九寨沟国家级自然保护区长海夏季浮游植物群落结构及生态评价

高山湖泊对于全球气候变化及人类影响是一个极为敏感的参照系统.九寨沟国家级自然保护区长海作为一个独特的高山湖泊,研究其浮游植物群落结构及其与环境的关系,评估其水质现状及影响因素,有着重要的意义.本文于2014年7月对长海浮游植物群落结构进行了研究.全湖共布设12个采样点,并在中心采样点进行了垂直分层采样.本次调查共发现浮游植物6门38属63种,平均丰度为6.98×10~5cells/L,平均生物量为0.31 mg/L.浮游植物的水平分布差异不大;在垂直分布上,浮游植物的丰度从表层0.5 m至水下50 m呈现先增加后减少的趋势,在20 m水深处达到最大.长海浮游植物的优势种是长海小环藻(Cyclotella changhai)和飞燕角甲藻(Ceratium hirundinella),长海小环藻数量较多,飞燕角甲藻生物量较大.长海浮游植物多样性指数较低,综合各类水质评价方法,可以得出九寨沟长海处于贫-中营养状态.     

Light climate as the key factor controlling the spring dynamics of phytoplankton in Lake Zürich

During the spring seasons of 1983, 1986 and 1987 the development of phytoplankton in Lake Zürich was investigated (from February to May) using samples taken at short term intervals. The aim was to describe the effects of the short term dynamics of environmental factors on the algal growth. The results could then be used to discuss the existing theories to assess the start of phytoplankton growth pulses in spring. Only 7 to 10 days without wind driven vertical mixing were required in spring to start the first growth pulse, despite of a still very unstable water column (sometimes inverse thermal stratification). Mainly flagellates andStephanodiscus hantzschii increased their biomass and achieved net growth rates of 0.1 and up to 0.65 d⁻¹ respectively. During such a phase the mixing depth was always smaller than the euphotic depth. Later on, at the start of the spring bloom (=last growth pulse in spring before the clear water stage), the intensity of vertical mixing as well as the mixing depth were markedly reduced due to an increase in heat input and low wind. Then flagellates dominated (contribution up to 75.5% of the areal biomass reaching 60 g fresh weight m⁻²) and the growth rate rose to a maximum of 0.65 d⁻¹. Standard models of critical depth considers that there is only a biomass increase if the mixing depth is smaller than the depth of a water layer positive balanced between production and respiration. This model for determining the beginning of a phytoplankton growth pulse in spring takes no account of the favorable light conditions for phytoplankton cells at calm and sunny days in February and March. The newly developed threshold value model takes these situations into account: It assumes that the phytoplankton biomass increases when the calculated effective light climate is equal or greater than a previously fixed threshold. The calculations are based on the mean light intensity within the mixed layer at windy days or within the euphotic depth (z _eu) at calm days. In Lake Zürich a minimum of 0.2 10⁶ J m⁻²d⁻¹ (=0.9 mol quanta m⁻²d⁻¹) has to be reached or surpassed in at least 3 days before an exponential increase of algal biomass can occur. The value does not depend on short term fluctuations in neither radiation nor mixing depth. It seems that this value is rather low comparing with those of investigations in other water bodies (up to 0.8 10⁶ J m⁻² d⁻¹) but high related to values from algal cultures (0.02 10⁶ J m⁻²d⁻¹). As the weather can only be forecasted a few days ahead with any certainty the period for a more or less accurate prediction of an algal bloom is restricted to about 1 to 5 days.     

The seasonal productivity cycle of phytoplankton and controlling factors in Lake Constance

Annual phytoplankton productivity in Lake Constance is about 300 g C m⁻², a value typical for mesoeutrophic lakes. Seasonal variations in phytoplankton biomass and productivity are exceptionally great because of a sequence of factors controlling the production process. During winter productivity is controlled by low energy inputs and high respiratory losses due to deep water column mixing. Biomass is low and water transparancy high. The spring phytoplankton growth is triggered by the thermal stabilization of the water column. The summer phytoplankton biomass maximum mainly depends on phosphorus availability. However, biomass yields comprise only 15–20% of values to be expected from the Redfield ratio because large proportions of POM are detritus and non-algal biota. Moreover, sedimentation during the second half of the year removes biomass from the euphotic zone. Water transparency and thus vertical distribution of algal photosynthesis is highly dependent on phytoplankton biomass. Self-shading causes considerably smaller seasonal variations in areal biomass and photosynthetic rates than in volume-based values. By light-shade adaptation effects of seasonal fluctuations in mean daily surface radiance fluxes on algal photosynthesis can to a significant extent be compensated for. At any given level of biomass daylength is the major determinant of daily production rates. Dedicated to Professor Elster on his 80th birthday.     

