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22841. 题目: Interacting effects of urea and water addition on soil mineral‐bound phosphorus dynamics in semi‐arid grasslands with different land use history | |||||
22842. 题目: Seasonality of dissolved organic carbon exchange across the Strait of Gibraltar Exchange of mass, heat and solutes across the Strait of Gibraltar is fundamental to understand the circulation and biogeochemistry of the Mediterranean. Here we focus on the exchange of dissolved organic carbon (DOC) using data from 12 surveys conducted between 2008 and 2015. DOC exchange exhibits a marked bimodal distribution with minima in late June and late October and maxima in mid April and late August. This pattern is mainly due to seasonal variation of the DOC gradient between the Atlantic Surface Water entering the Mediterranean and the deep opposite flow of Mediterranean Overflow Water. The gradient is controlled by the different seasonal cycles followed by the DOC in the two layers. Annual average DOC import from the Atlantic is equivalent to 4.2 ± 1.5 Tg C y–1, which represents 53% of the external DOC inputs and contributes to support 32% of the net heterotrophy of the Mediterranean. | |||||
22843. 题目: Photochemistry After Fire: Structural Transformations of Pyrogenic Dissolved Organic Matter Elucidated by Advanced Analytical Techniques Pyrogenic organic matter (pyOM) is the solid residue left after pyrolysis of organic matter, a process in nature during forest fires. Upon rain events, pyrogenic dissolved organic matter (pyDOM) leaches and is transferred to the aquatic environment where it has been identified as an important component of the global carbon cycle. Overall, pyDOM consists of highly condensed aromatic compounds (ConAC) and poorly characterized aliphatic molecules. While the ConAC are thought to be persistent in the environment, there has not been observed a large accumulation that would match the calculated fluxes of pyDOM formation and export. Photo-degradation has been identified as a major pyDOM sink, and it can potentially account for the discrepancy in pyDOM's global mass balance. Photochemistry of pyDOM has been studied to a certain extent, but neither the structural transformation pathways of pyDOM nor how they relate to pyrolysis temperature and parent feedstocks are well understood. Thus, we have examined the photo-irradiated products of pyDOM derived from a temperature series (250, 400, 525, 650 OC) of biochars made under controlled laboratory conditions, which can be considered model pyrogenic substances. Ultrahigh resolution mass spectrometry (FT-ICR-MS), one-dimensional 1H NMR, and two-dimensional 1H-1H total correlation spectroscopy (TOCSY) NMR were used to evaluate the compositional changes that occurred with photo-irradiation. In agreement with previous studies, pyDOM aryl groups were the most photo-labile, and alkyl and O-alkyl groups were photo-produced. A new finding is that polysubstituted olefinic moieties of pyDOM were also photo-degraded. Using TOCSY we identified several small molecular weight compounds whose abundance changed non-linearly across the combustion continuum which suggests that different radical processes occur in the different char leachates. Using mass spectrometric data we observed that pyDOM from oak chars made at lower temperatures (250 and 400 OC), as well as pyDOM from a grass char prepared at 650 OC, photo-transform to a more hydrogenated and oxygenated composition. In contrast, pyDOM from higher temperature char leachates (525 and 650 OC) transformed predominantly into small aliphatic compounds. To explain these differences, we propose a photo-transformation mechanism for ConAC which includes oxygenation of ConAC, ring-opening reactions, and sequential decarboxylation yielding small aliphatic N-rich molecules (marine-like composition). These structures could be further polymerized by reactive oxygen species to form straight-chain alkanes if not consumed by microorganisms. Results from these controlled experiments reveal that photo-transformation appears to be a function of production temperature and parent feedstock. This study enhances our understanding of ConAC and pyDOM, their terrestrial-to-marine transfers, geochemical stability, and eventual fate in sunlit environments. Here we also show the value of structural characterization of pyDOM, and reveal the many unknowns left to be answered for this complex and analytically challenging type of organic matter. | |||||
