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1.
本文从地球化学和环境保护的角度,用8180—4Kγ谱仪直接测定方法确定了天然放射性元素U,Ra,Th,~(40)K,及人工核素~(137)Cs的含量,讨论了它们的分布特点及其影响因素,指出了河口区与下游段元素变化的差异及其制约条件。 相似文献
2.
3.
Longitudinal and transverse dispersion in estuaries may be determined in principle by measuring the change in time of the concentration field of a water soluble dye. In practice, measurements may take the form of several sampling runs crossing the dye patch. The coefficients of dispersion are usually estimated from the second moments of the concentration field; the use of second moments, in particular, introduces errors because measurements at long times or distance are unduly emphasized.A self-consistent method, free of the disadvantages inherent in the use of higher moments, is described in which the distribution of concentration in space is related to the zeroth spatial moment of concentration. In this formulation, based upon sampling runs across the dye patch, the concentration field in the estuary may be directly and simply related to the dispersion coefficients in both the intercept and gradient of a linear graph.The methods are illustrated by the characterization of a series of experiments in the Inner Estuary of Milford Haven. 相似文献
4.
本文报道2015年9月和2016年5月期间天然放射性核素224Ra和223Ra在吕宋海峡及周边海域表层和垂向水体的分布特征。为理解日本福岛核事故的影响，本文亦分析研究区域内人工放射性核素137Cs的分布特征。结果表明，224，223Ra和137Cs比活度水平均处于我国南海海洋天然放射性本底变化范围之内。224Ra在吕宋海峡以西南海北部海域比活度较高，在吕宋海峡以东菲律宾海域比活度较低。137Cs没有明显的分布趋势。基于三站位（LS3，LS5和LS8）224Ra、137Cs以及温盐的垂向分布特征，本文揭示224Ra和137Cs在热带表层水、次表层水和中-深层水中比活度水平和梯度变化的差异特征。彩虹台风事件扭转了整个吕宋海峡及周边海域的海流循环过程。大量以低水平224Ra为特征的西太平洋海水涌入南海，降低水体224Ra比活度水平。但是，西太平洋和南海北部海域水体137Cs比活度水平没有明显差异，台风导致的海流变化对水体137Cs比活度没有明显影响。 相似文献
5.
The distribution and inventory of artificial radionuclides,239,240Pu and137Cs were determined in the East China and the Yellow Seas in 1987. Almost all of239,240Pu and 50 to 80% of137Cs in the continental shelf area are retained in the sediment column.239,240Pu sediment inventory in the sea area is larger than the fallout input and tends to increase southwardly. This excess239,240Pu and the lateral distribution are attributable to the supply of239,240Pu by the Yangtze River discharge. On the contrary,137Cs sediment inventory shows a decrease to the south, and the fact can be accounted for by the southward dispersion of fine silt particles discharged from the Yellow River. Total137Cs inventory is smaller than the estimated fallout input, and the fact seems to indicate dispersion of137Cs out of the shelf region. Vertical profiles of239,240Pu and137Cs contents in sediments differ from that of natural210Pb, implying the effect of varied accumulation rates of the artificial radionuclides over the sediment particle mixing by benthic organisms. Apparent maximum sediment particle mixing coefficient (D
B
) calculated from the excess210Pb profiles in stations located between the inner and outer shelves ranged from 1.4 to 8.3 cm2y–1. ThisD
B
value is higher than that in the Okinawa Trough (1.0 cm2y–1), but lower than previously estimatedD
B
value (26 cm2y–1) in the outer shelf mud. 相似文献
6.
几种近海沉积物吸附137Cs的初步研究 总被引：1，自引：0，他引：1
在对青岛近海放射性污染调查研究中发现,该海区与对照海区(石岛海区和连云港海区)海水中~(137)Cs的含量处于同一水平,而所取沉积物中~(l37)Cs的含量却存在明显差异。同 相似文献
7.
