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

Abstract

This study first examined the spatial distribution of dissolved cadmium (Cd) along with other hydrochemical parameters in a large subtropical river estuary system (the Jiulong River–Estuary, China) between 2008 and 2010, aiming to evaluate the impacts of the recently increasing anthropogenic perturbation in natural waters. The results showed that dissolved Cd was variable in the watershed with sporadically high concentrations (>0.6nmolL−1). The significantly positive correlation of dissolved Cd with phosphate in the watershed (May 2008: dissolved Cd=0.22*P+0.0062, r=0.64, p<0.05) indicated that dissolved Cd levels have been elevated along with P by the increasing agricultural discharges and/or sewage effluents.The estuary was characterized with decreased levels of dissolved Cd in the highly turbid upper part (salinity: <5; dissolved Cd: <0.1nmolL−1; Total Suspended Matter: 100–300mg/L), and a mid-salinity maximum of dissolved Cd in the middle part, which were higher in Summer high river discharge period (0.40-0.54nmolL−1) than in Fall low river discharge period (0.25–0.35nmolL−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 ~0.2nmolL−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.