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Sorption–Diffusion Model of 137Cs Absorption by Bottom Deposits of Lakes in the Reconstruction of 137Cs Fallout to Water Basins
... To further explore the relationship between climatic factors and water turbidity and understand the potential meteorological factors of interannual turbidity variation, we analyzed the correlation between the average turbidity of each lake in each landscape image and local wind, temperature, and precipitation (which were collected from the National Meteorological Information Center. 2 These climate data mainly include the averaged wind speed, averaged temperature and cumulative precipitation data (e.g., of the day, the last ten days when the satellite image was captured) from corresponding five meteorological stations (see Fig. 10). The average water turbidity of most lakes demonstrate positive correlations with temperature and wind speed (R < 0.5). ...
Water turbidity is an important proxy to measure water quality and environmental conditions. Based on extensive field data and Landsat data (2011-2018), this article developed a retrieval model suitable for turbidity. The determination coefficient (R
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) of the model was 0.946 and the root-mean-square error was 23.82 NTU. The model was implemented to obtain the turbidity information of hundreds of lakes in Northeast China (1984-2018). The results revealed the distinctive spatial pattern of water turbidity values of the lakes (i.e., high turbidity in the south; low turbidity in the northwest; and moderate turbidity in the east). In terms of temporal pattern, the water turbidity values of most lakes trended downward at an average rate of 1.39 NTU/a (P <; 0.05) with obvious seasonal differences (i.e., decreased from May to the lowest in July, and then increased from September onward). Finally, we quantitatively examined how several typical factors affect turbidity variation at different scales. We found that water turbidity was highly correlated with NDVI (R = 0.56, P <; 0.001), followed by water temperature and wind speed (0.02 <; R <; 0.5, P <; 0.05). Water turbidity varies because of the interaction of multiple factors (e.g., area, temperature, water depth, precipitation, and land use) instead of one factor. This article highlights the potential of remote sensing in large-scale and long-term monitoring of lake water quality, and provides important information and support for water quality management in China.
Contamination of waters of lake–river systems after many-year migration of ¹³⁷Cs in water bodies was studied. In lakes with the ¹³⁷Cs fallout density lower than 8 kBq m–2, the radionuclide concentrations in water after 24–29 years did not exceed 2–3 Bq m–3, and at a fallout level of 37 kBq m–2 it was in the range 11–34 Bq m–3. The natural half-clearance time Т of lake waters from ¹³⁷Cs was 6–7 years at the exposure of up to 20 years. The ¹³⁷Cs migration in the lake–river systems that occurred during ~30 years did not lead to structural changes in the water contamination: The initially low ¹³⁷Cs level in lake waters did not become high, and vice versa. Among rivers feeding Lake Ladoga, the ¹³⁷Cs level in the Vuoksa River is ~3 times higher than in waters of the Volkhov and Svir rivers. During the period 1988–2015, 21.3 TBq of ¹³⁷Cs was supplied to Lake Ladoga with Vuoksa waters. The Vuoksa source from the Saima lake system with increased contamination with ¹³⁷Cs of Chernobyl origin leads to long-term supply of this radionuclide to Lake Ladoga.
The 5–17-year migration of ¹³⁷Cs in bottom sediments (BSs) of five oligotrophic lakes located on the “Chernobyl” ¹³⁷Cs fallout plume was studied. The layer-by-layer analysis of the ¹³⁷Cs levels in BS cores allowed determination of the ¹³⁷Cs migration mechanism and of the numerical characteristics of its transfer into the thickness of BSs of low-trophy water bodies. The exponential decrease in the ¹³⁷Cs concentration from the core surface to the BS depth was evaluated by the half-loss layer h. The value of h for “Chernobyl” ¹³⁷Cs for BSs of oligotropic lakes was 1.2–2.3 cm. The ¹³⁷Cs transfer in BSs of oligotrophic lakes occurred by the diffusion mechanism. The diffusion coefficients (D) of “Chernobyl” ¹³⁷Cs in the lake BS columns were (2.0–4.7) × 10⁻⁸ cm² s⁻¹. The diffusion coefficients in ¹³⁷Cs migration increased from the near-surface layer of bottom sediments (∼0–2 cm) to the depth of the bottom soil in the range n × (10⁻⁹–10⁻⁸) cm² s⁻¹. The numerical characteristics of the ¹³⁷Cs migration (h and D) refer to BSs of oligotrophic lakes in which the flow of sediments to the lake bottom did not exceed 1.8 mm year⁻¹. In Lake Sukhodol’skoe at a sedimentation rate of 6 mm year⁻¹ and radionuclide exposure of 31 years, the bulk of BSs was contaminated with ¹³⁷Cs by the mixed mechanism: diffusion from the primary accumulation site and sedimentation of suspended matter with ¹³⁷Cs.