呼伦湖浮游植物群落季节动态及其与环境因子的关系

为探究呼伦湖浮游植物群落的季节变化特征及其与环境因子的关系,本研究分别于2019年3、5 10月对呼伦湖浮游植物的种类、细胞密度和生物量及湖水水质进行调查.结果显示,共鉴定出120种浮游植物,隶属于7门72属.从浮游植物群落季节组成差异上来看,春季绿藻门种类数最多,其次是硅藻门、蓝藻门;夏秋季绿藻门种类数最多,蓝藻门次之;冬季硅藻门种类数最多,绿藻门次之.呼伦湖浮游植物优势种主要为硅藻门的梅尼小环藻(Cyclotella meneghiniana)、蓝藻门的卷曲长孢藻(Anabaena circinalis)和细小平裂藻(Merismopedia minima),种类数在春季最多,秋冬季最少.浮游植物细胞密度在春季(123.52×10⁴cells/L)和冬季(16.41×10⁴cells/L)较夏季(280.80×10⁴cells/L)和秋季(380.63×10⁴cells/L)低,春冬季绿藻门细胞密度最高,夏秋季蓝藻门细胞密度最高.就浮游植物生物量而言,夏季(0.38mg/L)最大,其次是秋季(0...     

基于浮游植物的城市湖泊生态健康评价——以长江下游铜陵市西湖为例

为了解铜陵西湖浮游植物群落结构与水生态健康状况,于2016年9月至2017年7月进行6次调查.结果显示：（1）浮游植物共检出6门88种,总密度变化范围为8.20×10⁵~1.60×10⁸ cells/L,均值为2.19×10⁷cells/L,生物量变化范围为1.34~27.76 mg/L,均值为9.45 mg/L,优势种为铜绿微囊藻（Microcystis aeruginosa）、浮游蓝丝藻（Planktothrix sp.）和微囊藻（Microcystis sp.）;（2） RDA分析表明浮游植物生物量主要受水温、悬浮物、总氮、亚硝态氮和总磷影响;（3）浮游植物隶属于22组功能群,基于功能群的Q指数表明,铜陵西湖水质整体处于“中等”状态,7月水生态状况最差,11月最佳;（4）依据候选参数与环境因子的相关性,最终选定生物量、密度和Margalef指数来构建铜陵西湖浮游植物生物完整性指数（P-IBI）,其评估结果与Q指数呈显著正相关,但P-IBI评估结果（整体为“较差”状态）更为严格.本研究阐述铜陵西湖浮游植物群落结构特征,并基于浮游植物Q指数和P-IBI评估其生态健康状况,相关研究结果可为其水环境管理及城市湖泊生态健康评估提供一定的科学参考.     

Torn between extremes: the ups and downs of phytoplankton

We present a model to investigate the success and resulting patterns of phytoplankton migration, based on motility which depends exclusively on the internal energy and nutrient state of the cells. The model consists of migrating and non-migrating sub compartments for phytoplankton, and migration is a function of the prescribed threshold values for internal quotas. The different modes of phytoplankton behavior are evaluated in the framework of a coupled physical–biological model that includes wind-driven up- and downwelling. The results show that (1) migration is almost always advantageous with respect to biomass, (2) a wide variety of migration patterns (e.g., subsurface maxima, surface-avoidance behavior) can be reproduced by a relatively simple treatment of motility, (3) multiple deep chlorophyll maxima can be explained as the result of certain threshold values in combination with negligible vertical movement of the water, and (4) descending tongues of high phytoplankton concentration may be caused by migratory behavior and not necessarily by subduction due to frontal convergence. Thus, our model offers explanations for a large variety of observed phytoplankton distributions and migration patterns.The comments of two anonymous reviewers are gratefully acknowledged.     

