Showing papers on "Environmental isotopes published in 2019"

Occurrence of Uranium in Groundwater Along the Lithological Contacts in Central Tamilnadu, India: An Isotope Hydrogeochemical Perspective

Abstract: Groundwater contributes to the highest exposure level of naturally occurring uranium (U) to biosphere, and hence, the source and concentration of uranium in groundwater needs to be monitored periodically. In the present study, groundwaters from different lithologic locations were collected and measured for uranium concentration and major ions in order to establish any possible link with the lithology on the uranium distribution in central parts of Tamil Nadu, South India. About 11% of the samples contain U in excess of the permissible limit of WHO (Guidelines for drinking-water quality, WHO, Geneva, 2011), and the contamination was limited to mostly hard rock terrain, which is granitic in nature. The correlations among U, major ions, and environmental isotopes were studied to understand the mechanism governing uranium dissolution and transport in groundwater of this region. Observations lead us to infer that the older water with near-neutral pH and oxidizing condition contains higher dissolved U compared with relatively young groundwater. The results also reflect the possible health risk to the local population through long-term consumption of uranium-containing groundwater without any pretreatment.

Characterization of recharge mechanisms in a Precambrian basement aquifer in semi-arid south-west Niger

Abstract: In the central part of the semi-arid Dargol Basin of southwestern Niger, most of the groundwater resource is contained in the fractured aquifers of the Precambrian basement. The groundwater resource is poorly characterized and this study is the first attempt to better describe the recharge mechanisms and hydrogeochemical behaviour of the aquifers. Hydrogeochemical and piezometric methods were combined to determine changes in recharge rate and origin of groundwaters for the shallow weathered aquifer and the deep fissured/fractured aquifer. At the basin scale, the groundwater fluxes towards the Niger River are influenced mainly by topography, with no visual long-term trend in groundwater levels (1980–2009). The hydro-geochemical signature is dominated by the calcic-bicarbonate to magnesian (70%) type. It shows evolution from an open environment with CO2 and low mineralized water (granitoids, alterites) towards a more confined environment with more mineralized waters (schists). Stable water isotopes (δ18O, δ2H) analysis suggests two main groundwater recharge mechanisms: (1) direct recharge with nearly no post-rainfall fractionation signature and (2) indirect recharge from evaporated surface waters and/or stream-channel beds. Groundwater tritium content indicates that recharge is mostly recent, with an age less than 50 years (3H > 3 TU), with only 10% indicating low or even no recharge for the past decades. A median value of the groundwater renewal rate estimated from individual values of tritium is equivalent to 1.3% year−1, close to the one determined for groundwater samples dating to the early 1980s, thus indicating no measurable long-term change.

Delineation of spring recharge zones using environmental isotopes to support climate-resilient interventions in two mountainous catchments in Far-Western Nepal

Abstract: Though springs are the primary source of water for communities in the mid-hills of Nepal, an in-depth scientific understanding of spring systems is missing, preventing the design of effective climate-resilient interventions for long-term sustainability of springs. This study marks the first attempt to combine environmental isotopes analysis with hydrometric and hydrogeological measurements to identify dominant recharge zones for springs in two mountainous catchments—Banlek and Shikarpur—in Far-Western Nepal. In total, 422 water samples collected from rainfall, springs and streams between March 2016 and March 2017 were analyzed for their isotopic composition (δ18O and δD). Isotopic composition of rainwater shows seasonality, suggesting that different sources of water vapor cause rains in monsoon and in dry season. Rainfall responses of individual springs were used to identify connections to unconfined and deeper groundwater strata. The isotopic composition of springs in the two catchments ranges from −9.55 to −8.06‰ for δ18O and −67.58 to −53.51‰ for δD. The isotopic signature of the spring sources falls close to the local meteoric water line for the corresponding season, indicating strong rainfall contribution to springs. Altitudinal isotopic gradients suggest mean recharge elevation of 2,600–2,700 m asl for springs in Shikarpur, which lies beyond the surface-water catchment, and a recharge elevation of 1,000–1,100 m asl for Banlek, which partially extends beyond the surface-water catchment. The demarcated recharge zones will be used by government agencies to implement recharge interventions to increase the resiliency and reliability of springs in Far-Western Nepal.

