基于着生硅藻指数的梧桐河水生态健康评价

在黑龙江省梧桐河,调查了13个点位的着生硅藻群落结构和水环境特征,应用8种硅藻指数对该河流水生生态系统进行健康评价,并在此基础上应用主成分分析、相关分析、冗余分析、箱型图分析等统计分析方法研究了影响梧桐河着生藻类群落的主要环境因子和8种硅藻指数在梧桐河的适用情况。结果显示:梧桐河存在一定程度的环境污染,优势种以小型异极藻(Gomphonema parvulum)等耐污种为主。8个硅藻指数中,硅藻属指数(Generic Index of Diatom,GI)、澳大利亚河流硅藻生物评价指数(Diatom Index for Australian Rivers,DIAR;Diatom Species Index for Bioassessment of Australian Rivers,DSIAR)评价结果偏差较大,在梧桐河不适用;相似度指数(Jaccard Index,JI)与富营养化硅藻指数(Trophic Diatom Index,TDI)评价结果较为严格,评分明显偏低;硅藻污染耐受指数(Pollution Tolerance Index,PTI)、硅藻生物评价指数(Diatom Bioassessment Index,DBI)和生物硅藻指数(Biological Diatom Index,BDI)在梧桐河流域适用性最好。根据冗余分析(RDA),将梧桐河流域点位分为3组,第一组点位为中-重度污染,主要影响因子为流速和总磷;第二组点位为轻-中度污染,主要影响因子为磷酸盐、氨氮和溶解氧;第三组点位为轻污染-清洁,主要影响因子为p H和电导率。     

太子河着生藻类群落与氮、磷营养盐的定量关系研究

着生藻类是河流水生生物群落的重要组成部分,其与栖境水环境因子有着紧密的关联性。国内外关于着生藻类群落与栖息地环境因子关系的研究多是通过多元统计分析,评价影响着生藻类群落时空分布的环境要素,这种定性分析仅能判断环境驱动因子,而无法精确定量着生藻类群落与环境因子(如氮、磷)的响应关系。本研究以辽宁省太子河为范例,基于3次全流域的水生态调查所获得的141个站位的生态数据,运用临界指示物种分析法(TITAN)和加权平均回归分析(WA),定量评价着生藻类群落与河流水环境中氮、磷营养盐的定量响应关系(最适值和阈值)。结果表明,采用TITAN在太子河共确定了22种总氮(TN)指示物种,其中,13种为负响应物种,9种为正响应物种。TN负响应指示种中,普通等片藻(Diatoma vulgare)为出现频数较高的物种; TN正响应指示种中,小片菱形藻(Nitzschia frustulum)出现的频数最高。TITAN确定的太子河流域总磷(TP)指示物种为19种,其中,9种为负响应物种,10种为正响应物种。TP指示种中,负响应种近缘桥弯藻(Cymbella affinis)出现频数最高,TP指示种所对应的正响应突变点中,小片菱形藻和急尖舟形藻(Navicula cuspidata)出现频数最高。总体上看,太子河TN和TP对着生藻类最适值范围分别为0.025～0.47 mg·L~(-1)和0.65～12.14 mg·L~(-1),直链藻属(Melosira)和菱形藻属(Nitzschia)的种类,适宜栖息于TP较高的水环境中;异极藻属(Gomphonema)和桥弯藻属(Cymbella)适宜栖息于TP较低的水环境中;裸藻属(Euglena)和菱形藻属(Nitzschia)适宜栖息于TN较高的水环境中;而桥弯藻属和舟形藻属(Navicula)适宜栖息于TN较低的水环境中。通过定量分析水环境因子氮、磷对着生藻类群落的最适值和阈值,可以相对准确地评估着生藻类群落与河流营养盐含量的定量响应关系,对于在太子河开展对氮、磷等典型营养物的流域"污染物"排放的总量控制等流域生态管理决策和环境保护提供基础数据和科学依据。     

