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25401. 题目: A new software of calculating the pH values of coastal seawater: Considering the effects of low molecular weight organic acids
文章编号: N19031804
期刊: Marine Chemistry
作者: Li-Na Lyu, Daoming Lu, Chengjun Sun, Haibing Ding, Liang-Min Yu, Gui-Peng Yang
更新时间: 2019-03-18
摘要: Effects of low molecular weight organic acids (LMWOAs) on the pH value of seawater were investigated in the surface seawater of the Jiaozhou Bay, China. The new software of Org·TCO2TA was developed to calculate the pH values of seawater based on the alkalinity (Alk) equation where organic acid Alk (Org-Alk) was separated into LMWOA Alk (LMWOA-Alk) and humic acid Alk (HA-Alk). In the calculations, all dissociation constants of organic acids were from previous literature. In our study, the average concentration of total LMWOAs was 14.5 ± 11.2 μmol·kg⁻¹ SW. pH values from the Org·TCO2TA software were closer to the pH values from spectrophotometric measurement than those from the CO2SYS program, indicating pH values can be influenced by high concentrations of LMWOAs in coastal seawater of the Jiaozhou Bay. Although the differences still existed between the pH values from the spectrophotometric method and the calculated pH values from the Org·TCO2TA software due to the influence of various factors, including the analytical errors of dissolved inorganic carbon and nutrients, the new software can calculate the pH values of coastal seawater more accurately by considering the effects of LMWOAs.

25402. 题目: Diagenetic transformation of organic matter in sapropel sediments of small lakes (southern West Siberia and eastern Transbaikalia)
文章编号: N19031803
期刊: Quaternary International
作者: G.A. Leonova, A.E. Maltsev, V.N. Melenevsky, S.K. Krivonogov, L.M. Kondratyeva, V.A. Bobrov, M.Y. Suslova
更新时间: 2019-03-18
摘要: Sapropels, biogenic lake sediments, are characterized by a reduction type of diagenesis, during which decomposition of organic compounds, modification of the pore water chemical composition and precipitation of authigenic minerals, mostly pyrite, occur. Pyrolysis data indicate that organic matter undergoes radical transformations already in the uppermost sapropel layers, and composition of the organic matter in the sediments is principally different from the composition of the organic matter of live organisms, which produce the sediments. The sapropels lose labile protein–carbohydrate compounds in the horizon of unconsolidated sediment (0–5 cm), and kerogen appears, whose macromolecular structures start to develop in the very early stages of diagenesis. Various physiological groups of microorganisms provide diagenetic transformations of the organic matter, where heterotrophic, ammonifying and sulfate-reducing bacteria play key role. Their effect is well-seen from the pore water transformation: a decrease in concentrations of SO₄^2– and consequent increase of reduced Fe and S as pyrite in the solid phase of the sediment. Comparative analysis shows that, unlike in lakes of the Baikal area, sapropels in southern West Siberia are affected by more active sulfate reduction, which can depend on both the composition of the organic matter and the SO₄^2– concentration in the pore waters.

25403. 题目: Long-term impact of no-till conservation agriculture and N-fertilizer on soil aggregate stability, infiltration and distribution of C in different size fractions
文章编号: N19031802
期刊: Soil and Tillage Research
作者: Nkanyiso J. Sithole, Lembe S. Magwaza, Guy R. Thibaud
更新时间: 2019-03-18
摘要: Soil degradation associated with the loss of soil organic carbon (SOC) has been a major concern in sub-Saharan Africa because of the subsequent yield reduction. It is not fully understood how long-term additional C through biomass and N-fertilizers impact on C distribution in soil aggregates and its effects on soil aggregate stability and infiltration in sub-tropical maize monocropping system. The study, therefore, assessed long-term changes in total SOC (TSOC), aggregate-associated C, particulate organic C (POC), aggregate stability and infiltration in the 0–10, 10–20 and 20–30 cm depths under different tillage systems after 13 years of implementation of the trial. The three tillage systems were no-till (NT), rotational tillage (RT) both with permanent residue cover and conventional tillage (CT) with residue removed. N-fertilizer was applied at a rate of 0, 100 and 200 kg/ha. On average TSOC did not vary (p > 0.05) across the tillage treatments, 27.1 t/ha NT vs 26.0 t/ha RT and 26.6 t/ha CT, but varied with depth where it was stratified in the 0–10 cm depth in NT and RT. Particulate organic C, however, varied significantly (p < 0.05) across the treatments where it decreased with increase in tillage intensity but only in the 0–10 cm depth. Carbon associated with large aggregates (>2000 μm) differed marginally (p = 0.085) with tillage treatment with NT having 38.0 t/ha, RT 36.6 t/ha and CT 29.7 t/ha. However, differences (p < 0.05) were observed in small macroaggregates (250–2000 μm) with NT having 37.8 t/ha, RT 33.5 t/ha and CT 30.4 t/ha in the surface depth. Fertilizer application rate did not seem to affect soil aggregate stability & SOC. The results found a strong effect of residue retention in NT and RT in the soil surface with aggregate stability which, was correlated with the high rate of infiltration rate in these treatments. The results of this study indicate that reduced soil disturbance improves physical protection of SOC, soil structure and infiltration, however, it also indicated that TSOC takes time to improve in maize continuous monocrop system in the studied soil.

