The nutrient forms, cycling and exchange flux in the sediment and overlying water system in lakes from the middle and lower reaches of Yangtze River

This paper is a review of research works concerning the nutrient transportation, transformation and exchange between water, sediment and biota in the lakes from the middle and lower reaches of the Yangtze River conducted in the context of project entitled "The Processes and Mechanism of Lake Eutrophication in Middle and Lower Reaches of Yangtze River". All the lakes from this area are shallow lakes. According to the typical lake site research, the lakes from the middle and lower reaches of Yangtze River have a higher baseline of nutrition in the history. Normally the trophic status of these lakes can be categorized into medium-trophic or eutrophic. Human activities have been enhanced during the last decades, which speed up the lake eutrophic process. Lake eutrophication control needs to reduce not only the external nutrient inputs from watershed but also the internal loading from the sediments. Investigations revealed that the lake sediments in this area are considerablly high in nutrition in which at most about 30% of phosphorus exists in the form of bio-available in the sediment. The surface sediment will exert great effects on the nutrient exchange between water-sediment interface via adsorption and release of nutrient. The nutrient release from the sediment in these shallow lakes is mainly in two ways, i.e. in the undisturbed condition the nutrient is released through diffusion created by the nutrient gradient from sediment to overlying water; whereas in disturbed condition, the nutrient release is determined by the hydrodynamic forcing intensity and the sediment resuspension. Metallic elements such as the iron, manganese and aluminium and the aerobic-anaerobic ambience will affect the release of nutrients. The disturbed release will increase the total nutrients in the water column significantly in the short period. At the beginning of sediment resuspension, the dissolved nutrient concentration will increase. This increase will be damped if the ferric oxide and aluminium are rich in sediment because of the adsorption and flocculation. This means that the lakes have capability of eliminating the nutrient loadings. Investigations for the lakes from middle and down stream of Yangtze River have suggested that most lakes have the self-cleaning capability. Dredging the control of the internal loading, therefore, is only applicable to the small lakes or undisturbed bays which normally are situated nearby the city or town and rich in organic materials in the sediment. In addition, the strong reduction condition and weak aeration of these lakes and bays make these small lakes and bays release much more bio-available nutrient and without much self-eliminating capability. Moreover, eutrophication induced algal bloom in these lakes will change the pH of water, which further induces the increase in the nutrient release. In turn, the increase in nutrient release promotes the growth of phytoplankton and results in severe algal bloom. For the heavily polluted water, research suggests that the biomass of bacteria and alkaline phosphatase activity will be higher corresponding to the higher concentration of nutrients, which accelerates the nutrient recycling between water, sediment and biota. Quick recycling of nutrient, in turn, promotes the production and biomass growth of microorganism and leads to more severe eutrophication. Further research work should focus on the nutrient transformation mechanism and the effects of microbial loop on the eutrophication.     

湖泊底泥疏浚环境效应：Ⅰ.内源磷释放控制作用

通过为期一年的疏浚模拟试验,在试验室培养疏浚与对照柱样研究了底泥疏浚对内源磷释放的控制效果,结果发现,疏浚表层30cm能够有效的消减沉积物中不同形态磷含量与孔隙水中PO43-p含量,在一年的试验周期内,疏浚和对照柱沉积物-水界面的PO43-P通量分别为-143.8至14.4与-237.3至3047.6μg(m2·d),疏浚柱沉积物-水界面的磷通量总体上低于未疏浚对照的磷通量,尤其是在温度较高的月份,从2006年3-10月疏浚柱沉积物-水界面磷释放通量显著低于未疏浚对照柱,疏浚沉积物的磷的释放潜力低于未疏浚对照沉积物,研究结果表明,在外源磷得到有效控制的前提下,底泥疏浚是消减研究区内源磷负荷有效的技术手段.     

偏最小二乘法回归 (PLS)研究酸性森林土壤中铝的释放过程

采集了华南和西南酸性森林小流域中的土壤和土壤水并分析其化学组成,利用偏最小二乘法回归(PLS)研究了土壤中铝的释放过程,以综合评价各种影响因素的相对重要性。连续3年(2000～2002)的现场监测数据表明,尽管土壤水中铝的浓度存在显著差异,但铝的形态分布在各流域之间基本相似。大多数土壤水中单体铝(Ala)主要以无机态(Ali)存在,有机铝(Alo)一般不足10%。在pH3.6～5.6范围内,土壤水中Al3 活度(pAl)与土壤水pH值呈显著正相关关系(P<0.001),上层和下层土壤中pH-pAl拟合直线的斜率分别为1.28和2.00,明显偏离三水铝石(gibbsite)的溶解平衡模式。偏最小二乘法回归分析显示,上层和下层土壤中铝具有不同的来源和主导影响因素。上层土壤中,铝主要来源于有机键合铝(Alorg),土壤水离子强度(I)是造成铝浓度差异的主导因素。与此同时,铝的释放过程明显受到离子交换反应的影响。下层土壤中,铝近乎全部来源于无机键合铝(Alinorg),土壤水H 浓度成为影响铝释放过程的最主要因素。与上层土壤相比,离子交换对土壤铝释放过程影响明显减小。     

降水量对连古城自然保护区荒漠植被凋落物分解和氮状态的影响

对连古城自然保护区不同降雨梯度(不截留和分别截留30％、50％、80％)下荒漠典型植被土壤无机氮和原位净氮矿化的凋落物分解和养分释放进行了连续的观测分析.结果表明:(1)随着水分输入减少,凋落物的分解速率减小,凋落物分解速率与年降水量正相关.与此相反,净氮矿化与降水量无关.(2)土壤NO3-浓度随着降水输入的增加而显著...     

