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1.
The aim of this research was to measure the rate of carbon dioxide (CO2) exchange between the soil and atmosphere in the inter-tidal forest floor of the Indian Sundarbans mangrove ecosystem and to study its response with soil temperature and soil water content. Soil CO2 effluxes were monitored every month at two stations (between April, 2011 and March, 2012); one situated at the land–ocean boundary of the Bay of Bengal (outer part of the mangrove forest) and the other lying 55 km inshore from the coast line (inner part of the mangrove forest). The static closed chamber technique was implemented at three inter-tidal positions (landward, seaward and bare mudflats) in each station. Fluxes were measured in the daytime every half an hour by circulating chamber headspace air through a sampling manifold assembly and a closed-path non-dispersive infrared gas analyser. The fluxes ranged between 0.15 and 2.34 μmol m?2 s?1 during the annual course of sampling. Effluxes of higher magnitude were measured during summer; however, it abruptly decreased during the monsoon. CO2 flux from the forest floor was strongly related to soil temperature, with the highest correlation found with temperature at 2 cm depth. No such significant relationship between soil water content and CO2 efflux could be properly ascertained; however, excessively high soil water content was found to be the only reason which hampered the rate of effluxes during the monsoon. On the whole, landward (LW) sites of the mangrove forest emitted more than the seaward (SW) sites. Q 10 values (obtained from simple exponential model) which denote the multiplicative factor by which the efflux rate increases for a 10 °C rise in temperature ranged between 2.07 and 4.05.  相似文献   

2.
In situ carbon flux measurements and calculated burial rates are utilized to construct an organic carbon budget for the upper meter of sediment at a single station in Cape Lookout Bight, a small marine basin located on the Outer Banks of North Carolina, U.S.A. (34°37′N, 76°33′W). Of 149 ± 20 mole · m?2 · yr?1 of total organic carbon deposited, 35.6 ± 5.2 mole · m?2 · yr?1 is recycled to overlying waters, 84 ± 18% as ∑CO2 and 16 ± 8% as CH4. Approximately 68 ± 20% of the upward carbon flux is supported by sulfate reduction while 32 ± 16% takes place as the result of underlying methanogenesis. Measured ∑CO2 and CH4 sediment-water fluxes range seasonally from 1900–6300 and 50–2500 μmole · m?2 · hr?1 respectively.The mean residence time of metabolizable organic carbon in the upper 80 cm of sediment is approximately four months with greater than 98% of the calculated total remineralization taking place within three years. In spite of large upward fluxes of methane, larger molecules derived from metabolizable sedimentary organic carbon appear to be the dominant reductants for dissolved sulfate.  相似文献   

3.
Numerous studies of marine environments show that dissolved organic carbon (DOC) concentrations in sediments are typically tenfold higher than in the overlying water. Large concentration gradients near the sediment–water interface suggest that there may be a significant flux of organic carbon from sediments to the water column. Furthermore, accumulation of DOC in the porewater may influence the burial and preservation of organic matter by promoting geopolymerization and/or adsorption reactions. We measured DOC concentration profiles (for porewater collected by centrifugation and “sipping”) and benthic fluxes (with in situ and shipboard chambers) at two sites on the North Carolina continental slope to better understand the controls on porewater DOC concentrations and quantify sediment–water exchange rates. We also measured a suite of sediment properties (e.g., sediment accumulation and bioturbation rates, organic carbon content, and mineral surface area) that allow us to examine the relationship between porewater DOC concentrations and organic carbon preservation. Sediment depth-distributions of DOC from a downslope transect (300–1000 m water depth) follow a trend consistent with other porewater constituents (ΣCO2 and SO42−) and a tracer of modern, fine-grained sediment (fallout Pu), suggesting that DOC levels are regulated by organic matter remineralization. However, remineralization rates appear to be relatively uniform across the sediment transect. A simple diagenetic model illustrates that variations in DOC profiles at this site may be due to differences in the depth of the active remineralization zone, which in turn is largely controlled by the intensity of bioturbation. Comparison of porewater DOC concentrations, organic carbon burial efficiency, and organic matter sorption suggest that DOC levels are not a major factor in promoting organic matter preservation or loading on grain surfaces. The DOC benthic fluxes are difficult to detect, but suggest that only 2% of the dissolved organic carbon escapes remineralization in the sediments by transport across the sediment-water interface.  相似文献   

