Picoplankton structure in clear and turbid eutrophic shallow lakes: A seasonal study

The relative abundance of the different picoplankton components (eukaryotic picophytoplankton (Peuk), picocyanobacteria (Pcy) and bacterioplankton), and their relationships with the lake conditions were studied in three types of shallow lakes from the Pampa Plain (Argentina) that differ in their optical properties: clear-vegetated, phytoplankton-turbid and inorganic-turbid. All the selected lakes, but one, are characterized by their different alternative steady state (clear-vegetated and phytoplankton-turbid water phases) following the model proposed by Scheffer et al. (1993).Autotrophic and heterotrophic picoplankton abundances were analyzed seasonally in relation to environmental variables. All the lakes presented high concentrations of total nitrogen (TN) (>229 μg L⁻¹), total phosphorus (TP) (>46 μg L⁻¹) and dissolved organic carbon (DOC) (>13.7 mg L⁻¹). Clear-vegetated lakes were characterized by vertical diffuse PAR (photosynthetic active radiation) attenuation coefficient (kd_PAR) lower than 11 m⁻¹, whereas inorganic-turbid lake always showed values higher than 21.1 m⁻¹. The euphotic zone depth (Z_1%) was wider in clear-vegetated lakes (40–140 cm) and thinner in the inorganic-turbid (10–20 cm). The phytoplankton-turbid lakes presented a wide range in the values of these variables (kd_PAR: 5.2–35.8 m⁻¹; Z_1%: 10–90 cm). Phytoplankton chlorophyll-a (Chl-a) strongly differed, ranging from 1.6 to 334.6 μg L⁻¹. Picophytoplankton was mainly represented by phycocianine-rich (PC-rich) Pcy in all cases, dominating over Peuk algae. The total and relative abundances of eukaryotic picophytoplankton, Pcy and bacterioplankton, as well as the size structure of the phytoplankton community differed among the water bodies. In general, clear-vegetated water bodies exhibited similar abiotic characteristics, picophytoplankton/bacterioplankton ratios, and phytoplankton size structure. Contrarily, no clear trend was identified for the group of turbid lakes. The contrasting results obtained for the importance of the picoplankton components in phytoplankton-turbid shallow lakes evidence that the availability of the energetical and nutrient resources cannot be solely considered to predict their relative importance in this type of shallow lake.     

The effects of wet and dry seasons on concentrations of solutes and phytoplankton biomass in seven Ethiopian rift-valley lakes

The chemical characteristics and phytoplankton biomass (measured as chlorophyll-a concentrations) of seven lakes and one reservoir in the Ethiopian rift-valley were studied during the wet and dry seasons between 1990 and 2000. Mean concentrations of three major plant nutrients (nitrate-nitrogen, soluble reactive phosphorus, and silicate) increased during the wet seasons in four of the seven lakes, presumably as a result of mixing events and input from runoff. The changes in the major nutrient concentrations in the rest of the lakes were variable, but concentrations were usually higher during the dry seasons, most likely as a response to temporal variation in the phytoplankton biomass. pH measurements of the lakes did not show marked differences between the wet and dry seasons. Salinity (measured as conductivity) and total ions seemed to increase during the wet seasons in some of the lakes, possibly as a result of inflows that might carry high concentrations of solutes due to the heavy rains. Chlorophyll-a concentrations were higher during the dry seasons in most lakes except in three relatively more productive lakes. The results suggest that there could be light limitation in some of the Ethiopian rift-valley lakes, and events associated with the wet and dry seasons could bring about contrasting changes in nutrient levels and phytoplankton biomass in lakes, depending on the physical characteristics of the lakes.     

