Cyclotella Meneghiniana Research Articles

Isolation of Diatom Cyclotella meneghiniana Kützing and Characterization of Oil Extracted for Biodiesel Production

Isolation of Diatom Cyclotella meneghiniana Kützing and Characterization of Oil Extracted for Biodiesel Production

Diversity of Cyanobacteria and Microalgae in the Shallow Mountain Lake Paučko, Konjuh Mountain

Shallow mountain lakes are highly sensitive to eutrophication. Cyanobacteria and microalgae in planktonic communities are the main producers in lake ecosystems, but stability of its communities is impacted by numerous factors. The aim of this study is to analyze seasonal diversity and community structure of cyanobacteria and microalgae in plankton and periphyton of the lake Paučko, physical and chemical properties of water and evaluate trophic status. The mountain lake Paučko is the shallow natural lake in Protected landscape Konjuh in northeastern Bosnia and Herzegovina. Sampling of net – phytoplankton, periphyton and water for physical and chemical analysis was caried in two seasons in 2018. Light microscopes and immersion objective (magnification 1000x) were used for the identification and quantification of microalgae. Non metric multimensional scaling and Simper analysis were used to describe communities in periphytic and planktic samples. In total, 70 taxa were identified. The most numerous were Bacillariophyta with 52, and Chlorophyta with 7 taxa. Seasonal dynamics in plankton communities were observed in the direction of shift of abundant Cyclotella meneghiniana, Dinobryon divergens, Peridinum cinctum and Ankistrodesmus fusiformus in spring season to Rabdoderma lineare and Pantocsekiella comensis in summer sampling season. Physical and chemical analysis of water revealed high values of total phosphorus, which correspond to the evaluated meso to eutrophic status of the lake calculated by Rott Trophic Index. The lake Paučko is under high pressure caused by the influx and retention of nutrients, which makes it susceptible to eutrophication. The results of the study provide the first insight into the diversity of cyanobacteria and microalgae for this lake and can be useful in planning of restoration measures in the context of ecological monitoring.

Diatom complexes from bottom sediments of Lake Semenovskoe (Murmansk)

For the first time, the composition of diatom complexes of the bottom sediments of Lake Semenovskoe was studied, located within the city of Murmansk. In the core 44 cm thick, 117 species and intraspecific taxa of diatoms were found. Significant rearrangements in the taxonomic composition and structure in the direction from the lower layers to the upper ones were revealed. In the lower layers of the core are benthic acidophilic forms of Frustulia rhomboides (Ehrb.) De Toni (32%), Brachysira serians (Bréb.) Round & Mann (8,5%), Semiorbis hemicyclus (Ehrb.) Patrick (6,1%). In modern layers, the dominant steel species are: planktonic alkalibiont Aulacoseira subarctica (Müll.) Haworth (46%), planktonic-benthic alkaliphile Cyclotella meneghiniana Kütz. (10%). The benthic acidophilic species S. hemicyclus and Oxyneis binalis (Ehrb.) Round completely disappeared.

Đa dạng sinh học thực vật phù du ở vùng hạ lưu sông Vàm Cỏ, tỉnh Long An

The study was conducted at ten sites in the lower of Vam Co river, Long An province from January to July 2018. The samples were collected by phytoplankton net and fixed with 5% formalin at the field. A total of 223 phytoplankton species were recorded, belonging to 106 genera, 66 families, 37 orders, and 6 divisions, of which the diatom group dominated in the species number. The average cell density ranged from 27 144 ± 8 508 cells/liter to 153 743 ± 45 300 cells/liter. The dominant species recorded in the study area include Merismopedia punctata, Oscillatoria acuta, Oscillatoria perornata, Oscillatoria sp., Microcystis aeruginosa, Microcystis panniformis, Lyngbya martensiana, Cyclotella meneghiniana, Skeletonema costatum, Coscinodiscus jonesianus, Melosira granulata. The high densities of phytoplankton were rich food sources for larvae, zooplankton, shrimp, fish, and bivalves. The Shannon - Weiner index, Simpson index, and Margalef index showed that the phytoplankton of lower Long An was diverse and abundant.

