Variação espaço-temporal da biomassa fitoplanctônica (clorofila-a) no alto e médio Rio Araguari - AP

Abstract

The pigment chlorophyll-a is common to all the algae used to estimate the phytoplankton biomass through their concentrations in the aquatic environment. Economic activities that promote the discharge of effluents and even without treatment tank construction can provide an increased concentration of pigment. This is used to assess the trophic status of aquatic ecosystems, their monitoring is very important for decision making, how to avoid the occurrence of algal blooms resulting from environmental impacts on aquatic ecosystems. In this context, the present study aimed to determine the concentrations of chlorophyll a and check whether there is a correlation between the variation of algal biomass in relation to spatial and temporal gradient along a stretch of the River Araguari upstream reservoir dam. The study area includes a stretch of 90 km, starting in the affluent River Falsino, Araguari Alto and close to National Forest of Amapá (FLONA). The stretch of river studied finalizes the reservoir hydroelectric Coaracy Nunes (UHECN). The study comprised four quarterly measures in fourteen sampling sites of water for determination of physico-chemical parameters and quantification of the concentration of chlorophyll-a. Throughout the period studied stretch and the concentration of chlorophyll-a was less than 10 microg.L-1, with peak recorded in the dry period of 8.16 microg.L-1. Therefore, seasonal variations, represented by the liquid discharge of the river were correlated with the variation of the values of biomass during the annual hydrological cycle. Conversely, there was no consistent correlation between algal biomass and the spatial gradient. Moreover, the concentration of chlorophyll significantly been explained by physico-chemical variables conductivity, total dissolved solids and temperature. It was concluded that both the Araguari River, including the reservoir and tributary Falsino were considered oligotrophic, meeting the standard of Class II river, contained in resolution 357/2005 of CONAMA