Amendment-driven soil health restoration through soil pH and microbial robustness in a Cd/Cu-combined acidic soil: A ten-year in-situ field experiment.

Soil health arguably depends on biodiversity and has received wide attention in heavy-metal (HM) contaminated farmland remediation in recent years. However, long-term effects and mechanisms of soil amendment remain poorly understood with respect to soil microbal community. In this in-situ field study, four soil amendments (attapulgite-At, apatite-Ap, montmorillonite-M, lime-L) at three rates were applied once only for ten years in a cadmium (Cd)-copper (Cu) contaminated paddy soil deprecated for over five years. Results showed that after ten years and in compared with CK (no amendment), total Cd concentration and its risk in plot soils were not altered by amendments (p > 0.05), but total Cu concentration and its risk were significantly increased by both Ap and L, especially the former, rather than At and M (p < 0.05), through increased soil pH and enhanced bacterial alpha diversity as well as plant community. Soil microbial communities were more affected by amendment type (30%) than dosage (11%), microbial network characteristics were dominated by rare taxa, and soil multifunctionality was improved in Ap- and L-amended soils. A structural equation model (SEM) indicated that 57.3% of soil multifunctionality variances were accounted for by soil pH (+0.696) and microbial network robustness (-0.301). Moreover, microbial robustness could be potentially used as an indicator of soil multifunctionality, and Ap could be optimized to improve soil health in combined with biomass removal. These findings would advance the understanding of soil microbial roles, especially its network robustness, on soil multifunctionality for the remediation of metal contaminated soils and metal control management strategies in acidic soils. ENVIRONMENTAL IMPLICATION: Farmland soil contamination by heavy metals (HMs) has been becoming a serious global environmental challenge. However, most studies have been conducted over the short term, leading to a gap in the long-term remediation efficiency and ecological benefits of soil amendments. For the successful deployment of immobilization technologies, it is critical to understand the long-term stability of the immobilized HMs and soil health. Our study, to the best of our knowlege, is the first to state the long-term effects and mechanisms of soil amendments on soil health and optimize an effective and eco-friendly amendment for long-term Cd/Cu immobilization.

Hippuris vulgaris could replace Myriophyllum aquaticum for efficiently removing water phosphorus under low temperature conditions in China.

Phytoremediation is widely used for the restoration of aquatic environments. However, the phytoremediation effects and mechanisms of special submerged species of native aquatic plants, especially under low-temperature conditions, are not yet clear. In this study, two typical submerged plants, Myriophyllum aquaticum (M. aquaticum; an exotic species) and Hippuris vulgaris (H. vulgaris; a native species), in China were investigated for their phosphorus (P) removal efficiencies (REp) and the related mechanisms of phytophysiology and microorganisms in a low-temperature incubator (10 °C during the day and 2 °C at night). At an initial P level of 0.5 mg L-1, the two plants exhibited similar REp, with the highest values (73.5%-92.1%) observed on days 3-6. After 18 days, the residual P concentration in the water was less than the Grade III limit value (0.2 mg L-1; GB 3838-2002). However, M. aquaticum had a faster REp velocity than H. vulgaris at an initial P level of 3.0 mg L-1, which was attributed to the mechanisms of plant and its interactions with microorganisms. Compared to the control group, the superoxide dismutase activity of H. vulgaris was significantly increased and its catalase activity was decreased, whereas for that of M. aquaticum was the opposite. Micro region X-ray fluorescence analysis revealed that there may be synergic absorption effects between P, S, and K, and antagonistic absorption action between P and Mn in H. vulgaris. In addition, Acinetobacter, Novosphingobium and Pseudomonas were enriched at 3.0 mg L-1 P level with these two plants, but Chlorophyta only accumulated with H. vulgaris, respectively. Overall, the native species, H. vulgaris, could replace the exotic M. aquaticum to efficiently remove P from polluted water at low temperatures. These findings provide a theoretical foundation for submerged plants P removal capabilities, and the protection of local ecosystem diversity at low temperatures.

Insights into Adaptive Regulation of the Leaf-Petiole System: Strategies for Survival of Water Lily Plants under Salt Stress.

