1. 题目: Role of crystalline iron oxides on stabilization of inositol phosphates in soil
Inositol phosphates selective retention in soil is related to their great affinity to iron (Fe) oxides, with which they interact by the formation of ligand exchange complexes. Soils contain from amorphous to crystalline Fe oxides forms, as goethite (Gt), whose effect on inositol phosphates retention is well-known. The contribution of other widespread crystalline Fe oxides as haematite (Hm), magnetite (Mt) and maghemite (Mh) is instead less known. These oxides display different phosphorus (P) retention and release capacities due to their specific surface properties and stability towards protons, organic acids and complexing agents. We therefore investigated: i) the extent and mechanisms of myo-inositol hexaphosphate (InsP6) and inorganic phosphate (Pi) adsorption on Gt, Hm, Mt and Mh, also studying the computational geometries of InsP6 molecule; ii) the reversibility of the reaction as affected by pH and in the presence of citrate; iii) the efficiency of NaOH-EDTA on P extraction. Compared to Gt, Hm retained less InsP6, due to the distribution of superficial –OH groups allowing for the interaction of two phosphate groups instead of four, as for Gt. Mt and Mh retained more InsP6 than Hm, also through precipitation processes due to a partial dissolution of the oxides caused by InsP6. Desorption of InsP6 in the pH range 3.5–8.5 was negligible, except for Hm, while citrate led to larger desorption, with no release from Gt. NaOH-EDTA extraction of InsP6 was instead particularly effective from Gt and less from the other oxides. The four crystalline Fe oxides thus showed different capacity to retain organic P in the form of InsP6 as a function of surface properties and stability of the mineral-P complexes, therefore influencing the extent of release, accumulation and turnover in soils.
2. 题目: Light Absorption Properties of Organic Aerosol from Wood Pyrolysis: Measurement Method Comparison and Radiative Implications
3. 题目: Persistent free radicals on N-doped hydrochar for degradation of endocrine disrupting compounds
Metal-free carbocatalysts are raising increased interest in advanced oxidation processes (AOPs) for green degradation of aqueous organic pollutants. In the present study, a series of N-doped hydrochars (NHCs) was prepared from pinewood biomass and used in carbocatalysis toward catalytic peroxymonosulfate (PMS) activation to degrade refractory endocrine disrupting compounds. Nitrogen-doping was found to regulate the concentrations and types of persistent free radicals (PFRs) on hydrochar, promoting the electron transfer and oxidative degradation of the contaminants. Mechanistic studies revealed that graphitic N not only shows a strong electron transfer to facilitate PMS activation in a nonradical pathway, but also induces the formation of oxygen-centered PFRs from the structure defects for a radical oxidation pathway. More importantly, the PMS/NHC system demonstrates efficient degradation and satisfactory stability for real water treatment. This study has gained in-depth understanding on the roles of N-dopants in radical and nonradical pathways of biomass-based carbocatalysis, and will provide a promising and environmental-friendly route for efficient degradation of refractory endocrine disrupting compounds for green remediation.
4. 题目: Waste-derived biochar: Applications and future perspective in microbial fuel cells
Application of microbial fuel cell (MFC) is coming to the forefront as a dual-purpose system for wastewater treatment and energy recovery. Future research should emphasize on developing low cost field-scale MFCs for removal of organic matter, nutrients, xenobiotic and recalcitrant compounds from wastewaters and powering low energy devices. For achieving this, low cost electrodes, low cost yet efficient cathode catalysts and proton exchange membrane (PEM) should be developed from waste-based resources to salvage the waste-derived material as much as possible, thereby reducing the fabrication cost of this device. Biochar is one such low cost material, which has wide range of applications. This review discusses different applications of biochar in MFC, viz. in the form of standalone electrodes, electrocatalyst and material for PEM in light of different characteristics of biochar. Further emphasis is given on the future direction of research for implementation of biochar-based PEMs and electrodes in field-scale MFCs.
