Impacts of hydrous manganese oxide on the retention and lability of dissolved organic matter     

Jason W. Stuckey  Christopher Goodwin  Jian Wang  Louis A. Kaplan  Prian Vidal-Esquivel  Thomas P. BeebeJr.  Donald L. Sparks 《Geochemical transactions》2018,19(1):6

Minerals constitute a primary ecosystem control on organic C decomposition in soils, and therefore on greenhouse gas fluxes to the atmosphere. Secondary minerals, in particular, Fe and Al (oxyhydr)oxides—collectively referred to as “oxides” hereafter—are prominent protectors of organic C against microbial decomposition through sorption and complexation reactions. However, the impacts of Mn oxides on organic C retention and lability in soils are poorly understood. Here we show that hydrous Mn oxide (HMO), a poorly crystalline δ-MnO₂, has a greater maximum sorption capacity for dissolved organic matter (DOM) derived from a deciduous forest composite O_i, O_e, and O_a horizon leachate (“O horizon leachate” hereafter) than does goethite under acidic (pH 5) conditions. Nonetheless, goethite has a stronger sorption capacity for DOM at low initial C:(Mn or Fe) molar ratios compared to HMO, probably due to ligand exchange with carboxylate groups as revealed by attenuated total reflectance-Fourier transform infrared spectroscopy. X-ray photoelectron spectroscopy and scanning transmission X-ray microscopy–near-edge X-ray absorption fine structure spectroscopy coupled with Mn mass balance calculations reveal that DOM sorption onto HMO induces partial Mn reductive dissolution and Mn reduction of the residual HMO. X-ray photoelectron spectroscopy further shows increasing Mn(II) concentrations are correlated with increasing oxidized C (C=O) content (r = 0.78, P < 0.0006) on the DOM–HMO complexes. We posit that DOM is the more probable reductant of HMO, as Mn(II)-induced HMO dissolution does not alter the Mn speciation of the residual HMO at pH 5. At a lower C loading (2 × 10² μg C m^?2), DOM desorption—assessed by 0.1 M NaH₂PO₄ extraction—is lower for HMO than for goethite, whereas the extent of desorption is the same at a higher C loading (4 × 10² μg C m^?2). No significant differences are observed in the impacts of HMO and goethite on the biodegradability of the DOM remaining in solution after DOM sorption reaches steady state. Overall, HMO shows a relatively strong capacity to sorb DOM and resist phosphate-induced desorption, but DOM–HMO complexes may be more vulnerable to reductive dissolution than DOM–goethite complexes.  相似文献   

Evaluating Tidal Wetland Restoration Performance Using National Estuarine Research Reserve System Reference Sites and the Restoration Performance Index (RPI)     

Kenneth B. Raposa  Scott Lerberg  Craig Cornu  John Fear  Nina Garfield  Christopher Peter  Robin L.J. Weber  Gregg Moore  David Burdick  Michelle Dionne 《Estuaries and Coasts》2018,41(1):36-51

Evaluations of tidal wetland restoration efforts suffer from a lack of appropriate reference sites and standardized methods among projects. To help address these issues, the National Estuarine Research Reserve System (NERRS) and the NOAA Restoration Center engaged in a partnership to monitor ecological responses and evaluate 17 tidal wetland restoration projects associated with five reserves. The goals of this study were to (1) determine the level of restoration achieved at each project using the restoration performance index (RPI), which compares change in parameters over time between reference and restoration sites, (2) compare hydrologic and excavation restoration projects using the RPI, (3) identify key indicator parameters for assessing restoration effectiveness, and (4) evaluate the value of the NERRS as reference sites for local restoration projects. We found that the RPI, modified for this study, was an effective tool for evaluating relative differences in restoration performance; most projects achieved an intermediate level of restoration from 2008 to 2010, and two sites became very similar to their paired reference sites, indicating that the restoration efforts were highly effective. There were no differences in RPI scores between hydrologic and excavation restoration project types. Two abiotic parameters (marsh platform elevation and groundwater level) were significantly correlated with vegetation community structure and thus can potentially influence restoration performance. Our results highlight the value of the NERRS as reference sites for assessing tidal wetland restoration projects and provide improved guidance for scientists and restoration practitioners by highlighting the RPI as a trajectory analysis tool and identifying key monitoring parameters.  相似文献   

Magma evolution beneath Bequia,Lesser Antilles,deduced from petrology of lavas and plutonic xenoliths   总被引：1，自引：0，他引：1  

Michal?Camejo-HarryEmail authorView author&#;s OrcID profile  Elena?Melekhova  Jon?Blundy  William?Attridge  Richard?Robertson  Thomas?Christopher 《Contributions to Mineralogy and Petrology》2018,173(10):77

