Exploring the stemflow dynamics and driving factors at both inter- and intra-event scales in a typical subtropical deciduous forest     

Haixia Zhang  Congsheng Fu  Aimin Liao  Can Zhang  Jiufu Liu  Niu Wang  Bin He 《水文研究》2021,35(3):e14091

Numerous efforts have been made to understand stemflow dynamics under different types of vegetation at the inter-event scale, but few studies have explored the stemflow characteristics and corresponding influencing factors at the intra-event scale. An in-depth investigation of the inter- and intra-event dynamics of stemflow is important for understanding the ecohydrological processes in forest ecosystems. In this study, stemflow volume (F_V), stemflow funnelling ratio (F_R), and stemflow ratio (F_%) from Quercus acutissima and Broussonetia papyrifera trees were measured at both inter- and intra-event scales in a subtropical deciduous forest, and the driving factors, including tree species and meteorological factors were further explored. Specifically, the F_V, F_R and F_% of Q. acutissima (52.3 L, 47.2, 9.6%) were lower than those of B. papyrifera (85.1 L, 91.2, 12.4%). The effect of tree species on F_V and F_% was more obvious under low intensity rainfall types. At the inter-event scale, F_V had a strong positive linear correlation with rainfall amount (G_P) and event duration (D_E) for both tree species, whereas F_R and F_% had a positive logarithmic correlation with G_P and D_E only under high-intensity, short-duration rainfall type. F_R and F_% were mainly affected by wind speed and the maximum 30-min rainfall intensity under low-intensity, long-duration rainfall type. At the intra-event scale, for both tree species, the mean lag time between the start of rainfall and stemflow was the shortest under high-intensity, short-duration rainfall type, while the mean duration and amount of stemflow after rain cessation were the greatest under high-amount, long-duration rainfall type. The relationship between stemflow intensity and rainfall intensity at the 5-min interval scale also depended greatly on rainfall type. These findings can help clarify stemflow dynamics and driving factors at both inter- and intra-event scales, and also provide abundant data and parameters for ecohydrological simulations in subtropical forests.  相似文献   

纳米气泡改性矿物颗粒的湖泊沉积物-水界面增氧效果实验研究     

余萍萍  王敬富  陈敬安  张耀  陈权  卢耀庭 《湖泊科学》2019,31(1):65-71

季节性缺氧导致夏季沉积物内源磷强烈释放，加剧水体富营养化，是我国西南地区深水湖泊（水库）面临的重要挑战.有效增加夏季缺氧期深水沉积物-水界面的含氧量，是减少内源磷释放的关键.现有的深水增氧技术由于缺乏对沉积物-水界面增氧的针对性，因此治理效果有限.近年来，纳米气泡已被证实具有的稳定性好、氧传质速率高和环境风险低等优点，为新型深水增氧技术研发提供了巨大潜力.本文以天然矿物材料白云母、绢云母、硅藻土和沸石为基底，负载纳米气泡，研发纳米气泡改性矿物颗粒技术，开展湖泊沉积物-水界面增氧模拟实验研究，运用平面光电极技术评估其界面增氧效果.结果表明，纳米气泡改性矿物颗粒对沉积物-水界面具有比较明显的增氧效果.其中，改性白云母、绢云母和沸石的界面持续增氧时间可达7天以上，增氧后的界面最大溶解氧（DO）浓度达4.40 mg/L，而改性硅藻土不具有增氧能力.其次，矿物粒度对改性颗粒的增氧效果有一定影响：粒度越细，界面的最大增氧浓度越高，且持续增氧时间越长.纳米气泡改性矿物颗粒技术有望成为夏季缺氧期深水沉积物-水界面精准增氧和内源污染控制的有效技术手段.  相似文献   

Geochemical study of the Neoproterozoic clastic sedimentary rocks of the Khambal Formation (Sindreth Basin), Aravalli Craton,NW Indian Shield: Implications for paleoweathering,provenance, and geodynamic evolution     

《Chemie der Erde / Geochemistry》2020,80(1):125596

Petrographic and geochemical studies characterize lithologies of the Khambal Formation deposited in the Sindreth Basin as arkosic, subarkosic, and quartzarenite. Weathering indices, such as CIA and CIW in conjunction with the ACNK diagram, prescribe mostly moderate chemical weathering with intermittent pulses of extreme weathering in the source area. The discrimination diagrams suggest that these Neoproterozoic clastics were deposited in an active rift basin. Provenance indicators of the detritus components point to a terrane possessing subordinate mafic material in conjunction with large felsic components. A comparison of immobile element ratios with probable source rocks suggest that the Mesoproterozoic Delhi arc situated to the east of the Sindreth Basin could be the possible source. Our mixing calculation defines the proportion of end member components in the Delhi arc. Geodynamic considerations relate the origin of the Sindreth Basin to the processes of disintegration and reassembly of supercontinents.  相似文献   

