Abstract: A coastal karstic aquifer highly exposed to anthropogenic pollution and seawater intrusion is the main water supply source for Merida-Progreso inhabitants (Yucatan, Mexico). In this investigation fresh/ brackish water interface changes linked to precipitation events were identified and correlated with the Ghyben-Herzberg principle. Water level elevations and electrical conductivity values were manual and automatic recorded in a 26 wells monitoring network. Results indicate a fast water level increase (hours) to precipitation events, for example a 19 cm water level increase and 570 µmhos·cm-1 decrease measured at the fresh/brackish water interface were recorded in an observation well located west of Merida city less than 24 hours after a 60 mm rainfall. Predictions using the Ghyben-Herzberg principle do not correlate with in-situ measurements. Actual thickness of the freshwater lens change from rainy (33 m) to dry (31.5 m) season below Merida city, minor thickness changes along the year were identified north to Merida city (26 m freshwater lens thickness). | Resumen: La población en la región Mérida-Progreso, Yucatán, México, depende totalmente del agua subterránea que es obtenida de un acuífero kárstico costero, vulnerable a la contaminación antropogénica y natural por los efectos de la intrusión salina. El objetivo de estudio fue describir, espacial y temporalmente, el comportamiento de las interfases de agua dulce y agua salobre ante eventos de precipitación, y proponer alternativas que ayuden a explicar la respuesta observada y su relación con el principio de Ghyben-Herzberg. Se utilizó una red de 26 pozos de observación para determinar elevaciones del nivel del agua y cambios en la conductividad eléctrica en las interfases mediante mediciones manuales y una red automatizada. Los resultados indican que en general existe una respuesta rápida (del orden de horas) del nivel freático a la precipitación, por ejemplo un incremento de 19 cm en la elevación del nivel del agua al occidente de Mérida y un comportamiento irregular de las elevaciones de las interfases de agua salina (decremento de 570 µmhos·cm-1) y salobre ante eventos de precipitación (60 mm). De acuerdo con los resultados obtenidos, el principio de Ghyben-Herzberg no es aplicable para la determinación de la posición de la interfase de agua salina en la región. Finalmente, se definieron espesores de agua dulce bajo la zona urbana de Mérida para las temporadas de lluvia (33 m) y estiaje (31.5 m), y un espesor promedio de 26 m al norte de Mérida a 15 km de la línea de costa donde no hay una variación entre ambos periodos.

Neste trabalho, estudaram-se os efeitos de cinco níveis (N) de salinidade da água de irrigação (1,51; 2,79; 3,93; 5,15 e 7,22 dS m-1), no desenvolvimento inicial de duas cultivares de melão amarelo (Gold mine e AF646). O cultivo foi realizado na horta do Departamento de Fitotecnia da ESAM, localizada no município de Mossoró, RN, no período de 4 de novembro a 12 de dezembro de 1998, em recipientes plásticos com capacidade para 9 L, conduzidos ao ar livre, tendo como substrato Argissolo vermelho-amarelo eutrófico abrupto do horizonte Ap1, utilizando-se o delineamento em blocos inteiramente casualizados arranjados no esquema fatorial 2x5, com três repetições. As características: peso seco da parte aérea, área foliar e salinidade média e final do solo, foram avaliadas mediante análise de variância (teste F) e estudo de regressão. As cultivares Gold mine e AF646 apresentaram comportamento semelhante quanto a tolerância à salinidade da água de irrigação, com perda de fitomassa seca da parte aérea (FSPA) de 6,8% por aumento unitário da condutividade elétrica na água de irrigação. O comportamento da área foliar foi similar ao da FSPA. Observou-se efeito linear e quadrático da salinidade da água de irrigação sobre a salinidade média e final do solo, respectivamente.<br>The effect of five irrigation water salinity levels (N: 1.51, 2.79, 3.93, 5.15 and 7,22 dS m-1), on initial development of two yellow melon cultivars (Gold mine and AF646) was studied. The trial was conducted under field conditions in an orchard belonging to Department of Phytotechnic - ESAM, at Mossoró in the State of RIo Grande do Norte, Brazil, during the period of November 4 to December 12, 1998. Plastic pots with 9 L capacity filled with Alfisol soil (horizon Ap1) were used. Experimental design was a completely randomized block in a factorial scheme, with three replications. Shoot dry matter, leaf area, mean soil salinity and final soil salinity were evaluated through variance and regression analysis. Salinity tolerance was similar for Gold mine and AF646, with a loss of 6.8% of shoot dry matter for unit increase of electrical conductivity of irrigation water. A similar behavior was observed for leaf area. Irrigation water salinity induced linear effect on mean soil salinity and quadratic effect on final soil salinity.

