论文检索

总访问量：2137575次

总访客量：105678人

所有论文

24641. 题目: A Neolithic palaeo-catena for the Xagħra Upper Coralline Limestone plateau of Gozo, Malta, and its implications for past soil development and land use
文章编号: N18072801
期刊: CATENA
作者: Charles French, Sean Taylor, Rowan McLaughlin, Alan Cresswell, Tim Kinnaird, David Sanderson, Simon Stoddart, Caroline Malone
更新时间: 2018-07-28
摘要: Geoarchaeological survey on the island of Gozo combined with test excavations and new chronometric dating of two Neolithic temple sites at Santa Verna and Ġgantija on the Xagħra plateau have revealed well-preserved buried soils which tell a new story of soil development and change for the early-mid-Holocene period. Micromorphological analysis has suggested that the earlier Neolithic climax soil type was a thick, well-developed, humic and clay-enriched argillic brown Mediterranean soil. With human intervention on the Xagħra Upper Coralline Limestone plateau from at least the early 4th millennium BCE, the trajectory of soil development quickly changed. Radical soil change was marked by the removal of scrub woodland, then consequent poorer organic status and soil thinning, and rubefication and calcification, no doubt exacerbated by Neolithic agricultural activities and a more general longer-term aridification trend. The beginnings of this transitional brown to red Mediterranean soil change process has been observed at Santa Verna temple by the early 4th millennium BCE, and appears to be much further advanced by the time of the latter use of Ġgantija temple in the early-mid-3rd millennium BCE. There is also evidence of attempts at amending these deteriorating soils during this period and into the 2nd millennium BCE, a practice which probably underpinned the viability of later Neolithic agricultural society in the Maltese Islands. The changes observed ultimately resulted in the creation of the thin, xeric, red Mediterranean soils on the Coralline Limestone mesa plateaux which are typical of much of Gozo and Malta today.

24642. 题目: Uranium Retention in a Bioreduced Region of an Alluvial Aquifer Induced by the Influx of Dissolved Oxygen
文章编号: N18072713
期刊: Environmental Science & Technology
作者: Donald Pan, Kenneth H. Williams, Mark J. Robbins, Karrie A. Weber
更新时间: 2018-07-27
摘要: Reduced zones in the subsurface represent biogeochemically active hotspots enriched in buried organic matter and reduced metals. Within a shallow alluvial aquifer located near Rifle, CO, reduced zones control the fate and transport of uranium (U). Though an influx of dissolved oxygen (DO) would be expected to mobilize U, we report U immobilization. Groundwater U concentrations decreased following delivery of DO (21.6 mg O₂/well/h). After 23 days of DO delivery, injection of oxygenated groundwater was paused and resulted in the rebound of groundwater U concentrations to preinjection levels. When DO delivery resumed (day 51), groundwater U concentrations again decreased. The injection was halted on day 82 again and resulted in a rebound of groundwater U concentrations. DO delivery rate was increased to 54 mg O₂/well/h (day 95) whereby groundwater U concentrations increased. Planktonic cell abundance remained stable throughout the experiment, but virus-to-microbial cell ratio increased 1.8–3.4-fold with initial DO delivery, indicative of microbial activity in response to DO injection. Together, these results indicate that the redox-buffering capacity of reduced sediments can prevent U mobilization, but could be overcome as delivery rate or oxidant concentration increases, mobilizing U.
图文摘要:

24643. 题目: Effects of anthropogenic nitrogen deposition on soil nitrogen mineralization and immobilization in grassland soil under semiarid climatic conditions
文章编号: N18072712
期刊: Environmental Monitoring and Assessment
作者: Ambreen Bhatti, Jawad Ahmad, Muhammad Qasim, Muhammad Riaz, Malcolm S. Cresser
更新时间: 2018-07-27
摘要: Earlier studies by the authors on English soils under grassland strongly supported their hypothesis that soil/plant systems have naturally evolved to conserve nitrogen (N) by having a close match between the dynamics of mineral-N production in soils and the dynamics of plant N requirements. Thus, maximum mineral-N production in soils occurred in spring when plant N requirements were greatest and were very low in mid to late summer. Low temperature and a high C:N ratio of senescing material helped to conserve N in winter, but mobile N was associated with pollution inputs. We test the hypothesis that under the much more arid conditions of Pakistan, soil/plant systems naturally have evolved to conserve mineral-N, especially over the very dry and cooler months between October and February. When soils from a grassland site were incubated at ambient temperatures after removal of plant roots and exclusion of atmospheric N inputs, there was consistent evidence of immobilization of nitrate and immobilization and possibly volatilization of ammonia/ammonium. In the wetter months of July and August, the soil at 0–10 cm depth showed no evidence of significant ammonium-N production in July and only small ammonium production at 10–20 cm depth in August, but was associated with significant nitrate-N immobilization in August. Nitrate leaching only appeared likely towards the end of the rainy season in September. The results strongly suggest that, under grass, the retention of atmospheric N inputs over the long dry periods is regulating the pools of available N in the soils, rather than the N produced by mineralization of soil organic matter.

