三峡小江回水区藻类集群与主要环境要素的典范对应分析研究

三峡成库后支流回水区水华频繁发生,备受关切。基于2年的野外跟踪观测结果,利用典范对应（CCA）分析方法,建立了藻类生境要素同藻类集群演替的多元统计模型。研究发现,所建立的CCA模型有效且具有较高的显著性;水库季节性调蓄所形成的不同藻类生境条件是诱导集群出现演替的关键。在低水位运行下,藻类生境近似于天然河道,总悬浮颗粒物和流量变化对集群影响明显,水体扰动剧烈迫使耐受于不稳定水动力条件的藻种易于形成优势;而在高水位运行状态下,藻类生境接近深水湖泊,适宜于低温和具有运动功能的藻类将耐受于该生境状态并在集群中占优。     

Seasonal and spatial distribution of chlorophyll-a concentrations and water conditions in the Gulf of Tonkin, South China Sea

The Gulf of Tonkin is a semi-closed gulf northwest of the South China Sea, experiencing reversal seasonal monsoon. Previous studies of water conditions have been conducted in the western waters of the gulf, but very few studies of the Chlorophyll-a (Chl-a) distribution have been carried out for the entire gulf. The present study investigates seasonal and spatial distributions of Chl-a and water conditions in the Gulf of Tonkin by analyzing Sea-viewing Wide Field-of-View Scanner (SeaWiFS) derived Chlorophyll-a (Chl-a), in situ measurements, sea surface temperatures (SST), and other oceanographic data obtained in 1999 and 2000. The results show seasonality of Chl-a and SST variations in the Gulf of Tonkin, and reveal phytoplankton blooming events in the center part of the gulf during the northeast monsoon season. In summer, Chl-a concentrations were relatively low (<0.3 mg m⁻³) and distributed uniformly throughout most of the area, with a belt of higher Chl-a concentrations along the coast, particularly the coast of Qiongzhou Peninsula; in winter, Chl-a concentration increased (0.5 mg m⁻³) in the entire gulf, and phytoplankton blooms offshore-ward from the northeast coast to the center of the gulf, while Chl-a concentrations reached high levels (0.8-1 mg m⁻³) in the center of the blooms. One peak of Chl-a concentrations was observed during the northeast monsoon season in the year. SST were high (27-29 °C) and distributed uniformly in summer, but lower with a large gradient from northeast (17 °C) to southwest (25 °C) in winter, while strong northeast winds (8-10 m/s) were parallel to the east coast of the gulf. Comparison of Chl-a values shows that SeaWiFS derived Chl-a concentrations match well with in situ measurements in most parts of the gulf in May 1999, but SeaWiFS derived Chl-a are higher than in situ data in river mouth waters. The seasonal variation of Chl-a concentrations and SST distribution were associated with the seasonally reversing monsoon; the winter phytoplankton blooms were related to vertical mixing and upwelling nutrients drawn by the northeast wind.     

A practical application of Droop nutrient kinetics (WR 1883)

Algal growth kinetics based on internal phosphorus concentration were incorporated into an existing eutrophication model. Application to a closed system resulted in damped oscillations in algal biomass and phosphate relative to a model with fixed composition. Peak biomass did not differ substantially, however, from that attained using a model with fixed, minimal phosphorus-to-carbon ratio. Sensitivity analyses were conducted following model application to the lower St. Johns River, Florida. Factor-of-two changes in key parameters had little influence on computed chlorophyll. Varying model parameters exerted a larger influence on dissolved phosphate concentration. We conclude Droop kinetics present a mechanism for regulating computed nutrient concentrations rather than computed chlorophyll concentrations.     

