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Titre : Eutrophication assessment in the Kavango river system from Rundu to Divundu, Namibia

Auteur : Haikola, Ester Ishiwa

Université de soutenance  : University of Namibia

Grade : Master of Science (Biodiversity Management) 2022

Résumé partiel
Eutrophication is one of the most serious problems facing freshwater ecosystems globally. Nutrient enrichment of these freshwater ecosystems results in excessive plant and algal growth that have negative effects on biodiversity and water quality. The present study was conducted at six selected sites from Rundu to Divundu along the Kavango River namely ; Rundu, Mashare, Shitemo Irrigation schemes, Quito, Shadikongoro Irrigation systems and Divundu. The overall objective of the study was to assess the level of eutrophication of the Kavango river downstream from Rundu to Divundu in Namibia by assessing concentration levels of Total Nitrogen, Total phosphate and Ortho-phosphate in the water. Water samples were collected in 50 ml plastic bottles from the main flow along the Kavango river gradient. Each site was sampled upstream (Before the site) and downstream (After the site) from Rundu to Divundu. Water samples were collected 3-5 cm below the surface following United States Environmental Protection Agency standards. Sampled water was analysed for Total Nitrogen (N), Total Phosphate (P), Ortho-phosphate using Inductively coupled plasma-atomic emission spectrometry (ICP-AES). Dissolved oxygen was also measured 3-5 cm below the water surface. Simple Linear Regression was used to test the effect of distance on the concentration levels of Total Nitrogen, Total Phosphates and Ortho-phosphate. The Wilcoxon Signed Rank test was used to compare nutrient concentration levels, flow rates and dissolved oxygen before and after sites. To test for compliance with acceptable standards International Water Quality Guidelines (IWQES) and South African Water Quality Guidelines for Aquatic Ecosystems (SAWQG), one Sample Wilcoxon Signed Rank test was used for non-parametric data and one -sample t test was used for parametric data. There was no significant relationship between concentrations of Total Nitrogen and Total phosphate concentration in the Kavango river and the distance downstream from Rundu to Divundu. However, there was a significant relationship between the concentration of Ortho-phosphate (mg/l) and distance along the Kavango River (p= 0.028 ; R 2 =0.42971). Furthermore, there was no significant difference in concentrations of Total nitrogen, Total phosphate and Ortho-phosphate.

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