Effects of anthropogenic activities on macroinvertebrate assemblages in the littoral zone of Lake Hawassa, a tropical Rift Valley Lake in Ethiopia

Abstract

AbstractIn developing tropical countries, the littoral region of lakes is exposed to high human pressures, and the degradation effects are more evident on riparian vegetation and macrophytes. Human impacts on other biological entities, such as plankton and macroinvertebrates, are rarely investigated and reported. The present study focuses on assessing the effects of habitat disturbance on the littoral macroinvertebrate assemblages in Lake Hawassa, Ethiopia. Samples were taken from February to November 2015/16 from 12 sampling sites purposefully selected on the basis of percentage disturbance score (PDS) and categorized into minimally disturbed (four sites), moderately disturbed (five sites) and highly disturbed (three sites). Macroinvertebrate samples were collected from each site using a D‐frame net of 500 µm, with both in situ measurement and laboratory analysis of the environmental variables being conducted. A total of 23,051 macroinvertebrates belonging to 43 families were identified. Analysis of similarities (ANOSIM) and non‐metric multidimensional scaling (NMDS) analyses revealed significantly different macroinvertebrate assemblages among the disturbance levels (ANOSIM: p = .004, R = .55). Variables such as Biological Monitoring Working Party, Shannon diversity index, Ephemeroptera and Trichoptera (ET) family richness, and family richness exhibited a flawless pattern of decrease with increasing human disturbances and a negative correlation with nutrients. The reduction of these metrics for highly disturbed sites was attributable to the deterioration of vegetation and bottom substrate qualities, increasing stormwater inputs, lack of buffer zones and well‐planned land use induced by human interventions. It was evident anthropogenic activities in and around the littoral zone of the lake contributed to the degradation of habitat quality and decreased macroinvertebrate richness and abundance. Thus, effective lake management practices are recommended to rehabilitate the degraded littoral habitat quality in order to realize the sustainable use of this natural resource.