Stratification in the filling phase of the man-made lake Brokopondo in Surinam (S. America)

Summary Temperature and dissolved oxygen content measured weekly at various depths during 3 1/2 years in the filling phase of a tropical man-made lake, show that at the dam-site fluctuations of epilimnion values occurred, whereas the hypolimnion remained almost constant in temperature and permanently devoid of oxygen. This confirms previous reports concerning another mid-lake station. Apart from rather steep superficial temperature gradients, classical thermoclines did not occur. It is proposed that the lake could not become fully mixed by wind action because of the great vertical density differences at the prevailing temperatures, and because of the drowning forest still giving shelter by the extending crowns. On the other hand, the stratification was not static. Fluctuations between high and low epilimnion values for temperature, oxygen content and transparency oocurred yearly, but could not be related satisfactorily to the prevailing seasons. The depth of the epilimnion increased each year. It is suggested that the observed kind of stratification was effective though not absolute. Vertical exchange may have been reduced by increasing density differences, but it was not fully eliminated. This explains the varying degree of incorporation of upper hypolimnetic layers in the epilimnion in relation with epilimnetic temperature. Comparison with large African reservoirs accentuates the exceptional limnological development of Lake Brokopondo during ifs filling phase.