22844. 题目: Effects of five different biochars on aggregation, water retention and mechanical properties of paddy soil: A field experiment of three-season crops Biochar can improve a number of soil physical properties but few studies focused on the impacts of different biochars on soil Atterberg limits and mechanical strength in paddy fields. A field experiment was performed to evaluate the influences of five different biochars on soil physical properties of a paddy soil (Stagnic Anthosol). Biochars produced from rice straw (RB), maize straw (MB), wheat straw (WB), rice husk (HB) and bamboo (BB) were applied to the paddy field with the rate of 0, 11.25, and 22.5 t ha−1, respectively. After three consecutive crops (rice-rape-maize) plantation, the biochar-amended soils were collected to determine a number of soil physical parameters. Compared with control treatment, the application of five biochars at the rate of 22.5 t ha−1 significantly (p < 0.05) increased the content of macroaggregates larger than 5 mm in diameter and aggregate stability evaluated by Le Bissonnais's methodology. Biochar treatments significantly (p < 0.05) increased soil water retention capacity at matric potential of -0.033 and -1.5 MPa, and consequently, enhanced available water content (AWC) in soil. Biochars at the rate of 22.5 t ha-1 treatments increased the AWC by 15.5, 17.1, 26.4, 42.4, and 15.2 % for RB, MB, WB, HB, and BB, respectively. Biochar application could significantly increase the plastic index (PI) of soil, thus effectively extend soil cultivable water range. The application of biochar significantly reduced the tensile strength and cohesion, but no significant effect on internal frication angle of soil was observed. The application of biochars at the rate of 22.5 t ha−1, on average, increased the yield of first season crop (rice) by 6.3∼13.3 %, but only RB and HB treatments significantly increased the yield of second season crop (rape), and RB, WB, and HB significantly increased the yield of third season crop (maize). The scanning electron microscope (SEM) image and elemental mapping of biochars indicated that biochar could alter pore characteristics (size distribution, shape, connectivity, and porosity) of soil, consequently affecting water retention and mechanical strength of soil. Overall, the HB exhibited the largest effect on the AWC, Atterberg limits, and crop yield. The biochar amendment increased the crop yield by improving soil workability for tillage operations and reducing mechanical resistance to crop root growth. | |||||
22845. 题目: Divergent consequences of different biochar amendments on carbon dioxide (CO2) and nitrous oxide (N2O) emissions from the red soil Climate change due to greenhouse gas (GHG) emissions is one of the global environmental matters of the 21st century. Biochar (BC) amendments have been proposed as a potential solution for improving soil quality and to mitigate GHGs emissions. Therefore, we evaluated the influence of different BCs on soil CO2 and N2O emissions in an outdoor pot experiment. The soil was mixed with three different types of BCs; bamboo, hardwood, and rice straw BCs as BB, BH, and BR, respectively, and control as B0 with four levels (0, 5, 20, and 80 g kg−1 of soil). Gas samples were collected on a bi-monthly basis for six months. A polyvinyl chloride (PVC) static chamber was placed on each replicate to collect the gas samples at 15, 30, 45, and 60 min, respectively. Compared to B0, the lowest cumulative N2O emissions were observed in BH80 (11%) followed by BH20, BH5, and BR80. However, for cumulative CO2 emissions, B0 and BC treatments showed no significant differences except for BB80 (>11%) and BB5 (<2%). BC type and level both had a significant (P < 0.001) impact on the cumulative N2O emissions with a significant interaction (P < 0.001). However, cumulative CO2 emissions were unaffected by BC type but BC level showed a significant influence on cumulative CO2 emissions (P < 0.05) and there was a significant (P < 0.001) interaction between the BC type and level on cumulative CO2 emissions. Overall, higher doses of BR and BB showed a pronounced effect on soil pH over BH. The soil pH and moisture showed a negative correlation with N2O emissions whereas soil temperature showed a positive correlation with the cumulative fluxes of N2O. Our results demonstrate that BC incorporation to soil may help to mitigate GHGs emissions but its influence may vary with BC type and level under different conditions and soil type. | |||||
