Quantifying Ecological Stability: From Community to the Lake Ecosystem

We performed a methodological study aimed at extending our previously developed approach to quantify the ecological stability of biotic communities and an entire ecosystem, using Lake Kinneret as a case study. The ecological stability of the biotic communities (phytoplankton and zooplankton) of Lake Kinneret was estimated using two different aggregating schemes. The first scheme used the combined stability index, based on the combined indices of the individual phytoplankton (SI[Comb]_P) and zooplankton (SI[Comb]_Z) taxonomic groups. The total community stability index was calculated based on the total abundances of these communities. The stability of the entire ecosystem was estimated for two sets of ecosystem state variables, a lake “trophic state” set and a “water quality” set, which provided considerably different estimates of the lake ecosystem stability. Good agreement between the results of this study and qualitative estimates of Lake Kinneret stability validates the suitability of this approach to estimate the stability of different ecological units.     

The dynamics of freshwater phytoplankton stability in the Naroch Lakes (Belarus)

The phytoplankton community of the Belarus Lakes Naroch, Myastro and Batorino, which have a Trophic State Index of 42.3, 60.7 and 66.8, respectively, underwent drastic changes to their structure during the period between 1968 and 2012. Thanks to an extensive monitoring program, these changes were well-documented and were qualitatively interpreted as signs of the community destabilization. The main objective of this study was the quantification of the ecological stability of the phytoplankton community in the Naroch Lakes. The approach to the quantification of ecological stability was based on defining the stability index as an inverse of the Euclidean Distance between the current and the reference states of the algal community (EuD-approach). The stability of the phytoplankton community was characterized by two indices: a “combined” index (SI[Comb]), and a “total community” index (SI[TotB]). SI[Comb] was calculated based on the individual taxonomic group biomasses and thus characterizes the stability of a community structure. SI[TotB] was calculated based on the values of the total algal biomass. Analyses of the results of this study extended the plausibility of the EuD-approach for the quantification of lake phytoplankton stability and allowed us to identify the dynamics of the stability of the Naroch Lakes phytoplankton. For the Naroch Lakes, we observed relatively larger SI[TotB] values in comparison with the SI[Comb] values. The results enabled us to examine the relationship between the lake trophic status and the stability of the phytoplankton community.     

The structure and dynamics of the phytoplankton assemblages in Lake Kinneret, Israel

The phytoplankton of Lake Kinneret, a warm monomictic lake,is dominated by a Pyrrhophyta-Chlorophyta assemblage. Four stagesof succession of planktonic algae occur in the lake, startingwith thermal and chemical destratification and ending with stratification. The index of diversity of the phytoplankton communities is highduring the destratification and mixed periods. The index reachesminimal values during late summer, when the ecosystem is subjectto strong physical, chemical and biological stresses. The diversityin Lake Kinneret increases with the increase in nutrients andnot with the increase in temperature. During most of the year, the nanoplanktonic forms are in greaternumbers than the netplankton species. This fact is correlatedwith the amounts of available nutrients in the lake. The annual averages of the wet autotrophic biomass in Lake Kinneretare very high in comparison with other warm lakes. The contributionof the nanoplanktonic species to the total algal biomass isvery small during the Peridinium bloom, but represents approximatelyhalf of the total algal biomass during the rest of the year. The concentration of nutrients in the water, together with theadverse competitive effect of Peridinium on other algae, areto a large extent responsible for the composition, successionand abundance of the phytoplankton assemblages in Lake Kinneret.     

