| dc.description.abstract | Inner Murchison Bay (IMB) gets polluted through both point and non-point sources due to anthropogenic activities in the catchment. The shape, water movement dynamics, water quality of joining wetlands in the IMB including local processes determines the distribution of dissolved and suspended materials. IMB experiences total mixing (July-August) and total stratification (February-March) periods, and how this impacts on physico-chemical variables and Escherichia coli numbers in vertical and horizontal profiles was investigated. This study applied quantitative methods where numerical data from the vertical and horizontal sampling of water generated raw data. In-situ water quality variables namely electrical conductivity (EC), pH, temperature, turbidity, total dissolved solids (TDS), dissolved oxygen (DO), total suspended solids (TSS), and E.coli were monitored at 12 sampling points (700 m apart) for two months each during total mixing and stratification periods. There were several intersecting and divergent currents in the IMB with main flow towards the center and later diverging away. However, three (3) major surface water interfaces entering the IMB were observed. Electrical conductivity was significant at distance of 200 m during stratification but insignificant with depth in both thermal regimes. Vertical and horizontal distance accounted for 36% and 9% for stratification and total mixing, an indication of more spread of wastewater during stratification. The pH values were significant from 0.5 m to 1 m depth at 200 m during both total mixing and stratification. Variation of pH along horizontal distance was not significantly different. Changes in depth and distances could explain pH variance by 27% and 46% during stratification and total mixing respectively. Significant temperature differences during total mixing occurred within 1 m to 2.5 m depth at horizontal distance of 200 m and 1500 m. Temperature was significantly different at 0.5 and 2.5 m depth but with relatively similar values in the horizontal distance. The depth and distance accounted for more change during total mixing (52%) compared to stratification (23%). Higher dissolved oxygen (4-6 mg/l) occurred in surface water (up to 1 m deep) during stratification compared to 2-4 mg/l during total mixing attributed to diffusion into entire water column. Total mixing and stratification conditions exhibited significant DO at horizontal distance of 200 m but stratification period also presented significant DO at 800 m. The effect of horizontal distance (59%) and depth profile (56%) on DO was relatively the same for total mixing and stratification. Overall, both stratification and total mixing exhibited no significant changes in E.coli numbers. In comparison of E.coli with distance and depth between transects was significantly different during total mixing (p = 0.001) and stratification (p = 0.000) respectively. The depth and distance accounted for 4% and 11% of E.coli numbers during total mixing and stratification. Higher TSS concentration range (20-80 mg/l) was recorded during total mixing compared to stratification (20-60 mg/l). However, TSS concentration was not significantly influenced by the conditions of stratification and total mixing. Depth and distance could explain TSS changes by 13% and 5% during total mixing and stratification periods respectively. Turbidity was similar in the depth but significantly different at 200 m into open water during both total mixing and stratification regimes. The depth and horizontal distance accounted for 15% and 23% of turbidity changes during stratification and total mixing. TDS concentration was highest at the deeper end closer to the edge. At 200 m from edge, TDS was significant during both total mixing and stratification but the depth exhibited non-significant difference in both thermal regimes. Distance and depth had relatively similar influence on TDS variance during total mixing (37%) and stratification (34%). In conclusion, thermal regimes in IMB have marked effect on water quality in the horizontal distance (at 200 m) and depth of 0.5-2.5 m. Depth and distance accounted for major changes (>50%) in DO during both regimes while the effect was higher (>50%) for temperature during total mixing only. Except for temperature and DO that exhibited significant differences between the thermal regimes, other variables (EC, pH, TDS, TSS and turbidity) were not significantly different, confirming temperature and DO as major players of metabolic processes in IMB. | en_US |
