Batch Dissolution Kinetics: The Shrinking Sphere Model with Salts and Its Potential Application to Biogenic Silica     

Victor W. Truesdale 《Aquatic Geochemistry》2007,13(4):267-287

The full potential of batch dissolution experiments in geochemical and industrial applications has been hampered by the lack of an equation to describe the increase in dissolved solid concentration with time. This study provides new experimental results on the dissolution of salts and new equations, which describe dissolution according to the shrinking sphere model. Sieved salts were found to dissolve according to the shrinking sphere model while the dissolution of the parent material, raw (agglomerated) salt, fitted an exponential dissolution curve. The implications of this to the development of a systematic approach to batch dissolution, irrespective of the solid, is explored. Mathematical equations are derived for the dissolution of solids in under-saturated systems, which are much simpler than ones available, so far. In turn these provide easier comprehension of the workings of the shrinking sphere model. Finally, existing results for biogenic silica dissolution are reviewed in the light of the above-mentioned experimental and modelling advances. An earlier claim that shrinking sphere dissolution had been observed is refuted.  相似文献   

海南岛万泉河口沉积物有机碳、 氮同位素的特征及其环境意义^*   总被引：4，自引：0，他引：4  

葛晨东  王颖  T.F.Pedersen  O.Slaymaker 《第四纪研究》2007,27(5):845-852

对海南岛万泉河口沙美内海柱样K3和K4沉积物进行生物地球化学指标总有机碳(TOC)、总氮(TN)、有机碳同位素(δ¹³ C)、氮同位素(δ¹⁵ N)的分析,以及²¹⁰ Pb定年了解其近代变化特征,追踪沉积物有机质来源的变化,提取沉积环境演变及人类活动的信息。K3中TOC的变化介于0.51 ％ ~1.12 ％ ,K4变化介于0.43 ％ ~1.49 ％ ,而其随时间的变化反映了流域内人类活动的历史。17世纪TOC含量明显增加记录了明末清初开始流域内广泛种植农作物的活动,19世纪以来TOC含量逐渐增加,至现代达最高值,对应了工业革命以来人类活动的增强。K3和K4的δ¹³ C值变化分别在-24.38 ‰ ~-21.02 ‰ 之间和-24.74 ‰ ~-20.17 ‰ 之间,δ¹⁵ N值变化分别在2.20 ‰ ~4.62 ‰ 之间和2.39 ‰ ~5.02 ‰ 之间,映证了本区沉积物有机质是陆源物质和海洋物质混合的特点。明末清初开始流域内广泛种植玉米等农作物造成δ¹³ C值增加和δ¹⁵ N值减少; 自19世纪以来至现在,该区的经济活动增加,人口的持续增长,尤其是近50年来化肥农药的大量使用,造成陆源输入的有机碳含量大幅增加,使δ¹³ C值减少和δ¹⁵ N比值增加。 δ¹³ C值自19世纪以来就逐渐变轻,说明陆源和海洋有机碳的比例发生了变化,较轻的陆源有机碳比例相对增加,较重的海洋有机碳比例相对减少,反映了玉带滩沙坝的增长、沙美内海封闭、海水交换作用减少的状况。C/N比值分别从底部的16.19和17.36到顶部减小为11左右,自19世纪以来呈明显减小的趋势也反映了沙美内海泻湖自生的藻类有机质供应越来越多,也说明了其逐渐封闭、水动力条件越来越弱,与外海的交换作用逐渐减少的状况。  相似文献   

基于弹性脆弱性的环巢湖自行车赛风险辨识     

王学林 《沙漠与绿洲气象(新疆气象)》2020,14(2):123-128

为提高环巢湖自行车公开赛的气象保障服务能力。本研究基于2013-2016年环巢湖自行车赛举办期间收集到的问卷调查资料，总结归纳出自行车骑行比赛的气象适宜性指标，并从强化措施和规避措施两个方面出发，构建基于脆弱性指标体系的环巢湖自行车公开赛风险辨识概念模型，并利用巢湖国家基本气象站1957-2016年逐日气象观测资料对2017年环巢湖自行车赛做个例分析。研究结果表明：（1）2017年4月23日我市降水适宜性和温度适宜性概率普遍较高，分别为70%和39%，而相对湿度和风速适宜度概率略偏低，因此，相对湿度和湿度是制约运动员发挥的重要因子。（2）各参评因子在4月份均具有明显的震荡特征，降水和相对湿度在四月上旬适宜度较高，而日平均气温和风速呈现明显相反的趋势。（3）降水适宜度综合指数在4月份普遍高于风速、温度、湿度，表明四月份无降水的概率普遍较高；综合适宜度指数四月中下旬优于上旬，表明环巢湖赛事选择下旬举行最佳。（4）分析综合因子重现期发现，四月下旬重现期普遍短于上中旬。本研究结果可为环巢湖自行车公开赛的赛前安排、赛事评估等方面提供科学依据。  相似文献   

