Algal Density Research Articles

Zirconium-Modified Attapulgite Composite for Phosphorus Removal and Algae Control in Lake Water

Phosphorus removal is critical for effective water treatment and the prevention of eutrophication. This study focuses on the modification of attapulgite, an economical clay material, with zirconium (Zr@ATP) to enhance its phosphorus adsorption capacity. Zr@ATP was comprehensively characterized, and its phosphorus-removal mechanisms were investigated. Additionally, its performance in water treatment was evaluated using a lake water-sediment system. Zr@ATP exhibited a high surface area of 329.29 m2/g. The static adsorption experiments revealed that Zr@ATP achieved a phosphorus-removal efficiency of 95.8% at an adsorbent dosage of 5 g/L. Kinetic studies indicated that the adsorption followed a pseudo-second-order model, with the primary mechanism being chemisorption via ion exchange. Application of Zr@ATP in a lake water-sediment system resulted in an 83.6% reduction in total phosphorus. The chlorophyll concentration significantly decreased from 32.33 μg/L to 8.56 μg/L, and the algal density decreased by 84.6%, effectively inhibiting algal growth. These results suggest that Zr@ATP is a promising adsorbent for sustainable phosphorus removal and eutrophication control in aquatic environments.

Spatial patterns of hydroecological health in the semi-arid yellow river basin: Revelations from machine learning models

The ecosystem of semi-arid watersheds is influenced by a combination of natural climate factors, rainfall, and habitat destruction, resulting in complex mechanisms of spatial differentiation and evolution of water ecological health. Indicator selection in mainstream water ecological health assessment methods, such as the Index of Biotic Integrity (IBI), often relies on subjective reference point choices. This approach tends to overlook the comprehensive impacts and interactions among various environmental stressors. For watersheds significantly influenced by natural climatic factors, considerable uncertainties arise, leading to a lack of scientific justification for establishing water ecological health protection goals. In this study, the nonlinear capabilities of the random forest (RF) model were applied to reduce subjectivity in traditional water ecological health assessments and to more accurately reveal the emerging spatial differentiation patterns and underlying causes of water ecological health in the Wei River Basin (WRB), the largest typical semi-arid watershed of the Yellow River in China. Our findings indicate: (1) Traditional evaluation indices indicate that the overall water ecological health of the WRB is classified as sub-healthy (60 %). The core indicators include dominant species, total algal density, and the percentage of diatom density, with no significant spatial differentiation observed. (2) An improved water ecological health assessment method for semi-arid watersheds, based on the RF model, has been developed to replace traditional subjective judgment steps. This method establishes a complex multi-input–output response relationship (R2 > 0.85) between environmental stress indicators and the biological integrity index for the WRB. (3) The model results identify key driving factors affecting changes in water ecological health in semi-arid watersheds, with the sensitivity of the new model increasing nearly 11-fold compared to traditional IBI methods. (4) Following improvements, the water ecological health characteristics of the WRB exhibit significant spatial heterogeneity, with a higher dispersion coefficient (1.21), and demonstrate enhanced nonlinear response trends to climatic factors. The application of machine learning models indicates that traditional methods may underestimate the extent of ecological health degradation in watersheds and tend to oversimplify spatial heterogeneity characteristics.

Biomass Productivity and Photosynthetic Activity in Ulva compressa (Chlorophyta) in Raceway Photobioreactors Under Stress Conditions.

Research in seaweed cultivation technologies aims to increase production and reduce costs, leading to more efficient and sustainable processes. In this study, we analyzed the outdoor production of Ulva compressa cultured in summertime at different stocking densities of 0.6, 0.8 and 1.0 kg Fresh weight (FW) m-2 in a raceway photobioreactor with 30 m2 surface (3000 L), and its relation to photosynthetic activity. Under the experimental conditions of high temperature (>28-30 °C) and pH > 9 in culture water, higher seaweed density resulted in lower specific growth rate. The biomass production has been related to photosynthetic activity by using in vivo chlorophyll a fluorescence. Dynamic photoinhibition was observed at noon, which was less severe in cultures with higher algal densities. However, photosynthesis recovered in the afternoon. Seaweeds that were acclimatized for a week to the conditions of 1.0 kg FW m-2 stocking density showed an increase in biomass growth and absence of photoinhibition compared to non-acclimatized thalli. In conclusion, the cultivation of U. compressa in a mid-scale raceway photobiorreactor under conditions of high irradiance and temperature and low nutrient input, exhibited the best photosynthetic performance and hence the highest growth rates for the highest culture density assayed (1.0 kg FW m-2).

Impacts of counting protocols for light microscopy on estimates of biodiversity and algal density of phytoplankton

AbstractKnowledge on the biodiversity and abundance of phytoplankton is key for many ecological and societal (e.g., blue growth) questions. Gathering temporal variation and spatial patterns on key indicators requires reliable and standardized protocols on sampling, species identification and counting. Numerous methods are used but consequences for comparing the biodiversity and abundance of phytoplankton of these different techniques are not well known. We evaluated the consequences of different counting protocols using light microscopy (i.e., subsampling transects or wedges within counting chambers) for these indices using samples collected weekly to bi‐weekly (n = 398, 2009–2018) from the Wadden Sea (southern North Sea). Phytoplankton cells were counted (by one person under similar conditions) in a fixed number of viewing fields (58, 70, and 29) at three respective magnifications (10 × 100, 10 × 40, and 10 × 10). Patterns in the spatial distribution of phytoplankton cells varied among species and clustering of cells occurred in more than one‐fifth of the samples. This will induce error in the conversion from counts (per viewing field) to abundance (cells mL−1). Our present effort resulted in a high accuracy (95%) in overall cell abundances. This was not the case for species richness, for example, capturing 90% of all species present in the sample would require an almost threefold increase in effort for the 10 × 40 and 10 × 10 magnifications. We recommend that counting methods be tailored to the main research objectives and that counting protocols should quantify uncertainty as well as potential bias to provide an estimation of the error in phytoplankton abundance and species composition.

Eutrophication promotes resource use efficiency and toxin production of Microcystis in a future climate warming scenario

Addressing the risks of cyanobacterial blooms and toxin production under ongoing and accelerating eutrophication and climate warming is crucial for both water ecosystem services and human health. Therefore, we here explored the interactive effects of eutrophication and warming on freshwater ecosystems, focusing on Microcystis and its cyanotoxin production. We employed a large-scale mesocosm system simulating future climate warming scenarios in concert with varying degrees of nutrient enrichment. We explored the full range of identified cyanobacterial toxins and cyanotoxin-producing genes under different experimental conditions and assessed the effects of both eutrophication and warming on both phytoplankton community structure (algal densities, community stability) and function (resource use efficiency, RUE). We show here that eutrophication increases the RUE of Microcystis and promotes an increase in toxin-producing genes, leading to a substantial increase in the dominance of Microcystis. This increase correlates with enhanced cyanotoxin production, a trend exacerbated under the influence of future climate warming, suggesting interactions between eutrophication and climate warming on Microcystis ecology and cyanotoxin dynamics. Hence, heatwaves and eutrophication lead the phytoplankton community to be dominated by a minority of algal species with higher toxic capacity. In a broader context, our study underscores the urgent need for holistic management strategies, addressing both nutrient control and climate mitigation, to effectively manage the escalating ecological risks associated with cyanobacterial dominance and toxin production.

