Lukaw,Y.S., Celestino Ladu, J.,L. and Kenyi, D.D
Abstract
Seasonal influence of physiochemical variables on the phytoplankton abundance was studied for one year from January 2003 to December 2003 in Jebel Aulia reservoir in Khartoum, Sudan. Selected physicochemical variables such as water temperature, rainfall, sechi depth, water discharge, pH, dissolved oxygen, dissolved organic matter; nitrate, phosphate and silicate were measured at the time of phytoplankton collection. All raw data were log transformed Log10(X+1) for normality and parametric statistical test requirements were statistically analyzed using SPSS 16 for windows. Generally, the reservoir and its surrounding water was alkaline (pH- 7.99 ± 0.09 μgl-l-1). The mean water temperature was (28.05 ±2.22o C); rainfall, (26.58 ±9.64mm); discharge, (65.75 ±7.10 (106 m3) and the mean sechi depth measured was (120.59 ±23.77cm). Dissolved oxygen level was generally (7.98 ±0.303 mg/l); dissolved organic matter, (14.28±0.58 mgO2/l); nitrate, (3858.50 ±1087.37 μgl-1); phosphate, (340.83 ±12.44 μgl-1) and silicate level was (29716.67±2621.47 μgl-1). A total phytoplankton biomass of 13275.5 cells L-1 was recorded in the reservoir of which 8397.5 cells L-1 occurred in the rainy season, 4898 cell L-1 in the dry season. All the physicochemical variables did not vary (P>0.05) between the rainy and the dry seasons, water temperature, transparency and rainfall varied significantly between the rainy and the dry seasons. All the phytoplankton classes indicated positive correlations ( P < 0.05) with the nutrients PO4 and SiO2 , no correlation with NO3; positive correlation ( P < 0.05 ) with rainfall, negative correlations with water temperature and transparency and were not correlated with water discharge. A total of 33 phytoplankton genera were recorded, the phytoplankton classes dominated by Bacillariophyceae >Chlorophyceae> Cyanophyceae>Zygnemataphyceae>Dinophyceae >Oedogoniophyceae. Phytoplankton Density is influenced by both physicochemical variables and biotic, hydrobiological and hydrographic features of the reservoir. [Yatta S. LUKAW; Denis D. KENYI ; John Leju Celestino LADU. Seasonal Influence of Physicochemical Variables on Phytoplankton Abundance in Jebel Aulia Reservoir in Khartoum – Sudan.
Keywords: phytoplankton; biomass; biotic; physicochemical variables; sechi depth; hydrobiological.
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