17481. 题目: The stoichiometry of carbon, hydrogen and oxygen in peat
期刊: Journal of Geophysical Research: Biogeosciences
作者: Tim R. Moore, David Large, Julie Talbot, Meng Wang, John L. Riley
摘要: Carbon (C), hydrogen (H) and oxygen (O) form ~90% by mass of peat, a product of the input of plant tissues and litter and the output of decomposition under aerobic and anaerobic conditions. We examined patterns of these elements, as the O:C and H:C atomic ratios, in over 1300 peat samples collected from over 400 profiles in Ontario, Canada, representing bogs, fens and swamps. The overall O:C ratio decreased from the surface (0.6 to 0.7) to ~0.5 at a depth of 50 cm and showed little further change to a depth of 5 m. In contrast, the H:C ratio decreased only slightly (1.30 to 1.25) over the top 1 m and showed no further significant decline with depth. The carbon oxidative state (Cox) and oxidation ratio (OR) showed strong decreases and increases, respectively, with depth with most changes occurring in the top 0.5 m. The O:C ratio, and Cox and OR values were significantly correlated with the von Post Humification Index, with most changes occurring in Index values 1 through 4, the latter representing a slight degree of decomposition. Collation of the Ontario peats with other data sets revealed the very large range in O:C and H:C values, with a general decrease from temperate to tropical and sub‐tropical peatlands. Estimation of the O:C and H:C ratios of input (litter) and output (mineralization to CO2, methanogenesis to CH4 and CO2 and loss as dissolved organic carbon) allowed an estimation of the degree of decomposition or C loss.
17482. 题目: The Extent and Regulation of Summer Methane Oxidation in Northern Lakes
期刊: Journal of Geophysical Research: Biogeosciences
作者: Shoji D. Thottathil, Paula C. J. Reis, Paul A. del Giorgio, Yves T. Prairie
摘要: Inland waters have a significant influence on atmospheric methane (CH4) levels. However, processes determining the strength of CH4 emissions from these systems are not well defined. Aerobic oxidation is a major sink of CH4 in freshwater environments and thus an important determinant of aquatic CH4 emissions, yet strikingly little is known about its drivers. Here, we assessed the extent of water column CH4 oxidation at the whole ecosystem‐scale using stable carbon isotopic (δ13C) mass balance of CH4 in 14 northern lakes spanning wide range of dissolved organic carbon (DOC) concentrations. We show that the extent of oxidation can vary from near zero to near complete, and for concentrations of 1.9 – 11 mg L‐1, DOC is a key modulator of CH4 oxidation during the summer stratification period. Increasing DOC concentrations enhances oxidation in the upper layers by reducing light inhibition on methanotrophic activity, while reducing oxygen available for oxidation in the deeper layers. The effect of this light inhibition was also observable over the diurnal cycle. We developed simple predictive empirical models (r2 > 0.82) to estimate the extent of oxidation in the different layers of lakes for the summer period. Applying our surface layer model to a larger dataset suggests that about 30% of CH4 transported to or generated within the epilimnion of Québec lakes is oxidized during summer. Our results imply that DOC concentration, through its effect on the light regime of lakes, has the potential to affect strongly the magnitude and patterns of summer CH4 emissions.
17483. 题目: Multidecadal persistence of organic matter in soils: investigations at the submicrometer scale
作者: Suzanne Lutfalla, Pierre Barré, Sylvain Bernard, Corentin Le Guillou, Julien Alléon, and Claire Chenu
摘要: The mineral matrix, particularly clay-sized minerals, protects soil organic matter (SOM) from decomposition by microorganisms. Here we report the characterization of SOM and associated minerals over decades of biodegradation, in a French long-term bare fallow (LTBF) experiment started in 1928. The amounts of carbon (C) and nitrogen (N) declined with time for six fractions (sand, coarse silt, fine silt, coarse clays, intermediate clays and fine clays). The C:N ratios of SOM associated to silt fractions remained constant whereas they significantly decreased in clays, reaching very low values in intermediate and fine clays (C:N<5) after 8 decades of LTBF. X-ray absorption spectroscopy revealed that (i) bulk-scale SOM chemical speciation remained almost constant, (ii) submicrometric particulate OM was present in coarse clays, even after 79 years of LTBF, (iii) illite particles became progressively SOM-free with time whereas mixed layered illite/smectite and smectites were always associated to OM throughout the bare fallow. Altogether, these results suggest that clay-sized minerals preferentially protect N-rich SOM and that smectites and mixed layered illite/smectite protect SOM more efficiently than illites.
