Chemical and Strontium Isotopic Compositions of the Hanjiang Basin Rivers in China: Anthropogenic Impacts and Chemical Weathering

The Hanjiang River, the largest tributaries of the Changjiang (Yangtze) River, is the water source area of the Middle Route of China’s South-to-North Water Transfer Project. The chemical and strontium isotopic compositions of the river waters are determined with the main purpose of understanding the contribution of chemical weathering processes and anthropogenic inputs on river solutes, as well as the associated CO₂ consumption in the carbonate-dominated basin. The major ion compositions of the Hanjiang River waters are characterized by the dominance of Ca²⁺ and HCO₃ ⁻, followed by Mg²⁺ and SO₄ ²⁻. The increase in TDS and major anions (Cl⁻, NO₃ ⁻, and SO₄ ²⁻) concentrations from upstream to downstream is ascribed to both extensive influences from agriculture and domestic activities over the Hanjiang basin. The chemical and Sr isotopic analyses indicate that three major weathering sources (dolomite, limestone, and silicates) contribute to the total dissolved loads. The contributions of the different end-members to the dissolved load are calculated with the mass balance approach. The calculated results show that the dissolved load is dominated by carbonates weathering, the contribution of which accounts for about 79.4% for the Hanjiang River. The silicate weathering and anthropogenic contributions are approximately 12.3 and 6.87%, respectively. The total TDS fluxes from chemical weathering calculated for the water source area (the upper Hanjiang basin) and the whole Hanjiang basin are approximately 3.8 × 10⁶ and 6.1 × 10⁶ ton/year, respectively. The total chemical weathering (carbonate and silicate) rate for the Hanjiang basin is approximately 38.5 ton/km²/year or 18.6 mm/k year, which is higher than global mean values. The fluxes of CO₂ consumption by carbonate and silicate weathering are estimated to be 56.4 × 10⁹ and 12.9 × 10⁹ mol/year, respectively.     

Weathering rates and anthropogenic influences in a sedimentary basin,São Paulo State,Brazil

The weathering rate of rocks and chemical dynamics of the Corumbataı́ River basin, São Paulo State, Brazil, were evaluated using major elements as natural tracers. This basin has serious environmental problems in terms of quality of surface and rainwater, which affect the determination of weathering rate. The Corumbataı́ River, downstream from Rio Claro City, receives several elements/compounds through anthropogenic activities, with only K, SO₄²⁻ and alkalinity yielding positive flux values. The negative flux of some anions/cations can be attributed to atmospheric loading mainly related to anthropogenic inputs, providing K a value of 16.7 ton/km⁻²a⁻¹ for the material removed by weathering in the Corumbataı́ River basin. This is equivalent to 26×10⁶ kg of rock being removed each year by the Corumbataı́ River. The instantaneous flux was found to be a function of discharge, with the majority of dry residue (dissolved load) being transported during the summer (wet) months. The removed material in Corumbataı́ River basin derives mainly from two sub-basins (Cabeças River and Passa Cinco River), where the sandstones weather more easily than siltstones and claystones in the basin.     

Application of the stable isotope composition of S04 to tracing anomalous TDS in Nose Creek,southern Alberta,Canada

Nose Creek, a tributary of the Bow River, has a TDS load that is significantly higher than the Bow River or its other tributaries. Chemical and stable isotope analyses were used to elucidate the sources of TDS in Nose Creek. Oxygen and H isotopes indicate that water is added to Nose Creek by leaky municipal pipes, via groundwater infiltration, as the creek flows through the cities of Airdrie and Calgary. Upstream of Airdrie, the high δ³⁴S of dissolved S0₄ (+ 17‰), is consistent with derivation from the local sour gas industry. The S0₄ concentration of Nose Creek doubles as the creek flows through agricultural land between Airdrie and Calgary, while the δ³⁴S composition remains a consistent 5‰. This is indicative of S derived from local soils. Within Calgary, S0₄ is derived from oxidation of reduced forms of S in the till, related to the influx of municipal groundwater.     

