Planktonic Algae Research Articles

Impact and Mechanism of Medium and Small Flood Regulation in the Three Gorges Reservoir on the Phytoplankton in Tributary Bays

The regulation of small- and medium-sized floods （RSMF） has become the main mode of regulation in the flood season of the Three Gorges Reservoir （TGR）. To study the response of phytoplankton in the tributary bays of the TGR to the RSMF, a typical eutrophic tributary of the TGR, Xiangxi River, was investigated for the spatiotemporal distribution characteristics of phytoplankton and nutrients in the main and tributary streams from 2020 to 2021. The response characteristics of phytoplankton in the tributary bays to the RSMF were analyzed. The results indicated that during the RSMF, the chlorophyll a （Chl-a） in the water body of the Xiangxi River decreased with the increase in the water level in front of the dam, whereas during the reservoir impounding at the end of flood season, the concentration of Chl-a increased again. During the RSMF, the Chlorophyta and Diatoma were the main communities of planktonic algae in the Xiangxi River. The phytoplankton community changed with the RSMF. When the water level fluctuation increased, diatoms were the main species, whereas when the water level fluctuation was small, blue and green algae were the main species. The concentration of Chl-a was more sensitive to changes in TN concentration. When the flow velocity was >0.25 m·s-1 or the suspended sediment content was >10 mg·L-1, the concentration of Chl-a in the water was inhibited. After 2010, the typical outbreak time of algal blooms in the Xiangxi River Reservoir Bay shifted to the flood season, with only two non-flood season algal blooms. Further attention needs to be paid to the response of algal blooms in the reservoir to small- and medium-sized flood control during the flood season.

Exploring the prospects of deep natural gas resources from the geochemical parameters of the Shahejie Formation source rocks in the Banqiao depression

Deep natural gas is an important field and direction for oil and gas exploration and development in the Banqiao depression. The geochemical characteristics of the Paleogene Shahejie Formation source rocks in the Banqiao Sag were investigated based on pyrolysis, Total Organic Carbon (TOC), chloroform bitumen A, vitrinite reflectance, saturated hydrocarbon gas chromatography–mass spectrometry, and maceral determination. The results showed that the Es3 source rocks of the Paleogene Shahejie Formation were generally of better quality than the Es1 source rocks. Regarding the Es1 source rocks, the abundance of organic matter was variable, with mixed types and low maturity. The source rocks were formed in a saline-water reductive environment. Regarding the Es3 source rocks, the abundance of organic matter was relatively high, meaning that they were of medium–high quality, with mixed types of, yet highly mature, organic matter. The hydrocarbon generation environment was oxidative, and the source rocks were mainly deposited in fresh water with localized salinization. The main hydrocarbon-generating components of organic matter in the Shahejie Formation were amorphous humic components formed by intensive microbial modification of lower planktonic algae and terrestrial higher plants. Aquatic organisms were the main sources of organic matter, with localized mixing of higher-plant organic matter. The organic matter derived from these higher plant debris sources provided beneficial conditions for the generation of natural gas. At present, the Shasan source rock is at the peak of hydrocarbon generation. Under deep conditions, the maturity of organic matter increases, and organic matter rich in terrestrial higher plants can make a significant contribution to the generation of natural gas, especially shale gas.

Contribution of groundwater-borne nutrients to eutrophication potential and the share of benthic algae in a large lowland river

