Sources and factors controlling the distribution of metals in mudflat sedimentary environment, Ulhas estuary, Mumbai

Abstract

Vertical variations for various physico-chemical parameters such as pH, TOC, TP, TN, sediment components and metals such as Fe, Mn, Cu, Pb, Co, Ni, Zn, Cr, V and Al of a sediment core collected from a mudflat bordering the Ulhas estuary, near Retibandar in Mumbai, was analysed at every 2 cm interval. Based on the distribution pattern of sediment, the core is divided into three parts. The upper and the lower portions are found to be dominated by clay and silt fractions while in the middle portion, sand is found to be in higher percentage. The varying thickness and the variations in sediment size of the three parts suggest that sedimentation rate and processes are not the same along the length of the core. The hydrodynamic conditions of the depositional environment of the mudflat was assessed using the triangular diagram proposed by Pejrup (1988), which indicates that the sediment deposition took place under relatively calmer conditions. Higher TOC, TP and TN in the upper portion of the core compared to middle and lower portions indicate increasing impact of human activities on the estuary in recent years. The results of metal concentration indicate a significant upward enrichment of Cu and Pb, with the highest concentrations in the uppermost 0-12 cm layer, supporting the effect of increasing anthropogenic influence in recent years. Correlation coefficients, dendogram hierarchical cluster and factor analysis has been applied to the data, to assess the diverse sources and mechanisms influencing the metal distribution in the sedimentary column of the estuary.