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1.
A case of new particle formation observed during dissipation stage of a thunderstorm at a tropical station, Pune, India on
3 June 2008 is reported. The flash rate and rainfall intensity increased as high as 110 flashes per 5 minutes and 150 mm hour − 1 respectively during the active stage of thunderstorm, and then gradually decreased during the dissipation stage. The number
concentration of particles in the size range of 10–100 nm sharply increased from 350 particles cm − 3 to ∼8000 particles cm − 3 during the dissipation stage of a thunderstorm and grew to larger diameter subsequently. Observations suggest that the atmospheric
conditions such as (i) reduced background aerosol concentration after heavy rain, (ii) high humidity condition, and (iii)
increased ion concentration during the dissipation stage by corona discharges, favoured generation of new particles by ion-induced
nucleation (IIN). Observations also suggest that generation of unipolar ions by corona discharges may be more favourable for
IIN and subsequent growth of the particles. 相似文献
2.
This paper presents the results of experimental investigation on the effect of geotextile ties on uplift capacity of anchors
embedded in sand. Uplift capacity of anchor increases with increase in embedment depth to base diameter (H/D) ratio irrespective of type of anchor. With the introduction of tie to anchors, uplift capacity of anchors increases and
optimum number of layers of ties is found to be 2. A non linear power model has been developed to predict the uplift capacity
at any settlement (Q
R) of anchors with tie in terms of uplift capacity at any settlement (Q
URs) of anchor without tie, H/D ratio, number of layers of tie and displacement to base diameter ratio (Δ/D). The model is applicable for predicting Q
R having the values of Q
RS, H/D, N and Δ/D in the range of 0.257 ≤ Q
URs ≤ 1.420, 1.5 ≤ H/D ≤ 3.0, 1 ≤ N ≤ 4, 0.8 ≤ Δ/D ≤ 8. 相似文献
3.
María del Carmen Blanco Juan Darío Paoloni Hector Morrás Carmen Fiorentino Mario Eduardo Sequeira Nilda N. Amiotti Oscar Bravo Silvana Diaz Martín Espósito 《Environmental Earth Sciences》2012,66(7):2075-2084
Excessive arsenic concentrations above the Argentinean and WHO guidelines for drinking water (10 μg L−1) affects shallow aquifers of the southern Pampean Plain (Argentina) hosted in the Pampean and the Post Pampean formations
(loess and reworked loess; Plio-Pleistocene–Holocene). Health problems related to high As concentrations in drinking waters
are known as Endemic Regional Chronic Hydroarsenicism. Hydrochemistry of shallow groundwaters and soil geochemistry were investigated
aiming to (1) understand the partition of As in the solid phase and its relationship with unacceptable As concentrations in
waters, (2) identify the provision source of As to groundwaters. Only 5% of the samples had As concentrations <10 μg L−1; in 27% As concentrations ranged from 10 to 50 μg L−1 and in 58% it reached 60–500 μg L−1. The coarse fraction (50–2,000 μm) hosts about 27% of the total As in the solid phase, being positively correlated to Ba
(p < 0.01; r
2 = 0.93). About 70% is included in the <2 μm fraction and had positive correlations of As–Fe (p < 0.05; r
2 = 0.85) and As–Cr (p < 0.05; r
2 = 0.68). Soils and sediment sand fractions of vadose zones are the primary sources of As in shallow groundwater while adsorption–desorption
processes, codisolution–coprecipitation, and evaporation during the dry seasons raise As concentrations in waters exceeding
the guideline value for drinking water. 相似文献
4.
