Residual Exchange Flows in Subtropical Estuaries

Observations of residual exchange flows at the entrance to four subtropical estuaries, two of them semiarid, indicate that these flows are mainly tidally driven, as they compare favorably with theoretical patterns of tidal residual flows. In every estuary examined, the tidal behavior was that of a standing or near-standing wave, i.e., tidal elevation and tidal currents were nearly in quadrature. The pattern of exchange flow that persisted at every estuary exhibited inflow in the channel and outflow over the shoals. Curiously, but also fortuitously, this pattern coincides with the exchange pattern driven by density gradients in other estuaries. The tidal stresses and the residual elevation slopes should be the dominant mechanisms that drive such tidal residual pattern because the Stokes transport mechanism is negligible for standing or near-standing waves. Time series measurements from the semiarid estuaries showed fortnightly modulation of the residual flow by tidal forcing in such a way that the strongest net exchange flows developed with the largest tidal distortions, i.e., during spring tides. This modulation is opposite to the modulation that typically results in temperate estuaries, where the strongest net exchange flows tend to develop during neap tides. The fortnightly modulation on tidal residual currents could be inferred from previous theoretical results because residual currents arise from tidal distortions but is made explicit in this study. The findings advanced herein should allow the drawing of generalities about exchange flow patterns in subtropical estuaries where residual flows are mainly driven by tides.     

Salinity Variability and Water Exchange in Interconnected Estuaries

A high-resolution coastal ocean model is used to investigate salinity variability and water exchange in a complex coastal system off the southern U.S. characterized by three adjacent sounds that are interconnected by a network of channels, creeks, and intertidal areas. Model results are generally highly correlated with observations from the Georgia Coastal Ecosystem Long Term Ecological Research (GCE-LTER) program, revealing a high degree of salinity variability at the Altamaha River and Doboy Sound, decreasing sharply toward Sapelo Sound. A Lagrangian particle tracking method is used to investigate local residence time and connectivity in the system. Local residence time is highly variable, increasing with distance from the Altamaha River and decreasing with river flow, revealing that discharge plays a dominant role on transport processes and estuary-shelf exchange. The Altamaha River and Doboy Sound are connected to each other in all seasons, with exchange occurring both via coastal and estuarine pathways. While particles released at the Altamaha and Doboy rarely reach Sapelo Sound, particles released at Sapelo Sound and the creeks surrounding its main channel can reach the entire estuarine system.     

黑潮与毗邻陆架海域的碳交换

作为沟通陆架边缘海与开放大洋的北太平洋西边界流,黑潮对毗邻中国陆架海域碳循环有着不可忽视的影响。分析总结了黑潮与毗邻陆架海域海水中溶解有机碳(DOC)、颗粒有机碳(POC)、溶解无机碳(DIC)和颗粒无机碳(PIC)分布与交换的现有研究成果。分析表明,黑潮通过表层水涡旋、入侵以及次表层以下水体上涌等形式携碳进入毗邻陆架海域。在黑潮与毗邻陆架海域,DOC和POC的分布受生物活动、水团混合以及沉积物—水界面相互作用的共同影响,表层与陆架水中含量较高,DIC受海水碳酸盐体系平衡影响,表层含量低于底层,在陆架海域与上升流区有高值,PIC含量较低。在台湾东北海域,DOC,POC和DIC由东海陆架海域向黑潮有净输出,输出量分别为2 431×109,1 051×109和21 733×109mol C/a,PIC通过陆架源悬浮颗粒物向黑潮主流输送,通量为1 852×109mol C/a。DOC,POC和PIC由南海经吕宋海峡向黑潮有净输出,输出量分别为2 652×109,1 009×109和230×109mol C/a,但DIC由黑潮向南海有净输出,通量为13 005×109mol C/a。台湾海峡碳循环受黑潮输运的影响,但影响机制及过程至今并不清楚。因此,黑潮与毗邻陆架海域的碳交换过程研究还有若干重大科学问题亟待解决,尚需深入系统的研究。     

