Phytoplankton Production in Lake Arenguade (Hora-Hado), Ethiopia.

No Thumbnail Available



Journal Title

Journal ISSN

Volume Title


Addis Ababa University


Dynamics of Chl a biomass, abundance amd photosynthetic production of phytoplankton in relation to some phyico-chemical factors were studied in Lake Arenguade from December, 2008 to October, 2009. Water transparency in Lake Aranguade varied from 0.21 to 0.37 indicating the shallowness of the trophogenic zone owing to high turbidity, which seems to be largely of biological origin. Depth profiles of temperature showed the occurrence of a superficial type of thermal stratification which is created by solar heating and destroyed by nocturnal cooling although oxygen depth profiles determined on two days seem to sugggsest the formation of stable and deep-seated thermal stratification at times. Total Alkalinity of the lake ranged from 33 to 50.6 while pH varied from 9.62 to 9.84. SRP, nitrate and silica varied temporally from about 702 to 2123 μg L- , 1, 4.1 to 78 μg L-1 and 3.5 to 37.3 mg L-1, respectively. The phytoplankton community of Lake Arenguade was co-dominated by two species of blue-green anlgae, Spirulina platensis (Arthospira fusiformsi) and Anabaenopsis elenkinii, chl a biomass of phytoplankton varied temporally ranging from 41.7 to 271 mg L-1 and with peaks coinciding with those of phosphate and silicate and low levels of nitrate. The depthdistribution of gross photosynthesis per unite water volume (A, mg C m-3 h-1) exhibited the typical pattern for phytoplankton with maximum production rates at depths below the surface on most sampling dates.The light-saturated rate of gross photosynthesis (Amax), which ranged from 76.14 to 650 mg C (243.64–2080 mg O2) m-3 h-1. was positively but modestly (r=0.53, r2=0.28 at p=0.061 ) correlated with Chl a biomass. Biomassspecific rates at light-saturation (φmax, photosynthetic capacity) ranged from 2.3 to 13.2 mg O2 (mg Chl a)-1 h-1 with most values between 8 and 11 mg O2 (mg Chl a)-1 h-1. Hourly integral rates of photosynthesis (ΣA) ranged from 0.13 to 1.67 g O2 m-2 h-1. The seasonal peaks of hourly integral rates were associated with peaks of chlorophyll a concentration and light-saturated rate of gross photosynthesis (Amax). The correlations between hourly integral rates and chlorophyll a concentration (r=0.53, r2=0.28 at p=0.06 and Amax (r = 0.78, r2=0.62 at p=0.0014), were positive and strong. The causal relationship between biological parameters and physico-chemical variables are examined and discussed