高原河流着生藻类群落沿海拔梯度的变化特征——以西藏黑曲、雪曲为例

海拔对生物群落的空间格局具有重要影响。探究生物群落随海拔变化规律不仅可以确定生物的地理分布范围,而且可为预测生物响应气候变化提供基础信息。然而,目前对于生物群落海拔格局的研究多集中于陆生大型生物,对水生微型生物的研究相对不足。基于西藏昌都市境内金沙江上游支流黑曲和雪曲着生藻类的调查数据,运用广义线性混合模型和分段结构方程模型探究着生藻类密度、生物量、物种丰富度、均匀度和样点对β多样性的贡献（Local contribution to beta diversity,LCBD）等生物群落指标的海拔格局及其驱动机制。结果表明：两条河流共鉴定出161个分类单元,分属硅藻门、蓝藻门和绿藻门。其中着生硅藻种类最多,占总分类单元数的78.9%,极小曲丝藻（Achnanthidium minutissimum,平均相对丰度：28.3%）、波状瑞氏藻（Reimeria sinuata,平均相对丰度：11.5%）、偏肿内丝藻（Encyonema ventricosum,平均相对丰度：9.3%）和细端菱形藻（Nitzschia dissipata,平均相对丰度：7.2%）为主要优势种。不同海拔的着生藻类群落...     

太子河流域本溪段水生生物的群落特征及其主要水质影响因子分析

着生藻类和底栖动物作为指示生物评价水环境状况已被广泛应用于各类水体状况的监测与评价中,以此对太子河流域的水生生物群落和水环境因子关系进行研究,对整个流域的水环境管理有着极其重要的作用。基于2009年7月丰水期和2010年1月平水期太子河流域本溪段着生藻类和底栖动物的调查数据,通过因子分析和典范对应分析,探讨水生生物群落结构与水质污染因子的空间分布特征。结果表明：太子河本溪段着生藻类为4门22科29属,以硅藻门为优势门类;底栖动物3门10科13属,以环节动物门为优势门类。NH3-N是影响水生生物空间格局的主要水质污染因子,水量是影响太子河流域水生生物群落结构的重要环境因子。     

适于北江水质生物评价的附着硅藻指数研究

采用主成分、层次聚类、箱型图和双向指示种分析(TWINSPAN)等方法,研究了15项附着硅藻指数在北江流域的适用性。在北江流域25个监测点中,共鉴定出附着硅藻2目6科30属98个种和亚种,相对丰度为5%以上的硅藻属有曲壳藻属(Achnanthes)、菱形藻属(Nitzschia)、舟形藻属(Navicula)和直链藻属(Melosira),分别为34.4%、18.1%、8.6%和7.3%。相对丰度为5%以上的硅藻种有极小曲壳藻(Achnanthes minutissima),极小曲丝藻(Achnanthidium minutissimum),克劳斯菱形藻(Nitzschia clausii)和可变直链藻(Melosira varians)。附着硅藻指数间,罗特营养指数(Rott Trophic Index,ROTT)和洛博指数(Lobo Index,LOBO)与其他指数相关性较弱,硅藻生物指数(Biological Diatom Index,IBD)和富营养污染硅藻指数(Diatom Eutrophication Pollution Index,EPI-D)呈极显著相关(r=0.915,P0.01)。硅藻指数与水质指标的相关性分析表明,斯雷德切克指数(Sláde?ek Index,SLA)和LOBO与电导率(Cond)、溶解氧(DO)和总磷(TP)等10项水质指标间均无相关性,其他指数与某个或某几个水质指标有一定的相关性。对10项水质指标加权后进行层次聚类,结果表明阿图瓦-皮卡第硅藻指数(Artois-Picardy Diatom Index,IDAP)、特定污染敏感指数(Specific Polluosensitivity Index,IPS)、硅藻属指数(Generic Diatom Index,IDG)和IBD与水质分类结果较一致。利用TWINSPAN对样点和硅藻群落进行分类后绘制箱型图,结果表明,IBD对样点水质的变化最为敏感。结果表明,IBD是适合北江流域水质评价的硅藻指数。     