Groundwater inflow can be a significant source of nutrients for riverine ecosystems, which can affect eutrophication i.e., the elevated primary production and the corresponding accumulation of algal biomass. Experimental and modelling work has shown that benthic algae (autotrophic biofilms) in particular benefit, as they have direct access to the inflowing groundwater-borne nutrients. Primarily the supply of phosphorus (P) enhances pelagic algal biomass, as it is the limiting nutrient for primary production in most freshwater systems. In this study, we estimate the effect of groundwater inflow on overall eutrophication of a large, European lowland river and tested its seasonal effect on biofilms in particular. We calculated the effects on overall eutrophication during summer according to the estimated input of groundwater-borne P and the C:P stoichiometry of planktonic algae in the Elbe River. Our model indicated that these diffuse P inputs have the potential to significantly increase eutrophication. Groundwater-P can contribute up to 1.5 t/d PO4 over the investigated 450 km stretch of the Elbe River under low flow conditions. This would result in an additional planktonic load of about 46 t/d of particulate organic carbon, thereby contributing to eutrophication at the regional scale in this river. In contrast, at the local scale, biofilms were collected seasonally from artificial substrata exposed in the river either in hydrogeologically active areas with groundwater inflow, or in areas of varying hydraulic connectivity. Analyses of biofilm macronutrients, structural components and biofilm community composition show distinct effects of season, hydrogeology and groundwater inflow. The dominant predictors were season and the interaction between hydrogeology and groundwater. Benthic eutrophication is most likely to occur in autumn in areas of loose rock with high groundwater inflow. The strong interaction of environmental factors in determining benthic eutrophication highlights the need to assess these factors in combination rather than in isolation.

Intensified anthropogenic disturbances impair planktonic algae in an urban river

Anthropogenic activities have posed significant threats to water quality and aquatic organisms in urban rivers, yet the understanding of how planktonic and sedimentary algal communities respond to different levels of anthropogenic disturbances remains limited. To address this knowledge gap, we conducted a systematic investigation on the effects of three anthropogenic-disturbance levels (i.e., low in the upstream, moderate in the midstream, and high in the downstream reach) on algal communities in water and sediment of the Bahe River. Our results revealed that planktonic rather than sedimentary algae were more vulnerable to anthropogenic activities in the urban river. Notably, we found the lowest biodiversity and niche breadth of planktonic algae in the downstream subjected to the high anthropogenic stress. Furthermore, the lowest complexity and stability of co-occurrence patterns of planktonic algae as well as planktonic algae-bacteria were witnessed under the highest human disturbance. Anthropogenic activities, followed by physicochemical variables, geographical patterns, and bacteria co-occurring with algae, played essential roles in shaping the niche differentiation and community assembly of planktonic algae. This study suggested that anthropogenic disturbances (represented by nighttime light, gross domestic product, and impervious surface) can alter physiochemical conditions (such as nitrogen and phosphorus contents) and thereby damage algal compositions along the urban river, highlighting the importance of effective measures for mitigating the impacts of anthropogenic activities and protecting the ecological health of river systems.

Re-evaluation of Padre Secchi’s visual method for modern oceanography

Secchi-disk is an instrument that enables investigating water transparency, being reflective of sunlight to be used to measure the depth of light penetration in the water column. In biological marine research, the device is used to determine the intensity of primary production of planktonic algae. In the present study, we re-evaluated the practicality of Secchi’s method, developed some 160 years ago, for modern oceanography by using the same locations, methods, objectives, and comparable Secchi disk that were used in his survey in 1865. We show that the Secchi-disk is still a valid scientific method in environmental marine research and therefore defends its place reliably among modern electronical research infrastructure. Observer’s subjectivity didn’t have a significant effect on measuring but environmental conditions can influence ZSD determination in general. It is therefore justified to follow, for example, the general recommendations for the use of the Secchi net issued by HELCOM. Our results also revealed that ZSD was located about twofold deeper in 1865 than presently which cannot be explained only by annual variation. We show that green(ish) sea areas have today extended to larger sea areas than they were 160 years ago, due to an increase in the turbidity of the water resulting from, e.g., general eutrophication.

