Impacts of hydrodynamics and pollutants on foraminiferal fauna distribution in the Santos Estuary (SE Brazil)

Abstract

Superficial sediment samples of the Santos Estuary (SE Brazil) were analyzed for benthic foraminifera (dead fauna), aliphatic hydrocarbons (AHs), polycyclic aromatic hydrocarbons (PAHs), total organic carbon, total nitrogen, and trace metals. The foraminiferal fauna results were related to estuarine hydrodynamics and pollution parameters. The residual circulation of the estuary drives the transport of particles into the Santos channel. Thereby, tidal currents promote an advective transport of the species, including Pararotalia cananeiaensis, Discorbis sp. and Pseudononion japonicum from the Santos Bay to the upper estuary. Additionally, the dredging of the Santos channel leads to the suspension of sediments, favoring the post mortem transport. Enrichment factor and pollution load index for trace metals evidenced a contamination (mainly by Zn) in the Piacaguera River, and AHs and PAHs analyses revealed a widespread presence of petroleum-related residues and petroleum combustion products in the region of the upper estuary, with values of unresolved complex mixtures ranging from 95.2 to 402.3 µg g−1 and total PAHs concentrations from 1176 to 32,153.3 ng g−1. Although, the data obtained are from dead fauna, the impact of anthropogenic activities is also pointed by the benthic foraminifera, revealing that the pollutants impact are acting for some years in the upper estuary. The ecological indices show lowest values of richness and density, and low values of diversity for benthic foraminifera mainly in the upper estuary. Moreover, high values of dominance were observed due to the high abundance of the opportunistic species Ammonia sp1.