近30 a云贵高原湖泊表面水体面积变化遥感监测与时空分析

以云贵高原湖泊近30 a来的TM、ETM~+和OLI遥感影像为数据源,采用归一化水体指数(NDWI)、改进归一化水体指数(MNDWI)、新型水体指数(NWI)、增强型水体指数(EWI)和自动水体提取指数5种水体指数提取了1985—2015年云贵高原10个湖泊表面水体面积,并对各种算法进行精度对比分析.针对湖泊各自特点采用不同的水体指数提取其表面水体面积,并进行水体面积变化时空分析.结果表明:云贵高原湖泊表面水体面积总体呈现先增加后缩减趋势,1985—1995年湖泊表面水体面积增加了30.86 km~2,1995—2015年湖泊水体表面面积减少了48.12 km~2,其中,面积变化最大的是杞麓湖与异龙湖.对云贵高原湖泊表面水体面积变化与该区域的年降水量、蒸发量、平均气温、流域植被覆盖面积和人类活动时空进行相关分析,结果表明:1)高原湖泊对区域气候变化的响应具有明显的空间差异性,云贵高原湖泊的表面水体面积与气候相关性较显著,气温升高引起蒸发加速,降水量下降,湖面不断缩小,与逐年上升的气温呈负相关,与逐年波动上升的蒸发量呈负相关,与逐年减少的降水量呈正相关;2)云贵高原湖泊各流域的植被覆盖面积与湖泊面积变化相关性较弱;3)人类活动是影响湖泊面积变化的重要因素,大肆围湖造田、围湖养殖以及旅游开发等人类活动直接导致云贵高原湖泊面积的锐减,并对湖泊生态环境产生重要影响.     

Factors promoting persistence of the bloom-forming Gonyostomum semen in temperate lakes

The nuisance large flagellate Gonyostomum semen (Raphidophyceae) is typical for brown-water lakes in temperate and boreal regions. This study is focused on two annual cycles of G. semen in shallow temperate lakes (one of which stratifies) with a particular emphasis on the species’ ecology and its potential impact on the alternation of phytoplankton assemblages. Temperature and phosphorus were the main forces driving seasonal growth of the raphidophyte. G. semen occurred at a broad temperature range and prevailed for the extended period from spring to late autumn at maximum biovolume and forming up to 98.7% of total phytoplankton in June–July and/or September. The species exclusively dominated under phosphate-replete conditions and caused heavy blooms in the stratified lake. The species outcompeted other flagellates in the lakes; considerable fluctuations in phytoplankton species composition occurred during the periods at low G. semen biovolume.     

富营养化湖泊典型水华蓝藻的固有光学特性

固有光学特性是水体光学特性的重要内容,掌握富营养化湖泊水体内典型水华蓝藻的固有光学特性,是开展不同水华蓝藻遥感识别的理论基础.利用AC-S吸收衰减仪、BB9后向散射仪,通过实验室纯藻培养,研究微囊藻（Microcystis）、鱼腥藻（Dolichospermum）和束丝藻（Aphanizomenon）3种典型水华蓝藻的固有光学特性,并探讨色素浓度、色素占比以及藻类等效粒径对不同水华蓝藻固有光学特性的影响.结果表明,3种典型水华蓝藻的吸收光谱曲线均具有440、620和675 nm吸收峰,微囊藻620和675 nm的比吸收系数最大,鱼腥藻440 nm处的比吸收系数最大;束丝藻单位色素浓度的散射和后向散射能力最高,鱼腥藻次之,微囊藻最低;固有光学特性影响因子分析表明,色素浓度和藻蓝素占比是影响3种水华蓝藻固有光学特性的主要因素.3种蓝藻的吸收系数、散射系数以及鱼腥藻、束丝藻的后向散射系数均随着色素浓度（叶绿素a或藻蓝素）的增加而增大;当蓝藻中藻蓝素占比增加时,3种蓝藻的单位色素浓度的后向散射系数逐渐下降;而藻细胞粒径与固有光学特性之间并未表现出很好的相关性.因此,3种水华蓝藻单位色素浓度的固有光学特性将为典型水华蓝藻的遥感识别提供重要的理论基础和数据支持.     

Effects of nitrogen and phosphorus on phytoplankton composition and biomass in 15 subtropical, urban shallow lakes in Wuhan, China

