Sediment Physicochemical Properties Research Articles

Microorganisms Directly Affected Sediment Carbon–Nitrogen Coupling in Two Constructed Wetlands

Clarifying the carbon–nitrogen coupling pattern in wetlands is crucial for understanding the driving mechanism of wetland carbon sequestration. However, the impacts of plants and environmental factors on the coupling of carbon–nitrogen in wetland sediments are still unclear. Sediment samples from plant (Typha angustifolia and Phragmites australis)-covered habitats and bare land were collected in two constructed wetlands in northern China. The contents of different forms of carbon and nitrogen in sediments and plants, and the sediment microbial community were detected. It was found that the sediment carbon to nitrogen (C/N) ratios did not differ significantly in the bare sites of different wetlands, but did in the plant-covered sites, which highlighted the different role of plants in shifting the carbon–nitrogen coupling in different constructed wetlands. The effects of plants on the sediment carbon–nitrogen coupling differed in two constructed wetlands, so the structural equation model was used and found that sediment microorganisms directly affected sediment C/N ratios, while water and sediment physicochemical properties indirectly affected sediment C/N ratios by altering sediment microbial functions. Multiple linear regression models showed that water pH, sediment moisture content, water dissolved oxygen, and water depth had a greater influence on the carbon metabolism potential of the sediment microbial community, while sediment moisture content had the greatest impact on the sediment microbial nitrogen metabolism potential. The study indicates that variations in environmental conditions could alter the influence of plants on the carbon and nitrogen cycles of wetland sediments. Water environmental factors mainly affect microbial carbon metabolism functions, while soil physicochemical factors, especially water content, affect microbial carbon and nitrogen metabolism functions.

Response of microbial communities and biogeochemical cycling functions to sediment physicochemical properties and microplastic pollution under damming and water diversion projects

Understanding the interactions among flow-sediment, microorganisms, and biogeochemical cycles is crucial for comprehending the ecological response mechanisms of dams and water diversion. This study focused on the spatial patterns of carbon, nitrogen, phosphorus, and sulfur (CNPS) cycle functional genes in the water resource for the middle route of the South-to-North Water Diversion Project in China, specifically the Danjiangkou Reservoir (comprising the Han and Dan reservoirs). The investigation incorporated sediment physicochemical properties and microplastic pollution. Numerous microbial species were identified, revealing that microbial communities demonstrated sensitivity to changes in sedimentary mud content. The communities exhibited greater β diversity due to finer sediment particles in the Han Reservoir (HR), whereas in the Dan Reservoir (DR), despite having higher sediment nutrient content and MPs pollution, did not display this pattern. Regarding the composition and structure of microbial communities, the study highlighted that sediment N and P content had a more significant influence compared to particle size and MPs. The quantitative microbial element cycling (QMEC) results confirmed the presence of extensive chemolithotrophic microbes and strong nitrogen cycle activity stemming from long-term water storage and diversion operations. The denitrification intensity in the HR surpassed that of the DR. Notably, near the pre-dam area, biological nitrogen fixation, phosphorus removal, and sulfur reduction exhibited noticeable increases. Dam construction refined sediment, fostering the growth of different biogeochemical cycling bacteria and increasing the abundance of CNPS cycling genes. Furthermore, the presence of MPs exhibited a positive correlation with S cycling genes and a negative correlation with C and N cycling genes. These findings suggest that variations in flow-sediment dynamics and MPs pollution have significant impact the biogeochemical cycle of the reservoir.

Effect of temperature on surface fluid sediment properties with cyanobacterial bloom biomass accumulation