25404. 题目: Effects of pH on redox proxies in a Jurassic rift lake: Implications for interpreting environmental records in deep time
文章编号: N19031801
期刊: Geochimica et Cosmochimica Acta
作者: Eva E. Stüeken, Aaron Martinez, Gordon Love, Paul E. Olsen, Steve Bates, Timothy W. Lyons
更新时间: 2019-03-18
摘要: It is widely agreed that the Earth’s atmosphere and oceans have undergone major redox changes over the last 2.5 billion years. However, the magnitude of these shifts remains a point of debate because it is difficult to reconstruct concentrations of dissolved O₂ from indirect proxies in sedimentary archives. In this study, we show that an additional complicating factor that is rarely considered may be the pH of the water column. We analyzed rock samples from the early Jurassic Towaco Formation in the Newark basin (eastern USA), comprising deposits of a rift lake that became temporarily redox stratified. New biomarker evidence points to increasingly saline aquatic conditions during the second half of the lake’s history, with a salinity stratification that induced redox stratification, including evidence for water column anoxia, and that state may also explain the disappearance of macrofauna at this time. Distinctive lipid biomarker assemblages and stable nitrogen isotope data support previous mineralogical indications that the lake was alkaline (pH ≥ 9) during its saline episode. Despite the biomarker and macrofaunal evidence for anoxia, ratios of Fe/Al and Fe_HR/Fe_T show only small to no enrichments in the anoxic horizon compared to oxic facies in the same section – counter to what is commonly observed in anoxic marine settings. Molybdenum, As, V, U and to some degree Cd show enrichments in the anoxic interval, whereas Co, Ni, Cu, Zn and Cr do not. These patterns are most parsimoniously explained by differential pH effects on the solubility of these elements. Extrapolating from these observations in lacustrine strata, we speculate that a secular increase in seawater pH over Earth’s history as recently proposed may have helped modulate the magnitude of trace metal enrichments in marine shales, although other factors such as atmospheric and oceanic redox likely dominated the observed enrichment patterns. Further, a decrease in the solubility of ferrous iron, a major O₂ sink, with increasing pH may have contributed to ocean oxygenation. In summary, our results highlight the potential importance of pH in influencing global biogeochemical cycles for multiple elements and for the interpretation of ancient nitrogen isotope signatures.

25405. 题目: Distribution of carbon and nitrogen along hillslopes in three valleys on Herschel Island, Yukon Territory, Canada
文章编号: N19031708
期刊: CATENA
作者: Justine L. Ramage, Daniel Fortier, Gustaf Hugelius, Hugues Lantuit, Anne Morgenstern
更新时间: 2019-03-17
摘要: Thermokarst results from the thawing of ice-rich permafrost and alters the biogeochemical cycling in the Arctic by reworking soil material and redistributing soil organic carbon (SOC) and total nitrogen (TN) along uplands, hillslopes, and lowlands. Understanding the impact of this redistribution is key to better estimating the storage of SOC in permafrost terrains. However, there are insufficient studies quantifying long-term impacts of thaw processes on the distribution of SOC and TN along hillslopes. We address this issue by providing estimates of SOC and TN stocks along the hillslopes of three valleys located on Herschel Island (Yukon, Canada), and by discussing the impact of hillslope thermokarst on the variability of SOC and TN stocks. We found that the average SOC and TN 0–100 cm stocks in the valleys were 26.4 ± 8.9 kg C m-² and 2.1 ± 0.6 kg N m-². We highlight the strong variability in the soils physical and geochemical properties within hillslope positions. High SOC stocks were found at the summits, essentially due to burial of organic matter by cryoturbation, and at the toeslopes due to impeded drainage which favored peat formation and SOC accumulation. The average carbon-to‑nitrogen ratio in the valleys was 12.9, ranging from 9.7 to 18.9, and was significantly higher at the summits compared to the backslopes and footslopes (p < 0.05), suggesting a degradation of SOC downhill. Carbon and nitrogen contents and stocks were significantly lower on 16% of the sites that were previously affected by hillslope thermokarst (p < 0.05). Our results showed that lateral redistribution of SOC and TN due to hillslope thermokarst has a strong impact on the SOC storage in ice-rich permafrost terrains.

25406. 题目: Organic carbon mineralization in soils of a natural forest and a forest plantation of southeastern China
文章编号: N19031707
期刊: Geoderma
作者: Jinxue Huang, Teng-Chiu Lin, Decheng Xiong, Zhijie Yang, Xiaofei Liu, Guangshui Chen, Jinsheng Xie, Yiqing Li, Yusheng Yang
更新时间: 2019-03-17
摘要: Understanding soil organic carbon (SOC) mineralization under different temperature regimes is critical for predicting SOC responses to climate change. Yet, the effects of altering temperature regimes on SOC mineralization remain poorly understood in forest plantations converted from natural forests. Forest conversion is extensive and could have major impact on SOC dynamics, so that this knowledge limits our ability of predicting the consequences of such land use change on carbon cycling. To fill this knowledge gap, we conducted a 360-day incubation experiment under constant and varying temperature regimes for soils of a natural forest and a Chinese fir (Cunninghamia lanceolata) plantation. Results showed that SOC mineralization was greater in the forest plantation soil than in the natural forest soil in both temperature treatments, possibly due to greater labile SOC in the forest plantation soil by 27–28%. The results suggested that replacing natural forests with forest plantations may increase CO₂ emission via the mineralization of SOC. In the natural forest soil, SOC mineralization was greater in the varying temperature treatment relative to the constant temperature treatment but no difference was found in the forest plantation soil. Moreover, temperature sensitivity (Q₁₀) of SOC mineralization was greater in the natural forest soil than the Chinese fir soil for the 0–180 day of the incubation. The difference in the response to the two temperature treatments between the two forest soils which was accompanied by difference in soil microbial communities. It was likely that soil microbes of the closed-canopy natural forest were less adapted to temperature fluctuations than soil microbes of the forest plantation soil as the canopy was rarely closed. Our results highlight that soil incubation experiments need to take temperature fluctuations into consideration to more accurately reflect SOC dynamics in the field, especially when evaluating the impacts of replacing natural forests with forest plantations on soil carbon dynamics.

25407. 题目: Application of denitrifying bioreactors for the removal of atrazine in agricultural drainage water
文章编号: N19031706
期刊: Journal of Environmental Management
作者: Bahareh Hassanpour, Larry D. Geohring, Annaleise R. Klein, Shree Giri, Ludmilla Aristilde, Tammo S. Steenhuis
更新时间: 2019-03-17
摘要: Atrazine and nitrate NO3N are two agricultural pollutants that occur widely in surface and groundwater. One of the pathways by which these pollutants reach surface water is through subsurface drainage tile lines. Edge-of-field anaerobic denitrifying bioreactors apply organic substrates such as woodchips to stimulate the removal of NO3N from the subsurface tile waters through denitrification. Here we investigated the co-removal of NO3N and atrazine by these bioreactors. Laboratory experiments were conducted using 12-L woodchips-containing flow-through bioreactors, with and without the addition of biochar, to treat two concentrations of atrazine (20 and 50 μg L⁻¹) and NO3N (1.5 and 11.5 mg L⁻¹), operated at four hydraulic retention time, HRT, (4 h, 8 h, 24 h, 72 h). Additionally, we examined the effect of aerating the bioreactors on atrazine removal. Furthermore, we tested atrazine removal by a field woodchip denitrifying bioreactor. The removal of both NO3N and atrazine increased with increasing HRT in the laboratory bioreactors. At 4 h, the woodchip bioreactors removed 65% of NO3N and 25% of atrazine but, at 72 h, the bioreactors eliminated all the NO3N and 53% of atrazine. Biochar-amended bioreactors removed up to 90% of atrazine at 72-h retention time. We concluded that atrazine removal was primarily via adsorption because neither aeration nor NO3N levels had an effect. At 4-h retention time, the field bioreactors achieved 2.5 times greater atrazine removal than the laboratory bioreactors. Our findings thus highlighted hydraulic retention time and biochar amendments as two important factors that may control the efficiency of atrazine removal by denitrifying bioreactors. In sum, laboratory and field data demonstrated that denitrifying bioreactors have the potential to decrease pesticide transport from agricultural lands to surface waters.
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25408. 题目: Macroaggregates as biochemically functional hotspots in soil matrix: Evidence from a rice paddy under long-term fertilization treatments in the Taihu Lake Plain, eastern China
文章编号: N19031705
期刊: Applied Soil Ecology
作者: Zichuan Li, Zhipeng Rui, Dengxiao Zhang, Xiao Feng, Haifei Lu, Shengyuan Shen, Jufeng Zheng, Lianqing Li, Zhaoliang Song, Genxing Pan
更新时间: 2019-03-17
摘要: Abundance and allocation of organic matter, microbial community and their extracellular enzyme activities in soil aggregates had been increasingly concerned for mediating biogeochemical cycle and biodiversity provided by soil. In this study, the variations of soil organic carbon (SOC) accumulation and extracellular enzyme activities in aggregate size fractions of a rice paddy with long-term fertilization treatments were analyzed. These treatments included no fertilizer application (NF) as a control, chemical fertilizer only (CF), chemical fertilizer combined with swine manure (CFM), and with straw residue return (CFS). Hereby, size fractions of soil aggregates respectively of >2000 μm (large macroaggregates), 250–2000 μm (macroaggregates), 53–250 μm (microaggregates), 2–53 μm (fine aggregates), and <2 μm (fine clay) were obtained from undisturbed soil cores following water-dispersion and subsequent wet-sieving using a low energy separation protocol. Of these aggregate fractions, SOC and total nitrogen (N) contents were determined with wet digestion