Stream water quality is controlled by the interaction of natural and anthropogenic factors over a range of temporal and spatial scales. Among these anthropogenic factors, land cover changes at catchment scale can affect stream water quality. This work aims to evaluate the influence of land use and seasonality on stream water quality in a representative tropical headwater catchment named as Córrego Água Limpa (Sao Paulo, Brasil), which is highly influenced by intensive agricultural activities and urban areas. Two systematic sampling approach campaigns were implemented with six sampling points along the stream of the headwater catchment to evaluate water quality during the rainy and dry seasons. Three replicates were collected at each sampling point in 2011. Electrical conductivity, nitrates, nitrites, sodium superoxide, Chemical Oxygen Demand (DQO), colour, turbidity, suspended solids, soluble solids and total solids were measured. Water quality parameters differed among sampling points, being lower at the headwater sampling point (0m above sea level), and then progressively higher until the last downstream sampling point (2500m above sea level). For the dry season, the mean discharge was 39.5ls⁻¹ (from April to September) whereas 113.0ls⁻¹ were averaged during the rainy season (from October to March). In addition, significant temporal and spatial differences were observed (P<0.05) for the fourteen parameters during the rainy and dry period. The study enhance significant relationships among land use and water quality and its temporal effect, showing seasonal differences between the land use and water quality connection, highlighting the importance of multiple spatial and temporal scales for understanding the impacts of human activities on catchment ecosystem services.

A necessidade de uso de águas salinas na agricultura é crescente, devido à pressão sobre águas de boa qualidade, principalmente para consumo humano. Com este objetivo, foram estudados os efeitos de quatro níveis de condutividade elétrica da água de irrigação (CEa: 0,1; 5,0; 10,0 e 15,0dS m-1), obtidos mediante adição de NaCl sobre o desenvolvimento do coqueiro (Cocos nucifera L.) cv. "Anão Verde", com 3,5 anos de idade. O experimento foi conduzido em blocos casualizados, em solo arenoso, irrigado por microaspersão, no município de Parnamirim-RN, no período de janeiro de 2000 a março de 2001. A salinidade da água aumentou os intervalos de emissão foliar e de inflorescência e o número de flores femininas, bem como os teores de Na e de Cl na folha número 14, acompanhado de relações antagônicas entre Na-Ca, Na-K e Cl-N e sinergismo entre Na-Mg, mas sem manifestar sintomas visuais de efeitos tóxicos. Os teores ótimos de Na e Cl na folha 14 foram, respectivamente, 0,207 e 0,580%.<br>The necessity to use saline waters in agriculture has increased due to pressure on good quality water, principally, for human consumption. With this objective, the effects of four levels of electrical conductivity (0.1, 5.0, 10.0 and 15.0dS m-1) of irrigation water obtained by addition of NaCl were studied on the development of 3.5 years old coconut (Cocos nucifera L.) cv. 'Anão Verde'. The experiment was conducted in a sandy soil adopting a completely randomized block design and micro sprinkler irrigation system in the municipality of Parnamirim - RN, Brazil, during the period of January, 2000 to March, 2001. The salinity of water increased the interval of leaf emission and inflorescences and the number of female flowers per inflorescence as well as the contents of Na and Cl in leaf 14, accompanied by antagonism between Na-Ca, Na-K and Cl-N, and synergism between Na-Mg but without any visual symptoms of toxic effects. The optimum levels of Na and Cl in 14th leaf were found to be 0.207 and 0.580%.

