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1.
Spatial distribution of soil salinity can be estimated based on its environmental factors because soil salinity is strongly affected and indicated by environmental factors. Different with other properties such as soil texture, soil salinity varies with short-term time. Thus, how to choose powerful environmental predictors is especially important for soil salinity. This paper presents a similarity-based prediction approach to map soil salinity and detects powerful environmental predictors for the Huanghe(Yellow) River Delta area in China. The similarity-based approach predicts the soil salinities of unsampled locations based on the environmental similarity between unsampled and sampled locations. A dataset of 92 points with salt data at depth of 30–40 cm was divided into two subsets for prediction and validation. Topographical parameters, soil textures, distances to irrigation channels and to the coastline, land surface temperature from Moderate Resolution Imaging Spectroradiometer(MODIS), Normalized Difference Vegetation Indices(NDVIs) and land surface reflectance data from Landsat Thematic Mapper(TM) imagery were generated. The similarity-based prediction approach was applied on several combinations of different environmental factors. Based on three evaluation indices including the correlation coefficient(CC) between observed and predicted values, the mean absolute error and the root mean squared error we found that elevation, distance to irrigation channels, soil texture, night land surface temperature, NDVI, and land surface reflectance Band 5 are the optimal combination for mapping soil salinity at the 30–40 cm depth in the study area(with a CC value of 0.69 and a root mean squared error value of 0.38). Our results indicated that the similarity-based prediction approach could be a vital alternative to other methods for mapping soil salinity, especially for area with limited observation data and could be used to monitor soil salinity distributions in the future.  相似文献   

2.
Using hydrographic measurements from three recent surveys in the western tropical Pacific, this study revealed the existence and general features of thermohaline finestructure near the northern Philippine coast. Pronounced finestructures were detected in the layers of the North Pacific Tropical Water (NPTW) and the North Pacific Intermediate Water (NPIW) during all three cruises and shown to be mainly thermohaline intrusions. Characteristics of the intrusions were further investigated with spiciness curvature and salinity anomaly methods. The vertical scale of the intrusions was 20-50m and 50-100m in the NPTW and NPIW layers, respectively. Within the NPTW layer, the Turner angle distribution and correlation between salinity and density anomalies suggested that diffusive convection between surface fresh water and subsurface saline water played an important role in the development and maintenance of the intrusions. In addition, connection between thermohaline finestructure and larger-scale oceanic processes was explored using historical hydrographic data. The results reveal that the salinity field and the distribution of the intrusions in this region were largely determined by mesoscale eddies. As a result of eddy stirring, both isopycnal and diapycnal temperature/salinity gradients were strengthened, which gave rise to the development of thermohaline intrusions. The intrusions acted to enhance heat and salt fluxes and resulted in the mixing of water masses being more efficient. By linking mesoscale eddy stirring to micro-scale diffusion, thermohaline finestructure plays a vital role in the ocean energy cascade and water mass conversion in the northern Philippine Sea.  相似文献   

3.
Actinomycetes population from continental slope sediment of the Bay of Bengal was studied. Samples were collected during two voyages of FORV Sagar Sampada in 2004 （May-June） and 2005 （July） respectively from 11 transects （each transect had ca. 200 m, 500 m, and 1 000 m depth stations）. The physicochemical parameters of overlying water, and sediment samples were also recorded. The actinomycete population ranged from 5.17 to 51.94 CFU/g dry sediment weight and 9.38 to 45.22 CFU/g dry sediment weight during the two cruises respectively. No actinomycete colony was isolated from stations in 1 000 m depth. Two-way analysis of variance showed significant variation among stations （ANOVA two-way, P〈0.05）, but no significance was found between the two cruises （ANOVA two-way, P〈0.05）. Populations in stations in 500 m depth in both cruises were higher than that of 200 m depth stations with statistically insignificant difference （ANOVA two-way, P〉0.05）. Three actinomycetes genera were identified. Streptomyces was found to be the dominating one in both the cruises, followed by Micromonospora, and Actinomyces. The spore of Streptomyces isolates showed the abundance in spiral spore chain. Spore surface was smooth. Multiple regression analysis revealed that the influencing physico-chemical factors were sediment pH, sediment temperature, TOC, porosity, salinity, and pressure. The media used in the present study was prepared with seawater. Thus, they may represent an autochthonous marine flora and deny the theory of land runoff carriage into the sea for adaptation to the salinity of the seawater and sediments.  相似文献   

