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1.
Isotope data of precipitation and groundwater in parts of the Voltaian Basin in Northern Ghana were used to explain the groundwater recharge regime in the area. Groundwater recharge is an important parameter in the development of a decision support system for the management and efficient utilization of groundwater resources in the area. It is therefore important to establish the processes and sources of groundwater recharge. δ18O and δ2H data for local precipitation suggest enrichment relative to the Global Meteoric Water Line (GMWL) and indicate that precipitation takes place at a relative humidity less than 100%. The groundwater data plot on an evaporation line with a slope of 5, suggesting a high degree of evaporative enrichment of the precipitation in the process of vertical infiltration and percolation through the unsaturated zone into the saturated zone. This finding is consistent with the observation of high evapotranspiration rates in the area and ties in with the fact that significant clay fraction in the unsaturated zone limits vertical percolation and thus exposes the percolating rainwater to the effects of high temperatures and low humidities resulting in high evapotranspiration rates. Groundwater recharge estimates from the chloride mass balance, CMB, method suggest recharge in the range of 1.8–32% of the annual average precipitation in the form of rainfall. The highest rates are associated with areas where open wells encourage significant amount of groundwater recharge from precipitation in the area. In the northern parts of the study area, groundwater recharge is lower than 12%. The recharge so computed through the application of the CMB methodology takes on a spatial distribution akin to the converse of the spatial pattern of both δ18O and δ2H in the area. As such, the locations of the highest recharge are associated with the most depleted values of the two isotopes. This observation is consistent with the assertion that low vertical hydraulic conductivities slow down vertical percolation of precipitation down to the groundwater water. The percolating precipitation water thus gets enriched in the heavier isotopes through high evapotranspiration rates. At the same time, the amount of water that finally reaches the water table is considerably reduced. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

2.
Jordan is classified as an arid to semi‐arid country with a population according to 1999 estimates of 4·8 millions inhabitants and a growth rate of 3·4%. Efficient use of Jordan's scarce water is becoming increasingly important as the urban population grows. This study was carried out within the framework of the joint European Research project ‘Groundwater recharge in the eastern Mediterranean’ and describes a combined methodology for groundwater recharge estimation in Jordan, the chloride method, as well as isotopic and hydrochemical approaches. Recharge estimations using the chloride method range from 14 mm year?1 (mean annual precipitation of 500 mm) for a shallow and stony soil to values of 3·7 mm year?1 for a thick desert soil (mean annual precipitation of 100 mm) and values of well below 1 mm year?1 for thick alluvial deposits (mean annual rainfall of 250 mm). Isotopically, most of the groundwater in the Hammad basin, east Jordan, falls below the global meteoric water line and far away from the Mediterranean meteoric water line, suggesting that the waters are ancient and were recharged in a climate different than Mediterranean. Tritium levels in the groundwater of the Hammad basin are less than the detection limit (<1·3 TU). However, three samples in east Hammad, where the aquifer is unconfined, present tritium values between 1 and 4 TU. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

3.
We characterize the precipitation and groundwater in a mountainous (peaks slightly above 3000 m a.s.l.), semi‐arid river basin in SE Spain in terms of the isotopes 18O and 2H. This basin, with an extension of about 7000 km2, is an ideal site for such a study because fronts from the Atlantic and the Mediterranean converge here. Much of the land is farmed and irrigated both by groundwater and runoff water collected in reservoirs. A total of approximately 100 water samples from precipitation and 300 from groundwater have been analysed. To sample precipitation we set up a network of 39 stations at different altitudes (800–1700 m a.s.l.), with which we were able to collect the rain and snowfall from 29 separate events between July 2005 and April 2007 and take monthly samples during the periods of maximum recharge of the aquifers. To characterize the groundwater we set up a control network of 43 points (23 springs and 20 wells) to sample every 3 months the main aquifers and both the thermal and non‐thermal groundwater. We also sampled two shallow‐water sites (a reservoir and a river). The isotope composition of the precipitation forms a local meteoric water line (LMWL) characterized by the equation δD = 7·72δ18O + 9·90, with mean values for δ18O and δD of − 10·28‰ and − 69·33‰, respectively, and 12·9‰ for the d‐excess value. To correlate the isotope composition of the rainfall water with groundwater we calculated the weighted local meteoric water line (WLMWL), characterized by the equation δD = 7·40δ18O + 7·24, which takes into account the quantity of water precipitated during each event. These values of (dδD/dδ18O)< 8 and d‐excess (δD–8δ18O)< 10 in each curve bear witness to the ‘amount effect’, an effect which is more manifest between May and September, when the ground temperature is higher. Other effects noted in the basin were those of altitude and the continental influence. The isotopic compositions of the groundwater are represented by the equation δD = 4·79δ18O − 18·64. The groundwater is richer in heavy isotopes than the rainfall, with mean values of − 8·48‰ for δ18O and − 59·27‰ for δD. The isotope enrichment processes detected include a higher rate of evaporation from detrital aquifers than from carbonate ones, the effects of recharging aquifers from irrigation return flow and/or from reservoirs' leakage and enrichment in δ18O from thermal water. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

4.
Despite its location in the rain shadow of the southern Sierra Nevada, the Panamint Range hosts a complex mountain groundwater system supporting numerous springs which have cultural, historical, and ecological importance. The sources of recharge that support these quintessential desert springs remain poorly quantified since very little hydrogeological research has been completed in the Panamint Range. Here we address the following questions: (i) what is the primary source of recharge that supports springs in the Panamint Range (snowmelt or rainfall), (ii) where is the recharge occurring (mountain-block, mountain-front, or mountain-system) and (iii) how much recharge occurs in the Panamint Range? We answer questions (i) and (ii) using stable isotopes measured in spring waters and precipitation, and question (iii) using a chloride mass-balance approach which is compared to a derivation of the Maxey–Eakin equation. Our dataset of the stable isotopic composition (δ18O and δ2H) of precipitation is short (1.5 years), but analyses on spring water samples indicate that high-elevation snowmelt is the dominant source of recharge for these springs, accounting for 57 (±9) to 79 (±12) percent of recharge. Recharge from rainfall is small but not insignificant. Mountain-block recharge is the dominant recharge mechanism. However, two basin springs emerging along the western mountain-front of the Panamint Range in Panamint Valley appear to be supported by mountain-front and mountain-system recharge, while Tule Spring (a basin spring emerging at the terminus of the bajada on the eastern side of the Panamint Range) appears to be supported by mountain-front recharge. Calculated recharge rates range from 19 mm year−1 (elevations < 1000 mrsl) to 388 mm year−1 (elevations > 1000 mrsl). The average annual recharge is approximately 91 mm year−1 (equivalent to 19.4 percent of total annual precipitation). We infer that the springs in the Panamint Range (and their associated ecosystems) are extremely vulnerable to changes in snow cover associated with climate change. They are heavily dependent on snowmelt recharge from a relatively thin annual snowpack. These findings have important implications for the vulnerability of desert springs worldwide.  相似文献   

5.
Soil and vadose zone profiles are used as an archive of changes in groundwater recharge and water quality following changes in land use in an area of the Loess Plateau of China. A typical rain‐fed loess‐terrace agriculture region in Hequan, Guyuan, is taken as an example, and multiple tracers (chloride mass balance, stable isotopes, tritium and water chemistry) are used to examine groundwater recharge mechanisms and to evaluate soil water chloride as an archive for recharge rate and water quality. Results show that groundwater recharge beneath natural uncultivated grassland, used as a baseline, is about 94–100 mm year?1 and that the time it takes for annual precipitation to reach water table through the thick unsaturated zone is from decades to hundreds of years (tritium free). This recharge rate is 2–3 orders of magnitude more than in the other semiarid areas with similar annual rainfall but with deep‐rooted vegetation and relatively high temperature. Most of the water that eventually becomes recharge originally infiltrated in the summer months. The conversion from native grassland to winter wheat has reduced groundwater recharge by 42–50% (50–55 mm year?1 for recharge), and the conversion from winter wheat to alfalfa resulted in a significant chloride accumulation in the upper soil zone, which terminated deep drainage. The paper also evaluates the time lag between potential recharge and actual recharge to aquifer and between increase in solute concentration in soil moisture and that in the aquifer following land‐use change due to the deep unsaturated zone. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

6.
According to the precipitation and δ18O data obtained during the GEWEX Asian Monsoon Experiment–Tibet Intensive Observation Period, based on the knowledge that δ18O is lower in precipitation formed from ocean air mass vapour than that from local evaporation vapour, the water vapour sources can be identified from the δ18O values in precipitation. We attempt to give the identification criterion of δ18O values in precipitation. The threshold values chosen to distinguish between ocean and local sources are δ18O < ?20‰ and δ18O > ?13‰ respectively. According to this criterion, the proportion of local evaporation‐formed precipitation and ocean air‐mass‐formed precipitation in total precipitation was estimated. The average value of precipitation at three sites (NODA, Amdo and AQB) is 249·76 mm. Among this, precipitation formed directly by the ocean air mass vapour is 80·08 mm at most. Precipitation formed by water vapour evaporated from local places is 117·05 mm at least. That is to say that precipitation formed directly by the ocean air mass vapour accounts for 32·06% of the total precipitation at most. Precipitation formed by water vapour evaporated from local places accounts for 46·86% of the total precipitation at least. At least 21·8% of the total precipitation came from water vapour that was evaporated on the way and transported by the monsoon circulation. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

7.
The stable isotope composition (18O and 2H) in the tropical precipitation collected from 18 locations throughout the Deduru Oya river basin in Sri Lanka, has been studied during August and September 2001, in order to characterize the isotopic composition of precipitation in the dry and intermediate climatic zones of Sri Lanka. The isotope compositions are described with respect to the distance from the coast and the altitude. The analyses show that δ18O vary from ? 5·11 to 1·39‰ and δD vary from ? 35·71 to 12·55‰. The d‐excess values range from ? 0·65 to 13·17 with an average value of ～7. Regression for the δ18O ? δD is y = 6·8x + 4·9 (R2 = 0·9) which is compatible with the precipitation in other tropical regions. The lower slope in the regression line and the lower d‐excess value indicate high temperature events which were possibly aided by concentration through successive evaporation within the atmosphere. The spatial variation of isotope composition indicates two different cloud contributions for the rain events, of which one may be linked to the Indian Ocean contribution and the other to the high altitude condensation. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

8.
The development of intense agriculture in semiarid areas modifies intensity and spatial distribution of groundwater recharge by summing irrigation return flow to limited rainfall infiltration. Environmental tracers provide key information, but their interpretation is complicated by more complex groundwater flow patterns. In multilayered aquifers, the real origin of the groundwater samples is hard to assess because of local mixing processes occurring inside long‐screened boreholes. We use environmental tracers (14C, 13C, 2H, 18O, 3H) to investigate the long‐term evolution of recharge in the five‐layer Campo de Cartagena aquifer in South‐Eastern Spain, in addition to high‐resolution temperature loggings to identify the depth of origin of groundwater. Despite the complex background, this methodology allowed a reliable interpretation of the geochemistry and provided a better understanding of the groundwater flow patterns. The tritium method did not give good quantitative results because of the high variability of the recharge signal but remained an excellent indicator of recent recharge. Nonetheless, both pre‐anthropization and post‐anthropization recharge regime could be identified and quantified by radiocarbon. Before the development of agriculture, recharge varied from 17 mm.year‐1 at the mountain ranges to 6 mm.year‐1 in the plain, whereas the mean annual rainfall is about 300 mm. In response to the increase of agricultural activity, recharge fluxes to the plain were amplified and nowadays reach up to 210 mm.year‐1 in irrigated areas. These values are strengthened by global water budget and local unsaturated zone studies. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

