Origin of the groundwater salinization in La Aldea coastal aquifer (Gran Canaria, Canary Islands)

[EN] Groundwater chemistry in La Aldea aquifer (Gran Canaria, Canary Islands) shows high contents of chloride and nitrate ions. The salinization process has been modelled using the geochemical data, taking into account the results of a previous flow model. The results allow to identify the salinity of the recharge from the rainfall under aridity conditions and the irrigation returns like the main causes of the groundwater salinization.

Temporal evolution of emerging contaminants, priority substances and heavy metals most frequently detected in reclaimed water and grounwater in a volcanic aquifer

[EN] The presence of emerging contaminants has been previously described in reclaimed water and groundwater of Gran Canaria (Spain). Despite of the environmental risk associated to irrigation with reclaimed water (R), this practice is necessary considering sustainability of the hydrological cycle in semiarid zones, especially regarding agricultural activity. The aim of this study was: i) to analyse the evolution during two years of contaminants of emerging concern, priority substances (2008/105/EC) and heavy metals in reclaimed water (R) and in a volcanic aquifer in the NE of Gran Canaria where a golf course has been irrigated with R since 1976 and ii) to relate this presence with physicochemical water properties and hydrogeological media. Reclaimed water and groundwater (GW) were monitoring quarterly from July 2009 to September 2011. Sorption and degradation processes in soil account for more compounds being detected in R. Diazinon and chlorfenvinphos were detected always in R and terbuthylazine, terbutryn and diuron at 90% of frequency. Considering all the samples, the most frequent compounds were chlorpyrifos ethyl, fluorene, phenanthrene and pyrene. Although their concentrations were frequently below 50 ngL-1, some contaminants, were occasionally detected at higher concentrations. Chlorpyrifos ethyl and diuron are priority substances detected frequently and at high concentrations so they must be included in monitoring studies. Geology and location seem to be related to the emerging compounds presence due to occasional contamination events (not related to R irrigation) and therefore not to an existence of a dangerous diffuse contamination level. Thus, it is preferable to select wells with less stable chemical water quality, in order to monitor the risk of emerging compounds presence. Considering the relationship between contaminant presence, chemical water quality, seasonal variation, hydrogeological characteristics and wells location we can conclude that chlorpyrifos ethyl and diuron were the most dangerous priority substances in terms of GW quality so they must be included in all of the monitoring studies, at least in Canary Islands.

Reconstruction of the aquifer history of Gran Canaria

[EN]A study on the recent history and current state of the aquifer in the Island of Gran Canaria (Canary Is., 28oN, 15oW) is performed. Though rainfall is scarce on the island, traditional agricultural practices and small population were able to keep the aquifer in a constant state for centuries. Nevertheless, at the beginning of the 20th Century, culture of several water-consuming species was introduced on a commercial basis due to the relative proximity of the Canaries to continental Europe and to the possibility of more than one yearly harvest. This led to generalised well digging (more than 300m deep in many cases) and to the appearance of a chronic hydraulic deficit, as well as to spoiling vastcoastal areas of the aquifer through intrusion of brackish water. In the mid 1960’s, coincident with the apex of agricultural exploitation, massive tourism appeared in the scene. This new activity soon became a susbstitute for Agriculture, but it attracted more new labour force to the island, and a fast growth of population was the main result. Moreover, new water use practices entered the scene. As a consequence, the main causes for the aquifer decline are population growth and extensive Agriculture practices in use during the last half of the 20th Century. Some remarks on sustainability issues in order to cope with Climate Change are also offered.

Radon in Groundwater of the Northeastern Gran Canaria Aquifer

[EN]Rn has been detected in 28 groundwater samples from the northeast of Gran Canaria (Canary Islands, Spain) utilizing a closed loop system consisting of an AlphaGUARD monitor that measures radon activity concentration in the air by means of an ionization chamber, and an AquaKIT set that transfers dissolved radon in the water samples to the air within the circuit. Radon concentration in the water samples studied varies between 0.3 and 76.9 Bq/L. Spanish radiological protection regulations limit the concentration of 222Rn for drinking water to 100 Bq/L, therefore the values obtained for all the analyzed samples are below this threshold. The hydrogeological study reveals a significant correspondence between the radon activity concentration and the material characteristics of the aquifer.

Estimating Natural Recharge by Means of Chloride Mass Balance in a Volcanic Aquifer: Northeastern Gran Canaria (Canary Islands, Spain)

[EN]The chloride mass balance method was used to estimate the average diffuse groundwater recharge on northeastern Gran Canaria (Canary Islands), where the largest recharge to the volcanic island aquifer occurs. Rainwater was sampled monthly in ten rainwater collectors to determine the bulk deposition rate of chloride for the 2008–2014 period. Average chloride deposition decreases inwardly from more than 10 g·m−2 ·year−1 to about 4 g·m−2 ·year−1 . The application of the chloride mass balance method resulted in an estimated average recharge of about 28 hm3 /year or 92 mm/year (24% of precipitation) in the study area after subtracting chloride loss with surface runoff.