Spatial patterns of the evolution of the chemical composition and discharge of river water in the Ob River basin

The discharge of major cations and dissolved organic carbon (C_org) with water of the Ob River and its tributaries along the natural zones within the Ob River basin was calculated, and the contribution of the underground component to the volumes of total discharge of the Ob River basin was estimated. It was demonstrated that the total chemical composition of river water and the geochemical discharge in the Ob River basin were consistent with the zoned hydroclimatic conditions controlling the character and duration of interaction in the water–rock system. It was established that the average ionic discharge of the Ob River increased from 6–7 × 10⁶ t/year near Barnaul to 46–47 × 10⁶ t/year near Salekhard; the discharge of dissolved C_org increased from 0.1 × 10⁶ to 3.8 × 10⁶ t/year. Multiple enrichment of underground waters of the Ob River in dissolved organic matter from the upper to the lower reaches was revealed.     

Chloride imbalance in a catchment undergoing hydrological change: Upper Barwon River,southeast Australia

Documenting whether surface water catchments are in net chemical mass balance is important to understanding hydrological systems. Catchments that export significantly greater volumes of solutes than are delivered via rainfall are not in hydrologic equilibrium and indicate a changing hydrological system. Here an assessment is made of whether a saline catchment in southeast Australia is in chemical mass balance based on Cl. The upper reaches of the Barwon River, southeast Australia, has total dissolved solids, TDS, concentrations of up to 5860 mg/L and Cl concentrations of up to 3370 mg/L. The high river TDS concentrations are due to the influxes of groundwater with TDS concentrations of up to 68,000 mg/L. Between 1989 and 2011, the median annual Cl flux from the upper Barwon catchment was 17.8 × 10⁶ kg (∼140 kg/a/ha). This represents 340–2230% of the annual Cl input by rainfall to the catchment. Major ion and stable isotope geochemistry indicate that the dominant source of solutes in the catchment is evapotranspiration of rainfall, precluding mineral dissolution as a source of excess Cl. The upper Barwon catchment is not in chemical mass balance and is a net exporter of solutes. The chemical imbalance may reflect the transition within the last 100 ka from an endorheic lake system where solutes were recycled producing shallow groundwater with high TDS concentrations to a better drained catchment. Alternatively, a rise in the regional water table following land clearing may have increased the input of groundwater with high TDS concentrations to the river system.     

Carbon river fluxes and weathering CO2 consumption in the Congo and Amazon river basins

Data on carbon river fluxes recently obtained by the authors for the Congo basin within the framework of the PIRAT Program (INSU-CNRS/ORSTOM) are compared with results previously obtained for the Amazon basin. A special interest is devoted to the bicarbonate river fluxes and to their relationships with river discharges. The flux of atmospheric and soil CO₂ consumed by rock weathering is estimated to be 3.1 × 10⁵ and 0.5 × 10⁵ moles/a/km² respectively for the Amazon and the Congo basin. These CO₂ fluxes represent, respectively, 67.4% and 74.7% of the total bicarbonate river fluxes. A comparison to other large river basins shows that this contribution is directly related to the proportion of carbonate rock areas. A transfer function between the weathering CO₂ flux and the river discharge is calculated for each basin and allows the reconstitution of the variations of this flux using the river discharge fluctuations during the last century. These interannual CO₂ fluctuations present average increasing trends of 10% for Amazon basin and only 0.7% for the Congo basin during the last century.     

