Chemical structural models for coalified wood (vitrinite) in low rank coal     

Patrick G. Hatcher 《Organic Geochemistry》1990,16(4-6)

Examination of a series of coalified gymnospermous woods ranging in rank from brown coal to subbituminous coal by solid-state ¹³C NMR and analytical pyrolysis has provided sufficient information to construct structural models depicting the changes that occur to lignin, the primary precursor of vitrinite, during coalification. Progressive changes in the chemistry of coalified wood suggest the following series of reactions: (1) demethylation to form catechol-like structures that are dominant components of brown coal and lignite A; (2) cleavage of aryl ether linkages to form phenols and reactive carbocations that alkylate the catechol rings; (3) dehydration of the catechol rings; (3) dehydration of the catechol-like structures to form the structures of subbituminous coal dominated by alkylphenols; and (4) reduction of the 3-carbon alkyl side chain derived from lignin to form propyl substituents. The models developed for each stage of coalification are derived from chemical modifications of the structure of lignin.  相似文献   

Trace elements and mineral chemistry of silicified wood from Thailand: colours and elemental distribution     

S. Saminpanya 《Australian Journal of Earth Sciences》2016,63(7):873-884

Thai silicified woods were examined using electron probe microanalysis, yielding chemical data that characterised the samples into two groups: low and high silica contents (82—94 wt% and 94—98 wt%). The elements analysed in order of abundance include Si > Fe > Ca > Na > Al > Ti > K > Mg > Mn > Zr. Iron plays a major role in the colour range (red, orange, yellow, brown, grey and black) of the samples. Calcium is associated with Fe in the darker colours of the wood. Pseudo-crystallochemistry has been used for the substitution of trace elements for Si⁴⁺ in silica polymorphs. The atomic channels that run parallel to the c-axis of silica polymorphs or lattice defects, or even the charge balance for trivalent-ion substitution for Si⁴⁺, can accommodate monovalent ions (K⁺ and Na⁺). Vacant and atomic cavities, which are charged balanced by trivalent ions [Al³⁺ or Fe³⁺ substituting for Si⁴⁺], are commonly occupied by divalent ions (Ca²⁺, Mg²⁺ and Mn²⁺). Quadrivalent ions, Ti⁴⁺ and Zr⁴⁺ are non-structurally incorporated but form clusters of mineral inclusions in the samples. Several other trace-element contents are also in the form of mineral/fluid inclusions hosted in the woods.  相似文献   

Mats of Beggiatoa bacteria reveal that organic pollution from lumber mills inhibits growth of Zostera marina     

Joel K. Elliott  Erin Spear  & Sandy Wyllie-Echeverria 《Marine Ecology》2006,27(4):372-380

The objectives of this study were to determine the distribution and abundance of Zostera marina (eelgrass) in relation to the distribution of the mat forming bacteria Beggiatoa spp., and the levels of sulfide and organic material (wood waste) in the sediment. Underwater videography and intertidal surveys were used to map the distribution and abundance of Z. marina beds and Beggiatoa in the nearshore area of Commencement Bay, WA (USA), a location that has a long history of sawmill activity. Zostera marina occurred from the intertidal to ?6 m mean lower low water (MLLW) on sandy substrates in areas with low levels of sulfide (<50 μm ) and organic material (<5 % total volatile solids). Areas with high sulfide levels (>200 μm ) occurred where there were significant amounts of organic material in the sediments, which was found to be wood waste that had been discarded from sawmills. Zostera marina was absent from the intertidal and occurred at lower densities in areas with high sulfide levels. In contrast, mats of Beggiatoa were only found in areas where the sulfide levels were >1000 μm and there were significant deposits of wood. Thus, the negative correlation between the distribution and abundance of Z. marina and Beggiatoa suggests that the presence of Beggiatoa mats could be used as a biological indicator of inhibiting levels of hydrogen sulfide in the marine environment.  相似文献   

Environmental controls of wood entrapment in upper Midwestern streams     

Eric Christopher Merten  Jacques Finlay  Lucinda Johnson  Raymond Newman  Heinz Stefan  Bruce Vondracek 《水文研究》2011,25(4):593-602

Wood deposited in streams provides a wide variety of ecosystem functions, including enhancing habitat for key species in stream food webs, increasing geomorphic and hydraulic heterogeneity and retaining organic matter. Given the strong role that wood plays in streams, factors that influence wood inputs, retention and transport are critical to stream ecology. Wood entrapment, the process of wood coming to rest after being swept downstream at least 10 m, is poorly understood, yet important for predicting stream function and success of restoration efforts. Data on entrapment were collected for a wide range of natural wood pieces (n = 344), stream geomorphology and hydraulic conditions in nine streams along the north shore of Lake Superior in Minnesota. Locations of pieces were determined in summer 2007 and again following an overbank stormflow event in fall 2007. The ratio of piece length to effective stream width (length ratio) and the weight of the piece were important in a multiple logistic regression model that explained 25% of the variance in wood entrapment. Entrapment remains difficult to predict in natural streams, and often may simply occur wherever wood pieces are located when high water recedes. However, this study can inform stream modifications to discourage entrapment at road crossings or other infrastructure by applying the model formula to estimate the effective width required to pass particular wood pieces. Conversely, these results could also be used to determine conditions (e.g. pre‐existing large, stable pieces) that encourage entrapment where wood is valued for ecological functions. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Spatial variation in sap flow velocity in semiarid region trees: its impact on stand‐scale transpiration estimates     

Tomonori Kume  Kyoichi Otsuki  Sheng Du  Norikazu Yamanaka  Yi‐Long Wang  Guo‐Bin Liu 《水文研究》2012,26(8):1161-1168