17484. 题目: Qualitative and quantitative correlation of physicochemical characteristics and lead sorption behaviors of crop residue-derived chars
期刊: Bioresource Technology
作者: Yanfei Li, Xian Liu, Peizhen Zhang, Xinlei Wang, Yaoyao Cao, Lujia Han
摘要: This study investigated the key physicochemical characteristics of char that control its ability to absorb Pb2+. Three type of crop residue-derived chars and their ball milled powder were characterized using multiple approaches. The Pb2+ sorption mechanisms of biochar were caused mainly by coprecipitation reactions, which were governed by ionic minerals on chars instead of mineral crystallization (e.g., SiO2 and Al2O3), while coprecipitation reactions and π electronic interaction were the dominant mechanisms of activated carbon. Pearson analysis showed that adsorption quantity (Q) highly correlated with the cation exchange capacity (CEC) (P<0.01)/oxygen functional groups (OFGs) (P<0.05) and Q closely correlated with coprecipitation amount (P<0.01)/complexation amount (P<0.01). Linear regression equations of sorption amount and CEC (R2＞0.8)/OFGs (R2＞0.7) were established. CEC and OFGs of chars are the key factors controlled Pb2+ sorption. These results may promote the development of low-cost, engineered biochar with superior sorption qualities for environmental remediation.
17485. 题目: Improved lignocellulose-degrading performance during straw composting from diverse sources with actinomycetes inoculation by regulating the key enzyme activities
期刊: Bioresource Technology
作者: Yuquan Wei, Di Wu, Dan Wei, Yue Zhao, Junqiu Wu, Xinyu Xie, Ruju Zhang, Zimin Wei
摘要: This study was conducted to assess the effect of thermophilic actinomycetes inoculation on the lignocellulose degradation, enzyme activities and microbial community during different types of straw composting from wheat, rice, corn and soybean. The results showed that actinomycetes inoculation not only changed the structure of actinomycetic and bacterial community but also accelerated the degradation of cellulose, hemicellulose and lignin and increased the key enzymes activities including CMCase, Xylanase, manganese peroxidase, lignin peroxidase and laccase during composting particularly from wheat straw and rice straw. The key enzyme and physiochemical parameters which affected organic fractions degradation have been identified by redundancy analysis. The combined application of actinomycete inoculation and urea addition as a source of nitrogen was suggested to regulate the key enzyme activities and lignocellulose degradation, which lays a foundation for effectively managing organic wastes from different types of crop straws by composting.
17486. 题目: Fast Dissolution Pretreatment of the Corn Stover in Gamma-valerolactone Promoted by Ionic Liquids: Selective Delignification and Enhanced Enzymatic Saccharification
期刊: Bioresource Technology
作者: Longming Jin, Xue Yu, Chang Peng, Yuanlong Guo, Lihua Zhang, Qinqin Xu, Zongbao Kent Zhao, Yu Liu, Haibo Xie
摘要: The dissolution of corn stover was investigated in gamma-valerolactone (GVL) assisted by ionic liquids. An enhanced subsequent enzymatic saccharification was reached with a total reducing sugar yield of 0.69 g.g-1 and a glucose of 0.38 g.g-1 within 24 h. The treatment effects on the physical-chemical features of corn stover in terms of the natural recalcitrance to the subsequent biological digest were systematically investigated using composition analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The structures of the associated enzymatic hydrolysis lignin (EHL) and ionic liquid extracted lignin (IEL) were characterized by gel permeation chromatography (GPC), fourier transform infra-red spectroscopy (FTIR), phosphorous nuclear magnet resonance spectrometry (31P NMR), and heteronuclear single quantum coherence spectroscopy (HSQC) for an in-depth understanding of the delignification process and the basic structural information for further lignin valorization.
