Planktonic Algae Research Articles

Biological sources, paleoenvironment, and organic matter enrichment in source rocks of the Ordovician Majiagou Formation, Ordos Basin, China: Evidence from biomarkers, microfossils, and inorganic geochemical analyses

Carbonate deposits in the Ordovivian Majiagou Formation are significant source rocks for natural gas generation in the Ordos Basin, northwestern China. Previous studies mainly focused on the organic matter enrichment mechanism of shales rather than carbonate rocks. The biological sources and paleoenvironment of carbonate source rocks, and the main controlling factors of organic matter enrichment in the carbonate source rocks were studied in this paper in combination with evidence from biomarkers, microfossils and inorganic geochemistry analysis. The results show that four types of microfacies were identified in the Majiagou Formation, respectively as: mud flat microfacies, mud–dolomite flat microfacies, dolomite flat microfacies, and open marine microfacies. The biological sources of organic matter are chiefly planktonic algae, followed by bacteria. The mud flat and mud–dolomite flat contain a high abundance of terrigenous detrital inputs, as indicated by the high content of Al2O3, TiO2, Th, and Zr. The low Sr/Cu and high Rb/Sr values reveal warm and humid paleoclimate conditions in the mud flat and mud–dolomite flat, whereas the dolomite flat and open marine were likely formed in hot and arid paleoclimate conditions. The mud flat and mud–dolomite flat deposits were characterized by high paleoproductivity of the Majiagou Formation. Low Sr/Ba values were found in the mud flat samples, indicating fresh to brackish water condition, whereas samples of other facies have a relatively high degree of salinity. Based on Uauth, Moauth, Crauth, Coauth, δCe, and δEu values, the mud flat microfacies was formed in a suboxic and anoxic environment, whereas the mud–dolomite flat, dolomite flat and open marine microfacies were within dysoxic to oxic conditions. A model of organic matter enrichment in the Majiagou Formation is thus established. The level of terrigenous detrital inputs is the principal factor of organic matter enrichment in the Majiagou Formation, secondly are redox condition and then paleoproductivity. The mud flat and mud–dolomite flat microfacies show abundant terrestrial detrital inputs and nutrient elements, indicative of warm and humid climate that facilitated biotic productivity, including an abundance of planktonic algae (microfossils). The suboxic and anoxic environments promoted the preservation of organic matter, as evidenced by the relatively high TOC content. The mud flat as well as the mud–dolomite flat of the Majiagou Formation is prospecting for forming source rocks.

Present Condition of the Protected Area of Endangered Asian Arowana (Scleropages formosus) Golden-Red in East-Central Sumatra, Indonesia

Abstract The only location for the protection of Arowana golden-red in its natural habitat is in east-central Sumatra. Currently, the area is being invaded by oil palm plantations. This research identified the present conditions in that conservation area, specifically focusing on land-use situation and aquatic organism distribution and diversity. We designated four sampling sites according to the stratification of river flows that pass through the Arowana golden-red conservation area and present land use. The research showed that oil palm plantation was the largest land use in the Arowana golden-red conservation area covering 61.2% (2,310.84 ha). The swamp forest which is the habitat of Arowana golden-red only remained at 6.99% (263.98 ha). In the study area, aquatic organisms were identified as 47 species with a total of 424 individuals: 7 genera of Benthos, 11 species of Planktonic algae, and 29 species of Fish. The diversity index was in the range of 0.46–2.45. The diversity of aquatic organisms was found to be comparable to or higher than other areas in Malaysia and Indonesia such as Aceh province and Kalimantan. However, only 31 individuals of Arowana golden-red were found in the swamp forest in Middle Mahato. This site should be a priority area to save the Arowana golden-red.