4.
Net ecosystem metabolism (NEM) was measured in the Piauí River estuary, NE Brazil. A mass balance of C, N, and P was used to infer its sources and sinks. Dissolved inorganic carbon (DIC) concentrations and fluxes were measured over a year along this mangrove dominated estuary. DIC concentrations were high in all estuarine sections, particularly at the fluvial end member at the beginning of the rainy season. Carbon dioxide concentrations in the entire estuary were supersaturated throughout the year and highest in the upper estuarine compartment and freshwater, particularly at the rainy season, due to washout effects of carbonaceous soils and different organic anthropogenic effluents. The estuary served as a source of DIC to the atmosphere with an estimated flux of 13 mol CO2 m?2 year?1. Input from the river was 46 mol CO2 m?2 year?1. The metabolism of the system was heterotrophic, but short periods of autotrophy occurred in the lower more marine portions of the estuary. The pelagic system was more or less balanced between auto- and heterotrophy, whereas the benthic and intertidal mangrove region was heterotrophic. Estimated annual NEM yielded a total DIC production in the order of 18 mol CO2 m?2 year?1. The anthropogenic inputs of particulate C, N, and P, dissolved inorganic P (DIP), and DIC were significant. The fluvial loading of particulate organic carbon and dissolved inorganic nitrogen (DIN) was largely retained in two flow regulation and hydroelectric reservoirs, promoting a reduction of C:N and C:P particulate ratios in the estuary. The net nonconservative fluxes obtained by a mass balance approach revealed that the estuary acts as a source of DIP, DIN, and DIC, the latter one being almost equivalent to the losses to the atmosphere. Mangrove forests and tidal mudflats were responsible for most of NEM rates and are the main sites of organic decomposition to sustain net heterotrophy. The main sources for this organic matter are the fluvial and anthropogenic inputs. The mangrove areas are the highest estuarine sources of DIP, DIC, and DIN.  相似文献   

5.
在2001年秋季对贵州省荔波县茂兰国家喀斯特森林公园林地、草地植被下土壤CO2呼吸释放及岩溶表层泉水HCO3及其δ13C值的变化进行了日动态的野外监测,表明岩溶系统中土-气-水界面间存在着碳交换的日动态变化以及所伴随的同位素交换的变化,这种变化与土温的日动态有密切的关系。林地植被显示了平抑这种日动态幅度的效应,而草地植被则显示响应于温度变化的较灵敏的动态变化。这种短尺度的变化构成了表层岩溶系统对外界条件的灵敏响应,进一步揭示了在生物作用下岩溶地质作用在碳循环过程及其同位素交换上的灵敏性和动态性。其不同植被系统下的日动态差异在解释岩溶沉积记录和讨论岩溶作用与碳循环时值得充分注意  相似文献   

6.
Release of CO2 from surface ocean water owing to precipitation of CaCO3 and the imbalance between biological production of organic matter and its respiration, and their net removal from surface water to sedimentary storage was studied by means of a quotient θ = (CO2 flux to the atmosphere)/(CaCO3 precipitated). θ depends not only on water temperature and atmospheric CO2 concentration but also on the CaCO3 and organic carbon masses formed. In CO2 generation by CaCO3 precipitation, θ varies from a fraction of 0.44 to 0.79, increasing with decreasing temperature (25 to 5°C), increasing atmospheric CO2 concentration (195–375 ppmv), and increasing CaCO3 precipitated mass (up to 45% of the initial DIC concentration in surface water). Primary production and net storage of organic carbon counteracts the CO2 production by carbonate precipitation and it results in lower CO2 emissions from the surface layer. When atmospheric CO2 increases due to the ocean-to-atmosphere flux rather than remaining constant, the amount of CO2 transferred is a non-linear function of the surface layer thickness because of the back-pressure of the rising atmospheric CO2. For a surface ocean layer approximated by a 50-m-thick euphotic zone that receives input of inorganic and organic carbon from land, the calculated CO2 flux to the atmosphere is a function of the CaCO3 and Corg net storage rates. In general, the carbonate storage rate has been greater than that of organic carbon. The CO2 flux near the Last Glacial Maximum is 17 to 7×1012 mol/yr (0.2–0.08 Gt C/yr), reflecting the range of organic carbon storage rates in sediments, and for pre-industrial time it is 38–42×1012 mol/yr (0.46–0.50 Gt C/yr). Within the imbalanced global carbon cycle, our estimates indicate that prior to anthropogenic emissions of CO2 to the atmosphere the land organic reservoir was gaining carbon and the surface ocean was losing carbon, calcium, and total alkalinity owing to the CaCO3 storage and consequent emission of CO2. These results are in agreement with the conclusions of a number of other investigators. As the CO2 uptake in mineral weathering is a major flux in the global carbon cycle, the CO2 weathering pathway that originates in the CO2 produced by remineralization of soil humus rather than by direct uptake from the atmosphere may reduce the relatively large imbalances of the atmosphere and land organic reservoir at 102–104-year time scales.  相似文献   