Complex hydrochemical characteristics of the Middle–Upper Pleistocene aquifer in Soc Trang Province, Southern Vietnam

Abstract: Environmental isotope techniques were applied to study the hydrochemical characteristics of groundwater in Soc Trang Province, Southern Vietnam, in frame of the project Improvement of Groundwater Protection in Vietnam (IGPVN). Groundwater samples were collected from various monitoring wells (newly drilled by the IGPVN project), national monitoring wells, private tube wells and production wells. Surface water samples were collected from rivers, ponds or canals. The aquifer system is more complex than presumed as the hydrochemical and stable isotope compositions of groundwater samples in the Middle-Upper Pleistocene (qp2-3) aquifer differ significantly in lateral direction. Furthermore, observed changing redox reactions within the target aquifer from dry to wet season make it probable that some interaction with overlying aquifers exists. The stable isotope signatures of the qp2-3 groundwater samples can be divided into two distinct groups which, respectively, originated from paleo-meteoric water and either was located in paleo-salinized areas of the qp2-3 aquifer or resulted from evaporation effect of recharging water prior or during infiltration process. In fact, individual parts of "the same" aquifer seem not to be hydraulically connected to each other. The environmental isotope data provided neither evidences of hydraulic connection between the rivers and the qp2-3 aquifer nor of recent groundwater recharge in the Province. As a result, saltwater from the sea intruded inland to some extent via the Hau River during the dry season, but it did not affect the target aquifer. Any recharge from surface water to the qp2-3 aquifer in Soc Trang should occur outside the boundaries of Soc Trang Province. Considering the low groundwater transit velocities roughly estimated in this study (3.6 m/year and 7.8 m/year), it may take several ten thousands to hundred thousands of years for recharging water from beyond the Vietnam's national border to reach the qp2-3 aquifer in Soc Trang Province. Consequently, natural recharge cannot help to reduce groundwater declining in the short-to-middle term.

Application of environmental isotopes to identify recharge source, age, and renewability of phreatic water in Yinchuan Basin

Abstract: The accurate understanding of groundwater circulation pattern and its renewable capacity is vital for groundwater resource assessment and the rational exploitation and utilization of groundwater. Estimation of groundwater recharge is difficult in arid or semiarid area due to the low amount and variability of recharge. A combination of isotope investigation with hybrid model allows a direct calculation of renewability of the aquifer. In this paper, the phreatic water circulation pattern and its renewable capacity of phreatic water in Yinchuan Basin, a semiarid area located at the northwest China, are investigated by the application of environmental isotope method, which mainly focusses on the isotope characteristics of different water bodies, phreatic water isotope age, phreatic water circulation pattern, and phreatic water renewal rate. The results demonstrate that the two dominant recharge sources of groundwater in Yinchuan Basin, local atmospheric precipitation and Yellow River, account for 13% and 87%, respectively. The average residence time of phreatic water in Yinchuan Basin is about 48 years, and the average renewal rate is 3.38%/a. The results indicate that the phreatic water has a strong renewable capacity and the regeneration rate distribution is consistent with that indicated by isotope age.

Evaluation of surface water–groundwater interaction using environmental isotopes (D, 18 O and 222 Rn) in Chongli Area, China

Abstract: In order to understand the interaction between surface water and groundwater in Qingshuihe Basin of Chongli Area, the environmental isotopic D, 18O and 222Rn in surface water and groundwater have been analysis, the study results show that: the calculation results based on the D and 18O, the surface water in middle stream of Donggou River has been recharged by groundwater and river water upstream, the percentage of groundwater recharge is 56%; the calculation results based on the 222Rn, the average seepage rate of surface water is 27.8 m3/d/m in the upstream section, and the average recharge rate of groundwater is 17.6 m3/d/m. It is concluded that, the groundwater and surface water interaction is the main characteristics and processes of water cycle in Qingshuihe Basin, and groundwater recharge is the main sources of surface water in draught seasons.

Combining multiple isotope and noble gas data with seismic profiles in an interpretation of hydro-geochemical anomalies

Abstract: Environmental isotopes (δ 18 O, δD, δ 13 C, 14 C, 87 Sr/ 86 Sr), combined with hydrogeochemical data and seismic profile interpretation, have been used in studying regional groundwater flow systems in the Pannonian Basin. An interpretation of seismic profiles indicates the existence of faults systems, some of them being traceable from the Pre-Cenozoic basement up to near-surface Quaternary sediments. The Lakitelek study area shows high He contents (22 to 25 %) of mantle origin, where fault lines might have been reactivated during recent geological times and facilitated the occurrence of mantle-derived He in the groundwater. The Mezőtur study area, where most H- and O-isotope compositions are shifted from the global meteoric water line, exhibits 7.6 to 10.6 % He of mantle origin,. The deepest sample indicates mixing with formation waters. Here basement faults might not have been reactivated, since they do not seem to have an active role on the groundwater composition and effects of the regional flow system seem to be the dominant factor determining the groundwater isotope compositions.