Migration of Cs in tributaries,lake water and sediment of Lago Maggiore (Italy,Switzerland) – analysis and comparison with Lago di Lugano and other lakes

This paper describes the behaviour of ¹³⁷Cs in Lago Maggiore and other pre-alpine lakes as a consequence of atmospheric nuclear weapons testing fallout and the fallout from the nuclear accident in Chernobyl. It presents data on the ¹³⁷Cs distribution in tributaries, lake water, bottom sediments and reveals the role of ¹³⁷Cs as a marker of the sedimentation processes. The run-off of ¹³⁷Cs from the watershed to the lake is described with a simple compartment model. Measurements of the activity concentration of ¹³⁷Cs in sediments are compared with the output of a model (diffusion–convection type) which describes the input of ¹³⁷Cs into and its vertical distribution within the sediment. Varying sedimentation rates (0.05–0.90 g (cm² y)⁻¹) in Lago Maggiore are compared with data of other authors. Sedimentation rates and total distribution coefficients (of about 10⁵ L kg⁻¹) in Lago Maggiore are discussed and compared with those of Lago di Lugano, Lake Constance, and Lake Vorsee.     

Predicting the transfer of radiocaesium from organic soils to plants using soil characteristics

A model predicting plant uptake of radiocaesium based on soil characteristics is described. Three soil parameters required to determine radiocaesium bioavailability in soils are estimated in the model: the labile caesium distribution coefficient (kd1), K+ concentration in the soil solution [mK] and the soil solution-->plant radiocaesium concentration factor (CF, Bq kg-1 plant/Bq dm-3). These were determined as functions of soil clay content, exchangeable K+ status, pH, NH4+ concentration and organic matter content. The effect of time on radiocaesium fixation was described using a previously published double exponential equation, modified for the effect of soil organic matter as a non-fixing adsorbent. The model was parameterised using radiocaesium uptake data from two pot trials conducted separately using ryegrass (Lolium perenne) on mineral soils and bent grass (Agrostis capillaris) on organic soils. This resulted in a significant fit to the observed transfer factor (TF, Bq kg-1 plant/Bq kg-1 whole soil) (P < 0.001, n = 58) and soil solution K+ concentration (mK, mol dm-3) (P < 0.001, n = 58). Without further parameterisation the model was tested against independent radiocaesium uptake data for barley (n = 71) using a database of published and unpublished information covering contamination time periods of 1.2-10 years (transfer factors ranged from 0.001 to 0.1). The model accounted for 52% (n = 71, P < 0.001) of the observed variation in log transfer factor.     

Radiocaesium soil-to-wood transfer in commercial willow short rotation coppice on contaminated farm land

The feasibility of willow short rotation coppice (SRC) for energy production as a revaluation tool for severely radiocaesium-contaminated land was studied. The effects of crop age, clone and soil type on the radiocaesium levels in the wood were assessed following sampling in 14 existing willow SRC fields, planted on radiocaesium-contaminated land in Sweden following Chernobyl deposition. There was only one plot where willow stands of different maturity (R6S2 and R5S4: R, root age and S, shoot age) and clone (Rapp and L78183 both of age category R5S4) were sampled and no significant differences were found. The soils differed among others in clay fraction (3-34%), radiocaesium interception potential (515-6884 meq kg(-1)), soil solution K (0.09-0.95 mM), exchangeable K (0.58-5.77 meq kg(-1)) and cation exchange capacity (31-250 meq kg(-1)). The soil-to-wood transfer factor (TF) of radiocaesium differed significantly between soil types. The TF recorded was generally small (0.00086-0.016 kg kg(-1)), except for willows established on sandy soil (0.19-0.46 kg kg(-1)). Apart from the weak yet significant exponential correlation between the Cs-TF and the solid/liquid distribution coefficient (R2 = 0.54) or the radiocaesium interception potential, RIP (R2 = 0.66), no single significant correlations between soil characteristics and TF were found. The wood-soil solution 137Cs concentration factor (CF) was significantly related to the potassium concentration in the soil solution. A different relation was, however, found between the sandy Tr?dje soils (CF = 1078.8 x m(K)(-1.83), R2 = 0.99) and the other soils (CF = 35.75 x m(K)(-0.61), R2 =0.61). Differences in the ageing rate of radiocaesium in the soil (hypothesised fraction of bioavailable caesium subjected to fast ageing for Tr?dje soils only 1% compared to other soils), exchangeable soil K (0.8-1.8 meq kg(-1) for Tr?dje soils and 1.5-5.8 meq kg(-1) for the other soils) and the ammonium concentration in the soil solution (0.09-0.31 mM NH4+ for the Tr?dje soils compared to 0.003-0.11 mM NH4+ for the other soils) are put forward as potential factors explaining the higher CF and TF observed for the Tr?dje soils. Though from the dataset available it was not possible to unequivocally predict the Cs-soil-to-wood-transfer, the generally low TFs observed point to the particular suitability for establishment of SRC on radiocaesium-contaminated land.     

