361. 题目: Rhizosphere Effect on Physicochemical Properties and Immobilization Performance of Biochar
The application effect of biochar in soil is often affected by environmental factors, but the effect of rhizosphere processes on the properties and functions of biochar remains unclear. The purpose of this study was to explore the effect of the rhizosphere process on biochar characteristics and heavy metal immobilization through different wheat rhizosphere simulation experiments. After aging in the wheat rhizosphere, the physicochemical properties of rice husk biochar (RH BC) and sludge biochar (Sl BC) changed significantly. In general, ash content, specific surface area (SAA), and thermal stability were significantly reduced, while the oxygen (O) content, polarity, and surface O–containing functional groups content were significantly increased. Meanwhile, the increase of C = O and O = C–OH on the aged biochar surface promotes its adsorption capability for Cd2+ and Pb2+ in solution. However, in heavy metal–contaminated rhizosphere soils, the immobilization effect of RH BC on heavy metals was significantly weakened by the rhizosphere process, which may be due to the elevated dissolved organic matter (DOM) content of the rhizosphere soil, but that of Sl BC was not affected. Therefore, although the rhizosphere process may enhance the adsorption performance of biochar for heavy metals, the actual immobilization effect of biochar in the rhizosphere soil was still at risk of being weakened, depending on the type of biochar. An in-depth understanding of how biochar properties change in soil–plant systems will help to scientifically evaluate the long-term effectiveness of biochar.
362. 题目: Characterizing the spatiotemporal distribution of dissolved organic matter (DOM) in the Yongding River Basin: Insights from flow regulation
Artificial flow regulation is an important measure to alleviate water shortages and improve the ecological quality of river basins. Dissolved organic matter (DOM) plays a crucial role in the carbon cycle and regulates biogeochemical and ecological processes in aquatic systems. Among the numerous studies on the effects of anthropogenic activities on the quality and quantity of river DOM, few studies have focused on the influence of different artificially regulated flow on the composition, source, and fate of fluvial DOM. This study aims to elucidate the impact of different artificial regulation modes of river flows on the source, migration, and transformation of DOM. The optical properties of DOM were used to explore the temporal and spatial distribution characteristics of DOM in the Yongding River Basin, where artificial regulation of river flows by cross-basin and inner-basin water transfers were implemented. Excitation–emission matrix fluorescence spectroscopy coupled with parallel factor analysis revealed four fluorescent substances of DOM in the water: one microbial humic-like (C1), one terrestrial humic-like (C2), one non-point source pollution humic-like (C4), and one tryptophan-like (C3) substance. Due to cross-basin water transfer from the Yellow River, the flow is the highest (21.79 m3/s) during spring, which was the reason that the signal of C2 was stronger during spring (71.45 QSU) compared to summer (57.12 QSU) and autumn (51.78 QSU). Due to inner-basin water transfer from upstream reservoirs, C3 derived from autochthonous sources were higher during autumn (130.81 QSU) than during spring (77.17 QSU) and summer (93.16 QSU). With no water transfer, more C1 were present at higher temperatures during summer (141.51 QSU) than during spring (126.73 QSU) and autumn (128.8 QSU). Moreover, C4 originating from urban and/or agricultural non-point source runoff increased during summer (57.07 QSU) than during spring (33.29 QSU) and autumn (52.27 QSU) because of increased rainfall. The different modes of artificial regulation of river flows changed the hydrological characteristics of the basin, which in turn altered the temporal and spatial distribution characteristics of the quantity and quality of DOM. The finding of this study can help promote the development of appropriate management strategies for artificial regulation of river flows in the basin. Furthermore, this study provides a basis for investigating the effects of different artificial flow regulations on the carbon cycles and ecological risks of rivers in the basin.
