Determine Anzali lagoon sediment age based on Cesium-137

Abstract

From descending sedimentation rate viewpoint, accumulation of sediments in Anzali lagoon may be accompanies with rising water level in Anzali lagoon and descending the depth of the lagoon. Thus getting knowledge about the rate and the degree of sedimentation in lagoon can provide planners with useful approaches. Cesium-137 is an artificial Radionuclide with Gamma rays and half- life of 2/30 years which is produced as a by-product resulting from nuclear experiments of previous decades and released in stratosphere. Considering the high-powered of this approach in accuracy of assessment and easiness of data collecting, it has been used in surveying the age of sedimentation in Anzali lagoon. In this research, sampling is done in three spots, to the depth of 4 meters, with a core drilling machine. Grading, moisture and plastic limit of samples are measured in the laboratory. Then 10 samples in different levels from three boreholes (BH) are taken for Cesium 137experiment and are sent to Atomic Energy Organization laboratory. As well, MPSIAC model is used to calculate the degree of sedimentation empirically. Results of the grading show that samples of sediments are mostly fine-grade in different

layers of the earth. An overview shows that soil layers at the first BH is silt with low plastic attributes. In the second BH, soil layers from the surface to the depth of three meters is silt with low plastic attributes and from the depth of three or four meters is silt with sand and low plastic attributes. Soil layers in the BH3, from the surface to the depth of three meters is silt with low plastic attributes and from the depth of 3 to 4 is silt with sand and low plastic attributes. Age measurement of the different layers shows that most Cesium is in the depth of 2.4-2.7 considering mentioned depth and time interval of the incidence, density of the sedimentation equals to 8.5 meters per year.