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1.
On the basis of different photosynthetic pathways.there is an obvious difference in δ^13C values between C3 and C4 plants,In terms of this characteristic,we analyzed the organic carbon content (forestlands:1.81%-16.00%;farmland:0.45%-2.22%) and δ^13C values(forestlands:-23.86‰--27.12‰;farmland:-19.66‰--23.26‰)of three profile-soil samples either in farmland or in forestland near the Maolan Karst virgin forest,where there were developed plant C3 plants previously and now are C4 plants.Results showed that the deforestation has accelerated the decomposition rate of soil organic matter and reduced the proportion of active components in soil organic matter and thus soil fertility.  相似文献   

2.
Study on Modern Plant C－13 in Western China and Its Significance   总被引：2，自引：0，他引：2  
Organic carbon isotopic composition(δ^13C) is one of the important proxies in paleoenvironment studies.In this paper modern plant δ^13C in the arid areas of China and Tibetan Plateau is studied.It is found that most terrestrial plant species in western China are C3 plants with δ^13C values ranging from -32.6‰ to -23.2‰ and only few species are C4 plants with δ^13C values from -16.8‰ to -13.3‰.The δ^13C is closely related to precipitation (or humidity),i.e., light δ^13C is related to high precipitation(or humid climate),while heavy δ^13C to low precipitation (or dry climate),but there is almost no relation between plant δ^13C and temperature.Submerged plants have δ^13C values ranging from -22.0‰ to -12.7‰,like C4 plants,while merged plants have δ^13C values ranging from -28.1‰ to -24.5‰，like C3 C4 plants,while marged plants have δ^13C values ranging from -28.1‰ to -24.5‰,like C3 plants.It can then be concluded that organic δ^13C variations in terrestrial sediments such as loeas and soil in western China can indicate precipitation changes,but those in lake sediments can reflect organic sources and the productivity of different types of aquatic plants.  相似文献   

3.
There is considerable discussion and uncertainty in the literature regarding the importance of fresh litter versus older soil organic matter as sources of soil dissolved organic carbon (DOC) in forest floor. In this study, the differences of organic carbon concentration and stable isotope composition were analyzed under different background conditions to identify the origins of DOC in forest soil. The data show that there is no significant difference in SOC content between these collected soil samples (P > 0.05), but the litter-rich surface soils have relatively higher DOC concentration than the litter-lacking (P < 0.01) ones, and the δ 13C values of DOC (δ 13CDOC) are closer to δ 13C of litter than δ 13C values of SOC (δ 13CSOC). In the litter-lacking surface soil samples, the range of δ 13CDOC is between δ 13CSOC and δ 13C of dominant plant leaves. These results suggest that DOC mainly derive from litter in the litter-rich surface soil with, and the main path of DOC sources may change with surrounding conditions. In addition, δ 13CSOC and δ 13CDOC become more positive, and the absolute values of Δ (δ 13CDOC − δ 13CSOC) decrease with depth in the soil profiles, which indicate that the percentage of DOC below 5 cm, derived from degradation of humus, may increase with soil depth.  相似文献   

4.
Natural gases of shallow reservoirs with the carbon isotopic compositions of methane ranging from -50‰ to -60‰ (PDB) were considered as mixed gases of biogenic and thermogenic origins previously and some of them were considered as low-mature (or low temperature thermogenic) gases lately. In this paper natural gases with the carbon isotopic compositions of methane in the above range were identified using the molecular and stable carbon isotopic compositions of methane, ethane and propane. The mixed gases of biogenic and mature thermogenic origins display the characteristics of δ 13 C1 ranging from -50‰to -60‰,δ13C2 ＞ -35‰,Δvalues (δ13C3 -δ13C2) ＜ 5‰ and C1/∑C2 ratios ＜ 40. Immature to low-mature gases display the characteristics of δ 13 C1 ranging from - 50‰ to - 60‰, δ13 C2 ＜- 40‰,Δ values (δ13C3 -δ13C2) ＞7‰, and C1/∑C 2 ratios ＞60.  相似文献   

