Impacts of Hydroclimatic and Land Use/Cover Variability on Water Quality Parameters in Densely Populated Urban Tropical Basins

Abstract Understanding how hydroclimatic (HC) and land use and land cover (LULC) variabilities affect surface water quality is very important for effective water resources management. In this study, seven water quality parameters were analyzed in four watersheds in the city of Fortaleza, the Brazilian capital with the highest population density: biochemical oxygen demand (BOD), chlorophyll-a (Chl-a), dissolved oxygen (DO), total coliforms (TC), total nitrogen (TN), total phosphorus (TP), and total suspended solids (TSS). Data were grouped into two periods: the wet period (January to June) and the dry period (July to December). The results showed that intra-annual variability of precipitation and land use/cover had a considerable impact on water quality. The values of Chl-a and BOD were higher during the dry period, while all other parameters tended to show higher concentration during the wet period. According to the results, dilution was the primary factor influencing BOD and chlorophyll-a concentrations, whereas surface runoff played a predominant role in shaping the dynamics of the other water quality parameters.TN was the most responsive parameter to seasonal variations, with higher values in the wet season, possibly due to nutrient transport during rainfall. The degradation of water quality was strongly associated with urban and agricultural land uses, which contribute both point and diffuse sources of pollution. These areas often release excessive amounts of nutrients, organic matter, and sediments into water bodies, mainly through wastewater discharges and stormwater runoff.