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1.
Areal distributions and complete time histories since 1952 are presented of the tritium and90Sr concentrations in North Atlantic surface water. The distributions are based on a compilation of measured North Atlantic surface water tritium concentrations which is part of this paper and includes hitherto unpublished measurements, and on available90Sr compilations. To reconstruct the insufficiently represented early concentrations, a two-box North Atlantic mixing model with tropospheric input is employed, for which the input is specified (on relative scales), and which is fitted to the available surface water observations. This procedure gives a natural tritium concentration of 0.2 TU (±30%), and furthermore suggests that part of the old oceanic tritium and90Sr measurements are high. The fit requires characteristic model mixing times of 2.5 years (exchange with an intermediate-depth reservoir about three times the size of the surface box) and 30 years (loss into the deep ocean), and a tritium/90Sr input ratio of 310 Ci/Ci. The areal distributions and time histories can serve as boundary value data for evaluations of subsurface tritium and90Sr measurements.  相似文献   

2.
Tritium is one of the most important environmental tracers in isotope hydrology for understanding the dynamics of groundwater and connected surface water and has been used in a wide range of applications at different scales. A key requirement for using tritium as a tracer is the knowledge of its spatial and temporal distribution in different water types. As a fundamental input, quantity long-term time series of tritium in precipitation are of particular importance. In this paper, the authors present an overview of tritium data sets of the Federal Institute of Hydrology (BfG), the Helmholtz Zentrum München (HMGU) and the German Weather Service (DWD). Since the 1970s, all three institutions have monitored the tritium concentration at 53 surface water and 37 precipitation stations on a monthly basis. The primary purpose of the data set was to provide baseline information for different water types all over Germany as an integral part of the German radiation protection monitoring system. Additionally, as geochemically inert tracer, tritium provides a unique tool to different user groups in a wide range of research questions and applications.  相似文献   

3.
Tritium in the Arctic Ocean and East Greenland Current   总被引：1，自引：0，他引：1  
High concentrations of tritium are found in the surface water of the Arctic Ocean (up to 50 TU) and in the East Greenland Current (up to 70 TU). These high tritium values are a direct result of atmospheric testing of nuclear weapons in the early 1960's. A box model with a time-dependent input of highly tritiated precipitation predicts that high tritium concentrations are to be expected in the surface layer of the Arctic Ocean and its various outflows. We suggest that a few tritium stations in the Arctic Ocean would provide a powerful analytical tool for assigning time scales to exchange processes.  相似文献   

4.
Surface-water and ground-water flow are coupled in the central Everglades, although the remoteness of this system has hindered many previous attempts to quantify interactions between surface water and ground water. We modeled flow through a 43,000 ha basin in the central Everglades called Water Conservation Area 2A. The purpose of the model was to quantify recharge and discharge in the basin's vast interior areas. The presence and distribution of tritium in ground water was the principal constraint on the modeling, based on measurements in 25 research wells ranging in depth from 2 to 37 m. In addition to average characteristics of surface-water flow, the model parameters included depth of the layer of ‘interactive’ ground water that is actively exchanged with surface water, average residence time of interactive ground water, and the associated recharge and discharge fluxes across the wetland ground surface. Results indicated that only a relatively thin (8 m) layer of the 60 m deep surfical aquifer actively exchanges surface water and ground water on a decadal timescale. The calculated storage depth of interactive ground water was 3.1 m after adjustment for the porosity of peat and sandy limestone. Modeling of the tritium data yielded an average residence time of 90 years in interactive ground water, with associated recharge and discharge fluxes equal to 0.01 cm d−1. 3H/3He isotopic ratio measurements (which correct for effects of vertical mixing in the aquifer with deeper, tritium-dead water) were available from several wells, and these indicated an average residence time of 25 years, suggesting that residence time was overestimated using tritium measurements alone. Indeed, both residence time and storage depth would be expected to be overestimated due to vertical mixing. The estimate of recharge and discharge (0.01 cm d−1) that resulted from tritium modeling therefore is still considered reliable, because the ratio of residence time and storage depth (used to calculated recharge and discharge) is much less sensitive to vertical mixing compared with residence time alone. We conclude that a small but potentially significant component of flow through the Everglades is recharged to the aquifer and stored there for years to decades before discharged back to surface water. Long-term storage of water and solutes in the ground-water system beneath the wetlands has implications for restoration of Everglades water quality.  相似文献   

