210 Po and 210 Pb distributions and residence times in the nearshore region of Lake Superior (original) (raw)
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Marine Chemistry, 1993
Many bays and estuaries of the USA are heavily impacted by man's activities. It is therefore important to characterize the self-cleansing capacity of these waters. To this effect, Th, Pb and Be nuclides in the water column can be used as tracers for the removal behavior of particle-reactive substances. Both sub-and supra-micron sized particles play a major role in the transport of particle-reactive nuclides and pollutants in estuarine and coastal waters. We report here the results of a study of the fate of radionuclides, carried out during different times of the year in six Texas bays and estuaries, and in Galveston's coastal waters, after a one-time pulse injection by wet fallout of Pb and Be nuclides. We investigated both removal residence times and the partitioning of Th, Pb and Be isotopes between filter-retained particles (0.5 m or greater), filter-passing dissolved (0.5 m or less) and, in a separate experiment, a colloidal phase.
Journal of Geophysical Research, 1991
Atmospheric and sedimentary fluxes of natural (i.e., 2'øpb, 2'øpo, 7Be, and 'øBe) and artificial (i.e., Chernobyl mCs) radionuclides and particles through Lake Zurich (at 50 m and 130 m depth) between 1983 and 1987 were compared in order to establish trr. ce metal pathways and their kinetics. Atmospheric fluxes averaged 0.83 dpm cm -2 yr" for 2'øpb and 16.0 dpm cm '2 yr" for 7Be during 1984 to 1987. Vertical fluxes of 2'øpb and 7Be, associated with settling particles, were measured in sediment traps deployed at 50 m and 130 m depth at a station near the deepest part of Lake Zurich. Average fluxes of 2'øFo and 7Be at 50 m depth were 0.94 and 4.90 dpm cm '2 yr 4, respectively, and 16.5 x 107 atoms m '2 d" for 'øBe. Sediment traps at 50 m quantitatively collected atmospherically deposited 2'øpb falli.ng through the water column. At 130 m depth, immediately above seasonally anoxic bottom waters, 2'øpb, 'øl•e, and'37Cs fluxes were higher than at 50 m by up to 60% at times during the summer stagnation period. Sediment inventories of :mPb and 'øBe are in agreement with atmospheric nuclide fluxes, suggesting only moderate recycling of these nuclides in the bottom waters, whereas mCs inventory in the sediments is lower than expected from sediment trap fluxes, indicating remobilization of this nuclide.
Radionuclide fluxes and particle scavenging in Cariaco Basin
2004
234 Th, 228 Th and 210 Pb fluxes were measured in a series of sediment trap samples in Cariaco Basin from November 1995 to 8 May 1996. Sediment traps were located at 275, 455, 930 and 1255 m depth, with the 275 m trap just above the oxic/anoxic interface. Total mass, organic carbon, carbonate, biogenic opal, and lithogenic fluxes were also determined. Our results found that 234 Th, 228 Th and 210 Pb fluxes are highly correlated with total mass (r 2 ¼ 0:92 À 0:94), major sediment component fluxes (r 2 ¼ 0:82 À 0:93), and one another (r 2 ¼ 0:94 À 0:99). Decreases in radionuclide, total mass and major sediment component fluxes with depth were attributed to physical disaggregation and remineralization. While the 210 Pb specific activity loss from settling particles is the same as the bulk specific activity of the trapped particles between 455 and 930 m, the 210 Pb specific activity loss is substantially higher than the bulk specific activity of the trapped particles between 930 and 1255 m. We attributed this fractionation to a loss of minor components from settling particles. This suggests that minor components are responsible for the initial water column scavenging of 210 Pb in the Cariaco Basin. Steady state release of 210 Pb from settling particles would produce an anoxic water column activity an order of magnitude greater than previously reported. Therefore, a non-steady state removal mechanism must exist and is potentially caused by high sediment flux events from earthquake triggered turbidity currents or major plankton blooms. r (J.M. Smoak).
Journal of Environmental Radioactivity
Polonium-210 and Pb-210 were measured in surficial benthic sediments and particulate matter collected in sediment traps deployed at five different locations in the Clinton River, a dynamic system, in Lake St. Clair in Southeast Michigan to quantify the sediment resuspension rates and determine the particle residence time. The mean 210 Po xs / 210 Pb xs activity ratio of suspended trap and surficial bottom sediments were 0.72 � 0.12 (n ¼ 16, range: 0.42-0.89) and 0.79 � 0.15 (n ¼ 15, range: 0.40-1.00) indicating that a major fraction of trapped material is from resuspended bottom sediments. Sediment resuspension rate calculated using a single box model approach yielded a resuspension rate of 0.1-1.0 g cm À 2 yr À 1 using 210 Po and 0.2-1.4 g cm À 2 yr À 1 using 210 Pb. Particle residence time varied from 0.3 to 3.9 days using 210 Pb and 0.9-13.4 days for 210 Po. This present study indicates that sediment resuspension is considerably high in Clinton River and thus any decision on remedial action towards the restoration such as dredging, natural attenuation is challenging. This present study has direct relevance to the transport and resuspension of other sulfur group elements (Se, O, etc) and lithogenic elements (e.g., Th).