Diversity and ecology of freshwater diatoms as pollution indicators from the freshwater Ponds of Kanyakumari district, Tamilnadu

The present study explores the diversity and ecology of freshwater diatom in the Kanyakumari district, Tamilnadu. Six freshwater ponds namely, Thuckalay pond, Eraniel pond, Pampanvilai pond, Villukuri pond, Erachakulam and Thottiyodu pond were selected from Kalkulam Taluk in Kanyakumari district. A total of 27 taxa of 17 genera were recorded from these freshwater ponds. Among the freshwater diatom species, Gomphonema montanum was found to be the predominant species in all stations except St- 2. The correlation analysis between diatom density and physico-chemical parameters revealed a significant positive correlation of diatoms (Nitzschia sp., Navicula sp., Cyclotella meneghiniana and Stauroneis sp) with nitrate, phosphate and lead at sampling statins St- 2 and 6. CCA analysis revealed that the concentration of calcium, chloride, pH, alkalinity, silica, and ammonia were found to favor the occurrence of dominant species such as Cymbella turgiduta, Gomphonema sp., Rhopalodia sp., in St-3 and St-4. Among all ponds, certain parameters like total alkalinity, nitrite, phosphate, sodium, cobalt, potassium perhaps reflect the influence of agricultural waste, sewage waste, or anthropogenic activities. The statistical indices in coherence with the dominance of pollution indicator species such as Nitzschia palea, Melosira granulata and Cyclotella meneghiniana revealed that the stations St-2, 4 and 6 were heavily polluted, whereas St- 1, 3 and 5 were less polluted.

Phytoplankton Community Structure Dynamics in Relation to Water Environmental Factors in Zhalong Wetland.

Phytoplankton, as the primary producer of the wetland water ecosystem's food chain, are very sensitive to environmental changes. In order to explore the significance of phytoplankton in protecting ecosystem integrity, the wetland ecosystem in Zhalong wetland, one of the most important international wetlands, was selected as the research area. For the study, 81 sampling sites were set up in the whole wetland, and phytoplankton samples and water quality environmental factors were measured in spring, summer, and autumn of 2019. The phytoplankton community structure and water environmental factors were evaluated by canonical correspondence analysis (CCA). The main research findings are as follows: a total of 292 species and variants of phytoplankton belonging to 8 phyla and 110 genera were identified within Zhalong wetland in spring, summer, and autumn 2019. The total phytoplankton abundance and biomass in summer were higher than in spring and autumn, and Cyclotella meneghiniana was the most dominant species in three seasons and three areas. The results of random forest are generally consistent with the results of CCA in spring, when the main environmental factors affecting phytoplankton were NTU and WT; the result in summer and autumn agreed with those of CCA, which awaits further study. In addition, the phytoplankton is mainly affected by WT, depth, and DO in the lake area, TP, DO, and NTU in the river area, and WT in the wetland area.

Conservation of triplet-triplet energy transfer photoprotective pathways in fucoxanthin chlorophyll-binding proteins across algal lineages

Detailed information on the photo-generated triplet states of diatom and haptophyte Fucoxanthin Chlorophyll-binding Proteins (FCPs and E-FCPs, respectively) have been obtained from a combined spectroscopic investigation involving Transient Absorption and Time-Resolved Electron Paramagnetic Resonance. Pennate diatom Phaeodactylum tricornutum FCP shows identical photoprotective Triplet-Triplet Energy Transfer (TTET) pathways to the previously investigated centric diatom Cyclotella meneghiniana FCP, with the same two chlorophyll a-fucoxanthin pairs that involve the fucoxanthins in sites Fx301 and Fx302 contributing to TTET in both diatom groups. In the case of the haptophyte Emilianina huxleyi E-FCP, only one of the two chlorophyll a-fucoxanthins pairs observed in diatoms, the one involving chlorophyll a409 and Fx301, has been shown to be active in TTET. Furthermore, despite the marked change in the pigment content of E-FCP with growth light intensity, the TTET pathway is not affected. Thus, our comparative investigation of FCPs revealed a photoprotective TTET pathway shared within these classes involving the fucoxanthin in site Fx301, a site exposed to the exterior of the antenna monomer that has no equivalent in Light-Harvesting Complexes from the green lineage.

