[en] The concentrations of ²³⁸Pu, /sup 239,240/Pu, ²⁴¹Am, ²⁴⁴Cm, and ¹³⁷Cs have been determined in the waters, sediments, and interstitial waters of two reservoirs located in the southeastern US. Limnological data are also presented which demonstrate that both reservoirs undergo thermal stratification with attendant hypolimnetic anoxia for significant periods in their annual hydrologic cycles. Seasonal concentration patterns of ¹³⁷Cs and the actinide elements are discussed relative to the hypothesis that seasonal anoxia of the hypolimnion and sediments can lead to remobilization of these elements from the sediments to the overlying water column. The results of this study support such a hypothesis for ¹³⁷Cs in both reservoirs. The data for /sup 239,240/Pu in one reservoir, however, indicate that no remobilization of that element has occurred in that system. In the second reservoir, the data show an increased concentration of ²³⁹Pu, /sup 239,240/Pu, ²⁴¹Am, and ²⁴⁴Cm in deep waters coincident with anoxic, hypolimnetic conditions. The data are not complete enough to delineate the source of the actinide elements in either the overlying water column or the sediments. It is suggested, however, that ²³⁹Pu is being added from an external source and that the chemically similar elements Am and Cm are being controlled by different mechanisms. 18 references, 7 figures, 10 tables

[en] The cycling of iron, manganese and other metals can have important ecological implications in acidic southeastern lakes and reservoirs. When water in a lake's hypolimnion is anoxic, as typically occurs in summer, the solubility of certain elements, such as iron and manganese, increases. During such anoxic conditions, remobilization of elements from lake sediments into the hypolimnion may also occur. Concentrations of these elements can reach levels that are toxic to organisms. Perhaps more importantly, when turnover of the water column occurs in autumn, oxygenation of the anoxic hypolimnion may cause precipitation of metal oxides, forming colloids that can be harmful to fish and other organisms, e.g., by physically obstructing gills. all of these processes can have bearing on the development of a balanced biological community in L-Lake. The inventory of metal and radionuclide concentrations in L-Lake basin sediments will be used to assess potential remobilization of these elements from the lake sediments into the overlying water column. These data will be used in conjunction with laboratory microcosm studies and lake measurements to determine the potential for element remobilization under existing lake conditions. 1 figure, 2 tables

[en] Research is being conducted in Pond B to determine the relative importances of (1) changes in particles settling rates, (2) changes in remobilization rates, and (3) the influence of the macrophytes on the annual cycle in /sup 239,240/Pu inventories. The initial research has emphasized (1) an evaluation of the importance of particle adherence to macrophytes in reducing Pu inventories in the water column and (2) measurements of particle settling rates at different times of the year. This report describes the research on measurements of particle settling rates. 3 figures, 1 table

[en] The interrelationships among plant biomass, plant surface area and interception fraction were determined for the interception by corn of ²³⁸Pu-bearing particles released to the atmosphere from the H-Area nuclear fuels chemical separations facility on the U.S. Department of Energy's Savannah River Plant in Barnwell County, South Carolina. The relationship between interception fraction and corn biomass was accurately approximated by a filtration model with an absorption coefficient of 3.60 m2 kg-1. A filtration model with an absorption coefficient of 2.91 m2 kg-1 accurately approximated the relationship between biomass and interception fraction for data compiled from the literature for a variety of grass species. A linear regression model accurately approximated the relationship between interception fraction and surface area, but was not a better predictor of interception fraction than the filtration model for biomass

[en] Although radionuclide cycling studies have been performed in Pond B, Par Pond and other lake and pond habitats on the Savannah River Plant, there have been few studies designed to estimate total radionuclide inventories or the inventories in various components of these ecosystems. Because inventory data were lacking for SRP lakes and for southeastern lakes in general, a study was initiated in 1983 to inventory the ⁹⁰Sr, ¹³⁷Cs and /sup 239,240/Pu contents of Pond B sediments and biota. The inventory study was conducted concurrently with research on radionuclide cycling processes in the water column. The radionuclide inventories in the sediments were determined from randomly located sediment cores taken from throughout the pond. Samples were also collected at various times of the year to estimate the radionuclide contents of the water column. The appropriate samples were also collected to estimate the biomass and radionuclide inventories in the major biological components of the pond. Data were obtained on macrobenthic organisms and various vertebrate species, but the greatest emphasis was placed on estimating the biomass and radionuclide contents of the aquatic macrophytes. Approximately 40% of the 87 ha area of Pond B is less than 3 m deep, and this large shallow area supports approximately 140 metric tons of macrophyte biomass. 4 figures

[en] The distribution of ¹³⁷Cs, ⁹⁰Sr, ²³⁸Pu, ^239,240Pu, ²⁴¹Am, and ²⁴⁴Cm was studied in the biotic and abiotic components of an abandoned reactor cooling impoundment, Pond B. The impoundment is located at the US Department of Energy's Savannah River Plant in South Carolina, USA. It received radioactive contaminants via cooling water discharges from R Reactor from September 1961 to June 1964. The radionuclde inventories were estimated in water, seston, sediments, and biotic components after 20 yr of equilibration. Chemical, physical, and biological relationships to the radionuclide distribution patterns were investigated. Biotic components contained some of the highest radionuclide concentration ratios observed to date. However, most of the radioactivity resides in sediments. The principal mechanisms of loss from the system are radioactive decay and periodic outflow of water and suspended materials; biotic export and seepage appear to be inconsequential. Strontium-90 was much more mobile in the system than the other radionuclides. Aquatic macrophytes dominated the biotic component radionuclide inventories and their dynamics exert a strong influence on the spatial distribution and turnover of radioactivity in the ecosystem. Pond B supports a diverse and productive flora and fauna. Cleanup of the system is not indicated. Use of Pond B for recreation is feasible with adequate attention to monitoring and radiological health guidelines

[en] To evaluate the importance of particle settling on the behavior of ^239,240Pu inventories in the water column of a monomictic reservoir, the sedimentation fluxes of ^239,240Pu were measured using sediment traps and compared to the Pu inventories. Sedimentation flux from surface to deeper waters averaged 5.4 mBq ^239,240Pu m^-2 d^-1 which represented ≥ 3% of the surface water inventory of Pu per day. The fluxes were large enough to account for (1) the observed declines in the Pu inventories of surface waters following stratification and (2) the rapid increase in Pu inventories in deeper waters immediately following stratification. (Author)

[en] Previous studies in Pond B, a 12-m deep, 82 ha reservoir that once served as a reactor cooling pond, had (i) suggested the preferential accumulation of ¹³⁷Cs in sediments at a water depth of 3 m within the littoral zone and (ii) attributed this accumulation to the effects of either macrophyte vegetation or sediment slope. To test for the preferential accumulation of ¹³⁷Cs at intermediate depths within the littoral zone, sediment cores were taken at water depths of 0.5, 1,2,3,4 and 5 m along 6 transects in Pond B. The sediment structure was similar at all water depths in the littoral zone with a surface layer of 0.02-0.04m of plant debris and fine sediments over a base of sandy sediments. The ¹³⁷Cs was largely restricted to the surface layer of fine sediments, and there was no indication of preferential accumulation of fine sediments or ¹³⁷Cs at water depths of 3m. There was no apparent relationship between sediment slope and ¹³⁷Cs content. Although the ¹³⁷Cs entered Pond B more than 20 years ago, its prevalance in the surface layers of littoral zone sediments resembles the pattern observed for ¹³⁴Cs deposited in European lakes from the recent Chernobyl accident. (Author)

[en] A pond which undergoes seasonal anoxia as a result of thermal stratification was studied to assess the possible release of actinide elements from anoxic sediments to the pond waters. Concentration profiles of sup(239,240)Pu, ²⁴¹Am, ²³²Th, iron and manganese in the water column show significant increases in concentration for all elements in the anoxic deep waters. However, calculated total inventories of the elements in the pond water indicate no apparent input of actinide elements to the system during summer stratification. Similar inventory calculations for sup(239,240)Pu, in a previously studied system support the results of this study. The lack of a significant increase in pond inventories of actinide elements coupled with a lack of correspondence of concentration profiles of the actinide elements to the seasonal Fe and Mn concentration profiles argues that the increases in concentrations observed for these elements in anoxic bottom waters result from the downward transport of material already in the water column rather than release from the sediments. (author)

[en] An annual cycle occurs in the ^239,240Pu inventories of the water column of Pond B, an 87-ha warm monomictic reservoir on the US Department of Energy's Savannah River Site in Barnwell Co., South Carolina. The pond has elevated concentrations of ²³⁸Pu and ^239,240Pu in sediments due to releases from former reactor operations and continues to receive additional Pu input from atmospheric deposition. For surface waters, the ^239,240Pu inventory increases following turnover in November to a maximum in March followed by a decline until later summer when minimum inventories occur. For deeper waters, the ^239,240Pu inventories increase rapidly following turnover and reach maximum values in March. The inventories in deeper waters remain large from March until turnover. Maximum inventories for the entire water column occur in March with minimum inventories at turnover in October and November. Turnover results in a redistribution of Pu across water depth but no measurable Pu loss from the water column. Ratios of ²³⁸Pu: ^239,240Pu indicate that the cycle involves primarily Pu from sediment sources with little influence from atmospheric sources. Thus, the cycle represents net remobilization of ^239,240Pu from the sediments to the water column during the oxic, holomictic portion of the year followed by a net loss of Pu from the water column once stratification occurs. (author)