This study aims at investigating the composition and biomass of the phytoplankton community in 15 urban shallow eutrophic lakes as well as the effects of main environmental factors, including nutrient concentrations and the ratio of nitrogen to phosphorus, temperature, COD, BOD, water depth, etc. on the phytoplankton community structure. Lake water samples were taken and analyzed on a bimonthly basis during the period from March 2004 to March 2006. The redundancy analysis (RDA) and regression analysis (RA) were performed to identify the effects of nutrients on the phytoplankton community and biomass in these typical urban lakes. The results indicate that most of these urban lakes were hypertrophic due to high concentrations of total phosphorus (TP) and total nitrogen (TN), with mean levels of 490 and 5380 mg m⁻³, respectively. The phytoplankton community was dominated by Microcystis aeruginosa and Euglena caudate in summer and Cryptomonas ovata and Cyclotella meneghiniana in winter. The mean biomass of the phytoplankton reached 456.87 mg L⁻¹ in summer months and the annual level was 189.24 mg L⁻¹. Temperature and TP content were found to be the principal limiting factors for phytoplankton growth on an annual basis. On the other hand, the results of RDA and RA demonstrate that the dominant phytoplankton species were not nutrient-limited during summer months. Low TN:TP ratios (<10) were detected accompanied with fewer occurrences of N-fixing cyanobacteria and other filamentous algae in most lakes in summer, which implies that low N:P ratio does not always shifts the dominance of phytoplankton community to the N-fixing cyanobacteria. Moreover, TP always had higher correlation with chlorophyll a (Chl-a) than TN, even when the TN:TP ratios of most samples were lower than 10. Therefore, it is concluded that the TN:TP ratio is not always a suitable index to determine whether nitrogen or phosphorus limits the phytoplankton biomass in urban shallow eutrophic lakes.     

Differential piscivory of the native Percichthys trucha and exotic salmonids upon the native forage fish Galaxias maculatus in Patagonian Andean lakes

The present paper analyses predation patterns, of Percichthys trucha and salmonid fish upon Galaxias maculatus in five lakes of northern Patagonia with differing community and environmental characteristics. Tank experiments were performed to evaluate relative efficiency of native and exotic predators of G. maculatus under treatments with and without cover (aquatic vegetation). Important differences were found between predators with regards to distribution and consumption of G. maculatus. Salmonids are more efficient than P. trucha in consuming G. maculatus in deep environments with scarcely vegetation; in contrast to native species they frequently use the pelagic environment. Although pelagic habitat might have served in the past as a refuge from native predators in the past, G maculatus now experiences intense predation in the pelagic zone by exotic salmonids. It is suggested that the widespread distribution of G. maculatus in Patagonian lakes may have facilitated the success of salmonids throughout Patagonia.     

鄱阳湖阻隔湖泊沉积物中溞属枝角类卵鞍密度的长期变化及其与营养盐的关系:以军山湖为例

本文研究了典型的鄱阳湖阻隔湖泊——军山湖沉积物(0~36 cm)中溞属枝角类卵鞍密度的长期变化.1~#和2~#采样点36 cm沉积层对应的年代分别为1839和1857年.1958年前,军山湖沉积物的沉积速率呈现较高的水平,而1959年建坝后的沉积速率明显减小.1958年前,军山湖沉积物中总氮和总磷含量相对稳定,但建坝后总氮含量呈现明显增加的趋势.在军山湖沉积物中,鉴定出中华拟同形溞(Daphnia similoides sinensis)、盔形溞(D.galeata)和蚤状溞(D.pulex)的卵鞍.1~#和2~#沉积柱中3种溞属种类总卵鞍和含休眠卵卵鞍的累积速率和密度呈现较一致的变化.1958年前,3种溞属种类总卵鞍和含休眠卵卵鞍的累积速率和密度均处于较低水平(1~#沉积柱:0~1.51×10~3ind./(m~2·a)和0~0.63 ind./(g·dw);2~#沉积柱:0~0.70×10~3ind./(m~2·a)和0~0.22 ind./(g·dw));1959年建坝后,10~1 cm的沉积层中3种溞属种类总卵鞍和含休眠卵卵鞍的累积速率和密度呈现逐步增加的趋势,尤其是在3~1 cm(2009-2015年)的沉积层.Pearson相关性显示,军山湖1~#沉积柱中的总氮含量与3种溞属种类的总卵鞍和含休眠卵卵鞍的累积速率之间均存在极显著相关性.2~#沉积柱中的总氮和总磷含量均与3种溞属种类总卵鞍的累积速率之间存在显著相关性.2~#沉积柱的总氮和总磷含量还与中华拟同形溞的含休眠卵卵鞍的累积速率之间均存在显著相关性.结果表明,沉积物中营养盐含量和溞属种类卵鞍(或休眠卵)的长期变化能够反映湖泊富营养化和溞属种群的历史演变过程.     

