Resuspension and redistribution of radionuclides during grassland and forest fires in the Chernobyl exclusion zone: part I. Fire experiments

Controlled burning of experimental plots of forest or grassland in the Chernobyl exclusion zone has been carried out in order to estimate the parameters of radionuclide resuspension, transport and deposition during forest and grassland fires and to evaluate the working conditions of firemen. An increase of several orders of magnitude of the airborne radionuclide concentration was observed in the territory near the fire area. The resuspension factor for (137)Cs and (90)Sr was determined to range from 10(-6) to 10(-5) m(-1), and for the plutonium radionuclides from 10(-7) to 10(-6) m(-1) (related to the nuclides in the combustible biomass). These values are 2 orders of magnitude lower if they are calculated relatively to the total contamination density (including the nuclides in the soil). The radionuclide fallout along the plume axis is negligible in comparison to the existing contamination. However, the additional inhalation dose for firemen exposed in the affected area can reach the level of the additional external irradiation in the period of their mission. The plutonium nuclides constitute the dominating contribution to the inhalation dose.     

Monitoring of firefighters exposure to smoke during fire experiments in Portugal

Forest fires represent a serious threat to public security in Europe due to the large burned area. Moreover, smoke pollution due to forest fire events is an important public health issue for the communities directly affected, and particularly for the personnel involved in firefighting operations. Aiming to contribute to the scientific knowledge concerning firefighters exposure to forest fires smoke, data of individual exposure to carbon monoxide, nitrogen dioxide, volatile organic compounds, and particulate matter were obtained during experimental field fires for a group of 10 firefighters equipped with portable “in continuum” measuring devices. Measured values are very high exceeding the Occupational Exposure Standard limits, in particular for peak limit thresholds. These are the first measurements and analysis of firefighter's individual exposure to toxic gases and particles in fire smoke experiments in Europe. However, they already indicate that urgent measures to avoid these levels of exposure are needed.     

A study of the atmospheric dispersion of a high release of krypton-85 above a complex coastal terrain, comparison with the predictions of Gaussian models (Briggs, Doury, ADMS4)

Atmospheric releases of krypton-85, from the nuclear fuel reprocessing plant at the AREVA NC facility at La Hague (France), were used to test Gaussian models of dispersion. In 2001-2002, the French Institute for Radiological Protection and Nuclear Safety (IRSN) studied the atmospheric dispersion of 15 releases, using krypton-85 as a tracer for plumes emitted from two 100-m-high stacks. Krypton-85 is a chemically inert radionuclide. Krypton-85 air concentration measurements were performed on the ground in the downwind direction, at distances between 0.36 and 3.3 km from the release, by neutral or slightly unstable atmospheric conditions. The standard deviation for the horizontal dispersion of the plume and the Atmospheric Transfer Coefficient (ATC) were determined from these measurements. The experimental results were compared with calculations using first generation (Doury, Briggs) and second generation (ADMS 4.0) Gaussian models. The ADMS 4.0 model was used in two configurations; one takes account of the effect of the built-up area, and the other the effect of the roughness of the surface on the plume dispersion. Only the Briggs model correctly reproduced the measured values for the width of the plume, whereas the ADMS 4.0 model overestimated it and the Doury model underestimated it. The agreement of the models with measured values of the ATC varied according to distance from the release point. For distances less than 2 km from the release point, the ADMS 4.0 model achieved the best agreement between model and measurement; beyond this distance, the best agreement was achieved by the Briggs and Doury models.     

Forest fires and adaptation options in Europe

This paper presents a quantitative assessment of adaptation options in the context of forest fires in Europe under projected climate change. A standalone fire model (SFM) based on a state-of-the-art large-scale forest fire modelling algorithm is used to explore fuel removal through prescribed burnings and improved fire suppression as adaptation options. The climate change projections are provided by three climate models reflecting the SRES A2 scenario. The SFM’s modelled burned areas for selected test countries in Europe show satisfying agreement with observed data coming from two different sources (European Forest Fire Information System and Global Fire Emissions Database). Our estimation of the potential increase in burned areas in Europe under “no adaptation” scenario is about 200 % by 2090 (compared with 2000–2008). The application of prescribed burnings has the potential to keep that increase below 50 %. Improvements in fire suppression might reduce this impact even further, e.g. boosting the probability of putting out a fire within a day by 10 % would result in about a 30 % decrease in annual burned areas. By taking more adaptation options into consideration, such as using agricultural fields as fire breaks, behavioural changes, and long-term options, burned areas can be potentially reduced further than projected in our analysis.     