The effects of molecular diffusivity of H2SO4 and NH3 vapours on nucleated particles of SO42− and NO3− species are reported. Condensation sink and source rate of H2SO4 and NH3 vapours, growth rates and ratios of real to apparent nucleation rates are calculated for SO4– and NO3− aerosols using fractional contributions of them in total aerosol size-distribution during the measurement period at Pune,
reported in Chate and Pranesha (2004). The percentage of nucleated SO42− and NO3− aerosols of mid-point diameter 13 nm are 2% and 3% respectively of the total particles (13 nm ≤ D
p
≤ 750 nm) for both H2SO4 and NH3 diffusion. In the diameter range 75 nm ≤ D
p
≤ 133 nm, it is 48% and 45% of SO42− and NO3− aerosols, respectively for NH3 diffusion and 43% and 36% of SO42− and NO3− for H2SO4 diffusion. Increase in percentage of nucleated particles of these species corresponding to mid-point diameter 133 nm around
0900 h IST is significantly higher than that of mid-point diameter 13 nm and it is due to photo-chemical nucleation, coagulation
and coalescence among nucleated clusters. The ratios of real to apparent formation rates for SO42− and NO3− aerosols are 12% and 11% respectively, corresponding to mid-point diameter 13 nm, 17% and 13%, for midpoint diameter 133
nm and 12% and 9.5%, for mid-point diameter 750 nm. The results indicate that nucleation involving H2SO4 and acidic NH3 diffusion on SO42− and NO3− particles is the most relevant mechanism in this region. 相似文献
5.
Source and distribution of trace metals and nutrients in Narmada and Tapti river basins,India 总被引:2,自引:1,他引:1
The study was designed to establish the distributions of trace metals, dissolved organic carbon, and inorganic nutrients as
well as to assess the extent of anthropogenic inputs into the Narmada and Tapti rivers. Water and sediment qualities are variable
in the rivers, and there are major pollution problems at certain locations, mainly associated with urban and industrial centers.
The metal concentrations of samples of the aquatic compartments investigated were close to the maximum permissible concentration
for the survival of aquatic life, except for higher values of Cu (5–763 μg l−1), Pb (24–376 μg l−1), Zn (24–730 μg l−1), and Cr (70–740 μg l−1) and for drinking water except for elevated concentrations of metals such as Pb, Fe (850–2,060 μg l−1), Cr, and Ni (20–120 μg l−1). In general, the concentrations of trace metals in the rivers vary down stream which may affect the “health” of the aquatic
ecosystem and may also affect the health of the rural community that depends on the untreated river water directly for domestic
use. The assessment of EF, I
geo, and PLI in the sediments reveals overall moderate pollution in the river basins. 相似文献
6.
Sulfate reduction rates were measured over the course of a year in the sediments of aJuncus roemerianus marsh located in coastal Alabama. Sulfate reduction rates were typically highest in the surface 0–2 cm and at depths corresponding
to peak belowground biomass of the plants. The highest volume-based sulfate reduction rate measured was 1,350 μmol liter-sediment−1 d−1 in September 1995. Areal sulfate reduction rates (integrated to 20 cm depth) were strongly correlated to sediment temperature
and varied seasonally from 15.2 mmol SO
4
2−
m−2 d−1 in January 1995 to 117 mmol SO
4
2−
m−2 d−1 in late August 1995. Despite high sulfate reduction rates porewater dissolved sulfide concentrations were low (<73 μM), indicating
rapid sulfide oxidation or precipitation. Sulfate depletion data indicated that net oxidation of sediment sulfides occurred
in March through May, following a period of infrequent tidal flooding and during a period of high plant production. Porewater
Fe(II) reached very high levels (maximum of 969 μM; mean for all dates was 160 μM), particularly during periods of high sulfate
reduction. The annual sulfate reduction rate integrated over the upper 20 cm of sediment was 22.0 mol SO
4
2−
m−2 yr−1, which is among the highest rates measured in a wetland ecosystem. Based on literature values of net primary production inJ. roemerianus marshes, we estimate that an amount equivalent to 16% to 90% of the annual belowground production may be remineralized through
sulfate reduction. 相似文献
7.