Research Advance in Air-Water CO2 Exchange of Estuaries

Estuary holds a key position in linking the four geo-spheres, i.e., atmosphere, lithosphere, hydrosphere and biosphere. Figuring out the transfer mechanisms of estuarine carbon, especially the exchange ofCO₂ at the air water interface is conducive to understanding the carbon pattern in coastal oceans. To date, many fruitful studies have been conducted on the control mechanism towards the partial pressure of CO₂ (pCO₂) in different estuarine areas around the world. By a thorough research on the latest studies of estuarineCO₂ exchange with the atmosphere, it is concluded as follows: ①A common pattern is found on the spatial distribution of pCO₂in different estuarine areas. However, the concrete seasonal change of pCO₂ shows great differences, and the corresponding control factors also vary considerably. ②Estuaries are believed to be large sources ofCO₂ to the atmosphere. It is estimated that the global estuarineCO₂ degassing fluxes, although the global surface area of estuariesis small, are up to 0.25×10¹⁵~0.50×10¹⁵g C/a; and about 1/3 of riverine carbon is released into the atmosphere during the estuarine transit. ③Degradation of organic matter, lateral transfer of marsh derivedCO₂ , mineral deposits in water and turbulence in the liquid phase are the main factors that are responsible for the emission of estuarineCO₂ . At present, this estimate of estuarineCO₂ exchange with the atmosphere is based on limited spatial data, therefore problems such as the limitation in the depth and scope of studies still exist. There are also varieties of uncertainties in the estimation of gas transfer velocity and the whole areas of global estuaries, all of them make it difficult to reach an accurate evaluation ofCO₂ fluxes at the air water interface. It is difficult to predict the future trend of theCO₂ exchange at the air-water interface due to the complexities of the driving forces and feedback mechanisms in estuarine carbon cycle and the intense anthropogenic disturbance. Investigating the mechanism of pCO₂ in estuarine areas, improving the accuracy of evaluation ofCO₂ fluxes and comparing studies of different estuaries would be new scopes in the future researches on the exchange ofCO₂ at the air-water interface in estuaries.     

Carbon Dioxide and Methane Dynamics in Three Coastal Systems of Cadiz Bay (SW Spain)

The partial pressure of CO₂ (pCO₂) and concentration of dissolved CH₄ in surface waters have been studied in three coastal systems connected to Cadiz Bay (southwestern coast of Spain) over different time scales. The concentration of CH₄ varied from 1 to 4200 nmol kg^?1 (192.1 ± 463.6 nmol kg^?1) and the saturation percent from 19 to 159,577% (6645 ± 16,921%), and pCO₂ from 315 to 3240 μatm (841.9 ± 466.3 μatm), with saturation percent values varying between 72 and 981% (220 ± 133%). The seasonal variation of pCO₂ mainly depends on the temperature. On the contrary, the annual distribution of dissolved CH₄ is associated with the precipitation regime. In addition, pCO₂ and dissolved CH₄ showed spatial variation. pCO₂ increased toward the inner part of the systems, with the proximity to the discharge points from human activities. Dissolved CH₄ is influenced by both anthropogenic inputs and natural processes such as benthic supply and exchange with the adjacent salt marshes. pCO₂ and dissolved CH₄ also varied with the tides: The highest concentrations were measured during the ebb, which suggests that the systems export CO₂ and CH₄ to the Bay and adjacent Atlantic Ocean.     

