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   

The role of aerosols and greenhouse gases in Sahel drought and recovery     

Giannini  Alessandra  Kaplan  Alexey 《Climatic change》2019,152(3-4):449-466

Climatic Change - We exploit the multi-model ensemble produced by phase 5 of the Coupled Model Intercomparison Project (CMIP5) to synthesize current understanding of external forcing of Sahel...  相似文献   

A Lagrangian Particle Transport and Diffusion Model for Non-passive Scalars     

H. Kaplan 《Boundary-Layer Meteorology》2015,156(1):37-52

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Flooding of the continental shelves as a contributor to deglacial CH4 rise     

Andy Ridgwell  Mark Maslin  Jed O. Kaplan 《第四纪科学杂志》2012,27(8):800-806

The transition from the last glacial and beginning of Bølling–Allerød and Pre‐Boreal periods in particular is marked by rapid increases in atmospheric methane (CH₄) concentrations. The CH₄ concentrations reached during these intervals, ～650–750 ppb, is twice that at the last glacial maximum and is not exceeded until the onset of industrialization at the end of the Holocene. Periods of rapid sea‐level rise as the Last Glacial Maximum ice sheets retreated and associated with ‘melt‐water pulses’ appear to coincide with the onset of elevated concentrations of CH₄, suggestive of a potential causative link. Here we identify and outline a mechanism involving the flooding of the continental shelves that were exposed and vegetated during the glacial sea‐level low stand and that can help account for some of these observations. Specifically, we hypothesize that waterlogging (and later, flooding) of large tracts of forest and savanna in the Tropics and Subtropics during the deglacial transition and early Holocene would have resulted in rapid anaerobic decomposition of standing biomass and emission of methane to the atmosphere. This novel mechanism, akin to the consequences of filling new hydroelectric reservoirs, provides a mechanistic explanation for the apparent synchronicity between rate of sea‐level rise and occurrence of elevated concentrations of ice core CH₄. However, shelf flooding and the creation of transient wetlands are unlikely to explain more than ～60 ppb of the increase in atmospheric CH₄ during the deglacial transition, requiring additional mechanisms to explain the bulk of the glacial to interglacial increase. Similarly, this mechanism has the potential also to play some role in the rapid changes in atmospheric methane associated with the Dansgaard–Oeschger cycles. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

WIMPs and solar evolution code     

Yannick Giraud-Héraud  Jean Kaplan  François De Volnay Martin  Charling Tao  Sylvaine Turck-Chièze 《Solar physics》1990,128(1):21-33

The Saclay solar evolution code is used to check the effect of WIMPs on solar evolution. In this paper we study the effects of various types of Cosmion-matter interactions, give constraints on the crosssections compatible with the measured neutrino rate of 2 SNU on chlorine, and relate these constraints to ongoing dark matter detection experiments.Unité associée au CNRS UA 280, F-75251 Paris Cedex 05, France.On leave from LPC, Collège de France.  相似文献   

Growth pattern and 13C12C isotope fractionation of Cyanidium caldarium and hot spring algal mats     

J. Seckbach  I.R. Kaplan 《Chemical Geology》1973,12(3):161-169

A study was undertaken with the thermophilic green alga Cyanidium caldarium which grows optimally at low pH and high concentrations of CO₂. Carbon-isotope fractionation was not found to be a simple linear function of temperature. Maximum enrichment of ¹²C in cellular material occurred under optimum growth conditions (at approximately pH 2 and at temperatures between 40–50°C in a CO₂ atmosphere). A maximum measured fractionation of ?24‰ may account for low values ($\text{δ}{}^{13}\text{C}\text{< ?30‰}{}_{\mathrm{<mtext>PDB</mtext>}}$) in Precambrian kerogen presumably derived from algal mats.  相似文献   

Vertical and lateral transport of organic carbon and the carbon budget in Santa Monica Basin, California     

M.I. Venkatesan  I.R. Kaplan 《Progress in Oceanography》1992,30(1-4)

The flux and compositions of solvent-extractable lipid fractions were measured in particulate matter collected periodically by moored sediment traps in the Santa Monica Basin from 1985–1988. The purpose was to assess the compositional changes during settling, the carbon dynamics in the basin and to estimate the impacts of energy-related by-products on the surface sediments. Sediment traps recorded consistently high lipid fluxes in the eastern slope relative to the central basin, reflecting elevated terrigenous carbon inputs possibly from land-based human activities. Generally, lipid fluxes decrease offshore but increase vertically with water depth below 500m, implying lateral transport of particles. The steep decline of flux in the top 500m of the water is related to the rapid decomposition and mineralization of the marine-derived cellular carbon compounds. Less than 5% of the marine lipid components reach the seabed. In contrast, preferential preservation of terrigenous lipid is clearly evident from the chemistry of deeper traps and surface sediments.The lateral transport of particles is reflected in the presence of higher plant-derived lignin phenols and sewage-derived coprostanol and epicoprostanol in the deep trap material as well as in surface sediment throughout the basin. Petroleum triterpanes characteristic of natural seepage also permeates through the entire basin. Based on the data collected from both the trap particulte matter and surface sediments, a carbon budget for the Santa Monica Basin has been constructed.  相似文献   

Forum On Role Of Genetically Modified Organisms In The Future Of Food And Agriculture          下载免费PDF全文

David H. Kaplan  Antoinette M.G.A. Winklerprins 《Geographical review》2017,107(4):557-558

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Is there diversity in the New Urbanism? Analyzing the demographic characteristics of New Urbanist neighborhoods in the United States   总被引：1，自引：1，他引：0  

Dan Trudeau  Jeffrey Kaplan 《Urban geography》2016,37(3):458-482

The New Urbanism (NU) planning movement aspires to create socially diverse neighborhoods. It is unclear, however, whether this movement lives up to its aspirations in practice. In an effort to systematically examine this aspect of the movement, this paper analyzes age, family type, income, and race data of 70 NU neighborhoods in the United States. The paper uses a diversity index to compare the NU neighborhoods with control sites. Findings show that NU neighborhoods have lower racial diversity, but may have higher income diversity. Consideration of variations within the way NU is implemented reveals that the low racial diversity is associated with a single approach, but higher income diversity is associated with all variants. This paper argues that NU generates places that are more socially diverse than what is described in the literature and uses two case studies to explore the ways in which diversity is produced and its relation to gentrification.  相似文献   

Where Are the Women? Accounting for Discrepancies in Female Doctorates in U.S. Geography     

David H. Kaplan  Jennifer E. Mapes 《The Professional geographer》2016,68(3):427-435

Although there have been noticeable improvements in recent years, geography continues to be a predominantly male discipline. The percentage of women receiving PhDs in geography has tracked lower than the U.S. average of female PhDs. Previous studies of women's contribution to geography have focused on personal accounts or on the study of some of the most prominent practitioners, with a few studies using basic data on PhDs awarded and Association of American Geographers membership to determine trends. This article provides a comprehensive overview of doctoral degrees in geography by gender, over time, and across all universities in the United States by examining an alternative database, that of doctoral dissertations. The analysis yields three separate types of results. First, historical and contemporary variations among U.S. universities are examined. Second, data indicate that male and female doctoral students differ in the sex of their advisor. Third, a simple regression model explains some of the discrepancies in the proportion of female doctoral students by department. In sum, this article provides a comprehensive empirical study of the factors that might contribute to the continued disparities in female doctoral students in geography.  相似文献