Biomineral Flocculation of Kaolinite and Microalgae: Laboratory Experiments and Stochastic Modeling

AbstractIn estuaries and coastal waters, the flocculation of cohesive sediments is significantly affected by extracellular polymeric substances secreted by microalgae. In this study, laboratory experiments are carried out to explore the role of two typical microalgae (Skeletonema costatum and Cyclotella meneghiniana) on suspended fine‐grained sediments under various turbulent shear and environmental conditions. The results show that the shear rate is a dominant factor in controlling the biomineral flocculation processes, and the existence of microalgae generally enhances the aggregation of mineral sediments with microalgae. It is also found that floc size distributions (FSDs) and mean sizes are clearly influenced by different algal species and concentrations, especially under intensive turbulent environments. Moreover, a quasi‐Monte Carlo (QMC) based bivariate population balance model is developed to simulate the FSDs of sediment‐algae flocs. This model is reasonably validated by two analytical solutions and laboratory observations, and indicates a potential extension for tracking the properties of microalgae‐associated fine sediment flocs due to the discrete nature of the QMC method.

Diversity of Coastal Phytoplankton in Balayan Bay, Batangas, Philippines

Phytoplankton composition, density, and their relation with 10 abiotic water parameters in six coastal stations [four marine (Anilao, San Luis, Calatagan, and Balayan) and two freshwater (Palanas and Pansipit)] in Balayan Bay, Batangas, Philippines were examined monthly for one year (February 2006–January 2007). A total of 97 taxa of phytoplankton in four phyla were observed. About 85% of these taxa were diatoms (Bacillariophyta). The mean monthly density of phytoplankton ranged from 2,367 (Pansipit Station) to 2,992 units · mL–1 (San Luis Station), with as much as 93% of the total phytoplankton density being made up of diatoms. Cyclotella meneghiniana, a centric diatom, had the highest mean monthly density (143 units · mL–1) in all the stations. Among the six stations, the marine stations generally showed higher phytoplankton density (maximum monthly value = 4,700 units · mL–1, Anilao, in January), species diversity index (maximum monthly value, H’ = 1.402, Balayan, in March), and species richness (maximum monthly value, 29, Balayan, in March) than the freshwater stations. Clear differences were also detected in the physico-chemical characteristics between the freshwater and marine stations. Among the 10 abiotic parameters monitored, mean monthly salinity ranged from 0.92–1.02 psu in freshwater stations and 29.1–32.6 psu in marine stations. Mean monthly water temperatures ranged from 23–33.5 °C and pH ranged from 7.87–8.23. Conductivity in the two freshwater stations ranged from 2,006.17–2,051.92 μS · cm–1 and was 45x of that of the marine stations, which ranged from 44.57–50.48 μS · cm–1. Generally, marine stations showed higher values of total solids, total dissolved solids, and total suspended solids than the freshwater stations. However, marine stations recorded greater water clarity than the freshwater stations (mean monthly depth of Secchi disc ranged from 1.68–3.65 m). Freshwater stations recorded higher mean monthly orthophosphate-P values but generally lower nitrate-N values than the marine stations. These values (1.65–4.31 ppm PO4-P or 0.29–1.41 ppm P; 2.58–5.35 ppm NO3-N or 0.428–1.509 ppm N) are within or near the Philippine standard value of 1.0 ppm for P and N for clean marine water. Changes in some of these abiotic parameters were correlated with changes in the population density of some of the dominant species, to total mean monthly phytoplankton density, species diversity index, and species richness in some of the stations, but no single parameter can explain the biological patterns observed for all stations. No algal bloom was observed during the course of this study, although a potentially harmful dinoflagellate, Ceratium furca, was observed. It was never a dominant alga in any of the stations.