The water lily (Nymphaea tetragona) is an ancient angiosperm that belongs to the Nymphaeaceae family. As a rooted floating-leaf plant, water lilies are generally cultivated in fresh water, therefore, little is known about their survival strategies under salt stress. Long-term salt stress causes morphological changes, such as the rapid regeneration of floating leaves and a significant decrease in leaf number and surface area. We demonstrate that salt stress induces toxicity soon after treatment, but plants can adapt by regenerating floating leaves that are photosynthetically active. Transcriptome profiling revealed that ion binding was one of the most-enriched GO terms in leaf-petiole systems under salt stress. Sodium-transporter-related genes were downregulated, whereas K+ transporter genes were both up- and downregulated. These results suggest that restricting intracellular Na+ importing while maintaining balanced K+ homeostasis is an adaptive strategy for tolerating long-term salt stress. ICP-MS analysis identified the petioles and leaves as Na-hyperaccumulators, with a maximum content of over 80 g kg-1 DW under salt stress. Mapping of the Na-hyperaccumulation trait onto the phylogenetic relationships revealed that water lily plants might have a long evolutionary history from ancient marine plants, or may have undergone historical ecological events from salt to fresh water. Ammonium transporter genes involved in nitrogen metabolism were downregulated, whereas NO3--related transporters were upregulated in both the leaves and petioles, suggesting a selective bias toward NO3- uptake under salt stress. The morphological changes we observed may be due to the reduced expression of genes related to auxin signal transduction. In conclusion, the floating leaves and submerged petioles of the water lily use a series of adaptive strategies to survive salt stress. These include the absorption and transport of ions and nutrients from the surrounding environments, and the ability to hyperaccumulate Na+. These adaptations may serve as the physiological basis for salt tolerance in water lily plants.

Anthocyanin metabolism in Nelumbo: translational and post-translational regulation control transcription.

BACKGROUND: Lotus (Nelumbo Adans.) is used as an herbal medicine and the flowers are a source of natural flavonoids. 'Da Sajin', which was firstly found in the plateau area, is a natural mutant in flower color with red streamers dyeing around white petals. RESULTS: The LC-MS-MS results showed that eight anthocyanin compounds, including cyanidin 3-O-glucoside, cyanidin 3-O-galactoside, malvidin 3-O-galactoside, and malvidin 3-O-glucoside, were differentially enriched in red-pigmented tissues of the petals, whereas most of these metabolites were undetected in white tissues of the petals. Transcriptome profiling indicated that the relative high expression levels of structural genes, such as NnPAL, NnF3H, and NnANS, was inconsistent with the low anthocyanin concentration in white tissues. Members of the NnMYB and NnbHLH transcription factor families were presumed to play a role in the metabolic flux in the anthocyanin and proanthocyanidin biosynthetic pathway. The expression model of translational initiation factor, ribosomal proteins and SKP1-CUL1-F-box protein complex related genes suggested an important role for translational and post-translational network in anthocyanin biosynthesis. In addition, pathway analysis indicated that light reaction or photo destruction might be an important external cause for floral color determination in lotus. CONCLUSIONS: In this study, it is supposed that the natural lotus mutant 'Da Sajin' may have originated from a red-flowered ancestor. Partial loss of anthocyanin pigments in petals may result from metabolic disorder caused by light destruction. This disorder is mainly regulated at post translation and translation level, resulting in a non-inherited phenotype. These results contribute to an improved understanding of anthocyanin metabolism in lotus, and indicate that the translational and post-translational regulatory network determines the metabolic flux of anthocyanins and proanthocyanidins under specific environmental conditions.

Improving earthworm quality and complex metal removal from water by adding aquatic plant residues to cattle manure.

