Groundwater flow in a relatively old oceanic volcanic island: the Betancuria area, Fuerteventura Island, Canary Islands, Spain

A multi-perspective exploration of the salinization mechanisms of groundwater in the Guanzhong Basin, China

A comprehensive understanding of the salinization of groundwater in the Guanzhong Basin, China, is crucial for ensuring sustainable groundwater development. However, the mechanism driving salinization in different regions of the basin remains unclear. Therefore, this study employed multivariate statistical methods, hydrochemical analysis, isotope studies, and hydrochemical modeling to uncover the factors and processes influencing groundwater salinization. The results indicate significant regional variations in total dissolved solids (TDS), with concentrations exceeding 1000 mg/L predominantly occurring to the north of the Weihe River and the east of the Jinghe River. The correlations of groundwater chloride (Cl-) with Cl/Br molar ratio and stable isotopes show that groundwater salinity in the Guanzhong Basin is mainly controlled by mineral dissolution, and evaporation. In addition, human activities, such as vertical irrigation recharge and excessive fertilizer use, exacerbate local salinity levels. Irrigation activities worsen the shallow groundwater salt enrichment in the runoff zone of the central basin, revealed by the high salinity (TDS>3000 mg/L), high Cl/Br ratios (>2000), moderate δ2H (-57.5 to -67.5 ‰) and moderate δ18O (-8.1 to -8.9 ‰). High salinity (TDS>1000 mg/L), high nitrate concentration (>100 mg/L), and moderate Cl- (100 to 500 mg/L) indicate the impact of excessive fertilizer use. It is worth noting that intensive groundwater withdrawal disrupts the dynamic balance within the aquifer, causing shallow high-saline groundwater to percolate downward, thereby increasing the risk of deep groundwater pollution. The research enhances the understanding of groundwater salinity transport and provides insights into the effects of groundwater salinization in the irrigation area.

Groundwater origin and recharge in the hyperarid Cordillera de la Costa, Atacama Desert, northern Chile

The Cordillera de la Costa is located along the coastline of northern Chile, in the hyperarid Atacama Desert area. Chemical and isotopic analyses of several small coastal springs and groundwater reservoirs between 22.5 °S and 25.5 °S allow understanding groundwater origin, renewal time and the probable timing of recharge. The aquifers are mostly in old volcanic rocks and alluvial deposits. All spring waters are brackish, of the sodium chloride type due to intensive concentration of precipitation due aridity and for deep groundwater to additional water-rock interaction in slowly renewed groundwater and mixing with deep seated brines. The heavy δ¹⁸O and δ²H values in spring water are explained by recharge by the arrival of moist air masses from the Pacific Ocean and the originally lighter values in the deep wells can be associated to past recharge by air masses coming from the Atlantic Ocean. Current recharge is assumed almost nil but it was significant in past wetter-than-present periods, increasing groundwater reserves, which are not yet exhausted. To explain the observed chloride content and radiocarbon (¹⁴C) activity, a well-mixed (exponential) flow model has been considered for aquifer recharge. The average residence time of groundwater feeding the springs has been estimated between 1 and 2kyr, up to 5kyr and between 7 and 13kyr for deep well water, assuming that current recharge is much less than during the previous wetter period. The recharge period feeding the coastal springs could have been produced 1 to 5kyr BP, when the area was already inhabited, and recharge in the Michilla mine was produced during the 10 to 14.5kyr BP CAPE (Central Andean Pluvial Event) pluvial events of the central Andes. The approximate coincidence of turnover time with the past wet periods, as revealed by paleoclimate data, points to significant recharge during them.

Groundwater flow in a closed basin with a saline shallow lake in a volcanic area: Laguna Tuyajto, northern Chilean Altiplano of the Andes

Laguna Tuyajto is a small, shallow saline water lake in the Andean Altiplano of northern Chile. In the eastern side it is fed by springs that discharge groundwater of the nearby volcanic aquifers. The area is arid: rainfall does not exceed 200mm/year in the rainiest parts. The stable isotopic content of spring water shows that the recharge is originated mainly from winter rain, snow melt, and to a lesser extent from some short and intense sporadic rainfall events. Most of the spring water outflowing in the northern side of Laguna Tuyajto is recharged in the Tuyajto volcano. Most of the spring water in the eastern side and groundwater are recharged at higher elevations, in the rims of the nearby endorheic basins of Pampa Colorada and Pampa Las Tecas to the East. The presence of tritium in some deep wells in Pampa Colorada and Pampa Las Tecas indicates recent recharge. Gas emission in recent volcanoes increase the sulfate content of atmospheric deposition and this is reflected in local groundwater. The chemical composition and concentration of spring waters are the result of meteoric water evapo-concentration, water-rock interaction, and mainly the dissolution of old and buried evaporitic deposits. Groundwater flow is mostly shallow due to a low permeability ignimbrite layer of regional extent, which also hinders brine spreading below and around the lake. High deep temperatures near the recent Tuyajto volcano explain the high dissolved silica contents and the δ(18)O shift to heavier values found in some of the spring waters. Laguna Tuyajto is a terminal lake where salts cumulate, mostly halite, but some brine transfer to the Salar de Aguas Calientes-3 cannot be excluded. The hydrogeological behavior of Laguna Tuyajto constitutes a model to understand the functioning of many other similar basins in other areas in the Andean Altiplano.

Groundwater Recharge and Hydrogeochemical Evolution in Leizhou Peninsula, China

An analysis of the stable isotopes and the major ions in the surface water and groundwater in the Leizhou Peninsula was performed to identify the sources and recharge mechanisms of the groundwater. In this study, 70 water samples were collected from rivers, a lake, and pumping wells. The surface water was considered to have a lower salinity than the groundwater in the region of study. The regression equations forδD andδ18O for the surface water and the groundwater are similar to those for precipitation, indicating meteoric origins. TheδD andδ18O levels in the groundwater ranged from −60‰; to −25‰; and −8.6‰; to −2.5‰, respectively, and were lower than the stable isotope levels from the winter and spring precipitation. The groundwater in the southern area was classified as the Ca2+-Mg2+-HCO3--type, whereas the groundwater in the northern area included three types (Na+-Cl−-type, Ca2+-Mg2+-HCO3--type, and Ca2+-Mg2+-Cl−-type), indicating rapid and frequent water-rock exchange in the region. A reasonable conclusion is that the groundwater chemistry is dominated by rock weathering and rainwater of local origin, which are influenced by seawater carried by the Asian monsoon.