Effect of abrupt post‐fire ash inputs on water quality and the phytoplankton community in lentic freshwaters

Abstract One of the major threats to biodiversity is changing fire regimes, particularly increasingly frequent fires, especially during the dry season. However, studies on the direct and indirect effects of fire on biotic responses in aquatic ecosystems are still scarce. In this study, we investigated how water quality and phytoplankton community structure were affected by different ash concentrations from burning vegetation of a tropical savanna. We used a microcosm experiment to simulate the aquatic ecosystem with different ash concentration scenarios and evaluated the water quality and the composition, richness and density of phytoplankton over time. We found increased total phosphorus and ammoniacal nitrogen concentrations after ash addition, in addition to changes in electrical conductivity. We identified 242 phytoplankton taxa throughout the experiment and identified changes in species composition among treatments. We identified changes in the taxonomic richness of total phytoplankton, green algae and desmids over time. The density of total phytoplankton, diatoms, green algae, desmids and cyanobacteria also changed over time. Our results suggest that ash from terrestrial fires affects water quality and phytoplankton communities depending on the proportion of ash input. Our results serve as a basis for further investigations of the effects of fire on abiotic conditions in aquatic ecosystems and their communities over long periods of time. Finally, longer‐term experiments are needed to evaluate delayed responses by the phytoplankton community.

Winter Season Outdoor Cultivation of an Autochthonous Chlorella-Strain in a Pilot-Scale Prototype for Urban Wastewater Treatment

The global population increase during the last century has significantly amplified freshwater demand, leading to higher wastewater (WW) production. European regulations necessitate treating WW before environmental. Microalgae have gained attention for wastewater treatment (WWT) due to their efficiency in remediating nutrients and pollutants, alongside producing valuable biomass. This study investigates the phycoremediation potential of a Chlorella-like strain isolated from urban WW in a 600L-scale system under winter conditions. Experiments in December 2021 and February 2022 tested the strain’s adaptability to varying environmental conditions, particularly temperatures (min-max temperature range: from −3.69 to 10.61 °C in December and −3.96 to 17.61 °C in February), and its ability to meet legal discharge limits. In December, low temperatures algal growth. Nitrates showed an RE of about 92%, while ammonia slightly decreased (RE, about 32%), and phosphorous remained unchanged. In February, mild temperatures increased algal density (33.3 × 106 cell mL−1) and, at the end of experiment, all nutrients were below legal limits with very high RE % (NH4+, 91.43; PO43− 97.32). Both trials showed an E. coli RE, % = 99%. The study highlights the potential of microalgae for WWT and the importance of considering seasonal variations when implementing these systems.

River algal blooms can be estimated by remote sensing reflectance

Abstract River eutrophication is difficult to diagnose and estimate quantitatively because of its complex degradation mechanism in large river systems. Conventional monitoring and modeling methods are limited to accurately revealing the evolution process and trends of river aquatic organisms. In the present study, based on HJ-1A/1B CCD sensor, combined with genetic algorithm (GA) and regression tree (GART), a remote sensing inversion prediction model was established; the model can estimate algal blooms in the Han River affected by China’s Middle Route of the South-to-North Water Diversion Project (SNWTP). During the outbreak of algal blooms, the near-infrared band reflectance evidently increased between 2009 and 2015, with increasing algal density. The algal density in the downstream of the Han River has a nearly synchronous positive change with the reflectance in the B4 (near-infrared) band and a nearly synchronous reverse change with the B1 (blue) band. B1 and B4 screened by GA reduced redundancy by 14%, leading to a good prediction performance (R 2 = 0.88). According to GART and partial dependence analysis, the B4 band is a crucial characterization factor of algal blooms in the Han River. When the remote sensing band was in the range of B1 ⩾ 0.085 and B4 ⩽ 0.101, the algal density was lower than 0.15 × 107 cells l−1, indicating no algal bloom in the downstream of the Han River. When B4 was >0.103 and B1 ⩽ 0.076, algal density was higher than 1 × 107 cells l−1 and algal blooms were very likely to occur. These findings could provide a scientific reference for diagnosing and predicting large-scale water ecological degradation in similar watersheds.