Dissolved and particulate concentrations of silver in Tokyo Bay estuarine waters and Japanese rivers were determined in this
study. The dissolved silver concentrations in the surface water of Tokyo Bay range from 5.9 to 15.1 pmol kg−1, which is comparable to those in the surface water of the Japan Sea, but two or three times higher than those in the surface
water of the open ocean. However, elevated concentrations of dissolved silver are not found in Tokyo Bay compared with those
in other highly urbanized estuaries, such as San Francisco Bay (20∼243 pmol kg−1). In the Tokyo Bay estuary, silver typically exhibits non-conservative mixing behavior, which is a common feature in the
other estuaries reported previously. Dissolved silver concentrations decrease with salinity from the rivers to the mouth of
Tokyo Bay. Silver is efficiently scavenged by suspended particulates, as evidenced by the high conditional distribution coefficients
for silver throughout the estuary (log Kd > 5.0 ± 0.6). The silver fluxes into Tokyo Bay via inflowing rivers and atmospheric deposition were estimated as 83 kg y−1 and 15 kg y−1, respectively. A simple budget calculation shows that the silver supplied from rivers and atmosphere must be rapidly scavenged
within the Tokyo Bay estuary. 相似文献
8.
AbstractIn this paper, two analytical models used worldwide to assess salinity variation in alluvial estuaries are applied to the Ashtamudi estuary, a Ramsar site, southwest coast of India; and Bouregreg estuary, in northwest part of Morocco. The estuaries’ bathymetry is described by an exponential function. Both models are quite similar and use a predictive equation for the dispersion in the estuary mouth (D0). The major difference between the two models is the use of the constant value of K?=?0.5 for the Van der Burgh coefficient (K) and the introduction of the correction factor ζ, which is a function of damping (δ) and shape (γ). The performance of these two models was evaluated by comparing their results with field measurements; this revealed that both analytical models apply well to both the estimation of salinity distribution and the prediction of salt intrusion in the Ashtamudi and Bouregreg estuaries (Ashtamudi: RMSE = 0.60–1.22 ppt; Bouregreg: RMSE = 0.92–2.71 ppt). One model agrees more with the field measurements of salinity distribution along the estuaries axis; the second underestimate and overestimate some values of salinity distribution along the estuaries. Possibly, the constant value of K?=?0.5 for the Van der Burgh coefficient (K) has applicability limits for the estuaries under tidal conditions. The specifying of the parameterization may be a field of research. 相似文献
9.
历次核试验进入海洋的~(137)Cs对中国近海影响的模拟研究 总被引：1，自引：0，他引：1
1945年以来,世界各主要核国家进行了数千次核试验,这些核试验产生的绝大部分放射性物质通过多种途径进入海洋,对海洋环境造成放射性污染。本文建立了一个准全球海洋的放射性物质输运和扩散数值模式,通过数值模拟手段评估了历史核试验释放的放射性物质137 Cs对中国近海海洋环境的影响。本文借助前人工作评估了核试验释放137Cs进入海洋的途径和总量;通过比较模拟结果与观测资料,表明本文建立的放射性物质模式能够较好地模拟出137Cs在中国近海及其邻近海域的分布情况和随时间演变特征;模拟结果表明中国近海里的137Cs浓度在20世纪50年代中期达到最大,其中吕宋海峡海域137Cs浓度最高,达80.99Bq/m3;进一步分析了2011年3月份日本福岛核事故前中国近海137Cs浓度分布状况,2011年整个中国近海137Cs浓度介于1.0~1.6Bq/m3间,且其浓度垂向分布较均匀,相对封闭的南海浓度略高于其他海域。 相似文献
10.
A 3-D dispersion model has been developed to simulate the dispersion of nuclear contaminants in marine ecosystems. This model is characterized by presenting high spatial resolution, by taking into account the possible sedimentation of a fraction of the contaminants, and by formulating the diffusion processes using an original approach.The model has been applied and validated taking the Baltic Sea as its scenario, and using the 137Cs originating from the Chernobyl accident as the substance which experienced the dispersion. The simulation of a year’s dispersion of the 137Cs in the Baltic sea (just after the Chernobyl accident) has been performed. 相似文献
11.
