Dual effects of precipitation and evaporation on lake water stable isotope composition in the monsoon region

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 (δ¹⁸O_L) 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, δ¹⁸O_L was substantially positive and d_L 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.     

Seasonal variations of deuterium and oxygen‐18 isotopes and their response to moisture source for precipitation events in the subtropical monsoon region

Deuterium and oxygen‐18 are common environmental tracers in water used to investigate hydrological processes such as evaporation and groundwater recharge, and to trace moisture source. In this study, we collected event precipitation from 01 January 2010 to 28 February 2011 at a site in Changsha, Yangtze River Basin to estimate the influence of moisture source and atmospheric conditions on stable isotope compositions. The local meteoric water line, established as δD = (8.45 ± 0.13) δ¹⁸O + (17.7 ± 0.9) (r² = 0.97, n = 189), had a higher slope and intercept than global meteoric water line. Temperature–δ¹⁸O exhibited complex correlations, with positive correlations during Nov.–Apr. superior to during Jun.–Sep., which was attributed to distinctive moisture sources, but vague the overall period; amount effect examined throughout the year. Linear regressions between δ¹⁸O and δD value in different precipitation event size classes revealed progressively decreasing slope and intercept values with decreasing precipitation amount and increasing vapour pressure deficit, indicating that small rainfall events (0–5 mm) were subject to secondary evaporation effects during rainwater descent. In contrast, snowfall and heavy precipitation events exhibited high slope and intercepts for the regression equation between δ¹⁸O and δD. High concentrations of heavy isotopes were associated with precipitation events sourced from remote westerly air masses, degenerated tropical marine air masses from the Bay of Bengal (BoB), and inland moisture in the pre‐monsoon period, as determined from backward trajectories assessed in the HYSPLIT model. Meanwhile, low concentrations of heavy isotopes were found to correspond with remote maritime moisture from BoB, the South China Sea, and the west Pacific at three different air pressures in summer monsoon and post‐monsoon using HYSPLIT and records of typhoon paths. These findings suggest that stable isotope compositions in precipitation events are closely associated with the meteorological conditions and respond sensitively to moisture source in subtropical monsoon climates. Copyright © 2013 John Wiley & Sons, Ltd.     

Assessing waterbird habitat use in coastal evaporative systems using stable isotopes (δC, δN and δD) as environmental tracers

Isotopic patterns of biota across salinity gradients in man-made evaporative systems could assist in determining the use of these habitats by animals. Here we report δ¹³C, δ¹⁵N and δD measurements of a euryhaline fish, the Mediterranean toothcarp (Aphanius fasciatus), inhabiting a range of salinities in the Thyna saltworks near Sfax (Tunisia). The contribution of these salinity niches to egg formation of two typically piscivorous bird species breeding in the area and feeding within saltworks, Little Tern (Sternula albifrons) and Little Egret (Egretta garzetta), was inferred trough a triple-isotope (δ¹³C, δ¹⁵N and δD) Bayesian mixing model. Isotopic trends for fish δ¹⁵N and δD across the salinity gradient followed the equations: δ¹⁵N = e^{(1.1 + 47.68/Salinity)} and δD = −175.74 + Salinity + Salinity²; whereas fish δ¹³C increased as salinity rose (δ¹³C = −10.83 + 0.02·Salinity), after a sudden drop in fish isotopic values for salinities >60 (Practical Salinity Scale) (average fish δ¹³C for salinities <60 = −5.92‰). Both bird species fed largely on low hypersalinity ponds (salinity = 43; average contribution = 37% and 22% for Little Egrets and Little Terns, respectively), although the use of intermediate hypersalinities (salinities 63 and 70) by Little Terns also occurred (16% and 21%, respectively). Isotopic patterns across salinity gradients allow the use of isotopic measurements to inform studies of habitat occupancy within evaporative systems and provide further insights into how wildlife communities interact with them.     

Estimation of mean residence times of subsurface waters using seasonal variation in deuterium excess in a small headwater catchment in Japan

We measured deuterium excess (d = δD ? 8δ¹⁸O) in throughfall, groundwater, soil water, spring water, and stream water for 3 years in a small headwater catchment (Matsuzawa, 0·68 ha) in the Kiryu Experimental Watershed in Japan. The d value represents a kinetic effect produced when water evaporates. The d value of the throughfall showed a sinusoidal change (amplitude: 6·9‰ relative to Vienna standard mean ocean water (V‐SMOW)) derived from seasonal changes in the source of water vapour. The amplitude of this sinusoidal change was attenuated to 1·3–6·9‰ V‐SMOW in soil water, groundwater, spring water, and stream water. It is thought that these attenuations derive from hydrodynamic transport processes in the subsurface and mixing processes at an outflow point (stream or spring) or a well. The mean residence time (MRT) of water was estimated from d value variations using an exponential‐piston flow model and a dispersion model. MRTs for soil water were 0–5 months and were not necessarily proportional to the depth. This may imply the existence of bypass flow in the soil. Groundwater in the hillslope zone had short residence times, similar to those of the soil water. For groundwater in the saturated zone near the spring outflow point, the MRTs differed between shallow and deeper groundwater; shallow groundwater had a shorter residence time (5–8 months) than deeper groundwater (more than 9 months). The MRT of stream water (8–9 months) was between that of shallow groundwater near the spring and deeper groundwater near the spring. The seasonal variation in the d value of precipitation arises from changes in isotopic water vapour composition associated with seasonal activity of the Asian monsoon mechanism. The d value is probably an effective tracer for estimating the MRT of subsurface water not only in Japan, but also in other East Asian countries influenced by the Asian monsoon. Copyright © 2006 John Wiley & Sons, Ltd.     

Short‐term variability in isotopic composition of precipitation: A case study from the Midwestern United States

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.     

四川牟尼沟水体的同位素地球化学特征

运用同位素地球化学的方法，对牟尼沟各水体中的δD、δ^18O、T值、氘过量参数(d)和元素化学分析数据进行研究，基本查明牟尼沟内大气降水、地表水、地下水以及主要泉水之间的循环和补、径、排关系。珍珠泉和翡翠泉为沟内出露的主要泉水：二道海沟珍珠泉系地下深循环热水的露头，是由补给高度在3700m以上的大气降水渗入地下，再通过深大断裂循环至地下深部，与深部热流进行热交换后，返回地表出露。作为天然温泉开发具有较大的潜力；矿泉水厂沟的翡翠泉是典型的酸性岩溶冷泉，含水层水的径流较珍珠泉慢且滞留时间相对长些，含有一定的CO2，系一深部含水层地下水的露头。它源自补给高度全区最高(3800m以上)的大气降水。泉水流量大而且稳定，水质好，作为矿泉饮用水开发具有重要的经济价值；沟内大多数地表径流来源于大气降水和浅层地下水补给，夏季以大气降水为主，冬季浅层地下水补入到地表径流中的比例相对增加。这种对地表径流的调节作用，对于保持风景区内的景观具有重要作用。     

四川盆地卤水同位素组成及氘过量参数演化规律

运用岩石地球化原理对四川盆地卤水的同位素及氘过量参数进行分析,结果发现其具有明显的分布规律特征,盆地内以中三叠世为界同位素的显示出海、陆两大体系,海相沉积含卤层卤水中氢同位素组成均低于海水,而氧同位素则高于海水.卤水(主体)源于海水,不同时期海水的蒸发程度有所差异.由震旦系舍卤层卤水分布区向上,经寒武系、二叠系茅口组至三叠系嘉陵江组、雷口坡组,卤水的δD值随时代变新而相对富重同位素.陆相沉积含卤层卤水,源于大气降水,同位素组成落在大气降水线附近.海、陆过渡相含卤层(上三叠系须家河组)卤水,同位素组成落在海相沉积含卤层卤水与大气降水端员之间,系大气降水和蒸发海水的混合.盆地内不同时代的含卤层,卤水的氘过量参数(d值)有明显随含卤层时代变老逐步降低的趋势.三叠系雷口坡组-嘉陵江组、二叠系茅口组、寒武系及震旦系含卤层均系碳酸盐地层,水/岩作用十分强烈,同时显示出卤水的氘过量参数的变化是时间的函数.所有含卤层,凡是分布于盆地周边或处在断裂构造发育或经过长期开采卤资源的卤井,明显受到大气降水渗漏补给的影响,它们的氘过量参数(d)都有不同程度的升高,升高的程度取决于现代大气降水混入的数量.三叠系不同组含卤层的卤水,卤水d值的变化与平面分布和含卤层的埋深有一定的关联,含卤层埋深愈深,卤水的氘过量参数(d)值就愈低.     

新疆夏季云下二次蒸发对雨滴稳定同位素影响的定量研究

在干旱区,雨滴在云下降落易受到二次蒸发的影响,明确降水从云层底部降落到地面过程中稳定氢氧同位素的变化在同位素水文学研究中很有必要。基于新疆地面气象站逐小时的观测资料,采用改进后的Stewart模型,研究了新疆雨滴云下蒸发剩余比（从云下到近地面雨滴蒸发后剩余体积占原体积的百分率f）、雨滴中δD变化量（△δD）和过量氘变化量（△d）的时空特征,并分析了△d与气象要素的关系。结果表明：（1）新疆降水中△d和蒸发剩余比存在明显的空间差异。（2）当在气温低、相对湿度大、降水强度大、雨滴直径大的情况下,蒸发剩余比较大,△d接近于0,蒸发剩余比与△d间的线性关系明显,斜率较低。不同气象条件下,蒸发剩余比与△d的关系并不固定,利用这一线性关系反推蒸发剩余比应慎重。（3）敏感性分析可以得出,如果各气象站的气温升高2℃,△d降幅为0.26%~3.10%;如果相对湿度升高5%,△d升幅为1.23%~8.34%;如果雨强增大10%,△d升幅为0.06%~0.89%;如果雨滴直径增加0.2 mm,△d升幅为0.98%~8.16%,但雨滴直径增加量大于1.2 mm时,△d变化量趋于稳定。     

中国西部降水中/D及相关气候研究(英文)

The spatial variation of δD in precipitation in West China is discussed in this paper, and the relationship between δD in precipitation and temperature is analyzed as well based on the measured δD in precipitation samples collected in 6 sites in West China during mainly the summer of 1996. δD in precipitation in West China shows an intensive spatial variation: lower in the south of the Tibetan Plateau and higher in the north of West China. Analysis shows that the low value of δD is caused by obvious impact of southwest monsoon, and a very high value is due to the regional water cycle in the arid regions. δD in precipitation in the interior of the continent shows a strong “temperature effect”, while not in the south of the Tibetan Plateau.