Decreased mobility of heavy metals in Haihe River sediments: The possible role of tide gate

•It is the first discussion of impact of tide gates on heavy metal mobility.•Seawater increases Cd, Zn, and Cu mobility in the Haihe River sediments.•Low salinity caused by constructing tide gates is responsible for restricting Cd and Cu mobility from river to Bohai Bay.•Cd and Zn were not, but Cu and Pb were, affected by the increase of salinity and ionic strength in acidification processes.

The impact of tide gate on heavy metal mobility in Haihe River sediments was studied in a laboratory leaching simulation experiment. The results indicated that seawater promoted a higher release of Cd and Cu than deionized water and river water, and river water extracts high amounts of Zn. This release may be a result of both the formation of chloride complexes and ion exchange. However, the salinity induced by seawater did not significantly enhance the mobility of Pb. This implied that the mobility of Cd and Cu can be reduced by the insufficiency of the salinity when constructing tide gates in the brackish zones of an estuary. In the acidification processes, Cd and Zn were not, but Cu and Pb were, affected by an increase of salinity and ionic strength.