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1.
Chromophoric dissolved organic matter (CDOM) is an important component in the aquatic environment and plays a key role in light attenuation and in carbon biogeochemical cycles. We examined CDOM production in each of two laboratory experiments in which phytoplankton and macrophyte degradation were monitored using absorption and excitation–emission matrix fluorescence spectroscopy (EEMs). During the incubation period, CDOM was produced from phytoplankton and macrophytes, and partly decomposed by microorganisms. The absorption spectra of the phytoplankton derived and the macrophyte derived CDOM were distinct and characterized by peaks and shoulders in the UV bands. Production of CDOM absorption at 350 nm, a(350), was 0.0125 m2/g per unit of chlorophyll a from phytoplankton CDOM from 0–3 d. Meanwhile a(350) production was 2.708 × 10−4 m2/g per unit of wet biomass from macrophytes CDOM from 1–7 d. Despite the high production of CDOM by phytoplankton and macrophytes, extrapolation of these values to the field indicated that about 15% of total CDOM was produced from phytoplankton during algal blooms in Meiliang Bay in summer and about 8% of total CDOM was produced from macrophytes in the macrophyte dominated littorals. The mean value of the spectral slope (S) describing the exponential decrease of the absorption spectrum, which was strongly correlated to an optical index of molecular size, for the phytoplankton derived CDOM was 10.26 ± 2.05 μm−1, which was significantly lower than the mean S of 14.47 ± 2.88 μm−1 for the macrophyte derived CDOM (t-test, p < 0.001). The mean value of the spectral slope ratio (SR) for the phytoplankton derived CDOM was 1.79 ± 0.52, which was significantly higher than that of 0.35 ± 0.58 for the macrophyte derived CDOM (t-test, p < 0.001). Three fluorescent components were validated in parallel factor analysis (PARAFAC) models calculated separately for phytoplankton derived and macrophyte derived CDOM, each CDOM source resulting in distinct excitation and emission maxima for each component. The significant differences in CDOM absorption spectra, S, SR and PARAFAC fluorescence component characteristics, all showed that phytoplankton derived CDOM was compositionally distinct from macrophyte derived CDOM. Overall both sources were important to the CDOM pool in the shallow temperate lake. 相似文献
2.
Spatial-seasonal dynamics of chromophoric dissolved organic matter in Lake Taihu, a large eutrophic, shallow lake in China 总被引：3，自引：0，他引：3
Yunlin Zhang Yan Yin Xiaohan Liu Zhiqiang ShiLongqing Feng Mingliang LiuGuangwei Zhu Zhijun GongBoqiang Qin 《Organic Geochemistry》2011,42(5):510-519
From 2005 to 2009, the spatial distribution and the seasonal dynamics of chromophoric dissolved organic matter (CDOM) were explored in Lake Taihu in eastern China. The spatial-seasonal dynamics of CDOM absorption and three CDOM composition variables, including spectral slope (S), spectral slope ratio (SR) and the M value, defined as the ratio of absorption at 250 nm/365 nm, were analyzed and discussed. Furthermore, river input processes and degradation of phytoplankton were studied to assess their impact on CDOM composition and the factors involved in the spatial-seasonal variability of CDOM. The CDOM absorption coefficient at a wavelength of 350 nm, a(350), ranged from 1.37-9.55 m−1 with a mean of 3.33 ± 1.32 m−1. Spatially, higher a(350) values, but lower spectral slope, spectral slope ratio and M values, were recorded in the northern algae dominated bays while lower values were recorded in southeastern macrophyte dominated bays. The a(350) was significantly higher in inshore waters than in offshore waters. Values of S, SR and M decreased during the flood and algal bloom season in spring and summer whereas a(350) increased. In the three river profiles, the gradual decrease of a(350) along the trajectory from the river mouth into the lake during the flood season showed the contribution of allochthonous CDOM. A laboratory phytoplankton degradation experiment was conducted to determine the contribution of CDOM production from phytoplankton. The significant increase of a(350) with time in the CDOM production experiment underlines the importance of autochthonous CDOM production during the algal bloom season. In summary, the significant increase of a(350) in spring and summer (algal bloom season) may be due to both the allochthonous CDOM input from the surrounding rivers and the autochthonous production of CDOM from degrading phytoplankton. 相似文献
3.
