Downstream carbon transport and surface CO2 evasion in the Hanjiang River Network and their implications for regional carbon budget.

Fluvial carbon fluxes have been increasingly recognized as important components of the global carbon budget. However, it is challenging to accurately quantify carbon fluxes in river networks; therefore, the role of carbon fluxes in the regional carbon budget remains poorly understood. The Hanjiang River Network (HRN) is located in a subtropical monsoon climate zone, and its material transport has a notable impact on the Changjiang River. In this study, it was hypothesized that the total fluvial carbon fluxes from the river network in the subtropical monsoon climate zone are dominated by vertical CO2 evasion and account for a large fraction of terrestrial net primary productivity (NPP) (e.g., 10 %) and fossil CO2 emissions (e.g., 30 %), which is roughly equivalent to the global average. Therefore, the downstream export of three carbon fractions and CO2 evasion were estimated in the HRN over the last two decades and the findings were compared with NPP and fossil CO2 emissions in the basin. The results suggest that approximately 2.14-6.02 Tg C year-1 (1 Tg = 1012 g) of carbon is exported in the HRN. Vertical CO2 evasion represents the largest destination at 1.22-5.34 Tg C year-1 or 68 % of the total fluvial carbon flux component, corresponding to 1.5 %-11 % of the fossil CO2 emissions. Downstream export of dissolved inorganic carbon is the second largest destination with a magnitude of 0.56-1.92 Tg C year-1. Downstream organic carbon export plays a relatively small role with a magnitude of 0.04-0.28 Tg C year-1. The findings also indicate that the offset of total fluvial carbon fluxes from terrestrial NPP is unexpectedly small (2.0 %-5.4 %). Data availability and the simplification of carbon processes introduced uncertainty; therefore, future research should incorporate a fuller representation of fluvial carbon processes and fractions to improve regional-scale carbon accounting.

Autochthonous sources and drought conditions drive anomalous oxygen-consuming pollution increase in a sluice-controlled reservoir in eastern China.

Freshwater reservoirs are an important type of inland waterbody. However, they can suffer from oxygen-consuming pollution, which can seriously threaten drinking water safety and negatively impact the health of aquatic ecosystems. Oxygen-consuming pollutants originate from both allochthonous and autochthonous sources, and have temporally and spatially heterogeneous drivers. Datanggang Reservoir, China, is located in a small agricultural watershed; it is controlled by multiple sluice gates. Anomalously high oxygen consumption indicators were observed in this reservoir in March 2021. Here, it was hypothesized that autochthonous sources were the primary drivers of oxygen-consuming pollution in the reservoir under drought conditions. Datasets of water quality, precipitation, primary productivity, and sediment were used to analyze water quality trends in the reservoir and inflow rivers, demonstrating the effects of allochthonous inputs and autochthonous pollution. No correlation was found between reservoir oxygen consumption indicators and allochthonous inputs; reservoir oxygen consumption indicators and chlorophyll-a concentration were significantly positively correlated (p < 0.05). Substantially lower precipitation and higher water temperature and pH (compared to historical levels) were also observed before the pollution event. Therefore, during this period the hydrological conditions, water temperature, pH, and other variables caused by short-term drought conditions may have facilitated phytoplankton growth in the reservoir. This contributed to a large increase in autochthonous oxygen-consuming pollutants, as reflected by the abnormally high indicators. Sediments contaminated with organic matter may also have been an important contributor. As the effects of environmental management and pollution control continue to emerge, exogenous pollutants imported from the land to reservoirs are currently effectively controlled. However, endogenous pollutants driven by a variety of factors, such as meteorology and hydrology, will likely become the main drivers of short-term changes in oxygen-consuming pollution in freshwater reservoirs in the foreseeable future.

Microplastic pollution in the Yangtze River Basin: Heterogeneity of abundances and characteristics in different environments.

