Application of environmental indexing for water quality assessment – case of Nasolo River, Blantyre

By: Blessings Mtchuka, Francis Chauluka, Emmanuel Chinkaka, Harold Yapuwa ,

Abstract

Water quality is critical to ecosystem health as it threatens biodiversity when degraded by anthropogenic or geogenic activities. As an urban river, the Nasolo River can be impaired by various anthropogenic activities arising from urbanization and industrialization. This study assessed the effects of the activities above on the Nasolo River in Blantyre, through the application of environmental indexing approaches. Four sampling sites, S1, S2, S3, and S4 sites were purposefully selected to provide an upstream-to-downstream characterization of the river health. Selected water quality variables including pH, electrical conductivity (EC), temperature, salinity, total dissolved solids (TDS), and dissolved oxygen (DO) were measured using a multi-probe AP800 aqua meter. Membrane filtration technique (MFT) was employed to determine fecal and total coliforms, and a hydrotest photometer was used to analyze turbidity and total suspended solids (TSS), nitrate and ammonia. A National Sanitation Foundation Water Quality Index (NSFWQI) was used to depict water quality status and a Stream Assessment Scoring System (miniSASS) biomonitoring technique was employed to collect and identify macroinvertebrates in Nasolo River whose presence or absence reflected varying environmental conditions along the river. Six orders of macroinvertebrates, Ephemeroptera, Diptera, Trichoptera, Annelida, Coleoptera, and Turbellaria were identified in the river. The macroinvertebrates data were interpreted by calculating average scores per taxon (ASPT) to develop a biotic index. Lastly, a correlation analysis between the NSFWQI and macroinvertebrate biotic index (MBI) was performed to quantify the degree to which the two indices are related. The findings showed a significant correlation between the two indices. Both indices have shown that upstream station S1 was mildly contaminated whereas further downstream, sites S2, S3, and S4 were severely polluted. The overall outcome indicated that the water quality in the Nasolo River is poor, posing an ecological risk to aquatic life while rendering the river unable to offer ecological services. Therefore, it is necessary to use good catchment management strategies to improve the quality of the rivers.