7621. 题目: Rates of anthropogenic transformation of soils in the Botanical Garden of Jagiellonian University in Kraków (Poland)
作者: ?ukasz Musielok, Marek Drewnik, Mateusz Stolarczyk, Magdalena Gus, Sylwia Bartkowiak, Krzysztof Ko?yczkowski, Jakub Lasota, Alicja Motak, Karolina Szczechowska, Miko?aj W?t?y
摘要: Soils in botanical gardens play a crucial role as they condition the growth and vegetation of huge diversity of plant species on relatively small areas. Creating favourable habitats for the planted vegetation's development frequently leads to the formation of soils with thick surface horizons with a very well developed structure, rich in organic matter and nutrients, described as hortisols. Despite significant human influence, the environments of botanical gardens are often considered to be seminatural enclaves in urban areas. The main objectives of the presented paper were to explain soil cover differentiation noted across the Botanical Garden of Jagiellonian University in Kraków and determine the share of natural and anthropogenic features in the studied soils. Moreover, the usefulness of the WRB system in the evaluation of the rate of anthropogenic transformation in soils was tested. All the investigated soils showed significant evidences of anthropogenic transformations. Both digging and overbuilding with allochthonous material rich in artefacts caused disturbances in soil morphology. On the other hand, formerly intensive liming and fertilizing with organic materials has resulted in the homogenization of soil chemical properties in the studied botanical garden. No significant relationships between the spatial differentiation of soil properties and diversity of planted vegetation or time span from the area's inclusion to the botanical garden were detected. The results of the bonitation of specific soil properties not considered by the classification system (e.g. thickness of soil profile overheap) were compatible with the WRB 2015 systematic position. This confirmed good definition of actual WRB criteria for soils disturbed by human activity and undergoing natural development.
7622. 题目: Soil organic carbon stabilization changes with an altitude gradient of land cover types in central Himalaya, India
作者: J. Dinakaran, Abhishek Chandra, K.P. Chamoli, Jyotishman Deka, K.S. Rao
摘要: Soil organic carbon (SOC) stabilization in a mountain forest ecosystem is a key component of the global carbon cycle to mitigate the rising level of atmospheric carbon dioxide. We investigated the effects of different types of land cover at different altitudes on SOC stabilization in the Himalayan region, India. We chose four different land covers at different altitudes, viz., pasture land (~2500 m), mixed cover (~2200 m), chirpine (~950 m) and agricultural land (~950 m). Organic carbon (OC), total nitrogen (N), and total microbial activity (MAt) in soils up to depths of 100 cm and under different types of land cover were assessed to study the impact of vegetation cover on the storage of SOC and N. Hydrofluoric acid (HF) soluble carbon, FeDCB/AlDCB oxides and stable carbon isotopes (δ13C) were determined in the soils under different types of land cover to evaluate the amounts of mineral-associated carbon and understand the organic carbon stabilization process. The maximum SOC stock was observed under a mixed land cover (281.86 t ha-1), followed by pasture land cover (229.61 t ha-1), chirpine (182.16 t ha-1) and agricultural land cover (70.20 t ha-1) up to a depth of 100 cm. Higher SOC contents, N contents and MAt were closely linked to the surface layers (0–30 cm), while HF-soluble carbon, FeDCB and AlDCB oxides were linked to sub-surface layers (30–100 cm) of soils under different types of land cover. HF-soluble carbon was more abundant in mixed and pasture land covers compared with chirpine and agricultural land covers. The linear relationship between δ13C values and HF-soluble carbon, FeDCB/OC, δ13C, AlDCB/OC and δ13C in soils under mixed and pasture land covers confirmed that the subsurface soil constituted more decomposed carbon and its associated FeDCB/AlDCB minerals. Nevertheless, this trend was not observed in other types of land cover located at lower altitudes and might be due to the root exudates and/or mixing of young and old carbon. These results suggest that the land cover types at higher altitudes in central Himalaya may be considered as a potential sink for the sequestration of atmospheric carbon and as potential sites for the stabilization of sequestered carbon in soils. However, land cover types at lower altitudes in central Himalaya must be managed by better soil management practices to sequester and stabilize more carbon in soils.
7623. 题目: Contributions of Condensable Particulate Matter to Atmospheric Organic Aerosol over Japan
期刊: Environmental Science & Technology
作者: Yu Morino, Satoru Chatani, Kiyoshi Tanabe, Yuji Fujitani, Tazuko Morikawa, Katsuyuki Takahashi, Kei Sato, and Seiji Sugata
摘要: Because emission rates of particulate matter (PM) from stationary combustion sources have been measured without dilution or cooling in Japan, condensable PM has not been included in Japanese emission inventories. In this study, we modified an emission inventory to include condensable PM from stationary combustion sources based on the recent emission surveys using a dilution method. As a result, emission rates of organic aerosol (OA) increased by a factor of 7 over Japan. Stationary combustion sources in the industrial and energy sectors became the largest contributors to OA emissions over Japan in the revised estimates (filterable-plus-condensable PM), while road transport and biomass burning were the dominant OA sources in the previous estimate (filterable PM). These results indicate that condensable PM from large combustion sources makes critical contributions to total PM2.5 emissions. Simulated contributions of condensable PM from combustion sources to atmospheric OA drastically increased around urban and industrial areas, including the Kanto region, where OA concentrations increased by factors of 2.5–6.1. Consideration of condensable PM from stationary combustion sources improved model estimates of OA in winter but caused overestimation of OA concentrations in summer. Contributions of primary and secondary OA should be further evaluated by comparing with organic tracer measurements.
7624. 题目: 13C isotopic signature and C concentration of soil density fractions illustrate reduced C allocation to subalpine grassland soil under high atmospheric N deposition
期刊: Soil Biology and Biochemistry
作者: Matthias Volk, Seraina Bassin, Moritz F. Lehmann, Mark G. Johnson, Christian P. Andersen
摘要: We followed soil C fluxes in a subalpine grassland system exposed to experimentally increased atmospheric N deposition for 7 years. Earlier we found that, different from the plant productivity response, the bulk soil C stock increase was highest at the medium, not the high N input as hypothesized. This implies that a smaller N-deposition rate has a greater potential to favor the biological greenhouse gas-sink. To help elucidate the mechanisms controlling those changes in SOC in response to N deposition, we produced four soil density fractions and analyzed soil organic C concentration [SOC], as well as δ13C signatures (δ13CSOC) of SOC components. Soil respired CO2 (δ13CCO2) was analyzed to better distinguish seasonal short term dynamics from N-deposition effects and to identify the predominant substrate of soil respiration. Both at the start of the experiment and after 7 years we found a strong, negative correlation between [SOC] and δ13CSOC of the soil density fractions in the control treatment, consistent with an advanced stage of microbial processing of SOC in fractions of higher density. During the experiment the [SOC] increased in the two lighter density fractions, but decreased in the two heavier fractions, suggesting a possible priming effect that accelerated decomposition of formerly recalcitrant (heavy) organic matter pools. The seasonal pattern of soil δ13CCO2 was affected by weather and canopy development, and δ13CCO2 values for the different N treatment levels indicated that soil respiration originated primarily from the lightest density fractions. Surprisingly, [SOC] increases were significantly higher under medium N deposition in the <1.8 fraction and in bulk soil, compared to the high N treatment. Analogously, the depletion of δ13CSOC was significantly higher in the medium compared to the high N treatment in the three lighter fractions. Thus, medium N deposition favored the highest C sequestration potential, compared to the low N control and the high N treatment. Clearly, our results show that it is inappropriate to use plant productivity N response as an indicator for shifts in SOC content in grassland ecosystems. Here, isotopic techniques illustrated why atmospheric N deposition of 14 kg N ha-1 yr-1 is below, and 54 kg N ha-1 yr-1 is above a threshold that tips the balance between new, assimilative gains and respiratory losses towards a net loss of [SOC] for certain soil fractions in the subalpine grassland.
7625. 题目: Metagenomic and 13C tracing evidence for autotrophic atmospheric carbon absorption in a semiarid desert
期刊: Soil Biology and Biochemistry
作者: Zhen Liu, Yanfei Sun, Yuqing Zhang, Wei Feng, Zongrui Lai, Keyu Fa, Shugao Qin
摘要: Atmospheric carbon dioxide (CO2) absorption by desert soils has received increasing interests in recent years; however, the underlying physical and chemical mechanisms are not commonly acceptable. Here, we hypothesised that autotrophic carbon fixation of soil microbes contributes to this process. To test this postulate, we investigated the genomic and biochemical potential of autotrophic carbon fixation and traced atmospheric autotrophic carbon absorption using metagenomics and 13CO2 labelling approaches in the Mu Us Desert in northern China. More than 30000 genes involved in the six carbon fixation pathways (approximately 2% of the assembled metagenomes, in relative abundance) were found in the metagenome of the desert soil, and the relative abundance for genes encoding for the reductive citrate cycle was the highest among the six pathways. The main autotrophic microbes employing the six pathways belong to Actinobacteria, Proteobacteria, Chloroflexi, Acidobacteria, Gemmatimonadetes, Firmicutes, Thaumarchaeota, Nitrospirae, Planctomycetes, and Bacteroidetes, respectively. 13CO2 labelling revealed that the contents of microbially incorporated soil organic carbon (13C-SOC) and dissolved organic carbon were 0.572–1.45 mg kg-1 and 0.290–0.914 mg kg-1, respectively. Further, the 13C-SOC correlated with the relative abundance of genes of the total six pathways, reductive citrate cycle, 3-hydroxypropionate bi-cycle, and reductive acetyl-CoA pathway. Another in situ labelling experiment showed a significant increase in δ13C of SOC, and the incorporated carbon (13C) in SOC accounted for 3.85% of total atmospheric carbon absorption. These results showed that desert soil microbes containing genetic potential for autotrophic carbon fixation spread over a broad taxonomic range, and incorporated atmospheric carbon into organic components, which contributed to atmospheric carbon absorption. Although more research is required to accurately evaluate the portions of autotrophic carbon in the amount of atmospheric carbon absorption, the biotransformation of carbon from the atmosphere to soil via autotrophic carbon fixation represents a microbial pathway for persistent atmospheric CO2 absorption in desert soils, and further implicates an important carbon biochemical cycle for carbon accumulation in oligotrophic desert soils.