Journal of Geophysical Research: Oceans, 2013
1] The timescale of transport processes in estuarine and coastal regions can be evaluated using natural radionuclides with different half-lives. The distribution patterns of 7 Be, 210 Pb, and 234 Th in the water column from April to July 2008 were used to calculate the removal and residence times in the Changjiang Estuary. The results showed that the maximum particulate activities of 7 Be, 210 Pb, and 234 Th were observed approximately 150 km downstream (the turbidity maximum zone) of the freshwater end-number. The mean distribution coefficients (K d , cm 3 g À1 ) of the high suspended particulate matter (SPM) group are higher than those of the lower-SPM group for 7 Be and 210 Pb; for 234 Th, the reverse is true. Based on a material balance in two-dimensional models of 7 Be, 210 Pb, and 234 Th in the Changjiang River mouth, the removal times of these nuclides were approximately 0.66-12, 1.6-21, and 1.2-5.4 days, respectively. The residence times increased toward the seaward side. In the coastal region, the removal times of 7 Be, 210 Pb, and 234 Th calculated by material balance in onedimensional models were approximately 1.1-26, 1.2-27, and 0.70-23 days, respectively. Moreover, an enhanced resuspension process not only controlled the partitioning of 7 Be, 210 Pb, and 234 Th between the particulate and dissolved phases, but also, this process may play a dominant role in controlling the dynamic behavior of SPM in the water column compared with the advection input/output fluxes of the SPM in the river mouth areas. The removal and the resuspension fluxes were comparable in the estuary. Meanwhile, old composition (whose deposition into the seabed for a long time is enough for 7 Be to decay completely) occupied only a small part in the resuspended sediment during resuspension process.
Activities of the naturally occurring, short-lived and highly particle-reactive radionuclide tracer 234Th in the dissolved and particulate phase were measured at three shallow-water stations (maximumwater depths: 15.6, 22.7 and 30.1m) in Mecklenburg Bay (south-western Baltic Sea) to constrain the time scales of the dynamics and the depositional fate of particulate matter. Activities of particle-associated (N0.4 μm) and total (particulate+dissolved) 234Th were in the range of 0.08–0.11 dpm L−1 and 0.11–0.20 dpm L−1, respectively. The activity ratio of total 234Th and its long-lived and conservative parent nuclide 238Uwas well below unity (range: 0.09–0.19) indicating substantial radioactive disequilibria throughout the water column, very dynamic trace-metal scavenging and particle export from the water column at all three stations. For the discussion the 234Th data of this study were combined with previously published water-column 234Th and particulate-matter data from Mecklenburg Bay ( Kersten et al., 1998. Applied Geochemistry 13, 339–347). The resulting average vertical distribution of total 234Th/238U disequilibria was used to estimate the depositional 234Th flux to the sediment. There was a virtually constant net downward flux of 234Th of about 28 dpmm−2 d−1 leaving each water layer of one meter thickness. Thorium-234-derived net residence times of particulate material regarding settling from a given layer in the water column were typically on the order of days, but with maximum values of up to a couple of weeks. Based on an average ratio of particulate matter (PM) to particle-associated 234Th a net flux of about 145 mg PM m−2 d−1 was estimated to leave each water layer of one meter thickness. The estimated cumulative water-columnderived particulate-matter fluxes at the seafloor are higher by a factor of about 2 than previously published sediment-derived estimates for Mecklenburg Bay. This suggests that about half of the settling particulate material is exported from the study area and/or subject to processes such as mechanical breakdown, remineralisation and dissolution. Lateral particulatematter redistribution and particle breakdown in the water column (as opposed to the sediment) seem to be favoured by (repeated) particle resuspension from and resettling to the seafloor before ultimate sedimentary burial. The importance of net lateral redistribution of particulate material seems to increase towards the seafloor and be particularly high within the bottommost few meters of the water column.
Radioprotection, 2005
In freshwater, radionuclide transfers depend both on exchanges between liquid and solid phases and on mass transfers between suspended and bottom sediment. Whereas the former ones depend on chemical processes (sorption/desorption, complexation…), the latter ones are regulated by hydrological and sedimentary considerations (dispersion, erosion, deposit…) closely related to the interactions between flow, suspended matter and bed sediment. Previous studies highlight the need to consider the matter heterogeneity and its specific sediment dynamics to correctly report the in homogeneity of fluxes in time and in space. These considerations lead us to develop an experimental method to distinguish the different particle groups present in natural water, mainly according to their settling kinetics. In this context, this paper presents the experimental protocol TALISMEN to characterize a natural bulk suspension according to its main settling kinetics groups. In a first step, this identification is achieved by the use of a settling tank that allows the monitoring of the suspended solid concentrations at various depths, combined to a settling model applying a multi-class approach. In a second step, the particle groups are isolated and characterized. The sorption property of each group toward 137 Cs is determined by estimation of its distribution coefficients (k d) and sorption kinetics.
Journal of Marine Research, 1987
The "mobilities" of radioactive trace elements across the water sediment boundary of a coastal marine ecosystem were investigated. The studies carried out included chemical speciation experiments ofthe solution and solid phases, as well as verification experiments in controlled model ecosystems ("MERL" tanks). The latter included backdiffusion experiments under oxic and anoxic conditions and experiments with artificially increased sediment resuspension rates. These studies have produced seven general conclusions: