Proposal of a trophic state index in semiarid reservoirs using data of the Banabuiú Basin, state of Ceará, Brazil

Abstract

Aim This study aimed to develop a Trophic State Index that simulates the cumulative impact in 18 reservoirs in the Banabuiú basin, located in the semiarid region of the State of Ceará. Methods Analyses were made for physical (temperature, transparency and turbidity), chemical (dissolved oxygen, pH and total phosphorus) and biological (chlorophyll-a) variables as indicators of reservoir water quality. Data used in this study were made available by the Water Resources Management Company of the State of Ceará (COGERH), in the years between 2010 and 2013. An adaptation was developed for trophic classification (TSISA), incorporating the three most relevant variables for trophic evaluation, total phosphorus, chlorophyll-a and transparency. For interpreting the data set, we used multivariate statistics as Hierarchical Cluster Analysis (HCA) and Factor Analysis/Principal Component Analysis (PCA). Results The similarity of Banabuiú basin reservoirs in relation to water eutrophication gave rise to three distinct groups: I, II and III consisting of nine, four and five reservoirs, respectively. The calculation of minimum and maximum values and percentiles of the correlated parameters defined four classes of trophic state; it was observed that the reservoirs in the group I showed trophic classification predominantly between oligotrophic (54.7%), mesotrophic (30.2%), group II, eutrophic (44.4%) and hypertrophic (33.3%) and those of the group III, eutrophic (39.1%) and hypertrophic (60.9%). Conclusions The TSISA presented a simple methodology and easy interpretation of the data, grounded in the quality of water of reservoirs located in the semiarid region of Ceará. Thus, its use can contribute for the reduction of errors in the inference of the trophic state of reservoirs in this region and should be considered as an indicator for more detailed studies.

Análise de atributos limnológicos em reservatórios do semiárido nordestino

“…As águas dos reservatórios analisados são no geral utilizadas para fins de abastecimento, mas ao longo dos anos, tiveram os seus usos expandidos para outras finalidades, como irrigação, recreação, aquicultura, pesca, piscicultura e turismo, a permutação do uso da água, é comum e já foi observada em outros trabalhos como o de Pessoa et al (2017) e Chaves et al (2019). As informações das atividades desenvolvidas nesses reservatórios são importantes para o entendimento dos processos que integram esses corpos d'água (Chaves et al, 2019), demonstrando como os usos impactam diretamente na conservação ou deterioração da qualidade da água desses ambientes aquáticos (Rolim et al, 2019 (Lacerda et al, 2018;Chaves et al, 2019).…”