磷的生物地球化学循环研究进展     

周强  姜允斌  郝记华  季峻峰  李伟 《高校地质学报》2021,27(2):183-199

磷是生命体的必需元素,也是粮食生产的重要限制因素。磷的生物地球化学循环不仅调控着海洋的初级生产力,而且影响着全球气候系统,并决定着磷矿资源的形成和分布,与地球上生命的生存繁衍息息相关。当前“地球系统科学”理论将大气圈、水圈、岩石圈（地壳和上地幔）和生物圈等子系统有机整合,为研究磷的生物地球化学循环提供了更加广阔的视野。基于已有研究,结合“地球系统科学”理论观点,针对磷的生物化学循环获得了以下重要认识： 磷在地质历史时期的演化决定了现今磷在全球范围内（陆地生态系统与海洋生态系统）的循环模式;人类的工业和农业活动作为重要的地质营力,改变了磷的生物地球化学循环过程,造成了磷矿枯竭的资源危机及水体富营养化的环境问题;解决磷短缺的资源危机问题和磷过剩的环境污染问题的关键在于调控引起这些问题的生物地球化学循环过程。  相似文献   

Towards a heterogeneous environmental responsibility: sustainability and cycling fundamentalism     

Julie Cupples  Elisabeth Ridley 《Area》2008,40(2):254-264

This article explores the urban governmentalities that are emerging through the discursive constitution of cycling as a form of sustainable transport. It has two main aims. The first is to explore and critique the strategies and discourses used to promote cycling as a sustainable form of transport. We argue that cycling advocacy displays totalising tendencies which obscure social and cultural difference, ignore the embodied and affective dimensions of transport practices and fail in part to apprehend the heterogeneity of environmental responsibility. Our second aim is to tentatively suggest a more productive way of knowing and talking about cycling that might be constitutive of a less exclusionary affective ethical sensibility.  相似文献   

The response of drainage basins to the late Quaternary tectonics in the Sicilian side of the Messina Strait (NE Sicily)     

Pierpaolo Guarnieri  Claudia Pirrotta 《Geomorphology》2008,95(3-4):260-273

Despite more than 40 yr of research attributing temporal changes in streambank erosion rates to subaerial processes, little quantitative information is available on the relationships between streambank erodibility (k_d) and critical shear stress (τ_c) and the environmental conditions and processes that enhance streambank erosion potential. The study goal was to evaluate temporal changes in k_d and τ_c from soil desiccation and freeze–thaw cycling. Soil erodibility and τ_c were measured monthly in situ using a multiangle, submerged jet test device. Soil moisture, temperature, and bulk density as well as precipitation, air temperature, and stream stage were measured continuously to determine changes in soil moisture content and state. Pairwise Mann–Whitney tests indicted k_d was 2.9 and 2.1 times higher (p < 0.0065) during the winter (December–March) than in the spring/fall (April–May, October–November) and the summer (June–September), respectively. Regression analysis showed 80% of the variability in k_d was explained by freeze–thaw cycling alone. Study results also indicated soil bulk density was highly influenced by winter weather conditions (r² = 0.86): bulk density was inversely related to both soil water content and freeze–thaw cycling. Results showed that significant changes in the resistance of streambank soils to fluvial erosion can be attributed to subaerial processes. Water resource professionals should consider the implications of increased soil erodibility during the winter in the development of channel erosion models and stream restoration designs.  相似文献   

地下水中稳定铬同位素的生物地球化学作用   总被引：2，自引：0，他引：2  

徐芬  马腾  Andre Ellis  刘存富  高永娟  李理 《地学前缘》2012,19(4):183-193

铬是地下水中常见的一种变价重金属污染物,在自然界中广泛分布且应用广泛。将Cr(Ⅵ)还原为Cr(Ⅲ)是地下水铬污染防治中的主要策略。在Cr(Ⅵ)的非生物还原过程中存在铬同位素分馏现象,通过地下水中铬同位素组成的变化情况可以定量地指示Cr(Ⅵ)的还原程度和速率。这被认为是一个重要发现,在地下水铬污染防治中有着广阔的应用前景。文中对铬与铬的来源、地下水中铬同位素的测定方法、铬同位素的生物地球化学作用、铬同位素在地下水污染防治中的应用等进行了系统综述。研究认为：微生物广泛参与地下水中铬的氧化与还原作用,并有可能产生显著的铬同位素分馏。地下水中被还原的Cr(Ⅵ)在微生物作用下有可能被活化,用非生物还原条件下的铬同位素分馏规律指示地下水中Cr(Ⅵ)还原程度可能会产生较大的误差。开展地下水中铬同位素的生物地球化学作用研究,特别是生物氧化Cr(Ⅲ)过程中的铬同位素分馏规律研究,对于更全面地认识铬同位素的指示作用具有重要意义。  相似文献   