7.
The quantification of carbon burial in lake sediments, and carbon fluxes derived from different origins are crucial to understand modern lacustrine carbon budgets, and to assess the role of lakes in the global carbon cycle. In this study, we estimated carbon burial in the sediment of Lake Qinghai, the largest inland lake in China, and the carbon fluxes derived from different origins. We find that: (1) The organic carbon burial rate in lake sediment is approximately 7.23 g m−2 a−1, which is comparable to rates documented in many large lakes worldwide. We determined that the flux of riverine particulate organic carbon (POC) is approximately 10 times higher than that of dissolved organic carbon (DOC). Organic matter in lake sediments is primarily derived from POC in lake water, of which approximately 80% is of terrestrial origin. (2) The inorganic carbon burial rate in lake sediment is slightly higher than that of organic carbon. The flux of riverine dissolved inorganic carbon (DIC) is approximately 20 times that of DOC, and more than 70% of the riverine DIC is drawn directly and/or indirectly from atmospheric CO2. (3) Both DIC and DOC are concentrated in lake water, suggesting that the lake serves as a sink for both organic and inorganic carbon over long term timescales. (4) Our analysis suggests that the carbon burial rates in Lake Qinghai would be much higher in warmer climatic periods than in cold ones, implying a growing role in the global carbon cycle under a continued global warming scenario.  相似文献   

8.
《Atmósfera》2014,27(1):61-76
The Carbon Tracker system will play a major role in understanding CO2 sinks and sources, gas exchange between the atmosphere and oceans, and gas emissions from forest fres and fossil fuels in Latin America and the Caribbean. This paper discusses the trends in carbon fluxes in the biosphere and ocean, as well as emissions from forest fres and fossil fuel use in the above-mentioned region, using the Carbon Tracker (CT) system. From 2000 to 2009, the mean carbon fluxes for the biosphere, fossil fuel use, wildfires and the ocean in Latin America and the Caribbean were −0.03, 0.41, 0.296, −0.061 Pg C/yr, respectively, and −0.02, 0.117, 0.013, −0.003 Pg C/yr, respectively, in Mexico. The mean net carbon flux for Latin America and the Caribbean was 0.645 Pg C/yr, and 0.126 Pg C/yr for Mexico. The terrestrial sinks in Latin America and the Caribbean are dominated by the forest, agricultural, grass and shrub regions, as well as the Andes mountain range and the net surface-atmosphere fluxes including fossil fuel are dominant in regions around large cities in Mexico, Brazil, Chile, and areas undergoing deforestation along the Amazon River. The results confirm that forest fres are an important source of CO2 in Latin America and the Caribbean. In addition, we can confirm that policies encouraging the use of ethanol in light vehicles in Brazil have helped to decrease carbon emissions from fossil fuel, and assume the effects of the Proárbol program on carbon sinks from the biosphere and from fire emissions sources in Mexico. Based on this analysis, we are confident that the CT system will play a major role in Latin America and the Caribbean as a scientific tool to understand the uptake and release of CO2 from terrestrial ecosystems, fossil fuel use and the oceans, and for long-term monitoring of atmospheric CO2 concentrations.  相似文献   