Vermicomposting is an economical and environmentally friendly process. However, related knowledge of vermicomposting aquatic plant residues (APRs), earthworm quality, and mechanisms for metal removal from water is still lacking. Nelumbo and Oenanthe javanica residues and their mixture were treated with Eisenia foetida and cattle manure for 45 days. Compared with the control comprising only cattle manure, addition of the APR mixture improved earthworm quality, mainly for low crude ash, high alkaloid compounds and different fat compositions in the Nelumbo residue and the balanced protein proportion of the APR mixture. All the vermicompost especial O. javanica residue added (VO) played efficient roles in removing metals from water initially containing 2.0 mg Cu L-1 and 8.0 mg Zn L-1. There were higher removal efficiencies (Ers) at the dosage of 4 g L-1 with a small microbial contribution. VO significantly increased Ers, which could be from the decrease of phylum Firmicutes (especial Bacteroides) abundance, stronger CH2, C = O, and CH, the addition of COOH groups, and higher organic matter and total phosphorus contents. The combination of VO and Hippuris vulgaris was optimized as an ecological and economical method for treating complex-metal polluted water. Moreover, our study widened the route for APR reuse.

Linking ecological niches to bacterial community structure and assembly in polluted urban aquatic ecosystems.

Introduction: Bacterial communities play crucial roles in the functioning and resilience of aquatic ecosystems, and their responses to water pollution may be assessed from ecological niches. However, our understanding of such response patterns and the underlying ecological mechanisms remains limited. Methods: In this study, we comprehensively investigated the effects of water pollution on the bacterial structure and assembly within different ecological niches, including water, sediment, submerged plant leaf surfaces, and leaf surfaces, using a 16S high-throughput sequencing approach. Results: Ecological niches had a greater impact on bacterial community diversity than pollution, with a distinct enrichment of unique dominant phyla in different niches. This disparity in diversity extends to the bacterial responses to water pollution, with a general reduction in α-diversity observed in the niches, excluding leaf surfaces. Additionally, the distinct changes in bacterial composition in response to pollution should be correlated with their predicted functions, given the enrichment of functions related to biogeochemical cycling in plant surface niches. Moreover, our study revealed diverse interaction patterns among bacterial communities in different niches, characterized by relatively simply associations in sediments and intricate or interconnected networks in water and plant surfaces. Furthermore, stochastic processes dominated bacterial community assembly in the water column, whereas selective screening of roots and pollution events increased the impact of deterministic processes. Discussion: Overall, our study emphasizes the importance of ecological niches in shaping bacterial responses to water pollution. These findings improve our understanding of the complicated microbial response patterns to water pollution and have ecological implications for aquatic ecosystem health.

Removal effects of aquatic plants on high-concentration phosphorus in wastewater during summer.

Aquatic plants are widely used in depth treatment of wastewater; however, the phosphorus (P) removal mechanisms of aquatic plants at high temperatures in summer are not well understood. Eight aquatic plants, including two floating species (Ludwigia peploides and Hydrocharis dubia) and six emergent species (Lythrum salicaria, Sagittaria sagittifolia, Canna indica, Sparganium stoloniferum, Rotala rotundifolia, and Ludwigia ovalis), were treated with five P solutions (3.0, 3.5, 4.0, 4.5, and 5.5 mg L-1) for 5 weeks in a greenhouse during summer at air temperatures ranging from 25 to 35 °C. H. dubia, L. peploides, L. salicaria, and S. sagittifolia showed high water P removal efficiencies (exceeded 95%). Furthermore, their corresponding residual P concentrations in water were almost lower than the limit value of 0.2 mg L-1 of Grade III in the Chinese Environmental Quality Atandards for Surface Water (GB3838-2002). Plants have different water P removal paths. For example, H. dubia enriched more P with water P concentration increasing significantly. As the culture time increased, the water pH fluctuated significantly in the fall, and then H. dubia used the produced H+ enrich P. L. peploides did not enrich P, but proliferated rapidly, to remove P from water by increasing its fresh weight (FW). L. salicaria and S. sagittifolia showed two paths of enrich-P and FW increase. During the growth process of L. salicaria, the stem diameter and leaf length increased with an increase in P concentration in water or plant or both; however, the height and root length of L. peploides were reduced. Moreover, SOD and CAT activities responded to high P concentrations in water or high temperatures or both, which protected against oxidative damage. These findings could offer theoretical foundation and practical guidance for selection of aquatic plant species in depth treatment of wastewater during summer.

