INTERNATIONAL JOURNAL OF NATURAL AND APPLIED SCIENCES (IJNAS), VOL. 17, NOS.1& 2 (2024); P. 52 – 59, 1TABLE, 8FIGS. Spatial variation of heavy metals in coastal waters of the Cross River Estuary, Southeast Nigeria V. I. Emeka 1,4 , C. N. Emeka 2 , E. Agi-Odey 1 , S. U. Eteng 3 , A. E. Itam 2 INTRODUCTION A significant number of the world’s population and many industries are located along the coast, making the coastal ecosystem highly vulnerable to pollution. Coastal pollution can be derived from water and land-based sources. Water based sources include navigation, dredging and land reclamation, offshore crude oil and natural gas exploration while land-based sources may include oil terminals, gas plants, municipal and industrial development, tourism, beach creation, agricultural and defense activities (Pati and Patra, 2012). Major pollutants generated from these sources are heavy metals, pesticides, toxic chemicals, garbage, oil sewage, radioactive wastes etc. These pollutants have harmful effects on the coastal eco- system causing harm to living resources, human health as well as affecting water quality. There is a growing need for environmental monitoring in view of the anthropogenic impacts of pollution on coastal and marine systems. The distribution of heavy metals in rivers and estuaries have been widely studied (Eddy, 2004; Ip et al., 2007; Li et al., 2007; Uwah et al., 2013; Jia et al., 2021; Agi-Odey et al., 2025; Emeka et al., 2025). The distribution of heavy metals within the Cross River estuary system had been investigated (Ntekim et al. 1993; Essien et al., 2009; Dan et al., 2022). Ntekim et al. (1993) related elevated metal concentrations around industrial establishments to industrial effluents and metal leaching from refuse and municipal solid wastes. Essien et al. (2009) related high enrichment of V, Zn and Cr in Cross River estuary sediments to industrial effluent discharge. In this study, the concentration of six heavy metals in water samples obtained from the Cross River estuary is examined and compared with established reference values. Spatial distribution maps and along channel profiles of heavy metal levels in water within the estuary are presented. MATERIALS AND METHODS Twenty bottom water samples were collected from the Cross River estuary using a Nansen bottom water sampler (FIG. 1) at Geo- referenced sampling stations. Bottom water samples were collected immediately above the sediment-water interface using a Nansen water bottle with an in-built thermometer. Samples were immediately transferred into pre-labelled plastic bottles and kept cool. In the laboratory, water samples were digested because of the presence of fine sediments in the water. 100 ml of the water sample was digested with 0.5 ml of dilute nitric acid and heated until the volume of the solution reduced to 20 ml. The solution was allowed to cool, and subsequently filtered into volumetric flask. Purified water was added to the volumetric flask until a volume of 100 ml was attained. The solution was transferred into a sample bottle and covered for heavy metal analysis. Heavy metals in water were analyzed using Atomic Absorption Spectrometer (Unicam Model, SOLAAR 969). For quality control, the reagent blank and regular samples were measured and monitored under optimized conditions. Materials used for the analysis were thoroughly cleaned with 5% nitric acid, non-ionic soap and purified water following standard procedures recommended by APHA-AWWA-WEF (1998). All water samples were analyzed in duplicate, and the average values were calculated. Instruments were calibrated according to manufacturer’s recommendation. The descriptive statistics (minimum, maximum and mean concentrations) of heavy metals were calculated using Microsoft excel. Spatial distribution maps of heavy metals within the estuary channel were plotted using ArcGIS. ABSTRACT The spatial variation of heavy metals (Pb, Zn, Cu, Cd, Ni, Fe) in bottom waters of the Cross River estuary were examined to understand the effect of anthropogenic pressures on the estuary eco-system. The average concentrations of heavy metals in water followed the order of Fe>Zn>Ni>Cu> Cd>Pb.The concentrations of Pb, Zn, Cu, Cd, Ni, Fe are low and less likely to have negative effects on aquatic biota. Along channel profile of Cu and Fe demonstrated an increasing distance downstream while Pb and Cd showed an increasing upstream trend. A near uniform distribution was observed for Zn and Ni. Growing industrialization along the estuary vicinity may lead to enhanced metal concentrations in the water thereby impacting negatively on the eco-system. 52 *Corresponding author. Email: emekavictoria@unical.edu.ng 1 Department of Physical Oceanography, University of Calabar, Calabar 2 Department of Geology, University of Calabar, Calabar 3 Department of Mariculture and Marine Fisheries Resources, University of Calabar © 2024 International Journal of Natural and Applied Sciences (IJNAS). All rights reserved.