落结构的影响, 以湖北省荆州市太湖农场稻虾模式试验基地为场所, 于2019年4—5月进行试验, 设置施化肥、施有机肥和施有机-无机复混肥3个处理。每块稻田中克氏原螯虾的放养密度为2.30ind/m2。结果发现, 施化肥、施有机肥和施有机-无机复混肥稻田中分别鉴定出浮游植物74、81和81种; 浮游植物丰度和生物量变化范围分别为 (0.78—30.32) ×106 ind./L、0.55—26.00 mg/L, 且均以绿藻和隐藻占优势, 群落动态主要表现为这两类植物的变动, 浮游植物丰度和生物量总体表现为化肥>有机-无机复混肥>有机肥。施有机肥和施有机-无机复混肥的浮游植物均匀度指数和多样性指数均高于施化肥, 且浮游植物群落能维持更加稳定的状态。浮游植物群落随时间表现出明显的动态变化, 其中水温和营养盐对浮游植物的影响最大。在稻田养殖水体中施用有机-无机复混肥具有促进浮游植物生长、改善浮游植物群落结构的效果, 施有机-无机复混肥优于单施化肥或有机肥。  相似文献   

6.
富营养水体生物修复中浮游植物的群落特征   总被引:26,自引:1,他引:26       下载免费PDF全文
通过对生物修复中富营养小水体浮游植物群落的分析 ,探讨了生物修复对浮游植物的影响以及浮游植物对环境因子改变的响应。生物修复实施后的浮游植物种类数比实施前多 ;浮游植物细胞数和生物量却有明显的下降 ;而对于Shannon Weaver多样性指数 ,实施后较实施前有明显的上升 ;生物修复过程中美丽胶网藻水华得到控制 ,优势种的指示性由中污变为寡污 ,优势度也由极度的高优势变为中低度优势 ,水体治理的前期阶段浮游植物群落的种类组成和结构有明显的改变 ;浮游植物种类数分别与正磷酸盐和氮磷比呈显著负、正相关 ,正磷酸盐的浓度与氮磷比的大小对水体浮游植物的种群结构变化具有重要影响。  相似文献   

7.
库容大小是影响水体水动力学过程的一个重要变量,它能在很大程度决定生态系统的结构,特别是浮游植物的群落结构.为了解小型贫营养水库浮游植物的群落特点,于2006年4、8、12月对位珠海市的贫营养小型水库-吉大水库的浮游植物群落结构进行采样和计数分析.3次采样共检出浮游植物32种,浮游植物细胞丰度的变化范围在69~342 cells·mL-1,生物量的变化范围在1.34~3.69 mg·L-1,夏季浮游植物的丰度和生物量明显高于冬季.甲藻是最主要的优势种类,且相对优势度较为稳定.夏季,隐藻门的隐藻(Cryptomonas sp.)和绿藻门的鼓藻(Cosmarium spp.)大量出现,甲藻的相对优势度有所降低.冬季,隐藻数量急剧下降,但硅藻门的颗粒直链藻(Aulacoseira granulata)大量出现,与甲藻共同成为水体中的优势种.由降雨引起的营养盐浓度增加是浮游植物变化的主要影响因子,而透明度全年维持较高的水平为浮游植物的生长形成了有利条件,此外,较为稳定的水体和甲藻利用营养盐的能力使得甲藻成为浮游植物中的最主要的优势种.  相似文献   

