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131.
Brandon M. Stephens Elizabeth C. Minor 《Aquatic Sciences - Research Across Boundaries》2010,72(4):403-417
The chemical characteristics of bulk (sterile-filtered) and high molecular-weight dissolved organic matter (HMW DOM) were
analyzed for freshwater (St. Louis River, Minnesota to Lake Superior) and saline (Elizabeth River, Virginia to Chesapeake
Bay) river-to-receiving basin transects. Dissolved organic carbon concentrations and UV–Visible spectroscopy of bulk DOM demonstrated
a reduction in organic carbon, colored DOM and aromatic compounds downstream in both transects. The proportion of DOM recoverable
via ultrafiltration as HMW material also decreased downstream in both transects, although there was an offset in recoveries
between the transects that may be explained by the effects of ionic strength and/or differences in ultrafiltration technique.
The analysis of HMW DOM by Fourier transform infrared spectroscopy illustrated similar trends between transects, with a general
shift from aromatic/carboxylic compounds nearshore to aliphatic/carbohydrate materials offshore. The parallel changes observed
along saline and freshwater transects imply that similar processes play significant roles in the down-gradient alteration
of DOM and that ionic strength or pH changes cause second-order effects. 相似文献
132.
Daniel B. Stephens 《Journal of Hydrology》1983,61(4):391-408
In the southern San Juan Basin, New Mexico, strata of Permian and younger age dip gently toward the center of the basin. Most previous investigators believed that recharge to these strata occurred by precipitation on the outcrops and groundwater flowed downdip to the north and northeast. Recent water-level measurements in an undeveloped part of the basin near Prewitt, New Mexico, show that groundwater at shallow depths in alluvium and bedrock flows southward, opposite to the dip direction, and toward a major ephemeral drainage in a strike valley. North of this area, groundwater in deep bedrock aquifers does appear to flow northward. This information suggests that there are two groundwater circulation patterns; a shallow one controlled by topography and a deeper one controlled by geologic structure.Significant amounts of recharge to sandstone aquifers by infiltration through outcrops is unlikely due to the near-vertical exposures on cliffs, the gentle dip of the strata, and small annual precipitation. Numerical model results suggest that recharge to bedrock aquifers may be from downward leakage via aquitards over large areas and leakage from narrow alluvial aquifers in the subcrop area. The recharge mechanism is controlled by the hydraulic conductivity of the strata.As the flow path is controlled by hydraulic conductivity contrasts, geologic structure, and topography, contamination movement from surface impoundments is likely to be difficult to predict without a thorough hydrogeological site investigation. 相似文献
133.
134.
Summary This paper presents a comparison of column water vapor (CWV) information derived from both infrared measurements as part of the TIROS-N Operational Vertical Sounder (TOVS) and Special Sensor Microwave/Imager (SSM/I) in an attempt to assess the relative merits of each kind of data. From the analyses presented in this paper, it appears that both types of satellite data closely reproduce the bulk climatological relationships introduced in earlier studies using different data. This includes both the bulk relationship between CWV and the sea surface temperature and the annual variation of CWV over the world's oceans. The TOVS water vapor data tends to be systematically smaller than the SSM/I data and when averaged over the ocean covered regions of the globe this difference is between 2–3 kgm–2. Using a cloud liquid water threshold technique to establish clear sky values of SSM/I water vapor, we conclude that the differences between TOVS and SSM/I are largely a result of the clear sky bias in TOVS sampling except in the subsidence regions of the subtropics. The clear sky bias is considerably smaller than previously reported and we attribute this improvement to the new physical retrieval scheme implemented by NOAA NESDIS. While there is considerable agreement between the two types of satellite data, there are also important differences. In regions where there is drying associated with large scale subsidence of the atmosphere, the TOVS CWV's are too moist relative to both radiosonde and SSM/I data and this difference may exceed 10 kgm–2. The explanation for this difference lies in the limitations of infrared radiative transfer. By contrast, in regions of deep convection, such as in the ITCZ, TOVS CWV is systematically lower than the SSM/I CWV. Both TOVS and SSM/I data demonstrate similar kinds of gross effects of large scale circulation on the water vapor except in these subsidence regions where TOVS data leads to an under-prediction of the effects of subsidence drying.With 11 Figures 相似文献