Drivers and ecological consequences of dominance in periurban phytoplankton communities using networks approaches

Temporal shifts in the phytoplankton network in a large eutrophic shallow freshwater lake subjected to major environmental changes due to human interventions

Phytoplankton communities are crucial components of aquatic ecosystems, and since they are highly interactive, they always form complex networks. Yet, our understanding of how interactive phytoplankton networks vary through time under changing environmental conditions is limited. Using a 29-year (339 months) long-term dataset on Lake Taihu, China, we constructed a temporal network comprising monthly sub-networks using "extended Local Similarity Analysis" and assessed how eutrophication, climate change, and restoration efforts influenced the temporal dynamics of network complexity and stability. The network architecture of phytoplankton showed strong dynamic changes with varying environments. Our results revealed cascading effects of eutrophication and climate change on phytoplankton network stability via changes in network complexity. The network stability of phytoplankton increased with average degree, modularity, and nestedness and decreased with connectance. Eutrophication (increasing nitrogen) stabilized the phytoplankton network, mainly by increasing its average degree, while climate change, i.e., warming and decreasing wind speed enhanced its stability by increasing the cohesion of phytoplankton communities directly and by decreasing the connectance of network indirectly. A remarkable shift and a major decrease in the temporal dynamics of phytoplankton network complexity (average degree, nestedness) and stability (robustness, persistence) were detected after 2007 when numerous eutrophication mitigation efforts (not all successful) were implemented, leading to simplified phytoplankton networks and reduced stability. Our findings provide new insights into the organization of phytoplankton networks under eutrophication (or re-oligotrophication) and climate change in subtropical shallow lakes.

Daily process and key characteristics of phytoplankton bloom during a low-water level period in a large subtropical reservoir bay

Reservoirs, heavily influenced by artificial management, often harbor phytoplankton assemblages dominated by cyanobacteria or dinoflagellates, triggering significant changes in aquatic ecosystems. However, due to limited sampling frequency and insufficient attention to species composition, the bloom processes and key characteristics of phytoplankton community structure have not been systematically elucidated. During the low-water level period when blooms are most likely to occur (June to September) in a tributary bay of the Three Gorges Reservoir, daily sampling was conducted to investigate phytoplankton community composition, identify significant environmental factors, and evaluate important structure characteristics of phytoplankton community. The results showed that Microcystis aeruginosa maintained a clear dominance for almost a month in stage 1, with low Shannon and evenness but a high dominance index. Phytoplankton total density and biomass decreased drastically in stage 2, but Microcystis aeruginosa still accounted for some proportion. The highest Shannon and evenness but the lowest dominance index occurred in stage 3. Peridiniopsis niei occurred massively in stage 4, but its dominant advantages lasted only one to two days. NH4-N was responsible for the dominance of Microcystis aeruginosa, while TP and PO4-P was responsible for the dominance of Peridiniopsis niei; however, precipitation contributed to their drastic decrease or disappearance to some extent. The TN : TP ratio could be considered as an important indicator to determine whether Microcystis aeruginosa or Peridiniopsis niei dominated the phytoplankton community. Throughout the study period, physiochemical factors explained more variation in phytoplankton data than meteorological and hydrological factors. Pairwise comparisons revealed an increase in average β diversity with stage progression, with higher β diversities based on abundance data than those based on presence/absence data. Repl had a greater effect on β diversity differences based on presence/absence data, whereas RichDiff had a greater effect on β diversity differences based on species abundance data. Co-occurrence networks for stage 1 showed the most complex structure, followed by stage 4, while the network for stage 3 was relatively sparse, although the overall community division remained compact. This study provides a useful attempt to explore the status and changes in phytoplankton community structure during the bloom process through high-resolution investigation.

Re-oligotrophication and warming stabilize phytoplankton networks

Phytoplankton taxa are strongly interconnected as a network, which could show temporal dynamics and non-linear responses to changes in drivers at both seasonal and long-term scale. Using a high quality dataset of 20 Danish lakes (1989-2008), we applied extended Local Similarity Analysis to construct temporal network of phytoplankton communities for each lake, obtained sub-network for each sampling month, and then measured indices of network complexity and stability for each sub-network. We assessed how lake re-oligotrophication, climate warming and grazers influenced the temporal dynamics on network complexity and stability of phytoplankton community covering three aspects: seasonal trends, long-term trends and detrended variability. We found strong seasonality for the complexity and stability of phytoplankton network, an increasing trend for the average degree, modularity, nestedness, persistence and robustness, and a decreasing trend for connectance, negative:positive interactions and vulnerability. Our study revealed a cascading effect of lake re-oligotrophication, climate warming and zooplankton grazers on phytoplankton network stability through changes in network complexity characterizing diversity, interactions and topography. Network stability of phytoplankton increased with average degree, modularity, nestedness and decreased with connectance and negative:positive interactions. Oligotrophication and warming stabilized the phytoplankton network (enhanced robustness, persistence and decreased vulnerability) by enhancing its average degree, modularity, nestedness and by reducing its connectance, while zooplankton richness promoted stability of phytoplankton network through increases in average degree and decreases in negative interactions. Our results further indicate that the stabilization effects might lead to more closed, compartmentalized and nested interconnections especially in the deeper lakes, in the warmer seasons and during bloom periods. From a temporal dynamic network view, our findings highlight stabilization of the phytoplankton community as an adaptive response to lake re-oligotrophication, climate warming and grazers.

Strategies for regulating the intensity of different cyanobacterial blooms: Insights from the dynamics and stability of bacterioplankton communities

The occurrence of cyanobacterial blooms is increasing in frequency and magnitude due to climate change and human activities, which poses a direct threat to drinking water security. The impacts of abiotic and biotic factors on the development of blooms have been well studied; however, control strategies for different bloom intensities have rarely been explored from the perspective of the dynamics and stability of bacterioplankton communities. Here, a network analysis was used to investigate the interactions and stability of microbial communities during different periods of R. raciborskii bloom in an inland freshwater lake. The abundance and diversity of rare taxa were significantly higher than that of abundant taxa throughout the bloom cycle. At the pre-bloom (PB) stage, microbial interactions among the different bacterial groups were weak but strongly negatively correlated, indicating low robustness and weak disturbance resistance within the community. However, community stability was better, and microbial interactions became more complicated at the high-bloom (HB) and low-bloom (LB) stages. Interestingly, rare taxa were significantly responsible for community stability and connectivity despite their low relative abundance. The Mantel test revealed that Secchi depth (SD), orthophosphate (PO43--P), and dissolved oxygen (DO) were significantly positively correlated with abundant taxa, rare taxa and PB. DO was significantly positively correlated with HB, intermediate taxa, and rare taxa, while water temperature (WT), N/P and total nitrogen (TN) were significantly positively correlated with LB, abundant taxa, intermediate taxa, and rare taxa. These findings suggest that reducing the PO43--P concentration at the PB stage may be an effective approach to preventing the development of R. raciborskii blooms, while regulating rare taxa at the HB and LB stages may be a key factor in controlling R. raciborskii blooms.