鄱阳湖流域柘林水库秋季浮游植物群落结构及其构建过程驱动机制

研究环境过滤过程和空间扩散限制过程在构建水生浮游植物群落结构中的作用是了解这些因素如何驱动物种分布和影响群落结构的关键步骤.为了揭示鄱阳湖流域柘林水库浮游植物群落结构特征与环境因子的关系,以及明确环境因子和空间扩散限制性因子在浮游植物群落构建过程中的影响机制,于2020年10月,对柘林水库33个采样点的浮游植物和水质理...     

Phytoplankton biomass size structure and its regulation in the Southern Yellow Sea (China): Seasonal variability

Phytoplankton size structure plays a significant role in controlling the carbon flux of marine pelagic ecosystems. The mesoscale distribution and seasonal variation of total and size-fractionated phytoplankton biomass in surface waters, as measured by chlorophyll a (Chl a), was studied in the Southern Yellow Sea using data from four cruises during 2006–2007. The distribution of Chl a showed a high degree of spatial and temporal variation in the study area. Chl a concentrations were relatively high in the summer and autumn, with a mean of 1.42 and 1.27 mg m⁻³, respectively. Conversely, in the winter and spring, the average Chl a levels were only 0.98 and 0.99 mg m⁻³. Total Chl a showed a clear decreasing gradient from coastal areas to the open sea in the summer, autumn and winter cruises. Patches of high Chl a were observed in the central part of the Southern Yellow Sea in the spring due to the onset of the phytoplankton bloom. The eutrophic coastal waters contributed at least 68% of the total phytoplankton biomass in the surface layer. Picophytoplankton showed a consistent and absolute dominance in the central region of the Southern Yellow Sea (>40%) in all of the cruises, while the proportion of microphytoplankton was the highest in coastal waters. The relative proportions of pico- and nanophytoplankton decreased with total biomass, whereas the proportion of the micro-fraction increased with total biomass. Relationships between phytoplankton biomass and environmental factors were also analysed. The results showed that the onset of the spring bloom was highly dependent on water column stability. Phytoplankton growth was limited by nutrient availability in the summer due to the strong thermocline. The combined effects of P-limitation and vertical mixing in the autumn restrained the further increase of phytoplankton biomass in the surface layer. The low phytoplankton biomass in winter was caused by vertical dispersion due to intense mixing. Compared with the availability of nutrients, temperature did not seem to cause direct effects on phytoplankton biomass and its size structure. Although interactions of many different environmental factors affected phytoplankton distributions, hydrodynamic conditions seemed to be the dominant factor. Phytoplankton size structure was determined mainly by the size-differential capacity in acquiring resource. Short time scale events, such as the spring bloom and the extension of Yangtze River plume, can have substantial influences, both on the total Chl a concentration and on the size structure of the phytoplankton.     

云南程海浮游植物初级生产力的时空变化及其影响因子

2016年4月-2017年2月,采用黑白瓶法研究了云南程海单点（码头点位）浮游植物初级生产力的垂直分布及其季节变化,同时基于全湖9个点位的现场调查和生产力垂向归纳模型（VGPM）估算并探讨了程海浮游植物初级生产力的时空变化及其主要影响因子.结果显示,码头点位的年均（均值±标准误）水柱（0~3 m）总初级生产力（GPP_C）、净初级生产力（NPP_C）和呼吸消耗量（R_C）分别为5.40×10³±0.64×10³、2.36×10³±0.63×10³和3.06×10³±0.82×10³ mg O₂/（m²·d）;不论春夏季（4-8月）、秋冬季（9月-次年2月）还是全年,码头点位的单位生物量GPP（GPP/Chl.a）和单位生物量NPP（NPP/Chl.a）的最大值和最小值均分别出现在水下0.5 m和3.0 m处.经VPGM估算,程海全湖的初级生产力（PP_eu）年均值为6.54×10³±0.30×10³ mg C/（m²·d）（2.74×10³~18.62×10³ mg C/（m²·d））.PP_eu的时空变化方面,春夏季是PP_eu快速上升的时节,秋冬季PP_eu的月变化则呈波动状态,春夏季与秋冬季PP_eu无显著性差异;PP_eu整体空间异质性较弱,仅在降水最为充沛的7、8月表现出南北向的异质性,这与降水条件和流域营养盐输入的空间异质性有关.回归分析发现,虽然程海PP_eu的主要影响因子具有季节异质性,但不论春夏季、秋冬季还是全年,浮游植物生物量均是重要的影响因子,水温亦是春夏季的重要影响因子.     