17487. 题目: A review on lignin structure, pretreatments, fermentation reactions and biorefinery potential
期刊: Bioresource Technology
作者: Vinoth Kumar Ponnusamy, Dinh Duc Nguyen, Jeyaprakash Dharmaraja, Sutha Shobana, Rajesh Banu, Rijuta Ganesh Saratale, Soon Woong Chang, Gopalakrishnan Kumar
摘要: In recent years, lignin valorization is commercially an important and advanced sustainable process for lignocellulosic biomass-based industries, primarily through the depolymerization path. The conversion of the lignin moieties into biofuels and other high value-added products are still challenging to the researchers due to the heterogeneity and complex structure of lignin-containing biomass. Besides, the involvement of different microorganisms that carries varying metabolic and enzymatic complex systems towards degradation and conversion of the lignin moieties also discussed. These microorganisms are frequently short of the traits which are obligatory for the industrial application to achieve maximum yields and productivity. This review mainly focuses on the current progress and developments in the pretreatment routes for enhancing lignin degradation and also assesses the liquid and gaseous biofuel production by fermentation, gasification and hybrid technologies along with the biorefinery schemes which involves the synthesis of high value-added chemicals, biochar and other valuable products.
17488. 题目: Mapping topsoil organic carbon concentrations and stocks for Tanzania
作者: Bas Kempen, Søren Dalsgaard, Abel K. Kaaya, Nurdin Chamuya, Maria Ruipérez-González, Anssi Pekkarinen, Markus G. Walsh
摘要: Tanzania is one of the countries that has embarked on a national programme under the United Nations collaborative initiative on Reducing Emissions from Deforestation and forest Degradation (REDD). Tanzania is currently developing the capacity to enter into a carbon monitoring REDD+ regime. In this context spatially representative soil carbon datasets and accurate predictive maps are important for determining the soil organic carbon pool. The main objective of this study was to model and map the SOC stock for the 0–30-cm soil layer to provide baseline information for REDD+ purposes. Topsoil data of over 1400 locations spread throughout Tanzania from the National Forest Monitoring and Assessment (NAFORMA), were used, supplemented by two legacy datasets, to calibrate simple kriging with varying local means models. Maps of SOC concentrations (g kg−1) were generated for the 0–10-cm, 10–20-cm, 20–30-cm, 0–30-cm layers, and maps of bulk density and SOC stock (kg m−2) for the 0–30-cm layer. Two approaches for modelling SOC stocks were considered here: the calculate-then-model (CTM) approach and the model-then-calculate approach (MTC). The spatial predictions were validated by means of 10-fold cross-validation. Uncertainty associated to the estimated SOC stocks was quantified through conditional Gaussian simulation. Estimates of SOC stocks for the main land cover classes are provided. Environmental covariates related to soil and terrain proved to be the strongest predictors for all properties modelled. The mean predicted SOC stock for the 0–30-cm layer was 4.1 kg m−2 (CTM approach) translating to a total national stock of 3.6 Pg. The MTC approach gave similar results. The largest stocks are found in forest and grassland ecosystems, while woodlands and bushlands contain two thirds of the total SOC stock. The root mean squared error for the 0–30-cm layer was 1.8 kg m−2, and the R2-value was 0.51. The R2-value of SOC concentration for the 0–30-cm layer was 0.60 and that of bulk density 0.56. The R2-values of the predicted SOC concentrations for the 10-cm layers vary between 0.46 and 0.54. The 95% confidence interval of the predicted average SOC stock is 4.01–4.15 kg m−2, and that of the national total SOC stock 3.54–3.65 Pg. Uncertainty associated with SOC concentration had the largest contribution to SOC stock uncertainty. These findings have relevance for the ongoing REDD+ readiness process in Tanzania by supplementing the previous knowledge of significant carbon pools. The soil organic carbon pool makes up a relatively large proportion of carbon in Tanzania and is therefore an important carbon pool to consider alongside the ones related to the woody biomass. Going forward, the soil organic carbon data can potentially be used in the determination of reference emission levels and the future monitoring, reporting and verification of organic carbon pools.
