Assessing social-ecological coupling: Agriculture and hypoxia in the Gulf of Mexico

Analysis and enhancement of “coupling” of social-ecological systems (SES) has emerged as a leading theme in sustainability studies. However, as an analytical concept that can support empirical research, coupling has not been adequately developed. This study synthesizes concepts from environmental sociology and ecological sciences to derive three criteria to assess adaptive coupling of an SES: prevention orientation, spatial targeting and temporal targeting. We apply our criteria to the case of nitrogen pollution from agriculture in the Mississippi River Basin (MRB) and resulting hypoxia in the Gulf of Mexico. We analyzed the federal agricultural research and development portfolio to assess the character of investments in knowledge creation and how patterns of investment have changed over time. While superficial assessment of the data suggests that public spending on nitrogen relevant research constitutes a substantive response to the problem of Gulf hypoxia, disaggregating the data highlights an ineffectual response. Specifically, we find that spatial and temporal targeting of investment of socioeconomic resources in the MRB is poorly aligned with the nature of ecological risks confronting the region. In addition to this policy relevant result, our study highlights the importance of geographically referenced data and attention to relevant scales of analysis. Further, the paper demonstrates opportunities to advance concepts and empirical understanding of social-ecological coupling through interdisciplinary research on interfaces that mediate interactions in SES, for example publicly funded research aimed at agricultural practice and environmental conservation in the MRB.     

Numerical simulation of pile installation

During installation of a displacement pile, the soil around the pile is heavily distorted. The resulting changes in soil density and stress state around the pile determine the ultimate pile capacity. In most finite element models, the installation phase is not explicitly modelled. In this paper the full installation phase is modelled in two different ways, in a numerical code capable of large deformations.     

Numerical modeling of stress effects on solute transport in fractured rocks

The effects of stress/deformation on fluid flow and contaminant transport in fractured rocks is one of the major concerns for performance and safety assessments of many subsurface engineering problems, especially radioactive waste disposal and oil/gas reservoir fields. However, very little progress has been made to study this issue due to difficulties in both experiments and numerical modeling. The objective of this study is to systematically investigate the influence of stress on solute transport in fractured rocks for the first time, considering different stress and hydraulic pressure conditions. A hybrid approach combining discrete element method (DEM) for stress-flow simulations and a particle tracking algorithm is developed. The impact of matrix diffusion (diffusion of molecular size solutes in and out of the rock matrix, and sorption onto the surface of micropores in rock matrix) is also included. The numerical results show that stress not only significantly changes the solute residence time through the fracture networks, but also changes the solute travel paths. Matrix diffusion plays a dominant role in solute transport when the hydraulic gradient is small, which is often encountered in practice.     

Extending a time/frequency domain hybrid method for riser fatigue analysis

Fully coupled time domain analysis of a floating system is rigorous but time-consuming, thus an efficient hybrid method was developed in a prior work. The method simulates the coupled slow-drift responses in the time domain and analyzes the wave-frequency dynamics in the frequency domain. The hybrid method was shown to compare well with time domain analysis in predicting the mean-square vessel motions and line tensions. In this paper, the hybrid method is extended for the fatigue analysis of moorings and risers. The fatigue damage thus calculated is found to closely agree with the result from time domain analysis in conjunction with rainflow counting. Several spectral fatigue techniques are also compared, and these methods are significantly less accurate, thus attesting to the complexity of the problem.     

改进BCR法-电感耦合等离子体发射光谱法测定矿产品堆场土壤中镉砷铅的化学形态

矿产品堆场土壤中重金属在环境中富集,随着元素的迁移、转化及地下水的循环,成为环境污染问题。本文将改进的顺序提取法(BCR)应用于矿产品堆场土壤中Cd、As、Pb的化学形态分析,结合这三种元素的性质,将堆场土壤中Cd、As、Pb分为可交换态、可还原态、可氧化态和残渣态,并利用电感耦合等离子体发射光谱法测定其含量。采用形态分析标准参考物质GBW 07436验证了三步提取态的准确性,并对6个矿产品堆场土壤中Cd、As、Pb形态含量进行分析,三步提取态加上残渣态质量分数之和与重金属总量进行了比较,回收率为85.54%~102.88%。通过对矿产品堆场土壤实际样品分析,Cd、As、Pb三种元素非残渣态含量顺序为Cd(79.40%~94.94%)Pb(24.27%~37.73%)As(22.89%~31.51%),表明Cd元素较为容易进入生物圈。该方法解决了港口堆场土壤中重金属化学形态提取问题,对污染土壤的治理具有指导意义。     