and soil enzyme activities were analyzed with substrate-induction incubation assays. Contents of SOC and total N were both highest in macroaggregates, followed by large macroaggregates and microaggregates, but depleted in fine microaggregates. Activities of carbon-degrading enzymes and N-acetyl-glucosaminidase were markedly enriched in soil aggregate fractions in size >53 μm. Whereas, activity of phenol oxidase was generally concentrated in soil aggregate fractions in size between 2 and 2000 μm while that of peroxidase in size between 53 and 2000 μm. Activity of β-glucosidase and cellobiohydrolase was both significantly elevated under CFS and that of peroxidase under CF, CFM and CFS treatments, but phenol oxidase activity was suppressed under CFS treatment. The enzyme activities of β-xylosidase, β-glucosidase, cellobiohydrolase and N-acetyl-glucosaminidase varied greatly (CVs up to 50%), rather with size fractions than with treatments, while those of α-Glucosidase and phenol oxidase varied moderately (CVs up to 35%), rather with treatments than with size fractions. However, those of acid phosphatase and peroxidase changed slightly (CVs up to 20%), regardless of both size fractions and fertilization treatments. Thus, abundance and enrichment of all the soil enzyme activities analyzed depended not on SOC although the overall extracellular enzyme activity was generally well correlated to SOC abundance, among aggregate size fractions. Only activities of carbon-degrading enzymes were greatly enriched in macroaggregates, which were seen reduced under combined organo/mineral fertilization. This study highlighted macroaggregates as biochemically active micro- hotspots and lower activities of carbon-degrading enzymes with SOC accumulation under long-term rational fertilization in the rice paddy.
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25409. 题目: Storage, patterns and controls of soil organic carbon in the alpine shrubland in the Three Rivers Source Region on the Qinghai-Tibetan Plateau
文章编号: N19031704
期刊: CATENA
作者: Xiuqing Nie, Lucun Yang, Fan Li, Feng Xiong, Changbin Li, Guoying Zhou
更新时间: 2019-03-17
摘要: Alpine shrubland ecosystems in the Three Rivers Source Region (TRSR) store substantial soil organic carbon (SOC), but the storage, patterns and control of SOC in those ecosystems have rarely been investigated. In this study, using data from 66 soil profiles surveyed from 22 sites between 2011 and 2013, we estimated the storage and patterns of SOC, and their relationships with climatic factors, elevation, ground cover and slope. Our results showed that SOC storage in the top 100 cm across the TRSR shrubland was 0.68 ± 0.38 Pg C, with an average SOC density (soil carbon storage per area) of 26.21 ± 14.58 kg m⁻². Spatially, SOC density increased with longitude and latitude. Vertically, SOC in the topsoil at 30 cm and 50 cm accounted for 56% and 75%, respectively, of the total at 100 cm. SOC density showed a decreasing trend with increasing elevation, but it was greater in regions of higher ground cover. The density had no relationship with either mean annual precipitation or slope. Increasing mean annual temperature had positive effects on SOC density, which is inconsistent with the global trend. With increasing soil depth, however, the effects of temperature on SOC density were not significant. Therefore, in a global warming scenario, increasing temperature gives shrubland considerable C sink potential on the topsoil, and the regions of C sequestration differ as a result of uneven increases in temperature. Hence, further monitoring of dynamic changes is necessary to provide a more accurate assessment of potential C sequestration in TRSR shrubland.

25410. 题目: Long-term organic matter application reduces cadmium but not zinc concentrations in wheat
文章编号: N19031703
期刊: Science of The Total Environment
作者: Roman Grüter, Benjamin Costerousse, Jochen Mayer, Paul Mäder, Cécile Thonar, Emmanuel Frossard, Rainer Schulin, Susan Tandy
更新时间: 2019-03-17
摘要: Wheat is a staple food crop and a major source of both the essential micronutrient zinc (Zn) and the toxic heavy metal cadmium (Cd) for humans. Since Zn and Cd are chemically similar, increasing Zn concentrations in wheat grains (biofortification), while preventing Cd accumulation, is an agronomic challenge. We used two Swiss agricultural long-term field trials, the “Dynamic-Organic-Conventional System Comparison Trial” (DOK) and the “Zurich Organic Fertilization Experiment” (ZOFE), to investigate the impact of long-term organic, mineral and combined fertilizer inputs on total and phytoavailable concentrations of soil Zn and Cd and their accumulation in winter wheat (Triticum aestivum L.). “Diffusive gradients in thin films” (DGT) and diethylene-triamine-pentaacetic acid (DTPA) extraction were used as proxies for plant available soil metals. Compared to unfertilized controls, long-term organic fertilization with composted manure or green waste compost led to higher soil organic carbon, cation exchange capacity and pH, while DGT-available Zn and Cd concentrations were reduced. The DGT method was a strong predictor of shoot and grain Cd, but not Zn concentrations. Shoot and grain Zn concentrations correlated with DTPA-extractable and total soil Zn concentrations in the ZOFE, but not the DOK trial. Long-term compost fertilization led to lower accumulation of Cd in wheat grains, but did not affect grain Zn. Therefore, Zn/Cd ratios in the grains increased. High Zn and Cd inputs with organic fertilizers and high Cd inputs with phosphate fertilizers led to positive Zn and Cd mass balances when taking into account atmospheric deposition and fertilizer inputs. On the other hand, mineral fertilization led to the depletion of soil Zn due to higher yields and thus higher Zn exports than under organic management. The study supports the use of organic fertilizers for reducing Cd concentrations of wheat grains in the long-term, given that the quality of the fertilizers is guaranteed.
