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1.
Spatial variability in the primary productivity in the East China Sea and its adjacent waters 总被引：7，自引：0，他引：7
Primary productivity in the East China Sea and its adjacent area was measured by the13C tracer method during winter, summer and fall in 1993 and 1994. The depth-integrated primary productivity in the Kuroshio
Current ranged from 220 to 350 mgC m−2d−1, and showed little seasonal variability. High primary productivity (above 570 mgC m−2d−1) was measured at the center of the continental shelf throughout the observation period. The productivity at the station nearest
to the Changjiang estuary exhibited a distinctive seasonal change from 68 to 1,500 mgC m−2d−1. Depth-integrated primary productivity was 2.7 times higher in the shelf area than the rates at the Kuroshio Current. High
chlorophyll-a specific productivity (mgC mgChl.-a−2d−1) throughout the euphotic zone was mainly found in the shelf area rather than off-shelf area, probably due to higher nutrient
availability and higher activity of phytoplankton at the subsurface layer in the shelf area. 相似文献
2.
Dissolved nitrous oxide (N2O) dynamics in agricultural field drains and headwater streams in an intensive arable catchment 
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下载免费PDF全文 Indirect nitrous oxide (N2O) emissions produced by nitrogen (N) leaching into surface water and groundwater bodies are poorly understood in comparison to direct N2O emissions from soils. In this study, dissolved N2O concentrations were measured weekly in both lowland headwater streams and subsurface agricultural field drain discharges over a 2‐year period (2013–2015) in an intensive arable catchment, Norfolk, UK. All field drain and stream water samples were found to have dissolved N2O concentrations higher than the water–air equilibrium concentration, illustrating that all sites were acting as a net source of N2O emissions to the atmosphere. Soil texture was found to significantly influence field drain N2O dynamics, with mean concentrations from drains in clay loam soils (5.3 μg N L?1) being greater than drains in sandy loam soils (4.0 μg N L?1). Soil texture also impacted upon the relationships between field drain N2O concentrations and other water quality parameters (pH, flow rate, and nitrate (NO3) and nitrite (NO2) concentrations), highlighting possible differences in N2O production mechanisms in different soil types. Catchment antecedent moisture conditions influenced the storm event mobilisation of N2O in both field drains and streams, with the greatest concentration increases recorded during precipitation events preceded by prolonged wet conditions. N2O concentrations also varied seasonally, with the lowest mean concentrations typically occurring during the summer months (JJA). Nitrogen fertiliser application rates and different soil inversion regimes were found to have no effect on dissolved N2O concentrations, whereas higher N2O concentrations recorded in field drains under a winter cover crop compared to fallow fields revealed cover crops are an ineffective greenhouse gas emission mitigation strategy. Overall, this study highlights the complex interactions governing the dynamics of dissolved N2O concentrations in field drains and headwater streams in a lowland intensive agricultural catchment. 相似文献
3.
Boubacar KANE Pierre Y. JULIEN 《国际泥沙研究》2007,22(2):114-119
An extensive database of reservoir sedimentation surveys throughout continental United States is compiled and analyzed to determine specific degradation SD relationships as function of mean annual rainfall R, drainage area A, and watershed slope S. The database contains 1463 field measurements and specific degradation relationships are defined as function of A, R and S. Weak trends and significant variability in the data are noticeable. Specific degradation measurements are log normally distributed with respect to R, A, and S and 95% confidence intervals are determined accordingly. The accuracy of the predictions does not significantly increase as more independent variables are added to the regression analyses. 相似文献
4.
A thermoelastic model for calculating the high-pressure and high-temperature properties of isotropic solids is presented
by extending the formalism by Thomsen and combining the resulting one with the Vinet model for static lattice and the Debye
model for lattice vibration. Applying it to polycrystalline corundum, we have shown that the calculated values of entropy
and heat capacity at constant pressure are in agreement with literature values to 2325 K at zero pressure and that the calculated
values of thermal expansivity agree reasonably with experimental data to 1100 K at zero pressure. The model reproduces experimental
data of sound velocities v
p
and v
s
of compressional and shear waves to 1825 K at zero pressure and those to 62 GPa at room temperature, and it reproduces also
experimental shock-wave equation of state to 150 GPa. The velocity correlation (∂ln v
s
/∂ln v
p
)
S
was found to have weak pressure and temperature dependences and the results under lower mantle conditions are compared with
those of magnesian and calcium silicate perovskites and magnesiowüstite, and the PREM values of the Earth's lower mantle.
