Temporal variation of attenuation of the visible radiation in four lakes of Parque Estadual do
Rio Doce (PERD), Minas Gerais
BEZERRA-NETO1, J.F; BARBOSA2, P.M. & BARBOSA2, F.A.R.
1 Programa de Pós-Graduação em Ecologia, Conservação e Manejo da Vida Silvestre, Universidade Federal de Minas Gerais. CP 486, 31270-901, Belo Horizonte, Minas Gerais, Brasil.
2 Laboratório de Limnologia, Departamento de Biologia Geral, Universidade Federal de Minas Gerais. CP 486, 31270-901, Belo Horizonte, Minas Gerais, Brasil.
ABSTRACT: The present study aimed at characterizing seasonal variation of photosynthetic solar radiation (PAR) within the water column of four natural lakes of the middle Rio Doce basin (Carioca, Dom Helvécio, Gambazinho, and Jacaré lakes) during the period July 2004 to June 2005. Depths of PAR penetration within the water columns were measured in order to estimate the scalar light attenuation coefficient (Ko) for each lake. Chemical and biological water variables were also determined (total suspended solids - TSS, dissolved organic carbon -DOC, colored dissolved organic matter -CDOM, and chlorophyll a -Chl a) in order to determine their relative contribution to light attenuation. Measurements of Ko in the analyzed lakes showed marked variation with higher (0.92-1.74 m-1) and lower Ko values (0.58-0.77 m-1) recorded for lakes Carioca and Gambazinho, respectively. Among the lakes the variation of Ko can be explained mainly due to changes of Chl a and CDOM concentrations. When all lakes are considered together CDOM is the major component of Ko and explains 76% (p < 0.001) of its variation. Patterns of visible radiation penetration were analysed with potential contributions of allochthonous material and argued the possible causes in optical water quality differences among the studied lakes.
Key-words: colored dissolved organic matter; attenuation of visible radiation; temporal variation; Rio Doce State Park.