Early succession of the macroinvertebrate community in a shallow lake: Response to changes in the habitat condition

In the present study the initial succession of the aquatic macroinvertebrate communities of a newly created shallow lake in a wetland area was monitored during 15 months. Three different types of macroinvertebrate samples (multihabitat, associated to the Phragmites australis stands and associated to the sediment) were collected monthly from May 2004 to July 2005. Additional samples were collected in the reed stand in 2007, when the reed belt had become much taller and thicker. Colonization of the lake was fast, and the colonization sequence was mainly related to the dispersal abilities of the taxa. Habitat-specific changes in the assemblage's structure and composition were registered. The communities associated to the sediment showed a decrease in overall biomass, density and species richness along time. The density of the gastropod Physella acuta and the chironomid species Dicrotendipes pallidicornis, Polypedilum nubifer and Tanytarsus horni decreased significantly, after Chara stands declined; while the chironomid Chironomus riparius became dominant. The epiphytic macroinvertebrate communities associated with the reed stands followed a seasonal pattern, with a warm-period community dominated by the chironomid species Ablabesmyia monilis and Psectrocladius sordidellus-group, and a cold-period community dominated by the chironomid species Cricotopus ornatus and D. pallidicornis.     

江汉平原湖群藻相特征及其环境状况评价

于2011年4月—2012年5月丰、平、枯3个水期对江汉平原水面面积为10 km2以上的22个湖泊进行了水质和藻类同步监测.结果显示:江汉平原主要湖泊中鉴定出藻类7门100属191种(亚种、变种),其中蓝藻门17属29种,绿藻门45属99种,硅藻门26属40种,隐藻门2属5种,裸藻门4属9种,甲藻门3属5种,金藻门3属4种;全年平均藻细胞丰度为0.93×106~84.18×106cells/L,细胞丰度以蓝藻门最高(50.65%),其次是绿藻门(29.56%),再次是硅藻门(12.30%)、隐藻门(6.19%)、裸藻门(0.56%)、甲藻门(0.39%)和金藻门(0.35%);丰水期生物量显著高于平水期和枯水期,Shannon-Wiener多样性指数年均值在1.44~2.10之间,丰水期的多样性指数略高于其他水期;藻类种类组成及优势种有明显的季节变化和空间差异.依据藻相特征的PCA分析将22个湖泊分为4个类群,不同类群具有显著不同的环境状况,氮磷营养负荷、水质状况和开发利用程度的不同是导致湖泊分化的内在原因;研究结果显示,江汉平原湖群总体上属于轻度污染状况,水体主要是中营养状态,丰水期与枯水期的湖泊生态环境状况具有显著差异;以藻相特征判断22个湖泊存在明显的时空异质性,部分湖泊因过度开发利用存在严重的富营养化风险;基于湖泊生态状况的显著时空异质性,对江汉平原湖群的管理应"因湖而异"制订科学合理的方法.     

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.     

五个湖泊中华刺鳅(Mastacembelus sinensis)种群线粒体细胞色素b遗传多样性分析

采用特异性引物对中华刺鳅基因组DNA进行扩增和测序,获得了江苏省5个湖泊的中华刺鳅种群线粒体cyt b基因767 bp的序列.分析表明,cyt b基因中A+T含量略高于G+C含量,144个中华刺鳅共获得cyt b基因单倍型28个,变异位点38个,其中单倍型Hap1分布最为广泛,可能为祖先型单倍型.平均单倍型多样性和平均核苷酸多样性指数分别为0.58751和0.00214,遗传多样性较低.群体间遗传分化系数为0.0356,绝大多数的遗传变异都来自群体内部,而群体间的遗传分化极小.构建的系统进化树未出现明显的以单个湖泊群体的聚簇,5个湖泊的种群间基因交流极其强烈.研究结果表明,当前5个湖泊的中华刺鳅遗传多样性水平比较低,亟待加强保护.     