Kainsaz(CO3)陨石中两个富Al球粒的氧同位素组成特征与形成演化     

戴德求  包海梅  刘爽  尹锋 《岩石学报》2020,36(6):1850-1856

富Al球粒是原始球粒陨石中一种矿物岩石学特征介于富钙铝包体(CAIs)和镁铁质硅酸盐球粒之间的特殊集合体,所以常常认为富Al球粒在认识CAIs和镁铁质硅酸盐球粒形成演化过程中的相互联系具有特殊意义。然而,对富Al球粒的初始物质组成以及形成演化过程一直存在较多争议,而氧同位素组成研究能够对球粒演化和早期星云环境等提供重要的信息。在本文中我们报导了来自Kainsaz(1937年降落于俄罗斯,CO3型)碳质球粒陨石中的2个富Al球粒(编号K1-CH1和K2-CH2)的矿物岩石学和氧同位素组成特征。K1-CH1的矿物组成主要为橄榄石、低钙辉石和富钙长石,K2-CH2为橄榄石和富钙长石。2个球粒中的矿物均具有贫~(16)O同位素组成特征。K1-CH1中矿物的△~(17)O组成基本上位于2个区间:-11.1‰～-8.7‰和-3.9‰～0.4‰;而K2-CH2的△~(17)O介于-6.6‰～-0.6‰之间,且具有从中部至边部升高的趋势。矿物岩石学和氧同位素特征表明,这2个富Al球粒的初始物质组成为富CAIs和镁铁质硅酸盐。在球粒熔融结晶过程中,与贫~(16)O同位素组成(△~(17)O:-8.7‰～-7.8‰)的星云发生了氧同位素交换。球粒形成后,发生迁移进入陨石母体,在相对更贫~(16)O同位素组成(△~(17)O:-0.6‰～0.4‰)的母体中(流体参与)发生变质作用,并再次发生了氧同位素交换。  相似文献   

Fluvial dynamics and 14C-10Be disequilibrium on the Bolivian Altiplano     

Kristina Hippe  Tiemen Gordijn  Vincenzo Picotti  Irka Hajdas  John D. Jansen  Marcus Christl  Christof Vockenhuber  Colin Maden  Naki Akçar  Susan Ivy-Ochs 《地球表面变化过程与地形》2019,44(3):766-780

Determining sediment transfer times is key to understanding source-to-sink dynamics and the transmission of environmental signals through the fluvial system. Previous work on the Bolivian Altiplano applied the in situ cosmogenic ¹⁴C-¹⁰Be-chronometer to river sands and proposed sediment storage times of ~10–20 kyr in four catchments southeast of Lake Titicaca. However, the fidelity of those results hinges upon isotopic steady-state within sediment supplied from the source area. With the aim of independently quantifying sediment storage times and testing the ¹⁴C-¹⁰Be steady-state assumption, we dated sediment storage units within one of the previously investigated catchments using radiocarbon dating, cosmogenic ¹⁰Be-²⁶Al isochron burial dating, and ¹⁰Be-²⁶Al depth-profile dating. Palaeosurfaces appear to preserve remnants of a former fluvial system, which has undergone drainage reversal, reduction in catchment area, and local isostatic uplift since ~2.8 Ma. From alluvium mantling the palaeosurfaces we gained a deposition age of ~580 ka, while lower down fluvial terraces yielded ≤34 ka, and floodplains ~3–1 ka. Owing to restricted channel connectivity with the terraces and palaeosurfaces, the main source of channel sediment is via reworking of the late Holocene floodplain. Yet modelling a set of feasible scenarios reveals that floodplain storage and burial depth are incompatible with the ¹⁴C-¹⁰Be disequilibrium measured in the channel. Instead we propose that the ¹⁴C-¹⁰Be offset results from: (i) non-uniform erosion whereby deep gullies supply hillslope-derived debris; and/or (ii) holocene landscape transience associated with climate or human impact. The reliability of the ¹⁴C-¹⁰Be chronometer vitally depends upon careful evaluation of sources of isotopic disequilibrium in a wide range of depositional and erosional landforms in the landscape. © 2018 John Wiley & Sons, Ltd.  相似文献   