8.
安徽沱湖夏季浮游植物群落结构特征与环境因子关系   总被引:3,自引:0,他引:3  
为了揭示沱湖浮游植物群落结构特征及其与水环境因子的关系,于2016年7月(夏季),对沱湖流域上游至下游11个采样点浮游植物种类组成、细胞丰度、生物量等进行调查研究。结果显示,沱湖共有浮游植物96种(含变种),隶属8门48属,其中绿藻门(Chlorophyta)和硅藻门(Bacillariophyta)种类最多,绿藻门有23属39种,占总种数的40.63%,硅藻门有7属20种,占总种数的20.83%;其次为裸藻门(Euglenophyta),有5属17种,占总种数的17.71%,蓝藻门(Cyanophyta) 8属14种,占14.58%;甲藻门(Pyrrophyta) 2属2种,隐藻门(Cryptophyta) 1属2种,各占总种数的2.08%,黄藻门(Xanthophyta)与金藻门(Chrysophyta)均有1属1种,均占总种数的1.04%。绿藻和硅藻类物种在沱湖浮游植物群落结构中处于优势地位,沱湖夏季浮游植物种类组成表现为绿藻-硅藻型。沱湖夏季浮游植物细胞丰度与生物量从上游到下游呈逐渐增加趋势,细胞丰度与生物量平均值分别为4.022×106cells/L与3.046 mg/L,蓝藻门和绿藻门类群为沱湖浮游植物细胞丰度主体,硅藻门和裸藻门类群为沱湖浮游植物生物量的主体;上游浮游植物多样性指数与均匀度指数均略高于下游采样点,沱湖水质呈β中污型-无污染型,上游水质优于下游水质。浮游植物群落结构与水环境因子的典型对应分析(CCA)结果表明,电导率、透明度、水深及pH值等环境因子与沱湖夏季浮游植物群落结构有较强的相关性。  相似文献   

9.
淮北采煤塌陷区小型湖泊浮游植物群落结构和季节动态   总被引:1,自引:0,他引:1  
深入了解煤矿塌陷湖泊生态系统的结构与功能,有助于开展淮北煤矿塌陷水域的生态保护和资源的可持续利用.该文从2005年3月至2007年2月,研究了淮北采煤塌陷区两个小型湖泊(南湖和乾隆湖)浮游植物的群落结构和季节动态.结果表明:乾隆湖中总氮和总磷的浓度均高于南湖.蓝藻和绿藻均为南湖和乾隆湖的优势类群,其总和分别约占两湖泊年平均总浮游植物生物量的69.8%和63.3%,且南湖浮游植物生物量明显低于乾隆湖.另外,南湖夏季出现了以铜绿微囊藻(Microcystis aeruginosa)为主的蓝藻水华,而富营养湖泊中常见的微囊藻属(Microcystis)和水华束丝藻(Aphanizomenon flos-aquae)等蓝藻种类在乾隆湖中没有被观察到.除营养盐、温度外,鱼类和硬度水质可能是影响淮北采煤塌陷区小型湖泊浮游植物群落演替和生物量季节变化的重要原因.  相似文献   

10.
胡韧  雷腊梅  韩博平 《生态学报》2008,28(10):4652-4664
新丰江水库是我国第四大的水库,也是广东省最大的水库和重要的水源地。于2004~2005年2月一次调查了新丰江水库水文、水质和浮游植物分布,分析了浮游植物群落季节动态特征。新丰江水库浮游植物生物量比较低,在0.037—1.497mg·L^-1之间变化。浮游植物种类较多,11次采样共检到158种。在丰度上,水库浮游植物主要以小环藻、蓝纤维藻、小球藻和纤维藻等优势种为主,而在生物量上则以微小多甲藻为优势。浮游植物组成随季节变化而不同,春季以硅藻、甲藻和绿藻为优势类群;夏季以蓝藻、绿藻和硅藻为优势类群;秋季蓝、绿藻减少而硅藻和甲藻增加。2004年的浮游植物季节性变化更为明显,有从硅藻-绿藻优势(2月和4月份),到蓝藻-绿藻优势(6月和8月份),到混合优势(10月份)和金藻优势(12月份)这样一个变化过程。2005年硅藻的相对丰度比2004年高出很多。两年浮游植物组成的差异与两年的降水量有关。水动力学对丰水期(6~8月份)浮游植物组成结构有较大影响,导致硅藻和绿藻相对丰度的增加。与温带贫营养型水库相比,新丰江水库的浮游植物群落具有春季和秋季种类多、夏季的蓝藻种类丰富的特点。从细胞大小分布上看,小于20μm浮游植物是生物量的主要贡献者,其次是大于45μm的浮游植物。在粒径小于20μm的浮游植物中,微小多甲藻是最主要的贡献者。浮游植物群落的大小分布受水动力学条件和营养盐浓度动态的影响。  相似文献   