富营养化浅水湖泊生态修复中背角无齿蚌(Anodonta woodiana)对水质改善的影响

滤水速率的快慢是决定滤食性河蚌对水质改善与否的关键,但受蚌龄大小、食物多少和季节变化的影响.以背角无齿蚌（Anodonta woodiana）为研究对象,设置幼龄蚌组、成年蚌组和无蚌对照组,在惠州西湖生态修复后的清水态和未修复的富营养化水体同时进行中型系统原位实验,测定了各处理组水层中氮、磷、总悬浮物（TSS）浓度和浮游藻类生物量（用叶绿素a（Chl.a）浓度表示）的季节变化,以研究蚌龄、食物和季节变化对背角无齿蚌水质改善的影响.结果表明,与对照组相比,背角无齿蚌提高了清水态水体总磷（TP）和铵态氮浓度,但对总氮（TN）、TSS和浮游藻类Chl.a浓度的影响不显著,表明其不能有效改善清水态水体水质;富营养化水体中,背角无齿蚌虽对水中TN浓度影响不显著,但显著降低了TP浓度、浮游藻类Chl.a浓度和TSS浓度;表明背角无齿蚌可改善富营养化水体水质;且富营养化水体中幼龄蚌的滤水速率显著高于成年蚌;幼龄蚌的滤水速率春季最大（0.132±0.018 L/（g·h））,夏季最小.因此,在富营养化水体修复前期,可通过放养本地滤食性河蚌,如背角无齿蚌,以改善水质,春季放养幼龄蚌更佳,为接下来的修复创造有利条件;而在生态修复后期的清水态水体中,单独的河蚌对水质改善效果不明显.本研究可为水生态系统保护和富营养化水体生态修复提供参考.     

Macrophyte diversity of lakes in the Pannon Ecoregion (Hungary)

We examined the distribution of submerged and emergent macrophyte species and the entire macrophyte community within and between five lake types (highland reservoirs, alkali lakes, large shallow lakes, small to medium sized shallow lakes, marshes) in the Pannon Ecoregion, Hungary. The lowest submerged, emergent and total species richness was found in alkali lakes. The highest submerged macrophyte richness was in small to medium sized lakes, while the highest emergent macrophyte species richness was in reservoirs, small to medium sized lakes, and marshes. The values of within-lake type beta diversity were generally lower than the values of alpha diversity, especially for submerged macrophytes, indicating between site homogeneity in species composition within the lake types. Emergent macrophyte communities contributed the most to within and between lake type diversity and total (gamma) diversity. Canonical correspondence analyses showed that the main environmental variables which influenced the distribution of submerged macrophytes were conductivity, Secchi transparency and water nitrogen contents. For emergent macrophytes conductivity, lake width, altitude and water depth proved to be the most influential variables. Our results contribute to the knowledge of large-scale distribution of macrophytes in the Pannon Ecoregion and to the identification of conservation value of lakes using macrophytes. The results support the importance of small lakes and artificial lakes in the conservation of macrophyte diversity compared to large and natural lakes in the Pannon Ecoregion.     

东洞庭湖浮游藻类粒级结构组成及其关键影响因子

不同粒径大小浮游藻类的养分吸收速率、沉降特性和能流方向等都不相同,浮游藻类生物量的粒级组成变化对湖泊生态系统的结构与功能具有重要影响.为了解通江湖泊浮游藻类粒级组成演替规律及其驱动机制,于2018年9月2019年9月对东洞庭湖进行了年度采样调查,研究了不同粒级浮游藻类的时空分布特征及其与环境因子的关系.结果表明:东洞庭湖浮游藻类叶绿素a总浓度呈现显著的时空分布差异;季节上表现为夏季(22.43μg/L)秋季(16.95μg/L)春季(11.69μg/L)冬季(3.28μg/L),空间上表现为北部湖区(26.12μg/L)南部湖区(15.81μg/L)东部行洪道(5.88μg/L).纳微型藻(3～20μm)是东洞庭湖浮游藻类生物量的主要贡献者,其在冬季优势度最高,为68.0%;春季开始,超微型藻(0～3μm)的贡献量逐渐增加,到夏季达到最高值,为42.1%;粒径最大的微型藻(20μm)占比最低,全年平均占比16.2%. RDA限制性排序结果表明,不同粒级浮游藻类对环境因子的响应趋势相同,但适应能力不同;温度、水位、营养盐和pH等是影响东洞庭湖浮游藻类粒级结构的重要因素.     

