Variability of chlorophyll a and photosynthetic parameters in a nutrient-saturated tropical great lake

Diurnal measurements of Secchi depth, light attenuation, thermal structure, photosynthetic irradiance (PE) parameters, and chlorophyll a (Chl a) were performed at weekly intervals in three inshore bays in Lake Victoria, Uganda. The only statistically significant diurnal patterns observed were a decline in PE parameters normalized to Chi a and a decline in gross integral phytoplankton production. On a weekly timescale, Chl a was positively correlated to changes in the mean water-column temperature (T-WC) in each bay. Meteorologic data in one of these bays suggest that the synchronous increases and decreases in Chl a and T-WC are related to the extent of advective exchange with deeper areas of the lake. Analysis of all data from this study, as well as available historic data, reveals that the optical properties of Lake Victoria covary with the concentration of Chl a. On weekly timescales, the PE parameters alpha(B) and P-BM covary, and both parameters generally decline as Chl a increases, a pattern consistent with historic data from Lake Victoria. Empirical relations are developed that relate optical properties and PE parameters to Chl a. These relations provide a mathematical representation of the limnologic changes that Lake Victoria has experienced through eutrophication and can be used to predict these parameters over larger spatial and temporal scales and facilitate estimates of whole-lake primary production.