11.
1. An in situ enclosure experiment was conducted in a deep reservoir of southern China to examine (i) the effects of a low biomass (4 g wet weight m?3) of silver carp (Hypophthalmichthys molitrix) and nutrients on the plankton community and (ii) the response of Daphnia to eutrophication. 2. In the absence of fish, Daphnia galeata dominated the zooplankton community, whereas calanoids were dominant in the fish treatments, followed by D. galeata. Silver carp stocking significantly reduced total zooplankton biomass, and that of D. galeata and Leptodorarichardi, but markedly increased the biomass of smaller cladocerans, copepod nauplii and rotifers. In contrast, nutrient enrichment had no significant effect on the plankton community except for cyclopoids. 3. Chlorophyta, Cryptophyta and Bacillariophyta were dominant phytoplankton groups during the experiment. Chlorophyta with high growth rates (mainly Chlorella vulgaris in the fish enclosures and Ankyra sp. in the fishless enclosures) eventually dominated the phytoplankton community. Total phytoplankton biomass and the biomass of edible phytoplankton [greatest axial linear dimension (GALD) < 30 μm], Chlorophyta, Cryptophyta, Bacillariophyta and Cyanobacteria showed positive responses to fish stocking, while inedible phytoplankton (GALD ≥ 30 μm) was significantly reduced in the fish enclosures. However, there was no significant effect on the plankton community from the interaction of fish and nutrients. 4. Overall, the impact of fish on the plankton community was much greater than that of nutrients. High total phosphorus concentrations in the control treatment and relatively low temperatures may reduce the importance of nutrient enrichment. These results suggest it is not appropriate to use a low biomass of silver carp to control phytoplankton biomass in warmer, eutrophic fresh waters containing large herbivorous cladocerans.  相似文献   

12.
鲤鱼种和鲢鳙对池塘浮游生物的影响   总被引:9,自引:0,他引:9  
赵玉宝 《生态学报》1993,13(4):348-355
本文根据1990年-9月对9个鱼池的研究,报道鲤鱼种和鲢鳙对浮游生物的影响,结果表明:鲤鱼种使浮游植物和浮游动物生物量增加,浮游植物大型化,浮游动物小型化,并使浮游植物多样性增加,浮游动物多样性下降;鲢鳙密度增加,浮生物小型明显,微型藻类和超微在在浮植物中所占比重显著增加,小型浮游动物(原生动物和轮虫)在浮游动物中比重也明显增;鲢鳙密度对浮游生物多样性和浮游生物量的影响具有阶段性,当鲢鳙密度低时,  相似文献   

13.
14.
报道了单养链(Hypophthalmichthys molitrix)和施肥对盐碱池塘围隔生态系统浮游生物群落的影响,链的放养使浮游植物丰度,叶绿素a 含量和和初组生产力增大,浮游植物小型化,生物量以小型硅藻和绿藻占优势,裸藻和金藻占有相当比重;浮游动物生物量减少,特别是枝角类的生物量无鱼围隔大于有鱼围隔,且多是较大型的种类,施肥特别是施无机肥能显著地提高浮游植物丰度和初级生产力,浮游动物生物量也增大,施有机肥围隔浮游植物和浮游动物生物量虽高于有鱼对照围隔,但其浮游植物初级生产力,叶绿素a含量,浮游生物多样性指数,P/R系数均较低,链鱼的生长最差,文中讨论了滤食性鱼类和施肥对浮游生物的影响。  相似文献   

15.
1. Nutrient and fish manipulations in mesocosms were carried out on food‐web interactions in a Mediterranean shallow lake in south‐east Spain. Nutrients controlled biomass of phytoplankton and periphyton, while zooplankton, regulated by planktivorous fish, influenced the relative percentages of the dominant phytoplankton species. 2. Phytoplankton species diversity decreased with increasing nutrient concentration and planktivorous fish density. Cyanobacteria grew well in both turbid and clear‐water states. 3. Planktivorous fish increased concentrations of soluble reactive phosphorus (SRP). Larger zooplankters (mostly Ceriodaphnia and copepods) were significantly reduced when fish were present, whereas rotifers increased, after fish removal of cyclopoid predators and other filter feeders (cladocerans, nauplii). The greatest biomass and diversity of zooplankton was found at intermediate nutrient levels, in mesocosms without fish and in the presence of macrophytes. 4. Water level decrease improved underwater light conditions and favoured macrophyte persistence. Submerged macrophytes (Chara spp.) outcompeted algae up to an experimental nutrient loading equivalent to added concentrations of 0.06 mg L?1 PO4‐P and 0.6 mg L?1 NO3‐N, above which an exponential increase in periphyton biomass and algal turbidity caused characean biomass to decline. 5. Declining water levels during summer favoured plant‐associated rotifer species and chroococcal cyanobacteria. High densities of chroococcal cyanobacteria were related to intermediate nutrient enrichment and the presence of small zooplankton taxa, while filamentous cyanobacteria were relatively more abundant in fishless mesocosms, in which Crustacea were more abundant, and favoured by dim underwater light. 6. Benthic macroinvertebrates increased significantly at intermediate nutrient levels but there was no relationship with planktivorous fish density. 7. The thresholds of nutrient loading and in‐lake P required to avoid a turbid state and maintain submerged macrophytes were lower than those reported from temperate shallow lakes. Mediterranean shallow lakes may remain turbid with little control of zooplankton on algal biomass, as observed in tropical and subtropical lakes. Nutrient loading control and macrophyte conservation appear to be especially important in these systems to maintain high water quality.  相似文献   