Origin of K-rich diamond-forming immiscible melts and CO2 fluid via partial melting of carbonated pelites at a depth of 180–200 km     

《Gondwana Research》2019

Melt inclusions in kimberlitic and metamorphic diamonds worldwide range in composition from potassic aluminosilicate to alkali-rich carbonatitic and their low-temperature derivative, a saline high-density fluid (HDF). The discovery of CO₂ inclusions in diamonds containing eclogitic minerals are also essential. These melts and HDFs may be responsible for diamond formation and metasomatic alteration of mantle rocks since the late Archean to Phanerozoic. Although a genetic link between these melts and fluids was suggested, their origin is still highly uncertain. Here we present experimental results on melting phase relations in a carbonated pelite at 6 GPa and 900–1500 °C. We found that just below solidus K₂O enters potassium feldspar or K₂TiSi₃O₉ wadeite coexisting with clinopyroxene, garnet, kyanite, coesite, and dolomite. The potassium phases react with dolomite to produce garnet, kyanite, coesite, and potassic dolomitic melt, 40(K_0.90Na_0.10)₂CO₃·60Ca_0.55Mg_0.24Fe_0.21CO₃ + 1.9 mol% SiO₂ + 0.7 mol% TiO₂ + 1.4 mol% Al₂O₃ at the solidus established near 1000 °C. Molecular CO₂ liberates at 1100 °C. Potassic aluminosilicate melt appears in addition to carbonatite melt at 1200 °C. This melt contains (mol/wt%): SiO₂ = 57.0/52.4, TiO₂ = 1.8/2.3, Al₂O₃ = 8.5/13.0, FeO = 1.4/1.6, MgO = 1.9/1.2, CaO = 3.8/3.2, Na₂O = 3.2/3.0, K₂O = 10.5/15.2, CO₂ = 12.0/8.0, while carbonatite melt can be approximated as 24(K_0.81Na_0.19)₂CO₃·76Ca_0.59Mg_0.21Fe_0.20CO₃ + 3.0 mol% SiO₂ + 1.6 mol% TiO₂ + 1.4 mol% Al₂O₃. Both melts remain stable to at least 1500 °C coexisting with CO₂ fluid and residual eclogite assemblage consisting of K-rich omphacite (0.4–1.5 wt% K₂O), almandine-pyrope-grossular garnet, kyanite, and coesite. The obtained immiscible alkali‑carbonatitic and potassic aluminosilicate melts resemble compositions of melt inclusions in diamonds worldwide. Thus, these melts entrapped by diamonds could be derived by partial melting of the carbonated material of the continental crust subducted down to 180–200 km depths. Given the high solubility of chlorides and water in both carbonate and aluminosilicate melts inferred in previous experiments, the saline end-member, brine, could evolve from potassic carbonatitic and/or silicic melts by fractionation of Ca-Mg carbonates/eclogitic minerals and accumulation of alkalis, chlorine and water in the residual low-temperature supercritical fluid. Direct extraction from the hydrated marine sediments under conditions of cold subduction would be another possibility for the brine formation.  相似文献   

Influence of shallow gas on the geotechnical properties of pockmark soil: A case study in the East China Sea     

《Applied Ocean Research》2019

Several incidents involving damage to submarine pipelines indicate that there will be potential hazards for many submarine structures if the geotechnical properties of the soil in pockmarks remain unclear. Based on a geophysical survey, geological drilling, in-situ measurement, and shallow gas eruption experiment, two large pockmarks near the Zhongjieshan Archipelago in the East China Sea were analyzed comprehensively. The geophysical and in-situ data indicated that the soil below the two pockmarks contains free or dissolved shallow gas, which continues to migrate upward from the deep zones, but there is no high-pressure gas reservoir in the pockmark soil. In-situ piezocone data, geotechnical results, and shallow gas eruption experiments have demonstrated that the pockmark soil has strengthened mechanical properties and zoning characteristics. After analyzing the pockmark soil in the area where the study was conducted, it was concluded that the pockmark soil in this area is not suitable for the accumulation of high-pressure, shallow gas. It also was concluded that the pockmark soil had stronger mechanical properties than virgin sediment due to the compaction of the soil caused by the eruption of the shallow gas. The zoning characteristics of pockmark soil are due to the regional differences in the ability of shallow gas to carry soil particles, which is a new finding that is worthy of attention in off-shore engineering.  相似文献   