Individual and combined toxicity of microplastics and diuron differs between freshwater and marine diatoms

Microplastics are considered as the emerging pollutants, which not only directly affect aquatic organisms, but also causes combined pollution by adsorbing other pollutants. Diuron, as one of the most widely used herbicides, is frequently monitored in the aquatic environment for its adverse effects on aquatic organisms. However, little is known about the combined toxicity of microplastics and diuron to aquatic organisms, especially diatoms. In this study, freshwater diatom (Cyclotella meneghiniana) and marine diatom (Skeletonema costatum) were selected to study the individual and combined toxicity of microplastics (polystyrene, 0.6– 1.0 μm) and diuron. Experimental concentrations of microplastics and diuron were set at 50 mg/L and 100 μg/L, respectively, which have been shown to significantly inhibit the growth of aquatic organisms. Results suggested that both single microplastics and single diuron significantly inhibited the growth of the two diatoms, while significant SOD and MDA increase were only found in single diuron exposure. For diatoms exposed to individual microplastics, the microplastic particles adsorbed inside Cyclotella sp. and those aggregated around Skeletonema sp. were the major factor inhibiting the growth of diatom, respectively. According to the independent action model, the combined toxicity for both diatoms were all antagonistic. The adsorption behavior of microplastics to diuron alleviated the intracellular damage to diatoms caused by diuron, and the oxidative stress induced by diuron mitigated the physical damage to diatoms caused by microplastics. Collectively, our findings suggest that the co-existence of microplastics and diuron may affect their respective toxicity to diatoms. The mechanism of this “cross-phenomenon” between microplastics and diuron and their combined toxicity to different aquatic organisms need to be further studied.

Hydrological disconnection from the Yangtze River triggered rapid environmental degradation in a riverine lake

Interactive River-Flood Ecosystem (RFE) is an important feature characterizing the dynamics of the hydrological connectivity between lake and river worldwide. Any disruption in the RFE can impose significant effects on the functioning of floodplain ecosystems. However, due to the lack of long-term monitoring data, the understanding of the process and mechanism behind limnological responses to the changes in hydrological alterations and nutrient loading in floodplain lakes is restricted. The middle and lower reaches of the Yangtze river floodplain lake system of China is one of the significant food bowls of the nation, and makes important contribution to ecosystem services including drinking water and food to the society for generations. The interactive RFE of the Yangtze floodplain lakes is profoundly disrupted by anthropogenic activities over the recent decades. However, the response of such changes in river-lake connectivity is not comprehensively investigated yet. Here, we studied Cehu Lake in the lower reaches of the Yangtze floodplain system to examine the long-term environmental changes with altered river-lake connectivity and increased nutrient loading using high-resolution paleolimnological multi-proxy analyses including geochemistry, grain size and diatom assemblages of a 210Pb/137Cs dated core. Our results suggest that Cehu Lake have experienced two pronounced shifts: immediately after the damming in Yangtze river (1964) completely ceasing the lake-river connectivity, and in 1994. The disruption in the hydrological connectivity in 1964 led to an abrupt decrease in the abundance of Aulacoseira granulata, and an increase in the organic matter (loss-on-ignition), epiphytic and benthic diatoms, while the disruption in 1994 led to increased total phosphorus (TP), lead (Pb), dry mass accumulation rate, and a decline in Fe/Mn, and consequently enhanced lake eutrophication with emergence of enriched nutrient tolerant diatoms (Cyclotella meneghiniana, Cyclostephanos tholiformis). The redundancy analysis (RDA) showed increased TP loads in lake sediment after damming in the Yangtze river. The condition stimulated macrophyte growth with, but altered diatom flora. Reconnecting Cehu lake with Yangtze river together with reducing nutrient loading to the lake from the incoming river may be an effective management practice to relieve the ecological stress.

Effective dilution rate to suppress the risk of Microcystis blooms in Lake Tega, Japan, based on a competitive growth simulation model

Abstract Although water transfer as an efficient method to improve water quality and control Microcystis blooms in lakes has been executed for several decades, few studies have examined effective dilution rates depending on various water qualities. Therefore, to clarify the effective dilution rate to suppress Microcystis blooms, a competitive growth simulation model developed for eutrophic conditions was utilized. A competition experiment between Microcystis sp. and Cyclotella meneghiniana under limited phosphorus and sufficient nitrogen concentration was conducted to investigate the mechanism of dilution effect and verify the broad applicability of the simulation model. Experimental results revealed that there was no remarkable discrepancy in Microcystis sp. cell density among different dilution groups (p>0.05), while C. meneghiniana cell density was significantly different between groups (p<0.05). The accuracy of the simulation model under limited phosphorus as well as sufficient nitrogen concentration was verified by comparing the simulated value with experimental results. Based on the simulated results, it was suggested that a dilution rate of over 13.3% can suppress Microcystis blooms effectively in Lake Tega, Japan, as a case study. The predicted data was also compared with the field data collected over years in Lake Tega, and its effectiveness has been confirmed.