9.
Recharge patterns, possible flow paths and the relative age of groundwater in the Akaki catchment in central Ethiopia have been investigated using stable environmental isotopes δ18O and δ2H and radioactive tritium (3H) coupled with conservative chloride measurements. Stable isotopic signatures are encoded in the groundwater solely from summer rainfall. Thus, groundwater recharge occurs predominantly in the summer months from late June to early September during the major Ethiopian rainy season. Winter recharge is lost through high evaporation–evapotranspiration within the unsaturated zone after relatively long dry periods of high accumulated soil moisture deficits. Chloride mass balance coupled with the isotope results demonstrates the presence of both preferential and piston flow groundwater recharge mechanisms. The stable and radioactive isotope measurements further revealed that groundwater in the Akaki catchment is found to be compartmentalized into zones. Groundwater mixing following the flow paths and topography is complicated by the lithologic complexity. An uncommon, highly depleted stable isotope and zero‐3H groundwater, observed in a nearly east–west stretch through the central sector of the catchment, is coincident with the Filwoha Fault zone. Here, deep circulating meteoric water has lost its isotopic content through exchange reactions with CO2 originating at deeper sources or it has been recharged with precipitation from a different rainfall regime with a depleted isotopic content. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

10.
Understanding flow pathways and mechanisms that generate streamflow is important to understanding agrochemical contamination in surface waters in agricultural watersheds. Two environmental tracers, δ18O and electrical conductivity (EC), were monitored in tile drainage (draining 12 ha) and stream water (draining nested catchments of 6‐5700 ha) from 2000 to 2008 in the semi‐arid agricultural Missouri Flat Creek (MFC) watershed, near Pullman Washington, USA. Tile drainage and streamflow generated in the watershed were found to have baseline δ18O value of ?14·7‰ (VSMOW) year round. Winter precipitation accounted for 67% of total annual precipitation and was found to dominate streamflow, tile drainage, and groundwater recharge. ‘Old’ and ‘new’ water partitioning in streamflow were not identifiable using δ18O, but seasonal shifts of nitrate‐corrected EC suggest that deep soil pathways primarily generated summer streamflow (mean EC 250 µS/cm) while shallow soil pathways dominated streamflow generation during winter (EC declining as low as 100 µS/cm). Using summer isotopic and EC excursions from tile drainage in larger catchment (4700‐5700 ha) stream waters, summer in‐stream evaporation fractions were estimated to be from 20% to 40%, with the greatest evaporation occurring from August to October. Seasonal watershed and environmental tracer dynamics in the MFC watershed appeared to be similar to those at larger watershed scales in the Palouse River basin. A 0·9‰ enrichment, in shallow groundwater drained to streams (tile drainage and soil seepage), of δ18O values from 2000 to 2008 may be evidence of altered precipitation conditions due to the Pacific Decadal Oscillation (PDO) in the Inland Northwest. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

11.
Atmospheric chloride deposition in continental Spain   总被引：1，自引：0，他引：1  
F. J. Alcalá  E. Custodio 《水文研究》2008,22(18):3636-3650
The atmospheric bulk deposition rate of chloride in continental Spain was studied to get basic information in order to help in the evaluation of diffuse recharge to aquifers through an environmental chemical balance. Both new, recent data and bibliographic data have been used. Most sampling records are less than 5 years long and often only 1 year long. This means that the calculated mean yearly bulk deposition rate of chloride is quite uncertain by 30% on average, and larger than the values derived form records up to 15 years long. A map of atmospheric bulk deposition of chloride has been drawn using ordinary kriging. The mean bulk deposition rate of chloride varies from 1 to 30 g m?2 year?1 in coastal areas, with strong negative landward gradients between 0·1 and 1 g m?2 year?1 km?1. In the centre of the Iberian Peninsula, chloride deposition rates vary from 0·2 to 0·5 g m?2 year?1, with gradients around or less than 5 × 10?3 g m?2 year?1 km?1. The coefficient of variation of the mean bulk atmospheric deposition rate of chloride, for any place, ranges from 0·1 to 1. Values larger than ～0·5 are not a good indicator of natural uncertainty for this series of data that has a skewed distribution. The map of bulk deposition rate and its error is one of the terms needed for aquifer recharge estimation by means of the chloride ion balance. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