Recently we showed that visible-UV spectra in aqueous solution can be accurately calculated for arsenic (III) bisulfides, such as As(SH)3, As(SH)2S- and their oligomers. The calculated lowest energy transitions for these species were diagnostic of their protonation and oligomerization state. We here extend these studies to As and Sb oxidation state III and v sulfides and to polysulfides S n 2- , n = 2–6, the bisulfide anion, SH-, hydrogen sulfide, H2S and the sulfanes, S n H2, n = 2–5. Many of these calculations are more difficult than those performed for the As(iii) bisulfides, since the As and Sb(v) species are more acidic and therefore exist as highly charged anions in neutral and basic solutions. In general, small and/or highly charged anions are more difficult to describe computationally than larger, monovalent anions or neutral molecules. We have used both Hartree-Fock based (CI Singles and Time-Dependent HF) and density functional based (TD B3LYP) techniques for the calculations of absorption energy and intensity and have used both explicit water molecules and a polarizable continuum to describe the effects of hydration. We correctly reproduce the general trends observed experimentally, with absorption energies increasing from polysulfides to As, Sb sulfides to SH- to H2S. As and Sb(v) species, both monomers and dimers, also absorb at characteristically higher energies than do the analogous As and Sb(III)species. There is also a small reduction in absorption energy from monomeric to dimeric species, for both As and Sb III and v. The polysufides, on the other hand, show no simple systematic changes in UV spectra with chain length, n, or with protonation state. Our results indicate that for the As and Sb sulfides, the oxidation state, degree of protonation and degree of oligomerization can all be determined from the visible-UV absorption spectrum. We have also calculated the aqueous phase energetics for the reaction of S8 with SH- to produce the polysulfides, S n H-, n = 2–6. Our results are in excellent agreement with available experimental data, and support the existence of a S6 species. 相似文献
4.
收集了来自俄罗斯、新西兰、婆罗洲、马达加斯加、哥伦比亚和苏门答腊6个不同产地的柯巴树脂,采用宝石显微镜、红外光谱、紫外荧光观察和三维荧光光谱等测试方法对柯巴树脂谱学特征进行了对比研究。婆罗洲、苏门答腊柯巴树脂的红外光谱主要特征为存在3000~2800 cm-1范围内4个吸收峰,1732 cm-1肩峰和1708 cm-1吸收峰,888 cm-1处的弱吸收峰。新西兰柯巴树脂红外光谱主要特征为存在3000~2800 cm-1范围内3个吸收峰,1642 cm-1和888 cm-1处的弱吸收峰。马达加斯加、哥伦比亚和俄罗斯柯巴树脂的红外光谱相似,主要特征为存在与C=C相关的3处组合特征吸收峰以及1270 cm-1和1180 cm-1处的2个吸收峰。在长波紫外荧光下,婆罗洲和新西兰柯巴树脂荧光强度明显强于其他产地样品,马达加斯加柯巴树脂荧光强度最弱。由三维荧光光谱可知,婆罗洲和苏门答腊柯巴树脂中存在445、474、505 nm 3个发射峰,可被416、447 nm波长有效激发;新西兰柯巴树脂的最强发射峰位于385 nm,其最佳激发波长352 nm;俄罗斯柯巴树脂最强发射峰在399 nm,可被354 nm波长最佳激发;哥伦比亚柯巴树脂的最强发射峰为470 nm,被400 nm波长最佳激发;马达加斯加柯巴树脂的最强荧光峰在465 nm,被378 nm波长最佳激发。综合分析认为,三维荧光光谱特征和红外光谱特征可为柯巴树脂的鉴别和分类提供依据。 相似文献
5.
Y. Sadhuram V. V. Sarma T. V. Ramana Murthy B. Prabhakara Rao 《Journal of Earth System Science》2005,114(1):37-49
Physical and chemical characteristics of the Hooghly estuary during winter (December 1997–January 1998), summer (May 1998)
and post-monsoon (November 1998) seasons have been studied. Salinity varied spatially and temporally and seasonally during
ebb and flood tide conditions. Water temperature showed a difference of 10‡C in winter to summer. Temperature did not vary
much vertically as it is a well-mixed estuary. Strong currents exceeding 100 cm S-1 were observed during peak ebb and flood tide conditions irrespective of the season. Longitudinal eddy diffusion coefficient
(K
x
) was estimated as 757m S-1 and 811m2 S-1 during summer and post-monsoon seasons, respectively. The vertical eddy diffusion coefficient (εv) was estimated as 0.0337 m2 S-1 during post-monsoon season. The salinity and current observations are compared with those obtained from models reported earlier.