Seasonal dynamics of bacterial community and co-occurrence with eukaryotic phytoplankton in the Pearl River Estuary

In this study, we investigated the taxonomic composition of the bacteria and phytoplankton communities in the Pearl River Estuary (PRE) through Illumina sequencing of the V3-V4 region of the 16 S rRNA gene. Furthermore, their relationships as well as recorded environmental variables were explored by co-occurrence networks. Bacterial community composition was different in two size fractions, as well as along the salinity gradient across two seasons. Free-living (FL) communities were dominated by pico-sized Cyanobacteria (Synechococcus CC9902) while Exiguobacterium, Halomonas and Pseudomonas were predominantly associated with particle-associated (PA) lifestyle, and Cyanobium PCC-6307 exhibited seasonal shifts in lifestyles in different seasons. In wet season, bacterial community composition was characterized by abundance of Cyanobacteria, Actinobacteria, and Bacteroidetes, which were tightly linked with high riverine inflow. While in dry season, Proteobacteria increased in prevalence, especially for Psychrobacter, NOR5/OM60 clade and Pseudomonas, which were thrived in lower water temperature and higher salinity. Moreover, we discovered that differences between PA and FL composition were more significant in the wet season than in the dry season, which may be due to better nutritional conditions of particles (indicated by POC%) in the wet season and then attract more diverse PA populations. Based on the analysis of plastidial 16 S rRNA genes, abundant small-sized mixotrophic phytoplankton (Dinophyceae, Euglenida and Haptophyta) were identified in the PRE. The complexity of co-occurrence network increased from FL to PA fractions in both seasons, which suggested that suspended particles can provide ecological niches for particle-associated colonizers contributing to the maintenance of a more stable community structure. In addition, the majority of phytoplankton species exhibited positive co-occurrences with both other phytoplankton species and bacterial counterparts, indicating the mutual cooperation between phytoplankton assemblages and specific bacterial populations e likely benefited from phytoplankton-derived organic compounds. This study enhances our understanding of the seasonal and spatial dynamics of bacterial communities and their potential relationship with phytoplankton assembly in estuarine waters.

Temporal patterns of algae in different urban lakes and their correlations with environmental variables in Xi'an, China

Urban lakes were critical in aquatic ecology environments, but how environmental factors affected the distribution and change characteristics of algal communities in urban lakes of Xi'an city was not clearly. Here, we investigated the algal community structure of six urban lakes in Xi'an and evaluated the effects of water quality parameters on algae. The results indicated that the significant differences on physicochemical parameters existed in different urban lakes. The maximum concentration of total phosphorus in urban lakes was (0.18 ± 0.01) mg/L and there was a phenomenon of phosphorus limitation. In addition, 51 genera of algae were identified and Chlorella sp. was the dominant algal species, which was affiliated with Chlorophyta. Network analysis elucidated that each lake had a unique algal community network and the positive correlation was dominant in the interaction between algae species, illustrating that mature microbial communities existed or occupied similar niches. Redundancy analysis illustrated that environmental factors explained 47.35% variance of algal species-water quality correlation collectively, indicating that water quality conditions had a significant influence on the temporal variations of algae. Structural equation model further verified that algal community structure was directly or indirectly regulated by different water quality conditions. Our study shows that temporal patterns of algal communities can reveal the dynamics and interactions of different urban ecosystem types, providing a theoretical basis for assessing eutrophication levels and for water quality management.

The phyto-bacterioplankton couple in a shallow freshwater ecosystem: Who leads the dance?

Bloom-forming phytoplankton dynamics are still unpredictable, even though it is known that several abiotic factors, such as nutrient availability and temperature, are key factors for bloom development. We investigated whether biotic factors, i.e. the bacterioplankton composition (via 16SrDNA metabarcoding), were correlated with phytoplankton dynamics, through a weekly monitoring of a shallow lake known to host recurrent cyanobacterial blooms. We detected concomitant changes in both bacterial and phytoplankton community biomass and diversity. During the bloom event, a significant decrease in phytoplankton diversity, was detected, with a first co-dominance of Ceratium, Microcystis and Aphanizomenon, followed by a co-dominance of the two cyanobacterial genera. In the same time, we observed a decrease of the particle-associated (PA) bacterial richness and the emergence of a specific bacterial consortium that was potentially better adapted to the new nutritional niche. Unexpectedly, changes in PA bacterial communities occurred just before the development the emergence of the phytoplanktonic bloom and the associated modification of the phytoplanktonic community composition, suggesting that changes in environmental conditions leading to the bloom, were first sensed by the bacterial PA community. This last was quite stable throughout the bloom event, even though there were changes in the blooming species, suggesting that the association between cyanobacterial species and bacterial communities may not be as tight as previously described for monospecific blooming communities. Finally, the dynamics of the free-living (FL) bacterial communities displayed a different trajectory from those of the PA and phytoplankton communities. This FL communities can be viewed as a reservoir for bacterial recruitment for the PA fraction. Altogether, these data also highlight s that the spatial organization within these different microenvironments in the water column is a relevant factor in the structuring of these communities.

Shift of phytoplankton assemblages in a temperate lake located on the eastern route of the South-to-North Water Diversion Project

There remains no consensus on the effects of changes in the environment factors under the action of water diversions on phytoplankton communities. Herein the changing rules applying to phytoplankton communities subject to water diversion were unveiled based on long-term (2011-2021) time-series observations on Luoma Lake, located on the eastern route of the South-to-North Water Diversion Project. We found that nitrogen decreased and then increased, while phosphorus increased after operation of the water transfer project. Algal density and diversity were not affected by water diversion, while the duration of high algal density was shorter after water diversion. Phytoplankton composition had dramatic differences before and after water transfer. The phytoplankton communities exhibited greater fragility when they first experienced a human-mediated disturbance, and then they gradually adapted to more interferences and acquired stronger stability. We furthermore found the niche of Cyanobacteria narrowed while that of Euglenozoa widened under the pressure of water diversion. In addition to WT and DO, the main environmental factor before water diversion was NH₄-N, whereas the effect of NO₃-N and TN on phytoplankton communities increased after water diversion. These findings fill the knowledge gap as to the consequence of water diversion on water environments and phytoplankton communities.

Disruption of fish gut microbiota composition and holobiont's metabolome during a simulated Microcystis aeruginosa (Cyanobacteria) bloom

BACKGROUND

Cyanobacterial blooms are one of the most common stressors encountered by metazoans living in freshwater lentic systems such as lakes and ponds. Blooms reportedly impair fish health, notably through oxygen depletion and production of bioactive compounds including cyanotoxins. However, in the times of the "microbiome revolution", it is surprising that so little is still known regarding the influence of blooms on fish microbiota. In this study, an experimental approach is used to demonstrate that blooms affect fish microbiome composition and functions, as well as the metabolome of holobionts. To this end, the model teleost Oryzias latipes is exposed to simulated Microcystis aeruginosa blooms of various intensities in a microcosm setting, and the response of bacterial gut communities is evaluated in terms of composition and metabolome profiling. Metagenome-encoded functions are compared after 28 days between control individuals and those exposed to highest bloom level.

