Análise e modelagem das relações entre nutrientes e fitoplâncton em reservatórios no Ceará

Abstract

This research aimed to analyze the relationships between total phosphorus (P), total nitrogen (N), and chlorophyll a (Cla) in a small urban reservoir and in rural reservoirs. A field study was carried out on the urban reservoir, located at Fortaleza, Ceará, to analyze the water quality parameters and then compare the results with historical data of 35 rural reservoirs located in the semiarid region of the Brazilian northeast, in the state of Ceará. Empirical correlations were developed among these nutrients and Cla. Then, different levels of nutrient load reduction were analyzed with the empirical correlations obtained and the water quality complete moisture hypothesis, whose phosphorus decay coefficient used was the one developed for semiarid regions. The results showed that P best described the concentration of Cla in all reservoirs, using power adjustment equations. It was also shown that the concentrations of P in the urban reservoir were higher than those of the rural ones, with a mean of 1,76 mg/L and a N:P correlation of approximately 1, while the rural reservoirs had mean concentrations between 0,04 – 0,59 mg/L and N:P between 5 – 50. The analysis of the different load scenarios showed that different levels of P load reduction could be adopted depending on the P and Cla concentrations desired. Finally, it was concluded that the models proposed are applicable and useful as a means to aid decision making in the management of water resources.