Preliminary geochemical evidence of groundwater contamination in coral islands of Xi-Sha, South China Sea

Geochemical data on dissolved major, minor and trace constituents in groundwater samples from Xi-Sha coral islands (Paratas Islands) reveal the main processes responsible for their geochemical evolution. Multivariate statistical analysis indicates four sources of solutes: (1) seawater intrusion due to limited groundwater recharge; (2) leaching of heavy metals from imported granite soil; (3) leaching of toxic elements such as As due to guano-soil erosion and historical phosphatic guano mining; and (4) local and regional contamination characterized by high loadings of Cu, Ag and Hg. Although process 1 dominates the geochemical characteristics of the groundwater, process 4 indicates the significant role of anthropogenic impact by local (e.g., Cu) and regional (e.g., Hg) sources. Such contamination in groundwater will potentially impose adverse effects on the fragile ecosystem of the coral islands. It is necessary to monitor microorganisms associated with human feces in the nearshore water column as well as nutrient levels in coastal waters in order to further assess the impact of human activities on the ecosystem of these islands.