Impacts of future land use/land cover on wildfire occurrence in the Madrid region (Spain)

This paper assesses the relative importance of socioeconomic factors linked to fire occurrence through the simulation of future land use/land cover (LULC) change scenarios in the Madrid region (Spain). This region is a clear example of the socioeconomic changes that have been occurring over recent decades in the European Mediterranean as well as their impact on LULC and fire occurrence. Using the LULC changes observed between 1990 and 2006 as a reference, future scenarios were run up to 2025 with the conversion of land use and its effects model. Simultaneously, the relationship between LULC arrangement (interfaces) and historical fire occurrence was calculated using logistic regression analysis and used to quantify changes in future fire occurrence due to projected changes in LULC interfaces. The results revealed that it is possible to explain the probability of fire occurrence using only variables obtained from LULC maps, although the explanatory power of the model is low. In this context, border areas between some LULC types are of particular interest (i.e., urban/forest, grassland/forest and agricultural/forest interfaces). Results indicated that expected LULC changes in Euro-Mediterranean regions, particularly given the foreseeable increase in the wildland–urban interface, will substantially increase fire occurrence (up to 155 %). This underlines the importance of future LULC scenarios when planning fire prevention measures.     

Modelling the trade-off between fire and grazing in a tropical savanna landscape, northern Australia.

As savannas are widespread across northern Australia and provide northern rangelands, the sustainable use of this landscape is crucial. Both fire and grazing are known to influence the tree-grass character of tropical savannas. Frequent fires open up the tree layer and change the ground layer from perennials to that dominated by annuals. Annual species in turn produce copious quantities of highly flammable fuel that perpetuates frequent, hot fires. Grazing reduces fuel loads because livestock consumes fuel-forage. This trade-off between fire and grazing was modelled using a spatially explicit, process-orientated model (SAVANNA) and field data from fire experiments performed in the Victoria River District of northern Australia. Results of simulating fire (over 40 years) with minimal or no grazing pressure revealed a reduction in the shrub and woody plants, a reduction in grasses, and no influence on the tree structure given mild fires. While mature trees were resistant to fire, immature trees, which are more likely associated with the shrub layer, were removed by fire. The overall tree density may be reduced with continual burning over longer time periods because of increasing susceptibility of old trees to fire and the lack of recruitment. Increases in stocking rates created additional forage demands until the majority of the fuel load was consumed, thus effectively suppressing fire and reverting to the grazing and suppressed fire scenario where trees and shrubs established.     

Human impacts on fire occurrence: a case study of hundred years of forest fires in a dry alpine valley in Switzerland

Forest fire regimes are sensitive to alterations of climate, fuel load, and ignition sources. We investigated the impact of human activities and climate on fire occurrence in a dry continental valley of the Swiss Alps (Valais) by relating fire occurrence to population and road density, biomass removal by livestock grazing and wood harvest, temperature and precipitation in two distinct periods (1904–1955 and 1956–2006) using generalized additive modeling. This study provides evidence for the role played by humans and temperature in shaping fire occurrence. The existence of ignition sources promotes fire occurrence to a certain extent only; for example, high road density tends to be related to fewer fires. Changes in forest uses within the study region seem to be particularly important. Fire occurrence appears to have been negatively associated with livestock pasturing in the forest and wood harvesting, in particular during the period 1904–1955. This study illustrates consistently how fire occurrence has been influenced by land use and socioeconomic conditions. It also suggests that there is no straightforward linear relationship between human factors and fire occurrence.     

Ventomod: a dynamic model for leaf to fruit transfer of radionuclides in processing tomato plants (Lycopersicon esculentum Mill.) following a direct contamination event

This paper presents results on the calibration and validation of a model (Ventomod) for leaf to fruit transfer of (134)Cs, (85)Sr and (65)Zn in processing tomato plants after leaf contamination. Several models (e.g. FARMLAND) that deal specifically with the transfer of radionuclides to fruits are adaptations of models that were developed for agricultural crops such as leafy green vegetables. "Ventomod" represents a dynamic evaluation model exclusively built for the short-term behaviour of radionuclide depositions. It forecasts the level of radionuclide contamination in ripe processing tomato fruits following an accidental radionuclide release into the atmosphere. A validation of the developed model by data sets from an independent experiment showed that the model successfully reproduced the observed radionuclide distribution and dynamics in tomato fruits. The level of uncertainty was within the normal range of similar assessment models. For a more general use of this model further testing with independent data sets from experiments obtained under different environmental conditions and data from other horticulturally important plant species would be desirable.     

