Aluminum phytotoxicity induced structural and ultrastructural changes in submerged plant Vallisneria natans.

Aluminum (Al) is a concentration-dependent toxic metal found in the crust of earth that has no recognized biological use. Nonetheless, the mechanism of Al toxicity to submerged plants remains obscure, especially from a cell/subcellular structure and functional group perspective. Therefore, multiple dosages of Al3+ (0, 0.3, 0.6, 1.2, and 1.5 mg/L) were applied hydroponically to the submerged plant Vallisneria natans in order to determine the accumulation potential of Al at the subcellular level and their ultrastructural toxicity. More severe structural and ultrastructural damage was determined when V. natans exposed to ≥ 0.6 mg/L Al3+. In 1.2 and 1.5 mg/L Al3+ treatment groups, the total chlorophyll content of leaves significantly reduced 3.342, 3.838 mg/g FW, some leaves even exhibited chlorosis and fragility. Under 0.3 mg/L Al3+ exposure, the middle-age and young leaves were potent phytoexcluders, whereas at 1.5 mg/L Al3+, a large amount of Al could be transferred from the roots to other parts, among which the aged leaves were the most receptive tissues (7.306 mg/g). Scanning/Transmission electron microscopy analysis displayed the Al-mediated disruption of vascular bundle structure in leaf cells, intercellular space and several vegetative tissues, and demonstrated that Al in vacuole and chloroplast subcellular segregation into electron dense deposition. Al and P accumulation in the roots, stolons and leaves varied significantly among treatments and different tissues (P < 0.05). Fourier transform infrared spectroscopy of plant biomass also indicated possible metabolites (amine, unsaturated hydrocarbon, etc.) of V. natans that may bind Al3+. Conclusively, results revealed that Al3+ disrupts the cellular structure of leaves and roots or binds to functional groups of biological tissues, thereby affecting plant nutrient uptake and photosynthesis. Findings might have scientific and practical significance for the restoration of submerged vegetation in Al-contaminated lakes.

Potential effects of Cladophora oligoclora Decomposition: Microhabitat variation and Microcystis aeruginosa growth response.

Excessive proliferation of filamentous green algae (FGA) is a new ecological problem in lake systems that have not yet reached a steady state. However, knowledge on how FGA decomposition affects the physical and chemical properties of microhabitats, and whether FGA decomposition stimulates the growth of harmful microalgae in the same niche and promotes the formation of harmful algal blooms remains unclear. In this study, we investigated the decomposing effect of a typical FGA, Cladophora oligoclora, on the density and photosynthetic capacity of Microcystis aeruginosa. C. oligoclora decomposition was characterized under different conditions, namely, unshaded and aerobic, unshaded and anoxic, shaded and anaerobic, and shaded and anoxic, which represented different environmental states in the sedimentation process of decaying C. oligoclora mats from water surface to sediment. The shaded and anaerobic treatment significantly decreased the dissolved oxygen and pH of the culture medium by 66.48 % and 7.21 %, respectively, whereas the conductivity and total organic carbon increased by 71.17 and 70.19 times compared with the control group, respectively. This indicated that the decomposing C. oligoclora deposited at the bottom under dark and anaerobic conditions in natural waters had the greatest impact on the lake environment. Further, the cell density of M. aeruginosa was higher than that in the control group with low concentration (10 % of decomposing solution), whereas the cell density and photosynthetic activity decreased significantly at high concentration of the decomposing solution. Fatty acids and phenolic acids were identified as the main Cyanobacteria-inhibiting active substances in the organic acid components of the decomposing solution. Furthermore, phenol, 4-methyl- and indole compounds were active organic lipophilic compounds in the residue and solution of decomposing C. oligoclora were difficult to degrade. Our findings will be valuable for understanding the succession relationships between FGA and cyanobacteria, which have the same niche in lake ecosystems.

Effect of submerged plant coverage on phytoplankton community dynamics and photosynthetic activity in situ.