滦河干流浮游生物群落结构特征及水质环境评价

为研究滦河干流浮游生物群落和评价水质状况,对滦河干流河源段、上游段、中游段和下游河口段在两水期的浮游生物群落结构和多样性指数以及水体理化指标进行分析,计算综合污染指数与生物多样性指数综合评价滦河水质,最后利用统计方法研究水体理化指标与浮游生物群落之间关系. 结果表明：滦河干流浮游植物以绿藻和硅藻为主,除下游河口段外,其他河段在丰水期的平均密度超过枯水期. 浮游动物在丰、枯水期都是以原生动物为主,丰水期在中、下游段平均密度较高,超过1.6 × 10⁶个/L,枯水期在上、中和下游段的浮游动物平均密度接近,且丰水期的平均密度高于枯水期. 两类浮游生物多样性指数显示滦河干流水质受到中度污染. 滦河水体中溶解氧(DO)、五日生化需氧量(BOD₅)、氨氮(NH₃-N)和总磷(TP)浓度均达到了国家地表水体Ⅳ类标准;化学需氧量(COD)浓度在丰水期的中游段和枯水期的下游河口段超过了地表水Ⅳ类标准;水体中总氮(TN)浓度普遍超过Ⅳ类标准,在两个水期中游段和下游河口段均超过了Ⅴ类标准. Pearson相关性分析和冗余分析(RDA)表明滦...     

辽宁省主要河流底栖动物群落结构及水质评价研究

利用2021年辽宁省主要河流47个点位的底栖动物监测数据分析其群落结构的空间分布、群落结构与环境因子的关系、不同评价指数以及它们与环境因子的相关关系,为辽宁省水生态监测与评价方法的优化提供参考。结果表明,（1）辽宁省主要河流共检出底栖动物4门8纲22目57科98属120种,以水生昆虫为主,其种类数和生物密度均占据优势地位。上游点位以水生昆虫和甲壳动物为优势类群,33%的上游点位以蜉蝣目、襀翅目和毛翅目（EPT）为优势类群;中游点位以甲壳动物为优势类群,软体动物和环节动物明显增多;下游点位以甲壳动物和环节动物为优势类群,水生昆虫和软体动物的相对密度明显减少;从上游到下游整体呈现水生昆虫相对密度不断减少、环节动物相对密度不断增多、软体动物相对密度先增多后减少、甲壳动物基本稳定的趋势。（2）RDA分析结果表明,氟化物、化学需氧量、生化需氧量和总磷与底栖动物群落数显著负相关,溶解氧和锌与底栖动物群落数显著正相关。溶解氧与总分类单元数相关性最高（F=2.37,P=0.02）,锌与环节动物相关性最高（F=3.30,P=0.01）。（3）构建了涵盖总分类单元数、EPT分类单元数、耐污种分类单元数和香...     

安徽省石塘湖过去百余年湖水总磷浓度的定量重建

湖水总磷浓度对湖泊富营养化有很好的预警作用,历史湖水总磷浓度的定量重建能揭示湖泊营养演化历史.依据安徽省石塘湖沉积物钻孔的高分辨率硅藻研究结果,结合长江中下游湖泊硅藻-总磷转换函数模型,定量重建了其过去百余年来硅藻组合演替与历史湖水总磷浓度的变化过程.结果表明:石塘湖硅藻经历了从颗粒直链藻(Aulacoseira granulate)优势组合(1867-1981年)向富营养属种高山直链藻(Aulacoseira alpigae)优势组合(1981年以来)的变化.1981年以前,水体ρ(总磷)为50～60μg.L-1,湖泊一直维持在中等营养水平;1981年之后水体ρ(总磷)呈现明显升高趋势(＞100 μg·L-l),硅藻组合以高山直链藻占绝对优势,同时伴有喜好富营养环境的属种如极微小环藻(Cyclotella atomus)、梅尼小环藻(Cyclotella meneghiniana)、谷皮菱形藻(Nitzschia palea)和汉斯冠盘藻(Stephanodiscus hantzschii)等的增加,标志着湖泊富营养化的发生.20世纪80年代以来,农业及城市生活污水排放、农业化学肥料的大量使用以及过度养殖是硅藻种群转变和富营养化发生的主要根源.增温在一定程度上也影响着硅藻群落变化和富营养化的加重.根据重建的硅藻-水体总磷浓度结果,提出石塘湖治理的营养物基准水体ρ(总磷)为60 μg·L-1,为该湖整治和修复方案的制定提供可参考的目标,也为当地大量类似湖泊的治理提供重要参考.     

