Self-Purification and Rainfall Events in a Tropical Rural Catchment,Nigeria

Abstract

This paper studies self-cleansing processes in an urbanized stream in a Nigerian city. The stream under study took its source from a refuse heap in the Central open-place-city market and empties its water into a University Dam 15 kilometres away.

Twenty-seven water samples were taken from nine sample points, which were selected with distances downstreams and according to land use changes in the period before and after the 1st and the 2nd rainfall events. The results showed that some parameters decrease progressively with rain events while some equally increase progressively. The result of the Pearson moment product correlation showed that in the period before rainfall onsets five water parameters (Ca $^+$ , P, total hardness, suspended particles, NO $^-_3$ ) significantly decreased in their concentration downstream; and after the first rainfall only NO $^-_3$ significantly decreased downstream from the source to the dam/ site (downstream) while in the period after the 2nd rainfall event all the water parameters decreased in concentration downstream with seven parameters significantly decreasing (i.e. Na $^+$ , Ca $^+$ , K $^+$ , Mg $^+$ , P, NO $^-_3$ and pH). The overall results indicated that the processes of self-cleansing become more active with increasing rainfall events.