洞庭湖、鄱阳湖白鱀豚和长江江豚的生态学研究

１９９７年至１９９９年对洞庭湖和鄱阳湖的湖区及其支流的白豚和长江江豚的分布、数量和活动规律进行了系统的调查。调查结果表明,白豚已在洞庭湖和鄱阳湖绝迹。长江江豚随着水位的变化,其分布范围、数量和活动规律也随之而变化。长江江豚在洞庭湖的分布范围主要集中在从城陵矾到鲶鱼口一带,其种群数量大致力１００～１５０头。洞庭湖各支流中已看不到江豚的踪迹。在鄱阳湖主要分布在湖口至龙口一带,老爷庙至小矶山是其集中分布区。赣江南北支、抚河下游及康山河在涨水季节也有少量江豚活动。洞庭湖和鄱阳湖大规模的围湖造田,湖区的迅速淤积变浅,大桥的修建,有害渔具渔法的大量使用,船舶数量的大量增加是长江江豚迅速减少的重要原因,两大湖泊中的长江江豚急待保护。     

Radiocaesium soil-to-plant transfer in tropical environments

In this work, soil-to-plant transfer factors of radiocaesium are predicted based on soil properties such as pH, organic matter content, exchangeable K+ and clay content valid for the tropical environments in Bangladesh, China and Japan, and using a previously published model. Due to insufficient data of soil properties in the selected regions, the average values of pH, organic matter content, exchangeable K+ and clay content were taken as the input model parameters within the ranges given for Asia. Nevertheless, a complete set of soil properties of Japanese soils was used to compare the measured and calculated TF values of radiocaesium for radish. The calculated TF values for radiocaesium are comparable with the measured values especially for leafy parts of a plant. However, calculated values for rice, an important crop in Asia are found to overestimate the measured values due to an overestimate of calculated CECs in soils in the selected regions. The empirical parameters used in the model need to be re-evaluated for the specific part of a plant and/or for a variety of different plants. Alternatively, a general conversion factor for each part of a plant and/or for a variety of different plants for a specific region is suggested for tropical environments.     

Modelling the long-term dynamics of radiocaesium in closed lakes

During the years after the Chernobyl accident the radioceasium activity concentration in most contaminated aquatic ecosystems decreased markedly. Lakes with no permanent inflows and outflows (closed lakes), however, still present a radioecological problem which is expected to continue for some time. In this paper, a mechanistic model for the long-term prediction of radiocaesium behaviour in closed lakes is developed. The model of Prokhorov (Radiokhimiya (Radiochemistry) 11 (1969) 317) was modified to describe the effects of bottom sediment bioturbation, surface runoff from the catchment and suspended solids formation and sedimentation. The model input parameters are the effective diffusion coefficient in bottom sediments, depth of the completely mixed layer, the distribution coefficient in the sediment-water system, the runoff coefficient, sedimentation rate, and deposition density. Values of all these parameters can be independently estimated or measured in a short-term experiment. Given negligible runoff and sedimentation, the dynamics of radiocaesium in lake water is described by a simple equation with only one unknown parameter. This allows us to make long-term predictions on the basis of a series of measurements carried out during the relatively short period. The model was tested against 137Cs activity concentrations measured between 1993 and 1999 in Svyatoe lake in the Bryansk region of Russia. Calculated and measured activity concentrations are in good agreement.     