9.
We report the results of a 5-year fertilization experiment in a central Long Island Sound salt marsh, aimed at understanding the impacts of high nutrient loads on marsh elevational processes. Fertilization with nitrogen led to some significant changes in marsh processes, specifically increases in aboveground primary production and in CO2 fluxes from the soil. However, neither nitrogen nor phosphorus fertilization led to elevation loss (relative to controls), reduced soil carbon, or a decrease in belowground primary production, all of which have been proposed as links between elevated nutrient loads and marsh drowning. Our data suggest that high nutrient levels increase gross carbon loss from the sediment, but that this is compensated for by other processes, leading to no net deleterious effect of nutrient loading on carbon storage or on marsh stability with respect to sea level rise.  相似文献   

10.
土壤碳蓄积量变化的影响因素研究现状   总被引：37，自引：2，他引：37  
土壤碳库的动态平衡影响作物产量和土壤肥力的高低，是土壤肥力保持和提高的重要研究内容。简要评述了土壤理化特性、温度和降水变化、大气CO2浓度上升、人类的农业活动对土壤有机碳蓄积量的影响，介绍了当前对土壤碳蓄积量动态变化的研究进展，认为应加强气候变化和土地利用/土地覆被变化与土壤碳循环研究的结合，提高对陆地生态系统碳循环变化的认识，并需要从生态环境保护的利益和可持续发展的理论出发，进一步加强土地管理方式的改变，促进土壤有机质的积累，提高土壤对碳的固定。  相似文献   

11.
Mangrove water biogeochemistry has been frequently studied under tropical climates, but less is known regarding mangroves in semi-arid climates. In this study, we examine the carbon and nutrient biogeochemistry in a mangrove tidal creek and in the main branch of a semi-arid estuary in New Caledonia. Porewater seepage represents a source of nutrients (DON, NH4 +, and DIP), carbon (DOC and CO2), and alkalinity for the water column, but seawater dilution of the mangrove inputs is observed. Spatial and tidal variations in CO2 fluxes along the tidal creek suggest that porewater seepage is a driver of CO2 emission into the atmosphere. Large seasonal and spatial differences in the biogeochemical functioning of the main channel are observed and are mainly related to the seasonal rainfall pattern. During the rainy season, the watershed influences the entire estuary, which exhibits a typical positive circulation. During the dry season, the estuary turns into a salt-plug region with positive and negative circulations in the upper and lower reaches, respectively. In this case, the upper and lower reaches seem to function independently, and the biogeochemical functioning of their water column is not controlled by the same processes. Surprisingly, pCO2@27 °C values tend to be higher during the dry season, as do the total alkalinity (TAlk) values, while the pH values exhibit an opposite trend. Moreover, the TAlk values are higher in the lower reaches during the wet season and in the upper reaches during the dry season. These results indicate high in situ biogeochemical reactions and high porewater influence during the dry season, likely because of a low flushing rate and high water residence time after salt plug establishment. Although our results suggest that salt plugs may significantly affect the water column’s biogeochemistry and may promote CO2 emissions of mangrove-derived carbon, further investigations, especially mass balance studies, are required to quantify their role in the biogeochemical functioning of such estuarine systems.  相似文献   

12.
We used enclosures to quantify wetland-water column nutrient exchanges in a dwarf red mangrove, (Rhizophora mangle L.) system near Taylor River, an important hydraulic linkage between the southern Everglades and eastern Florida Bay, Florida, USA. Circular enclosures were constructed around small (2.5–4 m diam) mangrove islands (n=3) and sampled quarterly from August 1996 to May 1998 to quantify net exchanges of carbon, nitrogen, and phosphorus. The dwarf mangrove wetland was a net nitrifying environment with consistent uptake of ammonium (6.6–31.4 μmol m−2 h−1) and release of nitrite +nitrate (7.1–139.5 μmol m−2 h−1) to the water column. Significant flux of soluble reactive phosphorus was rarely detected in this nutrient-poor, P-limited environment. We did observe recurrent uptake of total phosphorus and nitrogen (2.1–8.3 and 98–502 μmol m−2 h−1, respectively), as well as dissolved organic carbon (1.8–6.9 μmol m−2 h−1) from the water column. Total organic carbon flux shifted unexplainably from uptake, during Year 1, to export, during Year 2. The use of unvegetated (control) enclosures during the second year allowed us to distinguish the influence of mangrove vegetation from soil-water column processes on these fluxes. Nutrient fluxes in control chambers typically paralleled the direction (uptake or release) of mangrove enclosure fluxes, but not the magnitude. In several instances, nutrient fluxes were more than twofold greater in the absence of mangroves, suggesting an influence of the vegetation on wetland-water column processes. Our findings characterize wetland nutrient exchanges, in a mangrove forest type that has received such little attention in the past, and serve as baseline data for a system undergoing hydrologic restoration.  相似文献   