7626. 题目: Nitrogen removal in pilot-scale partially saturated vertical wetlands with and without an internal source of carbon
期刊: Science of The Total Environment
作者: Nancy B. Martínez, Allan Tejeda, Aarón Del Toro, Martha P. Sánchez, Florentina Zurita
摘要: The aim was to evaluate and compare total nitrogen (TN) removal in pilot-scale partially saturated vertical wetlands (PSVWs) with and without an internal solid source of organic carbon (corncob) in order to distinguish the role of nitrification-denitrification and ANAMMOX in the removal process. The height of the free-drainage zone (FDZ) was 40 cm and the saturated zone (SZ) was 30 cm in system I (SI) and system II (SII) and 40 cm in system III (SIII) and system IV (SIV). In SII and SIV, approximately 30 kg of dry, 5 cm–length corncob was added. The systems were evaluated during two periods, that is, P1 and P2. Measurements of water quality parameters including BOD5, COD, organic nitrogen (Org-N), ammonium, nitrate and nitrite were taken in the influent and effluents on a weekly basis; nitrate measurements were also taken at the interface. Measurements of pH, dissolved oxygen (DO) and oxidation-reduction potential (ORP) were taken in the SZ. The height of both SZ (40 cm vs. 30 cm in P1) and FDZ (40 vs. 25 and 30 cm in SI/SIII in P2) did not affect the efficiencies (p > 0.05) but the presence or absence of corn cob did (p < 0.05). Thus, SII and SIV were superior when compared to SI and SIII (p < 0.05) with TN average removal efficiencies of 72.9% and 73.2% in P1, and 59.8% and 64.2% in P2, respectively; showing a tendency to lower values when the biodegradable organics supplied by the corncob diminished. In SI and SIII, TN removals were 47.6% and 40.3% in P1, and 46.1% and 44.1% in P2, respectively. In SII and SIV, denitrification took place in both the lower semi-saturated part of the FDZ (probably also ANAMMOX) and SZ; whereas in SI and SIII, ANAMMOX took place in the lower semi-saturated part of the FDZ.
7627. 题目: Treatment of oil sands produced water using combined electrocoagulation and chemical coagulation techniques
期刊: Science of The Total Environment
作者: Laleh Shamaei, Behnam Khorshidi, Basil Perdicakis, Mohtada Sadrzadeh
摘要: Hybrid electrocoagulation-chemical coagulation (EC-CC) process has attracted a growing attention for the removal of various types of wastewaters contaminants. In this paper, the feasibility of EC-CC technique as an alternative to conventional chemical processes for the treatment of steam assisted gravity drainage (SAGD) produced water has been systematically studied. Eight parameters, namely electrode material, cell configuration, pH and temperature of the solution, chemical coagulant dosage, intensity of the electrical current, mixing rate, and treatment time were studied. To explore the synergistic effect of the design parameters, the experimental trials were arranged using Taguchi method. Analysis of variance (ANOVA) was performed to evaluate the effect of each design parameter on the organic matter removal from the SAGD produced water. It was found that all parameters except the electrode arrangement had a significant effect on the removal efficiency of the EC-CC process. Among these parameters, the chemical coagulant and the treatment time had the most significant contribution to the efficiency by 40% and 26%, respectively. The optimum condition for the highest TOC removal efficiency (39.8%) was obtained by applying 0.34 A to Al electrode in a bipolar (BP) configuration when the pH, temperature, coagulant concentration, mixing rate, and reaction time were set to 8, 60 °C, 200 mg/L, 700 rpm, and 90 min, respectively. Moreover, a second-order polynomial regression model was proposed to predict the removal efficiency in terms of design parameters. An excellent agreement between the model predictions and experimental data was obtained with the adjusted R2 of about 99%.
