Hydrogeochemical and isotopic evidences of unique groundwater recharge patterns in the Mongolian Plateau

Abstract

In arid and semi‐arid areas, local precipitation is insufficient to fulfil the water requirements of the fragile local environment; hence, water is obtained from groundwater. The Hulun Lake Basin is located in the Mongolian Plateau, which is home to numerous lakes. In this study, we used remote sensing and isotopic tracing of naturally occurring isotopes (δ18O, δ2H, and 87Sr/86Sr) to identify and quantify the various water inputs into the basin. Based on the lake water balance calculation and precipitation and river inputs, a 5.4 × 108 m3/year groundwater recharge rate was determined. Groundwater and river water with depleted δ18O and δ2H were identified close to the faults near Hulun Lake. The groundwater recharge into Hulun Lake is aided by the faults. The δ18O and δ2H compositions of the groundwater, rivers, and lakes were consistent and more depleted than those of precipitation in the local mountains and plains. Therefore, the rivers and lakes are assumed to be primarily recharged by groundwater. The low strontium isotopes (87Sr/86Sr) in the samples suggest that the water was primarily recharged by basalt groundwater, which was identified under the Cenozoic strata instead of the sandstones, granites, and tuffs, which are the primary rocks in the study area. Moreover, the faults were widely distributed in the study area, allowing for groundwater upwelling from basalts. For the areas with volcanic rocks and faults, particularly in arid and semi‐arid areas, the basalt groundwater recharge through faults is critical for environmental sustainability. This research provides necessary information for future hydro‐ecosystem resource management in arid and semi‐arid areas.

Basalt and Dune: Critical Factors in Desert Water Resource Development

“…Artesian basins in the arid area of northern China have also received external rapid water recharge, and the water isotope signatures further suggest that the most likely recharge source is the leakage water from the Tibetan Plateau (TP). − The imbalance of the water budget in the Qiangtang Basin (internal flow region) on the TP was previously revealed to have been caused by the leakage of rivers and lakes out of the basin (approximately 54 ± 4 km 3 ) through underground passages . The leakage occurred along the southern Qiangtang rift valleys and basement fault zones, under which low-speed layers with high conductivity that extended 100 km deep underground were observed .…”

“…To determine whether there was a recharge of groundwater in the dunes stemming from heavy rainfall, a simulated rainfall infiltration test was conducted on the top of the mega-dune around the basin where borehole 5# was located (Figure 1i). Desert groundwater (27), drilling water (47), lakes (9), and rain (4) were collected from the BJD, as well as some groundwater samples from surrounding areas, including Gaurinai (10), Wintour gol (8), and Longshou Mts. (3), as shown in Figure 1a.…”

Analysis of the Interaction between Lake and Groundwater Based on Water–Salt Balance Method and Stable Isotopic Characteristics

“…Based on the composition characteristics of D and 18 O isotopes in different water bodies, the source, migration, mixing, and other hydrologic processes can be analyzed [9]. Natural isotope tracing can also be used to identify and quantify various water catchment input pathways, including sources of various water types, based on calculations of lacustrine water balance, precipitation, and river inputs [10,11]. Stable isotopes are increasingly used as tracers in environmental studies.…”