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Original Article • Acta Limnol. Bras. 31 • 2019 • https://doi.org/10.1590/S2179-975X12517 linkcopy

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

Proposta de índice de estado trófico em reservatórios do semiárido a partir de dados da bacia do Banabuiú, estado do Ceará, Brasil

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    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.

    Keywords:  index; eutrophication; water quality; Ceará semiarid region

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