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1.
Stable isotope variability and fractionation associated with transformation of precipitation/accumulation to firn to glacial river water is critical in a variety of climatic, hydrological and paleoenvironmental studies. This paper documents the modification of stable isotopes in water from precipitation to glacier runoff in an alpine catchment located in the central Tibetan Plateau. Isotopic changes are observed by sampling firnpack profiles, glacier surface snow/ice, meltwater on the glacier surface and catchment river water at different times during a melt season. Results show the isotopic fractionation effects associated with glacier melt processes. The slope of the δD‐δ18O regression line and the deuterium excess values decreased from the initial precipitation to the melt‐impacted firnpack (slope from 9.3 to 8.5 and average d‐excess from 13.4‰ to 7.4‰). The slope of the δD‐δ18O line further decreased to 7.6 for the glacier runoff water. The glacier surface snow/ice from different locations, which produces the main runoff, had the same δD‐δ18O line slope but lower deuterium excess (by 3.9‰) compared to values observed in the firnpack profile during the melt season. The δD‐δ18O regression line for the river water exhibited a lower slope compared to the surface snow/ice samples, although they were closely located on the δD‐δ18O plot. Isotope values for the river and glacier surface meltwater showed little scatter around the δD‐δ18O regression line, although the samples were from different glaciers and were collected on different days. Results indicate a high consistency of isotopic fractionation in the δD‐δ18O relationships, as well as a general consistency and temporal covariation of meltwater isotope values at the catchment scale. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

2.
ABSTRACT

Glacier-melt-induced changes in runoff are of concern in northwestern China where glacier runoff is a major source for irrigation, industries and ecosystems. Samples were collected in different water mediums such as precipitation, glacial ice/snowcover, meltwater, groundwater and streamwater for the analysis of stable isotopes and solute contents during the 2009 runoff season in the Laohugou Glacial Catchment. The multi-compare results of δ18O values showed that significant difference existed in different water mediums. Source waters of streamflow were determined using data of isotopic and geochemical tracers and a three-component hydrograph separation model. The results indicated that meltwater dominated (69.9 ± 2.7%) streamflow at the catchment. Precipitation and groundwater contributed 17.3 ± 2.3% and 12.8 ± 2.4% of the total discharge, respectively. According to the monthly hydrograph, the contribution of snow and glacier meltwater varied from 57.4% (September) to 79.1% (May), and that of precipitation varied from 0% (May) to 34.6% (September). At the same time, the monthly contribution of groundwater kept relatively steady, varying from 9.7% (June) to 20.9% (May) in the runoff season. Uncertainties for this separation were mainly caused by the variation of tracer concentrations. It is suggested that the end-member mixing analysis (EMMA) method can be used in the runoff separation in an alpine glacial catchment.
Editor Z.W. Kundzewicz; Associate editor Not assigned  相似文献   

3.
ABSTRACT

Runoff generation and dynamics is an important issue in watershed and water resource management. Taking the Aksu River as a typical inland river, the spatial and temporal variations of δ18O and δD of the river water and its sources component pattern were investigated from May 2012 to May 2013. The results showed the following three main findings. Firstly, we analysed the runoff generation and mechanism over a longer time-scale in two tributaries of the Aksu River. Secondly, 46–54% of the runoff in the Aksu River was derived from groundwater, 31–36% from glacier meltwater, 5–8.8% from snow meltwater and 10% from precipitation. The third major finding was the significant inconsistency of the climate change impact on water resources. Specifically, our results showed that the Toxkan River is recharged by more glacier meltwater (36%), and responds to sensitive temperature changes. Autumn runoff is more sensitive to changes of precipitation and temperature.
Editor Z.W. Kundzewicz Associate editor Not assigned  相似文献   

4.
ABSTRACT

We investigated the isotopic composition of the Urumqi River and documented seasonal variability attributable to the mixing of various flow sources. Next, we applied these isotopic signals to partition the sources and studied their temporal variability in summer. The isotope hydrology separation results indicated that groundwater is the dominant streamflow source (approximately 62.7%) in the Urumqi River. Precipitation is an important source for the Urumqi River; approximately 19.1–20.7% of the runoff came from precipitation during summer and early autumn. In summer, approximately 21.1% of the runoff is derived from glacial meltwater. In summer, with the increasing distance to the glacier front, groundwater accounts for a larger and larger percentage of the river water, and the contributions of precipitation and glacial meltwater gradually diminish. Throughout 2012, the proportions of precipitation and glacial meltwater in the streamflow were 17.6% and 14.7%, respectively, and only 5% of the streamflow was derived from snowmelt.
Editor Z. W. Kundzewicz; Associate editor not assigned  相似文献   

5.
The significance of the baseflow component of glacier river discharge in summer varies with geographical location, altitude, glacier geometry and glacier size. Baseflow is maintained by meltwater generated above the transient equilibrium line and by water released from temporary storage on, in or beneath the glacier. At the Norwegian glacier Austre Okstindbreen, where precipitation is generally high throughout the year and the summers are cool and wet, observations in three successive, but contrasting, years have shown that Na+ ion concentrations in the glacier river water are influenced strongly by the amount of snowmelt. This itself depends on the preceding winter conditions, which determine the amount of accumulation, and on the current summer's weather. The efficiency of the glacier's drainage systems depends on the general progress of summer ablation. The speed with which the systems develop influences ion provision from subglacial sources. Ca2+ ion concentrations are largely determined by subglacial conditions. Oxygen isotope variations in glacier river water reflect the relative contributions made to total discharge by snow meltwater and other sources; the composition of the snow cover, which is a function of winter temperatures, has a strong influence. Ice meltwater has low isotopic variability, but the isotopic composition of rainfall varies markedly. A simple model of mixing of englacial and subglacial waters, each of a constant composition, cannot be applied to a high-latitude glacier of the size and altitudinal range of Austre Okstindbreen.  相似文献   

6.
Streamflow generation was investigated using isotopic and geochemical tracers in semiarid, glacier-covered, montane catchments in the upper Shule River, northeastern Tibetan Plateau. Samples from stream water, precipitation, glacier meltwater, and groundwater were collected at the Suli and Gahe catchments along the Shule River, with an area of 1908 and 4210 km2, respectively. The samples were analysed for stable isotopes of water and major ions. Results of diagnostic tools of mixing models showed that Ca2+, Mg2+ and Cl−, along with δ18O and δ2H, behaved conservatively as a result of mixing of three endmembers. The three endmembers identified by the mixing analysis were surface runoff directly from precipitation, groundwater, and glacier meltwater. Streamflow was dominated by groundwater, accounting for 59% and 60% of streamflow on average in the Suli and Gahe catchments, respectively, with minimum groundwater contribution in July (47% and 50%) and maximum contribution in October (69% and 70%). The contributions of surface runoff were slightly higher in the Suli catchment (25%) than in the Gahe catchment (19%). However, the contributions of glacier meltwater were higher in the Gahe catchment (21%) compared to the Suli catchment (17%), as a result of a higher percentage of glacier covered area in the Gahe catchment. This difference followed well the non-linear power–law trend of many glacier-covered catchments around the world. As glacier retreat continues in the future, the reduction of streamflow in glacier-covered upper Shule catchment likely will be accelerated and possibly elsewhere in the Tibetan Plateau. This study suggests that it is critical to define the turning point of an accelerated reduction in glacier meltwater for glacier-covered catchments around the world in order to better assess and manage water resources.  相似文献   

7.
ABSTRACT

The temporal variations in electrical conductivity and the stable isotopes of water, δD and δ18O, were examined at Chhota Shigri Glacier, India, to understand water sources and flow paths to discharge. Discharge is highly influenced by supraglacially derived meltwater during peak ablation, and subglacial meltwaters are more prominent at the end of the melt season. The slope of the best fit linear regression line for δD versus δ18O, for both supraglacial and runoff water, is lower than that for precipitation (snow and rain) and surface ice, indicating strong isotopic fractionation associated with the melting processes. The slope of the local meteoric water line (LMWL) is close to that of the global meteoric water line (GMWL), reflecting that the moisture source is predominantly oceanic. The d-excess variation in rainwater confirms that the southwest monsoon is the main contributor during summer while the remainder including winter is mostly influenced by westerlies.  相似文献   

8.
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   

9.
Snow and glaciers are known to be important sources for freshwater; nevertheless, our understanding of the hydrological functioning of glacial catchments remains limited when compared with lower altitude catchments. In this study, a temperate glacial region located in the southeast margin of the Tibetan Plateau is selected to analyse the characteristics of δ18O and δD in different water sources and the contribution of glacier–snow meltwater to streamflow. The results indicate that the δ18O of river water ranges from ?16.2‰ to ?10.2‰ with a mean of ?14.1‰ and that the δD values range from ?117.0‰ to ?68.0‰ with a mean of ?103.1‰. These values are more negative than those of glacier–snow meltwater but less negative than those of precipitation. The d ‐excess values are found to decrease from meltwater to river to lake/reservoir water as a result of evaporation. On the basis of hydrograph separation, glacier–snow meltwater accounts for 51.5% of river water in the Baishui catchment in the melting season. In the Yanggong catchment, snow meltwater contributes 47.9% to river water in the premonsoon period, and glacier meltwater contributes only 6.8% in the monsoon period. The uncertainty in hydrograph separation is sensitive to the variation of tracer concentrations of streamflow components. The input of meltwater to a water system varies with local climate and glacier changes. The results confirm that hydrograph separation using water isotopes is valuable for evaluating the recharge sources of rivers, especially in ungauged glacial regions. This study provides insights into the hydrological processes of glacial catchments on the Tibetan Plateau, which is important for water resource management.  相似文献   

10.
Recent understanding of chemical weathering in glacierized catchments has been focused on mid-latitude, Alpine catchments; comparable studies from the high latitudes are currently lacking. This paper attempts to address this deficiency by examining solute provenance, transport and denudation in a glacierized catchment at 78°N in the Svalbard High Arctic archipelago. Representative samples of snow, glacier ice, winter proglacial icing and glacier meltwater were obtained from the catchment during spring and summer 1993 and analysed for major ion chemistry. Seasonal variations in the composition of glacier meltwater occur and are influenced by proglacial solute acquisition from the icing at the very start of the melt season, and subsequently by a period of discharge of concentrated snowmelt caused by snowpack elution; weathering within the ice-marginal channels that drain the glacier, particularly carbonation reactions, continues to furnish solute to meltwater when suspended sediment concentrations increase later in the melt season. Partitioning the solute flux into its various components (sea-salt, crustal, aerosol and atmospheric sources) shows that c. 25% of the total flux is sea salt derived, consistent with the maritime location of the glacier, and c. 71% is crustally derived. Estimated chemical denudation, 160 meq m−2 a−1 sea salt-corrected cation equivalent weathering rate, is somewhat low compared with other studied glacierized catchments (estimates in the range 450–1000 meq m−2 a−1), which is probably attributable to the relatively short melt season and low specific runoff in the High Arctic. A positive relationship was identified between discharge and CO2 drawdown owing to carbonation reactions in turbid meltwater. © 1997 John Wiley & Sons, Ltd.  相似文献   

11.
Glaciers are of crucial importance for the livelihood of the local populations, which depend on their meltwater for water and energy supplies. For this reason, seasonal variations of oxygen‐18 of glacial stream water and their sources within a small glacial catchment in south western China were investigated during the wet season. The results showed significant difference of oxygen‐18 existed among meltwater, rainwater, ground water and stream water, and significantly seasonal variation of precipitation occurred during the observed period. The streamflow of Baishui catchment was separated into components of ice‐snowmelt and precipitation using oxygen‐18. As shown by the result of the two‐component mixing model, on average, 53.4% of the runoff came from ice‐snowmelt during the wet season, whereas the remaining 46.6% were contributed by precipitation in the catchment. According to monthly hydrograph, the contribution of snow and glacier meltwater varied from 40.7% to 62.2%, and that of precipitation varied from 37.8% to 59.3% in wet season. Uncertainties for this separation were mainly caused by the variation of tracer concentrations. The roles of glacier and snow meltwater should be noticed in water resource management in those glacial regions in south western China. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

12.
Studies on hydrological processes are often emphasized in resource and environmental studies. This paper identifies the hydrological processes in different landscape zones during the wet season based on the isotopic and hydrochemical analysis of glacier, snow, frozen soil, groundwater and other water sources in the headwater catchment of alpine cold regions. Hydrochemical tracers indicated that the chemical compositions of the water are typically characterized by: (1) Ca? HCO3 type in glacier snow zone, (2) Mg? Ca? SO4 type for surface runoff and Ca? Mg? HCO3 type for groundwater in alpine desert zone, (3) Ca? Mg? SO4 type for surface water and Ca? Mg? HCO3 type for groundwater in alpine shrub zone, and (4) Ca? Na? SO4 type in surface runoff in the alpine grassland zone. The End‐Members Mixing Analysis (EMMA) was employed for hydrograph separation. The results showed that the Mafengou River in the wet season was mainly recharged by groundwater in alpine cold desert zones and shrub zones (52%), which came from the infiltration and transformation of precipitation, thawed frozen soil water and glacier‐snow meltwater. Surface runoff in the glacier‐snow zone accounted for 11%, surface runoff in alpine cold desert zones and alpine shrub meadow zones accounted for 20%, thawed frozen soil water in alpine grassland zones accounted for 9% of recharge and precipitation directly into the river channel (8%). This study suggested that the whole catchment precipitation did not produce significant surface runoff directly, but mostly transformed into groundwater or interflow, and finally arrived in the river channel. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

13.
Twelve modified passive capillary samplers (M‐PCAPS) were installed in remote locations within a large, alpine watershed located in the southern Rocky Mountains of Colorado to collect samples of infiltration during the snowmelt and summer rainfall seasons. These samples were collected in order to provide better constraints on the isotopic composition of soil‐water endmembers in the watershed. The seasonally integrated stable isotope composition (δ18O and δ2H) of soil‐meltwater collected with M‐PCAPS installed at shallow soil depths < 10 cm was similar to the seasonally integrated isotopic composition of bulk snow taken at the soil surface. However, meltwater which infiltrated to depths > 20 cm evolved along an isotopic enrichment line similar to the trendline described by the evolution of fresh snow to surface runoff from snowmelt in the watershed. Coincident changes in geochemistry were also observed at depth suggesting that the isotopic and geochemical composition of deep infiltration may be very different from that obtained by surface and/or shallow‐subsurface measurements. The M‐PCAPS design was also used to estimate downward fluxes of meltwater during the snowmelt season. Shallow and deep infiltration averaged 8·4 and 4·7 cm of event water or 54 and 33% of the measured snow water equivalent (SWE), respectively. Finally, dominant shallow‐subsurface runoff processes occurring during snowmelt could be identified using geochemical data obtained with the M‐PCAPS design. One soil regime was dominated by a combination of slow matrix flow in the shallow soil profile and fast preferential flow at depth through a layer of platy, volcanic rocks. The other soil regime lacked the rock layer and was dominated by slow matrix flow. Based on these results, the M‐PCAPS design appears to be a useful, robust methodology to quantify soil‐water fluxes during the snowmelt season and to sample the stable isotopic and geochemical composition of soil‐meltwater endmembers in remote watersheds. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

14.
ABSTRACT

In this study, we characterized the glacial meltwater flow through a proglacial area with a focus on proglacial lakes, their hydrological regime and their connection to the stream. The studied lakes – the Adygine ice-debris complex, northern Tien Shan – showed a distinct development throughout an ablation season: at Lake 2, the mean daily water-level fluctuation amplitude increased from 0.07 m to 0.18 m (June, August), then dropped to 0.07 m in September. Glacial meltwater flows through the lakes and further downstream through a rock glacier rather fast, moving at 0.085 m s?1. However, based on the low dye recovery in the stream (0.03%), only a small portion of water was routed efficiently. The complexity of the site’s drainage system was supported by varying isotopic composition of water in the tarns situated on the rock glacier, with Tarn a (δ2H: –36.08‰; δ18O: –6.25‰) being the most enriched and Tarn c (δ2H: 78.68‰; δ18O: 11.9‰) the most depleted in heavy isotopes.  相似文献   

15.
There are still relatively few hydrochemical studies of glacial runoff and meltwater routing from the high latitudes, where non-temperate glacier ice is frequently encountered. Representative samples of glacier meltwater were obtained from Scott Turnerbreen, a ‘cold-based’ glacier at 78° N in the Norwegian high Arctic archipelago of Svalbard, during the 1993 melt season and analysed for major ion chemistry. Laboratory dissolution experiments were also conducted, using suspended sediment from the runoff. Significant concentrations of crustal weathering derived SO2−4 are present in the runoff, which is characterized by high ratios of SO2−4: (SO2−4+HCO−3) and high p(CO2). Meltwater is not routed subglacially, but flows to the glacier terminus through subaerial, ice marginal channels, and partly flows through a proglacial icing, containing highly concentrated interstitial waters, immediately afront the terminus. The hydrochemistry of the runoff is controlled by: (1) seasonal variations in the input of solutes from snow- and icemelt; (2) proglacial solute acquisition from the icing; and (3) subaerial chemical weathering within saturated, ice-cored lateral moraine adjoining drainage channels at the glacier margins, sediment and concentrated pore water from which is entrained by flowing meltwater. Diurnal variations in solute concentration arise from the net effects of variable sediment pore water entrainment and dilution in the ice marginal streams. Explanation of the hydrochemistry of Scott Turnerbreen requires only one major subaerial flow path, the ice marginal channel system, in which seasonally varying inputs of concentrated snowmelt and dilute icemelt are modified by seepage or entrainment of concentrated pore waters from sediment in lateral moraine, and by concentrated interstitial waters from the proglacial icing, supplied by leaching, slow drainage at grain intersections or simple melting of the icing itself. The ice marginal channels are analogous neither to dilute supra/englacial nor to concentrated subglacial flow components. © 1998 John Wiley & Sons, Ltd.  相似文献   

16.
In high elevation cold regions of the Tibetan Plateau, suspended sediment transfer from glacier meltwater erosion is one of the important hydrological components. The Zhadang glacier is a typical valley‐type glacier in the Nyainqentanglha Mountains on the Tibetan Plateau. To make frequent and long period records of meltwater runoff and sediment processes in the very high elevation and isolated regions, an automatic system was installed near the glacier snout (5400 m a.s.l) in August 2013, to measure the transient discharge and sediment processes at 5‐min interval, which is shorter than the time span for the water flow to traverse the catchment from the farthest end to the watershed outlet. Diurnal variations of discharge, and suspended sediment concentration (SSC) were recorded at high frequency for the Zhadang glacier, before suspended sediment load (SSL) was computed. Hourly SSC varied from the range of 0.2 kg/m3 to 0.5 kg/m3 (at 8:00–9:00) to the range of 2.0 kg/m3 to 4.0 kg/m3 (at 17:00–18:00). The daily SSL was 32.24 t during the intense ablation period. Hourly SSC was linearly correlated with discharge (r = 0.885**, n = 18, p < 0.01). A digit‐eight hysteresis loop was observed for the sediment transport in the glacier area. Air temperature fluctuations influence discharge, and then result in the sediment variations. The results of this study provide insight into the responses of suspended sediment delivery processes with a high frequency data in the high elevation cold regions. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