Carbonate equilibrium in the water of the Razdol’naya River

The paper suggests an accurate approach to studying carbonate equilibrium in the water of the Razdol’naya River. The approach involves measuring pH by Pitzer’s scale, using a cell without liquid junction; measuring the total alkalinity by Bruevich’s technique; and using apparent constants of carbonate equilibrium with regard for the organic alkalinity. The Pitzer technique was employed to calculate the apparent constants of carbonate equilibrium in solution that models the riverine water: Ca(HCO₃)₂–NaCl–H₂O within the range of alkalinity of 0–0.005 mol/kg and temperatures of 0–25°C. Carbonate equilibrium in the water of the Razdol’naya River was sampled for studying at eight sites during all four seasons. Although the contents of biogenic compounds in the water are high, they can merely insignificantly affect the acid–base equilibrium, which is controlled in the riverine water by carbonate equilibrium and the concentrations of humic substances, which play the greater role, the greater the discharge of the river. In addition to the production and destruction of organic matter, carbonate equilibrium in the river is also affected by the supply of humic substances with soil waters and total alkalinity with groundwaters. The fluxes of alkalinity and humic substances annually brought by the Razdol’naya River to Amur Bay are evaluated at 1.33 × 10⁹ mol and 9.9 × 10⁶ kgC, respectively. The carbon dioxide export with the Razdol’naya River is equal to the alkalinity flux and does not depend on the weathering mechanisms.     

Ion chemistry of groundwater and the possible controls within Lhasa River Basin,SW Tibetan Plateau

In order to study the major ion chemistry and controls of groundwater, 65 groundwater samples were collected and their major ions measured from wells within Lhasa River Basin. Groundwater has the characteristics of slightly alkaline and moderate total dissolved solid (TDS). TDS concentration ranged from 122.0 to 489.9 mg/L with a median value of 271.2 mg/L. Almost all the groundwater samples suited for drinking and irrigation. The major cations of groundwater are Ca²⁺ and Mg²⁺, accounting for 59.6 and 31.3% of the cations, respectively. Meanwhile, HCO₃^? and SO₄^2? constituted about 56.7 and 36.9% of the anions, respectively, in Lhasa River Basin. The hydrochemical type of groundwater is HCO₃-SO₄-Ca-Mg. The chemical composition of groundwater samples located in the middle of Gibbs model, which indicates that the major chemical process of groundwater is controlled by rock weathering. Carbonate weathering was the dominant hydro-geochemical process controlling the concentration of major ions in groundwater within Lhasa River Basin, but silicate weathering also plays an important role.     

青藏高原东部长江流域盆地陆地化学风化研究

长江河水主要离子由流域盆地碳酸盐岩的风化所控制,沱沱河和楚玛尔河受蒸发盐岩影响较为明显;河水溶质载荷Si,Si/TZ *,Si/(Na* K)等指标表明,长江流域盆地地表硅酸盐岩风化还是浅表层次的;金沙江地表化学剥蚀速率为1.74×103mol/yr.km2,雅砻江为1.69×103mol/yr.km2,大渡河为1.57×103mol/yr.km2,岷江为1.88×103mol/yr.km2,长江河源区楚玛尔河为2.32×103mol/yr.km2,沱沱河为1.37×103mol/yr.km2,流域地表化学剥蚀速率可与世界上其它造山带的河流进行对比。     

Rare earth elements (REE) of dissolved and suspended loads in the Xijiang River, South China

The Xijiang River is the main channel of the Zhujiang (Pearl River), the second largest river in China in terms of water discharge, and flows through one of the largest carbonate provinces in the world. The rare earth element (REE) concentrations of the dissolved load and the suspended particulate matter (SPM) load were measured in the Xijiang River system during the high-flow season. The low dissolved REE concentration in the Xijiang River is attributed to the interaction of high pH and low DOC concentration. The PAAS-normalized REE patterns for the dissolved load show some common features: negative Ce anomaly, progressively heavy REE (HREE) enrichment relative to light REE (LREE). Similar to the world’s major rivers the absolute concentration of the dissolved REE in the Xijiang River are mainly pH controlled. The degree of REE partitioning between the dissolved load and SPM load is also strongly pH dependent. The negative Ce anomaly is progressively developed with increasing pH, being consistent with the oxidation of Ce (III) to Ce (IV) in the alkaline river waters, and the lack of Ce anomalies in several DOC-rich waters is presumably due to both Ce (III) and Ce (IV) being strongly bound by organic matter. The PAAS-normalized REE patterns for the dissolved load and the SPM load in rivers draining the carbonate rock area exhibit middle REE (MREE) enrichment and a distinct maximum at Eu, indicating the preferential dissolution of phosphatic minerals during weathering of host lithologies. Compared to the Xijiang River waters, the MREE enrichment with a maximum at Eu disappeared and light REE were more depleted in the South China Sea (SCS) waters, suggesting that the REE sourced from the Xijiang River must be further fractionated and modified on entering the SCS. The river fluxes of individual dissolved REE introduced by the Xijiang River into the SCS vary from 0.04 to 4.36 × 10⁴ mol a⁻¹.     