In eutrophic shallow lakes, cyanobacterial blooms will occur frequently and then settle into sediment, leading the formation of fluid sediment. Several factors including temperature can influence surface sediment properties. In this study, the influence of temperatures on surface sediment properties was determined in microcosm experiments through monitoring sediment physicochemical and rheological properties. During one-month incubation, it was found that surface sediment density and water content varied exponentially with increase in temperatures from 10 ℃ to 35 ℃. The results of particle size distribution indicated that cyanobacterial blooms biomass (CBB) degradation in sediment led to sediment flocculation and agglomeration. In the meantime, there were high ratios polysaccharide/protein in extracellular polymeric substances (EPSs), which enhanced the sediment particle agglomeration. Further, the yield stress in rheological test for sediment with (R2 = 0.97) and without (R2 = 0.85) CBB presented an exponential decay with increase in temperatures. And a threshold value at 20 ℃ for sediment critical shear stress (τcr) indicated that sediment could be resuspended easier when temperature was more than 20 ℃. Altogether, this study showed that the increase in temperatures with a threshold at 20 ℃, can cause sediment particle flocculation, resulting in a loose and fragile structure. And the results would be helpful to sediment management considering environmental effects of sediment suspension for eutrophication shallow lakes.

Occurrence, source apportionment and ecological risk of bisphenol analogues in river sediments in areas with different land use patterns

Bisphenol analogues (BPs) have gained increasing attention in recent years due to their ubiquitousness and potential endocrine disrupting properties in environments. However, little information is available on their spatiotemporal distribution, source apportionment and ecological risk in river sediments, especially the case in river basins with a high population density and those typical regions with agricultural-urban gradient, where land use patterns and intensity of human activity are varying. In this study, field investigations of BPs in the sediment of the entire Qinhuai River Basin, a typical agricultural-suburban agricultural-urban gradient area, were conducted before and after the flood period. Thirty-two sites were sampled for six types of BPs, resulted in no significant difference in the concentration of ΣBPs between the two periods, with ΣBPs ranging from 3.92 to 151 ng/g and 2.16–59.0 ng/g, respectively. Bisphenol A (BPA) was the main contributor. Whereas a multivariate analysis of variance (MANOVA) suggested that the composition structure of BPs had been influenced by water periods. The land use patterns had an impact on the distribution of ΣBPs in river sediments, which was more significant in after the flood period, with ΣBPs in urban rivers was 1.85 times, 3.44 times, and 3.08 times higher than the suburban rivers, agricultural rivers, and reservoirs, respectively. Yet land use types did not significantly alter the composition structure of BPs. The correlation analysis between BPs and the physicochemical properties of sediments showed a significant positive correlation between BPA and total organic carbon (TOC). The positive matrix factorization model (PMF) suggested that BPs in sediments of the basin might be influenced by industrial coatings, textiles, electronics and biopharmaceuticals, as well as urban wastewater or solid waste generated from daily life. The ecological risk assessment posed by BPA, based on the risk quotient, indicated that the ecological risk of BPA in sediments was low for three indicator benthic organisms: crustaceans, worms, and mollusks. However, the risk of BPA in river sediments varied among different land use patterns, with the risk ranking as follows: reservoirs < agricultural rivers < suburban rivers < urban rivers.

Microplastics enhance the invasion of exotic submerged macrophytes by mediating plant functional traits, sediment properties, and microbial communities

Plant invasions and microplastics (MPs) have significantly altered the structure and function of aquatic habitats worldwide, resulting in severe damage to aquatic ecosystem health. However, the effects of MPs on plant invasion and the underlying mechanisms remain largely unknown. In this study, we conducted mesocosm experiments over a 90-day period to assess the effects of polystyrene microplastics on the invasion of exotic submerged macrophytes, sediment physicochemical properties, and sediment bacterial communities. Our results showed that PS-MPs significantly promoted the performance of functional traits and the invasive ability of exotic submerged macrophytes, while native plants remained unaffected. Moreover, PS-MPs addition significantly decreased sediment pH while increasing sediment carbon and nitrogen content. Additionally, MPs increased the diversity of sediment bacterial community but inhibited its structural stability, thereby impacting sediment bacterial multifunctionality to varying degrees. Importantly, we identified sediment properties, bacterial composition, and bacterial multifunctionality as key mediators that greatly enhance the invasion of exotic submerged macrophytes. These findings provide compelling evidence that the increase in MPs may exacerbate the invasion risk of exotic submerged macrophytes through multiple pathways. Overall, this study enhances our understanding of the ecological impacts of MPs on aquatic plant invasion and the health of aquatic ecosystems.

