Submarine groundwater discharge: Natural radioactivity accumulation in a wetland ecosystem
Résumé
Submarine groundwater discharge (SGD) has attracted the interest from the scientific community over the past decade for its impact on biogeochemical cycles of coastal ecosystems and/or management of water resources. SGD is associated with a flow of natural radionuclides (Ra isotopes and Rn-222), which are often used as SGD tracers that can significantly increase the natural background radiation. Although in many circumstances the discharge is produced directly to the sea and therefore the increase of natural radioactivity levels can generally be considered negligible due to a dilution processes, the discharge into coastal wetlands (marshes, coastal lagoons or ponds), with somewhat restricted exchange with the open sea, may require a detailed study of the distribution of natural radionuclides and their effects on the coastal ecosystem. The Peniscola marsh is a Mediterranean coastal wetland where such studies may be of special interest because it is fed exclusively by groundwater, mainly discharging from a deep aquifer with high natural radioactivity content. In the Peniscola marsh, brackish groundwater discharging through the wetland sediments is enriched in radionuclides to maximum values of 2.8 and 616 kBq m(-3) of Ra-226 and Rn-222, respectively. These high dissolved concentrations result in high levels of Rn-222 in air (up to 36 Bq m(-3)) and Pb-210 and Po-210 dissolved in water (20 and 5.7 Bq m(-3), respectively). These elevated levels of natural radionuclides in the Peniscola marsh are also responsible of the significant increase in Po-210 and Pb-210 contents in both fish and plants. (C) 2013 Elsevier B.V. All rights reserved.