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25411. 题目: Local habitat heterogeneity determines the differences in benthic diatom metacommunities between different urban river types
文章编号: N19031702
期刊: Science of The Total Environment
作者: Shan Chen, Wei Zhang, Jiahui Zhang, Erik Jeppesen, Zhaoying Liu, J. Patrick Kociolek, Xiaoying Xu, Liqing Wang
更新时间: 2019-03-17
摘要: Benthic diatoms are useful indicators of the ecological state of river systems. To understand the factors determining benthic diatom metacommunity composition in urban rivers, we studied in situ surface sediment diatom communities from 23 rivers in Shanghai City. Based on our study results on the metacommunity structure of benthic diatoms and hierarchical cluster analysis (HCA), we found substantial differences between restored (G1) and unrestored rivers (G2–G4) in taxa richness, relative abundances, and dominant and indicator taxa of benthic diatoms. The epiphytic diatoms Cocconeis placentula and Amphora libyca var. baltica were representative of the restored rivers (G1), where aquatic macrophytes were more abundant and the water was clearer. The motile epipelic diatoms Navicula recens and Navicula germainii dominated the moderately polluted rivers (G2). The eutrophic taxa Cyclotella meneghiniana, Aulacoseira granulata, and Cyclostephanos tholiformis dominated in G3, which comprised relatively heavily polluted rivers with low organic matter sediment and high disturbance. The polysaprobic taxon Nitzschia palea and the halophilous taxon Fallacia pygmaea represented relatively heavily polluted rivers with a comparatively higher sedimentary salinity (SSal) (G4). Redundancy analysis (RDA) revealed that total phosphorus (TP), dissolved organic carbon (DOC), silicon dioxide (SiO₂), dissolved oxygen (DO), Secchi depth (SD), SSal, and the ratio of carbon to nitrogen (C/N) in the sediment were important environmental factors explaining variation among benthic diatom metacommunity composition. Partial RDA (pRDA) implied that the relative importance of environmental factors in structuring benthic diatom metacommunity was much higher than spatial factors. Classification and regression trees (CART) further indicated that DOC, the sediment C/N ratio, and SSal were the key local environmental factors affecting grouping patterns of benthic diatom metacommunities. Our study proposes that benthic diatom metacommunities respond to the complex characteristics of local environment in urban rivers and provides useful knowledge for consideration in the ecological monitoring of urban river systems.
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25412. 题目: Effects of tillage, crop establishment and diversification on soil organic carbon, aggregation, aggregate associated carbon and productivity in cereal systems of semi-arid Northwest India
文章编号: N19031701
期刊: Soil and Tillage Research
作者: H.S. Jat, Ashim Datta, M. Choudhary, A.K. Yadav, V. Choudhary, P.C. Sharma, M.K. Gathala, M.L. Jat, A. McDonald
更新时间: 2019-03-17
摘要: Intensive tillage based management practices are threatening soil quality and systems sustainability in the rice-wheat belt of Northwest India. Furthermore, it is accentuated with puddling of soil, which disrupts soil aggregates. Conservation agriculture (CA) practices involving zero tillage, crop residue management and suitable crop rotation can serve as better alternative to conventional agriculture for maintaining soil quality. Soil organic carbon is an important determinant of soil quality, playing critical role in food production, mitigation and adaptation to climate change as well as performs many ecosystem functions. To understand the turnover of soil carbon in different forms (Total organic carbon-TOC; aggregate associated carbon-AAC; particulate organic carbon- POC), soil aggregation and crop productivity with different management practices, one conventional agriculture based scenario and three CA based crop management scenarios namely conventional rice-wheat system (Sc1), partial CA based rice-wheat-mungbean system (Sc2), full CA-based rice-wheat-mungbean system (Sc3) and maize-wheat-mungbean system (Sc4) were evaluated. TOC was increased by 71%, 68% and 25% after 4 years of the experiment and 75%, 80% and 38% after 6 years of the experiment in Sc4, Sc3 and Sc2, respectively, over Sc1 at 0–15 cm soil depth. After 4 years of the experiment, 38.5% and 5.0% and after 6 years 50.8% and 24.4% improvement in total water stable aggregates at 0–15 and 15–30 cm soil depth, respectively was observed in CA-based scenarios over Sc1. Higher aggregate indices were associated with Sc3 at 0–15 cm soil depth than others. Among the size classes of aggregates, highest aggregate associated C (8.94 g kg⁻¹) was retained in the 1-0.5 mm size class under CA-based scenarios. After 6 years, higher POC was associated with Sc4 (116%). CA-based rice/maize system (Sc3 and Sc4) showed higher productivity than Sc1. Therefore, CA could be a potential management practice in rice-wheat cropping system of Northwest India to improve the soil carbon pools through maintaining soil aggregation and productivity.

