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Abstract:
In two tropical lakes, one of the white water floodplain with an amount of suspended solids
(tripton) of 100 mg/l, and one of the black water floodplain stained by humic substances (gilvin) of
130 - 170 HAZEN, situated in Central Amazonia, measurements of the light regime were made.
Mainly two types of collectors were used measuring the hemispherical (cosine) and the spherical
(scalar) incident solar radiation in the PAR wave band (photosyntethetically active radiation). From
these data the coefficients for the irradiance reflectance, extinction for downward irradiance, and the
depth of the euphotic zone were calculated for the so-called Várzea (white water) and lgapó (black
water) lakes and all values compared to those obtained in the water body of an oligotrophic lake in
Northern Germany.
Besides comments concerning methodological details, remarks are given on the consequences of
the very extreme light regimes for the biota in the two tropical lakes.
