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25941. 题目: Degradation of haloacetonitriles with UV/peroxymonosulfate process: Degradation pathway and the role of hydroxyl radicals
文章编号: N19013004
期刊: Chemical Engineering Journal
作者: Xing Zhang, Jilun Yao, Zhiwei Zhao, Jie Liu
更新时间: 2019-01-30
摘要: Haloacetonitriles (HANs), a specie of new emerging halogenated nitrogenous disinfection by-products (N-DBPs) including trichloroacetonitrile (TCAN), dichloroacetonitrile (DCAN), monochloroacetonitrile (MCAN) and dibromoacetonitrile (DBAN), were more cytotoxic and genotoxic than the conventional DBPs. In this study, kinetics and mechanisms in the oxidization of HANs by UV/peroxymonosulfate (PMS) process were investigated. The degradation of chloroacetonitriles (CANs) in UV/PMS process was more remarkable than UV alone, PMS alone and UV/H₂O₂ process. And the order of the rates of degradation of HANs was followed: TCAN > DCAN > MCAN, while DBAN was remarkably degraded by UV alone. The degradation of DCAN was accelerated by humic acid and Cl⁻, while suppressed by bicarbonate. Scavenging experiments showed that hydroxyl radical (^radOH) was the predominant species in the reaction. According to the gas chromatography/mass spectrometer (GC/MS) analysis, the breakage of CCl bond was the dominant pathways in degradation of CANs.
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25942. 题目: CO₂-mediated Chicken Manure Biochar Manipulation for Biodiesel Production
文章编号: N19013003
期刊: Environmental Research
作者: Jong-Min Jung, Jeong-Ik Oh, Young-Kwon Park, Jechan Lee, Eilhann E. Kwon
更新时间: 2019-01-30
摘要: This study employs chicken manure as a feedstock to produce different forms of energy to abate environmental burdens. To achieve ultimate carbon management, the possible utilization of CO₂ during pyrolysis of chicken manure was fundamentally investigated. The roles of CO₂ in pyrolysis of chicken manure include enhanced thermal cracking and shifting of the carbon distribution via reaction between volatile organic compounds and CO₂. The identified roles induced by CO₂ were catalytically enhanced because of the inorganic content in the feedstock. The morphology of biochar created from the chicken manure pyrolysis was significantly affected by CO₂. For example, a well-developed pore structure was observed in the biochar developed under a CO₂ environment; this biochar was used as an effective porous material for biodiesel synthesis.

25943. 题目: Effect of water depth on the TEX₈₆ proxy in volcanic lakes of northeastern China
文章编号: N19013002
期刊: Organic Geochemistry
作者: Yuan Yao, Jiaju Zhao, Thorsten Bauersachs, Yongsong Huang
更新时间: 2019-01-30
摘要: The TEX₈₆ index, based on the distribution of isoprenoid glycerol dialkyl glycerol tetraethers (iGDGTs), has been widely applied for reconstructing past sea surface temperature (SST). However, its successful application in lacustrine environments has been limited to certain large lakes in which aquatic Thaumarchaeota are thought be the dominant iGDGT producers. In small lakes, multiple factors, such as iGDGTs from soil and non-thaumarchaeotal sources, could complicate the use of TEX₈₆ as a temperature proxy (Powers et al., 2010). Here we investigate iGDGTs from surface sediments and suspended particulate matter (SPM) in a series of small volcanic lakes (areas: ∼ 0.1 to 8.2 km²) from three main volcanic fields of northeastern China. The iGDGT distribution patterns from surface sediments of these lakes differ significantly from those of surrounding soils, global marine sediments, as well as cultured Group I.1a and Group I.1b Thaumarchaeota, suggesting a substantial contribution of autochthonous non-thaumarchaeotal sources. Interestingly, however, the correlation between TEX₈₆ values in the SPM samples and in situ water temperatures remain strong and display temperature sensitivity similar to previously published linear calibrations from global marine and lake sediments. Our results suggest that the in situ TEX₈₆-temperature relationship is little affected by the non-thaumarchaeotal iGDGT sources in these lakes. However, the TEX₈₆-inferred temperatures from surface sediments show increasingly colder offsets relative to air temperatures with increasing lake depth, which can be explained by the observed increase in iGDGTs production and decrease in water temperatures in water column as depth increases. Our results thus suggest that TEX₈₆ values in the sediments of these volcanic lakes are affected by both temperature and lake depth, and when temperature can be constrained independently or remains constant over a given period of time, have potential application as a lake level proxy in deep volcanic lakes.