363. 题目: Improving pedotransfer functions for predicting soil mineral associated organic carbon by ensemble machine learning
Soil organic carbon (SOC) sequestration is a promising natural climate solution for capturing atmospheric CO2, and it provides crucial co-benefits in improving soil functions and services at the same time. Given that SOC is not a single and uniform entity, a deep understanding of SOC response to environmental changes requires additional information on SOC fractions with distinct characteristics such as particulate organic carbon (POC) and mineral associated organic carbon (MAOC). Despite their great importance, POC and MAOC information is still scarce in the soil databases, particularly on a broad scale. Pedotransfer function (PTF) is a good strategy to estimate missing soil properties, while its application in SOC fractions has been poorly explored. Based on 352 representative mineral topsoil samples (0–20 cm) across Europe, we evaluated the potential of MAOC prediction using machine learning based PTF (random forest (RF), Cubist, and gradient boosted machine (GBM)) together with predictor selection methods (recursive feature elimination (RFE) and forward recursive feature selection (FRFS)). The repeated validation (100 times) showed that MAOC could be well predicted by machine learning based PTFs (R2 of 0.877–0.9, RMSE of 2.994–3.269 g kg−1). RFE can effectively reduce the number of predictors from 21 to 12 with comparable performance to the models using all predictors. The proposed FRFS algorithm had the best model parsimony with only 6 predictors (SOC, silt + clay, nitrogen, nitrogen deposition, soil erosion and sand) and performed similar to or even better than RFE. In combination with FRFS, Cubist performed best among the three machine learning models (R2 of 0.9, RMSE of 2.994 g kg−1). Our results also showed that five model ensemble methods had similar model performance and can improve model accuracy and robustness compared to a single machine learning model. This study provides a valuable reference for coupling PTF and legacy soil databases to increase the spatial coverage and the performance of machine learning based SOC fraction predictions.
364. 题目: Phosphorus species in sequentially extracted soil organic matter fractions
The majority of organic P (Porg) in soil is considered to be part of soil organic matter (SOM) associations, but its chemical nature is largely ‘unresolved’. In this study, we investigated the Porg composition in different SOM fractions of a Gleysol soil using the Humeomics sequential chemical fractionation (SCF) procedure combined with nuclear magnetic resonance (NMR) spectroscopy.
In summary, SCF procedure with subsequent NaOH-EDTA extraction of the soil residue extracted a total of 1769 mg P/kgsoil compared to 1682 mg P/kgsoil of a single-step NaOH-EDTA extraction. Approximately 38 % of the extracted Porg was present in the form of the unresolved Porg pool, which was represented by one or two underlying broad signals in the phosphomonoester region of solution 31P NMR spectra. The SCF revealed that phosphomonoesters were recovered in each fraction: 47 % of the unresolved phosphomonoesters were associated with the SOM fraction released by breaking ester bonds (40 %) and ether bonds (7 %), whereas about 30 % of this unresolved Porg pool appeared in the SOM fraction closely associated with the soil mineral phase. Furthermore, the extractability of inositol phosphates (IP) was increased from 312 mg P/kgsoil to 534 mg P/kgsoil (factor 1.7) using the SCF procedure compared to a single-step NaOH-EDTA extraction. Previous studies have reported the presence of IP in molecular size fractions greater than 10 kDa. Our findings on the removal of IP with the fractionation of the SOM could explain the presence of IP in these large associations.
We demonstrate that major pools of Porg are closely associated with SOM structures, comprising a diverse array of chemical species and bonding types. These results forward our understanding of Porg stabilisation, P transformation, and P cycling in terrestrial ecosystems towards an association point of view.
365. 题目: A field incubation approach to evaluate the depth dependence of soil biogeochemical responses to climate change
366. 题目: Effect of pyrolysis temperature of biochar on Cd, Pb and As bioavailability and bacterial community composition in contaminated paddy soil
To further investigate the effect of pyrolysis temperature on bioavailable Cd, Pb and As, as well as the bacterial community structure in multi-metal(loid) contaminated paddy soil, six types of biochar derived from wood sawdust and peanut shell at 300 °C, 500 °C and 700 °C were prepared and incubated with Cd, Pb and As contaminated paddy soil for 45 days. The results showed that adding biochar decreased bioavailable Cd by 31.3%− 42.9%, Pb by 0.61–56.1%, while bioavailable As changed from 9.68 mg kg−1 to 9.55–10.84 mg kg−1. We found that pyrolysis temperature of biochar had no significant effect on Cd bioavailability while Pb bioavailability decreased obviously with pyrolysis temperature raising. Biochar reduced the proportion of soluble and exchangeable Cd from 45.0% to 11.2–15.4% in comparison with the control, while no significant effect on the speciation of Pb and As. Wood sawdust biochar (WSBs) had more potential in decreasing bioavailable Cd and Pb than peanut shell biochar (PSBs). Although high-temperature biochar resulted a larger increase in bacterial species than low-and mid- temperature biochar, feedstock played a more important role in altering soil bacterial diversity and community composition than pyrolysis temperature. PSBs increased the diversity of soil bacteria through elevating soil dissolved carbon (DOC). Biochar altered soil bacterial community structure mainly by altering the level of soil electricity conductivity, DOC and bioavailable Cd. In addition, applying high-temperature PSBs increased the genus of bacteria that relevant to nitrogen cycling, such as Nitrospira, Nitrosotaleaceae and Candidatus_Nitrosotalea.