Microplastic pollution in the Yangtze River Basin has become a major concern; however, the variations in different environmental compartments are unknown. Here, we compiled published information including detection methods, occurrence, and characterization of microplastics from 624 sampling sites in river water, river sediment, lake and reservoir water, and lake and reservoir sediment in the Yangtze River Basin. The spatial distribution of sampling sites shows fractal pattern and was uniformly concentrated around the main stream of the Yangtze River and the lake geographical zone. Collection, pretreatment, identification, and quantification processes varied among different studies. Non-parametric tests were performed to compare the different microplastic indices. A Pearson correlation analysis was used to study the relationship between microplastic pollution and local socioeconomic conditions. We found that the microplastic size and abundance distribution in river water and lake and reservoir water showed different patterns for different sampling methods, indicating that different methods influenced the results. Population density and urbanization rate are suggested to be important factors influencing the spatial heterogeneity of microplastic abundances in water, rather than in sediment. The microplastic abundances in lake and reservoir water were higher than that in river water in bulk samples. However, microplastic abundances among different sediment environments shows no significant difference. For bulk water samples and sediment samples overall, the proportion of small microplastics (<1 mm, i.e. SMP), fibers, transparent debris, and polypropylene (PP) were 65.1%, 67.8%, 31.8%, and 29.7%, respectively. The microplastic characteristics of lake and reservoir water and sediment were similar, differing from those of river water and sediment. This study provides the first basin scale insight into microplastic occurrence and characteristics in different environments in the Yangtze River Basin.

A data-driven framework for spatiotemporal characteristics, complexity dynamics, and environmental risk evaluation of river water quality.

To evaluate the evolution of river water quality in a changing environment, measuring the objective water quality is critical for understanding the rules of river water pollution. Based on the sample entropy theory and a nonlinear statistical method, this study aims to identify the spatiotemporal dynamics of water quality and its complexity in the Yangtze River basin using time series data, to separate the contributions of human activity and climate change to water quality, and to establish a data-driven risk assessment framework for the spatial (potential risk) and temporal (direct risk) aspects of water pollution. The results demonstrate that the spatiotemporal dynamics of water quality and sample entropy in each monitoring section are closely related to the characteristics of the corresponding location. The water quality of the main stream is superior, and its complexity is less than that of the tributaries. Cascade reservoir operation and vegetation status, agricultural production, and rainfall patterns exert great influences in the upper, middle, and lower reaches, respectively. Dam construction, urban agglomeration development, and interactions between river and lake are also influencing factors. An attributional analysis found that climate change and human activities negatively contributed to the evolution of NH3-N concentration in most of the monitored sections, and the average relative contribution rates of human activities to changes in water quality in the main and tributary streams were -55.46% and -48.49%, respectively. In addition, the construction of data-driven risk assessment framework can efficiently and accurately assess the potential and direct water pollution risks of rivers.

Effects of harvest time and desalination of feedstock on Spartina alterniflora biochar and its efficiency for Cd2+ removal from aqueous solution.

Cadmium (Cd2+), as the primary contaminant in Chinese soils, is dangerous to human health and ecological security. Invasive plant Spartina alterniflora in Chinese coastal wetlands presents a promising feedstock for biochar, which is an efficient adsorbent for heavy metal removal. S. alterniflora harvested in summer, autumn and winter were pyrolyzed to produce biochars. We analyzed the effects of harvest time and desalination of feedstock on biochar properties and Cd2+ adsorption capacity in aqueous solution. Biochars were characterized by pH probe, elemental analyzer, SEM, BJH, BET, and FTIR, and the Cd2+ concentrations were measured using AAS. Except pH (9.85-10.95) and nitrogen contents (0.71-1.59%), other biochar properties had no linear correlations with harvest time. Biochars produced from feedstock harvested in autumn had the highest carbon contents (73.25%) and lowest functional groups diversity (CC and -CHx). The pH and carbon contents (64.44-73.25%) were increased by desalination treatment. The surface area (0.48-2.27 m2/g), total pore volume (0.0015-0.0055 mL/g), mesopore volume (0.0015-0.0052 mL/g), and Cd2+ adsorption capacities (16.29-32.34 mg/g) were affected by desalination treatment, and the effects varied with harvest time. Biochars produced from desalted feedstock harvested in summer and untreated feedstock harvested in winter showed higher surface area, porosity, and Cd2+ adsorption capacity. Moderate salt contents (1.5-3.0% in chloride content) in feedstock promote the formation of biochars with higher surface area and porosity.

A systematic approach for watershed ecological restoration strategy making: An application in the Taizi River Basin in northern China.

