Natural Forest Fires Research Articles

Effects of aged and fresh biochars on soil acidity under different incubation conditions

Biochar has positive effects as a soil acidity amendment which is a global concern. However, few studies have been reported on the effect of aged biochar on soil acidity. Incubation methods with different ventilation conditions may induce different effects on soil acidity amendment using biochar. This study analyzed the effects of fresh and aged biochars on soil acidity amendment with different incubation methods. Samples of typical acidic soil (plinthudults) and fresh Pinus massoniana bark were collected from the hilly red soil region of southern China and used to create biochar (PB) with the oxygen-limited pyrolysis method at 450°C. A 4-month-aged PB (PBa) which was produced by a natural forest fire was collected from the same area as that of biochar PB. A 69 days incubation experiment was conducted using an improved incubation method. The treatments comprised 100g soil+2g PBa (PBA), 100g soil+2g PB (ventilated incubation, PBV), 100g soil+2g PB (sealed incubation, PBS) and 100g soil only incubated under ventilated (CKV) and sealed (CKS) conditions. Soil pH was measured periodically. Soil exchangeable base cations, exchangeable acidity, exchangeable aluminum (Al3+) and cation exchange capacity (CEC) were measured after incubation. Throughout the incubation period, PB and PBa positively enhanced soil pH (P<0.05), with PB exhibiting more remarkable effects. A similar effect was also observed for soil exchangeable Al3+ and exchangeable acidity. After incubation, soil pH values of PBV (5.05±0.02) and PBS (4.99±0.03) were than the value of PBA (4.98±0.03), with nonsignificant differences (P>0.05) between values in PBV and PBS. PB addition improved soil exchangeable base cations and base saturation compared to PBa addition. Soil CEC levels in PBA, PBV, and PBS were not significantly different from those in CKV and CKS, but CEC in PBV and PBS were significantly higher than the CEC in PBA. All parameters in PBV were not significantly different from the parameters in PBS. Biochar PB can be used to amend soil acidity, but the efficiency declines to a certain extent if biochar PB has undergone a short-term aging before being added to soils. The different ventilation conditions had little influence on soil acidity amendment using biochar.

Physical and psychological determinants of injury in Ontario forest firefighters.

Forest firefighters are faced with multiple physical and psychological challenges as a result of their duties. Little is known about the determinants of injury among these workers. The Ontario Ministry of Natural Resources (OMNR) Aviation, Forest Fire and Emergency Services (AFFES) records detailed information on two mutually exclusive types of workplace injury: First aid (self-reported) and Workplace Safety Insurance Board (WSIB, i.e. received medical attention). To identify the contributions of physical and psychological factors on the likelihood of injury among forest firefighters. Participants were male and female forest firefighters aged between 18 and 65. Data were collected using two self-administered instruments: The NEO Personality Inventory and the Job Stress Survey. Secondary data were collected from the OMNR AFFES and data were analysed by way of multivariate statistical procedures. There were 252 participants. Those who were older, had a history of injury, had high scores for the personality construct of Neuroticism or low scores for the Openness construct were significantly more likely to incur a first aid injury, while those with high experience levels were significantly less likely to incur injury (P < 0.05). High job stress was the only significant predictor of WSIB injury (P < 0.05). First aid and WSIB injuries in the OMNR AFFES were quite distinct phenomena and different factors need consideration in their prediction. It is recommended that managers and decision-makers in this field consider factors such as job stress, personality and the prior occurrence of injuries in their assessment of risk.