RESULTS

The gut bacterial community of O. latipes exhibits marked responses to the presence of M. aeruginosa blooms in a dose-dependent manner. Notably, abundant gut-associated Firmicutes almost disappear, while potential opportunists increase. The holobiont's gut metabolome displays major changes, while functions encoded in the metagenome of bacterial partners are more marginally affected. Bacterial communities tend to return to original composition after the end of the bloom and remain sensitive in case of a second bloom, reflecting a highly reactive gut community.

CONCLUSION

Gut-associated bacterial communities and holobiont functioning are affected by both short and long exposure to M. aeruginosa, and show evidence of post-bloom resilience. These findings point to the significance of bloom events to fish health and fitness, including survival and reproduction, through microbiome-related effects. In the context of increasingly frequent and intense blooms worldwide, potential outcomes relevant to conservation biology as well as aquaculture warrant further investigation. Video Abstract.

Succession dynamics of microbial communities responding to the exogenous microalgae ZM-5 and analysis of the environmental sustainability of a constructed wetland system

Constructed wetlands (CWs) are economical and effective swine tailwater treatment systems. However, nitrogen removal in CWs is limited by the lack of carbon source for denitrification. In this study, we studied the feasibility of dosing the microalgae ZM-5 to improve the nitrogen removal ability in CWs. Compared to the control CW, a 20 % higher removal capacity of COD and TN was observed for the coupled system (EG). The microalgae ZM-5 could interact with denitrifying bacteria to compensate for the deficiency of denitrifying stage in CWs. HT-qPCR chip analysis also provided evidence that denitrification genes significantly increased (p < 0.05). According to the life cycle assessment (LCA), ultrasonic extraction had the best environmental sustainability among four lipid extraction processes. As an improvement strategy, clean energy could be utilized to optimize the electricity source to reduce environmental load (45 %-60 %). These findings offer new insights into the feasibility of EG for environmentally sustainable wastewater treatment.

The role of nutrients, wind speed, and rainfall in determining the composition of the algal community of shallow lakes in the Taoge water system, upstream from Lake Taihu, China

Gaining a deeper understanding of factors that influence changes in phytoplankton community has significant implications for shallow lake management. The present study examined changes in the algae community of three shallow eutrophic lakes of the Taoge water system between 2008 and 2018 and the related factors influencing these changes. The composition of the algal community varied significantly during this period with the relative diatom biomass in lakes Changdanghu and Gehu increasing between 2014 and 2016 and again decreasing after 2017. However, relative cyanobacteria biomass initially decreased and later increased; meanwhile, the proportion of biomass of other phyla decreased continuously in the study period. Lake Zhushanhu showed similar trends, although it eventually returned to its initial state with absolute Microcystis dominance. Furthermore, the analysis of driving factors revealed that the concentrations of total nitrogen (TN), nitrate (NO₃), and orthophosphate (PO₄) were significantly associated with a significant increase in Microcystis biomass. Meteorological conditions also influenced changes in total algal and diatom biomasses, which were inversely related to the daily mean and daily maximum wind speeds. Monthly cumulative precipitation was only significantly associated with diatom biomass. Meanwhile, rainfall primarily affected the algal community structure between 2013 and 2017; an increase in the relative biomass of diatoms coincided with increased precipitation. Coordinating nitrogen and phosphorous use within the Taoge water system should improve lake habitat management; a broader perspective in attempts to control global and regional climate change may be needed.

Ancient DNA reveals potentially toxic cyanobacteria increasing with climate change

Cyanobacterial blooms in freshwater systems are a global threat to human and aquatic ecosystem health, exhibiting particularly harmful effects when toxin-producing taxa are present. While climatic change and nutrient over-enrichment control the global expansion of total cyanobacterial blooms, it remains unknown to what extent this expansion reflected cyanobacterial assemblage due to the scarcity of long-term monitoring data. Here we use high-throughput sequencing of sedimentary DNA to track ∼100 years of changes in cyanobacterial community in hyper-eutrophic Lake Taihu, China's third largest freshwater lake and the key water source for ∼30 million people. A steady increase in the abundance of Microcystis (as potential toxin producers) during the past thirty years was correlated with increasing temperatures and declining wind speeds, but not with temporal trends in lakewater nutrient concentrations, highlighting recent climate effects on potentially increasing toxin-producing taxa. The socio-environmental repercussions of these findings are worrisome as continued anthropogenic climate change may counteract nutrient amelioration efforts in this critical freshwater resource.

Distinct indicators of land use and hydrology characterize different aspects of riverine phytoplankton communities

Given the many threats to freshwater biodiversity, we need to be able to resolve which of the multiple stressors present in rivers are most important in driving change. Phytoplankton are a key component of the aquatic ecosystem, their abundance, species richness and functional richness are important indicators of ecosystem health. In this study, spatial variables, physiochemical conditions, water flow alterations and land use patterns were considered as the joint stressors from a lowland rural catchment. A modeling approach combining an ecohydrological model with machine learning was applied. The results implied that land use and flow regime, rather than nutrients, were most important in explaining differences in the phytoplankton community. In particular, the percentage of water body area and medium level residential urban area were key to driving the rising phytoplankton abundance in this rural catchment. The proportion of forest and pasture area were the leading factors controlling the variations of species richness. In this case deciduous forest cover affected the species richness in a positive way, while, pasture share had a negative effect. Indicators of hydrological alteration were found to be the best predictors for the differences in functional richness. This integrated model framework was found to be suitable for analysis of complex environmental conditions in river basin management. A key message would be the significance of forest area preservation and ecohydrological restoration in maintaining both phytoplankton richness and their functional role in river ecosystems.