17.
We present the results of a 3‐year monitoring programme of the stable isotope composition of lake water and precipitation at Taozi Lake, in the East Asian monsoon region of China. Our aims were to reveal the spatiotemporal pattern of variation of stable isotopes in a small closed‐basin lake and to quantitatively determine the impacts of precipitation and evaporation on the stable isotope composition of lake water under a humid monsoon climate. In the time domain, the stable oxygen isotopic ratio of the lake water (δ18OL) exhibited substantial seasonal and interannual variations, but the isotope variations between different precipitation events substantially exceeded seasonal and interannual variations. Compared with the stable isotopes in precipitation, δ18OL was substantially positive and dL was negative. In the space domains, the lake water was homogeneously mixed. Indicated by statistic analyses, precipitation plays a dominant role in dynamic of the lake stable isotope during precipitation events of relatively large magnitude, whereas the effect of evaporation is dominant during smaller precipitation events. Results advance our understanding of the stable isotope change rule in the process of lake water evaporation, and it is helpful to identify the climatic significance recorded in stable isotopic compositions of lake bottom sediments.  相似文献   

18.
Forest canopies alter the amount and isotopic composition of precipitation reaching the forest floor. Thus retention, evaporation and transport processes in forest canopies, and their effects on water isotopes, are key to understanding forest water cycling. Using a two-year isotope dataset from a mixed beech/spruce forest in Zurich, Switzerland, we assessed the isotopic offsets between precipitation, throughfall and stemflow. We also analysed how these offsets affect estimates of the fraction of soil water that is derived from winter precipitation. Throughfall was typically enriched in heavy isotopes compared to precipitation, but isotopically lighter than stemflow, with average δ2H of −64.3 ‰, −59.9 ‰ and − 56.3 ‰ in precipitation, throughfall and stemflow, respectively. The differences between beech and spruce were rather small compared to the seasonal differences in precipitation isotopes. Isotopic offsets between precipitation and throughfall/stemflow were smaller during the spring and summer months (March through August) than during fall and winter (September through February). Bulk and mobile soil waters at 10 and 40 cm showed smaller seasonal variations than those in precipitation, throughfall and stemflow, and were isotopically lighter than recent precipitation, with the largest offsets occurring during the summer months (June through August) for bulk soil waters. Thus, bulk soil waters at both depths contain a mixture of precipitation from previous events and seasons, with over-representation of isotopically lighter winter precipitation. Mobile soil waters were more similar to recent precipitation than bulk soil waters were. Throughfall isotopes were slightly heavier than precipitation isotopes, resulting in different sinusoidal fits for seasonal isotopic cycles in precipitation and throughfall. These differences lead to small underestimates in the fraction of soil water originating from winter precipitation, when open-field precipitation rather than throughfall is used as the input data. Together our results highlight the importance of isotope measurements in throughfall and stemflow for the assessment of precipitation seasonality and water cycling across forested landscapes.  相似文献   

19.
Abstract

Stable isotopes are powerful research tools in environmental sciences and their use in ecosystem research is increasing. Stable isotope measurements allow the study of evapotranspiration fluxes, soil evaporation and leaf transpiration phenomena. Soil water and leaf water are the sources of the evapotranspiration that transfers large quantities of water from land to the atmosphere; as a result the isotopic composition of water left in the leaves is modified towards enrichment. Evaporation also changes the isotopic composition of water bodies creating a natural isotopic signal. The isotopic identity of soil water affects the oxygen isotopic signature of leaf and stem water. In this paper we present the isotopic data of bulk leaf water, showing the enrichment in isotopic value of oxygen due to evapotranspiration from leaves in conjunction with the isotopic signal of rainwater and other environmental factors such as humidity and temperature. Results suggest that the variation in the values of δ18O of Eucalyptus citriodora, Dalbergia sissoo, Melia azedarach and Pinus roxburghii is due to the seasonal changes in the δ18O of the source water for plants, i. e. rain. It is further observed that leaf water δ18O values are depleted during the months of July, August and September. This occurs due to the following reasons: (a) the sampling areas receive about 50% of the average annual rain during these months, and (b) rainfalls during these months are isotopically depleted compared with winter rains.

Citation Butt, S., Ali, M., Fazil, M. & Latif, Z. (2010) Seasonal variations in the isotopic composition of leaf and stem water from an arid region of Southeast Asia. Hydrol. Sci. J. 55(5), 844–848.  相似文献   

20.
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   

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