title: Spatial and temporal variability of (7)Be and (210)Pb wet deposition during four successive monsoon storms in a catchment of northern Laos.
abstract: Fallout radionuclides (7)Be and (210)Pb have been identified as potentially relevant temporal tracers for studying soil particles dynamics (surface vs. subsurface sources contribution; remobilization of in-channel sediment) during erosive events in river catchments. An increasing number of studies compared (7)Be: (210)Pb activity ratio in rainwater and sediment to estimate percentages of freshly eroded particles. However, the lack of data regarding the spatial and temporal variability of radionuclide wet deposition during individual storms has been identified as one of the main gaps in these estimates. In order to determine these key parameters, rainwater samples were collected at three stations during four storms that occurred at the beginning of the monsoon (June 2013) in the Houay Xon mountainous catchment in northern Laos. Rainwater (7)Be and (210)Pb activities measured using very low background hyperpure Germanium detectors ranged from 0.05 to 1.72 Bq L(-1) and 0.02 to 0.26 Bq L(-1), respectively. Water δ(18)O were determined on the same samples. Total rainfall amount of the four sampled storms ranged from 4.8 to 26.4 mm (51 mm in total) at the time-fractionated collection point. Corresponding cumulative (7)Be and (210)Pb wet depositions during the sampling period were 17.6 and 2.9 Bq m(-2), respectively. The (7)Be: (210)Pb activity ratio varied (1) in space from 6 to 9 for daily deposition and (2) in time from 3 to 12 for samples successively collected. Intra-event evolution of rainwater (7)Be and (210)Pb activities as well as δ(18)O highlighted the progressive depletion of local infra-cloud atmosphere radionuclide stock with time (washout), which remains consistent with a Raleigh-type distillation process for water vapour. Intra-storm ratio increasing with time showed the increasing contribution of rainout scavenging. Implications of such variability for soil particle labelling and erosion studies are briefly discussed and recommendations are formulated for the collection of rainwater signature in studies based on the (7)Be: (210)Pb ratio method, especially in tropical areas under high erosive pressure.
authors: Laboratoire des Sciences du Climat et de l'Environnement (LSCE), UMR 8212 (CEA-CNRS-UVSQ/IPSL), Domaine du CNRS, avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France. Electronic address: elian.gourdin@lsce.ipsl.fr.
authors: E
authors: E
authors: Gourdin
authors: Laboratoire des Sciences du Climat et de l'Environnement (LSCE), UMR 8212 (CEA-CNRS-UVSQ/IPSL), Domaine du CNRS, avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France.
authors: O
authors: O
authors: Evrard
authors: Université Pierre et Marie Curie (UPMC), UMR 7618 Bioemco, Case 120, 4 Place Jussieu, 75252 Paris Cedex 05, France.
authors: S
authors: S
authors: Huon
authors: Laboratoire des Sciences du Climat et de l'Environnement (LSCE), UMR 8212 (CEA-CNRS-UVSQ/IPSL), Domaine du CNRS, avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France.
authors: J-L
authors: JL
authors: Reyss
authors: Géosciences Environnement Toulouse (GET), UMR 5563 (CNRS, UPS, IRD), 14 Avenue Edouard Belin, 31400 Toulouse, France.
authors: O
authors: O
authors: Ribolzi
authors: CNRS, UMR 7618 Bioemco, Campus INRA - AgroParisTech, Bâtiment EGER, 78550 Thiverval-Grignon, France.
authors: T
authors: T
authors: Bariac
authors: National Agriculture and Forestry Research Institute (NAFRI), P.O. Box 4199, Ban Nogviengkham, Xaythany District, Vientiane, Lao People's Democratic Republic.
authors: O
authors: O
authors: Sengtaheuanghoung
authors: Laboratoire des Sciences du Climat et de l'Environnement (LSCE), UMR 8212 (CEA-CNRS-UVSQ/IPSL), Domaine du CNRS, avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France.
authors: S
authors: S
authors: Ayrault
mesh_terms: D001608:Beryllium / Q000032:analysis*; D019015:Geologic Sediments / Q000032:analysis*; D007812:Laos; D007856:Lead Radioisotopes / Q000032:analysis*; D010103:Oxygen Isotopes / Q000032:analysis; D011834:Radiation Monitoring; D011847:Radioactive Fallout; D011868:Radioisotopes / Q000032:analysis*; D011891:Rain; D045483:Rivers
chemical_list: D007856:Lead Radioisotopes; D010103:Oxygen Isotopes; D011847:Radioactive Fallout; D011868:Radioisotopes; D001608:Beryllium
keywords: Be-7; Local spatial temporal variability; Monsoon storm; Pb-210; Rainwater; Wet deposition