Sedimentation rates and heavy metal concentrations in the tidal flats of North Vietnam

Tidal flats in the north of Vietnam from Quang Ninh to Ninh Binh provinces are impacted by land-ocean interaction processes and human activity. The flats are experiencing erosion in some parts and accretion in others, as well as the accumulation of pollutants. This study examines core samples extracted from the region to systematically quantify changes in sedimentary processes and the accumulation of heavy metals. A total of 11 sediment cores were collected from the tidal flats and analyzed for ²¹⁰Pb, ²²⁶Ra, grain size, and heavy metal content. Sedimentation rates, according to the constant rate supply model (CRS), ranged from 0.04 to 15.00 cm/year. There was evidence of spikes in sedimentation rates for brief episodes; however, the average ranged from 0.14 to 3.04 cm/year. In the north of the study area, the sedimentation rate was low, then increased to the center and the south. The concentrations of heavy metals (Cu, Zn, Pb, As, and Cd) in the sediments were found to increase with time. Additionally, an increasing trend was observed from the north to the south of the study area. The concentrations of heavy metals Cu, Pb, and As in the sediments from the center to the south exceeded the ISQG levels.