Diphosphine-based hypothesis of wetland autoignition is not confirmed

В работе рассматривается «дифосфиновая» гипотеза самовозгорания болот. Ее суть состоит в следующем: в болотах образуется Р 2Н 4 в количествах, достаточных для того, чтобы он, самопроизвольно воспламеняясь на воздухе, инициировал бы воспламенение фосфина, что, в свою очередь, может привести к возгоранию метана. Такое цепное возгорание компонентов болотного газа рассматривается некоторыми исследователями как реальная причина возникновения естественных лесных и торфяных пожаров. Показано, что поскольку данная гипотеза предполагает достаточно маловероятные процессы, она является весьма сомнительной. В частности, с высокой вероятностью можно утверждать, что самовозгорание дифосфина в той концентрации и в той газовой смеси, которые имеют место в болоте или в приземном слое атмосферы, не происходит. Но даже если бы самовозгорание дифосфина произошло, то от этого торфяной пожар, скорее всего, не начался бы, поскольку, во-первых, температура не поднялась бы до тех значений, при которых можно ожидать возгорание фосфина и, во-вторых, окружающая газовая смесь не поддерживает горение. В крайнем случае могла бы произойти лишь вспышка, недостаточная по времени для того, чтобы поджечь мох. Статья представляет собой адаптированный к формату журнала вариант лекции, прочитанной первым автором в МГУ им. М.В. Ломоносова на семинаре «Парниковые газы: актуальные вопросы».

The Zoning of Forest Fire Potential of Gulestan Province Forests Using Granular Computing and MODIS Images

Abstract. There are many vegetation in Iran. This is because of extent of Iran and its width. One of these vegetation is forest vegetation most prevalent in Northern provinces named Guilan, Mazandaran, Gulestan, Ardebil as well as East Azerbaijan. These forests are always threatened by natural forest fires so much so that there have been reports of tens of fires in recent years. Forest fires are one of the major environmental as well as economic, social and security concerns in the world causing much damages. According to climatology, forest fires are one of the important factors in the formation and dispersion of vegetation. Also, regarding the environment, forest fires cause the emission of considerable amounts of greenhouse gases, smoke and dust into the atmosphere which in turn causes the earth temperature to rise up and are unhealthy to humans, animals and vegetation. In agriculture droughts are the usual side effects of these fires. The causes of forest fires could be categorized as either Human or Natural Causes. Naturally, it is impossible to completely contain forest fires; however, areas with high potentials of fire could be designated and analysed to decrease the risk of fires. The zoning of forest fire potential is a multi-criteria problem always accompanied by inherent uncertainty like other multi-criteria problems. So far, various methods and algorithm for zoning hazardous areas via Remote Sensing (RS) and Geospatial Information System (GIS) have been offered. This paper aims at zoning forest fire potential of Gulestan Province of Iran forests utilizing Remote Sensing, Geospatial Information System, meteorological data, MODIS images and granular computing method. Granular computing is part of granular mathematical and one way of solving multi-criteria problems such forest fire potential zoning supervised by one expert or some experts , and it offers rules for classification with the least inconsistencies. On the basis of the experts’ opinion, 6 determinative criterias contributing to forest fires have been designated as follows: vegetation (NDVI), slope, aspect, temperature, humidity and proximity to roadways. By applying these variables on several tentatively selected areas and formation information tables and producing granular decision tree and extraction of rules, the zoning rules (for the areas in question) were extracted. According to them the zoning of the entire area has been conducted. The zoned areas have been classified into 5 categories: high hazard, medium hazard (high), medium hazard (low), low hazard (high), low hazard (low). According to the map, the zoning of most of the areas fall into the low hazard (high) class while the least number of areas have been classified as low hazard (low). Comparing the forest fires in these regions in 2010 with the MODIS data base for forest fires, it is concluded that areas with high hazards of forest fire have been classified with a 64 percent precision. In other word 64 percent of pixels that are in high hazard classification are classified according to MODIS data base. Using this method we obtain a good range of Perception. Manager will reduce forest fire concern using precautionary proceeding on hazardous area.

Predicting fire occurrence patterns with logistic regression in Heilongjiang Province, China

Prediction of forest fire ignition may aid in forest fire vigilance and monitoring, and in prioritizing forest fuel treatments. In this paper, we chose easily obtained spatial variables pertaining to topography, vegetation types, meteorological conditions, climate, and human activity to predict forest fire ignition in Heilongjiang province, China, using logistic regression. Results showed fire ignition prediction through logistic regression had good accuracy. Climatic variables (e.g., average annual mean temperature and precipitation) and meteorological conditions (e.g., daily minimum temperature, daily minimum humidity, daily mean humidity, and mean wind speed) are the main determinants of natural forest fires. In the case of anthropogenic fires, vegetation types and human activity as indicated by distances to roads and settlements combined with suitable meteorological conditions (e.g., daily mean humidity) are the main driving factors. The fire ignition probability map can be easily used to prioritize areas for vigilance, to make decisions on allocating firefighting resources, and to select vulnerable spots for forest fuel treatments. It was found that forest fuel treatments should be focused on the Great Xing’an Mountains.