In this study, we aimed to clarify spatial variations in xylem sap flow, and to determine the impacts of these variations on stand‐scale transpiration (E) estimates. We examined circumferential and radial variations in sap flow velocity (F_d) measured at several directions and depths in tree trunks of black locust (Robinia pseudoacacia) and native oak (Quercus liaotungensis), both of which have ring‐porous wood anatomy, in forest stands on the Loess Plateau, China. We evaluated the impacts of circumferential variations in F_d on stand‐scale transpiration estimates using a simple scaling exercise. We found significant circumferential variations in F_d in the outermost xylem in both species (coefficients of variation = 20–45%). For both species, F_d measured at the inner xylem was smaller than that of the outermost xylem and the F_d at the depth of > 10 mm was almost zero. The simple exercises showed that omitting circumferential variations in F_d affected the E estimate by 16–21%, which was less than the effects of omitting within‐tree radial and tree‐to‐tree variations in F_d in both species. These results suggest that circumferential variations in F_d can be a minor source of error for E estimates compared with within‐tree radial and tree‐to‐tree variations in F_d, regardless of the significant circumferential variations. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Spatial Integration,Adjustment, and Structural Transformation in Sub‐Saharan Africa: Some Linkage Pattern Changes in Ghana     

J. Henry Owusu 《The Professional geographer》2001,53(2):230-247

In 1983, Ghana embarked on a program of structural adjustment under the auspices of the World Bank and the International Monetary Fund, to resuscitate the economy and to foster development. This paper utilizes the Lagos Plan of Action, a comprehensive, continent‐wide effort and African‐led policy strategy for the economic development of the African continent, to examine the contribution of adjustment to the development of an integrated economy in Ghana. Adjustment is examined as a form of structural transformation, as evidenced by the emergent intranational (intra‐ and inter‐sectoral) and international linkages in the formal wood processing industry, a key sector with tremendous potential for such linkages. Intranationally, this study shows that, as in the pre‐adjustment years, inter‐sectoral linkages, although important, were not dynamic enough to play a significantly galvanizing role in the nation's economic development. However, intra‐sectorally, a dramatic expansion in lumber exports led to an unprecedented constriction in the traditional forward linkage between sawmills and downstream processors. This forced the latter to depend on the informal sector for inputs. Internationally, Ghanaian firms operated as subcontractors of convenience for firms overseas (particularly in Europe) via an expanded forward linkage, reflecting a new “colonial relationship” under the program.  相似文献   

The impact of small-scale wood harvesting on neem Azadirachta indica A. Juss stands in the coastal savanna of Ghana     

Michael O'Neal Campbell 《Area》2005,37(1):8-16

Although the introduced neem tree Azadirachta indica A. Juss is a very important energy source in the coastal savanna of Ghana, the sustainability of small-scale wood harvesting (SSWH) has not been investigated with regard to this species. This paper assesses the sustainability of SSWH on neem stands in the coastal savanna, using a socio-economic and ecological survey. The results show that SSWH, incorporating coppicing, stand tolerance, balanced with total bole cutting and root removal, and based on socio-cultural supports, has created a modified yet sustainable system of SSWH. It is concluded that these systems may contribute to tree stand conservation.  相似文献   

Large wood potential,piece characteristics,and flood effects in Swiss mountain streams     

Christian Rickli  Alexandre Badoux  Dieter Rickenmann  Nicolas Steeb  Peter Waldner 《自然地理学》2018,39(6):542-564

We present results of two studies on the (1) potential wood load in steep headwater streams and (2) properties of large wood (LW) transported in mountain rivers during the large August 2005 flood event in Switzerland. Ten headwater reaches of 1000 m length were surveyed in different regions of Switzerland. The potential wood load was estimated for in-channel deadwood, and possible driving factors were explored. Correlations were found with dead wood volume on hillslopes and mean channel width. We established size distributions of LW pieces and identified probable recruitment processes. Four reaches were resurveyed after an exceptionally severe flood in August 2005, showing limited LW transport in channels but considerable wood input by mass wasting processes. In addition, characteristics of deposits of LW along mountain rivers affected by the 2005 flood were investigated. Diameter and length distribution of transported and deposited pieces were comparable to those of LW from steep headwater streams, yet with considerably fewer long pieces in the deposits of mountain rivers. Most LW pieces were fresh wood, indicating that the portion of in-channel deadwood transported during the 2005 flood was limited. Findings of the study contribute to a better understanding of LW dynamics in Alpine mountain streams.  相似文献   

冀东铁精矿的物化性能测试   总被引：1，自引：0，他引：1  

亢立明李福民  刘曙光吕庆 《岩矿测试》2007,26(3):201-204

对冀东铁精矿进行了系统的物化性能测试。结果表明，铁精矿粒度较粗、颗粒表面光滑、比表面积小、SiO2含量较高。结合矿相结构分析了冀东铁精矿成球性能比较差的原因。采用3％的优质膨润土作铁精矿球团的黏结剂，制得球团的性能能够满足生产要求。  相似文献   

X射线荧光光谱法测定土壤样品中碳氮硫氯等31种组分   总被引：3，自引：3，他引：3  

徐海刘琦  王龙山 《岩矿测试》2007,26(6):490-492

利用新型的ZSX Primus Ⅱ型X射线荧光光谱仪采用粉末压片法直接测定土壤样品中的C、N、S、Cl等31种元素。各元素分析晶体为N采用RX45，C采用RX61，Na、Mg采用RX25，C1、S、P采用Ge，Si、Al采用PET，其余元素均采用LiF200。结果表明，方法的检出限、精密度和准确度对绝大多数元素而言，均可满足多目标地球化学调查样品分析的质量要求：  相似文献