三峡澎溪河高阳平湖碳通量初步分析及不确定性

为明确三峡水库支流澎溪河回水区的碳收支特征,以澎溪河高阳平湖水域为研究对象,建立了河道型水库主要路径碳收支估算方法,对高阳平湖从2011年9月至2012年8月一个完整水文周年内主要路径的碳通量进行了收支动态分析.结果表明,2011年9月至2012年8月,澎溪河高阳平湖水域河流输入的碳通量为133548.55 t C,输出的碳通量为125651.82 t C,水-气界面的扩散碳通量为762.56 t C,消落带土-气界面的扩散碳通量为123.74 t C,水中气泡的释放碳通量为0.38 t C,降水输入的碳通量为104.58 t C,全年高阳平湖水域碳的净积累量为7114.63 t C,宏观上呈现碳积累特征;澎溪河高阳平湖水域水体碳素总体上呈现出河道型水库特有的纵向输移特征.高阳平湖水域上游大量碳素的输入及其在高阳平湖水域的滞留可能会是该水域水-气界面温室气体释放的主要来源.尽管总体上高阳平湖全年呈现出碳积累的特点,但一些方法依然存在不确定性(水-气界面扩散碳通量和气泡释放碳通量的时空异质性等),需要更系统、更长期的工作予以验证或改进.     

一种气泡释放过程连续监测方法及其在三峡水库香溪河CH4通量监测的应用

气泡释放是天然水体释放CH₄的主要途径之一,准确量化水体气泡释放量对于辨析其“汇、源”特性至关重要。自然水体释放气泡的不连续性、不确定性使得监测其过程较为困难。本研究针对水体气泡释放监测难题,通过改进倒置漏斗型气泡通量监测装置提出了一种气泡释放过程连续监测方法。本方法测量对象为定长时间监测水域释放气泡的体积,经室内外实验验证,其理论量程为3.6～132 mL/(m²·min),测量结果能够较好的表征10～40 m水深缓流水体气泡体积通量变化特征。运用该方法于2021年6—11月对三峡水库支流香溪河库湾开展CH4气泡通量连续监测,并分析不同环境因子对其产生的影响。结果表明:监测期间,研究水域CH₄气泡通量变化范围为0.02～8.13 mg/(m²·d),且各采样点间CH₄气泡通量呈现较高的时空变异性;CH₄气泡通量与水温、水体pH呈显著正相关关系,与水深及水体电导率呈显著负相关关系。其中,水深可能是决定水体是否通过气泡形式释放CH₄的重...     

三峡水库澎溪河水-气界面CO2、CH4扩散通量昼夜动态初探

三峡水库温室气体效应近年来备受关注.为揭示三峡水库典型支流澎溪河水-气界面CO₂和CH₄通量的昼夜动态规律,明晰短时间尺度下该水域温室气体释放的影响因素,在2010年6月至2011年5月的一个完整水文周年内,选择4个具有代表性的时段(2010年8、11月和2011年2、5月)对澎溪河高阳平湖水域开展昼夜跟踪观测.结果表明:2010年8、11月和2011年2、5月4次采样的CO₂日总通量值分别为-8.34、73.94、28.13和-20.12 mmol/(m²·d),相应的CH₄日总通量值分别为2.22、0.11、0.32和7.16 mmol/(m²·d),不同时期昼夜变化明显.研究水域CO₂和CH₄通量过程不具同步性:CO₂昼夜通量变化可能更显著地受到水柱光合/呼吸过程的影响,但瞬时气象过程(水汽温差、瞬时风速等)在高水位时期亦可对CO₂通量产生显著影响;CH₄昼夜通量变化与水温条件改变更为密切.     

三峡澎溪河回水区流速对藻类原位生长速率的影响

为明晰不同流速水平对三峡支流回水区库湾藻类原位生长的影响,本文采用可调速的环形实验槽,选择三峡水库不同运行状态(低水位、高水位),对三峡澎溪河高阳平湖库湾藻类生物量(用叶绿素a浓度表示)变化特征进行原位受控实验.通过流速在0(对照)、0.1、0.2和0.3 m/s的实验发现,夏季低水位阶段澎溪河水域光热充足,但流速升高(0.2m/s)对藻类原位比生长速率具有一定影响.大体上,高阳平湖水域藻类原位比生长速率与流速水平呈对数关系.冬季高水位运行期间,流速的升高将可能在一定程度上促进水柱扰动,成为维持藻类在上层水体受光生长、避免下沉的主要因素.该时期,采用调节流速、流量的方法抑制藻类生长的难度相对较大.     

