Spatial variability of dissolved organic carbon to nitrogen oxides ratio in the Nsooba-Lubigi channel

Abstract

Urban streams receive huge amounts of nutrients from land coming from domestic homes, agricultural fields and factories containing large amounts of nitrogen compounds and organic matter. Intermediate reactions of the denitrification process tend to produce NO2 which has a high global warming potential, its rate of production is affected by carbon to nitrogen ratio and dissolved oxygen. Nsooba-Lubigi channel transports heavily polluted waters which it collects from various slums around Kampala hence a potential source of NO2. During this research, samples were collected from seven sampling sites from the start of the channel in Kamwokya to its mouth in Bwaise and analysed for NOX--N, DO and DOC from which DOC: NOX--N was calculated for each site. Sampling, S1 had the highest ratio (1.92±0.06) while S3 had the lowest (0.12±0.01). S2 had the lowest DOC while S4 had the highest, NOX--N was generally low except for sampling sites S3 and S4. S1 and S4 had lower DO values than the other four sites. From the results, it shows that the channel has low DOC: NOx--N hence high denitrification rates. Therefore, Nsooba-Lubigi channel is a potential source of nitrous oxide gas.