H. S. Chaudhari G. K. Sawaisarje M. R. Ranalkar P. N. Sen 《Journal of Earth System Science》2010,119(5):603-615
In this study, an attempt has been made to bring out the observational aspects of vertical wind shear in thunderstorms over
Minicoy. Case studies of thunderstorm events have been examined to find out the effect of vertical wind shear and instability
on strength and longevity of thunderstorms. Role of vertical wind shear in thunderstorms and its mechanism has been explored
in this study. Results reveal that for prolonged thunderstorms high and low instability along with moderate to high vertical
wind shear (moderate: 0.003 S−1 ≤ vertical wind shear ≤ 0.005 S−1 and high: > 0.005 S−1) play a significant role in longevity and strength of thunderstorms. The mechanism of vertical wind shear in thunderstorms
was investigated in a few cases of thunderstorm events where the duration of thunderstorm was covered by the radiosonde/rawin
ascent observation taken at Minicoy. Empirical model has been developed to classify thunderstorm type and to determine the
strength and longevity of thunderstorms. Model validation has been carried out for selected cases. Model could classify thunderstorm
type for most of the cases of thunderstorm events over island and coastal stations. 相似文献
8.
We performed comparative study of phase relations in Fe1−x
Ni
x
(0.10 ≤ x ≤ 0.22 atomic fraction) and Fe0.90Ni0.10−x
C
x
(0.1 ≤ x ≤ 0.5 atomic fraction) systems at pressures to 45 GPa and temperatures to 2,600 K using laser-heated diamond anvil cell and
large-volume press (LVP) techniques. We show that laser heating of Fe,Ni alloys in DAC even to relatively low temperatures
can lead to the contamination of the sample with the carbon coming from diamond anvils, which results in the decomposition
of the alloy into iron- and nickel-rich phases. Based on the results of LVP experiments with Fe–Ni–C system (at pressures
up to 20 GPa and temperatures to 2,300 K) we demonstrate decrease of carbon solubility in Fe,Ni alloy with pressure. 相似文献
9.
Leucine and thymidine incorporation were examined in size-fractionated estuarine communities and in cultures of phytoplankton
known to use dissolved organic nitrogen (DON). Cultured phytoplankton species were used to establish that phytoplankton took
up leucine and thymidine into protein and DNA, respectively. Subsequently, incorporation of leucine and thymidine was measured
in size-fractionated populations collected from the Lafayette River, VA, a eutrophic estuary where resident populations contain
bloom-forming phytoplankton known to take up DON, and the Gulf of Mexico during a bloom of the mixotrophic red tide dinoflagellate,
Karenia brevis. We examined the efficacy of size fractionation for determining phytoplankton versus bacterial incorporation of leucine and
thymidine under conditions employed during bacterial productivity bioassays, and antibiotics were used to distinguish between
bacterial and phytoplankton incorporation in cultured and natural populations. Results suggest that cultures and natural assemblages
of phytoplankton can take up both leucine and thymidine when supplied at low concentrations (10 and 12 nmol L−1, respectively) and during short incubations (15 min to 1 h). In natural populations, up to 95% of the leucine and thymidine
incorporation during short bioassays was recovered in the >5.0-μm size fraction that contained ≤4.2% of the bacterial biomass. 相似文献
10.
Global regression relations for conversion of surface wave and body wave magnitudes to moment magnitude 总被引:1,自引:0,他引:1
A homogenous earthquake catalog is a basic input for seismic hazard estimation, and other seismicity studies. The preparation
of a homogenous earthquake catalog for a seismic region needs regressed relations for conversion of different magnitudes types,
e.g. m
b
, M
s
, to the unified moment magnitude M
w. In case of small data sets for any seismic region, it is not possible to have reliable region specific conversion relations
and alternatively appropriate global regression relations for the required magnitude ranges and focal depths can be utilized.
In this study, we collected global events magnitude data from ISC, NEIC and GCMT databases for the period 1976 to May, 2007.