Seasonally chemical weathering and CO<Subscript>2</Subscript> consumption flux of Lake Qinghai river system in the northeastern Tibetan Plateau

The major cation and anion compositions of waters from the Lake Qinghai river system (LQRS) in the northeastern Tibetan Plateau were measured. The waters were collected seasonally from five main rivers during pre-monsoon (late May), monsoon (late July), and post-monsoon (middle October). The LQRS waters are all very alkaline and have high concentrations of TDS (total dissolved solids) compared to rivers draining the Himalayas and the southeastern Tibetan Plateau. Seasonal variations in the water chemistry show that, except the Daotang River, the TDS concentration is high in October and low in July in the LQRS waters. The forward models were used to quantify the input of three main rivers (Buha River, Shaliu River, and Hargai River) from rain, halite, carbonates, and silicates. The results suggest that (1) atmospheric input is the first important source for the waters of the Buha River and the Shaliu River, contributing 36–57% of the total dissolved cations, (2) carbonate weathering input and atmospheric input have equal contribution to the Hargai River water, (3) carbonate weathering has higher contribution to these rivers than silicate weathering, and (4) halite is also important source for the Buha River. The Daotang River water is dominated by halite input owing to its underlying old lacustrine sediments. The water compositions of the Heima River are controlled by carbonate weathering and rainfall input in monsoon season, and groundwater input may be important in pre-monsoon and post-monsoon seasons. After being corrected the atmospheric input, average CO₂ drawdown via silicate weathering in the LQRS is 35 × 10³ mol/km² per year, with highest in monsoon season, lower than Himalayas and periphery of Tibetan Plateau rivers but higher than some rivers draining shields.     

Understanding the Cyclicity of Chemical Weathering and Associated CO<Subscript>2</Subscript> Consumption in the Brahmaputra River Basin (India): The Role of Major Rivers in Climate Change Mitigation Perspective

Weathering of rocks that regulate the water chemistry of the river has been used to evaluate the CO₂ consumption rate which exerts a strong influence on the global climate. The foremost objective of the present research is to estimate the chemical weathering rate (CWR) of the continental water in the entire stretch of Brahmaputra River from upstream to downstream and their associated CO₂ consumption rate. To establish the link between the rapid chemical weathering and thereby enhance CO₂ drawdown from the atmosphere, the major ion composition of the Brahmaputra River that drains the Himalaya has been obtained. Major ion chemistry of the Brahmaputra River was resolved on samples collected from nine locations in pre-monsoon, monsoon and post-monsoon seasons for two cycles: cycle I (2011–2012) and cycle II (2013–2014). The physico-chemical parameters of water samples were analysed by employing standard methods. The Brahmaputra River was characterized by alkalinity, high concentration of Ca²⁺ and HCO₃ ^? along with significant temporal variation in major ion composition. In general, it was found that water chemistry of the river was mainly controlled by rock weathering with minor contributions from atmospheric and anthropogenic sources. The effective CO₂ pressure (log\({{\text{P}}_{{\text{C}}{{\text{O}}_{\text{2}}}}}\)) for pre-monsoon, monsoon and post-monsoon has been estimated. The question of rates of chemical weathering (carbonate and silicate) was addressed by using TDS and run-off (mm year^?1). It has been found that the extent of CWR is directly dependent on the CO₂ consumption rate which may be further evaluated from the perspective of climate change mitigation The average annual CO₂ consumption rate of the Brahmaputra River due to silicate and carbonate weathering was found to be 0.52 (×10⁶ mol Km^?2 year^?1) and 0.55 (×10⁶ mol Km^?2 year^?1) for cycle I and 0.49 (×10⁶ mol Km^?2 year^?1) and 0.52 (×10⁶ mol Km^?2 year^?1) for cycle II, respectively, which were significantly higher than that of other Himalayan rivers. Estimation of CWR of the Brahmaputra River indicates that carbonate weathering largely dominates the water chemistry of the Brahmaputra River.     