High performance self-assembled sulfidized nanoscale zero-valent iron for the immobilization of cadmium in contaminated sediments: Optimization, microbial response, and mechanisms

Sulfidized nanoscale zero-valent iron (S-nZVI) showed excellent removal capacity for cadmium (Cd) in aqueous phase. However, the remediation effects of S-nZVI on Cd-contaminated sediment and its interactions with microorganisms in relation to Cd fate remain unclear. The complexity of the external environment posed a challenge for Cd remediation. This study synthesized S-nZVI with different S and Fe precursors to investigate the effect of precursors and applied the optimal material to immobilize Cd in sediments. Characterization analysis revealed that the precursor affected the morphology, Fe0 crystallinity, and the degree of oxidation of the material. Incubation experiments demonstrated that the immobilization efficiency of Cd using S-nZVIFe3++S2- (S/Fe = 0.14) reached the peak value of 99.54%. 1% and 5% dosages of S-nZVI significantly reduced Cd concentration in the overlying water, DTPA-extractable Cd content, and exchangeable (EX) Cd speciation (P < 0.05). Cd leaching in sediment and total iron in the overlying water remained at low levels during 90 d of incubation. Notably, each treatment maintained a high Cd immobilization efficiency under different pH, water/sediment ratio, organic acid, and coexisting ion conditions. Sediment physicochemical properties, functional bacteria, and a range of adsorption, complexation and precipitation of CdS effects dominated Cd immobilization.

Distribution Characteristics and Factors Controlling Different Phosphorus Fractions in the Soils and Sediments of an Inland Lagoon

Lagoons, significant coastal wetlands, stand out for their vital role in the cycles and transformations of phosphorus. However, the relationship between the spatial distributions of various phosphorus forms in the soil and sediments of lagoon areas remains unclear. This study investigated the phosphorus fractions and distribution patterns in the soil and sediments from Shimei Inland Sea, Hainan Province, China, and identified the factors controlling phosphorus distribution and its relationship with lagoon eutrophication. The results revealed significant enrichment of inorganic phosphorus (IP) in the Shimei Inland Sea (64.1–679.0 mg/kg) and offshore areas (56–627.2 mg/kg), while organic phosphorus (OP) was relatively concentrated in land (60–744.3 mg/kg), suggesting that the productivity of the terrestrial ecosystem controlled the OP content and IP formed from the mineralization of OP was more likely to leach into the water and combine with minerals. Total phosphorus (TP) content was negatively affected by pH, and organic matter, cation exchange capacity and iron/aluminum oxides showed significant positive correlations with TP content. These findings highlighted the coupled impact of soil and sediment physicochemical properties on phosphorus enrichment and transformation, providing theoretical support for the ecological restoration of ecosystems in tropical coastal wetlands.

Insight into the role of niche concept in deciphering the ecological drivers of MPs-associated bacterial communities in mangrove forest

Myriad inherent and variable environmental features are controlling the assembly and succession of bacterial communities colonizing on mangrove microplastics (MPs). However, the mechanisms governing mangrove MPs-associated bacterial responses to environmental changes still remain unknown. Here, we assessed the dissimilarities of MPs-associated bacterial composition, diversity and functionality as well as quantified the niche variations of each taxon on plastispheres along river–mangrove–ocean and mangrove landward–to–seaward gradients in the Beibu Gulf, China, respectively. The bacterial richness and diversity as well as the niche breadth on mangrove sedimentary MPs dramatically decreased from landward to seaward regions. Characterizing the niche variations linked the difference of ecological drivers of MPs-associated bacterial populations and functions between river–mangrove–ocean (microplastic properties) and mangrove landward–to–seaward plastispheres (sediment physicochemical properties) to the trade-offs between selective stress exerted by inherent plastic substrates and microbial competitive stress imposed by environmental conditions. Notably, Rhodococcus erythropolis was predicted to be the generalist species and closely associated to biogeochemical cycles of mangrove plastispheres. Our work provides a reliable pathway for tackling the hidden mechanisms of environmental factors driving MPs-associated microbe from perspectives of niches and highlights the spatial dynamic variations of mangrove MPs-associated bacteria.