5. 题目: Biochar alters nitrogen and phosphorus dynamics in a western rangeland ecosystem
Application of biochar to soils has been proposed as a novel approach to managing wood residuals, enhancing soil carbon (C) storage and improving soil fertility; however, the majority of biochar studies have been conducted in agricultural systems that rely on tillage and nutrient inputs associated with annual cropping schemes. Few studies have evaluated the influence of biochar on soil processes in semi-natural rangeland ecosystems that feature more complex plant communities, lack deep soil disturbance, and have relatively few external nutrient inputs. In August 2018, biochar produced using wood waste from a lumber mill in Columbia Falls, MT, USA was applied to surface soils in replicated plots at an experimental ranch in western Montana to test the impact of biochar on soil C storage and nutrient management. A series of soil biochemical properties including total soil C and nitrogen (N), microbial N functional genes, available phosphorus (P) and the net accumulation of nutrients below surface soil layer were evaluated over a one-year period following biochar addition with or without a poultry litter based organic fertilizer. Biochar used alone slightly reduced soil NH4+, significantly increased soil nitrification potential, increased the relative abundance of the bacterial amoA gene, and increased the soil nitrate (NO3−) pool size, while having no net effect on soil inorganic N accumulation below surface soil. By contrast, biochar previously charged with poultry litter (termed charged biochar) had no effect on NH4+ availability, but a positive effect on amoA abundance. Charged biochar significantly reduced NH4+ accumulation below 25 cm depth compared to poultry litter alone. Biochar additions led to a shift towards a more fungal dominated community and a general increase in P availability. However, biochar used alone also contributed to a greater amount of soluble P collected below surface soil, an effect slightly attenuated when biochar was applied with poultry litter. Soil pH increased from 5.7 to 6.9 in response to biochar addition and was one of the dominant factors governing much of the observed changes in soil processes. Charged biochar helped retain soil nutrients and promoted soil C storage in this semi-natural rangeland system over one growing season. Changes in these soil pools and fluxes may influence various trophic groups affecting ecosystem functioning over time.
6. 题目: Nitrate migration and transformations in groundwater quantified by dual nitrate isotopes and hydrochemistry in a karst World Heritage site
Karst aquifers are extremely vulnerable to pollution, including from nitrate. This research advances a systematic evaluation of water quality dynamics and processes in a relatively pristine karst flow system impacted by seasonal tourism, in particular migration and transformation of nitrate. Water samples from the Shuifang Spring basin (Jinfoshan Karst World Heritage Site, Chongqing, China) were collected for analysis of ion concentrations and dual nitrate isotopes. The principal sampling sites included untreated tap water from the Jinfoshan Holiday Hotel (JHH), JHH septic system effluent, discharged effluent at Sinkhole #1, and groundwater at Shuifang Spring (SFS, the resurgence of the basin). Sampling from April 2017 through April 2018 showed that higher nitrate concentrations were observed at SFS during busy tourist seasons that occurred in the summer drought and winter dry seasons. Between the septic system and SFS, nitrate was diluted by rainwater and infiltration from the matrix regions of the karst aquifer in the wet season. The MixSIAR model quantitatively revealed that nitrate from manure and sewage (M&S), soil organic nitrogen (SON) and atmospheric precipitation (AP) contributed roughly 55%, 41% and 4% on average, respectively. The mixture of effluent and oxygen-rich tap water from the JHH underwent nitrification at the septic system and Sinkhole #1. After the nitrification and decomposition of organic matter with oxygen consumption in the effluent, denitrification was the dominant response to nitrate attenuation in the effluent of Sinkhole #1 during peak tourism periods. The septic effluent sinking into the aquifer deteriorated the groundwater quality, which was controlled by nitrification in the summer drought and winter dry seasons. In contrast, microorganisms in groundwater assimilated nitrate from effluent in the wet season. Because of the relatively pristine ambient background conditions and seasonal tourism, these results can inform interpretation of background and impacted nitrogen processes in a range of karst settings.