The Safety of Consuming Water Dropwort Used to Purify Livestock Wastewater Considering Accumulated Antibiotics and Antibiotic Resistance Genes.

Research is lacking on the health risks of antibiotics and antibiotic resistance genes (ARGs) in water dropwort grown in livestock wastewater. Our results showed that antibiotics from livestock wastewater were absorbed and bioaccumulated by water dropwort. The concentration of antibiotics was higher in the roots than in the stems and leaves. The health-risk coefficients of antibiotics in water dropwort were below the threshold (<0.1), indicating that in this case study, the consumption of water dropwort used to purify livestock wastewater was safe for humans considering accumulated antibiotics. ARGs were closely correlated between livestock wastewater and water dropwort, with the results showing that all 13 ARGs detected in the livestock wastewater were also found in the water dropwort. Tetracycline resistance genes were more abundant than the other ARGs in both the livestock wastewater and water dropwort. The estimated daily intake of ARGs in water dropwort for humans ranged from 2.06 × 106 to 7.75 × 1012 copies g−1, suggesting the potential risk of intaking ARGs in water dropwort cannot be ignored. Although the safety of consuming water dropwort used to purify livestock wastewater, considering accumulated antibiotics and ARGs, was assessed in this study, more studies should be conducted to ensure we fully understand the health risks.

Phytoremediation performance of three traditional ornamental hydrophytes and the structure of their rhizosphere microorganism populations.

The use of phytoremediation technology in urban and rural landscapes can permit both aesthetic and water purification functions to be achieved sustainably. Here, the ability of three ornamental aquatic plant species (Lythrum salicaria L., Sagittaria trifolia L., and Typha orientalis C. Presl) to remove nutrients from simulated contaminated water over 35 days and the structure of their rhizosphere microorganism populations were evaluated to examine their potential to be used for landscape phytoremediation as well as determine the mechanism of nutrient removal. L. salicaria had the highest nutrient removal ability (86.91-96.96% removal efficiency of total nitrogen and 46.04-66.70% removal efficiency of total phosphorus). The population structure of rhizosphere microorganisms was mainly affected by plant species and not the nutrient level of the water body according to principal coordinates analysis and non-metric multi-dimensional scaling. Betaproteobacteriales and Chitinophagales were highly correlated with the content of nutrients in water according to redundancy analysis. The accumulation of the two orders by L. salicaria and higher biomass might explain the stronger removal ability of L. salicaria. The findings of this study indicate that these plants could enhance urban and rural water landscape design; our results also shed new light on the mechanism of phytoremediation by rhizosphere microorganisms.

Trends and Causes of Raw Water Quality Indicators in the Five Most Famous Lakes of Jiangsu Province, China.

Due to pollutants from industrial and agricultural activities, the lakes in China are faced with ecological and environmental problems. The five most famous lakes of Jiangsu Province, Taihu Lake, Gehu Lake, Gaobaoshaobo Lake, Hongze Lake, and Luoma Lake, have long-term fixed monitoring points for water body-related indicators. Over a five-year period, the monitoring showed that Gehu Lake had the highest average total nitrogen (TN) and total phosphorus (TP) concentrations among all lakes which were close to the Grade V critical value of the China's Environmental Quality Standards for Surface Water (CEQSW). The NH3-N concentrations in all lakes were Grade IV according to the China's Water Quality Standard for Drinking Water Sources (CWQSDWS) and Grade II according to the CEQSW. In addition, although TP concentrations in Taihu Lake did not exceed Grade V in the CEQSW, TP removal was the main factor controlling eutrophication. It was also found that the petroleum concentrations in all lakes were lower than the Grade I according to the CEQSW. Despite this relatively low petroleum pollution, the concentration of petroleum was negatively correlated with the phytoplankton densities in all lakes. This indicated that phytoplankton density was very sensitive to petroleum concentration. For heavy metals, the concentrations of Pb, Cu, As, and Cd in all lakes were significantly lower than Grade I (CEQSW) from 2013 to 2017. However, the accumulated heavy metals in sediments will remain an important pollution source affecting water quality and aquatic products in the future. The comprehensive pollution index analysis showed that the five lakes were often moderately polluted, indicating that the protection of lake resources in China should not be relaxed for a long time in the future.