367. 题目: Adsorption of norfloxacin from wastewater by biochar with different substrates
The type of feedstock and pyrolysis temperature are the main reasons affecting the properties of the resulting biochar. Therefore, this paper investigates the effects of different feedstocks (peanut shell, corn straw and soybean straw) and different pyrolysis temperatures (300, 450 and 600 ℃) on the structural morphology and elemental composition of the resulting biochar. The optimum pyrolysis temperature of 600 ℃ was selected based on the comparison of the adsorption of NFX (norfloxacin) by the biochar prepared at different temperatures. Characterization of biochar materials using x-ray diffractometer, fourier transform infrared spectrometer and scanning electron microscope to study the changes in the physicochemical and structural properties of biochar. The results showed that the pH, surface area and ash content of biochar are increased with increasing temperature. The results of isothermal adsorption and adsorption kinetics experiments showed that the adsorption processes of the three biochar species on NFX were consistent with the Langmuir model and Pseudo-second order kinetic model. The adsorption process occurred in the surface layer of the biochar and was dominated by chemisorption. The inhibition of the adsorption of NFX was more obvious with the higher valence state of cations and the higher ion concentration. The adsorption mechanism of biochar on NFX includes pore filling, hydrogen bonding and electrostatic interactions.
368. 题目: Efficient aqueous molybdenum removal using commercial Douglas fir biochar and its iron oxide hybrids
Molybdenum (Mo) is a naturally-occurring trace element in drinking water. Most commonly, molybdate anions (MoO42-) are in well water and breast milk. In addition, it is used in medical image testing. Recently, the EPA classified Mo as a potential contaminant, as exposure can lead to health effects such as gout, hyperuricemia, and even lung cancer. We have assessed the sorptive removal of aqueous molybdate using Douglas fir biochar (DFBC) and a hybrid DFBC/Fe3O4 composite containing chemically-coprecipitated iron oxide (Fe3O4). Adsorption was studied at various: pH values, equilibrium times (5 min-24 h), initial Mo concentrations (2.5-1000 mg/L), and temperatures (5, 25, and 40 °C) using batch sorption and fixed-bed column equilibrium methods. Langmuir capacities for DFBC and DFBC/Fe3O4 (at pH 3, 2 hrs equilibrium) were within 459.3-487.9 mg/g and 288-572 mg/g, respectively. These adsorbents and their Mo-laden counterparts were characterized by elemental analysis, BET, PZC, SEM, TEM, EDS, XRD, and XPS. MoO42- adsorption on DFBC is thought to be governed primarily via electrostatic attraction. Adsorption by DFBC/Fe3O4 is primarily governed by chemisorption onto magnetite surface hydroxyl groups, while electrostatics prevail in the DFBC-exposed phase. Stoichiometric precipitation of iron molybdates triggered by iron dissolution was also considered. The data suggest that DFBC and DFBC/Fe3O4 are promising candidates for molybdate sorption.
