Seasonal nutrient cycling of Lake Bosomtwe

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Seasonal nutrient cycling of Lake Bosomtwe was investigated from February-December 2008. Bimonthly samples were collected at both inshore and offshore zones of three selected sites namely Abono, Asisriwa and Dompa. Levels of the parameters covered (surface water temperature, transparency, pH, conductivity, phosphorus, nitrogen, organic carbon and primary production) were determined for contrasting seasons. A survey on attitude of fair use and conservation of the catchment area by farmers in the two inhabited sampling sites Abono and Dompa was also conducted. The results showed that lowest surface water temperature of Lake Bosomtwe was in August. Transparency from Secchi disk measurement was low in the dry season and the lowest was recorded at Abono and Dompa. Statistically insignificant correlation existed between transparency and chlorophyll-a at all the three study sites. Mean transparency during the study ranged from 0.64 to 1.49 m. pH of the lake was lowest in the dry season and highest in the main wet season. Organic carbon influenced pH in the inshore zones and mean pH range recorded during the study was 8.77-9.33. Conductivity was highest in October after the main wet season and lowest during the dry season. A correlation analysis between conductivity and all the nutrients (phosphorus, nitrogen and organic carbon) covered in this study revealed non uniform correlation. Mean conductivity recorded ranged from 1047.8 to1268.5 µscm-1. Phosphorus did not follow a marked seasonality and mean phosphorus recorded during the study ranged from 0.025 to 0.48 mg-1 with the highest recorded at Dompa in December. Organic carbon levels were high during the heavy rains in June and August at Abono and Dompa. Mean organic carbon levels recorded during the study ranged from 0.667 to 4.339 mg-1 with the highest at Abono. Highest mean total nitrogen determined as Total Kjedahl Nitrogen was recorded in June and August in Abono and Dompa. Mean nitrogen levels fluctuated within eutrophic status during the study and levels recorded ranged between 0.89 and 75.37 mg-1. Chlorophyll-a followed a strict seasonality with the highest chlorophyll-a in August. Seasonal nitrogen appeared influential on chlorophyll-a. Mean chlorophyll-a levels recorded during the study ranged from 1.65 to 16.1 mg-1. Primary production determined from the light- dark bottle technique did not follow a marked seasonality, however values from offshore zones were generally higher than inshore zones. The gross primary production (G.P.P) levels recorded during the study ranged from 3.49 to 21.722 mgCm-2d-1. Most of the inhabitants engaged in activities within the catchment of Lake Bosomtwe used slash and burn method of land preparation and were oblivious of the impact of their activities on the water body. Little information on conservational processes to sustain the lake was available to the inhabitants.
A Thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the Degree of Master of Philosophy,