Tadahiko Tsuruta Hisaya Harada Toshiharu Misonou Toshiyuki Matsuoka Yasuyuki Hodotsuka 《Journal of Oceanography》2017,73(5):547-558
Investigations including a bathymetric survey, sonic prospecting, and vibrocoring were performed to understand the horizontal and vertical distribution of 137Cs in seabed sediments in shallow seas with depths less than 30 m near the Fukushima Daiichi Nuclear Power Plant. Especially, features of 137Cs distributions in deeper sections of the seabed sediments were studied to evaluate the vertical heterogeneity of 137Cs distribution in the seabed sediments in shallow seas. The distribution area of the seabed sediments was less than half of the investigation area, and the locations of the seabed sediments were divided into flat and terrace-like seafloors based on their topographical features. The thicknesses of the seabed sediment layers were mostly <2 m. The 137Cs inventories in the seabed sediments varied from 13 ± 1 to 3,510 ± 26 kBq m?2, and continuous distributions of 137Cs at depths greater than 81 cm were observed. The 137Cs distributions were not uniform; however, the 137Cs inventories tended to be larger near the base of the steeper ascending slopes than in the terrace-like seafloors themselves. Based on the relationship between the 137Cs inventories and mean shear stress, features of the seafloor topography were inferred to be significant control factors governing the horizontal and vertical distribution of 137Cs in the seabed sediments. Rapid changes and multiple peaks in the vertical profile of the 137Cs distributions suggest that they are related to pulse input caused by heavy-rain events. Change in the 137Cs inventories with depth in this study are larger than those reported in previous studies, indicating earlier results of 137Cs inventories per unit in seabed sediments in shallow seas, especially near the river mouth, which drains a radiologically highly-contaminated basin, were underestimated. 相似文献
12.
Peter Hamilton 《Progress in Oceanography》1990,25(1-4)
Simulations of the time and depth-dependent salinity and current fields of the Columbia River Estuary have been performed using a multi-channel, laterally averaged estuary model. The study simulated two periods. The first, in October 1980, with low riverflow of about 4,000m3s−1, which showed marked changes in the salinity intrusion processes between neap and spring tides; and second, in spring 1981, with high riverflow varying between 7,000 and 15,000m3s−1, which showed the rapid response of the salinity intrusion to changes in riverflow and that vertical mixing did not change character with increasing tidal energy because of the maintenance of stratification by freshwater flow. An extreme low flow simulation (riverflow of 2,000m3s−1) showed a more partially mixed character of the estuary channels with tidal dispersion of salt across the Taylor Sands from the North Channel to the upper reaches of the Navigation Channel. Asymmetries in the non-linear tidal mean flows, in the flood and ebb circulations, and salinity intrusion characteristics between the two major channels were observed at all riverflows. The model confirms Jay and Smith's (1990) analysis of the circulation processes in that tidal advection of salt by the vertically sheared tidal currents is the dominant mechanism by which the salinity intrusion is maintained against large freshwater flows. An accurate finite-difference method, which minimized numerical dispersion, was used for the advection terms and was an important component in reasonably simulating the October neap-spring differences in the salinity intrusion. The simulations compare favorably with elevation, current and salinity time series observations taken during October 1980 and spring 1981. 相似文献
13.
D. Knapinska-Skiba R. Bojanowski Z. Radecki G. E. Millward 《Estuarine, Coastal and Shelf Science》2001,53(6):779
The activity concentrations of dissolved137Cs have been determined in the water column and137Cs and134Cs in the sediments and the sediment porewaters of the southern Baltic Sea. The mean activity concentration of dissolved137Cs in the Gdansk Deep declined from 109 Bq m−3in June 1986 to 61 Bq m−3in 1999. In sediments, the activity concentrations of137Cs (33-231 Bq kg−1) were highest in muds and the activity concentrations of134Cs were about 6% of the total Cs activity. The Chernobyl contribution to137Cs activity was between 43% and 77%. The porewater activity concentrations of137Cs in muddy sediments were in the range 71 to 3900 Bq m−3and were higher than those in the overlying seawater. The diffusive flux of dissolved137Cs from the muddy sediments was estimated in the range 5 to 480 Bq m−2year−1. The flux of137Cs from sediment porewaters of the southern Baltic Sea was about 45% of the total, including fluxes of137Cs from wet and dry atmospheric deposition and the fluvial inputs. The results were used to elucidate the rate of recovery of the sediments and the waters of the southern Baltic from Chernobyl-derived137Cs. 相似文献
14.