369. 题目: Regulating the exposed crystal facets of α-Fe2O3 to promote Fe2O3-modified biochar performance in heavy metals adsorption
α-Fe2O3 modified biochar (Fe2O3/BC) was prepared to remove Cu(II), Pb(II) and As(V). By adjusting the calcination temperature, the morphology and exposed crystal facets of α-Fe2O3 on the biochar were changed which further affected the adsorption performance. The kinetics and isotherms were investigated systematically to reveal adsorption effect of the adsorbent on Cu(II), Pb(II) and As(V). The results indicated that chemisorption process was the dominant adsorption mechanism. Fe2O3/BC-350 exhibited superior adsorption capacity for Cu(II) (258.22 mg/g) and Pb(II) (390.60 mg/g), and Fe2O3/BC-250 showed relatively good adsorption capacity for As(V) (5.78 mg/g). By adsorption mechanism analysis, electrostatic adsorption, ion exchange, precipitation and complexation were coexisted in the process of removing metal ions by Fe2O3/BC. The repeatability test and the effect of ion strength exhibited the strong stability of Fe2O3/BC. Meanwhile, density functional theory (DFT) calculations manifested that the (202) facet of α-Fe2O3 on Fe2O3/BC-350 possessed the lowest adsorption energies of Cu(II) and Pb(II). While for As(V), it was the (104) facet of α-Fe2O3 on Fe2O3/BC-250 that exhibited the lowest adsorption energy. DFT results revealed that different Fe2O3/BC had different adsorption affinities to various heavy metals. In general, this work not only prepared a promising adsorbent via a simple procedure, but also served as a reference for researchers in designing absorbents with specific active facet for efficient heavy metals remediation.
370. 题目: Properties of river organic carbon affected by wastewater treatment plants
Tracking the sources of organic carbon (OC) is critical not only for understanding riverine carbon dynamics but also for providing management options to improve water quality. We collected water samples from upland forest streams to the mainstream Geumho River (GHR) of South Korea, which included a variety of wastewater treatment plants (WWTP) effluents. We analyzed the concentrations, optical properties, and dual carbon isotope ratios of these samples to identify the sources of OC. Dissolved organic carbon (DOC) was the dominant form of OC in the GHR compared to particulate organic carbon (POC), as the former accounted for 87 % of OC. The concentrations of DOC and POC ranged from 1.2 to 11.2 mg L−1 and from 0 and 3.6 mg L−1, respectively, aside from the livestock WWTP effluent. Dominant fluorescence components were terrestrial humic substances in upper reaches whereas protein-like materials in lower reaches of the GHR whose watershed includes a large city with many WWTPs. Significantly lower Δ14C-DOC and Δ14C-POC were observed in industrial WWTP effluents than the other sites due to the contribution of fossil OC. Livestock WWTP effluents had higher δ13C-DOC and δ13C-POC than most of the sites, possibly due to the animal feed derived from C4 plants such as corn. Fossil OC contributed 29–52 % of [DOC] and 36–56 % of [POC] from industrial WWTP effluents, whereas C4-plants derived OC contributed about half of [DOC] and [POC] from a livestock WWTP effluent. The results suggest that anthropogenic sources of organic carbon could alter river carbon dynamics, and that caution is needed when we interpret isotope ratios of riverine organic carbon, particularly when the river passes through highly populated areas wherein WWTP effluents are large.
371. 题目: Evaluating the impacts of alternative grazing management practices on soil carbon sequestration and soil health indicators
Globally, grazing lands represent a major carbon (C) sink. However, improper use of these ecosystems can degrade their soils and their C storage capacity. Specifically, prolonged high stocking rates in livestock production can result in significantly less soil organic carbon (SOC) and soil fertility in grazing lands. This underlines the need to assess key soil health indicators to determine the ecological efficacy of grazing management. The objective of this study was to identify the impacts of alternative grazing management practices, including heavy continuous (HC), light continuous (LC), and adaptive multi-paddock (AMP) grazing, on SOC and soil health indicators at the ranch and watershed scales in the Lower Prairie Dog Town Fork Red River Watershed in Northwest Texas. The stocking rate was the same under AMP and HC grazing, and it was reduced by half under LC grazing. The Soil and Water Assessment Tool-Carbon (SWAT-C) model was modified and used to conduct this assessment over a 40 year period (1979–2018), after a 900-year spin-up simulation (800 years under natural condition and 100 years under the HC grazing) to initiate the SOC pool. The simulated SOC was validated using observed data from several sampling locations. The study results indicated that when grazing management at the study ranch was changed from the current AMP grazing to hypothetical HC grazing, simulated average annual SOC decreased from 84 to 81.8 Mg/ha (a 2.6% decline). At the watershed-scale, when the grazing management was changed from the baseline HC grazing to AMP grazing, the simulated average annual SOC increased from 35.6 to 38.3 Mg/ha (a 7.5% increase). The net primary productivity (NPP), evapotranspiration (ET), biomass C, and soil nitrogen (N) increased, while C losses from runoff, and sediment loads decreased under AMP grazing. These results indicate that compared to HC, AMP grazing performed better with respect to SOC increase, and improvement of soil ecosystem and hydrological functions at both the ranch and watershed scales in the study watershed. Our findings suggest the need to shift from continuous to AMP grazing in order to improve soil health at multiple spatial scales.