24644. 题目: Phytolith content in Vietnamese paddy soils in relation to soil properties
文章编号: N18072711
期刊: Geoderma
作者: Minh N. Nguyen, Stefan Dultz, Andrew Meharg, Quang V. Pham, Anh N. Hoang, Than T.N. Dam, Van T. Nguyen, Khai M. Nguyen, Huan X. Nguyen, Nghia T. Nguyen
更新时间: 2018-07-27
摘要: Understanding of the fate of phytolith in soils is important because of its role as an agronomical nutrient resource and for carbon sequestration. Accumulation of phytolith derived silica occurs in paddy soils when phytolith input, here through straw incorporation, is higher than silica removal through crop offtake, dissolution and leaching. Phytolith dissolution is thought to be the main reason for diminishing of phytolith derived silica in soil, with this dissolution being highly dependent on soil chemical properties. In this study, phytolith content from 78 paddy soils sampled in the Red River (RRD) and Mekong River (MRD) Deltas, Vietnam, were quantified and related to pH, electrical conductivity (EC), oxalate-extractable Al and Fe (Al_ox and Fe_ox), organic carbon (OC) and clay content. Average phytolith contents within the topsoil (0–20 cm) were 4.8 ± 1.98 and 7.74 ± 2.97 mg g⁻¹ for the RRD and MRD, respectively. Positive correlation coefficients obtained for Al_ox, OC, clay content and EC, implying that these parameters might enhance phytolith resistance to dissolution. Soil pH had a negative correlation coefficient with phytolith content. Lower pH and higher Al_ox content explained the predominance of the phytolith in the MRD compared to the RRD. Soil pH adjustment can be proposed as an active management strategy to maintain phytolith added Si, source for crops and for carbon sequestration.
图文摘要:

24645. 题目: Evaluation of the anaerobic biodegradation of linear alkylbenzene sulfonates (las) using oecd 308 water/sediment systems
文章编号: N18072710
期刊: Journal of Hazardous Materials
作者: Carmen Corada-Fernández, Eduardo González-Mazo, Pablo A. Lara-Martín
更新时间: 2018-07-27
摘要: Linear alkylbenzene sulfonates (LAS) are the most widely used anionic surfactants in household detergents and cleaning products. We have evaluated LAS anaerobic degradation in sediments following OECD 308 guidelines. Four different classes of sediments were collected from non-polluted areas and tested to check the influence of: fine and coarse texture, low and high organic carbon content, and freshwater and marine origin. The concentrations of LAS and possible degradation metabolites in sediment and water phases were monitored by high resolution mass spectrometry over an incubation period of 160 days. LAS removal was between 0 and 63%, depending on the sediment used, and it was accompanied by formation of sulfophenyl carboxylic acids (SPCs). The best results were observed for marine sediments having low organic carbon and silt + clay contents (0.5% and 13%, respectively), whereas degradation was negligible in freshwater sediments. The large differences in degradation observed across the sediments tested were attributed to their physicochemical properties influencing LAS bioavailability and the heterogeneity of microbial communities. Further research is also needed to address some shortcomings observed during the application of the OECD 308 and to ensure that test results obtained with these guidelines model anaerobic biodegradation under realistic environmental conditions.

24646. 题目: Interpreting the effects of natural organic matter on antimicrobial activity of Ag₂S nanoparticles with soft particle theory
文章编号: N18072709
期刊: Water Research
作者: Yulei Liu, Tao Yang, Lu Wang, Zhuangsong Huang, Juan Li, Haijun Cheng, Jin Jiang, Suyan Pang, Jingyao Qi, Jun Ma
更新时间: 2018-07-27
摘要: Natural organic matter (NOM) ubiquitously exists in natural waters and would adsorb onto the particle surface. Previous studies showed that NOM would alleviate the toxicity of nanomaterials, while the mechanism is seldom quantitatively interpreted. Herein, the effects of humic substances [Suwannee River fulvic acid (SRFA) and Suwannee River humic acid (SRHA)] and biomacromolecules [alginate and bovine serum albumin (BSA)] on the aggregation and antimicrobial effects of silver sulfide nanoparticles (Ag₂S-NPs) were investigated. The aggregation kinetics of Ag₂S-NPs in electrolyte solutions were in agreement with the results based on Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The dynamic light scattering (DLS) results showed that the SRFA, SRHA, alginate and BSA molecules coated on the Ag₂S-NPs surfaces. The NOM coating layer prevented salt-induced coagulation of Ag₂S-NPs, and the effects of BSA and SRHA on Ag₂S-NPs stabilizing were more obvious than that of SRFA and alginate. Flow cytometry results showed that BSA and SRHA were more effective on alleviating the Ag₂S-NPs induced cell (Escherichia coli) membrane damage than SRFA and alginate. After interpreting the electrophoretic mobility (EPM) data of the NOM coated Ag₂S-NPs by Ohshima's soft particle theory, it was found that the thickness of the NOM coating layers followed the orders of BSA > SRHA > alginate > SRFA. The E.coli cell membrane damage level was negatively correlated with the thickness and softness of the coating layer. NOM coating may physically alleviate the contact between NPs and E. coli cells and thus attenuate the extent of cell membrane damage caused by the NP-cell interaction. This work provides a new perspective for quantitatively interpreting the influence of NOM on the environmental behaviors and risks of nanomaterials.
图文摘要:

24647. 题目: Dissolved organic matter binding with Pb(II) as characterized by differential spectra and 2D UV–FTIR heterospectral correlation analysis
文章编号: N18072708
期刊: Water Research
作者: Huacheng Xu, Mingquan Yan, Wentao Li, Helong Jiang, Laodong Guo
更新时间: 2018-07-27
摘要: Dissolved organic matter (DOM) in aquatic environment significantly influences the behavior and fate of heavy metals via binding, complexation and thus changes the metal speciation; however detailed interfacial processes and mechanisms are still unclear. Here, differential absorbance and fluorescence spectra and two dimensional UV–FTIR heterospectral correlation analysis were applied to probe into the Pb(II)–DOM interaction at a wide range of pH and ionic strength (IS). The absorbance of DOM molecules under all conditions increased with metal addition, while the different extents of absorbance variations along the wavelength range in the differential zero-order and log-transformed absorbance spectra indicated the site heterogeneity within the DOM pool for metal binding. Spectral parameters, namely differential fluorescent components 1 and 2 (DFC1 and DFC2) and differential slopes of log-transformed absorbance in the range of wavelength 350–400 nm (DSlope_350–400) were found to be highly correlated with the total amounts of DOM-bound Pb(II) predicted by the NICA-Donnan model, while the differential absorbance spectra at 235 nm (DA₂₃₅) was related to the extent of Pb(II) bound by carboxylic groups. Thus, these parameters are an indicator or proxy for the in situ Pb(II)–DOM interaction extent. Aryl C–H gave the fastest response to Pb(II) binding at lower pH and IS (e.g., pH 4.7 and IS = 0.01 M), followed by carboxyl C=O and polysaccharide C–OH and then chromophoric groups at 265 nm (CDOM₂₆₅). However, the CDOM₂₆₅ bound to Pb(II) prior to aryl C–H and polysaccharide C–OH groups at higher pH and IS (6.0 and 0.1 M, respectively), showing that the binding sequences were highly dependent on solution chemistry. Differential spectra combined with two dimensional UV–FTIR heterospectral correlation analysis can be used as a promising approach to elucidate metal–DOM interaction processes, including site heterogeneity, binding sensitivity and sequence at the functional group level.
图文摘要:

24648. 题目: Comparative evaluation of influence of aging, soil properties and structural characteristics on bioaccessibility of polychlorinated biphenyls in soil
文章编号: N18072707
期刊: Chemosphere
作者: Qingqing Ti, Chenggang Gu, Chang Liu, Jun Cai, Yongrong Bian, Xinglun Yang, Yang Song, Fang Wang, Cheng Sun, Xin Jiang
更新时间: 2018-07-27
摘要: Though bioaccessibility commonly recognized as a guideline for risk assessment is closely related with pollution occurrence and chemical species of compounds, the mechanistic links are barely evaluated particularly for widespread polychlorinated biphenyls (PCBs) in soil. With the biomimetic extraction of hydroxypropyl-β-cyclodextrin (β-HPCD), the temporal and spatial influences of soil properties, aging and structural characteristics, e.g. polarity of PCB congeners on bioaccessibility were investigated for PCBs. Sensitive variation of bioaccessibility with aging, soil organic matter (SOM), particle size and soil moisture were clearly evidenced for different PCB congeners. Due to aging, the bioaccessibility decreased in the long term after stabilization for 36 h. In concert with the first-order kinetics, the decay rates of bioaccessibility were shown with congener-specificity and were well correlated with dipoles of PCBs. The increment of SOM diminished the bioaccessibility for the strengthened adsorption while the increased particle size and soil moisture elevated it possibly due to the less adsorption on soil particles and more accommodation of PCBs in soil pore water. Except the positive correlations with particle size, soil moisture and dipole moment, the greater dependency on aging and SOM was highlighted for bioaccessibility by partial least squares (PLS) analysis. The mutual relationship with influential factors was quantitatively formulated for accelerative prediction of bioaccessibility, and the comparative evaluation and detailed insights into the mechanistic links would thus help enhance the precise determination of bioaccessibility and risk assessment of PCBs in soil.

