The contribution of various types of settling particles to the flux of organic carbon in the Gulf of St. Lawrence

The contents of 31 samples from free-drifting sediment traps deployed in the Gulf of St. Lawrence (GSL) were analyzed for the individual contribution of the different types of particles encountered to the total particulate organic carbon (POC) flux. Two trap models were used in 1993-1994: small traps at 50 m depth and large traps at 50 and 150 m. Total POC fluxes averaged 42 mg C m⁻² d⁻¹ for the more reliable large trap and 149 mg C m⁻² d⁻¹ for the small trap. The POC fluxes were attributed to different classes of particles based upon microscopically determined particle dimensions and carbon/volume algorithms available in the literature. Fecal pellets, followed by phytoplankton, were the major attributable components, with important contributions by microzooplankton, particularly during the summer of 1994. The mean fluxes for pellets (6 and 60 mg  C m⁻² d⁻¹, for the large and small traps, respectively) and phytoplankton (3.2 and 42.9 mg C m⁻² d⁻¹) were in the range of those encountered in other areas of moderate primary productivity. Mean zooplankton carbon fluxes (1.8 and 8.5 mg C m⁻² d⁻¹, respectively), however, reflect higher than average zooplankton abundances in the GSL. The C fluxes of specific algal groups confirmed the existence of three trophic regimes previously identified from water column studies and numeric cell fluxes: (1) a period when diatoms were dominant during the spring, (2) a longer interval, which was dominated by dinoflagellates at most others times of the year, and (3) a period of transition during summer. Carbon of animal origin dominated the attributable flux, including an important fraction associated with heterotrophic dinoflagellates. The contribution of marine snow to the total flux (estimated as the difference between the total POC flux and the sum of the attributed components) frequently amounted to more than 60%. The true importance of marine snow remains uncertain, however, because the errors associated with each of the measured components accumulate to produce large uncertainties. The methodological problems involved are discussed.     

太湖水质时空特性及其与蓝藻水华的关系

以太湖2005-2007年的连续监测资料为基础,运用聚类分析和自相关分析方法,针对总无机磷,总无机氮、水温等环境理化因素与叶绿素a进行时空序列分析,初步归纳了当前太湖水质指标变化的空间特点、时问周期性及其与蓝藻水华暴发的关系.结果表明,太湖水质的空间分布大致分为三个人湖河口、四个湖湾、湖心区、西部湖区、东部湖区等十个区...     

贵州百花湖麦西河河口浮游植物群落结构及与环境因子关系

2009年7月至2010年6月,以每月一次的频率对百花湖(水库)麦西河河口浮游植物群落结构和环境因子进行调查.监测到浮游植物66种(属),浮游植物主要由绿藻、硅藻和蓝藻组成,夏秋季湖泊假鱼腥藻(Pseudanabaena limnetica)为优势浮游植物,而冬春季梅尼小环藻(Cyclotella meneghinia...     

贵州高原水库冬季浮游植物中汞及甲基汞分布特征

为了解贵州高原水库浮游植物中汞和甲基汞的分布特征及浮游植物对汞及甲基汞的富集特点,于2012年12月对贵州省的5座高原水库中浮游植物和汞形态进行采样调查.研究结果表明:冬季贵州高原水库浮游植物群落主要是由硅藻组成,5座水库浮游植物丰度有明显差异.百花湖大坝处浮游植物丰度最高,为29.05×104cells/L;三板溪水库浮游植物丰度最低,仅为0.49×104cells/L.浮游植物中总汞和甲基汞的浓度分别在29.29~277.07 ng/g和1.12~10.93 ng/g之间,总汞含量以百花湖岩脚寨最高,甲基汞含量以百花湖大坝最高.总汞和甲基汞在浮游植物中的生物富集系数分别在1.42×104~9.78×104和3.10×104~4.43×105之间.在浮游植物富集无机汞及甲基汞的系数中,百花湖中浮游植物对无机汞生物富集系数最高,而红枫湖中浮游植物对甲基汞的生物富集系数最高.浮游植物种类组成不同对汞及甲基汞的生物富集有影响.浮游植物中的总汞与水体中的总汞、甲基汞和溶解态甲基汞都存在显著的相关关系,浮游植物中的甲基汞与水体中的总汞及甲基汞不存在显著相关性.甲基汞在浮游植物中富集不是简单的吸收,存在着影响甲基汞在浮游植物中富集的其它因素.浮游植物中的甲基汞与水体富营养化环境因子(透明度、总氮、硝氮)均呈负相关关系,表明水体富营养化的程度不同对浮游植物中的甲基汞浓度有影响.     

太湖蓝藻水华灾害灾情评估方法初探

通过对太湖蓝藻水华灾害影响分析,探讨了太湖蓝藻水华灾害灾情评估指标的选取和评价标准的划分,并采用模糊评价模型构建太湖蓝藻水华灾害灾情综合评估方法.评价指标分为影响人口、影响范围、生态环境影响和经济损失四个方面,其中影响人口指标为受灾人口,影响范围指标包括蓝藻水华面积发生百分比和影响时间,生态环境影响指标包括藻细胞浓度、...     

