Spatial and temporal scale dependent variability in water and habitat quality of Afromontane streams

Abstract

Study region Major Afrotropical streams draining the Dwangwa River, North Rukuru River, and South Rukuru River catchments in northern and central Malawi. Study focus Although human pressures have long been linked to aquatic ecosystem decline, there remains limited clarity on whether management and conservation efforts should prioritize reach-scale or catchment-scale interventions. We therefore, assessed the relative influence of catchment-scale land-use and reach-scale disturbances on water and habitat quality in selected Afrotropical streams. Water and habitat quality attributes were measured and assessed respectively in two sampling campaigns, once per season, during the dry (September–November 2024) and wet (January–April 2025) seasons across a gradient of land-use (forest, agriculture, urban, and mixed) and reach disturbance intensity (low, moderate, and high). Principal component analysis (PCA), permutational multivariate analysis of variance (PERMANOVA), and generalized linear mixed-effects models (GLMMs) were used to evaluate spatial and seasonal variability in stream condition and identify dominant environmental drivers. New hydrological insights for the region The findings showed that agricultural, urban, and highly disturbed sites exhibited significantly degraded conditions, including elevated temperature, particulate organic matter (POM), total suspended solids (TSS), and nutrient concentrations (nitrite, nitrate, and SRP), alongside reduced canopy cover and poor bank stability (p < 0.05), with clear seasonal variation. GLMMs showed scale-dependent controls on stream condition, with catchment-scale land-use exerting stronger influence on suspended solids, canopy cover, instream cover, and nutrient enrichment, whereas reach-scale disturbance more strongly affected temperature, dissolved oxygen, riparian width, and bank stability. These findings underscore the importance of integrated, multi-scale watershed management strategies to protect freshwater ecosystems.