5.
Groundwater-surface water interactions (GSI) connect rivers and streams with riparian areas and the adjacent aquifer. Although these interactions exert a substantial control of quantity and quality of both groundwater and surface water, knowledge on GSI along rivers at the regional scale, particularly for inland waterways, is still limited. We investigated GSI along the river Moselle, an important federal inland waterway in Germany, by using radon and tritium to identify gaining (water flux from the aquifer to the surface water) and losing (water flux from the surface water to the aquifer) stream conditions, respectively. Gaining stream conditions were identified by continuously measuring radon along the river during boat surveys with a high spatial resolution (every 2 km) during intermediate (October 2020) and near low flow conditions (August/September 2021). The tritium concentrations in surface water and groundwater and the resulting tritium inventories were used to characterize losing stream conditions Monthly tritium inventories from 2017 to 2022 revealed a mean loss for the whole period of 20.3 % and a mean gain of 21.8%. Both were probably triggered by a combination of losing stream conditions and flood-induced mass transfer of water from the aquifer back into the river as well as discharge fluctuations. At the investigated site Lehmen there were direct indications of an influence of surface water due to elevated tritium concentrations in the groundwater (up to 13.3 Bq L−1). Using radon mass balance modelling, good agreements of simulated versus measured radon data with respect to two groundwater end-member scenarios were obtained during intermediate flow (Spearman's ρ: 0.97 and 0.99; MAE: 10.1 and 3.4 Bq L−1) and near low flow (Spearman's ρ: 0.97 and 0.99; MAE: 11 and 6.5 Bq L−1). Considerable groundwater inflow was limited to the meander of Detzem, where cumulated groundwater inflow of about 19 m3 s−1 (9.5% of total discharge) and 4.2 m3 s−1 (3.8% of total discharge) was simulated during intermediate and near low flow, respectively. However, the groundwater inflow was relatively low compared to alpine streams, for example. The study will help to better identify and quantify GSI at the regional scale and provide methodological guidance for future studies focusing on inland waterways.  相似文献   

6.
Tritium data in the Dead Sea for the period 1960–1979 are given. Tritium levels have increased until 1965 in the upper layers of the Dead Sea reaching a level of 170 TU, in response to the atmospheric buildup of tritium from thermonuclear testing. The levels have been decreasing ever since, both because of rapidly declining atmospheric concentrations of tritium and because of mixing of the surface layers with tritium deficient, deeper water masses. The depth of penetration of the tracer delineated the depth of meromictic stratification and successfully monitored the deepening of the pycnocline, until the overturn in 1979 homogenised the entire tritium profile. Modelling the changing tritium inventory over this period showed the predominance of the direct exchange across the air/sea interface, both in the buildup of tritium in the lake and also in its subsequent removal from it. The good fit between calculated and measured tritium inventories confirmed the evaporation estimate of 1.46 m/yr (the mean value for the period) with a precision unattained by other methods.  相似文献   

7.
Depth profiles of the chlorofluoromethanes (CFM), CFCl3 and CF2Cl2, have been obtained together with tritium profiles from water samples collected in the Norwegian Sea between surface and 2800 m depth. CFM analysis was performed by vacuum extraction of the dissolved gases from 500 ml samples of seawater and subsequent gaschromatographic measurement. The CFM concentration decreases with depth to about 10 percent of surface concentration at depths below 2000 m. The same behaviour is found for the tritium content. From a correlation of the CFM and tritium concentration the upper limit of the preindustrial atmospheric CFM levels can be estimated to 5 percent of the present day concentrations.  相似文献   

8.
It is very interesting and meaningful to investigate the rainfall-groundwater recharge process under the humid climatic condition of Japan, where mean annual precipitation is about 1600 mm. The present study has investigated soil water movement in the unsaturated zones of a volcanic ash layer, called the ‘Kanto Loam formation’, using environmental tritium as a tracer. The site selected is a flat ground surface on a terraced upland which has a deep unsaturated zone (about 20 m) with a relatively high water content (about 70 per cent) consisting of nearly uniform Kanto Loam formation. The tritium concentrations in groundwater, soil waters having different matric potentials, precipitation, and the seepage water moving through the formation into a man-made cave were measured to characterize the rainfall-groundwater recharge process and the effect of large pore spaces in the formation mentioned by previous studies. Because of the humid climate of Japan, there appears to be a unique soil water flow characteristic which may involve percolation through large pore spaces during heavy rainfall. However, in a fine grained and high water content soil like the Kanto Loam formation, the existence of this flow through large pore spaces does not have a significant effect upon the whole recharge process. The recharge model of displacement flow with dispersion is useful in estimating the tritium concentration profile of soil water. The calculated result shows a recharge rate of 2.5 mm/day. The value obtained reflects the hydrological characteristics of the uplands covered with volcanic ash.  相似文献   