Values of pH, Dissolved Oxygen and Biological Oxygen Demand are within the threshold limits of the estuarine environment.
Nutrients show seasonal variation in the estuarine environment. High values (160-2686 mg l-1) of total suspended matter were noticed both at surface and bottom in the study region showing the impact of fresh water
and sediment transportation. 相似文献
6.
7.
Virender K. Sharma Ria A. Yngard Zoltan Homonnay Abhishek Dey Chun He 《Aquatic Geochemistry》2010,16(3):483-490
The kinetics of the formation of the purple-colored species between FeIII-EDTA and peroxynitrite were studied as a function of pH (10.4–12.3) at 22°C in aqueous solutions using a stopped-flow technique.
A purple-colored species was immediately formed upon mixing, which had an absorbance maximum at 520 nm. The increase in absorbance
with time could be fit empirically by a power function with two parameters a and b. The power equation determined was absorbance = a*t
b
, where a increased linearly with pH and the concentration of peroxynitrite, while b almost remained constant with a value of ~0.25. The molar extinction coefficient ε520 nm for the colored species was determined as 13 M−1cm−1, which is much lower than ε520 nm = 520 M−1 cm−1 for the [FeIII(EDTA)O2]3−, a purple species observed in the FeIII–EDTA–H2O2 system. The results of kinetics and spectral measurements of the present study are briefly discussed and compared with those
of the reaction between Fe(III)-EDTA and hydrogen peroxide. 相似文献
8.
The electrical conductivity in the temperature range from 298 to 873 K and the optical absorption in the spectral range from 4000 to 20000 cm-1 (at T = 298 K) of four natural samples of trioctahedral phyllosilicates with varying iron contents have been investigated. It is observed that the values of anisotropy systematically increase with increasing iron content. The increase in conductivity for the electrical field (E) polarized parallel to the (001) plane is explained by using a two dimensional percolation model with conducting paths related to the Fe ions in the octahedral layer of the structure. The conductivity perpendicular to the (001) plane is suggested to be due to defects (conducting bridges between the layers).The E (001) polarized absorption spectra exhibit a strong increase in the absorption with increasing wavenumbers with features at 9000, 12000 and 14000 cm-1. The E (001) polarized spectra show similar line profiles with, however, lower intensities and without the 14000 cm-1 feature. The analysis of the spectra is based on the model of small polaron absorption in disordered systems. The result shows that the polaron absorption is always the dominant contribution in the near infrared spectral range. A polaron stabilization energy of about 4800 cm-1 (0.6 eV) is deduced and is related to the energetical separation between Fe2+ and Fe3+ states. The 9000, 12000 and 14000 cm-1 features are superimposed to the polaron absorption. 相似文献
9.
H. Cynn A. M. Hofmeister P. C. Burnley A. Navrotsky 《Physics and Chemistry of Minerals》1996,23(6):361-376
Infrared absorption measurements were taken from 100 to 5000 cm?1 of a natural chondrodite and three dense hydrous magnesium silicates: phase A, phase B, and superhydrous phase B (shy-B). Raman spectra were also acquired from phase B and the chondrodite. Roughly half of the lattice modes are represented and our data are the first report of the low frequency modes. Comparison of our new spectra to symmetry analyses suggests that multiple sites for hydrogen exist for all the phases. The shy-B we examined crystallizes in P21 nm with two OH sites. Models for the density of states are constructed based on band assignments for the lattice modes and for the OH stretching vibrations. Heat capacity CP and entropy S calculated using Kieffer's formulation should be accurate within 3% from 200 to 800 K. Model values for CP at 298 K are 299.6 J/mol-K for chondrodite, 421.5 J/mol-K for phase A, 529.4 J/mol-K for shy-B, and 618.9 J/mol-K for phase B. Model values for S298 0 are 234.2 J/mol-K for chondrodite, 303.5 J/ mol-K for phase A, 377.9 J/mol-K for shy-B, and 473.3 J/mol-K for phase B. Debye temperatures are near 1000 K. 相似文献
10.
