Sediment and nutrient loads into river Lwiro, in the Lake Kivu basin, Democratic Republic of Congo

Abstract

This study assessed sediment and nutrient loads in Lwiro river, Lake Kivu basin in the Democratic Republic of Congo. Water discharge was measured and water samples were collected twice a month from 6 sites in Lwiro river system and analyzed for total suspended sediment (SS), temperature, pH, dissolved oxygen (DO), chemical oxygen demand (COD), five-day biological oxygen demand (BOD5), alkalinity and nutrients (P, N, PO₄^3-, NO₃^- and NH₄⁺) using standard methods. Results show that the concentration of BOD₅ was low (1.08 ± 0.83 mg/L); but COD (13.13 ± 6.26 mg/L) and SS (1.15 ± 0.36 mg/L) were high in the industrial effluent than in agricultural effluent (2.7 ± 0.77 mg/L for BOD₅; 9.05 ± 3.55 mg/L for COD and 0.81 ± 0.36 mg/L for TSS). It was observed that all these values were low compared to the standard limit proposed by UNECE and Uganda standard. TSS, nutrient and other chemicals parameters load analyzed were high in agriculture effluent than in industrial effluent except for NH₄⁺ load. Temporal variation and site difference between TSS and nutrient load were significantly different (F=5.54, p< 0.005 for SS; F= 8.59, p< 0.005 for TP and F=7.63, p< 0.005 for TN). Techniques for reducing nutrient and TSS loads should be initiated in the microcatchment to protect the Lake Kivu.

Keywords: Sediment; nutrient load; industrial; agriculture effluent; Lwiro river; Lake Kivu.