以鲢、鳙养殖为主的长江中下游武山湖浮游植物群落结构特征

武山湖是紧邻长江的通江型富营养化湖泊,是国家级湿地公园.为切实了解该湖在以鲢、鳙养殖为主的情况下浮游植物结构特征,于2017年9月-2018年8月对其浮游植物群落结构特征及水质开展了监测.监测结果表明武山湖水质全年处于轻度富营养到重度富营养水平之间;12次共采集浮游植物7门100种（属）,浮游植物优势种共有23种,其中蓝藻门有9种,绿藻门有8种,硅藻门和隐藻门各有3种.夏季和秋季蓝藻门优势种最多且优势度高,冬季和春季绿藻门和硅藻门优势种多且优势度高.武山湖浮游植物每月优势度最大的种类主要有蓝藻门微囊藻和细小平裂藻、绿藻门小球藻以及硅藻门小环藻.浮游植物生物量峰值出现在6月,达34.77 mg/L;丰度峰值出现在7月,达341.46×10⁶ cells/L.冗余分析（RDA）和线性相关分析均表明浮游植物丰度和生物量与总磷、温度和pH均呈显著正相关,且蓝藻门生物量和丰度以及优势属与总磷和温度均呈显著正相关.研究结果表明武山湖浮游植物丰度和生物量在夏季均很高,发生蓝藻水华的风险较大.相对于氮,磷是更重要的限制浮游植物生长的营养元素.     

丹江口水库浮游植物时空变化特征

为研究丹江口浮游植物的群落特征,探讨影响浮游植物时空分布的环境因子,于2014年5月2015年4月对丹江口水库进行了为期1年的调查.此次调查共采集到浮游植物66种,隶属于7门21科38属.浮游植物全年平均生物量为0.35 mg/L,平均密度为9.08×10~5cells/L.优势种为脆杆藻、小环藻、直链藻和栅藻,其中脆杆藻所占比例最大,平均生物量为0.089 mg/L,占总生物量的25.43%.近些年丹江口水库营养水平的提高可能是脆杆藻生物量升高的主要原因.绿藻和蓝藻在夏季大量繁殖,硅藻为春、秋和冬季优势门类.汉江库区浮游植物生物量大于丹江库区,两个库区的浮游植物种类组成存在明显的差异,丹江库区优势门类为硅藻门,而汉江库区为绿藻门.浮游植物生物量与环境因子的相关分析表明,浮游植物生物量的主要影响因子是总磷浓度、pH值和溶解氧浓度.RDA分析表明,影响浮游植物组成的主要环境因子是溶解氧浓度、pH值、总磷浓度和水温.为控制浮游植物的生物量,防止其异常增殖造成水华,应严格控制外源营养盐特别是磷元素的输入.本研究可为丹江口水库的水质改善及富营养化防治提供一定的科学依据.     

Differences in zooplankton feeding rates and isotopic signatures from three temperate lakes