A framework for exploring environmental risk of the longest inter-basin water diversion project under the influence of multiple factors: A case study in China

Multi-factor risk assessment is an important prerequisite for water quality protection and the safe operation of mega hydro-projects. As the largest long-distance inter-basin water diversion project in the world, the Middle Route of the South-to-North Water Diversion Project of China (MRSNWDPC) has been in operation for 8 years and has benefited 79 million people along the canal. However, concerns have been raised in recent years about the potential negative effects of abnormal algal proliferation in the MRSNWDPC. It is very important for the safety of water supply to carry out relevant risk analysis and formulate regulatory management. In order to quantitatively evaluate the risk of algal proliferation in the MRSNWDPC under the influence of multiple factors, a multivariate risk assessment method based on Vine Copula theory and Monte Carlo simulation was proposed. Five key factors (water temperature, flow velocity, flow rate, algal cell density, and dissolved oxygen) were used and multiple dependency models in each section of the MRSNWDPC from January 2016 to January 2019 were established to study the risk of algal proliferation under multiple scenarios. The results demonstrate that water temperature can be used as an appropriate early-warning indicator of algal proliferation. The early-warning interval (unit: °C) of water temperature in the upper, middle, and lower reaches are 26-29°C, 23-26°C, and 21-23°C, respectively. Unlike bivariate analysis, the multiple dependency model describes the relationship between variables more accurately and enriches the scenarios of multiple conditional probabilities. When the water temperature fluctuates in the early-warning interval, regulating the upstream, midstream, and downstream flow velocity to be higher than 0.6 m/s, 0.5 m/s, and 0.6 m/s, respectively, can effectively reduce the risk of algal proliferation. This research not only provides a reference for the ecological control of algae in the MRSNWDPC and similar mega hydro-projects but also enriches the application of the Vine Copula theory coupled with the random sampling method for multi-variable risk analysis.

Cyanobacterial bloom intensities determine planktonic eukaryote community structure and stability

The intensity of cyanobacterial blooms that predominate in the world's lakes and reservoirs is variable, which may lead to differing effects on the freshwater ecosystem. Planktonic eukaryotes play key roles in the structure and function of freshwater ecosystems; however, little is known about the influence of cyanobacterial blooms on eukaryotic plankton communities and their function. Herein, the dynamics of eukaryotic plankton communities in Hongze Lake, which is the fourth largest freshwater lake in China, with a range of bloom levels occurred, from low to high, were studied to reveal the effect of cyanobacterial blooms' spatial heterogeneity on planktonic eukaryotes. Results showed that the diversity, richness, and evenness of eukaryotic plankton community were not affected by low level of bloom; however, they were decreased obviously by high level of bloom. Metazoa, Ochrophyta, Chloroplastida, Cryptomonadales, and Ciliophora were the main planktonic eukaryotes in this lake. Metazoa relative abundance declined 25.1% and relative abundance of eukaryotic phytoplankton (mainly Ochrophyta, Chloroplastida, and Cryptomonadales) and Ciliophora increased 17.4% and 2.0%, respectively, during the period with low level of bloom; conversely, the site with the high bloom level manifested the opposite changes. The linkage density of planktonic eukaryotic network was 0.188 and 0.138 with low and high level of bloom, respectively, indicating the stability of planktonic eukaryotes was lower when a high level of bloom occurred compared to that of a low bloom level. Our findings indicate that cyanobacterial blooms should be controlled at low level to avoid their obvious negative impact on microeukaryotes in lakes or reservoirs.

Water depth and land-use intensity indirectly determine phytoplankton functional diversity and further regulate resource use efficiency at a multi-lake scale

Biodiversity-ecosystem functioning relationships under multiple pressures have recently been the subject of broad studies. For the key primary producer in aquatic ecosystems, phytoplankton, several studies have focused on trait-based functional diversity (FD) and the related functioning (e.g., resource use efficiency, RUE), and their linkages. However, investigations of the effects of environmental factors at different levels (e.g., land use, lake morphometry, climate and nutrients) on FD and RUE are sparse. We developed a data-driven-model framework to simultaneously elucidate the effects of multiple drivers on FD (functional diversity based on dendrograms, FDc and functional richness, FRic) and RUE (of nitrogen and phosphorus) of phytoplankton based on data from 68 Yunnan-Guizhou Plateau lakes, Southwest China. We found that the concentration of total phosphorus, which is mainly affected by land-use intensity and influenced by water depth, was the primary (positive) driver of changes in both FDc and FRic, while RUE was mainly explained by phytoplankton FD (i.e., FRic). These results indicate that water depth and land-use intensity influence indirectly phytoplankton FD and further regulate RUE. Moreover, nonlinear correlations of RUE with FRic were found, which may be caused by interspecific competition and niche differentiation of the phytoplankton community related to nutrient levels. Our finding may help managers to set trade-off targets between FD and RUE in lake ecosystems except for extremely polluted ones, in which the thresholds derived from the Bayesian network, of total phosphorus, total nitrogen and land-use intensity were approximately 0.04 mg/L, 0.50 mg/L and 244 (unitless), respectively. The probability of meeting the RUE objectives was lower in shallow lakes than in deep lakes, but for FRic the opposite was observed.

Changes in Phytoplankton Community Composition and Phytoplankton Cell Size in Response to Nitrogen Availability Depend on Temperature

The climate-driven changes in temperature, in combination with high inputs of nutrients through anthropogenic activities, significantly affect phytoplankton communities in shallow lakes. This study aimed to assess the effect of nutrients on the community composition, size distribution, and diversity of phytoplankton at three contrasting temperature regimes in phosphorus (P)–enriched mesocosms and with different nitrogen (N) availability imitating eutrophic environments. We applied imaging flow cytometry (IFC) to evaluate complex phytoplankton communities changes, particularly size of planktonic cells, biomass, and phytoplankton composition. We found that N enrichment led to the shift in the dominance from the bloom-forming cyanobacteria to the mixed-type blooming by cyanobacteria and green algae. Moreover, the N enrichment stimulated phytoplankton size increase in the high-temperature regime and led to phytoplankton size decrease in lower temperatures. A combination of high temperature and N enrichment resulted in the lowest phytoplankton diversity. Together these findings demonstrate that the net effect of N and P pollution on phytoplankton communities depends on the temperature conditions. These implications are important for forecasting future climate change impacts on the world’s shallow lake ecosystems.

Salinity Is a Key Determinant for the Microeukaryotic Community in Lake Ecosystems of the Inner Mongolia Plateau, China

The arid and semiarid areas experienced remarkable lake shrinkage during recent decades due to intensive human activities and climate change, which would result in unprecedented changes of microeukaryotic communities. However, little is known about how climate change affects the structure and ecological mechanisms of microeukaryotic communities in this area. Here, we used an 18S rRNA gene-based high-throughput sequencing approach to explore the structure, interspecies interaction, and assembly processes of the microeukaryotic community in lake ecosystems of the Inner Mongolia Plateau. As a direct result of climate change, salinity has become the key determinant of the lacustrine microeukaryotic community in this region. The microeukaryotic community in this ecosystem can be divided into three groups: salt (Lake Daihai), brackish (Lake Dalinuoer) and freshwater lakes. Co-occurrence network analysis revealed that salinity shapes the interspecies interactions of the microeukaryotic community. This causes interspecies interactions to change from antagonistic to cooperative with an increase in salinity. Phylogenetic-based β-nearest taxon distance analyses revealed that stochastic processes mainly dominated the microeukaryotic community assembly in lake ecosystems of the Inner Mongolia Plateau, and salinity stress drove the assembly processes of the microeukaryotic community from stochastic to deterministic. Overall, these findings expand the current understanding of interspecies interactions and assembly processes of microeukaryotic communities during climate change in lake ecosystems of the Inner Mongolia Plateau.