Contrasting styles of Sn-W mineralisation in peninsular Thailand and SW England

The Sn-W deposits of SW England and SE Asia are associated with crustally derived granitic rocks with late volatile-enriched (F, Li, B, P) differentiates. In peninsular Thailand, primary ores are principally pegmatitic, and hydrothermal vein systems are only locally important. In SW England, wolframite and cassiterite mainly occur in hydrothermal vein systems, and are associated with greisening and tourmalinisation; mineralised pegmatites are rare. These two styles of mineralisation are thought to arise because of differences in the character of late magmatic processes. In peninsular Thailand, late-stage tourmaline-bearing granitic rocks are enriched in B, but not Li and F, compared to earlier biotite granites. Similar late-stage granitic rocks occur also in SW England, but a later topaz granite, enriched in F, Li and P, also occurs. The Thai pegmatitic Sn-W deposits are thought to have formed by late magmatic crystallisation from an aqueous phase enriched in metals and derived by exsolution from a B and metal-rich magma, whereas the SW England mineralisation involved essentially post-magmatic hydrothermal processes. Complexing agents (especially F) and metals may have been derived from granitic or country rocks during hydrothermal circulation at the current level of emplacement.     

Contrasting styles of Taconian, Eastern Acadian and Western Acadian metamorphism, central and western New England

The two major Early to Middle Palaeozoic tectonic/metamorphic events in the northern Appalachians were the Taconian (Middle to Late Ordovician) in central to western areas and the Acadian (Late Silurian to early Middle Devonian) in eastern to west-central areas. This paper presents a model for the Acadian orogenic event which separates the Acadian metamorphic realm into eastern and western belts based on distinctively different styles. We propose that the Acadian metamorphism in the east was the delayed consequence of Taconian back-arc lithospheric modification. East of the Taconian island arc, thick accumulations of Late Ordovician and Silurian sediments, coupled with plutons rising along a magmatic arc, produced crustal thermal conditions appropriate for anomalously high-T, low-P metamorphism accompanied by major crustal anatexis. In this zone, upward melt migration was coupled with subsequent E-W crustal shortening (possibly due to outboard collision with the Avalon terrane) to produce mechanical conditions that favoured formation of fold and thrust nappes and resultant tectonic thickening to the west (and probably to the east as well). The basis for the distinction between the Eastern and Western Acadian events lies in the contrasting styles of metamorphism accompanying each. Evidence for contrasting metamorphic styles consists of (1) estimated metamorphic field gradients (MFGs) based on thermobarometric studies, and (2) petrological evidence for contrasting P–T trajectories. West of the Acadian metamorphic front, the Taconian zone has an MFG in which peak temperatures of 400-600° C were reached at pressures of about 4–6 kbar, with both P and T increasing to the east. Near its western edge, the Western Acadian metamorphic overprint has a similar MFG to the Taconian, and is mainly discriminated by ⁴⁰Ar/³⁹Ar dating and microtextural evidence. East of this narrow zone, the Western Acadian overprint is characterized by progressively higher temperatures (600–725° C) and pressures (6.5–10 kbar, or more) to the east, yielding an overall MFG that lies along, or slightly above, the kyanite–sillimanite boundary on a P–T diagram. There is little or no plutonism accompanying Western Acadian metamorphism. In contrast, thermobarometry in the Eastern Acadian, east of the Bronson Hill Belt, yields high-T, intermediate-P conditions for the highest grade rocks known in New England: T= 650–750° C, P= 4.5–6.5 kbar for granulite facies assemblages which apparently formed along an ‘anticlockwise’P–T path. The Bronson Hill Belt lies geographically between the Eastern and Western Acadian zones and shows transitional petrological behaviour: anomalously high temperatures at intermediate pressures, but a ‘clockwise’ path with decompression cooling. Radiometric dating indicates peak Taconian conditions may have been achieved as early as 475 Ma in the Taconian hinterland and as late as 445 Ma in the Taconian foreland (including the Taconic allochthons). Eastern Acadian magmatism may have started as early as 425 Ma, and most nappe-stage deformation and metamorphism in the Eastern Acadian zone appears to have ended by about 410 Ma. Tectonic thickening in the Western Acadian (including the western counterparts of the nappe-stage deformation documented in the Eastern Acadian) must pre-date attainment of peak metamorphic conditions dated at 395–385 Ma. Dome-stage deformation clearly post-dates peak metamorphism and deforms metamorphic isograds. The end of Western Acadian deformation is well constrained by 370-375 Ma radiometric ages of late pegmatites and granitoids which cross-cut all structures.     

