Variations of Groundwater Dynamics in Alluvial Aquifers with Reclaimed Water Restoring the Overlying River, Beijing, China

Abstract

Some of the rivers in northern China are dried, and reclaimed water (RW) is used to restore these degraded river ecosystems, during which the RW could recharge the aquifer by river bank infiltration. From 2007 to 2018, 2.78 × 108 m3 of RW has been replenished to the dried Chaobai River (Shunyi reach), Beijing, China, which is located on the edge of one depression cone in groundwater caused by groundwater over-pumping. The groundwater hydrodynamic variations and the flow path of the RW were identified by eight-year hydrological, hydrochemical, and stable isotopic data, together with multivariate statistical analysis. The RW infiltration drastically impacts the groundwater dynamics with a spatiotemporal variation. The 30-m depth groundwater levels at Perennial intake reach increased quickly around 3 m after 2007, which indicated that they were dominated by RW infiltration. Other 30-m depth groundwater levels were controlled by precipitation recharge from 2007 to 2011, showing significant seasonal variations. In 2012, with more RW transferred to the river, the hydrodynamic impact of the RW on 30-m depth aquifer expanded downstream. However, the 50-m and 80-m depth groundwater levels showed decreasing trend with seasonal variations, due to groundwater pumping. The 30-m depth aquifer was mainly recharged by RW, being evidenced by the enriched δ2H and δ18O. The depleted δ2H and δ18O of the 50-m and 80-m depth groundwater indicated that they were dominated by regional groundwater with meteoric origin. The heterogenous properties of the multi-layer alluvial aquifer offer the preferential flow path for RW transport in the aquifers. The proportion of the RW in the aquifers decreases with depth that was calculated by the chloride conservative mixing model. The increased lateral hydraulic gradient (0.43%) contributes to the RW transport in the 30-m depth aquifer. RW usage changed 30-m depth groundwater type from Ca·Mg-HCO3 to Na·Ca·Mg-HCO3·Cl. RW preferentially recharged the 50-m and 80-m depth aquifers by vertical leakage.

Numerical modeling of changes in groundwater storage and nitrate load in the unconfined aquifer near a river receiving reclaimed water

“…Besides RW, industrial pollution in the study area is also the source of Cl − inputting into groundwater. But the latter didn't affect the uncon ned groundwater surrounding the monitoring wells except G32 (He et al, 2021). The high Cl − concentrations in the uncon ned groundwater along the river are mainly affected by the RW in ltration.…”

“…Many studies have been carried out on characterizing variations in physical and chemical parameters of groundwater after RW recharge in the study area, with the most signi cant changes in the uncon ned aquifer. The groundwater table increased by ~3 m after RW supply to the Chaobai River from 2007 to 2018 (He et al, 2021). Column experimental results indicated that cation exchange took place between K + in the RW and Ca 2+ in the riverbed medium during RW in ltration (Liu et al, 2018).…”

“…The NO 3 -N contents near the Xiangyang sluice are relatively high due to the existing thick gravel layer, which is not conducive to remove NO 3 -N (Xiong, 2009). The north channel of the earth dam has been replenished only in May andThe RW in ltration has quickly replenished the uncon ned groundwater, resulting in the groundwater table around the river channel to rose rapidly by 3~4 m in the rst two years (2007-2009)(Zheng et al, 2015;He et al, 2021). However, increased recharge via the RW in ltration may not necessarily result in a corresponding increase in the groundwater storage volume(Maliva, 2020b).…”

“…The hydraulic travel time of RW in ltration into the 30 m depth was about 6.5 months(Li et al, 2019). The average proportion of the RW in the uncon ned aquifers is about 53% from 2007 to 2018(He et al, 2021). NO 3 -N in the RW was well attenuated with an attenuation rate of 99.6% during in ltration(Li et al, 2019).…”

Molecular Responses of Dissolved Organic Matter to Anthropogenic Groundwater Recharge: Characteristics, Transformations, and Sensitive Molecules

“…However, owing to excessive exploitation, groundwater resources were over-consumed, resulting in a sharp drop in groundwater levels in some regions. − To alleviate the groundwater crisis, managed aquifer recharge, an intentional measure of anthropogenic groundwater recharge (AGR), is usually applied along rivers, infiltration basins, or lakes, where clean surface water can easily infiltrate into highly permeable shallow aquifers, thereby increasing groundwater resources. , However, contaminants from the surface and vadose zone can be introduced into the aquifer through AGR, resulting in groundwater pollution . In addition, since there are differences in water quality between recharge surface water and natural groundwater, AGR can change water-rock interactions to degrade groundwater quality. , For example, many studies have reported that AGR can result in nitrate pollution. , Thus, the groundwater quality risks and regional applicability of AGR remain to be explored. , …”