Characteristics and origin of low-organic-matter carbonate source rocks in the Middle–Upper Ordovician, Tarim Basin, northwestern China

The continually-discovered large volumes of marine hydrocarbons indicate a huge exploration potential within the carbonate rocks of Ordovician in the Tarim Basin, northwestern China. The Middle–Upper Ordovician (O2+3) carbonate source rocks are at a highly mature stage. These rocks presently contain a low amount of total organic carbon (TOCpd ≤0.5%) (TOCpd means the present-day TOC). A mass balance approach is used to identify the source rocks that have expelled hydrocarbons. The characteristics and origin of hydrocarbon expulsion from low-TOCpd source rocks are studied, which are significant for oil exploration in the basin. The results showed that a low-TOCpd O2+3 source rock having expelled hydrocarbons was type I and had a very narrow oil window. With a high rock maturity and a high original TOC (TOCo) value exceeding 1%, nearly 80% of the generated hydrocarbons were expelled. The content of gammacerane and C28 steranes in the oil and source rock extracts were relatively lean, with a V-shaped distribution of regular steranes, suggesting a possible genetic relation between the low-TOCpd source rocks and the marine oil in the Tabei area. Hydrogen-rich planktonic algae or acritarchs were the main hydrocarbon parent materials, distributed in the subsiding platform-slope facies. Organic matter was preserved under reducing conditions, and source rocks were formed with a favorable kerogen type and a moderate hydrocarbon generation potential. This study illustrates the hydrocarbon expulsion of low TOCpd source rocks in northern Tarim Basin, which is greatly significant for analyzing the genesis of marine crude oil in Tarim Basin, and evaluating the distribution of marine source rocks. This research method is theoretically significant for oil and gas exploration in the same type of highly-mature carbonate paleobasins.

The influence of the degree of surface water pollution from the urban ecosystem Balti and Floresti on the planktonic algae

The influence of the degree of surface water pollution from the urban ecosystem Balti and Floresti on the planktonic algae

First record of Chelonian coprolites from the Early-Middle Miocene Kutch Basin, western India, and their palaeodietary and palaeobiological implications

In this paper, we provide the first data on large (cm-sized) coprolites (represented by three morphotypes) comprising a rare occurrence of eight specimens from a total of three vertebrate-bearing horizons identified within the Early Miocene (Aquitanian) Khari Nadi Formation and Middle Miocene (Burdigalian-Langhian) Chassra Formation, Kutch Basin, western India. The geochemical data confirm the phosphatic character of the investigated ichnofossils. The dominance of partly digested bone matter and presence of plant remains in all the three coprolite morphotypes reflects the omnivorous diet of the producers, which were most likely chelonians. The occurrence of an inclusion (in a coprolite specimen recorded in this study) showcasing an ultrastructure similar to mammalian dental enamel is a rarity in Neogene coprolite records. Additional biotic inclusions observed in the investigated coprolites include ostracods (assigned to genera Paractinocythereis, Hermanites, and Propontocypris); large planispiral benthic foraminifera including the genus Quinqueloculina; uniserial and biserial benthic foraminifera belonging to genus Textularia; marine calcareous algae genus Actinoporella; chrysophytes (resting spores or cysts of planktonic algae); sponge spicules (represented by the morphotypes Acanthoxea and Strongyle); freshwater diatom genus Aulacoseira; unidentified fungal remains; and phytoliths. Taken together, the biotic and abiotic (e.g., pyrite) inclusions, geochemical data and associated microbiota suggest that these ichnofossils were deposited in a dominantly coastal marine (intertidal) setting linked to a lacustrine/palustrine environment.

Organic geochemistry of the middle Paleozoic Ora Formation in Iraq: Implications for source rock assessment and hydrocarbon potentiality

