Physicochemical Characterization of Water Quality - Lagoa dos Índios in Macapá, Brazil

Aims: To characterize relevant physicochemical parameters of water quality in an Amazonian tropical lake and compare them with the reference values of the Brazilian Resolution CONAMA 357/2005 and those recommended by the similar US-EPA law. In addition, to correlate statistically the parameters in two different climatic periods.

Study Design: The sampling procedures occurred in five sites of a tropical lagoon (Lagoa dos Índios) in Macapá-Amapá-Brazil. The investigation occurred during the rainy season (November / 2010) and dry season (March / 2011). Seventeen physical and chemical parameters were analyzed according to APHA (1998). The metal ions were determined by atomic absorption spectrometry, with a Shimadzu device (AAS model 6300). The pH was determined in situ with the portable pH-meter, mark ORION, Model 3 STARS THERMO.

Place and Duration of Study/Methodology: The physicochemical analyses were performed at the Laboratory of Chemistry, Sanitation and Environmental Systems Modeling, and the General Laboratory of Analytical Chemistry of the Federal University of Amapá (UNIFAP). The period was from November 2010 to March 2011. Data were analysed using the BioStat 5.0 software to elaborate a Correlation Matrix (Spearman Method and non-parametric test).

Results: Alkalinity presented values ​​outside the EPA standards, unlike hardness, that presented accordingly. The other variables studied ​​could be considered normal when compared to other as the nearby waters of the Amazon River. The results for biochemical oxygen demand (BOD), dissolved aluminum, ammonia nitrogen, total dissolved solids (TDS), nitrate, chloride and turbidity measurement showed in accordance with the reference values ​​of CONAMA and US-EPA. Then a nonparametric test (Kruskal Wallis) showed significant differences in water quality between both seasonal periods as among at the five sampling sites. Kruskal Wallis test showed also significant differences space-seasonal in the water quality. So, the Spearman correlation showed good fitness with some physicochemical parameters: a positive correlation between pH and alkalinity, EC and pH, alkalinity, TDS, and negative correlation between DO and BOD.

Conclusion: We concluded that the Spearman correlation matrix describes reasonably well the behavior of the heterogeneous quality of the Lagoa dos Índios to the different sampling sites, both in the dry season and in the rainy season. The water quality is yet within legal standards expected to CONAMA Resolution 357/2005 and EPA-USA. However, there is evidence of imbalances of some parameters of water quality resulting from likely effects of urban pollution on the water quality of the lagoon.