Environmental isotopes as a hydrogeological tool in Nicaragua

Variations in the environmental isotopic composition of precipitation and groundwater have been used to determine the relative importance of recharge from precipitation on the Chinandega Plain with respect to precipitation on the higher slopes of the Cordillera de Marrabios. The variation of the δ18O content of precipitation with altitude was found to be -0.26 per mille/100 m. The best estimate of the long-term δI8O value for recharge from precipitation at a given altitude was obtained from the isotopic composition of a spring at 800 m and groundwater which was deemed to represent recharge on the plain on the basis of isotope and hydrogeological information. It was concluded that recharge to the deep aquifer from elevations higher than 280 m is more significant than recharge by precipitation on the plain. (author)