The Ora Formation (late Devonian–early Carboniferous) is thought to be a potential source rocks for the Paleozoic petroleum system of Iraq. The source potential from the Ora Formation is evaluated for the first time ever in this study from western and northern Iraq which integrates data from organic geochemistry including Total Organic Carbon (TOC) analysis, HAWK pyrolysis, gas chromatography (GC), and gas chromatography mass spectrometry (GC-MS) and mineralogical X-ray diffraction and scanning electron microscopy. The shale and muddy carbonate succession within the Ora Formation from surface section in northernmost Iraq and subsurface section from two wells (Akkas-1 and Akkas −3) from western Iraq have been employed to assess the source rock potentiality, thermal maturity, kerogen type, organic content, and depositional environment. In addition to organic geochemical analyses, mineralogical XRD and SEM-EDS were used to support the paleoenvironmental interpretation of the Ora Formation. The results from TOC and HAWK analyses reveal that the Ora Formation ranges from poor to good as a source rock. However, the HAWK data suggests that the surface samples from northernmost Iraq are highly mature, highly weathered, or both. Kerogen analysis revealed that the Ora Formation contains immature type III and mixed II-III kerogens. Low TOC values were attributed to factors such as significant clastic input, weathering effects, and the prevailing oxic environment during deposition. The presence of detrital influx of quartz and feldspars, along with the occurrence of illite and kaolinite clay minerals, suggest a detrital input with weathering influence under hot arid and warm humid conditions. Biomarker analysis of the light hydrocarbons using GC and GC-MS revealed that these light hydrocarbons were generated from marine planktonic algae sources, possibly with some contributions from terrestrial and/or microbially reworked organic matter. These high mature light hydrocarbons in subsurface section were originated from anoxic marine shale source rocks. They were most likely from the Cambro-Ordovician Khabour Formation and were contaminated from another source.

Organic Petrologic Characterization and Paleoenvironmental Analysis of Permian Shale in Northeast Sichuan Province, China

The Permian shale in Northeast Sichuan is an important shale oil and gas resource potential area, and the study of its organic matter characteristics and paleoenvironmental analysis is of great significance for revealing the shale oil and gas formation mechanism and resource evaluation. In this study, the organic matter of Permian shales in northeast Sichuan was carefully studied based on various analytical tools, such as petrology, laser Raman, microscopy, and principal trace elements, and the paleoenvironmental parameters of the shales were comprehensively analysed. A detailed study of the organic matter characteristics of Permian shales in northeast Sichuan reveals important features such as organic matter fractions, structural characteristics, maturity and sources. The results show that the organic matter of the shale consists mainly of solid bitumen, putrescine group, specular group and multicellular planktonic algae. Petrological observations and laser Raman analyses indicate a high maturity of the organic matter and a high content of organic carbon (TOC), showing good hydrocarbon potential. In this study, we reconstructed the palaeoenvironmental parameters and inferred the palaeoenvironmental evolution through palaeoenvironmental analyses of Permian shales in northeast Sichuan. The results of the comprehensive multi-indicator study show that the type of palaeoenvironment at the time of shale deposition was mainly an anoxic-reducing environment, and the depositional conditions were favourable to the enrichment and preservation of organic matter. In summary, the organic matter characteristics and paleoenvironmental analyses of the Permian shales in Northeast Sichuan provide important geological background information for an in-depth understanding of the formation mechanism, exploration potential and development prospect of shale hydrocarbons in this area. The results of this study can provide a scientific basis for the evaluation and development of shale oil and gas resources in this area, which is of great significance to geologists and the energy industry.

River Control Points for Algal Productivity Revealed by Transport Analysis

AbstractMeasurement of planktonic chlorophyll‐a—a proxy for algal biomass—in rivers may represent local production or algae transported from upstream, confounding understanding of algal bloom development in flowing waters. We modeled 3 years of chlorophyll‐a transport through a 394‐km portion of the Illinois River and found that although algal biomass is longitudinally widespread, most net production occurs at river control points in the upper reaches (up to 3.7 Mg chlorophyll‐a y−1 km−1). Up to 69% of the algal biomass in the upper river was a result of within‐reach production, with the remainder recruited from headwaters and tributaries. High chlorophyll‐a measured farther downstream was largely because of transport from source‐area control points, with substantial net losses of algal biomass occurring in the lower river. Modeling the often‐overlooked river transport component is necessary to characterize where, when, and why planktonic algae grow and predict how far and fast they move downstream.

