Evidence for a recent increase in delivery of atmospheric 210 Pb to Oualidia lagoon, coastal Morocco

• Published in: Environmental monitoring and assessment 2018-10, Vol.190 (11), p.642
• Main Authors: Laissaoui, Abdelmourhit, Mejjad, N, Ziad, N, Ait Bouh, H, El Hammoumi, O, Benkdad, A, Fekri, A
• Format: Article
• Language: English
• Subjects: Air Pollution, Radioactive - analysis; Air Pollution, Radioactive - statistics & numerical data; Atmosphere - chemistry; Cesium Radioisotopes - analysis; Environmental Monitoring - methods; Geologic Sediments - chemistry; Lead Radioisotopes - analysis; Morocco; Radiation Monitoring; Radon - analysis; Water Pollutants, Radioactive - analysis
• ISSN: 1573-2959
• DOI: 10.1007/s10661-018-7046-z

Two sediment cores were collected from the Oualidia lagoon, on the Atlantic coast of Morocco, and analyzed for Pb and Cs activity by gamma spectrometry. The Pb profiles were characterized by high activity at specific depths in each core, which were attributed to substantial increases in atmospheric Pb input to the sediment. A modified CRS model was applied to develop age-depth relations (chronologies) for the cores and calculate sediment accumulation rates, taking into account changing unsupported Pb delivery and specifying the year when the increase began. Calculated Pb inventories (activity/area) and fluxes (activity/area/time) depend strongly on sedimentation rates and were much higher than mean values in similar coastal systems worldwide. We attempted to use Cs as a time marker to support the modified CRS chronologies for both cores. The Cs profiles, however, were affected by post-depositional cesium migration in the sediment which made it difficult to identify the 1963 atmospheric bomb-testing peak, especially in the core with low sedimentation rate. We conclude that the high activities of Pb detected at specific depths in the Oualidia lagoon sediment cores are a consequence of decay of radioactive Rn, which displayed periodic high concentrations in the overlying atmosphere.