三江平原湿地同江地区水域夏季浮游植物群落结构特征

2012年6月对三江平原湿地同江地区水域浮游植物群落结构进行了初步研究。设置了13个采样点,生境类型包括大型开阔水体、小型封闭水体、湿地型水体以及河流型水体。结果在该水域发现浮游植物共计312个分类单位,包括276种33变种3变型,隶属于8门10纲21目36科92属。浮游植物细胞密度变化范围为2.68×104–2.53×106 cells·L–1。大型开阔水体种类丰富,细胞密度最大,以绿藻为优势种群;小型封闭水体中藻类的适应性强,群落结构最为复杂;湿地型水体受人为活动影响较大,发现了一些耐有机污染的种类;在河流型水体中,有一些适低温的隐藻出现并成为优势种,如啮蚀隐藻(Cryptomonas erosa)等。此外,在三江平原湿地同江地区还发现了大量β-中污染指示种类。经聚类和多维尺度分析,将不同采样点各生境水体的浮游植物群落分为4组。综合多样性指数表明,同江地区水域浮游植物群落结构较丰富且稳定性较好。     

西安城市河流浮游植物群落结构及其与环境因子的关系

为探究西安市城市河流浮游植物群落结构特征及其与环境因子的关系,分别于2020年10月和2021年6月对灞河、浐河、沣河及黑河共计24个采样点进行了浮游植物群落组成、细胞密度和生物量的调查研究,并利用冗余分析(RDA)研究环境因子对浮游植物群落结构的影响。调查结果显示,枯水期共鉴定出浮游植物6门115种,主要包括蓝藻门(11.30%)、硅藻门(54.78%)及绿藻门(26.96%),浮游植物细胞密度均值为(3.36±3.50)×106 cells/L,生物量均值为(1.79±3.59) mg/L。丰水期共鉴定出浮游植物7门168种,主要包括蓝藻门(7.74%)、硅藻门(51.79%)及绿藻门(29.76%),浮游植物细胞密度均值为(9.17±9.73)×10⁶ cells/L,生物量均值为(6.54±11.57) mg/L。与枯水期相比,丰水期在物种数量、细胞密度和生物量都大于枯水期。聚类分析结果表明,西安城市河流大部分采样点之间浮游植物群落结构及水环境状况具有相似性,而人类活动可能是导致其余点位具有空间差异性的主要原因。冗余分析(RNA)结果表明影响西安市城市河流...     

安徽沱湖夏季浮游植物群落结构特征与环境因子关系

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。     

怀洪新河浮游植物群落结构与水环境因子的关系研究

为研究怀洪新河水域浮游植物的群落结构及其与水环境因子的关系, 分别于丰水期(2014 年6 月)和枯水期(2014 年12 月)在怀洪新河进行采样分析, 并对调查区域内的浮游植物及主要环境因子进行了主成分分析(PCA)和典范对应分析( CCA)。结果表明, 共发现浮游植物7 门45 属83 种, 种类绿藻门最多。怀洪新河水域各采样点浮游植物细胞密度平均为1.96×106 ind. ·L-1, 生物量平均为1.71 mg·L-1。利用生物学指标对湖泊进行营养状况评价, 怀洪新河属于中营养型湖泊。PCA 分析表明, TN 和NH3-N 是影响水体富营养化的主要因素; 典范对应分析表明, Chl-a、NH3-N、T、TN、DO、水深和浊度是影响浮游植物群落结构的主要驱动因子。     

嘉兴石臼漾湿地冬季浮游植物群落结构特征

2010年冬季对嘉兴石臼漾饮用水水源人工湿地水体的浮游植物群落结构进行了调查,以探索湿地净化措施对浮游植物群落结构的影响.结果表明:在石臼漾湿地共发现浮游植物77种,隶属7门39属,其中硅藻门最多,为14属33种;优势种有变异直链藻、梅尼小环藻、菱形藻、色球藻、针晶蓝纤维藻、四尾栅藻、小型黄丝藻等,梅尼小环藻优势度最大,为0.144.石臼漾湿地冬季浮游植物平均密度为1.28×106 cell·L-1;出水口密度最低,为6.80×105cell·L-1,并且出水口蓝藻细胞的密度仅为进水口的14.9％(P＜0.05).各采样点Shannon多样性指数为0.94 ～1.27.经聚类和多维尺度分析,石臼漾湿地冬季浮游植物群落可分为根孔沿岸带群落、根孔植物床流水型群落(2种)、深度净化湖区静水型群落和湿地源水群落五大类;各采样点生态环境及水体流速的不同是五类群落产生的主要影响因素.     