17489. 题目: Changes in the Rock-Eval signature of soil organic carbon upon extreme soil warming and chemical oxidation - A comparison
作者: Christopher Poeplau, Pierre Barré, Lauric Cécillon, François Baudin, Bjarni D. Sigurdsson
摘要: Soil warming can increase soil organic carbon (SOC) mineralization, triggering a positive climate‑carbon cycle feedback loop. Globally, many soil warming experiments have examined losses of bulk SOC, but few have assessed changes in quality. Accurate knowledge of the latter is required for an in-depth understanding and improved prediction of SOC feedback to climate change. In this study, we used Rock-Eval thermal analysis (RE6) to characterize shifts in SOC thermal stability and bulk chemistry after six years of geothermal warming by 0.6 °C, 1.8 °C, 3.9 °C, 9.9 °C, 16.3 °C, 40 °C, and 80 °C in an Icelandic grassland topsoil (0–10 cm). We also used the strong warming-induced depletion of SOC (up to 92% in the 80 °C soil) in comparisons of chemical oxidation-resistant and biogeochemically resistant SOC, which are generally assumed to be similar in nature. Sodium hypochlorite (NaOCl) and hydrogen peroxide (H2O2) were used for oxidation. Warming-resistant SOC was strongly depleted in hydrocarbons and enriched in oxygen, confirming that SOC oxidation state, and thus energy content, is an important driver for biogeochemical stability. This was supported by findings that thermal stability, i.e., the amount of energy (temperature) necessary to pyrolyze or oxidize SOC, strongly increased with warming intensity. Of the 31 RE6 parameters tested, the most warming-sensitive were hydrogen index (HI, ρ = −0.84), oxygen index (OIRE6, ρ = 0.83), proportion of total pyrolyzed carbon released as hydrocarbons at 200–650 °C (S2/PC, ρ = −0.86), and the temperature at which a certain proportion of CO2 evolved during pyrolysis (ρ > 0.8). Chemical oxidation of unwarmed soil caused average relative SOC losses of 61% (NaOCl) and 91% (H2O2) and shifts in RE6 properties that differed strongly from warming-induced shifts at comparable SOC losses. Chemical oxidation-resistant SOC was more enriched in oxygen, but slightly enriched in hydrocarbons, and less thermostable than comparable naturally depleted SOC at the same time. A certain overlap, especially for NaOCl-treated soils, is likely, while H2O2-oxidized soils showed very distinct RE6 properties. We concluded that i) soil warming leads to strong shifts in SOC bulk chemistry and thermal stability and ii) H2O2 should be avoided in isolation of a slow SOC kinetic pool.
17490. 题目: Charge fingerprint in relation to mineralogical composition of Quaternary volcanic ash along a climatic gradient on Java Island, Indonesia
作者: Sri Rahayu Utami, Florias Mees, Mathijs Dumon, Nikolla P. Qafoku, Eric Van Ranst
摘要: We studied the relationship between the mineralogical composition and surface charge properties of representative Quaternary volcanic ash soils, classified as Andosols, along an East-West sequence on Java Island in Indonesia. The soil charge characteristics were determined using ‘charge fingerprinting’ procedures. Most of the studied soils have a limited ability to retain cations under their forest or grass vegetation. The surface charge properties of these soils are mainly related to allophane and organic matter contents and, to a lesser degree, to ferrihydrite content and layer silicate characteristics. In East Java, the soils are Andosols with low allophane content, dominated either by halloysitic clays or by a mixture of 2:1 and 1:1 layer silicate clays; these soils are characterized by a low to moderate permanent charge. In West Java, the soils are rich in allophane, with subordinate kaolinitic clays, gibbsitic material or a mixture of 1:1 and 2:1 layer silicate clays; in contrast to the allophane-poor soils of East Java, these soils have extreme variable charge characteristics, creating a net ‘positive’ variable surface charge at soil pH. Differences in mineralogical composition of the clay fraction are attributed mainly to more pronounced seasonality in East Java, with variations in parent ash composition, becoming more acidic from east to west, as subordinate factor. The more severely leaching environment in West Java results in a higher degree of desilication, which led to a higher point of zero net charge (PZNC) and pHo in the allophane-rich soils. This study demonstrates how a climatic gradient can affect regional variations in charge properties, through the impact of climate on the mineralogical composition of the clay fraction. Regional patterns of this type must be understood to correctly assess of variations in soil fertility status and to make correct soil management choices for sustainable crop production.