13.
The distribution of mangrove biomass and forest structure along Shark River estuary in the Florida Coastal Everglades (FCE) has been correlated with elevated total phosphorus concentration in soils thought to be associated with storm events. The passage of Hurricane Wilma across Shark River estuary in 2005 allowed us to quantify sediment deposition and nutrient inputs in FCE mangrove forests associated with this storm event and to evaluate whether these pulsing events are sufficient to regulate nutrient biogeochemistry in mangrove forests of south Florida. We sampled the spatial pattern of sediment deposits and their chemical properties in mangrove forests along FCE sites in December 2005 and October 2006. The thickness (0.5 to 4.5 cm) of hurricane sediment deposits decreased with distance inland at each site. Bulk density, organic matter content, total nitrogen (N) and phosphorus (P) concentrations, and inorganic and organic P pools of hurricane sediment deposits differed from surface (0–10 cm) mangrove soils at each site. Vertical accretion resulting from this hurricane event was eight to 17 times greater than the annual accretion rate (0.30 ± 0.03 cm year−1) averaged over the last 50 years. Total P inputs from storm-derived sediments were equivalent to twice the average surface soil nutrient P density (0.19 mg cm−3). In contrast, total N inputs contributed 0.8 times the average soil nutrient N density (2.8 mg cm−3). Allochthonous mineral inputs from Hurricane Wilma represent a significant source of sediment to soil vertical accretion rates and nutrient resources in mangroves of southwestern Everglades. The gradient in total P deposition to mangrove soils from west to east direction across the FCE associated with this storm event is particularly significant to forest development due to the P-limited condition of this carbonate ecosystem. This source of P may be an important adaptation of mangrove forests in the Caribbean region to projected impacts of sea-level rise.  相似文献   

14.
We estimated CO2 and CH4 emissions from mangrove-associated waters of the Andaman Islands by sampling hourly over 24 h in two tidal mangrove creeks (Wright Myo; Kalighat) and during transects in contiguous shallow inshore waters, immediately following the northeast monsoons (dry season) and during the peak of the southwest monsoons (wet season) of 2005 and 2006. Tidal height correlated positively with dissolved O2 and negatively with pCO2, CH4, total alkalinity (TAlk) and dissolved inorganic carbon (DIC), and pCO2 and CH4 were always highly supersaturated (330–1,627 % CO2; 339–26,930 % CH4). These data are consistent with a tidal pumping response to hydrostatic pressure change. There were no seasonal trends in dissolved CH4 but pCO2 was around twice as high during the 2005 wet season than at other times, in both the tidal surveys and the inshore transects. Fourfold higher turbidity during the wet season is consistent with elevated net benthic and/or water column heterotrophy via enhanced organic matter inputs from adjacent mangrove forest and/or the flushing of CO2-enriched soil waters, which may explain these CO2 data. TAlk/DIC relationships in the tidally pumped waters were most consistent with a diagenetic origin of CO2 primarily via sulphate reduction, with additional inputs via aerobic respiration. A decrease with salinity for pCO2, CH4, TAlk and DIC during the inshore transects reflected offshore transport of tidally pumped waters. Estimated mean tidal creek emissions were ～23–173 mmol m?2 day?1 CO2 and ～0.11–0.47 mmol m?2 day?1 CH4. The CO2 emissions are typical of mangrove-associated waters globally, while the CH4 emissions fall at the low end of the published range. Scaling to the creek open water area (2,700 km2) gave total annual creek water emissions ～3.6–9.2?×?1010 mol CO2 and 3.7–34?×?107 mol CH4. We estimated emissions from contiguous inshore waters at ～1.5?×?1011 mol CO2?year?1 and 2.6?×?108 mol CH4?year?1, giving total emissions of ～1.9?×?1011 mol CO2?year?1 and ～3.0?×?108 mol CH4?year?1 from a total area of mangrove-influenced water of ～3?×?104 km2. Evaluating such emissions in a range of mangrove environments is important to resolving the greenhouse gas balance of mangrove ecosystems globally. Future such studies should be integral to wider quantitative process studies of the mangrove carbon balance.  相似文献   