Restoration of submerged plants in eutrophic lakes can reduce nutrients and phytoplankton biomass in the water body. However, the effect of submerged plants on phytoplankton communities and their photosynthetic activity in situ are still poorly understood. Here, we studied the response of phytoplankton community structure and fluorescence parameters to different submerged plants coverage, the relationship of phytoplankton community and fluorescence parameters with submerged plants coverage and water physicochemical parameters were analysed in sampling area of Hangzhou West Lakes. The results showed that the coverage and biomass of submerged plants were negatively correlated with nitrogen and phosphorus contents in water body but positively correlated with total phenol content. The ratio of nitrogen to phosphorus in the study site changed greatly (32.25-124.54). In spring and summer, Oscillatoria and Leptolyngbya (Cyanophyta) were the dominant species, while in autumn and winter, the dominant species were Cyclotella (Chlorophyta), and Melosira and Cymbella (Bacillariophyta). Compared with Chlorophyta and Bacillariophyta, fluorescence parameters of Cyanophyta were more sensitive to total phosphorus, N:P ratio, total phenols, pH, and electric conductivity. Fluorescence parameters of Chlorophyta and Bacillariophyta were only affected by underwater light. Total phosphorus (TP) and N:P had a negative effect on the maximum photochemical electron yield of Cyanophyta. Furthermore, Cyanophyta was inhibited by total phenols from submerged plants. When phytoplankton were under stress, photochemical electron yield decreased significantly, whereas non-photochemical quenching increased. The structural equation model showed that the coverage of submerged plants might indirectly affect the fluorescence parameters of Cyanophyta by affecting nitrogen, phosphorus, and total phenol contents in the water body. These findings contribute to the understanding of the mechanisms underlying the impact of submerged plant restoration on phytoplankton community dynamics in subtropical eutrophic shallow lakes and provide a theoretical basis for the management of lakes.

Effects of maifanite on growth, physiological and phytochemical process of submerged macrophytes Vallisneria spiralis.

The restoration of submerged plants is critical for the reconstruction of eutrophic lake ecosystems. The growth of submerged plants is influenced by many factors. For the first time in this study, the effects of silicate-mineral maifanite supplement on the growth, physiological and phytochemical process of Vallisneria spiralis (V. spiralis) were investigated by an outdoor PVC barrel experiment, to provide a technical reference for further applications in aquatic ecological restoration. The results show that the maifanite could significantly promote the growth of V. spiralis. Specifically, the biomass, height, number of leaves, leaf width, root length, and root activity of V. spiralis in the maifanite-supplemented group were better than those of the control (P < 0.05). Moreover, the modified maifanite group performed better than the raw maifanite group (P < 0.05). The photosynthetic pigment, root activity, and the malondialdehyde and peroxidase activity of the maifanite-treated V. spiralis were better than those of the control to some extent. It was found that maifanite contained abundant major and trace elements, which are required for the growth of V. spiralis. It is concluded that maifanite is beneficial to the growth of V. spiralis and can be further applied to the ecological restoration of eutrophic lakes.

Bacterial Communities and Their Predicted Functions Explain the Sediment Nitrogen Changes Along with Submerged Macrophyte Restoration.

Submerged vegetation biomass fluctuation usually occurs during the preliminary stage of vegetation restoration in shallow lakes, which impacts the final status and duration for achieving a macrophyte-dominant state. This study uncovered the sediment N characteristics and the sediment bacterial community and their predicted functions during the preliminary stage of vegetation recovery in the West Lake, a typical subtropical degenerated shallow lake in China. Results showed increased amounts of sediment TN and NH4-N, reaching 3425.76 and 345.5 mg kg-1, respectively, when the vegetation biomass decreased from its maximum to its minimum. The maximum concentration of sediment NH4-N reached 508.60 mg kg-1 with the decline in vegetation, which might restrict further growth of the submerged macrophytes. The bacterial community structure during the high macrophyte biomass (HMB) period was distinct from that observed during the low macrophyte biomass (LMB) period. Specific taxa such as the phyla Chloroflexi and Acidobacteria and the genus Anaerolineaceae that are related to organic carbon degradation were significantly higher during the LMB period. Potential denitrifiers, such as Lactococcus and Bacillus genera decreased during the LMB period. Accumulation of sediment ammonia could be attributed to the enhanced production by assimilatory nitrate reduction, organic N degradation, and/or the decreased consumption by nitrification. Our findings highlight that the unstable preliminary stage of vegetation restoration brings drastic fluctuation of sediment N loading, of which NH4-N accumulation caused by bacterial communities prevents further growth of the submerged macrophytes. Therefore, extra management measures for the vegetation recovery areas should be taken to avoid excess NH4-N accumulation in sediments.