25944. 题目: A new strategy for assessing the binding microenvironments in intact soil microaggregates
文章编号: N19013001
期刊: Soil and Tillage Research
作者: Jian Xiao, Yong-Li Wen, Sen Dou, Benjamin C. Bostick, Xin-Hua He, Wei Ran, Guang-Hui Yu, Qi-Rong Shen
更新时间: 2019-01-30
摘要: Adsorption to soil minerals and occlusion within soil aggregates are two critical mechanisms to shield soil organic carbon (SOC) from microbial decomposition. Here, we combined the synchrotron radiation based Fourier transform infrared (SR-FTIR) spectroscopy, synchrotron radiation based micro X-ray fluorescence microscopy (μ-XRF) and two-dimensional correlation spectroscopy (2DCOS) analysis to in situ visualize the interiors of intact microaggregates from a typical Ferralic Cambisol in China, which had endured 25-year organic fertilization. Results showed that the spatial distribution and correlation between clay clusters and biopolymers were heterogeneous and significant, and also demonstrated that clay clusters were associated as nuclei with the potential of binding carbon at the submicron scale. Furthermore, the combination of SR-FTIR mapping and 2DCOS analysis could explore the strategy of identifying overlapped spectra and quantifying the sequestration reactivity for the first time. Specifically, carbon retention correlated as the binding sequence orders: 3630 cm⁻¹ > 3610 cm^-1, 985 cm^-1 > 898 cm^-1, indicating that Fe/Al oxyhydroxides and phyllosilicates could regulate the organic matter sequestration without the influence of spatial perturbations. Together, we conclude a combined methodology to assess the heterogeneous binding microenvironments between the mineral assemblages and biopolymers, which could also contribute to understand the process of carbon sequestration interrestrial ecosystems.

25945. 题目: Multi-proxy evidence for paleoclimate evolution performed on a paleolake sediment core in the East Asian Monsoon Region
文章编号: N19012903
期刊: Environmental Earth Sciences
作者: Longjuan Cheng, Wei Ye
更新时间: 2019-01-29
摘要: A sediment succession from a paleolake in the Hangjiahu Plain, Southeast China, covering the period 11.4–5.0 cal ka BP was studied using grain size, total organic carbon (TOC), organic carbon isotope (δ¹³C_org), C/N ratio, pollen, carbonate and its carbon and oxygen isotopes (δ¹⁸O_carb and δ¹³C_carb) analysis to reconstruct climate changes. The methods of redundancy analysis (RDA) ordination and correlation analysis (CA) were employed to quantify the influence of geochemical indexes on the biological index (the pollen) and to explain the environmental significance of each proxy more scientifically and accurately, so as to provide more reliable indication for the reconstruction of the paleoclimate. The reconstruction, supported by the AMS ¹⁴C age modelling, indicates climatic evolution during the Early–Middle Holocene period, at least, experienced four stages: (1) a period of gradual warm and humid during the early Holocene (11.4–8.7 cal ka BP). (2) A middle continuous cold–dry stage (8.7–8.0 cal ka BP), precipitation and temperature declined revealed by the proxies. (3) 8.0–6.6 cal ka BP, which was the wettest and warmest stages in the climate change sequence, precipitation, and temperature increased markedly, and this stage was consistent with the Holocene Climate Optimum. (4) A cold–dry period during the middle Holocene (6.6–5.0 cal ka BP), and particularly worth mentioning was that a large number of Oryza pollens were found which indicated the rice-based agriculture developed. In particular, the Liangzhu Culture in this region appeared at this time.