Modelling the long-term behaviour of radiocaesium and radiostrontium in two Italian lakes

The present paper describes the application of a state-of-the-art model to two lakes in central Italy (Trasimeno and Monterosi) for the assessment of migration parameters of (137)Cs and (90)Sr (migration velocity to sediment, transfer rates from sediment to water and to bottom sediment). Applications of a compartment model and a model based on the diffusion equation to predict the behaviour of pollutants in water and through bottom sediment are presented and discussed. The application of the diffusion equation shows some difficulties of a general nature and typical of such a modelling approach. Moreover, there is no evidence of significant improvements of the model performances when the diffusion equation is applied. Very low levels of sedimentation rate of suspended matter in Lake Monterosi were evaluated by the quantitative assessment of radiocaesium migrating to bottom sediment. This suggests that, in this lake, the removal of radionuclide from the water column is mainly due to the turbulent mixing of bottom sediment causing radionuclide burial.     

A critical review of measures to reduce radioactive doses from drinking water and consumption of freshwater foodstuffs.

Following a radioactive fallout event, there are a number of possible intervention measures to reduce radioactive doses to the public via the surface water pathway. We have critically reviewed the options available to decision-makers in the event of radioactive contamination of surface waters. We believe that the most effective and viable measures to reduce radioactivity in drinking water are those which operate at the water treatment and distribution stage. Intervention measures to reduce concentrations of radioactivity in rivers and reservoirs are expected to be much less viable and efficient at reducing doses via the drinking water pathway. Bans on consumption of freshwater fish can be effective, but there are few viable measures to reduce radioactivity in fish prior to the preparation stage. Lake liming and biomanipulation have been found to be ineffective for radiocaesium, although the addition of potassium to lakewaters appears promising in some situations. Lake liming may be effective in reducing radiostrontium in fish, though this has not, to our knowledge, been tested. De-boning fish contaminated by strontium is probably the most effective food preparation measure, but salting and freezing can also reduce radiocaesium concentrations in fish. The provision of accurate information to the public is highlighted as a key element of countermeasure implementation.     

Uptake and elimination of radiocaesium in fish and the "size effect."

A number of hypotheses have previously been developed concerning the rates of uptake and elimination of radiocaesium (137Cs) in fish. These include the influence of potassium and other water chemical parameters on both uptake and elimination, and the effect of fish size on accumulation. In order to test these hypotheses, we have assembled a data set comprising more than 1,000 measurements of radiocaesium (137Cs) in predatory fish (perch, pike and brown trout) in nine European lakes during the years after Chernobyl. These data have been analysed using simple models for uptake and excretion of 137Cs in fish, showing that: 1. Fish-water concentration factors (CF) were inversely proportional to potassium [K+] concentration of the different lakes, in agreement with previous studies. 2. The uptake rate of 137Cs in fish was negatively correlated with lake [K+], but excretion rate was independent of [K+]. 3. Lower than expected CF values were found in one lake, Iso Valkj?rvi, Finland. This is attributed to inhibition of the K+ (and therefore 137Cs) high affinity transport system in aquatic plants and fish by low pH and/or low Ca2+. 4. The inclusion of fish weight as a parameter in our dynamic model significantly improves the ability of the model to fit the observed measurements of 137Cs. 5. The model developed from the above hypotheses was able to fit the data from nine different lakes to within approximately a factor of 3 of the observed values.     