Data for mb magnitudes for 3,48,423 events for ISC and 2,38,525 events for NEIC, M
s
magnitudes for 81,974 events from ISC and 16,019 events for NEIC along with 27,229 M
w
events data from GCMT has been considered. An epicentral plot for M
w
events considered in this study is also shown. M
s
determinations by ISC and NEIC, have been verified to be equivalent. Orthogonal Standard Regression (OSR) relations have
been obtained between M
s
and M
w
for focal depths (h < 70 km) in the magnitude ranges 3.0 ≤ M
s
≤ 6.1 and 6.2 ≤ M
s
≤ 8.4, and for focal depths 70 km ≤ h ≤ 643 km in the magnitude range 3.3 ≤ M
s
≤ 7.2. Standard and Inverted Standard Regression plots are also shown along with OSR to ascertain the validation of orthogonal
regression for M
s
magnitudes. The OSR relations have smaller uncertainty compared to SR and ISR relations for M
s
conversions. ISR relations between m
b
and M
w
have been obtained for magnitude ranges 2.9 ≤ m
b
≤ 6.5, for ISC events and 3.8 ≤ m
b
≤ 6.5 for NEIC events. The regression relations derived in this study based on global data are useful empirical relations
to develop homogenous earthquake catalogs in the absence of regional regression relations, as the events catalog for most
seismic regions are heterogeneous in magnitude types. 相似文献
11.
Ahmed I. Rushdi Peter U. Clark Alan C. Mix Vasile Ersek Bernd R. T. Simoneit Hai Cheng R. Lawrence Edwards 《Environmental Earth Sciences》2011,62(6):1245-1261
We analyzed speleothem calcite from the Oregon Caves National Monument, southwestern Oregon, to determine the preservation,
distribution, concentrations and sources of aliphatic lipid compounds preserved in the calcite. Maximum speleothem growth
rate occurs during interglaciations and minimum during glacial intervals. Concentrations of the total lipid compounds range
from 0.5 to 12.9 μg g−1. They increase at times of low speleothem growth rate, suggesting dilution, whereas the apparent accumulation rate of lipid
compounds tends to be highest during times of fastest speleothem growth rate. Such increased accumulation generally corresponds
to times of warm (interglacial) climate, suggesting either a greater source of organic materials during interglacial times
and/or greater efficiency of compound capture during more rapid calcite growth. Aliphatic lipid compounds include homologous
n-alkanoic acids, n-alkanols and methyl n-alkanoates and sterols with concentrations ranging from 0.3 to 7.8 μg g−1, 0.4 to 1.1 μg g−1, 0.5 to 9.6 μg g−1 and 0.1 to 2.7 μg g−1, respectively. Minor amounts of branched methyl n-alkanoates and dimethyl n-alkanedioates are also present. The high concentrations of methyl n-alkanoates are the result of esterification reactions of free fatty acids in alkaline solutions with high pH values associated
with the dripping cave waters. The distribution patterns and geochemical parameters and indices indicate that the major sources
of the aliphatic lipids involved leaching from higher plants and microbial residues derived from the soil zone above the cave
system. The estimated percentage of microbial inputs ranged from 42 to 90% of the total lipids and also showed an increase
in accumulation during warm climates. These well-preserved lipid compounds in speleothem calcite could be used as biomarkers
for paleoenvironmental study. 相似文献
12.
Paolo Paronuzzi 《Environmental Geology》2009,58(7):1451-1466
This paper reports the field evidence and the kinematical study of the motion of two blocks (A and B) mobilised by a rockfall
in Lavone (Valtrompia, northern Italy) on 14 February 1987. The two sequences of impact marks left by the blocks on the ground
surface were measured and the lithostratigraphical features of the debris slope were surveyed. On the basis of the field-collected
input data, several computer simulations were carried out to calculate the coefficients of restitution (E) satisfying the trajectory conditions. The computed output values show that rebound trajectories require high coefficients
of restitution (0.8 ≤ E ≤ 0.9). Back-calculated impact velocities range from 9.2 to 19.8 m/s. Trajectory heights vary from 0 to 2.4 m above the slope
surface. Block trajectories differ considerably according to the circumstances of initial air projection, i.e. to initial
rebound angle (αr). The calculated values of (αr) denote a considerable range (36°), emphasising the random nature of this parameter. The described case-history shows that
rockfall computer analyses can be an effective tool to describe the bouncing propagation of single blocks but care must be
taken in choosing the restitution coefficient E and the geometrical parameters of initial air projections. 相似文献
13.