9.
Tritium concentrations in river and stream waters from different locations can be compared by normalizing them using the ratio of tritium concentrations in precipitation and surface water (Cp/Cs) in the study area. This study uses these ratios in a hydrological residence time context to make regional‐ and global‐scale comparisons about river basin dynamics. Prior to the advent of nuclear weapons testing, the Cp/Cs ratio was greater than or equal to 1 everywhere because of the decay of tritium in the watershed after it was deposited by precipitation. After an initial increase in the ratios during the bomb peak, the ratio dropped to less than 1 for most surface waters in the following years. This post‐bomb change in the ratio is due to the retention of the bomb‐pulse water in watersheds on timescales that are long relative to the residence time of tritium in the atmosphere. Ratios were calculated for over 6500 measurements of tritium in river and stream waters compiled by the International Atomic Energy Agency. These measurements span the post‐nuclear era (1940s to present) and include many long‐term datasets, which make it possible to examine residence times of waters in watersheds on a global basis. Plotting Cp/Cs versus time shows that ratios tended to reach a minimum in approximately one to two decades after the bomb peak for most locations. This result suggests that changes affecting quantity and quality of river flows need to be assessed on a multi‐decadal timescale. These long lag times have significant implications for assessing climate or land‐use change impacts on a large number of river systems around the world. The continuing value of tritium in studying surface water systems for both the Southern and Northern Hemisphere is also demonstrated. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.  相似文献   

10.
Tritium and14C data of the “GOGO I” station at 28.5°N, 121.6°W in November 1971 are reported. The tritium decline between 150 and 350 m depth is as pronounced as was observed on a previous occupation of the same position, station “Geosecs I” in September 1969, and the tritium concentrations below 200 m are unchanged.14C data from the depth range of tritium decline are corrected for fallout14C contribution. The correcting procedure requires simultaneous measurements of14C, ΣCO2, and tritium. It is concluded that the natural absolute14C concentration attains a maximum near 400 m depth, of 7.5% excess over that of surface water.  相似文献   

11.
Deuterium and tritium measurements were made on firn samples taken along a central axis across Greenland. Accumulation values determined from tritium profiles decrease regularly from 54.7 cm of water per year on the west coast to 18.1 cm of water per year on the east coast. A correlation is demonstrated between the tritium deposition rate and the altitude of the precipitation collection site.  相似文献   

12.
Rose S 《Ground water》2007,45(3):309-317
An iterative algorithm is presented that allows the user to model the subsurface residence time of shallow ground water comprising stream base flow based on decadal scale variation of tritium concentrations. The algorithm accounts for the effects of radioactive decay, the shallow subsurface mixing of ground water with precipitation, and ground water flux. The inverse of the best-fitting modeled flux through the saturated zone is equivalent to the residence time. The data required for this model include at least two measurements of tritium in base flow for a given stream location made at least a decade apart and the long-term tritium input in precipitation for the region of interest. The model is sensitive to relatively small changes in tritium concentrations and is limited by analytic uncertainties to an accuracy of approximately +/-5 years. The algorithm was applied to stream base flow for several basins in the Piedmont Province of Georgia in which tritium concentrations were measured during the early 1990s and again in the 2000s. The model results produced highly concordant residence times for three hydrogeologically similar basins in the Upper Ocmulgee Basin in North Central Georgia. The best estimate of the average residence time for ground water comprising base flow in this Piedmont basin using this new method is between approximately 14 and 18 years. These results are generally consistent with calculations made in previous studies, and these relatively long residence times can be attributed to the storage of water in the clay soils that dominate Piedmont Province watersheds.  相似文献   