Extrusive and intrusive igneous rocks represent different parts of a magmatic system and ultimately provide complementary information about the processes operating beneath volcanoes. To shed light on such processes, we have examined and quantified the textures and mineral compositions of plutonic and cumulate xenoliths and lavas from Bequia, Lesser Antilles arc. Both suites contain assemblages of iddingsitized olivine, plagioclase, clinopyroxene and spinel with rare orthopyroxene and ilmenite. Mineral zoning is widespread, but more protracted in lavas than xenoliths. Plagioclase cores and olivine have high anorthite (An?≤?98) and low forsterite (Fo?≤?84) compositions respectively, implying crystallisation from a hydrous mafic melt that was already fractionated. Xenolith textures range from adcumulate to orthocumulate with variable mineral crystallisation sequences. Textural criteria are used to organize the xenoliths into six groups. Amphibole, notably absent from lavas, is a common feature of xenoliths, together with minor biotite and apatite. Bulk compositions of xenoliths deviate from the liquid line of descent of lavas supporting a cumulate origin with varying degrees of reactive infiltration by evolved hydrous melts, preserved as melt inclusions in xenolith crystals. Volatile saturation pressures in melt inclusions indicate cumulate crystallization over a 162–571 MPa pressure range under conditions of high dissolved water contents (up to 7.8 wt% H₂O), consistent with a variety of other thermobarometric estimates. Phase assemblages of xenoliths are consistent with published experimental data on volatile-saturated low-magnesium and high-alumina basalts and basaltic andesite from the Lesser Antilles at pressures of 200–1000 MPa, temperatures of 950–1050 °C and dissolved H₂O contents of 4–7 wt%. Once extracted from mid-crustal mushes, residual melts ascend to higher levels and undergo H₂O-saturated crystallization in shallow, pre-eruptive reservoirs to form phenocrysts and glomerocrysts. The absence of amphibole from lavas reflects instability at low pressures, whereas its abundance in xenoliths testifies to its importance in mid-crustal differentiation processes. A complex, vertically extensive (6 to at least 21 km depth) magmatic system is inferred beneath Bequia. Xenoliths represent fragments of the mush incorporated into ascending magmas. The widespread occurrence of evolved melts in the mush, but the absence of erupted evolved magmas, in contrast to islands in the northern Lesser Antilles, may reflect the relative immaturity of the Bequia magmatic system.  相似文献   

A Rhaetian microvertebrate fauna from Stowey Quarry,Somerset, U.K.     

Iacopo Cavicchini  H. Cecilia Heyworth  Christopher J. Duffin  Claudia Hildebrandt  Michael J. Benton 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(2):144-158

Rhaetian bone beds have been described from many locations in south-west England, around Bristol. One site that has never been reported is Stowey Quarry, some 13?km south of Bristol. This quarry yielded Lias, and revealed thin Rhaetian units in the quarry floor, including two bone beds, the basal Rhaetian bone bed, and a second, higher bone bed, also within the Westbury Formation. The fossil fauna of both includes elements typical of Rhaetian bone beds elsewhere, but showing differences in faunal composition between the two. The basal bone bed yielded more specimens and more species, with three taxa (Sargodon tomicus, Rhomphaiodon minor and Hybodus cloacinus) exclusive to this bed and eleven identified in total. Severnichthys acuminatus accounts for more than 50% of the countable teeth from the basal bone bed, followed by Gyrolepis albertii with 20%, Lissodus minimus with 14% and Rhomphaiodon minor with 9%. The basal bone bed, as ever, is dominated by chondrichthyans, whereas the upper bone bed is dominated by osteichthyans, which form 90% of the non-dental remains. The only unique taxon is Dapedium, and Gyrolepis albertii is the most abundant species with 45% of countable teeth, followed by Severnichthys acuminatus with 38% and Duffinselache holwellensis with 11%. These faunal differences, and the equally good condition of specimens between both samples confirms that the upper bone bed is independent of the basal bone bed, and is not a reworked subsample.  相似文献   

The Carboniferous coal swamp floras of England: a window on an ancient tropical ecosystem     

Christopher J. Cleal 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(3):329-351

England has an exceptional range of Westphalian—Stephanian (late Bashkirian—Moscovian) fossil floras spanning some 10 million years. They represent vegetation growing in part of a swamp that covered large areas of tropical Euramerica and which was responsible for the removal of vast quantities of carbon from the atmosphere. This coincided with significant global climatic cooling—the Late Palaeozoic Ice Age. The cratonic Pennine Basin in central and northern England has some of the best preserved fossil floras of this age anywhere in the world, especially notable being those of the Barnsley Thick Seam in Yorkshire and Derbyshire, the Bensham Seam in Northumberland and Durham, and the Coseley Ten Foot Ironstone in the West Midlands. The floras in southern England are mostly not as well preserved but include the historically important Radstock flora of Somerset. The taxonomic diversity dynamics of the fossil floras of the Pennine Basin are rather different from those seen in South Wales, probably due to differences in landscape and habitat, which in turn probably reflect the different tectonic settings. However, evidence of a significant change from lycophyte- to fern-dominated vegetation in latest Westphalian times, recognisable across Euramerica, can be seen in the English floras.  相似文献   