Changes in the leaf functional traits of mangrove plant assemblages along an intertidal gradient in typical mangrove wetlands in Hainan, China

The understanding of biodiversity-ecosystem functioning linkages under environment change has been advanced immensely by the development and application of the functional trait theory. Intertidal zones, characterized by significant environmental gradient differences, are severely threatened by sea-level rises caused by global warming. The functional trait distribution pattern for mangrove communities along the intertidal gradient and underlying mechanisms remain unclear. We investigated differences in the leaf functional traits of mangrove plant assemblages among the high, middle, and low intertidal zones, and their relationships to sediment physicochemical properties, in Dongzhaigang and Qinglan Harbor reserves, Hainan, China. In both reserves, most sediment physicochemical properties (pH; salinity; total potassium, carbon, nitrogen, and sulfur concentrations; organic carbon content; ammonium nitrogen and available phosphorus concentrations) differed significantly among gradient zones. The sediment pH, total phosphorus, and available potassium concentrations differed significantly between the dry and wet seasons. From the low to the high intertidal zone, the mangrove specific leaf area and leaf nitrogen and phosphorus concentrations increased significantly and the leaf thickness decreased significantly. The leaf tannin and lignin concentrations were significantly lower and the leaf phosphorus concentration, nitrogen concentration and hardness were significantly higher in the dry season than in the wet season. The sediment salinity, pH, and total sulfur and potassium contents were key factors affecting the distribution of mangrove leaf functional traits along the intertidal gradient. The changes in mangrove leaf functional traits reflect gradient-level responses to environmental stress and the sediment nutrient status. Our findings improve the understanding of the functional trait diversity and maintenance mechanisms of mangrove communities under environmental change and provide a new perspective for the prediction of how coastal mangroves will respond to future global warming.

Reuse of sediment as a soil conditioner in a semiarid region dominated by subsistence farming: sediment characterization at the regional scale and effects on maize crop

PurposeThe increasing demand for fertilizers and their rising prices has led to the search for new nutrient sources, especially in rural areas where family farming predominates. In this study, we assessed the potential of reusing sediment deposited in surface reservoirs as a soil conditioner in a semiarid region, focusing on two features: the characterization of sediment physicochemical properties at the regional scale and the effect of the substrate containing sediment on the growth and physiology of maize.MethodsSediment from the beds of 14 reservoirs was investigated, and two of them were used for the preparation of substrate for maize cultivation. Differences between the physicochemical properties of the sediments were analyzed using ANOVA and Tukey’s test at a significance level of 0.05. The experimental design of the plant experiment was entirely randomized, in a factorial arrangement of two sources and four doses of sediment: 25, 50, 75, and 100% of the economic dose of 100 t ha−1 previously proposed in the study region. Two treatments were considered as controls: a substrate containing only soil and a treatment containing soil and chemical fertilizer. The data for each treatment were submitted independently considering the doses and sediment sources, and the means were compared by Tukey’s test.ResultsIn general, nutrient contents were higher in the sediment of the surface reservoirs than in the soil. For instance, the concentrations of nitrogen and potassium were three to 10 times higher in the sediment, compared to the soil, and the organic matter content was up to six times higher. In the plant experiment, the dose and source of the sediments influenced all of the analyzed variables. The addition of sediments to the soil increased the chlorophyll content, photosynthesis rate, and growth of the leaves in relation to the treatment containing only soil. There were no significant differences between the biomass production and the plants’ nutrient extraction with the largest dose of the most enriched sediment when compared to the treatment with chemical fertilizer.ConclusionsThe experiment of maize plant growth showed the feasibility of using sediment deposited in reservoirs as a soil conditioner due to the enrichment of nutrients, organic matter, and fine particles. Therefore, sediment reuse has potential to improve livelihoods and food security, as well as contributing to a circular economy. However, prior analysis is required to avoid soil contamination and to set the most appropriate sediment dose, due to the high spatial variability of the sediment characteristics.