Infiltration of freshwater food chain by nanoplastics: An examination of trophic transfer and biological impact

The contamination of freshwater by nanoplastics (NPs) poses a significant threat to various organisms. However, the influence of food factors on the NPs toxicity and the associated risks to water safety remains poorly understood. In this study, we employed highly fluorescent NPs incorporating aggregation-induced emission fluorogens to quantify and visualize the interactions of NPs with freshwater phytoplanktonic alga Chlamydomonas reinhardtii and zooplankton Daphnia magna, including the uptake of NPs by algae and daphnids, as well as gut environment responses through both waterborne and foodborne routes. NPs at environmentally relevant concentrations were capable of aggregating and internalizing in planktonic algae, thus permeating the food chain and potentially causing ecological risks. Notably, positively charged NPs exhibited greater infiltration than the negatively charged NPs. Our findings indicated that NPs had a greater tendency to accumulate in Daphnia via the food chain rather than through direct exposure to water. This was attributed to the loss of selectivity, suggesting a potential mechanism for NP accumulation in aquatic food chains. However, daphnids exposed to NPs through waterborne route exhibited more gut pH acidification, esterase activity, and gut inflammation compared to those exposed via the foodborne route. Moreover, chronic exposure to NPs through waterborne routes significantly disrupted the growth, molting, and reproduction of Daphnia compared to the foodborne group. These findings provided valuable insights into the complexities of plastic pollution on primary trophic levels in aquatic environments.

Geochemical characteristics and origin of the ultra-deep hydrocarbons from the Shunbei Oilfield in the Tarim Basin, China: Insight from molecular biomarkers and carbon isotope geochemistry

To better evaluate the exploration prospects of ultra-deep hydrocarbon resources in the Tarim Basin, origin of the newly discovered ultra-deep hydrocarbons from the Shunbei Oilfield are investigated thoroughly concerning the maturity, secondary variations, and source kitchens based on molecular biomarkers and carbon isotope geochemistry. Given the physical and chemical properties of the studied oils and gases, they are classified into five families: A, B, C, D, and E. Newly proposed maturity parameters are employed for evaluating the maturity of the studied oils and gases as Family D > E > B > A, except for Family C hydrocarbons, which may be a mixture of relatively high-maturity natural gas with relatively low-maturity oil. Secondary alterations are concentrated in the southern part of the Shunbei region, primarily including oil cracking and TSR effects, both of which may occur in deeper strata than in situ. Furthermore, the simulated maturity evolution and variation of sedimentary facies of the Yuertusi Formation (Є1y) source rocks in the Shuntuoguole Low Uplift (STLU) area match well with the genesis of the studied hydrocarbons, which suggests that the studied hydrocarbons may be derived from the Є1y source rocks in the STLU area. Collectively, Family A hydrocarbons originate from the western Є1y source kitchen in the STLU region where the water column is shallow, rich in planktonic algae, and the maturity is relatively low; in contrast, Family E hydrocarbons are derived from the eastern Є1y source kitchen in the STLU region where the water column is deep, rich in benthic algae, and the maturity is relatively high; Families B and C hydrocarbons originate between them. This research also contributes to the establishment of a geochemical evaluation system for ultra-deep hydrocarbons.

Impact of critical eddy diffusivity on seasonal bloom dynamics of Phytoplankton in a global set of aquatic environments

The intensity of eddy diffusivity and the spatial average of water velocity at the depths of the water column in oceans and lakes play a fundamental role in phytoplankton production and phytoplankton and zooplankton biomass, and community composition. The critical depth and intensity of turbulent mixing within the water column profoundly affect phytoplankton biomass, which depends on the sinking characteristic of planktonic algal species. We propose an Nutrient-Phytoplankton-Zooplankton (NPZ) model in 3D space with light and nutrient-limited growth in a micro-scale ecological study. To incorporate micro-scale observation of phytoplankton intermittency in bloom mechanism in stationary as well as oceanic turbulent flows, a moment closure method has been applied in this study. Experimental observations imply that an increase in turbulence is sometimes ecologically advantageous for non-motile planktonic algae. How do we ensure whether there will be a bloom cycle or whether there can be any bloom at all when the existing phytoplankton group is buoyant, heavier, motile, or non-motile? To address these questions, we have explored the effects of critical depth, the intensity of eddy diffusivity, spatial average of water velocity, on the concentration as well as horizontal and vertical distribution of phytoplankton and zooplankton biomass using a mathematical model and moment closure technique. We quantify a critical threshold value of eddy diffusivity and the spatial average of water velocity and observe the corresponding changes in the phytoplankton bloom dynamics. Our results highlight the importance of eddy diffusivity and the spatial average of water velocity on seasonal bloom dynamics and also mimic different real-life bloom scenarios in Mikawa Bay (Japan), Tokyo Bay (Japan), Arakawa River (Japan), the Baltic Sea, the North Atlantic Ocean, Gulf Alaska, the North Arabian Sea, the Cantabrian Sea, Lake Nieuwe Meer (Netherlands) and several shallower lakes.

