Isotopes as Tracers of Water Origin in and Near a Regional Carbonate Aquifer: The Southern Sacramento Mountains, New Mexico

Mixed-Unit-Model-Based and Quantitative Studies on Groundwater Recharging and Discharging between Aquifers of Aksu River

The confined aquifer in the Aksu River Basin is the main aquifer for drinking water within the area. In this study, the unconfined aquifer and the confined aquifer in the Aksu River Basin were divided into different water circulation units through analysis of their flow field. After the hydrochemistry and isotope characteristics of each unit were analyzed, these data were used as water volume quantitative information of the aquifer according to the mixed-unit model. With this quantitative information, the transformation relationship between the unconfined aquifer and the confined aquifer, the recharging source, recharging amount, recharging proportion, and discharging amount of the confined aquifer were revealed. The results showed that the confined aquifer receives a recharge of 21.48 × 106 m3/a from the unconfined aquifer. The recharging sources of the confined aquifer in the middle and upper stream of the Aksu River mainly included side recharging and leakage recharging from the unconfined aquifer, while the confined aquifer received little recharging from unconfined aquifer downstream of the Aksu River and did not receive recharging from the unconfined aquifer in the southeast of the basin. Additionally, drainage methods of the confined aquifer were mainly lateral flowing and artificial well-group pumping. The side discharging volume through the whole area was 15.67 × 106 m3/a, and the artificial pumping volume was 21.20 × 106 m3/a. The confined aquifer was in a negative balance state from the middle-upper stream to the downstream. The downstream confined aquifer and its unconfined aquifer had a plane laminar flow movement, and the unconfined aquifer provided very little recharging to the confined one, which was further enhanced by the artificial well pumping and caused an accumulating negative balance state of the downstream aquifer.

Groundwater Isotopes in the Sonoyta River Watershed, USA-Mexico: Implications for Recharge Sources and Management of the Quitobaquito Springs

Groundwater resources in the southwestern United States are finite and riparian and wetland areas are vulnerable to aquifer overdraft and unregulated groundwater use. Environmental isotopes and water chemistry were used to distinguish water types, recharge mechanisms, and residence time along several reaches of the Sonoyta River and Quitobaquito Springs located near the U.S.-Mexico border. Areas located upgradient from the Sonoyta River, such as the Puerto Blanco Mountains and La Abra Plain, are supported by local recharge which corresponds to water from the largest 30% of rain events mainly occurring during winter. For Quitobaquito Springs, the δ18O and δ2H values are too low to be derived from local recharge. Stable isotope data and Cl/SO4 mass ratios indicate that the Sonoyta River supplied Quitobaquito Springs through flow along a suggested fault system. Based on these results, Quitobaquito Springs flow could be diminished by any activity resulting in increased groundwater extraction and lowering of water elevations in the Sonoyta River regional aquifer.

Hydrology of Mountain Blocks in Arizona and New Mexico as Revealed by Isotopes in Groundwater and Precipitation

Mountain-block groundwater in the Southern Basin-and-Range Province shows a variety of patterns of δ18O and δ2H that indicate multiple recharge mechanisms. At 2420 m above sea level (masl) in Tucson Basin, seasonal amount-weighted means of δ18O and δ2H for summer are −8.3, −53‰, and for winter, −10.8 and −70‰, respectively. Elevation-effect coefficients for δ18O and δ2H are as follows: summer, −1.6 and −7.7 ‰ per km and winter, −1.1 and −8.9 ‰ per km. Little altitude effect exists in 25% of seasons studied. At 2420 masl, amount-weighted monthly averages of δ18O and δ2H decrease in summer but increase in winter as precipitation intensity increases. In snow-banks, δ18O and δ2H commonly plots close to the winter local meteoric water line (LMWL). Four principal patterns of (δ18O, δ2H) data have been identified: (1) data plotting along LMWLs for all precipitation at >1800 masl; (2) data plotting along modified LMWLs for the wettest 30% of months at <1700 masl; (3) evaporation trends at all elevations; (4) other patterns, including those affected by ancient groundwater. Young, tritiated groundwater predominates in studied mountain blocks. Ancient groundwater forms separate systems and mixes with young groundwater. Recharge mechanisms reflect a complex interplay of precipitation season, altitude, precipitation intensity, groundwater age and geology. Tucson Basin alluvium receives mountain-front recharge containing 50%–90% winter precipitation.