Scale-dependent effects of rural activities on benthic macroinvertebrates and physico-chemical characteristics in headwater streams of the Mara River, Kenya

We studied streams in a rural landscape mosaic of the upper Mara River basin (Mau Forest, Kenya), where native forest has been converted to land uses dominated by various kinds of farming, agriculture and rural human settlements. We investigated scale-dependent effects of these anthropogenic rural activities on macroinvertebrates and physico-chemical variables by separately testing for effects of reach-scale disturbance and catchment-scale land use. Physico-chemical variables like conductivity, turbidity and total suspended solids reacted equally well to reach-scale disturbance and catchment-scale land use, demonstrating the high spatial integration potential of these variables and calling for farsighted large-scale water resource management. In contrast, macroinvertebrates reacted more sensitively at the reach-scale than at the catchment-scale, suggesting a stronger influence of local habitat conditions. These results highlight the importance of local stream ecosystem management, e.g., the restoration and protection of stream banks, to protect against agriculture-driven biodiversity losses. However, we also found responses of selected taxa to catchment-scale land use, suggesting that localized management efforts may not suffice to maintain full stream ecosystem integrity and regional biodiversity. Our results also suggest that macroinvertebrates may allow a scale-specific assessment of stream ecosystem integrity and pressures by a scale-dependent bioindicatory approach.