草地异戊二烯排放通量影响因子的研究

2002年夏季对中国内蒙古草原挥发性有机物的排放通量进行的首次测量结果表明,其主要成分异戊二烯的排放有明显的日变化和季节变化.采样箱对太阳辐射有非常明显的衰减作用,其衰减率为17%～35%.为准确估算异戊二烯的排放通量,建立其排放模式是非常必要的.基于可见光辐射传输与守恒的观点,在观测数据的基础上建立了异戊二烯排放通量的经验模式.结果表明,对日变化、季节变化和日总量的模拟值与测量值比较一致.在使用箱方法时,应该考虑箱内外辐射、温湿度、水汽含量之差引起的排放通量的差别,特别是箱内外辐射之差所引起排放通量的差别.同时也说明,可见光辐射是影响异戊二烯排放的最主要因子.利用异戊二烯排放通量的日总量与11:00通量之比和可见光辐射日总量与11:00时累计值之比的定量关系,可以由某日11:00的排放通量来推算该日的日总量,其平均相对偏差小于14%.     

Isotopic and microbial indicators of sewage pollution from Stone Town, Zanzibar, Tanzania

In Stone Town, Zanzibar, sewage treatment is minimal, with a biological oxygen demand reduction to 60% and no removal of bacteria or nutrients. Here, Stone Town's sewage pollution was studied by measuring Enterococci and NH(4)(+) concentrations in seawater and δ(15)N of benthic organisms; samples were collected along the Stone Town shoreline and from offshore coral reefs. Public perceptions of sewage pollution were investigated via interviews. Enterococci from the Stone Town shoreline exceeded USEPA guidelines for recreational use. Benthic organisms from two of the four reefs were relatively enriched (δ(15)N>10 ‰), indicative of sewage derived N. δ(15)N values of organisms from Stone Town exceeded 16 ‰. A strong correlation was found between Enterococci and δ(15)N across sites, while step-wise regression indicated rainfall and tidal stage as important predictors for bacterial concentrations. These data provide an important impact assessment from which the efficacy of future policy and management change can be assessed.     

Occurrence of negative epsilon in seismic hazard analysis deaggregation,and its impact on target spectra computation

This paper investigates circumstances behind the occurrence of negative ε (the normalized difference between the spectral acceleration of a recorded ground motion and the median response predicted by a ground motion prediction equation) in probabilistic seismic hazard deaggregation. Negative ε values are of engineering interest because of their impact on the conditional mean spectrum (CMS), which is a proposed alternative to the uniform hazard spectrum (UHS) as a target spectrum for ground motion selection. In the case where target ε values from deaggregation are positive, the CMS calculation produces relatively lower response spectra than the UHS. Positive target ε values occur almost universally in active seismic regions at long return periods of engineering interest, but the possibility of negative target ε values is important because in the case of negative target ε, some relationships between the CMS and UHS would reverse. This paper describes the calculation of target ε, performs parametric studies to determine when negative ε values occur in deaggregation, and investigates the potential impact on target spectrum calculation and ground motion selection. The case studies indicate that special seismicity models and certain ground motion prediction equations have the most significant effect on ε values and a combination of these characteristics in Eastern North America creates the most likely situation for negative target ε to occur. CMS results are nonintuitive when the target ε is negative, but it is not clear that this is a common practical concern because negative target ε occurs only in well‐constrained areas. Copyright © 2011 John Wiley & Sons, Ltd.     

Ground motion directionality in the 2010–2011 Canterbury earthquakes

This paper examines the observed directionality of ground motions in the Christchurch urban area during the 2010–2011 Canterbury, New Zealand earthquakes. A dataset of ground motions recorded at 20 strong motion stations over 10 different earthquake events is utilized to examine the ratios of various response spectral directionality definitions and the orientation of the maximum direction. Because the majority of previous related studies have utilized overlapping ground motion datasets from the NGA database, the results of this study provide a largely independent assessment of these ground motion aspects. It is found that the directionality ratio between the maximum (100th percentile) and 50th percentile orientation‐independent spectral acceleration is similar to that obtained from recent studies. Ground motions from the 4 September 2010 Darfield earthquake are shown to exhibit strong directionality for source‐to‐site distances up to R_rup = 30 km, notably further than results from a previous study, which suggests that such effects are generally limited to R_rup < 5 km. The adopted dataset also offers the unique potential to consider site‐specific effects on directionality ratios and maximum direction orientations; however, in both cases, site‐specific effects are found not to be significant in the observed empirical results. Copyright © 2014 John Wiley & Sons, Ltd.     

