Accepted April 5th, 2014
The economic meltdown in Zimbabwe which started around 2000 and lasted almost a decade led to the intensification of already existing environmental problems. Local authorities were not able to fully regulate the treatment and disposal waste and some sewerage system often burst and raw sewage flowed into streams and rivers unmonitored. In Marlborough, Harare, sewage from burst Marlborough sewerage system was flowing into Marlborough stream which flows through the suburb. Water quality in Marlborough river was monitored by collecting benthic macro-invertebrates once a month from February to April 2012 at four sites, one upstream and three downstream of the point of sewage discharge. Macroinvertebrates metrics of abundance, taxa richness, Shannon Wiener diversity index, tolerance average score per taxon (ATSPT) and South African Scoring System (SASS) scores were used in the determinations of water quality of the stream. Abundance, taxa richness and Shannon Wiener index differed significantly (p<0.05) spatially but no significant differences were found among the sampling months. SASS scores and ATSPT differed significantly (p<0.05) among sampling sites in each sampling month indicating that water quality differed significantly among sampling sites but no significant difference were found among the sampling months. The reference site had the highest number of pollution sensitive families, while the site 1, just after point of discharge had the highest number of pollution tolerant families. The abundance of pollution tolerant families decreased from site 1 going down stream possibly due to self-purification and dilution. The outcomes of the research showed that the inflow of sewage into the stream reduced water quality of the stream.
Keywords: Water quality, Benthic macro-invertebrates, Bio-assessment; Marlborough river, Sewage effluent