Impact of weathered and virgin polyethylene terephthalate (PET) micro- and nanoplastics on growth dynamics and the production of extracellular polymeric substances (EPS) of microalgae

The ever-increasing plastic waste accumulation in the marine environment necessitates a deeper understanding of microalgae interactions with micro- and nanoplastics (MNP), and the role of extracellular polymeric substances (EPS). EPS, known for its adhesive properties and produced as an algal stress response, may facilitate aggregation of both algae and MNPs, thereby impacting ecological and hydrodynamic processes such as the trophic transfer or vertical transport of MNPs. Moreover, gaining a deeper understanding of the impact of weathering processes on the potential toxicological effects of plastic particles, and the comparative significance of plastic-specific effects relative to those of naturally occurring particles such as kaolin clay, is imperative. Therefore, this study investigated the impact of fragmented, polydisperse virgin polyethylene terephthalate (PET, Daverage = 910 nm) and weathered PET (Daverage = 1700 nm) on the growth and the production of EPS of Rhodomonas salina. Algae were exposed to a range of low MNP concentrations (10, 100 and 1000 and 10,000 MNPs ml-1) for 11 days. A natural particle control (kaolin, Daverage = 1600 nm) was deployed to differentiate particle effects from plastic effects. It was observed that exposure to both weathered PET and virgin PET resulted in initially increased growth rates (7.80 % and 7.28 % respectively), followed by significant decreases in algae cell density (−30.1 % and −11.2 % respectively). Furthermore, exposure to weathered PET caused a simultaneous elevation in cellular EPS production (76.51 %). The effects of plastics were significantly larger than the effect of kaolin. Also, the observed effects were amplified by the weathering of the plastics. These observations underscore the interactions between particle type, age and concentration, and their distinct impacts on algae density and growth inhibition. The observations indicate a role for EPS as an algal protection mechanism, potentially affecting the environmental fate of MNP – microalgae aggregates.

Dynamics of the risk of algal blooms induced by surface water temperature in an alpine eutrophic lake under climate warming: Insights from Lake Dianchi

Climate change-induced higher water temperature is increasing the risk of algal blooms (ABs) in eutrophic water bodies. However, it is not well known how and to what extent warming affects ABs risk. In this work, with simple data input (satellite product, lake surface observation, and climate) and method structure (ensemble learning, statistical downscaling, and hierarchical clustering), a systematic lake surface water temperature (LSWT) and ABs risk evaluation system are constructed and applied in a typical eutrophic freshwater lake. The main results are as follows: 1. The warming rate of LSWT and air temperature from 2000 to 2023 reached 0.21 °C/10a and 0.30 °C/10a respectively, resulting in an extended ABs risk in the historical period. 2. The Nash–Sutcliffe efficiency between climate and LSWT reached 0.89, and LSWT showed a significant (p < 0.05) positive correlation with algal density. 3. The escalation of ABs risks mainly spread to spring and autumn in the forthcoming future, the adverse effect of high emission scenarios will evidently emerge in the mid-21st century. Policymakers and catchment managers should be cautious of lake warming and develop countermeasures in advance.

Metal Mixture Effects of Ni, Cu, and Zn in a Multispecies, Two-Trophic-Level Algal-Daphnid Microcosm Can Be Predicted From Single-Trophic-Level Effects: The Role of Indirect Toxicity.

Effect assessments of metals are mostly based on single-metal, single-species tests, thereby ignoring metal-mixture effects and indirect effects through species interactions. We tested the combined effects of metal and species interactions in two-trophic algal-daphnid microcosms. Metal-mixture effects on daphnid communities may propagate from effects on the generally more sensitive algal communities. Four different algal communities (three species each), with and without addition of the same daphnid community (three species) were exposed to single metals and one metal mixture (17:17:51 µg/L Ni:Cu:Zn). Daphnid densities were negatively affected by metals in the two-trophic test, the magnitude of which depended on the algal community composition. Algal densities were overall positively affected by the metals in the two-trophic test but negatively in the single-trophic test, illustrating an indirect positive effect in the two-trophic system due to a reduced grazing pressure. Metal effects on daphnid communities in the two-trophic test (day 21) were correlated with metal effects on the single-trophic-level algal communities during exponential growth (R2 = 0.55, p = 0.0011). This finding suggests that metal effects propagate across trophic levels due to a reduced food quantity. However, the indirect positive effects on algal densities, resulting in abundant food quantity, suggests that metal effects can also propagate to daphnids due to a reduced food quality (not measured directly). Metal-mixture interactions on daphnid densities varied during exposure, but were additive or antagonistic relative to independent action when final daphnid densities were considered (day 56). This suggests stronger indirect effects of the mixture compared with the single metals. Overall, our study highlights the dynamic aspect of community-level effects, which empirical reference models such as independent action or concentration addition cannot predict. Environ Toxicol Chem 2024;43:2350-2364. © 2024 SETAC.