15.
Carbon dioxide (CO2) emission from the river-type reservoir is an hotspot of carbon cycle within inland waters. However, related studies on the different types of reservoirs are still inadequate. Therefore, we sampled the Three Gorges Reservoir (TGR), a typical river-type reservoir having both river and lake characteristics, using an online system (HydroCTM/CO2) and YSI-6600v2 meter to determine the partial pressure of carbon dioxide (pCO2) and physical chemical parameters in 2013. The results showed that the CO2 flux from the mainstream ranged from 26.1 to 92.2 mg CO2/m2 h with average CO2 fluxes of 50.0 mg/m2 h. The CO2 fluxes from the tributary ranged from ?10.91 to 53.95 mg CO2/m2 h with area-weighted average CO2 fluxes of 11.4 mg/m2 h. The main stream emits CO2 to the atmosphere the whole year; however, the surface water of the tributary can sometimes act as a sink of CO2 for the atmosphere. As the operation of the TGR, the tributary became more favorable to photosynthetic uptake of CO2 especially in summer. The total CO2 flux was estimated to be 0.34 and 0.03 Tg CO2/year from the mainstream and the tributaries, respectively. Our emission rates are lower than previous estimates, but they are in agreement with the average CO2 flux from temperate reservoirs estimated by Barros et al. (Nat Geosci 4(9):593–596, 2011).  相似文献   

16.
Despite their primary contribution to climate change, there are still large uncertainties on the sources and sinks of the main greenhouse gases: carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). A better knowledge of these sources is necessary to understand the processes that control them and therefore to predict their variations. Indeed, large feedbacks between climate change and greenhouse gas fluxes are expected during the 21st century. Sources and sinks of these gases generate spatial and temporal gradients that can be measured either in situ or from space. One can then estimate the surface fluxes, either positive or negative, from concentration measurements through a so-called atmospheric inversion. Surface measurements are currently used to estimate the fluxes at continental scales. The high density of spaceborne observations allows potentially a much higher resolution. Several remote sensing techniques can be used to measure atmospheric concentration of greenhouse gases. These techniques have motivated the development of spaceborne instruments, some of them already in space and others under development. However, the accuracy of the current estimates is still not sufficient to improve our knowledge on the greenhouse gases sources and sinks. Rapid improvements are expected during the forthcoming years with a strong implication of the scientific community and the launch of dedicated instruments, optimized for the measurement of CO2 and CH4 concentrations.  相似文献   

17.
In global carbon cycle models, orogenesis is often viewed as a sink for atmospheric CO2, acting on tectonic timescales. However, recent attempts to quantify fluxes for CO2 produced by metamorphic reactions and released to the atmosphere suggest that these are an order‐of‐magnitude greater than CO2 uptake by chemical weathering of silicate minerals, and that metamorphic CO2 is released on millennial timescales. These hypotheses have gained support from both measurements of CO2 emissions from present‐day orogenic hot springs and chromatographic modelling of carbonation reactions in metamorphic rocks from ancient orogens. In this article I review research that attempts to quantify metamorphic CO2 release fluxes, focussing specifically on studies conducted in the SW Scottish Highlands.  相似文献   