蓄水初期三峡水库草堂河水-气界面CO2和CH4通量日变化特征及其影响因素

为查明三峡水库蓄水初期典型支流水-气界面CO_2和CH_4通量的日变化特征,采用LGR在线分析仪-通量箱法,于2015年9月初在库腹一级支流草堂河回水区开展连续24 h的定位观测.结果表明,24 h监测期内,支流库湾水-气界面CO_2通量变幅为-81.642~180.991 mg/(m~2·h),呈"昼吸夜放"特征,均值为17.346 mg/(m~2·h),总体为释放特征;CH_4全天均表现为释放状态,释放通量均值为0.064 mg/(m~2·h),呈"昼弱夜强"变化.相关分析结果表明,CH_4和CO_2释放通量与风速呈正相关,与表层水温、溶解氧浓度、叶绿素a浓度呈负相关,说明风速物理扰动、浮游植物光合作用是控制草堂河水-气界面气体通量最重要的环境因素.同时,干-支流相互作用形成的特殊水环境(如异重流、水温分层)也与水-气界面温室气体通量过程密切相关,但是其作用机制更为复杂,应开展进一步系统观测和深入研究.     

三峡水库澎溪河流域高阳回水区夏季水体CO2分压日变化特性

水柱中CO2分压(pCO2)的时空分布在一定程度上可反映水中碳的环境地化特征.本研究在夏季分层期间对三峡水库澎溪河(小江)流域高阳回水区段进行了昼夜连续观测发现,恒定的温跃层中pCO2随水深增加而显著增大,表层0.5 m处pCO2均值为152±71μatm,而在水深10.0 m处pCO2均值为4568±1089μatm,同水温、pH及DO存在明显的负相关关系,进一步分析认为水温等将影响微生物、浮游植物的代谢过程及水气界面对流传输,进而对pCO2分布产生影响.对水气界面CO2扩散通量的估算结果表明,夏季分层期间高阳水域总体上表现为CO2的汇,其对大气CO2的吸收量最大值于15:00左右,达到-0.33 mmol/(m2.h);最弱在次日凌晨3:00左右,吸收量仅为-0.17 mmol/(m2.h).     

三峡水库典型支流库湾沉积物CH4产生和氧化规律

以三峡水库香溪河库湾为研究对象,采用原位加密采样(2021年5月)和室内培养方法,结合沉积物特性与水环境因子分析,探讨了香溪河库湾沉积物甲烷(CH₄)释放潜力、沉积物-水界面CH₄产生和氧化通量空间分布规律及其影响因素。结果表明:三峡水库泄水期间,香溪河库湾沉积物CH₄释放潜力的变化范围是6.35-2029.37 mg/(kg·d),沉积物-水界面CH₄产生通量和氧化通量的变化范围分别为0.04～0.73、0.03～0.62 mmol/(m²·d);空间上,沉积物CH₄释放潜力、沉积物-水界面CH₄产生及氧化通量在香溪河库湾和各典型横切面(XX02、XX05和XX06)间表现出空间差异性,主要受水深、TOC和温度的影响。垂向上,CH₄产生速率随沉积物深度的增加而减小,表层20 cm沉积物CH₄释放潜力占整柱沉积物的70%,可以用于估算库湾沉积物CH₄释放潜力。此外,沉积...     

水-气界面CO_2通量监测的静态箱法与薄边界层模型估算法比较

模型估算法与静态箱法是水-气界面气体通量监测的主要方法,因原理不同监测结果通常存在一定差异.目前对引起上述差异的主要环境因素仍不清晰.本研究使用自行设计的静态箱对三峡支流澎溪河水-气界面CO2通量进行监测,并与同步开展的CO2通量薄边界层模型估算法结果相比较,探讨该水域引起这两种监测方法结果产生差异的主要环境因素.结果表明,瞬时风速、水汽温差及水深均会对静态箱法及模型估算法的监测结果产生影响.风速越强、水汽温差越大、水深越大,这两种方法监测结果的差异就越小;而水域面积对两种方法的差异没有影响.比较发现,两种方法所获通量数据呈显著正相关,但静态箱法所获通量数据离散性显著高于薄边界层模型估算法.从方法的稳定性角度,在峡谷河道型水库水体温室气体监测中薄边界层模型估算法可能更为适宜.     