Complex Plastids and the Evolution of the Marine Phytoplankton

Photosynthesis allows for the formation of biomass from inorganic carbon and therefore greatly enhances the amount of organic material on planet Earth. Especially, oxygenic photosynthesis removed a major bottleneck in the formation of biomass by utilising ubiquitous water (H2O) and CO2 molecules as raw materials for organic molecules. This, over billions of years, shaped the world into the form we know today, with an oxygen-containing atmosphere, largely oxygenated water bodies and landmasses consisting of sediment rocks. Oxygenic photosynthesis furthermore enabled the evolution of aerobic energy metabolism, and it would be very difficult to imagine animal (including human) life in the absence of molecular oxygen as an electron acceptor. Oxygenic photosynthesis first, and exclusively, evolved in cyanobacteria. However, eukaryotes also learned to photosynthesise, albeit with a trick, which is the integration of formerly free-living cyanobacteria into the eukaryotic cell. There, the former bacteria became endosymbionts, and from these endosymbionts, the photosynthetic organelles (termed plastids) evolved. In almost all major groups of eukaryotes, plastid-containing members are found. At the same time, plastid-related features also indicate that these plastids form a monophyletic group. This can be explained by the transfer of plastids between the eukaryotic super-groups, leading to plastids being found in groups that are otherwise non-photosynthetic. In this chapter, we discuss the evolutionary origin of plastids, with a special emphasis on the evolution of plankton algae, such as diatoms or dinoflagellates, who acquired their plastids from other photosynthetic eukaryotes.

Hydrological disturbances enhance stochastic assembly processes and decrease network stability of algae communities in a highland floodplain system

Floodplains are hotspots for biodiversity research and conservation worldwide. Hydrological disturbances can profoundly influence the ecological processes and functions of floodplain systems by altering key biological groups such as algae communities. However, the impacts of flood disturbance on the assembly processes and co-occurrence patterns of algae communities in floodplain ecosystems are still unclear. To ascertain the response patterns of algae communities to flood disturbance, we characterized planktonic and benthic algae communities in 144 water and sediment samples collected from the Tibetan floodplain during non-flood and flood periods based on 23S ribosomal RNA gene sequencing. Results showed that planktonic algae exhibited higher diversity and greater compositional variations compared with benthic communities after flood disturbance. Flooding promoted algae community homogenization at horizontal (rivers vs. oxbow lakes) and vertical levels (water vs. sediment). Stochastic processes governed the assembly of distinct algae communities, and their ecological impacts were enhanced in response to flooding. In the non-flood period, dispersal limitation (81.78 %) was the primary ecological process driving algae community assembly. In the flood period, the relative contribution of ecological drift (72.91 %) to algae community assembly markedly increased, with dispersal limitation (22.61 %) being less important. Flooding reduced the interactions among algae taxa, resulting in lower network complexity and stability. Compared with the planktonic algae subnetworks, the benthic subnetworks showed greater stability in the face of flooding. Findings of this study broaden our understanding of how algae communities respond to hydrological disturbances from an ecological perspective and could be useful for the management of highland floodplain ecosystems.