Bacteria and phytoplankton are integral in the mobilization and transfer of organic matter to higher trophic levels. Hence, we examined their role in zooplankton diets and assessed trends in their nitrogen isotopic variability. We performed feeding experiments with natural particulate organic matter (POM) and four zooplankton groups (Daphnia, Holopedium, large calanoids and small calanoids) to (1) examine whether there are differences in consumption (presented as clearance and ingestion rates) of phytoplankton and bacteria, and (2) determine whether differences in zooplankton clearance and ingestion rates are correlated with their δ¹⁵N isotopic signatures. In general, phytoplankton and bacteria clearance rates and biomass ingested per animal varied significantly among different zooplankton groups within lakes and between lakes for a given zooplankton group. Within a given lake, Daphnia and Holopedium had the highest phytoplankton and bacteria clearance and ingestion rates, followed by large calanoids, and then small calanoids. For a given zooplankton group, bacteria and phytoplankton clearance rates varied among lakes. In contrast, phytoplankton ingestion rates were consistently highest in Dickie Lake for all taxa, whereas bacteria ingestion rates were more variable among lakes for the different zooplankton taxa. The percentage contribution of different phytoplankton taxa to the biomass of phytoplankton ingested also varied significantly among lakes for a given taxa, but there were few differences within a given lake among zooplankton. Zooplankton δ¹⁵N_DOMC values were correlated with their size adjusted phytoplankton and bacteria clearance and ingestion rates. The correlations were stronger with (1) phytoplankton compared to bacteria, and (2) clearance rates compared to ingestion rates of biomass. Together our results suggest that zooplankton taxa with low phytoplankton and bacteria clearance and ingestion rates and higher δ¹⁵N_DOMC are likely exploiting food sources from higher trophic levels.     

河蟹生态养殖池浮游植物功能类群的结构特征

为探究河蟹生态养殖池浮游植物群落的结构及动态,2013年4-10月对上海松江泖港地区河蟹养殖池的浮游植物进行了调查,分析其种类构成、密度、生物量和生物多样性.共检测到浮游植物105种,其中河蟹生态养殖池优势种11种,分别属于B、D、J、LO、X1、WO、X2、S1和MP功能群.河蟹养殖池浮游植物平均密度为282.58×10~4cells/L,平均生物量为1.59 mg/L,Shannon-Wiener多样性指数变化范围为2.11~3.09.水源浮游植物平均密度为175.13×104cells/L,平均生物量为0.99 mg/L,Shannon-Wiener多样性指数变化范围为1.70~2.79.河蟹养殖池浮游植物平均密度分别于5月14日-6月14日和7月29日-8月29日与水源差异显著;河蟹养殖池浮游植物平均生物量分别于5月30日、6月14日和7月29日-8月29日与水源差异显著;河蟹养殖池浮游植物Shannon-Wiener生物多样性指数分别于5月14日-6月14日和8月14日-9月15日与水源差异显著.河蟹养殖池浮游植物的平均密度、平均生物量和生物多样性指数与水源水体变化趋势基本一致,均高于水源,群落稳定.     

Size-fractionated phytoplankton biomass,primary production and respiration in the Nervión–Ibaizabal estuary: A comparison with other nearshore coastal and estuarine ecosystems from the Bay of Biscay

The seasonal pattern of size-fractionated phytoplankton biomass, primary production and respiration was investigated along the longitudinal axis of the Nervión–Ibaizabal estuary (Bay of Biscay) from April 2003 to September 2004. Environmental factors influencing phytoplankton dynamics were also studied. Chlorophyll a biomass showed a longitudinal pattern of increase from the outer Abra bay to the inner estuary. On a seasonal scale, in the intermediate and inner estuary phytoplankton biomass maxima were registered in summer, the warmest and driest season, whereas in the outer bay chlorophyll a peaks occurred in May 2004, but were delayed to August 2003, likely due to a very rainy spring. Data suggest that river flow exerts a marked influence on the timing of phytoplankton biomass maxima in this estuary, decreased river flows providing a lowering of turbidity and an increase in water residence time needed for chlorophyll a to build up. Nutrient concentrations were high enough not to limit phytoplankton growth throughout the annual cycle, except silicate and occasionally phosphate in the outer bay during summer. Silicate concentration correlated positively with river flow, whereas ammonium and phosphate maximum values were generally measured in the mid-estuary, suggesting the importance of allochthonous anthropogenic sources. In the intermediate and inner estuary phytoplankton biomass was generally dominated by >8 μm size-fraction (ca. 60%), but in August 2003 <8 μm size-fraction increased its contribution in the intermediate estuary. It is argued that the lower nutrient concentrations measured in August 2003 than in August 2004 could have played a role. This is the first study in which phytoplankton primary production rates have been measured along the longitudinal axis of the Nervión–Ibaizabal estuary. Throughout the annual cycle these rates ranged from 0.001 to 3.163 g C m^?3 d^?1 and were comparable to those measured in nearby small estuaries of the Basque coast and other larger estuaries on the Bay of Biscay. Surface plankton community respiration rate maxima were measured during the spring 2004 chlorophyll a peak in the Abra bay and in summer months at the mid and inner estuary, coinciding with chlorophyll a biomass and primary production maxima. In general, respiration rates showed a positive correlation with temperature. In order to compare results from the Nervión–Ibaizabal estuary with other nearshore coastal and estuarine ecosystems within the Bay of Biscay a review of existing information on phytoplankton biomass and primary production dynamics was performed.     

