Reactive Transport of NH 4 + in the Hyporheic Zone from the Ground Water to the Surface Water.

Nowadays, ammonia nitrogen (NH₄⁺) pollution gets more and more attention in drinking water sources. This study investigated the main behavior of biogeochemical NH₄⁺ from groundwater to surface water in a hyporheic zone (HZ) sediment from a reservoir. The experiments were conducted using synthetic groundwater to investigate ammonium transformation. The results indicated that ammonium concentration decreased, apparently resulting from the influence of microbial oxidation and ion exchange with Ca²⁺, Mg²⁺, K⁺, and Na⁺. However, all the ammonium in the sediment was oxidized, then the adsorbed NH₄⁺ became bioavailable by being released back when NH₄⁺ concentration decreased in the aqueous phase. The results showed NH₄⁺ behavior in a HZ where the aerobic and anaerobic environments frequently exchange, with different hydrological conditions controlled by a strong coupling between microbial activities, geochemistry, hydrology, and ion exchange. [ABSTRACT FROM AUTHOR]