Transport and fate of radionuclides in aquatic environments--the use of ecosystem modelling for exposure assessments of nuclear facilities

In safety assessments of nuclear facilities, a wide range of radioactive isotopes and their potential hazard to a large assortment of organisms and ecosystem types over long time scales need to be considered. Models used for these purposes have typically employed approaches based on generic reference organisms, stylised environments and transfer functions for biological uptake exclusively based on bioconcentration factors (BCFs). These models are of non-mechanistic nature and involve no understanding of uptake and transport processes in the environment, which is a severe limitation when assessing real ecosystems. In this paper, ecosystem models are suggested as a method to include site-specific data and to facilitate the modelling of dynamic systems. An aquatic ecosystem model for the environmental transport of radionuclides is presented and discussed. With this model, driven and constrained by site-specific carbon dynamics and three radionuclide specific mechanisms: (i) radionuclide uptake by plants, (ii) excretion by animals, and (iii) adsorption to organic surfaces, it was possible to estimate the radionuclide concentrations in all components of the modelled ecosystem with only two radionuclide specific input parameters (BCF for plants and Kd). The importance of radionuclide specific mechanisms for the exposure to organisms was examined, and probabilistic and sensitivity analyses to assess the uncertainties related to ecosystem input parameters were performed. Verification of the model suggests that this model produces analogous results to empirically derived data for more than 20 different radionuclides.     

Two thresholds determine climatic control of forest fire size in Europe and northern Africa

Fire weather indices predict fire extent from meteorological conditions assuming a monotonic function; this approach is frequently used to predict future fire patterns under climate change scenarios using linear extrapolation. However, the relationship between weather and fire extent may potentially depend on the existence of fuel moisture content thresholds above which this relationship changes dramatically, challenging this statistical approach. Here, we combine the continuous and the threshold approaches to analyze satellite-detected fires in Europe during 2001–2010 in relation to meteorological conditions, showing that fire size response to decreasing fuel moisture content follows a ramp function, i.e., with two plateaus separated by a phase of monotonic increase. This study confirms that at continental and high-resolution temporal scales, large fires are very unlikely to occur under moist conditions, but it also reveals that fire size stops to be controlled by fuel moisture content above a given threshold of dryness. Thus, fuel moisture content control only applies when fire is not limited by other factors such as fuel load, as large fires were virtually absent during the considered period in dry regions with less than 500 mm of average annual precipitation, i.e., low-productive areas where fuel amount would be scarce and discontinuous. In regions with sufficient fuel, other factors such as fire suppression or fuel discontinuity can impede large fires even under very dry weather conditions. These findings are relevant under current climatic trends in which the fire season length, in terms of number of days with drought code values above the observed thresholds (break points), is increasing in many parts of the Mediterranean, while it is decreasing in eastern Europe and remains unchanged in central Europe.     

Resuspension of coarse fuel hot particles in the Chernobyl area

Measurements of resuspended aerosol in the Chernobyl 30-km exclusion zone have shown coarse fuel hot particles in the activity range 1-12 Bq 137Cs per particle. The particles were sampled with newly designed rotating arm impactors which simultaneously collect during the same experiment three samples with fuel particles in the size ranges larger than 3 microns, larger than 6 microns and larger than 9 microns in geometric diameter. The radionuclide ratios, determined after gamma-spectrometry, were in good agreement with the theoretical calculations for the radionuclide-composition of the Chernobyl Nuclear Power Plant at the moment of the accident and the measured hot particles in soil in the early years after the accident. The number concentrations of airborne hot particles were derived from digital autoradiography. For wind resuspension, maximal concentrations of 2.6 coarse hot particles per 1000 m3 and during agricultural activities 36 coarse hot particles per 1000 m3 were measured. The geometric diameter of single hot particles was estimated to be between 6 and 12 microns.     

长江上游不同地形条件下的土地利用/覆盖变化

基于1〖DK〗∶10万的1980、2000和2005年的土地利用/覆盖数据和90 m分辨率的DEM数据,采用转移概率矩阵和地形 面积频度方法,分析了1980~2005年长江上游地区不同地形因子条件下的土地利用/覆盖变化。结果表明：1）1980~2000年,草地、林地和农业用地面积变化趋势与2000~2005年相反。后5 a,可能由于退耕的土地出现反弹现象增多,草地和林地面积出现缩减而农业用地面积增加。两个分析时段主要的土地利用/覆盖类型变化趋势类似,包括农业用地向林地和草地的转化,林地向农业用地的转化以及草地向裸地的转化。2）农业用地和城镇用地主要分布于低海拔区而林地、草地则主要分布于高海拔区。低海拔区主要是退耕还林和城市化过程。高海拔区主要是林地的退化消失和草地退化沙化过程。3）农业用地在坡度段10~25°所占面积比例最大。林地用地面积比例随坡度变陡呈现规则递增,城镇用地分布趋势与之相反。近年裸地趋向分布于缓坡区。坡度0~5°的区域主要是草地退化沙化过程;5~10°坡度段主要是退耕还林过程;大于10°的区域造林工程与森林退化并存。4）各种土地利用/覆盖类型对不同坡向的适宜性相差不大。各种坡向上土地利用/覆盖类型变化类似.     