Prediction and sensitivity analysis of chlorophyll a based on a support vector machine regression algorithm

Outbreaks of planktonic algae seriously affect the water quality of rivers and are difficult to control. Based on the analysis of the temporal and spatial variation characteristics of environmental factors, this study uses a support vector machine regression (SVR) algorithm to establish a chlorophyll a (Chl-a) prediction model and conduct Chl-a sensitivity analysis. In 2018, the average Chl-a content was 126.25 ug/L. The maximum total nitrogen (TN) content was 16.68mg/L and high year-round. The average NH4+-N and total phosphorous (TP) contents were only 0.78 and 0.18mg/L. The content of NH4+-N was higher in spring and increased significantly along the water flow, while TP decreased slightly along the water flow. We used a radial basis function kernel SVR model and tenfold cross-validation method to optimize parameters. The penalty parameter c was 1.4142, the kernel function parameter g was 1, and the training and verification errors were only 0.032 and 0.067, respectively, indicating a good model fit. Based on a sensitivity analysis of the SVR prediction model, the maximum sensitivity coefficients of Chl-a to TP and WT were 0.571 and 0.394, respectively, and the contributions were 33% and 22%, respectively. The next highest sensitivity coefficients were those of DO (0.28, 16%) and pH (0.243, 14%). The sensitivity coefficients of TN and NH4+-N were the lowest. According to the current water environment pollution conditions, TP is the limiting factor of Chl-a in the Qingshui River, and it is also the main prevention and control factor of phytoplankton outbreak.

Differences of Organic Matter Types of High Maturity Marine Organic-Rich Shale from Wufeng-Longmaxi Formation: Implication for Shale Gas “Sweet Spots” Prediction

Based on the identification of visual kerogen assessment, a subdivision method of organic matter types was proposed. Combined with GR curve, the distribution was further studied, the relationship between shale reservoir parameters and organic matter types was analyzed, and the significance was discussed. The results show that the kerogen types of organic rich shale in the lower part of Wufeng-Longmaxi Formation in the south of the Sichuan Basin are mainly of type I, II1a and II1b, while type II2 and type III are not developed. In Wufeng Formation, the shale organic matter is mainly of type II1a and II1b. From Long111 to Long114, the shale displays a trend of “Type I-II1b-II1a-II1b”. Type I was characterized by higher TOC, porosity and gas bearing capacity of shale reservoirs than the other organic matter. The reservoir parameter of type II1a was better than type II1b, indicating that the organic matter type control on the quality of shale reservoirs. Type difference is closely related to the bio-precursors component, among which type I and type II1a are related to the content of planktonic algae, while type II1b is related to the content of benthic algae. This study provides a good reference for the subdivision of marine shale organic matter types and the evaluation and prediction of gas bearing properties.

Origin of the Ultra-Deep Hydrocarbons from the Shunbei No. 1 Fracture Zone in the North of Shuntuoguole Low Uplift, Tarim Basin, North-Western China

In order to have a deeper insight into the accumulation mechanism of ultra-deep hydrocarbons, in this paper, the recently discovered ultra-deep Ordovician light oil and gas deposits (>7200 m) in the Shunbei No. 1 fracture zone are studied intensively, including maturity, source kitchens, the extent of secondary alterations, and possible migration directions, based on an analysis of the molecular compositions and stable carbon isotopes of crude oils and natural gases. The average equivalent vitrinite reflectance (Rc) of these oils, estimated from light hydrocarbons (H versus I), MDI, DNR, and MDR, are about 1.50%, 1.58%, 1.48%, and 1.51%, respectively, which suggests that most of the oils are in the late stages of crossing the oil window. The two maturity grades (1.06–1.25% and 1.36–1.67%) of the oil samples calculated from the aromatic compounds indicate the presence of at least two stages of hydrocarbon charge. In addition, the positive correlation plot of DNR and MDR (y = 3.59x − 12.84; R2 = 0.96) indicates that oils in the southwestern region of the F1 (S1-11–S1-16) are slightly more mature than oils in the northeastern region of the F1 and the well at SL1, far from the No. 1 main fault zone. In addition, the study shows that these hydrocarbons belong to the same source kitchen of a reduced marine sedimentary environment with mixed organic matter comprising benthic and planktonic algae, based on biomarker parameters, light hydrocarbons, and carbon isotope compositions. The oil–oil correlation analyses suggest that the studied oil samples are probably derived from the in situ Lower Cambrian Yuertusi formation source rocks. Various geochemical parameters consistently show limited significant hydrocarbon alteration processes, indicating favorable preservation conditions in the study area. The integrated geochemical characteristics of the hydrocarbons allow us to infer that they mainly migrate vertically from the in situ Lower Cambrian Yuertusi formation source rocks toward the Ordovician reservoirs, followed by a certain degree of lateral migration from southwest to northeast.

Structure and Productivity of the Phytoplankton Community in the Southwestern Kara Sea in Early Summer

Knowledge of the features of the structure and productivity of the Arctic communities of marine planktonic algae is necessary to identify possible changes in the pelagic ecosystem functioning under the changing climate condition of the Kara Sea. This study shows that the species diversity, abundance of phytoplankton, and production activity of algae are at a maximum at the beginning of summer during a seasonal ice melting period. The studies were carried out in the southwestern Kara Sea and in the estuarine zone of the Ob and Yenisei rivers from 29 June to 15 July 2018. The concentrations of nutrients and dissolved organic carbon were determined. The optical properties of chromophoric dissolved organic matter, species composition, abundance and biomass of all size groups of phototrophic and heterotrophic phytoplankton, and parameters of primary production and potential photosynthetic capacity were considered. Statistical data analysis showed that the leading factors influencing changes in the abundance of phytoplankton and its productivity are the content of silicates and salinity. At the same time, the production potential of algae is realized as short-lived and small phytoplankton assemblages differed in number taxa and diversity, with an equally rapid decrease in photosynthetic activity. Such changes affect the Marine Zone to a greater extent and the Estuarine Zone to a lesser extent.

Water Quality Change Trend and Risk Analysis of Wuhan Hanjiang River Water Source

Hanjiang River is closely related to the middle route of the South-to-North Water Diversion Project, the Water Diversion Project from the Hanjiang River to the Wei River, and the Water Diversion Project in Northern Hubei. The Wuhan Hanjiang River water source is one of the important drinking water sources in China; its water quality safety is significant to living and production for millions of residents in Wuhan. Based on data from 2004 to 2021, the water quality variation trend and risk of Wuhan Hanjiang River water source were studied. The results showed that a certain gap existed between the concentrations of some pollutants such as total phosphorus, permanganate index, ammonia nitrogen, and correspondent water quality target, especially for the total phosphorus. The growth of algae in the water source was marginally limited by the concentrations of nitrogen, phosphorus, and silicon. When other factors remained unchanged, diatoms tended to grow rapidly when the water temperature was appropriate (6-12℃). The quality of water upstream had a great impact on the water quality of the Hanjiang water source. There may have been pollutants entering into the reach during the West Lake Water Plant and Zongguan Water Plant. There were differences in the temporal and spatial variation trend of concentrations between permanganate index, total nitrogen, total phosphorus, and ammonia nitrogen. Significant changes in the ratio of nitrogen and phosphorus in the water body will affect the population structure and quantity of planktonic algae and ultimately affect the safety of water quality. The water body in the water source area was generally in the state of medium nutrition to mild eutrophication, and middle eutrophication may have occurred in a few periods. In recent years, the nutritional level of the water source has been on the decline. It is necessary to make an in-depth investigation on the source, quantity, and change trend of pollutants in water sources in order to eliminate potential risks.

Current anthropogenic warming threatens shallow Lake ecosystems on the Tibetan plateau: A palaeolimnological study covering the past 1,600 years in Genggahai Lake