4.
Study of the surface morphology of gas hydrate is of great importance in understanding its physical properties and occurrence.In order to investigate the surface morphology of different types(sI and sII)and occurrences(pore-filling and fracture-filling)of gas hydrate,both lab-synthesized and drilled-gas hydrate samples were measured using cryo-scanning electron microscopy(cryo-SEM).Results showed that the surface of s I hydrate was relatively smooth,and spongy nano-pores(200–400 nm)gradually occurred at the surface during continuous observation.The surface of sII hydrate was more compact,showing a tier-like structure.Hydrate occurred in quartz sand and usually filled the pores of the sediments and both hydrate and sediments were cemented with each other.SEM observation of the gas hydrates collected from the South China Sea showed that the surface morphology and contact relation with sediments varied with hydrate occurrence.For instance,hydrates dispersed in sediments mainly filled the pores of the sediments.The existence of microorganism shells,such as foraminifera,was beneficial to the formation of gas hydrate.When hydrate occurred as a massive or vein structure,it was easily distinguished from the surrounding sediments.The surface of hydrate with massive or vein structure showed two distinct characters:one was dense and smooth,the other is porous(several to tens of micrometers in diameter).The occurrence of different hydrate morphologies was probably caused by the supplement rates of methane gas.  相似文献   

5.
Temperature and salinity profile data, collected by southern elephant seals equipped with autonomous CTD-Satellite Relay Data Loggers(CTD-SRDLs) during the Antarctic wintertime in 2011 and 2012, were used to study the evolution of water property and the resultant formation of the high density water in the Mackenzie Bay polynya(MBP) in front of the Amery Ice Shelf(AIS). In late March the upper 100–200 m layer is characterized by strong halocline and inversion thermocline. The mixed layer keeps deepening up to 250 m by mid-April with potential temperature remaining nearly the surface freezing point and sea surface salinity increasing from 34.00 to 34.21. From then on until mid-May, the whole water column stays isothermally at about~(-1).90℃while the surface salinity increases by a further 0.23. Hereafter the temperature increases while salinity decreases along with the increasing depth both by 0.1 order of magnitude vertically. The upper ocean heat content ranging from 120.5 to 2.9 MJ m~(-2), heat flux with the values of 9.8–287.0 W m~(-2) loss and the sea ice growth rates of 4.3–11.7 cm d~(-1) were estimated by using simple 1-D heat and salt budget methods. The MBP exists throughout the whole Antarctic winter(March to October) due to the air-sea-ice interaction, with an average size of about 5.0×10~3 km~2. It can be speculated that the decrease of the salinity of the upper ocean may occur after October each year. The recurring sea-ice production and the associated brine rejection process increase the salinity of the water column in the MBP progressively, resulting in, eventually, the formation of a large body of high density water.  相似文献   

6.
A field observation was carried out in the Changjiang （Yangtze） River Estuary from May 19 to 26, 2003. A total of 29 stations, including 2 anchored stations, were occupied through almost the whole salinity gradient. Based on the observation data, biogeochemistry of chemical oxygen demand （COD） was examined. Spatial distribution pattern of COD shows that it decreased downstream. The COD concentration varied generally within a narrow range of 1.24-1.60 mg/L in the zone around the river mouth, beyond which it decreased rapidly to 0.20 mg/L. In the mixed water zone, the fluctuation in COD was smaller at 2 m above the bottom layer than at the surface layer in 48 h. In the seawater zone, the 48-h fluctuation at the surface was the largest, followed by that of 5 m below the surface and 2 m above the bottom layers in a range of from 2.50 to 0.55 mg/L. Freshwater discharge was the dominant source of COD in the estuary. The average COD beyond the river mouth was 2.7 mg/L, which accorded with the Chinese seawater quality Grade I. Relationships between dissolved oxygen and biogeochemical parameters such as suspended particulate matter, dissolved organic matter and chlorophyll-a were also discussed.  相似文献   