Solubility of Pt in sulphide mattes: Implications for the genesis of PGE-rich horizons in layered intrusions 总被引：1，自引：0，他引：1
Raúl O.C. Fonseca Ian H. Campbell Hugh St. C. O&#x;Neill Charlotte M. Allen 《Geochimica et cosmochimica acta》2009,73(19):5764-5777
The partitioning of Pt in sulphide melt (matte) has been studied as a function of fS2 and fO2 at 1200 and 1300 °C. The results show that the solubility of Pt in mattes increases strongly with increasing fS2 and decreases weakly with increasing fO2. The increase in Pt solubility with increasing fS2 is attributed to Pt dissolving in the melt as a sulphide species and the weak inverse dependence of Pt solubility on fO2 to the diluting effect of increasing O in the melt at high fO2. These results, coupled with measurements of Pt solubility in silicate melts taken from the literature, allow the calculation of Pt matte/silicate-melt partition coefficients () for a range of conditions pertinent to the formation of Pt-rich horizons in layered intrusions. The calculated values range between 107 and 1011, depending on fO2 and fS2, several orders of magnitude higher than previously published values. Our preferred value for for conditions appropriate to the Merensky Reef is 107 and for the Stillwater Pt-rich horizon 108. The new results are consistent with the magmatic hypothesis for Pt-rich horizons in layered intrusions. 相似文献
11.
基于相机摄影测量的冰面反照率反演方法研究 总被引：1，自引：1，他引：0
雪冰反照率是冰川与积雪能量平衡计算的关键参数,也是观测的难点. 为测量冰面反照率,试验采用相机摄影测量技术,在祁连山十一冰川开展了自动拍摄、并利用共线方程进行冰川正射制图,在此基础上于2012年7月28日-8月18日在冰川表面开展了不同海拔梯度的反照率观测. 通过统计分析晴天与阴天观测反照率与对应点相机拍摄获取的RGB归一化指数之间的关系,对十一冰川进行冰面反照率参数化方法研究. 结果表明：晴天冰面反照率与RGB归一化指数存在明显的指数关系,拟合R2达到0.79;而阴天的统计关系较差,线性拟合R2仅为0.52. 据此尝试利用晴天的拟合公式对整个冰面进行反照率参数化,计算表明：在晴天冰川表面地形阴影区的反照率存在低估现象,而无阴影区的反照率估算结果可信度较高. 利用2013年的反照率观测数据进行了参数化方案的验证,结果表明：观测值与模拟值平均误差仅为0.037,表明利用RGB影像对反照率参数化具有一定的可用性和可靠性. 相似文献
12.
Eunyoung Choe Kyoung-Woong Kim Sunbaek Bang In-Ho Yoon Keun-Young Lee 《Environmental Geology》2009,58(3):477-482
Reflectance spectroscopy covering the visible and near-infrared ranges (400–2,400 nm) is known as a rapid and nondestructive
method in the characterization and quantitative analysis of many components of interest. In this study, the potential use
of spectral absorption feature parameters (SAFPs) in the range of 400–2,400 nm was investigated in terms of the prediction
of heavy metals and mapping of their distribution. Parameters such as absorption depth, area, and peak ratio were derived
from variations in spectral absorption shape associated with concentrations of heavy metals. Heavy metals were quantified
from SAFPs using stepwise multiple linear regression (SMLR) and enter multiple linear regression (EMLR). The EMLR model showed
qualitative prediction performance for As and Cu, with R
2 values of 0.60 and 0.81, respectively. A contour map of As and Cu concentrations based on EMLR-derived values showed similar
spatial patterns to a map based on measured values. 相似文献
13.
