Evaluation of the in situ, time-integrated DGT technique by monitoring changes in heavy metal concentrations in estuarine waters

Various natural and anthropogenic processes influence heavy metal concentrations within estuaries. In situ, time-integrated DGT measurements made over concurrent tidal phases found significantly higher concentrations of Cu (probability p = 0.017), Zn ( p = 0.003) and Ni ( p = 0.003) during the flood phase, because the incoming tide passes several point sources. DGT-reactive Cu concentrations significantly decreased with increased tidal-flushing and vice versa within a marina (correlation r = −0.788, p = 0.02). DGT measurements also recorded significant increases in Cu (4 out of 4 sites, p < 0.001) and Zn (3 out of 4 sites, p ≤ 0.015) after a 24 mm rainfall event. Finally, DGT-reactive Cu increased significantly ( p < 0.001) during peak boating times, due to increased numbers of Cu-antifouled boats. This study demonstrates that, with judicious selection of deployment times, DGT measurements enable changes in heavy metal concentrations to be related to various cycles and events within estuaries. Demonstration of the usefulness of DGT as a monitoring tool for heavy metals in dynamic estuaries.