Controlling toxic cyanobacteria: effects of dredging and phosphorus-binding clay on cyanobacteria and microcystins

Mitigating harmful cyanobacterial blooms in drinking water reservoirs through in-situ sediment resuspension

Mitigating harmful cyanobacterial blooms is a global challenge, particularly crucial for safeguarding source water. Given the limitations of current technologies for application in drinking water reservoirs, we propose an innovative strategy based on in-situ sediment resuspension (SR). This method's effectiveness in cyanobacterial control and its potential impacts on water quality were assessed through laboratory culture experiments and further validated via field applications in five drinking water reservoirs. The results revealed that SR could significantly mitigate cyanobacterial growth, evidenced by the treated sets (removal rate: 3.82×106 cells L-1d-1) compared to the control set (growth rate: 2.22×107 cells L-1d-1) according to the laboratory experiments. The underlying mechanisms identified included underwater light reduction (2.38× increase in extinction coefficient) and flocculation and entrainment of cells by resuspended particles (30 % reduction per operation). Additional contributions were noted in the reduction of bioavailable phosphate and remediation of anaerobic sediment characterized by increased redox potential. This facilitated the oxidation of iron, which in turn promoted the co-precipitation of phosphate (removal rate: 46 μg L-1d-1) and inhibited its release from the sediment. The SR operation, devoid of importing extra substances, represents a safe and economical technology for controlling harmful cyanobacteria in drinking water reservoirs.

The shifts in microbial interactions and gene expression caused by temperature and nutrient loading influence Raphidiopsis raciborskii blooms

Climate change and the trophic status of water bodies are important factors in global occurrence of cyanobacterial blooms. The aim of this study was to explore the cyanobacteria‒bacterial interactions that occur during Raphidiopsis raciborskii (R. raciborskii) blooms by conducting microcosm simulation experiments at different temperatures (20 °C and 30 °C) and with different phosphorus concentrations (0.01 mg/L and 1 mg/L) using an ecological model of microbial behavior and by analyzing microbial self-regulatory strategies using weighted gene coexpression network analysis (WGCNA). Three-way ANOVA revealed significant effects of temperature and phosphorus on the growth of R. raciborskii (P < 0.001). The results of a metagenomics-based analysis of bacterioplankton revealed that the synergistic effects of both climate and trophic changes increased the ability of R. raciborskii to compete with other cyanobacteria for dominance in the cyanobacterial community. The antagonistic effects of climate and nutrient changes favored the occurrence of R. raciborskii blooms, especially in eutrophic waters at approximately 20 °C. The species diversity and richness indices differed between the eutrophication treatment group at 20 °C and the other treatment groups. The symbiotic bacterioplankton network revealed the complexity and stability of the symbiotic bacterioplankton network during blooms and identified the roles of key species in the network. The study also revealed a complex pattern of interactions between cyanobacteria and non-cyanobacteria dominated by altruism, as well as the effects of different behavioral patterns on R. raciborskii bloom occurrence. Furthermore, this study revealed self-regulatory strategies that are used by microbes in response to the dual pressures of temperature and nutrient loading. These results provide important insights into the adaptation of microbial communities in freshwater ecosystems to environmental change and provide useful theoretical support for aquatic environmental management and ecological restoration efforts.

Manipulating geological phosphorus resources for improved production and environmental outcomes during plant establishment

Phosphorus (P) fertilisers are under scrutiny due to resource constraints and environmental impacts. Simple rock phosphate (RP) modifications with acids and co-applied with microbial inoculum could offer sustainable alternative P fertiliser products. We evaluated the effects of acid-treated rock phosphate (RP) in combination with fungal inoculum on plant establishment, environmental impacts (nutrient leaching) and soil quality in a 5-month pot trial. The treatments were evaluated in a clayey Vertisol and a silty Acrisol using cotton (Gossypium hirsutum) as a model plant. The RP treatments - apart from the unmodified and HCl products - were effective in promoting plant establishment with two of the microbial formulations superior to conventional P fertilisers by an average factor of 2 in both soil types (p < 0.05). All RP products restricted P leaching compared with conventional P fertilisers (p < 0.05), by an average factor of 5 for diammonium phosphate (DAP) in both soil types and 3 for the triple superphosphate TSP (only in Acrisol). Nitrate leaching from all treatments was high although much lower from the RP treatments compared with the conventional fertilisers towards the end of the establishment trial, by an average factor of 1.5 (p < 0.05). Ranking analysis revealed that some RP treatments showed evidence for improved ongoing soil quality, including decreased P leaching and soil acidification risks. Microbial analysis showed complex interactions between treatment and soil type. Nonetheless, inoculum persistence at the end of the plant establishment phase was observed for all pots analysed. Our results demonstrate that relatively simple modifications to RP could pave the way for developing sustainable P fertilisers.

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.

Biological and Chemical Approaches for Controlling Harmful Microcystis Blooms

The proliferation of harmful cyanobacterial blooms dominated by Microcystis aeruginosa has become an increasingly serious problem in freshwater ecosystems due to climate change and eutrophication. Microcystis-blooms in freshwater generate compounds with unpleasant odors, reduce the levels of dissolved O2, and excrete microcystins into aquatic ecosystems, potentially harming various organisms, including humans. Various chemical and biological approaches have thus been developed to mitigate the impact of the blooms, though issues such as secondary pollution and high economic costs have not been adequately addressed. Red clays and H2O2 are conventional treatment methods that have been employed worldwide for the mitigation of the blooms, while novel approaches, such as the use of plant or microbial metabolites and antagonistic bacteria, have also recently been proposed. Many of these methods rely on the generation of reactive oxygen species, the inhibition of photosynthesis, and/or the disruption of cellular membranes as their mechanisms of action, which may also negatively impact other freshwater microbiota. Nevertheless, the underlying molecular mechanisms of anticyanobacterial chemicals and antagonistic bacteria remain unclear. This review thus discusses both conventional and innovative approaches for the management of M. aeruginosa in freshwater bodies.

Combining dredging with modified zeolite thin-layer capping to control nitrogen release from eutrophic lake sediment

Dredging is widely used to control internal sediment nitrogen (N) pollution during eutrophic lake restoration. However, the effectiveness of dredging cannot be maintained for long periods during seasonal temperature variations. This study used modified zeolite (MZ) as a thin-layer capping material to enhance dredging efficiency during a year-long field sediment core incubation period. Our results showed that dredging alone more effectively reduced pore water N, N flux, and sediment N content than MZ capping but showed more dramatic changes during the warm seasons. The N flux in dredged sediment in summer was 1.8 and 2.5 times that in spring and autumn, respectively, indicating a drastic N regeneration process in the short term. In contrast, the combination method reduced the extra 10% pore water N, 22% N flux, and 8% sediment organic N content compared with dredging alone and maintained high stability during seasonal changes. The results indicated that the addition of MZ to the surface of dredged sediment not only enhanced the control effect of dredging by its adsorption capacity but may also smooth the N regeneration process via successive accumulation (in the channel of the material) and activation of bacteria for months, which was evidenced by the variation in microbial diversity in the MZ treatment. As a result, the combination of dredging with modified zeolite simultaneously enhanced the efficiency and stability of the single dredging method in controlling sediment N content and its release, exhibiting great prospects for long-term application in eutrophic lakes with severe pollution from internal N loading.

The effects of different doses of lanthanum-modified bentonite in combination with a submerged macrophyte (Vallisneria denseserrulata) on phosphorus inactivation and macrophyte growth: A mesocosm study

The combination of chemical phosphorus (P) inactivation and submerged macrophyte transplantation has been widely used in lake restoration as it yields stronger effects than when applying either method alone. However, the dose effect of chemical materials on P inactivation when used in combination with submerged macrophytes and the influences of the chemicals used on the submerged macrophytes growth remain largely unknown. In this study, we investigated P inactivation in both the water column and the sediment, and the responses of submerged macrophytes to Lanthanum modified bentonite (LMB) in an outdoor mesocosm experiment where Vallisneria denseserrulata were transplanted into all mesocosms and LMB was added at four dosage levels, respectively: control (LMB-free), low dosage (570 g m-2), middle dosage (1140 g m-2), and high dosage (2280 g m-2). The results showed that the combination of LMB dosage and V. denseserrulata reduced TP in the water column by 32%-38% compared to V. denseserrulata alone, while no significant difference was observed among the three LMB treatments. Porewater soluble reactive P, two-dimensional diffusive gradient in thin films (DGT)-labile P concentrations, and P transformation in the 0-1 cm sediment layer exhibited similar trends along the LMB dosage gradient. Besides, LMB inhibited plant growth and reduced the uptake of mineral elements (i.e., calcium, manganese, iron, and magnesium) in a dosage-dependent manner with LMB. LMB may reduce plant growth by creating a P deficiency risk for new ramets and by interfering with the uptake of mineral elements. Considering both the dose effect of LMB on P inactivation and negative effect on macrophyte growth, we suggest a "small dosage, frequent application" method for LMB application to be used in lake restoration aiming to recover submerged macrophytes and clear water conditions.

