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Hydrochemistry and groundwater isotopes
Published in Ian Acworth, Investigating Groundwater, 2019
Appello and Postma (2005) identify the deuterium excess as a parameter that could explain enrichment above the meteoric water line. The deuterium excess is calculated from the global meteoric water line (GMWL) in Equation 14.11 as: d=δ2Hrain−8.0δ18Orain Values of the deuterium excess > 10 would indicate additions of the heavier isotope 18O. Appello and Postma (2005) suggest that the deuterium excess can be an indication of a contribution from evaporated water in an arid climate with lower humidity, as would occur from rainfall beginning to evaporate before it gets to the ground, or a contribution from previously evaporated inland water to the rain. The latter process is indicated on the right-hand side of Figure 14.10.
Groundwater and surface water interactions and impacts of human activities in the Hailiutu Catchment, Northwest China
Published in Zhi Yang, Quantitative Assessment of Groundwater and Surface Water Interactions in the Hailiutu River Basin, Erdos Plateau, China, 2018
A linear relationship between deuterium and oxygen-18 was established for average global meteoric waters, which is well known as the Global Meteoric Water Line (GMWL) (Craig, 1961): δD=8δ18O+10. Monthly isotopes values in precipitation at the nearby Taiyuan, Baotou, and Yinchuan stations from the Global Network of Isotopes in Precipitation ((GNIP IAEA/WMO 2016)) are collected for providing localized relations between δD and δ18O known as the Local Meteoric Water Line (LMWL). The isotopic signatures of deuterium and oxygen-18 are often enriched in surface water bodies due to evaporative effects, while the isotopes remain unaffected in the groundwater system. The relation between the values of isotopes in different water bodies can be used to determining the interactions between groundwater and surface water. The isotopic and chemical profiles of the Hailiutu River were obtained from the analysis results of the river water samples with EC values, isotopic composition, and chemical components. The lengths from the origin of the Hailiutu River to the water samples sites range from 4 to 56.5 km (Figure 5.1).
Application of Natural and Artificial Isotopes in Groundwater Recharge Estimation
Published in M. Thangarajan, Vijay P. Singh, Groundwater Assessment, Modeling, and Management, 2016
Although wind speed and temperature can influence the kinetic fractionation, relative humidity is the most important driving force. The deuterium excess values of regional precipitation deviate from that of global meteoric water line (GMWL). If deuterium excess values are greater than 10, then evaporation under low humidity conditions takes place at the source area. Significant re-evaporation of local surface waters under low humidity creates vapor mass with high deuterium excess. If such vapor mixes with atmospheric reservoir and recondenses, the resultant precipitation will have high deuterium excess (Clark and Fritz, 1997). The deuterium excess value thus serves as a tool to differentiate air masses causing rainfall in a region. In this study, for the southwest monsoon rain, the value was close to that of the global meteoric line (+10), whereas greater values were obtained for the northeast monsoon rains. Thus, two types of air masses of different origin can be inferred. The southwest monsoon rains are caused by the marine vapors, carrying moisture from the Indian Ocean and Arabian Sea. The relative humidity at the vapor source region is around 85%, and correspondingly the deuterium excess value is around 10%o. In the case of northeast monsoon rains, the winds are in the reverse direction, that is, oriented toward the southern hemisphere. The vapors reach the peninsular region after traversing the vast northern Indian plains. During its journey, the air mass acquires re-evaporated vapor from the land and the relative humidity of the vapor source region is also considerably less (<70%). The combined effect of the two processes produces rainfall with high deuterium excess value. The two different vapor source origins were reported in this region earlier (Deshpande et al., 2003; Gupta et al., 2004; Resmi> 2011).
The importance of groundwater to the upper Columbia River floodplain wetlands
Published in Canadian Water Resources Journal / Revue canadienne des ressources hydriques, 2023
Casey R. Remmer, Rebecca Rooney, Suzanne Bayley, Catriona Leven
An isotopic framework was developed to interpret the dominant hydrological processes influencing wetlands. Isotope framework parameters were calculated (in decimal notation) using approaches described in Gonfiantini (1986), Gibson and Edwards (2002), Edwards et al. (2004), and Yi et al. (2008), which are based on the linear resistance model of Craig and Gordon (1965). The framework consists of two linear trends. The Global Meteoric Water Line (GMWL), described by δ2H = 8 δ18O + 10, represents the observed global relationship between δ18O and δ2H in amount‐weighted annual precipitation. In a region, the isotopic composition of precipitation will cluster along a Local Meteoric Water Line (LMWL). For the Columbia Valley the LMWL was approximated by δ2H = 8.21 δ18O − 9.36, based on precipitation collected at the nearest Global Network of Isotopes in Precipitation (GNIP) site (Calgary, Alberta). The Local Evaporation Line (LEL) represents the trajectory of surface water undergoing evaporation (Gibson and Edwards 2002). Here we use a predicted LEL, based on the linear resistance model of Craig and Gordon (1965), which allows water isotope compositions to be interpreted independently based on their position along or about the LEL. This is advantageous to the more common technique of applying linear regression through measured water isotope compositions, as it allows isotope compositions to be interpreted independently based on their position along (degree of evaporation) and about (i.e. above/below; relative influence of different input waters such as snowmelt and rainfall) the LEL.