Seasonal Rotifer Dynamics in the Long-term (1969–2002) Record from Lake Kinneret (Israel)

Long-term (1969–2002) data record of biomass distribution of rotifers in Lake Kinneret is combined with previously published information on their metabolic activity and newly calculated population dynamics parameters to synthesize a model of their seasonal dynamics in Lake Kinneret. Nineteen rotifer species were recorded in routine samples collected in Lake Kinneret (Israel) in 7 offshore (deeper than 5 m), stations, at 12 discrete depths during 1969–2002. Organisms were sorted and counted (including external egg carrying females), biomass was measured and calculated for the entire lake stock (g_w.w m⁻²; mg l⁻¹). Rates of grazing, respiration and production were measured experimentally at three different temperature ranges. Results were extrapolated to the lake community for months with similar temperatures. Rotifera comprised 7% of total zooplankton biomass in Lake Kinneret whilst Cladocera and Copepoda 58 and 35% respectively. Rotifers were found to be more abundant during December–June and decline in summer months. Monthly (1969–2001) means indicated total grazing capacity of rotifers as 11%, respiration as 9% and production as 3.7% of the total zooplankton metabolic activity. Positive relations were indicated between rotifer and small bodied cladoceran numerical concentrations. Population growth models suggest that rotifers are not food limited in Lake Kinneret but that fish predation plays an important role in regulating abundance in spring-summer and fall.     

Physico-chemical limnology and plankton dynamics of Mazvikadei,a tropical reservoir in Zimbabwe

The limnology of Mazvikadei Reservoir, northern Zimbabwe, was investigated in 2015 to determine whether it had changed since filling in 1990. The reservoir is characterised by low algal biomass, low nutrients (i.e. N and P) and high water clarity/transparency. Fifty-four species of phytoplankton were recorded, comprising Bacillariophyta, Chlorophyta, Cyanophyta, Desmids, Dinophyta and Euglenophyta. Chlorophyta numerically dominated in the hot dry season, whereas Bacillariophyta, Desmids, Dinophyta and Euglenophyta dominated in the cool dry season. Species richness was highest at the onset of the cool dry season, in response to high nutrient concentrations. Phytoplankton abundance and composition were significantly correlated with temperature, nitrates and total nitrogen. Nineteen zooplankton species were recorded, including Copepoda, Cladocera and Rotifera. Overall, Cladocera were numerically dominant and became most abundant during the cool dry season. Rotifers and copepods dominated during the hot dry season. The zooplankton abundance was correlated with reactive phosphorus and phytoplankton abundance. The trophic state of Mazvikadei Reservoir seems to have stabilised and to have assumed the physico-chemical characteristics and plankton community typical of an oligotrophic lake.     

Changes to the phytoplankton assemblage of Lake Kinneret after decades of a predictable, repetitive pattern

1. Phytoplankton abundance and species composition in Lake Kinneret, Israel, have been monitored at weekly or fortnightly intervals since 1969. This paper summarises the resulting 34‐year phytoplankton record with a focus on the last 13 years of new data, and reassesses an earlier conclusion that the lake phytoplankton shows remarkable stability despite a wide range of external pressures. 2. The Kinneret phytoplankton record can be split into two major periods. The first, from 1969 till 1993, was a period of distinct stability expressed by a typical annual pattern revolving around a spring bloom of the dinoflagellate Peridinium gatunense that repeated each year. The second period, starting around 1994 and ongoing, is characterised by the loss of the previously predictable annual pattern, with both ‘bloom years’ and ‘no‐bloom years’. 3. In the second period, deviations from the previous annual pattern include: the absence of the prevailing spring P. gatunense blooms in some years and increased variability in the magnitude of the bloom in others; intensification of winter Aulacoseira granulata blooms; higher summer phytoplankton biomass with replacement of mostly nanoplanktonic, palatable forms by less palatable forms; new appearance and establishment of toxin‐producing, nitrogen fixing cyanobacteria in summer; increase in the absolute biomass and percentage contribution of cyanobacteria to total biomass; and fungal epidemics attacking P. gatunense. 4. The 34‐year record serves to validate Schindler's (1987) assessment that phytoplankton species composition will respond to increased anthropogenic stress before bulk ecosystem parameters.     