Chemical evolution of seawater in the Transvaal Ocean between 2426 Ma (Ongeluk Large Igneous Province) and 2413 Ma ago (Kalahari Manganese Field)     

《Gondwana Research》2020

Drill core and outcrop samples of pure marine chemical sediments (banded iron formation (BIF), manganese formation (MnF), jaspilites, lutites, and cherts) from the transition of the ~2426 Ma old Ongeluk Formation into the 2413 Ma old Hotazel Formation, Transvaal Supergroup, South Africa, reveal remarkable changes of seawater chemistry in the Transvaal Ocean. Similar to pre-Ongeluk chemical sediments, the shale-normalized rare earths and yttrium (REY_SN) patterns of jaspilites intercalated with the volcanic rocks of the Ongeluk large igneous province and directly overlying cherts do not show positive Eu_SN anomalies, indicating that high-temperature (>250 °C) hydrothermal fluids did not contribute significantly to the REY budget of ambient waters. However, a 10 cm drill core section in the lower Hotazel Formation is characterized by conspicuous positive Eu_SN anomalies, revealing temporary inflow of water masses strongly affected by high-temperature hydrothermal fluids. After this short episode, the REY_SN pattern of Transvaal seawater returned to that of pre-Ongeluk times, showing heavy REY_SN enrichment, positive La_SN, Gd_SN and Y_SN anomalies, but no Ce_SN or Eu_SN anomalies. Higher up in the stratigraphy, the Hotazel Formation shows negative Ce_SN anomalies in some of the lutites, BIFs and MnFs, reflecting Ce depletion in ambient seawater. All Hotazel lutite, BIF, and MnF samples studied show unradiogenic εNd_(t) values (−0.5 ± 0.2 to −2.4 ± 0.2), indicating a mostly continental REY source. The REY distribution and Nd isotope data combined suggest that oxidative terrestrial weathering of this continental crustal source supplied most of the dissolved REY to local “Transvaal seawater”. Precipitation of the Hotazel lutites, BIFs and MnFs with negative Ce_SN anomalies, therefore, suggests that oxic conditions prevailed on the Kaapvaal Craton and in Hotazel seawater already at ~2.413 Ga, i.e. 80 m.y. before the disappearance of mass-independent sulfur isotope fractionation (MIF-S) that defines the Great Oxidation Event at ~2.33 Ga.  相似文献   

Freshwater Sources in the Bays of Yuzhnyi Island of the Novaya Zemlya Archipelago According to Isotopic (δD, δ18O) Data     

Kossova  S. A.  Dubinina  E. O.  Chizhova  Ju. N.  Miroshnikov  A. Yu. 《Doklady Earth Sciences》2020,492(2):475-479

Doklady Earth Sciences - An isotope–geochemical study was performed on the waters of Abrosimov and Stepovoi bays along the southeastern coasts of the Novaya Zemlya Archipelago. The waters...  相似文献   

Refined chronostratigraphy of the late Mesozoic terrestrial strata in South China and its tectono-stratigraphic evolution     

《Gondwana Research》2019

The late Mesozoic terrestrial strata in numerous basins in S (South) China provide important sedimentary archives to understand the tectonic evolution of S China and East Asia. However, establishing regional stratigraphic framework within a basin and precisely correlating strata among basins remain challenging due to limited chronological constraints. In this study, we report zircon U-Pb ages of 21 samples and a compilation of 132 reliable age data from 15 type sections of the volcanic-sedimentary basins in S China. The synthesized geochronology allows us to establish a refined chronostratigraphy for the late Mesozoic terrestrial strata. New calibrated results indicate that most of the lithostratigraphic units are diachronic, laterally stacking, and/or interfingering. Six stacking styles are classified for the relationship of lithostratigraphic units. Analysis of the refined chronostratigraphy and the stratal stacking styles, together with lithological composition, reveals three episodes of tectono-stratigraphic evolution. Episode I (~145–125 Ma) is characterized by intense volcanism, as evidenced by widespread occurrence of volcanic strata and (137–120 Ma) A-type granites, and was probably related to the rollback of the subducting Paleo-Pacific plate; The strata deposited during Episode II (~125–100 Ma) are composed of variegated sediments associated with/without volcanic intercalations in sedimentary faulted-depression basins, indicating the waning of volcanism and tectonism attributed to the ending of the Izanagi/Kula plate subduction; In Episode III (<~100 Ma), red strata occurred along the NE-SW sinistral strike-slip faulting or failed rifting in small basins, which probably resulted from the drastic directional change of the Paleo-Pacific plate subduction from NW to SN.  相似文献