25946. 题目: Effects of early diagenesis on Mg isotopes in dolomite: the roles of Mn(IV)-reduction and recrystallization
文章编号: N19012902
期刊: Geochimica et Cosmochimica Acta
作者: Weiqiang Li, Or M. Bialik, Xiaomin Wang, Tao Yang, Zhongya Hu, Qingyu Huang, Shugao Zhao, Nicolas D. Waldmann
更新时间: 2019-01-29
摘要: Sedimentary dolomite plays an important role in global Mg cycling, and Mg isotopes in massive dolostones may be used to infer secular changes in seawater chemistry through geological history. However, sedimentary dolomite is generally regarded as a diagenetic product, and many details about the effects of early diagenesis on the Mg isotope composition of dolomite remain unclear. The mid-Cretaceous (Albian) Soreq and Givat Ye’arim formations near Jerusalem, Israel, contain exceptionally well-preserved massive dolostones, which provide an ideal opportunity to investigate the Mg isotope responses to early diagenesis. Dolomite samples from this section show large variations in δ¹³C values and Mn contents that are negatively correlated, reflecting degradation of organic matter and mineralization of organic carbon in the Mn(IV) reduction zone within soft sediment during dolomite formation. This is a rare example of a clear link between Mn(IV) reduction and dolomite precipitation based on geochemical evidence in the rock record. The dolomite samples also exhibit large variations in d(104) values and the degree of cation ordering. The latter is negatively correlated with Sr contents, implying that variable degrees of dolomite recrystallization occurred during diagenesis. δ²⁶Mg values of >50 dolomite samples from this section vary from –2.28‰ to –1.78‰, but do not correlate with indicators of organic matter degradation (δ¹³C values and Mn contents) or dolomite recrystallization (e.g., Sr contents), suggesting that Mg isotopes behave conservatively after initial dolomite (or proto-dolomite) precipitation during the very early stages of diagenesis. We propose that the Mg isotope composition of dolomite formed due to Mn(IV) reduction is buffered by seawater due to the shallowness of the Mn(IV) reduction zone in platform sediments, which is different from the dolomitization associated with bacterial sulfate reduction or methanogenesis, where Mg supply can be diffusion-limited. Furthermore, Mg isotopes in dolomite are robust to resetting by recrystallization during burial. Magnesium isotope compositions of platform dolomite that show variable and negatively correlated δ¹³C values and Mn contents can, therefore, be considered robust archives for reconstructing paleo-seawater Mg isotope compositions. The variation in δ²⁶Mg values of the dolostones in the Soreq and Givat Ye’arim formations is interpreted to reflect Rayleigh fractionation in response to dolomitization in a restricted water body. Therefore, the lowest δ²⁶Mg value is considered to be the Mg isotope composition of dolomite that was in equilibrium with coeval seawater in the open ocean, and thus the δ²⁶Mg value of Albian seawater was around –0.4‰.

25947. 题目: Whale carcass leachate plumes in beach groundwater: A potential shark attractant to the surf?
文章编号: N19012901
期刊: Marine Pollution Bulletin
作者: James P. Tucker, Isaac R. Santos, Kay L. Davis, Paul A. Butcher
更新时间: 2019-01-29
摘要: With the recovery of whale populations, carcass strandings on beaches are growing. Beach burial is a common management option for stranded carcasses. However, communities fear shark attraction following leachate transport to the ocean via submarine groundwater discharge. Here, a sediment column mesocosm experiment indicated that carcasses can be a localised source of dissolved organic carbon (DOC), phosphate and ammonium to groundwater. The spatial reach of the leachate plume was <2.5 m, while the temporal stabilisation occurred over 100–300 days. No significant chemical signals were observed under a beach-buried carcass, implying effective attenuation of decomposition plumes. For beaches with conditions similar to our one-directional, fast-flowing sediment experiment generating extreme groundwater contamination, it is unlikely that any leachate from a whale carcass would reach the ocean if buried >25 m onshore. Therefore, carcass leachate plumes would only potentially attract sharks to the surf under specific conditions not experienced during our experiments.

25948. 题目: River channel connectivity shifts metabolite composition and dissolved organic matter chemistry
文章编号: N19012802
期刊: Nature Communications
作者: Laurel M Lynch, Nicholas A Sutfin, Timothy S Fegel, Claudia M Boot, Timothy P Covino, Matthew D Wallenstein
更新时间: 2019-01-28
摘要: Biogeochemical processing of dissolved organic matter (DOM) in headwater rivers regulates aquatic food web dynamics, water quality, and carbon storage. Although headwater rivers are critical sources of energy to downstream ecosystems, underlying mechanisms structuring DOM composition and reactivity are not well quantified. By pairing mass spectrometry and fluorescence spectroscopy, here we show that hydrology and river geomorphology interactively shape molecular patterns in DOM composition. River segments with a single channel flowing across the valley bottom export DOM with a similar chemical profile through time. In contrast, segments with multiple channels of flow store large volumes of water during peak flows, which they release downstream throughout the summer. As flows subside, losses of lateral floodplain connectivity significantly increase the heterogeneity of DOM exported downstream. By linking geomorphologic landscape-scale processes with microbial metabolism, we show DOM heterogeneity increases as a function of fluvial complexity, with implications for ecosystem function and watershed management.

