A numerical investigation for dating 210Pbex and 137Cs vertical profiles in a coastal area: The Eastern Ligurian Sea, Italy (original) (raw)
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Time-averaged fluxes of lead and fallout radionuclides to sediments in Florida Bay
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Recent, unmixed sediments from mud banks of central Florida Bay were dated using 210 Pb/ 226 Ra, and chronologies were verified by comparing sediment lead temporal records with Pb/Ca ratios in annual layers of coral (Montastrea annularis) located on the ocean side of the Florida Keys. Dates of sediment lead peaks (1978 Ϯ 2) accord with prior observations of a 6 year lag between the occurrence of maximum atmospheric lead in 1972 and peak coral lead in 1978. Smaller lags of 1-2 years occur between the maximum atmospheric radionuclide fallout and peaks in sediment temporal records of 137 Cs and Pu. Such lags are consequences of system time averaging (STA) in which atmospherically delivered particle-associated constituents accumulate and mix in a (sedimentary?) reservoir before transferring to permanent sediments and coral. STA model calculations, using time-dependent atmospheric inputs, produced optimized profiles in excellent accord with measured sediment 137 Cs, Pu, lead, and coral lead distributions. Derived residence times of these particle tracers (16 Ϯ 1, 15.7 Ϯ 0.7, 19 Ϯ 3, and 16 Ϯ 2 years, respectively) are comparable despite differences in sampling locations, in accumulating media, and in element loading histories and geochemical properties. For a 16 year weighted mean residence time, STA generates the observed 6 year lead peak lag. Evidently, significant levels of nondegradable, particle-associated contaminants can persist in Florida Bay for many decades following elimination of external inputs. Present results, in combination with STA model analysis of previously reported radionuclide profiles, suggest that decade-scale time averaging may occur widely in recent coastal marine sedimentary environments.
Estuaries, 1998
Various anthropogenic radionuclides and uOPb were analyzed in a 4.3-m-long core, sampled near the Rhone River mouth in March 1991, to evaluate the extent of industrial releases that accwnulate in this area. The whole core was significantly marked by radionuclide inputs from the nuclear facilities located along the river (137CS, I34CS, 60CO). Irregular profiles in natural and artificial radionuclides should be related to variations in their respective inputs from the Rhone River to the Mediterranean Sea. Minimwn concentrations were found during high flow periods. Using both the 137CS/134CS profile in the core and the range of this ratio in Rhone waters, mean apparent accwnulation rates were estimated to range between 37 em yr-I and 48 em yr-I. This core would then represent a sedimentary record over a 7-10 year period. However, the presence of a signal from the Chernobyl accident, which occurred on April 26, 1986, was not clearly observed in the core. Inventories of both artificial and natural radionuclides were greater than expected from atmospheric inputs. The increased sedimentation occurring in close vicinity to the mouth of the Rhone River is thus responsible for trapping of elements transported by the river to the Mediterranean Sea. In this area, inventories of artificial radionuclides are well in excess of aerial deposition from Chernobyl and atmospheric weapons tests and are linked primarily to industrial releases.
Land, 2021
Given the importance of understanding long-term dynamics of radionuclides in the environment in general, and major gaps in the knowledge of 137Cs particulate forms in Chernobyl exclusion zone water bodies, three heavily contaminated water bodies (Lakes Glubokoe, Azbuchin, and Chernobyl NPP Cooling Pond) were studied to reconstruct time changes in particulate concentrations of 137Cs and its apparent distribution coefficient Kd, based on 137Cs depth distributions in bottom sediments. Bottom sediment cores collected from deep-water sites of the above water bodies were sliced into 2 cm layers to obtain 137Cs vertical profile. Assuming negligible sediment mixing and allowing for 137Cs strong binding to sediment, each layer of the core was attributed to a specific year of profile formation. Using this method, temporal trends for particulate 137Cs concentrations in the studied water bodies were derived for the first time and they were generally consistent with the semiempirical diffusional...
Various anthropogenic radionuclides and 210Pb were analyzed in a 4.3-m-long core, sampled near the Rhone River mouth in March 1991, to evaluate the extent of industrial releases that accumulate in this area. The whole core was significantly marked by radionuclide inputs from the nuclear facilities located along the river (l1337Cs, 134Cs, 60Co). Irregular profiles in natural and artificial radionuclides should be related to variations in their respective inputs from the Rhone River to the Mediterranean Sea. Minimum concentrations were found during high flow periods. Using both the 137Cs/134Cs profile in the core and the range of this ratio in Rhone waters, mean apparent accumulation rates were estimated to range between 37 cm yr-1 and 48 cm yr ~. This core would then represent a sedimentary record over a 7-10 year period. However, the presence of a signal from the Chernobyl accident, which occurred on April 26, 1986, was not clearly observed in the core. Inventories of both artificial and natural radionuclides were greater than expected from atmospheric inputs. The increased sedimentation occurring in close vicinity to the mouth of the Rhbne River is thus responsible for trapping of elements transported by the fiver to the Mediterranean Sea. In this area, inventories of artificial radionuclides are well in excess of aerial deposition from Chernobyl and atmospheric weapons tests and are linked primarily to industrial releases.