Received: 12 February 2000 / Accepted: 15 July 2000 相似文献
5.
Takeo Hama Shoko Kawashima Koichi Shimotori Yuhi Satoh Yuko Omori Shigeki Wada Taiki Adachi Shun Hasegawa Takashi Midorikawa Masao Ishii Shu Saito Daisuke Sasano Hiroko Endo Tsuyoshi Nakayama Isao Inouye 《Journal of Oceanography》2012,68(1):183-194
The effect of ocean acidification, caused by the increase in pCO2 in seawater, on phytoplankton population and on related organic nitrogen production was experimentally examined by use of a natural coastal microbial population. pCO2 and pH were controlled by aeration with air in which pCO2 was at the current level (control), for which ambient air was used, and with air in which pCO2 was ??800?? and ??1200?? ppm, in 500-L culture vessels. The experiment was continued for 15?days after addition of the inorganic nutrients such as nitrate, phosphate, and silicate. During most of the experimental period, a minor increase in phytoplankton biomass was noted, probably because of low irradiance, an increase in phytoplankton biomass was observed at the end of the experiment. Flow cytometric and microscopic observations revealed that this increase was because of Chrysochromulina sp. (Haptophyceae). The growth of Chrysochromulina sp. was most obvious in the control vessel, and tended to be obscured by increasing pCO2 (decrease in pH), indicating the possibility that ocean acidification inhibits the growth of specific phytoplankton groups, for example Chrysochromulina sp. Production of particulate organic nitrogen (PON), determined by the 15N tracer method, also diminished under acidified conditions compared with that at the current level. 相似文献
6.
Interpretation of undisturbed hydrogeochemical conditions in Neogene sediments of the Horonobe area, Hokkaido, Japan 总被引：1，自引：0，他引：1
Empirical, geostatistical and geochemical modeling techniques were used to determine whether chemical, isotopic and mineralogical data collected in surface-based borehole investigations at the Horonobe Underground Research Laboratory (URL) site in Hokkaido, Japan were representative of the natural environment before it was disturbed by borehole drilling, hydraulic testing and sampling. Water samples collected either by pumping groundwaters to the surface from borehole sections that had been isolated by inflatable packers or by squeezing porewaters from drillcores sampled from the same borehole and sampling depth were found to be similar in certain respects (mNa+, mCl−, δ18O and δD) but not others (mSO42−, mCa2+, mMg2+ and mK+). The inconsistencies suggest that a majority of the porewater samples were contaminated as a result of pyrite oxidation and dissolution of carbonate minerals during sampling, storage and/or squeezing of the drillcores. Multivariate geostatistical analyses support this hypothesis, and further suggest that uncontaminated porewaters and groundwaters can be divided into three representative groups: a low salinity, low δ18O and low δD group; a moderate salinity, low Ca-Mg group; and a high salinity, high K and moderate Ca-Mg group. The groundwaters also contain high concentrations of dissolved gases, including CH4(g), CO2(g), H2S(g) and various hydrocarbons, which exsolve from the groundwaters as they are pumped to the surface for sampling. The effects of such degassing on the chemistry of groundwater samples was evaluated by using a reaction-path model to simulate the titration of gases collected at the surface back into the samples. Results suggest that undisturbed groundwaters are slightly more acidic than their sampled counterparts, and contain roughly equivalent activities of dissolved CH4(aq) and carbonate species. Redox potentials calculated using the corrected groundwater compositions and assuming equilibrium for the CH4(aq)/CO2(aq) redox couple are significantly more negative than those determined in situ in one borehole using a downhole chemical probe, and those that can be inferred from the ubiquitous presence of small amounts of framboidal pyrite and siderite in siliceous biogenic sediments of the Horonobe area. The empirical, geostatistical and geochemical modeling techniques considered in this study can be adapted for use in characterizing the hydrogeochemical environment of a site that will eventually be selected to host a geologic repository for high-level nuclear waste in Japan. 相似文献
7.