5.
The stable carbon isotope composition in surface soil organic matter (δ13Csoil) contains integrative information on the carbon isotope composition of the standing terrestrial plants (δ13Cleaf). In order to obtain valuable vegetation information from the δ13C of terrestrial sediment, it is necessary to understand the relationship between the δ13C value in modern surface soil and the standing vegetation. In this paper, we studied the δ13C value in modern surface soil organic matter and standing vegetation in arid areas in China, Australia and the United States. The isotopic discrepancy between δ13Csoil and δ13Cleaf of the standing dominant vegetation was examined in those different arid regions. The results show that the δ13Csoil values were consistently enriched compared to the δ13Cleaf. The δ13Cleaf values were positively correlated with δ13Csoil, which suggests that the interference of microorganisms and hydrophytes on the isotopic composition of surface soil organic matter during soil organic matter formation could be ignored in arid regions. The averaged discrepancy between δ13Csoil and δ13Cleaf is about 1.71%in Tamarix L. in the Tarim Basin in China, 1.50% in Eucalytus near Orange in Australia and 1.22% in Artemisia in Saratoga in the United States, which are different from the results of other studies. The results indicate that the discrepancies in the δ13C value between surface soil organic matter and standing vegetation were highly influenced by the differences in geophysical location and the dominant species of the studied ecosystems. We suggest that caution should be taken when organic matter δ13C in terrestrial sediment is used to extract paleovegetation information (C3/C4 vegetation composition), as the δ13C in soil organic matter is not only determined by the ratio of C3/C4 species, but also profoundly affected by climate change induced variation in the δ13C in dominant species.  相似文献   

6.
This is the first study of δ13C values that considers elevational influences of the Qilian mountains of China. The δ13C values of different parts of the Qilian juniper (Sabina przewalskii Kom.) at different elevations of the Qilian mountains, China, were measured. Relatively constant differences in δ13C values existed between the tree leaves and the trunk wood. No strong dependency of δ13C values on elevation was found. The temporal changes of wood δ13C values with directions, elevations and height in the tree showed general similarity. These results suggest that the isotopic effects of environmental factors expressed initially at the site of photosynthesis, i.e., the leaves could be contained in the trunks of a tree. Regardless of elevation, direction or height in the tree, wood δ13C values have been decreasing during the past 60 years. A composite 600-year δ13C chronology developed from four trees showed that δ13C values remain relatively constant before 1800. After 1800 AD, however, δ13C values became significantly more negative. The trend in wood δ13C values was consistent with that obtained for δ13C values in atmospheric CO2. The results showed that for Qilian juniper, tree-ring δ13C chronology could be established to ascertain fluctuations of the atmospheric δ13C.  相似文献   

7.
The seasonal variation of foliar δ13C values in Sabina przewalskii Kom. and Sabina chinensis (Lin.) Ant. was measured. The relationships between foliar δ13C values and branch δ13C values as well as environmental factors (monthly total precipitation, monthly average air temperature, monthly average soil temperature, monthly total solar duration, relative humidity, atmospheric pressure, vapor pressure, wind speed and potential evaporation) were investigated. The results showed that the foliar δ13C values were negatively correlated with air pressure, and positively correlated with air temperature, precipitation, vapor pressure, potential evaporation, solar duration, wind speed and soil temperature. No significant relationship between δ13C values and relative humidity was detected. This demonstrates that the foliar δ13C of Sabina is a successful empirical indictor of these meteorological factors within the usual range of C3 whole-leaf δ13C values. Furthermore, the δ13C signature of leaf tissue is similar to that of wood tissue and the responses of δ13C values in S. przewalskii Kom. to environmental factors are also relatively stronger than that of S. chinensis (Lin.) Ant. These results provided strong evidence that it is feasible to extract climatic information from tree-ring δ13C series and S. przewalskii Kom. is a dendroclimatologically promising tree species.  相似文献   

8.
A series of samples, including vegetation, soil organic matter, soil waters, spring, bedrock, pool water, drip waters (upper-drip waters and ground-drip waters) and their corresponding speleothems were collected at Liangfeng Cave (LFC) system of Guizhou Province, southwest of China, respectively, from 2003 to 2004 year, then their stable carbon isotopes were measured and analyzed. Results reveal that vegetation is C3 type in LFC system; cave overlying δ 13C signals, including values and variations, could be transmitted to drip water (speleothem); speleothem δ 13C mainly shows a biogenic δ 13C value character (soil CO2 from plant respiration and decay); and there are remarkable seasonal variations of δ 13C values for drip water TDIC (speleothem), which are lighter at least 2.0‰ in the rainy seasons than in the dry ones. So, it could be feasible to reconstruct high-resolution changes of paleoecology and paleoclimate by using speleothem δ 13C values.  相似文献   

9.
Studies of carbonate carbon isotope of loess/paleosol (δ13Ccarb) in the Chinese Loess Plateau (CLP) have shown δ13Ccarb less negative in loess and more negative in paleosol, which is opposite to that of bulk organic matter. Although some mechanisms have been proposed to explain this inconsistency, few studies have been conducted to investigate how carbonate migration could affect the reliability of utilizing δ13Ccarb as an effective indicator. Here, a loess/paleosol profile with a nodule horizon intercalated in the loess layer, located on the southeastern edge of the CLP, was investigated to understand the influence of carbonate eluviation and reprecipitation on δ13Ccarb along the section. The mean grain size and magnetic susceptibility generally conform to the field observed loess/paleosol stratigraphy. However, carbonate content shows distinct differences in the two sides of the nodule horizon, clearly indicating eluviation along the section. The variation of carbon and oxygen isotopic compositions of soil carbonate (δ13CSC and δ18OSC) and nodule carbonate (δ13CNC and δ18ONC) along the profile does not present a clearly meaningful picture. Generally, δ13CSC and δ18OSC have a similar change trend along the profile and are positively correlated, but there is no apparent relationship between δ13CNC and δ18ONC. More importantly, δ18ONC values fall in the range of δ18OSC, whereas δ13CNC values are much more positive than δ13CSC. Detailed analyses of the data indicate migration of carbonate along the profile, which is an important factor that determines that loess/paleosol δ13Ccarb could not be employed as a high-resolution paleovegetational and paleoenvironmental indicator in the CLP, at least on or below the glacial/interglacial scales.  相似文献   

10.
Natural and anthropogenic impacts on karst ground water, Zunyi, Southwest China, are discussed using the stable isotope composition of dissolved inorganic carbon and particulate organic carbon, together with carbon species contents and water chemistry. The waters can be mainly characterized as HCO3–Ca type, HCO3 · SO4–Ca type, or HCO3 · SO4–Ca · Mg type, according to mass balance considerations. It is found that the average δ13CDIC values of ground waters are higher in winter (low-flow season) than in summer (high-flow season). Lower contents of dissolved inorganic carbon (DIC) and lower values of δ13CDIC in summer than in winter, indicate that local rain events in summer and a longer residence time of water in winter play an important role in the evolution of ground water carbon in karst flow systems; therefore, soil CO2 makes a larger contribution to the DIC in summer than in winter. The range of δ13CDIC values indicate that dissolved inorganic carbon is mainly controlled by the rate of carbonate dissolution. The concentrations of dissolved organic carbon and particulate organic carbon in most ground water samples are lower than 2.0 mg C L−1 and 0.5 mg C L−1, respectively, but some waters have slightly higher contents of organic carbon. The waters with high organic carbon contents are generally located in the urban area where lower δ13CDIC values suggest that urbanization has had an effect on the ground water biogeochemistry and might threaten the water quality.  相似文献   

