Groundwater Selenium Level and its Enrichment Dynamics in Seawater Intrusion Area along the Northern Coastal Zones of Shandong Province, China

Abstract

The variation of groundwater properties caused by seawater intrusion, such as OH–, TDS, $${\\text{SO}}_{4}^{{2 - }},$$ can potentially affect the groundwater Se levels. But there are no researches detailing the mechanism of groundwater selenium characteristics in seawater intrusion areas along coastal zones. Buzhuang town has been selected for study and groundwater is sampled to discuss the behavior of groundwater selenium with the intrusion of seawater. The groundwater Se levels range from 1.43 to 15.60 µg/L, with an average of 6.23 µg/L. All are within the limit of 10 µg/L except Wanglu village, but the local groundwater Se levels in 8 villages exceed the chronic criterion of 5 µg/L, and the Se levels in local groundwater are higher than those in the supplied water which has a non-seawater source. The groundwater Se levels have been shown to be elevated by seawater intrusion. The groundwater Se levels are positively correlated with Cl–, TDS, Br–, Na+, Mg2+, $${\\text{SO}}_{4}^{{2 - }},$$ Ca2+ and Fe and negatively correlated with pH. Ion competition effects and the Na-Mg-sulfate minerals play an important role in the adsorption and desorption for $${\\text{SeO}}_{3}^{{2 - }}$$ and $${\\text{SeO}}_{4}^{{2 - }}$$, which are the important dynamic species for groundwater selenium enrichment. However, Ca and Fe ions have less contribution to groundwater Se variation because of the lower affinity for $${\\text{SeO}}_{3}^{{2 - }}$$ and $${\\text{SeO}}_{4}^{{2 - }}$$ and lesser content in groundwater of seawater intrusion areas.