Removal effects of a biomass bottom ash composite on tailwater phosphate and its application in a rural sewage treatment plant.

Tailwater phosphate from sewage treatment plants and biomass bottom ash (BA) from power plants has become a global concern for the sustainable environmental development and resource management. However, there are large gaps in the understanding of the removal mechanisms and application conditions of BA on tailwater phosphate. In this study, the removal effect and mechanism of BA and its composites were fully discussed using a series of experiments, including adsorption, desorption, characterization, and incubation experiments. It was found that the combination of BA and red soil at a rate of 4:1 (CBA) could remove 92.44% of phosphate from tailwater in 3-10 h. Its adsorption process was well fitted by the pseudo-second-order kinetic and Freundlich isotherm adsorption models. The mechanism of phosphate adsorption primarily included ligand exchange, physical adsorption, chemical precipitation, electrostatic attraction, and ion exchange. The CBA could be used as a better substrate for constructed wetlands because it was effective under wide application conditions, which varying pH values (4.0-8.0), initial concentrations of tailwater phosphate (0.5-5.0 mg L-1), and even extreme temperatures (heat and cold). Moreover, Hippuris vulgaris L. was optimized and combined with the CBA to deeply remove 57.45-76.06% of phosphate from a rural sewage treatment plant. The phosphate concentration after treatment could reach below the limit values of the Grade III or IV standard (GB 3838-2002), though the CBA contained and released phosphate. This study can help provide a recycling route for both BA and tailwater phosphate resources, extend the industrial chain of biomass power plants, and improve the surrounding water environment.

Abundant Allelochemicals and the Inhibitory Mechanism of the Phenolic Acids in Water Dropwort for the Control of Microcystis aeruginosa Blooms.

In recent years, with the frequent global occurrence of harmful algal blooms, the use of plant allelopathy to control algal blooms has attracted special and wide attention. This study validates the possibility of turning water dropwort into a biological resource to inhibit the growth of harmful Microcystis aeruginosa blooms via allelopathy. The results revealed that there were 33 types of allelopathic compounds in the water dropwort culture water, of which 15 were phenolic acids. Regarding water dropwort itself, 18 phenolic acids were discovered in all the organs of water dropwort via a targeted metabolomics analysis; they were found to be mainly synthesized in the leaves and then transported to the roots and then ultimately released into culture water where they inhibited M. aeruginosa growth. Next, three types of phenolic acids synthesized in water dropwort, i.e., benzoic, salicylic, and ferulic acids, were selected to clarify their inhibitory effects on the growth of M. aeruginosa and their mechanism(s) of action. It was found that the inhibitory effect of phenolic acids on the growth of M. aeruginosa increased with the increase of the exposure concentration, although the algae cells were more sensitive to benzoic acid than to salicylic and ferulic acids. Further study indicated that the inhibitory effects of the three phenolic acids on the growth of M. aeruginosa were largely due to the simultaneous action of reducing the number of cells, damaging the integrity of the cell membrane, inhibiting chlorophyll a (Chl-a) synthesis, decreasing the values of F0 and Fv/Fm, and increasing the activity of the antioxidant enzymes (SOD, POD, and CAT) of M. aeruginosa. Thus, the results of this study indicate that both culture water including the rich allelochemicals in water dropwort and biological algae inhibitors made from water dropwort could be used to control the growth of noxious algae in the future.

NiCo2S4nanosheets decorated on nitrogen-doped hollow carbon nanospheres as advanced electrodes for high-performance asymmetric supercapacitors.