25413. 题目: The Speciation and Mobility of Mn and Fe in Estuarine Sediments
文章编号: N19031608
期刊: Aquatic Geochemistry
作者: Véronique E. Oldham, Matthew G. Siebecker, Matthew R. Jones, Alfonso Mucci, Bradley M. Tebo, George W. Luther
更新时间: 2019-03-16
摘要: Dissolved and solid-phase speciation of Mn and Fe was measured in the porewaters of sediments recovered from three sites in the Greater St. Lawrence Estuary: the Saguenay Fjord, the Lower St. Lawrence Estuary (LSLE) and the Gulf of St. Lawrence (GSL). At all sites and most depths, metal organic ligand complexes (Mn(III)–L and Fe(III)–L) dominated the sedimentary porewater speciation, making up to 100% of the total dissolved Mn or Fe. We propose that these complexes play a previously underestimated role in maintaining oxidized soluble metal species in sedimentary systems and in stabilizing organic matter in the form of soluble metal–organic complexes. In the fjord porewaters, strong (log KCOND > 13.2) and weak (log KCOND −2 year−1 at the pelagic site (GSL), 11 µmol cm−2 year−1 at the hemipelagic site (LSLE) and 2.0 µmol cm−2 year−1 in the fjord. The higher benthic flux in the LSLE reflects the lower oxygen concentrations (dO2) of the bottom waters and sediments at this site, which favor the reductive dissolution of Mn oxides as well as the decrease in the oxidation rate of dissolved Mn(II) diffusing through the oxic layer of the sediment and its release to the overlying water.

25414. 题目: On-line vis-NIR spectroscopy prediction of soil organic carbon using machine learning
文章编号: N19031607
期刊: Soil and Tillage Research
作者: S. Nawar, A.M. Mouazen
更新时间: 2019-03-16
摘要: Accurate on-line visible and near infrared (vis-NIR) spectroscopy prediction of soil organic carbon (OC) is essential for food security and environmental management. This paper aims at using on-line vis-NIR spectra coupled with random forest (RF) modelling approach for the prediction of soil organic carbon (OC), comparing between single field (SF), non-spiked UK multiple-field (NSUK) and spiked UK multiple-field (SUK) calibration models. Fresh soil samples collected from 6 fields in the UK (including two target fields) were scanned with a fibre-type vis-NIR spectrophotometer (tec5 Technology for Spectroscopy, Germany), with a spectral range of 305–2200 nm. After dividing spectra into calibration and independent validation sets, RF was run on the calibration set to develop calibration models for OC for the three studied datasets. Results showed that the model prediction performance depends on the dataset used and varies between fields. Less accurate prediction performance was obtained for the on-line prediction compared to laboratory (samples scanned in the laboratory under non-mobile measurement) prediction, and for non-spiked models compared to spiked models. The best model performance in both laboratory and on-line predictions was obtained when samples from the SF were spiked into the UK samples, with coefficients of determination (R²) values of 0.80 to 0.84 and 0.74 to 0.75, root mean square error of prediction (RMSEP) values of 0.14% and 0.17 to 0.18%, and ratio of prediction deviation (RPD) values of 2.30 to 2.5 and 1.98 to 2.04, respectively. Therefore, these results suggest that RF modelling approach when coupled with spiking provides high prediction performance of OC under both non-mobile laboratory and on-line field scanning conditions.

25415. 题目: Spectroscopic study of the effects of dissolved organic matter compositional changes on availability of cadmium in paddy soil under different water management practices
文章编号: N19031606
期刊: Chemosphere
作者: Zhongwu Li, Mei Huang, Ninglin Luo, Jiajun Wen, Chuxiong Deng, Ren Yang
更新时间: 2019-03-16
摘要: It is well established that water management can influence the availability of Cd in paddy soil but the role of dissolved organic matter (DOM) characteristics in this process is still unclear. Here, we measured and compared the DOM quantity and quality between flooded and wetted treatments by spectroscopic and chemometric analysis and applied correlation analysis to relate DOM characteristics with availability concentrations of Cd. Ultraviolet–visible showed that aromaticity and hydrophobicity of DOM significantly decreased with time in wetted paddy soil (p < 0.05) but had no significant difference in flooded paddy soil (p > 0.05). According the results from two-dimensional correlation spectroscopy analytical method, humic- and protein-like substances had fast response during cultivation process. Two humic-like substances (C1, C2) and two protein-like substances (C3, C4) were identified from paddy soil-derived DOM by combining emission and excitation matrix spectroscopy with parallel factor. Compared to component C1, C3, and C4, component C2 has stronger aromaticity and hydrophobicity and higher molecular size (665–1000 Da). Its proportion declined markedly during the wetting periods but increased slightly during flooding. Pearson correlation analysis illustrated that flooding was more helpful in immobilizing Cd than wetting due to the aromatic, hydrophobic, and high molecular weight constituents remained in flooded treatments and the substantial decomposition of component C2 in wetted treatments. These results suggested that spectroscopic and chemometric methods are helping to further explain the impacts of DOM quality on Cd availability under different water management practices.
