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51.
Benthic fluxes of C, N, P and Si have been measured at two sites in Great Bay Estuary, New Hampshire. Higher fluxes of reactive phosphate, nitrate and reactive silicate were observed at the site where bioturbation is known to occur and the fluxes of NH4 +, PO4 ?3 and reactive silicate at this location were from 3 to 6 times higher than that calculated by simple pore water diffusion models. *** DIRECT SUPPORT *** A01BY019 00010 相似文献
52.
Susan E. Hogg 《Earth》1982,18(1):59-76
Following McGee's (1897) use of the term sheetflood, there developed a variety of conflicting opinions and numerous terminologies relating to this process, many of which are ill-considered and poorly defined. A classification system is devised on both a hydrologic and geomorphic basis which dispenses with many superfluous terms that have been used with respect to sheetfloods. Magnitude of a storm is expressed in terms of the amount of surface runoff generated from a given storm due to the surface conditions.A sheetflood is defined as a sheet of unconfined flood water moving down a slope. The frequency of a sheetflood is relatively low while its magnitude is relatively great. Sheetflow is defined as relatively high-frequency, low-magnitude overland flow occurring in a continuous sheet and is restricted to laminar flow conditions. Sheetwash, a term of geomorphic origin, is considered to be redundant and is superseded by the more meaningful term rainwash defined as the washing action of rain on slopes. 相似文献
53.
Steven Emerson Susan Kalhorn Lucinda Jacobs Bradley M Tebo Kenneth H Nealson Reinhardt A Rosson 《Geochimica et cosmochimica acta》1982,46(6):1073-1079
A simple mass balance for dissolved manganese(II) in waters containing low levels of oxygen in Saanich Inlet indicates that the residence time for Mn(II) removal to the solid phase is on the order of a few days. The average oxidation state of Mn in particulate material sampled from the region of Mn removal was 2.3–2.7, and electron micrographs revealed structures characteristic of bacterially formed Mn precipitates. Radiotracer experiments utilizing 54Mn(II) indicated that removal of Mn from solution in the region of active uptake was substantially blocked by a poison mixture, demonstrating that Mn(II) binding to particulates is catalyzed by bacteria in this environment. 相似文献
54.
55.
Natural background and pollution levels of some heavy metals in soils from the area of Dayton,Ohio 总被引:2,自引:0,他引:2
In a reconnaissance study, trace amounts of Cd, Cu, Pb, and Zn were determined in “A-zone” soil from 22 locations in the Dayton,
Ohio, area. Soil samples were collected at high-volume air monitoring sites in urban, suburban, and rural areas. Measurable
amounts of the elements were found in all of the samples. Positive correlations occur between each metal and particulate matter,
with correlation coefficients of aboutr=0.70, at the 99% confidence level. Natural background values for the elements were measured in soil from rural areas. Theoretical
background values, which are very close to those measured, were calculated from the individual regression equations. Natural
background levels do not exceed 1.00 ppm Cd, 15 ppm Cu, 25 ppm Pb, and 55 ppm Zn. The heavy metal contents of most soils in
the area exceed background by factors of up to 3.0 for Cd, up to 4.5 for Cu, up to 11 for Pb, and up to 4.5 for Zn.
Significant positive correlations among the metals suggest a common source (or sources) for at least some, if not most, of
the heavy metals. For the most part, the highest metal values are found in soils near coal-burning plants. Fly ash from a
local plant contains substantial amounts of the elements. The high lead values are largely due to vehicular exhaust. However,
there is evidence that the metals can also come from the normal deterioration of vehicles.
It appears that airborne pollution is an important source of heavy metals in Dayton area soils. 相似文献
56.
57.
Susan Ellis Silke Wissing Adrian Pfiffner 《International Journal of Earth Sciences》2001,90(1):168-180
Published strength profiles predict strength discontinuities within and/or at the base of continental crust during compression. We use finite element models to investigate the effect of strength discontinuities on continental collision dynamics. The style of deformation in model crust during continued subduction of underlying mantle lithosphere is controlled by: (1) experimental flow-law data; (2) the crustal geotherm; (3) strain localization by erosion; (4) strain-softening and other localization effects. In the absence of erosion and other factors causing strain localization, numerical models with typical geothermal gradients and frictional/ductile rheologies predict diffuse crustal deformation with whole-scale detachment of crust from mantle lithosphere. This prediction is at odds with earlier model studies that only considered frictional crustal rheologies and showed asymmetric, focused crustal deformation. Without localization, model deformation is not consistent with that observed in small collisional orogens such as the Swiss Alps. This suggests that strain localization by a combination of erosion and rheological effects such as strain softening must play a major role in focusing deformation, and that strength profiles derived under constant strain rates and uniform material properties cannot be used to infer crustal strength during collision dynamics. 相似文献
58.
59.
Impact of the Montreal protocol and its amendments on the rate of change of global radiative forcing
Increases in chlorinated and brominated halocarbons are believed to be responsible for the depletion of stratospheric ozone observed over much of the globe in the past decade or so. Ozone depletion is in turn believed to lead to a negative radiative forcing, tending to cool the stratosphere and the surface. We show that the increasing atmospheric concentrations of ozone-depleting halocarbons and onset of related ozone depletion likely led to a negative forcing of the climate system in the 1980s that slowed significantly the rate of change of total anthropogenic radiative forcing due to the combined effect of all greenhouse gases over that decade. Within the next decade, emissions of these halocarbons are expected to rapidly decrease, with corresponding impacts on ozone and radiative forcing. As the emissions of ozone-depleting gases are reduced and eventually phased out, the rate of ozone depletion is expected to decrease and eventually reverse. All other things being equal, we show that the change from deepening ozone depletion in the 1980s to ozone increases in the future should lead to a pronounced increase in the decadal rate of change of anthropogenic greenhouse forcing of the next few decades, perhaps to levels unprecedented in this century. 相似文献
60.
Comparability of Large-Scale Studies of Agricultural Chemical Contamination of Rural Private Wells 总被引:1,自引:0,他引:1
Detection of agricultural chemicals in ground water has prompted numerous studies. Federal, state, and regional studies were conducted in the last 10 years in order to assess the occurrence of agricultural chemicals in ground water. The results of the studies present the number or percentage of samples with agricultural chemicals above the drinking water standard or health advisory levels as well as samples with detections of one or more compounds. Data comparison from one state or region to another are frequently referred to by regulatory and agency personnel involved in water quality and agriculture issues. Unless the history of pesticide use, method of chemical analyses, detection limits, statistical design of the sampling plan, well type, well depth, geology of the formation material, and typical land use around the wellhead are known, such comparisons can be misleading. Reporting the limitations or presenting a disclaimer should be a key element for a study so that "apples and oranges" are not compared. 相似文献