Data availability statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.
372. 题目: A review of long-term change in surface water natural organic matter concentration in the northern hemisphere and the implications for drinking water treatment
Reduced atmospheric acid deposition has given rise to recovery from acidification – defined as increasing pH, acid neutralization capacity (ANC), or alkalinity in surface waters. Strong evidence of recovery has been reported across North America and Europe, driving chemical responses. The primary chemical responses identified in this review were increasing concentration and changing character of natural organic matter (NOM) towards predominantly hydrophobic nature. The concentration of NOM also influenced trace metal cycling as many browning surface waters also reported increases in Fe and Al. Further, climate change and other factors (e.g., changing land use) act in concert with reductions in atmospheric deposition to contribute to widespread browning and will have a more pronounced effect as deposition stabilizes. The observed water quality trends have presented challenges for drinking water treatment (e.g., increased chemical dosing, poor filter operations, formation of disinfection by-products) and many facilities may be under designed as a result. This comprehensive review has identified key research areas to be addressed, including 1) a need for comprehensive monitoring programs (e.g., larger timescales; consistency in measurements) to assess climate change impacts on recovery responses and NOM dynamics, and 2) a better understanding of drinking water treatment vulnerabilities and the transition towards robust treatment technologies and solutions that can adapt to climate change and other drivers of changing water quality.
373. 题目: SOC mediates the contribution of generalists and specialists to changes in soil nirK bacterial diversity: Evidence from apple orchards in main production areas of China
nirK-Denitrifying bacteria are closely related to N2O emissions and they have been studied widely in agro-ecosystems. However, the mechanisms associated with maintenance of the diversity of nirK bacterial communities in agro-ecosystems are unclear. In particular, the ecological roles of “generalists” and “specialists” in nirK bacterial communities under different soil organic carbon (SOC) levels have not been characterized. In this study, we divided 102 soil samples (0–20 and 20–40 cm) from 62 apple orchards in China's main apple producing areas (Shaanxi and Shandong provinces) into four groups according to the SOC content and soil depth, i.e., high organic carbon soils in the 0–20 cm depth, low organic carbon soils in the 0–20 cm depth, high organic carbon soils in the 20–40 cm depth, and low organic carbon soils in the 20–40 cm depth. In the nirK bacterial community, 4187 operational taxonomic units (OTUs) (∼51.32 %) were classified as specialists and 1781 OTUs (∼21.83 %) as generalists. The α-diversity of generalists was higher in the high SOC soils than the low SOC soils, which was consistent with the α-diversity of the whole nirK bacterial community. However, the observed number of specialist species was lower in high SOC soils than low SOC soils. Analysis based on the Spearman's correlation coefficients also showed that the α-diversity and relative abundances of generalists and specialists responded differently to environmental factors. Both deterministic and stochastic processes contributed to the assembly of generalists and specialists. Among the deterministic processes, variable selection was important for the assembly of the generalist community, whereas homogeneous selection was important for the assembly of the specialist community. The niche breadth of generalists was higher than that of specialists, whereas the niche overlap of specialists was higher than that of generalists. The niche breadth of generalists was higher in high SOC soils than low SOC soils. In both networks, generalists had higher degrees than specialists, although the number of generalists was much lower than that of specialists. Our findings demonstrate the contributions of generalists and specialists to the changes in the diversity of the nirK bacterial community at different SOC levels as well as providing new insights into the mechanisms responsible for maintaining the diversity of the nirK bacterial community.