三峡支流澎溪河消落带落干初期N2O释放与反硝化特征初探

水库近岸湿地(消落带)土壤N2O释放和反硝化作用是消落带氮的生物地球化学过程的重要组成部分.以三峡水库支流澎溪河高阳平湖库湾消落带为研究对象,于2013年落干初期,采用C2H2抑制-原状土柱培养法研究该处自然植被恢复区、农耕区和对照组等不同土地类型土壤的N2O释放速率和反硝化速率,并测定了土壤p H值、氧化还原电位、温度、有机质、总氮、铵态氮、硝态氮和土壤孔隙含水量等环境指标.结果表明,自然植被恢复区土壤N2O释放速率为9.88±6.49 g N/(hm2·d),反硝化速率为58.94±52.84 g N/(hm2·d);农耕区土壤N2O释放速率和反硝化速率分别为7.71±4.44和30.70±25.68 g N/(hm2·d).不同土地类型间N2O释放速率差异显著,落干初期土壤氧含量、含水量及氮含量对不同土地类型N2O释放和反硝化作用影响明显.土壤氧含量的升高促进了自然植被恢复区的N2O释放,并在一定程度上抑制了该区域反硝化作用.农耕区土壤含水量高于自然植被恢复区,可能致使N2O释放速率低于自然植被恢复区,而反硝化速率高于自然植被恢复区.消落带土壤氮含量降低同反硝化速率降低有一定联系.     

三峡澎溪河水-气界面温室气体模型估算及其敏感性分析

模型估算法是水-气界面温室气体通量监测的主要方法,所得成果也不胜枚举.然而监测过程中诸多环境因素会对最终结果产生不确定的影响.结合三峡库区澎溪河背景条件,利用模型估算法进行水-气界面温室气体通量(以CO_2为例)估算,并且采用修正Morris筛选法尝试分析模型估算法中各个参数对温室气体扩散通量(以CO_2为例)的局部敏感性.研究结果表明:利用模型估算法计算三峡澎溪河流域水-气界面温室气体通量具有较高的可行性和可靠性;风速、水温以及pH值会对监测结果产生影响,且风速越强、水温越高、pH值越小,CO_2扩散通量就越大;pH值是高灵敏参数,风速和水温是灵敏参数.在三峡库区澎溪河监测过程中更应注意pH值的精确性,每次采样前需校正仪器.     

Elasticity of single-crystal SmAlO3, GdAlO3 and ScAlO3 perovskites

The adiabatic single-crystal elastic moduli of SmAlO₃, GdAlO₃ and ScAlO₃, all with the orthorhombic perovskite structure, have been measured by Brillouin spectroscopy under ambient conditions. These 3 compounds display various degrees of crystallographic distortion from the ideal cubic perovskite structure. We find that longitudinal moduli in directions parallel to the axes of a pseudocubic subcell are nearly equal and insensitive to distortions of the crystal structure from cubic symmetry, whereas, the moduli C₁₁ and C₂₂, parallel to the orthorhombic axes, display pronounced anisotropy with the exception of ScAlO₃. The shear moduli also correlate with distortion from cubic symmetry, as measured by rotation, or tilt angles, of the AlO₆ octahedra. Our data support the observations of Liebermann et al. that perovskite-structure compounds define consistent elasticity trends relating bulk modulus and molar volume, and sound speed and mean atomic weight. These relationships have been used to estimate bulk and shear moduli for the high-pressure polymorphs of CaSiO₃ and MgSiO₃ with the perovskite structure.     

High-temperature elasticity of the fluorite-structure compounds CaF2, SrF2 and BaF2

The elastic moduli of single-crystal CaF₂, SrF₂ and BaF₂ have been determined by the ultrasonic pulse superposition technique as a function of temperature from T = 298 to T = 650°K. These new data are consistent with other data obtained by ultrasonic pulse techniques in the region of room temperature and are superior to previous high-temperature data from resonance experiments. The elastic moduli (c) are represented by quadratic functions in T over the experimental temperature range with the curvature in the same sense for all the moduli. Evaluation of the temperature derivatives of the elastic moduli at constant volume indicates that the dominant temperature effect is extrinsic for (?K_S/?T)_P and intrinsic for (?μ/?T)_P, where K_S and μ are the isotropic bulk and shear moduli, respectively. For the series CaF₂SrF₂BaF₂, |(?c/?T)_p| decreases with increasing molar volume for all moduli; however there are no theoretical or empirical grounds on which to derive a simple relationship between (?c/?T)_P and crystallographic parameters.     

Pyroxene-garnet solid-solution equilibria in the systems Mg4Si4O12Mg3Al2Si3O12 and Fe4Si4O12Fe3Al2Si3O12 at high pressures and temperatures

Pyroxene-garnet solid-solution equilibria have been studied in the pressure range 41–200 kbar and over the temperature range 850–1,450°C for the system Mg₄Si₄O₁₂Mg₃Al₂Si₃O₁₂, and in the pressure range 30–105 kbar and over the temperature range 1,000–1,300°C for the system Fe₄Si₄O₁₂Fe₃Al₂Si₃O₁₂. At 1,000°C, the solid solubility of enstatite (MgSiO₃) in pyrope (Mg₃Al₂Si₃O₁₂) increases gradually to 140 kbar and then increases suddenly in the pressure range 140–175 kbar, resulting in the formation of a homogeneous garnet with composition Mg₃(Al_0.8Mg_0.6Si_0.6)Si₃O₁₂. In the MgSiO₃-rich field, the three-phase assemblage of β- or γ-Mg₂SiO₄, stishovite and a garnet solid solution is stable at pressures above 175 kbar at 1,000°C. The system Fe₄Si₄O₁₂Fe₃Al₂Si₃O₁₂ shows a similar trend of high-pressure transformations: the maximum solubility of ferrosilite (FeSiO₃) in almandine (Fe₃Al₂Si₃O₁₂) forming a homogeneous garnet solid solution is 40 mol% at 93 kbar and 1,000°C.If a pyrolite mantle is assumed, from the present results, the following transformation scheme is suggested for the pyroxene-garnet assemblage in the mantle. Pyroxenes begin to react with the already present pyrope-rich garnet at depths around 150 km. Although the pyroxene-garnet transformation is spread over more than 400 km in depth, the most effective transition to a complex garnet solid solution takes place at depths between 450 and 540 km. The complex garnet solid solution is expected to be stable at depths between 540 and 590 km. At greater depths, it will decompose to a mixture of modified spinel or spinel, stishovite and garnet solid solutions with smaller amounts of a pyroxene component in solution.     

High-pressure disproportionation of Co2SiO4 spinel and implications for Mg2SiO4 spinel

Co₂SiO₄ spinel has been found to disproportionate into its isochemically mixed oxides with rocksalt and rutile structures at pressures between 170 and 190 kbar and temperatures between 1400 and 1800°C in a diamond-anvil press. The exact disproportionation pressure is not certain due to transient increases in pressure during the local and rapid heating by a continuous YAG laser. The slope of the phase boundary between the spinel phase and the mixed oxides is calculated to be?33 ± 20bar/deg. This negative slope is consistent with the observed anomalously large entropy of CoO (relative to its isostructural oxides) in entropy vs.(MV)^?1/2 systematics, whereM is the formula weight andV the molar volume. The sign of the slope for a phase boundary in the disproportionation of spinel depends on the values of entropy of the rocksalt oxides as well as the inverse character exhibited in the spinel phases. The normal entropy of MgO suggests that the phase boundary for the disproportionation of Mg₂SiO₄ spinel has positive slope.     

High-pressure phases of Co2GeO4, Ni2GeO4, Mn2GeO4 and MnGeO3: implications for the germanate-silicate modeling scheme and the Earth's mantle

In a diamond-anvil press coupled with YAG laser heating, the spinels of Co₂GeO₄ and Ni₂GeO₄ have been found to disproportionate into their isochemical oxide mixtures at about 250 kbar and 1400–1800°C in the same manner as their silicate analogues. At about the same P-T conditions MnGeO₃ transforms to the orthorhombic perovskite structure (space group Pbnm); the lattice parameters at room temperature and 1 bar are a₀ = 5.084 ± 0.002, b₀ = 5.214 ± 0.002, and c₀ = 7.323 ± 0.003Å with Z = 4 for the perovskite phase. The zero-pressure volume change associated with the ilmenite-perovskite phase transition in MnGeO₃ is ?6.6%. Mn₂GeO₄ disproportionates into a mixture of the perovskite phase of MnGeO₃ plus the rocksalt phase of MnO at P = 250kbar and T = 1400–1800°C. The concept of utilizing germanates as high-pressure models for silicates is valid in general. The results of this study support the previous conclusion that the lower mantle comprises predominantly the orthorhombic perovskite phase of ferromagnesian silicate.     

