Seasomal Studies Of Phytoplankton Primary Production In Relation To Light And Nutrients In Lake Awasa

Phytoplankton primary production of Lake Avmsa wasrnstudied from Novembelj 1983 to Mnrch, 1985 by the oxygen lightrnand dark bottle technique. Supporting data include waterrnchemistry, light penetration, thermal characteristics andrnstanding crop of phytoplankton.rnThe solar radiation falling on the lake surface didrnnot show pronounced variation apart from one low valuernrecorded on a cloudy day. The lake is of fairly highrntranspOlrency with red and green the most penetrating components.rnThere has been no indication of deep-seated thermalrnstratification in Lake Awasa apart from the superficialrntype of stratification which is generated by solar heatingrnand destroyed by nocturnal cooling or wind-induced verticalrnmixing.rnThe chemistry of the lake water is basically similarrnto other East African lake waters with sodium as thern'. prec}(lntinant cntion [md bioarbonate+ a nrbonll1Jtt, .. " the predominantrnanion. The lake 'las found to have high concentrationrnof silica ~.nd 101'1 concentration of phosphate and nitrate.rnAlmost all nutrients were found to show some seasonalrn''f ariations •.rnThe algal crop is fairly high and 'las found to changernseasonally. The vertic".l distribution of photosyntheticrnactivity per unit water volume was of a typical pattern for viiphytoplanktonrnwith light inhibition on nll but the mostrnovercast days, The threshold of inhibition at the lakern-2 .rnsurface was around 1500 f Em • Haximum net photosynthesisrnaveraged 211r.6 mg0 ) -3-1rn2rn(66.95mgG m h and integral photosynthesisrnran~;ed from 0.3 to 0.73 g 02 (0.094 to 0.226 gG)rn-2 -1 m h • The estimated velues of daily integral gross photosynthesisrnwere in the range of 3.3 to 7.8 g 02 (1.03 torn2.4 g G) m-2d-1 • The correlation between gross photosynthesisrnand standing crop was poor though there was a general tendencyrnfor the maximum photosynthesis to increase with the standingrncrop.rnThough not pronounced, spatial (vertical) and temporalrnvariations of phytoplankton standing crop and primary productionrnwere observed. The vertical va.riations appear to be the resultrnof variation in the underwater radiation which is a function ofrnthe lake's transparency and amount of surface radiation. Thernobserved terolporal variations in phytoplankton standing crop andrnprimary production seem to be controlled more by nutrient supplyrnthan energy supply. The seasonality of rainfall seems, therefore,rnto play the pradominant role in determing the nutrient statusrnand extent of algal growth and primary production.

Get Full Work

Report copyright infringement or plagiarism