一座河道型水库浮游植物与附着硅藻群落对环境变化的响应比较

浮游植物是湖泊或湖泊型水库的常规调查要素,而附着硅藻则是河流监测常用的方法,河道型水库监测中是采用浮游植物还是附着硅藻依赖于浮游植物与附着硅藻群落对环境要素的响应特征.在热带地区一座典型河道型水库中采集浮游植物的同时,设置人工基质采集附着硅藻;鉴定出的浮游植物和附着硅藻分别为131种和138种;浮游植物和浮游硅藻群落变化主要体现在优势种的演替上,空间差异小;附着硅藻群落的变化则体现在种类组成和优势种演替两个方面,群落的空间差异较大.多元回归分析和冗余分析表明影响浮游植物和附着硅藻群落的环境因子不同,温度是浮游植物、浮游硅藻和附着硅藻的关键解释变量(P 0.01),溶解氧和硝氮也是附着硅藻的解释变量(P 0.05);环境因子对附着硅藻群落变化具有更高解释度(R2=0.27).因此,对于河道型水库而言,附着硅藻群落对环境变化的响应更灵敏,与浮游植物反映的环境信息有一定的差异,结合附着硅藻和浮游植物群落的变化能更好地反映水环境的变化.     

基于SOM的乌梁素海浮游植物群落结构研究

浮游植物能够产生氧气并为其他生物提供食物,维持其他生命的生存,进而保证水生态系统的平衡,在水生态系统中具有重大意义。为研究寒旱区乌梁素海浮游植物群落结构特征及其与环境因子的关系,运用自组织特征映射网络(SOM),并结合完全连接法,将乌梁素海浮游植物分为8个群落类型,分别为群落Ⅰ(蓝藻Cyanobacteria-绿藻Chlorophyta-硅藻型Bacillariophyta)、群落Ⅱ(蓝藻型)、群落Ⅲ(硅藻型)、群落Ⅳ(硅藻-绿藻型)、群落Ⅴ(硅藻-蓝藻型)、群落Ⅵ(绿藻-硅藻型)、群落Ⅶ(绿藻-硅藻型)、群落Ⅷ(绿藻-硅藻-蓝藻型)。分类结果显示,各群落结构的物种组成呈现明显特征,优势种的分布具有显著的规律性。利用Kruskal-Wallis方法分析群落类型间环境因子的差异性,结果显示,各群落类型的水深、水温、p H、总磷具有极显著性差异(P0.01),而透明度、总氮、电导率显著性差异不显著(P0.05)。通过对群落类型与其环境因子的分析,结合国内外浮游植物功能群及其生境的研究,发现优势属小环藻(Cyclotella)、舟形藻(Navicula)、衣藻(Chlamydomonas)适应低温、浅水及高营养盐的水域环境;栅藻(Scenedesmus)、绿球藻(Chlorococcum)、针杆藻(Synedra)适应总氮、总磷浓度均较高的水域环境;而平裂藻(Merismopedia)、色球藻(Chroococcus)适应高温、深水、总磷浓度较低的水域环境。温度是乌梁素海浮游植物群落结构组成的决定因子,而氮磷比可能是影响群落组成的又一重要环境因子。     

