Carbonate weathering is sensitive to tectonic and climatic settings due to its rapid dissolution kinetics, playing an important role in the carbon cycle at short time scales (102 2 to 104 4 years). Under global warming, extreme weather and hydrological events have become more frequent worldwide. How carbonate weathering and its associated carbon budget respond to these extreme events remains unclear. Here, high-temporal-resolution (weekly) riverine chemistry during 2010 was investigated in the upper Min Jiang, a highly-erosion river catchment on the eastern Tibetan Plateau. River water chemistry during the monsoon season fluctuated with six storm events (9 days in total) that were characterized by 7-14 times higher water discharge and 10-40 times higher erosion than those of the non-monsoon seasons. Based on a forward model, riverine chemistry was dominated by carbonate dissolution in the upper Min Jiang. Compared to the non-monsoon seasons, the storm events triggered 270% and 264% increases in the average fluxes of carbonate weathering and associated CO2 2 consumption, respectively. Furthermore, an incongruent carbonate dissolution (ICD) model as a possible mechanism was employed to reveal the preferential leaching of Mg2+ 2 + and Sr2+ 2 + relative to Ca2+ 2 + during carbonate weathering under extremely-high erosion at basin scale. Accompanying the ICD, the storm-derived carbonates were likely carried downstream as suspended particles for further weathering. This study demonstrates the intensification of carbonate weathering and a carbon sink by storm events, with incongruent carbonate dissolution under storm-induced high erosion.

In order to better understand how stable metal isotope signals in large rivers can be used to constrain present and past weathering, the seasonal riverine Mg-Sr isotopic pattern in the middle Yellow River was systematically investigated based upon weekly collected samples for the whole year of 2013. The results demonstrate that Mg is mainly transported in the dissolved form (65%) in this river system and that 45% of the total dissolved Mg is transported during the monsoon seasons, with 2% exported over 4 days during a single storm event. Dissolved Mg in the middle Yellow River is dominantly derived from both silicate and carbonate (82-89%) in this semi-arid region, with limited evaporite contribution (similar to 7%). Lithological mixing is the first order control on riverine dissolved Mg and Sr isotopes, with a contribution from similar to 40% carbonate dissolution and similar to 60% from silicate dissolution in the dry seasons, and similar to 50% carbonate and similar to 50% silicate during the monsoon seasons according to delta 26Mg signals. Furthermore, a significant role of prior calcite precipitation (PCP) can be quantified, which fractionates Mg isotopes by about 0.17%o to 0.39%o positively depending on the choice of elemental and isotope partition of Mg in secondary carbonates. Clay formation following the PCP further fractionates riverine Mg isotopes to the negative side. An similar to 0.2%o decrease of riverine Mg isotopes is attributable to (1) a single storm event causing carbonate dissolution and (2) delayed delivery of depleted waters to rivers (similar to 3 months after the storm event) because of subsurface hydrological circulation. Annually, the weighted average riverine delta 26Mg (- 1.05%o) in the middle Yellow River is identical to the global average (-1.09%o). Despite the significant impact of lithology on the riverine dissolved Mg isotope signature, the mixing proportions of different Mg sources remain virtually constant, even when there are huge contrast of temperature, hydrology, and precipitation seasonally along the year, providing a basis for dissolved delta 26Mg response to climatic forcing on the continental scale. This means that significant changes in the sedimentary Mg isotope records would reflect extreme conditions in deep time.