Post-eruptive lahars at Kali Putih following the 2010 eruption of Merapi volcano,Indonesia: occurrences and impacts     

Hadmoko  Danang Sri  de Belizal  Edouard  Mutaqin  Bachtiar Wahyu  Dipayana  Gilang Arya  Marfai  Muh Aris  Lavigne  Franck  Sartohadi  Junun  Worosuprojo  Suratman  Starheim  Colette C. A.  Gomez  Christopher 《Natural Hazards》2018,94(1):419-444

Following the 2010 VEI 4 eruption of Merapi volcano, more than 250 lahars were triggered during two rainy seasons from October 2010 to March 2012. This high number of post-eruption lahars mainly occurred in the Kali (valley) Putih watershed and was mostly associated with high-magnitude rainstorms. A lahar occurring on January 8, 2011, caused significant damage to homes in several communities, bridges, sabo dams, and agricultural crops. The aims of this contribution are to document the impacts of lahars on the Kali Putih watershed and specifically (1) to analyze the lahar frequency during the period of 1969–2012 on an inter-annual and intra-annual basis and to determine the link between the volume of tephra and the frequency of lahars; (2) to detail the lahar trajectory and channel evolution following the January 8th lahar; (3) to map the spatial distribution of the thickness and geomorphic effects of the lahar deposit; and (4) to determine the impacts of the lahar on the infrastructure (sabo dams and roads) and settlements in the distal area of the volcano. The Kali Putih watershed has experienced 62 lahars, which represent 22% of all lahars triggered on 17 rivers at Merapi between 2010 and 2012. The main geomorphic impacts are: (1) excessive sedimentation in valleys, settlements and agricultural areas; (2) undercutting of the river banks by as much as 50 m, accompanied by channel widening; and (3) abrupt changes in the river channel direction in the distal area (15–20 km downstream of the volcano). About 19 sabo dams were damaged, and 3 were totally destroyed. Over 307 houses were damaged, and the National Road Yogyakarta–Semarang was regularly cut (18 times during approximately 25 days). Although the sabo dams on Kali Putih were originally constructed to protect distal areas from lahar damage, they had little effect on the 2010–2012 rain-triggered lahars. The underlying design of those dams along this river is one of the main reasons for the major destruction in this sector of the volcano’s lower slope. The catch basin capacity of the sabo dam was only 1.75?×?10⁶ m³, whereas the total volume of the 2010–2011 lahars exceeded 5?×?10⁶ m³. In order to prepare for future lahars, the government has invested in significant mitigation measures, ranging from structural approaches (e.g., building new sabo dams and developing an early warning system) to non-structural approaches (e.g., contingency and preparedness planning and hazard education).

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A novel approach to leveraging social media for rapid flood mapping: a case study of the 2015 South Carolina floods     

Zhenlong Li  Cuizhen Wang  Christopher T. Emrich  Diansheng Guo 《制图学和地理信息科学》2018,45(2):97-110

Rapid flood mapping is critical for local authorities and emergency responders to identify areas in need of immediate attention. However, traditional data collection practices such as remote sensing and field surveying often fail to offer timely information during or right after a flooding event. Social media such as Twitter have emerged as a new data source for disaster management and flood mapping. Using the 2015 South Carolina floods as the study case, this paper introduces a novel approach to mapping the flood in near real time by leveraging Twitter data in geospatial processes. Specifically, in this study, we first analyzed the spatiotemporal patterns of flood-related tweets using quantitative methods to better understand how Twitter activity is related to flood phenomena. Then, a kernel-based flood mapping model was developed to map the flooding possibility for the study area based on the water height points derived from tweets and stream gauges. The identified patterns of Twitter activity were used to assign the weights of flood model parameters. The feasibility and accuracy of the model was evaluated by comparing the model output with official inundation maps. Results show that the proposed approach could provide a consistent and comparable estimation of the flood situation in near real time, which is essential for improving the situational awareness during a flooding event to support decision-making.  相似文献   

Late Quaternary chironomid community structure shaped by rate and magnitude of climate change     

