Spatial distribution of dissolved cadmium in the Jiulong river-estuary system: Relevance of anthropogenic perturbation

The estuary was characterized with decreased levels of dissolved Cd in the highly turbid upper part (salinity: <5; dissolved Cd: <0.1 nmol L−1; Total Suspended Matter: 100-300 mg/L), and a mid-salinity maximum of dissolved Cd in the middle part, which were higher in Summer high river discharge period (0.40-0.54 nmol L−1) than in Fall low river discharge period (0.25-0.35 nmol L−1). Dissolved Cd generally decreased outwards in the lower estuary and nearby coastal waters as mixed with the low Cd-content seawater offshore (dissolved Cd= −0.025*Salinity+0.96, r=0.60, p<0.05). In particular, an enhancement of dissolved Cd (by ~0.2 nmol L−1) was observed in the lower estuary and estuarine plume zone as a result of sewage discharges nearby and/or Cd-enriched submarine groundwater discharges. Summarily, our exemplary study provides clear evidence that China's natural waters are currently subject to local perturbation due to the recently increasing anthropogenic activities.