Spatial and temporal variations of phytoplankton composition and biomass in Lake Bunyonyi, South-Western Uganda

The purpose of this study was to examine the spatial and temporal variations of phytoplankton species composition and biomass in Lake Bunyonyi, South-Western Uganda. Samples were collected monthly from nine fixed stations in the lake from October 2019 to September 2020. Based on the morphological characterization, 52 different species of phytoplankton were recorded. These were dominated by cyanobacteria (21 species) and chlorophytes (15 species) followed by diatoms (10 species), euglenophytes (4 species), dinoflagellates (2 species), and cryptophytes (1 species). The biomass (Chl-a concentration) ranged from 0.019 ± 0.009 mg/L at Heissesero station to 0.045 ± 0.013 mg/L obtained at Nyombe station. On a temporal basis, the highest mean Chl-a concentration of 0.044 ± 0.03 mg/L was recorded in March 2020 while the least concentration of 0.015 ± 0.011 mg/L was obtained in September 2020. Significant differences existed in the Chl-a concentration values between stations and across sampling months. Chl-a concentration was significantly positively correlated with dissolved oxygen (DO), turbidity but negatively correlated with temperature. The Shannon-Wiener index and evenness put it clear that the distribution of phytoplankton species in the lake is inequitable. Besides, 94.2% of the phytoplankton species revealed had never been reported by the previous studies in the study area. The dominance of species cyanobacteria (such as Microcystis spp., Cylindrospermopsis raciborskii, Anabaenopsis sp., and Anabaena sp.) presents potential future challenges to water quality management. Therefore, the establishment of a strong and committed committee dubbed "Lake Bunyonyi Water Management Committee" to oversee the activities and avert potential water quality challenges is strongly recommended. The existence of some toxic phytoplankton species calls for regular monitoring and careful use of the lake and its food products.

Environmental Factors Drive Periphytic Algal Community Assembly in the Largest Long-Distance Water Diversion Channel

Periphytic algae exist widely in different waters. However, little is known about periphytic algae in long-distance water diversion channels across watersheds. We investigated the periphytic algae and the environmental factors at twenty sampling sites in the middle route of the South-to-North Water Diversion Project (MRP). The dominant species were Desmodesmus intermedius (Hegewald), Calothrix thermalis (Bornet & Flahault), Calothrix parietina (Bornet & Flahault) and Leptolyngbya benthonica (Anagnostidis) (dominance > 0.02) as measured in a whole year. Habitat heterogeneity in the MRP led to lower spatial heterogeneity and higher temporal heterogeneity of the periphytic algal community. Stochastic processes are the major process in periphytic community assembly. In deterministic processes, homogeneous selection had the major role in structuring the periphytic community, whereas the role of heterogeneous selection was less significant. In stochastic processes, dispersal limitations had the major role in structuring the periphytic community, whereas the role of homogenizing dispersal and drift were less significant. The variation in total nitrogen and total phosphorus promoted more stochastic processes (−1.96 < βNTI < 1.96). The variations in water temperature and water velocity promoted more heterogeneous selection (βNTI > 1.96). In integrating all of this empirical evidence, we explore the role of environmental factors in the action of ecological processes shaping thecommunity assembly of the periphytic algal community.

Trophic states regulate assembly processes and network structures of small chromophytic phytoplankton communities in estuarine and coastal ecosystem

Small chromophytic phytoplankton (SCP) are anticipated to be more important for a significant proportion of primary production in estuarine-coastal ecosystems. However, responses of SCP community to coastal eutrophication are still unclear. In this study, we investigated diversity, co-occurrence and assembly features of SCP communities, as well as relationship with environmental factors in subtropical Beibu Gulf. The results exhibited that the alpha diversity and beta diversity of SCP communities were significantly different among eutrophic states. Co-occurrence network revealed a complex interaction that most amplicon sequence variants (ASVs) in modules of the network were specific to trophic states. Further, phylogenetic based β-nearest taxon distance analyses revealed that stochastic processes mainly provided 69.26% contribution to SCP community assembly, whereas deterministic processes dominated community assembly in heavy eutrophic state. Overall, our findings elucidate the mechanism of diversity and assembly in SCP community and promote the understanding of SCP ecology related to subtropical coastal eutrophication.

Strong reorganization of multi-domain microbial networks associated with primary producers sedimentation from oxic to anoxic conditions in an hypersaline lake

Understanding the role of microbial interactions in the functioning of natural systems is often impaired by the levels of complexity they encompass. In this study, we used the relative simplicity of an hypersaline crater lake hosting only microbial organisms (Dziani Dzaha) to provide a detailed analysis of the microbial networks including the three domains of life. We identified two main ecological zones, one euphotic and oxic zone in surface, where two phytoplanktonic organisms produce a very high biomass, and one aphotic and anoxic deeper zone, where this biomass slowly sinks and undergoes anaerobic degradation. We highlighted strong differences in the structure of microbial communities from the two zones and between the microbial consortia associated with the two primary producers. Primary producers sedimentation was associated with a major reorganization of the microbial network at several levels: global properties, modules composition, nodes and links characteristics. We evidenced the potential dependency of Woesearchaeota to the primary producers' exudates in the surface zone, and their disappearance in the deeper anoxic zone, along with the restructuration of the networks in the anoxic zone toward the decomposition of the organic matter. Altogether, we provided an in-depth analysis of microbial association network and highlighted putative changes in microbial interactions supporting the functioning of the two ecological zones in this unique ecosystem.

Chemical contamination alters the interactions between bacteria and phytoplankton

Bacteria and phytoplankton are key players in aquatic ecosystem functioning. Their interactions mediate carbon transfer through the trophic web. Chemical contamination can alter the function and diversity of phytoplankton and bacterioplankton, with important consequences for ecosystem functioning. The aim of the present study was to assess the impact of chemical contamination on the interactions between both biological compartments. Two contrasting marine coastal ecosystems, offshore waters and lagoon waters, were exposed to chemical contamination (artificial or produced from resuspension of contaminated sediment) in microcosms in four seasons characterized by distinct phytoplankton communities. Offshore waters were characterized by a complex phytoplankton-bacterioplankton network with a predominance of positive interactions between both compartments, especially with Haptophyta, Cryptophyta, and dinoflagellates. In contrast, for lagoon waters, the phytoplankton-bacterioplankton network was simpler with a prevalence of negative interactions with Ochrophyta, Cryptophyta, and flagellates. Contamination with an artificial mix of pesticides and trace metal elements resulted in a decrease in the number of interactions between phytoplankton and bacterioplankton, especially for offshore waters. Resuspension of contaminated sediment also altered the interactions between both compartments. The release of nutrients stored in the sediment allowed the growth of nutrient limited phytoplankton species with marked consequences for the interactions with bacterioplankton, with a predominance of positive interactions, whereas in lagoon waters, negative interactions were mostly observed. Overall, this study showed that chemical contamination and sediment resuspension resulted in significant effects on phytoplankton-bacterioplankton interactions that can alter the functioning of anthropogenic coastal ecosystems.