Aiming to protect freshwater ecosystems, river ecological restoration has been brought into the research spotlight. However, it is challenging for decision makers to set appropriate objectives and select a combination of rehabilitation acts from numerous possible solutions to meet ecological, economic, and social demands. In this study, we developed a systematic approach to help make an optimal strategy for watershed restoration, which incorporated ecological security assessment and multi-objectives optimization (MOO) into the planning process to enhance restoration efficiency and effectiveness. The river ecological security status was evaluated by using a pressure-state-function-response (PSFR) assessment framework, and MOO was achieved by searching for the Pareto optimal solutions via Non-dominated Sorting Genetic Algorithm II (NSGA-II) to balance tradeoffs between different objectives. Further, we clustered the searched solutions into three types in terms of different optimized objective function values in order to provide insightful information for decision makers. The proposed method was applied in an example rehabilitation project in the Taizi River Basin in northern China. The MOO result in the Taizi River presented a set of Pareto optimal solutions that were classified into three types: I - high ecological improvement, high cost and high benefits solution; II - medial ecological improvement, medial cost and medial economic benefits solution; III - low ecological improvement, low cost and low economic benefits solution. The proposed systematic approach in our study can enhance the effectiveness of riverine ecological restoration project and could provide valuable reference for other ecological restoration planning.

Characterization of dissolved organic matter in Dongjianghu Lake by UV-visible absorption spectroscopy with multivariate analysis.

UV-visible absorption spectroscopy coupled with principal component analysis (PCA) and hierarchical cluster analysis (HCA) was applied to characterize spectroscopic components, detect latent factors, and investigate spatial variations of dissolved organic matter (DOM) in a large-scale lake. Twelve surface water samples were collected from Dongjianghu Lake in China. DOM contained lignin and quinine moieties, carboxylic acid, microbial products, and aromatic and alkyl groups, which in the northern part of the lake was largely different from the southern part. Fifteen spectroscopic indices were deduced from the absorption spectra to indicate molecular weight or humification degree of DOM. The northern part of the lake presented the smaller molecular weight or the lower humification degree of DOM than the southern part. E2/4, E3/4, E2/3, and S2 were latent factors of characterizing the molecular weight of DOM, while E2/5, E3/5, E2/6, E4/5, E3/6, and A2/1 were latent factors of evaluating the humification degree of DOM. The UV-visible absorption spectroscopy combined with PCA and HCA may not only characterize DOM fractions of lakes, but may be transferred to other types of waterscape.

[Response Behaviors of Heavy Metals at Tidal Currents Interface and Salinity Interface in the Estuary Area].

In China, trace metals (such as dissolved Cu, Zn, Pb, Cd, and Cr) are the routine mandatory monitoring indicators in existing Freshwater Quality Standard (FWQS, 2002) and Seawater Quality Standard (SWQS, 1997). Using Daliao River estuary as an example, we tried to research the general response patterns of these metals in estuarine system. Firstly, we determined the location of FSI (freshwater-seawater interface) and TCI (tidal currents interface), which were based on biological, chemical and geographic similarities by descriptive and quantitative methods, respectively. Secondly, two hypotheses were proposed to explain the difference based on distribution coefficient Kd along salinity and SS (suspended solids) gradient, these results revealed that the indicators for As, Cd and Cr may be prone to be affected by salinity, and the ones in the second pattern may be more sensitive to SS. Finally, we classified the response behaviors into two patterns based on the changing trends along the distance and magnitudes affected by the FSI and TCI: 1the obvious boundary break point from FSI for As, Cd and Cr; 2 the boundary zones from TCI for Zn, Cu, Pb and Ni. The partitioning behaviors showed similar changing trends at particle and sediment phases, especially for particle phase, depending on the concentration of SS along the salinity. The difference between general behaviors for the two patterns mainly existed at water phase. In general, this paper highlighted the need to consider the background difference of trace metals and identified the sensitive indicators controlled by different environment factors (such as salinity and SS) based on the native estuarine characteristics. Our work will assist the implementation of updating the current water quality standards in China.

Bioassessment of marine sediment quality using meiofaunal assemblages in a semi-enclosed bay.

In order to assess marine sediment quality of a semi-enclosed bay, sediment and meiofaunal samples were analyzed at 35 stations in coastal waters of Bohai Bay, China. Concentrations of heavy metals (Cd, Cr, Cu, Ni, Pb, Zn, Co and Mn) in sediment were measured and the Hakanson potential ecological risk index coupled with the ratio of nematodes to copepods (N/C ratio) was used. Results showed that the concentration of Mn was the highest while Cd was the main risk contributor. The Hakanson potential ecological risk index indicated that all pollutants posed low risks in the study area. However, the N/C ratio exhibited different results compared with Hakanson potential ecological risk index. BIOENV analysis identified the concentration of Ni and sediment grain size as the most important environmental variables influencing meiofaunal assemblages. The present study indicated that, in marine sediment quality assessments, meiofaunal assemblages should be involved besides pollutant concentrations.

Bacterial community structure and its regulating factors in the intertidal sediment along the Liaodong Bay of Bohai Sea, China.