Long–range transport of soil dust and smoke pollution in the South Asian region

Transboundary transport of air pollution in the South Asian region has been an issue of increasing importance over the past several decades. Long–range transport of anthropogenic pollution is contrasted with that of pollution produced by natural processes such as dust storms or natural forest fires. Airborne particulate matter datasets covering the period from 2002 to 2007 from the neighboring countries like Bangladesh, India, Pakistan and Sri Lanka were used to find the source areas that are primarily responsible for long range transported pollutants. All four countries collected samples with the same type of sampler and follow the same technique for mass and BC measurements. It was found that high fine soil contributions were from dust storms. On the other hand, smoke in this region mainly comes from northern India where agricultural waste is often burned.

Assessment of Fragmentation and Disturbance Patterns in Eastern Ghats: A Case Study in R.V. Nagar Range, Visakhapatnam District, Andhra Pradesh, India

At present the biodiversity in Eastern Ghats is threatened by loss of habitats, exploitation and unscientific management of natural resources, forest fire, biological invasion and other anthropogenic pressures. In this context, we have assessed the forest cover changes, fragmentation and disturbance in the R.V. Nagar Range of Eastern Ghats region, Andhra Pradesh using satellite remote sensing and GIS techniques. Satellite data of IRS-1A LISS II of 1988 and IRS-P6 LISS III of 2006 were assessed for forest cover changes in 1 sq.km grid and generated as Sensitivity Index map. Further the road and settlement buffer of 1000 m was generated to represent Threat Index map. From 1988 to 2006, the forest cover had a total cover loss of 35.2 sq.km and increase in scrub cover by 7.2%. Over all change analysis from 1988 to 2006 with reference to forest cover indicates, negative changes (loss of forest area) accounted for 48.1 sq.km area and positive changes (gain of forest) for an area of 12.1 sq.km of area. The results of the change detection using multi-date satellite imagery suggest degradation in forest cover over two decades, which necessitates the conservation measures in this range with high priority.

Short- and long-term effects of fire on the Collembola communities of a sub-alpine dwarf pine ecosystem in the Austrian Alps

We compared the Collembola communities of three sub-alpine sites in the Limestone Alps to evaluate the short- and long-term effects of natural forest fires. SITE 1 was burned in August 2003, SITE 2 was burned 50 years ago and sampled to assess the long-term effects of fire and the recovery of soil animals. A reference site (REF) was sampled to represent the undisturbed dwarf pine community. All sites are close to each other on a steep slope between 1 400 and 1 650 m above sea level. We found a total of 41 species of Collembola, as well as clear differences in the species composition and abundance between the sites. Most species (29) were found on the REF site. The highest abundance was found on SITE 1 (48 960 individuals*m-2, 22 species). We assume that some species survived the fire in deeper soil layers and others migrated or were passively dispersed from unburned patches and surrounding sites. The lowest abundance and species number (8 160 individuals*m-2, 18 species) were found on the 50-year-old site. This site was covered with a typical community for moving substratum, consisting mainly of alpine grasses, yet the dwarf pine vegetation had not yet recovered. The soil layer was still very thin and we therefore assume that a recovery of the Collembola community will take much longer than 50 years.

On physical and mathematical modeling of the initiation and propagation of peat fires

Works devoted to experimental and theoretical investigations of peat fires under laboratory and natural conditions have been reviewed. Evaluations show that the smoldering of surface combustible materials in peatlands involves half the biomass burnt during natural (forest, steppe, and peat) fires. These fires are of first importance in emission of combustion products into the atmosphere, destruction of the soil structure, and damage to the environment. Many investigations have been carried out on the problem of peat-fire behavior, and they have been published in various journals and materials of conferences.