22846. 题目: Microcystin-LR sorption and desorption by diverse biochars: Capabilities, and elucidating mechanisms from novel insights of sorption domains and site energy distribution This study accurately assessed microcystin-LR (MCLR)-trapping capabilities of diverse biochars based on sorption and sequential desorption (SDE), and elucidated MCLR sorption-desorption mechanisms from novel views of sorption domains and site energy distribution along sorption-SDE process. Results showed that maize straw biochar (MSB) and chicken manure biochar (CMB) excelled in trapping MCLR (91.0%–97.4% and 85.7%–96.4%, respectively, at 60–600 μg/L of initial MCLR amount), followed by their respective HCl-treated ones (HCMB, HSMB), while HCl-treated bamboo biochar and pine sawdust biochar poorly trapped MCLR (48.9%–77.8% for HBB, 22.6%–67.2% for HPSB). Non-partition sorption domains (NPSD) contributed more than partition sorption domain (PSD) to MCLR sorption by each biochar. Higher NPSD contribution to MCLR sorption in CMBs and MSBs than other biochars resulted from their higher pHPZC and mesoporosity, which provided stronger electrostatic and pore-filling interaction for MCLR. Desorption hysteresis was weaken with rising aqueous MCLR amount for most biochars. Along SDE process, remaining MCLR in PSD of MSBs, HPSB and HBB could transfer to NPSD, thus desorption ratio continuously decreased with increasing desorption cycle. Differently, remaining MCLR in NPSD of CMBs converted into PSD during 1st–3rd desorption, causing fluctuated desorption ratio without obvious decrease as desorption cycle increased. These implied that MCLR in PSD was more easily desorbed than NPSD for each biochar. Site energy distribution dynamics supported the results of PSD and NPSD contribution changes along SDE. This study was greatly implicated in cost-efficient emergent MCLR-pollution remediation and deeply understanding MCLR sorption-desorption mechanisms of diverse biochars. | |||||
22847. 题目: Treatment of leachate concentrate by electrocoagulation coupled with electro-Fenton-like process: Efficacy and mechanism The efficient treatment of leachate concentrate is a key issue in the application of membrane technology to leachate treatment. Here a process coupling electrocoagulation with an electro-Fenton-like process was developed and tested for the treatment of leachate concentrate using a dual-anode system. The effects of pH, electrode gap, electrical charge, and suspended solids on the performance of organics and ammonia removal were evaluated with leachate concentrates from a municipal waste incineration facility. 57% of the organics and 60% of the ammonia were removed at the electrical charge of 7Ah/L, the potential of 7 V, and pH of 7. Electro-oxidation by hypochlorite ions generated in situ, electrocoagulation and electro-Fenton-like reaction via hypochlorite and ferrous ions achieved the removal. Higher levels of suspended solids and a smaller electrode gap both benefitted the removal of organics. Most of the fulvic acid and humic acid-like substances in the concentrate were removed, with the treatment effectiveness following the order coupled process > electro-Fenton-like process > electrocoagulation process. This coupled process shows an alternative potential as a preliminary process in the treatment of leachate concentrates. | |||||
22848. 题目: Primary sludge as solid carbon source for biological denitrification: System optimization at micro-level Commercial carbon source (e.g. methanol) has been frequently used to enhance heterotrophic denitrification for nitrate removal. However, this is not sustainable due to the high cost of chemical purchasing and excessive sludge production. To address these issues, this study reports an integrated denitrification system using primary sludge as solid carbon source. Complete denitrification without any nitrite accumulation achieved at the primary sludge dosage of 6.0 g VSS/g N with the maximum specific nitrate reduction rate of 6.4 mg N/g VSS/h, which was comparable with the reported soluble carbon source. More importantly, as a solid waste in municipal wastewater treatment plants (WWTPs), the primary sludge was simultaneously reduced by 65.3%–85.1%, and this avoids the intensive denitrification biomass generation that generally occurs in using the commercial carbon source. Ammonium, phosphate, and recalcitrant organic matter were released meantime. Interestingly, the concentration of ammonium and phosphate declined during the denitrification process. The refractory dissolved organics mainly composed of aromatic protein and microbial by-products. The detailed cycle study suggests that an appropriate denitrification cycle/duration time would largely lower the effluent organics concentration, which can be achieved by monitoring the pH turning point. This study clearly demonstrates that primary sludge is a promising alternative carbon source for biological denitrification with great economic benefits and environmental sustainability. | |||||