二氧化碳洗井中相关问题的探讨

二氧化碳洗井方法具有设备简单、用时少,效果好的特点,但随着钻孔深度和孔径加大,井管材料的更新换代,有时也会难以出现壮观的井喷场面,达不到理想的洗井效果,使用范围受到限制的问题。总结多年的洗井经验,依据二氧化碳洗井原理,运用洗井过程中起动压力和用气量的计算公式,进而对洗井深度和影响用气量的因素进行了分析,结果表明:1该方法比较适用于井深300m左右、孔径Φ325mm以内、泥浆相对密度小于1.1g/cm3的新打水井,对大于300m的深井,可采用分层洗井法或压风机引喷法进行洗井。2井喷形成时的二氧化碳气体用量,与瓶内气体的压力、钻杆的下入深度、环空体积、地面管路的长度与直径、钻杆内径、钻井液的密度等成正比,而与水温、气温等成反比;当井的含水层的水柱高度低于70m时,一般不易形成井喷。3二氧化碳洗井适用于井内下入钢管、铸铁管等抗压强度较高的井。对水泥管、塑料管等强度较低的井管则要视情况具体分析。     

Carbon Dioxide in igneous petrogenesis: I

A number of experimental CO₂ solubility data for silicate and aluminosilicate melts at a variety of P- T conditions are consistent with solution of CO₂ in the melt by polymer condensation reactions such as SiO _4(m ^4? +CO_2(v)+Si _n O _3n+1(m) ⁽²ⁿ⁺¹⁾ ?Si _n+1O _3n+4(m) ^(2n+4)? +CO _3(m ^)2? . For various metalsilicate systems the relative solubility of CO₂ should depend markedly on the relative Gibbs free change of reaction. Experimental solubility data for the systems Li₂O-SiO₂, Na₂O-SiO₂, K₂O-SiO₂, CaO-SiO₂, MgO-SiO₂ and other aluminosilicate melts are in complete accord with predictions based on Gibbs Free energies of model polycondesation reactions. A rigorous thermodynamic treatment of published P- T-wt.% CO₂ solubility data for a number of mineral and natural melts suggests that for the reaction CO_2(m) ? CO_2(v)

1. CO₂-melt mixing may be considered ideal (i.e., { \(a_{{\text{CO}}_{\text{2}} }^m = X_{{\text{CO}}_{\text{2}} }^m \) );
2. \(\bar V_{{\text{CO}}_{\text{2}} }^m \) , the partial molal volume of CO₂ in the melt, is approximately equal to 30 cm³ mole^?1 and independent of P and T;
3. Δ C _p ⁰ is approximately equal to zero in the T range 1,400° to 1,650 °C and
4. enthalpies and entropies of the dissolution reaction depend on the ratio of network modifiers to network builders in the melt. Analytic expressions which relate the CO₂ content of a melt to P, T, and \(f_{{\text{CO}}_{\text{2}} } \) for andesite, tholeiite and olivine melilite melts of the form

$$\ln X_{{\text{CO}}_{\text{2}} }^m = \ln f_{{\text{CO}}_{\text{2}} } - \frac{A}{T} - B - \frac{C}{T}(P - 1)$$ have been determined. Regression parameters are (A, B, C): andesite (3.419, 11.164, 0.408), tholeiite (14.040, 5.440,0.393), melilite (9.226, 7.860, 0.352). The solubility equations are believed to be accurate in the range 3<P<30 kbar and 1,100°<T<1,650 °C. A series of CO₂ isopleth diagrams for a wide range of T and P are drawn for andesitic, tholeiitic and alkalic melts.     

