Luiz Carlos Guerreiro Chaves

A new proposal of the classification of irrigation water.

A study on surface water quality in the Acarau Basin, in the North of the state of Ceara, Brazil was performed. Qualitative dynamics of water flowing to the Acarau River that supplies water to the irrigation project in the area was evaluated. Multivariate Factor Analysis/Principal Component Analysis was used for evaluation of water quality in order to develop a water quality index (WQI) that reflects soil salinity and sodicity risks and water toxicity to plants. From April/2003 to September/2005 water were sampled from ten sampling sites covering the basin, where physical and chemical parameters that contribute to the WQI were evaluated. The results showed that the use of water for irrigation in the Acarau basin, according to the proposed WQI, are potentially prone to cause toxicity (crop cycle) and sodicity problem in the long run, if the soil-water-plant is not carefully monitored.

Similaridade e fatores determinantes na salinidade das águas superficiais do Ceará, por técnicas multivariadas

Tecnicas de estatistica multivariada foram empregadas com o objetivo de identificar a similaridade dos reservatorios superficiais do Ceara, com relacao a salinidade das aguas e identificar os fatores determinantes da qualidade das aguas. Os dados utilizados foram provenientes do banco de dados da Companhia de Gestao dos Recursos Hidricos do Ceara, no periodo de 1998/2009, no total de 807 amostras de 48 reservatorios. Os parâmetros considerados foram: Cl-, Ca2+, Mg2+, Na+, HCO3 -, CE e RAS. A analise de agrupamento hierarquico formou quatro grupos distintos, sendo determinantes os tipos e concentracoes dos sais analisados. Nos grupos 1 e 2 a salinidade da agua e definida principalmente pelas condicoes naturais de solo e clima da regiao e nos grupos 3 e 4, alem desses fatores, a influencia antropica. O emprego da analise de fator/analise de componente principal promoveu a reducao de sete caracteristicas das aguas superficiais do Estado Ceara, para dois componentes, sendo que o primeiro componente explicou 57,28% e o segundo, 26,77% da variância contida nas sete variaveis. Os parâmetros mais representativos na variabilidade da salinidade das aguas foram Cl-, CE, Na+ e Mg2+, relacionados com a solubilidade dos sais.

Impacto da irrigação sobre os solos de perímetros irrigados na Bacia do Acaraú, Ceará, Brasil

To identify the soil salinity and sodium risk, due to irrigation management, was carried out a comparative study of the Electric Conductivity (EC) and Sodium Adsorption Ration (SAR) values, between an irrigated area and an undisturbed land (MN). The investigation occurred at two Irrigated Districts: Baixo Acarau (DIBAU) and Araras Norte (DIPAN) sited in Acarau watershed, Ceara, Brazil. Soils samples were collected, in 0-30 m; 30-60 m; 60-90 m and 90-120 cm layers, in bimestrial period, from May/2003 to September/2005. Analyses were carried out at Embrapa Soil and Water Laboratory. To identify if the addition of salts in the soils were statistically significant the Wilcoxon paired test was applied. The EC increments were higher in DIPAN with an average of 250%, while in DIBAU the average reached 50%. The total rainfall registered in 2004 was enough to guide the irrigated soils in DIBAU to a similar condition of undisturbed land area. The same did not occur with the soil in DIPAN. The medium values of SAR increments in DIBAU were around 200%. An increasing of SAR was not registered at DIPAN. Therefore, the soils of DIBAU showed higher tendency to sodium problems, while the soils at DIPAN presented a higher risk of salinity. Despite of the registered increments, EC and SAR values were lower than those of salinity and sodium soils, respectively. Also, results showed that the action of rainfall in the leaching process of salts was higher at DIBAU, due to the soil texture (sand soils).

Water as Capital and Its Uses in the Caatinga

Due to climate and local geology, the only source of water for the entire Caatinga is rainfall. Annual rainfall averages 773 mm, and 70% of this amount may precipitate in a single month. The rainfall regime in the region is more strongly affected by the great spatio-temporal variability of the rains than by the total amount of rainfall precipitated annually. This variability results in several microclimates, from a desert climate in the central region to a rainy climate along the coastal areas and mountainsides due to orographic effects, with alternating drought and flood years. The scarcity of water in the region is also linked to the physical environment, such as shallow soils, high evaporative demand, the reduction of vegetative cover, and social organization. The waterways that make up the drainage network of the Caatinga are almost entirely intermittent or ephemeral, and throughout the dry season water is available from artificial lakes and artificial perennial use of rivers. These constitute the main source of water for many uses, making the prevention and control of pollution in these sources essential to ensuring a safe water supply. This natural asset has many uses, from soil and vegetation development to climate thermoregulation. In fact, water, soil, and vegetation act in a complementary way; if the existence of vegetation is dependent on water availability, then vegetation is crucial to the infiltration of water into the soil and the maintenance of water quality.

PRECIPITAÇÃO PLUVIOMÉTRICA NA VARIABILIDADE ESPAÇO-TEMPORAL DA CE E RAS EM UM RESERVATÓRIO DA REGIÃO SEMIÁRIDA

Resumo – Em reservatorios localizados no semiarido nordestino, variacoes nas concentracoes de sais soluveis se tornam mais evidentes devido as condicoes climaticas da regiao. Objetivou-se identificar a influencia da precipitacao pluviometrica na variabilidade espaco-temporal dos parâmetros de condutividade eletrica (CE) e razao de adsorcao de sodio (RAS) no reservatorio Oros, Ceara. Os dados foram coletados no periodo de janeiro de 2010 a dezembro de 2012 a 30 cm de profundidade, em 3 pontos (P02, P03 e P06). Observou-se que tanto no periodo seco como no chuvoso dos anos analisados, valores de CE variaram de 0,12 a 0,62 dS∙m -1 , sendo maximo na estacao seca de 2010 em todos os pontos. Com relacao a RAS, observou-se uma tendencia de reducao de seus valores na estacao chuvosa em todos os anos, ocorrendo o inverso no periodo seco. Esses valores superiores mostram uma predominância do ion sodio em relacao aos ions calcio e magnesio. Observa-se que em todos os pontos amostrais e em ambos os periodos analisados, os valores da RAS foram inferiores ao limite que restringe o uso da agua para irrigacao que e 3,0. Foram verificados valores medios de CE e RAS elevados na bacia de contribuicao do ponto P02, com valores de CE medio de 0,29 dS∙m -1 e RAS medio de 1,21. Isso pode ser explicado pela maior area de drenagem e lavagem dos sais provenientes nessa bacia, bem como devido a maior pluviosidade.