Carbonate weathering plays a significant role in regulating global carbon budget at short time scales, and thus needs to be better constrained in the context of global warming. Riverine magnesium isotopes (delta 26Mg) have the potential to trace carbonate weathering intensity (CWI) but require further testing under various climatic and geological settings. Cation exchange is an important mechanism buffering river water chemistry, especially in catchments characterized by high erosion. However, field evidence on the influence of cation exchange on riverine delta 26Mg is rare. In this study, spatial riverine delta 26Mg variation within the Three Rivers (i.e., the Jinsha Jiang, the Lancang Jiang, and the Nu Jiang), three extremely-high-erosion catchments in the southeastern Ti-betan Plateau, was investigated to address this issue. The results showed that riverine delta 26Mg values present a wide range from -1.11 %o to -0.59 %o in the Jinsha Jiang, from -1.39 %o to -0.65 %o in the Lancang Jiang, and from -1.19 %o to -0.50 %o in the Nu Jiang. An inversion model was used to partition riverine Mg2+ sources and confirmed that the riverine Mg2+ budget was dominated by carbonate weathering, followed by evaporite dissolution. However, conservative mixing could not explain riverine delta 26Mg variation within the Three Rivers catchments, because measured delta 26Mg values (delta 26Mgmeasured) systematically deviated from the modeled ones (delta 26Mgmodeled), with Delta 26Mgmeasured-modeled (delta 26Mgmeasured - delta 26Mgmodeled) up to 0.79 %o. The positive correlations between Delta 26Mgmeasured-modeled and suspended particulate matter (SPM) concentrations indicate Mg isotopic fractionation was related to high suspended loads owing to extremely-high erosion rates. Given the significant cation exchange capacity of SPM, Mg2+-Na+ exchange is proposed for the first time as an explanation for the observed delta 26Mg variations in the rivers draining the Tibetan Plateau, although the role of carbonate precipitation could not be excluded. The strong positive correlations between riverine delta 26Mg and exchangeable Mg/Na ratios in the Three Rivers further support that light Mg isotopes may be preferentially retained in the riverine exchange pool during Mg2+-Na+ exchange, driving riverine delta 26Mg towards higher values. Expanding our finding to global rivers, the negative correlation between riverine delta 26Mg and CWI can be interpreted by a competition between the fast dissolution of carbonates leading to the enrichment of 24Mg in waters and Mg isotope fractionation induced by cation exchange leading to the depletion of 24Mg in the residual waters. This study provides new insight into cation exchange as a regulator of riverine delta 26Mg and Mg cycling, highlighting the robustness of riverine delta 26Mg in tracing CWI and constraining the carbon cycle.

Carbonate weathering regulates the short-term carbon (C) cycle and global climate due to its fast response to hydrological processes. The carbonate weathering flux needs to be well constrained to better understand the climate change at short time scale. Riverine magnesium (Mg) isotopes are sensitive to primary mineral dissolution and so have great potential to trace carbonate weathering. Global large rivers draining continental crust dominate weathering flux to the oceans, but how riverine Mg isotopes respond to carbonate weathering remains unclear. The Yangtze River drainage basin (YRDB) was selected to test the robustness of riverine Mg isotopes (δ26Mg) in tracing continental carbonate weathering because it spans a wide range in lithology, geomorphology and climate. The riverine δ26Mg values within the YRDB show a decreasing trend from the headwater to the mainstream ranging from −1.36‰ to −0.59‰. The dissolved δ26Mg have strong negative correlations with carbonate weathering rate and intensity within the YRDB, indicating a sensitive response of riverine δ26Mg to the carbonate weathering flux. In a compilation of Mg fluxes and δ26Mg in the world's largest rivers, there is similar dominance of carbonate weathering on riverine Mg fluxes and isotopes. Therefore, we propose that riverine δ26Mg in large rivers are a robust tracer of carbonate weathering intensity. Intensifying carbonate weathering under global warming tends to increase riverine Mg and C fluxes to the oceans and thus the atmospheric CO2 sink at the millennial time scale.

