Mapping spatial - temporal variations of phosphate, sulphate, nitrate and escherichia coli (e.Coli) pollution in Ngong river, Kenya

Abstract

The spatial and temporal variations of phosphates, nitrates, sulphates and E. coli in water and sediment from Motoine-Ngong River system were investigated in this study. 13 sampling sites were selected between Motoine Dam (elevation 1,842 m) and Kangundo Road (elevation 1,526 m). Grab sampling method was used to collect water and sediments from each site between January - February 2012 (Dry season) and May- June 2012 (Wet season). Arc GIS software version 10.1 was used to generate colour-coded projection maps to establish spatial and temporal distribution of contaminants in selected sites. Statistical analysis of spatial and temporal changes in water quality was conducted at 5% confidence level ( p≤0.05) by Analysis of Variance (ANOVA), Pearson correlation coefficient (r) and Regression analysis using QI Microsoft excel 2010. Phosphate concentration in water ranged from 1.59±0.01 mg/L to 11.34±0.01 mg/L, with a mean concentration of 5.50 mg/L for the dry season and a range of 0.96±0.27 mg/L to 9.96±0.54 mg/L, with a mean of 4.95 mg/L for the wet season. Sulphates levels ranged from below detectable limit to 1.15±0.02 mg/L with a mean of 0.54 mg/L in the dry season, and 0.42±0.12 mg/L to 0.79±0.02 mg/L, with a mean of 0.67 mg/L in the wet season. The concentration of nitrates ranged from below detectable limit to 13.74±0.08 mg/L, with a mean of 6.14 mg/L in the dry season and from below detectable limit to 26.65±1.36 mg/L, with a mean of 16.92 mg/L during the wet season. E. coli levels ranged between 140 and 1,800 MPN/100 mL, with a mean of 1,661 MPN/100 mL in the dry season and between 94 and 1,800 MPN/100 mL, with a mean of 1,525 MPN/100 mL during the wet season. For sediments, phosphate levels ranged from 1,985±2 mg/Kg to 8,805±150 mg/Kg, with a mean of 4,602 mg/Kg during the dry season and from 1,866±162 mg/Kg to 9,157±540 mg/Kg, with a mean of 4,767 mg/kg in the wet season. Sulphates ranged from 1,045±104 mg/Kg to 21,033±1,197 mg/Kg, with a mean of 10,739 mg/Kg for the dry season and 18,120±364 mg/Kg to 32,373±4,283 mg/Kg, with a mean of 24,407 mg/Kg in the wet season. Nitrates ranged from below detectable limit to 4,178±20 mg/Kg, with a mean of 1,327 mg/Kg in the dry season and from below detectable limit to 3,524±39 mg/Kg, with a mean of 1,136 mg/Kg for the wet season. Statistical data analysis revealed a positive temporal correlations for different parameters in water at r (PO43-) = 0.71, r (NO3-) = 0.16, r (SO42-) = 0.25 and sediments at r (PO43-) = 0.19, r (NO3-) = 0.32, r (SO42-) = 0.21. Weak correlations were observed for both water and sediments. Sulphate levels in water were within the World Health Organization’s recommended standards (0 -500) mg/L for drinking water. Phosphates and Nitrates level were higher at some sampling sites than the recommended WHO standards of phosphates (0-5) mg/L and Nitrates (0-10) mg/L, respectively. There was no significant difference in Escherichia coli (E. coli) levels in both seasons. The results suggest random sources of pollution in Ngong-Motoine River system. Therefore, greater attention should be paid to the anthropogenic activities along the river system in order to restore the river water quality.