Analyzing water quality monitoring data of environmentally protected water bodies

Preserving water quality is fundamental for public health and ecosystem sustainability. This study presents a comprehensive environmental assessment of the Maranguapinho River and four urban lagoons-Parangaba, Maraponga, Messejana, and Mondubim-in Fortaleza, Brazil, examining the influence of land use and seasonal variation on water quality. A total of 16 physicochemical and microbiological parameters were analyzed, including pH, dissolved oxygen (DO), biochemical oxygen demand (BOD), total Kjeldahl nitrogen (TKN), total phosphorus (P), turbidity, sulfate (SO₄^2-), sulfide (S^2-), total iron (Fe), copper (Cu), cadmium (Cd), lead (Pb), chromium (Cr), nickel (Ni), zinc (Zn), and thermotolerant coliforms. Spatial analysis revealed contrasting urbanization levels, with the Maranguapinho River surrounded by less developed areas and the lagoons embedded in more urbanized zones. Although pH values remained within legal limits (6.00 to 8.71), DO concentrations fell below the regulatory threshold (5.0 mg L^-1) at over half of the sampling sites during the rainy season, with the lowest value (3.2 mg L^-1) recorded at a point along the Maranguapinho River. The Maranguapinho River exhibited multiple exceedances of environmental standards, particularly for S^2- (1.6 mg L^-1), total Fe (1.2 mg L^-1), Cd (0.002 mg L^-1), and Cr (0.42 mg L^-1, below the 0.5 mg L^-1 limit but still elevated). In addition to the river, several lagoons also showed values above the recommended limits, with biochemical oxygen demand (BOD) reaching 18.5 mg L^-1 in Maraponga Lagoon, exceeding the limit of 5.0 mg L^-1. The results underscore the cumulative impact of urbanization and seasonal dynamics on water quality, revealing widespread exceedances of regulatory thresholds for nutrients, metals, and microbial contaminants. The findings highlight the urgent need for integrated urban planning, improved waste management, and sustainable water resource governance to protect aquatic ecosystems in rapidly developing urban regions.