Enhanced nutrient control efficiency in sediments using modified clay inactivation coupled with aquatic vegetation in the confluence area of a eutrophic lake

Developing a long-term method for controlling sediment N and P release is important for enabling lake restoration. In this study, inactivation methods using lanthanum-modified clay, modified zeolite, or planting aquatic vegetation and their combinations were used in the control internal sediment loading (pore water N and P concentrations and their fluxes), and the efficacies of the methods were analyzed. The results indicated that compared to the control sediment, the addition of P sorbent, which was La and Al co-modified attapulgite (ACLA), and N sorbent, which was NaCl-modified zeolite (modified zeolite), planting of aquatic vegetation Vallisneria spiralis (V. spiralis), and a combination of sorbents and plants effectively reduced the porewater nutrient content and its fluxes across the sediment-water interface. However, the reduction in pore water nutrients and flux were superior when using a combination of clay inactivation and aquatic planting. The poorest sediment N and P control was achieved by planting V. spiralis alone. The addition of La and Al co-modified attapulgite (ACLA) and modified zeolite efficiently reduced N and P in the sediment, but the N and P sorbents did not achieve long-lasting nutrient release control. The high efficiency obtained by the combination of modified clay-based inactivation and V. spiralis was likely due to the strong chemical sorption capacity of clay and oxygenation by the rhizosphere of aquatic vegetation. These results show that a combination of chemical and ecological methods would be the most effective approach to remediate polluted sediments in the long term.

Assessing the impacts of fine sediment removal on endogenous pollution release and microbial community structure in the shallow lakes

Resuspension is a crucial process for releasing endogenous pollution from shallow lakes into the overlying water. Fine particle sediment, which has a higher contamination risk and longer residence time, is the primary target for controlling endogenous pollution. To this end, a study coupling aqueous biogeochemistry, electrochemistry, and DNA sequencing was conducted to investigate the remediation effect and microbial mechanism of sediment elution in shallow eutrophic water. The results indicated that sediment elution can effectively remove some fine particles in situ. Furthermore, sediment elution can inhibit the release of ammonium nitrogen and total dissolved phosphorous into the overlying water from sediment resuspension in the early stage, resulting in reductions of 41.44 %-50.45 % and 67.81 %-72.41 %, respectively. Additionally, sediment elution greatly decreased the concentration of nitrogen and phosphorus pollutants in pore water. The microbial community structure was also substantially altered, with an increase in the relative abundance of aerobic and facultative aerobic microorganisms. Redundancy analysis, PICRUSt function prediction, and the correlation analysis revealed that loss on ignition was the primary factor responsible for driving changes in microbial community structure and function in sediment. Overall, the findings provide novel insights into treating endogenous pollution in shallow eutrophication water.

Comparison of dredging, lanthanum-modified bentonite, aluminium-modified zeolite, and FeCl2 in controlling internal nutrient loading

The eutrophic Bouvigne pond (Breda, The Netherlands) regularly suffers from cyanobacterial blooms. To improve the water quality, the external nutrient loading and the nutrient release from the pond sediment have to be reduced. An enclosure experiment was performed in the pond between March 9 and July 29, 2020 to compare the efficiency of dredging, addition of the lanthanum-modified bentonite clay Phoslock® (LMB), the aluminum-modified zeolite Aqual-P™ (AMZ) and FeCl2 to mitigate nutrient release from the sediment. The treatments improved water quality. Mean total phosphorus (TP) concentrations in water were 0.091, 0.058, 0.032, 0.031, and 0.030 mg P L-1 in controls, dredged, FeCl2, LMB and AMZ treated enclosures, respectively. Mean filterable P (FP) concentrations were 0.056, 0.010, 0.009, 0.005, and 0.005 mg P L-1 in controls, dredged, FeCl2, LMB and AMZ treatments, respectively. Total nitrogen (TN) and dissolved inorganic nitrogen (DIN) were similar among treatments; lanthanum was elevated in LMB treatments, Fe and Cl in FeCl2 treatments, and Al and Cl in AMZ treatments. After 112 days, sediment was collected from each enclosure, and subsequent sequential P extraction revealed that the mobile P pool in the sediments had reduced by 71.4%, 60.2%, 38%, and 5.2% in dredged, AMZ, LMB, and FeCl2 treatments compared to the controls. A sediment core incubation laboratory experiment done simultaneously with the enclosure experiment revealed that FP fluxes were positive in controls and cores from the dredged area, while negative in LMB, AMZ and FeCl2 treated cores. Dissolved inorganic nitrogen (DIN) release rate in LMB treated cores was 3.6 times higher than in controls. Overall, the applied in-lake treatments improved water quality in the enclosures. Based on this study, from effectiveness, application, stakeholders engagement, costs and environmental safety, LMB treatment would be the preferred option to reduce the internal nutrient loading of the Bouvigne pond, but additional arguments also have to be considered when preparing a restoration.

Combined impacts of algae-induced variations in water soluble organic matter and heavy metals on bacterial community structure in sediment from Chaohu Lake, a eutrophic shallow lake

Many lakes are suffering from eutrophication and heavy metals-contamination. However, the combined impacts of algae bloom and its induced variations in heavy metals on microbial community in sediment from eutrophic lakes remain unclear. In this study, we performed field experiments to investigate how algae bloom impacted water soluble organic matter (WSOM) and heavy metals in sediment from Chaohu Lake, a eutrophic shallow lake, and probed their combined impacts on sediment bacterial community structure. The results showed that algae bloom increased WSOM quantity, in particular, the soluble microbial by-product-like (SMP) and fulvic acid-like (Fa-L) components markedly enhanced by 203.70 % and 70.17 %, respectively. We also found that algae bloom redistributed the spatial patterns of heavy metals and altered their chemical species in sediment, then promoted contamination degree and potential ecological risk of heavy metals in sediment. Moreover, sediment bacterial community richness and diversity obviously decreased after algae bloom, and the variance partitioning analysis (VPA) results showed that combined impacts of algae-induced changes in WSOM and heavy metals explained 66.56 % of the variations in bacterial community structure. These findings depicted how algae bloom influence sediment WSOM and heavy metals, and revealed the combined impacts of algae-induced variations on microbial community structure in shallow eutrophic lake.

The role of Ca2+ in the improvement of phosphate adsorption in natural waters: Establishing an environmentally friendly La/Ca bimetallic organic framework

Modified metal-organic framework (MOF) materials are promising adsorbents for phosphate removal in aquatic environment. Herein, a high-efficiency and eco-friendly La/Ca composite (La/Ca-BTC) was designed by calcining La/Ca MOFs for phosphate adsorption. Batch adsorption experiments showed that La/Ca-BTC-3/1 (La: Ca molar ratio of 3: 1) had an excellent phosphate sorption capacity of 101.01 mg P/g, and could also maintain relatively high adsorption in the range of pH 4-8. Anion coexistence experiments showed that, except for carbonate ions, common anions have little effect on adsorption. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) analysis indicated that oxygen vacancies formed in the La/Ca-BTC, probably by metal doping. The density functional theory (DFT) calculation showed that oxygen vacancies could affect the orbital hybridization energy during phosphate adsorption by changing the state density, reducing the bond energy barrier for phosphate adsorption, thereby enhancing the adsorption effect of La/Ca-BTC. Phosphate adsorbents generally incur severe environmental risk by their gradual release of metal ions due to changes in water quality, especially where there is high natural organic matter (NOM). The DFT calculation further demonstrated that Ca²⁺ in the La/Ca-BTC was more inclined to combine with humic acid (HA) than La³⁺. Therefore, due to the introduction of Ca²⁺, La/Ca-BTC exhibited lower La-release in the presence of HA than La-BTC, which could be reduced by about 52.04%. Furthermore, La/Ca-BTC had the potential to simultaneously remove NOM which has important implication for aquatic remediation. These results are of great significance for the development of environmentally friendly phosphate adsorbents.

Phosphorus control and dredging decrease methane emissions from shallow lakes

Freshwater ecosystems are an important source of the greenhouse gas methane (CH₄), and their emissions are expected to increase due to eutrophication. Two commonly applied management techniques to reduce eutrophication are the addition of phosphate-binding lanthanum modified bentonite (LMB, trademark Phoslock©) and dredging, but their effect on CH₄ emissions is still poorly understood. Here, this study researched how LMB and dredging affected CH₄ emissions using a full-factorial mesocosm design monitored for 18 months. The effect was tested by measuring diffusive and ebullitive CH₄ fluxes, plant community composition, methanogen and methanotroph activity and community composition, and a range of physicochemical water and sediment variables. LMB addition decreased total CH₄ emissions, while dredging showed a trend towards decreasing CH₄ emissions. Total CH₄ emissions in all mesocosms were much higher in the summer of the second year, likely because of higher algal decomposition and organic matter availability. First, LMB addition lowered CH₄ emissions by decreasing P-availability, which reduced coverage of the floating fern Azolla filiculoides, and thereby prevented anoxia and decreased surface water NH₄⁺ concentrations, lowering CH₄ production rates. Second, dredging decreased CH₄ emissions in the first summer, possibly it removed the methanogenic community, and in the second year by preventing autumn and winter die-off of the rooted macrophyte Potamogeton cripsus. Finally, methanogen community composition was related to surface water NH₄⁺ and O₂, and porewater total phosphorus, while methanotroph community composition was related to organic matter content. To conclude, LMB addition and dredging not only improve water quality, but also decrease CH₄ emissions, mitigating climate change.

