Importance of heavy metal-organic matter interactions in natural waters     

J.H Reuter  E.M Perdue 《Geochimica et cosmochimica acta》1977,41(2):325-334

The role of organic ligands in metal complexing in natural waters has received little attention because of uncertainties regarding both the abundance and nature of dissolved organic carbon compounds. Recent data show that the bulk of dissolved organic matter in natural waters consists of highly oxidized and chemically and biologically stable polymeric compounds closely resembling soil humic substances. Average molar concentrations of these aquatic humics in major U.S. rivers range from 5 × 10^?6to 3 × 10^?5 moles 1^?1. Fractional elution of soil organic matter by meteoric waters may be considered to be the main process contributing to the presence of humic matter in rivers. The aquatic humic polymers participate in complex formation through ionizable functional groups with a range of differential acidities. The stabilities of metal-humic complexes in natural waters are higher than those of the corresponding inorganic metal complexes. Quantitative evaluation of the metal-organic interactions can be approached by applying variable equilibrium functions which take into account the differential physico-chemical characteristics of the active complexing sites on the polymer molecule. Assuming an average humic concentration of 10 mg 1^?1, complexation of trace metals can be significant even in the presence of excess concentrations of major cations.  相似文献   

Protoconch morphology of Conoteuthis (Diplobelida,Coleoidea) and its implications on the presumed origin of the Sepiida     

《Cretaceous Research》2012

The phylogenetic origin of the Sepiida is still unclear. The presumed derivation from diplobelid belemnoids can be tested by comparison of their initial chambers (protoconchs). The first investigation of a juvenile phragmocone of the diplobelid Conoteuthis hayakawai from the Cenomanian of Hokkaido (northern Japan) yielded surprising insights into the internal protoconch morphology of the Diplobelida. The Conoteuthis protoconch exhibits in many aspects a mosaic of the belemnitid and the spirulid protoconch types. Whereas the sepiid protoconch represents most probably a modification of the spirulid type, the Conoteuthis protoconch is unique in having a closed (imperforated) proseptum. Apart from this, Conoteuthis differs in many other characters from the earliest sepiids (Ceratisepia, Belosepia), which makes a closer relationship unlikely.  相似文献   

Long‐term trend of precipitation and runoff in Korean river basins     

Deg‐Hyo Bae  Il‐Won Jung  Heejun Chang 《水文研究》2008,22(14):2644-2656

The spatial and temporal variations of precipitation and runoff for 139 basins in South Korea were investigated for 34 years (1968–2001). The Precipitation‐Runoff Modelling System (PRMS) was selected for the assessment of basin hydrologic response to varying climates and physiology. A non‐parametric Mann–Kendall's test and regression analysis are used to detect trends in annual, seasonal, and monthly precipitation and runoff, while Moran's I is adapted to determine the degree of spatial dependence in runoff trend among the basins. The results indicated that the long‐term trends in annual precipitation and runoff were increased in northern regions and decreased in south‐western regions of the study area during the study period. The non‐parametric Mann–Kendall test showed that spring streamflow was decreasing, while summer streamflow was increasing. April precipitation decreased between 15% and 74% for basins located in south‐western part of the Korean peninsula. June precipitation increased between 18% and 180% for the majority of the basins. Trends in seasonal and monthly streamflow show similar patterns compared to trends in precipitation. Decreases in spring runoff are associated with decreases in spring precipitation which, accompanied by rising temperatures, are responsible for reducing soil moisture. The regional patterns of precipitation and runoff changes show a strong to moderate positive spatial autocorrelation, suggesting that there is a high potential for severe spring drought and summer flooding in some parts of Korea if these trends continue in the future. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Shock and thermal history of Northwest Africa 4859, an annealed impact‐melt breccia of LL chondrite parentage containing unusual igneous features and pentlandite     

Niina JAMSJA  Alex RUZICKA 《Meteoritics & planetary science》2010,45(5):828-849

Abstract– Northwest Africa 4859 (NWA 4859) is a meteorite of LL chondrite parentage that shows unusual igneous features and contains widely distributed pentlandite. The most obvious unusual feature is a high proportion of large (≤3 cm diameter) igneous‐textured enclaves (LITEs), interpreted as shock melts that were intruded into an LL chondrite host. One such LITE appears to have been produced by whole rock melting of LL chondrite, initial rapid partial crystallization, and subsequent slow cooling of the residual melt in the host to produce a differentiated object. Other unusual features include mm‐sized “overgrowth objects,” fine‐grained plagioclase‐rich bands, and coarse troilite (≤7 mm across) grains. All these features are interpreted as having crystallized from melts produced by a single transient shock event, followed by slow cooling. A subsequent shock event of moderate (S3) intensity produced veining and transformed some of the pyroxene into the clinoenstatite polytype. Pentlandite (together with associated troilite) in NWA 4859 probably formed by the breakdown of a monosulfide precursor phase at low temperature (≤230 °C) following the second shock event. NWA 4859 is interpreted to be an unusual impact‐melt breccia that contains shock melt which crystallized in different forms at depth within the parent body.  相似文献   

Situating corporate framings of child labor: Toward grounded geographies of working children in globalized agriculture     

《Geoforum》2015

The expansion of multinational corporations into agricultural production around the world is resulting in new forms of engagement in specific places. In the context of neoliberal restructuring, these engagements are tied to shifting landscapes of societal, governmental and industry-based perceptions on the role of corporations in labor regimes. But how are these engagements developed and how do they connect to the everyday lives of workers? In India, when Monsanto expanded into hybrid cotton seed production in the early 2000s, the corporation came under pressure to address concerns over the widespread employment of children and young workers for seed pollination. In response, the corporation developed an approach to child labor that, I argue, works to reinforce generalized and problematic notions of childhood and work. Corporate engagements in global agriculture need to be situated in time and space, and alongside the experiences of workers. Children experience attempts to shape their patterns of work and mobility as a series of surmountable obstacles, disconnected from the process of deciding whether or not they will engage in this work. Drawing on qualitative fieldwork in Gujarat and Rajasthan, and documentary analysis of public documents, I outline the development of a corporate response to child labor and place it within the context of the rise of corporate social responsibility, global ideas of child labor, and in the specific case of cotton seed production in western India. I demonstrate that contextualized geographies of working children in globalized agriculture reveal the nature of multinational corporations’ engagements in specific places.  相似文献   

Assessment of future runoff trends under multiple climate change scenarios in the Willamette River Basin,Oregon, USA     

Il‐Won Jung  Heejun Chang 《水文研究》2011,25(2):258-277

We investigated trends in future seasonal runoff components in the Willamette River Basin (WRB) of Oregon for the twenty‐first century. Statistically downscaled climate projections by Climate Impacts Group (CIG), eight different global climate model (GCM) simulations with two different greenhouse gas (GHG) emission scenarios, (A1B and B1), were used as inputs for the US Geological Survey's Precipitation Runoff Modelling System. Ensemble mean results show negative trends in spring (March, April and May) and summer (June, July and August) runoff and positive trends in fall (September, October and November) and winter (December, January and February) runoff for 2000–2099. This is a result of temperature controls on the snowpack and declining summer and increasing winter precipitation. With temperature increases throughout the basin, snow water equivalent (SWE) is projected to decline consistently for all seasons. The decreases in the centre of timing and 7‐day low flows and increases in the top 5% flow are caused by the earlier snowmelt in spring, decreases in summer runoff and increases in fall and winter runoff, respectively. Winter runoff changes are more pronounced in higher elevations than in low elevations in winter. Seasonal runoff trends are associated with the complex interactions of climatic and topographic variables. While SWE is the most important explanatory variable for spring and winter runoff trends, precipitation has the strongest influence on fall runoff. Spatial error regression models that incorporate spatial dependence better explain the variations of runoff trends than ordinary least‐squares (OLS) multiple regression models. Our results show that long‐term trends of water balance components in the WRB could be highly affected by anthropogenic climate change, but the direction and magnitude of such changes are highly dependent on the interactions between climate change and land surface hydrology. This suggests a need for spatially explicit adaptive water resource management within the WRB under climate change. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献