南水北调东线湖群水体营养状态评价及其限制因子研究

湖泊富营养化问题是我国湖泊保护面临的紧迫问题,开展湖泊营养状态评价及其限制因子研究,对于富营养化湖泊治理和生态系统修复具有重要意义。该研究以南水北调东线工程调蓄湖群-高邮湖、洪泽湖、骆马湖、南四湖、东平湖为研究区域,于2018年4月非调水期和10月调水期对调蓄湖群109个样点开展了系统监测,采用综合营养状态指数法对调蓄湖群营养状态进行了评价,运用多元统计分析方法分析了湖群富营养化特征及其限制因子。结果表明:同一水期内调蓄湖泊间水质指标不尽相同,各调蓄湖泊非调水期水质优于调水期,影响水质达标的主要因子为总氮和总磷。调蓄湖群调水期均处于轻度富营养状态,非调水期均处于中营养状态,非调水期优于调水期。透明度和叶绿素a是决定调蓄湖群富营养化水平的限制性因子。     

Predictions of in situ solid/liquid distribution of radiocaesium in soils

Previous work has demonstrated that plant uptake of radiocaesium (RCs) is related to the activity concentration of RCs in soil solution, which is linked to the soil/soil solution distribution coefficient, K(D). The solid-liquid distribution of RCs is generally studied in soil suspensions in the laboratory and there are few reported measurements for in situ soil solutions. From a data set of 53 different soils (contaminated with either 134CsCl or 137CsCl) used in pot trials to investigate grass uptake of RCs, we analysed the variation of in situ K(D) with measured soil properties. The soils differed widely in % clay (0.5-58%), organic matter content (1.9-96%) and pH (2.4-7.0, CaCl2). The K(D) varied between 29 and 375,000 L kg-' (median 1460 L kg(-1)). Stepwise multiple regression analysis showed a significant correlation between the log K(D) and pH (p < 0.001), log %clay (p < 0.01) and log exchangeable K (p < 0.001) (overall R2 = 0.70). The in situ K(D) values were further compared to K(D)S predicted using an existing model, which assumes that RCs sorption occurs on specific sites and regular ion-exchange sites on the soil solid phase. Sorption of RCs on specific sites was quantified from the radiocaesium interception potential (RIP) measured for each soil and the soil solution concentrations of K+ and NH4+. The in situ log K(D) correlated well with the predicted K(D) (R2 = 0.85 before plant growth, R2 = 0.83 after plant growth). However, the observations were fivefold to eightfold higher than the predictions, particularly for the mineral soils. We attribute the under-prediction to the long contact times (minimum 4 weeks) between the RCs tracers and our experimental soils relative to the short (24 h) contact times used in RIP measurements. We conclude that our data confirmed the model but that ageing of RCs in soil is a factor that needs to be considered to better predict in situ KD values.     

汉阳湖群底栖动物群落及其对环境质量的指示

汉阳地区湖汊纵横、水系丰富,是汉阳地区工业和生活废水的主要纳污水体,水质多为劣V类。底栖动物已被广泛用于监测湖泊有机污染,因此,为探明汉阳地区湖泊群（三角湖、墨水湖、龙阳湖、月湖、后官湖）的污染状况和污染分布格局,于2002~2005年全面调查了各湖泊的底栖动物群落,并分析了其对环境的指示作用。除后官湖发现软体动物外,其他各湖泊均以耐污的颤蚓科寡毛类(霍甫水丝蚓,苏氏尾鳃蚓)和摇蚊科幼虫(长足摇蚊、红裸须摇蚊、羽摇蚊)占绝对优势。统计分析表明,颤蚓类和摇蚊幼虫的密度与水体氮、磷、叶绿素含量呈显著正相关（〖WTBX〗p<005）,且颤蚓类密度对水体氮、磷水平的预测能力（R2）〖WTBZ〗优于摇蚊幼虫。K 优势曲线和多样性指数的污染评价结果显示,墨水湖和龙阳湖属重污染,月湖和三角湖属中度污染,后官湖属轻度污染,这与理化指标表征的营养状况基本吻合,特别是在受苯酚化工废料污染的龙阳湖东片没有采集到底栖动物,这是底栖动物能够监测污染物长期效应的例证。进一步应用颤蚓类密度的水平分布指示了各湖泊的沉积物污染分布,结合湖体周边环境分析论证了这种指示作用的可信度     