Wind plays an important role in regulating mixing/stratification, estuarine circulation, and transport timescale in estuaries. A three-dimensional model was used to investigate the effect of wind on transport time by using the concept of water age (WA) in the tidal Rappahannock River, a western tributary of the Chesapeake Bay, USA. The model was calibrated for water level, current, and salinity. A series of experiments regarding the effects of wind on WA was conducted under various dynamic conditions. The effect of wind on transport timescale depends strongly on the competition between the wind and buoyancy forcings, and on the pre-status of the circulation. A down-estuary wind generally decreases WA along the estuary. An up-estuary wind increases WA substantially because it changes the vertical mixing and estuarine circulation more significantly. When the buoyancy forcing increases, the up-estuary wind effect decreases whereas the down-estuary wind effect increases. A 2-day period wind pulse with a maximum speed of 15 m s−1 can alter WA for 3 days; but the wind influence on WA lasts up to 40 days in the simulation. Both local and non-local wind forcings alter WA distribution. The local wind enhances vertical mixing and changes the gravitational circulation in the downstream portion of the estuary whereas it enhances transport in the freshwater portion of the estuary. Consequently, the local wind has a significant impact on WA distribution. In contrast, the non-local wind does not change the gravitational circulation significantly by imposing setup (setdown) of water level at the open boundary, resulting in a lesser impact on WA distribution. 相似文献
15.
The concentrations of90Sr and137Cs, derived from the radioactive fallout, in the surface layers of the adjacent seas of Japan and the North Pacific were determined radiochemically during 1969 to 1973. The90Sr and137Cs concentrations in sea water decreased markedly with increase of the depth and below the depth of 1,000 m, the concentrations were approximately uniform. The distribution of90Sr in the surface water of the North Pacific in spring of 1970 was approximately uniform, except two regions; rather large low-concentration region between 160°E and 170°W and relatively higher contamination area around 32°N and 146°W. 相似文献
16.
Observations of the velocity and salinity structure of the Tees estuary were made at eight stations along the estuary axis between Victoria Bridge and the sea during the summer of 1975. The measurements were made on ten separate tidal periods covering neap and spring tides.The data were collected over a period of relatively low freshwater flows and the residual current was found to have a strong dependence on the Stokes drift. At the upstream stations, the residuals were more than an order of magnitude greater than the currents anticipated from the freshwater discharge. Although the mean stratification decreased as the tidal range increased, the vertical circulation was stronger on spring tides than on neaps. Vertical variations in the amplitude and phase of the tidal current results in a current which strengthens the vertical circulation. However, this effect only made a relatively small contribution to the observed vertical circulation.The relative contribution of the individual salt flux terms to the net upstream transport of salt varies along the estuary. As the estuary narrows, the contribution by the oscillatory terms dominates that from the shear in the steady state flow. Of these oscillatory terms, the correlation of velocity and salinity fluctuations plays a key rôle in the salt transport. The depth mean values make a greater contribution than deviations from the depth mean and the flux due to phase variations over depth is smaller than either of these. Since the Stokes drift is compensated by a down-stream steady state flow, it does not contribute to the tidal mean transport of salt.At the seaward end of the estuary, the salt fluxes due to the steady state vertical shear and the convariance of the tidal fluctuations act in a complementary way to counter the seaward transport of salt by the freshwater flow. With the possible exceptions of the wide or narrow reaches of the Tees, the longitudinal fluxes of salt due to transverse variations in velocity, salinity and depth and turbulent fluctuations are of secondary importance as contributors to the estuary salt budget.On both neap and spring tides, the computed total salt transports at the Newport and Victoria bridges did not match the values required for a salt balance with the corresponding freshwater flows. These fluxes were probably the cause of the observed downstream displacement of the tidal mean salinity distribution between neap and spring tides. 相似文献
17.