Analysis of the structure of phytoplankton communities in the ecological monitoring of Lake Zaozernoe (Russia)

In this work, the taxonomic composition, biodiversity, abundance, biomass, ecological features of planktonic algae and water quality in Lake Zaozernoye of the Pskov Region were studied a year after the territory was recognized as a natural monument. A twofold increase in the species richness of plankton was revealed, a two-fold decrease in representatives of the Euglenozoa phylum and a 40% decrease in representatives of Cyanobacteria. 145 phytoplankton taxa ranked below the genus from 8 phylums have been identified: Bacillariophyta (50 species taxa), Chlorophyta (36), Ochrophyta (18), Cyanobacteria (12), Euglenozoa (12), Miozoa (8), Cryptophyta (5) and Charophyta (4). The biomass was dominated by diatoms and cryptophytic algae. Toxic cyanobacteria species Aphanocapsa delicatissima and Aphanothece sp. have been identified among the dominant species in terms of numbers. 2 rare species of algae have been identified for reservoirs in the Northwestern region – Anabaena sphaerica Bornet Flahault (Cyanobacteria) and Phacus monilatus (A. Stokes) Lemmerman (Euglenozoa). The analysis of species diversity using the Sierensen–Chekanovsky, Shannon, Simpson, and Margalef diversity indices revealed changes in the structure of the plankton community in different areas of the lake. The species composition of Zaozernoye is compared with the lakes closest to it.

Removal of algae from ballast water by cationic flocculant-composite titanium xerogel coagulant: Differences in freshwater and seawater

The treatment of ballast water has been garnering increasing attention, with planktonic algae removal being a crucial part. Coagulation has been demonstrated as an effective method for algae removal, albeit few coagulants exhibit excellent coagulation performance in both freshwater and seawater. To address this issue, the cationic flocculant poly dimethyl diallyl ammonium chloride (PDADMAC) was composited with titanium xerogel coagulant (TXC), abbreviated as PT. Using the algae Cyclotella meneghiniana as the research object, the algal removal performance and mechanisms of PT in freshwater and seawater were investigated. Cell integrity, superoxide dismutase (SOD) activity, and malondialdehyde (MDA) content of C. meneghiniana during floc storage were also evaluated. The PT composite coagulant exhibited excellent coagulation performance in both freshwater and seawater. Its algal removal ability was superior to TXC and the commercial coagulants polyaluminum chloride (PAC) and polymerized ferrous sulfate (PFS), with removal rates for C. meneghiniana reaching 98.3 % in freshwater and 98.4 % in seawater at a 80 mg/L dosage. PT also exhibited excellent removal performance over wide dosage and pH ranges. PT acted via distinct coagulation mechanisms in freshwater and seawater, with charge neutralization and bridging played major roles in freshwater and sweeping being important in seawater. The floc storage experiment indicated that the coagulation process did not directly lead to algal cell fragmentation, but PT accelerated and exacerbated oxidative stress and oxidative damage to algal cells during floc storage. Furthermore, PT also showed excellent removal performance for the marine diatom Skeletonema costatum and the freshwater cyanobacteria Cylindrospermopsis raciborskii. This work not only provides a novel approach for algae removal in ballast water, but also enhances our understanding of the coagulation behavior of titanium-based coagulants in different water environments.

Upper Miocene aragonite sediments of the Eastern Paratethys (Zheleznyi Rog section): Whiting events or not?