Radiocaesium fallout behaviour in volcanic soils in Iceland

The retention of 137Cs in various types of Andosols in Iceland was investigated. Soils were sampled at 29 sites with varying precipitation and environmental conditions. Samples were obtained from 0 to 5, 5 to 10, and 10 to 15 cm depths. The amount of radiocaesium present was quite variable, ranging between 300 and 4800 Bq m(-2) and correlated closely to total annual precipitation (r2=0.71). The majority of 137Cs, 82.7% on average, was retained in the uppermost 5 cm of the soil. The greatest penetration of 137Cs was observed for organic Histosols (76.3% in top 5 cm). The Icelandic Vitrisols (barren, poorly developed Andosols) are coarse grained with only 2-5% clay content and contain little organic matter (<1%). Yet these soils retained 74% of 137Cs in the top 5 cm. The results indicate that radiocaesium fallout is strongly retained by colloidal materials characteristic of Andosols, such as allophane and ferrihydrite. Most soils in Iceland are subject to severe and prolonged freezing and waterlogging; despite this, 137Cs is retained in the upper soil horizons and vertical migration is negligible in Icelandic Andosols. However, erosion and aeolian activity can markedly influence the amount and vertical distribution of radiocaesium in Icelandic soils.     

Land use influence on 137Cs levels in perch (Perca fluviatilis L.) and roach (Rutilus rutilus L.)

The environmental influence on Chernobyl-derived 137Cs levels in perch (Perca fluviatilis L.) and roach (Rutilus rutilus L.) was revealed using partial least-squares regression (PLS). The 53 environmental predictors used describe land use in catchment areas, various catchment area and lake characteristics, lake water chemistry, and fish stock composition. The study showed a profound effect of land use on the 137Cs levels in fish. Radiocaesium deposited on arable land was retained in the soil to a greater extent than was 137Cs deposited on wetlands, which more easily leached out to the lake ecosystems. The 137Cs deposition close to the lakes had a more pronounced effect on 137Cs levels in the fish than did more distant deposition. The radiocaesium bioavailability is mainly governed by lake water cation content, as hardwater lakes had significantly lower 137Cs content in fish. Resuspension of 137Cs contaminated sediments only had a limited influence on the observed levels in fish.     

月湖底栖动物的空间格局及其对水草可恢复区的指示

底质适宜是富营养湖泊恢复沉水植物(水草)的重要前提。大型底栖动物可综合指示底质的污染程度,于2002~2003年在武汉月湖开展了底栖动物水平分布对水草可恢复区指示作用的研究。首先通过月湖底栖动物与环境的相关分析,选择颤蚓科寡毛类作为底质营养状况的指示类群,然后利用同类湖泊群颤蚓与水草数据分析阈值,初步确定颤蚓密度≤100 ind/m2的底质适合水草生长,最后绘制月湖颤蚓分布的水平等值线,显示水草恢复的合适区域。在此基础上构建了应用底栖动物空间格局指示水草恢复区的技术原理框架。     

鄱阳湖越冬鸟类种群动态与保护研究

目前为止缺少对鄱阳湖全湖冬候鸟的种群动态和群落方面的研究分析,拟通过对鄱阳湖冬候鸟群落多样性和种群动态的分析,为该地区冬候鸟及其栖息地保护提出建设性建议。2010～2012年冬季,通过采用直接计数法和样线法调查鄱阳湖湿地冬季碟形湖内的越冬鸟类群落结构。总共记录到越冬鸟类88种,另有29种属于文献报道但本次调查中未发现的种类。总共117种鸟类分别属于目、鹈形目、鹳形目、雁形目、鹤形目、鸻行目和佛法僧目。在鄱阳湖,种类和数量分布最多的是冬候鸟,达到78种。小天鹅、鸿雁、豆雁、白额雁、绿翅鸭和斑嘴鸭是鄱阳湖湿地越冬鸟类中的绝对优势种,鸟类个体数量最多的冬季蝶形湖泊主要包括鄱阳湖自然保护区的蚌湖、大湖池、沙湖和大汊湖,都昌县的黄金嘴,南矶山湿地自然保护区的白沙湖,余干县的林充湖和南湖,以及鄱阳县的珠湖。各种越冬鸟类在鄱阳湖湿地的种群数量分布差异主要是与各碟形湖水位的高低和食物的分布密切相关。只有在冬季开始后,使碟形湖洼地的水位逐渐降低,越冬鸟类才能够更有效的利用湖泊中的食物     