Taking advantage of both Faradaic and carbonaceous materials is an efficient way to synthesize composite electrodes with enhanced performance for supercapacitors. In this study, NiCo2S4nanoflakes were grown on the surface of nitrogen-doped hollow carbon nanospheres (NHCSs), forming a NiCo2S4/NHCS composite with a core-shell structure. This three-dimensionally confined growth of NiCo2S4can effectively inhibit its aggregation and facilitate mass transport and charge transfer. Accordingly, the NiCo2S4/NHCS composite exhibited high cycling stability with only 9.2% capacitance fading after 10 000 cycles, outstanding specific capacitance of 902 F g-1at 1 A g-1, and it retained 90.6% of the capacitance at 20 A g-1. Moreover, an asymmetric supercapacitor composed of NiCo2S4/NHCS and activated carbon electrodes delivered remarkable energy density (31.25 Wh kg-1at 750 W kg-1), excellent power density (15003 W kg-1at 21.88 Wh kg-1), and satisfactory cycling stability (13.4% capacitance fading after 5000 cycles). The outstanding overall performance is attributed to the synergistic effect of the NiCo2S4shell and NHSC core, which endows the composite with a stable structure, high electrical conductivity, abundant active reaction sites, and short ion-transport pathways. The synthesized NiCo2S4/NHCS composite is a competitive candidate for the electrodes of high-performance supercapacitors.

A New Green Model for the Bioremediation and Resource Utilization of Livestock Wastewater.

The rapid growth of the livestock and poultry industries has resulted in the production of a large amount of wastewater, and the treatment of this wastewater requires sustainable and environmentally friendly approaches such as phytoremediation. A substrate-free floating wetland planted with water dropwort (Oenanthe javanica), a common vegetable in Southeast China, was constructed to purify a lagoon with anaerobically and aerobically treated swine wastewater in Suqian, China. The average removal rates of total nitrogen, ammonium nitrogen, nitrite nitrogen, and chemical oxygen demand were 79.96%, 95.04%, 86.14%, and 59.91%, respectively, after 40 days of treatment. A total of 98.18 g∙m-2 nitrogen and 19.84 g∙m-2 phosphorus were absorbed into plants per harvest through the rapid growth of water dropwort biomass, and the nitrogen accumulation ability was similar to that observed of other plants, such as water hyacinth. In addition, the edible part of water dropwort was shown to comply with the Chinese National Food Sanitation Standards and be safe for human consumption. Its low soluble sugar content also makes it a suitable addition to the daily diet. Overall, substrate-free floating constructed wetlands planted with water dropwort could be more widely used for livestock wastewater purification and could be integrated with plant-livestock production in China because of its high removal efficiency and recycling utilization of water dropwort biomass.

Removal effects of different emergent-aquatic-plant groups on Cu, Zn, and Cd compound pollution from simulated swine wastewater.

Aquatic plants play effective in removing heavy metal (HM) as a prominent factor of bioremediations, however, there are still knowledge gaps in species selection and configuration for high removal efficiency (RE) of compound HM and ornamental value. In this study, seven emergent-aquatic-plant species were configured into seven groups and planted in a simulated swine wastewater (SW) with Cu, Zn, and Cd for 75 days in summer. REs of Cu, Zn, and Cd were 45.06-86.93%, 42.40-87.22%, and 73.85-85.52% at day 75, respectively. Higher REs were observed from day 30-45 for Cu and Zn, whereas days 15-30 for Cd. The synergistic removal of Zn and Cu or Zn and Cd was almost observed (p < 0.05). The configuration of G5 (S. tabernaemontani, I. sibirica, and P. cordata) was generally efficient roles in the removal at day 45, with REs of 85.14%, 87.06%, and 83.56% for Cu, Zn, and Cd, respectively. The dry weight of roots, water NH4+-N, temperature, pH, and dissolved oxygen acted on heavy-metal removal. During days 45-75, concentrations of Cu, Zn, and Cd in G5 were 0.52-0.66, 0.54-0.65, and 0.23-0.33 mg L-1. The former two were below the limits of Grade Ⅱ (1.0 mg L-1) and the latter was above the limits of Grade Ⅴ (0.1 mg L-1; GB3838-2002). Thus, G5 could be optimal for Cu and Zn removal from simulated SW, however, efficient Cd removal is required to ensure efficient SW recycling.

Removal effects of Myriophyllum aquaticum on combined pollutants of nutrients and heavy metals in simulated swine wastewater in summer.