鄱阳湖不同水文期浮游生物群落结构特征和影响因素及水质评价

为阐明鄱阳湖不同水文期浮游生物群落结构特征及其影响因素,研究于2017年8月(丰水期)和12月(枯水期)在鄱阳湖湖区典型水域设置5个采样点进行浮游生物采样调查。研究期间共鉴定浮游植物8门75属186种,丰水期与枯水期均以硅藻门和绿藻门为主。共鉴定浮游动物4类76种,丰水期与枯水期均以原生动物和轮虫为主。方差分析显示:浮游植物密度与生物量在不同水文期之间的差异均为极显著(P<0.01),浮游动物丰水期密度高于枯水期,但无显著差异(P>0.05),浮游动物生物量(P<0.05)在不同水文期差异显著。冗余分析(RDA)显示:丰水期透明度和浮游生物呈显著负相关关系,电导率和浮游生物呈显著正相关。透明度、电导率与营养盐是影响丰水期浮游生物群落结构的主要环境因素,枯水期水温和溶解氧是驱动鄱阳湖浮游生物群落生态分布的主要环境因素。基于Shannon-Wiener(H′)、Margalef(d)和Pielou(J)等生物多样性指数的水质评价结果表明:鄱阳湖研究区域水质状态处于寡污-中污之间。研究揭示了2个水文期对通江湖泊浮游生物的影响:季节变化不改变湖泊浮游生物的物种组成及优势种,但...     

淀山湖浮游植物群落特征及其演替规律

为探明淀山湖浮游植物群落结构演变与富营养化之间的关系,于2004-2006年对上海市最大天然淡水湖泊淀山湖的浮游植物进行逐月采样调查,分析其群落结构特征.共采集到淀山湖浮游植物84属205种,主要由绿藻(种类数占50%)、硅藻(20%)、蓝藻(13%)、裸藻(13%)等组成.相邻两月之间种类相似性系数呈现冬春季高、夏秋季低的趋势:优势种为银灰平裂藻(Merismopedia glauca)、小席藻(Phormidium tenus)、铜绿微囊藻(Microcystis aeruginosa)、具缘微囊藻(M.marginata)、湖泊鞘丝藻(Lyngbya limnetica)、微小色球藻(Chroococcus minutus),颗粒直链藻最窄变种(Melosira granulata var.angustissima )、啮蚀隐藻(Cryptomonas erosa)、小球藻(Chlorella vulgate)和四尾栅藻(Scenedesmus quadricauda)等.浮游植物群落细胞数量主要由蓝藻(42.73%)、绿藻(37.75%)、硅藻(12.67%)和隐藻(6.06%)组成;生物量主要由硅藻(36.75%)、蓝藻(16.78%)、绿藻(16.36%)和隐藻03.53%)等组成.淀山湖浮游植物群落结构季节演替模式不同于PEG(Plankton Ecology Group)模型,其中蓝藻从春末开始大量出现,夏季大量繁殖,一直延续到秋初.综合文献资料看出,淀山湖浮游植物群落已从1959年的硅藻一金藻型、1987-1988年的隐藻-硅藻型演变为2004-2006年的蓝藻-绿藻型;数量由1959年的103 ind./L上升至2004-2006年的1.11×107 cells/L.演替的总体趋势表现为:贫中营养型的金藻、甲藻比例下降,富营养型的蓝藻、隐藻和微型绿藻增加.浮游植物数量和群落结构的演变指示了淀山湖水体的富营养化进程.     

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。     

Cyanobacteria and cyanotoxins in the source water from Lake Chivero,Harare, Zimbabwe,and the presence of cyanotoxins in drinking water

The phytoplankton community and cyanotoxins in Lake Chivero (formerly Lake McIlwaine) and the presence of cyanotoxins in treated drinking water were investigated between 2003 and 2004. A typical seasonal succession of Cyanobacteria species occurred from January to April, Bacillariophyta from May to July, and Cryptophyta and Chlorophyta from August to December. Microcystis aeruginosa and M. wesenbergii, known producers of the toxin microcystin, and the non-toxic cyanobacterium M. novacekii dominated during summer. The highest concentrations of microcystins and lipopolysaccharide endotoxins occurred when cyanobacterial biomass was highest. Lipopolysaccharide endotoxin concentrations in the lake ranged between 8 and 3 200 Endotoxin Units (EU) ml^?1. Microcystin concentrations in treated water were below the recommended safe limit for drinking water. Lipopolysaccharide endotoxin concentrations in treated water ranged from 0.15 to 11 EU ml^?1. The phytoplankton community comprised non-microcystin-producing species for the greater part of the study period.     