Effects of the decomposing liquid of Cladophora oligoclona on Hydrilla verticillata turion germination and seedling growth.

Excessive proliferation of filamentous green algae (FGA) has been considered an important factor resulting in the poor growth or even decline of submerged macrophytes. However, there is a lack of detailed information regarding the effect of decaying FGA on submerged macrophytes. This study aimed to investigate whether the decomposing liquid from Cladophora oligoclona negatively affects Hydrilla verticillata turion germination and seedling growth. The results showed that the highest concentrations of decomposing liquid treatments inhibited the turion germination rate, which was the lowest than other treatments, at only 84%. The chlorophyll a fluorescence (JIP test) and physiological indicators (chlorophyll a content, soluble sugars, Ca2+/Mg2+-ATPase and PAL activity) were also measured. The chlorophyll a content in the highest concentration (40% of original decomposing liquid) treatment group decreased by 43.53% than that of the control; however, soluble sugars, Ca2+/Mg2+-ATPase, and PAL activity increased by 172.46%, 271.19%, and 26.43% respectively. The overall results indicated that FGA decay has a considerable effect on submerged macrophyte turion germination and seedling growth, which could inhibit their expansion and reproduction. This study emphasized the need to focus on effects of FGA decomposition on the early growth stages of submerged macrophytes and offered technological guidance for submerged vegetation restoration in lakes and shallow waters.

Effects of Planted Versus Naturally Growing Vallisneria natans on the Sediment Microbial Community in West Lake, China.

Submerged macrophytes play an important role in aquatic ecosystems, which has led to an increase in studies on vegetation recovery in polluted lakes from which submerged macrophytes have disappeared. The comparison of microbial communities in sediment cloned with planted and naturally growing submerged macrophytes is an interesting but rarely studied topic. In this investigation, Maojiabu and Xilihu, two adjacent sublakes of West Lake (Hangzhou, China), were selected as aquatic areas with planted and naturally growing macrophytes, respectively. Sediment samples from sites with/without Vallisneria natans were collected from both sublakes. The results showed that sediment total nitrogen and organic matter were significantly lower in the plant-covered sites than that in the non-plant sites in Maojiabu. Additionally, the sediment microbial community characterized by 16S ribosomal RNA (rRNA) sequencing differed more significantly for Maojiabu than for Xilihu. The relative abundances of microbes involved in C, N, and S elemental cycling were significantly higher in the sediments with plants than in those without. Results from both fatty acid methyl ester analysis and 16S rRNA sequencing indicated that vegetation significantly influenced the sulfate-reducing bacteria (SRB). Thus, the gene copies and composition of SRB were explored further. The relative gene abundance of SRB was 66% higher with natural vegetation colonization but was not influenced by artificial colonization. An increase in dominant SRB members from the families Syntrophobacteraceae and Thermodesulfovibrionaceae contributed to the increase of total SRB. Thus, macrophyte planting influences sediment nutrient levels and microbial community more than natural growth does, whereas the latter is more beneficial to sediment SRB.

Impacts of residual aluminum from aluminate flocculant on the morphological and physiological characteristics of Vallisneria natans and Hydrilla verticillata.

