LIGHT GRADIENT AS TOOL FOR THE ASSESSMENT AND MANAGEMENT OF LAKES ECOSYSTEM HEALTH

Consequence of lakes eutrophication as well degradation of natural environments in many cases is numerous transformations of abiotic and biotic. The most visible effect of this is a decrease in the transmission solar radiation, which is mostly absorbed in the shallow surface layer mainly through an accumulation of primary production in subsurface layer. The paradigm of spring blooms or an annual maximum of phytoplankton biomass in spring in deep temperate lakes has been pervasive but many exceptions have been demonstrated including evidence of greater seasonality of chlorophyll a with decreasing health state of lake. The behavior of photosynthetically active radiation in vertical profile of water, especially light attenuation with depth, has important implications for water quality and ecological conditions. The transformation of light energy flux under the influence of optically active substances (dissolved yellow substances, tripton, plankton and others) may cause its strong absorption or transmission to larger depths. On one hand the high level of epilimnetic solar radiation inhibits photosynthesis, but from other the intensive utilization of light by phytoplankton occurs. Aim of study was to analysis the influence of optically active substances generated by phytoplankton blooms on range of PAR in lakes of similar trophic state. Variation in the underwater light regime was also indexed by Secchi disk, vertical attenuation coefficient and depth of the photic zone derived from using an underwater spherical quantum sensor of PAR. Analysis of the physical features of water in the photic zone, defined as the depth of 1% subsurface PAR, permitted identification of characteristic substances blocking the penetration of light in lakes.