The upper Sarmatian and lower Maeotian unlithified aragonite sediments of the Zheleznyi Rog section (Taman Peninsula, Eastern Paratethys, Russia) were investigated by field observations and laboratory methods, including scanning electron microscopy, X?ray diffraction and isotope analyses. Aragonite sediments occur at separate intervals of the studied section, forming thin (millimeter?sized) interlayers with clays. These carbonate sediments consist almost entirely of crystals (individuals and twins) and aggregates of aragonite, ranging in size from 5 to 23 ?m. It is assumed that the isotopic composition (?13C = 5.7 and 5.3?, ?18O = ?2.4 and ?2.8? for upper Sarmatian and lower Maeotian aragonites, respectively) reflects the sedimentation conditions, chara cterized by reduced basin salinity, increased surface water bioproductivity, and periods of aridization. Abiotic precipitation of these aragonites most likely occurred due to the action of triggering mechanisms, which could include planktonic algae blooms (e.g. diatoms). The obtained results do not contradict the hypothesis that the studied aragonites may be considered as sediments of whiting phenomenon.

Swimming ability and flagellar motility of sperm packets of the volvocine green alga Pleodorina starrii.

Eukaryotic flagella collectively form metachronal waves that facilitate the ability to cause flow or swim. Among such flagellated and planktonic swimmers, large volvocine genera such as Eudorina, Pleodorina and Volvox form bundles of small male gametes (sperm) called "sperm packets" for sexual reproduction. Although these sperm packets reportedly have flagella and the ability to swim, previous studies on volvocine motility have focused on asexual forms and the swimming characteristics of sperm packets remain unknown. However, it is important to quantify the motility of sperm packets and sperm in order to gain insights into the significance of motility in the sexual reproduction of planktonic algae. In this study, we quantitatively described the behavior of three flagellated forms of a male strain of Pleodorina starrii-asexual colonies, sperm packets, and single dissociated sperm-with emphasis on comparison of the two multicellular forms. Despite being smaller, sperm packets swam approximately 1.4 times faster than the asexual colonies of the same male strain. Body length was approximately 0.5 times smaller in the sperm packets than in asexual colonies. The flagella from sperm packets and asexual colonies showed asymmetric waveforms, whereas those from dissociated single sperm showed symmetric waveforms, suggesting the presence of a switching mechanism between sperm packets and dissociated sperm. Flagella from sperm packets were approximately 0.5 times shorter and had a beat period approximately twice as long as those from asexual colonies. The flagella of sperm packets were densely distributed over the anterior part of the body, whereas the flagella of asexual colonies were sparse and evenly distributed. The distribution of flagella, but not the number of flagella, appear to illustrate a significant difference in the speeds of sperm packets and asexual colonies. Our findings reveal novel aspects of the regulation of eukaryotic flagella and shed light on the role of flagellar motility in sexual reproduction of planktonic algae.

Changes in Phytoplankton of the Irpin River (Ukraine) as a Result of Military Activities in Its Basin

Phytoplankton structure was studied in a comparative aspect (before and after the beginning of military activities) in the section of the Irpin River belonging to a large lowland rivers flowing in silicate rocks. On the whole, 132 algal species of seven divisions were found in the water column of the Irpin River during the period of investigations. Bacillariophyta and Chlorophyta were highly diverse in their species composition (37.1 and 31.1% of the total number of species). The distribution of plankton algae at the studied stations even within the same massif of surface waters was non-uniform in terms of species composition (the Sorensen coefficient of community similarity on the average was 37%), species richness (18-49 species), cell numbers (1930 thousand cells/L - 24,450 thousand cells/L), and biomass (2.118 mg/L - 20.374 mg/L). Almost different algal species dominated at various stations (14 species among 20 dominated only at one station). Compared to the previous period of investigations (2018), the number of plankton algal species in the studied section of the Irpin River somewhat increased (from 121 to 132). Phytoplankton taxonomic structure also somewhat changed. The contribution of Bacillariophyta increased from 22.3 to 37.1% and that of Cyanoprokaryota - from 9.1 to 12.1%. In this case, the contribution of Chlorophyta decreased from 47.1 to 37.1%. The quantitative indices of phytoplankton development increased. The maximum numbers increased from 19,480 thousand cells/L to 24,450 thousand cells/L, whereas the maximum biomass - from 5.143 mg/L to 20.374 mg/L. As a consequence of the impact of military activities on phytoplankton of the Irpin River, it is possible to consider an increase in the number of its species, the maximum numbers and biomass, as well as the contribution of water bloom forming blue-green algae in the estuarine section of the Irpin River due to the disturbance of hydromorphology and the income of an additional amount of nutrients from flooded territories, which can lead to the formation of such a negative phenomenon as water bloom in this section of the river.