17491. 题目: Characterizing nitric oxide emissions from two typical alpine ecosystems
期刊: Journal of Environmental Sciences
作者: Fei Lin, Chunyan Liu, Xiaoxia Hu, Yongfeng Fu, Xunhua Zheng, Rui Wang, Wei Zhang, Guangmin Cao
摘要: A portion of alpine meadows has been and will continue to be cultivated due to the concurrent increasing demands for animal- and crop-oriented foods and global warming. However, it remains unclear how these long-term changes in land use will affect nitric oxide (NO) emission. At a field site with a calcareous soil on the Qinghai-Tibetan Plateau, the authors measured the year-round NO fluxes and related variables in a typically winter-grazed natural alpine meadow (NAM) and its adjacent forage oat field (FOF). The results showed that long-term plow tillage, fertilization and growing forage oats significantly yielded ca. 2.7 times more (p < 0.01) NO emissions from the FOF than the NAM (conservatively 208 vs. 56 g N/(ha·year) on average). The spring freeze–thaw period and non-growing season accounted for 17–35% of the annual emissions, respectively. The Q10 of surface soil temperature (Ts) was 8.9 in the NAM (vs. 3.8 in the FOF), indicating increases of 24%–93% in NO emissions per 1–3 °C increase. However, the warming-induced increases could be smaller than those due to land use change and management practices. The Ts and concentrations of ammonium, nitrate and water-extractable organic carbon jointly explained 69% of the variance in daily NO fluxes from both fields during the annual period (p < 0.001). This result indicates that temporally and/or spatially distributed NO fluxes from landscapes with calcareous soils across native alpine meadows and/or fields cultivated with forage oats can be predicted by simultaneous observations of these four soil variables.
17492. 题目: Evaluation of temporal changes in hydrostructural properties of regenerating permanent grassland soils based on shrinkage properties and μCT analysis
期刊: Soil and Tillage Research
作者: A.E. Ajayi, R. Horn, Jens Rostek, D. Uteau, S. Peth
摘要: In this study, structural recovery of degraded cropland, which was converted to permanent grassland and managed under no-till and no-renovation condition, was evaluated. We combined hydrostructural parameters with shrinkage characteristics and X-ray computed microtomography (μCT) analysis at three depths, to determine the mechanism for soil structural recovery over a 19-year period. The results showed that the total porosity and hydraulic properties were improved, with the age of the regenerating grassland, due to a better rearrangement of soil particles which in combination with the shrinkage induced realignment of pores in the soil matrix, resulted in better pore continuity. Changes in hydraulic stresses were most pronounced in the intensely rooted soil layers with further enhancement of the soil structure during restoration. This was similarly observed in the reconstructed images, which further highlight the strong contribution from the root development and organic matter conversion to the improved pore networks. Our result also showed that ignoring the depth and time dependent shrinkage behaviour of within the soil matrix resulted in overestimation of water retention potential in the first 8 years since the commencement of the restoration programme, and in the underestimation of water retention in the structurally stable soil beyond this period The results from these combined analyses; allowed a more methodical, detailed, quantitative and qualitative assessment of temporal soil structural recovery in naturally recovering grassland soil.
17493. 题目: Behind the Scenes: Mechanisms Regulating Climatic Patterns of Dissolved Organic Carbon Uptake in Headwater Streams
期刊: Global Biogeochemical Cycles
作者: N. Catalán, J. P. Casas-Ruiz, M. I. Arce, M. Abril, A. G. Bravo, R. del Campo, E. Estévez, A. Freixa, P. Giménez-Grau, A. M. González-Ferreras, Ll. Gómez-Gener, A. Lupon, A. Martínez, C. Palacin-Lizarbe, S. Poblador, R. Rasines-Ladero, M. Reyes, T. Rodríguez-Castillo, P. Rodríguez-Lozano, I. Sanpera-Calbet, I. Tornero, A. Pastor
摘要: Large variability in dissolved organic carbon (DOC) uptake rates has been reported for headwater streams, but the causes of this variability are still not well understood. Here, we assessed acetate uptake rates across eleven European streams comprising different ecoregions by using whole‐reach pulse acetate additions. We evaluated the main climatic and biogeochemical drivers of acetate uptake during two seasonal periods. Our results show a minor influence of sampling periods but a strong effect of climate and dissolved organic matter (DOM) composition on acetate uptake. In particular, mean annual precipitation explained half of the variability of the acetate uptake velocities (VfAcetate) across streams. Temperate streams presented the lowest VfAcetate, together with humic‐like DOM and the highest stream respiration rates. In contrast, higher VfAcetate were found in semi‐arid streams, with protein‐like DOM, indicating a dominance of reactive, labile compounds. This, together with lower stream respiration rates and molar ratios of DOC to nitrate, suggest a strong C limitation in semi‐arid streams, likely due to reduced inputs from the catchment. Overall, this study highlights the interplay of climate and DOM composition and its relevance to understand the biogeochemical mechanisms controlling DOC uptake in streams.
