Vertical distribution of al, cu, fe and zn in the soil salt marshes of the Sado estuary, Portugal

The vertical distribution of Al, Cu, Fe and Zn in the soil salt marsh of the river Sado estuary was studied. The results obtained by an acid digestion procedure, indicate that the mean values at the first sampling point (near the Atlantic Ocean and very close to a populous city) are lower when compared with those found at the other Stations (approximately 8.0 and 20.0 km upstream), where they are very similar. These findings are related to the different nature of the soil matrix (essentially sand at Station 1 and silt‐clay at Station 2 and 3), and the reduced availability of the sandy fraction to bind trace metals. A correlation analysis for all the metals in different soil cores indicate that the correlation values at Station 1 are, generally, not significant at a 0.05 significance level.