大型热带水库-松涛水库枯水期浮游植物群落特征

松涛水库是一个大型热带水库,分为两个主要水域:番加洋和南丰洋,2003年12月对该水库的这两个水域的浮游植物进行采样,共发现7门65种藻类。松涛水库番加洋库区水体的浮游植物总细胞密度为1.08×10⁶cells·L^-1,主要种类组成为蓝藻(Cyanophyta)-绿藻(Chlorophyta)型。松涛水库南丰洋库区水体的浮游植物群落为细胞密度为1.14×10⁶cells·L^-1,主要种类组成为绿藻(Chlorophyta)-硅藻(diatom)型。松涛水库库区水体总体已为避-富营养,其中富营养型浮游植物指示种类有:铜绿微囊藻(Microcystis aeruginosa Kütz.),针状蓝纤维藻(Dactylococcopsis acicularis),镰形纤维藻(Ankistrodesmus falcatus),小环藻(Cyclotella menighiniana),模糊直链藻(Melosira spp.)等。与亚热带和温带的水库比较,处于热带地区的松涛水库浮游植物,在湖泊区微囊藻等适应高温高光强的种类具有更高的细胞密度。松涛水库河流区最主要的优势种是硅藻门的针杆藻。     

金河湾城市湿地浮游植物功能类群演替及驱动因子

于2015年春(5月)、夏(8月)、秋(10月)三季,在金河湾湿地4类水体共设置12个采样点对浮游植物功能类群演替及与水环境变量关系进行分析。研究期间共鉴定浮游植物376个种,隶属于8门10纲19目19科101属。浮游植物种类组成主要以硅藻门(39.62%)和绿藻门(35.64%)为主,其次裸藻门(10.11%)和蓝藻门(9.84%)的藻类所占比例较高,甲藻门、隐藻门、金藻门和黄藻门所占比例较低。调查期间金河湾湿地浮游植物细胞丰度季节间差异显著(P0.05),整体上呈现夏季秋季春季的规律。春、夏、秋三季共划分20个不同的功能类群,双因素方差分析(Two-way ANOVA)和单因子交叉相似性检验(One-way ANOSIM)表明:代表性功能类群在季节间演替明显(P0.05),群落构成差异显著(P0.01)。SIMPER分析指出,S2/H1/B/D/Lo/X1/MP是引起金河湾湿地各季节之间浮游植物群落结构差异的主要贡献类群。通过代表性功能类群和10个水环境变量的典范对应分析(CCA)探索环境变量与功能类群演替的关系。经分析,总氮(TN)是驱动金河湾湿地浮游植物功能类群演替的主要环境变量,电导率(SpCond)、pH与功能类群演替密切相关。     

鹤地水库浮游植物群落的结构与动态

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.     

海珠国家湿地公园浮游植物群落结构时空变化

浮游植物是湿地生态系统的重要组成成分,其数量及群落结构变化会对湿地生态系统的结构和功能产生重要影响。为了解海珠国家湿地公园浮游植物群落结构及时空动态变化特征,于2017年冬、2018年夏两季分别进行了调查。结果表明:海珠国家湿地公园共检到浮游植物171种,隶属7门64属,其中绿藻门、硅藻门和蓝藻门种类分别占总种类的44%、26%和13%;广州平裂藻(Merismopedia cantonensis)和细小平裂藻(Merismopedia minima)在两季均为优势种,冬季啮蚀隐藻(Cryptomonas erosa)也较多;浮游植物群落结构、丰度与生物多样性指数具有明显季节变化,冬季硅藻和绿藻占优,分别占藻类总丰度的32%和29%;夏季蓝藻占绝对优势,占68%;夏季浮游植物平均丰度达(25.58±18.47)×10^6cells·L^-1,约为冬季的3倍;Shannon物种多样性指数和Pielou均匀度指数冬季分别为4.38和0.77,夏季分别为2.92和0.51;从空间上看,海珠湖浮游植物种类、多样性指数均较低,而丰度较高;塘涌和西江涌硅藻丰度最大,其他位点均以蓝藻占优;水体总氮和温度是影响浮游植物群落结构变化的重要因素。本研究可为海珠国家湿地公园的管理和保护提供参考。     