Thermal Impact Characteristics by Forest Fire on Porcelain Insulators for Transmission Lines

In this study the thermal impact characteristics by forest fire are extensively investigated using temperature controlled ovens. The test conditions for thermal impact damage are simulated according to the characteristics of natural forest fire. The test pieces are suspension porcelain insulators made by KRI in 2005 for transmission lines. In the thermal impact cycle tests with <TEX>$300\;^{\circ}C$</TEX> thermal impact gradient (-70 to <TEX>$230\;^{\circ}C$</TEX>), cycling in 10 minute periods, no critical failures occurred in the test samples even with long cycle times. But in tests with thermal impact gradient from room temperature to <TEX>$200-600\;^{\circ}C$</TEX>, cycling in 10 to 30 minute periods, there were critical failures of the porcelain insulators according to the thermal impact gradient and quenching method. In the case of thermal impact by forest fire, it was found of that duration time is more important than the cycling time, and the initiation temperature of porcelain insulator failures is about <TEX>$300\;^{\circ}C$</TEX>, in the case of water quenching, many cracks and fracture of the porcelain occurred. It was found that the thermal impact failure is closely related to the displacement in the cement by thermal stress as confirmed by simulation. It was estimated that the initiation displacement by the thermal impact of <TEX>$300\;^{\circ}C$</TEX> is about 0.1 %. Above 1% displacement, it is expected that the most porcelain insulators would fail.

Changing climate and endangered high mountain ecosystems in Colombia

High mountain ecosystems are among the most sensitive environments to changes in climatic conditions occurring on global, regional and local scales. The article describes the changing conditions observed over recent years in the high mountain basin of the Claro River, on the west flank of the Colombian Andean Central mountain range. Local ground truth data gathered at 4150m, regional data available at nearby weather stations, and satellite info were used to analyze changes in the mean and the variance, and significant trends in climatic time series. Records included minimum, mean and maximum temperatures, relative humidity, rainfall, sunshine, and cloud characteristics. In high levels, minimum and maximum temperatures during the coldest days increased at a rate of about 0.6°C/decade, whereas maximum temperatures during the warmest days increased at a rate of about 1.3°C/decade. Rates of increase in maximum, mean and minimum diurnal temperature range reached 0.6, 0.7, and 0.5°C/decade. Maximum, mean and minimum relative humidity records showed reductions of about 1.8, 3.9 and 6.6%/decade. The total number of sunny days per month increased in almost 2.1 days. The headwaters exhibited no changes in rainfall totals, but evidenced an increased occurrence of unusually heavy rainfall events. Reductions in the amount of all cloud types over the area reached 1.9%/decade. In low levels changes in mean monthly temperatures and monthly rainfall totals exceeded + 0.2°C and − 4% per decade, respectively. These striking changes might have contributed to the retreat of glacier icecaps and to the disappearance of high altitude water bodies, as well as to the occurrence and rapid spread of natural and man-induced forest fires. Significant reductions in water supply, important disruptions of the integrity of high mountain ecosystems, and dramatic losses of biodiversity are now a steady menu of the severe climatic conditions experienced by these fragile tropical environments.

Natural and anthropogenic forest fires recorded in the Holocene pollen record from a Jinchuan peat bog, northeastern China

Pollen and charcoal particles from a Jinchuan peat (northeastern China) were examined to investigate the fire origin and interaction between climate, vegetation, fire and human activity during the Holocene. Pollen results show that: (i) a broadleaved deciduous forest was dominant during the early Holocene; (ii) from ~ 5500 cal. yr B.P. there was a gradual increase in coniferous trees (mainly Pinus), and a decrease in broadleaved deciduous trees (e.g. Quercus, Juglans, and Ulmus– Zelkova); (iii) after ~ 4200 cal. yr B.P., the deciduous forest was replaced by a mixed forest of coniferous and deciduous trees; (iv) coniferous trees including Pinus, Abies and Picea further increased after ~ 2000 cal. yr B.P., reflecting a cooler and drier climate after ~ 5500–4200 cal. yr B.P. Two layers of abundant microfossil charcoal particles (250–10 μm) and the coexistence of macrofossil particles (> 2 mm) suggest two local fires: fire event 1 (5120 ± 66 cal. yr B.P.) and fire event 2 (1288 ± 8 cal. yr B.P., AD 662 ± 8). Charcoal layer 1, with a large amount of Monolete psilate spores, is superimposed on the long-term trend of vegetation changes, indicating a natural origin for fire event 1 that was probably facilitated by drying environmental conditions since the mid-Holocene. Cerealia-type pollen and a low percentage of Monolete psilate spores were observed in charcoal layer 2, indicating that fire event 2 was caused by clearing. We suggest that fire event 2 may be related to the spread of the Han farming culture accompanied by the territorial expansion of the Tang Dynasty to the studied area in AD 668.