7.
Long-term datasets of water temperature,salinity,dissolved oxygen,phosphate and nitrate from 1973 to 2013 were used to study interannual variations of these parameters along a transect(section PN)across the Kuroshio and shelf area in the East China Sea.Water temperature and salinity at depths of 0–200 m showed a low-high-low-high pattern over the 40-year period.Water temperature and salinity at 500 m were relatively high from 1985 to 1990 and decreased continuously thereafter.Salinity at 800 m was lowest around 1993 and increased thereafter.Nutrients were highest between 1980 and 1985.After 1985,nutrients at 500 m were increasing.The range of variation in nutrients was large before 1985 and the magnitude increased with greater depths.Apparent oxygen utilization at 500 m depth was decreasing before 1990 and started to increase after 1992.Significant changes after 1990 at 500 m depth may be due to the upward trend of the upper boundary of Kuroshio intermediate water.Interannual variation of water temperature,salinity,dissolved oxygen,phosphate and nitrate along section PN has a significant correlation with the Pacific Decadal Oscillation index.  相似文献   

8.
The decadal variations of the North Pacific Tropical Water(NPTW)at 137°E in the western North Pacific Ocean are investigated based on the repeated hydrographic observations along with two global gridded ocean products.The results indicate that the maximum salinity of NPTW experiences significant quasi-decadal variations,having maxima around 1979,1987,1995,2004,and 2012,while minima around1974,1983,1991,1999,and 2008 during the period of interest.The NPTW area also shows similar quasidecadal variation,expanding/shrinking as its maximum salinity increases/decreases at the 137°E section.These variations are induced mainly by changes in the mixed layer salinity in the source region and largescale circulation in the northwestern tropical Pacific Ocean,both of which are related to the Pacific Decadal Oscillation.The underlying processes at work are further confirmed through conducting the subsurface salinity budget analysis.Besides,short-term processes are also at work through nonlinear interactions,especially after 2000.  相似文献   

9.
With the use of historical data from their 1982-1985 special observation at the source area of the Taiwan Warm Current the authors conducted studies to clarify the temperature and salinity characteristics, variability, and origin of the Taiwan warm Current Water, and its influence on the expanding direction of the Changjiang Diluted Water.The main results are given below.(1)The Taiwan Warm Current Water can be divided into the "Surface Water of the Taiwan Warm Current" formed due to the mixing of the Kuroshio Surface Water flowing northward along the east coast of Taiwan with the Taiwan Strait Water, and the "Deep Water of the Taiwan Warm Current" originated from Kuroshio Subsurface Water to the east of Taiwan. It is characterized by stable low temperature and stable high salinity in summer. The maximum seasonal variation and maximum secular variation of temperature and salinity are 1.87℃, 0.26‰ and 2.96℃, 0.37‰, respectively.(2)The variation in strength of the Taiwan Warm Current is the main influe  相似文献   

10.
One of sea ice core samples was taken from Arctic by the First Chinese National Arctic Research Expedition Team in 1999. 20 vertical and 2 horizontal ice sections were cut out of the ice core sample 2.22 m in length, which covered the ice sheet from surface to bottom except losses for during sampling and section cutting. From the observation and analysis of the fabrics and crystals along the depth of the ice core sample, followings were found. Whole ice sheet consists of columnar, refrozen clastic pieces, granular, columnar, refrozen clastic pieces, granular, columnar and refrozen clastic pieces. This indicates that the ice core sample was 3-year old, and the ice sheet surface thawed and the melt water flowed into ice sheet during summer. Hence, the annual energy balance in Arctic can be determined by the ice sheet surface thawing in summer, and bottom growth in winter. The thickness of the ice sheet is kept constantly at a certain position based on the corresponding climate and ocean conditions; A new  相似文献   

