Abstract

AIM: There is currently no consensus regarding the physical and chemical variability of tropical reservoirs. In semiarid Northeastern Brazil, reservoirs are among other things used for human consumption, industrial water supply and intensive fish farming, all of which can impact water quality. The objective of this study was to evaluate the physical and chemical variability of the water in Sítios Novos, a reservoir in semiarid Northeastern Brazil, comparing samples collected in areas of intensive tilapia (Oreochromis niloticus) farming to samples from areas not directly impacted by aquaculture, in both the dry and the rainy season. METHODS: Between October 2010 and July 2011, data were collected on temperature, conductivity, pH, turbidity, salinity, chlorophyll a, dissolved oxygen, oxygen demand, total phosphorus and total nitrogen levels in the water column using a multiparametric probe at four different sampling locations. Physical and chemical differences between the four locations were evaluated with the Kruskal-Wallis (KW) test and Dunn's post test, while the t test, followed by Welchʼs correction, was used to compare samples collected in different seasons. RESULTS: No influence of intensive aquaculture was detected when comparing sampling locations near fish farms (180C and 300C) to locations not directly impacted by aquaculture (LIMN1, near the dam, and LIMN2, near the debouch of the São Gonçalo river). However, the sampling locations differed significantly (p<0.05) with regard to conductivity, pH, turbidity and chlorophyll a levels. CONCLUSIONS: The physical and chemical variability was greater between seasons than between locations when the data were analyzed with the t test. That analysis showed significant differences for 22 of 40 comparisons between the 10 physical and chemical parameters in the two seasons at the four sampling locations. In conclusion, the physical and chemical variability registered for the Sítios Novos reservoir throughout the study period indicates morphometric, meteorological and hydrological heterogeneity, with emphasis on the differences between LIMN2 and the other three sampling locations and between the rainy season and the dry season. According to the calculated trophic status index, the reservoir is supereutrophic in the rainy season and supereutrophic to hypereutrophic in the dry season.

Highlights

  • Over the last decades an increasing number of studies have been conducted on the dynamics of the physical and chemical variability of reservoirs around the world in order to subsidize the management of these resources (Carpenter et al, 1995)

  • The objective of this study was to evaluate the physical and chemical variability of the water in the Sítios Novos reservoir (Ceará, Brazil), comparing samples collected in areas of intensive tilapia (Oreochromis niloticus) farming to samples from areas not directly impacted by aquaculture, in both the dry season and the rainy season

  • The physical and chemical variables registered for the Sítios Novos reservoir in 2010-2011 yielded variation coefficients above 35% for turbidity, chlorophyll a, dissolved oxygen and oxygen demand (Table 1)

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Summary

Introduction

Over the last decades an increasing number of studies have been conducted on the dynamics of the physical and chemical variability of reservoirs around the world in order to subsidize the management of these resources (Carpenter et al, 1995). Studies range from simple environmental surveys to complex analyses, such as hydrodynamic modeling (Lindim et al, 2011) and trophic network modeling (Carpenter et al, 2008). Despite these efforts, no consensus has been reached regarding the physical and chemical variability of tropical reservoirs. An excessive number of reservoirs have been built, many of which small and shallow, creating a discontinuity between water bodies and compromising the efficiency of the water storage network (Medeiros et al, 2010)

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