Swine wastewater (SW) treatment by Myriophyllum aquaticum is an important biotechnology for its resource utilization. However, some knowledge gaps remain in compound-pollutant removal in SW, especially in practical applications. To clarify the responses of M. aquaticum to the compound pollutants as well as the related operational parameters in SW treatment, three initial doses (0.5, 1.0, and 1.5 kg per pond in 150 L simulated SW) of M. aquaticum and a control (no plant; CK) were allocated to 12 ponds under a plastic roof in Nanjing city of Eastern China during 75 days in the summer of 2019. Results showed that M. aquaticum could be used as a pioneer plant to efficiently remove compounded pollutants of nitrogen (N), phosphorus (P), and especially for heavy metals in simulated SW. Compared with CK, M. aquaticum assisted in improving the total N, NH4+-N, NO3--N, NO2--N, and dissolved organic N by 30.1%, 100%, 100%, 97.6%, 20.2%, 39.8% whereas Cu, Zn, and Cd by 50.4%, 36.4% and 47.9% on average during the 75-day experiment in summer, respectively. Moreover, concentrations of Cu and Cd at day 75 were in the ranges of 1.92-2.82 and 0.64-1.47 g kg-1 DW, respectively, exceeding the corresponding limits of the heavy-metal hyperaccumulator. For the operational parameters, the optimized initial dose was 1.0 kg per pond with M. aquaticum harvested after 45 summer days, respectively. Given that M. aquaticum has been widely used as animal feed in recent years and limit values for Cu and Zn in animal feed are not set in China, the toxicities of Cu and Zn should be assessed and the guideline of their limit values needs to be established for safe feed production. Interestingly, NH4+-N could dominate the removal of heavy metals especially Cd in the simulated SW, however, related mechanisms are needed for further study.

Sources and trends of oxidized and reduced nitrogen wet deposition in a typical medium-sized city of eastern China during 2010-2016.

Fluxes and composition dynamics of atmospheric nitrogen deposition play key roles in better balancing economic development and ecological environment. However, there are some knowledge gaps and difficulties in urban ecosystems, especially for small and medium-sized cities. In this study, both flux and composition (ratio of NH4+-N to NO3--N, RN) of wet-deposited dissolved inorganic nitrogen (DIN, sum of NO3--N and NH4+-N) were estimated and sources were identified at a long-term urban observation station in Tongling, a typical medium-sized city in eastern China during 2010-2016, respectively. Results showed that wet-deposited DIN fluxes were 33.20 and 28.15 kgN ha-1 yr-1 in Tongling city during 2010-2011 and 2015-2016, respectively. Compared to these two periods, both DIN and NO3--N fluxes decreased by 15.2% and 31.8% for a series of NOx abatement measures applied effectively, respectively. At the same time, the NH4+-N flux remained stable and ranged from 19.53 to 20.62 kgN ha-1 yr-1, and the RN increased from 1.7 to 2.2. Seasonally, winds from the southwest and west-southwest with higher frequencies and speeds in spring and summer brought more NH4+-N and DIN wet deposition from an ammonia plant, which could threaten the safety of regional hydrosphere ecosystems. On the whole, the wet-deposited NH4+-N was threatening regional ecosystems of both the hydrosphere and forest. The wet-deposited DIN including NH4+-N in Tongling city stemmed mainly from a combined source of coal combustion and dust from Cu extraction and smelting, ammonia production, and roads. Therefore, production lines should be updated for Cu extraction and smelting industries, thermal power generations and the ammonia plant, old vehicles should be eliminated, and the use of new energy vehicles should be promoted for regional sustainable development and human health in the medium-sized city.

Seasonal fluxes and sources apportionment of dissolved inorganic nitrogen wet deposition at different land-use sites in the Three Gorges reservoir area.