7628. 题目: Determining the effects of polyaluminum chloride alkalinities and dosage treatments on various microalgal growth phases for the treatment of microalgae-laden water
期刊: Separation and Purification Technology
作者: Cheng Yan, Xiaoqing Song, Miao Yu, Yifei Tong, Weijun Zhang
摘要: Harmful algal blooms have become critical threats to human health as they have occurred with increasing frequency and intensity in various water bodies. In the People’s Republic of China, thousands of people are exposed to water bodies heavily contaminated with microalga Microcystis aeruginosa and thus at grave risk of microcystin poisoning. This study investigated the characteristics of extracellular organic matters (EOMs), floc morphology, and microcystin in each microalgal growth phase for the treatment of microalgae-laden water. The characterization was performed under different alkalinities and dosage treatments of polyaluminum chloride (PAC). Results suggested fulvic-like and humic-like acids, C=C, and unsaturated aldehyde ketones were present in the supernatant liquor and dissolved EOM (dEOM) solution under logarithmic and stationary phase treatments for EOM. However, the same components along with aromatic protein and amidogen were detected in the supernatant liquor and dEOM solution under the decline phase treatments. The EOM of the supernatant liquor and dEOM solution nearly resembled willmigerl, which was different from bound extracellular organic matter (bEOM) in the three growth phases. Nonetheless, the highest particle size and most compact and roughest flocs were observed in the stationary phase. Meanwhile, no significant difference (P>0.05) was observed among the microcystin concentrations of microalgal cells before and after coagulation, although the concentrations increased after the coagulating treatment. Therefore, coagulation pH of 2.0 and 50 mg L-1 dose of PAC was a good practical application to treat microalgae laden water at the stationary growth phase.
7629. 题目: Polyvinyl chloride (PVC) ultrafiltration membrane fouling and defouling behavior: EDLVO theory and interface adhesion force analysis
期刊: Journal of Membrane Science
作者: Wanyi Fu, Lan Wang, Fangjuan Chen, Xuezhi Zhang, Wen Zhang
摘要: To unravel fouling and defouling mechanisms of protein, saccharides and natural organic matters (NOM) on polymeric membrane during filtration, this study investigated filtration characteristics on polyvinyl chloride (PVC) ultrafiltration membranes with bovine serum albumin, dextran, humic acid as model foulants. Membrane fouling and defouling performances were analyzed through monitoring the flux decline during filtration and flux recovery during physical backwash. Physico-chemical properties (e.g., hydrophobicity and surface charge) of PVC membrane and foulants were characterized, which were used in the extended Derjaguin–Landau–Verwey–Overbeek (EDLVO) theory to calculate the interaction energies between membrane-foulant and foulant-foulant. The results showed that at the later filtration stages the fouling rate was strongly correlated with the deposition rate, which was determined by the interaction energy profile calculated by EDLVO. Moreover, the adhesion forces of membrane–foulant and foulant–foulant were further measured by atomic force microscopy (AFM) with modified colloidal probes. A positive correlation (R2 = 0.845) between particle detachment rate (determined by adhesion force) and defouling rate was developed for BSA and HA foulants that led to cake layer formation. By contrast, dextran defouling rate was off this correlation as dextran partially clogged membrane pores due to its smaller size.
7630. 题目: Alteration of organic matter during remediation of acid sulfate soils
作者: Angelika K?lbl, Petra Marschner, Luke Mosley, Rob Fitzpatrick, Ingrid K?gel-Knabner
摘要: When acid sulfate soils with hypersulfidic material dry, oxidation of pyrite can cause strong acidification due to formation of sulfuric (pH < 4) material. Re-saturation of acid sulfate soils containing sulfuric material can lead to re-formation of pyrite and pH increase through activity of sulfate reducing bacteria, which require available organic carbon (OC). In the Lower River Murray region in Australia, a clayey acid sulfate soil had acidified during the severe “Millennium” drought between 2007 and early 2010. We investigated why it has not recovered for over a decade after being reflooded. We hypothesized that the low quality and availability of OC limits the activity of sulfate reducing bacteria. A long-term anoxic incubation experiment was conducted to test if OC additions can help to overcome OC limitation. Small-scale incubation vessels were used, allowing investigating general biochemical phenomena under controlled laboratory conditions. Pre-incubated acid sulfate soil with sulfuric material (approx. pH 3.5) was submerged and pre-adjusted to pH 5.0. We used different rates of wheat straw and cattle manure application to test different organic matter quantities and qualities. Both substrates were added in two portions, at the beginning of the experiment and after 190 days. With every addition, we added two different amounts of organic matter (2 mg g 1 soil and 9 mg g 1 soil), equivalent to approx. 10% and 50% of the native soil OC content. A control treatment without OC addition was also included. CO2 production as well as redox and pH values were monitored weekly over a year. At the start and the end of incubation, we determined OC concentrations and the proportion of available, non mineral-associated OC. OC composition was analyzed by solid-state 13C NMR spectroscopy to assess its chemical degradation. The pH values increased rapidly in treatments with high OC supply, reaching pH ≥ 6.0 within 3 weeks after the second OC addition. Treatments with low OC additions showed slower pH increases, reaching values between pH 5.5 and 6.0 after one year. The control treatment had pH values <5.0 at the end of the experiment. After one year of anoxic incubation, the control treatment lost 10% of the native OC. Treatments with OC additions lost between 13 and 19% of total OC (native + added OC), with higher percentage loss in treatments with high OC additions. Highest losses were observed for the non mineral-associated OC fraction (up to 69% in treatments with high OC additions), with up to 20% being converted to the mineral-associated OC. OC composition changed little compared to the start of the experiment, showing slightly reduced proportions of carbohydrates (≤10% loss) and slightly higher proportions of lipids and lignin. Best remediation success was achieved by adding 50% of the native soil OC as wheat straw, resulting in fast pH neutralization, strongly reducing conditions, and decreased sulfur and iron concentrations in the soil solution. However, the amount of bioavailable OC was reduced to one third after the incubation period. Repeated OC addition is therefore recommended to keep the total amount of bioavailable, undecomposed plant residues high and to ensure long-term remediation success.