Effects of the Water Diversion Project from the Three Gorges Reservoir to the Hanjiang River on diatom blooms in Middle and Lower reaches of the Hanjiang River

ABSTRACT The algal blooms in the Middle and Lower reaches of the Hanjiang River (MLHR) have become a great aquatic eco-environmental problem over recent years. The planned implementation of the Water Diversion Project from the Three Gorges Reservoir to the Hanjiang River (WDP-TH) would influence the growth and propagation of diatoms and the development of algal blooms. In this paper, a dynamic model of diatom growth is developed that considers factors such as light exposure, water temperature, total phosphorus, and flow velocity. The effects of the WDP-TH on algal density and blooms in the MLHR were predicted for a typical median year, a typical dry year, and an extremely dry year. The results showed that following the water recharge in a typical median year, the propagation of diatoms in the MLHR was significantly promoted because of an increase in total phosphorus concentration. However, following the water recharge in typical dry and extremely dry years, increased flow rate and improved hydrodynamic conditions significantly inhibited diatom growth and accelerated the transport process. The results of the hypothetical simulation showed that after the initiation of the WDP-TH, inhibition effects of improved hydrodynamic force on algae were more apparent than promotion effects of increased total phosphorus concentration in the MLHR.

Insights into the response mechanisms of Tetradesmus obliquus to aged polylactic acid and tetracycline exposure via transcriptome analysis and physiological evaluations

Microplastics (MPs) and antibiotics, identified as emerging pollutants, are extensively prevalent in aquatic environments and display prolonged durability. Unlike conventional plastics, biodegradable plastics are more susceptible to decomposition in the environment, resulting in the generation of microplastics and posing potential risks to the aquatic ecosystems. In this study, we assessed growth inhibition, chlorophyll a content, malondialdehyde content (MDA), and antioxidant enzyme activities. These measurements were integrated with transcriptome analysis to explore the response mechanisms of virgin and aged polylactic acid (vPLA and aPLA) and tetracycline (TC) following 14-day exposure to Tetradesmus obliquus, either individually or in combination. The findings indicated that exposure to vPLA did not significantly impact the growth of T. obliquus. Conversely, aPLA demonstrated growth-promoting effects on T. obliquus, particularly in the latter incubation stages. Moreover, a 14-day exposure significantly increased the chlorophyll a content and the activities of superoxide dismutase (SOD), catalase glutathione (CAT) and glutathione S-transferase (GST) within the algal cells. Apart from 1 mg L−1, the TC concentrations of 2.5, 5.0, and 10 mg L−1 exhibited significant toxic effects on T. obliquus, including growth inhibition, decreased chlorophyll a content, elevated activities of SOD, CAT, and GST, and increased MDA levels. Exposure to a combination of 300 mg L−1 aPLA and 5.0 mg L−1 TC, compared to solely 5 mg L−1 TC, demonstrated a notable reduction in TC toxicity to T. obliquus in the presence of aPLA. This was indicated by elevated algal cell density and chlorophyll a content, as well as a decrease in MDA content. Transcriptome analysis indicated an enrichment of differentially expressed genes (DEGs) in pathways linked to porphyrin metabolism, photosynthesis, carbon fixation, and metabolism within the aPLA + TC combined exposure. The study aid in expanding our knowledge of the potential ecological risks posed by biodegradable plastics and accompanying pollutants in aquatic environments.

