Bioaccumulation of heavy metals by the flora and benthic macrofauna of the Bouregreg estuary wetland

Laboratory of Civil Engineering and Environment (LGCE), Higher School of Technology, SALE, Mohammed V University in Rabat.

e-mail: m_khamar@yahoo.fr

Abstract

Estuarine systems account for a high proportion of wetlands in Morocco due to the development of the river system. These estuarine and coastal Moroccan environments are as rich in fauna and flora as their European equivalents and present much originality. However, these coastal areas are generally highly urbanized and industrialized, and therefore subject to domestic and industrial discharges. The Bouregreg Estuary represents a good example of this situation, in view of this pollution (organic, chemical and biological) and the absence of fresh water supply upstream of the estuary after the dam was built, is increasingly unable of restoring the equilibrium of this ecosystem. This tide can instead ensure the polluting discharge downstream or upstream. Metallic contamination affects the different compartments of the estuarine ecosystem (sediment, water) and benthic species (fauna and flora). The objective of this study is to assess the accumulation and bioaccumulation of five heavy metals (Cu, Fe, Zn, Cr and Pb) at the sediment level of two dominant plant species (Artiplex portulacoides and Sarcocornia fructicosa) and three species of benthic macrofauna (Scrobicularia plana, Venerupis decussata and Hediste diversicolor) from the wetland of this estuary. This work will enable us to clearly understand the nutritional relationships between plant, animal, water and sediment species. The results of the analysis revealed that bioaccumulation varies from one species to another and from one metal to another. Thus, the levels of Lead and Chromium at Sarcocornia fructicosa are higher than those found at Artiplex portulacoides. Nevertheless, the latter accumulates better the other metals: Cu, Zn and Fe. While, the macrofauna shows a fairly large variation depending on the life style and sensitivity of species. Thus, Hediste diversicolor showed high levels of the various metals analyzed compared to Scrobicularia plana and Venerupis decussata.