Efficiency and ecological safety of herbicide haloxyfop-R-methyl on removal of coastal invasive plant Spartina alterniflora

Spartina alterniflora is a global invasive plant and has caused considerable damage to coastal wetland ecosystem. This study evaluated the efficiency and ecological safety of herbicide haloxyfop-R-methyl (HPME) in removing S alterniflora in Laizhou Bay. The results showed that the density of regenerated S. alterniflora after 10 months of application of 0.01, 0.02 and 0.03 g/m2 HPME decreased by 86.67 %, 99.16 % and 99.31 %, respectively. Moreover, seed abortion rates were 62.25 %, 92.24 % and 94.82 %, and weight of roots in HPME groups were 56.63 %, 59.99 %, and 40.10 % of those in the control group. After 4 days of application, HPME could not be detected in S. alterniflora and sediments. In addition, HPME did not change sediment physicochemical properties, macrozoobenthos community and microbial community structure during 16 days, but increased the density of native macrozoobenthos after 1 year. Therefore, HPME might be an effective and ecologically safe chemical for the eradication of S. alterniflora.

Spatial variation of organic carbon storage and aggregate sizes in the sediment of the Zhangjiang mangrove ecosystem

Sediment organic carbon (SOC) in mangrove ecosystem, known as blue carbon, is a crucial component in estuarine carbon cycles. To get a deep insight into the mechanism of SOC accumulation, the sediment physicochemical properties, SOC density and aggregate sizes were investigated among mangrove (Kandelia obovata), saltmarsh (Spartina alterniflora) and mudflats at different elevations (upland mudflat, midland mudflat, lowland mudflat). The results showed that the higher SOC content was observed both in the 0–60 cm of mangrove and in the 0–40 cm of S. alterniflora compared with mudflats (P < 0.05). The SOC density in the top meter ranged from 99 to 202.7 Mg·ha−1 and had vertical difference at all sites. The highest SOC density were found in mangrove, while no difference was observed between S. alterniflora and mudflats. The mean weight diameter of aggregates was higher in the top 60 cm sediment of mangrove while S. alterniflora had no change indicating the capacity of aggregate formation. RDA analysis showed SOC storage could be more explained by the SOC content than bulk density, all sites in the top 40 cm could be well separated. The MWD had the 8.6 % individual effects on SOC content, reflecting the aggregated protection. The mangrove root system favored aggregates formation and physical protection, which facilitate the SOC accumulation. These findings revealed that mangroves restoration could effectively enhance SOC storage, and the mudflat is also significant SOC pool owning to the large bulk density and area. The invasive S. alterniflora did not enhance the SOC storage compared with mudflats and should be controlled in the future work.

Phthalate esters in the Largest River of Asia: An exploration as indicators of microplastics

Phthalate esters (PAEs) are the most ubiquitous and highly used plasticizers in plastic products globally, yet studies on the spatial variation, risks, and their correlation with microplastics (MPs) are limited, particularly throughout the Yangtze River (the largest river in China/Asia). Therefore, this study investigated for the first time the PAEs pollution characteristics throughout the Yangtze River sediments, studied the environmental factors linked to the distribution of PAEs, and explored their potential as chemical indicators for interpreting pollution patterns of MPs. Totally 14 out of 16 PAEs were detected in sediments, with total concentrations ranging from 84.67 ng/g to 274.0 ng/g (mean: 163.5 ng/g), dominated by Bis(2-ethylhexyl) phthalate (DEHP), Di-n-butyl phthalate (DBP), and Di-isobutyl phthalate (DIBP), with contributions of 38.9 %, 31.8 %, and 20.8 %, respectively. Spatial distribution of PAEs did not indicate significant differences, which may be related to anthropogenic activities (i.e., emission intensity), runoff, and sediment physicochemical properties (i.e., TOC and TN), with TOC and TN being potential predictors of PAEs. The quantitative relationships (p < 0.001) between DEHP/∑16PAEs ratio and MPs (both individual and total MPs) were found in sediments, which suggested that DEHP could be potentially used as an indicator for MPs. DEHP, DIBP, and DBP posed high risks, accounting for 100 %, 68.4 %, and 10.5 % of the monitoring sites, respectively. Further work is necessary to better understand the relationship between DEHP/∑16PAEs and MPs in the environment and to take corresponding management and control measures for these pollutants.

Effects of Florfenicol on nirS-Type Denitrification Community Structure of Sediments in an Aquatic Microcosm Model.

