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The processes of nitrate removal from the stream waters of 2 headwater catchments were studied. In study stretches where the stream channels were vegetated with thick mats of grass (Gly‐ceria fluitans), nitrate removal processes were particularly active. In such grassed stream channels, c. 75% of the nitrate removal was attributable to plant uptake and the remainder to denitrifica‐tion. Both of these nitrate removal processes were linearly dependent on nitrate concentration, resulting in an exponential decline of nitrate level from the springs along the stream's length. Regeneration of nitrogen, by plant decay within the stream channel, results in export of dissolved organic nitrogen and paniculate nitrogen from the catchments. The overall impact of vegetated stream channels in modifying nitrogen exports from catchments is discussed. 相似文献
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In past decades, remote sensing studies on water quality mapping mainly focused on lakes using medium resolution imagery. Little research utilizes hyperspectral images to assess river water quality. This study aims to assess the capability of using Airborne Real-time Cueing Hyperspectral Enhanced Reconnaissance (ARCHER) for river water quality mapping and to characterize spatial patterns of turbidity and chlorophyll in the Blue Earth River (BER) system of Minnesota. The BER was characterized by both hyperspectral imagery (HSI) and laboratory analysis of synchronously collected water quality data. The optimal bands for water quality mapping were determined using a method based on hyperspectral profiles and derivative analysis. Finally, based on the regression analysis and modelling, we mapped continuous surface water turbidity. The results revealed that the ratio of HSI band 17 to band 9 effectively determined turbidity and chlorophyll concentrations. The study also found that turbidity and chlorophyll in the river generally increases downstream. 相似文献
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Myfanwy Bryce 《Astronomy& Geophysics》2002,43(3):3.25-3.26
The 8 m class telescopes now coming on stream, the availability of new instruments on 4 m telescopes and mm/radio telescopes, are beginning to throw new light on post-main sequence stellar evolution. The February RAS discussion meeting, organized by Nye Bevan, described the impact of these facilities on our understanding of this phase. Myfanwy Bryce reports. 相似文献
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Exoplanets 总被引：1，自引：0，他引：1
George Cole reviews the properties and significance of the planetary systems discovered around stars other than our Sun.
There has been speculation for centuries that planets might exist around stars other than our Sun. Might they form planetary systems like our solar system? Will life be found elsewhere one day? Planets were, in fact, discovered orbiting a pulsar in 1991 but, more interestingly, companions were found to stars like our Sun four years later. More stars with companions are continually being discovered and some 50 systems are known at the present time. Can some of these orbiting bodies be planets and what might they be made of? Is there a pattern in the systems being found? How do they compare with the solar system? Can they sustain living material? This article attempts to throw light on these questions. 相似文献
There has been speculation for centuries that planets might exist around stars other than our Sun. Might they form planetary systems like our solar system? Will life be found elsewhere one day? Planets were, in fact, discovered orbiting a pulsar in 1991 but, more interestingly, companions were found to stars like our Sun four years later. More stars with companions are continually being discovered and some 50 systems are known at the present time. Can some of these orbiting bodies be planets and what might they be made of? Is there a pattern in the systems being found? How do they compare with the solar system? Can they sustain living material? This article attempts to throw light on these questions. 相似文献
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Agustín Udías FRAS 《Astronomy& Geophysics》2001,42(2):2.23-2.24
Agustín Udías reflects on the Jesuit scientific tradition in astronomy and geophysics, by considering those who were also Fellows of the RAS.
The Society of Jesus has a venerable tradition of scientific observation and enquiry, as has the Royal Astronomical Society. Their paths have frequently crossed over the years and this tradition of shared enquiry continues to this day. 相似文献
The Society of Jesus has a venerable tradition of scientific observation and enquiry, as has the Royal Astronomical Society. Their paths have frequently crossed over the years and this tradition of shared enquiry continues to this day. 相似文献
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Mike Bode and Phil Charles present the minutes of the 11th meeting of the Standing Conference of Astronomy Professors on 3 July 2001. 相似文献
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Detailed observations of the [Oiii]5007 Å emission from the elliptical rings around SN 1987A suggest a model wherein the two faint, outer rings are due to emission from two circular toroids moving outwards (at 25 km s–1) along a bipolar cone centred on the site of the supernova. The brighter, central ring is expanding radially outward at 8.3 km s–1. The rings must have been created 2-3 × 104 years before the supernova explosion and are thought to be a consequence of the interaction of stellar winds emanating from the progenitor system during the final stages of its evolution to a supernova. 相似文献
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Recognition of strong seasonality and climatic cyclicity in an ancient,fluvially dominated,tidally influenced point bar: Middle McMurray Formation,Lower Steepbank River,north‐eastern Alberta,Canada 
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下载免费PDF全文 Inclined heterolithic stratification in the Lower Cretaceous McMurray Formation, exposed along the Steepbank River in north‐eastern Alberta, Canada, accumulated on point bars of a 30 to 40 m deep continental‐scale river in the fluvial–marine transition. This inclined heterolithic stratification consists of two alternating lithologies, sand and fine‐grained beds. Sand beds were deposited rapidly by unidirectional currents and contain little or no bioturbation. Fine‐grained beds contain rare tidal structures, and are intensely bioturbated by low‐diversity ichnofossil assemblages. The alternations between the sand and fine‐grained beds are probably caused by strong variations in fluvial discharge; that are believed to be seasonal (probably annual) in duration. The sand beds accumulated during river floods, under fluvially dominated conditions when the water was fresh, whereas the fine‐grained beds accumulated during the late stages of the river flood and deposition continued under tidally influenced brackish‐water conditions during times of low‐river flow (i.e. the interflood periods). These changes reflect the annual migration in the positions of the tidal and salinity limits within the fluvial–marine transition that result from changes in river discharge. Sand and fine‐grained beds are cyclically organized in the studied outcrops forming metre‐scale cycles. A single metre‐scale cycle is defined by a sharp base, an upward decrease in sand‐bed thickness and upward increases in the preservation of fine‐grained beds and the intensity of bioturbation. Metre‐scale cycles are interpreted to be the product of a longer term (decadal) cyclicity in fluvial discharge, probably caused by fluctuations in ocean or solar dynamics. The volumetric dominance of river‐flood deposits within the succession suggests that accumulation occurred in a relatively landward position within the fluvial–marine transition. This study shows that careful observation can reveal much about the interplay of processes within the fluvial–marine transition, which in turn provides a powerful tool for determining the palaeo‐environmental location of a deposit within the fluvial–marine transition. 相似文献