Qualitative Analysis in a Second-Order Impact Model for Forest Fires

Natural forest fires are the problems that influence ecosystems, and they have been researched from of old. For solving this problem, a prediction model for forest fires was proposed. The model imitates fires that are seen in mediterranean forests, boreal forests and savannas. In recent years, it was simplified a second-order impact model. Furthermore, the model of mediterranean forests have been analyzed. However, the others are insufficient yet, and the qualitative property of forest fires has not been discussed enough. In this letter, we analyze the second-order impact model that is seen in boreal forests and savannas. Moreover, we consider what bifurcation phenomena essentially influences some periodic solutions.

Isotope and lignin signatures in tropical peat core (Rawa Danau, Indonesia): An approach to reconstruct past vegetation and climate changes

Peat samples from a 3.60 m core collected from Rawa Danau, West Java, Indonesia, were studied to reconstruct past vegetation and climate changes. The study carried out combining visual observations, elemental analyses, stable carbon and nitrogen isotope analyses as well as CuO oxidation of lignin residues. Variations of total organic carbon (TOC: 55.53-3.18 %, mean 23.31 %), total nitrogen (TN: 2.52-0.06 %, mean 0.94 %) and water content (WC: 46.8-93.2 %, mean 79.0 %) with core lithology reflected dry and wet cycles. Vertical profiles for TOC, TN, WC and core lithology also had signatures of heavy precipitations and consequent land sliding at the abrupt change of climate (wet cycles). Variations of (C/N)a (15-93, mean 27) and δ13C (-27.0 to -30.1 ‰, mean -28.5 ‰) of organic matter (OM) in the peat core indicated that the organic material was comprised of terrestrial C3 plant material. The direct input of aquatic plant matter was small or overwhelmed by high terrestrial input, although changes in lake productivity due to decreasing/increasing nutrient availability were reflected in δ15N profile. At low elevations in the tropical area, a large shift in vegetation zones was not likely observed. Most species might persist at the site when small-scale localized environmental changes and human disturbances or natural forest fires occurred, but the abundances of particular species might change, depending on the natural conditions in which a species could grow. However, vegetation changes associated with periodical sequence of dry and wet microenvironment were inferred from the total lignin phenol (TLP) profile.

Seasonal and Inter-Annual Variations in Methyl Mercury Concentrations in Zooplankton from Boreal Lakes Impacted by Deforestation or Natural Forest Fires

We compared the effects of natural and anthropogenic watershed disturbances on methyl mercury (MeHg) concentration in bulk zooplankton from boreal Shield lakes. MeHg in zooplankton was monitored for three years in nine lakes impacted by deforestation, in nine lakes impacted by wildfire, and in twenty lakes with undisturbed catchments. Lakes were sampled during spring, mid- and late summer. MeHg in zooplankton showed a seasonal trend: concentrations were the lowest in spring, then peaked in mid-summer and decreased in late summer. Over the three study years, MeHg concentrations observed in mid-summer in zooplankton from forest harvested lakes were significantly higher than in reference and fire-impacted lakes, whereas differences between these two groups of lakes were not significant. The pattern of distribution of MeHg in zooplankton during the different seasons paralleled that of dissolved organic carbon (DOC), which is known as a vector of Hg from watershed soils to lake water. Besides DOC, MeHg in zooplankton also showed a positive significant correlation with epilimnetic temperature and sulfate concentrations. An inter-annual decreasing trend in MeHg was observed in zooplankton from reference and fire-impacted lakes. In forest harvested lakes, however, MeHg concentrations remained higher and nearly constant over three years following the impact. Overall these results indicate that the MeHg pulse observed in zooplankton following deforestation by harvesting is relatively long-lived, and may have repercussions to the accumulation of MeHg along the food chain. Therefore, potential effects of deforestation on the Hg contamination of fish should be taken into account in forest management practices.