Abstract The Tibetan Plateau has ∼1,200 lakes larger than 1 km2 with a total area of ~46,000 km2. The annual mean air temperature of the Tibetan Plateau has increased 2.5°C over the past 60 years. Lakes in this region are extremely responsive to climate changes as a result of their low biodiversity and simple food webs. However, it is unclear whether the current anthropogenic warming will benefit or threaten the aquatic ecosystems in this region. We assessed patterns of change associated with climate change in a shallow, freshwater lake (Genggahai Lake) on the NE Tibetan Plateau over the past ~1,600 years based on diverse aquatic fossils (macrophytes, molluscs, cladocerans and diatoms), total organic carbon (TOC) and total nitrogen (TN) of a sediment core. The abundances of macrophytes, molluscs and cladocerans, and the concentrations of TOC and TN in the sediments were high during the Mediaeval Warm Period (MWP, ~940–1,410 CE) but low during the Dark Ages Cold Period (DACP, ~390–940 CE) and the Little Ice Age (LIA, ~1,410–1970 CE), suggesting that modest natural warming was associated with the biomass of macrophytes and consumers in the food web. By contrast, low abundance of macrophytes and high abundance of planktonic diatoms were recorded in the sediments during the Current Warm Period (CWP, ~1970–2020 CE). Current anthropogenic warming has resulted in significantly higher temperatures than during the MWP, associated with the development of planktonic algae rather than macrophytes. Our findings show that the current anthropogenic warming, coupled with increased atmospheric nitrogen deposition and activated nutrients from thawed permafrost, is associated with phytoplankton dominance in lakes on the Tibetan Plateau, and may lead to significant reductions in ecosystem services provided by the lakes.

Habitat and Features of Development of Plankton Communities in Salt Lakes (South-Eastern Transbaikalia, Russia)

Results of studies of plankton algae and invertebrates in salt lakes of the territory of a closed runoff in the south of South-Eastern Transbaikalia (Russia) carried out in 2021–2022 are presented. Phyto- and zooplankton of sixteen saline lakes were studied during the maximum vegetation period from July to August. Lakes are different in chemical type: chloride, soda and sulfate. For chloride, sulfate and some soda lakes, data on plankton have been obtained for the first time. Fifty-four taxa of phytoplankton and twenty-seven species of zooplankton were found in soda lakes; twenty-three taxa of phytoplankton and four species of zooplankton were found in the chloride lakes; fifteen phytoplankton species and five zooplankton species were found in the sulfate lakes. For phytoplankton in soda lakes, green algae, cyanobacteria and diatoms were dominant. Green algae dominated in species composition in sulfate lakes; cryptophyte algae and cyanobacteria dominated in chloride lakes. For zooplankton, in all types of lakes, Brachionus plicatilis, Moina brachiata and Metadiaptomus asiaticus dominated. The abundance and biomass of algae and invertebrates in the surveyed lakes varied widely. Based on the results of the correlation analysis, total dissolved solids (TDS) are a key factor in the formation of planktonic communities in soda lakes; depth, transparency and temperature—in chloride lakes and pH—in sulfate lakes.

Geographic characteristics and environmental variables determine the diversities and assembly of the algal communities in interconnected river-lake system

Algal blooms in lakes are a major hazard worldwide. Although various geographical and environmental patterns affect algal communities during river-lake transit, a thorough understanding of what patterns shape the algal communities is still rarely researched, particularly in complex interconnected river-lake systems. In this study, focusing on the most typical interconnected river-lake system in China, the Dongting Lake, we collected paired water and sediment samples in summer, when algal biomass and growth rate are at high levels. Based on 23S rRNA gene sequencing, we investigated the heterogeneity and the differences in assembly mechanisms of planktonic and benthic algae in Dongting Lake. Planktonic algae contained more Cyanobacteria and Cryptophyta, while sediment harbored higher proportions of Bacillariophyta and Chlorophyta. For planktonic algae, stochastic dispersal dominated the assembly of the communities. Upstream rivers and confluences were important sources of planktonic algae in lakes. Meanwhile, for benthic algae, deterministic environmental filtering shaped the communities, and the proportion of benthic algae exploded with increasing N:P ratio and Cu concentration until reaching thresholds of 1.5 and 0.013 g/kg respectively, and then started falling, showing non-linear responses. This study revealed the variability of different aspects of algal communities in different habitats, traced the main sources of planktonic algae, and identified the thresholds for benthic algal shifts in response to environmental filters. Hence, upstream and downstream monitoring as well as thresholds of environmental factors should be considered in further aquatic ecological monitoring or regulatory programs of harmful algal blooms in these complex systems.