Zhiwen Dong Zhongqin Li Cunde Xiao Feiteng Wang Mingjun Zhang 《Environmental Earth Sciences》2010,60(7):1361-1368
Windblown mineral aerosol dust derived from the crustal surface is an important atmospheric component affecting the earth’s
radiation budget. Deposition of atmospheric dust was measured in the fresh snow on glacier no. 1 at the headwater of the Urumqi
River in eastern Tian Shan, central Asia. An analysis of seasonal variation of concentrations of dust particles in the snow
suggests that the number concentration of dust particle is significantly high from April to June, which may be caused by Asian
dust storms in the spring. The comparison of mass-size distribution of dust particles from April to August shows an obvious
seasonal change trend. The distribution of particles changes from single model (3–21 μm) in the non-dust period before dust
events in April, to bi-model (3–21 and 20–80 μm) during the Asian dust period, and to single model (3–21 μm) after July in
the non-dust period again. The Ca2+ concentration in the fresh snow is also very high from April to June, while NH4
+ and SO4
2−, as water-soluble constituents, have concentration changes that are different from each other. Backward trajectory was also
employed to examine the transport process of air mass in this region. 相似文献
14.
Paolo Paronuzzi 《Rock Mechanics and Rock Engineering》2009,42(5):783-813
This paper reports the field evidence and the kinematical study of the motion of two blocks (A and B) mobilised by a rockfall
in Lavone (Valtrompia, northern Italy) on 14th February 1987. The two sequences of impact marks left by the blocks on the
ground surface were measured and the lithostratigraphical features of the debris slope were surveyed. On the basis of the
field-collected input data, several computer simulations were carried out to calculate the coefficients of restitution (E) satisfying the trajectory conditions. The computed output values, obtained by running a specific automatic program for rockfall
modelling, show that rebound trajectories require high coefficients of restitution (0.8 ≤ E ≤ 0.9). Back-calculated impact velocities range from 9.2 to 19.8 m/s. Trajectory heights vary from 0 to 2.4 m above the slope
surface. Block trajectories differ considerably according to the circumstances of initial air projection, i.e. to the initial
rebound angle (α
r). The calculated values of α
r denote a considerable range (36°), emphasising the high variability and the random nature of this parameter. The described
case history shows that rockfall computer analyses can be an effective tool to describe the bouncing propagation of single
blocks, but care must be taken in choosing the restitution coefficient E and the geometrical parameters of initial air projections. 相似文献
15.
This investigation represented the preliminary study to characterize Pt and Pd concentrations and enrichment ratios in urban
roadside soils. Roadside soil samples were analyzed by ICP-MS. Data from 21 roadside topsoil samples show medians of Pt and
Pd concentrations are 2.9 and 2.8 ng g−1, respectively. These values are higher than those of upper crust that average 0.4 and 0.4 ng g−1, respectively. The relatively lower Pt and Pd concentrations are expected due to recent introduction of catalysts to China
compared to the prolonged use of catalysts in Europe. Hierarchical clustering analysis indicates that Pt and Pd in Xuzhou
urban roadside soils were mainly from the traffic emissions. Computation of enrichment ratios using the upper crust values
as background levels suggests that the roadside soils had enrichment medians of 6.4 for Pt (range 2.5–11.75) and of 6.75 for
Pd (range 2.75–9.25). Lower Pt/Pd ratios (range 0.35–2.86) in relation to similar studies in other countries were observed
due to the different automobile catalytic converters. In general, fine fraction (<250 μm) contains higher Pt and Pd concentrations
compared to the coarse fraction (250–500 μm). 相似文献
16.