Florfenicol is one of the most widely used antibiotics in aquaculture and veterinary clinics because of its low side effects and strong bactericidal effect. A total of 45~60% of florfenicol is not absorbed by the animal body and accumulates in the aquatic environment through a variety of pathways, which affects denitrification. Indoor aquatic microcosm models were constructed and sediment samples were collected at different florfenicol concentrations (0.1, 1, 10, and 100 mg/L) on days 0, 7, 30, and 60 to extract the microbial genome DNA and determine the water properties. qPCR and amplicon sequencing were used to study the dynamic changes in the nirS gene and nirS-type denitrification community structure, diversity, and abundance, respectively. The results showed that high florfenicol stress influenced the sediment's physicochemical properties, reducing conductivity, alkaline dissolved nitrogen, and organic matter content. In addition, the abundance of nirS, a functional denitrification gene, increased obviously with increased florfenicol concentrations but decreased the diversity of nirS-type denitrification microorganisms. Proteobacteria was the dominant denitrifying phylum in the sediment. Our study provides a scientific basis for the rational use of florfenicol in aquaculture to maintain a healthy and stable microecological environment and also provides a preliminary understanding of the response characteristics of water denitrifying microorganisms to florfenicol exposure.

Sediment physicochemical properties of Maa-Dee-Tai River System in Sogho community, Ogoniland, Rivers State, Nigeria

Sediment physicochemical properties of Maa-Dee-Tai River System in Sogho community, Ogoniland, Rivers State, Nigeria

Distinct microplastics abundance variation in root-associated sediments revealed the underestimation of mangrove microplastics pollution

Mangrove sediment is acknowledged as the critical sink of microplastics (MPs). However, the potential effect of mangrove root systems on the MPs migration in sediment remains largely unknown. Here, our study characterized the spatial distribution of MPs trapped in root hair, rhizosphere, and non-rhizosphere zones, and analyzed their correlations with physicochemical properties of sediments. The significantly increased MPs abundances toward root systems shed light on the distinct effect on the migration of MPs exerted by mangrove root systems. Partial least squares path modeling (PLS-PM) analysis revealed that pore water content and pH influenced the abundances of different MP characteristics (shape, color, size, and type) and further promoted the accumulation of MPs toward the root systems. In different mangrove areas from landward to seaward, other sediment properties (median grain size, clay content, and salinity) also controlled MP distribution. Additionally, smaller-sized MPs (<1000 μm) were more easily transported to the root systems. Our study emphasizes the importance of considering root systems effect when investigating the mechanisms of MPs distribution and migration in mangrove sediments.

Spatio-temporal variation and hazard assessment of potentially toxic metal element contamination in sediments and water before and after a water-level fluctuation cycle in the Three Gorges Reservoir, Wanzhou, China.

Previous investigations on heavy metals in the water-sediment compartment focused on their spatial distribution, and the influence of sediment pH and organic matter (OM) on metal environmental occurrences. However, there are limited studies on the effects of physicochemical properties on the migration and transformation of heavy metals in the water-sediment compartments. This study investigated the relationship between the physicochemical properties of sediments and the distribution and chemical speciation of heavy metals, and the potential environmental risk of heavy metals in water and sediment using Risk Assessment Code (RAC) values and the Tessier five-step extraction method. Adsorption and desorption experiments showed that the sediment had weak adsorption and the strongest desorption capacity for Cd. Results of the pH, OM, surface element content, and X-ray diffraction (XRD) patterns suggested that cadmium (Cd) was more likely to partition into the water phase from the sediment during the flooding and water storage periods. When pH was 7-8 and OM content was 3.6-5.9%, the sediment-water distribution coefficient of Cd was low due to its large ionic radius, and the surface adsorption sites were saturated by other elements. These studies can provide a theoretical basis for the management and pollution control of the Three Gorges Reservoir.