Investigating the entire species composition of the microorganisms is crucial to understand their roles in the biogeochemical cycles. Metagenomic DNA was extracted from six intertidal sediment samples along the Liaodong Bay of Bohai Sea, China, and was sequenced which yielded a total of 64,496 high-quality sequences from 83,485 reads, with an average read length of 463 bp. The sequences were assigned to 20,718 operational taxonomic units (OTUs) which belong to 42 phyla, 90 classes and 376 genera. At the different taxonomic levels, both the dominants and their abundances varied significantly among the six sites. Phylum Proteobacteria predominated in all the six samples, however, not only the abundance of this phylum varied significantly but also the proportions of Alpha-, Beta-, Gamma-, and delta- and epsilon-Proteobacteria varied greatly. The site sediment median grain size and dissolved oxygen (DO) revealed to be key factors regulating the observed significant differences in the bacterial community between sampling sites. In addition, the bacterial composition might be more sensitive than the richness and diversity to the studied environmental conditions.

Towards a protocol for stream macroinvertebrate sampling in China.

Standard protocols are critical for maximizing data comparability and aggregation in national monitoring programs, and taxa richness is a common indicator of site condition and biological diversity. There are two general approaches for sampling stream macroinvertebrate assemblages: targeted richest habitat and site wide. At seven sites, we compared three methods: Ontario Benthic Biomonitoring Network (OBBN), Environmental Monitoring and Assessment Program (EMAP), and Rapid Bioassessment Protocol (RBP). The OBBN method produced a biased sample at a site with a single small riffle, the RBP method produced the most total taxa, and the EMAP method produced the most taxa at four sites and the most individuals at six sites. The RBP method produced asymptotes for percent tolerant individuals, percent chironomid individuals, and Hilsenhoff Biotic Index score after five to ten stations. The EMAP method produced asymptotes for those metrics after 10 to 20 stations per site. The EMAP method typically required half the number of stations as the RBP method to obtain 70-90% of true taxa richness as estimated by the Jaccard coefficient. We conclude that the EMAP method is preferable because of its greater precision in taxa richness estimates.

Eutrophication development and its key regulating factors in a water-supply reservoir in North China.

Yanghe Reservoir is an important source of drinking water for Qinhuangdao City, North China; however, in recent decades this water source has been eutrophic with recurrent summer cyanobacterial blooms. The trophic grade of the system in summer was mesotrophic-eutrophic in 1990 and became hypertrophic in 2011. The nutrient availability is extremely high during the entire year, and the water temperature should be the primary driver of the summer blooms. In May-October of 2010 and 2011, abrupt variations were observed in the Secchi depth (SD) and chlorophyll a (Chl-a), and both the correlated analysis of Chl-a-SD and trophic status indices (TSI) deviation (TSI(Chl-a)-TSI(SD)) showed that algal cell density dominated light attenuation. During the algal bloom outbreak, the microcystin concentration was found to vary between 0.35-2.12 microg/L in 2010 and 0.11-1.86 microg/L in 2011. The maximum microcystin content was more than two times the safety limit required for drinking water. Inflow discharges were most concentrated in the summer, with periods of lower residence time and the largest water level fluctuation over the entire year. When a high availability of nutrients promoted a high Chl-a concentration in the whole system, it appeared that the instability caused by the decrease in residence time could not produce effective changes in the cyanobacterial abundance. The results indicated that nutrient enrichment in the aquatic systems of Yanghe Reservoir is the most serious problem and that the status would not been modified effectively by increasing hydrological fluctuations (e.g., decreasing the residence time). Therefore, decreasing the nutrient concentrations is the only route to improve the water quality of this reservoir.

Phytoplankton and eutrophication degree assessment of Baiyangdian Lake wetland, China.

Eight typical sampling sites were chosen to investigate the phytoplankton community structure and to assess the eutrophication degree of Baiyangdian Lake in 2009. Our results showed that among the total 133 species identified, Cyanophyta, Chlorophyta, and Bacillariophyta dominated the phytoplankton community. In spring, Chlorophyta and Bacillariophyta were the dominant phyla, and the dominant species included Chlorella sp., Chroomonas acuta Uterm., and Microcystis incerta Lemm.; the density of the phytoplankton ranged from 496 × 10(4) to 6256 × 10(4) cells/L with an average of 2384 × 10(4) cells/L. However, Chlorophyta and Cyanophyta became the dominant phyla in summer, and the dominant species were Chlorella sp., Leptolyngbya valderiana Anagn., and Nephrocytium agardhianum Nageli.; the density of the phytoplankton varied from 318 × 10(4) to 4630 × 10(4) cells/L with an average of 1785 × 10(4) cells/L. The density of the phytoplankton has increased significantly compared to the previous investigations in 2005. The index of Carlson nutritional status (TSIM) and the dominant genus assessment indicated that the majority of Baiyangdian Lake was in eutrophic state.