7. 题目: Effect of clay on greenhouse gas emissions and humification during pig manure composting as supported by spectroscopic evidence
To evaluate the effect of clay on greenhouse gas (GHGs) emissions and humification during pig manure (PM) composting, two lab-scale composting experiments, a control and a 10% clay treatment, were established. The results showed that adding clay reduced the emissions of CH4 and N2O by 45.88% and 86.79%, respectively, promoted the degradation of organic matter (OM) and facilitated the synthesis of humic acid (HA). The spectrum of dissolved organic matter (DOM) indicated that adding clay promoted the formation of aromatic carbon compounds and the degradation of aliphatic carbon. Furthermore, compared with the control, the spectral parameters including the specific UV absorbance at 254 nm (SUVA254), the specific UV absorbance at 280 nm (SUVA280) and the ration of the area at 435-480 nm and at 300-345 nm (A4/A1) of DOM were increased by 5.45%, 3.66% and 29.26%, respectively. Combined with the excitation - emission matrix (EEM) and the percentage fluorescence response (Pi,n), the clay amendment promoted the decomposition of tyrosine and Tryptophan and the formation of humic-like substances, and thus increased humification. The variation in the HA/fulvic acid and the humification index confirmed these results. Therefore, clay amendment is beneficial for reducing GHG emissions, promoting humification and aromatization during pig manure composting.
8. 题目: Logging residue piles of Norway spruce, Scots pine and silver birch in a clear-cut: Effects on nitrous oxide emissions and soil percolate water nitrogen
We analysed how logging residue (LR) piles of common tree species in Finland, Norway spruce (Picea abies (L.) H. Karst.), Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth), affect nitrogen (N) losses in forest soil after final felling. A Norway sprucedominated stand was clear-cut and followed by two experimental setups to study the nitrous oxide (N2O) emissions and leaching of carbon (C) and N. Experiments consisted of four treatments: tree species treatments consisting of 40 kg m−2 of LR and a control treatment without residues. The C losses were monitored as dissolved organic carbon (DOC), the N losses as ammonium (NH4-N), nitrate (NO3-N) and dissolved organic nitrogen (DON) fluxes and concentrations in soil percolation waters and the N2O emissions as fluxes from the forest soil to the atmosphere. In addition the soil temperatures, the molecular size distribution of the DOC from the soil percolation waters and the origin of the N2O production were determined. The LR piles lowered the soil temperatures and, especially those of birch, increased the concentrations of NO3-N in the soil percolation waters already 1 year after the establishment of the piles. The LR piles increased the NH4-N concentrations. The smallest molecular size fraction (<1 kD) of DOC predominated in all treatments. The N2O fluxes peaked under the piles during the second and third growing seasons; however, the inconsistent fluxes tended to be low. The production of N2O was driven by both nitrification and denitrification processes, the proportion depending on the tree species. Our results indicate that LR piles accelerate N losses 1 year after the clear-cutting, especially NO3-N, which predominates in the soil percolation waters under the birch residues, whereas spruce residues tend to stimulate N2O emissions longer. These results have implications for sustainable forest management practices and nutrition of regrowing vegetation.
9. 题目: Exopolysaccharides may increase biocrust rigidity and induce runoff generation
The potential of biocrusts (biological soil crusts) to generate runoff is a matter of great controversy, especially in arid and semiarid regions. Most authors maintain that runoff in the presence of biocrusts is generated as a result of hydrophobicity, crust structure, texture or surface roughness. Hypothesizing that runoff over biocrusts may result from partial pore clogging, brought on by extracellular polymeric substances (EPS), we compare two crust types from Nizzana in the northwestern Negev, Israel (NIZID, NIZPON) that readily generate runoff under natural field conditions to a crust type from Nizzanim in the southern coast of Israel (NIMID) that fails to generate runoff. We hypothesize that biocrust-induced EPS of the NIZ crusts will have different biochemical and viscoelastic properties than that of NIM. We conducted sprinkling experiments on the crusts, measured the biochemical properties (thickness, water repellency, compressive strength, water-holding capacity, silt and clay content, roughness) and the adhesion and viscoelastic properties of the crust EPS using quartz crystal microbalance with dissipation monitoring (QCM-D). Both crusts were not water repellent and were characterized by a relatively smooth surface. The NIZ crusts were however characterized by higher water-holding capacity and compressive strength. As far as the EPS is concerned, higher shear viscosity and shear modulus characterized the NIZ crusts, indicating higher crust integrity and rigidity and the formation of durable mineral grain-EPS matrix of the NIZ crusts. The findings point to a possible link between crust rigidity and runoff coefficients providing supporting evident for the role played by EPS in crust formation and runoff generation. Knowledge regarding the potentiality of runoff and hence water redistribution may assist in ecosystem management and agroforestry practices.