Use of epilithic diatoms to evaluate water quality in the Karasu River of Turkey

Epilithic diatom assemblages were used to evaluate water quality in the Karasu River basin (Turkey), which was polluted by industrial, agricultural and urban wastes. A total of 73 diatom taxa belonging to 22 genera were found from all seven sampling stations located in the River basin. The most pollution tolerant species Gomphonema parvulum, Nitzchia palea, Navicula cryptocephala were found in high densities at the polluted stations. Organic load (COD), biological oxygen demand in 5 days (BOD5) and concentrations of nutrients NO3(-)-N, NO2(-)-N, NH4(+)-N and PO4(3-)-P) were correlated negatively with dissolved oxygen. Except for generic index of diatoms (GI), all diatom indices were correlated significantly with COD, BOD5 dissolved oxygen and concentrations of nutrients. Saprobity index (SI), trophic diatom index (TDI) and the percentage pollution tolerant valves values suggested that the stations III, IV located in the River basin were eutrophicated and organically polluted.     

漓江桂林市区段夏季浮游植物群落特征与水质评价

浮游植物是水生态系统的重要组成部分,其群落结构变化与水体环境条件密切相关,能直接影响水生态系统的功能,是水环境质量优劣的重要指示因子之一。为揭示漓江流域浮游植物群落结构特征及其与水质的相互关系,2012年8月对漓江桂林市区段干流（桂林赵家桥村至桂林王家村）的理化指标及浮游植物的群落组成分布进行了分析研究,并结合水体理化指标和生物指数对漓江水质进行了评价。结果表明,漓江水体高锰酸盐指数、总氮、总磷、氨氮的变化范围依次为1.80-6.20、1.12-2.68、0.022-0.282、0.34-1.73 mg·L-1,其含量在上游变化平稳,到三条支流汇入处大幅增高,最高值均出现在南溪河入口处。共调查到浮游植物7门60属128种,其中硅藻50种（占种类组成的39.06%）,绿藻52种（占40.63%）,蓝藻16种（占12.50%）,裸藻7种（占5.47%）,黄藻、金藻和甲藻各1种（分别占0.78%）。优势种依次为冠盘藻（S. tephanodiscus）、蛋白核小球藻（C. pyrenoidosa）、喙头舟形藻（N.rhynchocephala）、短小舟形藻（N.exigua）、广缘小环藻（C.Bodanica）、四尾栅藻（S.quadricanda）和肘状针杆藻（S. ulna）。浮游植物密度为10.3×10^4-1047.0×10^4ind.·L^-1,平均密度为474.7×10^4 ind.·L^-1,其中密度最小的是赵家桥村,密度最大的是南溪河入口;种类上绿藻门占据多数,密度和优势种分布上以硅藻居多,总体上属于硅藻-绿藻型水体。浮游植物多样性指数Shannon-Wiener指数（H）在1.60-4.27之间,Simpson指数（D）在2.24-12.74之间,水质总体上为清洁-轻度污染。Margalef指数（d）在1.85-4.23之间,Pielou指数（J）在0.40-0.83之间,指数值总体较高,漓江水体中浮游植物群落结构比较稳定,受外界环境的影响较小。漓江干流水质总体上属于Ⅱ-Ⅲ类水体,在支流汇入处理化指标浓度增加,浮游植物多样性指     

Responses of phytoplankton and periphytic diatoms to environmental factors in a tropical riverine reservoir北大核心CSCD