Monitoring microbial biomass and respiration in different soils from the Czech Republic--a summary of results

The microbial biomass (Cbio), respiration (basal respiration (BR) and potential respiration (PR)), and derived indices for 520 independent soil samples of 117 different soils from the Czech Republic were statistically analysed. The broad range of soil samples allowed the stepwise breakdown of the database into six reasonable categories of soil: arable soils, loamy grassland soils, sandy grassland soils with weak organic matter content, sandy grassland soils with moderate organic matter content, forest soils with moderate organic matter content, and forest organic soils with rich organic matter content. Because soil microbiology lacks benchmarking values, the ranges of the microbial characteristics for these categories were stated and are presented here. The separation into soil groups narrowed the ranges enough to be useful for comparative purposes. The groups displayed significant differences in basal microbial parameters. The lowest microbial biomass was found in arable soils and grassland sandy soils with weak organic matter content. The highest microbial biomass was shown by loamy grassland soils and organic forest soils. Respiration displayed similar results to the microbial biomass. The derived indices revealed less significant differences confirming their inner-standard nature. The relationships between the soil contamination and microbial parameters were not explored because of the confounding effect of soil organic matter. However, it was not shown by the category of grassland sandy soils with weak organic matter content suggesting they could be especially suitable for the biomonitoring of harmful effects of chemicals on soil microorganisms.     

National and regional determinants of tropical deforestation in Colombia

Global tropical deforestation continues to occur at high rates despite political attention. National-level forest baselines are being established all over the world to guide the implementation of several policy mechanisms. However, identifying the direct and indirect drivers of deforestation and understanding the complexity of their interlinkages are often difficult. We first analyzed deforestation between 1990 and 2005 at the national level and found an annual deforestation rate of 0.62 %. Next, we performed separate analyses for four natural regions in Colombia and found annual deforestation rates between 0.42 and 1.92 %. Using general linear models, we identified several direct causes and underlying factors influencing deforestation at the national level: rural population density, cattle, protected areas, and slope. Significant differences in deforestation rates and causes were found across regions. In the Caribbean region, drivers of loss are urban population, unsatisfied basic needs, slope, and precipitation and four land use variables (illicit crops, pastures, cattle, and fires). In the Orinoco region, crops are the main driver of forest loss, and in the Amazonian region, deforestation is primarily due to fires related to the colonization front. Policy mechanisms will have to take into account regional patterns to successfully balance development and forest preservation in Colombia.     

A method for determining the analytical form of a radionuclide depth distribution using multiple gamma spectrometry measurements

When characterizing environmental radioactivity, whether in the soil or within concrete building structures undergoing remediation or decommissioning, it is highly desirable to know the radionuclide depth distribution. This is typically modeled using continuous analytical expressions, whose forms are believed to best represent the true source distributions. In situ gamma ray spectroscopic measurements are combined with these models to fully describe the source. Currently, the choice of analytical expressions is based upon prior experimental core sampling results at similar locations, any known site history, or radionuclide transport models. This paper presents a method, employing multiple in situ measurements at a single site, for determining the analytical form that best represents the true depth distribution present. The measurements can be made using a variety of geometries, each of which has a different sensitivity variation with source spatial distribution. Using non-linear least squares numerical optimization methods, the results can be fit to a collection of analytical models and the parameters of each model determined. The analytical expression that results in the fit with the lowest residual is selected as the most accurate representation. A cursory examination is made of the effects of measurement errors on the method.     

Test of existing mathematical models for atmospheric resuspension of radionuclides

Atmospheric resuspension of radionuclides can be a secondary source of contamination after a release has stopped, as well as a source of contamination for people and areas not exposed to the original release. A test scenario based on measurements collected after the Chernobyl accident was used to evaluate existing mathematical models for contaminant resuspension from soil, to examine resuspension processes on both local and regional scales, and to investigate the importance of seasonal variations of these processes. Model predictions from 15 participants were compared with measured air concentrations and resuspension factors to investigate and explain the discrepancies both among model predictions and between model predictions and observations and thus to evaluate the predictive capabilities and drawbacks of commonly used generic resuspension models. The empirical models tested can give predictions within an order of magnitude of observations or better if adequately calibrated for site-specific conditions, but they do not describe the process-level events or account for spatial heterogeneity or temporal variations.     

