Limnological characteristics of a reservoir in semiarid Northeastern Brazil subject to intensive tilapia farming (Orechromis niloticus Linnaeus, 1758)

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.

<b>Cyanobacteria community in two tropical eutrophic reservoirs in northeastern Brazil

“…The phosphorous showed the highest concentration in the dry season, a result also found by in studies in eutrophic reservoirs. Nevertheless, higher concentrations of this macronutrient and nitrogen forms were found in the rainy season, confirming Moura et al (2007b), Teixeira de Oliveira et al (2011), Dantas et al (2012) and Bezerra et al (2014). The profile for nitrogen was confirmed in this study and may be due to the input of sediments and nutrients from the reservoir margins.…”

“…Although phosphorus is frequently considered as the most important limiting factor for algal growth (DELAZARI-BARROSO et al, 2007), nitrogen limitation is recognized as the ideal condition for the occurrence of cyanobacterial blooms, reported in several studies in eutrophic ecosystems, highlighting the predominance of heterocystous species (MOURA et al, 2007a, 2007b, DELAZARI-BARROSO et al, 2007BICUDO, 2008, BEZERRA et al, 2014, COSTA et al, 2014, including reservoirs of Northeastern Brazil, probably due the high availability of phosphorous . Nevertheless, studies also demonstrated the predominance of cyanobacteria under phosphorus limiting conditions (CHELLAPPA et al, 2008, FIGUEREDO;GIANI, 2009) or found no relationship between cyanobacterial dominance and TN: TP ratio in eutrophic reservoirs .…”

Prevalence of paralytic shellfish poison-producing Planktothrix agardhii and Cylindrospermopsis raciborskii in a Brazilian semi-arid reservoir

“…In the case of nitrogen abundance however, those organisms lose their competitive advantage. Bezerra et al (2014), studying the same reservoir (Sitios Novos) from October 2010 to July 2011, identified N:P ratios from 8 to 14 indicating that the limiting factor may be, in fact, nitrogen. In spite of that, C. raciborskii did not show dominance over P. agardhii in our study and therefore, other factors rather than temperature or N:P ratio may be driving their relationship in Sítios Novos Reservoir.…”

Avaliação Colorimétrica Em Tomate De Mesa Minimamente Processado

“…ainda explica que nos trabalhos realizados em corpos de água maiores do semiárido brasileiro que medem parâmetros físicos e químicos da água, geralmente, não se fazem medições de salinidade, pois os açudes já são classificados como dulcícolas pelas empresas que controlam o abastecimento dos estados. As temperaturas encontradas são superiores a alguns estudos em águas continentais(BEZERRA et al, 2014;LUCENA, 2015). Rio Grande do Norte Lucena et al, (2015).…”