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25416. 题目: Integrating terrestrial and aquatic processes toward watershed scale modeling of dissolved organic carbon fluxes
文章编号: N19031605
期刊: Environmental Pollution
作者: Xinzhong Du, Xuesong Zhang, Rajith Mukundan, Linh Hoang, Emmet M. Owens
更新时间: 2019-03-16
摘要: Dissolved organic carbon (DOC) is not only a critical component of global and regional carbon budgets, but also an important precursor for carcinogenic disinfection byproducts (DBP) generated during drinking water disinfection process. The lack of process based watershed scale model for carbon cycling has been a limiting factor impeding effective watershed management to control DOC fluxes to source waters. Here, we integrated terrestrial and aquatic carbon processes into the widely tested Soil and Water Assessment Tool (SWAT) watershed model to enable watershed-scale DOC modeling (referred to as SWAT-DOC hereafter). The modifications to SWAT mainly fall into two groups: (1) DOC production in soils and its transport to aquatic environment by different hydrologic processes, and (2) riverine transformation of DOC and their interactions with particular organic carbon (POC), inorganic carbon and algae (floating and bottom). We tested the new SWAT-DOC model in the Cannonsville watershed, which is part of the New York City (NYC) water supply system, using long-term DOC load data (from 1998 to 2012) derived from 1399 DOC samplings. The calibration and verification results indicate that SWAT-DOC achieved satisfactory performance for both streamflow and DOC at daily and monthly temporal scales. The parameter sensitivity analysis indicates that DOC loads in the Cannonsville watershed are controlled by the DOC production in soils and its transport in both terrestrial and aquatic environments. Further model uncertainty analysis indicates high uncertainties associated with peak DOC loads, which are attributed to underestimation of high streamflows. Therefore, future efforts to enhance SWAT-DOC to better represent runoff generation processes hold promise to further improve DOC load simulation. Overall, the wide use of SWAT and the satisfactory performance of SWAT-DOC make it a useful tool for DOC modeling and mitigation at the watershed scale.

25417. 题目: Comparative contributions of copper nanoparticles and ions to copper bioaccumulation and toxicity in barnacle larvae
文章编号: N19031604
期刊: Environmental Pollution
作者: Li Yang, Wen-Xiong Wang
更新时间: 2019-03-16
摘要: Cu nanoparticles (CuNPs) have been widely used in numerous products, and may become a potential threat to marine organisms, but their behavior in the marine environments and potential toxicity to marine organisms remain little known. In the present study, we investigated the behavior of CuNPs in seawater, as well as the toxicity and bioaccumulation of CuNPs and copper sulfate (CuSO₄) in barnacle larvae (Balanus amphitrite), a dominant fouling invertebrate in marine environment. CuNPs tended to aggregate in natural seawater and released Cu ion rapidly into seawater. The aggregation and release were especially higher at a lower concentration of CuNPs, e.g., 94–96% of CuNPs were released as Cu ions at 20 μg/L after 24 h. The larger size of CuNPs (40 nm) tended to display a higher solubility than the 20 nm CuNPs did. Humic acids enhanced the aggregation and inhibited the dissolution of CuNPs, and had a protective effect on the survival of nauplii II at higher Cu concentrations (100–200 μg/L). Comparison of the lethal concentrations showed that CuNPs were generally less toxic to the two stages of barnacle larvae (nauplii II and VI) than the Cu ions. The calculated 48-h LC₅₀ values for nauplii II were 189.5 μg/L, 123.2 μg/L, and 89.8 μg/L for 20 nm CuNPs, 40 nm CuNPs, and CuSO₄, respectively. However, the lethal concentrations of Cu bioaccumulation in the barnacle larvae were comparable between CuNPs and Cu ions when expressed by the actual tissue Cu bioaccumulation. Barnacle larval settlement decreased with an increase of Cu concentrations of both CuNPs and CuSO₄, and was significantly inhibited at 100 μg/L CuSO₄ and 150 μg/L CuNPs. Our results indicated that the toxicity of CuNPs could not be solely explained by the released Cu ions, and both CuNPs and the released Cu ion contributed to their toxicity and bioaccumulation in barnacle larvae.