Aluminate is generally used as a flocculant in water and wastewater treatment processes, but the residual aluminum (Al) may have toxic effects on aquatic organisms when the concentration accumulates beyond a threshold level. The in situ and laboratory tests were conducted to evaluate the impact of residual Al on submerged macrophytes in West Lake, Hangzhou, China, which receives Al flocculant-purified water diverted from the Qiantang River. The responses of Vallisneria natans and Hydrilla verticillata were investigated based on their morphological and physiological parameters in pot culture and aquarium simulation experiments. In the pot culture experiments, the biomass, seedling number, plant height, stolon number, stolon length, and root weight were significantly higher at a site located 150m from the inlet compared with those at a site located 15m from the inlet (P < 0.05), thereby indicating that the residual Al significantly inhibited the morphological development of V. natans and H. verticillata. The variations in the chlorophyll-a, protein, and malondialdehyde contents of the two species in both the pot culture and aquarium simulation experiments also demonstrated that the two submerged macrophytes were stressed by residual Al. V. natans and H. verticillata accumulated 0.052-0.227mg of Al per gram of plant biomass (fresh weight, mg/g FW) and 0.045-0.205mg Al/g FW in the in situ experiments, respectively, where the amounts of Al were significantly higher in the plants in the treatment aquaria during the laboratory experiments than those in the controls. These results may have important implications for the restoration of submerged macrophytes and ecological risk assessments in Al-exposed lakes. It is recommended that the Al salt concentration used for the control of lake eutrophication should be reduced to an appropriate level.

Effects of pyrogallic acid on Microcystis aeruginosa: oxidative stress related toxicity.

Pyrogallic acid (PA) is used in various industrial and consumer products. The molecular mechanisms underlying PA's toxicity was not fully understood. In this study, toxicity of PA on Microcystis aeruginosa with reactive oxygen species (ROS) generation as an end point was investigated. The results showed an increase in the percentage of cells with loss of membrane integrity and enhanced intracellular ROS production. Exposure to 50mgL(-1) PA for 48h caused the highest percentage of loss of membrane integrity (56.7%), and a 2.54-fold higher intracellular ROS level compared to control. Further investigation revealed that PA caused a dose-dependent increase in DNA strand breaks (DSB) of M. aeruginosa at exposure concentration from 2 to 50mgL(-1). The incubation of cells with ROS scavengers ascorbic acid, N-acetyl-l-cysteine (NAC) and tocopherol markedly alleviated the level of PA-induced DSB. Analysis of PA autoxidized products in culture solution showed that PA was quickly converted to purpurogallin (PG), and PG was further autoxidized to other polyphenolic compounds. PA and PG might participate a futile redox cycle, which mediated ROS production in M. aeruginosa. These results suggested DNA strands and cell membrane were two targets of ROS induced by PA, and oxidative damage was an important mechanism for the toxicity of PA against M. aeruginosa.

Structural and metabolic responses of microbial community to sewage-borne chlorpyrifos in constructed wetlands.

Long-term use of chlorpyrifos poses a potential threat to the environment that cannot be ignored, yet little is known about the succession of substrate microbial communities in constructed wetlands (CWs) under chlorpyrifos stress. Six pilot-scale CW systems receiving artificial wastewater containing 1mg/L chlorpyrifos were established to investigate the effects of chlorpyrifos and wetland vegetation on the microbial metabolism pattern of carbon sources and community structure, using BIOLOG and denaturing gradient gel electrophoresis (DGGE) approaches. Based on our samples, BIOLOG showed that Shannon diversity (H') and richness (S) values distinctly increased after 30days when chlorpyrifos was added. At the same time, differences between the vegetated and the non-vegetated systems disappeared. DGGE profiles indicated that H' and S had no significant differences among four different treatments. The effect of chlorpyrifos on the microbial community was mainly reflected at the physiological level. Principal component analysis (PCA) of both BIOLOG and DGGE showed that added chlorpyrifos made a difference on test results. Meanwhile, there was no difference between the vegetation and no-vegetation treatments after addition of chlorpyrifos at the physiological level. Moreover, the vegetation had no significant effect on the microbial community at the genetic level. Comparisons were made between bacteria in this experiment and other known chlorpyrifos-degrading bacteria. The potential chlorpyrifos-degrading ability of bacteria in situ may be considerable.

Revealing the response characteristics of periphyton biomass and community structure to sulfamethoxazole exposure in aquaculture water: The perspective of microbial network relationships.

