Suzana Maria Gico Lima Montenegro

Improving agricultural water management in the semi-arid region of Brazil: experimental and modelling study

Agricultural practice in the semi-arid region of Brazil is highly dependant on irrigation. As access to water is limited in the region, there is a need to guarantee its efficient use, especially in small-scale farming schemes. Models adequately calibrated for semi-arid conditions and for typical crops are useful tools for analysis of on-farm strategies to improve water use efficiency. A physically based agrohydrological model, SALTMED, is calibrated and validated for carrots (Daucus carota L., Brasília variety) and cabbage (Brassica oleracea var. capitata), two of the main crops in small-scale irrigated agriculture in the northeast of Brazil. SALTMED is also calibrated for castor beans (Ricinus communis L.) under rainfed conditions. The results demonstrated the suitability of the SALTMED model for simulating soil water dynamics and crop yield in the area. Predicted time series of soil water content and matric potential of root zone showed good agreement with observed values, as shown graphically and statistically. Using the calibrated and validated model, management scenarios were analysed in terms of applied irrigation water, irrigation frequency, soil and crop types. Impact of climate change on the irrigation water requirements was also briefly analysed for possible changes in annual temperature using two different emission scenarios. Analysis of possible impact of climate change on temperature related to two emission scenarios on the area showed an increase around 11% of the crop water requirement for carrots and cabbage, for the low emission scenario, and around 17% for the high emission scenario. The analysis of management scenarios indicated possible over-irrigation in the area. The simulation showed that the deficit irrigation was a useful water-saving strategy for the region. The simulations also indicated that irrigation frequency affected crop water use and differed according to the soil type.

Origins and processes of groundwater salinization in the urban coastal aquifers of Recife (Pernambuco, Brazil): A multi-isotope approach

In the coastal multilayer aquifer system of a highly urbanized southern city (Recife, Brazil), where groundwaters are affected by salinization, a multi-isotope approach (Sr, B, O, H) was used to investigate the sources and processes of salinization. The high diversity of the geological bodies, built since the Atlantic opening during the Cretaceous, highly constrains the heterogeneity of the groundwater chemistry, e.g. Sr isotope ratios, and needs to be integrated to explain the salinization processes and groundwater pathways. A paleoseawater intrusion, most probably the 120 kyB.P. Pleistocene marine transgression, and cationic exchange are clearly evidenced in the most salinized parts of the Cabo and Beberibe aquifers. All (87)Sr/(86)Sr values are above the past and present-day seawater signatures, meaning that the Sr isotopic signature is altered due to additional Sr inputs from dilution with different freshwaters, and water-rock interactions. Only the Cabo aquifer presents a well-delimitated area of Na-HCO3 water typical of a freshening process. The two deep aquifers also display a broad range of B concentrations and B isotope ratios with values among the highest known to date (63-68.5‰). This suggests multiple sources and processes affecting B behavior, among which mixing with saline water, B sorption on clays and mixing with wastewater. The highly fractionated B isotopic values were explained by infiltration of relatively salty water with B interacting with clays, pointing out the major role played by (palaeo)-channels for the deep Beberibe aquifer recharge. Based on an increase of salinity at the end of the dry season, a present-day seawater intrusion is identified in the surficial Boa Viagem aquifer. Our conceptual model presents a comprehensive understanding of the major groundwater salinization pathways and processes, and should be of benefit for other southern Atlantic coastal aquifers to better address groundwater management issues.

Variabilidade espacial de atributos físicos em solos de vale aluvial no semiárido de Pernambuco 1

Soil physical and hydraulic characteristics are relevant for agricultural management, particularly at irrigation districts. The objective of this study was to evaluate the spatial variability of physical attributes of soil in an alluvial valley in the semiarid region of Pernambuco State, at the Ipanema River Watershed. Statistical techniques and geostatistics were applied to observe the degree of dependence and the spatial variability of soil physical properties, in plots adopted for communal agriculture. The coefficient of variation for the hydraulic conductivity was high, medium for soil resistance to root penetration and for sand, clay and silt. For bulk density, particle density and porosity, however, such coefficient was low. Spatial dependence structures were investigated, with ranges spanning from 135 m, for soil hydraulic conductivity, to 465 m, for silt content. Contour map was produced by kriging interpolation, representing the spatial variability of hydraulic conductivity, which showed moderate spatial dependence. Resistance to root penetration, soil density and particle distribution presented spatial random behavior, for the adopted spatial scale. It was possible to identify regions with higher agricultural potential. From the produced map, it was highlighted that loam soils usually present higher resistance to root penetration, and low hydraulic conductivity.