22849. 题目: Rainfall and conduit drainage combine to accelerate nitrate loss from a karst agroecosystem: Insights from stable isotope tracing and high-frequency nitrate sensing Understanding where nitrate is mobilized from and under what conditions is required to reduce nitrate loss and protect water quality. Low frequency sampling may inadequately capture hydrological and biogeochemical processes that will influence nitrate behavior. We used high-frequency isotope sampling and in-situ nitrate sensing to explore nitrate export and transformation in a karst critical zone. Nitrate was mobilised during light rainfall, and transferred from soil layers to the karst matrix, where some nitrate was retained and denitrified. Nitrate isotopic composition changed rapidly during the rising limb of events and slowly during the falling limb. The main nitrate source was synthetic fertiliser (up to 80% during event flow), transported by conduit flow following high rainfall events, and this contribution increased significantly as discharge increased. Soil organic nitrogen contribution remained constant indicating at baseflow this is the primary source. Isotope source appointment of nitrate export revealed that synthetic fertilizer accounted for more than half of the total nitrate export, which is double that of the secondary source (soil organic nitrogen), providing valuable information to inform catchment management to reduce nitrate losses and fluvial loading. Careful land management and fertilizer use are necessary to avoid nitrate pollution in the karst agroecosystem, for example by timing fertilizer applications to allow for plant uptake of nitrate before rainfall can flush it from the soils into the karst and ultimately into catchment drainage. | |||||
22850. 题目: Coupling-oxidation process promoted ring-opening degradation of 2-mecapto-5-methyl-1,3,4-thiadizaole in wastewater | |||||
22851. 题目: Plant wax evidence for precipitation and vegetation change from a coastal sinkhole lake in the Bahamas spanning the last 3,000 years Plant wax hydrogen isotopic composition is commonly used to reconstruct the hydrogen isotopic composition of precipitation used by terrestrial vegetation. However, mangroves growing in coastal environments take up a mixture of freshwater and seawater. Biosynthetic fractionation (between source water and plant wax) differs between plant types and as a function of salinity, potentially complicating interpretations of past precipitation in coastal environments. In order to reconstruct Holocene hydrologic and ecologic changes archived within sediments from Blackwood Sinkhole on Abaco Island in The Bahamas, we adopt a multi-proxy approach using plant wax hydrogen isotopic composition (δ2H) to reconstruct paleohydrology, together with plant wax carbon isotopic composition (δ13Cwax), sterol biomarkers and pollen abundances to identify vegetation change. When pollen indicates a stable terrestrial plant community (2,950 to 850 cal yrs BP), variations of δ2H values measured on the plant wax C28 n-alkanoic acid are interpreted in terms of precipitation isotope (δ2Hprecip) changes, with 2H-depletion from 2,950 to ∼2,100 cal yrs BP and ∼1,700 to 1,000 cal yrs BP. However, interpretation is complicated at 850 cal yrs BP, when δ2H values decrease (−50‰) concurrent with increased Laguncularia racemosa (white mangrove) and Conocarpus erectus (buttonwood mangrove), and the mangrove-derived biomarker, taraxerol. We develop a pollen-based correction for mangrove inputs, yielding reconstructed precipitation isotope estimates (δ2Hprecip-corr). Low δ2Hprecip-corr values are synchronous with increased abundance of pine pollen, both of which may indicate wetter conditions from 850 cal yrs BP to present. This study provides additional evidence that mangroves can complicate hydrologic reconstructions from n-alkyl terrestrial plant wax biomarkers, and that such complication can be removed by pollen-based correction. After correcting for mangrove inputs, we obtain estimates of δ2Hprecip-corr from –33 to +25‰ throughout the last 2,950 years, with uncertainties on the order of 10-20‰. | |||||
22852. 题目: Molecular and bulk geochemical proxies in sediments from the Conwy Estuary, UK Owing to their restricted riverine flow and greater numbers, small estuaries (annual discharge < 2000 m3 s–1) are important sites of organic carbon (OC) storage in sediments. The Conwy Estuary is an exemplar small rural-agricultural catchment which delivers a diverse pool of terrestrial OC to the Irish Sea. Thirty-nine surface sediments, covering a distance of 10.5 km, were taken transversal as well as longitudinal to the estuary to examine local and distant catchment inputs. Biomarkers (branched Glycerol Dialkyl Glycerol Tetraethers - brGDGTs, n-alkanes) and molecular and bulk proxies (BIT, Paq, TAR, δ13C, C/N), showed sediments were dominated by terrestrial inputs, with only sediments of the three most seaward sites showing stronger physical and geochemical characteristics of a marine influence (e.g., sandier sediments and lower BIT). Biomarker concentrations in the Conwy were comparable to the more urbanised Thames and the Clyde estuaries. The three estuaries showed similar fractional abundance of the brGDGTs, recording an inverse trend between the hexamethylated and the tetramethylated brGDGTs, and showing the pentamethylated brGDGTs as the dominant group. A systematic decrease in terrestrial biomarkers from bank to the main channel confirmed either a strong localised erosion/runoff process or a decrease in water velocity leading to a higher deposition. | |||||