The widespread application of sulfonamide antibiotics in aquaculture has raised concerns about their adverse environmental impacts. Periphyton plays a crucial role in the aquatic ecosystem. In this study, we examined sulfamethoxazole (SMX) effects on the community structure and interactions of periphyton in simulated aquaculture water. Our findings indicated that the total biomass of periphyton decreased, while the biomass of periphytic algae and the secretion of extracellular polymeric substances (EPS) increased at 0.7 × 10-3 mg/L. Under higher SMX concentrations (5 mg/L and 10 mg/L), periphyton growth was severely inhibited, the microbial community structure of periphyton were sharply altered, characterized by the cyanobacteria growth suppression and decrease in the diversity index of community. Furthermore, elevated SMX concentrations (5 mg/L and 10 mg/L) increased the ratio of negative relationships from 45.4% to 49.4%, which suggested that high SMX concentrations promoted potential competition among microbes and disrupted the microbial food webs in periphyton. The absolute abundance of sul1 and sul2 genes in T2 and T3 groups were 2-3 orders of magnitude higher than those in control group after 30 days of SMX exposure, which elevated the risk of resistance gene enrichment and dissemination in the natural environment. The study contributes to our understanding of the detrimental effects of antibiotic pollution, which can induce changes in the structure and interaction relationship of microbial communities in aquaculture water.

Unraveling the ecological mechanisms of Aluminum on microbial community succession in epiphytic biofilms on Vallisneria natans leaves: Novel insights from microbial interactions.

The extensive use of aluminum (Al) poses an escalating ecological risk to aquatic ecosystems. The epiphytic biofilm on submerged plant leaves plays a crucial role in the regulation nutrient cycling and energy flow within aquatic environments. Here, we conducted a mesocosm experiment aimed at elucidating the impact of different Al concentrations (0, 0.6, 1.2, 2.0 mg/L) on microbial communities in epiphytic biofilms on Vallisneria natans. At 1.2 mg/L, the highest biofilms thickness (101.94 µm) was observed. Al treatment at 2.0 mg/L significantly reduced bacterial diversity, while micro-eukaryotic diversity increased. Pseudomonadota and Bacteroidota decreased, whereas Cyanobacteriota increased at 1.2 mg/L and 2.0 mg/L. At 1.2 and 2.0 mg/L. Furthermore, Al at concentrations of 1.2 and 2.0 mg/L enhanced the bacterial network complexity, while micro-eukaryotic networks showed reduced complexity. An increase in positive correlations among microbial co-occurrence patterns from 49.51% (CK) to 57.05% (2.0 mg/L) was indicative of augmented microbial cooperation under Al stress. The shift in keystone taxa with increasing Al concentration pointed to alterations in the functional dynamics of microbial communities. Additionally, Al treatments induced antioxidant responses in V. natans, elevating leaf reactive oxygen species (ROS) content. This study highlights the critical need to control appropriate concentration Al concentrations to preserve microbial diversity, sustain ecological functions, and enhance lake remediation in aquatic ecosystems.

Gastrodin protects porcine sertoli cells from zearalenone-induced abnormal secretion of glial cell line-derived neurotrophic factor through the NOTCH signaling pathway.

Zearalenone (ZEA) is a prevalent mycotoxin found in moldy diets and is associated with reproductive dysfunction. However, the molecular underpinning of ZEA in impairment of spermatogenesis remains largely unknown. To unveil the toxic mechanism of ZEA, we established a co-culture model using porcine Sertoli cells and porcine spermatogonial stem cells (pSSCs) to investigate the impact of ZEA on these cell types and their associated signaling pathways. Our findings showed that low concentration of ZEA inhibited cell apoptosis, while high concentration induced cell apoptosis. Furthermore, the expression levels of Wilms' tumor 1 (WT1), proliferating cell nuclear antigen (PCNA) and glial cell line-derived neurotrophic factor (GDNF) were significantly decreased in ZEA treatment group, while concurrently upregulating the transcriptional levels of the NOTCH signaling pathway target genes HES1 and HEY1. The addition of the NOTCH signaling pathway inhibitor DAPT (GSI-IX) alleviated the damage to porcine Sertoli cells caused by ZEA. Gastrodin (GAS) significantly increased the expression levels of WT1, PCNA and GDNF, and inhibited the transcription of HES1 and HEY1. GAS also efficiently restored the decreased expression levels of DDX4, PCNA and PGP9.5 in co-cultured pSSCs suggesting its potential in ameliorating the damage caused by ZEA to Sertoli cells and pSSCs. In conclusion, the present study demonstrates that ZEA disrupts pSSCs self-renewal by affecting the function of porcine Sertoli cell, and highlights the protective mechanism of GAS through the regulation of the NOTCH signaling pathway. These findings may offer a novel strategy for alleviating ZEA-induced male reproductive dysfunction in animal production.