Damage Inflicted by Extreme Drought on Poyang Lake Delta Wetland and the Establishment of Countermeasures

Due to the joint influence of climate change and human activities, the hydrological rhythm of Poyang Lake has changed in recent years, leading to an increasingly severe drought problem during autumn and winter in this region. Notably, the extreme drought that occurred in 2022 had profound impacts on shipping, water supply and the ecological environment of the wetlands in the Poyang Lake Delta, sparking widespread concern. Based on the historical hydrometeorological data of Poyang Lake, we used statistical models (such as Chow test, correlation analysis, etc.) to analyze the cause of the extreme drought in the Poyang Lake Delta from the perspectives of natural factors and human activity. Through correlation analysis, we found that the water level, discharge, and drought duration of the Poyang Lake Delta were all significantly affected by climate change, particularly rainfall in the Poyang Lake basin. Furthermore, combining the results of Chow test and correlation analysis, we also found that the operation of the Three Gorges Reservoir had a notable impact on the water level of the Poyang Lake Delta. Based on remote sensing images, ecological and environmental sampling monitoring, the damage inflicted by the extreme drought event on the Poyang Lake Delta was analyzed. The results show that the inundated area of the delta wetlands in the extreme-drought year (2022) decreased by 45.75% compared with that in a normal year (2017). In addition, the ecological environment of the wetlands deteriorated significantly. The water quality parameters (TN, TP, NH4+-N) increased by 50.2%, 240% and 64.7%, respectively. The concentrations of TN and TP were 3.8 mg/L and 0.17 mg/L, respectively, while the context values in the delta were 1.2 mg/L and 0.075 mg/L. The density and biomass of algae increased by 87.2% and 557.9%, respectively. In contrast, the density and biomass of benthos decreased by 59.9% and 78.5%, respectively. The control strategy for the Poyang Lake Delta under extreme drought was studied through an experiment on the operation of hydraulic controllers. The results show that under extreme drought conditions, the newly built hydraulic controllers could raise the water level of the delta from 9.1 ± 0.7 m to 14.2 ± 1.8 m, thus effectively solving the water cut-off problem in the four branches of the delta. Furthermore, by adjusting the distributive ratio of the main, north, middle and south branches of the delta to 50%, 4%, 24% and 22% through newly built hydraulic controllers, the water area can be increased by 56%.

Controlling algal growth using ultrasonic technology and conceptual implementation in the real-life system

ABSTRACT The present work reports a study on the interactive response of algae and other microorganisms coexisting in a natural water body to ultrasonic treatment for effective algal growth inhibition using ultrasonic treatments. The cellular damage caused by treatment was also visualised through SEM imaging. For an ultrasonic exposure of 10–30 min at 30 kHz frequency with ultrasonic power dissipated in the range of 4.2–12.5 W, the reduction in the algal cell density was changed from 37.82 to –52.73% after 7 days of observation period. The gradual decrease in the chlorophyll concentration signified the reduced photosynthetic activity after treatment. The damage created on the cell membrane by ultrasound was evaluated through the increased permeability of electrolytes from the cells and the rise in the conductivity of water. Following the lab-scale experimental studies and interpretation of the results obtained, field trials were carried out at a local natural pond (40*35 sq. metre) for 6 months and secondary clarifier in a local industry (20 m diameter) for 2 months, with some system working based on low power ultrasonic transmitters (power ∼ 25 W/h and frequency 20–40 kHz) and promising improvement in water quality could be observed with 85% and more than 95% algae removal efficiency, respectively.