17494. 题目: Simulating Biogenic Secondary Organic Aerosol During Summertime in China
期刊: Journal of Geophysical Research: Atmospheres
作者: Momei Qin, Xuesong Wang, Yongtao Hu, Xiang Ding, Yu Song, Mengmeng Li, Petros Vasilakos, Athanasios Nenes, Armistead G. Russell
摘要: Biogenic secondary organic aerosol (BSOA) contributes significantly to summertime organic particulate matter. In this study, a simulation of BSOA for summer 2012 over China is performed using the Community Multiscale Air Quality (CMAQ) model with an explicit representation of BSOA formation via reactive uptake of isoprene‐derived intermediates, species‐specific parameters for monoterpene‐derived BSOA production, and a multi‐generational oxidation scheme. Simulated BSOA tracks the measurements well (normalized mean bias of 1% and r2 of 0.59). Elevated BSOA occurs in the Sichuan Basin and southeastern China (except the coastal areas) where concentrations are mostly within the range of 5‐7.5 μg·m‐3. Nitrate oxidation dominates fresh BSOA originating from monoterpenes. Simulated monoterpene‐formed BSOA increases by a factor of 3‐11 with multi‐generational oxidation. Isoprene‐formed BSOA shows high concentrations in southwestern China, formed primarily by 2‐methyltetrols (2‐MT) and organosulfates (62‐83%). High concentrations in this region are driven by the abundance of IEPOX and high particle surface area of sulfate‐laden aerosols. NOX emissions influence the formation pathways of isoprene‐formed BSOA, as a high ratio of 2‐methylglyceric acid (2‐MG)/2‐MT is found in the North China Plain and part of the Yangtze River Delta Region. The simulated isoprene‐formed BSOA is more strongly correlated with sulfate than with particle water mass concentration or particle acidity, in part because sulfate increases the surface area increasing uptake for heterogeneous reactions. Decreases in isoprene‐formed BSOA were simulated with a pH increase of 2, implying that particle acidity mediates the BSOA formation.
17495. 题目: Characterizing fluxes of trace metals related to dissolved and suspended matter during a storm event: application to a karst aquifer using trace metals and rare earth elements as provenance indicators
期刊: Hydrogeology Journal
作者: Cybèle Cholet, Marc Steinmann, Jean-Baptiste Charlier, Sophie Denimal
摘要: The origin of suspended matter and colloids in karst aquifers during storm events is not well understood in spite of their potentially important role in the transport of poorly soluble inorganic, organic, and microbiological pollutants. This work aims to characterize the fluxes of trace metals related to dissolved and suspended matter during a storm event at the spring of a karst aquifer in the Jura Mountains in France that is mainly recharged by diffuse infiltration. Various natural tracers, including rare earth elements (REE), were used to identify the origin of the contributing dissolved and suspended fractions. The storm event was characterized by the temporally delayed arrival of two different fractions of suspended particulate matter (SPM). A first SPM peak corresponded to autochthonous conduit sediment mobilized by a piston effect at the beginning of the event. A second SPM peak, related to the arrival of allochthonous soil particulates, was characterized by elevated turbidity and high concentrations of K, Al, Fe, and Mn. In the dissolved fraction, this second SPM peak was accompanied by various poorly soluble trace elements, which were interpreted by the presence of nanoparticles and colloids (NPCs). The REE distribution patterns demonstrated that both the NPCs and the SPM were derived from soil particles whatever the storm stage. This suggests that the SPM of the first stage was reworked cave sediment from previous storms composed of residual clays and soil particles, which excludes authigenic precipitates (such as Fe-Mn oxyhydroxides and speleothems) as a significant source for autochthonous sediments.
