ABSTRACT
Fluxes of CO2, CH4, and N2O from forest soils were measured with an enclosed chamber technique between October 1990 and December 1991 in a deciduous forest near Darmstadt, Germany. Flux ...measurements were made before and after the removal of leaves and humus layer from the forest floor, and gas fluxes from the leaves and humus alone were also measured as well as depth profiles of CH4, N2O, and soil moisture. Except for N2O, large seasonal variations were observed with generally higher gas fluxes during the summer. CO2 and CH4 fluxes were significantly dependent on changes in ambient temperature, whereas N2O fluxes were more affected by soil moisture. A good correlation between CO2 production and CH4 uptake was observed, but no relationship was found between N2O emissions and either CO2 or CH4 fluxes. Depth profiles of the CH4 mixing ratio in soil air consistently showed an exponential decrease with depth, whereas N2O profiles were highly variable and appeared to be related to changes in soil moisture. The manipulated soil experiments indicate that the leaves and the humus layers contribute significantly to the soil‐atmosphere exchange of trace gases.
Undersaturation of CH3Br in the Southern Ocean Lobert, Jürgen M.; Yvon-Lewis, Shari A.; Butler, James H. ...
Geophysical research letters,
15 January 1997, Letnik:
24, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Dry mole fractions of methyl bromide (CH3Br) in marine boundary layer air and in air equilibrated with surface water were measured in the Southern Ocean. Saturation anomalies were consistently ...negative at −36±7%. The observed undersaturations do not support recently published predictions of highly supersaturated Antarctic waters, but instead suggest a net uptake of atmospheric CH3Br by cold, productive oceans. The observations do not appear to be supported by known chemical degradation rates and present strong evidence for an unidentified, oceanic sink mechanism such as biological breakdown. Our estimate for the global, net, oceanic sink for atmospheric methyl bromide remains negative at −21 (−11 to −32) Gg y−1.
The spreading of viral RNA within Swiss Albino mice orally inoculated with coxsackievirus B4 E2 strain (CVB4 E2) was studied by using RT‐PCR and semi‐nested‐RT‐PCR methods. Viral RNA was detected in ...various organs: pancreas, heart, small intestine, spleen, thymus, and blood at various postinfectious (p.i.) times ranging from 8 hr to 150 days. Our results show that (i) outbred mice can be infected with CVB4 E2 following an oral inoculation, which results in systemic spreading of viral RNA, (ii) CVB4 E2 infection can be associated with a prolonged detection of viral RNA in spleen, thymus and blood, up to 70 days p.i. and further in other organ tissues.
Carbon monoxide (CO) fluxes between soil and atmosphere were measured between October 1990 and December 1991 in a temperate, deciduous forest near Darmstadt, Germany. Flux measurements were made with ...an enclosed chamber technique before and after the removal of leaves and humus from the forest floor as well as from leaves and humus alone. CO depth profiles were obtained during the period July to December, 1991. A net uptake of CO was observed under all conditions with an average of - 47.3 ± 24.0 ng CO m
-2
s
-1
for undisturbed forest soils, which increased significantly when the leaves or both leaves and humus were removed from the forest floor. The mean deposition velocity in undisturbed conditions was 0.027 ± 0.008 cm s
-1
. Our results indicate that CO has a short lifetime within the soil and that the consumption of atmospheric CO occurs mainly in the top few centimeters of the humus layer (O horizon). We conclude that temperate forests are a significant net sink for atmospheric CO and that leaves and humus significantly affect CO fluxes. The global soil sink for atmospheric CO was estimated to be 115-230 Tg CO yr
-1
.
The main interface and interconnection materials normally used in complementary metal-oxide semiconductor (CMOS) integrated circuit processing, i.e. silicon oxides and aluminum, were evaluated with ...regards to deoxyribonucleic acid (DNA) attachment. We investigated and quantified the influence of various techniques of fabrication of the silicon oxide on DNA binding obtained by four different biochemical processes. Regarding aluminum, we found that it only binds DNA in the presence of its natural oxide and that it is severely degraded by one of the three typical biochemical processes. Optimal process conditions for DNA binding on silicon oxides with aluminum compatibility are finally derived.
A new class of receptor molecules is presented that is highly selective for N‐alkylpyridinium ions and electron‐poor aromatics. Its key feature is the combination of a well‐preorganized molecular ...clip with an electron‐rich inner cavity and strategically placed, flanking bis‐phosphonate monoester anions. This shape and arrangement of binding sites attracts predominantly flat electron‐poor aromatics in water, binds them mainly by π–cation, π–π, CH–π, and hydrophobic interactions, and leads to their highly efficient desolvation. NAD+ and NADP, the important cofactors of many redox enzymes, are recognized by the new receptor molecule, which embraces the catalytically active nicotinamide site and the adenine unit. Even nucleosides such as adenosine are likewise drawn into the clip's cavity. Complex formation and structures were examined by one‐ and two‐dimensional NMR spectroscopy, Job plot analyses, and isothermal titration microcalorimetric (ITC) measurements, as well as quantum chemical calculations of 1H NMR shifts. The new receptor molecule is a promising tool for controlling enzymatic oxidation processes and for DNA chemistry.
