Historical industrial activities have resulted in soil
contamination
at sites globally. Many of these sites are located along coastlines,
making them vulnerable to hydrologic and biogeochemical alterations
due to climate change and sea-level rise. However, the impact of hydrologic
dynamics on contaminant mobility in tidal environments has not been
well studied. Here, we collected data from pressure transducers in
wells, multi-level redox sensors, and porewater samplers at an As-contaminated
site adjacent to a freshwater tidal channel. Results indicate that
sharp redox gradients exist and that redox conditions vary on tidal
to seasonal timescales due to sub-daily water level fluctuations in
the channel and seasonal groundwater–surface water interactions.
The As and Fe2+ concentrations decreased during seasonal
periods of net discharge to the channel. The seasonal changes were
greater than tidal variations in both Eh and As concentrations, indicating
that impacts of the seasonal mechanism are stronger than those of
sub-daily water table fluctuations. A conceptual model describing
tidal and seasonal hydro-biogeochemical coupling is presented. These
findings have broad implications for understanding the impacts of
sea-level rise on the mobility of natural and anthropogenic coastal
solutes.