24649. 题目: Seagrass community-level controls over organic carbon storage are constrained by geophysical attributes within meadows of Zanzibar, Tanzania
文章编号: N18072706
期刊: Biogeosciences
作者: Elizabeth Fay Belshe, Dieuwke Hoeijmakers, Natalia Herran, Matern Mtolera, and Mirta Teichberg
更新时间: 2018-07-27
摘要: The aim of this work was to explore the feasibility of using plant functional traits to identify differences in sediment organic carbon (OC) storage within seagrass meadows. At 19 sites within three seagrass meadows in the coastal waters of Zanzibar, Tanzania, species cover was estimated along with three community traits hypothesized to influence sediment OC storage (above and belowground biomass, seagrass tissue nitrogen content, and shoot density). Sediments within four biogeographic zones (fore reef, reef flat, tidal channel, and seagrass meadow) of the landscape were characterized, and sediment cores were collected within seagrass meadows to quantify OC storage in the top 25cm and top meter of the sediment. We identified five distinct seagrass communities that had notable differences in the plant traits, which were all residing within a thin veneer (ranging from 19 to 78cm thick) of poorly sorted, medium to coarsely grained carbonate sands on top of carbonate rock. One community (B), dominated by Thalassodendron ciliatum, contained high amounts of above (972±74gDWm⁻²) and belowground (682±392gDWm⁻²) biomass composed of low-elemental-quality tissues (leaf C:N = 24.5; rhizome C:N = 97). While another community (C), dominated by small-bodied ephemeral seagrass species, had significantly higher shoot density (4178 shootsm⁻²). However, these traits did not translate into differences in sediment OC storage and across all communities the percentage of OC within sediments was similar and low (ranging from 0.15% to 0.75%), as was the estimated OC storage in the top 25cm (14.1±2.2Mg Cha⁻¹) and top meter (33.9±7.7Mg Cha⁻¹) of sediment. These stock estimates are considerably lower than the global average (194.2±20.2Mg Cha⁻¹) reported for other seagrass ecosystems and are on the lower end of the range of estimates reported for the tropical Indo-Pacific bioregion (1.9 to 293Mg Cha⁻¹). The uniformly low OC storage across communities, despite large inputs of low-quality belowground tissues in community B, indicates that the geophysical conditions of the coarse, shallow sediments at our sites were not conducive to OC stabilization and outweighed any variation in the quantity or quality of seagrass litter inputs. These results add to a growing body of evidence showing that geophysical conditions of the sediment modulate the importance of plant traits in regards to retention of OC within blue carbon ecosystems and cautions against the use of plant traits as a proxy for sediment OC storage across all seagrass ecosystems.
图文摘要:

24650. 题目: Temperature sensitivity of extracellular enzymes differs with peat depth but not with season in an ombrotrophic bog
文章编号: N18072705
期刊: Soil Biology and Biochemistry
作者: J. Megan Steinweg, Joel E. Kostka, Paul J. Hanson, Christopher W. Schadt
更新时间: 2018-07-27
摘要: Peatlands contain a large portion of Earth's terrestrial soil organic matter in part due to a reduction in decomposition rates. Organic matter decomposition is initially mediated by extracellular enzyme activity, which is in turn controlled by temperature, moisture, and substrate availability; and all are subject to seasonal variation. As depth increases in peatlands, temperature variability and labile carbon inputs decrease. We hypothesized that the more stable recalcitrant subsurface would contain a smaller less diverse enzyme pool, that is better adapted to a narrow temperature range. Thus temperature dependence would be diminished at depth compared to superficial peat. Potential enzyme activity rates were determined across seasons and with depth in peat samples collected from the Marcell Experimental Forest in northern Minnesota, USA. The temperature dependence, assessed by activation energy, was quantified for three hydrolytic enzymes involved in nutrient cycling at up to 15 temperature points ranging from 2 °C to 65 °C. Potential enzyme activity decreased with peat depth as expected and corresponded with changes in peat composition and microbial biomass from the acrotelm to the catotelm. In an environmentally relevant temperature range (2–23 °C), activation energy decreased with depth for β-glucosidase as predicted and leucine amino peptidase activation energy was the lowest of all enzymes. Stable temperatures at depth appear to result in a microbial community containing enzymes that have lower sensitivity to temperature increases. Surprisingly, there was no significant seasonal effect on enzyme temperature dependence observed in our study. Based on these results, and without shifts in microbial community composition, warming of peat could result in increased carbon and phosphorus cycling at the surface but little change at depth. Additionally differences in enzyme temperature sensitivity suggest nitrogen cycling could remain constant with warming, potentially resulting in proteolytic nitrogen cycling being decoupled from carbon and phosphorus cycling.

