Effect of point source pollution on the quality of water in river Enyau, arua Municipality, Uganda

Abstract

Pollution of streams, rivers, wetlands and lakes is a major problem in Uganda, yet many people draw water for domestic use from these sources. The objectives of the study were to (i) identify the sources of point pollution (ii) assess the effect of the identified sources of point pollution on the water quality and and compare the physical properties and nutrient concentrations after the point of pollution for River Enyau in Arua Municipality with national standards for potable water. A reconnaissance study was carried out and six major point sources were identified; Pajulu bridge washing bay (PBWB), Niva Primary School discharge point (NDP), Ediofe bridge washing bay (EBWB), Arua public/distillery discharge point (APDP), Onduparaka Bridge washing bay (OBWB) and the Municipal Abattoir (MA). Samples were collected before and after the points of discharge in the mornings and afternoons and analyzed following standard procedures. Results showed that physico-chemical parameters of water at the selected sources of point pollution ranged as follows: pH 7.14−7.58 for points before discharge (BD) and 6.97−7.56 for points after discharge (AD). For electrical conductivity (EC) the measurements ranged 68.0−118.00 μS/cm for points BD and 67.00−137.00 μS/cm for points AD. Total Dissolved Solids (TDS) ranged from 37.00− 65.00 mg/l for points BD and 37.00−74.00 mg/l for points AD. Measured temperature ranged from 10.70−22.5˚C for points BD and 9.80−22.30˚C for points AD. Ammonium-nitrogen concentrations were from 0.68−1.90 mg/l for points BD and 0.99−1.93 for points AD; nitrites were from 0.00−0.03 mg/l for points BD and 0.00−0.03 mg/l for points AD; nitrates, from 0.01−0.04 mg/l for points BD and 0.00−0.03 mg/l for points AD; sulphates from 17.00−32.5 mg/l for points BD and 20.00−32.5 mg/l for points AD and total phosphorus ranged 0.152−0.651 mg/l for points before discharge and 0.166−0.695 mg/l for points AD. The results showed significant differences for Electrical conductivity for points before and after discharge at Arua public discharge point (APDP) and Municipal Abattoir (MA) ranging from 88−95 mg/l for APDP and 105−118 mg/l for MA, with P = 0.02 for both points of discharge. The Chi-square test showed that results obtained after points of discharge were below the maximum allowable values of the national standards for un-treated potable water for all sampling points (P<0.01). However results after points of pollution showed higher values that demonstrate some level of contamination and impairment of the water quality in River Enyau by activities in the catchment that include discharges from the Municipal Abattoir, indiscriminate disposal of commercial, residential wastes and washing bays. Pollution reduction strategies should be put in place