Distribution, relationship, and environmental driving factors of chlorophyll-a and algal cell density: A national view of China

Chlorophyll-a (Chl-a) and algal cell density (ACD) are vital for assessing algal proliferation and eutrophication in aquatic ecosystems. Although Chl-a is often used as a proxy for ACD, its accuracy requires validation, and studies on their linear correlation are scarce. Additionally, Chl-a and ACD are influenced by various factors, including nutritional, economic, biochemical, physicochemical, and meteorological factors. However, the relative importance of these factors on Chl-a and ACD remains insufficiently studied. This study analyzed data from 57 lakes and reservoirs across China from March 2021 to February 2023, investigating the distribution patterns of Chl-a and ACD across different regions and seasons. The study employed a linear regression model to explore the correlation between Chl-a and ACD in various regions and seasons throughout China. Furthermore, Mantel test and generalized linear model were used to evaluated the relative importance of nutritional factors (total nitrogen (TN), total phosphorus (TP), TN/TP ratio (TN/TP), and ammonia nitrogen (NH3-N)), economic factors (gross domestic product), meteorological factors (surface pressure, net solar radiation, air temperature, wind speed (WS), and rainfall (RF)), as well as biochemical and physicochemical factors (turbidity (TUR), pH value, water temperature (WT), permanganate index, and dissolved oxygen) on Chl-a and ACD. Results showed that the average concentrations of Chl-a and ACD in South China were highest, at 12 μg/L and 19.5 × 106 cells/L, respectively. Seasonally, Chl-a peaked in spring and was lowest in winter, while ACD peaked in summer and was lowest in winter. Significant seasonal and regional variations in the Chl-a and ACD correlation were observed, with spring showing the strongest relationship. In Central China, Chl-a and ACD were significantly correlated throughout the four seasons, whereas correlations were less distinct in Eastern and Western regions. Therefore, Chl-a as a proxy for ACD requires caution. Nutrient factors (TN, TP, TN/TP, NH3-N) were identified as the primary drivers of Chl-a and ACD. Meteorological factors (WS, RF), along with biochemical and physicochemical factors (WT, TUR) also emerged as critical predictors of Chl-a and ACD, with spatial variations. This study validates Chl-a as a proxy for ACD, analyzes their spatiotemporal distribution, and assesses the influence of various factors on Chl-a and ACD, enhancing our understanding of algal dynamics in Chinese lakes and reservoirs.

Effects on fatty acids, biochemical composition and growth of rotifer (Brachionus plicatilis) fed with different concentrations of Nannochloropsis sp.

The density of microalgae and nutrient content have impact on the population growth rate, egg rate and nutritional values of rotifers. The aim of this study was to investigate the effects of different concentrations of the alga Nannochloropsis sp. (N10: 10x106, N20: 20x106, N30: 30x106 cells mL-1) on the growth, egg rate, biochemical composition and fatty acid profile of the rotifer Brachionus plicatilis. To maintain a consistent algae density, an equivalent quantity was supplemented to compensate for any reduction. The study was started with three replicates, each with an initial inoculation density of 200 Brachionus individuals mL-1 . The investigation spanned 5 days, during which population parameters (total number of individuals, proportion of individuals with eggs and growth rate) were calculated. After the study period, rotifers were harvested for subsequent biochemical and fatty acid analyses. Notably, the N30 group showed the highest proportions of crude protein (54.41%) and crude lipid (34.5%). The N20 group displayed the most substantial content of total fatty acids, recording a value of 70.69%. Consequently, the N30 group, with a concentration of 30x106 cells mL-1, emerged as the most proficient group, demonstrating superior performance in both population growth and biochemical composition.

