Contamination Levels of Potentially Toxic Elements and Foraminiferal Distribution Patterns in Lagos Lagoon: A Correlation Analysis

Abstract

The ecological response of benthic foraminifera to bioavailable Potentially Toxic Elements (PTEs) was evaluated in Lagos Lagoon (Nigeria). We sampled and analyzed PTEs across Lagos Lagoon with the aim to investigate the extent of contaminated sediments, to document their distribution, and to explore the relationship between PTE concentration and the spatial distribution, composition, abundance, and species richness of benthic foraminifera biotas. PTE’s recordings showed a wide range reflecting a diffuse contamination, where Contamination and Enrichment Factor suggest low to extremely polluted sediments. Findings of a previous survey of the benthic foraminifera inhabiting Lagos Lagoon revealed diverse assemblages of benthic taxa, species-specific distribution patterns, gradients of species richness and abundance, and a disjunct distribution of agglutinated and hyaline-perforate/porcelaneous taxa along a pronounced salinity gradient. Correlation matrix analysis shows that except for Selenium, all PTE total concentrations positively correlate with mud and Total Organic Carbon (TOC) and two of the most abundant agglutinated taxa, Ammotium salsum, and Trochammina sp. 1. Moreover, both species display significant positive correlations with CrF4-CoF2-F3-F4-total-CuF4-total-NiF3-F4-total-AlF4-total-FeF3-F4-total-ZnF3-F4-total. On the other hand, both foraminifers correlate negatively with PbF4-SeF3-Setotal. The overall significant positive correlation of these PTEs suggests that they behave as micronutrients when complexed with organic matter. No significant positive correlation with none of the PTEs in any fraction was found for neither species richness nor for the most abundant hyaline perforate species (Ammonia aoteana). Some PTE fractions were found to correlate either positively or negatively with individual species, suggesting that they function as either micronutrients and/or stressors. The resulting Contamination Factor of the PTE total concentrations shows that only a few sample sites can be classified as “moderately” polluted for chromium, zinc, and copper and that all sampled sites are classified as “highly polluted” for selenium. The highest concentrations for Cr, Cu, Ni, and Zn were found towards the industrialized western part, an area that is characterized by moderate to high diversity but low abundances.