River health assessment using macroinvertebrates and water quality parameters: A case of the Orange River in Namibia

• River health is key to ecological sustainability.
• The SSA tool proved to be useful in assessing the health of the Orange River.
• Physico-chemical analysis and bio-assessment results indicate that the Orange River’s health is within acceptable range.

Land use activities that have an effect on water quality and river health are believed to have increased along the Orange River in Namibia. These are mainly agricultural activities, notably irrigation, with more than 2000 ha currently under irrigation and approximately 2000 ha planned for future expansion. Other anthropogenic activities include urban development and weir construction along the Orange River. Population increase along the river has resulted in proliferation of unplanned settlements with no proper sanitation facilities.This study was aimed at assessing the current water quality and overall health status of the Orange River in Namibia. The South African Scoring System 5(SASS5) was applied in eight sites where samples for macroinvertebrates, physical and chemical water quality parameters such as nutrients in the water, pH, turbidity and presence of bacteria were obtained. Satellite images i.e. Landsat images were also used to assess the land-uses over time in the study area with the view of linking such changes to variance in water quality over time.The SASS5 results indicated a fair water quality and river health condition in category C, indicating that the river is moderately modified. Water quality parameters at all sites varied moderately and were within acceptable limits, except for turbidity and chlorophyll a. There was a significant difference in the mean concentrations of nine water quality parameters among sampling periods, whereby F-value > F-critical at α = 0.05 among sites, F-value < F-critical at α = 0.05, except for turbidity and chlorophyll a. The Landsat images also showed minimal changes in land-use activities between 2002 and 2012, with a net increase of 38 ha in irrigated area. According to National Water Policy White Paper of Namibia of 2000, it was found that policies and legislation address water resources management from a broader spectrum and not specific to river health. Thus, it was concluded that the river health of Orange River is still within acceptable range despite the fact that there is an urgent need to develop an effective and sustainable water quality monitoring and development programme.