Contrasting shale oil accumulation in the upper and lower sweet spots of the lacustrine Permian Lucaogou Formation, Junggar Basin, China

Shale oil enrichment and accumulation in lacustrine strata is rather heterogeneous (unlike that in marine strata), which is a challenging issue to study. Here we carried out a case study in the Permian Lucaogou Formation in the Jimusar Sag, Junggar Basin, northwestern China. Based on data from drill cores, thin sections, rock extracts, and crude oils (including well logging, petrophysics, nuclear magnetic resonance, organic geochemistry, and oil test), the differences of lithology, reservoir physical property, oil generation potential, shale oil content, and physical property and geochemistry of oil between the lower and upper sweet spots were comprehensively compared. Results show that a mixed sedimentary system comprising interbedded carbonate, siltstone, and mudstone was developed owing to terrigenous clastic sedimentation, volcanism, and carbonate deposition. The lower sweet spot has a relatively higher content of silt compared with the upper sweet spot. Due to spatial changes in the depositional environment, only the lower sweet spot occurs at the northeastern margin of the study area and only the upper sweet spot occurs at its southeastern margin, but both occur in the central part of the study area. The porosity and permeability of the sweet spots are highly heterogeneous, due to the complex sedimentary–diagenetic processes, and dissolution pores are common in the lower sweet spot. The hydrocarbon generation potential and shale oil content of the sweet spots are both excellent. Comparatively, the shale oil in the lower sweet spot has higher densities and lower wax contents than those in the upper sweet spot. Thus, the shale oil is more mobile in the upper sweet spot. This implies a high-salinity depositional environment for the lower sweet spot and the oils are generated from salt-tolerant planktonic algae. The oil saturation index (OSI) values are not entirely consistent with the test production results. This indicates that the shale oil productivity is comprehensively controlled by multiple factors, e.g., the hydrocarbon generation potential, reservoir physical properties, and shale oil mobility. These are key features that distinguish lacustrine from marine shale oil systems. The exploration and exploitation strategies of shale oil in lacustrine systems need to be carefully developed.

Response of OC, TN, and TP deposition mediated by aquatic photosynthetic community structures in shallow karst surface waters under different land uses

Land use change alters the hydrochemical features, nutrient outputs, and community structure of aquatic photosynthetic organisms in watersheds and has an important impact on C, N, and P biogeochemical processes. In shallow water environments, sediments are the most important burial sites for C, N, and P; however, the factors underlying the control of their deposition by land use changes remain unclear. In this study, the relationship among hydrochemical features, aquatic photosynthetic organism community structure, and C, N, and P deposition in surface waters associated with different land uses was studied at the Shawan Karst Water-Carbon Cycle Test Site, Puding, SW China, by combining field monitoring and laboratory experiments performed over a complete hydrological year from September 2018 to August 2019. The results indicate that (1) OC and TN deposition showed small differences among ponds associated with five land uses, while TP was significantly higher in ponds associated with shrubland and grassland than in ponds of cultivated land, bare soil, and bare rock. (2) Cultivated land increased OC and TN deposition by increasing N and P output and planktonic algae biomass in surface waters, while grassland and shrubland ponds mainly by increasing DIC output and macrophyte biomass. (3) Compared with cultivated land, grassland and shrubland significantly enhanced TP deposition by promoting the deposition of calcium-bound P and biogenic P from macrophytes and their epiphytic algae in surface waters. In conclusion, the shift of cultivated land and bare soil to grassland and shrubland may be conducive to the formation of benign aquatic ecosystems and stabilization of C, N, and P sinks in karst shallow surface waters.

Bacterial community are more susceptible to nanoplastics than algae community in aquatic ecosystems dominated by submerged macrophytes