Elaboración de un mapa de lixiviación de nitratos mediante una metodología de acople SIG-modelo de simulación : aplicación al acuífero de La Aldea (Gran Canaria)

[ES] La contaminación difusa por nitrato constituye una de las mayores amenazas actuales para la calidad de las aguas subterráneas. De hecho, varias directivas europeas, nacionales y regionales se han legislado con el fin de minimizar el efecto de las prácticas agrarias en la contaminación de los acuíferos por nitratos. El acuífero de La Aldea (Gran Canaria, España) se ha declarado como vulnerable a la contaminación por nitrato según dichas normas. En este estudio se presenta una metodología para desarrollar el acople de un sistema de información geográfica-SIG con el modelo de simulación de nitrato GLEAMS. Esta herramienta permite calcular la cantidad de nitrato lixiviado procedente de los cultivos de tomate bajo invernadero y da la oportunidad de simular otros rangos de fertilización para minimizar el riesgo de contaminación de las aguas subterráneas. Se comprueba que la pérdida de nitrato por lixiviación en la zona a partir de dichos cultivos podía llegar a los 500 kg N/ha, casi un 62% del aportado como fertilizante mineral en un manejo tradicional. Por ello, se aconseja la aplicación de las recomendaciones de abonado incluidas en el código de buenas prácticas agrarias de Canarias o cualquier otro sistema de recomendación de abonado mineral para reducir estas pérdidas, minimizando de esta forma el riesgo de contaminación de las aguas subterráneas. ABSTRACT: Nitrate diffuse pollution is one of the main risks that affect the groundwater quality. Several european directives, national and regional guidelines have been enacted to protect the aquifers against the effect of the agricultural management practices. The “La Aldea” aquifer was declared nitrate vulnerable area following these laws. In this study a methodology was developed to link a Geographical Information System (GIS) with a nitrogen simulation model (GLEAMS) in this area. This tool allows to assess the amount of nitrate leaching that coming from the traditional nitrogen fertilization rates in greenhouses tomato crops, and gives the opportunity to simulate other fertilization rates to reduce the risk of groundwater pollution. The nitrate leaching reached to 500 kg N/ha in several zones of the study area, that represent the 62% of the nitrogen fertiliser apply in a traditional management. It was recommended the application of the Code of Good Management Practices or other recommendation system to decrease the nitrate leaching, in order to reduce the risk of groundwater pollution.

La explotación del acuífero de la Aldea (Gran Canaria) desde el punto de vista de la directiva marco del agua

[ES] El valle de La Aldea, al oeste de Gran Canaria, se dedica a la agricultura intensiva en un clima semi-árido. El agua de riego proviene de aguas superficiales y subterráneas. El acuífero está aislado del resto de la isla por el borde impermeable de la Caldera de Tejeda. El aluvial principal de La Aldea se comporta como un depósito de almacenamiento de agua que se llena y vacía, con un tiempo medio de renovación de aproximadamente 2 años. Las aguas subterráneas muestran una alta salinidad de origen natural, debido a la evapoconcentración de la deposición atmosférica y la interacción agua-roca, y antropogénica debida a los retornos de riego que producen contenidos en nitratos que pueden alcanzar los 700 mg/L. Se ha establecido un modelo conceptual de funcionamiento del acuífero y se han cuantificado los términos del balance de agua. El uso actual del acuífero está en conflicto con los requerimientos de la Directiva Marco del Agua (DMA). Sin embargo, dado que su uso es clave para el desarrollo económico del valle de La Aldea en particular, cabe plantear las excepciones legales específicas previstas en la DMA.

Cuantificación de la recarga natural al acuífero del norte de Gran Canaria mediante el balance diario de agua en el suelo

[ES]La recarga al acuífero noreste de Gran Canaria ha sido calculada dentro del proyecto REDESAC mediante la realización de un balance diario de agua en el suelo. Para llevarlo a cabo ha sido necesario adaptar los datos de partida existentes referentes a la pluviometría, la evapotranspiración (ET0 y ETP) y los parámetros del suelo. La zona se ha dividido en subzonas según la situación de las estaciones pluviométricas y atendiendo a las características climáticas. Los cálculos realizados mediante la utilización del código Easy-Bal han arrojado una recarga de unos 15±4 hm3/a, lo que supone el 13±4% de la precipitación, la mayor parte de la misma concentrada en las zonas altas y de medianías