Justus E. E. van Beusekom Dirk Mengedoht Christina B. Augustin Mario Schilling Maarten Boersma 《International Journal of Earth Sciences》2009,98(2):251-260
From March 2002 to until April 2003 we investigated the seasonal nutrient and phytoplankton dynamics in the central Bornholm
Basin (Baltic Sea) within the framework of the German GLOBEC Project. We choose a nested approach consisting of vertical fluorescence
profiles, phytoplankton counts and nutrient analyses. The Fluoroprobe (MultiProbe, BBE Moldaenke) is capable of distinguishing
four algal groups (Cryptophyceae, Cyanophyceae, Chlorophyceae, Bacillariophyceae + Dinophyceae). Winter nutrient concentrations
were about 5 μM NO3 and 0.5 μM PO4 in the central Basin. The spring phytoplankton bloom was dominated by the diatom Skeletonema sp. and reached a maximum of about 270 μg C/l before the onset of the seasonal stratification. Protozooplankton was dominated
by the Mesodinium rubrum (a phototrophic ciliate = Myrionecta rubra) and reached a maximum biomass of about 200–300 μg C/l about 2 weeks after the demise of the diatom spring bloom. During summer,
the water column was stratified and a subsurface maximum developed near the thermocline consisting of Bacillariophyceae, Cryptophycea
and other phototrophic flagellates. Phytoplankton and protozooplankton biomass was generally low. Nutrient concentrations
point towards a nitrogen limitation during this period. The stratification period ended during September and surface nutrient
concentrations increased again. Protozooplankton reached a second maximum during September. With the Fluoroprobe small scale
structures in the plankton community could be detected like a subsurface Cryptophyceae maximum near the thermocline that however,
could not be confirmed by cell counts. The chlorophyll a estimate of the Fluoroprobe was in good agreement with the phytoplankton
biomass estimated from counts. We conclude that only by combining modern sensing technology with microscopy, the small-scale
dynamics and taxonomic spectrum of the plankton can be fully captured. 相似文献
17.
Method for Quantification of Wear of Sheared Joint Walls Based on Surface Morphology 总被引:4,自引:2,他引:2
Roughness and wear evolution of three different joint wall surfaces were characterized using surface roughness and surface
wear parameters. Parameters were defined by considering the two components of morphology: waviness (“primary” roughness) and
surface roughness (“secondary” roughness). Two surface roughness parameters are proposed: joint interface (or single wall)
specific surface roughness coefficient SR
s
(0 ≤ SR
s
≤ 1) for quantifying the amount of “pure” roughness (or specific roughness), and degree of joint interface (or single wall)
relative surface roughness DR
r
(0 ≤ DR
r
≤ 0.5). Two further parameters are also proposed in order to quantify the wear of wall surface: joint interface (or single
wall) surface wear coefficient Λinterface, and the degree of joint interface (or single wall) surface wear D
w(interface). The three test specimens were: man-made granite joints with hammered surfaces, man-made mortar joints with corrugated surfaces,
and mortar joints prepared from natural rough and undulated schist joint replicas. Shearing under monotonic and cyclic shearing
was performed using a computer-controlled bidirectional and biaxial shear apparatus. Joint surface data were measured using
a noncontact laser sensor profilometer prior to and after each shear test. Calculation of specific surface roughness coefficient
SR
s
, and degree of surface wear D
w
, indicated that the hammered joint interface with predominant interlocking wears much more (>90%) than the corrugated (27%)
and the rough and undulated (23%) joint interfaces having localized interlocking points. The proposed method was also successfully
linked to the classical wear theory. 相似文献
18.