11.
Continuous observation of sea water temperature and current was made at Wenchang Station (19°35′N, 112°E) in 2005. The data collected indicate vigorous internal waves of both short periods and tidal and near-inertial periods. The temperature and current time series during 18-30 September were examined to describe the upper ocean internal wave field response to Typhoon Damrey (0518). The strong wind associated with the typhoon, which passed over the sea area about 45 km south of Wenchang Sta- tion on 25 September, deepened the mixed layer depth remarkably. It decreased the mixed layer temperature while increasing the deep layer temperature, and intensified the near-inertial and high-frequency fluctuations of temperature and current. Power spectra of temperature and current time series indicate significant deviations from those obtained by using the deep ocean internal wave models characterized by a power law. The frequency spectra were dominated by three energetic bands: around the inertial frequency (7.75× 10-6 Hz), tidal frequencies (1.010-25 to 2.4×10-5 Hz), and between 1.4×10-4 and 8.3 × 10-4 Hz. Dividing the field data into three phases (before, during and after the typhoon), we found that the typhoon enhanced the kinetic energy in nearly all the frequency bands, es- pecially in the surface water. The passage of Damrey made a major contribution to the horizontal kinetic energy of the total surface current variances. The vertical energy density distribution, with its peak value at the surface, was an indication that the energy in- jected by the strong wind into the surface current could penetrate downward to the thermocline.  相似文献   

12.
Four climatologies on a monthly scale (January, April, May and November) of chlorophyll a within the South China Sea (SCS) were calculated using a Coastal Zone Color Scanner (CZCS) (1979-1983) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) (1998-2002). We analyzed decadal variability of chlorophyll a by comparing the products of the two observation periods. The relationships of variability in chlorophyll a with sea surface wind speed (SSW), sea surface temperature (SST), wind stress (WS), and mixed layer depth (MLD) were determined. The results indicate that there is obvious chlorophyll a decadal variability in the SCS. The decadal chlorophyll a presents distinct seasonal variability in characteristics, which may be as a result of various different dynamic processes. The negative chlorophyll a concentration anomaly in January was associated with the warming of SST and a shallower MLD. Generally, there were higher chlorophyll a concentrations in spring during the SeaWiFS period compared with the CZCS period. However, the chlorophyll a concentration exhibits some regional differences during this season, leading to an explanation being difficult. The deepened MLD may have contributed to the positive chlorophyll a concentration anomalies from the northwestern Luzon Island to the northeastern region of Vietnam during April and May. The increases of chlorophyll a concentration in northwestern Borneo during May may be because the stronger SSW and higher WS produce a deeper mixed layer and convective mixing, leading to high levels of nutrient concentrations. The higher chlorophyll a off southeastern Vietnam may be associated with the advective transport of the colder water extending from the Karimata Strait to southeastern Vietnam.  相似文献   

13.
To study the relationship between sediment transportation and saltwater intrusion in the Changjiang (Yangtze) estuary, a three-dimensional numerical model for temperature, salinity, velocity field, and suspended sediment concentration was established based on the ECOMSED model. Using this model, sediment transportation in the flood season of 2005 was simulated for the Changjiang estuary. A comparison between simulated results and observation data for the tidal level, flow velocity and direction, salinity and suspended sediment concentration indicated that they were consistent in overall. Based on model verification, the simulation of saltwater intrusion and its effect on sediment in the Changjiang estuary was analyzed in detail. The saltwater intrusion in the estuary including the formation, evolution, and disappearance of saltwater wedge and the induced vertical circulation were reproduced, and the crucial impact of the wedge on cohesive and non-cohesive suspended sediment distribution and transportation were successfully simulated. The result shows that near the salinity front, the simulated concentrations of both cohesive and non-cohesive suspended sediment at the surface layer had a strong relationship with the simulated velocity, especially when considering a 1-hour lag. However, in the bottom layer, there was no obvious correlation between them, because the saltwater wedge and its inducing vertical circulation may have resuspended loose sediment on the bed, thus forming a high-concentration area near the bottom even if the velocity near the bottom was very low during the transition phase from flood to ebb.  相似文献   

14.
This paper describes a precise method combining numerical analysis and limit equilibrium theory to determine potential slip surfaces in soil slopes. In this method, the direction of the critical slip surface at any point in a slope is determined using the Coulomb’s strength principle and the extremum principle based on the ratio of the shear strength to the shear stress at that point. The ratio, which is considered as an analysis index, can be computed once the stress field of the soil slope is obtained. The critical slip direction at any point in the slope must be the tangential direction of a potential slip surface passing through the point. Therefore, starting from a point on the top of the slope surface or on the horizontal segment outside the slope toe, the increment with a small distance into the slope is used to choose another point and the corresponding slip direction at the point is computed. Connecting all the points used in the computation forms a potential slip surface exiting at the starting point. Then the factor of safety for any potential slip surface can be computed using limit equilibrium method like Spencer method. After factors of safety for all the potential slip surfaces are obtained, the minimum one is the factor of safety for the slope and the corresponding potential slip surface is the critical slip surface of the slope. The proposed method does not need to pre-assume the shape of potential slip surfaces. Thus it is suitable for any shape of slip surfaces. Moreover the method is very simple to be applied. Examples are presented in this paper to illustrate the feasibility of the proposed method programmed in ANSYS software by macro commands.  相似文献   

