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181.
182.
Yongsong Huang Katherine H. Freeman Richard T. Wilkin Michael A. Arthur A. Daniel Jones 《Organic Geochemistry》2000,31(12):642
We measured δ13C values of free and sulfur-bound lipids and framboidal pyrite-size distributions in three sediment cores from the southern margins of the Black Sea. The margin cores show a marked difference in the occurrence of biomarkers from green sulfur bacteria compared with the deep-basin cores, as a result of deepening of the chemocline resulting from enhanced mixing and/or decreased light-penetration as a consequence of high turbidity and productivity in shelf waters. Quantitation of biomarkers suggests that photic-zone anoxia along the shelf margin was generally absent during the deposition of unit I, although occurred during the deposition of Unit IIb at two sites. 相似文献
183.
The level of complexity, and the number of parameters, to include in a hydrological model is a relatively contentious issue in hydrological modelling. However, it can be argued that explicitly representing important run‐off generation processes can improve the practical value of a model's outputs. This paper explores the benefits of including a new function into an existing semi‐distributed hydrological model (the Pitman model) that is widely used in the sub‐Saharan Africa region. The new function was designed to represent saturation‐excess surface run‐off processes at subcatchment scales and was motivated by the evidence of dambo (low topography riparian areas) type features in many sub‐Saharan river basins. The results for uncertainty versions of the model, with and without the new function, were compared for 25 catchments, which were divided up into those where evidence of dambos exists and those where there is no such evidence. The results suggest that the new function certainly improves the model results for the catchments where dambos exist, but not in situations where saturation‐excess surface run‐off is not expected to occur. The overall conclusion is therefore that the addition of the new function is justified. 相似文献
184.
Groundwater monitoring at the watershed scale: An evaluation of recharge and nonpoint source pollutant loading in the Clear Creek Watershed,Iowa
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Keith E. Schilling Matthew T. Streeter E. Arthur Bettis III Christopher G. Wilson Athanasios N. Papanicolaou 《水文研究》2018,32(4):562-575
Determining the groundwater contribution of nonpoint source pollution at a watershed scale is a challenging issue. In this study, we utilized a top‐down approach to characterize representative groundwater response units (GRUs) based on land use and landscape position (e.g., upland, sideslope, or floodplain) in the 275‐km2 Clear Creek Watershed, Iowa. Groundwater monitoring wells were then established along downslope transects in representative GRUs. This unique combination of top‐down/bottom‐up approaches allowed us to estimate groundwater pollutant loads at the watershed scale with minimal monitoring. For the 2015 study period, results indicated that more groundwater recharge occurred in the floodplain (404 mm) compared to the uplands or sideslopes (281 and 165 mm, respectively), irrespective of land use. Recharge in the floodplains consisted of 37% of the annual precipitation, whereas upland wells averaged 26% and sideslopes averaged 15% of the annual precipitation. Less recharge was found to occur beneath perennial grass compared to row crop and urbanized areas. Baseflow discharge accounted for 69% of the total NO3‐N exported from the Clear Creek Watershed, with row crop areas contributing approximately 95% of the annual load. Orthophosphorus (OP) yields were approximately 0.72 kg/ha beneath urban and suburban areas, three times higher than those in row crop or perennial areas. Urban and suburban areas accounted for 21.4% of groundwater orthophosphorus and chloride loads in the watershed compared to only 8.5% of the land area. Overall, the groundwater load allocation model for baseflow nutrient discharge to Clear Creek can be used to target future nonpoint source load reduction strategies at the watershed scale. The use of GRUs can pinpoint better areas of concern for controlling nutrient loads. 相似文献
185.
Arthur Goodwin Romain Tartèse Russell J. Garwood Rhodri Jerrett Katherine H. Joy 《Meteoritics & planetary science》2023,58(8):1099-1116
The Stac Fada Member (Stoer Group) is a ~1.2 Ga melt-rich impact breccia preserved and intermittently exposed along the NW coast of Scotland. Using a combination of x-ray diffraction and micro-Raman spectroscopy, we identify potential coesite that is spatially associated with micron-sized diamonds, as well as disordered carbon phases. Comparing the graphite G-band of disordered carbon phases in the impact breccia to samples from underlying units indicates that most of the carbon in the Stoer Group was ultimately derived from the underlying Lewisian basement. Disordered carbon phases within the Stac Fada Member have been modified by mild heating within a hot ejecta blanket rather than shock pressure. We also report the first evidence for impact diamonds discovered within the Stac Fada Member. These diamonds have an average Raman shift of 1328.5 cm−1 and are present within both the impact breccia and the shocked gneiss clasts that are present in sandstones directly underlying the Stac Fada Member contact, and within sandstone rafts entrapped in the unit. These findings have implications for the timing of deposition of the Stac Fada Member, which must have occurred after ballistic ejection of Lewisian basement clasts during the impact event. 相似文献
186.
Arthur P.J. Mol 《Global Environmental Change》2011,21(3):785-794
China's unprecedented economic growth path over the last two decades has been paralleled by an exponential growth in the consumption of natural resources and in pollution. Initially, China mainly exploited domestic resources to fuel its rapid industrial development. But over the last decade, increasing shares of China's natural resources consumption and environmental impacts relate to peripheral regions, including sub-Saharan Africa. China's environmental impacts in peripheral regions seem in line with World-Systems Theory predictions for ascending world powers. This paper assesses the extent to which the World-Systems Theory idea of ‘environmentally unequal exchange’ between ascending world powers and peripheral economies reflects current behaviour of Chinese governmental authorities and companies in sub-Saharan Africa. It concludes that the theory only partly does so. Behaviour of Chinese governmental authorities and firms is conditioned and guided by environmental norms, as well. World-Systems Theory has to make conceptual space for such new environmental behaviour of ascending world powers, to understand the contemporary and future world-systems. At the same time, China has a long way to go before becoming the ‘green’ exemplar for the world to follow. 相似文献
187.
Hydrocarbon composition and distribution in a coastal region under influence of oil production in northeast Brazil 总被引:1,自引:0,他引:1
Wagener Ade L Carreira RS Hamacher C Scofield Ade L Farias CO Cordeiro LG Luz LG Baêta AP Kalas FA 《Marine pollution bulletin》2011,62(8):1877-1882
Waters and sediments from the Potiguar Basin (NE Brazilian coast) were investigated for the presence and nature of polycyclic aromatic hydrocarbons (PAH) and aliphatic hydrocarbons. The region receives treated produced waters through a submarine outfall system serving the industrial district. The total dispersed/dissolved concentrations in the water column ranged from 10-50 ng L−1 for ∑16PAH and 5-10 μg L−1 for total aliphatic hydrocarbons. In the sediments, hydrocarbon concentrations were low (0.5-10 ng g−1for ∑16PAH and 0.01-5.0 μg g−1 for total aliphatic hydrocarbons) and were consistent with the low organic carbon content of the local sandy sediments. These data indicate little and/or absence of anthropogenic influence on hydrocarbon distribution in water and sediment. Therefore, the measured values may be taken as background values for the region and can be used as future reference following new developments of the petroleum industry in the Potiguar Basin. 相似文献
188.
Efficient scheme for the shallow water equations on unstructured grids with application to the Continental Shelf 总被引:1,自引:1,他引:0
Herman W. J. Kernkamp Arthur Van Dam Guus S. Stelling Erik D. de Goede 《Ocean Dynamics》2011,61(8):1175-1188
In this paper, a shallow-water flow solver is presented, based on the finite-volume method on unstructured grids The method
is suitable for flows that occur in rivers, channels, sewer systems (1D), shallow seas, rivers, overland flow (2D), and estuaries,
lakes and shelf breaks (3D). We present an outline of the numerical approach and show three 2D test cases and an application
of tidal propagation on the Continental Shelf. The benefits of applying an unstructured grid were explored by creating an
efficient model network that aims at keeping the number of grid cells per wavelength constant. The computational speed of
our method was compared with that of WAQUA/TRIWAQ and Delft3D (the commonly used structured shallow-flow solvers in The Netherlands),
and comparable performance was found. 相似文献
189.
Christopher K. Junium Brendan J. KeelyKatherine H. Freeman Michael A. Arthur 《Organic Geochemistry》2011,42(7):856-859
Liquid chromatography, multi-stage mass spectrometry (LC-MSn) of acetone extracts confirms the presence of mesochlorophyllone in the mid-Cretaceous black shales of Demerara Rise. This finding represents molecular confirmation of the oldest primary chlorins in the geologic record and is evidence for a chlorophyll a source for bicycloalkanoporphyrins in the Demerara Rise black shales. 相似文献
190.
Evidence shows that high field strength (HFS) elements commonly used to index chemical weathering are variably mobile. This mobility may be linked to redistribution of suspended solids. A mass-balance model is presented that can quantify such redistribution without assuming immobility for any single element. Two tropical weathering profiles on quartz diorite and basalt are examined and redistribution of the HFS elements Zr and Ti is documented, along with potential corrections for the resulting changes in measured concentrations. 相似文献