24651. 题目: Labile soil organic carbon for assessing soil quality: influence of management practices and edaphic conditions
文章编号: N18072704
期刊: CATENA
作者: Matias E. Duval, Juan A. Galantini, Juan M. Martínez, Fabiana Limbozzi
更新时间: 2018-07-27
摘要: Soil organic carbon (SOC) is a complex set of pools, and to understand its dynamics it is necessary to know which of these pools are sensitive to the edaphic and climatic conditions or the agricultural practices, or to both. The objectives of this study were to evaluate the relationships between permanganate oxidizable C (POX-C) and various soil organic carbon fractions in different land-uses and soil types, and to examine whether the POX-C fraction is sensitive to different agricultural management practices in soils under no-tillage. Three treatments were identified at four sites located in the Argentine Pampas region: two different agricultural scenarios in terms of crop rotation, fertilizers and use of agrochemicals (Good Agricultural Practices and Poor Agricultural Practices, GAP and PAP, respectively) and an undisturbed natural (NE) environment adjacent to the agricultural sites as the control treatment. The following organic fractions were quantified: SOC, coarse and fine particulate organic carbon (POC_c and POC_f, respectively), hot water and acid extractable organic carbon (HWC and HAC, respectively) and POX-C. Soil POC values ranged from 0.46 to 7.29 g kg⁻¹, HAC values ranged from 1.50 to 6.73 g kg⁻¹, HWC values ranged from 0.20 to 1.10 g kg⁻¹ and POX-C values ranged from 0.41 to 1.04 g kg⁻¹ soil, POC_c being the most variable fraction (CV = 72%) and POX-C the least (CV = 22%). Soil POC_c and POC_f at 0–10 cm, and POC_c at 10–20 cm were largely explained by management practices with a component of variance >50%. The relationship between POX-C and SOC was generally stronger (R² = 0.76–0.92) than POX-C with other organic fractions and where depth and site factors have a greater influence on this relationship than management practices. Among the labile fractions, the most sensitive indicators of soil quality in agricultural soils were POC_f and HWC, which displayed the highest F-statistic values. Despite the dilute solution used (0.02 mol L⁻¹ KMnO₄) the POX-C demonstrated limited sensitivity to different agricultural practices. However, this methodology could be used to estimate SOC regarding site conditions and depths. The POC_f was the fraction most affected by agricultural practices, indicated by high relationships with both the soil physical attributes (macroporosity, bulk density, and density, volume and stability of aggregates) and the agronomic parameters (soybean and maize yields).

24652. 题目: Effect of different components of single superphosphate on organic matter degradation and maturity during pig manure composting
文章编号: N18072703
期刊: Science of The Total Environment
作者: Juan Wu, Aiguo Zhang, Guoxue Li, Yuquan Wei, Shengzhou He, Zhong Lin, Xiufang Shen, Qiuju Wang
更新时间: 2018-07-27
摘要: Single superphosphate (SSP) as an additive could improve phosphorus availability and reduce nitrogen loss for composts, but few studies have explored the influence of SSP on the transformation of carbon fractions in composting. The aim of this work was to assess the effect of different components of SSP, including calcium dihydrogen phosphate (CDP), calcium sulfate (CS) and free acid (FA) on organic matter degradation and maturity during pig manure composting. The results showed that CDP had significantly negative effects on the duration of thermophilic phase and organic matter degradation, but lengthened the curing phase for the transformation of organic matter. FA could intensify the inhibiting effect of CDP and postpone the biodegradation process of composting, but CS could buffer the effect of CDP on the degradation of organic carbon fractions by controlling pH. The study reveals the roles of different components of SSP to the transformation of organic carbon fractions, which lays a foundation for regulating the effects of chemical additives during composting. Regulating the content of CDP in SSP or applying SSP with other chemical additives to control the biotoxicity of excess phosphate on microbial activity should be concerned for complete and efficient composting in further study.
图文摘要:

24653. 题目: Sorption of organic compounds to two diesel soot black carbons in water evaluated by liquid chromatography and polyparameter linear solvation energy relationship
文章编号: N18072702
期刊: Water Research
作者: Po-Hsin Su, Dave Ta Fu Kuo, Yang-hsin Shih, Chih-yu Chen
更新时间: 2018-07-27
摘要: Substantial variability in sorption capacity of black carbon (BC) has been a major challenge for accurate fate and risk assessment of organic pollutants in soils and sediments. 16 model organic sorbates (logK_OW = 0.38–4.21) encompassing diverse chemical functionalities were used to probe the sorption capacity of two diesel soot samples representative of graphitic BC (BC1, specific surface area (SSA) = 87 m²/g) and amorphous, oxygenated BC (BC2; SSA = 3.6 m²/g). The BC-water sorption coefficients (logK_BC) of the model sorbates were determined using reversed-phase liquid chromatography (RP-LC) on soot-filled columns. It was found that mass-based logK_BC's of BC1 (1.64–3.66 L/kg_BC) exceeded those of BC2 (0.68–3.48 L/kg_BC) consistently for all model sorbates. However, area-normalized logK_BC's of BC2 were larger than those of BC1, suggesting that the overall sorption was more favored on the oxygenated sorbent per area basis. Linear solvation energy relationships (LSERs) for sorption onto BC1 and BC2 were found to be logK_BC = (2.49 ± 0.65)E + (−2.71 ± 0.88)S + (1.17 ± 0.46)A + (2.52 ± 0.34)V and logK_BC = (1.12 ± 0.39)E + (−1.68 ± 0.32)S + (−3.70 ± 0.57)B + (4.37 ± 0.38)V + (−1.51 ± 0.22), respectively. The LSERs indicated that sorption onto soot was generally enhanced with increasing non-specific van der Waals and decreasing cavitation cost (i.e., eE, sS, and vV terms). The logK_BC difference between BC1 and BC2, ΔlogK_BC, appeared to be correlated with the H-bonding capacity of the sorbates but not logK_OW. Analysis of literature and experimental logK_BC's revealed that logK_BC and logSSA across different types of BC (i.e., soot, char, charcoal, activated carbon) were linearly correlated for benzene and toluene (r² = 0.88–0.91). This work illustrates the utility of RP-LC in determining the sorption coefficients of high-capacity sorbents and suggests the possibility of a unified sorption model for the continuum of black carbon.