25949. 题目: Methane oxidation in vertical flow constructed wetlands and its effect on denitrification and COD removal
文章编号: N19012801
期刊: Ecological Engineering
作者: Thomas Schalk, Johannes Effenberger, Alexander Jehmlich, Jens Nowak, Heribert Rustige, Peter Krebs, Volker Kühn
更新时间: 2019-01-28
摘要: Most types of subsurface flow constructed wetlands include pretreatment units for separation of particulate matter. Due to long retention times of the settled sludge in pretreatment units of small constructed wetlands (CWs), anaerobic degradation processes occur and cause methane emissions into the environment. To minimize methane emissions, small-scale trials were carried out, in order to investigate whether vertical subsurface flow CWs (VF wetlands) are suitable for removal of methane and whether it can be utilized to improve the denitrification rate of VF wetlands.The results show that methane was completely removed for surface loads of up to 19 g CH₄/(m²·d). Based on mass balancing, 2% of the fed methane was oxidized with nitrate while 22% were oxidized with oxygen. The major part was attributed to biomass build-up. A correlation between effluent COD load and removed methane load was observed. Published literature indicates that COD accumulation is a result of production of extracellular polymeric substances. Low methane loads have only a slight impact on COD accumulation. It is expected that typical methane loads resulting from pre-sedimentation units may cause effluent COD concentrations to increase by up to 20% for municipal wastewater treatment with VF wetlands. Hence, combined wastewater treatment and methane oxidation was successfully demonstrated, but enhanced denitrification could not be achieved.

25950. 题目: Effect of sulfur and sulfur-iron modified biochar on cadmium availability and transfer in the soil–rice system
文章编号: N19012703
期刊: Chemosphere
作者: Manikandan Rajendran, Lizheng Shi, Chuan Wu, Waichin Li, Wenhui An, Ziyu Liu, Shengguo Xue
更新时间: 2019-01-27
摘要: Cadmium (Cd) contamination in paddy soils has aroused global concern. Sulfur modified biochar (BC) could combine the benefits of BC and S for Cd remediation. However, no information is available on the impact of sulfur modified biochar on Cd phytoavailability in paddy soils. In this study, a pot experiment was conducted to investigate the effect of sulfur modified biochar (S-BC) and sulfur and iron (Fe) modified biochar (S-Fe BC) on Cd mobility and Cd transfer in the soil-rice system. The application of S-BC and S-Fe BC effectively reduced pore water Cd in the rhizosphere and non-rhizosphere pore water throughout the rice growth stages. S-BC and S-Fe BC addition increased the total chlorophyll content, as well as the root, shoot and grain biomasses of rice. Furthermore, S-BC and S-Fe BC amendments greatly increase the formation of Fe plaque on rice root surface, thus decreasing Cd accumulation in different rice tissues. In particular, S-Fe BC supplementation significantly reduced the Cd concentration in rice grains to 0.018 mg kg^-1 in Cd-contaminated soil, which was lower than the China National standard for food contamination limit (0.2 mg kg^-1 Cd). Sequential extraction results showed that S-BC and S-Fe BC can promote the transfer of exchangeable Cd to Fe-Mn oxide, organic and residual bound forms which reduce Cd in paddy soils. Thus, the amendment of S-Fe BC to Cd-contaminated paddy soil is an effective strategy to decrease Cd accumulation in rice grains and thereby protect public health.

25951. 题目: Effects of artificial reefs on the meiofaunal community and benthic environment - A case study in Bohai Sea, China
文章编号: N19012702
期刊: Marine Pollution Bulletin
作者: Xinyuan Yang, Chenggang Lin, Xiaoyue Song, Min Xu, Hongsheng Yang
更新时间: 2019-01-27
摘要: Artificial reefs are widely deployed for fishery enhancement and marine conservation. A comprehensive assessment on the effects of artificial reefs could minimize the negative consequence of blindly developing artificial reefs. We examined the meiofaunal community and benthic environment adjacent to and <5 m from artificial reefs in Xiangyun Bay, Bohai Sea, China. We found the highest total meiofaunal abundance beside the artificial reef. Shannon-Wiener and Pielou indexes had no significant difference among different distances from the artificial reefs. The presence of artificial reefs impeded the surrounding flow and provided additional substrate for bivalves and kelps, which could cause finer sediment and organic enrichment around it. Sediment grain size and total organic matter were the most important parameters influencing the meiofauna. We suggest that the shape, material, configuration and location of artificial reefs should be related with a specific goal to avoid mindless proliferation.