A model of vegetation pattern at the Verkhneussuriysky Biogeocenotic Station

A model of relationships between forest communities and basic parameters of environmental conditions, which is suitable for making prognostic maps of forest types, has been developed and tested on the territory of Verkhneussuriysky Biogeocenotic Station of the Institute of Biology and Soil Science. A comparative analysis of the spatial distribution of forest communities has been performed according to this model and to the large-scale map of recent forest vegetation on the territory of the station.     

The Spatiotemporal Pattern of Fires in Northern Taiga Larch Forests of Central Siberia

The periodicity of fires in larch forests of Evenkia and their relationship with landscape elements have been studied. Cross-sections with “burns” in them caused by past fires have been analyzed in 72 test plots; the fire chronology encompassed the period from the 15th to the 20th century. The between-fire intervals (BFIs) have been calculated by two methods: (I) on the basis of burns alone and (II) on the basis of burns and the start of growth of the new generation of larch after the earliest fire. The BFI depends on local orographic features; it is 86 ± 11 (105 ± 12), 61 ± 8 (73 ± 8), 139 ± 17 (138 ± 18), and 68 ± 14 (70 ± 13) years for northeastern slopes, southwestern slopes, bogs, and flatlands, respectively. The mean BFIs calculated by methods I and II are 82 ± 7 and 95 ± 7 years, respectively. The permafrost horizon rises at a mean rate of 0.3 cm per year after a forest fire. It has been shown that the number of fires regularly peaks at periods of 36 and 82 years. There is also a temporal trend in fire frequency: the mean BFI was approximately 100 years in the 19th century and 65 years in the 20th century.     

Artificial radionuclides in the atmosphere over Lithuania

Measurements of airborne radioactive aerosol concentration were carried out on the basis of 1-3 days samples after the Chernobyl disaster and during the period of 1992-2003. Transport of "hot" particles of different composition resulted in the high activity concentrations of (137)Cs, (238)Pu, (239,240)Pu and (241)Am in the atmosphere in Vilnius at the end of April 1986. The (240)Pu/(239)Pu atom ratio showed clear evidence of non-global plutonium originating from the Chernobyl accident in the atmosphere over Lithuania. The (240)Pu/(239)Pu atom ratio ranged from 0.14 to 0.40 in monthly samples in Vilnius in 1995-2003. An increase in activity concentration of (137)Cs by a factor of 100 (up to 300 microBq/m(3)) was found following forest fires in the Ukraine and Belarus. However, no transport of the Chernobyl plutonium was observed and the (240)Pu/(239)Pu atom ratio in samples collected during the forest fires was found to be 0.229 and 0.185, respectively. The exponential decrease in the (240)Pu/(239)Pu atom ratio from 0.30 to 0.19 (mean values) was observed in 1995-2003.     

Increasing extremes of heat and drought associated with recent severe wildfires in southern Greece

Mountains of the northern Mediterranean basin face two major threats under global change. Aridity and available fuel are both expected to increase because of climatic and land-use changes, increasing fire danger. There may already be signs of such effects in the case of the Pinus nigra and Abies cephalonica forests on Mt. Taygetos (southern Greece). We reconstructed climate (mid- to late-fire-season drought) using tree-rings for the last 150 years and compared it with the mountain’s fire history reconstructed from P. nigra fire scars. Seven, out of the ten, large fires Mt. Taygetos experienced were associated with below-normal precipitation (P) or above-normal maximum temperature (T _max). The largest fires occurred in late summer of 1879, 1944, 1998, and 2007. However, only the recent fires (1998 and 2007) had both low P and high T _max, also confirmed from long-term meteorological data. The synergy between climate and fuel availability may explain the very high intensity of 1998 and 2007 fires that burned mostly as stand-replacing crown fires. The other two large fire events (1879 and 1944) most likely occurred under reduced availability in burning fuel and were related to above-normal T _max. Our findings are among the first based on long-term and site-specific empirical data to support the prediction that Mediterranean mountainous areas will face a very large threat from wildfires in the twenty-first century, if socioeconomic changes leading to land abandonment and thus burning fuel accumulation are combined with the drought intensification projected for the region under global warming.