13.
Seth Rose 《水文研究》1992,6(1):67-78
Environmental tritium was measured in 33 natural water samples representative of precipitation, stream runoff, and groundwater (derived principally from production wells) within the Georgia Piedmont Province. Major ion analyses were used to assist in the interpretation of the tritium results. Tritium concentrations were significantly greater within shallow groundwater derived from the regolith (28–34 TU) and stream runoff (25–30 TU) than within recent rainfall (4–17 TU). Based upon the decay-corrected tritium input function, this probably indicates that at least some of the shallow water is stored within the regolith for a period of approximately 25 years. A ‘post-bomb’ component of recharge was present in all groundwater derived from production wells in the study area. Groundwater sampled from the bedrock aquifers was commonly less tritiated than either stream runoff or shallow water stored in the regolith. the lower tritium concentrations May, have resulted from the mixing of ‘pre-bomb’ water stored within the fractures or the transitional zone directly above the bedrock and modern water stored in the shallow regolith. the preponderance of modern water provides evidence that groundwater flow paths are areally restricted within this setting, probably confined to local surface water drainage basins. the residence time of groundwater in the Piedmont is limited by the lack of deep, gravity-driven regional flow and the localized vertical flow induced by pumping. the results of this study indicate that relatively small tritium concentration variations (10-20 TU) May, have regional hydrological significance in the southeastern Piedmont Province and similar settings.  相似文献   

14.
Discontinuous measurements of the isotopic composition of surface water samples of the Garda lake carried out between 1998 and 2006 showed almost constant δ18O, δD and d-excess values through time. During 2006 and 2007 monthly vertical profiles of water samples were collected in the northernmost section of the lake, not far from the main inflow (Sarca river) to check whether there was any detectable influence from this inflowing river and whether there was a vertical isotopic stratification of the lake water. The isotopic measurement of water samples from the vertical profiles yielded isotopic values which were almost equal to those obtained from surface waters showing no detectable effect of the inflowing river water and no isotopic vertical stratification. The attempt to evaluate the evaporation rate of lake water by means of current models was totally unsuccessful. Despite the marked summer warming of the surface layer no isotopic fractionation related to evaporation processes could be detected. This anomalous behaviour may be related to the large amount of spring and summer precipitation characteristic of this area. The water balance of the lake calculated according to the amount of the inflowing water (Sarca river water plus rain water on the lake plus 20% of the precipitations on the whole catchment basin) and to the amount of outflowing water (Mincio river) showed a large imbalance, the river outflow alone resulting on average, during the last decade, at least double the inflow. To explain this imbalance of the lake, a large recharge by concealed groundwater is suggested: its isotopic composition should be quite close to the mean isotopic composition of precipitations over that area. This would be in agreement with the almost constant isotopic composition of both surface and deep waters and with the lack of vertical isotopic stratification. A few measurements of the tritium concentration carried out on lake water show values that are considerably higher than modern tritium values either in precipitation or in the Sarca river water: these results are in good agreement with the hypothesis of a recharge of the lake by deep aquifers.  相似文献   

15.
Environmental tracers, such as tritium, have generally been used to estimate aquifer recharge under natural conditions. A tritium tracer test is presented for estimating recharge under semi‐arid and irrigated conditions. The test was performed along 429 days (June 2007–August 2008) on an experimental plot located in SE Spain with drip irrigation and annual row crops (rotation of lettuce and melon), in which common agricultural practices were followed in open air. Tritiated water was sprinkled (simulated rainfall) over the plot, soil cores were taken at different depths and a liquid scintillation analyzer was used to measure tritium concentration in soil water samples. Tritium transport, as liquid or vapor phase, was simulated with the one‐dimensional numerical code SOLVEG. Simulations show that the crop water use was below potential levels, despite regular irrigation. Continuous high water content in soil promoted a great impact of rainfall events on the aquifer recharge. The results obtained from tritium tracer test have been compared with other independent recharge assessment, soil water balance method, to evaluate the reliability of the first one. Total recharge from tracer test was 476 mm for the October 2007–September 2008 period versus 561 mm from soil water balance method for the same period, which represents 37.1% and 43.7% of the applied water (1284 mm, irrigation + precipitation), respectively. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

16.
Rainfall and wine samples have been analysed for tritium in order to obtain a record of tritium fallout since 1950 for use in hydrologic studies in southern Australia.The tritium concentrations of rainfall have been estimated for years when no samples are available by using measured values of the tritium concentration of wine samples together with Roether's (1967) exchange model and and a simple model for predicting the age of soil water used by vines.As expected, the tritium fallout pattern is similar to that obtained for Kaitoke in New Zealand and Pretoria in southern Africa.  相似文献   

17.
Two models which attempt to correlate the tritium concentration of water taken from aquifers to aquifer parameters are discussed. The first takes into account flow along individual streamlines and relates aquifer parameters to the observed tritium concentration at outflow. For the Gambier Plain unconfined aquifer in southern Australia, the calculated tritium concentration at outflow derived from known aquifer parameters and an environmental tritium input function for the area, is 0.7 T.U. The mean tritium concentration of several springs at outflow is also 0.7 T.U.Using the complete mixing model and the approximation that samples withdrawn from an aquifer on Eyre Peninsula, South Australia, are fully mixed, mean annual recharge for the area is estimated at 3 cm/year.  相似文献   

