| dc.description.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. | en_US |