7631. 题目: Bioremediation of arsenic-contaminated groundwater by sequestration of arsenic in biogenic pyrite
期刊: Applied Geochemistry
作者: James A. Saunders, Ming-Kuo Lee, Prakash Dhakal, Shahrzad Saffari Ghandehari, Ted Wilson, M. Zeki Billor, Ashraf Uddin
摘要: Pyrite (FeS2) is the most common sulfide mineral in the Earth's crust, and it commonly contains minor amounts of arsenic. Here we show that authigenic pyrite can remove arsenic from contaminated groundwater and this can be used as a new and relatively inexpensive remediation process. Laboratory batch experiments presented show that fine-grain natural pyrite is an effective sorber of dissolved arsenic. Arsenic sorption onto pyrite is shown to increase with increasing pH, particularly at pH > 5 and at elevated dissolved arsenic concentration. We also present results from a field experiment at an arsenic-contaminated industrial site, which demonstrates the results of stimulation of natural sulfate-reducing bacteria in groundwater by injection of a labile organic carbon source, iron, and sulfate. Within a week, bacterial sulfate reduction triggered the formation of biogenic pyrite nanoparticles, which sequestered arsenic by adsorption and co-precipitation. Microscopic and X-ray diffraction analyses confirmed that pyrite was the only iron-sulfide formed, and that no arsenic-only sulfide phase precipitated (e.g. orpiment or realgar). Pyrite occurs as either 1–10 μm euhedral crystals or similar-sized framboids both of which contain 500–4000 mg/kg arsenic. As a result, dissolved arsenic decreased from its initial concentration of 0.3–0.5 mg/L to below the regulatory clean-up standard for the site of 0.05 mg/L in a matter of weeks. In addition to the potential of this technique to remediate anthropogenic arsenic contamination, it is possible that it can be modified to inexpensively treat individual small drinking-water wells contaminated by natural sources of arsenic in many developing nations.
7632. 题目: Scenario modeling for spatial-temporal change detection of carbon storage and sequestration in a forested landscape in Northern Iran
期刊: Environmental Monitoring and Assessment
作者: Ardavan Zarandian, Jalil Badamfirouz, Roya Musazadeh, Alireza Rahmati, Seyedeh Bahareh Azimi
摘要: The present study was conducted, based on scenario modeling approach, in the Do-hezar and Se-hezar forested landscape in the Mazandaran Province in Northern Iran in order to detect spatial-temporal changes of carbon storage and sequestration in four different carbon pools, i.e., aboveground and belowground biomasses, dead organic matter, and organic soils. For this purpose, firstly, the changing trend of land use/land cover (LULC) was detected by analyzing and comparing remotely sensed data of the landscape during the period of 1984–2016. Then, the impacts of future LULC changes on carbon storage and sequestration were predicted and valued using the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) model under two future plausible scenarios of business as usual (BAU) and balanced development (BD). According to the results of BAU scenario, continuation of the current trend will lead to a significant reduction in the carbon sequestration and a huge amount of social cost due to the loss of carbon stored in the landscape and its release to the atmosphere. The BD scenario which refers to the principled and under control development of human settlements simultaneously with forest conservational and restoration activities, could potentially reverse the downtrend of carbon sequestration service and avoid future socioeconomic costs, hence add to the economic value of the forest landscape in terms of providing a better sink for carbon storage. The results of this research can facilitate the quantitative and accurate assessment of carbon storage and sequestration relying on more precise biophysical and economic data as well as provide insight for effective land-use planning.