[Characteristics of Phytoplankton Communities and Key Impact Factors in Three Types of Lakes in Wuhan].

To reveal the characteristics and key impact factors of phytoplankton communities in different types of lakes, sampling surveys for phytoplankton and water quality parameters were conducted at 174 sampling sites in a total of 24 lakes covering urban, countryside, and ecological conservation areas of Wuhan in spring, summer, autumn, and winter 2018. The results showed that a total of 365 species of phytoplankton from nine phyla and 159 genera were identified in the three types of lakes. The main species were green algae, cyanobacteria, and diatoms, accounting for 55.34%, 15.89%, and 15.07% of the total number of species, respectively. The phytoplankton cell density varied from 3.60×106-421.99×106 cell·L-1, chlorophyll-a content varied from 15.60-240.50 µg·L-1, biomass varied from 27.71-379.79 mg·L-1, and the Shannon-Wiener diversity index varied from 0.29-2.86. In the three lake types, cell density, Chla, and biomass were lower in EL and UL, whereas the opposite was true for the Shannon-Wiener diversity index. NMDS and ANOSIM analysis showed differences in phytoplankton community structure (Stress=0.13, R=0.048, P=0.2298). In addition, the phytoplankton community structure of the three lake types had significant seasonal characteristics, with chlorophyll-a content and biomass being significantly higher in summer than in winter (P<0.05). Spearman correlation analysis showed that phytoplankton biomass decreased with increasing N:P in UL and CL, whereas the opposite was true for EL. Redundancy analysis (RDA) showed that WT, pH, NO3-, EC, and N:P were the key factors that significantly affected the variability in phytoplankton community structure in the three types of lakes in Wuhan (P<0.05).

Long-term study of ecological restoration in a typical shallow urban lake.

We investigated the long-term effects (6 years) of sediment improvement and submerged plant restoration of a subtropical shallow urban lake, Hangzhou West Lake China. To reveal the lake ecosystems variations, we analyzed the sediment properties, submerged macrophyte characteristics, sediment microorganisms, and benthic macroinvertebrate communities from 2015 to 2020. The ecological restoration project decreased sediment TP and OM, increased submerged macrophyte biomass and sediment microbial diversity, and improved the benthic macroinvertebrate communities in the restored area. The sediment TP decreased from 2.94 mg/g in 2015 to 1.33 mg/g in 2020. The sediment OM of the restored area decreased from 27.44 % in 2015 to 8.08 % in 2020. Principal component analysis (PCA) confirmed that the restoration improved the sediment conditions, making it suitable for the growth of submerged macrophytes, and then sped up the restoration and reconstruction of the lake ecosystem. These results have significant implications on the ecological management of shallow lakes.

Potential ecological implication of Cladophora oligoclora decomposition: Characteristics of nutrient migration, transformation, and response of bacterial community structure.

During decay, the sediment microenvironment and water quality are severely affected by excessive proliferation of harmful algae such as filamentous green algae (FGA). The frequency of this FGA is increased through global warming and water eutrophication. In the present study, the degradation processes of a common advantage FGA Cladophora oligoclora and its effect on nitrogen and phosphorus nutrient structure and bacterial community composition at the sediment-water interface were investigated by stable isotope labelling and high-throughput sequencing. The results showed that the decomposition process of C. oligoclona was fast, stable, and difficult to degrade. The changes in sediment δ15N values reached 66.68 ‰ on day 40, which indicated that some of the nitrogen had migrated to the sediment from C. oligoclona litter. TN and NH4+-N in the overlying water rapidly increased between days 0-10, NH4+-N rose to 78.21% of TN on day 40, resulting in severe pollution of ammonia in the overlying water. The nitrogen forms and contents in the sediment are mainly derived from the increasing ammonia nitrogen release. The TP and IP in the overlying water increased to the highest concentrations of 6.68±0.64, 6.59±0.79 mg·L-1 during the decomposition process, respectively, resulting in the migration of phosphate to the sediments with increasing phosphorus content. The abundance of the main dominant bacterial communities, such as Acinetobacter (0.08%-62.48%) and Pseudomonas (0.13%-20.36%) in sediments and overlying water has changed significantly. The correlation analysis results suggested that the phosphorus was mainly related to the bacterial community in the overlying water, while the various forms of nitrogen demonstrated a high relevance with the bacterial community in the sediment. Our research results will be valuable in evaluating the potential ecological risk of FGA decomposition and provide scientific support for shallow lake management and submerged vegetation restoration.