374. 题目: Spatial complexity in dissolved organic matter and trace elements driven by hydrography and freshwater input across the Arctic Ocean during 2015 Arctic GEOTRACES expeditions
375. 题目: Simultaneous alleviation of Cd availability in contaminated soil and accumulation in rice (Oryza sativa L.) by Fe-Mn oxide-modified biochar
Fe-Mn oxide-modified biochar (BC-FM) was used to remediate Cd-contaminated soil and mitigate Cd accumulation in rice. The roles of Fe and Mn in soil Cd immobilization and in controlling Cd uptake by rice were investigated via X-ray photoelectron spectroscopy (XPS) characterization and chemical analysis. Fe and Mn loaded on BC-FM increased the removal efficiencies of CaCl2 extractable Cd in soil and Cd in pore water compared to those in only biochar (BC)-treated soil, with maximum removal rates at 67.9 % and 77.8 %, respectively. The XPS results indicated that the redox reactions of the Fe-Mn oxides on BC-FM surface affected Cd immobilization in the soil. The Fe (II/III) components on BC-FM were primarily converted to Fe3O4 in the soil system, which may form stable complexes with Cd2+ (Fe–O–Cd) during the entire rice growth period, and Cd may be bound to MnO or Mn2O3 in the form of CdMn2O4. The excellent adsorption performance of BC-FM enhanced by Fe-Mn oxides reduced the available Cd in the soil and stimulated Fe and Mn transport in rice, thereby inhibiting Cd accumulation in the aerial parts of rice. Cd concentrations in brown rice under BC-FM treatments reached the national safety standard (0.2 mg/kg, GB2762–2017). And BC-FM significantly increased the biomass of brown rice with a maximum rate of 26.8 %. These findings suggest that BC-FM could be used as an efficient material for Cd-contaminated soil remediation, and Fe-Mn plays important role in immobilizing Cd in soil and reducing Cd transport in rice.
376. 题目: Elevation dependent response of soil organic carbon stocks to forest windthrow
Storms represent a major disturbance factor in forest ecosystems, but the effects of windthrows on soil organic carbon (SOC) stocks are poorly quantified. Here, we assessed the SOC stocks of windthrown forests at 19 sites across Switzerland spanning an elevation gradient from 420 to 1550 m, encompassing a strong climatic gradient. Results show that the effect size of disturbance on SOC stocks increases with the size of the initial SOC stocks. The largest windthrow-induced SOC losses of up to 29 t C ha−1 occurred in high-elevation forests with a harsh climate developing thick organic layers. In contrast, SOC stocks of low-elevation forests with thin organic layers were hardly affected. A mineralization study further revealed high elevation forests to store higher amounts of easily mineralizable C in thick organic layers that got lost following windthrow. These findings are supported by a meta-analysis of available windthrow studies, showing an increase of storm-induced SOC losses with the size of the initial SOC stocks. Modelling simulations further indicate longer-lasting SOC losses and a slower recovery of SOC stocks after windthrow at high compared to low elevations, due to a slower regeneration of mountain forests and associated lower C inputs into soils in a harsh climate. Upscaling the experimental findings/observed patterns by linking them to a data base of Swiss forest soils shows a total SOC loss of ~0.4 Mt. C for the whole forested area of Switzerland after two major storm events, counteracting the forest net carbon sink of decades. Our study provides strong evidence that the vulnerability of SOC stocks to windthrow is particularly high in forests featuring thick and slowly forming organic layers, such as mountain soils. Thus, the risk of losing SOC to more frequent windthrows in mountain forests strongly limits their potential to mitigate climate change.
377. 题目: Molecular characteristics of microalgal extracellular polymeric substances were different among phyla and correlated with the extracellular persistent free radicals
Extracellular polymeric substance (EPS) plays essential roles in microalgal adaptation to the external environment and aggregate formation. The molecular characteristics of EPS and extracellular persistent free radicals (PFRs) of 15 microalgal species belonging to three phyla were analyzed using Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), three-dimensional fluorescence excitation-emission matrices combined with parallel factor analysis (EEM-PARAFAC), and Electron Paramagnetic Resonance Spectrometer (EPR). Lignin accounted for the highest proportion of EPS for Cyanophyta and the proportion of lipids was higher for Bacillariophyta. The presence of PFRs was detected on the cell surfaces of all microalgae species (excluding Cyclotella sp.). The intensity of carbon-centered PFRs was positively correlated with the proportions of humic-like component and lignin, but was negatively correlated with the proportion of lipids in microalgal EPS. Following EPS extraction, carbon- and oxygen-centered free radicals were still detectable on the surface of microalgae. Given the high intensity of PFRs produced by Cyanophyta, the level of PFRs in eutrophic lakes and reservoirs predominated by Cyanophyta may be considerably high. Other organisms in the water column, such as bacteria and zooplankton are bound to be stressed by elevated level of PFRs. The ecological functions and environmental risks of PFRs carried by microalgae still need to be explored in follow-up research.