陶粒浮床对草鱼养殖池塘水质和浮游植物的影响

为了探讨陶粒浮床对草鱼养殖池塘浮游植物群落结构的影响, 将6个池塘随机分为两组, 分别为浮床组和对照组, 2013年510月对养殖池塘的藻类群落结构和水质因子进行定期采样分析。结果表明: 浮床组池塘水体透明度显著高于对照组(P0.05), 养殖后期, 浮床组主要营养盐指标显著低于对照组(P0.05), 微生物总数显著高于对照组(P0.05)。水质理化指标波动范围小, 系统稳定性较强。试验期间共检出浮游藻类8门111属179种, 其中绿藻93种, 蓝藻25种, 硅藻23种, 裸藻17种, 黄藻6种, 甲藻5种, 金藻5种, 隐藻5种。在养殖中后期, 陶粒浮床对藻类的种类组成有显著影响, 藻类种数明显高于对照组, 浮床组和对照组浮游植物数量范围分别为101. 95106614.95 106 ind./L和151.43106612.60 106 ind./L, 生物量范围分别为90.79402.85 mg/L和116.33831.55 mg/L, 到养殖中后期(8月份以后), 对照组浮游植物的生物量显著高于浮床组(P0.05)。绿藻门和蓝藻门的贡献率一直占总密度的90%以上。浮游植物群落呈明显的季节变化, 绿藻门呈先降低后升高的趋势, 蓝藻门相反。试验初期浮游植物的优势种为栅藻; 在试验开始30d后, 浮床组栅藻继续保持优势藻的地位, 对照组的优势种则变为平裂藻和微囊藻; 78月份, 浮床组和对照组的优势种均为蓝藻门的平裂藻, 9月份后优势藻逐渐由栅藻和绿球藻取代。浮床组和对照组藻类多样性指数无显著差异, 物种丰富度均呈逐渐下降的趋势, 范围为3.165.59, Shannon指数和Simpson指数均呈先降低后升高的趋势, 范围分别为1.502.46和0.540.87。陶粒浮床对改善池塘水质、丰富藻类种类组成、降低过高生物量和微囊藻爆发的风险有一定作用。       

仙女湖及入湖河流浮游植物功能类群与环境因子的相互关系

文章分析了仙女湖及入湖河流浮游植物群落结构和功能类群的时空分布特征, 探讨了影响其时空分布规律的关键环境因子。调查期间共鉴定表层水体中浮游植物82种(属), 包括蓝藻15种(属), 绿藻33种(属), 硅藻23种(属), 甲藻3种(属), 裸藻5种(属), 隐藻2种(属), 金藻1种(属)。各季节平均密度和生物量分别在7.95×106—2.19×109 cells/L和10.52—792.91 mg/L变化。群落功能类群的结果表明, 冬、春河流生境中具硅质结构的无鞭毛个体浮游植物(硅藻门)占据主导地位(Ⅵ功能群), 而湖区生境中具鞭毛、中等到大型的单细胞或群体浮游植物(如隐藻和甲藻)具有明显优势(Ⅴ功能群); 而夏秋季节不同生境中虽然Ⅵ型浮游植物数量仍然相对较高, 但是具伪空胞的、较大表面积/体积比的丝状个体浮游植物(Ⅲ型)以及具胶质鞘、小的表面积/体积比的群体类的浮游植物(如蓝藻, Ⅶ功能群)在某些河流和湖泊生境中的比重有显著增长。功能类群与环境因子的相关分析表明: 冬、春季Ⅴ与Ⅵ功能群浮游植物生物量主要受到总氮和总磷水平影响; 而夏、秋季节Ⅲ与Ⅶ功能群浮游植物受到水温、浊度、总氮和总磷水平的多重影响。     

