SURFACE WATER QUALITY AND BENTHIC SOIL STUDY OF LEH NULLAH

Abstract

Heavy metals, in any stream are a damaging factor for the aquatic biota which naturally ingest the organic matter present in that stream. Also the presence of heavy metals in any stream decreases its self purification capacity. Samples from Leh Nullah, Rawalpindi/Islamabad, one of the major carriers of combined industrial and municipal effluents, were collected from six different locations between Katarian and Chaklala from September 2012 to April 2013. The objective was to study the temporal and xiii spatial variations in the concentration of heavy metals in stream water as well as in the benthic soil of Leh Nullah. Metals selected for scrutiny were Cr, Ni, Cd, Mn, Zn, Cu, Fe, Pb, As and Hg, however preliminary results revealed that only Fe, Pb, Cd and Zn were available in both the surface water and the benthic zone. Standard Methods were adopted for sample collection, preservation and analysis. Benthic zone soil samples were also analyzed for the same metals by using the Flame Atomic Absorption Spectrometer (FAAS). Concentrations of some metals in the Leh Nullah waste water were found below or in some cases marginally exceeding Pakistan National Environmental Quality Standards (NEQS). In addition, correlation between metals concentration in the surface water, metals concentration in the benthic soil and other physicochemical parameters such as pH, total suspended solids and Electrical Conductivity etc. were investigated. Geoaccumulation indices of selected metals were also assessed for benthic soil of the nullah. Significant correlation was found between metal concentrations and Electrical Conductivity (EC) in the water environments. Metal concentrations were found to be more sensitive to temporal variations than spatial ones. Moreover, major sources of heavy metals in the nullah were identified. Mass loading of metallic pollutants running into Soan River was calculated and possible pretreatment system for industries discharging heavy metals in their effluent was proposed so that metal concentration in the nullah water could be reduced in future.