The potential role of freshwater luminescence measurements in exploring runoff pathways in upland catchments

The forested Coalburn catchment (1·5 km²) in northern England experiences episodic stream acidification. To plan for sustainable management of the plantation forest cycle, an understanding is required of the flow pathways and hydrochemical routing signatures of the organic and mineral soils that make up the source areas for runoff. A tentative mixing model, based on simple water chemistry exists for the major (terrestrial) sources and buffers of acidification; it is being expanded and consolidated by a detailed approach to the organic components of runoff, via sampling and analysis of the luminescence of surface waters at the catchment outlet and in two distinctive feeder streams. Luminescence measurements are presented that permit a simple apportionment of source areas. However, the technique also appears to have potential for identifying differential flow sourcing between the acrotelm and catotelm of intact peat deposits and for clarifying the influence of forest root systems in altering the organic chemistry of infiltrating waters. Applications may include the monitoring and prediction of coloured water events for the water supply industry. Copyright © 2001 John Wiley & Sons, Ltd.     

Age,petrogenesis and metamorphism of the syn-collisional Prøven Igneous Complex,West Greenland

The Paleoproterozoic Prøven Igneous Complex (PIC) in West Greenland extends from ca. 72°15 to 73°10N, approximately 500 km north of the subduction-related intrusive complex in the core of the +1100 km wide, asymmetric collisional Nagssugtoqidian-Rinkian Orogen. A new U-Pb SHRIMP age for the PIC of 1869±9 Ma indicates that it intruded synchronously with the main collisional phase of the orogen into the passive margin side of the collision. Sm-Nd and Lu-Hf isotopic and A-type geochemical signatures are compatible with its derivation from melted Archean lower crustal material contaminated to varying degrees by pelitic sedimentary rocks of the Karrat Group. The timing, petrogenesis and position of the PIC within the orogen support a model of collisionally induced delamination of the mantle lithosphere following initial collision. Upwelling asthenospheric mantle replacing the partially or completely detached mantle lithosphere caused widespread partial melting of lower crust that resulted in the areally extensive (~ 250,000 km²) Cumberland-Prøven intrusive complexes of Baffin Island and West Greenland. Emplacement of the PIC at 1.87 Ga caused a high-temperature low- to medium-pressure metamorphic aureole that contrasts the regional, overprinting higher-pressure amphibolite facies metamorphism. The consequent high-temperature garnet-orthopyroxene-biotite-bearing assemblages occurring within the margin of the intrusion in the aureole are attributed to the intrusion event. Garnet-controlled Sm-Nd and Lu-Hf ages of 1.82–1.80 Ga require efficient diffusion of these elements during orogenic reheating at this time. This age range overlaps the post-collisional, north–south shortening in the Nagssugtoqidian Orogen to the south and serves to confirm the recently proposed genetic link between these two orogens. These new data infer that garnet-controlled isochrons based on the Lu-Hf and Sm-Nd systems cannot date high-grade events in slowly cooled or significantly reheated terrains in rocks possessing other phases that close at low temperatures.     

Sulfur diffusion in basaltic melts

We measured the diffusion coefficients of sulfur in two different basaltic melts at reduced conditions (i.e., in the sulfide stability field), temperatures from 1225°C to 1450°C, pressures of 0.5 and 1 GPa, and water concentrations of 0 and 3.5 wt%. Although each melt is characterized by slightly different sulfur diffusion coefficients, the results can be combined to create a general equation for sulfur diffusion in anhydrous basalts:

     

Evaluation of volatilization as a natural attenuation pathway for MTBE

Volatilization and diffusion through the unsaturated zone can be an important pathway for natural attenuation remediation of methyl tert-butyl ether (MTBE) at gasoline spill sites. The significance of this pathway depends primarily on the distribution of immiscible product within the unsaturated zone and the relative magnitude of aqueous-phase advection (ground water recharge) to gaseous-phase diffusion. At a gasoline spill site in Laurel Bay, South Carolina, rates of MTBE volatilization from ground water downgradient from the source are estimated by analyzing the distribution of MTBE in the unsaturated zone above a solute plume. Volatilization rates of MTBE from ground water determined by transport modeling ranged from 0.0020 to 0.0042 g m(-2)/year, depending on the assumed rate of ground water recharge. Although diffusive conditions at the Laurel Bay site are favorable for volatilization, mass loss of MTBE is insignificant over the length (230 m) of the solute plume. Based on this analysis, significant volatilization of MTBE from ground water downgradient from source areas at other sites is not likely. In contrast, model results indicate that volatilization coupled with diffusion to the atmosphere could be a significant mass loss pathway for MTBE in source areas where residual product resides above the capillary zone. Although not documented, mass loss of MTBE at the Laurel Bay site due to volatilization and diffusion to the atmosphere are predicted to be two to three times greater than mass loading of MTBE to ground water due to dissolution and recharge. This result would imply that volatilization in the source zone may be the critical natural attenuation pathway for MTBE at gasoline spill sites, especially when considering capillary zone limitations on volatilization of MTBE from ground water and the relative recalcitrance of MTBE to biodegradation.