16.
1. The succession of a phytoplankton community was investigated through an intensive period of sampling and related to physical, chemical and biological conditions sampled at an equal, or higher, temporal resolution. 2. Phytoplankton samples were taken on a weekly basis from June to September 2004 and analysed for diversity, species composition, and contribution of different functional groups to total biomass. Physical and chemical data were collected on the sampling days, and physical environmental factors were also logged continuously throughout the period by automatic measuring stations. This continuous logging allowed community structure to be compared with physical data averaged over periods from a day to a week before each sampling date. 3. The Schmidt stability of the lake, a measure of the strength of stratification calculated from thermal data, showed a negative correlation with phytoplankton species diversity. This is consistent with the hypothesis that mixing was preventing exclusion by species that would otherwise dominate in stratified conditions. 4. At a functional level, stress tolerant (S‐type) species dominated during the stratified summer conditions, with small, colonising species (C types) and ruderal, disturbance tolerant species (R types) contributing little to the overall biomass. Of the stress tolerant species, the faster growing (SC) phytoplankters were significantly favoured by more stable, stratified conditions and higher solar radiation. Increased abundance of this group resulted in decreased species diversity. Correlations were generally strongest when using the 6‐ to 7‐day averaged physical data, stressing the importance of continuous measurements of these drivers in phytoplankton studies.  相似文献   

17.
Water-column mixing is known to have a decisive impact on plankton communities. The underlying mechanisms depend on the size and depth of the water body, nutrient status and the plankton community structure, and they are well understood for shallow polymictic and deep stratified lakes. Two consecutive mixing events of similar intensity under different levels of herbivory were performed in enclosures in a shallow, but periodically stratified, eutrophic lake, in order to investigate the effects of water-column mixing on bacteria abundance, phytoplankton abundance and diversity, and rotifer abundance and fecundity. When herbivory by filter-feeding zooplankton was low, water-column mixing that provoked a substantial nutrient input into the euphotic zone led to a strong net increase of bacteria and phytoplankton biomass. Phytoplankton diversity was lower in the mixed enclosures than in the undisturbed ones because of the greater contribution of a few fast-growing species. After the second mixing event, at a high biomass of filter-feeding crustaceans, the increase of phytoplankton biomass was lower than after the first mixing, and diversity remained unchanged because enhanced growth of small fast-growing phytoplankton was prevented by zooplankton grazing. Bacterial abundance did not increase after the second mixing, when cladoceran biomass was high. Changes in rotifer fecundity indicated a transmission of the phytoplankton response to the next trophic level. Our results suggest that water-column mixing in shallow eutrophic lakes with periodic stratification has a strong effect on the plankton community via enhanced nutrient availability rather than resuspension or reduced light availability. This fuels the basis of the classic and microbial food chain via enhanced phytoplankton and bacterial growth, but the effects on biomass may be damped by high levels of herbivory. Received: 3 May 1999 / Accepted: 13 April 2000  相似文献   

