The physic-chemical assessment of urban river basin using macroinvertebrate indices for the environmental monitoring of urban streams

The major sources of pollution along the Mukuvisi River are industrial effluents from Msasa, Graniteside, and Southerton industrial sites, sewage effluent from Firle sewage works, pesticide and fertilizer runoff from Pension and surrounding farms, and domestic and diffuse pollution from residential areas. The primary objective of this study was to assess the impact of point and non-point pollution sources on macroinvertebrates variability and investigate the seasonal water quality deterioration along the Mukuvisi River. To evaluate macroinvertebrate community diversity using South African Scoring System 5 protocol for rapid bioassessment of water quality. The combined application of benthic macroinvertebrates and physic-chemical parameters was the focus of this research to validate the water quality status of the urban River systems concerning emerging pollutants in urban areas.

  According to the Harare municipality pollution control strategy and surveillance, only twelve accessible sampling points were chosen along the river. Macroinvertebrate samples and physic-chemical measurements were collected once or twice a month, according to the city of Harare’s sampling schedule. The ancillary information, temperature, pH, and conductivity were measured on-site with a mercury bulb thermometer, a pH meter, and a conductivity meter, respectively. The standard South African Scoring System 5 sampling protocol was used for the sampling and identification of the macroinvertebrates community.

The early assessments showed that water pollution was, in the 1st place and as a primary issue, a biological matter, and its primary effects could have been traced to living organisms. Eutrophication in Manyame catchment, Harare, Zimbabwe is subjected to prolonged and cumulative ecosystem stress because of human activities, sewage disposal, and industrial discharges, among other pollution sources. The Phosphorus-P, Biological Oxygen Demand, Chemical Oxygen Demand, and Ammonia-NH3 (from 0, 6.9, 118, and 0 to 3.8, 81.9, 840, and 31 mg/L respectively) concentration increases downstream in both seasons. The Dissolved Oxygen saturation was 75% and 67% upstream in the dry-and-wet season and was reduced to 0% downstream in both seasons. The evaluation of macroinvertebrate diversity provided evidence that Mukuvisi River water was polluted based on the South African Scoring System, especially in the dry season.

The physic-chemical parameters were significantly related to macroinvertebrates diversity. In the assessment of river water quality, both macroinvertebrate indices and physio-chemical parameters can be sampled together to avoid bias. The results indicated that human activities from the upstream were inducing water pollution. Industries need to adhere to the wastewater discharge guidelines.