24654. 题目: A simple approach to estimate daily loads of total, refractory, and labile organic carbon from their seasonal loads in a watershed
文章编号: N18072701
期刊: Environmental Science and Pollution Research
作者: Ying Ouyang, Johnny M. Grace, Wayne C. Zipperer, Jeff Hatten, Janet Dewey
更新时间: 2018-07-27
摘要: Loads of naturally occurring total organic carbons (TOC), refractory organic carbon (ROC), and labile organic carbon (LOC) in streams control the availability of nutrients and the solubility and toxicity of contaminants and affect biological activities through absorption of light and complex metals with production of carcinogenic compounds. Although computer models have become increasingly popular in understanding and management of TOC, ROC, and LOC loads in streams, the usefulness of these models hinges on the availability of daily data for model calibration and validation. Unfortunately, these daily data are usually insufficient and/or unavailable for most watersheds due to a variety of reasons, such as budget and time constraints. A simple approach was developed here to calculate daily loads of TOC, ROC, and LOC in streams based on their seasonal loads. We concluded that the predictions from our approach adequately match field measurements based on statistical comparisons between model calculations and field measurements. Our approach demonstrates that an increase in stream discharge results in increased stream TOC, ROC, and LOC concentrations and loads, although high peak discharge did not necessarily result in high peaks of TOC, ROC, and LOC concentrations and loads. The approach developed herein is a useful tool to convert seasonal loads of TOC, ROC, and LOC into daily loads in the absence of measured daily load data.

24655. 题目: Divergence of soil microarthropod (Hexapoda: Collembola) recovery patterns during natural regeneration and regeneration by planting of windthrown pine forests
文章编号: N18072614
期刊: Forest Ecology and Management
作者: Maria Sterzyńska, Jarosław Skłodowski
更新时间: 2018-07-26
摘要: Windthrows are natural disturbances that influence the functioning and structure of forest ecosystems and the belowground components of an ecosystem. Soil processes such as the recycling of organic matter, energy and nutrients are controlled by soil fauna. However, little is still known about the post-disturbance recovery of soil microarthropod communities in forest stands exposed to windthrow of various severity and post-windthrow forest management over time. This study assessed soil Collembola community recovery in pine forest stands over the long-term (between 9 and 14 years after the disturbance event). We predicted that (1) different severity of windthrow disturbance in a pine forest has different effects on the recovery of Collembola community composition and functional structure, even after 10 years; (2) The recovery of Collembola communities is similar during regeneration of a forest disturbed by windthrow and in a pine plantation planted after clearing of a windthrown forest and subsequent soil preparation; (3) The changes in the Collembola community during forest regeneration after windthrow disturbance can be explained by selected environmental variables, especially the leaf area index LAI. As expected, regeneration processes within forest stands shifted the species composition of collembolan communities and changed their functional structure. The surface dwelling collembolan species (epigeic and atmobiotic life form) responded to regeneration processes mainly in pine stands, especially in a pine plantation established after a clearing of broken pines and subsequent soil preparation. Our results suggest different sensitivity of collembolan communities to environmental changes induced by various degrees of opening of the tree canopy by windthrow and to those caused by the post disturbance treatment. These findings confirm that collembolan community composition recovery is slow and divergent during natural regeneration of pine stands and regeneration by planting but does not differ between moderately and severely successional trajectories. Our results also confirm the importance of canopy closure for the possibility of Collembola community regeneration. If canopies were more closed (higher leaf area index, LAI index), the possibility of regeneration increased, especially in the young pine plantations, as seen in the final years of our study.
图文摘要:

