Abstract

Land use land cover change is an important contributor to the trace element content of an aquatic system. Therefore, the study of the land use pattern is important in understanding the heavy metal pollution of the sediments of the aquatic system in an area. The aim of the study is to apply LULC pattern to understanding the heavy metal pollution of the stream sediments of River Ala and its tributaries.  Geologically, the area is underlain by rocks of the Precambrian Basement complex of Nigeria. The basement rocks are: granite gneiss, granite, quartzite and charnockite. High resolution Landsat imageries were utilized in determining the LULC pattern for the years 2010 to 2016. The Landsat were processed and classified using maximum likelihood algorithm for the LULC classes. Twenty stream sediment samples were systematically collected from the channels of River Ala and its tributaries. The pollution status of the stream sediment were assessed by two pollution indices viz: Enrichment factor (EF) and geo-accumulation index (Igeo). The heavy metal concentrations were also compared with United States Environmental Protection Agency (USEPA) stream sediment quality (SQG) values as well as with other similar studies in Nigeria. Results of the geochemical analysis revealed that the mean concentration of the analyzed elements are Pb (0.47 mgkg^-1), Fe (22.9 %), Co (0.395 mgkg^-1), Cd (0.014 mgkg^-1), Mn (5.109 mgkg^-1), Zn (1.233 mgkg^-1), Cu (0.549 mgkg^-1), Cr (0.28 mgkg^-1) and Ni (0.571 mgkg^-1). The mean concentrations of all the analyzed elements are lower than both the average world shale and USEPA SQG values except for Fe. Furthermore, both the EF and Igeo indices revealed that the mean concentrations of the elements fall within background concentrations. The LULC patterns also revealed the most dominant LULC trends in 2010 was forestland which covered 28.78 km². However, the area occupied by forest had been reduced in 2016. In conclusion, the LULC changes has not had any significant effect on the heavy metal contents of the stream sediment as they are unpolluted with respect to the analyzed elements.

Key Words: Land use, Heavy metals, Pollution, Landsat 8, NDVI