7633. 题目: Soil aggregates: a scale to investigate the densities of metal and proton reactive sites of organic matter and clay phases in soil
期刊: European Journal of Soil Science
作者: L. Spadini, A. Navel, J. M. F. Martins, E. Vince , I. Lamy
摘要: Determining site density of reactive sites of metals in the main soil phases remains a challenging task. This study aimed to show that densities of reactive sites in soil may be assessed by a fractionation procedure based on soil being spatially organized as aggregates. The method is described with copper as a model trace element and a common silty loam soil after applying a low energy fractionation method to maintain the integrity of soil aggregates. The reactivity of five soil size fractions (> 250, 250–63, 63–20, 20–2 and < 2 μm) to protons and copper was quantified by acid–base titrations. The total proton sorption capacities were assigned to the total concentration of copper reactive sites and fitted to a linear combination of the relevant reactivity data of each phase, namely the total contents of organic carbon, copper and acid‐extractable aluminium. Acid–base reactivity was linearly related to the distribution of copper, and differences between fractions were used to reconstruct the distribution of acid–base and copper‐complexing sites among the clay, organic and weakly reactive residual phases. In accordance with our hypothesis that key reactive phases are mainly organic materials and clays, we used this procedure to determine the site densities of (i) two size classes of particulate organic matter, (ii) strongly reactive organic matter (e.g. soil humic and fulvic acids) and (iii) clay. The site densities and the distributions of copper obtained were used to validate our conceptual model for predicting global soil reactivity to metals.
7634. 题目: Drivers of postfire soil organic carbon accumulation in the boreal forest
期刊: Global Change Biology
作者: Benjamin Andrieux, Julien Beguin, Yves Bergeron, Pierre Grondin, David Paré
摘要: The accumulation of soil carbon (C) is regulated by a complex interplay between abiotic and biotic factors. Our study aimed to identify the main drivers of soil C accumulation in the boreal forest of eastern North America. Ecosystem C pools were measured in 72 sites of fire origin that burned 2–314 years ago over a vast region with a range of mean annual temperature of 3°C and one of 500 mm total precipitation. We used a set of multivariate a priori causal hypotheses to test the influence of time since fire (TSF), climate, soil physico‐chemistry and bryophyte dominance on forest soil organic C accumulation. Integrating the direct and indirect effects among abiotic and biotic variables explained as much as 50% of the full model variability. The main direct drivers of soil C stocks were: TSF >bryophyte dominance of the FH layer and metal oxide content >pH of the mineral soil. Only climate parameters related to water availability contributed significantly to explaining soil C stock variation. Importantly, climate was found to affect FH layer and mineral soil C stocks indirectly through its effects on bryophyte dominance and organo‐metal complexation, respectively. Soil texture had no influence on soil C stocks. Soil C stocks increased both in the FH layer and mineral soil with TSF and this effect was linked to a decrease in pH with TSF in mineral soil. TSF thus appears to be an important factor of soil development and of C sequestration in mineral soil through its influence on soil chemistry. Overall, this work highlights that integrating the complex interplay between the main drivers of soil C stocks into mechanistic models of C dynamics could improve our ability to assess C stocks and better anticipate the response of the boreal forest to global change.
7635. 题目: Relationships between DOC and CDOM based on the total carbon‐specific fluorescence intensities for river waters across China
期刊: Journal of Geophysical Research: Biogeosciences
作者: Ying Zhao, Kaishan Song
摘要: Weak correlations between chromophoric dissolved organic matter (CDOM) absorption coefficient a(440) and dissolved organic carbon (DOC) were observed due to weak absorption for river waters especially in the Qinghai‐Tibetan Plateau and thus it is impossible to estimate DOC concentrations by CDOM absorption across China. Therefore, it is necessary to estimate DOC concentrations through the fluorescent fraction of CDOM (i.e., FDOM). FDOM was proposed as a new method for estimation of large‐scale DOC concentrations in river waters across China. A total of 301 water samples from eight river basins across China were selected to assess FDOM by excitation‐emission matrix (EEM) fluorescence. Five fluorescent regions were obtained by EEM coupled with fluorescence regional integration (FRI) (EEM‐FRI) method. However, weak correlations between the fluorescence intensities FR(1‐5), FSUM and DOC concentrations were observed for all water samples, respectively. Therefore, the total carbon‐specific fluorescence intensities FSUM/DOC were used to establish relationships between DOC and FDOM. All 301 water samples excluding five outliers with FSUM/DOC higher than 8000 nm·(mg L–1)–1), were divided into four groups based on the threshold values for FSUM/DOC and strong positive correlations between FSUM and DOC were observed in each group (R2 = 0.843, FSUM/DOC < 1000 nm·(mg L–1)–1; R2 = 0.928, 1000 < FSUM/DOC < 2000 nm·(mg L–1)–1; R2 = 0.964, 2000 < FSUM/DOC < 3000 nm·(mg L–1)–1; R2 = 0.953, 3000 < FSUM/DOC < 8000 nm·(mg L–1)–1), respectively. This result indicated the riverine DOC concentrations on large scale across China can be estimated directly by FDOM properties.
7636. 题目: Is the adsorption of soil organic matter to haematite (α‐Fe2O3) temperature dependent?
