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W. Okello

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Papers by W. Okello

Reference Module in Earth Systems and Environmental Sciences, 2022

firi.go.ug

... Prepared by Charles Ezekiel, Sitoki Lewis, John Gichuki, William Okello, Ephraim Odada, and G... more ... Prepared by Charles Ezekiel, Sitoki Lewis, John Gichuki, William Okello, Ephraim Odada, and Godfrey Magezi ... checked for accuracy twice at the start and end of the sampling cruise using the standard Winkler titration method for determining dissolved oxygen concentration. ...

African Journal of Aquatic Science

Lake Victoria in East Africa is a major ecosystem, whose size and importance has warranted the ex... more Lake Victoria in East Africa is a major ecosystem, whose size and importance has warranted the exploration of MODIS imagery to provide continuous and accurate water quality information. To this effect, two sea expeditions (in November 2014 and February 2015) were carried out to collect in situ lake surface temperature (LST), chlorophyll a (Chl) and Secchi disk depth (SDD) to compare with the corresponding satellite derived variables. Comparisons were made based on the following error matrices: coefficient of correlation (r), mean square error (MSE), root mean square error (RMSE), mean absolute deviation (MAD) and mean absolute percent error (MAPE). In general the results showed that satellite derived LST gives a good estimate of in situ LST. Conversely, the error matrices indicated that satellite derived Chl yielded more uncertainty when compared with in situ Chl. This could be because of the fact that the MODIS Chl product algorithm was designed for oceans and may not be appropriate for inland lakes. Satellite derived SDD compared fairly well with in situ SDD. From these results it is evident that with more in situ observations and improved algorithms, MODIS can be useful to improve how water quality is monitored on Lake Victoria.

Uganda Journal of Agricultural Sciences, 2004

Bench scale experiments were done to assess the effects of decomposition of water hyacinth on pho... more Bench scale experiments were done to assess the effects of decomposition of water hyacinth on phosphorus release and water quality. Hyacinth plants from the lake were chopped to fine pieces. In replicate incubation tubes, 50 g of plant material was stocked to which 1.6 L of lake water was added. One set was aerated while the other was sealed with rubber stoppers to exclude airflow. Soluble phosphorus, pH, conductivity, and dissolved oxygen were measured daily for one month. In nonaerated set-ups, highest increase in phosphorus concentration occurred between the third and fourth days, but with a plateau after Day 5, and a peak (2,871.4 ± 771.2 mg L-1) on Day 10. In the aerated trials with hyacinth, highest increase occurred between the fifth and ninth day, with a peak (2,041.1 ± 1,050.2 mg L-1) on Day 9. Highly significant differences were attributed to time and aeration, with hypoxic conditions enhancing phosphorus release than well aerated ones. Significantly lower dissolved oxygen...