25952. 题目: Preferable phosphate removal by nano-La(III) hydroxides modified mesoporous rice husk biochars: Role of the host pore structure and point of zero charge
文章编号: N19012701
期刊: Science of The Total Environment
作者: Qian Tang, Chenghao Shi, Wenmin Shi, Xueling Huang, Yuanyao Ye, Wei Jiang, Jianxiong Kang, Dongqi Liu, Yongzheng Ren, Daosheng Li
更新时间: 2019-01-27
摘要: Immobilizing La(OH)₃ nanoparticles (NPs) to porous hosts has been widely applied to inhibiting their inherent aggregation as well as the subsequent low utilization efficiency of La. In this study, a series of rice husk biochars (RHBCs) with high mesoporous rates were prepared and the effects of host pore structure and point of zero charge (pH_pzc) on phosphate adsorption by La-modified RHBCs was particularly focused. Characterization results confirmed that La(OH)₃ NPs were both confined in the pore channel and external surface of RHBCs. Adsorption kinetics and isotherms showed that La-modified RHBCs with higher mesoporous rates of the host showed a faster adsorption rate and La-modified RHBCs exhibited superior La utilization efficiency than many reported La-incorporated adsorbents. Phosphate could be effectively captured over a wide pH of 3–10 due to the high pH_pzc of La-modified RHBCs. Moreover, the La-modified RHBCs showed satisfactory affinity towards phosphate in the presence of coexisting anions and the phosphate adsorption by La-RHBC₉ was enhanced in the presence of Ca²⁺, while it was inhibited in the presence of Mg²⁺. The mesoporous structure of RHBCs strengthened the stability of La-modified RHBCs and weakened the inhibition of coexisting humic substances on phosphate adsorption through the “shielding effect”.
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25953. 题目: Holocene shifts in the primary producer community of large, shallow European Lake Peipsi, inferred from sediment pigment analysis
文章编号: N19012626
期刊: Journal of Paleolimnology
作者: Ilmar Tõnno, Kristiina Nauts, Simon Belle, Monika Nõmm, Rene Freiberg, Toomas Kõiv, Tiiu Alliksaar
更新时间: 2019-01-26
摘要: We used HPLC to identify and quantify pigments in a Holocene sediment record from large, shallow Lake Peipsi, Estonia. The aim of our study was to track the influence of long-term climate change (i.e. temperature fluctuations) on past dynamics of aquatic primary producers. Sedimentary pigments were separated and quantified in 182 samples that span the last ca. 10,000 years. There was an increasing trend in sedimentary pigment concentrations from basal to upper sediment layers, suggesting a gradual increase in lake trophic status through time. Using additive models, our results suggested that primary producer dynamics in Lake Peipsi were closely related to temperature fluctuations. We, however, identified two periods (early Holocene and after ca. 2.5 cal ka BP) when the relationship between primary producer composition and temperature was weak, suggesting the influence of additional drivers on the primary producer community. We postulate that: (a) the increase of primary producer biomass in the early Holocene could have been caused by input of allochthonous organic matter and nutrients from the flooded areas when water level in Lake Peipsi was increasing, and (b) changes in the abundance and structure of primary producer assemblages since ca. 2.5 cal ka BP was related to widespread agricultural activities in the Lake Peipsi catchment. These results suggest that human activities can disrupt the relationship between the primary producer community and temperature in large, shallow lakes.

25954. 题目: Impacts of Natural and Human-Induced Hydrological Variability on Particulate Organic Carbon Dynamics in the Yellow River
文章编号: N19012625
期刊: Environmental Science & Technology
作者: Meng Yu, Timothy I Eglinton, Negar Haghipour, Daniel B Montluçon, Lukas Wacker, Pengfei Hou, Hailong Zhang, Meixun Zhao
更新时间: 2019-01-26
摘要: Natural and human-induced hydrological changes can influence organic carbon (OC) composition in fluvial systems, with biogeochemical consequences in both terrestrial and marine environments. Here, we use bulk and molecular carbon isotopes (13C and 14C) to examine spatiotemporal variations in particulate OC (POC) composition and age from two locations along the course of the Yellow River during 2015 and 2016. Dual carbon isotopes enable deconvolution of modern, pre-aged (millennial age) soil, and fossil inputs, revealing heterogeneous OC sources at both sites. Pre-aged OC predominated at the upstream site (Huayuankou) throughout the study period, mostly reflecting the upper riverine OC. Strong downstream (Kenli) intra-annual variations in modern and pre-aged OC were caused by increased contributions from modern aquatic OC production under the drier and less turbid conditions during this El Niño year. The month of July, which included the human-induced water and sediment regulation (WSR) event at Kenli, accounted for 82% of annual POC flux, with lower modern OC contribution compared with periods of natural seasonal variability. Both natural and human-induced hydrological events clearly exert strong influence on both fluxes and composition of Yellow River POC which, in turn, affect the balance between OC remineralization and burial for this major fluvial system.

