Microbial phylogenetic divergence between surface-water and sedimentary ecosystems drove the resistome profiles.

Antibiotic pollution and the evolution of antibiotic resistance genes (ARGs) are increasingly viewed as major threats to both ecosystem security and human health, and have drawn attention. This study investigated the fate of antibiotics in aqueous and sedimentary substrates and the impact of ecosystem shifts between water and sedimentary phases on resistome profiles. The findings indicated notable variations in the concentration and distribution patterns of antibiotics across various environmental phases. Based on the partition coefficient (Kd), the total antibiotic concentration was significantly greater in the surface water (1405.45 ng/L; 49.5 %) compared to the suspended particulate matter (Kd = 0.64; 892.59 ng/g; 31.4 %) and sediment (Kd = 0.4; 542.64 ng/g; 19.1 %). However, the relative abundance of ARGs in surface water and sediment was disproportionate to the abundance of antibiotics concentration, and sediments were the predominant ARGs reservoirs. Phylogenetic divergence of the microbial communities between the surface water and the sedimentary ecosystems potentially played important roles in driving the ARGs profiles between the two distinctive ecosystems. ARGs of Clinical importance; including blaGES, MCR-7.1, ermB, tet(34), tet36, tetG-01, and sul2 were significantly increased in the surface water, while blaCTX-M-01, blaTEM, blaOXA10-01, blaVIM, tet(W/N/W), tetM02, and ermX were amplified in the sediments. cfxA was an endemic ARG in surface-water ecosystems while the endemic ARGs of the sedimentary ecosystems included aacC4, aadA9-02, blaCTX-M-04, blaIMP-01, blaIMP-02, bla-L1, penA, erm(36), ermC, ermT-01, msrA-01, pikR2, vgb-01, mexA, oprD, ttgB, and aac. These findings offer a valuable information for the identification of ARGs-specific high-risk reservoirs.

Enhanced nutrient removal in agro-industrial wastes-amended hybrid floating treatment wetlands treating real sewage: Laboratory microcosms to field-scale studies.

The use of natural agro-industrial materials as suspended fillers (SFs) in floating treatment wetlands (FTWs) to enhance nutrient removal performance has recently been gaining significant attention. However, the knowledge concerning the nutrient removal performance enhancement by different SFs (alone and in mixtures) and the major removal pathways is so far inadequate. The current research, for the first time, carried out a critical analysis using five different natural agro-industrial materials (biochar, zeolite, alum sludge, woodchip, flexible solid packing) as SFs in various FTWs of 20 L microcosm tanks, 450 L outdoor mesocosms, and a field-scale urban pond treating real wastewater over 180 d. The findings demonstrated that the incorporation of SFs in FTWs enhanced the removal performance of total nitrogen (TN) by 20-57% and total phosphorus (TP) by 23-63%. SFs further enhanced macrophyte growth and biomass production, leading to considerable increases in nutrient standing stocks. Although all the hybrid FTWs showed acceptable treatment performances, FTWs set up with mixtures of all five SFs significantly enhanced biofilm formation and enriched the abundances of the microbial community related to nitrification and denitrification processes, supporting the detected excellent N retention. N mass balance assessment demonstrated that nitrification-denitrification was the major N removal pathway in reinforced FTWs, and the high removal efficiency of TP was attributable to the incorporation of SFs into the FTWs. Nutrient removal efficiencies ranked in the following order among the various trials: microcosm scale (TN: 99.3% and TP: 98.4%) > mesocosm scale (TN: 84.0% and TP: 95.0%) > field scale (TN: -15.0-73.7% and TP: -31.5-77.1%). These findings demonstrate that hybrid FTWs could be easily scaled up for the removal of pollutants from eutrophic freshwater systems over the medium term in an environmentally-friendly way in regions with similar environmental conditions. Moreover, it demonstrates hybrid FTW as a novel way of disposing of significant quantities of wastes, showing a win-win means with a huge potential for large-scale application.

Vegetated urban streams have sufficient purification ability but high internal nutrient loadings: Microbial communities and nutrient release dynamics.