22853. 题目: Internal enhancement mechanism of biochar with graphene structure in anaerobic digestion: The bioavailability of trace elements and potential direct interspecies electron transfer The main aim of the work is to understand the internal mechanism of biochar improving anaerobic digestion (AD) performance. This study evaluated the impact of biochar produced at 400 °C and 900 °C pyrolysis on the AD performance. The results indicated that the methane content increased from an inhibited value of around 60% in the control group to the theoretical value of 75% in the reactor with biochar produced at 900 °C pyrolysis, and the specific methane production increased to 725 mL/g VS/d. The bioavailability of trace elements (TEs) including Fe, Co and Ni was enhanced with the addition of biochar. Correspondingly, enzymatic activity test and metagenomic analysis signified the abundance of the enzyme gene as well as enzyme activity increased with the enhancement of the bioavailability of TEs by biochar. According to the metagenomic analysis of the microbial community and the metabolism pathway, Pseudomonas could participate in direct interspecies electron transfer (DIET) with Methanosaeta via biochar with graphene structure as an electron contact through carbon dioxide reduction so as to heighten methane metabolism. The obtained findings may provide new insight into the internal enhancement mechanism between enzymes as well as the bioavailability of TEs by biochar. | |||||
22854. 题目: Refractory DOM in industrial wastewater: Formation and selective oxidation of AOPs The performances of advanced oxidation processes (AOPs) for the removal of refractory dissolved organic matter (DOM) are significantly different due to the various degradation mechanisms and competitive interactions between DOM and AOPs. This research traced the variation and removal of DOM components in tannery wastewater (TW) during conventional treatment, which includes coagulation, hydrolytic acidification/anoxic (H/A), and anaerobic/aerobic (A/O) stages. Electrochemical oxidation (EO) and ozone oxidation (OO) AOPs were conducted to treat a conventional treatment effluent based on selective oxidation and performance. The results demonstrated that the refractory DOM of the secondary effluent of the TW was mainly the hydrophilic neutrals (HIN) fraction (44.1%), which consisted of fatty acids and aliphatic compounds, and the hydrophobic acids (HOA) fraction (28.5%), which included the carboxylic-rich alicyclic molecules (CRAMs) and complex polycyclic aromatic structures. During the conventional treatment, lower molecular weight (MW) aliphatic and protein substances were preferentially removed by the H/A stage, while the A/O stage more completely eliminated hydrophobic aromatic substances of a lower MW. However, humus-like substances increased in both scenarios. With respect to the two AOPs, OO preferentially removed substances with a lower MW, and the HOA fraction converting to hydrophilic humus-like substances followed with more derived by-products. Comparing to OO, EO performed better on the removal of aromatic compounds, especially the humus-like substances (polycyclic aromatic and CRAM-like substances) in HOA fraction, therefore significantly improved the biodegradability of the effluent. The results indicate that EO has a better selectivity for humus-like substances and is suitable for the treatment of refractory DOM containing chloride. | |||||