Kunihiro T Miyazaki T Uramoto Y Kinoshita K Inoue A Tamaki S Hama D Tsutsumi H Ohwada K 《Marine pollution bulletin》2008,57(1-5):68-77
We monitored seasonal changes of the abundance and composition of microorganisms in the fish-farm sediment in Kusuura Bay, Amakusa, Japan, using the quinone profiling technique, during bioremediation by introducing cultured colonies of polychaete, Capitella sp. I. In November 2004, approximately 9.2 million cultured worms were transferred to the fish-farm sediment, which increased rapidly, and reached 458.5 gWW/m(2) (528,000 indiv./m(2)) in March 2005. During this fast-increasing period of Capitella, the microbial quinone content of the surface sediment (0-2 cm) also increased markedly, and reached 237 micromol/m(2) in January 2005, although the water temperature decreased to the lowest levels in the year. Particularly, the mole fraction of ubiquinone-10 in total quinones in the sediment, indicating the presence of alpha subclass of Proteobacteria, increased by 9.3%. These facts suggest that the bacterial growth was enhanced markedly by the biological activities of worms in the sediment, and the bacteria played an important role in the decomposition of the organic matter in the sediment. 相似文献
8.
Roderick J. Mclntosh Boubacar Hama Diaby Tér’ba Togola 《Natural Resources Research》1997,6(2):111-129
There is a civilization at risk. In the middle of West Africa, just south of the Sahara, where the Niger River spills into
a vast floodplain (the Middle Niger), an indigenous urban civilization emerged around two thousand years ago. The story of
that civilization is just beginning to be uncovered from the thousands of tells (ancient settlement mounds) that litter the
Middle Niger, but archaeologists have until recently been loosing the race with the looters who plunder these sites for ancient
statues and bronze art. The nation of Mali, and the local community of Jenne at the epicenter of this looting recently invented
effective shields for the remains of this civilization, protections against local looters in the employ of a syndicate of
wealthy European antiquities dealers. In the person of the new, democratically-elected archaeologist-President, the nation
has articulated a vision of Mali’s future linked to the preservation of its past. The government has promulgated effective
regulations and education programs, and initiated with the United States the world’s first bilateral import ban between a
major “source” and a major “market” nation. This 1993 bilateral accord has become a prototype for many nations. In that same
year, Mali established a Cultural Mission at Jenne to reinforce local pride in a local past. This local pride, in only a short
period, has turned into a total protection of some 200 sites within a ten-kilometer radius of Jenne. These indigenous actions
have, in less than a decade, transformed the nonrenewable archaeological resources of the Jenne region from surely one of
the world’s most endangered, to a case study in local and national protection 相似文献
9.
10.
Gerardo Rodríguez-Fuentes Sabine Devautour-Vinot Sekou Diaby François Henn 《Physics and Chemistry of Minerals》2011,38(8):613-621
Purified natural clinoptilolite from the Tasajeras deposit, Cuba, and some of its metal exchanged forms are studied, at the
dehydrated state, by means of dielectric relaxation spectroscopy (DRS) using two different modus operandi: complex impedance
spectroscopy and dielectric dynamic thermal analysis. Data analysis yields the determination of the extra-framework cation
(EFC) population into the various possible crystallographic sites of the zeolitic framework as well as of the activation energy
characterizing the localized hopping mechanism of EFC. First, it is shown that the DRS responses obtained here match well
with the previous reported data, which were previously localized EFCs in positions close to M1 and M2 sites when the clinoptilolite
is modified to almost homoionic form. From this outcome, it can be concluded that all EFCs are in the same crystallographic
situation regarding solvation or, in other terms, that no steric effect can be taken into account to explain cationic selectivity.
Second, based on the assumption that the activation energy for EFC hopping is directly connected to the EFC/framework interaction
and on simple thermodynamics consideration, we show this interaction does not govern the EFC exchange reaction. So, it is
emphasized that EFC/H2O interaction is the key factor for cation exchange selectivity. 相似文献