Temporal variability of two contrasting transient pollution events in a pastoral stream

Two transient pollution events were monitored in a pastoral stream in southwestern Kenya to evaluate their relative contribution to diffuse pollution. Peak loads of pollutants during storm-induced transients were within 3-4 orders of magnitude higher than the short-lived (30-60 minutes) diurnal epis...

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Bibliographic Details
Published in:Water science and technology 2010-01, Vol.61 (4), p.1053-1063
Main Authors: Yillia, P T, Kreuzinger, N, Mwetu, K K
Format: Article
Language:English
Subjects:
Bacteria
Base flow
Environmental monitoring
Environmental Monitoring - methods
Environmental Pollution
Fecal coliforms
Fresh Water
Geography
Geologic Sediments
Hydrographs
Inhabitants
Kenya
Livestock
Peak load
Pollutants
Pollution
Pollution monitoring
Pollution sources
Rain
Riparian environments
Rivers
Storms
Stormwater
Stream pollution
Suspended particulate matter
Suspended solids
Temporal variations
Time Factors
Turbidity
Water Microbiology
Water Movements
Water Pollutants, Chemical - chemistry
Water Pollutants, Chemical - isolation & purification
Water pollution
Water Purification - methods
Water quality
Water Supply
Weather
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Summary:Two transient pollution events were monitored in a pastoral stream in southwestern Kenya to evaluate their relative contribution to diffuse pollution. Peak loads of pollutants during storm-induced transients were within 3-4 orders of magnitude higher than the short-lived (30-60 minutes) diurnal episodes provoked by in-stream activities of people and livestock. Transient yields were striking during storm-induced events; 778,000, 8,400, 550 and 100 kg day(-1) for suspended solids, BOD(5), total P and total N, respectively, compared to wet weather base flow (150, 30, 0.8 and 1.4 kg day(-1), for the same parameters, respectively). Two forms of concentration-discharge relationships were observed: increases in concentration for turbidity, suspended solids, BOD(5), total P and the faecal indicator bacteria at the peak of the stream hydrograph, and concurrent decreases in concentration for conductivity and total N. Following each storm-induced transient event, a marked improvement in water quality was observed within 48-72 hrs of the receding limb of the stream hydrograph before the next base low was established. It was concluded that storm-induced transients are exceedingly important for the mobilization of pollutants from diffuse sources but both transient events affect stream-channel processes, especially water quality, with the possibility of attendant consequences on the health of riparian inhabitants.
ISSN:0273-1223
1996-9732
DOI:10.2166/wst.2010.566