抛掷型岩爆震源体能量动态释放机制与几何尺度特征

为了进一步理解岩爆的机制并解释岩爆发生的过程,通过对抛掷型岩爆能量来源、去处及大小的分析,提出了抛掷型岩爆的震源两体模型。抛掷型岩爆本质上是释能体-岩爆体相互作用下岩石裂纹动态扩展和能量快速释放的过程。从岩爆体张拉断裂机制出发,采用脆性内聚裂纹阵列扩展动力学模型分析了裂纹间距与应变率对岩爆体能量释放速率的影响。据此得出释能体对岩爆体的作用可归结为应变率效应,释能体能量释放速率越大,对岩爆体的动态加载速率就越大,使得岩爆体能量释放速率加快。岩爆体破裂能量释放速率越大,作用于释能体的动态卸载速率就越大,又使得释能体的能量释放速率增大,两体相互作用形成的动态加、卸载效应构成了岩爆能量释放的正反馈机制。基于上述理论推导得出岩爆震源体的几何尺度是岩爆体的几倍到几十倍,理论结果与现场实际监测分析基本吻合。     

巷道开挖围岩能量释放与偏应力应变能生成的分析计算

巷道开挖,围岩能量释放,同时在围岩中产生偏应力。围岩应力是原岩应力与偏应力的叠加,偏应力或偏应力能控制岩体破坏。在静水压力 和岩体体积应变为0的条件下,利用文[1]在弹性、非线性软化本构模型导得的巷道围岩应力分布表达式,用重积分计算了围岩弹性区和软化区中的偏应力应变能 ,证明了 可以简捷地用地应力 关于巷壁位移 做一次积分再乘巷壁周长的途径来得到,阐述了该计算途径的原理。巷道开挖过程围岩释放的能量等于围岩压力 关于 的积分乘巷壁周长。由此,可通过 ~ 曲线、 ~ 曲线所围面积的几何形式,表示围岩偏应力能、围岩弹性能释放量随 变化的情况。所得研究结果可以深化围岩由于开挖产生的力学响应及挖成后围岩工况规律的认识。     

四川康定温泉系统深源CO2释放研究

根据水化学分析和稳定碳同位素的测试数据,本文计算了四川康定温泉热水和热储的ＣＯ２含量和深源ＣＯ２的释放量,探讨了热水中ＣＯ２的成因。温泉热水中ＣＯ２含量最高为１８４０．１６ｍｇ／Ｌ,平均为１０６０．５３ｍｇ／Ｌ,属于富含深源ＣＯ２的温泉系统。热水和ＣＯ２气的碳同位素揭示深源ＣＯ２的成因为幔源和碳酸盐岩变质脱气以及两者的混合。康定１２个温泉深源ＣＯ２的排出量为１７６６．４３ｔ／ａ,其中至少４０％呈气     

鄂尔多斯盆地东部上古生界石千峰组低压气藏特征

鄂尔多斯盆地的气源主要来自于山西组-太原组的海陆交互相煤系地层, 上石盒子组沉积了一套巨厚的泥岩, 具有很强的封盖能力, 天然气很难穿层运移.近年来, 相继在盆地东部的石千峰组地层中发现了一系列次生气藏, 其形成机理逐步引起了勘探家的关注.根据次生气藏的特点, 结合包裹体测试计算, 认为其形成原因主要是由于下部超压地层进行超压释放, 从而在区域性盖层内部形成一系列泄压通道, 原生气藏泄漏而形成的.形成过程主要经历了下部高温高压原生气藏的形成、原生气藏泄压与次生气藏的形成、次生气藏的长时间调整3个阶段.      

华北地区强震活动状态研究

华北地区历史强震活动频繁,但自1998年张北6.2级地震后至今6级以上地震平静近22年。大家对该区域未来6级以上地震危险趋势非常关注,且有不同观点。本文分析了该区6级以上地震活跃—平静周期性,运用小波变换技术对周期成分进行了定量计算;对比研究了活跃期与平静期之间的过渡阶段(本文称其为过渡幕)地震活动特点及其持续时间;从1999—2018年地震应变释放率与第Ⅲ、第Ⅳ活跃期、第3平静期和第Ⅳ活跃期内第3、第4平静幕的对比、平静幕持续时间的统计特征、当前华北地区显著的5级地震平静以及该区6级和7级以上地震前5级以上地震活动状态等方面进行了研究。结果显示,支持当前华北地区进入平静期的依据相对较多。     

熔融制样X射线荧光光谱法测定岩盐中的主量成分

以XRF分析岩盐,需解决标准物质缺乏和Cl在分析过程中的损失问题,选择合适的前处理方法以保证结果重现性。经实验发现用于粉末压片法的人工标准物质中氯化钠、硫酸钙等组分经X射线照射后呈现向样片表面扩散的趋势,其中氯化钠进一步分解,难以建立稳定的工作曲线;熔融制样则不存在这一问题,具备定量基础。本文选择熔融制样作为前处理方法,将光谱纯盐类、氧化物与土壤、水系沉积物国家标准物质以不同比例混合,配制人工标准物质建立工作曲线。熔融制样条件为:取样量0.6000 g,四硼酸锂+偏硼酸锂(12:22)混合熔剂10.000 g,熔融温度1000℃,预熔时间300 s,熔样时间300 s,静置时间30 s,所得样片平整通透,因样品中所含Cl具有脱模效果无需补充脱模剂。本方法测定主量元素的精密度(RSD)均小于1.5%,与经典方法相比减少了分析时间与试剂消耗,可作为岩盐主量成分分析的备选方法。