滇池蓝藻水华光谱特征、遥感识别及暴发气象条件

通过研究滇池蓝藻水华在可见光、红外谱段的光谱特征,并利用假彩色合成法以及归一化植被指数(NDVI)法进行了滇池蓝藻水华信息的遥感识别和提取,进而对提取结果进行了对比分析.结果表明:假彩色合成图的绿色区域和NDVI值大于-0.1的区域,为蓝藻水华区域.-0.1≤NDVI≤0.2时,轻度水华,像元内水华覆盖度为0-30%;0.2NDVI≤0.4时,中度水华,像元内蓝藻水华覆盖度为31%-80%;NDVI0.4时,重度水华,水华浓厚,像元内蓝藻水华覆盖度为81%-100%.同时研究了激励滇池蓝藻水华暴发的关键气象因子和指标.滇池蓝藻水华暴发的关键时期是6-9月份,影响滇池蓝藻暴发的关键因子是日照和风速.6-9月份连续4-5h的光照,且风速≤2m/s的气象条件组合极易引起蓝藻水华暴发.     

Calcium alginate immobilized marine microalgae: experiments on growth and short-term heavy metal accumulation

Growth of 11 calcium alginate immobilized marine microalgal species belonging to eight taxonomical groups has been checked in the present work. Cellular densities inside the calcium alginate beads were monitored during 17 days. Good growth and maintenance of the structure of the beads were both found for some of the assayed species. One of those species (Tetraselmis chui, Prasinophyceae) was selected in order to perform a short term (up to 24 h) heavy metal accumulation experiment. Beads of calcium alginate containing (or not) cells of T. chui were exposed to 820 μg L⁻¹ Cu and 870 μg L⁻¹ Cd separately during a 24 h period, and accumulation of heavy metals in the beads was measured after this time and compared. Concentration of each metal in the supernatants was monitored at 5, 10, 60 min and 24 h from the beginning of the experiment. After 24 h, practically all Cu was removed by the beads. Beads with immobilized algae removed around 20% of total Cd, while beads without algae removed half of that percentage.     

Dinoflagellate cysts in recent marine sediments from Thermaikos Gulf, Greece: Effects of resuspension events on vertical cyst distribution

A qualitative and semi-quantitative study of recent dinoflagellate cysts has been undertaken in the NW part of Aegean Sea, Thermaikos Gulf (Eastern Mediteranean), before (September 2001), during (October 2001) and after 120 days (February 2002) of intensive trawling activities. This is the first survey of recent dinoflagellate cysts from Greek marine coastal environments. Sediment samples were collected with a corer and the vertical distribution of the cysts was studied at five different layers, from 0 to 10 cm. Dinoflagellate cysts were both abundant and diverse. Cysts were found over the whole sampling area and periods, with concentrations ranging between 247–3202 cysts cm⁻³. Thirty-six cyst types were encountered, of which 32 were identified to species level, representing 12 genera. It seems that significant local resuspension, related to the onset of the trawling period and stirring up of the sediment, contributed to mixing of the upper layers, resulting to more homogenous cyst profiles in the sediment. Viable cysts constituted 16–60% of the total cyst abundance. The abundance peaks of viable cysts within the subsurface sediment layers, observed during the undisturbed period, disappeared during October. In February, the reduction of cyst concentration was associated to a loss of viable cysts, whilst the ratio of viable/empty cysts ranged between 0.30 and 0.67. The abundance of the different dinoflagellate species, in their active form, was monitored in order to detect any relationship between the concentration of cysts in the top 10 cm of sediment and blooms of algae in the water column. Cysts of potentially toxic species, causing Paralitic Shellfish Poisoning (PSP), such as Alexandrium cf. tamarense, A. cf. affine, A. cf. minutum, as well as Gymnodinium catenatum, were detected in the cyst survey.     

Horizontal distribution and transport processes of bloom-forming Microcystis in a large shallow lake (Taihu, China)

The horizontal distribution of bloom-forming Microcystis in a specific lake area and the transport of Microcystis by wind-driven lake currents between Meiliang Bay and the open water of Taihu Lake were measured during continuous field observations from August 21 to 25, 2006. During the observations, the horizontal distributions of Microcystis, represented by Chlorophyll a, showed a clear concentration toward downwind lake areas. According to the lake currents and the Chl a concentrations on the boundary line between the Meiliang Bay and the open water, the transported Chl a was less than 2% of the total weight of Chl a in Meiliang Bay on August 22, 24 and 25. The results suggest that the horizontal distribution of the bloom-forming Microcystis was strongly affected by the wind conditions, and the wind-driven Microcystis accumulation was mainly determined by surface drift; the transport of Microcystis by lake currents was much less important in this large, shallow lake.     

Changes of the plankton community composition during chemical neutralisation of the Bockwitz pit lake

Lake Bockwitz, a pit lake in a former lignite open-cast mine south of Leipzig (Germany), was neutralised (from pH 2.65 to pH 7.1) by addition of soda ash (14,620 t) from 2004 to 2007. The additions had to be continued due to ongoing inflows of acid ground and surface water. This paper reports on the changes in the plankton community accompanying the neutralisation.At the beginning, the community composition and biomass was comparable to other acidic pit lakes, i.e. the pigmented flagellates Chlamydomonas and Ochromonas dominated the autotrophs, and ciliates and rotifers were the top predators. The biomass was small (maximum 2 mg fresh weight per litre) and decreased until the end of 2008. With increasing pH, the autotrophic community became more diverse, whereby diatoms, chrysophyceans and blue greens contributed significantly to biomass. Although neutral pH conditions were achieved in autumn 2007, picocyanobacteria were not present until the end of 2008. In addition, crustaceans were under-represented in terms of biomass and diversity. Daphnids were not found. We attributed this to short-term changes of the ionic composition of the water and to the limited time available for non-acido-tolerant organisms to colonise the system.