378. 题目: Exploring recycled agricultural wastes for high-rate removal of nitrogen in wastewater: Emphasizing on the investigation of the inner driving force and comparison with conventional liquid carbon sources
In this study, four typical recycled agricultural wastes (AWs), corn cob, wheat straw, sawdust and walnut shells (named AW1, AW2, AW3 and AW4, respectively), were selected as external solid carbon sources to enhance the removal of nitrogen in wastewater, and specifically, the driving mechanism was thoroughly investigated. The leaching experiments showed that the dissolved organic carbon (DOC) release capacity followed the order of AW1>AW2>AW3>AW4, ranging from 6.21 to 31.92 mg/g. DOC released from AWs mainly consisted of protein-like substances, fulvic acid-like substances and humic-like substances. AW1 and AW2 achieved comparable NOx−-N removal performance with a liquid carbon source of sodium acetate (SA) during the long-term denitrification experiments (>94.2%) but not for the other two AWs (only 16.8%-38.1%). Denitrification performance relied on DOC released from AWs at the beginning, while the enrichment of the functional CAZymes (including glycoside hydrolase and carbohydrate esterase) involved in cellulose and hemicellulose decomposition of AWs and functional genes (GAPDH, gap 2, PK, etc.) related to glycolysis were the inner driving force, which guaranteed the continuous supply of electron donors for denitrification. The relatively high abundances of napAB, narGHI, nirKS, norBC and nosZ, which encode nitrate reductase, nitrite reductase, NO reductase and N2O reductase, assured the better denitrification performance in the SA, AW1 and AW2 groups. In addition to denitrification-related functional genes, the relative abundances of nirBD and nrfAH associated with dissimilatory nitrate reduction were much higher in AW1 and AW2 groups than in SA group, implying that the nitrogen removal mechanism should be different in liquid carbon source and AW-based solid carbon source systems. In addition, GLU, gltBD and glnA, which participate in ammonia assimilation were the highest in the AW2 group, resulting in a large amount of organic nitrogen accumulation (peak concentration of approximately 24.5 mg/L), and this finally ruled it out as an alternative external carbon source. The abovementioned microbial mechanism was verified based on the correlation analysis of nutrient removal and functional genes combined with host bacterial analysis. Our study can provide valuable information for understanding the mechanism of using AWs as alternative external carbon sources to promote the removal of nitrogen in wastewater.
379. 题目: Nutrient enrichment decreases dissolved organic carbon sequestration potential of tropical seagrass meadows by mediating bacterial activity
Dissolved organic carbon (DOC) pool in seawater plays an important role in long-term carbon sequestration in seagrass meadows. Microbial activities (microbial communities and their extracellular enzymes) are the key determining factors of DOC decomposition and sequestration potential, and are affected by nutrient enrichment. However, there is little information on the response of microbial communities and carbon-degrading extracellular enzymes to nutrient loading within seagrass meadows, limiting our understanding of the driving mechanism of DOC decomposition under nutrient enrichment. Here, microbial communities (including bacteria and fungi) and representative extracellular enzyme activity (EEA) in three seagrass meadows with different nutrients levels were investigated across four seasons. Water temperature was the driving factor influencing the seasonal dynamics of EEAs. In addition, the hydrolysis rates of chitinase, β-glucosidase, and α-glucosidase were significantly higher at a high nutrient loading seagrass meadow than at a low nutrient loading meadow. Furthermore, higher relative abundance of bacterial groups, such as Actinobacteria, Bacteroidetes, Cellvibrionale, and Verrucomicrobia were in according with enhanced EEAs, suggesting that these K-strategists were likely involved in enzyme production and the subsequent remineralization of organic matter in seagrass meadows. In contrast with the bacterial community, fungal communities were not sensitive to nutrient concentrations, and there was no strong association between the given fungal groups and EEA. This may be attributed to the low taxonomic resolution of marine planktonic fungi or the minor role of fungi in EEA production. Overall, these results suggested that nutrient loading enhanced EEA levels, modified bacterial rather than fungal communities, and consequently accelerated DOC remineralization, thereby reducing DOC contribution potential of seagrass ecosystems to long term carbon sequestration.
380. 题目: Progress, Barriers, and Prospects for Achieving a “Hydrogen Society” and Opportunities for Biochar Technology