Phytoplankton community succession shaping bacterioplankton community composition in Lake Taihu, China

PCR-denaturing gradient gel electrophoresis (DGGE) and canonical correspondence analysis (CCA) were used to explore the relationship between succession of phytoplankton community and temporal variation of bacterioplankton community composition (BCC) in the eutrophic Lake Taihu. Serious Microcystis bloom was observed in July-December 2008 and Bacillariophyta and Cryptophyta dominated in January-June 2009. BCC was characterized by DGGE of 16S rRNA gene with subsequent sequencing. The DGGE banding patterns revealed a remarkable seasonality which was closely related to phytoplankton community succession. Variation trend of Shannon-Wiener diversity index in bacterioplankton community was similar to that of phytoplankton community. CCA revealed that temperature and phytoplankton played key roles in structuring BCC. Sequencing of DGGE bands suggested that the majority of the sequences were affiliated with common phylogenetic groups in freshwater: Alphaproteobacteria, Betaproteobacteria, Bacteroidetes and Actinobacteria. The cluster STA2-30 (affiliated with Actinobacteria) was found almost across the sampling time at the two study sites. We observed that the family Flavobacteriaceae (affiliated with Bacteroidetes) tightly coupled to diatom bloom and the cluster ML-5-51.2 (affiliated with Actinobacteria) dominated the bacterioplankton communities during Microcystis bloom. These results were quite similar at the two sampling sites, indicating that BCC changes were not random but with fixed pattern. Our study showed insights into relationships between phytoplankton and bacterioplankton communities at species level, facilitating a better understanding of microbial loop and ecosystem functioning in the lake.     

On the use of the FluoroProbe®, a phytoplankton quantification method based on fluorescence excitation spectra for large-scale surveys of lakes and reservoirs

Although microscope analysis is very useful for studying phytoplankton community composition, it does not allow for high frequency (spatial and/or temporal) data acquisition. In an attempt to overcome this issue, fluorescence-based approaches that use selective excitation of pigment antennae have spread rapidly. However, the ability of spectral fluorescence to provide accurate estimates of phytoplankton biomass and composition is still debated, and only a few datasets have been tested to date.In this study, we sampled of a wide range of water bodies (n = 50) in the Ile-de-France region (North Central France). We used the resulting extensive dataset to assess the ability of the bbe-Moldaenke FluoroProbe II (FP) to estimate phytoplankton community composition in lakes and reservoirs.We demonstrated that FP data yields better estimates of total phytoplankton biovolume than do spectrophotometric chlorophyll a measures and that FP data can be further corrected using the average chlorophyll a to biovolume ratio among phytoplankton groups. Overall, group-specific relationships between FP and biovolume data were consistent. However, we identified a number of cases where caution is required. We found that Euglenophytes are expected to depart from the global FP vs. biovolume relationship of the ‘green’ group due to varying Fv/Fm and pigment content in response to environmental conditions (photoautotrophic vs. photoheterotrophic growth). Then, it appears necessary to consider the composition of the Chromophytes community in order to obtain a good agreement between both biomass estimation methods. Finally, we confirmed the misattribution toward the ‘red’ group of phycoerythrin-containing cyanobacteria and the occurrence of a strong scattering in the relationship between the FP vs. biovolume of the ‘blue’ group that can be partly attributed to the occurrence of large colony-forming cyanobacteria (e.g., Microcystis spp, Aphanizomenon flos-aquae).We propose correcting procedures to improve the quality of data obtained from spectral fluorescence tools in the context of large-scale sampling of lakes and reservoirs.     

浮游植物细胞图像识别方法的研究

讨论了如何利用数学形态学方法提取浮游植物细胞图像的面积（A）、周长（P）以及通过图像细化提取细胞的长（L）等特征信息;提出了利用这3个特征参数的比值（A／P,A/L和P／L）形成的特征向量作为进行细胞分类的依据,然后提出了利用最近邻准则对浮游植物进行自动识别的试探聚类算法,该方法可以通过学习提高识别率。通过对17种浮游植物细胞图像的识别实验,证明了该方法的识别准确率在95％以上,可以有效预防大面积赤潮的发生,对于赤潮爆发后的鉴定也有一定意义。     

Effects of vertical mixing on phytoplankton blooms in Xiangxi Bay of Three Gorges Reservoir: implications for management

Since the initial filling of Three Gorges Reservoir (TGR), serious phytoplankton blooms have occurred in its tributary bays. Cyanobacteria blooms have been observed in a number of tributary bays and threaten the drinking water security of residents in the TGR region. To identify the key factors controlling phytoplankton blooms in tributary bays and propose an effective management strategy, a one-year water quality study (November 2009 to October 2010) was conducted in Xiangxi Bay (XXB) of TGR. The results show that a rapid decrease in mixing depth is associated with the spring bloom, fading of the fall bloom occurs with the rapid increase in mixing depth, and an extremely shallow mixing depth is associated with cyanobacteria blooms that predominate during the summer. Development of thermal stratification in XXB is the major cause of seasonal variation in mixing depth and density current intrusion from TGR is the major cause of short-term variation in mixing depth. The seasonal thermal stratification of XXB is disrupted by sufficiently large water level fluctuations in TGR. The density current is lifted from mid-depths to the surface and chlorophyll a concentrations rapidly decrease in response. Based on these findings, a conceptual model is proposed for a management strategy to control phytoplankton blooms in tributary bays via controlled releases from TGR.     