18.
鹤地水库浮游植物群落的结构与动态   总被引:4,自引:0,他引:4  
鹤地水库位于雷州半岛北部(21°42'~22°22'N,109°54'~110°25'E),是一座中营养化的大型水库.为了研究其浮游植物群落的结构与变化特点,在水库设置5个采样点,并于2003年2、7、9、12月对其采样.鹤地水库浮游植物生物量变化为O.156~2.548 mg L~(-1),主要由蓝藻和硅藻组成.5个采样点的浮游植物生物量具有明显的季节变化,且变化趋势相同,即丰水期的生物量高于枯水期,主要是由于丰水期水温较高以及入库河水带入的营养盐.5个采样点的浮游植物生物量从主要入库河流至大坝区呈下降趋势,与磷浓度的降低直接相关.浮游植物优势种主要以热带代表性种类为主,且有明显的季节变化,枯水期主要为硅藻的根管藻(Rhizosolenia sp.)、小环藻(Cyclotella sp.)、颗粒直链藻(Melosira granulata)以及模糊直链藻(Melosira ambigua)等.丰水期为蓝藻的拟柱孢藻(Cylindrospermopsis raciborskii)、湖泊假鱼腥藻(Pseudanabaena limnetica)等,浮游植物优势种类的变化主要受磷浓度的影响.浮游植物前8个优势种的生物量占浮游植物群落生物量的850%~92%,显著低于温带地区浮游植物群落结构稳定的湖泊.  相似文献   

19.
1. In situ enclosure experiments were performed in the mesotrophic Bermejales reservoir to evaluate the algal response to changes in the nutrient supply and in the zooplankton size structure and density in a 2 × 2 factorial design. The experiments were conducted during the spring bloom of nanoplanktonic diatoms in 1989. 2. Nutrient enrichment promoted a great increase of phytoplankton biomass indicating a strong nutrient limitation on phytoplankton growth. Total phytoplankton biomass was significantly lower in the Daphina-added enclosures at a given nutrient level and strong direct an indirect effect of zooplankton on phytoplankton community structure and nutrient availability were observed. 3. Most of the nanoplanktonic species were effectively grazed but species with protective coverings and large size colonies were favoured by grazers and small chlorococcales were unaffected probably because of their compensatory high growth rates. The decrease in total biomass imposed by grazers is attributable mainly to the decrease of Cyclotella ocellata, the most abundant species. This taxon suffers two net effects of zooplankton: direct grazing and the indirect decrease of Si availability caused by the growth of C. ocellata which was promoted by P excretion by zooplankton. Indirect effects of grazers on Si availability should, therefore, be taken into account in explaining phytoplankton succession and community structure. 4. In this experiment grazers affected considerably the nanoplanktonic community in Bermejales reservoir. The extent which they were affected, however, depended not only on the algal size as a determinant of edibility but also greatly on the specific nutrient requirements and taxonomic features of the algal species.  相似文献   

20.
1. A 2‐year study was carried out on the roles of nutrients and fish in determining the plankton communities of a shallow lake in north‐west Spain. Outcomes were different each year depending on the initial conditions, especially of macrophyte biomass. In 1998 estimated initial ‘per cent water volume inhabited’ (PVI) by submerged macrophytes was about 35%. Phytoplankton biomass estimated as chlorophyll a was strongly controlled by fish, whereas effects of nutrient enrichment were not significant. In 1999 estimated PVI was 80%, no fish effect was observed on phytoplankton biomass, but nutrients had significant effects. Water temperatures were higher in 1998 than in 1999. 2. In the 1998 experiment, cladoceran populations were controlled by fish and cyanobacteria were the dominant phytoplankton group. There were no differences between effects of low (4 g fresh mass m?2) and high (20 g fresh mass m?2) fish density on total zooplankton biomass, but zooplankton biomass was higher in the absence of fish. With the high plant density in 1999, fish failed to control any group of the zooplankton community. 3. Total biovolume of phytoplankton strongly decreased with increased nutrient concentrations in 1998, although chlorophyll a concentrations did not significantly change. At higher nutrient concentrations, flagellate algae became more abundant with likely growth rates that could have overcompensated cladoceran feeding rates. This change in phytoplankton community composition may have been because of increases in the DIN : SRP ratio. Both chlorophyll a concentration and total phytoplankton biovolume increased significantly with nutrients in the 1999 experiment. 4. A strong decline of submerged macrophytes was observed in both years as nutrients increased, resulting in shading by periphyton. This shading effect could account for the plant decline despite lower water turbidity at the very high nutrient levels in 1998.  相似文献   

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