12.
18O is an ideal tracer for characterizing hydrological processes because it can be reliably measured in several watershed hydrological compartments. Here, we present multiyear isotopic data, i.e. 18O variations (δ18O), for precipitation inputs, surface water and groundwater in the Shingobee River Headwaters Area (SRHA), a well‐instrumented research catchment in north‐central Minnesota. SRHA surface waters exhibit δ18O seasonal variations similar to those of groundwaters, and seasonal δ18O variations plotted versus time fit seasonal sine functions. These seasonal δ18O variations were interpreted to estimate surface water and groundwater mean residence times (MRTs) at sampling locations near topographically closed‐basin lakes. MRT variations of about 1 to 16 years have been estimated over an area covering about 9 km2 from the basin boundary to the most downgradient well. Estimated MRT error (±0·3 to ±0·7 years) is small for short MRTs and is much larger (±10 years) for a well with an MRT (16 years) near the limit of the method. Groundwater transit time estimates based on Darcy's law, tritium content, and the seasonal δ18O amplitude approach appear to be consistent within the limits of each method. The results from this study suggest that use of the δ18O seasonal variation method to determine MRTs can help assess groundwater recharge areas in small headwaters catchments. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

13.
A calibration study of oxygen and hydrogen isotopic composition from precipitation and cave dripwater was conducted in west‐central Florida at Legend Cave during 2007–2008. This study was performed to better understand how modern precipitation patterns can be discerned through examination of cave dripwater and speleothem calcite for paleoclimate reconstruction. The ‘amount effect’ was shown to be a dominant control on the oxygen isotopic composition of precipitation for the study area. A meteoric water line with a slope of 6·7 suggests evaporative effects occur either during precipitation or subsequent hydrological processes. However, δ18O values of cave dripwater averaged near the mean annual amount‐weighted average of precipitation, suggesting that the isotopic composition of dripwater tracks the long‐term average of rainfall. An observed weak seasonal influence occurred in the d‐excess values, with summer precipitation being more enriched due to increased evaporative effects. Comparison of precipitation δ18O values to synoptic weather data shows the dominant amount effect influence occurs due to strong convective storms producing highly 18O‐depleted rainfall at greater amounts during the year. Constant δ18O values of the dripwater indicate that paleoclimate reconstructions using speleothems from this area would record changes in annual to interannual shifts in precipitation amount above the cave. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

14.
《水文科学杂志》2013,58(5):961-973
Abstract

A study was carried out to investigate the use of the chloride profile method in conjunction with the water balance method to estimate the annual groundwater recharge in both natural and irrigation sites in Luanjing Irrigation Area, Inner Mongolia. Groundwater recharge from precipitation, estimated by the chloride profile method, is less than 0.1 mm year?1 which accounts for just 0.06% of the long-term average annual rainfall, indicating that rainfall presently plays a minor role in the groundwater recharge. It appears that recharge events only occurred after heavy rain or sustained rainfall events. In the cropped area, the chloride profile method indicated that the average annual recharge is 268 mm year?1 with an infiltration rate of 32.5%, which is reasonably consistent with the 33.1% obtained by the water balance method in 2007. The study shows that about one third of that water is discharged back to the groundwater.  相似文献   