The release of nutrients back into the water column due to macrophyte litter decay could offset the benefits of nutrient removal by hydrophytes within urban streams. However, the influence of this internal nutrient cycling on the overlying water quality and bacterial community structure is still an open question. Hence, litter decomposition trials using six hydrophytes, Typha latifolia (TL), Phragmites australis (PAU), Hydrilla verticillata (HV), Oenanthe javanica (OJ), Myriophyllum aquaticum (MA), and Potamogeton crispus (PC), were performed using the litterbag approach to mimic a 150-day plant litter decay in sediment-water systems. Field assessment using simple in/out mass balances and uptake by plant species was carried out to show the potential for phytoremediation and its mechanisms. Results from two years of monitoring (2020-2021) indicated mean total nitrogen (TN) retention efficiencies of 7.2-60.14 % and 9.5-55.6 % for total phosphorus (TP) in the studied vegetated urban streams. Nutrient retention efficiencies showed temporal variations, which depended on seasonal temperature. Mass balance analysis indicated that macrophyte assimilation, sediment adsorption, and microbial transformation accounted for 10.31-41.74 %, 0.84-3.00 %, and 6.92-48.24 % removal of the inlet TN loading, respectively. Hydrophyte detritus decay induced alterations in physicochemical parameters while significantly increasing the N and P levels in the overlying water and sediment. Decay rates varied among macrophytes in the order of HV (0.00436 g day-1) > MA (0.00284 g day-1) > PC (0.00251 g day-1) > OJ (0.00135 g day-1) > TL (0.00095 g day-1) > PAU (0.00057 g day-1). 16S rRNA gene sequencing analysis showed an increase in microbial species richness and diversity in the early phase of litter decay. The abundances of denitrification (nirS and nirK) and nitrification (AOA and AOB) genes also increased in the early stage and then decreased during the decay process. Results of this study conducted in seven urban streams in northern China demonstrate the direct effects of hydrophytes in encouraging nutrient transformation and stream self-purification. Results also demonstrate that macrophyte detritus decay could drive not only the nutrient conversions but also the microbial community structure and activities in sediment-water systems. Consequently, to manage internal sources and conversions of nutrients, hydrophytic detritus (e.g., floating/submerged macrophytes) must be suppressed and harvested.

Performance of various fillers in ecological floating beds planted with Myriophyllum aquaticum treating municipal wastewater.

The performance of different suspended fillers (zeolite, drinking water treatment residual, biochar, woodchip and stereo-elastic packing) and their combinations in treating municipal wastewater in ecological floating beds (Eco-FBs) planted with Myriophyllum aquaticum was assessed. Six sets of enhanced Eco-FBs were developed to assess the individual and synergistic effects of combinations of the various fillers and microorganisms on nutrient elimination. The results demonstrated mean TN, NH4-N, TP and COD purification efficiencies of 99.2 ±â€¯11.2 %, 99.82 ±â€¯16.4 %, 98.3 ±â€¯14.3 %, and 96.1 ±â€¯12.3 %, respectively in the Eco-FBs strengthened with all five fillers. The corresponding purification rates were 0.89 ±â€¯0.14, 0.75 ±â€¯0.12, 0.08 ±â€¯0.016, and 7.05 ±â€¯1.09 g m-2 d-1, which were 2-3 times higher than those of the conventional Eco-FB system. High-throughput sequencing showed that some genera related to nutrient transformation, including Proteobacteria (24.13-51.95 %), followed by Chloroflexi (5.64-25.01 %), Planctomycetes (8.48-14.43 %) and Acidobacteria (2.29-11.65 %), were abundantly enriched in the strengthened Eco-FBs. Enhancement of the Eco-FBs with various fillers significantly increased microbial species richness and diversity as demonstrated by Chao1, Shannon and Simpson's indexes, particularly when all the five fillers were combined. Therefore, introducing suspended fillers into Eco-FBs is an appropriate approach for improving nutrient elimination from municipal wastewater.

Nitrogen/phosphorus behavior traits and implications during storm events in a semi-arid mountainous watershed.

Seasonal rainfall events reinforce the link between terrestrial and fluvial domains and are crucial for assessing hydrological control over riverine nutrient dynamics and pollutant source behaviors, especially in a semi-arid watershed. Taking the Qingshuihe river basin, a semi-arid mountainous basin in China, as an example, this paper investigated storm effects on riverine nitrogen (N) and phosphorus (P) dynamics (i.e. concentration, load, and composition changes) through continuous sampling of four storm events of the 2019 rainy season, including one small storm, two moderate storms, and a large storm. Pollutant sources and transport pathways were then examined over the storm sequence via hysteresis analysis. The results revealed a strong linkage between N/P dynamics and hydrological processes. Storm runoff caused a 6-fold increase in particulate-P (PP) and a 4-fold increase in ammonia-N (NH4-N) fluxes through four storms (most sensitive nutrients to storms). On average, PP shared 86% of P exports, and nitrate-N (NO3-N) contributed 79% of N exports. PP and NH4-N were delivered primarily from overland sources and transported by surface runoff. Nonetheless, mobilization of channel sediment reserves was also an important way of PP supply during storms. The results suggested groundwater as the principal NO3-N source in the watershed, and subsurface flow was important for NO3-N and total dissolved-P (TDP) delivery during storms. The large storm (>20 mm) often registered the highest N/P load exports. However, there were other influencing factors/processes on stormflow N/P dynamics in the semi-arid watershed, which complicate/override the effects of different storm magnitudes. Total suspended solids (TSS)/PP source availability and inter- and intra-storm export trends influenced P behaviors through storms. Moreover, impacts of mobilization processes on NO3-N behavior appeared over the storm sequence. These findings enhance our understanding of storm events induced N/P exports in water-scarce regions and provide references for water quality predictions and control in flood seasons.