A decision support system for managing forest fire casualties

Southern Europe is exposed to anthropogenic and natural forest fires. These result in loss of lives, goods and infrastructure, but also deteriorate the natural environment and degrade ecosystems. The early detection and combating of such catastrophes requires the use of a decision support system (DSS) for emergency management. The current literature reports on a series of efforts aimed to deliver DSSs for the management of the forest fires by utilising technologies like remote sensing and geographical information systems (GIS), yet no integrated system exists. This manuscript presents the results of scientific research aiming to the development of a DSS for managing forest fires. The system provides a series of software tools for the assessment of the propagation and combating of forest fires based on Arc/Info, ArcView, Arc Spatial Analyst, Arc Avenue, and Visual C++ technologies. The system integrates GIS technologies under the same data environment and utilises a common user interface to produce an integrated computer system based on semi-automatic satellite image processing (fuel maps), socio-economic risk modelling and probabilistic models that would serve as a useful tool for forest fire prevention, planning and management. Its performance has been demonstrated via real time up-to-date accurate information on the position and evolution of the fire. The system can assist emergency assessment, management and combating of the incident. A site demonstration and validation has been accomplished for the island of Evoia, Greece, an area particularly vulnerable to forest fires due to its ecological characteristics and prevailing wind patterns.

Epiphytic lichens along gradients in topography and stand structure in western Oregon, USA

Epiphytic macrolichen communities were compared among forest stand types in the Blue River watershed of western Oregon. Stand types were defined by stand structure, according to age classes of the younger tree cohort and remnant tree retention. Remnant trees were those in an older cohort that remained following a stand disturbance that initiated tree regeneration, such as a timber harvest or natural forest fire. Stands were located in upland and riparian forests of two vascular plant series (western hemlock and true fir). Presence and abundance of all epiphytic macrolichen species were sampled in a 0.4 ha circular plot in 117 stands. Nonmetric multidimensional scaling (NMS) ordination revealed that the strongest differences in lichen community composition were related to elevation, which was correlated with vascular plant series. Cyanolichens were largely limited to lower elevation forests (470 – 950 m) of the western hemlock series, while matrix lichens and forage lichens with green-algal photobionts dominated high elevation stands (950 – 1470 m) of the true fir series. Lichen communities differed with stand age. In even-aged young stands, lichen communities were species poor and lichen community composition differed from all other stand types. In general, macrolichen species richness varied little among stand types. However, cyanolichen species were most diverse in old-growth and mature stands at lower elevations. Lichen communities in young stands (< 20 yr) with remnants differed from those in even-aged young forests in both plant series. As a stand develops, the presence of remnant trees may accelerate the development of the lichen community towards those found in older stands. We infer that remnant trees serve as refugia for lichens through a disturbance and provide lichen inoculum to younger trees. Hardwood patches were hotspots for lichen diversity, particularly cyanolichens that are infrequent on conifers. Hardwood patches were most prevalent along perennial streams. To maintain and enhance lichen communities at a landscape level, forest managers must consider the importance of features such as late-successional stands, remnant trees, hardwoods, and riparian areas to lichen communities. These features are especially important to retain in or near regenerating forests to promote colonization by dispersal-limited lichens.

Forest fire burn areas in Western Canada modeled as self-similar criticality

Forest fire burn areas in the western Canadian provinces of Alberta and British Columbia have cumulative frequency-area distributions that are well described by a power law or an upper-truncated power law. The power law scaling extends over as many as five orders of magnitude and is observed for different geographical regions and for time intervals ranging from 1 to 40 years. The observed scaling exponent varies both geographically within and between provinces and temporally between annual records. The temporal variability decreases at the decadal scale, suggesting that decadal distributions may be useful for long term fire control planning within a geographical region. For example, for all of Alberta, based on the scaling parameters that describe the 1961–2000 record, we expect approximately 24 fires per year of 100 ha or larger. Unlike the original self-organized criticality (SOC) forest fire model that produces a single scaling exponent, the self-similar criticality (SSC) model replicates the range of scaling exponents observed for cumulative frequency-area distributions of natural forest fires.