Quantifying change in pelagic plankton network stability and topology based on empirical long-term data

Over the last 34 years, Lake Müggelsee has experienced concurrent warming and nutrient reduction. While the effects of environmental change on single taxonomic or physical–chemical variables have been relatively well researched in isolation, understanding how environmental change propagates through the ecological network remains a major challenge. Capitalizing on the long-term monitoring program of the German Long-Term Ecosystem Research Network site Lake Müggelsee (1979-ongoing), we identified three time periods (1979–1995; 1996–2005; 2006–2013) which differed significantly in phytoplankton biomass and relative plankton community composition. Using multivariate first order autoregressive (MAR1) modeling on 13 pelagic plankton groups and four abiotic variables, we quantified interaction networks and indicators of stability and centrality for each period. Our results suggested that the Müggelsee network was bottom-up regulated in all periods and that stability increased over time. Moreover, in all three networks, non-trophic and indirect interactions appeared to be as commonly present as trophic and direct interactions. Using network centrality measures of betweenness and closeness, we identified keystone plankton groups and groups particularly responsive to environmental change based on variation in centrality ranks over time. Given a more comprehensive understanding of the interaction network at hand, MAR1 model-derived stability and centrality measures may potentially be used as integrated ecological indicators to monitor changes in stability of lake ecosystems and to identify particularly vulnerable components of the network.     

Seasonal distribution of vitamin B12 in Lake Kinneret.

Vitamin B12 is formed in Lake Kinneret in the hypolimnion and in the sediment. The highest value of B12 recorded in the lake water was about 100 ng/liter in November and December of 1975 at a 40-m depth. The vitamin was liberated from the hypolimnion during the turnover period. This supply of the vitamin to the photic zone was accompanied by increasing biomass of Dinoflagellates, Bacillariophyta, and Chlorophyta. The decrease in the vitamin concentration, followed by an increase, is correlated with a decline and subsequent rise in the algal biomass, respectively. Cyanophyta biomass, on the other hand, increased when the vitamin concentration in the photic zone was at its lowest level.     

大庆新华湖藻类植物群落结构与环境因子的相关性

2014年5-10月对大庆新华湖藻类植物群落结构与环境因子的关系进行了初步研究, 为湖泊状况的动态监测提供基本数据。调查期间, 共发现藻类植物135种, 隶属5门63属, 其中硅藻门56种, 绿藻门49种, 蓝藻门15种, 裸藻门12种, 甲藻门3种。新华湖优势种共24种, 包括绿藻门14种, 蓝藻门6种, 硅藻门3种, 裸藻门1种, 且季节更替明显, 可以初步推断新华湖藻类植物群落组成为绿藻-硅藻型。新华湖藻类植物细胞丰度变化范围为37.57×10⁶-72.37×10⁶ cells·L^-1, 平均值为52.13×10⁶ cells·L^-1。多样性指数变化为: Simpson生态优势度指数(D)在0.642-0.928之间, Shannon-Weaver多样性指数(H')在1.698-3.1之间, Pielou均匀度指数(J)在0.324-0.561之间, 3种指数变化趋势一致, 均在秋季最高, 春季最低。研究表明, 水温、pH值、总磷、生化需氧量、溶解氧和水动力是影响新华湖藻类植物群落结构的主要因子。     

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。     

A Short-Term Study of Vertical and Horizontal Distribution of Zooplankton During Thermal Stratification in Lake Kinneret,Israel