AN INVESTIGATION OF PHYSICOCHEMICAL PARAMETERS AND PHYTOPLANKTON COMMUNITY STRUCTURE OF EKO-NDE RESERVOIR IN OSUN STATE, NIGERIA

This research was carried out to determine the relationship between physicochemical variables and phytoplankton community of the Eko-Nde reservoir. Changes in physicochemical parameters of aquatic ecosystems have significant impact on the species that live therein. Eko-Nde reservoir is of socio-economic significance to communities that surround it, which necessitates a proper study of the phytoplankton composition and environmental status of the reservoir. Water samples were collected from two stations in the reservoir from January 2019 to August 2019. The physicochemical parameters that were determined include but not limited to temperature, total hardness, pH and biochemical oxygen demand. The composition and diversity of phytoplankton were analyzed. A total of 2039 cells ml-1 belonging to four (4) major divisions were dominant in the order; Bacillariophyta (898 cells ml-1) > Charophyta (788 cells ml-1) > Chlorophyta (302 cells ml-1) > Cyanophyta (51 cells ml-1). Principal Component Analysis and Canonical Corresponding Analysis showed that certain physicochemical variables such as temperature, pH and total hardness were key drivers of the phytoplankton community structure of the reservoir. Diversity indices showed moderate abundance and distribution of phytoplankton species, with the highest diversity of species in the months associated with the rainy season. The appearance of pollution tolerant species such as Anabaena circinalis, Oscillatoria limosa, Nitzschia gracilis, Cymbella mexicana, Pediastrum boryanum, Synedra ulna, Cyclotella meneghiniana and Gomphonema spp. suggest that the reservoir was on the verge of pollution. Anthropogenic activities around the reservoir should be closely monitored to avoid health risks to humans and endangerment of aquatic organisms.

Temperature-dependent growth characteristics and dominance trends of the cyanobacterium Microcystis sp. and the diatom Cyclotella meneghiniana

Temperature-dependent growth characteristics and dominance trends of the cyanobacterium Microcystis sp. and the diatom Cyclotella meneghiniana

Odor-producing response pattern by four typical freshwater algae under stress: Acute microplastic exposure as an example

Algae-induced odor problems in water have been repeatedly occurred concerns for drinking water quality. However, present researches mostly focus on the odor-producing pattern of algae in normal growth, and there is scarce discussion on those under stress. Microplastics (MPs) pollution have been global concern for their negative ecological impacts and frequently co-occurs with odor-producing algal bloom in freshwaters. Thus, this study aimed to elucidate the effects and mechanisms of MPs as an environmental stress on algal odorant production for good illustration of odor-producing response pattern under stress. Variation in MP size (polystyrene microspheres; 100 nm, 1000 nm and 10 μm) had significant effects on odorant formation (β-cycloidal, 2-methylisopropanol, 2,4-heptandienal and 2,4-decadienal) by four freshwater algae (Microcystis aeruginosa, Pseudanabaena sp., Cyclotella meneghiniana and Melosira varians). The size ratio of MPs over cells (SRMC) was proposed to categorize the size-ratio dependent effects on the algal odorant production. Interestingly, when SRMC was in the range of 0.1–1, there were always promoting effects; when SRMC < 0.1 or SRMC > 1, there exhibited inhibiting effects, and the inhibiting effects of SRMC < 0.1 were far more severe than those of SRMC > 1. The promotion on odorant production in the SRMC range of 0.1–1 was mainly attributed to the increase in cellular yield, which was related to the increased odorant precursors derived from the oxidation products of reactive oxygen species (ROS). Alternatively, the inhibition of odorant production caused by MPs with SRMC < 0.1 was the results of simultaneously inhibiting cellular density and cellular yield, which might be attributed to the cellular internalization of MPs, inducing the extensive toxic effects. This study illustrated the possibilities of MPs in impairing the esthetics of the source water and provided guidance for the future algal odor issues under stress.