As a ubiquitous emerging pollutant, microplastics can interact with algal and bacterial communities in aquatic ecosystems. Currently, knowledge on how microplastics influence algae/bacteria is mostly limited to toxicity tests using either monocultures of algae/bacteria or specific algal–bacterial consortium. However, information on the effect of microplastics on algal and bacterial communities in natural habitats is not easily available. Here, we conducted a mesocosm experiment to test the effect of nanoplastics on algal and bacterial communities in aquatic ecosystems dominated by different submerged macrophytes. The community structure of algae and bacteria suspended in the water column (planktonic) and attached to the surface of submerged macrophytes (phyllospheric) were identified, respectively. Results showed that both planktonic and phyllospheric bacteria were more susceptible to nanoplastics, and these variations driven by decreased bacterial diversity and increased abundance of microplastic-degrading taxa, especially in aquatic systems dominated by V. natans. The community composition of both algae and bacteria were influenced to varying degrees by nanoplastics and/or plant types, but RDA results showed that only bacterial community composition was strongly correlated with environmental variables. Correlation network analysis showed that nanoplastics not only reduced the intensity of associations between planktonic algae and bacteria (average degree reduced from 4.88 to 3.24), but also reduced proportion of positive correlations (from 64% to 36%). Besides, nanoplastics also decreased the algal/bacterial connections between planktonic and phyllospheric habitats. Our study elucidates the potential interactions between nanoplastics and algal-bacterial community in natural aquatic ecosystems. These findings suggest that in aquatic ecosystems, bacterial community are more vulnerable to nanoplastics and may serve as a protective barrier for algae community. Further research is needed to reveal the protective mechanism of bacteria against algae at the community level.

Effects of Pond Water Depth and Method of Aeration on Phytoplankton Communities in Macrobrachium rosenbergii Farming Ponds

Recently, profitable Macrobrachium rosenbergii farming has developed rapidly in Asia. The occurrence of cyanobacterial blooms is one of the major environmental problems usually encountered in freshwater prawn farms. This study investigated the effects of pond water depth and aeration mode on phytoplankton communities in selected M. rosenbergii farming ponds in China. We adjusted pond water depth and aeration mode (pond water depth: 1.2 m or 1.8 m; method of aeration: surface or both surface and bottom) to compare and analyze phytoplankton community structure and characteristics between ecological (pond water depth: 1.8 m, both surface and bottom aeration) and traditional (pond water depth: 1.2 m, surface aeration) farming ponds. Water quality parameters were compared in six aquaculture systems, which were measured in situ or lab. The results showed that ecological culture suppressed Cyanophyta abundance and significantly increased the numbers of phytoplankton species leading to a 30.43–136.84% increase in the number of species for ecological ponds compared with that in traditional ponds. In all seasons, ecological culture tended to have decreased total nitrogen and ammonia nitrogen, and significantly lower total phosphorus and reactive phosphate compared with traditional ponds. In conclusion, ponds should maintain deeper water depth (1.8 m) and higher N/P ratio (>3) to promote phytoplankton diversity and suppress blooms; applying optimized culture may resolve planktonic algae problems in aquaculture ponds in Asia.

Rapid diversification underlying the global dominance of a cosmopolitan phytoplankton

Marine phytoplankton play important roles in the global ecosystem, with a limited number of cosmopolitan keystone species driving their biomass. Recent studies have revealed that many of these phytoplankton are complexes composed of sibling species, but little is known about the evolutionary processes underlying their formation. Gephyrocapsa huxleyi, a widely distributed and abundant unicellular marine planktonic algae, produces calcified scales (coccoliths), thereby significantly affects global biogeochemical cycles via sequestration of inorganic carbon. This species is composed of morphotypes defined by differing degrees of coccolith calcification, the evolutionary ecology of which remains unclear. Here, we report an integrated morphological, ecological and genomic survey across globally distributed G. huxleyi strains to reconstruct evolutionary relationships between morphotypes in relation to their habitats. While G. huxleyi has been considered a single cosmopolitan species, our analyses demonstrate that it has evolved to comprise at least three distinct species, which led us to formally revise the taxonomy of the G. huxleyi complex. Moreover, the first speciation event occurred before the onset of the last interglacial period (~140 ka), while the second followed during this interglacial. Then, further rapid diversifications occurred during the most recent ice-sheet expansion of the last glacial period and established morphotypes as dominant populations across environmental clines. These results suggest that glacial-cycle dynamics contributed to the isolation of ocean basins and the segregations of oceans fronts as extrinsic drivers of micro-evolutionary radiations in extant marine phytoplankton.