Harmful algae and their potential impacts on desalination operations off southern California

Seawater desalination by reverse osmosis (RO) is a reliable method for augmenting drinking water supplies. In recent years, the number and size of these water projects have increased dramatically. As freshwater resources become limited due to global climate change, rising demand, and exhausted local water supplies, seawater desalination will play an important role in the world's future water supply, reaching far beyond its deep roots in the Middle East. Emerging contaminants have been widely discussed with respect to wastewater and freshwater sources, but also must be considered for seawater desalination facilities to ensure the long-term safety and suitability of this emerging water supply. Harmful algal blooms, frequently referred to as ‘red tides’ due to their vibrant colors, are a concern for desalination plants due to the high biomass of microalgae present in ocean waters during these events, and a variety of substances that some of these algae produce. These compounds range from noxious substances to powerful neurotoxins that constitute significant public health risks if they are not effectively and completely removed by the RO membranes. Algal blooms can cause significant operational issues that result in increased chemical consumption, increased membrane fouling rates, and in extreme cases, a plant to be taken off-line. Early algal bloom detection by desalination facilities is essential so that operational adjustments can be made to ensure that production capacity remains unaffected. This review identifies the toxic substances, their known producers, and our present state of knowledge regarding the causes of toxic episodes, with a special focus on the Southern California Bight.     

Which offers more scope to suppress river phytoplankton blooms: Reducing nutrient pollution or riparian shading?

River flow and quality data, including chlorophyll-a as a surrogate for river phytoplankton biomass, were collated for the River Ouse catchment in NE England, which according to established criteria is a largely unpolluted network. Against these data, a daily river quality model (QUESTOR) was setup and successfully tested. Following a review, a river quality classification scheme based on phytoplankton biomass was proposed. Based on climate change predictions the model indicated that a shift from present day oligotrophic/mesotrophic conditions to a mesotrophic/eutrophic system could occur by 2080. Management options were evaluated to mitigate against this predicted decline in quality. Reducing nutrient pollution was found to be less effective at suppressing phytoplankton growth than the less costly option of establishing riparian shading. In the Swale tributary, ongoing efforts to reduce phosphorus loads in sewage treatment works will only reduce peak (95th percentile) phytoplankton by 11%, whereas a reduction of 44% is possible if riparian tree cover is also implemented. Likewise, in the Ure, whilst reducing nitrate loads by curtailing agriculture in the headwaters may bring about a 10% reduction, riparian shading would instead reduce levels by 47%. Such modelling studies are somewhat limited by insufficient field data but offer a potentially very valuable tool to assess the most cost-effective methods of tackling effects of eutrophication.     

Microbiological and chemical study of the nile river water quality

This study aims to Integrate the biological and chemical characteristics of Nile river to evaluate the trophic and autotrophic state of the river. The use of biological indices especially phytoplankton as an indicator of pollution, and the relation between some chemical variables revealed that the Nile river has poor quality water and light pollution conditions. Regarding the bacteriological examination, the results showed seasonal fluctuation of the faecal indicator bacteria, new indicators of pollution and pathogenic bacteria with highly significant correlation between the faecal bacterial indicators. The use of total yeasts as indicators of pollution revealed significant negative correlation with classical bacterial indicators. The statistical analysis between some bacterial and chemical variables (algal groups and chlorophyll “a") indicated significant relation between each other. The variation of zooplankton counts in the four seasons was positively correlated with the chlorophyll “a” concentration, both zooplankton and chlorophyll “a” content peak in the winter. The virological examination showed only one sample which induced CPE in BGM cells, and the virus count was 12 plaque forming unit per liter (PFU/L).