科研之友
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摘要
AIM: chemical stratification and the patterns of light limitation and nutrients of two natural lakes, one shallow and the other one deep, were comparatively evaluated, both lakes located in the southeast Brazil. METHODS: pH, electrical conductivity, dissolved oxygen, total dissolved solids and nutrients were monthly collected during 5 consecutive years at the vertical profile of the two lakes. RESULTS: multivariate analysis indicated that the long thermal stratification period favored the occurrence of chemical stratification in the two lakes. However, in the deeper lake the stratified thermal profile with high hypolimnetic nutrient concentration, electrical conductivity, total dissolved solids and redox potential indicated that the mixing was not complete even during the annual circulation period, suggesting a slight meromixis and a high chemical stability at the hypolimnion. In the shallower lake, high light attenuation and high availability of nitrogen forms (mainly N-NH4) and phosphorus was observed along the water column, even during stratification. In the deeper lake, N and P co-limitation and low light attenuation coefficients were detected. CONCLUSION: thermal and chemical stratification patterns indicated that the Carioca lake is a shallow, turbid, nutrient rich, whereas the Dom Helvecio lake is a deep, clear, oligotrophic system with a tendency towards meromixis and the isolation of solutes in the hypolimnion. Consequently, meromixis was compared to a %26quot;hypolimnetic memory%26quot;, which was defined, in the case of the deeper lake, as the maintenance of the chemical stratification along the years, during the lake thermal circulation period. OBJETIVO: a estratifica o qu赤mica e os padr es de limita o por luz e nutrientes foram avaliados comparativamente em dois lagos naturais, sendo um raso e o outro profundo no sudeste do Brasil. M谷TODOS: as amostragens de pH, condutividade el谷trica, oxig那nio dissolvido, s車lidos totais dissolvidos e nutrientes foram realizadas mensalmente, durante cinco anos consecutivos no perfil vertical dos dois lagos. RESULTADOS: as an芍lises multivariadas indicaram que o longo per赤odo de estratifica o t谷rmica favoreceu a ocorr那ncia de estratifica o qu赤mica nos dois lagos. No entanto, no lago mais profundo, o perfil t谷rmico estratificado, com elevadas concentra es hipolimn谷ticas de nutrientes, condutividade, s車lidos totais dissolvidos e potencial redox indicaram que a mistura n o foi completa mesmo durante o per赤odo de circula o anual, sugerindo uma leve meromixia e alta estabilidade qu赤mica no hipol赤mnio. No lago mais raso, e