10. 题目: Disulfide polymer grafted polypropylene/polyethylene filter media for selective cadmium removal
Heavy metal pollution caused by stormwater runoff has triggered a demand for effective heavy metal sorbents. Effective heavy metal removal using conventional stormwater runoff treatment processes that employ filtration mechanisms as primary removal mechanisms is difficult. Therefore, we attempt to improve cadmium removal performance by attaching disulfide polymer (DiS-COP) containing soft bases, thiols, onto the surface of polypropylene/polyethylene (PP/PE) fiber media, which is widely used for stormwater runoff treatment. Material characterization demonstrated that DiS-COP was successfully grafted and grown on the surface of PP/PE (Dis-PP/PE). The batch and continuous flow adsorption capacities of Dis-PP/PE were 81.1 mg/g and 2.33 mg/g, respectively, which is 40 times higher than those of pristine PP/PE. Applicability of DiS-PP/PE at pH 6–8 was demonstrated, and effects of calcium and humic acid on cadmium adsorption were investigated. Calcium marginally affected cadmium adsorption, which can be explained using the Hard and soft (Lewis) acids and bases theory (HSAB), but cadmium removal efficiency decreased owing to humic acid (HA) -Cd complex formation and agglomeration in the presence of organic material. In a breakthrough test, the adsorption column exhibited complete cadmium uptake over 24 h until it reached the breakthrough point. Therefore, heavy metal adsorption performance of PP/PE was successfully enhanced by grafting DiS-COP on its surface.
11. 题目: The spontaneous secondary synthesis of soil organic matter components: A critical examination of the soil continuum model theory
The Soil Continuum Model questions the occurrence of any independent natural process of secondary synthesis that generates compounds structurally distinct from plant or microbial metabolites. This review shows that a vast volume of interdisciplinary scientific evidence supports the formation of relevant non-pre-existing complex molecules exhibiting various types of structures. These molecules form during degradation and decay of biological cell components. The spontaneous abiotic and enzymatically catalysed reactions of components of organic residues and of their oxidative decomposition products suggested by state-of-the-art studies are indeed those proposed by most of the classical descriptions of humification. The review also highlights the chemically active role of pedofauna, explaining why the apparently harsh conditions of alkaline extraction of HS cannot be considered un-natural. Many insects and larvae feeding on foliage of plants with a high content of tannins have a midgut pH above 9. Albeit, reducing conditions are often maintained to avoid oxidation, peroxidases are active in the intestinal tract and pass on to feces. Polyphenols are then immediately enzymatically oxidized to their reactive quinone form, once feces are excreted and exposed to oxygen. Implications of our current knowledge on the reactivity of plant components in soil are discussed in relation with the present state of the art research on humic substances. Contrary to claims by the Soil Continuum Model theory, complimentary modern approaches need to be used to understand the complexity of soil organic matter.
12. 题目: Biochar amendment mitigates greenhouse gases emission and global warming potential in dairy manure based silage corn in boreal climate
About 11% of the global anthropogenic greenhouse gases (GHGs) emissions result from agricultural practices. Dairy manure (DM) application to soil is regarded as a best management practice due to C sequestration and improvement of soil physiochemical properties. However, GHGs emissions from the soil following the DM application could offset its advantages. Biochar (BC) is known to affect N transformation and GHGs emissions from soil. There had been considerably less focus on the BC amendment and its effects on GHGs emissions following DM application under field conditions. The objectives of this study were; i) to determine the temporal patterns and cumulative GHGs fluxes following DM and inorganic nitrogen (IN) application and, ii) to investigate BC amendment impact on DMY, GWP, direct N2O emission factor (EFd) and the response of CH4 emissions (RC) in DM based silage corn. To achieve these objectives a two-year field experiment was conducted with these treatments: 1) DM with high N conc. (DM1: 0.37% N); 2) DM with low N conc. (DM2: 0.13% N); 3) IN; 4) DM1+BC; 5) DM2+BC; 6) IN + BC; and 7) Control (N0); and were laid out in randomized complete block design with four replications. BC amendment to DM1, DM2 and IN significantly reduced cumulative CO2 emission by 16, 25.5 and 26.5%, CH4 emission by 184, 200 and 293% and N2O emission by 95, 86 and 93% respectively. It also reduced area-scaled and yield-scaled GWP, EFd, RC and enhanced DMY. Thus, BC application showed great potential to offset the negative effects of DM application i.e GHGs emissions from the silage corn cropping system. Further research is needed to evaluate soil organic carbon and nitrogen dynamics (substrates for GHG emissions) after DM and BC application on various soil types and cropping systems under field conditions.