15.
Seasonal netzplankton samples from stations in the Changjiang (Yangtze River) Estuary were collected from May, 2004 to February, 2005. The dominant species and their contribution to the total zooplankton abundance were determined. Moreover, the relationship between the salinity and abundance was studied with stepwise linear regression. During the whole year, the salinity was positively correlated with the abundance, while the temperature, negatively. Linear regression analysis showed also a high positive correlation with salinity for total abundance in August and November, while in February and May, no obvious relations were found. The most abundant community was composed of neritic and brackish-water species. The North Passage (NP) (salinity <5) was greatly diluted by freshwater while the North Branch (NB) was brackish water with salinity range of 12–28. Consequently, clear decline in abundance of zooplankton was along the estuarine haloclines from the maximum in the area of high salinity to the minimum in the limnetic zone. Total zooplankton abundance and biomass were lower in NP than the NB in all seasons. In short, the salinity influenced the abundance of each species of zooplankton, and ultimately determined the total abundance of zooplankton. Furthermore, a winter peak in the abundance existed, which might be caused by the flourishing of Sinocalanus sinensis, a widely distributed species in the Changjiang Estuary.  相似文献   

16.
Methane(CH_4) is an important greenhouse gas and oceans are net sources of atmospheric CH_4. The effects of environmental factors on the CH_4 variation during different phases of the spring algal blooms were examined during two cruises conducted in the Yellow Sea(YS) from February to April of 2009. During the pre-bloom period from February to March, low CH_4 saturation( 134%) was observed in the surface water, except at two nearshore stations where the CH_4 levels were above 140% in March due to mixing with the coastal water. During the bloom period, CH_4 increased obviously at two bloom-tracking stations, especially at the surface with mean saturations of 140% and 170%. The increase in CH_4 concentration/saturation is thought to be the result of in situ CH_4 production. The particulate organic carbon(POC) and chlorophyll a contents were believed to be important factors that influenced the CH_4 production. In addition, the presence of different dominant phytoplankton species and the grazing pressure may have stimulated the CH_4 production by supplying potential methanogenic substrates(such as dimethylsulphoniopropionate(DMSP)). Both the incubation data and the in situ estimations further evidenced the significant influence of the spring blooms on the CH_4 production. The calculated sea-to-air CH_4 fluxes during the bloom period were not significantly higher than those during the pre-bloom period despite the bloom-increased CH_4 saturation. This is due to the variation in physical forcing(such as wind speed), which is the main driver for determining the CH_4 flux. Finally, we estimated the annual CH_4 flux in the YS as 9.0 μmol m~(-2) d~(-1); the findings suggest that the YS is a natural source of atmospheric CH_4.  相似文献   

17.
The characteristics of seasonal variation in phytoplankton biomass and dominant species in the Changjiang River Estuary and adjacent seas were discussed based on field investigation data from 1959 to 2009. The field data from 1981 to 2004 showed that the Chlorophyll-a concentration in surface seawater was between 0.4 and 8.5 μg dm-3. The seasonal changes generally presented a bimodal trend, with the biomass peaks occurring in May and August, and Chlorophyll-a concentration was the lowest in winter. Seasonal biomass changes were mainly controlled by temperature and nutrient levels. From the end of autumn to the next early spring, phytoplankton biomass was mainly influenced by temperature, and in other seasons, nutrient level(including the nutrient supply from the terrestrial runoffs) was the major influence factor. Field investigation data from 1959 to 2009 demonstrated that diatoms were the main phytoplankton in this area, and Skeletonema costatum, Pseudo-nitzschia pungens, Coscinodiscus oculus-iridis, Thalassinoema nitzschioides, Paralia sulcata, Chaetoceros lorenzianus, Chaetoceros curvisetus, and Prorocentrum donghaiense Lu were common dominant species. The seasonal variations in major dominant phytoplankton species presented the following trends: 1) Skeletonema(mainly S. costatum) was dominant throughout the year; and 2) seasonal succession trends were Coscinodiscus(spring) →Chaetoceros(summer and autumn) → Coscinodiscus(winter). The annual dominance of S. costatum was attributed to its environmental eurytopicity and long standing time in surface waters. The seasonal succession of Coscinodiscus and Chaetoceros was associated with the seasonal variation in water stability and nutrient level in this area. On the other hand, long-term field data also indicated obvious interannual variation of phytoplankton biomass and community structure in the Changjiang River Estuary and adjacent seas: average annual phytoplankton biomass and dinoflagellate proportion both presented increased trends during the 1950 s-2000 s.  相似文献   