Sedimentation and Organic Carbon Burial in the Yangtze River and Hudson River Estuaries: Implications for the Global Carbon Budget

One of the most important challenges in global climate change research is balancing the carbon budget within the global carbon cycle. Carbon burial in sediments at the land–ocean interface has been difficult to quantify and model because it represents non-steady-state boundary conditions that are also affected by human activities. In this study, we document carbon burial rates in the Yangtze River (1.6–4.9 × 10¹² gC year^?1) and Hudson River (1.8–3.6 × 10¹⁰ gC year^?1) estuaries and integrate our results with carbon burial rates determined by others in the world’s 25 largest river-estuarine systems (6–11 × 10¹³ gC year^?1). Our results indicate that carbon burial in estuaries, bays, coves, lagoons, mud flats, marshes, mangroves, and other highly productive or protected low-energy areas at the land–ocean interface along the entirety of the world’s coastlines may serve as an unrecognized sink within the global carbon budget.     

The Influence of Benthic Macrofauna on the Erodibility of Intertidal Sediments with Varying mud Content in Three New Zealand Estuaries

Fine sediment inputs can alter estuarine ecosystem structure and function. However, natural variations in the processes that regulate sediment transport make it difficult to predict their fate. In this study, sediments were sampled at different times (2011–2012) from 45 points across intertidal sandflat transects in three New Zealand estuaries (Whitford, Whangamata, and Kawhia) encompassing a wide range in mud (≤63 μm) content (0–56 %) and macrofaunal community structure. Using a core-based erosion measurement device (EROMES), we calculated three distinct measures of sediment erosion potential: erosion threshold (? _c ; N m^?2), erosion rate (ER; g m^?2 s^?1), and change in erosion rate with increasing bed shear stress (m _e ; g N^?1 s^?1). Collectively, these measures characterized surface (? _c and ER) and sub-surface (m _e ) erosion. Benthic macrofauna were grouped by functional traits (size and motility) and data pooled across estuaries to determine relationships between abiotic (mud content, mean grain size) and biotic (benthic macrofauna, microbial biomass) variables and erosion measures. Results indicated that small bioturbating macrofauna (predominantly freely motile species <5 mm in size) destabilized surface sediments, explaining 23 % of the variation in ? _c (p ≤ 0.01) and 59 % of the variation in ER (p ≤ 0.01). Alternatively, mud content and mean grain size cumulatively explained 61 % of the variation in m _e (p ≤ 0.01), where increasing mud and grain size stabilized sub-surface sediments. These results highlight that the importance of biotic and abiotic predictors vary with erosion stage and that functional group classifications are a useful way to determine the impact of benthic macrofauna on sediment erodibility across communities with different species composition.     

基性、超基性岩:二氧化碳地质封存的新途径

CO2地质封存是控制全球CO2净排放量的有效手段.自然界存在大量基性、超基性岩石的碳酸盐风化作用,与CO2反应生成稳定的碳酸盐矿物.影响基性、超基性岩石与CO2反应速率的因素有温度、压力、pH值、流体流动速率以及与矿物接触的表面积等.矿物在反应过程中放热可以使碳酸盐化体系进入自我加热的良性循环,同时控制流体的流动速率可以保持最佳温度并使反应速率最大化.蛇绿岩中的橄榄岩、大陆玄武岩和深海玄武岩在地球表层广泛分布,可贮存大量CO2.目前研究表明此方法在技术上可行,经济成本上有优势.因此,基性、超基性岩石具有封存CO2的巨大潜力,可以作为地质封存CO2的新途径.     

松辽盆地北部火山岩CO2脱气参数及其对CO2资源量估算的意义

为了定量评价火山岩脱CO2气量的潜力，选择松辽盆地北部火山岩进行了低温脱气实验。将火山岩加热到250℃时，脱出挥发份总量为0.0299～0.0790ml/g；其中CO2脱出量为0.0218～0.0706 ml/g（0.429～1.387wt％）。脱挥发份总量与其中CO2量具有良好的正线性相关；挥发份以CO2气为主，其次是Ｎ2气，还伴有H2、CO、CH4等还原性气体，以及更少量的低碳烷烃；基性火山岩比中、酸性火山岩脱出CO2数量较多。火山岩吸附大量CO2气，成为充足气源，火山岩脱出的吸附气主要是辗转而来的深源气，火山岩成为探索幔源气成藏的主要源岩，尤其是基性火山岩。估算CO2资源量，可将250℃时火山岩挥发份含量作为岩石挥发份及残余CO2量的下限值，而全岩分析的总碳含量可作为CO2脱出量的上限值。     