24656. 题目: Glomalin changes in urban-rural gradients and their possible associations with forest characteristics and soil properties in Harbin City, Northeastern China
文章编号: N18072613
期刊: Journal of Environmental Management
作者: Wenjie Wang, Qiong Wang, Wei Zhou, Lu Xiao, Huimei Wang, Xingyuan He
更新时间: 2018-07-26
摘要: Glomalin-related soil protein (GRSP) is a glycoprotein from the hyphae and spores of arbuscular mycorrhizal fungi. Despite urbanization being the leading cause of present-day land-use changes, there is limited information available on the effects of urbanization on GRSP. We sampled soil from 257 plots in Harbin City, China, and surveyed forest characteristics, soil properties, and urbanization gradients related to ring road development, urban history, and land use. Two glomalin components (easily extracted glomalin, EEG; and total glomalin, TG) and their relative contributions to soil organic carbon (SOC: EEG/SOC, TG/SOC) were measured in the laboratory. We found exponential increases in EEG/SOC and TG/SOC from the most urbanized to the most rural regions, indicating that urbanization sharply reduced glomalin-related SOC sequestration. In general, 1.3–1.4-fold higher glomalin levels were found in the newly urbanized, previously rural areas, while glomalin contribution to SOC sequestration was lower by 38–59% for EEG and 74–85% for TG in the most urbanized regions compared to rural regions. Accompanying these recorded changes in glomalin, linear decreases in soil pH and electrical conductance were observed in all three urban-rural gradients from the urban center to the rural area, and steep decreases in conifer ratio and shrub richness were seen in two of the gradients. The complex associations among glomalin and forest characteristics, soil properties, and urbanization gradients were decoupled and cross-checked using redundancy analysis variation partitioning and structural equation model analysis. Urbanization indirectly changed glomalin features by altering soil properties, with soil properties accounting for over 60% of the glomalin variation. Forest characteristics and urbanization gradients contributed to 10–15% of the glomalin variation. With rapid urbanization occurring in China and on a global scale, glomalin variation should be considered when evaluating soil carbon sequestration and in developing effective forest management strategies, with the aim of ameliorating soil degradation in urbanized regions by rehabilitating glomalin accumulation.

24657. 题目: Microbial and plant-derived compounds both contribute to persistent soil organic carbon in temperate soils
文章编号: N18072612
期刊: Biogeochemistry
作者: Pierre Barré, Katell Quénéa, Alix Vidal, Lauric Cécillon, Bent T. Christensen, Thomas Kätterer, Andy Macdonald, Léo Petit, Alain F. Plante, Folkert van Oort, Claire Chenu
更新时间: 2018-07-26
摘要: Our study tests the emerging paradigm that biochemical recalcitrance does not affect substantially long-term (50 years) SOC persistence. We analyzed the molecular composition of SOC in archived soils originating from four European long-term bare fallow experiments (Askov, Rothamsted, Versailles and Ultuna). The soils had been collected after various periods (up to 53 years) under bare fallow. With increasing duration of bare fallow without new organic inputs, the relative abundance of cutin- and suberin-derived compounds declined substantially, and the abundance of lignin-derived compounds was close to zero. Conversely, the relative abundance of plant-derived long-chain alkanes remained almost constant or increased during the bare fallow period. The relative abundance of N-containing compounds, considered to be abundant in SOC derived from microbial activity, increased consistently illustrating that microbial turnover of SOC continues even when plant inputs are stopped. The persistence of the different families of plant-derived compounds differed markedly over the scale of half a century, which may be ascribed to their contrasting chemical characteristics and recalcitrance, or to differences in their interactions with the soil mineral matrix, and likely some combination since chemical composition drives the degree of mineral association. Using soil from this unique set of long-term bare fallow experiments, we provide direct evidence that multi-decadal scale persistent SOC is enriched in microbe-derived compounds but also includes a substantial fraction of plant-derived compounds.

24658. 题目: A farm-scale investigation of the organic matter composition and soil chemistry of Andisols as influenced by land use and management
文章编号: N18072611
期刊: Biogeochemistry
作者: Ritha Kov, Marta Camps-Arbestain, Roberto Calvelo Pereira, Manuel Suárez-Abelenda, Qinhua Shen, Stanislav Garbuz, Felipe Macías Vázquez
更新时间: 2018-07-26
摘要: Andisols are characterised by having abundant reactive Al in the form of short-range ordered (SRO) Al constituents and organo-Al complexes, which facilitates the accumulation of soil organic matter (OM). However, recent studies of New Zealand pastoral systems have reported loss of carbon (C) from Andisols when under intense management. This study compares the organic and inorganic chemistry of Andisols on two adjacent pasture sites under different pastoral management regimes (Paddock 2 being more intensively managed than Paddock 1), as well as under a nearby pine stand (Forest). Mean soil pH-H₂O in Forest (5.3) was significantly lower (P < 0.05) than that in Paddock 1 (5.7), which itself was significantly lower (P < 0.05) than in Paddock 2 (6.1). Soil C concentrations were significantly higher (P < 0.05) in the soils under pasture than under pine (63.8 g C/kg), and C in Paddock 1 (98.1 g C/kg) was significantly higher (P < 0.05) than in Paddock 2 (84.1 g C/kg). The ratio of Al in organo-Al complexes (as estimated with sodium pyrophosphate) to the sum of Al in both SRO and organo-Al complexes (Al_p/Al_o) was significantly smaller (P < 0.05) as the alkalinity of the soils increased (0.38, 0.23, 0.16 for Forest, Paddock 1 and Paddock 2, respectively). At the molecular level, soils under Forest had a larger relative contribution of degraded products of plant polysaccharides than those under pasture, while these had a larger contribution of fresh (e.g. cellulose and cutan/suberan aliphatic structures) and N-rich OM (e.g., microbial fingerprints, denoting a high microbial activity). Dissolved organic C content in the rhizosphere of pasture species was similar between paddocks, but Paddock 2 had a significantly (P < 0.05) greater contribution of organic acids of MW < 500 Da and higher pH (6.8 vs. 6.2). The results (1) confirm the common enrichment in organic C of New Zealand top soils under pasture compared to those under pine, and (2) reveal that the changes in the soil chemistry associated with pasture management may weaken the ability of these soils to preserve OM.