15.
Stable isotopic compositions (δ18O and d-excess) from 25 rivers in Thailand were analysed monthly during 2013–2015. Results indicated that monsoon precipitation fundamentally influences the river isotopes. The overland flow supplied from monsoon precipitation and human-altered flow regimes produces considerable isotopic variability. Spatial and temporal variations were observed among four principal geographical regions. The seasonality of monsoon precipitation in mountainous Thailand produced large variations in isotopic compositions because most rainfall occurred during the southwest monsoon, and dry conditions prevailed during the northeast monsoon. The northern and northeastern regions are mountainous, highland areas. Low δ18O values were found in these regions, likely because of altitude effects on precipitation. Conversely, monsoonal precipitation continually supplies rivers in southern Thailand all year round, producing higher and more consistent δ18O values than in the other regions. The Chao Phraya plain in the central region experienced enrichment of δ18O river runoff related to evaporation in irrigation systems. Larger catchment areas and longer residence times resulted in more pronounced evaporation effects, producing lower values of d-excess and local river water line slopes compared with precipitation. The isotopic differences between river waters and precipitation were utilized to determine river recharge elevations and water transit time. The methods presented here can be used to explore hydrological interactions in other tropical river basins.  相似文献   

16.
Increasing groundwater salinity and depletion of the aquifers are major concerns in the UAE. Isotopes of oxygen, hydrogen, and carbon concentrations in groundwater were used to estimate evaporation loss using the isotopes of oxygen and hydrogen, and using a carbon isotope to trace inorganic carbon cycling in two main aquifers in the eastern part of the United Arab Emirates. The δD‐δ18O of groundwater samples plotted on a line given by: δD = 4 δ18O + 4 ·4 (r2 = 0·4). In comparison, the local meteoric water line (LMWL) has been defined by the line: δD = 8 δ18O + 15. In order to better understand the system investigated, samples were separated into two groups based on the δD‐δ18O relationship. These are (1) samples that plot above the LMWL (δD = 6·1 δ18O + 12·4, r2 = 0·8) and which are located predominantly in the north of the study area, and (2) samples that plot below the LMWL (δD = 5·6 δ18O + 6·2, r2 = 0·8) and which are mostly distributed in the south. Slopes for both the groups are similar and lower than that for LMWL indicating potential evaporation of recharging water. However, the y‐intercept, which differs between the two groups, suggests evaporation of return flow and evapotranspiration in the unsaturated zone to be more significant in the south. This is attributed to intense agricultural activities in the region. Samples from the eastern Gravel Plain aquifer have δ13C and dissolved inorganic carbon (DIC) values in the range from ? 10 to 17‰, and 12–100 mg C/l, respectively, while the range for those from the Ophiolite aquifer is from ? 11 to ? 16.4‰, and 16–114 mg C/l respectively. This suggests the control of C‐3 and C‐4 plants on DIC formation, an observation supported by the range δ13C of soil organic matter (from ? 18·5 to ? 22·1‰.) Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

17.
ABSTRACT

The aim of this paper is to estimate the effect that climate change will have on groundwater recharge at the Yucatan Peninsula, Mexico. The groundwater recharge is calculated from a monthly water balance model considering eight methods of potential and actual evapotranspiration. Historical data from 1961–2000 and climate model outputs from five downscaled general circulation models in the near horizon (2015–2039), with representative concentration pathway (RCP) 4.5 and 8.5 are used. The results estimate a recharge of 118 ± 33 mm·year–1 (around 10% of precipitation) in the historical period. Considering the uncertainty from GCMs under different RCP and evapotranspiration scenarios, our monthly water balance model estimates a groundwater recharge of 92 ± 40 mm·year–1 (RCP4.5) and 94 ± 38 mm·year–1 (RCP8.5) which represent a reduction of 23% and 20%, respectively, a result that threatens the socio-ecological balance of the region.  相似文献   