Patterns of internal nitrogen and phosphorus loadings in a cascade reservoir with a large water level gradient: Effects of reservoir operation and water depth

Internal nutrient loadings pose a high risk of being an additional N and P source, exacerbating eutrophication and deteriorating water quality. In this study, we selected the Daheiting Reservoir (DHTR) in North China, with a pronounced water level gradient, to investigate internal N and P loadings, estimate N and P fluxes across the sediment‒water interface based on the pore water profiles, and reveal the potential effects of water discharge from an upstream reservoir and high-intensity cage aquaculture on the risks of internal N and P release. The results indicated that DHTR presented with severe internal nutrient loadings, and the N and P fluxes showed significant spatiotemporal variations. NH₄⁺-N and soluble reactive phosphorus (SRP) fluxes were higher in deep areas (averages of 26.14 and 9.9 mgm^-2d^-1, respectively) than in shallow areas near inflows (averages of 5.0 and 1.24 mgm^-2d^-1, respectively). Unexpectedly, the estimated NH₄⁺-N and SRP fluxes were the lowest in summer (averages of 3.94 and 0.33 mgm^-2d^-1, respectively), which may have been influenced by seasonal thermal stratification and copious discharge from the hypolimnion of the upstream reservoir (Panjiakou Reservoir). Comparison of annual internal and external N and P loadings revealed that water discharge from the upstream Panjiakou Reservoir was the dominant source of N and P to the reservoir, contributing up to 83.6% of N input and 55.4% of P input. The internal P loading also contributed to water eutrophication to a great extent, accounting for 34.7% of the total P input. Our results highlight the impact of upstream reservoir discharge operation on downstream reservoir water quality and the importance of controlling the internal nutrient loading in cascade reservoirs, and further provide theoretical and practical foundations for the development of policies and strategies to conserve reservoir ecosystems.

Response of sediment phosphorus partitioning to lanthanum-modified clay amendment and porewater chemistry in a small eutrophic lake

Sustained eutrophication of the aquatic environment by the remobilization of legacy phosphorus (P) stored in soils and sediments is a prevailing issue worldwide. Fluxes of P from the sediments to the water column, referred to as internal P loading, often delays the recovery of water quality following a reduction in external P loads. Here, we report on the vertical distribution and geochemistry of P, lanthanum (La), iron (Fe) and carbon (C) in the culturally eutrophied Lake Bromont. This lake underwent remediation treatment using La modified bentonite (LMB) commercially available as Phoslock™. We investigated the effectiveness of LMB in decreasing soluble reactive phosphorus (SRP) availability in sediments and in reducing dissolved fluxes of P across the sediment-water interface. Sediment cores were retrieved before and after LMB treatment at three sites representing bottom sediment, sediment influenced by lakeside housing and finally littoral sediment influenced by the lake inflow. Sequential extractions were used to assess changes in P speciation. Depth profiles of dissolved porewater concentrations were obtained after LMB treatment at each site. Results indicate that SRP extracted from the sediments decreased at all sites, while total extracted P (P_TOT) bound to redox-sensitive metal oxides increased. ³¹P NMR data on P extract reveals that 20-43% of total solid-phase P is in the form of organic P (P_org) susceptible to be released via microbial degradation. Geochemical modelling of porewater data provides evidence that LaPO_4(s) mineral phases, such as rhabdophane and/or monazite, are likely forming. However, results also suggest that La³⁺ binding by dissolved organic carbon (DOC) hinders La-phosphate precipitation. We rely on thermodynamic modelling to suggest that high Fe²⁺ would bind to DOC instead of La³⁺, therefore promoting P sequestrations by LMB under anoxic conditions.

Phosphate removal and recovery by lanthanum-based adsorbents: A review for current advances

Controlling eutrophication and recovering phosphate from water bodies are hot issues in the 21st century. Adsorption is considered to be the best method for phosphate removal because of its high adsorption efficiency and fast removal rate. Among the many adsorbents, lanthanum (La)-based adsorbents have been paid more and more attention due to their strong affinity to phosphorus. This paper reviews research of phosphate adsorption on La-based adsorbents in different La forms, including lanthanum oxide/hydroxide, lanthanum mixed metal oxide/hydroxide, lanthanum carbonate, La³⁺, La-based metal-organic framework (La-MOF) and La-MOF derivatives. The La-based adsorbents can be loaded on many carriers, such as carbon material, clay minerals, porous silica, polymers, industrial wastes, and others. We find that lanthanum oxide/hydroxide and La³⁺ adsorbents are mostly studied, while those in the forms of lanthanum carbonate, La-MOF, and La-MOF derivatives are relatively few. The kinetic process of most phosphate adsorption is pseudo-second-order and the isotherm process is in accordance with the Langmuir model. The cost of La-based and other traditional adsorbents was compared. The adsorption mechanisms are categorized as electrostatic attraction, ligand exchange, Lewis acid-base interaction, ion exchange and surface precipitation. Besides, regeneration methods of La-based adsorbents are mainly acid, alkali, and salt-alkali. In addition, the La-based adsorbents after absorbing phosphate can be directly used as a slow-release fertilizer. This review provides a basis for the research on phosphate adsorption by La-based adsorbents. It should be carried out to further develop La-based materials with high adsorption capacity and good regeneration ability. Meanwhile, studies have been conducted on the reuse of phosphate after desorption, which needs more attention in future research.

Development of a Potentially New Algaecide for Controlling Harmful Cyanobacteria Blooms Which is Ecologically Safe and Selective

Harmful cyanobacterial blooms (HCBs) caused by Microcystis aeruginosa are of great concern as they negatively affect the aquatic environment and human health. Chemical methods could rapidly eradicate HCBs and have been used for many decades. However, many chemical reagents are not recommended to eliminate HCBs in the long term, given the possible destructive and toxic effects of the chemicals employed on non-target aquatic organisms. We developed a new algaecide, 2-((1,3,4-thiadiazol-2-yl)thio)-N-(4-chlorophenyl) acetamide (Q2), to control harmful cyanobacteria while being environmentally friendly and selective. In our study, Q2 effectively inhibited cyanobacterial growth, especially of M. aeruginosa, but did not affect eukaryotic algae in test concentrations. A critical mechanism was revealed by transcriptome and metagenomic results showing that Q2 affects multiple cellular targets of cyanobacteria for HCB control, including the destruction of organelles, damage in the photosynthesis center, as well as inhibition of gas vesicle growth, and these changes can be highly relevant to the decrease of quorum-sensing functional KEGG pathways. Furthermore, Q2 did not affect the microbial composition and could recover the disrupted aquatic functional pathways in a short period. This is different from the impact on ecosystem functioning of the traditionally used harmful algaecide diuron. All these results verified that Q2 could be friendly to the aquatic environment, providing a new directional choice in managing HCBs in the future.

Higher dissolved oxygen levels promote downward migration of phosphorus in the sediment profile: Implications for lake restoration

Lake restoration (typically sediment dredging) commonly involves producing a new sediment-water interface (SWI). This study comprehensively investigated the migration and transformation of P during the formation of a new SWI under different dissolved oxygen (DO) levels in the overlying water, based on Fe/Al-rich sediment. The results suggest that DO had a profound effect on the 0-7 cm sediment layer properties and higher DO levels in the overlying water resulted in the diffusion of DO deeper into the sediments. Importantly, besides preventing Fe reductive dissolution and sulfides competition, higher DO levels inhibited the release of P from sediment by inducing the mitigation of P from the upper (0-3 cm) into the bottom (3-7 cm) sediments. The migration of P was found to be closely related to the interactions between organic matter and Al, Fe, and Ca in the sediment profile caused by higher DO levels in overlying water. Particularly, the decrease in organic matter in the upper sediments increased the mobility of Ca and promoted aging of Al and Fe, which increased the migration of the different forms of P. The increased organic matter in the bottom sediments retained the mobile Ca and increased amorphous Fe, which immobilized the P that had migrated from the upper sediments. These results demonstrate the relatively high mobility of P in the upper sediments and the importance of P immobilization capability of bottom sediments on regulating P release from SWI under higher DO levels in overlying water. Accordingly, measures for lake restoration with producing a new SWI were recommended to be applied in combination with P immobilization method to develop more feasible strategies.

Towards climate-robust water quality management: Testing the efficacy of different eutrophication control measures during a heatwave in an urban canal

Harmful algal blooms are symptomatic of eutrophication and lead to deterioration of water quality and ecosystem services. Extreme climatic events could enhance eutrophication resulting in more severe nuisance algal blooms, while they also may hamper current restoration efforts aimed to reduce nutrient loads. Evaluation of restoration measures on their efficacy under climate change is essential for effective water management. We conducted a two-month mesocosm experiment in a hypertrophic urban canal focussing on the reduction of sediment phosphorus (P)-release. We tested the efficacy of four interventions, measuring phytoplankton biomass, nutrients in water and sediment. The measures included sediment dredging, water column aeration and application of P-sorbents (lanthanum-modified bentonite - Phoslock® and iron-lime sludge, a by-product from drinking water production). An extreme heatwave (with the highest daily maximum air temperature up to 40.7 °C) was recorded in the middle of our experiment. This extreme heatwave was used for the evaluation of heatwave-induced impacts. Dredging and lanthanum modified bentonite exhibited the largest efficacy in reducing phytoplankton and cyanobacteria biomass and improving water clarity, followed by iron-lime sludge, whereas aeration did not show an effect. The heatwave negatively impacted all four measures, with increased nutrient releases and consequently increased phytoplankton biomass and decreased water clarity compared to the pre-heatwave phase. We propose a conceptual model suggesting that the heatwave locks nutrients within the biological P loop, which is the exchange between labile P and organic P, while the P fraction in the chemical P loop will be decreased. As a consequence, the efficacy of chemical agents targeting P-reduction by chemical binding will be hampered by heatwaves. Our study indicates that current restoration measures might be challenged in a future with more frequent and intense heatwaves.