Controlled mechanism and removal performance of phosphorus in black and odorous water bodies by Fe-based layered double hydroxides

The effective approach for controlling internal phosphorus loading remains a longstanding challenge to the maintenance of remediated black and odorous water bodies. Here, three Fe-based LDHs materials were developed for alleviating the phosphorus pollution in black and odorous water through synergistic functions of phosphate adsorption, controlled release of phosphorus, and microbial metabolism. The mechanism of phosphate removal in overlying water is mainly specific electrostatic attraction and coordination. After the addition of Fe-based LDHs, the water quality indexes of black and odorous water bodies were significantly improved, including TP concentration (from 0.8 to 0.2 mg/L), the dissolved oxygen content (from 0.1 to 3.0 mg/L), COD, turbidity (from 34 to 18 FTU), and redox potential. Moreover, the morphology and physicochemical properties of sediments were regulated by Fe-based LDHs. Fluffier and smaller sediments particles due to the destruction of extracellular polymeric substances structure, which was beneficial to the release of endogenous phosphorus. Furthermore, the results of microbial community structure analysis illustrated that Proteobacteria and Dechloromonas played the most important role in phosphorus elimination in Fe-based LDHs system. That is, based on the biocompatibility of Fe-based LDHs, which act as a medium of the electron transfer in the microbial metabolism, combining with microorganisms for the synergistic remediation of black and odorous water bodies. Our study emphasizes the feasibility of Fe-based LDHs materials for the remediation of internal phosphorus loads in black and odorous water bodies, towards sustainable control.

Baseline occurrence of organochlorine and organophosphate pesticides in water, sediment, and fish in the Miankaleh wetland, Iran

Micropollutants such as pesticides and the prediction of water quality in aquatic environments have been known as a serious risk to the environment and human health. The pollution level of six pesticides—three organochlorines (OCPs: aldrin, dieldrin, and endrin) and three organophosphates (OPPs: diazinon, malathion, and azinphosmethyl)— in water, sediment, and fish samples was examined in the Miankaleh wetland, Iran. Water quality, including dissolved oxygen (DO), biological oxygen demand (BOD), chemical oxygen demand (COD), salinity, electrical conductivity (EC), turbidity, total dissolved solids (TDS), pH, temperature, and physicochemical properties of sediments, was analyzed. Low concentrations of OCPs (0.70 ± 0.01 μg/L) and OPPs (1.31 ± 0.1 μg/L) were observed in water. In contrast, OCPs and OPPs were not detected in sediment and fish samples in the Miankaleh wetland. Low concentrations of OCPs and OPPs in water and no pesticide concentrations in sediment and fish samples indicate low contamination of the aquatic environment in Miankaleh. The results of this study could be used as an effective reference for policy makers in the field of water resource management.

Co-proliferation of antimicrobial resistance genes in tilapia farming ponds associated with use of antimicrobials

The prevalence of antimicrobial resistance genes (ARGs) in aquaculture has raised serious public concerns for food safety and human health, but its relationships to the use of antimicrobials in aquacultural ponds and even to their residues in the whole aquatic environment remain unclear. In this study, a better coverage of 323 target ARGs and 40 mobile genetic elements (MGEs) was analyzed in sediment using a smart chip-based high-throughput quantitative PCR approach (HT-qPCR) in random 20 ponds of a tilapia farming base in southern China, whose antimicrobial residues were reported previously. In total, 159 ARGs and 29 MGEs were quantified in 58 surface sediment samples across the ponds. Absolute abundance of ARGs ranged from 0.2 to 13.5 × 106 copies g−1, dominated by the categories of multidrug and sulfonamides. The quantified ARGs abundance and the antimicrobial compound residues were significantly correlated instead with the antimicrobial categories, mainly compounds in categories of fluoroquinolones and sulfonamides and trimethoprim (TMP). Antimicrobial residues alone explained 30.6 % of the ARGs' variation quantified in sediment across the ponds, indicating the clear link between antimicrobials and the proliferation of ARGs in aquaculture. Co-proliferation of the ARGs with non-related antimicrobial compounds quantified in sediment was also observed, especially for aminoglycosides' ARGs, which were highly associated with integrons (intI 1) as argued being carried by the intI 1 gene cassette arrays. Physicochemical properties of sediment (pH, electric conductivity, and total sulfur content) highly contributed the variations of the quantified ARGs abundance (21 %) across all the sediment samples equaling to the MGEs (20 %), suggesting co-selection for ARGs' proliferation in the aquaculture environment. This study provides insights into the interactions between residual antimicrobials and ARGs, which would enhance the understandings on the use and management of antimicrobials in aquaculture worldwide to strategize mitigation of antimicrobial resistance in aquaculture.