Glacial recharge, salinisation and anthropogenic contamination in the coastal aquifers of Recife (Brazil)

Implying large residence times and complex water origins deep coastal aquifers are of particular interest as they are remarkable markers of climate, water use and land use changes. Over the last decades, the Metropolitan Region of Recife (Brazil) went through extensive environmental changes increasing the pressure on water resources and giving rise to numerous environmental consequences on the coastal groundwater systems. We analysed the groundwater of the deep aquifers Cabo and Beberibe that are increasingly exploited. The processes potentially affecting groundwater residence times and flow paths have been studied using a multi-tracer approach (CFCs, SF6, noble gases, 14C, 2H and 18O). The main findings of these investigations show that: (1) Groundwaters of the Cabo and Beberibe aquifers have long residence times and were recharged about 20,000years ago. (2) Within these old groundwaters we can find palaeo-climate evidences from the last glacial period at the tropics with lower temperatures and dryer conditions than the present climate. (3) Recently, the natural slow dynamic of these groundwater systems was significantly affected by mixing processes with contaminated modern groundwater coming from the shallow unconfined Boa Viagem aquifer. (4) The large exploitation of these aquifers leads to a modification of the flow directions and causes the intrusion through palaeo-channels of saline water probably coming from the Capibaribe River and from the last transgression episodes. These observations indicate that the current exploitation of the Cabo and Beberibe aquifers is unsustainable regarding the long renewal times of these groundwater systems as well as their ongoing contamination and salinisation. The groundwater cycle being much slower than the human development rhythm, it is essential to integrate the magnitude and rapidity of anthropogenic impacts on this extremely slow cycle to the water management concepts.

Análise quantitativa de parâmetros biofísicos de bacia hidrográfica obtidos por sensoriamento remoto

The objective of this work was to quantitatively evaluate the biophysical parameters, obtained by remote sensing, for the range area of the Tapacura River Basin, in Pernambuco state, Brazil. Landsat 5‑TM images of 7/10/1989, 7/6/2005, and 8/29/2007 were used. The images were registered with a polynomial geometric correction of first order. Radiometric calibration, reflectance, transmittance and planetary albedo were calculated and, subsequently, thematic maps of surface albedo, surface temperature and enhanced vegetation index (EVI) were generated. The surface albedo showed increasing average values between the 1989 and 2005 images, which indicates the urban territorial expansion. The image of 8/29/2007 showed the highest land surface temperature, followed by the temperatures showed in the images of 7/10/1989 and 7/6/2005, and the highest values were those of the urban networks. The 1989 image showed the highest average value for EVI, which indicates that there was a higher vegetation presence in that date.

Evapotranspiração e estimativa da água consumida em perímetro irrigado do Semiárido brasileiro por sensoriamento remoto

The objective of this work was to map the actual evapotranspiration (ETr) and to determine the volume of water used in the irrigation project of Sao Goncalo, PB, in the Brazilian Semiarid Region, using remote sensing. TM/Landsat 5 images were acquired from the study area, in 2008, and were used to obtain thematic maps of daily ETr. Two dwarf coconut crops were selected for validation of the results of evapotranspiration obtained by the surface energy balance algorithm for land (ETSebal) and the FAO‑56 method (ETFAO). In order to determine ETFAO, the product between the culture coefficient, the adjustment coefficient, and the reference evapotranspiration was used. The differences obtained by the two techniques resulted in root mean square error, mean relative error, and mean absolute error equal to 0.53 mm, 9.46%, and 0.43 mm, respectively. In the irrigated areas, ETr represented about 85% of net radiation and, in rainfed plots, only 12.5%. The mapping of ETr clearly delimitated the irrigated and nonirrigated plots, as well as the differences within the irrigated perimeter of the project under investigation. The volume of water applied in the irrigation project, only in the period from July to December, represents more than 60% of the capacity of the Sao Goncalo reservoir.