24659. 题目: A hard, high-carbon, lignomor with conchoidal fracture: Cunnite, from mature myrtle beech (Nothofagus cunninghamii (Hook. f.) Oerst.)
文章编号: N18072610
期刊: Geoderma
作者: Christopher Dean, Ernst Horn
更新时间: 2018-07-26
摘要: Introduced here is a newly discovered, hard, high‑carbon, macroscopically homogenous, solid lignomor that is part of the natural decomposition product of mature, rainforest hardwood trees of the species myrtle beech (Nothofagus cunninghamii (Hook. f.) Øerst.). The substance, named cunnite, exhibits conchoidal fracture (indicating isotropic bonding), whereas all other tree decomposition products noted were readily friable, with no evidence of strong bonding. It is a dehydrated form of lignomor and its pre-dehydrated form also has conchoidal fracture. Cunnite was examined by carbon assay, radiocarbon dating, scanning electron microscopy (SEM) and Fourier transform infra-red spectroscopy (FT-IR). All wood cell walls had decomposed but the FT-IR results suggested that cunnite is high in lignin, and therefore it is most likely formed by a brown-rot fungi. Cunnite appears to be unique in that it is a product of natural decomposition but has relatively strong bonding. This bonding may be either from re-polymerisation or hydrogen bonding. If original polymer segments remain then they are most likely often cross-linked. Although cunnite appears to be stable beyond the decomposition of the entire tree, the age determined from radiocarbon dating for our samples does not imply that it is particularly long-lived thereafter. Cunnite is part of the forest carbon cycle but forms only a small fraction of the soil organic carbon pool. If the composition of cunnite is determined accurately in future work, and a synthetic version made, then it may be useful on a commercial scale as an adsorbent of hydrogen (i.e. storage for renewable energy) or of toxic substances; or it may provide other products useful in materials science or chemical engineering.
图文摘要:

24660. 题目: The importance of bioconcentration into the pelagic food web base for methylmercury biomagnification: A meta-analysis
文章编号: N18072609
期刊: Science of The Total Environment
作者: Pianpian Wu, Martin J. Kainz, Andrea G. Bravo, Staffan Åkerblom, Lars Sonesten, Kevin Bishop
更新时间: 2018-07-26
摘要: Methylmercury (MeHg) transfer from water into the base of the food web (bioconcentration) and subsequent biomagnification in the aquatic food web leads to most of the MeHg in fish. But how important is bioconcentration compared to biomagnification in predicting MeHg in fish To answer this question we reviewed articles in which MeHg concentrations in water, plankton (seston and/or zooplankton), as well as fish (planktivorous and small omnivorous fish) were reported. This yielded 32 journal articles with data from 59 aquatic ecosystems at 22 sites around the world. Although there are many case studies of particular aquatic habitats and specific geographic areas that have examined MeHg bioconcentration and biomagnification, we performed a meta-analysis of such studies. Aqueous MeHg was not a significant predictor of MeHg in fish, but MeHg in seston i.e., the base of the aquatic food web, predicted 63% of the variability in fish MeHg. The MeHg bioconcentration factors (i.e., transfer of MeHg from water to seston; BCF_w-s) varied from 3 to 7 orders of magnitude across sites and correlated significantly with MeHg in fish. The MeHg biomagnification factors from zooplankton to fish varied much less (logBMF_z-f, 0.75 ± 0.31), and did not significantly correlate with fish MeHg, suggesting that zooplanktivory is not as important as bioconcentration in the biomagnification of fish MeHg across the range of ecosystems represented in our meta-analysis. Partial least square (PLS) and linear regression analyses identified several environmental factors associated with increased BCF, including low dissolved organic carbon, low pH, and oligotrophy. Our study reveals the widespread importance of MeHg bioconcentration into the base of the aquatic food web for MeHg at higher trophic levels in aquatic food webs, as well as the major influences on the variability in this bioconcentration.
图文摘要: