Impacts of aggregate dredging on sediment composition and associated benthic fauna at an offshore dredge site in the southern North Sea     

Robinson JE  Newell RC  Seiderer LJ  Simpson NM 《Marine environmental research》2005,60(1):51-68

Dredging and associated screening at a dredge site in the southern North Sea (Area 408) is associated with areas of well-sorted fine sand that extend for up to 3 km to the south-east of the dredged area and overlay sediments with a more variable particle size composition. This well-sorted fine sand may reflect deposition and transport of material mobilised by the dredging and screening processes at the dredge site. Multivariate analysis of the benthic community structure suggests that marine aggregate dredging, at the level of intensity employed in the study area prior to sample collection, has had a limited impact on benthic community composition compared with that reported from studies elsewhere. This is ascribed to the likely rapid rates of recolonisation by the mobile opportunistic polychaetes and crustaceans that dominate the macrofauna of the sandy gravel deposits at this particular dredge site. Analysis of variance showed, however, that significant differences existed between the sample treatments in terms of species evenness (Pielou's J). Dredged samples were found to have the lowest mean species evenness (0.71) when compared to controls (0.77). The present study highlights the inherent difficulties in the application of general impact/recovery predictions to dredged sites with varying environmental characteristics.  相似文献   

Simultaneous measurements of transparency and irradiance in the coastal waters of North Wales     

B.J. Topliss  J.R. Hunter  J.H. Simpson 《Marine environmental research》1980,4(1):65-79

Simultaneous measurements of the diffuse attenuation coefficient, k, and the collinated beam attenuation coefficient, c, were made on a continuous basis at a near-shore site off the north coast of Anglesey, North Wales. A statistical approach to calculating the diffuse attenuation coefficient, k, in coastal waters allowed variations in transparency to be taken into consideration. The ratio of c:k varied throughout the year between approximately 11:1 and 5:1, indicating the changes in the scattering and absorption properties of the water column. The major contribution to coastal turbidity was from the scattering of light by suspended material with the relationship between scattering and absorption being dependent on the nature of the suspended matter.  相似文献   

Atmospheric forcing, larval drift, and recruitment of capelin (Mallotus villosus)     

Dalley  Edgar L.; Anderson  John T.; deYoung  Brad 《ICES Journal of Marine Science》2002,59(5):929-941

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Ozone production potential following convective redistribution of biomass burning emissions     

Kenneth E. Pickering  Anne M. Thompson  John R. Scala  Wei-Kuo Tao  Joanne Simpson 《Journal of Atmospheric Chemistry》1992,14(1-4):297-313

The effects of deep convection on the potential for forming ozone (ozone production potential) in the free troposphere have been simulated for regions where the trace gas composition is influenced by biomass burning. Cloud dynamical and photochemical simulations based on observations in 1980 and 1985 Brazilian campaigns form the basis of a sensitivity study of the ozone production potential under differing conditions. The photochemical fate of pollutants actually entrained in a cumulus event of August 1985 during NASA/GTE/ABLE 2A (Case 1) is compared to photochemical ozone production that could have occurred if the same storm had been located closer to regions of savanna burning (Case 2) and forest burning (Case 3). In each case studied, the ozone production potential is calculated for a 24-hour period following convective redistribution of ozone precursors and compared to ozone production in the absence of convection. In all cases there is considerably more ozone formed in the middle and upper troposphere when convection has redistributed NO_x, hydrocarbons and CO compared to the case of no convection.In the August 1985 ABLE 2A event, entrainment of a layer polluted with biomass burning into a convective squall line changes the free tropospheric cloud outflow column (5–13 km) ozone production potential from net destruction to net production. If it is assumed that the same cloud dynamics occur directly over regions of savanna burning, ozone production rates in the middle and upper troposphere are much greater. Diurnally averaged ozone production following convection may reach 7 ppbv/day averaged over the layer from 5–13 km-compared to typical free tropospheric concentrations of 25–30 ppbv O₃ during nonpolluted conditions in ABLE 2A. Convection over a forested region where isoprene as well as hydrocarbons from combustion can be transported into the free troposphere leads to yet higher amounts of ozone production.  相似文献   

The influence of local hydrogeologic forcings on near‐stream event water recharge and retention (Upper San Pedro River,Arizona)     

Scott C. Simpson  Thomas Meixner 《水文研究》2013,27(4):617-627

The rise in stream stage during high flow events (floods) can induce losing stream conditions, even along stream reaches that are gaining during baseflow conditions. The aquifer response to flood events can affect the geochemical composition of both near‐stream groundwater and post‐event streamflow, but the amount and persistence of recharged floodwater may differ as a function of local hydrogeologic forcings. As a result, this study focuses on how vertical flood recharge varies under different hydrogeologic forcings and the significance that recharge processes can have on groundwater and streamflow composition after floods. River and shallow groundwater samples were collected along three reaches of the Upper San Pedro River (Arizona, USA) before, during and after the 2009 and 2010 summer monsoon seasons. Tracer data from these samples indicate that subsurface floodwater propagation and residence times are strongly controlled by the direction and magnitude of the dominant stream–aquifer gradient. A reach that is typically strongly gaining shows minimal floodwater retention shortly after large events, whereas the moderately gaining and losing reaches can retain recharged floodwater from smaller events for longer periods. The moderately gaining reach likely returned flood recharge to the river as flow declined. These results indicate that reach‐scale differences in hydrogeologic forcing can control (i) the amount of local flood recharge during events and (ii) the duration of its subsurface retention and possible return to the stream during low‐flow periods. Our observations also suggest that the presence of floodwater in year‐round baseflow is not due to long‐term storage beneath the streambed along predominantly gaining reaches, so three alternative mechanisms are suggested: (i) repeated flooding that drives lateral redistribution of previously recharged floodwater, (ii) vertical recharge on the floodplain during overbank flow events and (iii) temporal variability in the stream–aquifer gradient due to seasonally varying water demands of riparian vegetation. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Ice stream influence on West Greenland Ice Sheet dynamics during the Last Glacial Maximum     

David H. Roberts  Antony J. Long  Bethan J. Davies  Matthew J. R. Simpson  Christoph Schnabel 《第四纪科学杂志》2010,25(6):850-864

This paper investigates the processes governing bedrock bedform evolution in ice sheet and ice stream areas in central West Greenland, and explores the evidence for a cross‐shelf ice stream at the Last Glacial Maximum (LGM). To the east of Sisimiut the formation of streamlined bedforms with high elongation ratios and high bedform density has been controlled by geological structure and topography in slow‐flowing ice sheet areas. At the coast, the effects of regional flow convergence, caused by coastal fjord orientation, routed ice into the Sisimiut/Itilleq area where it formed an ice stream onset zone. This funnelled ice into an offshore trough (Holsteinsborg Dyb), resulting in a southwesterly regional ice flow direction and the formation of a topographically routed ice stream (Holsteinsborg Isbrae). To the south of this, striae and bedform evidence show that local valley glaciers initially flowed east to west across the coast, but were later redirected by the Itilleq Fjord ice which turned southwestward due to diffluent flow and deflection by Holsteinsborg Isbrae. Roches moutonnées in this area have low elongation ratios and high bedform density, but do not provide unequivocal support for ice streaming, as they are a product of both bedrock structure and changes in ice flow direction, rather than enhanced flow velocities. Cosmogenic surface exposure ages limit maximum ice sheet surface elevation to ca. 755–810 m above sea level in this region. Such ice thickness enabled Holsteinsborg Isbrae to reach the mid/outer continental shelf during the LGM, and to contribute to the formation of a trough mouth fan and the Outer Hellefisk moraines. Initial deglaciation across this region was driven by rising sea level and increasing air temperatures prior to the Bølling Interstadial at ca. 14.5 cal. ka BP. Between 12 and 10 cal. ka BP both increased air and ocean temperatures post the Younger Dryas, and peak sea‐level rise up to the marine limit, caused accelerated thinning and marginal retreat through calving, although dating evidence suggests ice streams remained along the inner shelf/coast boundary until at least ca. 10 cal. ka BP, their longevity maintained by increased ice thickness and ice discharge. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

The Landsat Global Archive: a valuable global resource     

Kamlesh Lulla  M. Duane Nellis  Brad Rundquist 《国际地球制图》2013,28(4)

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China-Brazil Earth Resources Satellite Collaboration is a success     

Kamlesh Lulla  M. Duane Nellis  Brad Rundquist 《国际地球制图》2013,28(5)

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Celebrating fifty years of NASA and Earth observations from space. Part IV: Global water cycle and water resources research     

Kamlesh Lulla  M. Duane Nellis  Brad Rundquist 《国际地球制图》2013,28(4)

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Vigorous star formation in a bulge-dominated extremely red object at z= 1.34     

Garret Cotter  Chris Simpson  Rosemary C. Bolton 《Monthly notices of the Royal Astronomical Society》2005,360(2):685-692

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