Norio Ogura Yoshiharu Tanaka Jun-ichi Itoh Katsufumi Takahashi 《Journal of Oceanography》1984,40(3):184-191
Behaviour of dissolved and particulate proteinaceous substances in the estuary of the Tama River was investigated through field observations and laboratory experiments. Concentrations of dissolved proteinaceous substances in estuarine water were determined at eight stations between the mouth of the Tama River (TA-15) and a point 16km upstream (TA-8), using the colorimetric method of Lowryet al. (1951) that employs Folin phenol reagent. The results were expressed in terms of Folin phenol active substances (FPAS). It was found that FPAS decreased with increasing salinity and that the proportion of high molecular weight FPAS (molecular weight greater than 100,000) decreased rapidly in the estuary.The shapes, sizes and numbers of amorphous particulate substances stained by Amido Black 10B, called Amido Black active substances (ABAS), were determined under a microscope. The numbers of ABAS retained on Millipore HA filters (mean diameter: 10–80µm) amounted to 450ml–1 in the estuarine water about 6km from the mouth of the estuary (Station TA-12M). Some of these aggregates are considered to be producedin situ by flocculation of high molecular weight FPAS during estuarine mixing. ABAS were also produced in experiments by mixing filtered river water with sea water. 相似文献
18.
Shigeyoshi Otosaka 《Journal of Oceanography》2017,73(5):559-570
Temporal changes in cesium-137 (137Cs) concentrations in the surface (0–10 cm) layer of seabed sediment were quantified from continuous observation data at 71 stations within a 150-km radius of the Fukushima Daiichi Nuclear Power Plant, and the primary processes affecting temporal changes were identified. From March 2011 to the end of 2015, about 80% of the initially deposited 137Cs in the surface sediment in the coastal region (bottom depth ≤100 m) region has dissipated (radioactive decay is not included). Such a remarkable change in the 137Cs concentration was not observed in the offshore (>100 m) region. This paper focuses on the following three processes that affected the decrease in the 137Cs concentrations, and assesses their relative importance; (1) resuspension and transport of 137Cs-bound sediment, (2) desorption of 137Cs from the sediment, and (3) dilution of 137Cs by vertical mixing of sediment. Consequently, it was estimated that the first two processes together have potentially contributed to reduce the 137Cs inventory in the top 10 cm of the coastal region by at most 35%. Furthermore, by applying a pulse input sediment mixing model to the observed vertical distribution of sedimentary 137Cs, it was also estimated that more than 43% of the 137Cs in the surface sediment was transported to deeper sediment layers by vertical mixing of the sediment. This indicates that the decrease of 137Cs concentrations in coastal sediments was mainly affected by mixing of 137Cs-bound surface sediment with less contaminated sediment in the deeper layers. 相似文献
19.
90Sr and137Cs concentrations and their vertical distributions were determined in deep waters in the western Northwest Pacific, including the adjacent seas of Japan, from 1976 to 1979.The profiles of the radionuclides show distribution patterns with two parts with an exponential variation of radioisotope content with depth in both parts.Generally speaking, the inventories of90Sr and137Cs in the open waters of the northwestern Pacific correspond fairly well to the fallout inputs, but in some circumstances there seems to be considerable removal of radionuclides from the water column or they are diluted with water of lower radioactivity from other regions.The possibility of radioisotope remobilization from the bottom sediment or particulate matter is also discussed. 相似文献
20.
Concentrations and inventories of137Cs and239,240Pu were determined in sea waters and sediments columns from the western North Pacific from 1980 to 1986.The239,240Pu/137Cs activity ratio in the water column shows a tendency to increase from the surface (10–3) to bottom waters (10–1), but the ratio in sediment is within a rather narrow range (10–2 to 10–1), indicating more effective removal of plutonium from the water column than137Cs. In regions south of 40N, the radionuclide inventories in the water column significantly exceed the estimated global fallout (stratospheric fallout due to the atmospheric nuclear explosion), especially in the case of239,240Pu. These excess inventories imply that local or close-in fallout derived from nuclear explosions in the equatorial North Pacific are well-preserved and retained in the regions, despite about 20 years since the atmospheric nuclear explosion moratorium. Data suggesting lateral transport of137Cs in surface water from north of 40N to southern regions is shown. Some data on90Sr contents are also shown. 相似文献