Assessing Sources, Levels and Discharge Loads of Nitrogen And Phosphorus of River KISAT into Lake Victoria - Kisumu Municipality, Kenya

Abstract

River Kisat is a perennial river draining the Mamboleo - Kisumu basin between Latitude 0°04'12.42" S and Longitude 34°46'33.86" E to the North and Latitude 0°05' 13.52" S and 34°45'00.15" E to the South. It drains a distance of about 10 Kms through Industrial, Slums and Sewerage Treatment Plant (STP) areas into Winam Gulf. The river is polluted from various sources of pollutants ranging from non-point to point sources. This has resulted in changes in the trophic status of the lake at Winam Gulf from mesotrophic to hypertrophic. Pollution in the lake has reduced biotic abundance and diversity. A study was therefore designed on River Kisat, which is believed by many researchers as one of the major source of pollution into Lake Victoria, to generate data and results that will aid in the management of Lake Victoria water pollution and its probable source River Kisat. The specific objectives of this study were; to identify main point and non-point sources of pollution to River Kisat, to determine the pollution status of River Kisat through measurement of Nitrogen and Phosphorus nutrient concentration levels, and to establish the amount of Nitrogen and Phosphorus discharge loads into Winam gulf from River Kisat. The study was conducted during wet and dry seasons for a period of one year (2009) in order to capture the seasonality and was confined to 8 stations (STN 1, 2, 3, 4, 5, 6, 7 & 8) within the course of River Kisat, located at probable sources of pollution. The samples were collected from the middle of the channel through scoop method while sediments were collected using grab method. Samples from selected run-offs causes, during rainy season, were also collected. Sampling containers were first cleaned and samples pretreated using 0.02N HCl. The samples were then stored under refrigeration at temperatures of 4°C before analyses. The data obtained from the analyses were then subjected to statistical analyses using Excel spreadsheet by comparing variations between stations and between months through line graphs, bar charts, and descriptive statistics and ANOVA. The DO concentration levels between stations ranged between 1.33,(STN 6) and 4.11 mg/l (STN 8). The pH levels ranged between 7.00 (STN 6) and 7.41 (STN 3). In terms of nutrient (N & P) concentrations at STN 6 exhibited low concentrations but probably one of the main pollutant of the river. The NH4+ concentrations within the river course between stations ranged between 0.15 (STN 7) and 1.89 mg/l (STN 4) with a maximum in STN 4. The NH/ concentration is high during dry season but low during wet season. The N02- concentrations between stations ranged between 0.04 (STN 7 & 8) and 0.23 mg/l (STN 5). N03- ranged between 0.35 (STN 8) and 0.96 mg/l (STN 5). The N03- concentrations increases with increase in discharge. SRP and TP concentrations ranged from 0.16 to 1.04 mg/l and 0.21to 1.39 mg/l respectively. STN 4 is the main contributor of SRP. The total discharge load in a year during the study period is estimated at 140.5 tons/year. The TN concentrations shoot with increasing discharge rates. TP load per year is estimated at 155.8 tons/year. The TP also increases with discharge rates but at a lower scale compared to TN. The DO concentrations are low compared to standard guidelines for drinking and aquatic life. The nitrogen species concentration levels for both fisheries and domestic use falls within recommendable levels except for NH/. The concentration levels of nitrogen species tend to increase with decreasing discharges except for N03- and to some extent N02-. The phosphorus levels are very high compared to water quality standard for fisheries but within recommendable levels for drinking. The major pollution sources, both point and nonpoint, lies between STN's 1-6. STN 7 and 8 are near the river source devoid of major developments and are therefore less polluted. The government should therefore introduce a policy of Polluter Pays Principle (PPP) with the revenue collected plowed back into cleaning the river. These data would be important to policy makers like Municipal Council of Kisumu (MCK),National Environmental Management Authority (NEMA), Kenya Marine and Ministry of Public Health, Lake Basin Development Authority (LBDA).