Variabilidade espaço-temporal da condutividade elétrica da água subterrânea na região semiárida de Pernambuco

RESUMO Quando mal-conduzida, a irrigacao pode causar degradacao dos solos e da agua subterrânea, por potencializar o risco de salinizacao. Este problema e mais evidente em regioes semiaridas, nas quais as caracteristicas fisico-climaticas contribuem para seu agravamento. Uma das variaveis mais utilizadas para avaliar a concentracao de sais soluveis na agua de irrigacao e no solo, e a condutividade eletrica. Neste trabalho, buscou-se avaliar a variabilidade espacial e temporal da condutividade eletrica da agua subterrânea utilizada para irrigacao em um assentamento rural, no semiarido pernambucano. Tecnicas estatisticas descritivas e geoestatisticas foram aplicadas para identificacao dos padroes de variabilidade e dependencia espacial da condutividade eletrica, visando ao mapeamento da salinidade da agua subterrânea. Verificou-se que a condutividade eletrica possui variabilidade media a alta, com dependencia espacial moderada, em que a textura do solo e o regime pluviometrico influenciam na variacao espacial e temporal da condutividade eletrica, que vem aumentando ao longo dos anos, na area estudada.

Determinação do saldo radiativo na Ilha do Bananal, TO, com imagens orbitais

Remote sensing may be used to identify changes that occur in land use of Earth, resulting from natural and/or anthropic processes. Many of these changes can be diagnosed from the monitoring of radiative exchanges that take place at the surface. In this sense, this study aims to determine the net radiation at surface, by means of sateLλite images covering Bananal Island, in the State of Tocantins, Brazil. TM-Landsat 5 images obtained in 2005 (cloud free), were used to generate maps of instantaneous and daily net radiation (Rn) based on SEBAL. The Rn values were validated with measurements performed in a micrometeorological tower installed within the Bananal Island. The instantaneous Rn values varied between 488.0 and 535.0 W m-2; while the daily Rn values varied between 132.7 and 145.3 W m-2. The disturbed areas showed decrease in net radiation. The daily net radiation presented relative mean error, mean absolute error and square root of mean square error equal to 1.95%, 2.78 W m-2 and 3.36 W m-2; respectively. According to the results, it may be concluded that the methodology used for Rn determination presented good accuracy.

Análise da variabilidade espaço-temporal e identificação do padrão da precipitação na bacia do Rio Tapacurá, Pernambuco

The study aimed to evaluate the space-time variability of rainfall for the period 1970-2000, in Tapacura river basin, located in Pernambuco State. Many statistical parameters were used to analyze the monthly and annual rainfall, such as mean standard deviation, normalized deviation, fitted equation and coefficient of variability. The study showed a major concentration of rainfall between March and July, when 60% of annual rainfall occurred, and that the dry season occurred between August to February. The annual variability showed a significant decrease of the rainfall in order of -20% compared to the mean rainfall. About rainfall spatial variability, it was verified that it decreases at the direction East-West, and that the periods with low rainfall depths have higher coefficient of variation.

Variabilidade espacial das frações granulométricas e da salinidade em um Neossolo Flúvico do semi-árido

Analysis of the physical attributes and salinity of soils is important for proposing management strategies in irrigated areas. The objective of this study was to evaluate the spatial dependence of the granulometric fractions and electric conductivity of the saturation extract in an area irrigated in the semi-arid of Pernambuco State. A 5 x 5m regular mesh was adopted, with 98 sampling points collected at depth 0-20cm. The variables have been analysed through statistics and geoestatistics. The variation coefficients of the saturation extract were 26.08; 14.81; 16.01 and 28.00% for sand, clay, silt and electrical conductivity of the saturation extract, respectively. The spatial dependence was identified as high for the granulometric fractions and as moderate for the electric conductivity, with ranges of 56; 50 and 55 and 35m, respectively. The electric conductivity has a strong spatial correlation with silt content, presenting range of 52m, for the cross semivariogram. The results highlight the importance of the silt fraction in the spatial distribution of salinity in loam soils, and its relevance for adequate management of these soils.