The Huanghe once had a sediment flux of >1,000 Mt/yr, but this has decreased by ∼90% as its river sediment routing systems have undergone dramatic changes influenced by human activities such as dam construction. However, the way in which the sediment geochemistry of the river has responded to the altered sediment routing processes is not well known. This study investigates the sediment source‐to‐sink routing regime of the Huanghe River using Nd isotope fingerprinting. Four major source terranes, namely the Songpan‐Ganzi (SG) Block, Ordos Desert (OD), Chinese Loess Plateau (CLP) and North China Craton (NCC) are recognized according to their distinct Nd isotopes. The gradual downstream decrease in εNd values in sediments of the upper Huanghe indicates a decreasing contribution of material from the SG Block and a corresponding increase contribution of local underlying basement rocks, which is inferred to be related to sediment capture by a cascade of hydroelectric dams. A gradual increase in εNd from Yinchuan to Tongguan suggests an increasing contribution from the CLP under intense erosion. Relatively low εNd in the downstream sediments suggest a contribution from proximal NCC basement, consistent with the shift from deposition to erosion in the lower channel in recent years. The marked heterogeneity in Nd isotopes in the Huanghe sediments corresponds well to sediment source‐to‐sink processes in response to increasing human impacts. In a setting of global rivers facing strong anthropogenic impacts, the ways in which altered sediment routing systems affect river sediment geochemistry deserve more research attention.

为评估2010-2019年成都市机动车防控措施的减排效果,以2010年为基准年,采用排放清单法计算了各减排措施下2019年的减排量,对比分析了4种控制措施的减排效益.结果表明:成都市机动车排污总量逐年下降,2019年PM2.5、NOx、VOCs、CO、SO2和NH3的排放量分别为0.27×104、4.63×104、1.70×104、28.99×104、0.21×104和0.45×104t,主要分布在中心城区,其中重型货车对PM2.5和NOx贡献最大,小型客车对VOCs、CO、SO2和NH3贡献最大;措施中加严标准的综合减排量最大,重点减排车型为小型客车、轻型货车、公交车等,2019年6种污染物减排量分别为0.14×104、2.27×104、1.29×104、6.77×104、0.07×104和0.38×104t;优化城市交通管理对小型客车和摩托车的减排效果显著,2019年6种污染物减排量分别为0.04×104、0.81×104、0.38×104、2.55×104、0.05×104和0.04×104t;淘汰高排放车辆对小型客车、轻型货车等的减排较明显,2019年6种污染物减排放量分别为0.13×104、0.98×104、0.34×104、2.62×104、0.01×104和0.007×104t;推广清洁能源汽车的重点减排车型为出租车和公交车,虽然可有效减少PM2.5、NOx的排放,但VOCs却有小幅增加,2019年6种污染物减排放量分别为0.12×104、0.62×104、-0.13×104、0.30×104、0.004×104和0.000 5×104t.

随着多接收电感耦合等离子体质谱技术的快速发展,越来越多非传统稳定同位素在地学的众多研究领域展现出巨大的应用潜力.钡同位素在早期主要用于行星演化研究,而随着其分析精度的提升,被较广泛地用来示踪研究地球表生过程和环境演变.近些年,钡同位素在海洋学研究中发展迅速,尤其是在示踪(古)海洋生产力方面具有巨大潜力.本次研究综述了海洋钡的主要储库——海水、沉积物和珊瑚的钡同位素组成特征,及其示踪(古)海洋生产力的研究现状与进展,分析当前研究薄弱点,进而展望钡同位素地球化学在海洋科学研究的广阔应用前景.

对MOVES、COPERT、MOBILE、IVE、CEME等五种常见的机动车尾气排放模型的应用进行了总结,从地域性、成熟度、不确定性等方面对比评价了这几种模型的优点和适用范围,并基于研究现状提出了未来我国机动车排放因子的研究方向.