11.
In this study, two sediment cores (~70 cm) were collected from separate mangrove forests straddling the Ba Lat Estuary, Red River of northern Vietnam, to examine the origins of sedimentary organic carbon (SOC) and reconstruct the paleoenvironment. In addition, mangrove leaves and particulate organic matter were collected and measured for δ13C to trace the origins of SOC. The cores were analyzed by high-resolution sections for δ13C, TOC, C/N ratios, sediment grain size, water content, and porosity, with values of δ13C, TOC, and C/N ratios ranging from −28.19 to −22.5‰, 2.14–30.94 mg/g, and 10.29–18.32, respectively. The δ13C and TOC relationship indicated that there were some small residual effects of diagenetic processes on TOC and δ13C values in mangrove sediments. However, the shifts of δ13C and C/N ratios from the bottom to the surface sediment of the cores explained the change in organic matter sources, with values of C/N > 12 and δ13C < −25‰, and C/N < 12 and δ13C > −25‰ indicated terrestrial (e.g., mangrove litter) and marine phytoplankton sources, respectively. The covarying δ13C, C/N ratios, and sediment grain sizes during the past 100 years in sediment cores showed that the paleoenvironment may be reconstructed into three environments (subtidal, tidal flat, and intertidal mangrove). General trends in δ13C and C/N followed a gradual increase in the C/N ratio and a concomitant decrease in δ13C from the subtidal, through to tidal flat, and to the intertidal mangrove. δ13C and C/N ratios are therefore effective in measuring the continuum of environmental change in mangrove ecosystem.  相似文献   

12.
High resolution carbon isotopic records in millennial, centennial and decadal timescales from three stalagmites from three different caves under a similar monsoon climate in Guangxi–Guizhou, China, provided detailed information on the paleo-ecological environmental conditions in the past 15,000 years. The results indicate that during the glacial period, or cold-dry period, such as Heinrich event H1 and Younger Dryas event karst development was poor as was pedogenesis, C3 vegetation didn’t grow well, resulting in C4 plants dominating and with heavy δ13C values in stalagmites. In a warm-humid stage, C3 vegetation grew well and predominated with negative δ13C values. The δ13C records from stalagmites could be indicative of sensitive vegetation changes and reflective of climate changes in precipitation, temperature, etc. The δ13C records may also be used to distinguish different effects from nature or human activity. Particularly since the late Holocene, human activities have increased disturbances to environment, even more than natural factors. Forest vegetation was destroyed, C4 plants became dominant, and rock desertification was aggravated because of severe water and soil loss, all resulting in sharply increasing δ13C values of stalagmites that are heavier than pre-middle Holocene δ13C values.  相似文献   

13.
Xinglongtai field has been an important petroleum-producing area of Liaohe Depression for 30 years. Oil exploration and production were the focus of this field, but the gas was ignored. This study examined twenty five gas samples with the purpose of determining the gas genetic types and their geochemical characteristics. Molecular components, stable carbon isotopic compositions and light hydrocarbons were also measured, and they proved that microbial activity has attacked some of the gas components which resulted in unusual carbon isotopic distributions. Propane seems to be selectively attacked during the initial stage of microbial alteration, with abnormally lower con-tent compared to that of butane as well as anomalously heavy carbon isotope. As a consequence, the carbon isotopic distribution among the gas components is partially reverse, as δ13C1<δ13C2<δ13C3>δ13C4. Besides, n-alkanes of C3+ gas components are preferentially attacked during the process of microbial alteration. This is manifested that n-alkanes are more enriched in 13C than corresponding iso-alkanes. As a result, the concentrations of n-alkanes be-come very low, which may be misleading in indentifying the gas genetic types. As to four gas samples, light hydro-carbon compositions display evidence for microbial alteration. The sequence of hexane isomers varies obviously with high content of 2,3-DMC4, which indicates that they have been in the fourth level of extensively bacterial al-teration. So the geochemical characteristics can be affected by microbial alteration, and recognition of microbial alteration in gas accumulations is very important for interpreting the natural gas genetic types.  相似文献   