海珠国家湿地公园浮游植物群落结构时空变化

浮游植物是湿地生态系统的重要组成成分,其数量及群落结构变化会对湿地生态系统的结构和功能产生重要影响。为了解海珠国家湿地公园浮游植物群落结构及时空动态变化特征,于2017年冬、2018年夏两季分别进行了调查。结果表明:海珠国家湿地公园共检到浮游植物171种,隶属7门64属,其中绿藻门、硅藻门和蓝藻门种类分别占总种类的44%、26%和13%;广州平裂藻(Merismopedia cantonensis)和细小平裂藻(Merismopedia minima)在两季均为优势种,冬季啮蚀隐藻(Cryptomonas erosa)也较多;浮游植物群落结构、丰度与生物多样性指数具有明显季节变化,冬季硅藻和绿藻占优,分别占藻类总丰度的32%和29%;夏季蓝藻占绝对优势,占68%;夏季浮游植物平均丰度达(25.58±18.47)×10~6cells·L~(-1),约为冬季的3倍; Shannon物种多样性指数和Pielou均匀度指数冬季分别为4.38和0.77,夏季分别为2.92和0.51;从空间上看,海珠湖浮游植物种类、多样性指数均较低,而丰度较高;塘涌和西江涌硅藻丰度最大,其他位点均以蓝藻占优;水体总氮和温度是影响浮游植物群落结构变化的重要因素。本研究可为海珠国家湿地公园的管理和保护提供参考。     

松花江哈尔滨段浮游植物群落格局及其与环境因子的相关性

松花江是黑龙江在我国境内的最大支流,流经吉林、黑龙江两省。松花江哈尔滨段是哈尔滨市工农业生产与生活用水的重要水资源,近年来由于人类活动的频繁影响,水体质量有所下降。鉴于此,于2018年春、夏、秋三季(4月、8月和10月),在松花江哈尔滨段设置14个采样点,对电导率、总氮和总磷等理化指标进行测定,同时对其浮游植物群落结构及环境因子相关性进行研究。利用群落相似性分析(ANOSIM)探讨浮游植物群落时空分布差异;通过SIMPER分析筛选出影响群落时空格局的关键物种。基于优势种和10项理化指标的冗余分析(RDA)揭示了浮游植物群落生态分布特征并对关键影响因子进行识别。研究结果表明,调查期间共鉴定浮游植物136种,其中优势种15种,群落结构主要以硅藻门和绿藻门的物种构成。松花江哈尔滨段浮游植物群落结构与过去10余年间相比较为稳定。ANOSIM和SIMPER分析表明,季节变化和人为活动干扰对浮游植物群落时空格局具有一定驱动作用,蓝藻门物种的空间分布活动干扰影响明显。RDA分析表明,浮游植物分布特征与水环境时空异质性关系密切,驱动松花江哈尔滨段浮游植物群落时空分布的主要水环境因子为电导率、总磷、浊度和pH。     

乌梁素海冰封期浮游植物分布特征及其与水质指标的关系北大核心CSCD

为揭示寒旱区冰封期富营养化湖泊水体中浮游植物群落结构及其与水质指标的响应关系,该研究以乌梁素海为对象,于2019年1月在湖区设立12个采样点采集水样及浮游植物,通过对浮游植物定性定量检测和水体理化性质测定分析,以明确冰封期乌梁素海浮游植物群落结构空间变化特征及主要水质指标的分布规律;结合RDA分析和Pearson相关性分析揭示了浮游植物与水质指标的响应关系,为水体富营养化程度评估及防控提供理论依据。结果显示:(1)冰封期乌梁素海12个样点的水质指标特征差异明显,各水质指标从北到南具有不同的变化趋势。(2)冰封期乌梁素海共检出浮游植物61种,其中隐藻门的丰度最高(4.76×10^(6)个·L^(-1)),甲藻门的生物量最高(18.09 mg·L^(-1)),但湖区不同位置的优势浮游植物类群有所差异,北湖区蓝隐藻和伪鱼腥藻丰度明显高于南湖区。(3)不同种类的浮游植物在空间分布上存在明显的差异,且在P3样点的多样性最低,P8样点的多样性最高,并发现中、下湖区物种类型多且组成较为均匀。(4)浮游植物的丰度与TP呈显著正相关关系,生物量与TP呈极显著正相关关系,多样性指数与TP呈正相关关系。研究表明,冰封期乌梁素海水体处于中等营养水平,水体中总磷(TP)含量是影响浮游植物物种丰度和生物量的主要影响因子;寒旱区冰封期富营养化湖泊浮游植物分布特征为北湖区隐藻门、蓝藻门和甲藻门占优势;南湖区中绿藻门丰度最高。     