This study documents for the first time both vertical and horizontal distribution patterns of the zooplankton community in Lake Kinneret during the period of thermal stratification. The zooplankton distribution patterns were explored in relation to abiotic (temperature, oxygen) and biotic (picocyanobacteria, ciliates, flagellates, phytoplankton, fish) environmental gradients. Sampling was carried out on 6–7 July 1992 at five stations and six depths from nearshore to offshore. Zooplankton abundance and biomass varied from 5 to 267 ind. l^–1(mean: 95 ind. l^–1), and from 0.1 to 65 d.w. mg m^–3(mean: 24 d.w. mg m^–3). Zooplankton taxonomic groups (Rotifera, Cladocera, Cyclopoida, Calanoida) and size classes (micro-, meso- and macrozooplankton) showed peaks of maximal density and biomass in the epilimnetic and metalimnetic strata (5 and 14 m). Depth, accounting for 31–39% of total spatial variation, reflected the vertical distribution of zooplankton in relation to temperature and oxygen declines, and the higher concentration of food resources (protists and phytoplankton) in the epilimnion and metalimnion. Onshore–offshore distance, accounting for 17–22% of the total spatial variance, reflected different distribution patterns shown among zooplankton groups and size classes. The macrozooplankton (Copepoda, Cladocera) was more abundant offshore, whereas microzooplankton (Rotifera and nauplii) predominated nearshore. These horizontal distribution patterns were related to small increases in temperature and phytoplankton biomass, and higher concentrations of fish in the littoral zone. Although limited to a short temporal scale, our study indicated that zooplankton spatial distribution in Lake Kinneret during the period of thermal stratification was related to physicochemical, food and predation factors, manifested differently along the vertical and nearshore–offshore gradients.     

太湖梅梁湾湖岸带浮游植物群落演替及其与水华形成的关系

利用2009～2010年周年观测数据,结合江苏太湖湖泊生态系统研究站15年监测数据,分析了太湖梅梁湾湖岸带浮游植物群落演替及其与蓝藻水华形成的关系.50次周监测结果表明:蓝藻门(Cyanophyta)、绿藻门(Chlorophyta)、硅藻门(Bacillariophyta)分别占浮游植物总生物量的60%、16%和22%.冬春季绿藻、硅藻为主要优势种,夏秋季蓝藻门的微囊藻占绝对优势.4月下旬～6月初,平均温度低于20℃,蓝藻没有大规模生长,硅藻门、绿藻门生物量急剧降低,总生物量小于1mg·L^-1;随后温度超过25℃,蓝藻迅速增长并很快成为绝对优势,蓝藻增加滞后于绿藻、硅藻的减少.在营养盐充足、物理因素合适的条件下,浮游植物群落结构自然演替是蓝藻水华形成的主要原因之一.     

Spatiotemporal and long-term variation in phytoplankton communities in the oligotrophic Lake Pyhäjärvi on the Finnish-Russian border

As part of the joint Finnish-Russian research and development project “Assessment of the ecological state of the transboundary waters”, seasonal and spatial variations in the phytoplankton communities of Lake Pyhäjärvi were studied in order to identify possible long-term (1963–2002) changes and to present recent data (since 2002) on phytoplankton biomass and species composition. Some changes in both phytoplankton biomass and species composition, particularly in the littoral zone and northern basins of the lake, were obvious at the end of the 1980s; in particular, the density of blue-greens increased during that period. Biomasses increased five-fold in 1980, decreased after 1990 and have remained low (0.14 mg l^?l) to the present time. The effective water protection measures applied, especially reducing the phosphorus load from municipal wastewaters and airborne pollution, can now be seen to have improved the water quality. Although no significant temporal differences were found in phytoplankton biomass during the intensive biweekly sampling in 2002, considerable spatial variation was seen within the lake. An obvious change in the species composition of phytoplankton and an increase in biomass were seen even in the loaded parts of the lake. Despite the spatial differences in phytoplankton biomass and community structure, the changed species composition in the northern part of the lake indicated a clear recovery from the blue-green and Chrysophyceae dominated high biomass of the 1980s.