Substrate influence and temporal changes on periphytic biomass accrual and metabolism in a tropical humic lagoon

We performed a field experiment in a tropical humic coastal lagoon to evaluate periphyton biomass accrual and metabolism on three different substrates (1) plastic ribbons, (2) green and (3) senescent leaves of the emergent macrophyte Typha domingensis) over 30 days. The contribution of autotrophic biomass decreased as total biomass increased over the time. Mean periphytic ash free dry weight ranged from 0.8 to 5.6 mg cm⁻², but periphyton chlorophyll a concentrations presented shorter amplitudes, which oscillated from 0.12 to 0.44 μg cm⁻² throughout the experiment. Periphyton metabolism was overall heterotrophic on all substrates, especially on senescent leaves. Our data show that substrate type influenced both biomass accrual and periphyton net productivity and respiration rates throughout periphyton development and highlighted the dominance of heterotrophic metabolism. The periphyton respiration may be subsidized by both water- and substrate-derived allochthonous energy pathways, shedding light on the role of periphytic assemblages to the carbon cycling, as a source of CO₂ to the system.     

温度波动对浮游藻类生长及多糖组成的影响

以铜绿微囊藻、蛋白核小球藻及梅尼小环藻为研究对象,分析了春季藻类演替期间主要门类藻对温度波动的响应,实验在恒温(20℃)和昼夜波动(20±5℃)2种温度模式下测定了3种藻的生长和不同形态多糖含量的变化.结果表明,蛋白核小球藻的生长曲线在不同处理条件下没有显著性差异,铜绿微囊藻和梅尼小环藻的生长曲线在波动温度组显著低于恒定温度组,而且温度波动对梅尼小环藻的生长抑制明显强于铜绿微囊藻.随着实验的进行,3种藻在2个温度处理组中的生长速率逐渐趋近,无显著差异,但是在实验中段3种藻的生长速率对2个温度处理的响应差异显著,其中温度波动对蛋白核小球藻的生长速率起到了显著的抑制作用,对梅尼小环藻起到短暂的显著抑制作用,而对铜绿微囊藻的生长速率无显著性影响,表明铜绿微囊藻对短期(3~6 d)的温度波动表现出较强的适应能力.铜绿微囊藻的游离多糖含量在温度波动条件下显著增加,而固着多糖和总多糖的含量显著减少;蛋白核小球藻和梅尼小环藻多糖的含量没有显著性变化,表明温度波动可能不利于铜绿微囊藻固着多糖的积累.因此,相对短期的温度波动有利于铜绿微囊藻生长优势的确立与维持,而相对长期的温度波动可能会通过影响铜绿微囊藻固着多糖的积累而影响其生长优势的维持.     

Variations of phytoplankton productivity and biomass over an annual cycle in Saanich Inlet,a British Columbia fjord

Saanich Inlet is a highly productive temperate fjord with the capability to record inter-annual patterns of water-column primary production in undisturbed laminated sediments. We investigated spatial and temporal variations in primary productivity, total and size-fractionated phytoplankton chl a, dissolved nutrients, temperature and salinity at the head and mouth of Saanich Inlet from May 2005 to November 2006. New primary productivity was also measured from May to October 2006. During the growing season (spring, summer and fall), primary productivity was 1.5 times higher at the mouth than at the head of Saanich Inlet and, averaged across stations, total productivity was 460 g C m⁻² y⁻¹. Average new productivity was 53% and 58% of total primary productivity at the head and mouth of the inlet, respectively, and during the growing season micro-phytoplankton (>20 μm; mainly diatoms) was the most abundant size-class of phytoplankton. These rates of primary production are as high as or higher than those measured in other fjords, possibly because of a tidally-driven fortnightly gravity exchange that supplies nutrients to surface waters that enhance biological production when nutrients would otherwise be limiting. This exchange delivers nutrients at least as far inland as the head station, while nutrients associated with an eddy near the mouth may be the cause of even higher productivity there. We discuss the impact of these nutrient sources to Saanich Inlet on the records of paleoproduction generated from two Ocean Drilling Program cores extracted from this fjord, and suggest that the fortnightly exchange buffers variations in nutrient supply occurring on sub-decadal or decadal scales.