COMPORTAMENTO DAS VARIAVEIS QUALITATIVAS DO AÇUDE PEREIRA DE MIRANDA – PENTECOSTE/CE, NO PERÍODO DE ESTIAGEM

Pesquisas demonstram que o processo de eutrofização que ocorre nos reservatórios do semiárido brasileiro, está relacionado às altas temperaturas e alterações antrópicas na bacia hidrográfica. Esse fenômeno tem atingido a qualidade da água, e resultado em prejuízos incomensuráveis, especialmente para a sustentabilidade da biota aquática e interferindo diretamente no abastecimento humano e de perímetros irrigados. O objetivo deste trabalho é avaliar a qualidade da água do açude Pereira de Miranda, localizado no município de Pentecoste, Ceará, a partir de dados limnológicos. A partir da contagem de fitoplâncton observou-se a predominância de espécies de cianobactérias potencialmente tóxicas, como a Plantothrix Agardhit, Plantothrix sp. e Cylindrospermopsis Raciborskii. Por conseguinte, o resultado da aplicação do Índice de Estado Trófico - IET indicou que o reservatório permaneceu eutrófico todo o ano de 2012, período de realização do estudo, e que a aceleração desse processo está ocasionando a redução do oxigênio na camada do hipolímnio, e intensificando os processos de estratificação e desestratificação nos perfis verticais da coluna de água referentes às variáveis temperatura, condutividade elétrica e pH da água

Environmental factors influencing CyanoHABS in climate change scenario: spatio-temporal analysis in Brazilian semi-arid reservoirs

Several environmental factors have been shown to promote cyanobacteria in semi-arid regions, including high temperature, long photoperiods, alkaline pH, and nutrient pollution. Furthermore, global warming trends are particularly intensified in these regions, with droughts becoming longer and more severe due to higher evaporation and lower precipitation volume. The goal of this study was through canonical correspondence analysis that incorporated environmental parameters (biotic and abiotic components) to prognosticate blooms of cyanobacteria and cyanotoxins in 20 drinking water reservoirs (2,489 samples) in the semi-arid region of Ceará, Brazil. Across four years, 114 different phytoplankton taxa were identified; however these reservoirs were dominated by cyanobacteria (24 taxa), interestingly, specific cyanobacterial taxa were influenced by different biotic and abiotic factors. For example, nitrogen-to-phosphorus (N:P) and evaporation were positively related to saxitoxin-producing taxa, especially Raphidiopsis raciborskii, while temperature, electrical conductivity, total phosphorus, and transparency were positively associated with microcystin-producing taxa, such as Microcystis aeruginosa. Climate forecasts predict higher evaporation and temperatures in the semi-arid Ceará region, which will likely magnify droughts and water scarcity as well as promote toxic cyanobacterial blooms in reservoirs in the future. Therefore, understanding the factors associated with algal blooms dominated by specific taxa is paramount for water resource management

Morfometria e uso e ocupação da bacia hidrográfica do Carão, Estado do Ceará, Brasil

The aim of this work was to analyze the morphometry and the type of use and occupancy of the basin Carão reservoir, located in the municipality of Tamboril - Ceará, seeking to understand the natural and anthropogenic processes acting in this enviroment, favoring thus the development of conservation plans and natural resources management. The reliefs morphometric characteristics and the basins ways to use and occupation were obtained by the software ArcGIS 9.3\uae, from techniques of remote sensing and GIS. The basin is considered small, with estimated area of 309.55 km2 and 103.16 km perimeter. Among other things, an elongated and narrow shape was verified, with low drainage density and flat terrain and slightly wavy, whose slopes are presented below 20%, configuring thus so little disposition to flooding in the basin. It was observed a relationship of use and occupation targeted by the lower slope of the terrain and hydrographic presence,determining a bigger pressure by humam activities in these areas, representing a potential modifier of the water quality of the reservoir Carão. Relationship was observed for use and occupation targeted by the lower slope of the terrain and the presence basin, causing increased pressure in these areas by human activities, representing a potential modifier of the water quality of the Carão reservoir.Pages: 8138-814

Influence of rainfall on the trophic status of a brazilian semiarid reservoir - doi: 10.4025/actascibiolsci.v35i4.18261

This study evaluated the trophic conditions of the reservoir located in the urban perimeter of the town General Sampaio, semiarid region of the Ceará State, Brazil and its relationship with seasonal variation in rainfall between 2010 and 2011. It was obtained data for Secchi disk transparency, total phosphorus, and chlorophyll a to calculate the Trophic State Index (TSI), as well as rainfall data. The Trophic State Index (TSI) proposed by Carlson (1977) and modified by Toledo Junior (1990) was used to test the influence of the seasonal variation in rainfall on hydrological variables and on trophic conditions of the reservoir in 2010 and 2011. There was seasonal variability in variables analyzed between climatic periods (rainy and dry) and trophic conditions determined through the trophic index indicated conditions ranging from oligotrophic to eutrophic during the two years analyzed in this reservoir. Under these circumstances, one may conclude that the trophic status is related to seasonal fluctuations in the hydrology of the system controlled by rainfall, which is a common feature of semiarid regions.

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

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