Diatom assemblage responses to multiple environmental stressors in a deep brackish plateau lake, SW China.

Eutrophication, climate change, water level fall, fish introduction, and salinity have been widely recorded to impact lake ecosystems around the world. However, the combined responding pattern in the lake ecosystem to the above multiple environmental stressors is not well understood. Here, we present diatom assemblage and geochemical indicators (total organic carbon (TOC), total nitrogen (TN), and total phosphorous (TP)) in lake sediment to investigate the long-term trends in the aquatic ecosystem in response to multiple environmental stressors in Lake Chenghai, a deep brackish lake located on Yunnan-Guizhou Plateau, SW China, during the past 80years. We identified 8 genera and 15 species of diatom reaching a relative abundance of ≥ 2% in at least one sample, with the dominant taxa such as Cyclotella rhomboideo-elliptica and Aulacoseira alpigena through the sediment core. There was a clear shift in the diatom community from oligotrophic species of C. rhomboideo-elliptica to eutrophic species such as Cyclotella meneghiniana and Cyclostephanos dubius becoming dominant since ca. 1998 CE. In addition, the changes in the fish introduction, water level, temperature, and salinity also resulted in the variation in abundance of planktonic and benthic diatoms. The increase in the abundance of diatoms of C. rhomboideo-elliptica since ca. 1986 CE may be related to the decline in water level and increasing fish production. For one thing, the decline in water level reduces the concentrations of benthic diatoms but increases the relative biomass of planktonic diatoms. For another, the increasing fish production results in the decrease in the zooplankton biomass, thus reducing the predation pressure on planktonic algae. Besides, some specific species such as C. meneghiniana may respond to the increased nutrient release and increased salinity since ca. 1998 CE. Combined, our findings demonstrate that trophic level is the main driver of diatom assemblage changes, and other environmental variables including water level, fish introduction, and climate warming also contribute to diatom community variation in this brackish plateau lake during the last 80years.

Phytoplankton community characteristics and the underlying drivers under organic and conventional agricultural management

为了解不同农业施肥管理方式对水体浮游植物群落的影响，本研究以江苏句容戴庄有机示范村和常规农业管理区池塘浮游植物为对象，分析冬夏两季浮游植物群落特征及相关水环境因子.结果表明：冬季有机和常规农业区域的浮游植物分别检到7门95种和7门111种，夏季分别检到7门102种和6门112种，有机农业区浮游植物由冬季的隐藻-绿藻型向夏季的蓝藻-绿藻型变化，常规农业区从隐藻-绿藻型向蓝藻-硅藻型变化，蓝藻逐渐取代隐藻的优势地位.夏季各池塘浮游植物alpha多样性没有显著的区域差异，但冬季常规农业区浮游植物物种丰富度、蓝藻和裸藻的Shannon-Wiener多样性指数显著较高.指示物种分析显示，谷皮菱形藻（Nitzschia palea）和梅尼小环藻（Cyclotella meneghiniana）为有机农业区指示物种，而梭形裸藻（Euglena acus）、针形纤维藻（Ankistrodesmus acicularis）、肘状针杆藻（Synedra ulna）和狭形纤维藻（Ankistrodesmus angustus）为常规农业区指示物种，此6种藻为中、富营养化藻类，说明水体氮磷营养盐浓度较高，这与周围农田氮磷流失密切相关.Pearson相关性分析表明，有机农业区浮游植物alpha多样性与氮磷浓度的相关性不显著，但常规农业区浮游植物物种丰富度和Pielou均匀度与磷酸盐、总氮、氨氮和pH值显著相关.Mantel检验表明，有机农业区群落相异性仅在冬季受到总氮和氨氮的显著影响；而常规农业区在冬夏季受到氮磷两类营养盐的交替影响.本研究结果初步揭示了有机和常规农业区水体浮游植物群落结构特征及其影响因素，为区域水生生物多样性保护与稻田施肥管理的优化提供科学基础.;In order to explore the effects of different agricultural fertilization management on the phytoplankton community, the phytoplankton community characteristic and water environmental factors were investigated in winter and summer in Daizhuang organic village and conventional farming area of Jurong, Jiangsu Province. Our results showed that the phytoplankton communities were composed of 95 and 111 species of 7 phyla in organic (OFR) and conventional farming regions (CFR) in winter, 102 species of 7 phyla and 112 species of 6 phyla in summer, respectively. The phytoplankton varied from Cryptophyta-Chlorophyta type in winter to Cyanophyta-Chlorophyta type in summer in OFR, and from Cryptophyta-Chlorophyta type to Cyanophyta-Bacillariophyta type in CFR, indicating that Cyanophyta gradually replaced the dominant position of Cryptophyta. There was no significant difference in phytoplankton alpha diversity between organic and conventional farming ponds in summer, but the phytoplankton species richness and Shannon-Wiener diversity of Cyanophyta and Euglenophyta in CFR was significantly higher than that in OFR in winter. The IndVal analysis further revealed that Nitzschia palea and Cyclotella meneghiniana were the indicative species in OFR, while Euglena acus, Ankistrodesmus acicularis, Synedra ulna and Ankistrodesmus angustus were the indicative species in CFR. These algae often occurred in meso-eutrophic waters, indicating that the concentration of nitrogen and phosphorus in water was higher. This may be closely related to the nitrogen and phosphorus runoff. Pearson correlation analysis showed that there was no significant relationship between phytoplankton alpha diversity and environmental factors in two regions, but species richness and Pielou's evenness in CFR were significantly correlated with phosphate, total nitrogen, ammonia nitrogen and pH. Mantel test showed that the community dissimilarity in OFR was only significantly affected by total nitrogen and ammonia nitrogen in winter. While in CFR, community dissimilarity was affected by the alternation of nitrogen and phosphorus nutrients in winter and summer. These findings should be useful for future efforts to recover biodiversity and optimize fertilization management.

