Seasonal dynamics of physicochemical properties and heavy metal burdens in Mangrove sediments and surface water of the brackish Qua Iboe Estuary, Nigeria

Abstract

The physicochemical properties and concentrations of heavy metals were determined in surface water, intertidal mudflats (epipellic) and benthic sediments obtained from the mangrove swamp ecosystem of the Qua Iboe Estuary, Nigeria. The monthly concentrations of the nutritive salts revealed that the sediments are halomorphic. Heavy metal concentrations in benthic sediments and surface water were generally lower than the values recorded for the intertidal mudflats. The mean concentrations of heavy metals obtained from estuarine surface water and intertidal and subtidal sediments were highly variable and seasonally dependent. The levels of heavy metals in the intertidal sediments were comparatively higher in the wet than the dry season. The range of concentration over the months increased by 1.3% (Cr), 1.6% (Pb), 6.0% (V), 7.5% (Ni), 10.5% (Fe), 12.0% (Zn), and 15.0% (Cu). Cr, Pb, Zn, and V concentrations in intertidal and subtidal sediments were below the Sediment Quality Guidelines (SQGs). However, Cu and Ni concentrations exceeded these effect levels, indicating potential ecological effects on local benthic, pelagic and benthopelagic communities of the estuary. Linear relationships and coefficients for concentrations of heavy metals in surface water, intertidal and subtidal sediments during wet and dry seasons were calculated. Moreover, the results indicated a common anthropogenic pollution origin for the heavy metals.