18.
This paper describes a geographic information system(GIS)-based method for observing changes in topography caused by the initiation, transport, and deposition of debris flows using highresolution light detection and ranging(LiDAR) digital elevation models(DEMs) obtained before and after the debris flow events. The paper also describes a method for estimating the volume of debris flows using the differences between the LiDAR DEMs. The relative and absolute positioning accuracies of the LiDAR DEMs were evaluated using a real-time precise global navigation satellite system(GNSS) positioning method. In addition, longitudinal and cross-sectional profiles of the study area were constructed to determine the topographic changes caused by the debris flows. The volume of the debris flows was estimated based on the difference between the LiDAR DEMs. The accuracies of the relative and absolute positioning of the two LiDAR DEMs were determined to be ±10 cm and ±11 cm RMSE, respectively, which demonstrates the efficiency of the method for determining topographic changes at an scale equivalent to that of field investigations. Based on the topographic changes, the volume of the debris flows in the study area was estimated to be 3747 m3, which is comparable with the volume estimated based on the data from field investigations.  相似文献   

19.
Located in southwestern China, Jiuzhaigou National Park is one of the most popular tourism destinations in China, famous for its unique aquatic ecosystems and beautiful forests. However, plants in the park may be at high ozone risk as a result of the intensive use of diesel tour buses in the park. In addition, Jiuzhaigou is close to a region with relatively high regional anthropogenic NO x emissions. During the growing season, also the peak season of tourism, we measured ozone concentration at two sites within the Park and these were: Jiuzhaigou Bureau (JB) and Long Lake (LL). The results indicate that ozone concentrations were not high enough to cause foliar injury during the monitoring period, although the risk of ozone to plants was higher in spring than in summer and autumn. Diurnal ozone cycles at JB and LL displayed significantly higher ozone concentrations in the daytime than in the nighttime, suggesting photochemical production of ozone during the day and ozone deposition during the night as a result of the nocturnal boundary layer. In parallel with the seasonal change of background surface ozone in the Northern Hemisphere, maximum daily 8-h average ozone concentration (MDA8) and daily ozone concentration decreased from spring to autumn at the two sites. This temporal variation in Jiuzhaigou was most likely associated with the downward mixing of ozone-rich air from the free troposphere, because all the high-ozone events (MDA8 > 70.0 ppb) were observed in spring and ozone-rich air from the free troposphere was the dominant cause. In summary, our data suggest that ozone concentrations in Jiuzhaigou were more affected by the regional-scale of background pattern in air quality and meteorological conditions than by local tourist activities.  相似文献   

20.
On the basis of an understanding of the ocean current produced under the combined forces of wind stress over the sea surface and horizontal pressure gradient force caused by the uneven distribution of seawater density and the elevation of sea surface , we obtained the unsteady analytic solution of the variation with time of ocean surface current velocity corresponding to the time variation of the above two forces , and the unsteady analytic solution for variation of seawater density with time by considering only the vertical turbulence . To meet different needs, the above solutions may be written in two forms for short and long time predictions . After some simplification the analytic solution was used to predict surface ocean current velocity for meteorological -navigation in the North Pacific . The monthly average current field was first obtained to get the necessary parameters for selecting the initial shipping route in the North Pacific and Bohai and Yellow Seas . The wind current field was then cal  相似文献   

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