Análise multivariada aplicada ao estudo do fósforo total em reservatórios da bacia hidrográfica do Acaraú - CE

Abstract

The state of Ceará was the precursor in the culture of the damming in the 20th century. Freshwater reservoirs, created essentially for human supply and animal watering, today are essential for the movement of the economy in municipalities in the interior of Ceará. However, the water quality of Ceará's reservoirs is deteriorated due to the intrinsic characteristics of the northeastern semi-arid region and anthropic actions, which accelerate the eutrophication process in lentic environments, caused by the hyperfertilization of trophic nutrients such as phosphorus and nitrogen. The objective of this work is to investigate limnological environmental variables and indices that have correlations with the concentrations of total phosphorus in the four largest reservoirs of the Acaraú watershed (Araras, Ayres de Sousa, Edson Queiroz and Taquara) from 2016 to the first half of 2021, through data provided by the Programa Nacional de Avaliação de Qualidade das Águas (PNQA). The technique of multivariate statistics by principal components (PCA) was used to verify the most relevant environmental parameters in the study of total phosphorus in each reservoir through the PAST software version 4.08. It was noted that the concentrations of total phosphorus in the Macaws and Edson Queiroz reservoirs decreased in periods of greater rainfall in the Ayres de Sousa reservoir while the constant rates remained, indicating constant recharges from external sources. All four reservoirs, based on the Lamparelli Trophic State Index, were eutrophic during the study period. Total phosphorus obtained relevant weightings and indicative of deterioration of water quality in the Araras and Taquara reservoirs, in which there is a tendency to increase the nutrient phosphorus at the expense of low depths and low wind speeds, respectively. In the Ayres de Sousa and Edson Queiroz reservoirs, total phosphorus obtained low weighting indexes, which indicates that other variables are more prone to deterioration in the water quality in them, such as the fraction of soluble reactive phosphorus, chlorides and chlorophyll-a. , the latter indicating the presence of photosynthetic microorganisms and potential toxin producers. The study of the main components of total phosphorus concentrations can help in the elaboration of water resources management plans and research for pollution indicators in the reservoirs that are part of the Acaraú hydrographic basin.