<p>This research investigates the diel variations in nutrient concentrations in preserved streams located in the Cerrado and Atlantic Forest biomes of Bahia, Brazil. By examining both organic and inorganic forms of nitrogen and phosphorus, the study aims to understand how these nutrients fluctuate in response to environmental factors such as precipitation and landscape features. This study contributes to a deeper understanding of nutrient cycling in tropical stream ecosystems, providing insights that could aid in conservation strategies. Water samples were collected every hour using an automatic sampler over a 24-h period, covering both dry and rainy seasons to reflect seasonal variability. The abiotic variables pH, DO, conductivity, and temperature were measured during sampling, and subsequent nutrient analyses were conducted (including nitrate, nitrite, ammonium, and both dissolved and particulate organic nitrogen and phosphorus) along with Chlorophyll-a. This system-wide analysis provides a more comprehensive understanding, enabling us to effectively link nutrient dynamics with environmental conditions. Results indicate that abiotic variables were the only parameters showing diel variation, with higher values during the daytime. A comparison of parameters between Cerrado (M1) and Atlantic Forest (M2) revealed that almost all values were higher in the Atlantic Forest during the rainy season. Our findings suggest that vegetation cover, soil characteristics, and biogeochemical processes in soil and water were more influential in the variations between areas than diel fluctuations.</p>