Abstract:
Nutrient pollution occurs when an excessive amount of nutrients, primarily nitrogen and
phosphorus, are introduced into water bodies and act as fertilizer, causing excessive algae
growth known as eutrophication. Therefore, the objective of the present study is to evaluate the
level of nutrient pollution in the rivers water and their water interfaces sediments and quality
status of upper Guder and upper Awash rivers, Ethiopia. A longitudinal-based experimental
design that includes both qualitative and quantitative primary data collection from water and
sediment of the study was used. Ten sites (six from Awash, and four sites from Guder River)
were selected for the collection of water and sediment samples. The water temperature, pH,
electrical conductivity (EC) and dissolved oxygen (DO) content in the water were measured in
situ using a multi probe meter. In addition, the spatial and temporal variation of nutrient
concentrations such as nitrite, nitrate, total phosphorus, total nitrogen, and ammonia in the water
and sediments was measured in the laboratory. Our result confirmed a significant spatial
physicochemical parameters difference with the highest result observed in Awash River
(p<0.05), but only temperature and DO contents showed a significant temporal variation
(p<0.05). However, the nutrient content the rivers water and sediment samples highest in Guder
river, but statistically difference is not significant (p>0.05), but showed a significant spatial
variation (p<0.05) with the highest result recorded in A2, A3, A4, GL and GC sites. Similarly,
the result showed a significant seasonal variation with the highest result recorded in dry season
in the water, but higher in wet season in the sediments (p<0.05). The log-ratio principal
component analysis (PCA) for nutrient content in water and sediment samples varied highly on
Axis 1 and Axis 2, which together accounted for 80.29% of the total variance. The chlorophyll a
content of the water samples ranged between 0.49 and 3.28 µg/L with a mean amount of
1.57±0.78 µg/L and the result showed a significant spatial and temporal variation (p<0.05). The
mean WQI were 468.27±78.83 and 404.62±34.60 in dry season and wet season, respectively.
Generally, the result showed that the nutrient load is very high both river and surpasses the
maximum permitted limit. Similarly, the WQI result shows a poor water quality for drinking in
both rivers. Therefore, effective pollutant source management is very important for the health
life in the both rivers and the community relaying on the rivers.