18.
Mean annual rates of tritium input into the ocean averaged over 5° latitude bands are presented for the major oceans, for the period 1952–1975. The rates are obtained by converting tritium concentrations in marine precipitation into net oceanic tritium input, by means of a hydrological model. The tropospheric tritium pattern is specified on the basis of available observations, and climatological means from the literature are used for the rates of evaporation and precipitation and for the relative humidity in ship's height, that enter the model. Tritium input by water vapor exchange exceeds that by precipitation about three-fold. Tritium input by river runoff and by net tropospheric tritium outflow from the continents is also accounted for. This contribution is small except for the northern Indian Ocean and the North Atlantic.The inputs have hemispheric maxima near 50° latitude. The northern hemisphere inputs were strongly peaked in 1963–1964, whereas temporal changes in the southern hemisphere were much more gradual. By 1972, about 75% of the total oceanic input had been received by the northern ocean. For the Pacific, the computed total input agrees with the actual tritium inventory within the limits of uncertainty (about ±20%). The global tritium inventory is estimated at 1.9 GCi in 1972, which corresponds to an average tritium yield of 0.9 kg tritium per megaton TNT equivalent of nuclear fusion.  相似文献   

19.
李红春  赵树森 《地震地质》1996,18(4):325-328
北京石花洞地区水系的δＤ平均值为（－６５．４±３．０）‰（ＳＭＯＷ），δ１８Ｏ平均值为（－９．４±０．３）‰（ＳＭＯＷ），氚含量平均值为（３０．８±４．５）ＴＵ。石花洞洞内滴水是由地表水很快下渗得来，受古老地下水的混合作用很小。因此，洞内滴水的稳定同位素组成能够灵敏地反映地表水同位素组成（即重量加权的年平均雨水的同位素组成）的变化。影响洞内滴水的稳定同位素组成的因素主要是年平均气温、年降雨量以及降水气团的来源的变化。利用高分辨率的洞穴碳酸盐的稳定同位素记录．可以建立以湿度变化为主的古气候信息．尤其是我国季风气候的变化历史  相似文献   

20.
The southern coastal plain of Laizhou Bay, which is the area most seriously affected by salt water intrusion in north China, is a large alluvial depression, which represents one of the most important hydrogeological units in the coastal region of northern China. Chlorofluorocarbons (CFCs, including CFC‐11, CFC‐12 and CFC‐113) and tritium were used together for dating groundwater up to 50 years old in the study area. There are two cones of depression, caused by intensive over‐exploitation of fresh groundwater in the south and brine water in the north. The assigned CFC apparent ages for shallow groundwater range from 8 a to >50 a. A binary mixing model based on CFC‐113 and CFC‐12 concentrations in groundwater was used to estimate fractions of young and pre‐modern water in shallow aquifers and to identify groundwater mixing processes during saltwater intrusion. Discordance between concentrations of different CFC compounds indicate that shallow groundwater around the Changyi cone of depression is vulnerable to contamination. Pumping activities, CFC contamination, mixing and/or a large unsaturated zone thickness (e.g. >20 m) may be reasons for some groundwater containing CFCs without tritium. Saline intrusion mainly occurs because of large head gradients between fresh groundwater in the south and saline water bodies in the north, forming a wedge of saline water below/within fresh aquifer layers. Both CFC and tritium dates indicate that the majority of the saline water is from >50 a, with little or no modern seawater component. Based on the distribution of CFC apparent ages, tritium contents plus chemical and physical data, a conceptual model of groundwater flow along the investigated Changyi‐Xiaying transect has been developed to describe the hydrogeological processes. Three regimes are identified from south to north: (i) fresh groundwater zone, with a mixing fraction of 0.80–0.65 ‘young’ water calculated with the CFC binary mixing model (groundwater ages <34 a) and 1.9–7.8TU of tritium; (ii) mixing zone characterized by a mixing fraction of 0.05–0.65 young groundwater (ages of 23–44 a), accompanied by local vertical recharge and upward leakage of older groundwater; and (iii) salt water zone, mostly comprising waters with ages beyond the dating range of both CFCs and tritium. Some shallow groundwater in the north of the Changyi groundwater depression belongs to the >50a water group (iii), indicating slow velocity of groundwater circulation and possible drawing in of saline or deep groundwater that is tracer‐free. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

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