期刊: European Journal of Soil Science
作者: M. L. Nguyen, W. C. Hockaday, B. L. T. Lau
摘要: Soil organic matter interactions with minerals are a key determinant in the long‐term protection and sequestration of carbon in soils and sediments. Climate warming could potentially alter the dynamics of the Earth's largest carbon pools through processes controlling the formation of mineral–organic associations (MOAs). We studied the adsorption of Elliott soil humic acid (HA) and fulvic acid (FA) to the iron oxide mineral haematite (α‐Fe2O3) at temperatures from 15 to 35°C through batch sorption experiments. The ΔG°, ΔH° and ΔS° of sorption were derived for HA and FA and suggested that formation of MOAs was spontaneous and exothermic. The Langmuir sorption coefficients for HA and FA decreased with warming, but the maximum sorption capacities were not temperature dependent. The decrease in sorption coefficient was less when the temperature was increased from 30 to 35°C than from 15 to 30°C. Our infrared, ultraviolet and visible spectroscopy analysis of the bound and unbound HA and FA revealed preferential adsorption of oxygen‐ and hydrogen‐substituted aromatic and aliphatic carbon, which was independent of temperature. The adsorption of a hydrophobic probe molecule, Rose Bengal, to haematite increased with warming. Our results suggest that (i) MOAs in warmer climates might be less sensitive to temperature changes, (ii) the amount of iron oxide‐associated organic matter might remain unchanged with warming and (iii) hydrophobic interactions with iron oxides may be temperature dependent.
7637. 题目: Distinct changes in composition of soil organic matter with length of cropping time in subsoils of a Phaeozem and Chernozem
期刊: European Journal of Soil Science
作者: Y.‐L. Zhang, L.‐J. Li, S.‐H. Yao, J.‐D. Mao, K. Schmidt‐Rohr, D. C. Olk, X.‐Y. Cao, J.‐F. Cui, B. Zhang
摘要: Deeper soil horizons might provide an opportunity to enhance C sequestration because soil organic matter (SOM) at depth is assumed to be stable. However, it is unknown whether the stable composition of organic carbon in subsoils changes with the length of cropping time and the type of soil. The objectives of this study were to determine the effects on the chemical structures of SOM of cropping time after conversion from grassland to arable land under a Phaeozem and Chernozem in northeast China. Near‐quantitative multiple cross‐polarization (multiCP) 13C nuclear magnetic resonance (NMR) spectroscopy was applied, and 11 types of carbon (C) functional groups were identified. Principal component analysis of these functional groups showed that the chemical composition of SOM was differentiated by soil type and depth. The Phaeozem and Chernozem profiles differed mainly in their relative proportions of aromatic C–C and (CH2)n groups: the Phaeozem contained relatively more aromatic C–C, whereas the Chernozem contained relatively more (CH2)n groups. The fused‐ring aromatic C–C carbon was probably derived from char‐like organic matter generated by burning of plant litter or from SOM humification, whereas the (CH2)n groups were likely to be from plant‐ or microbially‐derived residues. The main differences between top‐ and sub‐soils were the occurrence of more protonated C in the topsoils and more non‐protonated C in the subsoils. With increasing length of cropping time, aromatic C–C and C–O groups and COO/N–C=O groups increased, but (CH2)n groups decreased in the Phaeozem subsoils and increased in the Chernozem subsoils. Our findings suggested that leaching and soil moisture might influence the origin, redistribution and transformation of the recalcitrant components of SOM in the soil profile, resulting in changes in SOM composition under different climates and soil types.
7638. 题目: Dependency of Antarctic zooplankton species on ice algae‐produced carbon suggests a sea ice‐driven pelagic ecosystem during winter
期刊: Global Change Biology
作者: Doreen Kohlbach , Martin Graeve , Benjamin A. Lange , Carmen David , Fokje L. Schaafsma , Jan Andries van Franeker , Martina Vortkamp , Angelika Brandt , Hauke Flores
摘要: How the abundant pelagic life of the Southern Ocean survives winter darkness, when the sea is covered by pack‐ice and phytoplankton production is nearly zero, is poorly understood. Ice‐associated (‘sympagic’) microalgae could serve as a high‐quality carbon source during winter, but their significance in the food web is so far unquantified. To better understand the importance of ice algae‐produced carbon for the overwintering of Antarctic organisms, we investigated fatty acid (FA) and stable isotope compositions of 10 zooplankton species, and their potential sympagic and pelagic carbon sources. FA‐specific carbon stable isotope compositions were used in stable isotope mixing models to quantify the contribution of ice algae‐produced carbon (αIce) to the body carbon of each species. Mean αIce estimates ranged from 4 to 67%, with large variations between species and depending on the FA used for the modeling. Integrating the αIce estimates from all models, the sympagic amphipod Eusirus laticarpus was the most dependent on ice algal carbon (αIce: 54‐67%), and the salp Salpa thompsoni showed the least dependency on ice algal carbon (αIce: 8‐40%). Differences in αIce estimates between FAs associated with short‐term versus long‐term lipid pools suggested an increasing importance of ice algal carbon for many species as the winter season progressed. In the abundant winter‐active copepod Calanus propinquus, mean αIce reached more than 50% in late winter. The trophic carbon flux from ice algae into this copepod was between 3 and 5 mg C m-2 d-1. This indicates that copepods and other ice‐dependent zooplankton species transfer significant amounts of carbon from ice algae into the pelagic system, where it fuels the food web, the biological carbon pump and elemental cycling. Understanding the role of ice algae‐produced carbon in these processes will be the key to predictions of the impact of future sea ice decline on Antarctic ecosystem functioning.
