Assessment of bacterial contamination of Mytilus galloprovincialis, Cardium edule and water quality in Bouregreg estuary (Morocco, Atlantic Ocean)

Abstract

AbstractThe Moroccan marine environment is threatened by several types of pollution. Indeed, the littoral zone knew an urban, industrial and agricultural development without precedent; moreover, coastal waters have served as discharges for almost all activities linked to this development. The aim of this study is to determine the biological, physicochemical and bacteriological quality of waters and bivalve shells in the Bouregreg estuary. Sampling was carried out at four stations (S1, S2, S3 and S4) located downstream to upstream of the estuary. Thus, we analysed the degree of contamination by total coliform, faecal coliform and faecal streptococci in the water and in the flesh of Mytilus galloprovincialis and Cardium edule and determined the physicochemical parameters of seawater samples, which included temperature, dissolved oxygen, electrical conductivity, pH, total hardness, biological oxygen demand for five days (BOD5), complete alkalimetric title, NO2−, NO3−, NH4+, Fe2+, K+, SO42−, HCO3−, Cl−, Na+, Mg2+and Ca2+. The S1, S2 and S3 stations were shown to have more or less homogeneous physicochemical properties. The evolution of faecal bacteriological contamination of water and bivalves has shown that faecal pollution of the environment varies according to the stations and according to the seasons. The degree of contamination is high in autumn and winter and comes from wastewater and runoff discharges which, by leaching agricultural land, bring a large number of microorganisms to the environment. This influences the quality of the aquatic fauna, in particular, the infestation of lamellibranch molluscs such as in Mytilus galloprovincialis and Cardium edule. We have noted that the contamination of mussels by these types of microorganisms follows, more or less, that of the biotope. It should also be noted that in summer, the faecal contamination of the environment increases with the arrival of summer visitors.