13. 题目: Changes to soil organic matter decomposition rate and its temperature sensitivity along water table gradients in cold-temperate forest swamps
High-latitude forest swamp soil stores a large amount of carbon (C), because of its anaerobic condition and lower temperature. The combination of decreasing water table by artificial drainage and climate warming exert a considerable influence on soil C storage. In this study, we explored how the soil organic matter decomposition rate (Rs) and its temperature sensitivity (Q10) are altered with water-table gradients in high-latitude swamp soil. We sampled soil from cold-temperate forest swamps at three water-table gradients (permanently flooded, seasonally flooded, and non-flooded) in the high-latitude areas of Genhe and Mohe in China. We then conducted an incubation experiment using a new mode of varying incubation temperature, with rapid and continuous measurements of Rs. Our results showed that Rs at 20 °C (R20) was significantly higher in seasonally flooded (SF) swamp soil, compared to permanently flooded (PF) or non-flooded (NF) soil. Soil redox condition mainly controlled R20 during the early drying stage of forest swamps, while substrate quantity and quality dominated the latter stage. The highest Q10 was observed in SF soils in Genhe, but this was not significant compared to the Q10 in soils from Mohe. There were clear regional differences in Q10 driven by changes to soil substrate (dissolved organic C and nitrogen) and physicochemical properties. Our findings indicate that high-latitude forest swamp soils may emit more CO2 and act as a C source under the scenarios of artificial draining and climate warming.
14. 题目: One-pot synthesis of nZVI-embedded biochar for remediation of two mining arsenic-contaminated soils: Arsenic immobilization associated with iron transformation
Waste biomass derived biochar has been proven as an effective and friendly amendment for remediation of heavy metals-contaminated soil. However, biochar is less effective for soil arsenic (As) immobilization in most cases. To improve the ability of biochar for As immobilization, in this study, the composite of biochar embedded with nano zero valent iron (nZVI/BC) was prepared through simple one-step pyrolysis of biomass sawdust and Fe2O3 mixture and then applied for amendment of two mining As-contaminated soils. Pristine sawdust biochar (BC) and nZVI alone or in combination were included for comparison. Results show that the prepared nZVI/BC contained about 40% Fe which was mainly present as Fe°. All treatments except BC reduced As concentration in (NH4)2SO4 extraction and gastrointestinal solution. Particularly, nZVI/BC reduced the labile As in (NH4)2SO4 extraction in two soils by over 93% and bioaccessible As in gastrointestinal solution decreased by over 85%. Fe° on the surface of nZVI/BC was oxidized into amorphous FeOOH which adsorbed or co-precipitated with As. Meanwhile, Ca-Fe-As-O and Al-Fe-As-O co-precipitated at the interface between nZVI/BC and two soils enriched with Ca and Al, respectively. Results indicated that the simply-prepared nZVI/BC was a promising material for remediation of As-contaminated soils.
15. 题目: Petrological and geochemical characteristics of xylites and associated lipids from the First Lusatian lignite seam (Konin Basin, Poland): implications for floral sources, decomposition and environmental conditions
Single pieces of fossil wood fragments (xylites) were collected from the middle Miocene First Lusatian lignite seam at the Adamów, Jóźwin IIB and Tomisławice opencast mines and are characterized by maceral variety, cellulose contents and their molecular and isotopic composition. Biomarker composition of xylites and δ 13C of their total organic matter, lipids and cellulose are used to provide insights into woody plant community and the effects of wood decomposition.
The investigated xylites represent fragments of fossil wood from conifers, most likely species of Cupressaceae, indicated by terpenoid biomarkers characteristic for conifers and by the δ 13C values of the extracted cellulose. This conclusion is confirmed by paleobotanical data highlighting Taxodium and Nyssa as the main elements of the wet forest swamps. Due to the wet swamp habitat and the higher-decay resistance exclusively wood fragments of conifers are found in the lignite seam. Minor abundances of angiosperm-derived triterpenoids in the xylites are explained by impurities from inherent detritic lignite.
