Analysis of total nitrogen and chlorophyll a correlations in reservoirs in Ceará/Brazil

Abstract

Chlorophyll a (Chla) concentration is an important indicator to characterize algal biomass, reflecting water quality and the level of eutrophication of aquatic environments. This study analyzed 4315 total nitrogen (TN) and Chla samples in 155 reservoirs in Ceará, Brazil. Relationships were obtained between TN and Chla through simple linear regression and classified according to the statistical performance of the coefficient of determination (R²). The dynamics of these correlations were examined by analyzing the variance between classification groups concerning watershed, reservoir size, coefficient of variability, and trophic state. The concentration of pollutants was influenced by seasonality, which increased significantly from the wet to the dry period in most basins. The coefficients of determination between Chla and TN for the watersheds followed the trends of classic curves in the literature, with satisfactory models (R² > 0.3) in most reservoirs (53.3%). The variance analysis attested that the models’ performance was affected by the basins, the volumetric variation, and the change in the trophic state levels. There was no significant variance of R² between reservoirs of different sizes.