Growth characteristics and nutrient removal capability of eco-ditch plants in mesocosm sediment receiving primary domestic wastewater.

Eco-ditches are being explored to maximize their capability of capturing pollutants and mitigate any harmful side effects in rivers. In this study, mesocosm plastic drum sediment and field experiments were set up to screen 18 plant species found in ditches and identify those with potential for high biomass production and nutrients removal. Terrestrial plants grown in the mesocosm system were shown to be able to acclimate to aquatic conditions and to survive in primary domestic sewage. About 73-95% increase in plant biomass was recorded. Removal efficiencies for total nitrogen, total phosphorus, and ammonium-nitrogen from the sewage of 72-99%, 64-99%, and 75-100%, respectively, were recorded. Furthermore, complete removal of the applied nitrate-nitrogen load was achieved in mesocosm systems. Findings also show that all species, but especially Acorus calamus, Canna indica, Canna lily, Cyperus alternifolius, Colocasia gigantea, Eichhornia crassipes, Iris sibirica, and Typha latifolia had the highest efficiencies for nitrogen and phosphorous removal. The N and P mass balance analysis demonstrated that plant uptake and sediment N and P accumulation accounted for 41-86% and 18-49% of the total influent TN and TP loads, respectively. In addition, the amounts of nitrogen and phosphorous uptake by these plant species were influenced significantly by biomass. The field-culture experiment further identified Canna indica followed by Cyperus alternifolius as the most promising for high biomass production and nutrients uptake. Therefore, these plants may be recommended for extensive use in treating highly eutrophicated rivers. Outcomes of this work can be useful for model design specifications in eco-ditch mitigation of sewage pollution.

Estimation of the removal efficiency of heavy metals and nutrients from ecological drainage ditches treating town sewage during dry and wet seasons.

Vegetated drainage ditches (ecological drainage ditches, EDD) are commonly used for the treatment of nutrients, suspended solids, and pesticides, from agricultural lands and aquaculture effluent. However, their effectiveness to remove heavy metals/metalloids (HM/Ms) and fate remains largely unexplored. In addition, there exists some uncertainty concerning the performance of the EDD in treating HM/Ms. This study presents a thorough assessment on the removal efficiencies of HM/Ms and identifies the parameters affecting the HM/Ms removal process in the EDD receiving primary domestic sewage for 13 years. The mean concentrations of the studied HM/Ms in sediments were lower than those reported in the aquatic ecosystems affected by coal-mine drainage and industrial wastewaters. The results also showed that the concentrations of the selected HM/Ms in ditch sediment were generally far higher than the soil background values of Sichuan basin. Concentrations of all the studied HM/Ms and nutrients in water entering the EDD were significantly higher than the effluent. The annual mean removal efficiencies of Ni, Cu, Cr, Zn, Cd, Pb, As, Fe, Al, Mn, N, and P in the ecological drainage ditch were 50.6, 56.1, 63.3, 79.3, 67.5, 80.1, 60.3, 52.6, 19.8, 24.3, 72.0, and 59.7%, respectively. The study also displayed that dissolved oxygen levels at the outlet were significantly (p < 0.001) higher after passing into the EDD system. The pH was kept at neutral or alkaline. Removal of HM/Ms and nutrients was seasonal, generally peaking in the growing season. Sedimentation was the major mechanism removing HM/Ms within the EDD system. EDD was found to possess a favorable influence at mitigating HM/Ms and nutrients in situ and can be successfully utilized to resolve this type of environmental pollution.

Assessing the influence of different plant species in drainage ditches on mitigation of non-point source pollutants (N, P, and sediments) in the Purple Sichuan Basin.