Response of planktonic communities to environmental stress in the eutrophic waters of Xiaoping Island in China

Phytoplankton blooms were affected by external environmental nutrient input, while the interspecific interactions in plankton (phytoplankton and mesozooplankton) under the nutrient pollution gradient remain largely unknown. Here, we systematically collected samples for 9 months (from April to December 2018) in the coastal waters of Xiaoping Island in China to analyze the planktonic community structure and identify the main driving environmental factors along the nutrient gradient from the sewage outlet to the open sea. The results indicated that there existed obvious seasonal and spatial variations in the planktonic community. Procrustes test analysis showed that temperature, transparency, dissolved oxygen, nitrate (NO₃-N), phosphate (PO₄-P), and silicate (SiO₃-Si) significantly affected the community compositions and diversity of plankton (p < 0.05). Co-occurrence network showed that seasons and nutrients pollution had an important influence on the inter-specific interactions between phytoplankton and mesozooplankton. In different nutrient pollution gradients, diatom was the most associated with Copepods in Section 1 (9.38%), Section 2 (9.84%), and Section 3 (5.38%), respectively, and it was also associated with Planktonic larva in Section 1 (7.81%), followed by in Section 3 (4.30%) and 2 (1.64%). Dinoflagellates were associated with Chaetognatha only in Section 1 (4.69%). This study may provide new insights into the plankton dynamics and facilitate nearshore environmental management.

Influence of cyanobacterial blooms and environmental variation on zooplankton and eukaryotic phytoplankton in a large, shallow, eutrophic lake in China

Harmful cyanobacterial blooms are a widespread destruction to the processes and function of aquatic ecosystems. To study effects of cyanobacterial blooms on plankton diversity and composition, we analyzed data of cyanobacterial, eukaryotic phytoplankton, metazoan zooplankton, and physicochemical samples collected from 24 sites for four seasons in 2017 and 2018 from the large, shallow Lake Taihu. We found that cyanobacterial abundance significantly correlated with phytoplankton biomass, species richness, functional richness and evenness, and zooplankton biomass, Shannon's diversity, Simpson's evenness, and functional evenness and richness. High cyanobacterial abundance during summer did not result in low species and functional diversities for both phytoplankton and zooplankton compared with other seasons. Species and functional diversities of sites with high cyanobacteria abundance were not significantly lower than other sites with relatively low cyanobacteria abundance. Structure equation modeling indicated that cyanobacteria had direct influence on phytoplankton and zooplankton compositions. Physicochemical and temporal-spatial factors had direct influence on phytoplankton and zooplankton, and had indirect influence on phytoplankton and zooplankton through direct influence on cyanobacteria. Variance partitioning analysis quantified that cyanobacteria alone and interactions with physicochemical and spatial-temporal factors explained about 10% of phytoplankton variation and 26% of zooplankton variation. Our results indicate that cyanobacteria have substantial effects on phytoplankton and zooplankton biodiversity and community composition. Physicochemical and spatial-temporal factors could potentially obscure the detection of cyanobacterial effects on plankton in Lake Taihu that has cyanobacterial blooms in all seasons. Our findings may improve the understanding of dynamics and responses of plankton communities to environmental changes and cyanobacterial bloom disturbance and enhance the capability of assessing the effectiveness of eutrophication management and restoration of aquatic ecosystems.

Ecological impacts of freshwater algal blooms on water quality, plankton biodiversity, structure, and ecosystem functioning

Harmful algal blooms are among the emerging threats to freshwater biodiversity that need to be studied further in the Anthropocene. Here, we studied freshwater plankton communities in ten tropical reservoirs to record the impact of algal blooms, comprising different phytoplankton taxa, on water quality, plankton biodiversity, and ecosystem functioning. We compared water quality parameters (water transparency, mixing depth, pH, electrical conductivity, dissolved inorganic nitrogen, total dissolved phosphorus, total phosphorus, chlorophyll-a, and trophic state), plankton structure (composition and biomass), biodiversity (species richness, diversity, and evenness), and ecosystem functioning (phytoplankton:phosphorus and zooplankton:phytoplankton ratios as a metric of resource use efficiency) through univariate and multivariate analysis of variance, and generalized additive mixed models in five different bloom categories. Most of the bloom events were composed of Cyanobacteria, followed by Dinophyta and Chlorophyta. Mixed blooms were composed of Cyanobacteria plus Bacillariophyta, Chlorophyta, and/or Dinophyta, while non-bloom communities presented phytoplankton biomass below the threshold for bloom development (10 mg L^-1, WHO alert level 2). Higher phytoplankton biomasses were recorded during Cyanobacteria blooms (15.87-273.82 mg L^-1) followed by Dinophyta blooms (18.86-196.41 mg L^-1). An intense deterioration of water quality, including higher pH, eutrophication, stratification, and lower water transparency, was verified during Cyanobacteria and mixed blooms, while Chlorophyta and Dinophyta blooms presented lower pH, eutrophication, stratification, and higher water transparency. All bloom categories significantly impacted phytoplankton and zooplankton structure, changing the composition and dominance patterns. Bloom intensity positively influenced phytoplankton resource use efficiency (R² = 0.25; p < 0.001), while decreased zooplankton resource acquisition (R² = 0.51; p < 0.001). Moreover, Cyanobacteria and Chlorophyta blooms negatively impacted zooplankton species richness, while Dinophyta blooms decreased phytoplankton richness. In general, Cyanobacteria blooms presented low water quality and major threats to plankton biodiversity, and ecosystem functioning. Moreover, we demonstrated that biodiversity losses decrease ecosystem functioning, with cascading effects on plankton dynamics.

Biogeographic distribution patterns of algal community in different urban lakes in China: Insights into the dynamics and co-existence

Urban lake ecosystems are significant for social development, but currently we know little about the geographical distribution of algal community in urban lakes at a large-scale. In this study, we investigated the algal community structure in different areas of urban lakes in China and evaluated the influence of water quality parameters and geographical location on the algal community. The results showed that obvious differences in water quality and algal communities were observed among urban lakes in different geographical areas. Chlorophyta was the dominant phylum, followed by cyanobacteria in all areas. The network analysis indicated that algal community composition in urban lakes of the western and southern area showed more variations than the eastern and northern areas, respectively. Redundancy analysis and structural equation model revealed that nutrients and pH were dominant environmental factors that affected the algal community, and they showed higher influence than that of iron, manganese and COD _Mn concentration. Importantly, algal community and density exhibited longitude and latitude relationship. In general, these results provided an ecological insight into large-scale geographical distributions of algal community in urban lakes, thereby having potential applications for management of the lakes.