For a sample including 22 lakes, the 137Cs concentrations in water were determined by the sorption-diffusion model. The 137Cs levels in waters of lakes of the Kola Peninsula and Karelian Isthmus are satisfactorily described by the suggested model at the distribution coefficient K
d of 4000 L kg−1 and diffusion coefficient D of 1.0 × 10−7 cm2 s−1 for 2–4-year exposure. For mid-latitude lakes, the ranges of K
d and D of 137Cs were 6000–1200 L kg−1 and 1.0 × 10−7–0.2 × 10−7 cm2 s−1, respectively. The 137Cs concentration in water is determined by the major contribution of silts, which are characterized by high K
d of 137Cs and by large thickness of sediments on the bottom of lake hollows, to the watter-bottom sorption system. After 2-year exposure of “Chernobyl” 137Cs in lakes, its inventory in water relative to the amount that fell out in 1986 did not exceed 14% for deep lakes and 2–3.6% for shallow lakes.
The results of works performed in 2007 and 2008 to determine the contamination density (CD) of soil with 137Cs and its depth distribution in 45 settlements of the Volosovo and Kingisepp raions of Leningrad oblast, affected by the Chernobyl accident, are reported. With the lognormal distribution of CD values assumed, the confidence ranges for the CD values averaged for specific settlements were estimated on the basis of the results of the above-mentioned works and of the whole set of data accumulated by now. The shortcomings of the Methodical Recommendations of 1990 as applied to the contamination conditions characteristic of Leningrad oblast are noted. In 35 of the 45 settlements surveyed, the volume of data accumulated by now is insufficient for making substantiated management and legal decisions. One of possible ways to make the studies less labor-consuming within the framework of the statistical model used is discussed.
The long-term behaviour of 137Cs was studied in two freshwater ecosystems in southern Finland in an area most loaded by the Chernobyl fallout in 1986. Samples were taken from water, sediments, aquatic plants and fish in the lakes and from soil, mushrooms and seed plants in the catchments. The activity concentrations of 137Cs in fish have remained at a relatively high level and decreased much more slowly in these two lakes than in other lakes studied by us. One reason for the continuously high concentrations in fish is evidently the prolonged stay of caesium at a relatively high level in the water of these lakes, which is associated with a slow sedimentation rate. The hydrographical properties of the lakes, i.e. the oligotrophic character associated with a deficiency of potassium in water and a low pH are other reasons for the effective uptake and long retention time of 137Cs in fish. The effect of humic substances on the uptake and delay of caesium in fish could not be proved clearly in this study. The swampy soil type of the catchment associated with a more oligotrophic status and lower pH of the water in Lake Siikajärvi explain at least partly the difference in activity concentrations and transfer of 137Cs between the two lakes studied. This refers to the higher transfer from the catchment to the lake and the higher uptake of 137Cs by fish and other biota in Lake Siikajärvi than in Lake Vehkajärvi. Perch and pike were more efficient accumulators of caesium than the best indicators among the aquatic plants. In the terrestrial environment, caesium was most effectively accumulated by mushrooms.
Itogi izucheniya i opyt likvidatsii posledstvii avariinogo zagryazneniya territorii produktami deleniya urana (Results of Studies and Experience of Liquidation of the Consequences of an Emergency Contamination of the Territory by Uranium Fission Products
- A I Burnazyan
- Ed
Ekologicheskaya bezopasnost’ yaderno-energeticheskogo kompleksa Rossii (Ecological Safety of the Nuclear-Power Complex of Russia)
- I I Kryshev
- E P Ryazantsev
Ozera Srednego i Yuzhnogo Urala (Lakes of the Middle and Southern Urals)
- M A Andreeva
- M.A. Andreeva
Ozera Srednego i Yuzhnogo Urala (Lakes of the Middle and Southern Urals), Chelyabinsk: YuUKI
- M A Andreeva