To identify seasonal fluxes and sources of dissolved inorganic nitrogen (DIN) wet deposition, concentrations and δ15N signatures of nitrate (NO3-) and ammonium (NH4+) in wet precipitation were measured at four typical land-use types in the Three Gorges reservoir (TGR) area of southwest China for a one-year period. Higher DIN fluxes were recorded in spring and summer and their total fluxes (averaged 7.58 kg N ha-1) were similar to the critical loads in aquatic ecosystems. Significant differences of precipitation δ15N were observed for NH4+-N between town and wetland sites in spring and between urban and rural sites in summer. For NO3--N, significant differences of precipitation δ15N were observed between town and rural sites in spring and between urban and town sites in autumn, respectively. Quantitative results of NO3--N sources showed that both biomass burning and coal combustion had higher fluxes at the urban site especially in winter (0.18 ± 0.09 and 0.19 ± 0.08 kg N ha-1), which were about three times higher than those at the town site. A similar finding was observed for soil emission and vehicle exhausts in winter. On the whole, DIN wet deposition averaged at 12.13 kg N ha-1 yr-1 with the urban site as the hotspot (17.50 kg N ha-1 yr-1) and regional NO3--N fluxes had a seasonal pattern with minimum values in winter. The contribution to NO3--N wet deposition from biomass burning was 26.1 ± 14.1%, which is the second dominant factor lower than coal combustion (26.5 ± 12.6%) in the TGR area during spring and summer. Hence N emission reduction from biomass burning, coal combustion and vehicle exhausts should be strengthened especially in spring and summer to effectively manage DIN pollution for the sustainable development in TGR area.

Effects of Soil Amendments on Microbial Activities in a Typical Cd-Contaminated Purple Field Soil, Southwestern China.

In this study, three soil amendments (inorganic, liming, or organic-inorganic materials) were used in a Cd-contaminated purple field soil to investigate their impacts on soil Cd availability, enzyme (urease, catalase, sucrase, and acid phosphatase) activities, microbial biomass (carbon/nitrogen) and type (bacteria, fungi, and actinomycetes) in mustard and corn trials. Results showed that soil amendments generally decreased soil exchangeable Cd, fungi and bacterial populations while increasing the activities of all the four soil enzymes tested, microbial biomass carbon and populations of actinomycetes (p < 0.05). Soil pH and microbial biomass nitrogen did not exhibit any significant response (p > 0.05) whereas stronger effects appeared in soil organic matter and available nutrients (nitrogen, phosphorous and potassium; p < 0.05). However, only soil available phosphorous significantly correlated with soil microbial activity in both mustard and corn trails (p < 0.05). Thus, application of phosphorous-containing amendments should be considered for promoting soil health in the remediation of the Cd-contaminated purple soils.

Atmospheric deposition of hazardous elements and its accumulation in both soil and grain of winter wheat in a lead-zinc smelter contaminated area, Central China.

Hazardous elements (HEs) and its deposition from atmosphere have become a major healthy and environmental concern worldwide, however, the risks to food safety of deposited HE are still largely unknown, especially for wheat grains (Triticum aestivum L.). This research was to characterize atmospheric deposition of high HEs [such as lead (Pb), cadmium (Cd) and arsenic (As)] at deposited site (TS) and assess its impacts on the soil and winter wheat accumulation in a lead­zinc smelter contaminated area of Central China. Results indicated that deposited As, Cd and Pb at TS site were 31.15, 15.94 and 281.86 mg m-2 during the winter wheat growing season, contributing 86.9%, 81.7% and 80.4% to the annual total, respectively. Most of deposited HEs were retained in top 35-cm soil, resulting in soil Cd concentration above the national soil regulatory limit (0.6 mg kg-1; GB 15618-2018). The newly deposited HEs could contribute 57.7-88.2% and 16.2-29.1% to total HEs of wheat grains in clean soil based on a soil transplanted experiment and in contaminated soil based on a two-year in-situ experiment, respectively. Moreover, the newly deposited HEs significantly increased HE concentration of wheat grain by 22.9-57.5% in the contaminated soil when an immobilizing amendment were applied (p < 0.05), and grain Cd concentration exceeded the national grain limit (0.1 mg kg-1; GB 2762-2017). Thus, deposited HE could be accumulated in soil and wheat grain and decrease the remediation effectiveness of passivation amendments in contaminated soils, which would raise a public awareness of HE deposition and provide a scientific data in support of environmental pollution control and remediation.