17496. 题目: Ageing and molecular changes of dissolved organic matter between two deep oceanic end members
期刊: Global Biogeochemical Cycles
作者: S. K. Bercovici, B. P. Koch, O. J. Lechtenfeld, S. L. McCallister, P. Schmitt-Kopplin, D. A. Hansell
摘要: The global ocean contains a massive reservoir of dissolved organic carbon (DOC), rivaling the atmosphere's pool of CO2. The most recalcitrant fractions have mean radiocarbon ages of ~4,000 years in the Atlantic to ~6,000 years in the Pacific. Knowing the radiocarbon signatures of DOC and the molecular composition of dissolved organic matter (DOM) is crucial to develop understanding of the persistence and lifetime of the DOC pool. In this research, we collected samples from the deep North Pacific in August 2013 (aboard the RV Melville), to couple the Δ14C content of solid‐phase‐extracted DOM (Δ14C‐SPE‐DOM) with its molecular composition in the ocean's oldest deep waters. We find that deep waters in this region held a mean Δ14C‐SPE‐DOM value of ‐554±9 ‰ (~6,400 14C years), substantially more depleted than that in the deep Atlantic, which held a mean Δ14C‐SPE‐DOM value of ‐445±5‰. While we find a more degraded molecular composition of DOM in the deep Pacific than the deep Atlantic, the molecular formulae within the Island of Stability (Lechtenfeld et al., 2014), are largely retained. These results imply that a fraction of deep DOM is resistant to removal and present in both the deep Atlantic and Pacific Oceans.
17497. 题目: Natural regeneration on land degraded by coal mining in a tropical climate: Lessons for ecological restoration from Indonesia
期刊: Land Degradation & Development
作者: V. Novianti, R.H. Marrs, D.N. Choesin, D.T. Iskandar, D. Suprayogo
摘要: There are few examples of primary succession from tropical conditions, especially on land degraded by human activity, e.g. mine wastes. Such studies would assist in informing ecological restoration of these degraded sites. Here, a chronosequence approach was used to investigate early‐stage primary succession on overburden spoil wastes derived from coal mining in a tropical climate over a 64‐month period. Plant species composition and several micro‐climatic and spoil physico‐chemical and microbial properties were measured, and responses analysed using regression and multivariate (NMDS) analyses. A clear primary successional process was described showing that vegetation cover and species richness generally increased through time with a successional pathway from graminoids and herbs as the early dominants, shrubs in mid‐succession and trees in the later‐successional stages. Two important differences were noted between our results and primary successions elsewhere; a lower abundance of nitrogen‐fixing species and the colonization by some late‐successional shrubs and trees at the start. During the succession aggregate stability and organic matter (total C) increased –while electrical conductivity and some potentially toxic elements (Al, B) decreased. The constant high spoil moisture content appears to be an important determinant of vegetation development during primary succession and may be a factor in the rapid pace of succession detected here. The lessons for ecological restoration for coal overburden spoil under tropical conditions are that succession can proceed relatively rapidly.
17498. 题目: Effects of grazing exclusion on soil-vegetation relationships in a semi-arid grassland on the Loess Plateau, China
期刊: Land Degradation & Development
作者: Guohua Ren, Caixia Wang, Kuanhu Dong, Huisen Zhu, Yongcui Wang, Xiang Zhao
摘要: Grazing exclusion (GE) is regarded as an effective practice to restore degraded grasslands. However, the patterns of vegetation recovery and related regulating factors in response to fencing have not been fully recognized. Hence, quantitative analysis of vegetation‐soil relationships in response to GE was conducted in a semi‐arid grassland located on the Loess Plateau, North China. The results revealed that enclosure establishment significantly increased vegetation cover, height and productivity but reduced plant diversity. Soil bulk density (0–20 cm) and pH (0–50 cm) clearly decreased after GE, whereas soil water (0–20 cm), organic matter (0–10 cm and 30–40 cm) and nutrient concentration (0–20 cm) increased significantly. Redundancy analysis of vegetation and environmental variables suggested that edaphic properties, including soil water, soil pH, total N, bulk density and organic matter, were associated with plant community composition. Subsequent canonical correlation analysis indicated that soil bulk density, organic matter and total N played an important role in shaping vegetation patterns in response to fencing, whereas variations in soil pH and total N were the major contributors to variations in grazing rangeland. This work emphasized that fencing is a positive grassland management approach, and suitable changes in grazing stock and soil variability are required to quantify vegetation recovery in response to grazing exclusion.