7639. 题目: Differential responses of carbon‐degrading enzymes activities to warming: implications for soil respiration
期刊: Global Change Biology
作者: Ji Chen, Yiqi Luo, Pablo García‐Palacios, Junji Cao, Marina Dacal, Xuhui Zhou, Jianwei Li, Jianyang Xia, Shuli Niu, Huiyi Yang, Shelby Shelton, Wei Guo, Kees Jan van Groenigen
摘要: Extracellular enzymes catalyze rate‐limiting steps in soil organic matter decomposition, and their activities (EEAs) play a key role in determining soil respiration (SR). Both EEAs and SR are highly sensitive to temperature, but their responses to climate warming remain poorly understood. Here, we present a meta‐analysis on the response of soil cellulase and ligninase activities and SR to warming, synthesizing data from 56 studies. We found that warming significantly enhanced ligninase activity by 21.4% but had no effect on cellulase activity. Increases in ligninase activity were positively correlated with changes in SR, while no such relationship was found for cellulase. The warming response of ligninase activity was more closely related to the responses of SR than a wide range of environmental and experimental methodological factors. Furthermore, warming effects on ligninase activity increased with experiment duration. These results suggest that soil microorganisms sustain long term increases in SR with warming by gradually increasing the degradation of the recalcitrant carbon pool.
7640. 题目: Effect of contrasting tillage and cropping systems on soil aggregation, carbon pools and aggregate‐associated carbon in rainfed Vertisols
期刊: European Journal of Soil Science
作者: J. Somasundaram, R. S. Chaudhary, D. Awanish Kumar, A. K. Biswas, N. K. Sinha, M. Mohanty, K. M. Hati, P. Jha, M. Sankar, A. K. Patra, R. Dalal, S. K. Chaudhari
摘要: Worldwide, conservation agriculture practices involving minimal soil disturbances and retention of crop residue (>30%) have been practised increasingly and recognized to enhance soil health by optimizing key soil attributes. However, little information is available on the short‐term effects of conservation agriculture practices on soil properties under rainfed Vertisols of Central India. Thus, our aim was to study the short‐term effects of contrasting tillage treatments and cropping systems on soil aggregation, aggregate‐associated carbon (C), carbon pools and crop productivity. This study comprised three tillage systems (TS), reduced tillage (RT), no tillage (NT) with retention of crop residue and conventional tillage (CT), together with four cropping systems (CS), namely soya bean (Glycine max L.) + pigeon pea (Cajanus cajan L.) (2:1), soya bean–wheat (Titricum durum L.), maize (Zea mays L.) + pigeon pea (1:1), and maize–chickpea Cicer arietinum L.). The experiment was laid out in a split‐plot design with three replicates. Soil samples were collected at four depths: 0–5, 5–15, 15–30 and 30–45 cm from the experimental field after completion of four crop cycles. Results indicated that at depths 0–5 and 5–15 cm, tillage and cropping system had a significant effect on aggregate mean weight diameter (MWD). The MWDs of 0.97 and 0.94 mm were larger for NT than CT (0.77 and 0.83 mm) at 0–5‐ and 5–15‐cm depths, respectively. Water‐stable aggregates (WSAs) were also larger for NT (70.74%) and RT (70.09%) than CT (59.50%) at 0–5 cm. Tillage practice, cropping system and their interaction had a greater effect (P < 0.05) on the content of aggregate‐associated C for large macroaggregates (LM). There was more aggregate‐associated C for NT and RT at 0–5‐cm depth than for CT. Cropping system also had a significant effect (P < 0.05) on aggregate‐associated C at 0–5‐cm depth. Soil organic C (%) fractions were in the order of non‐labile >very labile >less labile >labile for 0–5‐ and 5–15‐cm depths after four crop cycles. Less labile and non‐labile C fractions contributed >50% of TOC, indicating a more recalcitrant form of carbon present in the soil. Tillage had no significant effect (P > 0.05) on crop yields after four crop cycles. Conservation agriculture can have a positive effect on aggregate stability, aggregate‐associated C and different carbon pools in a Vertisol.