25955. 题目: Real-time assessment of wintertime organic aerosol characteristics and sources at a suburban site in northern France
文章编号: N19012624
期刊: Atmospheric Environment
作者: Roger Roig Rodelas, Abhishek Chakraborty, Esperanza Perdrix, Emmanuel Tison, Véronique Riffault
更新时间: 2019-01-26
摘要: A high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was deployed during wintertime (5 February to 15 March 2016) at a suburban site in Douai, northern France, in order to investigate the characteristics and sources of the organic matter (OM). The campaign average concentration of non-refractory submicron particulate matter (NR-PM1) was 11.1 ± 9.3 μg m-3, and composed of 38% OM, 36% nitrate, 16% ammonium and 9% sulfate. The average values for the OM:OC, O:C and H:C ratios were 1.60 ± 0.15, 0.32 ± 0.11 and 1.55 ± 0.14, respectively, indicating a moderate level of aerosol oxidation. The positive matrix factorization (PMF) source apportionment method was applied to the high-resolution organic aerosol (OA) mass spectra, resulting in four factors: a hydrocarbon-like (HOA) factor; one associated with oxidized biomass burning (oBBOA); and two oxygenated factors (OOA) denoted as less oxidized (LO-OOA) and more oxidized (MO-OOA), with average contributions to OA of 20%, 28%, 17% and 35%, respectively. The oBBOA factor was found to be mainly local as shown by non-parametric wind regression (NWR) analysis, and to correlate well with relative humidity (RH), suggesting fast aqueous processing of locally emitted primary biomass burning emissions. During most part of the campaign, the sampling site was affected by different air masses. However, during the last period of the campaign (5-16 March 2016) the site was heavily impacted by air masses from Eastern Europe which were rich in secondary inorganic and organic aerosols. The H:C versus O:C (Van Krevelen, VK) diagram highlighted that the aerosol followed an oxidation process throughout the whole campaign, with an average slope of -1.05. The impact of continental air masses towards the end of the campaign confined the aerosol towards a narrower space in the VK diagram, suggesting a homogenization of the different aerosol sources due to OA ageing during transport. Several nocturnal NPF (new particle formation)-like events were observed and associated to the fast processing of BBOA emissions and the formation of ammonium nitrate.

25956. 题目: Sedimentary alkalinity generation and long-term alkalinity development in the Baltic Sea
文章编号: N19012623
期刊: Biogeosciences
作者: Erik Gustafsson, Mathilde Hagens, Xiaole Sun, Daniel C. Reed, Christoph Humborg, Caroline P. Slomp, Bo G. Gustafsson
更新时间: 2019-01-26
摘要: Enhanced release of alkalinity from the seafloor, principally driven by anaerobic degradation of organic matter under low-oxygen conditions and associated secondary redox reactions, can increase the carbon dioxide (CO2) buffering capacity of seawater and therefore oceanic CO2 uptake. The Baltic Sea has undergone severe changes in oxygenation state and total alkalinity (TA) over the past decades. The link between these concurrent changes has not yet been investigated in detail. A recent system-wide TA budget constructed for the past 50 years using BALTSEM, a coupled physical–biogeochemical model for the whole Baltic Sea area revealed an unknown TA source. Here we use BALTSEM in combination with observational data and one-dimensional reactive-transport modeling of sedimentary processes in the Fårö Deep, a deep Baltic Sea basin, to test whether sulfate (SO42-) reduction coupled to iron (Fe) sulfide burial can explain the missing TA source in the Baltic Proper. We calculated that this burial can account for up to 26% of the missing source in this basin, with the remaining TA possibly originating from unknown river inputs or submarine groundwater discharge. We also show that temporal variability in the input of Fe to the sediments since the 1970s drives changes in sulfur (S) burial in the Fårö Deep, suggesting that Fe availability is the ultimate limiting factor for TA generation under anoxic conditions. The implementation of projected climate change and two nutrient load scenarios for the 21st century in BALTSEM shows that reducing nutrient loads will improve deep water oxygen conditions, but at the expense of lower surface water TA concentrations, CO2 buffering capacities and faster acidification. When these changes additionally lead to a decrease in Fe inputs to the sediment of the deep basins, anaerobic TA generation will be reduced even further, thus exacerbating acidification. This work highlights that Fe dynamics plays a key role in the release of TA from sediments where Fe sulfide formation is limited by Fe availability, as exemplified by the Baltic Sea. Moreover, it demonstrates that burial of Fe sulfides should be included in TA budgets of low-oxygen basins.

