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Long-term nitrate and phosphate loading of river water in the Upper Manyame Catchment, Zimbabwe

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Relation http://oar.icrisat.org/7444/
 
Title Long-term nitrate and phosphate loading of river water in the Upper Manyame Catchment, Zimbabwe
 
Creator Nyamangara, J
Jeke, N
Rurinda, J
 
Subject Soil Science
Watershed management
Agriculture-Farming, Production, Technology, Economics
 
Description Urbanisation and agriculture represent a dramatic example of human interference in catchment hydrology. The impact of agricultural, domestic, industrial and municipal activities on river flow and water quality within the Upper Manyame Catchment Area (UMCA) was assessed using 7-year nitrate, phosphate and water flow rate data, collected by the Environmental Management Agency (EMA). Water samples for nitrate and phosphate analysis were collected at 8 points along the Manyame (2 points), Marimba (2 points) and Mukuvisi (4 points) rivers, and runoff volume was recorded at the mouth of each river. Annual runoff of each river was closely related to rainfall amount, with the lowest runoff being recorded during drought years. High nitrate and phosphate concentrations were recorded directly downstream of residential, municipal and industrial areas suggesting that these were the major sources of the pollutants found in the river water. For example, phosphate concentration at 2 sites along Mukuvisi River (downstream of domestic and industrial areas) exceeded the statutory limit (0.5 mg/ℓ) for ‘safe’ or good quality water (‘blue’ category) according to the Zimbabwe Water (Waste and Effluent Disposal) Regulations, and ranged from 0.78 mg/ℓ during the dry season to 2.23 mg/ℓ during the wet season. In the Marimba River phosphate concentration at Site 4 (downstream of domestic, industrial and sewage processing plant) also exceeded the safe water quality standard by 4–6 times. Although Marimba River contributes the lowest proportion of runoff (relative to the other two rivers sampled) entering Lake Chivero, it contributed the highest nitrate (114 840
kg/yr) and phosphate (84 324 kg/yr) loading. It was concluded that anthropogenic activities within the UMCA were the major sources of nitrate and phosphate pollution in the three rivers and pose a serious threat to the ecological sustainability of the rivers and lakes downstream, and to the economic wellbeing of nearby cities which rely on the water for potable uses
 
Publisher Water Research Commission
 
Date 2013
 
Type Article
PeerReviewed
 
Format application/pdf
 
Language en
 
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Identifier http://oar.icrisat.org/7444/1/LongTermNitrate_Nyamangara_2013.pdf
Nyamangara, J and Jeke, N and Rurinda, J (2013) Long-term nitrate and phosphate loading of river water in the Upper Manyame Catchment, Zimbabwe. Water SA , 39. pp. 637-642. ISSN 0378-4738