δ 34S-values have been determined in 248 sulfide samples from different profiles through the ore bodies of the Sulitjelma pyrite-copper deposits. The values range for pyrite from ?4,1‰ to +9,2‰, but for an individual orebody the spread is generally much lower. Some profiles exhibit a systematic δ 34S decrease from the footwall to the hanging wall of the ore bodies, whereas laterally the S isotope composition in a distinct layer is rather uniform. Another trend from heavier to lighter sulfur exists from the center towards the margin of large porphyroblastic pyrite crystalls. Among the trace elements only the Co concentration in pyrite appears to be correlated with the δ-values. The sulfur-isotopic fractionation between coexisting sulfides is in agreement with the experience from other deposits, namely δ34Spyrite>δ34Spyrrhotite≈δ34Ssphalerite>δ34Schalcopyite 相似文献
14.
Xing Chen Wangsheng Chu Dongliang Chen Zhonghua Wu A. Marcelli Ziyu Wu 《Chemical Geology》2009,268(1-2):74-80
The local and geometrical structure around gold (III) e.g., Au3+ ions in aqueous solution with different OH−/Cl− molar ratios, has been investigated by X-ray absorption spectroscopy (XAS). X-ray absorption near-edge structure (XANES) spectra of [AuCln(OH)4−n]− solutions have been calculated and the multiple-scattering spectral features have been attributed to Cl d-states, axial water molecules and the replacement of Cl− ligands by OH− ligands. A square–planar geometry for [AuCln(OH)4−n]− with two axial water molecules has been identified. Moreover, a spectral correlation between XANES features and the type of planar atoms has been identified. By extended X-ray absorption fine structure spectra (EXAFS), the planar Au bond distances in the solutions have also been determined, e.g., 2.28 Å for Au–Cl and 1.98 Å for Au–O, respectively. The same EXAFS analysis provides evidence that the peak at about 4.0 Å in solutions with the lowest OH−/Cl− molar ratio arises from collinear Cl–Au–Cl multiple-scattering contributions. For the first time, a complete detailed reconstruction of the hydration structure of an Au ion at different pH values has been achieved. 相似文献
15.
16.
Karen Heymann Johannes Lehmann Dawit Solomon Michael W.I. Schmidt Thomas Regier 《Organic Geochemistry》2011,42(9):1055-1064
Black carbon (BC) is considered ubiquitous in soil organic matter (OM) and therefore plays an important role in soil biogeochemistry. Its complexity, particularly within environmental matrices, presents a challenge for research, primarily as a result of techniques which may favor detection of certain functional group types rather than capturing total sample C. The objective of this study was to utilize carbon (C) 1s near edge X-ray absorption fine edge structure (NEXAFS) spectroscopy to characterize the C chemistry of a broad range of BC materials. Characteristic resonances in the NEXAFS spectra allowed direct molecular speciation of the total C chemistry of the reference materials, environmental matrices and potentially interfering materials, obtained from an earlier BC ring trial. Spectral deconvolution was used to further identify the functional group distribution of the materials. BC reference materials and soils were characterized by a large aromatic C region comprising around 40% of total absorption intensity. We were able to distinguish shale and melanoidin from BC reference materials on the basis of their unique spectral characteristics. However, bituminous coal shared chemical characteristics with BC reference materials, namely high aromaticity of more than 40% identified by way of a broad peak. Lignite also shared similar spectra and functional group distributions to BC reference materials and bituminous coal. We compared the results of spectral deconvolution with the functional group distributions obtained by way of direct polarization magic angle spinning (DPMAS) 13C nuclear magnetic resonance (NMR) spectroscopy. Correlations between aromatic type C values for DPMAS 13C NMR and NEXAFS gave r2 = 0.633 (p < 0.05) and the values for NEXAFS were around 30–40% lower than for 13C NMR. Correlations were also drawn between the aromatic C/O-alkyl C ratio values for the two methods (r2 = 0.49, p < 0.05). Overall, NEXAFS was applicable for a wide range of environmental materials, such as those measured, although some limitations for the technique were addressed. 相似文献
17.
F. M. F. de Groot M. O. Figueiredo M. J. Basto M. Abbate H. Petersen J. C. Fuggle 《Physics and Chemistry of Minerals》1992,19(3):140-147
Ti 2p X-ray absorption spectra for a series of minerals have been measured. Crystal field multiplet calculations can explain the spectral shape. The asymmetry of the e
g
, peak is shown to be related to distortions of the Ti
IV
octahedron. It is found, theoretically as well as experimentally, that the absorption spectra are more sensitive to tetragonal distortions than to trigonal distortions. A number of silicate minerals and metamict minerals containing titanium are measured and Ti
III
has not been observed in any of these minerals. A comparison is made to the 1s X-ray absorption, and the potential of both for the study of minerals is discussed. 相似文献
18.
Natural specimens of green gemological euclase (chemical formula BeAlSiO4(OH)) from Brazil were investigated by electron paramagnetic resonance (EPR) and optical absorption. In addition to iron-related
EPR spectra, analyzed recently in blue and colorless euclase, chromium and vanadium-related EPR spectra were also detected
in green euclase. Their role as color causing centers is discussed. The results indicate that Cr3+ ions substitute for Al3+ ions in the euclase structure. The EPR rotation patterns of Cr3+ with electron spin S = 3/2 were analyzed with monoclinic spin Hamiltonian leading to the parameters of g
xx
, g
yy
and g
zz
equal to 2.018, 2.001 and 1.956 and electronic fine structure parameters of D = −8.27 GHz and E = 1.11 GHz, respectively, with high asymmetry ratio E/D = 0.13. For the vanadium-related EPR spectra the situation is different. It is concluded that vanadium is incorporated as
the vanadyl radical VO2+ with electron spin S = 1/2 with nearly axial spin Hamiltonian parameters gzz = 1.9447, g
xx
= 1.9740 g
yy
= 1.9669 and axial hyperfine interactions due to the nuclear spin I = 7/2 of the 51V isotope leading to A
zz
= 502 MHz, A
xx
= 150 MHz and A
yy
= 163 MHz. The green color of euclase is caused by two strong broad absorption bands centered at 17,185 and 24,345 cm−1 which are attributed to the 4A2g → 4T2g, 4T1g transitions of Cr3+, respectively. Vanadyl radicals may introduce some absorption bands centered in the near infrared with tail extending into
the visible spectral range. 相似文献
19.
依据烃源岩地球化学实验手段和油气地化理论,对辽东湾地区辽中凹陷东营组东二下段(Ed2-1)和东三段(Ed3)地层进行了有机地化分析。在实验获取总有机碳(TOC)、生烃潜量(S1+S2)、氢指数(IH)、氢碳比(H/C)、氧碳比(O/C)、最大热解峰温(Tmax)、镜质体反射率(Ro)等有机地化参数的基础上,对有机质丰度、类型、成熟度等进行了系统分析,同时对东营组烃源岩进行了综合评价。研究表明,东二下段S1+S2集中在0~3 mg/g,TOC集中在0%~1.5%;东三段S1+S2集中分布在4~9 mg/g之间,TOC集中分布在1%~1.25%。东二下段有机质类型主要是III型,东三段有机质类型为II1、II2型。东二下段Ro0.5,东三段Ro0.5,并且随着深度的增加东三段烃源岩Ro相应的增加。Tmax随着深度的增加呈现出先增加后减少的异常现象,该种异常现象出现的原因与烃源岩有机质类型和有机质丰度之间存在很大关联。 相似文献
20.
Richard A. Robie Bruce S. Hemingway Philippe Gillet B. Reynard 《Contributions to Mineralogy and Petrology》1991,107(4):484-486
The heat capacity of glaucophane from the Sesia-Lanza region of Italy having the approximate composition (Na1.93Ca0.05Fe0.02) (Mg2.60Fe0.41) (Al1.83Fe0.15Cr0.01) (Si7.92Al0.08)O22(OH)2 was measured by adiabatic calorimetry between 4.6 and 359.4 K. After correcting the C
p
0
data to values for ideal glaucophane, Na2Mg3Al2Si8O22(OH)2 the third-law entropy S
298
0
-S
0
0
was calculated to be 541.2±3.0 J·mol-1·K-1. Our value for S
298
0
-S
0
0
is 12.0 J·mol-1·K-1 (2.2%) smaller than the value of Likhoydov et al. (1982), 553.2±3.0, is within 6.2 J·mol-1·K-1 of the value estimated by Holland (1988), and agrees remarkably well with the value calculated by Gillet et al. (1989) from spectroscopic data, 539 J·mol-1·K-1. 相似文献