Three different types of ditches, each 300 m in length, were employed in this study. One vegetated constructed ditch (VCD), three natural vegetated soil ditches (NVSD), and three constructed ditches left unvegetated (UCD) as controls were investigated using simple in/out mass balances and uptake by plant species with a potential for phytoremediation and their mechanisms. Significant differences in the ditches were observed, suggesting the importance of plant species in nutrient mitigation. The removal rates of TN (total nitrogen) and TP (total phosphorus) were 64.28 and 58.02, 31.16 and 27.49, and 3.91 and 2.97%, respectively, in the VCD, NVSD, and UCD. Canna indica (45.12 g m-2) and Oenanthe javanica (21.48 g m-2) had the highest total N and P storage in the VCD and NVSD. Furthermore, species C. indica possessed the highest annual N and P uptake in the VCD (216.59 kg N/ha/yr and 30.73 kg P/ha/yr). In the NVSD, species O. javanica had the greatest annual N and P uptake (96.66 kg N/ha/yr and 7.94 kg P/ha/yr). Both VCD and NVSD were found to have a reasonably good outcome compared to UCD. Retention of nutrients by ditch sediments was probably the major attenuation mechanism, with subsequent plant uptake and microbial nitrification-denitrification of the nutrients as secondary removal mechanisms. Results of this study highlight the importance of taking actions for establishment of appropriate plant species inside the ditches in order to enhance its direct and indirect roles and maximize purification rate in aquatic environments.

Effectiveness of Vegetated Drainage Ditches for Domestic Sewage Effluent Mitigation.

Plant species have an important role in eco-ditches; however, the Michaelis-Menten kinetic parameters of nutrient uptake, growth rate and purification efficiency of ditch plants and their influences on domestic sewage treatment efficiency are still unclear. Growth rates of all nine species, but especially Lemna gibba, Cladophora and Myriophyllum verticillatum were best in undiluted domestic sewage as opposed to a mixture of domestic sewage. Performance of species to accumulate nutrients was not only species-specific, but was also affected by both sewage treatments. Removal efficiency of nutrients was dependent on both plant species and treatment. Uptake kinetic parameters were significantly affected by both nutrient form and plant species. The maximum uptake rate (Vmax) of NH4-N was higher than NO3-N. Similarly, Km values for NH4-N were greater than NO3-N. These results could be used to identify plants for sewage treatment efficiency and enhance water quality in eco-ditch treatment systems.

Long-term impact of primary domestic sewage on metal/loid accumulation in drainage ditch sediments, plants and water: Implications for phytoremediation and restoration.

We evaluate the long-term performance of a vegetated drainage ditch (VDD) treating domestic sewage with respect to heavy metal/metalloid (HM/M) accumulation in sediments, plants and water. VDD sediment contained significantly higher macro and trace elements compared to an agricultural ditch (AD) sediment. However, concentrations of HM/Ms in VDD sediment were below the ranges considered toxic to plants. Most HM/Ms were efficiently removed in the VDD, whereby removal efficiencies varied between 11% for Al and 89% for K. Accumulation of HM/Ms varied among species and plant parts, although sequestration by plants represents only a small proportion (<1%) of the inflow load. Accumulation of Al, As, Cd, Pb, Cr, Fe and Ni in VDD plants were mostly distributed in the roots, indicating an exclusive strategy for metal tolerance. The opposite was found for Zn, Cu, K, Ca, P, K, Na, N and Mg, which were accumulated either in the stems or leaves. Overall, concentrations of metals in sediment showed significant positive correlations with those in ditch plants. None of the studied species were identified as metal hyper-accumulators (i.e. >10,000mgkg-1 of Zn or Mn). Nevertheless, the high translocation factor (TF) values for Mn, Ni, Cu, Zn, Na, Mg, P, K and Ca in the ditch plants make them suitable for phytoextraction from water/soil, while the low TF values for Pb, Cd, As, Fe, Cr and Al make them suitable for their phytostabilization.

Metal Distribution and Contamination Assessment in Drainage Ditch Water in the Main Rice/Vegetable Area of Sichuan Hilly Basin.

In order to assess the impact of four land use changes on metal concentrations in the hilly Sichuan Basin of China, 71 surface water samples were collected in July and November 2014. Samples from residential ditch water were found to have higher metal concentrations than those in other types of ditches, while the lowest occurred in barren land ditch water. However, the selected metals were below the Chinese surface water quality standards and WHO (2011). The pollution index of four determined land use types was also below the critical pollution index, suggesting there were low levels of pollution in Sichuan Basin. Arsenic was the most important pollutant of concern. Results indicate steps should be taken to control and reduce the risk of metals released from residential ditch water.