18.
The proposed harvesting of previously undeveloped forests in north coastal British Columbia requires an understanding of hydrological responses. Hydrometric and isotopic techniques were used to examine the hydrological linkages between meteoric inputs to the surface‐groundwater system and runoff response patterns of a forest‐peatland complex. Quickflow accounted for 72–91% of peak storm discharge. The runoff ratio was lowest for open peatland areas with thick organic horizons (0·02–0·05) due to low topographic gradients and many surface depressions capable of retaining surface water. Runoff ratio increased comparatively for ephemeral surface seep flows (0·06–0·40) and was greatest in steeply sloping forest communities with more permeable soils (0·33–0·69). The dominant mechanism for runoff generation was saturated shallow subsurface flow. Groundwater fluxes from the organic horizon of seeps (1·70–1·72 m3 day?1 m?1) were an important component of quickflow. The homogeneous δ2H? δ18O composition of groundwater indicated attenuation of the seasonal rainfall signal by mixing during recharge. The positive correlation (r2 = 0·64 and 0·38, α = 0·05) between slope index and δ18O values in groundwater suggests that the spatial pattern in the δ18O composition along the forest‐peatland complex is influenced by topography and provides evidence that topographic indices may be used to predict groundwater residence time. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

19.
M. Z. Iqbal 《水文研究》2008,22(23):4609-4619
Oxygen and deuterium isotopes in precipitation were analysed to define local isotopic trends in Iowa, US. The area is far inland from an oceanic source and the observed averages of δ18O and δ D are ? 6·43‰ and ? 41·35‰ for Ames, ? 7·53‰ and ? 51·33‰ for Cedar Falls, and ? 6·01‰ and ? 38·19‰ for Iowa City, respectively. Although these data generally follow global trends, they are different when compared to a semi‐arid mid‐continental location in North Platt, Nebraska. The local meteoric water lines of Iowa are δ D = 7·68 δ18O + 8·0 for Ames, δ D = 7·62 δ18O + 6·07 for Cedar Falls, and δ D = 7·78 δ18O + 8·61 for Iowa City. The current Iowa study compares well with a study conducted in Ames, Iowa, 10 years earlier. The differences between Iowa and Nebraska studies are attributed to a variable climate across the northern Great Plains ranging from sub‐humid in the east to semi‐arid in the west. Iowa being further east in the region is more strongly influenced by a moist sub‐humid to humid climate fed by the tropical air stream from the Gulf of Mexico. The average d‐excess values are 10·06‰ for Ames, 8·92‰ for Cedar Falls and 9·92‰ for Iowa City. Eighty seven percent of the samples are within the global d‐excess range of 0‰ and 20‰. The results are similar to previous studies, including those by National Atmospheric Deposition Programs and International Atomic Energy Agency. It appears that the impact of recycled water or secondary evaporation on δ18O values of area precipitation is minimal. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

20.
Precipitation is a major component of the hydrologic cycle in arid desert areas. To date, however, few studies have been conducted on investigating the isotope characteristics and moisture sources of precipitation in arid desert environments. The Alxa Desert Plateau is a critical arid desert area in North China. This study is the first to analyse the stable isotopic composition of precipitation to identify the sources of atmospheric moisture over this plateau. Our results show that the δD and δ18O values of precipitation across the plateau change greatly at both daily and monthly timescales, and exhibit seasonal variations. Among the main meteorological parameters, atmospheric temperature is the most predominant factor controlling the isotopic composition and the δD–δ18O relationship of local precipitation. Analyses of the precipitation isotopes with the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model reveal that (a) the westerly and polar moisture sources are the dominant controls on summer and winter precipitation and (b) the evaporation of local lake water significantly affects winter precipitation even though it only represents a small amount. Based on the isotope data of 2013–2016 precipitation, a local meteoric water line (LMWL) is derived: δD = (8.20 ± 0.22)·δ18O + (8.15 ± 2.16)‰ for the study site. Compared to the global meteoric water line, the LMWL has a greater slope and lower d‐excess. This can be explained by admixing of atmospheric moisture resulting from the evaporation of local lake water. Based on this LMWL, we are able to trace that groundwater of the Badain Jaran Desert originates from the surrounding mountains with altitudes of <4,000 m. The newly derived LMWL shows that the recharge altitudes of desert groundwater are overestimated on the basis of the previous LMWLs. This study not only provides insights into the hydrological cycle but also offers guidance for water resource management in arid desert areas of China. Additionally, this study provides techniques that can be applied to the analyses of precipitation isotopes in similar arid regions of the world.  相似文献   

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