Design, synthesis, high algicidal potency, and putative mode of action of new 2-cyclopropyl-4-aminopyrimidine hydrazones

Control of cyanobacteria harmful algal blooms remains a global challenge. In the present study, a series of novel 2-cyclopropyl-4-aminopyrimidine hydrazones were designed and synthesized as potential algicides. Compounds 4a, 4b, 4h, 4j, 4k, 4l, and 4m showed potent inhibition against Synechocystis sp. PCC6803 (median effective concentration, EC₅₀ = 1.1 to 1.7 μM) and Microcystis aeruginosa FACHB905 (EC₅₀ = 1.2 to 2.0 μM), more potent than, or comparably with, copper sulfate (PCC6803, EC₅₀ = 1.8 μM; FACHB905, EC₅₀ = 2.2 μM) and prometryne (PCC6803, EC₅₀ = 12.3 μM; FACHB905, EC₅₀ = 7.2 μM). Compound 4k exhibited algicidal activity in an expanded culture system, and was less toxic than copper sulfate to zebrafish. Electron microscope analyses showed that 4k damaged cyanobacterial cells and decreased the number of thylakoid lamellae. Transcriptomic and qPCR analyses suggest that 4k interfered photosynthesis-related pathways. Treatment with 4k significantly decreased the maximum quantum yield of photosystem II and the photosynthetic electron transfer rate, and the resulting reactive oxygen species damaged thylakoid membranes and photosystem I. The results suggest that 4k is a potential lead for further development of effective and safe algicides.

Responses of Different Submerged Macrophytes to the Application of Lanthanum-Modified Bentonite (LMB): A Mesocosm Study

Lanthanum-modified bentonite (LMB) has remarkable efficacy on eutrophication control, but the reduced bioavailable phosphorus and formed anaerobic horizon from LMB may be harmful to submerged macrophytes. We conducted this study to explore the influence of LMB on Hydrilla verticillata and Vallisneria natans in mixed-species plantings. The concentrations of TP, TDP, SRP, and TDN in the LMB treatments were lower than the Control, but the Chl a concentration in the HLMB treatment (850 g m−2) was higher than the Control by 63%. There were no differences of V. natans growth among the treatments. For H. verticillata, its biomass, RGR, height, branch number, root number, and length in the LLMB treatment (425 g m−2) were lower than the Control by 48%, 22%, 13%, 34%, 33%, and 8%, respectively. In addition, the biomass of H. verticillata was 62%, the RGR was 32%, the height was 19%, the branch number was 52%, the root length was 40%, and the root number was 54% lower in the HLMB treatment than those in the Control. In summary, LMB had negative effects on submerged macrophytes with underdeveloped roots. Submerged macrophytes with more developed roots are preferred when using combined biological–chemical methods for water restoration.

Effect of Eutrophication Control Methods on the Generation of Greenhouse Carbon Gases in Sediment

The accumulation of nutrients (eutrophication) in water bodies generally produces increased concentrations of organic matter that eventually are deposited in sediment, and partially mineralized, generating greenhouse carbon gases (GHCG). The application of eutrophication control methods includes the application of phosphate adsorbing materials such as Phoslock (PHOS), and hypolimnetic oxygenation systems (HOS). We evaluated the generation of GHCG in sediment subject to these eutrophication control methods. Combined water and sediment samples from the Valle de Bravo reservoir in Mexico, were incubated in reactors, where the following eutrophication control methods were applied: HOS, PHOS, HOS + PHOS, and compared to a reactor without treatment (CONTROL). Redox potential (Eh), pH, redox-sensitive ions, and GHCG emissions were monitored, observing the following rates: CONTROL (15.6 mmol m−2 d−1) > HOS (12.8) > HOS + PHOS (11.0) > PHOS (9.7 mmol m−2 d−1), with the CONTROL rate within values determined from published sediment core data. The GHCG emissions increased with time as Eh decreased, and sulfate reduction increased. Application of eutrophication control methods in the Valle de Bravo reservoir, would most probably result in lower GHCG generation and emission rates. This is due to the repression of sulfate-reduction in water-sediment systems where HOS and PHOS were applied both individually and combined.

Demonstration study of bypass stabilization pond system in the treatment of eutrophic water body

This study involved a comprehensive renovation of fish ponds to improve the water quality of a eutrophic river in Dongguan City. The abandoned fish ponds were transformed into three different types of stabilization ponds: facultative, aerated biological, and submerged plant stabilization ponds. The water of the eutrophic section of the river was pumped into the facultative stabilization pond and discharged into the Haizai River through an aerated biological pond and a submerged plant pond. In the aerated biological pond, secondary treatment was carried out using plant zoning and artificial floating island aeration system. The submerged plant pond used fountain-type aeration and an underwater forest for tertiary treatment. After four months of monitoring the water quality of the stabilization pond and the river, the ammonia nitrogen (NH₃-N), total phosphorus (TP), and chemical oxygen demand (COD_Cr) levels in the raw sewage reduced from 6.53 mg/L to 1.13 mg/L, 1.76 mg/L to 0.29 mg/L, and 63 mg/L to 22 mg/L, respectively; the transparency of water increased to 45 cm, and dissolved oxygen (DO) level increased to 5.32 mg/L. This study provides a reference for the ex-situ treatment of urban eutrophic waterbodies.

The spatial variations of water quality and effects of water landscape in Baiyangdian Lake, North China

Baiyangdian Lake (BYD), a large shallow lake in North China, has complex water landscape patterns that are underlies spatial variations in water quality. In this study, we collected 61 water samples from three water landscapes (reed littoral zones, fish ponds, and open water) and analyzed them for water quality parameters, such as dissolved organic carbon (DOC), total nitrogen (TN), and total phosphorus (TP). Water landscape distribution (determined using remote sensing imagery) was then used to assess correlations between water quality parameters and water landscape proportion in differently scaled buffer zones. There was substantial variation across all subareas, with TN and TP concentrations ranging from 0.90 to 4.10 mg/L and 0.06 to 0.18 mg/L, respectively, in class IV of water quality as a whole. Spatial variations in water quality were mainly caused by water landscape distribution and external nutrient inputs. There were negative correlations between DOC, TN, and TP concentrations and the area proportion of reed littoral zones in the 300 and 500 m buffers. In contrast, DOC, TN, and TP concentrations were significantly positively correlated with the area proportion of fish ponds in the 100 m buffer. Furthermore, compared with reed littoral zones, a lower ratio of nitrogen to phosphorus and a higher proportion of dissolved organic nitrogen and tyrosine-like proteins were found in fish ponds. These effects were mainly attributed to the development of internal sediment loadings due to nutrient exchange across the sediment-water interface. Therefore, dredging-based sediment removal from fish ponds should be considered to suppress internal phosphorus loading and accelerate recovery of the BYD ecosystem.

Effect of dredging and capping with clean soil on the mitigation of algae-induced black blooms in Lake Taihu, China: A simulation study

Sediment is an important source of matter that causes blackening and odor formation in a water body. The restoration of polluted sediment can suppress algae-induced black blooms to a certain degree. In this study, we compared the control effects of sediment dredging and capping with clean soil on algae-induced black blooms in Lake Taihu using indoor simulation experiments. In addition, we explored the driving effect of temperature on algae-induced black blooms using the method of gradual warming (18, 23, and 28 °C) during the experiment. No blackening of the water body was observed in the simulation stages I (18 °C) and II (23 °C), and the blackening and odor formation occurred within 3 d when the temperature increased to 28 °C in stage III, implying that high temperature was an important driving factor for algae-induced black blooms. Dredging and capping inhibited the blackening and odor formation to some extent, and the colorimetric values in the water columns were lower in the treatment groups than in the control group. At the end of the experiment, the colorimetric values of dredging and capping treatments were 56.5% and 96.7% of the colorimetric value of the control group, respectively. The control effect of dredging on the blackening elements, i.e., Fe²⁺ and S^2- and the main odor forming compounds, i.e., dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS) was observed in stage II (11-20 d) and stage III (21-27 d), respectively, and the inhibition ability of dredging to suppress algal-induced black blooms was superior than that of capping with clean soil.

Mitigation of CyanoHABs Using Phoslock® to Reduce Water Column Phosphorus and Nutrient Release from Sediment

Cyanobacterial blooms can be stimulated by excessive phosphorus (P) input, especially when diazotrophs are the dominant species. A series of mesocosm experiments were conducted in a lake dominated by a cyanobacteria bloom to study the effects of Phoslock^®, a phosphorus adsorbent. The results showed that the addition of Phoslock^® lowered the soluble reactive phosphate (SRP) concentrations in water due to efficient adsorption and mitigated the blooms. Once settled on the sediments, Phoslock^® serves as a barrier to reduce P diffusion from sediments into the overlying waters. In short-term (1 day) incubation experiments, Phoslock^® diminished or reversed SRP effluxes from bottom sediments. At the same time, the upward movement of the oxic-anoxic interface through the sediment column slightly enhanced NH₄⁺ release and depressed N₂ release, suggesting the inhibition of nitrification and denitrification. In a long-term (28 days) experiment, Phoslock^® hindered the P release, reduced the cyanobacterial abundance, and alleviated the bloom-driven enhancements in the pH and oxygen. These results suggest that, through suppression of internal nutrient effluxes, Phoslock^® can be used as an effective control technology to reduce cyanobacteria blooms common to many freshwater systems.

Research on application of a new bottom trap technology to catch particles rich in nutrients in a large shallow lake

The resuspension and sedimentation of particulate matter and the release of nutrients from sediment are important factors affecting the eutrophication of shallow lakes. The capture and removal of particles rich in nitrogen, phosphorus, and other nutrients at the bottom of lakes is of great significance for improving the management and eutrophication status of lakes. This study investigated the feasibility of applying lake bottom trap technology in seven different locations in Lake Chaohu, which is the fifth largest freshwater lake in China. The results showed that the trap in the western part of Lake Chaohu had the highest sedimentation rate and could capture most of the nutrients. The sedimentation rates were higher in spring and summer than in autumn and winter. The bottom trap effectively collected and preserved chlorophyll a, organic matter, total nitrogen, and total phosphorus. The trap per meter length (15-20 m wide) could catch 20.7-27.6 m³ of particles rich in nutrients with a water content of 50-70%, organic matter content of 281.9-375.8 kg, total nitrogen content of 24.5-32.6 kg, and total phosphorus content of 10.5-14 kg. The proposed bottom trap had little impact on the benthic organism system of the lake. The bottom trap technology used in this study could solve the problem of nitrogen, phosphorus, and algae accumulation in lakes and reservoirs, broaden the utility of lake hydrodynamics in environmental pollution control, and provide new ideas and strategies for the control and management of cumulative pollution in shallow lakes and reservoirs.

In situ control of internal nutrient loading and fluxes in the confluence area of an eutrophic lake with combined P inactivation agents and modified zeolite

In this study, a field in situ inactivation experiment was carried out to control the confluence area sediment nutrient loading and fluxes using modified zeolite (MZ) in combination with poly aluminum chloride (PAC) and lanthanum-modified bentonite (LMB). The results indicated that PAC + MZ and LMB + MZ can reduce 76% and 75% of the P flux and 20% and 27% of the N flux, respectively. These results are based on a comparison with a control treatment over four months under the influence of external loading. However, their control efficiency on sediment nutrient fluxes decreased largely during the summertime algal blooming season. Both of the treatments lost their N control efficiency at this time. In contrast, LMB + MZ can still reduce 27% of the P flux compared to the control treatment. Surface sediment extractable ammonium increased substantially from the PAC + MZ and LMB + MZ treatments, which is 1.8 and 2.2 times more than the extractable ammonium in the control sediment after 210 days of remediation. The P fractionation analysis indicated that, in the PAC + MZ and LMB + MZ, both NaOH-rP and HCl-P increased greatly at a rate of 1.5 and 3.9 times, respectively, compared to the control sediment. PAC + MZ and LMB + MZ reduced the mobile P by 21% and 43%, respectively compared with the control sediment after 210 days of remediation. Bacteria richness and diversity in the PAC + MZ and LMB + MZ treatments had no obvious distinction when compared with the control treatment after 210 days of remediation but had a transient decrease in the LMB + MZ and recovered as it returned back to the same level found in control after 60 days. The results indicated that the control efficiency of nutrient fluxes in sediment might vary with types of inactivation agents and dosing methods and can be largely reduced under the influence of external loading and algal blooms.

The combined effects of macrophytes (Vallisneria denseserrulata) and a lanthanum-modified bentonite on water quality of shallow eutrophic lakes: A mesocosm study

Establishment of submerged macrophyte beds and application of chemical phosphorus inactivation are common lake restoration methods for reducing internal phosphorus loading. The two methods operate via different mechanisms and may potentially supplement each other, especially when internal phosphorous loading is continuously high. However, their combined effects have so far not been elucidated. Here, we investigated the combined impact of the submerged macrophyte Vallisneria denseserrulata and a lanthanum-modified bentonite (Phoslock®) on water quality in a 12-week mesocosm experiment. The combined treatment led to stronger improvement of water quality and a more pronounced reduction of porewater soluble reactive phosphorus than each of the two measures. In the combined treatment, total porewater soluble reactive phosphorus in the top 10 cm sediment layers decreased by 78% compared with the control group without Phoslock® and submerged macrophytes. Besides, in the upper 0-1 cm sediment layer, mobile phosphorus was transformed into recalcitrant forms (e.g. the proportion of HCl-P increased to 64%), while in the deeper layers, (hydr)oxides-bound phosphorus species increased 17-28%. Phoslock®, however, reduced the clonal growth of V. denseserrulata by 35% of biomass (dry weight) and 27% of plant density. Our study indicated that Phoslock® and submerged macrophytes may complement each other in the early stage of lake restoration following external nutrient loading reduction in eutrophic lakes, potentially accelerating the restoration process, especially in those lakes where the internal phosphorus loading is high.

Microbial diversity characteristics and the influence of environmental factors in a large drinking-water source

Although the influence of environmental factors on the microbial community in water sources is crucial, it is seldom evaluated. The seasonal relationship between microbial diversity of bacteria and fungi and environmental factors was investigated in a large drinking-water reservoir using Illumina MiSeq sequencing. Forty-one bacterial phyla and nine fungal phyla were analyzed in the Qingcaosha Reservoir, Shanghai, China. The predominant bacterial phyla were Actinobacteria, Proteobacteria, Bacteroidetes, and Cyanobacteria, with the maximum relative abundance of 46%, 36.6%, 16.1%, and 14.9%, respectively. Actinobacteria were observed to be the predominant bacterial phylum during spring and summer. The maximum relative abundance of unclassified fungi appeared in summer (98.8%), which was higher than that of Ascomycota and Basidiomycota (11.7% and 8.2%, respectively). Principal coordinate analysis (PCoA) results showed that the structural similarity in the bacterial community was greater during summer and winter; however, the fungal community exhibited a greater similarity during spring and summer. 2-Methylisoborneol (2-MIB), an olfactory compound produced by microorganisms, was detected at a concentration of 8.97 ng/L during summer, which was slightly lower than the olfactory threshold (10 ng/L). The positive correlation between Actinobacteria and unclassified fungi and 2-MIB (p < 0.05) confirmed that Actinobacteria and unclassified fungi produced 2-MIB. The chemical oxygen demand (COD) was 1.48-1.94 mg/L, and the maximum concentrations of total nitrogen (TN) and total phosphorus (TP) were 2.1 mg/L and 0.5 mg/L, respectively. Chloroflexi were negatively correlated with COD (p < 0.05) but positively correlated with TP (p < 0.01). Nitrospirae were negatively correlated with COD (p < 0.05), but positively correlated with TN (p < 0.05). Among the classified fungi, Rozellomycota, Basidiomycota (p < 0.05), and Chytridiomycota (p < 0.01) were positively correlated with TP. Therefore, the relative abundance of predominant bacteria was affected by various environmental factors; however, fungi were mainly influenced by TP.

Effect of algae on phosphorus immobilization by lanthanum-modified zeolite

Phosphorus-inactivating agents (PIAs) as geoengineering tools in lakes have been investigated extensively, but PIA resuspension in the photic layer occurs frequently in shallow lakes and little is known about the influence of algae on PIA performance. Our results proved that algae increased the dissolved oxygen, pH and dissolved organic carbon concentration substantially. In the absence of sediment, lanthanum modified zeolite (LMZ) as a representative PIA and algae could deplete dissolved inorganic phosphorus (DIP) from water but the former was faster than the latter. When LMZ and algae coexisted, the amount of phosphorus that was captured by LMZ was 3.1 times greater than that taken up by algae. An increase in pH or dissolved organic carbon increased the zero-equilibrium phosphorus concentration (EPC₀) of the sediment but LMZ addition could lower the EPC₀ and reduce the risk of phosphorus release during the algal blooming season. In the presence of sediment, LMZ reduced the DIP concentration more rapidly and yielded a lower final DIP concentration compared with algae. In conclusion, the influence of algae on the performance of LMZ by (i) taking up DIP to reduce the availability of DIP and convert DIP into a releasable phosphorus form and (ii) increasing the pH and dissolved organic carbon concentration to hinder the adsorption ability of DIP were recognized. The LMZ performed well, even in the presence of algae.

The efficacy of Phoslock® in reducing internal phosphate loading varies with bottom water oxygenation

Eutrophication in lakes and reservoirs has prompted interest in using sediment capping technology to reduce the sediment contribution to internal nutrient loading. One such sediment capping technology is Phoslock®, a lanthanum-embedded clay, which can bind phosphate at the sediment surface and limit its diffusion into the water column. However, in well-oxygenated lakes, naturally occurring iron can bind phosphate by a similar mechanism. We sought to test the efficacy of Phoslock® in limiting phosphate (PO₄ ^3-) fluxes relative to untreated iron-rich lake sediment under conditions of bottom-water oxia and anoxia through laboratory batch core incubations of intact sediment cores from Jordan Lake, a reservoir in central North Carolina. We found that Phoslock® decreased phosphate fluxes relative to the control under anoxic conditions (7.5 ± 9.5 vs. 236 ± 74 µmol PO₄ ^3-•m^-2•d^-1), but provided no benefit relative to the control when the water column was oxygenated (4.5 ± 4.3 vs. 7.0 ± 11.4 µmol PO₄ ^3-•m^-2•d^-1). We also found that Phoslock® itself can act as a source of NH₄ ⁺ to Jordan Lake waters. Applied at recommended levels to the whole lake, Phoslock® addition would result in a pulse increase in water column NH₄ ⁺ concentrations of approximately 2.6 ± 0.8 μM (an increase of 10 to 275% compared to ambient).

Effect of juvenile omni-benthivorous fish (Carassius carassius) disturbance on the efficiency of lanthanum-modified bentonite (LMB) for eutrophication control: a mesocosm study

Lanthanum-modified bentonite (LMB) is widely used for eutrophication control and has demonstrated good efficiency in some eutrophic lakes. However, the efficiency of LMB on eutrophication control in some eutrophic lakes, where the structure of food webs is mainly dominated by omni-benthivorous fish, remains ambiguous. Omni-benthivorous fish usually disturbs sediment and promotes the release of internal nutrients, the effect of which on the efficacy of LMB remains to be studied. Thus, a 30-day mesocosm experiment was conducted to determine whether omni-benthivorous fish disturbance and LMB would cause antagonistic responses. LMB significantly reduced dissolved P concentration in overlying water, converting mobile P to bound P in the surface layer of sediment in the absence of crucian carp (Carassius carassius). However, there were significantly negative interaction effects between LMB and crucian carp. Although LMB still effectively reduced the total dissolved phosphorus (TDP) and soluble reactive phosphorus (SRP) concentrations of overlying water in the presence of crucian carp, it had limited efficacy on inhibiting the increased concentrations of suspended solids, particulate nutrients, and chlorophyll a (Chl a) due to crucian carp disturbance. Furthermore, the crucian carp disturbance also increased the risk of mobile P releasing from surface sediment, whether with or without LMB application. The results indicated that the efficacy of LMB was insufficient to offset the negative effect of omni-benthivorous fish disturbance on eutrophication control. Hence, the omni-benthivorous fish also need to be considered for eutrophication control in shallow eutrophic lakes. Some measures need to be taken to control the biomass of omni-benthivorous fish.

Spatiotemporal dynamics of succession and growth limitation of phytoplankton for nutrients and light in a large shallow lake

Understanding the limiting factors of phytoplankton growth and competition is crucial for the restoration of aquatic ecosystems. However, the role and synergistic effect of co-varying environmental conditions, such as nutrients and light on the succession of phytoplankton community remains unclear. In this study, a hydrodynamic-ecological modeling approach was developed to explore phytoplankton growth and succession under co-varying environmental conditions (nutrients, total suspended solids (TSS) and variable N:P ratios) in a large shallow lake called Lake Chagan, in Northeast China. A phytoplankton bloom model was nested in the ecological modeling approach. In contrast to the traditonal ecological modeling, competition between phytoplankton species in our study was modeled at both the species/functional group and phenotype levels. Six phytoplankton functional groups, namely diatoms, green algae, Anabaena, Microcystis, Aphanizomenon and Oscillatoria and each of them with three limitation types (i.e., light-limitation, nitrogen-limitation and phosphorus-limitation) were included in the bloom model. Our results demonstrated that the average biomass proportion of the three limitation types (light-limitation, nitrogen-limitation and phosphorus-limitation) in the six phytoplankton function groups accounted for approximately 50%, 37% and 23% of the total phytoplankton biomass, respectively. TSS suppressed the growth of diatoms and green algae, but favored the dominance of cyanobacteria in Lake Chagan, especially in the turbid water phase (TSS ≥ 60 mg/L). In addition, it was reported that the potential of either N-fixing or non-N-fixing cyanobacterial blooming along the gradients of N:P ratios could exist under the influence of the co-environmental factors in the lake. The proportion of non-N-fixing cyanobacteria (i.e., Microcystis and Oscillatoria) exceeded the proportion of N-fixing cyanobacteria (i.e., Anabaena and Aphanizomenon) when the N:P ratios exceeded 20. Non-N-fixing cyanobacteria would become dominant at higher TSS concentrations and lower light intensities in the turbid water. N-fixing cyanobacteria favored lower N:P ratios and higher light intensities in the clearwater phase (where TSS ≤ 60 mg/L). To sustain a good ecological status in the lake, our results suggest that nutrient and TSS levels in the lake should be maintained at or below the thresholds (TN ≤ 1.5 mg/L; TP ≤ 0.1 mg/L; N:P ratios between 15 and 20; and TSS ≤ 60 mg/L). These findings can help improve water quality management practices to restore aquatic ecosystems.

Nitrogen budget at sediment-water interface altered by sediment dredging and settling particles: Benefits and drawbacks in managing eutrophication

Internal nitrogen (N) loading of lakes is commonly controlled by sediment dredging, although its comprehensive effect on internal N loading remains unclear. Herein, we examined the long-term effects of sediment dredging on internal N loading from a new perspective on the N budget at the sediment-water interface (SWI) through a simulation of field dredging performed by incubating intact sediment cores from a shallow eutrophic lake (Lake Taihu). We further evaluated the role of settling particles (SP) in the recovery of N cycle processes after dredging and its potential impact on the N budget. Our results demonstrated that dredging could help reduce organic matter and total N in sediments; improve the redox environment of the SWI; slow down N mineralization, N fixation, denitrification, and anaerobic ammonia oxidation (anammox); and alter the N budget at the SWI and the contribution of various N cycle processes. However, the input of SP enriched in fresh organic matter and N could accelerate the recovery of N cycle processes at the SWI, reducing the variation in the N budget and the contribution of each N cycle process caused by dredging. Dredging significantly reduced the N flux at the SWI, which was evident from the reduction of inorganic N release flux and N removal through denitrification and anammox. Therefore, sediment dredging has its advantages and disadvantages in managing internal N loading in lakes. To maintain a long-term control on the release of internal N through sediment dredging, measures should be taken based on the in-lake and watershed to inhibit the inflow and settlement of particulate matter.

Cyanotoxins in drinking water supply reservoir (Legedadi, Central Ethiopia): implications for public health safety

Cyanobacterial blooms in drinking water supply affect its quality, which ultimately impacts ecosystem and public health. Thus, this cross-sectional study was conducted to perform a preliminary study on cyanotoxins via analysis of samples collected only once from two sites during the month of peak algal bloom and to subsequently prompt a comprehensive risk assessment in a major drinking water source, Legedadi Reservoir, of Addis Ababa, the capital city of Ethiopia. Samples were collected during peak algal bloom month (January 2018) from two sampling sites, near the dam (S1) and at the center of the reservoir (S2). Identification and enumeration of phytoplankton taxa were done and the measurement of common hepatotoxin (MCs and NOD) concentrations was conducted using liquid chromatography-tandem mass spectrometry. In the reservoir, cyanobacteria made up to 98% of total phytoplankton abundance, with Dolichospermum and Microcystis spp, dominating the phytoplankton community. In these first cyanotoxin analyses conducted for a drinking water supply source in Ethiopia, six major MC variants, namely MC-dmRR, MC-RR, MC-YR, MC-dmLR, MC-LR, and MC-LA, were detected in both algal seston and water samples. MC-LR was the most dominant MCs variant, while nodularin was not detected for both sampling sites. Extracellular total MC concentrations (μg L−1) of 453.89 and 61.63 and intracellular total MC concentrations (μg L−1) of 189.29 and 112.34 were recorded for samples from S1 and S2, respectively. The high concentrations of extracellular MCs, with MC-LR constituting the greatest proportion, indicate the extremely high potential public health risk for end-users.

Allelopathic effect of rhubarb extracts on the growth of Microcystis aeruginosa

With its advantages of ecological safety, environmental affinity, and high selectivity, allelopathic technology has been widely developed for algae inhibition. However, obtaining effective allelochemicals and realizing their mechanism are difficult. In this paper, a Chinese herbal medicine, namely, Rheum palmatum L. (Chinese rhubarb), was utilized as a source of allelopathic substances for the first time. Four units of rhubarb organic extracts were collected to study the inhibition of growth, photosynthesis, proteins, and algal toxin of Microcystis aeruginosa. Results showed that the ethyl acetate, n-butanol, and aqueous phases of the rhubarb extracts have notable inhibitory effects. After a 16-day treatment, the four extracts reduced M. aeruginosa by 64.1%, 59.3%, 61.9%, and 7.2% with disruption of algal photosynthesis and protein synthesis and reduction of algal toxin.

Dredging mitigates cyanobacterial bloom in eutrophic Lake Nanhu: Shifts in associations between the bacterioplankton community and sediment biogeochemistry

Cyanobacterial blooms are a worldwide environmental problem, which is partly attributed to their access to excessive nitrogen (N) and phosphorus (P). Preventing the blooms by reducing N and P from internal inputs is viewed as a challenge. To evaluate the effects of dredging on cyanobacterial abundances and bacterioplankton communities, water and sediment samples were collected from eutrophic Lake Nanhu (Wuhan, China) before dredging (2017) and after dredging (2018). After dredging, significant decreases were observed for sediment nutrients (e.g., C, N, and P sources); C-, N-, P-, and S-cycling-related enzyme activity; N- and P-cycling-related gene abundance; microbial abundance; and dramatic changes were observed in the composition of the sediment microbial community. The release rates of nutrient including nitrogen, phosphorus, and organic matter decreased after dredging, and sediment biogeochemistry was closely correlated to nutrient release rates. Additionally, our observations and analyses indicated that the abundance and diversity of the bacterioplankton community decreased significantly, the composition and interaction of the bacterioplankton community dramatically changed, and the bacterioplankton community function (e.g., N, P-cycling-related enzymes and proteins) down regulated after dredging. Water and sediment physicochemical factors explained 72.28% variation in bacterioplankton community composition, and these physicochemical factors were significantly correlated with diversity, composition, and function of bacterioplankton community. Our findings emphasized that cyanobacterial blooms in freshwater ecosystems were closely correlated with noncyanobacterial bacterioplankton that were largely conserved at the phylum level, with Proteobacteria, Actinobacteria, and Bacteroidetes as the main taxa. To our knowledge, this is the first report clarifying the mechanism of cyanobacterial blooms mitigation by dredging, via changing the association between the bacterioplankton community and sediment biogeochemistry. Our findings are of significance and indicate that dredging is effective for mitigating cyanobacterial blooms.

Interactions of phosphate and dissolved organic carbon with lanthanum modified bentonite: Implications for the inactivation of phosphorus in lakes

Lanthanum-modified bentonite (LMB) is a widely used phosphorus-inactivating agent in lakes. However, dissolved organic carbon (DOC) exists ubiquitously in lakes, and its influence on phosphate binding is still not adequately understood. Our results showed that both phosphate and DOC can be adsorbed by LMB. The Langmuir adsorption maxima of phosphate and DOC were 9.06 mg P/g and 5.31 mg C/g, respectively, generating a C/P molar ratio ∼1.5. When phosphate and DOC coexisted at this ratio, the adsorption of phosphate was not influenced by DOC and vice versa. However, the phosphate capture by LMB was significantly reduced by raising the ratio above ∼9, and the reduction was increased with increasing the ratio. Once adsorbed by LMB, phosphate was essentially not desorbed by DOC, while adsorbed DOC can be mostly liberated by phosphate. It is deemed that phosphate can interact preferentially with La on LMB. However, DOC can still be adsorbed by LMB, even after LMB was saturated with phosphate, which was attributed to (i) the high coordination capacity of La; (ii) the interaction of DOC with the hydroxyl group(s) of the adsorbed phosphate via hydrogen bonding; and (iii) the interaction of DOC with the La sites unoccupied by phosphate. We proposed that LMB can be applied in the season (time) when the DOC/P ratio in lakes is low enough to facilitate the adsorption of phosphate, which will no longer be released into water, even after the C/P ratio is raised later.

Does external phosphorus loading diminish the effect of sediment dredging on internal phosphorus loading? An in-situ simulation study

Sediment dredging is an effective method to reduce internal phosphorus (P) loading of eutrophic lakes. However, external P loading may diminish the longevity of the effect of sediment dredging on P internal loading, and the mechanism of the same is unclear. Here, we used one-year in-situ simulation experiments to study the migration and transformation processes of P under the effect of external loading (suspended particle matter, SPM) input and internal loading control by dredging. The results showed that dredging can effectively reduce the internal loading and mobility of P, increase the P adsorption and retention capacity of the sediment, and improve the oxidation environment at the sediment-water interface (SWI), thus, inhibiting the release of internal P. The input of SPM, however, can significantly inhibit the above processes and increase the risk of P resupply and release. Temperature, dissolved oxygen, and the P resupply capacity (R) are the key factors affecting the P flux across the SWI. Therefore, it is necessary to control the input of SPM to effectively inhibit eutrophication after dredging. More measures to control the input of SPM, such as establishing buffer zones, ecological wetlands, and forebays, should be explored and applied.

Anoxia remediation and internal loading modulation in eutrophic lakes using geoengineering method based on oxygen nanobubbles

Benthic anoxia and internal P release, widely occurring in eutrophic lakes, are major factors threatening the health of aquatic ecosystems. In this paper, we experimentally evaluated the efficacy of a new type of "flock-lock" geoengineering method based on oxygen nanobubble technology to remediate sediment anoxia and reduce the internal P release in waters with and without algal blooms. Oxygen-carrying materials (OCM) modified from natural zeolites were used as capping agents and an oxygen-locking layer consists of OCM and the oxidized sediment was formed between anoxic sediment and overlying water. The synergy of diffusion and retention of oxygen in this layer contributes to both the increase of DO and reversal of anoxic conditions. By capping with OCM, the DO in overlying water improved instantly from around 1.5 mg/L to 3.5-4 mg/L and 5-6 mg/L in the systems with algal blooms and without algal blooms, respectively, and maintained throughout the incubation period. The oxygen penetration depth in the sediment can be significantly enhanced from around 0 cm to 3 cm and form an oxygen-locking layer at the end of the experiment by capping with OCM. The labile P was effectively retained via the re-oxidation of ferrous iron in this layer compared with the obvious release of labile P and Fe in control. More importantly, the oxygen depletion and labile P increase at the sediment-water interface caused by the decomposition of the deposited algal biomass can be substantially eliminated after capping with OCM. The study shed insights on the sustainable modulation of sediment anoxia and internal loading in eutrophic waters.

Impact of application mode on the control of phosphorus release from sediments using zirconium-modified bentonite as geo-engineering material

In this study, the influence of zirconium-modified bentonite (ZMBT) addition, capping, and addition/capping on the transport and transformation of phosphorus (P) in sediments were comparatively investigated using incubation experiments to determine the effect of ZMBT application mode on the controlling efficiency. Results showed that the release of soluble reactive P (SRP) from sediment to the overlying water was effectively intercepted by all the ZMBT treatments. The inactivation of pore-water SRP, diffusive gradients in thin films-labile P (DGT-LP) and mobile P (Mob-IP) in sediment played a pivotal role in the regulation of SRP liberation from the sediment to the overlying water by ZMBT. An application mode change from capping and addition/capping to addition resulted in a decline of the reduction efficiency of overlying water SRP by the ZMBT treatment to some extent. The variation in the reduction efficiency of pore-water SRP and DGT-LP in the uppermost sediment were responsible for the change of the reduction efficiency of overlying water SRP by the ZMBT treatment. A change in application mode from capping to addition/capping and addition caused an obvious increase in the immobilization efficiency of pore-water SRP, DGT-LP and Mob-IP in the lower sediment by the ZMBT treatment. Results of this work indicate that, when the ZMBT capping layer on the top of sediment was completely mixed with the sediment, although the stability of P in the lower sediment obviously increases, the controlling efficiency of SRP liberating from the sediment to the overlying water decreases to some extent. Thus, the repeated addition of ZMBT to form a covering layer on the ZMBT-amended sediment is very necessary for the effective control of sediment-P release to the overlying water.

Factors related to aggravated Cylindrospermopsis (cyanobacteria) bloom following sediment dredging in an eutrophic shallow lake

In recent years, Cylindrospermopsis raciborskii blooms have been widely found worldwide. Topics dealing with the mitigation of C. raciborskii bloom is of great importance for toxins produced could threaten public health. The paper first investigated C. raciborskii dynamics over three years following sediment dredging in a shallow eutrophic Lake Dongqian (China). Based on rpoC1 gene copies, C. raciborskii bloom formed with average density of 1.30 × 10⁶ cells/L on July 2009. One year later after sediment dredging, C. raciborskii cell density decreased below 1.17 × 10⁵ cells/L or under detected limits during summer days on 2010. While two years later, the C. raciborskii bloom period was returned with markedly increased cell density reaching up to 4.15 × 10⁷ cells/L on October 2011, and the maximum peak density was shown at 20.3 °C that was much lower than reported optimal growth temperature. Inferred from Spearman correlation analysis, linear regression showed C. raciborskii density was significant and positive with pH and SD, whereas they were significant and negative with TP and DO. Multiple regression analysis further demonstrated that TN, TP, SRP, pH and DO provided the best model and explained 53.1% of the variance in C. raciborskii dynamics. The approaches managing nutrients reduction might not control C. raciborskii bloom as extremely low TN (avg. 0.18 mg/L) and TP concentrations (avg. 0.05 mg/L) resulted in the highest C. raciborskii cell density after sediment dredging.

Assessment of iron-modified calcite/zeolite mixture as a capping material to control sedimentary phosphorus and nitrogen liberation

Calcite/zeolite mixture (CZ) can be used to construct a capping layer for the simultaneous management of phosphorus (P) and nitrogen (N) liberation from sediments into the overlying water (OVER-water). However, its control efficiency of sedimentary P release still needs to be improved. To address this issue, an iron-modified CZ (Fe-CZ) was synthesized, characterized, and employed as a capping material to simultaneously prevent P and N release from sediments into OVER-water. Batch and microcosm incubation experiments were performed to study the efficiency and mechanism for the control of P and N release from sediments by capping Fe-CZ. Results showed that sediment capping with Fe-CZ resulted in the significant reduction of soluble reactive P (SRP) and ammonium-N (NH₃-N) in OVER-water, with reduction rates of 77.8-99.7% and 54.0-96.7%, respectively. Furthermore, the Fe-CZ capping layer decreased the SRP concentration in the pore water (PORE-water) at depth of 0-30 mm and reduced the concentration of PORE-water NH₃-N at depth of 0-50 mm. Moreover, the Fe-CZ capping layer gave rise to the great decrement of the concentration of the labile P measured by DGT (diffusive gradient in thin films) technology (P-DGT) in the profile of OVER-water and sediment. Additionally, the Fe-CZ capping resulted in the reduction of redox-sensitive P (P-BD) in the 0-50 mm sediment and caused the transformation of P-BD to calcium-bound P (P-HCl) and residual P (P-RES) in the 0-10 mm sediment as well as to P-RES in the 10-20 mm sediment. Results of this work indicate that the Fe-CZ capping has a high potential for the simultaneous management of P and N release from sediments, and the decrease of the contents of sediment P-DGT, sediment P-BD, PORE-water SRP and PORE-water NH₃-N as well as the conversion of mobile P to more stable P in the top sediment should have a significant role in the simultaneous interception of sedimentary P and N liberation into OVER-water by the Fe-CZ capping.

Direct Effects of Temperature on Growth of Different Tropical Phytoplankton Species

Temperature increase may influence competition among phytoplankton species, potentially intensifying cyanobacteria blooms that can be favored by direct and indirect effects of temperature. In this study, we aimed to clarify how cyanobacteria can be favored by the direct effects of increased temperature compared to diatoms and chlorophytes. Strains of the most representative species of a eutrophic coastal lagoon (Microcystis aeruginosa, Planktothrix agardhii, Desmodesmus communis, and Cyclotella meneghiniana) were used to test the hypothesis that cyanobacteria would be favored by the direct effect of temperature increase. First, we evaluated the effect of temperature increase on growth in monocultures (batch and chemostats) at 25 and 30 °C and after in mixed cultures (chemostats). In batch monocultures, the cyanobacteria showed higher growth rates in 30 °C than in 25 °C. However, in continuous culture experiments (chemostats), growth rates of M. aeruginosa and P. agardhii were not affected by temperature, but the strains showed higher biovolume in steady-state with the temperature increase. In continuous mixed cultures, M. aeruginosa was always dominant and C. meneghiniana was excluded, regardless of temperature tested. D. communis was able to coexist with lower biomass. This study shows that rising temperatures can be detrimental to diatoms, even for a tropical strain. Although some studies indicate that the dominance of cyanobacteria in warmer climates may be due to the indirect effect of warming that will promote physical conditions in the environment more favorable to cyanobacteria, the outcomes of mixed cultures demonstrate that the direct effect of temperature can also favor the dominance of cyanobacteria.

Simultaneous control of nitrogen and phosphorus release from sediments using iron-modified zeolite as capping and amendment materials

The use of zeolite as a geo-engineering tool has a high potential to control nitrogen (N) release from sediments, but its efficiency for controlling sedimentary phosphorus (P) release still need to be further increased. To address this issue, this work synthesized an iron-modified zeolite (IM-Z) by coating iron onto the surface of natural zeolite (NAT-Z) and then the as-obtained IM-Z was utilized as a geo-engineering material to block the upward mobilization of N and P from sediments to the overlying water. The efficiencies of IM-Z covering and amendment to prevent the liberation of N and P from sediments were evaluated, and the controlling mechanism was explored. Capping and amendment with IM-Z not only resulted in the tremendous reduction of the levels of ammonium-N (NH₄⁺-N) and reactive soluble P (RSP) in the overlying water, but also led to the decrease of the contents of NH₄⁺-N and RSP in the pore water. More importantly, sediment capping and amendment with IM-Z resulted in the formation of a static layer in the upper sediment directly below the sediment-water interface, with very low concentration of RSP in the pore water. In addition, IM-Z capping and addition effectively immobilized the diffusive gradients in thin films (DGT)-labile P in the overlying water and sediment. Furthermore, the decrease of the DGT-labile Fe concentrations in the overlying water as well as the top sediment were also observed after IM-Z capping and addition. Nearly 70% of P bound by IM-Z is stable and difficult to be released back into the overlying water under common pH and anoxic conditions. The adsorption of pore water NH₄⁺-N on IM-Z, the immobilization of pore water RSP and DGT-labile P by IM-Z and the uptake of DGT-labile Fe on IM-Z played a significant role in the simultaneous control of NH₄⁺-N and RSP liberation. Compared to NAT-Z, the efficiency of IM-Z to block the liberation of sedimentary P was higher. Results of this study demonstrate that IM-Z is suitable for use in the simultaneous interception of the upward transportation of NH₄⁺-N and RSP from sediments into the overlying water.

Dredging project caused short-term positive effects on lake ecosystem health: A five-year follow-up study at the integrated lake ecosystem level

Sediment dredging is a controversial technology for lake eutrophication control. A lengthy and holistic assessment is important to understand the effects of a dredging project on a lake ecosystem. In this study, a dredging project was followed for 5 years. To understand the variations of lake ecosystems before, during and after the project, water quality, phytoplankton, zooplankton and benthic animal biomass were monitored; Four subindicators, including eco-exergy (Ex), structural eco-exergy (Ex_st), buffer capacity of total phosphorus for phytoplankton (β_(TP)(phyto)) and trophic level index (TLI) were calculated and developed to an integrated ecosystem health indicator (EHI). The monitoring results showed that the dredging project caused many short-term positive effects such as decreased total nitrogen, total phosphorus, permanganate index and phytoplankton biomass throughout the entire lake water, increased Secchi disk depth in the whole lake and increased benthonic animal biomass in the nondredged regions. However, these positive effects disappeared overtime. Water chemistry and biomass returned to the initial state before dredging. EHI showed that the dredging project caused negative effects on the lake health in the dredged region at first. Subsequently, the health status of the entire lake, including the dredged and nondredged regions, improved until 1-2 years after the project finished. Because of the lack of other timely ecological restoration measures, the lake gradually returned to its initial health status. However, the health status in the dredged regions was only slightly better than before dredging and often worse than that of the nondredged regions. Our study suggested that dredging projects may only cause short-term positive effects on lake ecosystem health. The external interception and dredging ratio were important. A dredging project should be combined with other ecological lake restoration measures when the project has caused positive effects in a lake.

Cyanobacterial removal by a red soil-based flocculant and its effect on zooplankton: an experiment with deep enclosures in a tropical reservoir in China

As one kind of cheap, environmentally-friendly and efficient treatment materials for direct control of cyanobacterial blooms, modified clays have been widely concerned. The present study evaluated cyanobaterial removal by a red soil-based flocculant (RSBF) with a large enclosure experiment in a tropical mesotrophic reservoir, in which phytoplankton community was dominated by Microcystis spp. and Anabaena spp. The flocculant was composed of red soil, chitosan and FeCl₃. Twelve enclosures were used in the experiment: three replicates for each of one control and three treatments RSBF₁₅ (15 mg FeCl₃ l^-1), RSBF₂₅ (25 mg FeCl₃ l^-1), and RSBF₃₅ (35 mg FeCl₃ l^-1). The results showed that the red soil-based flocculant can significantly remove cyanobacterial biomass and reduce concentrations of nutrients including total nitrogen, nitrate, ammonia, total phosphorus, and orthophosphate. Biomass of Microcystis spp. and Anabaena spp. was reduced more efficiently (95%) than other filamentous cyanobacteria (50%). In the RSBF₁₅ treatment, phytoplankton biomass recovered to the level of the control group after 12 days and cyanobacteria quickly dominated. Phytoplankton biomass in the RSBF₂₅ treatment also recovered after 12 days, but green algae co-dominated with cyanobacteria. A much later recovery of phytoplankton until the day of 28 was observed under RSBF₃₅ treatment, and cyanobacteria did no longer dominate the phytoplankton community. The application of red soil-based flocculant greatly reduces zooplankton, especially rotifers, however, Copepods and Cladocera recovered fast. Generally, the red soil-based flocculant can be effective for urgent treatments at local scales in cyanobacteria dominating systems.

Role of divalent metals Cu2+ and Zn2+ in Microcystis aeruginosa proliferation and production of toxic microcystins

Cu²⁺ and Zn²⁺, two ubiquitous metals in water environments, can widely trigger algae blooms at favourable environmental conditions. This paper elucidates the roles of Cu²⁺ and Zn²⁺ in the proliferation of Microcystis aeruginosa (M. aeruginosa) and synthesis of Microcystins (MCs). Findings indicate significant influences of increasing Cu²⁺ and Zn²⁺ concentrations on cell proliferation at limited available phosphorus concentrations of less than 0.1 mg/L. By contrast, Cu²⁺ and Zn²⁺ notably affected MCs production at all the inoculated phosphorus concentrations. The critical concentrations of 1 μg/L and 5 μg/L for Cu²⁺ and Zn²⁺, respectively, are determined to trigger rapid cell proliferation and MCs production. Furthermore, the impacts of Cu²⁺ and Zn²⁺ on nitrogen absorption and, subsequently, on amino acids (AAs) formation in cells, is likely key in MCs synthesis. The two AAs Alanine (Ala) and glutamic acid (Glu) demonstrate the most notable variations with the concentrations of Cu²⁺ & Zn²⁺.