22855. 题目: The overlooked role of carbonaceous supports in enhancing arsenite oxidation and removal by nZVI: Surface area versus electrochemical property Carbonaceous supports (e.g. biochar) have been widely applied to enhance the performance of nanoscale zero-valent iron (nZVI) for removing heavy metals (e.g. arsenic; As) due to their large surface areas (SSA) to alleviate nZVI particles aggregation, while their electrochemical properties are largely overlooked. Herein, the role of these two characteristics in enhancing As(III) removal has been systematically investigated through designing two parallel experiments to identify the effects of the two characteristics of biochar. Our results suggest that biochar with varying surface areas (33.38–470.36 m2/g) supported nZVI exhibits a substantially higher the As(III) oxidation rate (29.7–34.3%) and removal [295.5–371.5 mg/(g·nZVI)] efficiency compared to that by nZVI [27.1%; 192.7 mg/(g·nZVI)]. Despite the importance of SSA, the biochar with extremely low SSA of 33.38 m2/g appears to have comparable capacity of enhancing nZVI's performance with a nZVI loading up to 50%. On the contrary, electrochemical analysis suggests that the oxidation and removal of As(III) are highly related to the electron accepting capacity of biochar, indicating a strong electrochemical effect of biochar in As(III) removal varying with pyrolysis temperature. Surface quinone moieties are found responsible for enhancing electron transfer between biochar [up to 0.25 mmol e·(g biochar)−1] and nZVI, promoting nZVI corrosion and the generation of reactive oxygen species (ROS; mainly ) for enhancing the As(III) oxidation and removal. These findings highlight the important role of electrochemical properties of carbonaceous supports rather than SSA in developing nZVI-based materials for further improving heavy metals removal. | |||||
22856. 题目: Enhanced elemental mercury removal via chlorine-based hierarchically porous biochar with CaCO3 as template Mercury emission from coal-fired flue gas has threatened the natural environment. It is an urgent demand for developing more effective and cheap sorbents to substitute the high-cost commercial activated carbon for removing elemental mercury. In this work, an innovative route is proposed to prepare hierarchical porous biochar via one-step co-pyrolysis of waste rice straw and polyvinyl chloride with CaCO3 as a template. The optimum material (RPC-313) delivers over 90% capture performance for Hg0 at 120 °C under 225000 h−1 of GHSV. Characterization results show that the high efficiency of this sorbent is attributed to the synergistic effect of high chlorine-containing active sites (2.02%) and the developed hierarchically pores (large specific surface area of 554.9 m2/g and pore volume of 0.6397 m3/g). It also indicates that during the preparation process, the H–Cl generated from PVC react with CC groups on the surface of bio-chars to form the C–Cl groups. The employed CaCO3 as a template creates a hierarchical structure for the sorbent. Moreover, the mercury reaction mechanism is identified as a chemisorption process which can be divided into two parts: adsorption and oxidation. An excellent mesoporous ratio (70%) accelerates mercury diffusion inside the CaCO3-activated adsorbent. And the C–Cl groups are directly beneficial for the adsorption of Hg0 according to DFT calculation. Furthermore, the C–Cl bonds and active oxygen species on the micropores surface of adsorbent act as reaction sites for oxidizing the adsorbed Hg0 into HgCl2 and HgO, respectively. The HgCl is considered as an intermediate in the reaction pathway. | |||||
22857. 题目: Is soluble protein mineralisation and protease activity in soil regulated by supply or demand? Protein represents a major input of organic matter to soil and is an important source of carbon (C) and nitrogen (N) for microorganisms. Therefore, determining which soil properties influence protein mineralisation in soil is key to understanding and modelling soil C and N cycling. However, the effect of different soil properties on protein mineralisation, and especially the interactions between soil properties, are poorly understood. We investigated how topsoil and subsoil properties affect protein mineralisation along a grassland altitudinal (catena) sequence that contained a gradient in soil type and primary productivity. We devised a schematic diagram to test the key edaphic factors that may influence protein mineralisation in soil (e.g. pH, microbial biomass, inorganic and organic N availability, enzyme activity and sorption). We then measured the mineralisation rate of 14C-labelled soluble plant-derived protein and amino acids in soil over a two-month period. Correlation analysis was used to determine the associations between rates of protein mineralisation and soil properties. Contrary to expectation, we found that protein mineralisation rate was nearly as fast as for amino acid turnover. We ascribe this rapid protein turnover to the low levels of protein used here, its soluble nature, a high degree of functional redundancy in the microbial community and microbial enzyme adaptation to their ecological niche. Unlike other key soil N processes (e.g. nitrification, denitrification), protease activity was not regulated by a small range of factors, but rather appeared to be affected by a wide range of interacting factors whose importance was dependent on altitude and soil depth [e.g. above-ground net primary productivity (NPP), soil pH, nitrate, cation exchange capacity (CEC), C:N ratio]. Based on our results, we hypothesise that differences in soil N cycling and the generation of ammonium are more related to the rate of protein supply rather than limitations in protease activity and protein turnover per se. | |||||