Continuous measurements of aerosol size distributions in the mid-point diameter range 20.5–500 nm were made from October 2005
to March 2006 at Pune (18°32′N, 73°51′E), India using Scanning Mobility Particle Sizer (SMPS). Volatilities of atmospheric
aerosols were also measured at 40°, 125°, 175°, 300° and 350°C temperatures with Thermodenuder–SMPS coupled system to determine
aerosol volatile fractions. Aerosols in nucleated, CCN and accumulated modes are characterized from the measured percentage
of particles volatized at 40°, 125°, 175°, 300° and 350°C temperatures. Averaged monthly aerosol concentration is at its maximum
in November and gradually decreases to its minimum at the end of March. The diurnal variations of aerosol concentrations gradually
decrease in the night and in early morning hours (0400–0800 hr). However, concentration attains minimum in its variations
in the noon (1400–1600 hr) due to higher ventilation factor (product of mixing height and wind speed). The half an hour averaged
diurnal variation of aerosol number concentration shows about 5 to 10-fold increase despite the ventilation factor at higher
side before 1200 hr. This sudden increase in aerosol concentrations is linked with prevailing conditions for nucleation bursts.
The measurement of volatile fraction of ambient aerosols reveals that there are large number of highly volatile particles
in the Aitken mode in the morning hours and these volatile fractions of aerosols at temperatures <150°C are of ammonium chloride
and ammonium sulfate, acetic and formic acids. 相似文献
19.
Xunming Wang Caixia Zhang Hongtao Wang Guangqiang Qian Wanyin Luo Junfeng Lu Li Wang 《Environmental Earth Sciences》2011,64(4):1039-1050
A series of experiments to determine the direct emission of dust-sized particles from Gobi surfaces by clean wind (wind without
sand), and the potential for aeolian abrasion of Gobi surfaces and beds of gravel and mobile sand to produce fine (<100 μm)
and dust-sized (<10 μm, PM10) particles under sand-laden winds were conducted. Parent material was obtained from Gobi areas of the Ala Shan Plateau, the
region with high dust emissions in arid China. The fine particles produced by aeolian processes were collected using sand
traps and sieved the captured materials to exclude particles >100 μm in diameter and then PM10 by sedimentation was acquired. The Gobi surface provided most of the emitted fine particles during the initial dust emission
processes, but subsequently, release of the clay coatings of particles by abrasion becomes the dominant source of fine materials.
Under sand-laden winds, PM10 production rates produced by aeolian abrasion of Gobi surfaces ranged between 0.002 and 0.244% of blown materials. After
removal of sand, silt, or clay with low resistance to erosion from the Gobi surfaces by the wind, the PM10 production rates caused by aeolian abrasion were similar to those from gravel and sand beds. The results also indicated that
after the dust-sized particles with low resistance to erosion were removed, the production of dust-sized particles was unrelated
to wind velocity. Under aeolian processes, Gobi deserts in this region therefore play a major role in dust emissions from
arid and semiarid China. 相似文献
20.
We measured seasonal variations in microzooplankton grazing in Long Island Sound (LIS) and San Francisco Bay (SFB). There
was consistent evidence of nutrient limitation in LIS, but not SFB. We found higher chlorophyll a concentrations in LIS compared with SFB. In spite of differences in phytoplankton, there were no differences in microzooplankton
abundance (summer: LIS, 12.4 ± 1.8 × 103 indiv. L−1; SFB, 14.1 ± 3.0 × 103 indiv. L−1), biomass (summer: LIS, 30.4 ± 5.0 μg C L−1; SFB, 26.3 ± 5.9 μg C L−1), or grazing rates (summer: LIS, 0.66 ± 0.19 day−1; SFB, 0.65 ± 0.18 day−1) between the two estuaries. In common with many other investigators, we found many instances of saturated as well as insignificant
grazing. We suggest that saturation in some cases may result from high particle loads in turbid estuarine systems and that
insignificant grazing may result from extreme saturation of the grazing response due to the need to process non-food particles. 相似文献