Ecological restoration for eutrophication mitigation in urban interconnected water bodies: Evaluation, variability and strategy

Many urban water bodies grapple with low flow flux and weak hydrodynamics. To address these issues, projects have been implemented to form integrated urban water bodies via interconnecting artificial lake or ponds with rivers, but causing pollution accumulation downstream and eutrophication. Despite it is crucial to assess eutrophication, research on this topic in urban interconnected water bodies is limited, particularly regarding variability and feasible strategies for remediation. This study focused on the Loucun river in Shenzhen, comprising an pond, river and artificial lake, evaluating water quality changes pre-(post-)ecological remediation and establishing a new method for evaluating the water quality index (WQI). The underwater forest project, involving basement improvement, vegetation restoration, and aquatic augmentation, in the artificial lake significantly reduced total nitrogen (by 43.58%), total phosphorus (by 79.17%) and algae density (by 36.90%) compared to pre-remediation, effectively controlling algal bloom. Rainfall, acting as a variable factor, exacerbated downstream nutrient accumulation, increasing total phosphorus by 4.56 times and ammonia nitrogen by 1.30 times compared to the dry season, and leading to algal blooms in the non-restoration pond. The improved WQI method effectively assesses water quality status. The interconnected water body exhibits obvious nutrient accumulation in downstream regions. A combined strategy that reducing nutrient and augmenting flux was verified to alleviate accumulation of nutrients downstream. This study provides valuable insights into pollution management strategies for interconnected pond-river-lake water bodies, offering significant reference for nutrient mitigation in such urban water bodies.

Exploring spatiotemporal patterns of algal cell density in lake Dianchi with explainable machine learning

The escalating global occurrence of algal blooms poses a growing threat to ecosystem services. In this study, the spatiotemporal heterogeneity of water quality parameters was leveraged to partition Lake Dianchi into three clusters. Considering water quality parameters and both the delayed and instantaneous effects of meteorological factors, ensemble learning, and quasi-Monte Carlo methods were employed to predict daily algal cell density (AD) between January 2021 and January 2024. Consistently, superior predictive accuracy across all three clusters was exhibited by the Stacking-Elastic-Net regularization model. Furthermore, the minimum combination of drivers that achieved near-optimal accuracy for each cluster was identified, striking a balance between accuracy and cost. The ranking of the effect of drivers on AD varied by cluster, while the delayed effect of meteorological factors on AD generally outweighed their instantaneous effect for all clusters. Additionally, the heterogeneous or homogeneous thresholds and responses between drivers and AD were explored. These findings could serve as a scientific and cost-effective basis for government agencies to develop regional sustainable strategies for managing water quality.

Heat stress in symbiotic dinoflagellates: Implications on oxidative stress and cellular changes

Global warming has been shown to harmfully affect symbiosis between Symbiodiniaceae and other marine invertebrates. When symbiotic dinoflagellates (the genus Breviolum) were in vitro exposed to acute heat stress of +7 °C for a period of 5 days, the results revealed the negative impact on all physiological and other cellular parameters measured. Elevated temperatures resulted in a severe reduction in algal density of up to 9.5-fold, as well as pigment concentrations, indicating the status of the physiological stress and early signs of photo-bleaching. Reactive oxygen species (ROS) were increased in all heated dinoflagellate cells, while the antioxidant-reduced glutathione levels initially dropped on day one but increased under prolonged temperature stress. The cell viability parameters were reduced by 97 % over the heating period, with an increased proportion of apoptotic and necrotic cells. Autofluorescence (AF) for Cy5-PE 660-20 was reduced from 1.7-fold at day 1 to up to 50-fold drop at the end of heating time, indicating that the AF changes were highly sensitive to heat stress and that it could be an extremely sensitive tool for assessing the functionality of algal photosynthetic machinery. The addition of the drug 5-AZA-2′-deoxycytidine (5-AZA), which inhibits DNA methylation processes, was assessed in parallel and contributed to some alterations in algal cellular stress response. The presence of drug 5-AZA combined with the temperature stress had an additional impact on Symbiodiniaceae density and cell complexity, including the AF levels. These variations in cellular stress response under heat stress and compromised DNA methylation conditions may indicate the importance of this epigenetic mechanism for symbiotic dinoflagellate thermal tolerance adaptability over a longer period, which needs further exploration. Consequently, the increased ROS levels and changes in AF signals reported during ongoing heat stress in dinoflagellate cells could be used as early stress biomarkers in these microalgae and potentially other photosynthetic species.