Seasonal resilience of benthic macroinvertebrate communities in a highly urbanized tropical river: The Case of the Lukina River (Kinshasa, DRC)

This study aimed to assess the seasonal resilience of benthic macroinvertebrate communities in the Lukina River, a highly urbanized tropical watercourse in the city of Kinshasa (DRC). The analyses focused on water physicochemical parameters, benthic community structure, ecological indices, as well as the relationships between environmental variables and biological assemblages during both the dry and rainy seasons. Physicochemical results showed mean temperatures of 24.5 ± 1.47 °C in the dry season and 27.6 ± 0.79 °C in the rainy season. Mean conductivity ranged from 150 ± 46.4 µS/cm to 158 ± 56.4 µS/cm, respectively. Dissolved oxygen concentrations remained low during both seasons, averaging 2.46 ± 1.08 mg/L in the dry season and 2.86 ± 0.86 mg/L in the rainy season, reflecting significant organic pollution conditions. High values of $BOD_5$ (21.8 ± 2.84 mg/L in the dry season; 19.2 ± 1.98 mg/L in the rainy season), COD (25.2 ± 3.81 mg/L; 20.2 ± 3.62 mg/L), nitrates (25.5 ± 13.7 mg/L; 20.9 ± 11.3 mg/L), and phosphates (4.54 ± 1.76 mg/L; 2.05 ± 0.44 mg/L) indicate substantial nutrient enrichment of the system. In total, 1,792 individuals belonging to 15 families were recorded in the dry season, compared to 2,085 individuals across 11 families in the rainy season, representing an overall abundance increase of 16.4%. Benthic communities were heavily dominated by Chironomidae, accounting for up to 94% of the abundance at station Luk1 in the dry season and over 55% across all stations during the rainy season. Tubificidae, Lumbriculid, and Physical were also abundant at the most disturbed stations. Diversity indices revealed a relative improvement in communities during the rainy season. Shannon index values ranged from 0.32 to 1.99 in the dry season and from 1.25 to 1.51 in the rainy season. Palou’s evenness values were generally above 0.60 during the rainy season, reflecting a more homogeneous distribution of taxa. Multivariate analyses (Bray–Curtis, UPGMA, and NMDS) demonstrated a seasonal structuring of benthic assemblages. Rainy season stations exhibited relatively homogeneous communities, whereas dry season stations were more differentiated. The low seasonal similarities observed (0.175 to 0.392) indicate limited ecological resilience. Principal Component Analysis (PCA) showed that nitrates, phosphates, conductivity, and turbidity were the main factors influencing benthic community structure. Overall, the results indicate that the Lukina River remains highly subject to urban anthropogenic pressures. Despite a slight improvement in ecological conditions during the rainy season, benthic assemblages remain dominated by pollution-tolerant taxa, reflecting low ecological resilience in this urbanized river system.