Seasonal and annual variations in the organic matter contributed by the St Lawrence River to the Gulf of St. Lawrence

The St. Lawrence River discharges a substantial volume of water (405 km³/a) containing suspended (SPM; 3.42 × 10⁶t) and dissolved (68.0 × 10⁶t) materials to the Gulf of St. Lawrence. The total load contains organic carbon in paniculate (POC; 3–14% of SPM), and dissolved (DOC; 3.76 ± 0.63 mg/l) form. The concentration of POC (and particulate organic nitrogen) is positively correlated with discharge (increased during the spring flood and the fall enhancement of flow), but concentration of DOC is not so simply related to discharge. In consequence, the total organic carbon (POC + DOC) load is relatively invariant, and increased annually by only 2–3% despite a progressive increase of 8% in discharge over the years of this study. Seasonal differences in the composition of the particulate organic matter (POM) are interpreted as reflecting dominant contributions from within-river production in summer and from terrestrial sources in spring and fall. In years when the annual discharge was greater than average, a higher proportion of the POM was terrigenous. The organic matter in surface sediments of the estuary to which the river discharges is predominantly of terrestrial provenance.     

Temporal and spatial variability of sediment flux into the sea from the three largest rivers in China

The Yellow, Yangtze and Pearl Rivers supply over 90% of the sediment flux from China to the western Pacific Ocean. Trends and abrupt changes in the water discharge and sediment load of the three rivers were examined and compared based on data updated to the year 2011 at the seasonal and annual scales. The total water discharge from the three rivers shows a statistically insignificant decreasing trend with a rate of 0.62 × 10⁹ m³/a, and the total sediment load shows a statistically significant decreasing trend at a rate of 31.12 × 10⁶ t/a from the 1950s to 2011. The water discharge of the entire Yellow River and the upstream portion of the Yangtze River shows significant decreasing trends, and that of the mid-lower stream of Yangtze River and the entire Pearl River shows insignificant trends. The sediment loads in the three river basins all show significant decreasing trends at the annual and seasonal scales, and a dramatic decrease in the 2000s resulted in a more obvious decreasing trend over the studied period. From the 1950s to the 2000s, the contribution of sediment flux from the Yellow River to the ocean decreased from 71.8% to 37.0%, and the contributions of the Yangtze and Pearl Rivers increased from 24.2% and 4.0% to 53.0% and 10.0%, respectively. Inter-annual variations in water discharge and sediment load were affected by climate oscillations, such as the El Niño/Southern Oscillation, and the long-term decreasing trend in sediment load was primarily caused by human activities. Dam constructions and soil conservation projects were the major causes of sediment reduction. From the 1970s to the 2000s, the decrease in total sediment load from the three rivers caused by climate change and human activities was 2.24 × 10⁸ t/a (23.0%) and 7.5 × 10⁸ t/a (77.0%), respectively. In the coming decades, the sediment flux from the three rivers into the sea will decrease further with intensifying human activities, resulting in many challenges for the management of river basins and river deltas.     

天山乌鲁木齐河源1号冰川融水径流水化学特征研究

2006年和2007年的整个消融期内,在天山乌鲁木齐河源1号冰川末端水文控制点逐日定时采集融水径流样品,对样品的主要可溶离子、pH、电导率EC、总溶解固体TDS和悬移质颗粒物SPM进行了分析. 结果表明：天山乌鲁木齐河源1号冰川融水径流离子类型为Ca²⁺-HCO₃^--SO₄^2-,呈弱碱性. 融水径流中TDS变化受日径流量调节显著,表现为消融初期和末期浓度较高,消融强烈时浓度较低;SPM以细颗粒物质为主,各粒度组分含量变化幅度较大,且质量浓度SSC年内变化与TDS呈相反的变化趋势. 融水径流中离子组成主要受岩石风化作用影响,离子摩尔比值和Piper图分析表明,控制冰川径流离子组成的主要过程是碳酸盐、黄铁矿和长石类矿物风化作用.     

The effects of the July 2005 catastrophic inundations in the Siret River��s Lower Watershed, Romania

The Siret River originates from the Wooded Carpathians (Ukraine) and has a length of 559 km on the Romanian territory. The upper river course is set on the Ukrainian territory, the middle course flows through the Suceava Tableland, and then the limit between the Moldavian Subcarpathians and the Bârlad Tableland, followed by the lower course crosses the Inferior Siret Plain. The hydrographical network includes 1,013 water tributaries (representing the richest river from this point of view in Romania) and has a length of 15,157 km, which represents 19.2% of the total length of the Romanian river network. This materializes in a density of 0.35 km/km², compared to 0.33 km/km² which is the average for Romania. The Siret River has the greatest watershed area, with a total surface of 42,890 km², which represents 18.1% of the Romanian territory. Its discharge is the highest of all internal rivers of Romania, with an average discharge of 210 m³/s at the river mouth, and this is caused by the fact that most of the tributaries come from mountainous sectors, namely the Eastern Carpathians. In the summer of 2005, the most powerful floods ever occurred in the Siret River watershed with significant negative effects on the country??s economy. Considering the multiannual average discharge of 210 m³/s, the maximum discharge recorded on July 16, 2005, was of 4,650 m³/s at Lungoci. The main cause of these events is the deforestation of the small watersheds located in the mountainous sector of the counties of Vrancea, Bacau and Neamt. The total surface affected by floods was of 58,323.936 hectares, of which: 34,142.349 ha (58.54%) arable land, 6,697.486 ha (11.48%) orchards and wine-growing plantations, 1,863.698 ha (3.20%) built areas, 2,866.313 ha (4.91%), forests 4,915.985 ha (8.43%), waters 2,081.047 ha (3.57%), and unproductive land 5,757.058 ha (9.87%). Besides the material losses (over 10,000 houses completely destroyed), 24 human deaths were recorded together with the loss of thousands of domestic animals, whose overall value exceeded two million Euros. The estimation of the extent of the flooding and its impact in the Siret River watershed has been performed using LANDSAT TM 2003 satellite images and the FAO-LCCS classification methodology, in the ASR-CRUTA remote sensing laboratory, with the images offered after activating the International CHARTER (Call ID-98).     

Quantifying baseflow and water-quality impacts from a gravel-dominated alluvial aquifer in an urban reach of a large Canadian river

Groundwater discharge and non-point source (NPS) loading were evaluated along an urban reach of an eastern-slopes Rocky Mountains river (Bow River, Canada) to understand sources of water-quality impacts and baseflow. The discharge did not increase measurably over a 16-km reach. Groundwater in the river-connected alluvial aquifer was a mixture of river and prairie groundwater, with elevated chloride concentrations (average 379 mg L^–1) from road salt. Alluvial groundwater was the major NPS of chloride discharging to the river. Although the mass-flux based estimates of groundwater discharge were small (mean 0.02 m³ s^–1 km^–1, SD = 0.04 m³ s^–1 km^–1, n?=?30), the associated chloride mass flux over 16 km was significant (equivalent to that discharged from the city’s largest wastewater-treatment-plant effluent). Although local groundwater baseflow was previously thought to contribute significantly to overwinter baseflow in this reach, little contribution was measured in this study. Low baseflow generation is consistent with long-term river discharge data that show almost all of the baseflow generation occurs in the Rocky Mountain reach. Thus, local watershed areas are important for water-quality protection, but climate change in the headwaters is most salient to long-term flow.     