[Assessing the benthic ecological status in Yangtze River Estuary using AMBI and M-AMBI].

Both AMBI and M-AMBI could effectively assess the benthic ecological status of estuaries and coastal systems with soft sediments, and show the response of benthic communities to human pressures and natural changes. To monitor the ecological status of Yangtze River Estuary, macroinvertebrate samples and environmental data were collected in April 2009. Results showed that the benthic habit of Yangtze River Estuary was disturbed to various degrees, especially in the watersheds of Hangzhou Bay, coastal areas of Zhoushan islands and in the inner part of Yangtze River Estuary, which was related to land resourced discharges, eutrophication and large amounts of coastal projects. No significant difference was found between the calculation results of AMBI and M-AMBI based on density and biomass, as indicated by one-way Analysis of Variance (ANOVA). Compared with AMBI, M-AMBI could be more effective to assess the ecological status of Yangtze River Estuary because M-AMBI matched the community structure and environmental variables better. Moreover, according to results of Pearson correlation and linear regression analysis, significant negative relationships were found between the eutrophication index both in the surface and bottom water layers and M-AMBI, but no significant relationship was found between the eutrophication index and AMBI. Therefore, M-AMBI could be more suitable in indicating the eutrophication stress of Yangtze River Estuary.

Temporal and spatial distribution of red tide outbreaks in the Yangtze River Estuary and adjacent waters, China.

Between 1972 and 2009, evidence of red tide outbreaks in the Yangtze River Estuary and adjacent waters was collected. A geographic information system (GIS) was used to analyze the temporal and spatial distribution of these red tides, and it was subsequently used to map the distribution of these events. The results show that the following findings. (1) There were three red tide-prone areas: outside the Yangtze River Estuary and the eastern coast of Sheshan, the Huaniaoshan-Shengshan-Gouqi waters, and the Zhoushan areas and eastern coast of Zhujiajian. In these areas, red tides occurred 174 total times, 25 of which were larger than 1000 km(2) in areal extent. After 2000, the frequency of red tide outbreaks increased significantly. (2) During the months of May and June, the red tide occurrence in these areas was 51% and 20%, respectively. (3) Outbreaks of the dominant red tide plankton species Prorocentrum dong-haiense, Skeletonema costatum, Prorocentrum dantatum, and Noctiluca scientillan occurred 38, 35, 15, and 10 times, respectively, during the study interval.

Analysis of the bacterial community in the two typical intertidal sediments of Bohai Bay, China by pyrosequencing.

For full understanding of the bacterial community in the intertidal zones of Bohai Bay, China, we used pyrosequencing-based approach to analyze the 16S rRNA gene of bacteria in the sediments from the two typically intertidal zones - Qikou (Qi) and Gaoshaling (Ga). Results showed that, at a 0.03 distance, the sequences from the Qi sediment were assigned to 3252 operational taxonomic units (OTUs) which belong to 34 phyla, 69 classes and 119 genera, while the 3740 OTUs from the Ga sediment were affiliated with 33 phyla, 66 classes and 146 genera. Comparing the bacterial communities inhabiting in the two intertidal sediments, we observed significant difference in the dominant composition and distribution at phylum, class and genus levels. Canonical correspondence analysis (CCA) showed that the median grain size and DO were the most important factors regulating the bacterial abundance and diversity, while the other environmental factors have effects with different degree.

[Comparison of trophic status analysis of the Daning River within the Three Gorges Reservoir before and after experimental impoundment].