Seasonal dynamics of phytoplankton and its relationship with environmental factors in Lake Hulun

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（123.52×10⁴ cells/L）和冬季（16.41×10⁴ cells/L）较夏季（280.80×10⁴ cells/L）和秋季（380.63×10⁴ cells/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（0.38 mg/L）最大，其次是秋季（0.26 mg/L）和春季（0.24 mg/L），冬季（0.13 mg/L）最小.香农-威纳（Shannon-Wiener）多样性指数、均匀度指数和综合营养状态指数均表明呼伦湖水体处于中营养状态.冗余分析（RDA）表明：水温、叶绿素a、pH和营养盐浓度是影响呼伦湖浮游植物群落分布的主要环境因子.;To understand the phytoplankton community characteristics and its relationships with environmental factors, we investigated the species, abundance and biomass of phytoplankton and environmental factors at eight sampling sites in Lake Hulun during March and from May to October of 2019. The results showed that:A total of 120 phytoplankton species were identified, belonging to 7 plyla and 72 genera. In terms of the seasonal composition of the phytoplankton community, Chlorophyta was the dominant groups in spring, followed by Bacillariophyta and Cyanophyta. The number of Chlorophyta was the largest in summer and autumn, followed by Cyanophyta. Bacillariophyta was the dominant group in winter, followed by Chlorophyta. The dominant species of phytoplankton in Lake Hulun were Cyclotella meneghiniana of Bacillariophyta, Anabaena circinalis and Merismopedia minima of Cyanophyta. The number of the dominant species was the most in spring and the least in autumn and winter. The phytoplankton abundance in spring (123.52×10⁴ cells/L) and winter (16.41×10⁴ cells/L) was lower than that in summer (280.80×10⁴ cells/L) and autumn (380.63×10⁴ cells/L). The abundance of Chlorophyta was the highest in spring and winter, and the abundance of Cyanophyta was the highest in summer and autumn. In terms of phytoplankton biomass, summer (0.38 mg/L) had the largest, followed by autumn (0.26 mg/L) and spring (0.24 mg/L), and winter (0.13 mg/L) had the smallest. Shannon-Wiener diversity index, evenness index J and comprehensive trophic state index all indicated that Lake Hulun was in mesotrophic condition. Redundancy analysis of phytoplankton abundance and water environmental factors showed that water temperature, chlorophyll-a, pH and nitrogen and phosphorus nutrients were the main environmental factors that affected the distribution of the phytoplankton community in Lake Hulun.