Atmospheric Carbon Dioxide and Climate: Historical-Geological Aspects

Insignificant role of anthropogenic carbon dioxide in the total balance of this gas in the atmosphere is shown. Relationship of the atmospheric CO₂ content with climate in geological history of the Earth and history of mankind is ambiguous. It is assumed that the influence of greenhouse effect on global climate was less significant than was thought previously. Its impact is governed by complex relationship of cosmic and terrestrial factors, including the position of continental massifs.__________Translated from Litologiya i Poleznye Iskopaemye, No. 4, 2005, pp. 368–380.Original Russian Text Copyright © 2005 by Kuznetsov.     

Frostquakes in New England

Frostquakes are generated by tensional fracturing of the ground due to relatively rapid freezing. They are often accompanied by explosive noise and may reach Intensity V effects, yet they are only felt in neighborhoods and are not recorded on seismic networks. Frostquakes may crack macadam, concrete slabs, shallow soil pipe and some foundation materials along the line of the fracture. They occur in the early hours of the morning in mid-winter during major cold snaps. The ones investigated occurred in glacial sand and silt and none were found on till or bedrock. The recognition of frostquakes is important in correcting the records for fault-caused earthquakes. Frostquakes in the historic record complicate the difficulty of predicting large earthquakes from small ones.     

青岛邻近海域海水中有机碳的分布特征

在2006年8月、12月和2007年4月、10月对青岛邻近海域进行了4个季节的调查,分析了溶解有机碳(DOC)和颗粒有机碳(POC)的分布特征及影响因素.结果表明,调查海区DOC的浓度范围为1.23-3.15 mg/L,年平均值为1.70 mg/L,POC的浓度范围为0.09-1.04 mg/L,年平均值为0.28 m...     

长江口-杭州湾及其邻近海域不同粒级沉积有机碳分布特征

通过对长江口、杭州湾、舟山海域及东海陆架4个海区表层沉积物样品的粒度敏感组分分析,发现东海陆架与长江口具有相似的三级组分物质组成,杭州湾与舟山海域具有相似的两级组分物质组成.综合4个区域粒级组分分布特征,采用湿分法将4个海域表层沉积物样品分成6个粒级:＜0.004 mm,0.004～0.025 mm,0.025～0.063 mm,0.063～0.125 mm,0.125～0.250 mm和＞0.250 mm,分别提取各级组分和全样进行有机碳及同位素测试.定量分析各级组分有机碳含量、来源及物质组分,除杭州湾海域粗粒级外,基本上＜0.004 mm的粘土组分有机碳含量最高;富集在杭州湾海域粗颗粒中的有机质主要来源于陆源植物碎屑.沉积物颗粒大小、物质组成类型是不同粒级有机质富集的主要控制因素.     

松辽盆地二氧化碳地质埋存研究

CO2地下储存可有效地减少人类活动排放到大气中的CO2量,从而缓解日趋严重的全球气候变化问题。沉积盆地地下深部存在体积巨大的咸水含水层,咸水不宜开发利用,可用来储存大量的CO2。研究结果表明,利用松辽盆地进行CO2的地质埋存是可行的;松辽盆地深部咸含水层的CO2储存容量大约为8.96×109t,约为2003年中国大陆地区CO2放量的25倍。     