As 70% of potable water on the planet is used in agriculture, alternatives are needed to reduce itsconsumption and optimize the use of water for cultivation. Hydrogels are hydro polymers capable of absorbinglarge quantities of water and have been used as an alternative to improve water storage in areas of shortage.This study aimed to assess the use of different doses of hydrogels for water storage in soil, emphasizing theadvantages and disadvantages of each dose. The doses of the hydrogel used were (4, 8 and 12 g per pot) to analysethe efficiency of the product compared to the control, depending on the availability of moisture and increase inelectrical conductivity. These variables were determined with the use of time-domain reflectometer (TDR) probe.The dose of 4 g per pot was more viable, compared to the manufacturer’s recommendation (8 g per hole, underfield conditions), because it presented similar moisture content, lower electrical conductivity and lower cost.The higher dose (12 g per pot) caused swelling of the soil resulting in loss of product and soil and possible rootstrangulation. | Frente ao uso de 70% de água potável do planeta que a agricultura consome, alternativas são necessáriaspara reduzir o consumo e otimizar o uso da água durante o cultivo. Os hidrogeis são polímeros hidrorretentorescapazes de absorver grande quantidade de água e estão sendo utilizados como alternativa viável para melhoraro armazenamento de água em áreas de escassez. O presente trabalho teve como objetivo avaliar a utilização dediferentes dosagens de hidrogel no armazenamento de água no solo destacando-se as vantagens e desvantagensde cada dosagem. Utilizaram-se três diferentes dosagens do hidrogel (4, 8 e 12 g por vaso com 8 kg de solo)permitindo analisar a eficiência do produto comparado à testemunha em função da disponibilidade de águae do aumento da condutividade elétrica do solo. Essas variáveis foram determinadas com o uso de sondas dereflectometria no domínio do tempo (TDR). A dosagem de 4 g por vaso mostrou-se viável pois comparada àrecomendação do fabricante (8 g por cova, em condições de campo), apresentou teor de água semelhante, menorcondutividade elétrica do solo e menor custo de implantação. A maior dosagem (12 g por vaso) causou inchaço dosolo acarretando em perda do produto, solo e possível estrangulamento radicular.

Se exponen algunos criterios sobre la calidad del agua para riego en lo que respecta a salinidad, sodicidad y toxicidad. Se señalan los parámetros a determinar cuando se evalúa la calidad de agua que incluyen Ph, contenido total de sales disueltas. Contenido de K, Cl, Na, B, índice de Mg, relación de adsorción de Na, Carbonato de Sodio residual y dureza. Se indican las normas de calidad de aguas de riego y su clasificació

Se exponen algunos criterios sobre la calidad del agua para riego en lo que respecta a salinidad, sodicidad y toxicidad. Se senalan los parametros a determinar cuando se evalua la calidad de agua que incluyen Ph, contenido total de sales disueltas. Contenido de K, Cl, Na, B, indice de Mg, relacion de adsorcion de Na, Carbonato de Sodio residual y dureza. Se indican las normas de calidad de aguas de riego y su clasificacio.

The objective of this study was to evaluate the inorganic parameters in the water of the Texcoco river. Sampling took place at 10 sites along the watershed (between 2500 and 2240 m above sea level) during the four seasons of the year for three years, with repetitions. The diagnostic parameters and methods used were, for potassium, sodium, magnesium, and calcium, the internal method MI-AM-011 (atomic absorption); phosphates with MI-FQUAR-012, chlorides NMX-AA-073-1981, electrical conductivity and nitrogen of nitrates NOM-AA-93-1984 and NOM-AA-79-1986, pH NMX-AA-08-1980. The three-year average concentrations of calcium, magnesium, potassium, sodium, chlorine, nitrates, and electrical conductivity were low. However, the concentrations of sodium and electrical conductivity were close to medium quality. The concentrations of sodium during Years 2 and 3 were classified as medium. The concentration of phosphates was high. Electrical conductivity during Years 1 and 3 were classified as medium. The concentrations of sodium and electrical conductivity in Seasons 1 and 4 grade a medium quality. The concentration of phosphates during the four seasons and three years were classified as high. Variability of cations and anions at different times of the year was an almost generalized behavior and statistically significant.