Abstract
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.
Highlights
Water is an indispensable and irreplaceable natural resource, since it is an essential element for the development of all life forms on the planet
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
An adaptation was developed for trophic classification (TSISA), incorporating the three most relevant variables for trophic evaluation, total phosphorus, chlorophyll-a and transparency
Summary
Water is an indispensable and irreplaceable natural resource, since it is an essential element for the development of all life forms on the planet. The problem of water shortage and the inappropriate use of natural resources is worse in semiarid regions, such as Northeast Brazil, where natural resources, soil and water, are limited and constitute fragile ecosystems. These regions are characterized by water deficit and high positive balance of solar energy, which has contributed to high evaporative rates of water bodies. Ceará is the State with the highest number of regulation reservoirs, standing out the Jaguaribe River basin, with a high number of impoundments with a capacity of accumulation of more than 10 hm, especially the Orós, Banabuiú and Castanhão dams In this basin, demands often exceed the drought flow, and, with the regulation of flows promoted by the dams, water availability is capable of increasing the water supply (ANA, 2015)
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