钱塘江干流夏季浮游植物群落结构特征及其对水文气象的响应

河流中浮游植物的动态变化能够较好的指示河流水质状况.为探索水文气象过程对筑坝河流浮游植物群落结构的影响,2020年夏季,以钱塘江干流为例,对包括富春江水库在内的11个河段开展了浮游植物群落结构及相关环境因子的调查分析.结果 表明:夏季在钱塘江干流共鉴定出浮游植物6门59属95种,优势属为沟链藻(Aulacoseir、菱...     

三峡水库香溪河库湾拟多甲藻(Peridiniopsis)的昼夜垂直迁移行为对碳磷分布的响应

于2015年2月26-27日在香溪河库湾高岚河段拟多甲藻(Peridiniopsis)水华发生地昼夜监测其在水体中的垂直迁移,分别在6个时间段(8:00、12:00、16:00、20:00、0:00、4:00)分层取样分析拟多甲藻在水中的叶绿素a浓度、细胞密度、碳酸酐酶(CA)与碱性磷酸酶(AP)活性;分析总磷(TP)、溶解性总磷(DTP)、溶解性反应磷(SRP)与溶解性有机磷(DOP)浓度在水中的垂直分布.结果显示,水华发生期拟多甲藻为绝对优势种,监测的6个时段中,拟多甲藻呈显著的昼夜垂直迁移规律,正午12:00,表层细胞密度最大,可达5.2×10~6cells/L,凌晨0:00表层细胞密度最低,仅为0.4×10~6cells/L;TP与DTP浓度无垂直分布规律,但SRP与DOP浓度呈现显著的垂直分布规律,SRP浓度随水深增加而减小,DOP浓度随水深增加而增加;CA活性日间高于夜间,日间CA活性呈垂直分布规律,随水深增加而减小,但夜间无垂直分布规律;AP活性在水中昼夜呈极其显著的垂直分布规律,随着水深增加逐渐增加.相关性分析结果表明,拟多甲藻细胞密度与水深、DOP浓度呈极显著负相关,水深与CA和AP活性分别呈极其显著负相关与正相关,拟多甲藻细胞密度与CA和AP浓度分别呈极其显著正相关与负相关.因此,拟多甲藻的垂直迁移行为可能是对日间迁移至表层获取光能和无机碳来源、夜间迁移至水下获取磷源的一种适应.     