Microbial community shift via black carbon: Insight into biological nitrogen removal from microbial assemblage and functional patterns

Understanding the ecological relationship of microbial community under external stimulation is crucial for environmental restoration. Black carbon (e.g., biochar) have been widely deemed as a strategy to enhance pollutants removal because of its structure and redox-active property. However, the underlying ecological mechanism of microbial community under black carbon addition is poorly understood. The major purposes of this study were to determine the microbial assemblage and functional patterns via null model test, network analysis, and function prediction. The results showed that the nitrate removal efficiency of modified black carbon system achieved 46.44%. Both deterministic and stochastic processes were significant for mediating the microbial assemblage and the deterministic process dominated (>95%) the assemblage of community. Keystone taxa in the black carbon systems, involving Sulfuricella, Allorhizobium, and Nitrospira, stimulated the shift of community composition regarding the nitrogen removal. The existence of black carbon and the biotic interactions increased biological nitrate utilization and promoted nitrogen removal. Overall, this study presents the mechanism of bacterial community assembly and provides insight into biological nitrogen removal from microbial ecological perspective.

Water-lifting aerator reduces algal growth in stratified drinking water reservoir: Novel insights into algal metabolic profiling and engineering applications

Water-lifting aerator (WLA) which was developed by Professor Tinglin Huang at Xi'an University of Architecture and Technology, China has multi-functional water quality improvement that significantly inhibits the occurrence of harmful algal blooms (HABs) in deep drinking water reservoirs. However, the biological mechanism of WLA to the suppress algal growth has not been comprehensively understood. Here, the cellular mechanism that allows WLA to control HABs was explored based on the combination of both laboratory simulation and field investigation. Under simulated hydrodynamic conditions, the results showed that the cell density, chlorophyll a content, chlorophyll fluorescence parameters, and dehydrogenase activity in Microcystis aeruginosa all peaked under light conditions at 25 °C. The metabolic activity of M. aeruginosa varied significantly under low temperature at 6 °C and light conditions when cultured for 48 h. The extracellular organic matter (EOM) and intracellular organic matter (IOM) contents of M. aeruginosa were both resolved into three components. Moreover, the total fluorescence intensities from EOM and IOM both peaked under light conditions at 25 °C. The field investigation showed that the growth of algae was decreased significantly in Lijiahe drinking water reservoir with WLA application. The chlorophyll fluorescence parameters decreased significantly after vertical mixing, thereby indicating that the WLA weakened the photosynthetic ability and reduced the biological activity of algae in situ. In addition, the WLA significantly affected the vertical distribution of the phytoplankton community composition. Altogether, these results shed new lights on understanding the control of algal blooms by WLA in stratified drinking water reservoirs. WLA has broad prospect of engineering applications, which can control algal blooms of water supply resources in situ, therefore, reduce the content of disinfection by-products in drinking water treatment plants.

Disentangling the drivers of Microcystis decomposition: Metabolic profile and co-occurrence of bacterial community

In aquatic ecosystems, water microbial communities can trigger the outbreak or decline of cyanobacterial blooms. However, the microbiological drivers of Microcystis decomposition in reservoirs remain unclear. Here, we explored the bacterial community metabolic profile and co-occurrence dynamics during Microcystis decomposition. The results showed that the decomposition of Microcystis greatly altered the metabolic characteristics and composition of the water bacterial community. Significant variations in bacterial community composition were observed: the bacterial community was mainly dominated by Proteobacteria, Actinobacteria, Planctomycetes, and Bacteroidetes during Microcystis decomposition. Additionally, members of Exiguobacterium, Rhodobacter, and Stenotrophomonas significantly increased during the terminal stages. Dissolved organic matters (DOM) primarily composed of fulvic-like, humic acid-like, and tryptophan-like components, which varied distinctly during Microcystis decomposition. Additionally, the metabolic activity of the bacterial community showed a continuous decrease during Microcystis decomposition. Functional prediction showed a sharp increase in the cell communication and sensory systems of the bacterial communities from day 12 to day 22. Co-occurrence networks showed that bacteria responded significantly to variations in the dynamics of Microcystis decomposition through close interactions between each other. Redundancy analysis (RDA) indicated that Chlorophyll a, nitrate nitrogen (NO₃^--N), dissolved oxygen (DO), and dissolved organic carbon (DOC) were crucial drivers for shaping the bacterial community structure. Taken together, these findings highlight the dynamics of the water bacterial community during Microcystis decomposition from the perspective of metabolism and community composition, however, further studies are needed to understand the algal degradation process associated with bacteria.

Sedimentary ancient DNA metabarcoding delineates the contrastingly temporal change of lake cyanobacterial communities

Harmful cyanobacterial blooms consisting of toxic taxa can produce a wide variety of toxins to threaten water quality, ecosystem functions and services. Of greater concern was the changing patterns of cyanobacterial assemblage were not well understood due to the lack of long-term monitoring data over the temporal scale. Biodiversity change in cyanobacterial community and paleoenvironmental variables over the past 170 years in Lake Chenghai were investigated based on sedimentary ancient DNA metabarcoding and traditional paleolimnological analysis. The results showed species richness and homogenization of cyanobacterial assemblage increased in the most recent decades, which were synchronized with the growth of artificial fertilization and decline in precipitation. Cyanobacterial co-occurrence network analysis revealed more complex interactions and weak community stability after the change point of ∼1987, while the rare cyanobacterial genera such as Anabaena, Planktothrix, Oscillatoria and Microcystis were identified to be keystone taxa affecting cyanobacterial assemblage. Furthermore, an increase of toxin-producing cyanobacterial taxa was significantly and positively associated with TN and TP, as well as TN/IP and TN/TP, which was verified by quantitative real-time PCR of mcyA and rpoC1 genes. Threshold in total nitrogen (TN) concentration should be targeted no more than 0.60 mg/L to alleviate nuisance cyanobacterial blooms in Lake Chenghai. These findings reinforce the comprehensive understanding for the long-term dynamics of cyanobacterial assemblage responding to environmental change, which could contribute to proactively regulate environmental conditions for avoiding undesirable ecological consequences.

Temporal patterns in the interaction between photosynthetic picoeukaryotes and their attached fungi in Lake Chaohu

The combination of flow cytometric sorting and high-throughput sequencing revealed the broad existence of photosynthetic picoeukaryote attached fungi (PPE-attached fungi) in Lake Chaohu. The relative sequence abundance of attached fungi was negatively correlated with that of the photosynthetic picoeukaryotes (PPEs). PPE-attached fungal communities were mainly composed of Basidiomycota, Chytridiomycota and Ascomycota. Temperature, Si and PPE community structure are the most important driving factors for the temporal succession of PPE-attached fungal communities. In particular, PPE-attached fungi can be divided into three groups from high to low temperatures. Phylogenetic molecular ecological network results indicated that the connectivity and the total number of links in the network of the high-temperature group (&gt; 21.82°C) are higher than those in the other two temperature groups (between  9.67 and  21.82°C, and &lt; 9.67°C, respectively). Moreover, the interaction between PPE-attached fungi and the PPEs changed from antagonistic to cooperative, with the decline in temperature. The most abundant operational taxonomic units of PPE-attached fungi were affiliated with the Cladosporium, the most common saprophytic fungus, whereas most fungal hub taxa were Chytridiomycota, the main parasite fungi of phytoplankton.

