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

Abstract

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.

Quality characterization and pollution source identification of surface water using multivariate statistical techniques, Nalagarh Valley, Himachal Pradesh, India

“…The significant inverse relationship between Cl -and PO 4 2-and NO 3 -could be due to different source of chemical origin. Increase in nutrient concentration, primarily PO 4 2-and NO 3 -, enhanced biological metabolism thereby decreasing dissolved oxygen (Hickman and Gray 2010;Nyamangara et al 2013). It is noted that the study area lacks proper sewage drainage system and also encounters tremendous surface/urban runoff (effluent) during monsoon season.…”

“…Lastly, Cluster 3 (C3) is distinguished by the highest level of HCO 3 -and PO 4 3-, which correlates well with PC2. The sampling locations group of C3 (8,9,13,15,11,14,18) may be attributed to the anthropogenic factor (domestic sewage and agricultural runoff) (Nyamangara et al 2013).…”

Physicochemical Properties and Total Coliform Distribution of Selected Rivers in Osun State, Southwestern Nigeria

“…The mean nitrate values obtained in the river water samples were lower than the WHO permissible limits for drinking water. Nitrates however were noted in low concentrations within the range of 0.03 and 0.05 mg/l water and fell within the WHO water quality target of 5.0 mg/L [39]. This implies that analysed water samples contained low level of oxidized organic matter.…”

Enrichment and geoaccumulation of metals in the superficial sediments of Lake Chivero, Zimbabwe

“…Over the last six decades, the human population in the lake's catchment and their settlements have increased exponentially (Tendaupenyu et al, ), coincident with the volume of sewage effluent generated (Nhapi, ) and non‐point sources of pollution (Nyarumbu & Magadza, ). The majority of the industrial activities in Zimbabwe, including agro‐processing and fertiliser manufacture, are concentrated within the Lake Chivero catchment (Nyamangara, Jeke, & Rurinda, ). Overloading of the existing wastewater treatment infrastructure (Nhapi, ) has led to the discharge of partially treated and raw sewage into the lake over past years through the Manyame River and its two tributaries, the Marimba and Mukuvisi Rivers, leading to deteriorating water and sediment quality within the lake (Nhapi, ).…”