Phytoplankton population dynamics along the Casablanca - El Jadida Atlantic coast

Our taxonomic study from March 2014 to November 2015 along the atlantic coast between Casablanca and El Jadida revealed that phytoplanktonic structure is mainly represented by Diatoms (Bacillariophyceae), Dinoflagellates (Dinophyceae), Silicoflagellates (Dictyophyceae) and Euglenophyceae with a clear dominance of Diatoms and Dinoflagellates. A total of 101 taxa of planktonic algae have been identified revealing a relatively diversified taxocenosis. In terms of respective diversity, the Diatoms are represented by 62 taxa (61.4%), the Dinoflagellates by 36 taxa (35.6%) whereas the other two groups of Silicoflagellates and Euglenophyceae are only represented by 3 species (3.0%). Regarding potentially toxic species, more than fifteen taxa have been identified, most of which were Dinoflagellates and Diatoms (Pseudo-nitzschia australis and Pseudo-nitzschia cuspidata). The total phytoplankton densities exhibited great spatial and temporal variations as shown by analyses of diversity (H') and equitability (E) indices at the different coast sites investigated throughout the 2014-2015 years. Massive proliferation of some toxic species (e.g. Pseudo-nitzschia australis and Pseudo-nitzschia cuspidata, Lingulodinium polyedrum, Karenia mikimotoi) was also noticed. In addition, our study revealed the presence of opportunistic species (e.g. Eutreptiella, Thalassiosira, Prorocentrum scutellum) and of the new ectoparasite Dinoflagellate Amyloodinium ocellatum for the first time in Morocco. The detection of such diversity of toxic species, sometimes with alarming concentrations, should prompt the competent authorities to broaden the spectrum and frequency of biomonitoring to uncontrolled seafood harvesting sites.

Alien Algae Species Invasions in Humic Rivers within Weakly Human Impact Basin.

Increasing anthropogenic influence and climate change are leading to significant transformations in living conditions for indigenous representatives of aquatic communities. The problem of alien species invasions is actively discussed in the example of large rivers and water reservoirs, but medium and small rivers with weak anthropogenic influence have been insufficiently studied in this aspect. With the help of analysis of literary data and the results of our own long-term observations of phytoplankton using morphological and molecular genetic methods in some left-bank Volga tributaries, we identified six invasive species of different taxonomic groups of algae, with a predominance of diatoms. The relevance of using both traditional and modern approaches to identifying invasive algae species is revealed. Such invasive species as Thalassiosira incerta, T. faurii, Skeletonema subsalsum, Unruhdinium kevei, and Gonyostomum semen were part of planktonic communities; the benthic species Plagiotropis lepidoptera var. proboscidea sometimes reached a significant level of development (up 6 to 44% from total biomass) in plankton. It was demonstrated that some algae species have firmly taken the position of dominants and subdominants in planktonic algae communities. The expansion of alien representatives of microphytobenthos was noted in the Volga River basin for the first time. For Gonyostomum semen, its European origin was revealed, for plankton and benthic diatom-Ponto-Caspian. Our study showed that the processes of invasion and subsequent development of alien species take place in habitats with weak anthropogenic influence, which is likely determined by the hydrological, hydrochemical, and climatic changes in river basins and the high adaptive capabilities of invasive species.