25957. 题目: Changes in Streamflow and Sediment for a Planned Large Reservoir in the Middle Yellow River
文章编号: N19012622
期刊: Land Degradation & Development
作者: Binquan Li, Zhongmin Liang, Zhenxin Bao, Jun Wang, Yiming Hu
更新时间: 2019-01-26
摘要: Changes in streamflow and sediment runoffs would affect the reservoir's functional operation and the construction of soil and water conservation (SWC) measures in China's Loess Plateau. In this study, the long‐term changes in streamflow and sediment were analyzed for a main stem section of the middle Yellow River where the to‐be‐built large Guxian Reservoir locates at. Results showed that both streamflow and sediment had significant downward trends with the rates of ‐9.4 m³ s^‐1 year^‐1 and ‐16.8 million t/year, respectively, during the period of 1961‐2017. Using the Range of Variability Approach (RVA), the change of streamflow regime in its post‐impact period (1986‐2017) was subjected to the moderate alteration, while the alteration of sediment regime was moderate and severe for the first (1980‐1996) and second (1997‐2017) post‐impact periods. As an example, the attribution analysis of annual streamflow and sediment changes were conducted in a typical tributary catchment (Qingjian River) on the right bank of Guxian Reservoir. For the periods of 1980‐2002 and 2003‐2016, climate variability occupied the primary and secondary proportions to both streamflow and sediment reductions, respectively. Overall, human activities demonstrated the underlying contribution to the sharp declines of streamflow and sediment, accounting for 68% and 74%, respectively, during the period of 1980‐2016. We suggest that, based on the operational life of warping dam, there are risks of flash flood and high sediment concentration events in the future because the streamflow/sediment‐reducing infrastructures may be damaged by extreme rainstorms and in turn become the flood and sediment amplifiers.

25958. 题目: Drought and its legacy modulate the post‐fire recovery of soil functionality and microbial community structure in a Mediterranean shrubland
文章编号: N19012621
期刊: Global Change Biology
作者: M. Belén Hinojosa, V. Armando Laudicina, Antonio Parra, Enrique Albert‐Belda, Jose M. Moreno
更新时间: 2019-01-26
摘要: The effects of drought on soil dynamics after fire are poorly known, particularly its longer‐term (i.e., years) legacy effects once rainfall returns to normal. Understanding this is particularly important for nutrient‐poor soils in semi‐arid regions affected by fire, in which rainfall is projected to decrease with climate change. Here, we studied the effects of post‐fire drought and its legacy on soil microbial community structure and functionality in a Cistus‐Erica shrubland (Spain). Rainfall total and patterns were experimentally modified to produce an unburned control (natural rainfall) and four burned treatments: control (natural rainfall), historical control (long‐term average rainfall), moderate drought (percentile 8 historical rainfall, five months of drought per year), and severe drought (percentile 2, seven months of drought). Soil nutrients and microbial community composition (ester‐linked fatty acid approach) and functionality (enzyme activities and C mineralization rate) were monitored during the first four years after fire under rainfall treatments, plus two additional ones without them (six post‐fire years). We found that the recovery of burned soils was lower under drought. Post‐fire drought increased nitrate in the short‐term and reduced available phosphorus, exchangeable potassium, soil organic matter, enzyme activities and carbon mineralization rate. Moreover, drought decreased soil total microbial biomass and fungi, with bacteria becoming relatively more abundant. Two years after discontinuing the drought treatments, the drought legacy was significant for available phosphorus and enzyme activities. Although microbial biomass did not show any drought legacy effect, the proportion of fungi and bacteria (mainly Gram‐positive) did, being lower and higher, respectively, in former drought‐treated plots. We show that drought has an important impact on soil processes, and that some of its effects persist for at least two years after the drought ended. Therefore, drought and its legacy effects can be important for modeling biogeochemical processes in burned soils under future climate change.