离子色谱-电感耦合等离子体质谱法测定乳粉的汞形态

对于乳粉的汞形态分析,由于基质的复杂性,有机汞非常容易与样品中蛋白质上的巯基结合,形成稳定的络合物,在前处理过程中须保证各形态提取完全且各形态之间不会发生相互转化,因此样品前处理是汞形态分析的难点;同时乳粉中汞含量极低,对方法检出限提出了更高的要求。本文通过优化样品前处理过程,建立了离子色谱-电感耦合等离子体质谱测定乳粉中三种汞形态(二价汞、甲基汞、乙基汞)的方法。实验采用多种复合酶(蛋白酶、脂肪酶、淀粉酶)对乳粉基质中的蛋白、脂肪、淀粉进行解离,采用L-半胱氨酸-盐酸-甲醇的混合溶液作为提取剂进行超声提取,样品过RP固相萃取小柱去除杂质后用C18色谱柱(5μm,4.6 mm×150 mm)进行分离,流动相采用10 mmol/L乙酸铵-0.12%L-半胱氨酸-5%甲醇混合溶液进行淋洗,5 min内即可实现三种汞形态的基线分离。二价汞、甲基汞和乙基汞的加标回收率在79.9%~111.2%之间,检出限分别为0.5μg/kg、0.6μg/kg、0.9μg/kg。实际样品分析表明,汞总量很低的乳粉,汞各形态的提取率也能达到70%以上,能够满足检测要求。本方法在样品前处理过程中采用酶解的方式解离复杂基体中的汞形态,提高了提取率至80%以上;仪器分析方面采用甲醇作为增敏剂,提高了检测灵敏度,适用于乳粉样品中痕量汞形态的检测。     

微波消解-电感耦合等离子体质谱法测定煤中的硼

煤中硼的准确测定对于研究成煤的沉积环境具有重要意义。微波消解-电感耦合等离子体质谱(ICP-MS)可以有效地测定煤中的大部分微量元素,但由于硼易挥发等特殊的物理化学性质,致使硼的测定过程较为繁琐,测试结果不够准确。本文对微波消解ICP-MS测定煤中硼含量的分析方法进行了改进。样品中加入磷酸、硝酸和氢氟酸,用微波消解仪消解完全,置于电热板加热赶酸完毕后用硝酸提取。硼的卤化物易挥发,磷酸的加入使硼与磷酸结合生成难挥发的稳定络合物,起到了固硼的作用。ICP-MS测定中采用铍作为内标,通过在线加入的方式有效地补偿了基体效应产生的影响;用稀氨水冲洗进样系统,很好地降低了硼的记忆效应;选择高分辨率模式来测定,避免了12C和40Ar4+等质谱峰的干扰。方法的仪器检出限(0.22ng/mL)和方法检出限(0.34 ng/mL)较低,方法精密度(RSD)小于0.6%,灵敏度高,且测定标准样品的准确度良好。该方法简单快速,适用于批量分析煤样中硼的含量。     