采用DustTRAK TM气溶胶(粉尘)监测仪对成都市112个不同类别的房建、市政工地施工扬尘进行测试,研究了不同类别施工扬尘的排放特征,分析了下风向扬尘浓度的变化趋势,并采用CALPUFF对成都市新都区某建筑工地的排放进行了模拟.结果表明:(1)成都市施工扬尘排放浓度约为0.13～2.91mg/m3,其中房建类施工平均浓度约为0.94mg/m3,高于市政施工;大型工地扬尘平均浓度约为0.61mg/m3,低于中型和小型工地;土方施工阶段平均浓度约为1.21mg/m3,远高于地基建设、主体建设、装饰阶段.(2)成都市施工扬尘呈现出高低浓度交替的周期性变化,其中房建工程土方施工阶段的高低浓度差值可达到0.6mg/m3以上.(3)施工扬尘在场界外下风向5～15m范围内会出现浓度增加的趋势,随后逐渐下降,在50m附近逐渐趋于稳定,稳定浓度介于0.1～0.2mg/m3.(4)CALPUFF模型能较好地从宏观角度来模拟成都地区施工扬尘的扩散趋势,但难以捕捉施工扬尘在下风向近距离的扩散特征.

利用ECMWF-ERA5和NCEP-FNL再分析资料作为中尺度气象模式WRF(The Weather Research and Forecasting)初始场,对四川盆地2018年1月一次大气污染过程气象要素进行了模拟,对比分析了气温、风速、风向、相对湿度、边界层高度、温廓线的模拟效果,并结合大气超级站观测数据对模拟结果进行评估.结果表明:两种资料均能较好地模拟出气象要素的变化情况,但由于两套资料时空分辨率、采用的模式、同化方案、数据来源和质量控制方案存在一定区别,导致各要素模拟效果并不一致.与NCEP-FNL相比,ECMWF-ERA5模拟的平均相对湿度(59.23％)与观测值差异更小,且均方根误差、偏差较小,分别为9.83％和-0.83％,但NCEP-FNL模拟的平均气温(8.99℃)更接近观测值,且偏差值较小,为-0.04℃.两组模拟结果均显示盆地内部为模拟区域的低风速区,相对湿度模拟值在60％以上,气温高于西部山地地区.NCEP-FNL模拟的盆地内部气温、相对湿度、风速小于ECMWF-ERA5模拟值,但边界层高度模拟值较大.ECMWF-ERA5模拟的逆温强度相比较小,且温度露点差较小.此次污染过程PM2.5和PM10日均浓度最大值分别为190.1 μg·m-3和261.0 μg·m-3,相对湿度增大引发的颗粒物吸湿增长是导致PM2.5和PM10质量浓度突增的主要原因.

Barium (Ba) isotopes have been used to trace water mass mixing and export productivity in the oceans. However, the sources, isotopic signature and seasonal variation of dissolved Ba in large rivers remain poorly constrained. In order to improve our understanding of sources and fractionation of riverine Ba isotopes at the continental scale, weekly sampling of river water was carried out in the middle Yellow River over the full hydrological year of 2013. Dissolved Ba was mainly sourced from silicate dissolution, whose flux was correlated with physical erosion rate in this arid to semi-arid basin, largely covered by loess. More than half of the annual dissolved Ba flux was transported during the monsoon season (June to mid-September), in particular during a storm event period (accounting for 4% of the annual dissolved Ba flux in 4 days). The dissolved Ba isotopic composition (delta (138) Ba-rw) ranged from +0.17 parts per thousand to +0.46 parts per thousand, all higher than delta Ba-138 of loess (0.00 +/- 0.04 parts per thousand). The seasonal variation in delta Ba-138(rw) is best explained via an adsorption model of light Ba isotopes onto solids in the river, which is sensitive to erosion of loess, in particular during the storm event and the spring-time ice melting intervals, with a potential role of barite precipitation in groundwater during the dry seasons. With one to three orders of magnitude higher particulate matter fluxes during the monsoon seasons in rivers such as the Yellow River, desorption of Ba could result an unaccounted strong variation of Ba concentration and isotopic composition in coastal environments, which further study requires. (C) 2019 Elsevier B.V. All rights reserved.