Nitrogen behavior during artificial groundwater recharge through ponds: A case study in Xiong'an New Area

The Xiong'an New Area (XA) was established as a development hub in China. Excessive exploitation of groundwater has caused a series of environmental and geological problems, restricting further development of XA. The widely distributed ponds in this area have been targeted as convenient and efficient sites of artificial groundwater recharge. However, nitrogen accumulation in the shallow vadose zone associated with agricultural activities may pose environmental risks to groundwater during the recharge and infiltration process. Therefore, this study investigated the effects, transfer, and transformation of nitrogen during artificial groundwater recharge. The aeration zone is thick and the medium comprises fine particles, with total nitrogen and nitrate accumulation mainly in the shallow aeration zone. In indoor experiments, the nitrate removal rate reached 83.5% when organic carbon in the source water was increased by 10 mg/L. For Baigou diversion river water(BW) with slightly higher (14.46 mg/L) and lower (5.04 mg/L) nitrate contents, the nitrate content decreased by 26.0% (10.70 mg/L) and 26.8% (3.69 mg/L), respectively, after 150 days. When the water head was increased by 20 cm to increase the recharge rate, the time required for nitrate and ammonium to reach the maximum and equilibrium concentration was reduced by 50%. These findings indicate that nitrogen concentration in the source water, aeration zone media, and groundwater should be considered in pond replenishment. It is also necessary to control the concentration of organic carbon and the rate of recharge, which would provide guidance for other similar projects.