Eutrophic Lake Water Research Articles

Adaptable Plasmonic Membrane Sensors for Fast and Reliable Detection of Trace Low-Micrometer Microplastics in Lake Water.

In freshwater environments, low-micrometer microplastics (LMMPs) have captured significant attention due to their prevalence and toxicity. Yet, rapid detection of LMMPs (1-10 μm) at the single-particle level within complex freshwater matrices remains a hurdle. We developed an adaptable plasmonic membrane sensor for fast detection of individual LMMPs in eutrophic lake waters. The plasmonic membrane sensor functions both as a membrane filter and as a sensor for LMMP collection and analysis. Among the four types of membrane sensors, polycarbonate track-etch (PCTE) membrane sensors exhibit superior imaging quality for LMMPs due to their flat and homogeneous surfaces. Besides the significantly improved imaging contrast and reduced background interferences, the Raman intensity of LMMPs is enhanced by 48% ± 25% on PCTE membrane sensors compared to unmodified membranes. The increased Raman intensities of a chemical probe with an increasing gold layer thickness and a decreasing membrane pore size suggest a surface-enhanced Raman scattering effect from the membrane sensors. The membrane sensors achieve a detection limit of 1 μg/L and an ultrafast scanning time of 0.01 s for individual LMMPs across natural eutrophic lake water. The developed membrane sensors offer an adaptable tool for the swift and reliable detection of individual LMMPs in complex environmental matrices.

Lacustrine groundwater discharge-derived carbon and nitrogen to regulate biogeochemical processes as revealed by stable isotope signals in a large shallow eutrophic lake

Eutrophic shallow lakes are hotspots of carbon (C) and nitrogen (N) accumulation and transformation, and are increasingly recognized as important sources of greenhouse gases (GHGs: CO2, CH4 and N2O). Lacustrine groundwater discharge (LGD) is a crucial component of the water budget and terrestrial material delivery for lakes, but its interplays with intrinsic CN biogeochemical processes remain less tackled. In this study, C and N ingredients and multiple stable isotopes (δ2H, δ18O, δ13C, and δ15N) were measured seasonally in groundwater, river water and lake water of a large eutrophic shallow lake in eastern China. The results revealed that groundwater is enriched with various forms of C and N that have similar sources and pathways as surface water in the lake and rivers. The isotope balance model also indicated that LGD derived C and N contribute significantly to lake inventories in addition to river runoff. These allochthonous C and N provide extra substrates for related biogeochemical processes, such as algae proliferation, organic matter degradation, methanogenesis and denitrification. Simultaneously, the excess oxygen consumption leads to depletion and hypoxia in the lake, further facilitating the processes of methanogenesis and denitrification. LGD functions not only as an external source of C and N that directly increases GHG saturations, but also as a mediator of internal CN pathways, which significantly affect hypoxia formation, GHG productions and emissions in the eutrophic lake. This study highlights the unrevealed potential regulation of LGD on biogeochemical processes in the eutrophic lake, and underscores the need for its consideration in environmental and ecological studies of lakes both regionally and globally.

Alkaline Phosphatase Activity and Phosphatase-Active Bacteria in Lake Baikal Water Column and Major Tributaries

Phosphorus is one of the major biogenic elements. Its inflow facilitates eutrophication of lake water. In aquatic ecosystems, phosphorus is present mostly in organic compounds. Ability of aquatic microorganisms to assimilate phosphorus from organophosphorous compounds results from activity of alkaline phosphatases; activity of these enzymes may be an indicator of the state of the ecosystem, phosphate load, and water quality. In the present work, alkaline phosphatase activity (APA) and abundance of phosphatase-active bacteria (PAB) in Lake Baikal pelagic zone and in the mouths of its major tributaries was studied. In the pelagic zone, APA and PAB abundance decreased with depth, indicating that the main processes of phosphate generation occurred in the trophic layer of the lake. In the main tributaries, both APA and PAB abundance were considerably higher than in the pelagic zone. These results indicate active biochemical processes of transformation of organophosphorous compounds occur in the estuarine zones of the rivers. The degradation processes result in regeneration of phosphates, which are completely incorporated in the biological turnover, providing for phytoplankton development.