滇池入湖河流大清河河口段浮游藻类格局研究

2006年7月至2007年12月对大清河3个样点的浮游藻类组成及密度、浮游叶绿素a浓度等指标进行逐月监测.共观察到浮游藻类65个分类单元,计53个属.所有样点的平均藻类密度是1.23×10⁸ ind·L^-1,最高密度为1.39×10⁹ ind·L^-1,最低密度为3.21×10⁵ ind·L^-1.铜绿微囊藻(Microcystis aeruginosa)为绝对优势种,监测期间其平均相对丰度为92.23%.随着离湖距离的增加,浮游藻类总密度、铜绿微囊藻的百分含量明显降低,而香农-威纳(Shannon-Wiener)、辛普森(Simpson 1/Dominance)多样性指数和均匀度(Evenness)则呈现升高趋势.同时,样点2、3的铜绿微囊藻百分含量与滇池的极为相似,而样点1则距离滇池较远,其铜绿微囊藻的百分含量及生物多样性指数方面均不同于样点2、3,说明滇池水的倒灌已显著影响到样点2、3的藻类组成.通过比较各样点间的群落相似性指数发现:样点1、3间的相似性指数显著低于样点1、2和样点2、3间的相似性指数.样点2、3间的相似性指数除2007年4、5及7月外,均超过60%.通过对样点1、2和3的浮游藻类群落在工程运行前后进行"非度量多维标度"(NMS)分析,发现示范工程运行后的1年内还未对大清河监测河段水生生物群落的恢复有显著作用.     

Spatial patterns and determinants of wetland vegetation distribution in the Kumasi Metropolis,Ghana

The contribution of wetlands to livelihood in the forms of resources of direct consumptive uses, fishing and agriculture are of great importance to riparian communities in sub-Saharan Africa. It is unfortunate to note that these same areas are being degraded and converted to informal settlements through uncontrolled urbanisation. To improve urban environments and meet the various development targets, efforts are being made to rid sub-Saharan African cities of these informal wetland associated slums. The difficulty, however, lies in delineating wetland boundaries. This research is therefore aimed at determining the vegetation diversity of wetlands in Kumasi, Ghana and to identify and characterise the typical urban wetland and factors that influence the small scale heterogeneity in distribution of the wetland vegetation. Ten relatively large wetland sites associated with streams within the Kumasi Metropolis were selected for this study. Sampling in each site was done using 1 m² quadrats laid at 10 m intervals from the water channel. All plant species in each quadrat were identified. The soil and hydrologic conditions of each site were studied. A total of 112 species were identified in the 10 study sites. The study sites were found to be significantly different from each other in environmental conditions and species distribution. Species in these study sites could, however, be grouped into clusters according to the presence or absence of surface water. A wetland in Kumasi was found to be typified by high percentage organic carbon with Thelypteris palustris as the dominant species.     

Conservation of arthropod diversity in montane wetlands: effect of altitude, habitat quality and habitat fragmentation on butterflies and grasshoppers

1. The patterns of arthropod diversity were investigated in 24 montane wetlands in Switzerland. These differed in altitude, management regime (cattle-grazing vs. mowing), vegetation structure (index combining vegetation height and density) and degree of habitat fragmentation.
2. The general arthropod diversity was determined by net sampling at 10 sampling points per site. The diversity of grasshoppers and butterflies was measured by counting species richness at the site and species density (species richness per unit area) on transects. The species richness of grasshoppers and butterflies was found to be more sensitive to the geographical attributes of the site whereas species density was more affected by the habitat quality.
3. Grasshopper diversity decreased within the observed altitudinal range (800–1400 m) and was higher at grazed sites, whereas butterfly diversity was higher at mown sites. Arthropod diversity but not abundance of arthropods was positively related to the vegetation structure.
4. The species richness of butterflies was negatively influenced by the degree of habitat fragmentation: both the size of habitat as well as the area of wetland habitats within 4 km were related positively to the number of specialist wetland butterflies.
5. Late mowing as well as low-density cattle-grazing are appropriate management actions to maintain arthropod diversity in montane wetlands. In order to establish site-specific management plans, the biology of the present target species as well as the historical context should be considered.
6. We suggest that the best protection for the species examined in this study would be a network of wetland sites managed using a variety of traditional, non-intensive methods. This can only be achieved by coordinated planning of conservation measures among sites.     