18.
Studies of the δ13C of pore water dissolved inorganic carbon (δ13C-DIC) were carried out in shallow water carbonate sediments of the Great Bahamas Bank (GBB) to further examine sediment-seagrass relationships and to more quantitatively describe the couplings between organic matter remineralization and sediment carbonate diagenesis. At all sites studied δ13C-DIC provided evidence for the dissolution of sediment carbonate mediated by metabolic CO2 (i.e., CO2 produced during sediment organic matter remineralization); these observations are also consistent with pore water profiles of alkalinity, total DIC and Ca2+ at these sites. In bare oolitic sands, isotope mass balance further indicates that the sediment organic matter undergoing remineralization is a mixture of water column detritus and seagrass material; in sediments with intermediate seagrass densities, seagrass derived material appears to be the predominant source of organic matter undergoing remineralization. However, in sediments with high seagrass densities, the pore water δ13C-DIC data cannot be simply explained by dissolution of sediment carbonate mediated by metabolic CO2, regardless of the organic matter type. Rather, these results suggest that dissolution of metastable carbonate phases occurs in conjunction with reprecipitation of more stable carbonate phases. Simple closed system calculations support this suggestion, and are broadly consistent with results from more eutrophic Florida Bay sediments, where evidence of this type of carbonate dissolution/reprecipitation has also been observed. In conjunction with our previous work in the Bahamas, these observations provide further evidence for the important role that seagrasses play in mediating early diagenetic processes in tropical shallow water carbonate sediments. At the same time, when these results are compared with results from other terrigenous coastal sediments, as well as supralysoclinal carbonate-rich deep-sea sediments, they suggest that carbonate dissolution/reprecipitation may be more important than previously thought, in general, in the early diagenesis of marine sediments.  相似文献   

19.
One possible way of mitigating carbon dioxide (CO2) emissions from fossil fuel combustion is using carbon dioxide capture and storage (CCS) technology. However, public perception concerning CO2 storage in the geosphere is generally negative, being particularly motivated by perceived leakage risks. Therefore, a main issue when attempting to gain public acceptance is ensuring provision of appropriate monitoring practices, aimed at providing health, safety and environmental risk assessment, so that potential risks from CO2 storage are minimized. Naturally occurring CO2 deposits provide unique natural analogues for evaluating and validating methods used for the detection and monitoring of CO2 spreading and degassing into the atmosphere. Geological and hydrological structures of the Cheb Basin (NW Bohemia, Czech Republic) represent such a natural analogue for investigating CO2 leakage and offer a perfect location at which to verify monitoring tools used for direct investigation of processes along preferential migration paths. This shallow basin dating from the Tertiary age is characterized by up to 300?m thick Neogene sediment deposits and several tectonically active faults. The objectives of this paper are to introduce the CO2 analogues concept to present the Eger Rift as a suitable location for a natural CO2 analogue site and to demonstrate to what extent such an analogue site should be used (with a case study). The case study presents the results obtained from a joint application of geoelectrical measurements in combination with soil CO2 concentration and flux determination methods, for the detection and characterization of natural CO2 releases at gas seeps (as part of a hierarchic monitoring concept). To highlight discharge-controlling structural near surface features was the initial motivation for the application of geoelectrical measurements. Soil-gas concentration and flux measurement techniques are relatively simple to employ and are valuable methods that can be used to monitor seeping CO2 along preferential pathways. Joint interpretation of both approaches yields a first insight into fluid paths and reveals that the thickness and permeability of site-specific near surface sedimentary deposits have a great influence upon the spatial distribution of the CO2 degassing pattern at surface level.  相似文献   

20.
全球变化条件下的土壤呼吸效应   总被引：52，自引：7，他引：52  
土壤呼吸是陆地植物固定CO2尔后又释放CO2返回大气的主要途径，是与全球变化有关的一个重要过程。综述了全球变化下CO2浓度上升、全球增温、耕作方式的改变及氮沉降增加的土壤呼吸效应。大气CO2浓度的上升将增加土壤中CO2的释放通量，同时将促进土壤的碳吸存；在全球增温的情形下，土壤可能向大气中释放更多的CO2，传统的土地利用方式可能是引发温室气体CO2产生的重要原因，所有这些全球变化对土壤呼吸的作用具有不确定性。认为土壤碳库的碳储量增加并不能减缓21世纪大气CO2浓度的上升。据此讨论了该问题的对策并提出了今后土壤呼吸的一些研究方向。其中强调，尽管森林土壤碳固定能力有限，但植树造林、森林保护是一项缓解大气CO2上升的可行性对策；基于现有田间尺度CO2通量测定在不确定性方面的进展，今后应继续朝大尺度田间和模拟程序方面努力；着重回答全球变化条件下的土壤呼吸过程机理；区分土壤呼吸的不同来源以及弄清土壤呼吸黑箱系统中土壤微生物及土壤动物的功能。当然，土壤呼吸的测定方法尚有待改善。  相似文献   

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