Human impacts on ecosystems in the Chibefwe river catchment area in Mkushi district, Zambia

Abstract

xvi ABSTRACT The main objective of the study was to assess the impacts of anthropogenic land use activities on river health conditions using aquatic macroinvertebrates as indicators of water quality in the Chibefwe River Catchment area in Mkushi district, Central Province, Zambia. Three study sites were selected on the Chibefwe River: One near the source of the Chibefwe River (this served as a reference site for the study); The second inside the built-up area of Mkushi town; and the third, just before the confluence of the Chibefwe River with the Lunsemfwa River. At each site the following physicochemical parameters were recorded; pH, water temperature, electro-conductivity, turbidity, dissolved oxygen content and total dissolved solids. The Zambia Invertebrate Scoring System (ZISS) was employed as a standard biomonitoring protocol. The sampling of aquatic macroinvertebrates was done using a one-millimetre kick-sized net, targeting three major biotopes namely; stones, aquatic vegetation and gravel (including sand, mud, silt and clay), if present at the site. Collected specimens were enumerated and identified to family level on-site using the ZISS photographic identification manual. Specimens that could not be identified in the field were preserved in 70% ethanol and taken to the lab for further study and subsequent identification. Data collected was analysed by computing the ZISS score, Average Score Per Taxon (ASPT) and the macroinvertebrate species diversity. To identify water and land-based habitats, the latest sentinel two image covering the study area was obtained from the open Copernicus portal and the dataset was subjected to a land cover classification for analysis. Generally, all water quality parameters except pH and Turbidity conformed to the required standards. Macroinvertebrate results in the wet season showed that sites one and three had moderate water quality conditions (with ASPT values of 6.66 and 7.75, respectively). In contrast, an ASPT value of 4.5 was recorded for site two suggesting an impaired environmental quality of river water at the site. A total of 26 specimens were collected at this site (C2). Sites one and three had macroinvertebrate species diversities of 1.12 and 1.34, respectively, suggesting moderate modifications to the environment. A species diversity value of 0.84 determined for site two indicated that the Chibefwe River inside Mkushi town was highly degraded with high levels of pollution. During the dry season, results showed that sites two and three indicated close to natural conditions with few impairments recording ASPT values of 6.18 and 6.63 respectively whereas an ASPT value of 5.08 was recorded at site one. Higher species diversity values were recorded across all the sites in the dry season than in the wet season. Land cover results showed that much of the area is predominantly covered by forests (90Km2), followed by croplands (77.7 km2), settlements (16.6 km2), open shrublands (14 km2) and finally wetlands (0.8 km2). The study concluded that there were changes in water quality and ecosystem conditions across the Chibefwe river along a gradient of human disturbance. This was demonstrated from the presence of pollution sensitive (Ecnomidae) and semi-tolerant species to pollution (Coenagrionidae) for the first and second sites respectively. Deterioration of habitats near the township was due to variability in land use activities associated with settlements and croplands which resulted in the depletion of vegetation cover. The study recommended that the existing vegetation be conserved while reducing disposal of untreated wastes in rivers in the Chibefwe River Catchment area. Key words: Land use, Aquatic macroinvertebrates, Water quality, Species diversity