A new class of receptor molecules is presented that is highly selective for N‐alkylpyridinium ions and electron‐poor aromatics. Its key feature is the combination of a well‐preorganized molecular clip with an electron‐rich inner cavity and strategically placed flanking bis‐phosphonate monoester anions. This shape and arrangement of binding sites attracts predominantly flat electron‐poor aromatics (e.g., the enzyme cofactors NAD+ and NADP) in water, binds them mainly by π–cation, π–π, CH–π, and hydrophobic interactions and leads to their highly efficient desolvation (an example is illustrated here).
Point counts are widely used for conducting ecological surveys of wild birds. Vocal output of birds varies with time of day, and therefore the results of ecological surveys should also vary with time ...of day. We modeled how males’ singing rates change over the morning. We calculated song rates in 3 min sampling periods (the standard sampling period used by the North American Breeding Bird Survey) and compared how detection rates vary as sampling period increases. We recorded singing activity in 15 neighbourhoods of breeding Black-capped Chickadees (Poecile atricapillus) with 16-element microphone arrays that recorded every song from every male in every neighbourhood. We calculated the proportion of males that produced one or more songs during 3, 5, and 10 min count periods between nautical twilight and late morning. our results show a strong peak in singing activity just before sunrise followed by a steady decline in singing activity over the course of the morning. We found that longer sampling periods yielded significantly higher detection rates at all times after sunrise. After sunrise, detection rates never exceeded 60%, even with 10 min sampling periods. We found that unpaired males had significantly higher detection rates than paired males but we found no difference between paired males with fertile versus incubating mates. our results provide strong evidence that, for black-capped Chickadees, surveys during the dawn chorus provide the most comprehensive assessment of the number of birds present, and that longer sampling periods yield significantly better estimates of population sizes at all times after sunrise.
A source analysis of carbon monoxide (CO) over the Indian Ocean is presented using marked tracers in a chemistry GCM. The model includes a nonmethane hydrocarbon chemistry scheme and has been used at ...two different resolutions (3.75 x 3.75 deg and 1.9 x 1.9 deg). European Center for Medium-Range Weather Forecasts meteorological analyses have been assimilated into the model to represent actual meteorology during February and March of 1999. A comparison with measurements indicates that the model simulates realistic CO distributions. In general, the model performance is more realistic at higher resolution. Discrepancies exist close to the Indian coasts, possibly related to a sea breeze circulation at the Indian west coast, not resolved by the model. Discrepancies are also found in the vicinity of convection at the ITCZ. The marked tracer study suggests that biofuel use and agricultural waste burning in India are major CO sources for the Indian Ocean north of the ITCZ, with minor contributions from Middle East, China, and Southeast Asia. In the much cleaner boundary layer over the southern Indian Ocean, CO from hydrocarbon oxidation is a dominant source. There are no other regions around the globe where biofuel use and biomass burning contribute so much to the CO mixing ratios. In general, most of the Asian CO over the Indian Ocean remains north of the ITCZ, although some of the CO is transported to the Southern Hemisphere in the free troposphere near the African east coast. (Author)
We give an overview of the regional meteorological situation during the Indian Ocean Experiment INDOEX intensive field phase (IFP) in February and March 1999. The INDOEX domain, reaching from 30 deg ...N to 30 deg S and from 50 deg E to 100 deg E, was chosen because the low-level outflow of pollution from India is carried by the northeasterly trades into the tropical convergence zone, where cloud processing modifies the properties of the aerosols. In contrast, there is also an inflow of pristine southern hemispheric air by the southeasterly trades into the convergence zone. However, during the 1999 IFP some deviations from the climatological mean were observed. In 1999 the ITCZ was broken into a northern convergence zone and a southern convergence zone. During February the northern zone was more active and the cross-equatorial flow (N - S) was weak, both suggesting that less pollution was transported to the Southern Hemisphere. In February it was occasionally possible to sample a southern hemispheric air mass on the southern side of the INDOEX domain. During March 1999 the southern convergence zone became dominant and moved to a more southern position (near 5-10 deg S). It is shown that four channels carry pollution into the INDOEX domain: (1) NE trades over the western Arabian Sea, (2) NW-NE flow along the west coast of India, (3) NE trades over the west Bay of Bengal, and (4) NE flow from SE Asia. (Author)
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