PMC

Schematic diagram of the study area and sampling location. (A) The black rectangle in the lower part of the plot indicates the location of Beihai City. (B) The southern coastal area of Beihai City and the location of the three monitoring sites involved in this study, the location of seawater (SW) collected from the Beibu Gulf and the location of groundwater discharge site (ZLV-CI) from the Zhuoluo beach. (C) The location of the three monitoring sites (G1, G2 and G3) illustrated in (B).

Variation of the Cl⁻ and SO₄²⁻ concentrations and tide level in different underground aquifers of the three monitoring sites. Blue bars in the plot represent the Cl⁻ concentration and the orange bars represent the SO₄²⁻ concentration. The black solid line above each graph indicates the tidal level of the Beihai Port of Beihai City. The green arrow indicates when microbial sampling was performed. The left y-axis represents the concentrations of Cl⁻ and SO₄²⁻, the right y-axis represents the tidal level, and the x-axis represents time. The tidal data in the figure was obtained from the China oceanic information network (http://www.nmdis.org.cn). G1, G2 and G3 indicate monitoring site. UC, unconfined aquifer; CI, confined aquifer I; CII, confined aquifer II.

Temporal and spatial variations of ambient VOCs in Beihai.