岩溶IGCP国际合作30年与岩溶关键带研究展望   总被引：2，自引：1，他引：1  

章程  蒋忠诚  Chris Groves  袁道先 《中国岩溶》2019,38(3):301-306

全球岩溶类型多样,对环境变化敏感,资源与环境问题突出,是地球关键带监测与研究的重点,IGCP661项目的执行为岩溶区关键带类型划分与监测对比研究提供了契机和国际合作平台。近30年岩溶IGCP执行始终强调岩溶系统与人类活动环境的相互作用,其轨迹实际上与地球系统科学到地球关键带理念是一脉相承的。IGCP299提出了岩溶形态组合概念,揭示各种岩溶形态与其形成环境之间的因果关系。岩溶动力系统(IGCP379), 岩溶生态系统(IGCP448)概念的提出有助于我们更好地理解岩溶系统的整体功能,及系统内水、生物地球化学过程、人类活动的相互作用,进而形成了一整套岩溶动力学研究方法体系。开辟了岩溶记录与全球变化、碳循环与应对气候变化、石漠化形成演变与生态修复等研究新领域,并取得了丰硕的研究成果,有力地推动了现代岩溶学的发展。   相似文献   

Distribution of petroleum hydrocarbons in soils and the underlying unsaturated subsurface at an abandoned petrochemical site,North China   总被引：1，自引：0，他引：1       下载免费PDF全文

Qian Zhang  Guangcai Wang  Norio Sugiura  Motoo Utsumi  Zhenya Zhang  Yingnan Yang 《水文研究》2014,28(4):2185-2191

Contamination characteristics of petroleum hydrocarbons in soils and the underlying unsaturated subsurface were analysed by investigating and sampling at different depth of five boreholes named SH1 through SH5 at a typical petrochemical site, North China. Topsoil volatile organic gas measurement revealed that SH‐3 was the center of one pollution plume. Soil samples analysis showed that aromatic hydrocarbons and chlorinated hydrocarbons were major pollutants. Their maximum concentration was found at 6.5 and 14.6 m of SH‐2, 13 m of SH‐5, and 18.5 m of SH‐3. These pollutants are mostly accumulated on the interface between two different lithological layers, especially between the sand and silt clay layers. Denitrifying and iron reducing were main biogeochemical processes in this site. Under the influence of groundwater level fluctuation, free NAPLs passed through the boundary and dissolved into the lower groundwater. Knowledge of these associations between contaminant distributions and affecting factors could have implications for soil and groundwater pollution prevention and control. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Modelling the impacts of semi-intensive aquaculture on the foodweb functioning of a Nile Delta coastal lake     

M Bocci  R Pastres  S Kholeif  D Dalla Barba 《African Journal of Marine Science》2017,39(3):237-249

Nutrient loadings are an important component of aquaculture impacts as they can lead to cascade effects at the ecosystem level. An evaluation of these effects on foodweb functioning is presented and discussed for the case study of Lake Burullus in the Nile Delta, Egypt, where semi-intensive aquaculture in earthen ponds has grown remarkably in recent decades. Estimations of nutrient loads into the lake's brackish water, from agriculture and fish ponds, were assessed. A biogeochemical model was set up and calibrated to simulate the loads from nitrogen, phosphorus and phytoplankton, with and without fish ponds. The biogeochemical model was coupled offline to a foodweb model to test the effects of additional nutrient loads from aquaculture on the lake's foodweb functioning. The results obtained by comparing the present conditions of aquaculture development with a no-aquaculture scenario allowed us to identify a set of indicators of foodweb functioning which are sensitive to changes in nutrient loads from aquaculture. The limited changes in phytoplankton concentration with respect to changes in nutrient loads suggested that primary production in Lake Burullus is presently controlled largely by factors other than nutrient influxes from aquaculture. This study emphasises the potential benefits of using a combination of biogeochemical and foodweb models to assess the cumulative effects of nutrient loading from aquaculture on a receiving water body.  相似文献