Present-day characteristics of phytoplankton, microphytobenthos and phytoepiphyton of the Kaniv Reservoir

The paper studies quantitative diversity and dominant complexes of phytoplankton, microphytobenthos and phytoepiphyton in lotic and lentic biotopes within the Kaniv Reservoir in summer seasons of 2017–2022, considers their association with some abiotic variables, assesses the trophic state, information diversity according to Shannon’s index and water quality. The cell count of planktonic algae varied within 2780–124155 thous. cells · dm–3, biomass – 0.631–11.636 mg · dm–3, benthic algae – 390–13874 thous. cells · 10 cm–2 and 0.162–2.651 mg mg · 10 cm–2, epiphytic algae – 50–680 thous. cells mg · 10 cm–2 and 0.050–1.679 mg · 10 cm–2 respectively. In lotic biotopes the phytoplankton cell count was higher than in lentic biotopes due to algal inflow from the Kyiv Reservoir and tributaries. The structural organization of phytoplankton and microphytobenthos is represented by oligodominant complexes of Cyanobacteria – Bacillariophyta and Bacillariophyta – Cyanobacteria respectively, and phytoepiphyton – by monodominant complex of Bacillariophyta. The necessity to distinguish dominant complexes according to cell count and biomass has been proven. The dominant complexes of algal communities clearly divide into three clusters (for plankton, benthos and epiphyton), and each of them – into two clusters (for lotic and lentic biotopes). The Sorensen similarity between phytoplankton and microphytobenthos was higher than between phytoplankton and phytoepiphyton, which can be explained by sedimentation of planktonic forms on the bottom under different ecological conditions. High cell count and biomass, diverse dominant complex of algal communities depend upon some abiotic variables (solar radiation, photic layer thickness, water temperature in summer, nutrient content). According to phytoplankton the trophic state of the Kaniv Reservoir is assessed as eutrophic–polytrophic, and according to contour algal communities – as oligo-mesotrophic–mesotrophic. This difference complies with the “alternative stable states” theory. That is, in summer the water reservoir is in “turbid state”, when planktonic Cyanobacteria grow intensively, screen the water surface and suppress the photosynthesis of benthic and epiphytic algal communities. The water quality of the Kaniv Reservoir is within the 1st–3rd classes (clean–satisfactory clean waters), there are no point of diffuse sources of water pollution, which mainly coincides with retrospective data.

Characteristics of phytoplankton functioning in urban water reservoires (based on the example of Basivkut Reservoir, Ukraine)

The study states fundamental patterns of development for species and taxonomic composition, structure and seasonal population dynamics, biomass and informational diversity of phytoplankton in Basivkut Reservoir. During the research (June–October, 2022) it has been identified 121 algae species represented with 125 intraspecific taxa that belong to 84 genera, 43 families, 29 orders, 12 classes and 8 divisions. Floristic aspect of plankton algae is presented with Chlorophyta (40.1% of the total species number), Bacillariophyta (26.4%), Euglenozoa (13.2%) and Cyanobacteria (12.4%). The population of phytoplankton in Basivkut water storage was ranging from 4654 thous. cells/dm3 to 14212 thous. cells/dm3 (August), and the population of biomass was changing from 0.8732 mg/dm3 (July) to 9.4828 mg/dm3 (October). Shannon index has changed within 0.62–5.07 bit/mg according to biomass, 2.13–4.50 bit/sp. according to the population. The average values of the saprobic index have ranged from 1.74 to 2.14 that correspond to the third class of water quality (poorly polluted). The author highlights the increasing of Cyanobacteria development whose population and biomass reached 86.1% and 33.2% that caused intensive algal blooms in all summer months and is the impact of algal groups on the anthropogenic factors effect and climate changes. Aphanizomenon flos-aquae (10.5–32.2% and 10.6–12.4%) and Cuspidothrix issatschenkoi (11.6–31.2% and 10.2–14.5%) have dominated according to their population and biomass. Bacillariophyta impacted on population (39.5–74.0%) and biomass (88.7–98.4%) in autumn. Small cell type Stephanodiscus hantzschii has been characterized with significant population (16.9–65.4%) and biomass (51.1–92.9%) that focuses on increasing degree of trophic level in the Basivkut water storage.