The xylites are characterized by minor to moderate extents of gelification, but elevated to high cellulose decomposition. The relationship between δ 13C values of xylites and their cellulose contents reflects wood decomposition removing preferentially the 13C-enriched compounds, but decomposition did not affect the δ 13C of cellulose. Despite of similar δ 13C of xylites and detritic lignite, differences in isotopic composition of hopanoids argue for slightly different microbial communities involved in the decomposition of the respective OM. Thus, we conclude that wood decomposition proceeded in a freshwater environment under acidic conditions by fungi and bacteria.
Variations in water availability during growth periods of the conifers are suggested as the most probable cause for the observed minor variations in isotopic composition of plant lipids. The positive relationship found between δ 2H and δ 13C of plant biomarkers, and cellulose of xylites can be explained by the ability of vascular plants to minimize evapotranspiration during dryer phases resulting in plant OM enriched in 13C and 2H. The significant differences in δ2H between diterpenoids of different structural types and n-alkanes are most likely caused by differences in isotopic fractionation during lipid biosynthesis.
16. 题目: Promoting plant growth and carbon transfer to soil with organic amendments produced with mineral additives
The quality of organic soil amendments such as composts and vermicomposts can be improved by using additives during their production. However, little is known about the impact of these materials on carbon flow in the plant-soil system. We investigated the impact of organic amendments produced through composting and vermicomposting in the presence of clay minerals (montmorillonite) and/or earthworms on plants (perennial ryegrass, Lolium perenne and common bean, Phaseolus vulgaris) and carbon flow in soil. We carried out a growth chamber experiment with continuous 13C labelling and analysed above-/below-ground biomass production, as well as biogeochemical parameters of plant and soil (rhizospheric and non-rhizospheric) compartments. Quantitative biogeochemical analyses were further merged with microscale elemental and isotopic information (NanoSIMS) to investigate carbon transfer in the rhizopheric soil. Our results showed lowest biomass production for treatments amended with organic amendments produced without minerals probably related to the release of harmful substances (excess of dissolved organic carbon, salts and inorganic nitrogen) due to the immature nature of these materials. The use of montmorillonite as additive during the preparation of the amendments alleviated these adverse effects and resulted in a significant increase of above-/below-ground plant biomass production. When the organic amendments were produced in the presence of eathworms and montmorillonite, the higher plant biomass promoted the release of root-derived carbon within the rhizospheric soil (compared with amendments without clay minerals), which was used as an energy-rich substrate by microorganisms. We conclude that the use of mineral additives during composting or vermicomposting favours plant biomass production and carbon transfer to the soil and its microorganisms, which could enhance soil carbon storage in the longer term.
17. 题目: Technical note: Measurements and data analysis of sediment-water oxygen flux using a new dual-optode eddy covariance instrument
18. 题目: Use of eco-friendly magnetic materials for the removal of polycyclic aromatic hydrocarbons and metals from environmental water samples
Highly toxic pollutants including polycyclic aromatic hydrocarbons (PAHs) and metals such as copper and lead are released into the environment from a variety of sources. One way to remove them from aqueous media is to use magnetic hybrid adsorbents that can be easily separated from the medium after the adsorption process. This work reports the synthesis of a magnetic hybrid matrix consisting of cobalt ferrite as the inorganic phase and natural organic matter (NOM) as the organic phase, where NOM was used instead of the traditional solvents. Tests showed that a hybrid produced using ferric sulfate (FAST) presented higher adsorption efficiency, compared to a hybrid produced using ferric chloride (FACT). PAH adsorption assays were performed using a deionized water solution containing benzo(a)anthracene (BaA), benzo(b)fluoranthene (BbF), benzo(k)fluoranthene (BkF), benzo(a)pyrene (BaP), and dibenzo(a,h)anthracene (DahA), which resulted in removal percentages in the range 83.9–97.6% (q = 41.3–53.7 mg g−1) at equilibrium after 30 min. Tests using real seawater and produced water samples confirmed the efficiency of the hybrid, with removal percentages in the range 86.5–96.3% (q = 43.2–48.1 mg g−1). The highest adsorption of PAHs was achieved using FAST, which was therefore selected for evaluation of metal removal, showing excellent adsorptive capacity, removing 84.5 and 92.0%, respectively, of the copper and lead present in seawater samples. Here, FAST provided efficient removal of both organic and inorganic species, demonstrating its potential for use in technological and environmental applications, including in the manufacturing sector.