A review of the socioecological causes and consequences of cyanobacterial blooms in Lake Victoria

Africa is experiencing high annual population growth in its major river basins. This growth has resulted in significant land use change and pollution pressures on the freshwater ecosystems. Among them, the Lake Victoria basin, with more than 42 million people, is a unique and vital resource that provides food and drinking water in East Africa. However, Lake Victoria (LV) has experienced a progressive eutrophication and substantial changes in the fish community leading to recurrent proliferation of water hyacinth and cyanobacteria. Based on an extensive literature review, we show that cyanobacterial biomasses and microcystin concentrations are higher in the bays and gulfs (B&Gs) than in the open lake (OL), with Microcystis and Dolichospermum as the dominant genera. These differences between the B&Gs and the OL are due to differences in their hydrological conditions and in the origins, type and quantities of nutrients. Using data from the literature, we describe the multiple ways in which the human population growth in the LV watershed is connected to the increasing occurrence of cyanobacterial blooms in the OL and B&Gs. We also described the consequences of cyanobacterial blooms on food resources and fishing and on direct water use and water supply of local populations, with their potential consequences on the human health. Finally, we discuss the actions that have been taken for the protection of LV. Although many projects have been implemented in the past years in order to improve the management of waste waters or to reduce deforestation and erosion, the huge challenge of the reduction of cyanobacterial blooms in LV by the control of eutrophication seems far from being achieved.

Alterations in viability and CYP1A1 expression in SH SY5Y cell line by pollutants present in Madín Dam, Mexico

Currently one of the problems facing global development is the availability of water. Although water is abundant the planet only a small portion is for human use and consumption. The problem is exacerbated due to different factors, mainly: meteorological phenomena, the presence of contaminants in the water and the increase in the number of inhabitants. Potential effects of pollutants not only can affect freshwater biota but also can be implicated in cancer development and neurodegenerative diseases in humans. The study was conducted in the Madín Dam, a reservoir of economic importance for the geographical area in which it is located, as well as catering to the population of nearby areas, and is a place where recreational activities such as fishing and kayaking are carried out. The aim of this study was to identify the toxic effects that the pollutants present in the water of the Madín Dam can generate on a human cell line (SH SY5Y) evaluating the cell viability and the participation of the Aril Hydrocarbon Receptor (AhR) and Pregnane X receptor (PXR) through of the expression of the CYP1A1 and CYP3A4 (canonical genes). In one of the five sites analyzed, cell viability was up to 50%, in this site a decrease in the normal expression of CYP1A1 was observed (p < 0.05) and the CYP3A4 gene was not expressed in the cells SH SY5Y. These results show that the SH SY5Y cell line is a good biomarker for assessing the human toxicity of environmental pollutants and relating it to neurodegenerative diseases.

Warming and CO2 effects under oligotrophication on temperate phytoplankton communities

Eutrophication, global warming, and rising carbon dioxide (CO₂) levels are the three most prevalent pressures impacting the biosphere. Despite their individual effects are well-known, it remains untested how oligotrophication (i.e. nutrients reduction) can alter the planktonic community responses to warming and elevated CO₂ levels. Here, we performed an indoor mesocosm experiment to investigate the warming × CO₂ interaction under a nutrient reduction scenario (40%) mediated by an in-lake management strategy (i.e. addition of a commercial solid-phase phosphorus sorbent -Phoslock®) on a natural freshwater plankton community. Biomass production increased under warming × CO₂ relative to present-day conditions; however, a Phoslock®-mediated oligotrophication reduced such values by 30-70%. Conversely, the warming × CO₂ × oligotrophication interaction stimulated the photosynthesis by 20% compared to ambient nutrient conditions, and matched with higher resource use efficiency (RUE) and nutrient demand. Surprisingly, at a group level, we found that the multi-stressors scenario increased the photosynthesis in eukaryotes by 25%, but greatly impaired in cyanobacteria (ca. -25%). This higher cyanobacterial sensitivity was coupled with a reduced light harvesting efficiency and compensation point. Since Phoslock®-induced oligotrophication unmasked a strong negative warming × CO₂ effect on cyanobacteria, it becomes crucial to understand how the interplay between climate change and nutrient abatement actions may alter the, ecosystems functioning. With an integrative understanding of these processes, policy makers will design more appropriate management strategies to improve the ecological status of aquatic ecosystems without compromising their ecological attributes and functioning.

Community Compositions of Phytoplankton and Eukaryotes during the Mixing Periods of a Drinking Water Reservoir: Dynamics and Interactions

In deep drinking water reservoir ecosystems, the dynamics and interactions of community compositions of phytoplankton and eukaryotes during the mixing periods are still unclear. Here, morphological characteristics combined with high-throughput DNA sequencing (HTS) were used to investigate the variations of phytoplankton and the eukaryotic community in a large canyon-shaped, stratified reservoir located at the Heihe River in Shaanxi Province for three months. The results showed that Bacillariophyta and Chlorophyta were the dominant taxa of the phytoplankton community, accounting for more than 97% of total phytoplankton abundance, which mainly consisted of Melosira sp., Cyclotella sp., and Chlorella sp., respectively. Illumina Miseq sequencing suggested that the biodiversity of eukaryotes increased over time and thatspecies distribution was more even. Arthropoda (6.63% to 79.19%), Ochrophyta (5.60% to 35.16%), Ciliophora (1.81% to 10.93%) and Cryptomonadales (0.25% to 11.48%) were the keystone taxa in common, contributing over 50% of the total eukaryotic community. Cryptomycota as a unique fungus was observed to possess significant synchronization with algal density, reaching a maximum of 10.70% in December (when the algal density distinctly decreased) and suggesting that it might affect the growth of algae through parasitism. Co-occurrence network patterns revealed the complicated and diverse interactions between eukaryotes and phytoplankton, suggesting that eukaryotes respond to variations in dynamic structure of the phytoplankton community, although there might be antagonistic or mutualistic interactions between them. Redundancy analysis (RDA) results showed that environmental variables collectively explained a 96.7% variance of phytoplankton and 96.3% variance of eukaryotic microorganisms, indicating that the temporal variations of phytoplankton and eukaryotic microorganisms were significantly affected by environmental conditions. This study shows that potential interactions exist between phytoplankton and eukaryotic microorganism communities, andcould improve our understanding of the ecological roles of phytoplankton and eukaryotic microorganisms in changing aquatic ecosystems. However, long-term investigations are necessary in order to obtain comprehensive understandings of their complicated associations.