Efeito da turbidez sobre a produção primária fitoplanctônica

Abstract

Aquatic trophic chains have as their first link the phytoplankton, group of photosynthetic organisms that transform the luminous energy that penetrates in the water into organic carbon. Factors such as nutrient availability and photosintetically active radiation (PAR) regulate phytoplanktonic metabolism. Turbidity is a regulating factor of the available light for photosynthesis and can be of organic or inorganic nature, if it is related to particles in suspension in the water column. It can be caused by resuspension of sediment or by anthropic impact that lead to the increase of inorganic particles in suspension, as the mining activity, that generates tailings that can reach aquatic environments and alter planktonic dynamics and trophic structure. Batata Lake (PA) is situated at Amazonian plains and will be used as a model system because it was impacted by bauxite tailing. The objective of this study was to evaluate the effect of turbidity on primary production, on the distribution of chlorophyll groups and on the photosynthetic yield and to evaluate the effect of progressive addition of sediment on primary production. Experiments were performed using sediments from Chapéu D’Uvas reservoir, from the impacted area of Batata Lake and from its natural area with the planktonic community from the lake located at Botanic Garden of UFJF. High, medium and low levels of turbidity were combined to high, medium and low chlorophyll levels to evaluate the effect of each of the variables. An experiment was carried out with progressive addition of sediment to high and low levels of chlorophyll to evaluate the effect of progressive increase of turbidity. The results showed that inorganic turbidity is capable of reducing primary production if the sediment does not provide nutrients to the system. The effect of sediment is stronger in higher levels of turbidity and the effect of chlorophyll is stronger in lower levels of turbidity. Yield reduces in higher turbidity and treatments more adverse to photosynthesis, the groups distribution showed more brown algae expression than in treatments with more nutrients. The progressive addition of sediment caused more pronounced chlorophyll reduction in high chlorophyll treatments.