Experiments on Methane Displacement by Carbon Dioxide in Large Coal Specimens

Carbon dioxide (CO₂) is considered to be the most important greenhouse gas in terms of overall effect. CO₂ geological storage in coal beds is of academic and industrial interest because of economic synergies between greenhouse gas sequestration and coal bed methane (CH₄) recovery by displacement/adsorption. Previously, most work focused on either theoretical analyses and mathematical simulations or gas adsorption?Cdesorption experiments using coal particles of millimeter size or smaller. Those studies provided basic understanding of CH₄ recovery by CO₂ displacement in coal fragments, but more relevant and realistic investigations are still rare. To study the processes more realistically, we conducted experimental CH₄ displacement by CO₂ and CO₂ sequestration with intact 100?×?100?×?200?mm coal specimens. The coal specimen permeability was measured first, and results show that the permeability of the specimen is different for CH₄ and CO₂; the CO₂ permeability was found to be at least two orders of magnitude greater than that for CH₄. Simultaneously, a negative exponential relationship between the permeability and the applied mean stress on the specimen was found. Under the experimental stress conditions, 17.5?C28.0 volumes CO₂ can be stored in one volume of coal, and the displacement ratio CO₂?CCH₄ is as much as 7.0?C13.9. The process of injection, adsorption and desorption, displacement, and output of gases proceeds smoothly under an applied constant pressure differential, and the CH₄ content in the output gas amounted to 20?C50% at early stages, persisting to 10?C16% during the last stage of the experiments. Production rate and CH₄ fraction are governed by complex factors including initial CH₄ content, the pore and fissure fabric of the coal, the changes in this fabric as the result of differential adsorption of CO₂, the applied stress, and so on. During CO₂ injection and CH₄ displacement, the coal can swell from effects of gas adsorption and desorption, leading to changes in the microstructure of the coal itself. Artificial stimulation (e.g. hydraulic fracturing) to improve coalbed transport properties for either CO₂ sequestration or enhanced coal bed methane recovery will be necessary. The interactions of large-scale induced fractures with the fabric at the scale of observable fissures and fractures in the laboratory specimens, as well as to the pore scale processes associated with adsorption and desorption, remain of profound interest and a great challenge.     

岩溶泉补给地表溪流二氧化碳脱气作用研究

碳酸盐岩风化作用(即岩溶作用)能够吸收大气二氧化碳(CO_2),形成溶解无机碳(DIC,dissolved inorganic carbon),被认为是一种重要的陆地碳汇,其在全球碳收支平衡和未来陆地增汇中可能会有重要贡献。然而,目前对岩溶碳汇的稳定性还存在争议,一些学者认为岩溶地下水出露地表后会发生CO_2脱气,对岩溶碳汇通量估算带来不确定性。本文以广西桂林长流水表层岩溶泉补给的溪流(约2.7km长)为例,利用水化学和同位素质谱仪测试技术,研究了溪水水化学指标和溶解无机碳同位素(δ~(13)C_(DIC))沿流程变化,探讨了溪流CO_2脱气过程、通量及其影响因素,以更好地了解岩溶碳汇的稳定性。结果表明:从泉口向下游,在陡坡地段(C1～C14段,长约270m,坡度约10°),溪水pH值、方解石饱和指数和δ~(13)C_(DIC)沿流程分别升高了0.9、0.9和1.8‰,而CO_2分压、电导率、Ca~(2+)浓度和DIC浓度分别下降了85%、34μS/cm、0.2mmol/L和0.7mmol/L,说明溪水发生了显著的CO_2脱气,并伴随碳酸钙沉淀。而在平缓地段(C18～C26段,长约2.1km,坡度1°),溪水各水化学指标和δ~(13)C_(DIC)变化较小,指示CO_2脱气作用较弱。这些发现表明溪流CO_2脱气受到了地形决定的水动力条件控制。另外,在下游渠段,受支流汇入影响,溪水pH值和方解石饱和指数有所降低,在一定程度上抑制了CO_2脱气。溪流CO_2脱气能够抵消部分岩溶作用固定的大气CO_2量,但是在长流水这一高地势、低流量且有碳酸钙沉积的环境下,其抵消的量也仅占29%。对于在低缓地区受流量很大的岩溶泉/地下河补给的河流,其CO_2脱气作用对岩溶碳汇的影响有限,加之受可能增强的水生光合生物固碳效应影响,岩溶碳汇应具有很高的稳定性。