Atmospheric chloride deposition in continental Spain

15 pages, 9 figures.The atmospheric bulk deposition rate of chloride in continental Spain was studied to get basic information in order to help in the evaluation of diffuse recharge to aquifers through an environmental chemical balance. Both new, recent data and bibliographic data have been used. Most sampling records are less than 5 years long and often only 1 year long. This means that the calculated mean yearly bulk deposition rate of chloride is quite uncertain by 30% on average, and larger than the values derived form records up to 15 years long. A map of atmospheric bulk deposition of chloride has been drawn using ordinary kriging. The mean bulk deposition rate of chloride varies from 1 to 30 g m-2 year-1 in coastal areas, with strong negative landward gradients between 0·1 and 1 g m-2 year-1 km-1. In the centre of the Iberian Peninsula, chloride deposition rates vary from 0·2 to 0·5 g m-2 year-1, with gradients around or less than 5 × 10-3 g m-2 year-1 km-1. The coefficient of variation of the mean bulk atmospheric deposition rate of chloride, for any place, ranges from 0·1 to 1. Values larger than 0·5 are not a good indicator of natural uncertainty for this series of data that has a skewed distribution. The map of bulk deposition rate and its error is one of the terms needed for aquifer recharge estimation by means of the chloride ion balance.We would like to thank the endowment of the Spanish Research Project HID1999-0205. The first author is also grateful to the Ministry of Education and Science of Spain for a ‘Juan de la Cierva’ Programme Contract (reference JCI-2007-334).Peer reviewe