湖泊沉积物中磷形态标准物质研制

水体富营养化与沉积物中磷元素的形态有密切关系。为了准确测定沉积物中不同形态的磷的含量,欧盟在2000年研制了第一个湖泊沉积物中磷形态标准物质(BCR 684),但基本用尽已不能满足需求,而且该标准物质采集于欧洲某湖泊,沉积物类型及污染情况与我国湖泊不相匹配。本文结合我国沉积物的类型和湖泊污染状况,研制了我国首批2个湖泊沉积物中磷形态标准物质(编号为 GBW 07462和GBW 07463)。候选物样品采集地点为江苏太湖和湖南洞庭湖,样品经过自然干燥、研磨、灭菌、陈化等加工处理,随机抽取15个子样采用单因素方差分析(F检验法)进行均匀性检验,检验的F实测值均小于临界值,表明样品均匀性良好。根据ISO导则35推荐方法对候选物样品在一年内进行四次稳定性检查,分析结果无方向性变化,再通过2次验证实验,样品稳定性良好。此批磷形态标准物质采用8家实验室联合定值,定值参数包括五种磷形态:总磷、无机磷、有机磷、磷灰石态磷、非磷灰石态磷;磷形态提取方法采用欧盟SMT法,测定方法采用钼锑钪光度法和电感耦合等离子体发射光谱法(实验过程中用欧盟BCR 684作为质量监控);按照《一级标准物质研制规范》(JJG 1006—1994)和ISO导则35的要求给出了五种磷形态的标准值和不确定度。此批磷形态标准物质样品代表了我国典型富营养化湖泊的沉积物类型,采样点的区域代表性强,定值项目选择合理、量值准确,可应用于环境、地质、农业、地球化学等研究领域沉积物的磷形态样品质量监控。     

铅同位素比值法研究辽宁东大杖子战国墓地出土铜器的矿料来源

东大杖子墓地作为辽宁乃至东北亚地区等级极高的战国时期墓地,自发掘以来一直受到学术界的高度关注,前期的研究工作主要集中在墓葬以及随葬品类型学、文化性质等方面,缺乏对该墓地出土青铜器矿料来源的研究。本文采用电感耦合等离子体发射光谱仪、扫描电镜能谱仪和表面电离型固体质谱仪对该墓地出土的7件青铜样品进行了成分和铅同位素比值分析。成分测试结果显示7件样品中有4件为铅锡青铜,2件为锡青铜,1件未知,器物功用和合金性能基本相匹配;铅同位素示踪结果显示部分器物的铜料不大可能来自内蒙古林西大井、辽宁红透山以及山西中条山等铜矿; 5件铅含量大于2%的样品铅同位素比值~(206)Pb/~(204)Pb、~(207)Pb/~(204)Pb、~(208)Pb/~(204)Pb变化范围分别为17. 685～17. 941、15. 530～15. 612、38. 080～38. 404,其铅料来自辽宁青城子铅锌矿的可能性极大。本研究有助于探索辽宁东大杖子战国墓地出土铜器的矿料来源,同时为研究战国时期辽西与辽东半岛的金属资源贸易和流通以及辽东半岛资源开发历史提供了科学的证据。     

过氧化钠碱熔-电感耦合等离子体发射光谱法测定钛铝合金中的铬铁钼硅

应用电感耦合等离子体发射光谱法(ICP-OES)测定高钛含量的钛铝合金中铬铁钼硅时,单一酸不能使钛铝合金完全溶解;混合酸溶解样品后仍会出现少量杂质、溶解不完全的现象,且复溶时易出现沉淀现象,即使用浓王水也难以将沉淀再溶解。本实验在700℃温度下,采用过氧化钠进行碱熔20 min,盐酸酸化,建立了应用ICP-OES测定钛铝合金中的铬铁钼硅的方法。实验中采用钛基体匹配的方法降低了试液中钛浓度大于200μg/m L时的钛基体干扰,通过控制过氧化钠使用量来降低待测溶液中的盐分含量保证了测定的稳定性。方法检出限为0.002~0.005μg/m L,测定下限为0.007~0.017μg/m L;采用国家标准物质(GBW02501)进行验证,方法的相对标准偏差(RSD)为0.90%~4.89%,相对误差为1.2%~3.6%,回收率为91.6%~103.8%。本方法与酸溶法相比,样品溶解完全,测定准确、可靠,适用于高钛含量的钛铝合金多元素测定。