[Spatial Distribution Characteristics of Phosphorus Fractions and Release Risk in Sediments of Honghu International Importance Wetland].

According to a spatial distribution analysis of phosphorus in sediments from Honghu Wetland, it was found that TP content in sediments at the mouth of Honghu Lake was 781.31-1955.84 mg·kg-1 and the average value was(1287.21±437.28)mg·kg-1. TP content in sediments in the open water area was 438.33-1554.04 mg·kg-1, with an average value of(718.10±238.15)mg·kg-1. The TP content of sediments in lake inlet was significantly higher than that of sediments in the open water area(P<0.05), and that in the enclosed aquaculture was higher than in the open water area, although no significant difference was observed (P>0.05). The TP content of sediments to the northwest and northeast of Honghu Lake was higher than that to the southwest of Honghu Lake, and the TP content of sediments in The Four-lake main canal was significantly higher than that of Luoshan main canal(P<0.05). The phosphorus input in the Four-lake main canal may be the main source of phosphorus in Honghu Lake sediments. The phosphorus fraction composition in sediments from different sampling sites were significantly different. Fe/Al-P and Ca-P were the main forms of phosphorus in sediments from the lake inlet, while OP and Ca-P were the main forms of phosphorus in sediments from the open water area. The variation in spatial phosphorus form composition was related to the influence of human activity and the distribution of aquatic plants. Fe/Al-P and OP contents were used to estimate the content of biological available phosphorus (BAP) in evaluated sediments, and the proportion of BAP in TP was used to estimate the risk of phosphorus release in Honghu sediments. BAP/TP was 39.8%-69%, with an average of(56.5±7.23)%, indicating a high risk of phosphorus release. OP and BAP were significantly correlated with TP in overlying water(P<0.01), and the correlation between BAP and phosphate in the overlying water was the highest. The results showed that phosphorus concentration in the overlying water may be related to the release of Fe/Al-P and OP into water bodies.

The changing characteristics of phytoplankton community and biomass in subtropical shallow lakes: Coupling effects of land use patterns and lake morphology.

The community composition and biomass of phytoplankton in shallow lakes are impacted by many environmental factors including water quality physicochemical parameters, land use in the watershed, and lake morphology. However, few studies have simultaneously evaluated the relative importance of these factors on the effect of community composition and biomass of phytoplankton. The relative importance of the water quality physicochemical parameters (water temperature [WT], total nitrogen [TN], total phosphorus [TP], pH, dissolved oxygen [DO], electrical conductivity [EC], turbidity and Secchi depth [SD]), land use (built-up land, farmland, waters, forest, grassland, and unused land) in the watershed, and lake morphology (area and depth) on the composition and biomass of phytoplankton communities were assessed in 29 subtropical shallow lakes in Wuhan, China, during different seasons from December 2017 to November 2018. The results showed that phytoplankton in all 29 lakes was mainly composed of Cyanophyta, Chlorophyta, and Bacillariophyta. Phytoplankton abundance was highest in summer and lowest in winter. We analyzed the relative importance of the three groups of variables to the community composition of the phytoplankton by variance decomposition. The results showed that the three groups of environmental variables had the highest explanation rate (> 80%) for the composition of the phytoplankton community in summer and autumn, and the explanation rates in spring and winter were 42.1% and 39.8%, respectively. The water quality physicochemical parameters were the most important variables affecting the composition of phytoplankton communities, followed by land use in the watershed. Through generalized additive model and structural equation model analysis, we found that the land use and lake morphology had minimal direct impact on the Chl-a and cell density of phytoplankton, mainly by altering the TN, TP, turbidity, SD, DO, and EC, which indirectly affected phytoplankton. WT and nutrients were still the main predictors of phytoplankton abundance. Built-up land was the main source of nitrogen and phosphorus in lakes. Correlation analysis found that forest and grassland had positive impacts on reducing lake nitrogen and phosphorus contents. This showed that increasing grassland and forest in the watershed could reduce the pollutants entering the lake. Our findings will contribute to water quality management and pollution control for subtropical shallow lakes.

