Retention and vertical distribution of heavy metals in mangrove sediments of the protected area swamp of Mallorquin, Colombian Caribbean

Abstract

The accumulation, retention and vertical distribution of six heavy metals (Fe, Cu, Zn, Ni, Pb and Hg) in two contrasting sedimentary environments of the Swamp of Mallorquín Colombian Caribbean, one with mangrove plants (M) and another without plant covering (SM), were analyzed in order to establish the incidence that such plants may have on the distribution of those metals in their adjacent sediments. Total metal concentrations (μg g−1, Fe in %) in the sediment profile for the different sampling areas was: Fe (M: 3.4 ± 0.6; SM: 3.0 ± 1.2), Zn (M: 64.9 ± 3.7; SM: 60.7 ± 13.9), Cu (M: 42.6 ± 6.2; SM: 33.3 ± 8.9), Ni (M: 28.5 ± 3.6; SM: 24.3 ± 6.9), Pb (M: 3.5 ± 0.4; SM: 2.9 ± 0.7), Hg (M: 0.14 ± 0.03; SM: 0.11 ± 0.04). Correlation analysis suggest that distribution of Cu, Zn and Ni in the M zone would be dominated by the formation of iron sulfides and oxyhydroxides in sediments, while the organic matter would be influencing the distribution of Pb and Hg. On the other hand, SM showed correlation for most of the variables, making it difficult to establish the sedimentary phases influencing metal distribution, due to the codependency between the different diagenetic processes. Cu, Ni and Hg concentrations exceed prescribed sediment quality guidelines (SQGs) indicating potential adverse effect on biota. The results corroborate the suitability of mangrove sediments as metal sinks and the importance of mangrove ecosystem restoration and conservation in the Swamp of Mallorquín.