Chemical and strontium isotopic characteristics of shallow groundwater in the Ordos Desert Plateau,North China: Implications for the dissolved Sr source and water–rock interactions

In this study, the chemical and Sr isotopic compositions of shallow groundwater and rainwater in the Ordos Desert Plateau, North China, and river water from the nearby Yellow River, are investigated to determine the dissolved Sr source and water–rock interactions, and quantify the relative Sr contribution from each end-member. Three groundwater systems have been identified, namely, GWS-1, GWS-2 and GWS-3 according to the watershed distribution in the Ordos Desert Plateau. Ca²⁺ and Mg²⁺ are the most dominant cations in GWS-1, while Na⁺ is dominant in GWS-3. In addition, there is more SO₄²⁻ and less Cl⁻ in GWS-1 than in GWS-3. The shallow groundwater in GWS-2 seems to be geochemically between that in GWS-1 and GWS-3. The ⁸⁷Sr/⁸⁶Sr ratios of the shallow groundwater are high in GWS-1 and GWS-2 and are low in GWS-3. By geochemically comparing the nearby Yellow River, local precipitation and deep groundwater, the shallow groundwater is recharged only by local precipitation. The ionic and isotopic ratios indicate that carbonate dissolution is an important process controlling the chemistry of the shallow groundwater. The intensity of the water–rock interactions varies among the three groundwater systems and even within each groundwater system. Three end-members controlling the groundwater chemistry are isotopically identified: (1) precipitation infiltration, (2) carbonate dissolution and (3) silicate weathering. The relative Sr contributions of the three end-members show that precipitation infiltration and carbonate dissolution are the primary sources of the shallow groundwater Sr in GWS-3 whereas only carbonate dissolution is responsible for the shallow groundwater Sr in GWS-1 and GWS-2. Silicate weathering seems insignificant towards the shallow groundwater's chemistry in the Ordos Desert Plateau. This study is helpful for understanding groundwater chemistry and managing water resources.     

珠江流域岩石风化作用消耗大气/土壤CO2量的估算

以流域的岩性、径流量和水化学分析数据为主要资料,利用基于GIS空间分析的GEM-CO2模型,估算珠江流域陆地岩石风化作用消耗大气/土壤空气中的CO2,评价河流流域的碳汇能力。结果表明,珠江流域因岩石溶蚀和风化作用消耗大气/土壤中的CO2量为252×109 mol·a-1(571×103 mol·km-2·a-1),从岩性分析,碳酸盐岩区大气/土壤CO2消耗量为180×109 mol·a-1(1030×103 mol·km-2·a-1),占总量的71.4%。二级流域以西江流域CO2消耗量最大,占珠江流域总CO2消耗量79.4%,北江、东江分别占总量的13.0%、4.9%。珠江流域大气/土壤CO2消耗量大约为世界大河流域平均值的2.3倍。     

珠江流域碳酸盐岩与硅酸盐岩风化对大气CO_2汇的效应

对珠江流域11个测站的河水1个水文年4次取样进行水化学和同位素测试分析,揭示无论是碳酸盐岩区还是硅酸盐岩区,岩石风化均使河流的离子成分以HCO3-、Ca2+、Mg2+为主,碳酸盐岩风化溶蚀速率和由碳酸盐岩风化溶蚀引起的大气CO2消耗量分别为27.60 mm/ka和540.21x103mol/(km2·a-1),是硅酸盐岩风化速率和由硅酸盐岩风化引起的大气CO2消耗量的10.8倍和6.7倍,说明碳酸盐岩风化是流域碳汇过程及效应的主体。由于有利的水热条件和高的碳酸盐岩面积比例,珠江流域平均岩石风化速率和由岩石风化作用引起的大气CO2消耗量分别为30.15mm/ka和620.36×103mol/(km2·a-1),为全球60条河流平均值的2.6倍。