22858. 题目: Forest management impacts on stream integrity at varying intensities and spatial scales: Do abiotic effects accumulate spatially? Though effects of forest harvesting on small streams are well documented, little is known about the cumulative effects in downstream systems. The hierarchical nature and longitudinal connectivity of river networks make them fundamentally cumulative, but lateral and vertical connectivity and instream processes can dissipate the downstream transport of water and materials. To elucidate such effects, we investigated how a suite of abiotic indicators changed from small streams to larger downstream sites (n = 6) within three basins ranging in forest management intensity (intensive, extensive, minimal) in New Brunswick (Canada) in the summer and fall of 2017 and 2018. Inorganic sediments, the inorganic/organic ratios and water temperatures significantly increased longitudinally, whereas nutrients and the fluorescence index of dissolved organic carbon (DOC; indication of terrestrial source) decreased. However, some longitudinal trends differed across basins and indicated downstream cumulative (inorganic sediments, the inorganic/organic ratios and to a lesser extent DOC concentration and humification) as well as dissipative (temperatures, nutrients, organic sediments) effects of forest management. Overall, we found that the effects previously reported for small streams with managed forests also occur at downstream sites and suggest investigating whether different management practices can be used within the extensive basin to reduce these cumulative effects. | |||||
22859. 题目: Electrocatalytic degradation of humic acid using particle electrodes of activated carbon loaded with metallic cobalt A column granular electrode loaded with metallic cobalt was prepared using powder activated carbon (namely Co/AC) and used in a continuous electrochemical reactor to degrade humic acid (HA). The results of XRD indicated that the form of catalyst prepared at 600 °C for 4 h mainly consisted of Co0, whereas it consisted of CoO when prepared at 450–500 °C for 4 h. The Co0 possessed better catalytic effects in the degradation of HA than CoO. When C0 of HA was 200 mg L−1, the C/C0 approached 0.06–0.12 under 0.1 A, pH of 7.0, 0.01 M Na2SO4, and 20 min of hydraulic retention time (HRT). The current, HRT, initial pH, electrolyte type and concentration influenced the degradation of HA. The ESR signals indicated that both H∗ and OH were catalytically generated by Co/AC electrode. Compared to AC electrodes, the Co/AC electrodes showed a faster reaction Tafel slope (68 mV dec−1) and larger electrochemical double-layer capacitance (Cdl = 1.93 mF cm−2). The degradation and removal of HA was achieved by both the electro-oxidation and electro-reduction in the Co/AC electrode system. | |||||
22860. 题目: Can N2O emissions offset the benefits from soil organic carbon storage? To respect the Paris agreement targeting a limitation of global warming below 2°C by 2100, and possibly below 1.5 °C, drastic reductions of greenhouse gas emissions are mandatory but not sufficient. Large‐scale deployment of other climate mitigation strategies are also necessary. Among these, increasing soil organic carbon (SOC) stocks is an important lever because carbon in soils can be stored for long periods and land management options to achieve this already exist and have been widely tested. However, agricultural soils are also an important source of nitrous oxide (N2O), a powerful greenhouse gas, and increasing SOC may influence N2O emissions, likely causing an increase in many cases, thus tending to offset the climate change benefit from increased SOC storage. Here, we review the main agricultural management options for increasing SOC stocks. We evaluate the amount of SOC that can be stored as well as resulting changes in N2O emissions to better estimate the climate benefits of these management options. Based on quantitative data obtained from published meta‐analyses and from our current level of understanding, we conclude that the climate mitigation induced by increased SOC storage is generally overestimated if associated N2O emissions are not considered but, with the exception of reduced tillage, is never fully offset. Some options (e.g, biochar or non‐pyrogenic C amendment application) may even decrease N2O emissions. | |||||