Effects of the herbicides metazachlor and flufenacet on phytoplankton communities – A microcosm assay

Agrochemicals are the main pollutants in freshwater ecosystems. Metazachlor and flufenacet are two common herbicides applied in fall (i.e., August–October) to agricultural fields in Northern Germany. High concentrations of these herbicides are often found in adjacent aquatic ecosystems. Phytoplankton are one of the highly susceptible non-targeted aquatic organismal groups for herbicides and effects on phytoplankton may initiate a chain of consequences in meta communities through trophic interactions. Few studies have focused on responses of the phytoplankton community for metazachlor and, no studies have focused on flufenacet. We studied the effects of metazachlor and flufenacet on the phytoplankton community by conducting a microcosm experiment exposing natural fall phytoplankton communities to environmentally realistic concentrations as 0 (control), 0.5, 5 and 50 µg L−1 of metazachlor and flufenacet treatments over a 4-week period. We measured changes in density, composition (i.e., in phyla and species level), taxonomic diversity indices, and functional features of phytoplankton communities as a response to herbicides. A reduction in the density of Chlorophyta species (e.g., Koliella longiseta, Selenastrum bibraianum) and Cyanobacteria species (e.g., Merismopedia tenuissima and Aphanocapsa elegans) was observed in herbicide treatments compared to controls. The phytoplankton community shifted towards a high density of species from Bacillariophyta (e.g., Nitzschia fonticola and Cyclotella meneghiniana), Miozoa (i.e., Peridinium willei), and Euglenozoa (i.e., Trachelomonas volvocina) in herbicide treatments compared to controls. Metazachlor and flufenacet showed significant negative effects on taxonomic diversity indices (e.g., species richness, the Shannon-Wiener index) and functional features (e.g., functional dispersion and redundancy) of the phytoplankton communities, with increasing herbicide concentrations. Our study provides insights into direct, selective, and irrecoverable effects of metazachlor and flufenacet on phytoplankton communities in the short-term. The comprehensive understanding of these effects of environmentally realistic herbicide concentrations on aquatic biota is essential for a sustainable management of aquatic ecosystems in agricultural areas.

Impacts des activités minières d’amiante sur l’évolution du lac à la Truite d’Irlande, région de Thetford Mines (Québec, Canada) Impacts of asbestos mining activities on the evolution of Lac à la Truite d’Irlande, Thetford Mines region (Quebec, Canada)

Lac à la Truite (Trout Lake) from the municipality of Irlande (southern Quebec, Canada) suffers from eutrophication and siltation. More than 100 years of mining activities in the Thetford Mines region (1877–2011 CE) and the accumulation of gigantic mining waste piles have often been blamed for these problems, but their real impacts have never been demonstrated. Paleolimnological analyses were undertaken on a sediment core collected in Lac à la Truite to provide insights into its long-term evolution since pre-mining times. Results indicate that its degradation was greatly enhanced by the drainage of upstream Lac Noir (Black Lake) from 1955 to 1959 CE for mining purposes. Radiometric dating (137Cs, 210Pb, 14C) showed that this event caused a strong increase in sediment inputs, which afterwards remained high (0.6–1.3 cm yr−1; 0.4–1.0 g cm−2 yr−1). Loss-on-ignition and spectrometry (ICP-AES/ICP-MS) analyses revealed that sediments deposited since 1960 CE mostly originate from the mining waste piles as they are organic-poor and highly enriched in metals associated with asbestos tailings (magnesium, chromium, nickel). During the drainage of Lac Noir, the emergence of diatom taxa typical of nutrient-rich waters in the sedimentary assemblages (e.g., Cyclotella meneghiniana, Cyclostephanos invisitatus) and the concomitant shift of biochemical proxies (C/N, δ13C) indicate that the disappearance of this water body has also caused the rapid eutrophication of Lac à la Truite by facilitating municipal wastewater inputs. Moreover, the pH and conductivity of the lake water are now considerably higher than during pre-mining times. Pollution generated by the mining waste piles and wastewater must be rapidly controlled to ensure the sustainability of Lac à la Truite.