NUTRIENT LOADS AND TROPHIC SATE OF AN URBAN SHALLOW LAKE IN THE METROPOLITAN REGION OF NATAL, RN
Rio Pitimbu, Mass balance, Water Quality, Water Polution
Eutrophication of urban water sources represents a challenge for water security and the maintenance of ecosystem services. This study analyzed the temporal variation of nutrient loads and the trophic state of the Jiqui Lake, an important water supply source for the Metropolitan Region of Natal. Between May and September 2025, weekly monitoring of total phosphorus (TP), total organic carbon (TOC), and chlorophyll-a (Chl-a) concentrations was carried out. The average external loads of TP and TOC were 52.9 mg/s and 4.4 g/s, respectively, with high variability (CV = 124.7% and 69.7%), this variation being mainly determined by variation in concentrations, and not by variation in flow rates. The lake acted predominantly as a nutrient sink, with an average retention of 27.4 mg/s (TP) and 1.2 g/s (TOC), which corresponds to 52% and 27% of the average external load of TP and TOC, respectively. The concentrations of PT and Chl-a in the lake water indicate a mesotrophic condition. However, because it is a shallow system dominated by aquatic macrophytes, the lake can maintain clear water even under high nutrient loads, limiting the isolated application of these indicators. Thus, the inclusion of macrophyte dynamics in the monitoring is recommended for a better assessment of the trophic state. It should be noted that the study did not encompass a complete hydrological cycle, and long-term monitoring is necessary.