Seasonal variation of the radiocaesium transfer soil-to-Swiss chard (Beta vulgaris var. cicla L.) in allophanic soils from the Lake Region, Chile

The transfer factor (TF) of radiocaesium from soil-to-Swiss chard (Beta vulgaris var. cicla L.) was studied in two different characteristic allophanic soils (umbric andosol and dystric fluvisol) of the Lake Region, an important agricultural region situated in central-south Chile. To investigate especially the time dependence and the effect of K-fertilisation on the TF, field experiments were conducted. Plots of 7.6 m2 were labelled with 100 kBq 134Cs m(-2) at Santa Rosa Experiment Station close to the city of Valdivia characterised by a temperate climate and high precipitation rates. The variation in time of the radiocaesium TF soil-to-Swiss chard was observed during two consecutive years after soil contamination by sequential harvests and radiocaesium analyses of the plants. The TFs showed no significant ageing effect, but a pronounced seasonal decrease with effective half-lives of about 140 and 160 days for the umbric andosol without and with K-fertilisation, respectively, and of 50 and 60 days for the dystric fluvisol without and with K-fertilisation, respectively. The effect of K-fertilisation on the absolute values of the TF was determined by the ratio between the median TF values obtained for corresponding dates without and with use of K-fertiliser. A ratio of TF(without K)/TF(with K) = 1.8 for the umbric andosol and TF(without K)/TF(with K) = 2.9 for the dystric fluvisol was obtained, indicating a reduction of the TF by applying 90 kg K ha(-1). The maximal values of the TF to chard predicted by the equation characterising the seasonal decrease of the TF at the beginning of the harvest periods are 0.19 for the umbric andosol and 0.11 for the dystric fluvisol, both values for soil treated with common K-fertilisation.     

Estimation of critical loads for radiocaesium in Fennoscandia and Northwest Russia

The application of the critical loads methodology for radioactive contamination of Arctic and sub-arctic ecosystems, where natural and semi-natural food products are important components of the diet of many people, is proposed and discussed. The critical load is herein defined as the amount of radionuclide deposition necessary to produce radionuclide activity concentrations in food products exceeding intervention limits. The high transfer of radiocaesium to reindeer meat gives this product the lowest critical load, even though the intervention limit is relatively high compared with other products. Ecological half-lives of radiocaesium in natural and semi-natural products are often very long, and it is therefore important to take account of contamination already present in the event of an accident affecting areas where such products are important. In particular, the long ecological half-life for radiocaesium in moose meat means that the critical load is highly sensitive to prior deposition. An example of the potential application of the method for emergency preparedness is given for the Chernobyl accident.     

Radiocaesium contamination of meadow vegetation--time-dependent variability and influence of soil characteristics at grassland sites in Austria

Long-term trends of 137Cs and 40K concentrations in meadow grass and soil-plant transfer data at eight different sites in Upper Austria are presented. Geometric means of 137Cs TF-data and Tagg values vary between 0.03-1.06 and 0.0005-0.0184 depending on site, respectively. 40K results are less variable with TF values covering a range of 0.31-2.01. Only at one site was a significant decrease of 137Cs concentration (decay-corrected) in meadow vegetation observed during the observation period 1992-1999. Seasonal trends of 40K and 137Cs were investigated at one site in 1996. Both elements show decreasing concentrations in plants from beginning of May-July, followed by a peak in September. Although this pattern was not very pronounced, there are some hints that it may explain deviations of long-term trends in 137CS levels in grass caused by unusual weather conditions as indicated by phenological climate data (beginning of sweet cherry and black elder blossoming). Finally, TF values were correlated with soil characteristics, revealing a negative correlation of radiocaesium soil-plant transfer with soil pH, exchangeable and extractable fractions of Mg, Ca and Na as well as a positive correlation with exchangeable Al.