Riverine reservoirs have a short water retention time, which is ecologically more similar to that of rivers. Generally, phytoplankton-based approaches are used for lakes and periphytic diatom-based approach for rivers. To understand the differences in the responses of phytoplankton and periphytic diatoms to environmental variables for riverine reservoirs, we collected periphytic diatom samples on artificial substrata as well as phytoplankton samples from a tropical reservoir with a resident time less than 10 days. Our results showed that 131 phytoplankton species and 138 periphytic diatoms were detected; the variation of phytoplankton community was mainly reflected by the dominant species with a strong response to the environmental variables at a time scale, whereas the variation of periphytic diatom community was noted in both the species composition and the dominant species, with a strong response at spatial-temporal scales. The multivariate regression analysis and redundancy analysis showed that environmental factors have higher explanations for the variance of the periphytic diatom community (R2 = 0.27). Temperature was the key explanatory variable for phytoplankton, planktonic diatoms and periphytic diatoms (P < 0.01). However, dissolved oxygen and nitrate were also detected as significant explanatory factors associated with periphytic diatom community (P < 0.01). Thus, the periphytic diatoms were concluded to be more sensitive to environmental change and were associated with more environmental variables than phytoplankton. Periphytic diatoms appear to provide more ecological information than phytoplankton for riverine reservoirs. © 2018 Science Press. All rights reserved.     

Combination of two indication systems in pre-alpine lakes — diatom index and macrophyte index

Since the climax of eutrophication in the early 1980s mainly greater lakes have been investigated and monitored in terms of their nutrient charge. In the future there will still be a need to develop guidelines for monitoring the trophic status of smaller lakes. Four small lakes were investigated by the author in the years 1996 and 1997. In order to define the nutrient charge of those lakes more precisely, special emphasis has been put upon the two criteria diatoms and macrophytes. Eventually an evaluation of the lakes' catchment areas will also be an important component of these studies. Benthic diatoms are the main part of periphyton. As unicellular fast reproducing organisms they are excellent indicators for trophic situations in lakes. The diatom index denotes the trophic status of the littoral zone during the last few weeks before sampling. The macrophytes, however, reflect the nutrient charge over a longer period, i.e. several years. The macrophyte index is based on the fact that some species are most prevalent at certain nutrient loads. The effort to combine these two indication systems carries a high resolution of spatial nutrient changes as well as in temporally changes.     

乐安江重金属污染对浮游植物群落结构的影响

１９９３年和１９９４年对乐安江６个采样站浮游植物的两次调查结果表明，藻类的群落结构因不同河段水质状况不同而不同：未受矿山废水污染的上游海口站，藻类多样性指数较高，密度较低，优势种多为清洁神和耐中污的种类，水质较好；接纳大量矿山及采矿化工废水和生活污水的沽口站，藻类受到明显抑制，多样性指数极低，耐污种占绝对优势，水质极差；随流程和净化时间的延长，下游各站藻类的种类、数量、多样性指数、种类数比均不断上升，优势比不断下降，体现出明显的水质净化趋势．乐安江水体Ｃｕ２＋浓度与藻类的种类、数量、种类多样性指数、种类数比呈负相关的关系，Ｃｕ２＋浓度与藻类的优势比呈正相关关系；ｐＨ值与上述指标关系正好与Ｃｕ２＋所呈现的关系相反．藻类群落结构在春季丰水期与秋季枯水期的变化表明，春季乐安江水质好于秋季．     

Longitudinal and seasonal variations of epilimnetic silica in a morphologically complex reservoir and the significance of flow regime and internal processes to their dynamics

Spatial and temporal dynamics of silica (SiO2) were examined in a morphologically complex reservoir, based on data collected between high-flow year and low-flow year. SiO2 averaged 3.4 mg/L and varied from 0.1 to 9.7 mg/L depending on the year and the location. The paired sample test of SiO2 showed that in mainstem sites, SiO2 was significantly (t = 3.577, p < 0.01) greater in the high-flow year than in the low-flow year, and this pattern was similar to that of embayment sites, indicating an importance of flow regime on the silica loading. During the high-flow year, SiO2 was significantly (t = 3.577, p < 0.01) greater in the mainstems than in the embayments, but during the low-flow year, there was no statistical difference between the two reaches. SiO2 showed a distinct longitudinal decline from the headwaters to the dam in the high-flow year, and it was modified by the plunging of metalimnetic density current in the mid-lake reach. Seasonal fluctuation of SiO2 was influenced by internal nutrient cycling and diatom populations. Dominant phytoplankton abundance had an inverse relation between the two algal populations of bluegreens and diatoms during August-December of the low-flow year. In other words, bluegreen algae dominated at the low SiO2 (< 2.5 mg/L) during the summer period of the low-flow year, whereas diatoms dominated with the increase of SiO2 in fall overturn. Overall results suggest that increase of silica in this system is primarily regulated by interannual flow regime, but the internal loading during fall overturn and biological up-take by seasonal growth of diatom community were also considered as an important process controlling the input of silica.     

