Abstract
Evaluation of levels and spatial characteristics of dissolved nutrients and heavy metals in the river bed sediment within a basin are critical to understanding the extent of land-use impact on the river systems. Surface river bed sediments across eight rivers in the Ogun-Osun River Basin in Nigeria were collected and analyzed for Total N, , Total P, Total organic carbon, Cd, Hg, Pb, Zn, Cu, Fe, Mn and Cr. Pollution Load Index (PLI), Accumulation Factor (AF) and Hierarchical Clustering Analysis (HCA) were used to identify the impact of the pollutants and also define the spatial variation across the basin. The pollution load indices of heavy metals were moderately high ranging from 0.41 - 0.60, while AFs were 0.43 - 2.00 and 0.61 - 1.29 for heavy metals and nutrients from upstream to downstream in the rivers systems, respectively. The HCA identified 7 distinct spatial patterns describing pollutant input from the land-use in the basin. Although, heavy metals contents were low in relation to the background values, and the potential for redistribution and secondary pollution was high hence, there was need to impose checks on the activities across agricultural, urban and grazing land-uses that had impact negatively on the river systems in the basin.
Highlights
Changes in land-use patterns are directly altering the functioning of ecosystems worldwide [1]
Soils may be contaminated by heavy metals such as Zn, Cd, Pb and Cu due to sludge from these land-uses [3,4] while nutrient from animal manure and other related agricultural activities contribute to the quality of sediments washed off the land surfaces [5]
Physical contribution of sediment to pollution includes increase in turbidity, sedimentation leading to loss of downstream reservoir capacity, destruction of coral reefs, loss of spawning grounds for certain fish while chemical pollution of sediment includes redistribution of adsorbed metals and nutrients as well as hydrophobic organic metals in the river systems [7]
Summary
Changes in land-use patterns are directly altering the functioning of ecosystems worldwide [1]. The changes, have significant impact on the nutrient concentrations, and concomitantly influence the quality of river water and water resources. These impacts can be negative and positive [2]. Soils may be contaminated by heavy metals such as Zn, Cd, Pb and Cu due to sludge from these land-uses [3,4] while nutrient from animal manure and other related agricultural activities contribute to the quality of sediments washed off the land surfaces [5]. Earlier observation by [6] shows that land-use has impact on water quality through changes in sediment and nutrient loads, salts, metals and agrochemicals, influx of pathogens and change in the temperature regime. Physical contribution of sediment to pollution includes increase in turbidity, sedimentation leading to loss of downstream reservoir capacity, destruction of coral reefs, loss of spawning grounds for certain fish while chemical pollution of sediment includes redistribution of adsorbed metals and nutrients as well as hydrophobic organic metals in the river systems [7]
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