Spatio-temporal variability in water quality and macroinvertebrates assemblage of Lunyangwa river, northern Malawi.

Abstract

Freshwater ecosystems in Sub-Saharan Africa are experiencing severe degradation due to agricultural expansion, urbanization, and poor sanitation, threatening the ecosystem services that riparian communities depend on. This study examined how land use affects water quality and benthic macroinvertebrate assemblages in the Lunyangwa River, Mzuzu City, Northern Malawi. Macroinvertebrates and water quality parameters were sampled at nine stations across three land use types (forested, agricultural, and urban; n=3 each) during dry (Oct-Nov 2024) and rainy (Feb Apr 2025) seasons. Data were analyzed using diversity indices, water quality standards, and multivariate statistics to assess spatial and temporal variation. Urban stations showed the most severe degradation, with very poor water quality (WQI: 186.40–204.25), lowest dissolved oxygen (3.07 ± 2.74 mg/L), highest biochemical oxygen demand (4.73 ± 1.17 mg/L), and macroinvertebrate communities dominated by pollution-tolerant taxa like Bellamya capillata and Tanypodinae, resulting in low diversity (Shannon H = 0.96). Agricultural stations displayed intermediate conditions, while forested stations maintained the highest water quality and macroinvertebrate diversity. Land use was the primary driver of variation in both water quality and macroinvertebrate composition, with temperature, dissolved oxygen, BOD, pH, conductivity, and salinity differing significantly among land-use types, while seasonal effects were minimal. The findings demonstrate that macroinvertebrates are effective bioindicators of water quality and provide scientific evidence for urgent conservation interventions, including riparian zone protection, improved wastewater treatment, and regular biomonitoring programs for sustainable river basin management in the Lunyangwa River and similar African freshwater systems.