We evaluated 4-year data set to assess the trophic state and limiting factors of the Three Gorges Reservoir (TGR) during the experimental impounding period (September 2005 to September 2007) and the normal operating period (September 2008 to September 2010). The results indicated that there had been appeared new characteristics in spatial and temporal distribution of trophic state indices after impoundment. The trophic state indices (TSI(TP)) showed increased trend after the TGR impoundment during the study area, but TSI(TN) and TSI(SD) had no significant changes after the TGR impoundment. The values of TSI(CHL) showed increased trend after the TGR impoundment in S1, and the values of TSI(CHL) did not show obvious changes in S2, S3 and S4 after the TGR impoundment. The values of TSI(TN), TSI(TP) and TSI(SD) show similar spatial variances with the highest value in S4, followed in a descending order by S3, S2 and S1. TSI(CHL) in the S2 and S3 were higher than that in S1 and S4. According to the characteristics of water level, the operational period of the TGR classified into following four stages: stage I (pre-November-April), stage II (May-July), stage III (July-September) and stage IV (September-November). The values of TSI(TN) and TSI(TP) in the Daning River and the TGR mainstream showed similar seasonal variances with the highest value in the stage II and III, followed in a descending order by stage I and IV. The values of TSI(CHL) varied substantially among the four stages, with the highest value in stage III, followed by stage II, IV and I. The trophic state indices differences were getting smaller between the four stages after the TGR impoundment. Using Carlson's two-dimensional approach, deviations of the TSI(S) indicated that factors other than phosphorous and nitrogen limited algal growth and that nonalgal particles affected light attenuation. These findings were further supported by the significant correlation among the values of TSI and hydrological factors.

[Study on the changes of macrobenthos communities and their causes in Bohai Bay].

Based on the analysis of macrobenthos samples collected from Bohai Bay, China in 2011 and the data obtained from the nearly the same sampling area during last six years, as well as the hydrological conditions, nutrients and dissolved oxygen, the characteristics of the changes in macrobenthos communities and their response to environmental variables were derived. Results showed that the distribution of the values of species number, abundance, biomass, richness index and diversity index reflected a gradient from the coastline to the open sea with the higher values concentrated at the open sea in the north part of Haihe estuary. The macrobenthos communities showed an obvious fluctuation over last six years, composed of three nodes. The first time node was in 2005 and 2008, the total species number, abundance and biomass maintained relatively high; the second time node was in 2009 and 2010, the values of the above three indices were the lowest in the three time nodes due to the increasing anthropogenic disturbances and natural changes; the third time node was in 2011, the values of the above three indices were the highest since many effective environmental protection measures had been carried out, indicating that the macrobenthos communities were recovered to a certain degree. The integrated impacts from the physical, chemical and biological variables induced by natural changes and anthropogenic disturbances, such as over-fishing, coastal land reclamation and sewage discharge were the triggers for the changes of macrobenthos communities. Furthermore, the variation characteristics of macrobenthic communities and environmental factors were generally in accordance with each other.

[Applications of diatom in river health assessment: a review].

Diatom, as a kind of autotrophic photosynthetic eukaryotic algae, is an important primary producer in aquatic ecosystem, and can reflect the average status of water environment. As the bio-indicators of the environment, Nitzschia communis, Navicula minuscula, and Gomphonema parvulum can indicate the eutrophication of waters, whereas Gomphonema angustum, Epithemia adnata, and Diatoma moniliformis can indicate the oligotrophication of waters. Cyclotella bodanica, Neidium affine, and Eunotia exigua are all the eosinophilic species that can indicate waters acidity, Aminutissimum nodusa can indicate water's Cu concentration, and Synedra ulna can indicate the Zn concentration in waters. Some other diatoms can also indicate water' s contamination. This paper reviewed the research progress on the applications of diatom and diatom indices in river health assessment, pointed out the related existing problems, and put forward some future research directions, e. g., further perfect the classification and identification of diatoms, broadly carry out the researches of diatom indices upon different areas and conditions, pay more attention to the screening of diatom bio-integrality indices, and establish a benchmark which suits for the assessment of water quality.

[Temporal and spatial distribution of red tide in Yangtze River Estuary and adjacent waters].

The events of red tide were collected in Yangtze River Estuary and adjacent waters from 1972 to 2009. Based on geographic information system (GIS) analysis on the temporal and spatial distribution of red tide, the distribution map was generated accordingly. The results show: (1) There are three red tide-prone areas, which are outside the Yangtze River estuary and the eastern of Sheshan, Huaniaoshan-Shengshan-Gouqi, Zhoushan and the eastern of Zhujiajian. The red tide occurred 174 times in total, in which there were 25 times covered the area was larger than 1 000 km2. After 2000, the frequency of red tide were significantly increasing; (2) The frequent occurrence of red tide was in May (51% of total occurrence) and June (20% of total occurrence); (3) In all of the red tide plankton, the dominant species were Prorocentrum danghaiense, Skeletonema costatum, Prorocentrum dantatum, Nactiluca scientillans. The red tides caused by these species were 38, 35, 15, 10 times separately.