Quantitative evidence concerning the stabilization of sediments by marine benthic diatoms

Six species of benthic diatoms and a natural benthic diatom community were cultured in flasks on a variety of sediments. Diatom species which secreted large quantities of mucilage were effective sediment stabilizers. These mucilage-secreting species significantly reduced resuspension and retarded laminar flow of the sediments when the culture flasks were agitated. Diatom species which secreted little or no mucilage were not effective sediment stabilizers. These non-mucilage-secreting species did not significantly effect resuspension or laminar flow of the sediments when the culture flasks were agitated. A sediment stabilizing mechanism based on the secretion of mucilage by pennate benthic diatoms is proposed. The effect such a process may have on distributional patterns of benthic invertebrates in areas where extensive diatom or other microalgal films occur is discussed.This work was supported by the Belle W. Baruch Foundation, and is Contribution No. 68 of the Belle W. Baruch Institute for Marine Biology and Coastal Research.     

常德柳叶湖及其连通水体浮游甲壳动物群落结构与水环境特征

为研究连通水体中浮游甲壳动物的群落结构,于2018年6月至2019年3月,对常德市柳叶湖、穿紫河和沅江常德市区河段组成的连通水体浮游甲壳动物和理化环境进行每季度一次的采样调查.共发现浮游甲壳动物27种,其中桡足类10种,枝角类17种.连通水体浮游甲壳动物丰度变化范围为1-132 ind./L,沅江常德市区河段浮游甲壳动...     

Phytoplankton in the Weddell Sea,Antarctica: composition,abundance and distribution in water-column assemblages of the marginal ice-edge zone during austral autumn

At the compacted, north-south line of the ice edge, phytoplankton were sampled during early austral autumn of 1986 in the northwestern Weddell Sea. Cells from discrete water bottle samples from 12 stations on two east-west transects were counted to gain quantitative information on the composition, abundance, distribution, and condition of the phytoplankton in water-column assemblages. Over 70 species were found. The highest numbers of total cells (integrated through the top 150 m) were found in open water, well-separated from and to the east of the ice edge on the southern transect, with 6.01×10¹⁰ cells m^-2. The relative abundance of diatoms was low at ice-convered stations (< 35% of the total phytoplankton in preserved samples) and high at open-water stations (> 80%); however, the relative abundance of the prymnesiophyte Phaeocystis sp. was high at ice-covered stations (> 60%) and low at open-water stations (< 16%), with lower absolute abundances than during a previous austral-spring phytoplankton increase. In the open ocean, the dominants were the pennate diatoms Fragilariopsis cylindrus, Pseudonitzschia prolongatoides, F. curta, and a small form of the centric diatom Chaetoceros dichaeta in chains. Although the three pennate diatoms were frequently dominant in number, they represented less biomass than C. dichaeta in open waters. Mean phytoplankton abundance was low (0.2×10⁶ cells l^-1) but, overall, the diatom cell density (0.14×10⁶ cells l^-1) was similar to that found previously during a northward transect from ice-covered to ice-free water at the Weddell-Scotia Sea ice edge (spring 1983). The phytoplankton spatial patterns in the two autumn transects differed, with the more southerly transect exhibiting a higher abundance of diatoms and dinoflagellates. The ratio of full to empty diatoms was higher on the southern transect, indicating a healthy population, while lower ratios of full/empty frustules on the northern transect suggested a generally declining population. However, Phaeocystis sp. was more abundant on the northern transect.