25959. 题目: Drainage enhances modern soil carbon contribution but reduces old soil carbon contribution to ecosystem respiration in tundra ecosystems
文章编号: N19012620
期刊: Global Change Biology
作者: Min Jung Kwon, Susan M. Natali, Caitlin E. Hicks Pries, Edward A. G. Schuur, Axel Steinhof, K. Grace Crummer, Nikita Zimov, Sergey A. Zimov, Martin Heimann, Olaf Kolle, Mathias Göckede
更新时间: 2019-01-26
摘要: Warming temperatures are likely to accelerate permafrost thaw in the Arctic, potentially leading to the release of old carbon previously stored in deep frozen soil layers. Deeper thaw depths in combination with geomorphological changes due to the loss of ice structures in permafrost, may modify soil water distribution, creating wetter or drier soil conditions. Previous studies revealed higher ecosystem respiration rates under drier conditions, and this study investigated the cause of the increased ecosystem respiration rates using radiocarbon signatures of respired CO₂ from two drying manipulation experiments: one in moist and the other in wet tundra. We demonstrate that higher contributions of CO₂ from shallow soil layers (0–15 cm; modern soil carbon) drive the increased ecosystem respiration rates, while contributions from deeper soil (below 15 cm from surface and down to the permafrost table; old soil carbon) decreased. These changes can be attributed to more aerobic conditions in shallow soil layers, but also the soil temperature increases in shallow layers but decreases in deep layers, due to the altered thermal properties of organic soils. Decreased abundance of aerenchymatous plant species following drainage in wet tundra reduced old carbon release but increased aboveground plant biomass elevated contributions of autotrophic respiration to ecosystem respiration. The results of this study suggest that drier soils following drainage may accelerate decomposition of modern soil carbon in shallow layers but slow down decomposition of old soil carbon in deep layers, which may offset some of the old soil carbon loss from thawing permafrost.

25960. 题目: Ecosystem carbon response of an Arctic peatland to simulated permafrost thaw
文章编号: N19012619
期刊: Global Change Biology
作者: Carolina Voigt, Maija E. Marushchak, Mikhail Mastepanov, Richard E. Lamprecht, Torben R. Christensen, Maxim Dorodnikov, Marcin Jackowicz‐Korczyński, Amelie Lindgren, Annalea Lohila, Hannu Nykänen, Markku Oinonen, Timo Oksanen, Vesa Palonen, Claire C. Treat, Pertti J. Martikainen, Christina Biasi
更新时间: 2019-01-26
摘要: Permafrost peatlands are biogeochemical hot spots in the Arctic as they store vast amounts of carbon. Permafrost thaw could release part of these long‐term immobile carbon stocks as the greenhouse gases (GHGs) carbon dioxide (CO₂) and methane (CH₄) to the atmosphere, but how much, at which time‐span and as which gaseous carbon species is still highly uncertain. Here we assess the effect of permafrost thaw on GHG dynamics under different moisture and vegetation scenarios in a permafrost peatland. A novel experimental approach using intact plant–soil systems (mesocosms) allowed us to simulate permafrost thaw under near‐natural conditions. We monitored GHG flux dynamics via high‐resolution flow‐through gas measurements, combined with detailed monitoring of soil GHG concentration dynamics, yielding insights into GHG production and consumption potential of individual soil layers. Thawing the upper 10–15cm of permafrost under dry conditions increased CO₂ emissions to the atmosphere (without vegetation: 0.74±0.49 vs. 0.84±0.60g CO₂–C m⁻²d⁻¹; with vegetation: 1.20±0.50 vs. 1.32±0.60g CO₂–C m⁻²d⁻¹, mean±SD, pre‐ and post‐thaw, respectively). Radiocarbon dating (¹⁴C) of respired CO₂, supported by an independent curve fitting approach, showed a clear contribution (9–27%) of old carbon to this enhanced post‐thaw CO₂ flux. Elevated concentrations of CO₂, CH₄, and dissolved organic carbon at depth indicated not just pulse emissions during the thawing process, but sustained decomposition and GHG production from thawed permafrost. Oxidation of CH₄ in the peat column, however, prevented CH₄ release to the atmosphere. Importantly, we show here that, under dry conditions, peatlands strengthen the permafrost–carbon feedback by adding to the atmospheric CO₂ burden post‐thaw. However, as long as the water table remains low, our results reveal a strong CH₄ sink capacity in these types of Arctic ecosystems pre‐ and post‐thaw, with the potential to compensate part of the permafrost CO₂ losses over longer timescales.