Hidroquímica dos lagos Bolonha e Água Preta, mananciais de Belém-Pará

Abstract

Water for Belem’s Metropolitan Area is supplied by COSANPA (Companhia de Saneamento do Pará), which uses the water source of the lakes Utinga, Bolonha and Água Preta. These lakes are considered the most important in the region, and are responsible for the provision of water to 75% of that population. These water sources receive continuously a contribution of waters from Guamá River in order to maintain their water level. The period of study was 12 months (feb/2006 to jan/2007), using 12 sampling points (surface and bottom), being 11 points in Água Preta Lake (point 1 to 11) and 1 point in Bolonha Lake (point 12). All samples were obtained using a hydrologic bottle (Niskin). The objective of this research is to study abiological parameters such as temperature, turbidity, apparent color, electric conductivity, pH, dissolved oxygen, nitrate, N-amoniacal, phosphate, solids in suspension and the water’s transparency, in order to evaluate it’s behavior related to the lake’s seasonality and hydrology. The hydrological variables studied were input and output water flow, precipitation, water level variation and variation in the volume of waters. The batimetry in Água Preta Lake was accomplished to obtain current mean depth data.. A statistical treatment was applied to the results in order to evaluate the relationship between the studied parameters. Turbidity, apparent color and solids in suspension parameters reached higher concentrations in the period of minor precipitation and they presented values varying between 4 and 59 UNT; 15 to 550 mg L-1 Pt Co and 1 to 57 mg L-1, respectively. The electric conductivity presented a similar distribution when compared to the analyzed physical parameters, with higher concentrations in the period of minor precipitation, and it varied from 35,40 μ S / cm - 1 to 149,70 μ S / cm -1. The studied nutrients (nitrate, N-amoniacal and phosphate) presented the maximum values of 1,4 mg L-1, 1,34 mg L-1 and 1,6 mg L-1, respectively.