Combined Effects of Allelopathic Polyphenols on Microcystis aeruginosa and Response of Different Chlorophyll Fluorescence Parameters.

Polyphenols are allelochemicals secreted by aquatic plants that effectively control cyanobacteria blooms. In this study, sensitive response parameters (including CFPs) of Microcystis aeruginosa were explored under the stress of different polyphenols individually and their combination. The combined effects on M. aeruginosa were investigated based on the most sensitive parameter and cell densities. For pyrogallic acid (PA) and gallic acid (GA), the sensitivity order of parameters based on the EC50 values (from 0.73 to 3.40 mg L-1 for PA and from 1.05 to 2.68 mg L-1 for GA) and the results of the hierarchical cluster analysis showed that non-photochemical quenching parameters [NPQ, q N, q N(rel) and q CN] > photochemical quenching parameters [YII, q P, q P(rel) and q L] or others [F v/F m, F' v /F' m, q TQ and UQF(rel)] > cell densities. CFPs were not sensitive to ellagic acid (EA) and (+)-catechin (CA). The sensitivity order of parameters for M. aeruginosa with PA-GA mixture was similar to that under PA and GA stress. The quantitative (Toxicity Index, TI) and qualitative (Isobologram representation) methods were employed to evaluate the combined effects of PA, GA, and CA on M. aeruginosa based on cell densities and NPQ. TI values based on the EC50 cells suggested the additive effects of binary and multiple polyphenols, but synergistic and additive effects according to the EC50 NPQ (varied from 0.16 to 1.94). In terms of NPQ of M. aeruginosa, the binary polyphenols exhibited synergistic effects when the proportion of high toxic polyphenols PA or GA was lower than 40%, and the three polyphenols showed a synergistic effect only at the ratio of 1:1:1. Similar results were also found by isobologram representation. The results showed that increasing the ratio of high toxic polyphenols would not enhance the allelopathic effects, and the property, proportion and concentrations of polyphenols played an important role in the combined effects. Compared with cell densities, NPQ was a more suitable parameter as evaluating indicators in the combined effects of polyphenols on M. aeruginosa. These results could provide a method to screen the allelochemicals of polyphenols inhibiting cyanobacteria and improve the inhibitory effects by different polyphenols combined modes.

Synergistic control of internal phosphorus loading from eutrophic lake sediment using MMF coupled with submerged macrophytes.

Sediment phosphorus (P) is the main source of endogenous P for lake eutrophication. An in-situ combined technology for determination the removal effect of sediment P in all fractions was first developed using the novel modified maifanite (MMF) and submerged macrophytes in this study. MMF was synthesized using an acidification process (2.5 mol/L H2SO4) and then a calcination (400 °C) method. The morphology and structure of MMF were characterized by XRD, SEM, XPS, and BET. We tested the removal effects of sediment P by MMF and submerged macrophytes in combination and separately. The results demonstrated that the synergistic removal capacity of sediment P using MMF coupled with submerged macrophytes was higher than the sum of them applied separately. MMF could promote the submerged macrophytes growth and enhance the adsorption of extra P on MMF through root oxygenation and nutrient allocation. The microcosm experiment results showed that sediment from fMMF+V. spiralis exhibited the most microbial diversity and abundance among the sediment. The combination of MMF and submerged macrophytes increased the Firmicutes abundance and decreased the Bacteroidetes. These results indicated that adsorption-biological technology can be regarded as a novel and competitive technology to the endogenous pollution control in eutrophic shallow lakes.