Correlations between13C and ΣCO2 in surface waters and atmospheric CO2

¹³C and ΣCO₂ data from the North and South Atlantic, the Antarctic, and the North and South Pacific are given. The δ¹³C of the ΣCO₂ in the deep water (～3000m) decreases from 1.7‰ in the North Atlantic to ?0.10‰ in the North Pacific. This change is attributed to the addition of about 158 μmoles of CO₂ per kg of seawater. The in-situ oxidation of organic matter accounts for 83% of this increase in ΣCO₂, while the remainder is attributed to dissolution of calcium carbonate.The δ¹³C of the dissolved CO₂ in mid-latitude surface water samples is controlled by a quasi-steady-state equilibrium with atmospheric CO₂ at a mean temperature of 16°C. The δ¹³C and ΣCO₂ values of Antarctic surface water samples suggest that these waters are derived from a mixture of North Atlantic deep water and equilibrated surface water.     

Melting of the silica isotypes SiO 2, BeF 2 and GeO 2 at elevated pressures

The melting curves of the structural analogues SiO ₂, BeF ₂ and GeO ₂ have been studied at pressures ?40 kbar in a piston-cylinder apparatus. The initial slopes dT_m/dP of the β-quartz-liquid boundaries for SiO ₂ and BeF ₂ are ～35° while the slope of the rutile-liquid boundary for GeO ₂ is approximately 32°C/kbar. These large values of dT/dP reflect the unusually low entropies of fusion for these compounds in which strong structural similarities exist between the crystalline phases and the melt. Implications for the extended phase diagram of silica are discussed and it is concluded that either: (1) a maximum exists on the coesite melting curve, or (2) estimates of the melting temperature of stishovite need to be revised upwards.     

Melting relationships in CaO-CO2 and MgO-CO2 to 36 kilobars with comments on CO2 in the mantle

The melting curves of CaCO₃ and MgCO₃ have been extended to pressures of 36 kb by experiments in piston-cylinder apparatus. At 30 kb, the melting temperatures of calcite and magnesite are 1610°C and 1585°C, respectively. New data for the magnesite dissociation reaction permit the location of an invariant point for the assemblage magnesite + periclase + liquid + vapor near 26 kb-1550°C. New data are also presented for the calcite-aragonite transition at 800°C, 950°C and 1100°C. At pressures above 36–50 kb, calcite and magnesite melt at temperatures lower than the solidus of dry mantle peridotite. Natural and experimental evidence suggests that carbon dioxide in the Earth's mantle could be present in a variety of forms: (a) a free vapor phase, (b) vapor dissolved in silicate magma, (c) crystalline carbonate, (d) carbonatite liquid, (e) carbon-bearing silicate analogs, or (f) carbonato-silicates (such as scapolite, spurrite, tilleyite, and related compounds).     

Synthesis of γ-Mg2SiO4

Magnesium orthosilicate with spinel structure (γ-Mg₂SiO₄) was synthesized at about 250 kbar and 1000°C. Unit cell dimension was established to be 8.076 ± 0.001Å. X-ray powder diffraction pattern revealed a significant difference between γ-Mg₂SiO₄ and other γ-M₂SiO₄ spinels (M = Fe, Co, and Ni) in the intensities of (111) and (331) reflections, both of which are virtually absent in the Mg₂SiO₄ spinel. This feature could be thoroughly understood by the calculation of the intensities for several silicate spinels.     

CO2/CaCl2 solution interfacial tensions under CO2 geological storage conditions: Influence of cation valence on interfacial tension

The effectiveness of CO₂ storage in deep saline aquifers and hydrocarbon reservoirs is governed, among other factors, by the interfacial tension between the injected CO₂ and formation water (brine). Experimental data on CO₂/water and CO₂/NaCl solution have revealed that the interfacial tension depends on the pressure, temperature and water salinity. However, there is still a lack of data for other salts (such as MgCl₂ and CaCl₂) which are also present in aquifers and carbonate reservoirs.