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25418. 题目: Interactive effects of biotic and abiotic environmental stressors on carbamazepine toxicity in the non-biting midge Chironomus riparius
文章编号: N19031603
期刊: Water Research
作者: Katharina Heye, Thorsten Lotz, Arne Wick, Jörg Oehlmann
更新时间: 2019-03-16
摘要: The toxicity of contaminants in freshwater ecosystems can increase in combination with environmental stress, leading to a potential underestimation of risk in conventional assessments. The number of multiple-stress experiments in ecotoxicology is growing constantly, but pharmaceuticals have mostly been disregarded. As an omnipresent pharmaceutical in the water cycle, the antiepileptic drug carbamazepine (CBZ) was chosen as test substance for our 28-day binary stress experiments with the non-biting midge Chironomus riparius. Elevated population densities, food limitation, temperature, and a reduction of organic matter (OM) were chosen as relevant environmental stressors. In five stress intensities, they were combined with the 10% lethal concentration (LC₁₀) of CBZ to investigate the joint effect of stress and CBZ exposure. We were able to demonstrate that the toxicity of CBZ increased with higher larval densities and reduced OM. Mortality of the midges exposed to CBZ increased by a factor of 1.69 with 100 larvae per vessel and by a factor of 2.87 at 0.25% OM compared to the conventional test protocol, while the stressors alone did not reduce survival. Conventional low-stress laboratory tests as conducted for the risk assessment of chemicals would have underestimated the toxicity of CBZ. Even though it is necessary that more than just binary stressor combinations are included in future experiments, the present results extend our knowledge about the toxicity of pharmaceuticals, such as CBZ, in stressful environments and emphasize the importance of including pharmaceuticals in multiple stress experiments.
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25419. 题目: Dynamics and sources of colloids in shallow groundwater in lowland wells and fracture flow in sloping farmland
文章编号: N19031602
期刊: Water Research
作者: Wei Zhang, Jian-Hua Cheng, Qing-Song Xian, Jun-Fang Cui, Xiang-Yu Tang, Gen-Xu Wang
更新时间: 2019-03-16
摘要: Field-scale studies of natural colloid mobilization and transport in finely fractured aquifer as well as the source identification of groundwater colloids are of great importance to the safety of shallow groundwater. In this study, the daily monitoring of fracture flow from a sloping farmland plot and the biweekly monitoring of three lowland shallow wells within the same catchment were carried out simultaneously in 2013. The effects of physicochemical perturbations on groundwater colloid dynamics were explored in detail using partial redundancy analysis, structural equation modeling, Pearson correlation and multi-linear regression analyses. The characterization and source identification of groundwater colloids were addressed via multiple parameters. The daily colloid concentration in the fracture flow varied between 0.54 and 31.90 mg/L (1.64 mg/L on average). Unique periods of high colloid concentration (5.59 mg/L on average) occurred during the initially generated flow following the dry season. In comparison, a narrower colloid concentration range of 0.24–11.66 mg/L was observed in the lowland shallow wells, with a smaller temporal variation than that of the fracture flow. A low percentage (2.4–7.0%) of colloids and a high percentage (47.7–92.0%) of coarse particles (2–10 μm) were present in the lowland well water. Hydraulic perturbation by rainwater infiltration in the sloping farmland was the dominant mechanism for colloid mobilization in general; this effect retreated to secondary importance behind chemical perturbations (pH, Mg²⁺ and DOC) at low flow discharges (<1.3 L/min). In contrast, water chemistry (e.g., EC, cations and DOC concentrations) exhibited a major effect on colloid dynamics in the water of the lowland wells, except for the extremely high-salinity water of one well, in which water temperature showed a negative dominant influence on colloid stability. The combined use of multiple parameters (e.g., mineral composition and organic matter, calcium carbonate and δ¹³C contents) traced groundwater colloids to the shallow soil in the upper farmlands. It is strongly advised that in finely fractured aquifers within agricultural catchments, not only the small colloids but also the coarse particles in the size range of 2–10 μm should be monitored in case of colloid-associated contamination from agricultural wastes e.g., N, P, pesticides and/or heavy metals, especially at the early stages of the rainy seasons.
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25420. 题目: Mercury speciation, transformation, and transportation in soils, atmospheric flux, and implications for risk management: A critical review
文章编号: N19031601
期刊: Environment International
作者: David O'Connor, Deyi Hou, Yong Sik Ok, Jan Mulder, Lei Duan, Qingru Wu, Shuxiao Wang, Filip M.G. Tack, Jörg Rinklebe
更新时间: 2019-03-16
摘要: Mercury (Hg) is a potentially harmful trace element in the environment and one of the World Health Organization's foremost chemicals of concern. The threat posed by Hg contaminated soils to humans is pervasive, with an estimated 86 Gg of anthropogenic Hg pollution accumulated in surface soils worldwide. This review critically examines both recent advances and remaining knowledge gaps with respect to cycling of mercury in the soil environment, to aid the assessment and management of risks caused by Hg contamination. Included in this review are factors affecting Hg release from soil to the atmosphere, including how rainfall events drive gaseous elemental mercury (GEM) flux from soils of low Hg content, and how ambient conditions such as atmospheric O₃ concentration play a significant role. Mercury contaminated soils constitute complex systems where many interdependent factors, including the amount and composition of soil organic matter and clays, oxidized minerals (e.g. Fe oxides), reduced elements (e.g. S²⁻), as well as soil pH and redox conditions affect Hg forms and transformation. Speciation influences the extent and rate of Hg subsurface transportation, which has often been assumed insignificant. Nano-sized Hg particles as well as soluble Hg complexes play important roles in soil Hg mobility, availability, and methylation. Finally, implications for human health and suggested research directions are put forward, where there is significant potential to improve remedial actions by accounting for Hg speciation and transportation factors.