Lanthanum and cerium functionalised forestry waste biochar for phosphate removal: Mechanisms and real-world applications

Phosphorus as a diminishing finite resource, yet is an essential element for the growth of biota. However, elevated concentrations in water can imbalance ecosystems and cause eutrophication. To address both problems, two highly efficient biochars, namely La-OB and CeLa-OB were synthesised by lanthanum and cerium doping. The performance of La-OB and CeLa-OB were evaluated in both batch and dynamic regimes with synthetic phosphate (PO43--P) solutions and eutrophic lake water. PO43--P adsorption mechanisms were investigated in terms of pH, kinetics, isotherms, activation energy, thermodynamics and using in-depth characterisation (XPS, FTIR, XRD, BET, pHpzc and SEM-EDX). The feasibility of using such biochar in ‘real life’ situations was studied with column filtration of lake water with low and high PO43--P concentrations. Reusability/desorption and toxicity in the water environment was also considered. The mechanistic study showed that both biochars predominantly had inner-sphere complexes with La and Ce ligands (as a monolayer), while outer-sphere complexation was less common. The exothermic adsorption process followed the Elovich kinetic and Langmuir isotherm models, with a maximum adsorption capacity of 112 mg/g for La-OB and 40 mg/g for CeLa-OB. In column filtration trials the adsorption capacity reached 78 mg/g, while low metal leaching (0.08 mg/L) and low toxicity to Lepidium sativum germination were detected. The results indicated that these biochars, especially La-OB, could be used in circular economy-based water treatment.

Photocatalytic peroxydisulfate activation for dissolved organic matter degradation in eutrophic lake water using S-scheme BiVO4/g-C3N4 3D/2D heterojunction under visible light

Large amounts of carbon are stored primarily in dissolved organic matter (DOM), which plays an important indicator of lake eutrophication. However, removing DOM from eutrophic lakes remains a major challenge. Herein, a novel S-scheme flower-like microsphere BiVO4/nanosheet g-C3N4 3D/2D heterojunction was successfully constructed using a two-step method for DOM degradation of real eutrophic lake water in the presence of peroxydisulfate (PDS). 1.0-BiVO4/g-C3N4/PDS exhibited highly efficient photocatalytic performance with an 87.8 % removal rate of DOM for 60 min, which was 5.3 and 8.9 times higher than BiVO4/PDS and g-C3N4/PDS, respectively. Sulfate radical (·SO4−), hydroxyl radical (·OH) and singlet oxygen (1O2) were mainly responsible for DOM degradation in the 1.0-BiVO4/g-C3N4/PDS system, and the transformation pathway of 1O2 was emphatically analyzed. In addition, the changes of fluorescence components in DOM were detected using synchronous fluorescence spectra, second derivative spectra, and two-dimensional correlated spectroscopy analysis. Humic-like fluorescence, fulvic-like fluorescence, and protein-like substances were removed higher than 85.30 %, 73.02 %, and 67.23 % by the 1.0-BiVO4/g-C3N4 catalyst activating the PDS under visible light (VL), respectively. When the toxicity of catalytically treated eutrophic lake water was estimated by growth inhibition of Escherichia coli, the biotoxicity of DOM decreased continuously in the BiVO4/g-C3N4/PDS/VL coupling process. Theoretical calculations and photoelectrochemical tests suggested that the BiVO4/g-C3N4/PDS catalytic activity enhancement was attributed to the S-scheme mechanism and hybrid advanced oxidation process. It is expected that this work can provide new insight into DOM degradation in eutrophic lake water by the heterogeneous photocatalysis combined with the PDS activation system.

Rates of palaeoecological change can inform ecosystem restoration

Abstract. Accelerations of ecosystem transformation raise concerns, to the extent that high rates of ecological change may be regarded amongst the most important ongoing imbalances in the Earth system. Here, we used high-resolution pollen and diatom assemblages and associated ecological indicators (the sum of tree and shrub pollen and diatom-inferred total phosphorus concentrations as proxies for tree cover and lake-water eutrophication, respectively) spanning the past 150 years to emphasize that rate-of-change records based on compositional data may document transformations having substantially different causes and outcomes. To characterize rates of change also in terms of other key ecosystem features, we quantified for both ecological indicators: (i) the percentage of change per unit time, (ii) the percentage of change relative to a reference level, and (iii) the rate of percentage change per unit time relative to a reference period, taking into account the irregular spacing of palaeoecological data. These measures document how quickly specific facets of nature changed, their trajectory, as well as their status in terms of palaeoecological indicators. Ultimately, some past accelerations of community transformation may document the potential of ecosystems to rapidly recover important ecological attributes and functions. In this context, insights from palaeoecological records may be useful to accelerate ecosystem restoration.

Factors of the slow decline in the activity concentration of 137Cs in eutrophic lake water

Factors of the slow decline in the activity concentration of ¹³⁷Cs in eutrophic lake water

Effects of the fungicide azoxystrobin in two habitats representative of mediterranean coastal wetlands: A mesocosm experiment

This paper investigates the effects of the fungicide azoxystrobin, a compound widely used in rice farming, on aquatic communities representative of two habitats characteristic of Mediterranean wetland ecosystems: water springs and eutrophic lake waters. The long-term effects of azoxystrobin were evaluated on several structural (phytoplankton, zooplankton, macroinvertebrate populations and communities) and functional (microbial decomposition, macrophyte and periphyton growth) parameters making use of freshwater mesocosms. Azoxystrobin was applied in two pulses of 2, 20, 200 µg/L separated by 14 d using the commercial product ORTIVA (23 % azoxystrobin w/w). The results show that these two habitats responded differently to the fungicide application due to their distinct physico-chemical, functional, and structural characteristics. Although overall sensitivity was found to be similar between the two (lowest NOEC < 2 µg/L), the taxa and processes that were affected differed substantially. In general, the most sensitive species to the fungicide were found in the water spring mesocosms, with some species of phytoplankton (Nitzschia sp.) or macrocrustaceans (Echinogammarus sp. and Dugastella valentina) being significantly affected at 2 µg/L. In the eutrophic lake mesocosms, effects were found on phytoplankton taxa (Desmodesmus sp. and Coelastrum sp.), on numerous zooplankton taxa, on chironomids and on the beetle Colymbetes fuscus, although at higher concentrations. The hemipteran Micronecta scholtzi was affected in both treatments. In addition, functional parameters such as organic matter decomposition or macrophyte growth were also affected at relatively low concentrations (NOEC 2 µg/L). Structural Equation Modelling was used to shed light on the indirect effects caused by azoxystrobin on the ecosystem. These results show that azoxystrobin is likely to pose structural and functional effects on Mediterranean wetland ecosystems at environmentally relevant concentrations. Moreover, it highlights the need to consider habitat-specific features when conducting ecotoxicological research at the population and community levels.

Differential response of Hg-methylating and MeHg-demethylating microbiomes to dissolved organic matter components in eutrophic lake water

Methylmercury (MeHg) production in aquatic ecosystems is a global concern because of its neurotoxic effect. Dissolved organic matter (DOM) plays a crucial role in biogeochemical cycling of Hg. However, owing to its complex composition, the effects of DOM on net MeHg production have not been fully understood. Here, the Hg isotope tracer technique combined with different DOM treatments was employed to explore the influences of DOM with divergent compositions on Hg methylation/demethylation and its microbial mechanisms in eutrophic lake waters. Our results showed that algae-derived DOM treatments enhanced MeHg concentrations by 1.42−1.53 times compared with terrestrial-derived DOM. Algae-derived DOM had largely increased the methylation rate constants by approximately 1−2 orders of magnitude compared to terrestrial-derived DOM, but its effects on demethylation rate constants were less pronounced, resulting in the enhancement of net MeHg formation. The abundance of hgcA and merB genes suggested that Hg-methylating and MeHg-demethylating microbiomes responded differently to DOM treatments. Specific DOM components (e.g., aromatic proteins and soluble microbial byproducts) were positively correlated with both methylation rate constants and the abundance of Hg-methylating microbiomes. Our results highlight that the DOM composition influences the Hg methylation and MeHg demethylation differently and should be incorporated into future Hg risk assessments in aquatic ecosystems.

Algal organic matter inhibits methylmercury photodegradation in eutrophic lake water: A dynamic study

Algal organic matter (AOM) is a major component of dissolved organic matter (DOM) in eutrophic lakes and could impact the photodegradation of neurotoxic methylmercury (MeHg) in water. Predicting these effects, however, is challenging, largely due to the dynamic changes of AOM during algal decomposition. Here, we investigated the effects of AOM on MeHg photodegradation throughout the algal decomposition process and elucidated these effects by characterizing dynamic changes of AOM and exploring the respective roles of various reactive oxygen species (ROS). Our results reveal that AOM derived from algal decomposition significantly inhibits MeHg photodegradation, and the extent of this inhibition varies depending on the specific lakes (8–21 %, p < 0.05) and their eutrophication states (16–28 %, p < 0.05). The inhibitory effect gradually weakened as the decomposition progressed, which may be attributed to the dynamic changes in the quantity and quality of AOM. Moreover, hydroxyl radical (·OH) was found to be the main contributor in driving MeHg photodegradation (15–23 %) during the early stages of decomposition (day 0–3), while in the later stage (day 12–24), the role of singlet oxygen (1O2, 15–20 %) and (3DOM*, 21–30 %) gradually strengthened and these three ROS jointly drove MeHg photodegradation. Based on our findings and recent studies, we propose that AOM derived from algal decomposition plays a vital role in increasing the risk of MeHg in eutrophic lakes. It promotes MeHg formation while simultaneously inhibiting its photodegradation. Integrating AOM-MeHg interactions into Hg biogeochemical cycling models would reduce uncertainties when predicting MeHg risks.

The effects of nutrient loading from different sources on eutrophication in a large shallow lake in Southeast China.

Lake water eutrophication has become one of the leading obstacles to sustainable economic development in China. Research on the effects of mainstream currents on reservoirs has been relatively underdeveloped compared with research on tributaries, though changes in the water-sediment transport regime in a downstream river may affect nutrient transport behavior in a lake connected to that river. This is particularly problematic because certain wastewater sources, including runoff from agricultural wastes and industrial discharges, adversely affect lake water. Our study focused on Sanshiliujiao Lake, a significant drinking water source in Fujian, Southeast China, that has suffered considerably from eutrophication over the past few decades. This study aimed to estimate the phosphorus and nitrogen loads to the lake, exploring their sources and their ecologic effects using in situ observation and the export coefficient model. Our results showed that the pollution loads of total phosphorus (TP) and total nitrogen (TN) were 2.390 and 46.040 t/year, respectively, most of which were derived from the water diversion (TP 45.7%, TN 29.2%) and non-point source (TP 30.2%, TN 41.6%). The TN input was the highest in East river (3.557kg/d), followed by Red river (2.524kg/d). During the wet season, the input of TP and TN increased by 14.6 and 18.7 times, respectively, but produced only slight variations in concentration. Water diversion enriched the nutrients inputs and altered the structure and abundance of phytoplankton communities. In addition, when water flows from the main river directly to Sanshiliujiao Lake, algal blooms in river-connected lakes are significantly exacerbated, so our study may also serve as a theoretical basis to regulate eutrophication in Sanshiliujiao Lake.

Practices for Eutrophic Shallow Lake Water Remediation and Restoration: A Critical Literature Review

Lake water has been impaired with nutrients due to the synergic action of human-made activities and climate change. This situation is increasing eutrophication around the globe faster than before, causing water degradation, loss of its uses, and water-associated economic and health effects. Following the Sustainable Development Goal 6, more precisely its target 6.6, nations are already behind schedule in protecting and restoring water-related ecosystems (i.e., rivers and lakes). As concerns with eutrophication are escalating, eutrophic water remediation practices are the keys for restoring those lake waters. Diverse methodologies have been investigated focusing on the nutrient that limit primary productivity (i.e., phosphorus), but few have been applied to in-lake eutrophic water remediation. Thus, the objective of this paper is to provide an overview and critical comments on approaches and practices for facing eutrophic lake water remediation. Information on the successful cases and possible challenges/difficulties in the peer-reviewed literature are presented. This should be useful for supporting further remediation project selection by the stakeholders involved. In summary, for a successful and durable restoration project, external nutrient inputs need to be managed, followed by holistic and region-specific methods to attenuate internal legacy nutrients that are continually released into the water column from the sediment. When aligned well with stakeholder participation and continuous monitoring, these tools are the keys to long-lasting water restoration.

Phosphorus Recovery from Eutrophic Lake Water Using Al/Fe Micro-Electrolysis

Phosphorus (P) is a critical and nonrenewable resource. P crisis threatens future global food security, while P-induced eutrophication is damaging aquatic ecosystems. In eutrophic lakes, P is often heavily concentrated in algae-accumulated zones, creating “P reserves” for reuse. In this study, P was harvested from eutrophic lake water using Al/Fe micro-electrolysis and the stability of the harvested P was tested through anoxia incubation. The results showed that, compared with Fe micro-electrolysis, Al micro-electrolysis was more effective at co-harvesting dissolved and particulate P, and the yields were stable under anoxia conditions, making them suitable as slow-release P fertilizers. At 15 V, the P harvesting efficiency of Al micro-electrolysis was 2.68 times higher than that of Fe micro-electrolysis. This could be attributed to the powerful netting–bridging of amorphous Al hydroxides, which favor floatation separation and thereby P harvesting. Under anoxia, the transformation of Fe species caused P release from Fe micro-electrolysis yields, potentially enhancing P loss through leaching if the yields are used as soil P fertilizers. This study provides a promising strategy for P resource recycling from eutrophic lakes, which may be beneficial to the restoration of lake ecosystems and mitigation of the P crisis.

Complete Genome Sequences of Three Polynucleobacter sp. Subcluster PnecC Strains, KF022, KF023, and KF032, Isolated from a Shallow Eutrophic Lake and a River in Japan.

The genus Polynucleobacter subcluster PnecC consists of bacteria representing the ubiquitous taxon of freshwater bacterioplankton. Here, we report the complete genome sequences of three Polynucleobacter sp. (PnecC) strains, namely, KF022, KF023, and KF032, which were isolated from surface water of a temperate shallow eutrophic lake and its inflow river in Japan.

Applying synchronous fluorescence spectra with Gaussian band fitting and two-dimensional correlation to characterize structural composition of DOM from soils in an aquatic-terrestrial ecotone

Dissolved organic matter (DOM), the primary participant of carbon and nitrogen cycle, has a great impact on the behavior and fate of organic pollutants and heavy metals in eutrophic lakes. The dynamic spectral properties of DOM fractions were revealed in an aquatic-terrestrial ecotone under the different types of land use. Composite soil samples of different depths (0–20, 20–40 and 40–60 cm) were collected from four different land uses along a disturbed-impact gradient in Taihu Lake, China, i.e., grassland (GRL), forest land (FOL), paddy field (PAF), and vegetable field (VEF). DOM mainly consisted of tyrosine-like material (TYLF), tryptophan-like material (TRLF), microbial humic-like material (MHLF), fulvic-like material (FLF) and humic-like material (HLF) within all soil profiles, where TRLF was the dominant component (61.30 %) using synchronous fluorescence spectroscopy (SFS) combined with principal component analysis and Gaussian band fitting. Based on two-dimensional correlation spectroscopy with SFS and Fourier transform infrared, the variation order of DOM fractions was FLF → MHLF → HLF → TRLF → TYLF within the GRL soil profile, and MHLF exhibited an oppositive change with aliphatic OH and amide I in protein. The order of DOM fractions was MHLF → FLF → HLF → TYLF → TRLF within the FOL soil profile, and the change trend of MHLF remained oppositive with aliphatic OH and CO in ester. The order of DOM within the PAF soil profile fractions was TRLF → MHLF → HLF → TYLF → FLF, and changing trends of TYLF were oppositive to aliphatic OH, CH bending vibration, CH bending vibration and CO in ester. The order of DOM fractions was HLF → TYLF → TRLF → FLF → MHLF within the VEF soil profile, where the changing trend TYLF remained oppositive to aliphatic OH, CH deformations in lignin and aliphatic group and amide I in protein. This study may provide important support for alleviating lake water eutrophication or pollution.

Amplified cyanobacterial bloom is derived by polyphosphate accumulation triggered by ultraviolet light

Cyanobacterial blooms appear more strongly, constantly and globally, yet the positive effect of surface solar ultraviolet radiation (UV) on cyanobacterial bloom in natural freshwater habitats is largely ignored. Here in-situ and laboratory studies were jointly designed to probe the mechanism of cyanobacterial bloom promoted by solar UV light. The results showed that solar UV light is a key trigger factor for the accumulation of total phosphorus, dissolved inorganic phosphorus and polyphosphate (polyP) in blooming cyanobacterial cells. The increase of UV dose induces polyP accumulation to result in the excessive phosphorus uptake of blooming cyanobacteria, which provides sufficient phosphorus for cyanobacterial growth in suitable environment. Solar UV light also can promote the contents of phycocyanin, allophycocyanin, and phycoerythrin, producing sufficient ATP by photosynthesis for polyP synthesis in cyanobacterial cells in lake enviroment. The frequent variations of UV irradiance exposure prompts cyanobacteria to absorb excessive phosphorus from suspended solid or sediment. Cyanobacterial intracellular phosphorus is accumulated for their growth. UV light promotes polyP accumulation in blooming cyanobacterial cells to avoid damage. The adsorption amount of phosphorus increases for exuberant growth and then more surface blooming cyanobacteria are exposed to UV light to absorb ample phosphorus. Thus, the positive feedback occurs in lake water bodies with abundant phosphorus. This amplified cycle of cyanobacterial density and phosphorus due to solar UV light in eutrophic water bodies is analogous to a triode to amplify visible photosynthesis by UV light as a base electric current in the energy flow process in lake environment, therefore, “Cyanobacterial Phosphorus Assimilation Ultraviolet Effect” is used to describe this phenomenon. A new explanation is provided for the continuing proliferating mechanism of cyanobacterial bloom. Besides, a new perspective appears on the outbreak of cyanobacterial blooms in natural eutrophic lake water bodies worldwide.

Impact of cyanobacterial bloom intensity on plankton ecosystem functioning measured by eukaryotic phytoplankton and zooplankton indicators

Cyanobacterial blooms are global threats to freshwater ecosystem functioning, human health, and ecoservices. We assessed impacts of cyanobacterial bloom intensity on plankton ecosystem functioning using eukaryotic phytoplankton and zooplankton indicators and associated key physicochemical data collected from four seasons of two years at 24 evenly distributed sites in Lake Taihu that has year-around cyanobacterial blooms. Our analyses involved comparison of four site-groups with different bloom intensities and analyzing all sampling sites together using comparison, hierarchical partitioning analysis, generalized additive mixed model, and structural equation model. We found that cyanobacterial abundance positively associated with TP and temperature (negatively with TN:TP), while phytoplankton positively associated with TN. There was an inverse relation trend between relative abundances of phytoplankton and cyanobacteria, but there was no clear trend between absolute abundances of phytoplankton and cyanobacteria. Rotifers were most dominant when cyanobacteria were unabundant, while cladocerans presented higher abundance when cyanobacteria were in high abundance. Phytoplankton functional richness and species richness negatively and zooplankton functional richness and species richness positively associated with cyanobacterial bloom intensity. Cyanobacterial bloom intensity negatively associated with resource use efficiencies (RUEs) of phytoplankton and rotifers, and positively associated with RUE of cladocerans. Our analytical approach of integrating comparison of site-groups and analyzing all sites together uncovered how cyanobacterial bloom intensity shifted and altered physicochemical and biological conditions and plankton ecosystem functioning, and identified the mechanism and strength of the interactive linkages among physicochemical and biological indicators. Although our results may be different from oligotrophic lakes or reservoirs, our findings provide new insights in understanding the impacts of cyanobacterial bloom intensity on the dynamics of plankton communities and ecosystem functioning for polymictic eutrophic lakes, which may have broad application in enhancing the knowledge of this subject and provides the science base for managing polymictic eutrophic lake water quality and ecosystem functioning.

Efficient Microcystis removal and sulfonamide-resistance gene propagation mitigation by constructed wetlands and functional genes analysis

Increasingly prevalent Microcystis blooms and the propagation of the associated resistance genes represent global environmental problems. Constructed wetlands (CWs) are a cost-effective technology used for wastewater treatment. In this study, the herb Alisma orientale and three industrial byproducts, namely, blast furnace slag, biochar, and sawdust, were selected to construct mini-CW units. Their potential to remediate toxic Microcystis and their influences on the behaviors of antibiotic-resistant genes (ARGs, sul1, sul2, and intl1) were analyzed. Approximately 98.46% of Microcystis cells were removed by the sawdust-based CW in just 2 d, wherein <0.37 μg/L residual microcystin (MC)-LR was detected, with a removal efficiency of >96.47%, which is potentially caused by the higher relative abundance of MC-degrading gene mlrA on the substrate. Lower target ARG accumulations in the sawdust-based CW may be attributed to the lower intl1 relative abundance and microbial function mobile element content, which could influence horizontal gene transfer. In three sequential batches for the treatment of eutrophic lake water, six sawdust-based CW units were assembled into CW microcosms. The efficiency of removal of Microcystis and MC-LR by planted CW microcosms ranged between 92.00% and 95.88% and between 86.48% and 94.82%, respectively; this was significantly (P < 0.05) higher than that by unplanted ones. Less accumulation of target ARGs was also observed in planted CWs. Planting considerably improved nitrogen removal, possibly owing to the enrichment of genes involved in the KEGG nitrogen metabolism pathway in the substrate through metagenomic analysis.

Drinking water treatment residual as a ballast to sink Microcystis cyanobacteria and inactivate phosphorus in tropical lake water

The combination of a low dose of coagulant with a ballast that can inactive phosphorus (P) in lake sediment—a technique known as “flock and lock”—is one method for restoration of eutrophic lakes. The effectiveness of a drinking water treatment residual (DWTR) as a ballast in flock and lock was assessed using assays of eutrophic lake water from Thailand dominated by Microcystis aeruginosa cyanobacteria colonies by measuring changes in chlorophyll-a, pH, and zeta potential. P sorption isotherms were developed from long-term batch equilibrium experiments; desorption of nutrients and metals was assessed via leaching experiments; and morphological changes to cellular structure were assessed using scanning electron microscopy. Results showed that combining DWTR with a low dose of aluminum sulfate (0.6-4.0 mg Al/L) effectively sank 74-96% of Microcystis, with DWTR dose (50-400 mg/L), initial chlorophyll-a concentration (92-976 µg/L), pH (7.4-9.3), and alkalinity (99-108 ppm CaCO3) identified as factors significantly associated with sinking efficacy. P sorption capacity of the DWTR (7.12 mg/g) was significantly higher than a local soil (0.33 mg/g), enabling the DWTR to inactivate P in lake sediment. Desorption of Al, Fe, Ca and N from the DWTR was estimated to contribute to a marginal increase in concentrations of those compounds in the water column of a small shallow lake (1.2, 0.66, 53.4, and 0.07 µg/L, respectively) following a simulated application. Therefore, pre-treated DWTRs may be a viable alternative ballast in the flock and lock approach to lake restoration, supplementing or replacing modified local soils or lanthanum modified clays.

Antibiotic-accelerated cyanobacterial growth and aquatic community succession towards the formation of cyanobacterial bloom in eutrophic lake water

Antibiotics can stimulate the growth of model cyanobacterial species under pure culture conditions, but their influence on cyanobacterial blooms in natural aquatic ecosystems remains unclear. In this study, three commonly detected antibiotics (sulfamethoxazole, tetracycline, and ciprofloxacin) and their ternary mixture were proved to selectively stimulate (p < 0.05) the growth and photosynthetic activity of cyanobacteria in an aquatic microcosm at an environmentally relevant exposure dose of 300 ng/L under both oligotrophic and eutrophic conditions. Under the eutrophic condition, cyanobacteria reached a bloom density of 1.61 × 106 cells/mL in 15 days without antibiotics, while the cyanobacteria exposed to tetracycline, sulfamethoxazole, ciprofloxacin, and their ternary mixture exceeded this bloom density within only 10, 8, 7, and 6 days, respectively. Principal coordinate analysis indicated that the antibiotic contaminants accelerated the prokaryotic community succession towards the formation of a cyanobacterial bloom by promoting the dominance of Microcystis, Synechococcus, and Oscillatoria under the eutrophic condition. After 15 days of culture, the antibiotic exposure increased the density of cyanobacteria by 1.38–2.31-fold and 2.28–3.94-fold under eutrophic and oligotrophic conditions, respectively. Antibiotic exposure generated higher stimulatory effects on cyanobacterial growth under the oligotrophic condition, but the antibiotic(s)-treated cyanobacteria did not form a bloom due to nutrient limitation. Redundancy analysis indicated that the three target antibiotics and their ternary mixture affected the prokaryotic community structure in a similar manner, while tetracycline showed some differences compared to sulfamethoxazole, ciprofloxacin, and the ternary antibiotic mixture with regard to the regulation of the eukaryotic community structure. This study demonstrates that antibiotic contaminants accelerate the formation of cyanobacterial blooms in eutrophic lake water and provides insights into the ecological effects of antibiotics on aquatic microbial communities.