14.
Primary producer (angiosperms, macroalgae, submerged aquatic vegetation), suspended particulate matter, andFundulus heteroclitus isotope values (δ13C, δ15N, δ34S) were examined to assess their use as indicators for changes in food web support functions in tidally-restored salt marshes. Study sites, located throughout the southern New England region (USA), ranged fromSpartina alterniflora-dominated reference marshes, marshes under various regimes and histories of tide restoration, and a severely tide-restrictedPhragmites australis marsh.Fundulus δ13C values were greater for fish from referenceSpartina marshes than for fish from adjacent tide-restricted or tide-restored marshes where higher percent cover of C3 plants, lower water column salinities, and more negative dissolved inorganic δ13C values were observed. The difference inFundulus δ13C values between a tide-restrictedPhragmites marsh and an adjacent referenceSpartina marsh was great compared to the difference between marshes at various stages of tide restoration and their respective reference marshes, suggesting that food web support functions are restored as the degree of tidal restriction is lessened. While a multiple isotopic approach can provide valuable information for determining specific food sources to consumers, this study demonstrates that monitoringFundulus δ13C values alone may be useful to evaluate the trajectory of ecological change for marshes undergoing tidal restoration.  相似文献   

15.
In order to investigate the distribution characteristics of stable carbon isotope ratios (δ 13C) in the desert plant Reaumuria soongorica, the δ 13C values of leaves were measured in 407 individuals of 21 populations. Soil physicochemical properties including soil water content, soil total dissolved solids, soil total nitrogen, soil total phosphorus and soil organic content were also analyzed in order to survey the major factors influencing δ 13C values on spatial variation. Leaves and soil samples were simultaneously collected from the ten major distribution areas in Northwest China at altitudes from 394 m to 1 987 m above sea level, at latitudes from 36°10′N to 44°33′N, and at longitudes from 81°43′E to 106°37′E. These ten areas include Shihezi, Baicheng, Yiwu areas in Xinjiang Uygur Autonomous Region; Anxi, Zhangye, Baiyin, Lanzhou areas in Gansu Province; Shapotou, Yinchuan areas in Ningxia Hui Autonomous Region; and Alashan County in Inner Mongolia Autonomous Region. The results show that the δ 13C value of R. soongorica ranges from −22.77‰ to −29.85‰ with an average of −26.52‰. Foliar d13C values in R. soongorica are not significantly correlated with altitude, latitude or longitude, and a spatial distribution trend of d13C values of R. soongorica is not obvious on a large scale. However, when d13C values of two R. soongorica populations under the same climate conditions are compared, δ 13C values increase obviously from east to west and from north to south. As none of the soil total dissolved solids, soil total nitrogen, soil total phosphorus, and soil organic content shows a uniform trend from east to west and from north to south, we suppose that the small-scaled spatial distribution pattern of δ 13C values of R. soongorica is mainly controlled by the soil water content. Translated from Quaternary Sciences, 2006, 26(6): 947–954 [译自: 第四纪研究]  相似文献   

16.
Total dissolved inorganic carbon (TDIC) and its stable isotope ratio δ13CTDIC are used to trace the evolution of the carbon system of groundwater in three UK Permo-Triassic sandstone aquifers. Samples were collected from multilevel piezometers, open boreholes and sewer sampling points in the British Midlands (Nottingham, Birmingham and Doncaster) to evaluate both local and regional variations in δ13CTDIC. δ13C samples of matrix and pore water have also been analysed in each aquifer to further constrain the interpretations. Combining δ13CTDIC ratios with measurements of TDIC and pH clearly distinguishes the principal processes underlying the geochemical evolution of groundwater in Triassic sandstone aquifers, where processes can be both natural (e.g. carbonate dissolution) and anthropogenic (sewer-derived recharge). The paper shows that δ13CTDIC resolves ambiguities that arise from the interpretation of TDIC and pH measurements in isolation. Field measurements demonstrate that, under natural conditions, the carbonate system evolves similarly in each aquifer. An open-system evolution during recharge largely saturates the groundwater with carbonate depending upon its availability in the sandstone matrix. The contribution of sewer exfiltration to urban recharge is readily distinguished by lower pH and higher TDIC values without significant changes in δ13CTDIC.  相似文献   