Roseanna J. Mayfield  Peter G. Langdon  C. Patrick Doncaster  John A. Dearing  Rong Wang  Gaute Velle  Kimberley L. Davies  Stephen J. Brooks 《第四纪科学杂志》2021,36(3):360-376

Much is known about how climate change impacts ecosystem richness and turnover, but we have less understanding of its influence on ecosystem structures. Here, we use ecological metrics (beta diversity, compositional disorder and network skewness) to quantify the community structural responses of temperature-sensitive chironomids (Diptera: Chironomidae) during the Late Glacial (14 700–11 700 cal a bp ) and Holocene (11 700 cal a bp to present). Analyses demonstrate high turnover (beta diversity) of chironomid composition across both epochs; however, structural metrics stayed relatively intact. Compositional disorder and skewness show greatest structural change in the Younger Dryas, following the rapid, high-magnitude climate change at the Bølling–Allerød to Younger Dryas transition. There were fewer climate-related structural changes across the early to mid–late Holocene, where climate change was more gradual and lower in magnitude. The reduced impact on structural metrics could be due to greater functional resilience provided by the wider chironomid community, or to the replacement of same functional-type taxa in the network structure. These results provide insight into how future rapid climate change may alter chironomid communities and could suggest that while turnover may remain high under a rapidly warming climate, community structural dynamics retain some resilience.  相似文献   

Sedimentology of the continental end‐Permian extinction event in the Sydney Basin,eastern Australia     

Christopher R. Fielding  Tracy D. Frank  Allen P. Tevyaw  Katarina Savatic  Vivi Vajda  Stephen McLoughlin  Chris Mays  Robert S. Nicoll  Malcolm Bocking  James L. Crowley 《Sedimentology》2021,68(1):30-62

Upper Permian to Lower Triassic coastal plain successions of the Sydney Basin in eastern Australia have been investigated in outcrop and continuous drillcores. The purpose of the investigation is to provide an assessment of palaeoenvironmental change at high southern palaeolatitudes in a continental margin context for the late Permian (Lopingian), across the end‐Permian Extinction interval, and into the Early Triassic. These basins were affected by explosive volcanic eruptions during the late Permian and, to a much lesser extent, during the Early Triassic, allowing high‐resolution age determination on the numerous tuff horizons. Palaeobotanical and radiogenic isotope data indicate that the end‐Permian Extinction occurs at the top of the uppermost coal bed, and the Permo‐Triassic boundary either within an immediately overlying mudrock succession or within a succeeding channel sandstone body, depending on locality due to lateral variation. Late Permian depositional environments were initially (during the Wuchiapingian) shallow marine and deltaic, but coastal plain fluvial environments with extensive coal‐forming mires became progressively established during the early late Permian, reflected in numerous preserved coal seams. The fluvial style of coastal plain channel deposits varies geographically. However, apart from the loss of peat‐forming mires, no significant long‐term change in depositional style (grain size, sediment‐body architecture, or sediment dispersal direction) was noted across the end‐Permian Extinction (pinpointed by turnover of the palaeoflora). There is no evidence for immediate aridification across the boundary despite a loss of coal from these successions. Rather, the end‐Permian Extinction marks the base of a long‐term, progressive trend towards better‐drained alluvial conditions into the Early Triassic. Indeed, the floral turnover was immediately followed by a flooding event in basinal depocentres, following which fluvial systems similar to those active prior to the end‐Permian Extinction were re‐established. The age of the floral extinction is constrained to 252.54 ± 0.08 to 252.10 ± 0.06 Ma by a suite of new Chemical Abrasion Isotope Dilution Thermal Ionization Mass Spectrometry U‐Pb ages on zircon grains. Another new age indicates that the return to fluvial sedimentation similar to that before the end‐Permian Extinction occurred in the basal Triassic (prior to 251.51 ± 0.14 Ma). The character of the surface separating coal‐bearing pre‐end‐Permian Extinction from coal‐barren post‐end‐Permian Extinction strata varies across the basins. In basin‐central locations, the contact varies from disconformable, where a fluvial channel body has cut down to the level of the top coal, to conformable where the top coal is overlain by mudrocks and interbedded sandstone–siltstone facies. In basin‐marginal locations, however, the contact is a pronounced erosional disconformity with coarse‐grained alluvial facies overlying older Permian rocks. There is no evidence that the contact is everywhere a disconformity or unconformity.  相似文献   

Methodological challenges to confirmatory latent variable models of social vulnerability     

Goodman  Zachary T.  Stamatis  Caitlin A.  Stoler  Justin  Emrich  Christopher T.  Llabre  Maria M. 《Natural Hazards》2021,106(3):2731-2749

Natural Hazards - Socially vulnerable communities experience disproportionately negative outcomes following natural disasters and underscoring a need for well-validated measures to identify those...  相似文献