Demonstration of an integrated watershed assessment using a three-tiered assessment framework

Watersheds are useful templates for wetland protection and land use planning because they integrate cumulative effects that better inform site-specific management decisions. The goal of this study was to demonstrate application of a three-tiered assessment paradigm in the San Gabriel watershed (Los Angeles County, California) that incorporates monitoring at varying spatial scales and intensities. Data on wetland extent and distribution, habitat condition using rapid assessment, and intensive site monitoring were used to show how different levels of assessment can be used together to provide a deeper contextual understanding of overall wetland condition. Wetland sites in the less developed portions of the watershed were of higher overall condition compared to sites located in the more urbanized portions of the watershed. GIS analysis revealed that percent impervious surface is a useful landscape-scale indicator of riverine wetland condition. Furthermore, rapid assessment metrics were significantly correlated with stressors found at sites. Significant correlations also existed between riverine habitat condition, water chemistry, and benthic macroinvertebrate communities across streams in this watershed. This study highlights the following key concepts: (1) application of a multiple indicator approach at different spatial scales and sampling intensities promotes a better understanding of the causal relationships between land use, wetland condition, and anthropogenic stress, (2) a multi-tiered monitoring approach can provide a cost-effective means of integrating wetland status and trends assessments into routine watershed monitoring programs, and (3) a three tiered approach to monitoring provides wetland managers with an effective organizational tool that can be used to prioritize management activities.     

ChAnge, Stress, Sustainability and Aquatic ecosystem Resilience In North African wetland lakes during the 20th century: an introduction to integrated biodiversity studies within the CASSARINA Project

The CASSARINA Project is a co-ordinated joint study of recent environmental change in North African wetland lakes. Nine primary sites were selected for detailed study comprising three sites in each of Morocco, Tunisia and Egypt. Multi-disciplinary studies were undertaken by scientists from each of these countries working in co-operation with colleagues in the UK and Norway. The detailed results are presented in a consecutive suite of papers that describe both modern ecosystem attributes and the recent environmental histories of each site. This paper presents an overview of the aims, structure and initial results of the project.Modern site attributes measured were water quality and phytoplankton (Fathi et al., 2001), zooplankton (Ramdani et al., 2001b), fish (Kraïem et al., 2001) and littoral vegetation (Ramdani et al., 2001a). Baseline water quality data showed that one site (Megene Chitane) was acid with low salinity but the others had high alkalinities with varying degrees of brackishness. All the sites tended to be eutrophic and the phytoplankton was mainly dominated by green or blue-green algae. Where fish were present, growth rates were high with marginally highest rates in the Egyptian Delta lakes (Kraïem et al., 2001). Marginal vegetation surveys showed that emergent macrophytes were still extensive only in the Delta lakes (Ramdani et al., 2001a) where they form important refuges and restrict water pollution. In 1998, one Moroccan wetland lake (Merja Bokka) was drained completely for cultivation.Site specific environmental change records for the 20th century period were obtained using palaeolimnological techniques. Sediment core chronologies (Appleby et al., 2001) were based mainly on radio-isotopes (²¹⁰Pb and ¹³⁷Cs). Sedimentary remains of aquatic biota, diatoms, zooplankton, higher plants and benthic animals (Flower et al., 2001; Ramdani et al., 2001c; Birks et al., 2001a) and pollen (Peglar et al., 2001) were investigated (Birks et al., 2001b). Major differences in past species abundances were found and were interpreted in terms relevant to biodiversity and water quality/availability change. Metals and pesticide residues in sediment cores indicated that lake contamination was generally lower than in some European sites but some DDE profiles showed a close correspondence with known usage histories (Peters et al., 2001).Hydrological changes affecting water quality and availability mainly arose from land-use intensification during the 20th century and are shown to be the main driver of biodiversity disturbance at all nine CASSARINA sites. Summarizing floristic and faunistic changes using species richness values indicated that freshening of the Delta lakes during this century generally increased aquatic diversity. Species richness also increased during the final drainage of Bokka but tended to decline in acid Chitane. Modern sampling showed that phytoplankton and epiphytic diatom diversity was higher in the Delta lakes but this was not so for zooplankton. Each biological group reacted differently to environmental disturbance and this lack of concordance makes overall diversity changes difficult to predict.     

Phytoplankton community similarity in a semiarid floodplain under contrasting hydrological connectivity regimes

In this study we compare phytoplankton community similarity between sites in a semiarid floodplain wetland over a 6-year period with variable hydroperiod and connectivity regimes. Phytoplankton communities showed a relatively high site idiosyncrasy during most parts of the study; however, during situations of low connectivity when individual sites were highly fragmented, phytoplankton communities occasionally became more similar between sites. This suggests that mass effects related to dispersal-mediated processes could be important. Viewed from a metacommunity perspective, phytoplankton community assembly at the wetland scale involves complex hierarchical processes that can act independently at different spatial extents. The main conclusion of this study is that the well-known effects of environmental variability associated with hydrological disturbance alone may not be sufficient for explaining, and by extension predicting, community assembly in this wetland. Other processes, perhaps involving overland dispersal, may eventually add a new dimension to, and complicate our understanding of, community processes in fluctuating wetlands.