19. 题目: Diel cycles of carbon, nutrient and metal in humic lakes of permafrost peatlands
Despite the importance of surface waters of permafrost landscapes in carbon (C) emission and dissolved C and metal storage and export, the majority of available observations in high latitude aquatic systems deal with punctual or seasonal sampling without accounting for diurnal variations in temperature and primary productivity-respiration cycles. Towards providing comprehensive understanding of diel variations in CO2 emission, organic C and element concentrations in lakes of frozen peatlands, we monitored, each 2 h over 2 days, the water temperature, pH, CO2 fluxes, CO2, CH4, dissolved organic and inorganic carbon (DOC and DIC, respectively), nutrients, carboxylic acids, bacterial number, and major and trace elements in two acidic (pH = 3.6 and 4.0) and humic (DOC = 15 and 35 mg L−1) thermokarst lakes of discontinuous permafrost zone in Western Siberia. We discovered a factor of 2 to 3 higher CO2 concentrations and fluxes during the night compared to daytime in the high-DOC lake. The emission fluxes in the low-DOC lake increased from zero to negative values during the day to highly positive values during the end of night and early morning. The methane concentration varied within a factor of 5 without any link to the diurnal cycle. The bulk of dissolved (< 0.45 μm) hydrochemical parameters remained highly stable with ±10% variation in concentration over 2 days of observation (DOC, DIC, SUVA254 nm, carboxylates (formate, oxalate, puryvate and glutarate), Mn, Fe, Al, other trace elements). Concentrations of Si, P, K, Cu varied within ±20% whereas those of Zn and Ni ranged by a factor of 2 to 4 without any link to diurnal pattern. Overall, the impact of diel cycle on CH4, DOC, nutrient and metal concentration was below 10%. However, neglecting night-time period may underestimate net CO2 emission by ca. 30 to 50% in small organic-rich thaw ponds and switch the CO2 exchange from uptake/zero to net emission in larger thermokarst lakes. Given the dominance of large lakes in permafrost regions, the global underestimation of the emission flux may be quite high. As such, monitoring CO2 concentrations and fluxes in thermokarst lakes during months of extended night time (August to October) is mandatory for assessing the net emissions from lentic waters of frozen peatlands.
20. 题目: The photochemical release of dissolved organic matter from resuspended sediments: Insights from fluorescence spectroscopy
Sediments exposed to sunlight can serve as an important source of dissolved organic carbon (DOC) and nutrients to overlying waters. However, the photochemical release processes of dissolved organic matter (DOM) from resuspended sediments and the characteristics of photoreleased DOM are not fully understood. In this study, excitation-emission matrix fluorescence combined with parallel factor analysis (EEMs-PARAFAC) was used to study the photochemical release of DOM qualitatively and quantitatively. The EEMs-PARAFAC demonstrated that the photoreleased DOM is dominated by humic-like substances, and the photorelease process could be consist of the photoproduction and photodegradation of DOM. The concurrent photodegradation may result in the underestimation of photoreleased DOM. Moreover, the significant increases in DOC content and fluorescence intensity of humic-like components along with increasing nitrate and ferric ion indicated that nitrate and ferric ion could facilitate the photoproduction of DOM through the photochemical produced hydroxyl radical. However, the decreases in DOC and fluorescence intensity were also observed at high concentration of nitrate and ferric ion, owing to the photodegradation of DOM by redundant hydroxyl radical. All of these results suggest that EEMs-PARAFAC is an effective and sensitive analytical technique for evaluating DOM photoreleased from suspended lake sediments and previous studies may underestimate photochemical release of DOM from sediments due to the overlook of the subsequently photodegradation of these released DOM. Thus, the photochemical release of DOM and its associated pollutants from suspended particles in shallow and eutrophic lakes should be more significant then should be paid more attention.