Radiative effects of natural aerosols: A review

In recent years, there has been a substantial increase in interest in the influence of anthropogenic aerosols on climate through both direct and indirect effects. Several extensive investigations and coordinated field campaigns have been carried out to assess the impact of anthropogenic aerosols on climate. However, there are far fewer studies on natural aerosols than on anthropogenic aerosols, despite their importance. Natural aerosols are particularly important because they provide a kind of base level to aerosol impact, and there is no effective control on them, unlike their anthropogenic counterparts. Besides, on a global scale the abundance of natural aerosols is several times greater than that of the major anthropogenic aerosols (sulphate, soot and organics). The major natural aerosol components are sea salt, soil dust, natural sulphates, volcanic aerosols, and those generated by natural forest fires. As with anthropogenic aerosols, the abundance of natural aerosols such as soil dust is also increasing, due to processes such as deforestation, which exposes more land areas which may then interact directly with the atmosphere, and due to other human activities. Since a major fraction of the natural aerosol (sea salt and natural sulphate) is of the non-absorbing type (and hygroscopic), it partly offsets the warming due to greenhouse gases as well as that due to absorbing aerosols (e.g., soot). The mineral dust transported over land and ocean causes surface cooling (due to scattering and absorption) simultaneously with lower atmospheric heating (due to absorption); this could in turn intensify a low-level inversion and increase atmospheric stability and reduce convection. To accurately predict the impact of dust aerosols on climate, the spatial and temporal distribution of dust is essential. The regional characteristics of dust source function are poorly understood due to the lack of an adequate database. The reduction of solar radiation at the surface would lead to a reduction in the sensible heat flux and all these will lead to perturbations in the regional and global climate. Enhanced concentration of sea salt aerosols at high wind speed would lead to more condensation nuclei, increase in the cloud droplet concentration and hence cloud albedo. Even though direct radiative impacts due to sea salt and natural sulphate are small compared to those due to anthropogenic counterparts, their indirect effects (and the uncertainties) are much larger. There is a considerable uncertainty in sea salt aerosol radiative forcing due to an inadequate database over oceans. The presence of natural aerosols may influence the radiative impact of anthropogenic aerosols, and it is difficult to separate the natural and anthropogenic aerosol contributions to radiative forcing when they are in a mixed state. Hence it is necessary to document the radiative effects of natural aerosols, especially in the tropics where the natural sources are strong. This is the subject matter of this review.

Alkane and PAH depositional history, sources and fluxes in sediments from the Fraser River Basin and Strait of Georgia, Canada

Hydrocarbon data for dated sediment cores from Fraser Basin lakes and the Strait of Georgia in Canada reveal a pristine pre-industrial background that remains unaltered in modern sediments far from human activities. These pristine sediments contain polycyclic aromatic hydrocarbons (PAHs) from combustion (natural forest and prairie fires), and alkanes and PAHs from weathering of soils containing vascular plant remains and natural petroleum hydrocarbons, and algal production. At other locations examined, however, these natural loadings have been augmented over the past century by hydrocarbons from petroleum, the combustion of liquid (oil, gasoline) and solid (coal, wood) fuels and from processing of wood either directly from disturbed land and slash burning or indirectly through pulp mill effluent. Although contamination is clearest where there are nearby human activities, alkane profiles, PAH distributions and alkane unresolved complex mixtures suggest a widespread contamination from petroleum. Combustion products from human activities can also be identified, although with less source specificity than with the petroleum products. Regional emissions from anthropogenic combustion processes appear to support modern PAH increases within the Fraser River Basin and there is little evidence of inputs from global emissions. Principal components analysis using the new centred log ratio normalisation procedure to normalise data discriminates well between PAHs entering lakes from runoff or the atmosphere and PAH formed diagenetically within lake sediments, as well as between combustion and petroleum PAHs.