17.
Morphological characters and multi-element isotopic compositions of carbonates from the loess-paleosol sequences in Northwestern China are examined to explore the origin of the minerals. Samples are collected from various sections ranging from Holocene to 0.9 Ma within the sequences and fractions with grain sizes >45 and <2 μm are separated from the bulk soil and examined by SEM and TEM. The results show that the grains >45 μm exhibit an almost perfect spherical shape while those <2 μm are dominated by nano-rods having diameters of 30-50 nm and lengths of 0.3-2 μm, presumably indicating the detrital origin of the coarse fractions and the authigenic characters of the fine ones. Such implications are corroborated by the multi-elemental isotopic compositions of the carbonate minerals. A comparison of the δ13C and δ18O values between minerals and biologically originated samples indicates that the <2 μm fractions have a similar composition to those of coexisting land snail shells. Additional differences between the two size fractions also manifest in the ratios of 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, and 87Sr/86Sr. These results suggest the utility of fine carbonate particles in the soil profile in reconstructing a potentially higher resolution δ13C and δ18O time series to elucidate the paleoclimatic fluctuation in the Chinese Loess Plateau during Pleistocene. The discovery of the nano-rod calcite in Chinese loess, together with previous findings of the similar mineral form in Asian dust, strongly suggests the possibility that these highly reactive CaCO3 form may alter the aerosol properties during transport.  相似文献   

18.
1 Introduction China’s widespread marine carbonate rock series are mostly characterized by intensive thermal evolution and low abundance of organic matter, especially the Lower Paleozoic carbonate rocks have experienced multi-episodes of tectonics and ap…  相似文献   

19.
The relation of two well-known ancient carbonate deposits to hydrocarbon seepage was confirmed by this study. Archaea are found to be associated with the formation of Oxfordian seep carbonates from Beauvoisin and with a Miocene limestone from Marmorito ("tube-worm limestone"). Carbonates formed due to a mediation by archaea exhibit extremely positive or extremely negative δ13Ccarbonate values, respectively. Highly positive values (+15‰) reflect the use of 13C-enriched CO2 produced by methanogenesis. Low δ13C values of the Marmorito carbonates (–30‰) indicate the oxidation of seepage-derived hydrocarbons. Likewise, the δ13C content of specific tail-to-tail linked isoprenoids, biomarkers for archaea, was found to be strikingly depleted in these samples (as low as –115‰). The isotopic signatures corroborate that archaea were involved in the cycling of seepage-derived organic carbon at the ancient localities. Another Miocene limestone ("Marmorito limestone") shows a strong imprint of methanotrophic bacteria as indicated by δ13C values of carbonate as low as –40‰ and biomarker evidence. Epifluorescence microscopy and field-emission scanning electron microscopy revealed that bacterial biofilms were involved in carbonate aggregation. In addition to lucinid bivalves previously reported from both localities, we infer that sponges from Beauvoisin and tube worms from Marmorito depended on chemosynthesis as well. Low δ13C values of nodules related to sponge taphonomy (–27‰) indicate that sponges might have been linked to an enhanced hydrocarbon oxidation. Tube worm fossils from Marmorito closely resemble chemosynthetic pogonophoran tube worms from Recent cold seeps and are embedded in isotopically light carbonate (δ13C –30‰). Received: 13 October 1998 / Accepted: 5 February 1999  相似文献   

20.
Mollusk shells contain geochemical information about environmental conditions that prevailed at the time of formation. We investigated ontogenetic and seasonal variations of δ13C in calcitic shells of Pecten maximus. Ontogenetic variations of δ13Cshell in three large specimens collected in Norway, France, and Spain exhibited a similar linear decrease with increasing shell height. We removed this linear drift (detrending). These three residual time series displayed variations that could be linked to environmental fluctuations. To check it, we reanalyzed the isotopic datasets of Lorrain et al. (Journal of Experimental Marine Biology and Ecology 275:47–61, 2002, Geochimica et Cosmochimica Acta 68:3509–3519, 2004), who worked on three scallops harvested in 2000 in the bay of Brest (France), a well-monitored ecosystem. Lowest values of δ13Cshell detrended were recorded in all shells in late spring–early summer, most likely reflecting corresponding variations in food availability. Our results indicate that ontogenetic and seasonal variations of δ13Cshell cannot be used as a proxy for past δ13CDIC variations but should be considered as promising tools for ecophysiological studies.  相似文献   

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