17499. 题目: Linking permafrost thaw to shifting biogeochemistry and food web resources in an arctic river
期刊: Global Change Biology
作者: Michael R. Kendrick, Alexander D. Huryn, William B. Bowden, Linda A. Deegan, Robert H. Findlay, Anne E. Hershey, Bruce J. Peterson, Josh Benes, Elissa Schuett
摘要: Rapidly increasing air temperatures across the Arctic are thawing permafrost and exposing vast quantities of organic carbon, nitrogen, and phosphorus to microbial processing. Shifts in the absolute and relative supplies of these elements will likely alter patterns of ecosystem productivity and change the way carbon and nutrients are delivered from upland areas to surface waters such as rivers and lakes. The ultra‐oligotrophic nature of surface waters across the Arctic renders these ecosystems particularly susceptible to changes in productivity and food web dynamics as permafrost thaw alters terrestrial‐aquatic linkages. The objectives of this study were to evaluate decadal‐scale patterns in surface water chemistry and assess potential implications of changing water chemistry to benthic organic matter and aquatic food webs. Data were collected from the upper Kuparuk River on the North Slope of Alaska by the U.S. National Science Foundation Long‐Term Ecological Research (LTER) program during 1978‐2014. Analyses of these data show increases in stream water alkalinity and cation concentrations consistent with signatures of permafrost thaw. Changes are also documented for discharge‐corrected nitrate concentrations (+), discharge‐corrected DOC concentrations (‐), total phosphorus concentrations (‐), and δ13C isotope values of aquatic invertebrate consumers (‐). These changes show that warming temperatures and thawing permafrost in the upland environment are leading to shifts in the supply of carbon and nutrients available to surface waters and consequently changing resources that support aquatic food webs. This demonstrates that physical, geochemical, and biological changes associated with warming permafrost are fundamentally altering linkages between upland and aquatic ecosystems in rapidly changing arctic environments.
17500. 题目: Early indicators of soil formation in the Icelandic sub-arctic highlands
作者: Utra Mankasingh, Guðrún Gísladóttir
摘要: Andisols are carbon-rich soils that persist in volcanic regions with cool climates. They are the main soil type in Iceland, where there are also large areas of premature or degraded mineral soils with the possible potential to become andisols. This study examines soils from vegetated and unvegetated sites to look at the earliest indicators of andisol formation and soil organic carbon accumulation. Soils from 12 sites in the southern Icelandic highlands, which are characterised by harsh climate, shallow soils and limited vegetation cover, were sampled at four depths (0–5 cm, 5–10 cm, 10–20 cm and 20–30 cm). Three sites were sparsely vegetated gravels (M1–M3) and nine were fully vegetated, including 8 grassland sites (G1–G8) with mosses and dwarf shrubs, and a sandy fluvial wetland (S) with grasses, mosses and dwarf shrubs. Soils with vegetative cover were characterised as weak or structureless ranging from loamy sand to silty clay loam, while soils at the sparsely vegetated sites were structureless and sandy. The soil depth is greater in the vegetated sites, indicating greater soil development. On average, the bulk density of soils (0.75–1.16 g cm−3) was lower at vegetated sites than sparsely vegetated sites (0.90–1.17 g cm−3). The average carbon (%C), nitrogen (%N) and the overall soil organic matter (%SOM) of vegetated sites were higher (1.60%C, 0.10%N, 4.9%SOM) than for sparsely vegetated sites (0.27%C, 0.02%N, 1.81%SOM) with lower pH at the vegetated sites (pH < 7.2) than the sparsely vegetated (pH > 7.2), indicating the difference in soil development. Silandic allophanic material is present throughout the study area: all soils had >10% amounts of amorphous clay minerals (allophane, ferrihydrite or aluminium-humus complexes) and high aluminium and iron percentages. Strong associations between pyrophosphate-extractable Fe and Al and the soil C, indicative of Al and Fe complexed with humus or allophane and ferrihydrite clays of vegetated sites were observed. The %C, %SOM, Fe/Al associations, soil structure and soil depth all suggest that there is gradient of increasing soil genesis from sparsely vegetated to vegetated sites. Although the soils at the vegetated sites may be considered to be andisols, they are still immature, while the less developed soils at the sparsely vegetated sites are vitrisols (<1% C) and have not yet developed into andisols. Both of these groups are still undergoing pedological transformation and have not yet reached the C content of more mature andisols but indicate the potential for increased C accumulation. This study suggests there is potential for these soils to develop into the more fertile andisols over time through vegetation and vegetative succession.