Coastal thin layer dynamics: Consequences to biology and optics

Thin layers are fine-scale structures with high concentrations of organisms or particles occurring over very small vertical scales (a few meters or less), but with large horizontal scales, often extending for many kilometers. Because of their small vertical scales, thin layers are traditionally under sampled, but when proper measurement techniques are used, thin layers have been found to be ubiquitous in stratified oceans. A multi-investigator, interdisciplinary study of thin layers was sponsored by the US Office of Naval Research under a research initiative termed: Layered Organization in the Coastal Ocean (LOCO). The goal of this program was to understand the properties of coastal thin layers and the interacting physical, chemical, biological and optical processes responsible for their formation, maintenance and dissipation. As part of this program, fine-scale vertical profiles (cm resolution) of biological, physical and chemical properties were made hourly over periods spanning 1–3 weeks during three summers in Monterey Bay, California USA. The vertical profiles were made using arrays of moored autonomous profilers. In total, these profilers made ~2000 individual vertical profiles and provided a unique view of phytoplankton thin layer spatial-temporal dynamics. The autonomous profiler data were supplemented with high-resolution ship-based profiling and discrete water sampling for identifications of organisms.Persistent phytoplankton thin layers were observed during each year in Monterey Bay; however, each year had very different biological and physical dynamics. During 2002, thin layers were dominated by the non-motile and potentially toxic diatom genus Pseudo-nitzschia; during 2005, thin layers were dominated by the highly motile dinoflagellate species Akashiwo sanguinea; and during 2006, a more complex phytoplankton assemblage was present, but thin layers of the toxic dinoflagellate species Alexandrium catenella frequently occurred. The variability in the vertical location of thin layers in 2002 was primarily controlled by physics, while behavior, e.g. diurnal vertical migration patterns and daytime near-surface aggregations, primarily controlled the location of thin layers in 2005 and 2006. In 2002, phytoplankton thin layers were present in the water column 87% of the time, in 2005, 56% of the time and in 2006, 21% of the time. The median integrated chlorophyll concentration within the thin layers was found to be approximately 47% of the total water column chlorophyll in 2002, 41% in 2005 and 33% in 2006. Additional results in this study describe the mechanisms driving the spatial-temporal dynamics of these phytoplankton thin layers with special emphasis on diel patterns and the specific relationships that thin layers have to biological and physical processes and water column optics.     

Relative effects of local and landscape factors on wetland algal biomass over a salinity gradient

Wetlands in south-eastern Australia and other arid regions of the world are experiencing increases in salinity due to dryland salinization and climate change. We investigated changes in wetland ecological function, measured as phytoplankton and benthic algal Chl a, over a large salinity gradient (0.047–226 mS cm⁻¹) and in relation to several local water chemistry variables that may be important predictors of algal biomass. We investigated the relative importance of landscape variables that may affect input pollution and hydrology of wetlands at four spatial scales (100, 500, 1,000 and 5000 m). We explored the strength and form of the relationships between algal biomass and local and landscape predictors with emphasis on the effects of local and landscape salinity. We found local variables were more important than landscape variables in influencing algal biomass. We also found salinity of wetlands was not a good predictor of phytoplankton biomass but it did predict benthic algal biomass.     

Seasonal variations in phytoplankton biomass and primary production in the Ethiopian Rift Valley lakes Ziway, Awassa and Chamo – The basis for fish production

Seasonal variations in the biomass (Chl a) and primary production (¹⁴C-method) of phytoplankton were studied during 12 months of 2005 in the three Ethiopian Rift Valley Lakes (ERVL) Ziway, Awassa and Chamo. Chl a showed an average value of 40, 20, and 30 mg m⁻³ for the three lakes, respectively. Integrated areal primary production for the total phytoplankton (g C m⁻² d⁻¹) varied 2-fold in the three lakes but on different levels, from 0.67–1.8 in L. Ziway, 1.8–4.6 in L. Awassa, and 1.0–2.6 in L. Chamo. The overall photosynthetic efficiency of utilizing photosynthetically active radiation by the phytoplankton on molar basis (mmol C mol of photons⁻¹) resulted in an average value of 1.4 for L. Ziway, 3.5 for L. Awassa and 1.6 for L. Chamo. Among the different factors regulating phytoplankton primary productivity, light penetration and nutrients were the most important in the three lakes. The seasonal variations of incident radiation (most values between 5 and 7 E m⁻² h⁻¹) and water temperature (most values between 22 and 24 °C) were small and unlikely to result in the marked differences in phytoplankton primary production. Although relative increase in nutrient concentrations occurred following the rainy periods, the major algal nutrients were either consistently low (nitrate and/or silicate) or high (phosphate and/or ammonium) and remained within a narrow range for most of the study period in all the three lakes. Consequently, phytoplankton biomass and primary production seem to be maintained more by nutrient regeneration or turnover (facilitated by high temperature) than by allochthonous nutrient input. This would be coupled with wind-induced mixing that would play an important role in determining hydrographic characteristics (water column structure) and the associated redistribution of nutrients and phytoplankton, the availability of light and subsequently the spatial (vertical) and temporal patterns of phytoplankton production in these three ERVL. Phytoplankton production (PP) is regarded as a good predictor of fish yield in lakes and seasonal measurements of PP is a prerequisite for good such estimates.