Comparing fire-history interpretations based on area, number and estimated volume of macroscopic charcoal in lake sediments

Sedimentary charcoal particles from lakes are commonly used to investigate fire history. Fire-history reconstructions are based on measuring the surface area or counting the number of charcoal fragments in adjacent samples. Recently, the volume of charcoal particles was advised as a more accurate method for quantifying past charcoal production. Large charcoal datasets, used to synthesize global fire history, include these different types of charcoal measurements and implicitly assume that they provide comparable fire-history information. However, no study has demonstrated that this assumption is valid. Here we compare fire-frequency reconstructions based on measurements of charcoal area and number, and estimates of charcoal volume from two lake sediment records from the eastern Canadian boreal forest. Results indicate that the three proxies provide comparable fire-history interpretations when using a locally defined threshold to identify fire events.     

Charcoal signatures defined by multivariate analysis of charcoal records from 10 lakes in northwest Wisconsin (USA)

We show how sedimentary charcoal records from multiple sites within a single landscape can be used to compare fire histories and reveal small scale patterns in fire regimes. Our objective is to develop strategies for classifying and comparing late-Holocene charcoal records in Midwestern oak- and pine-dominated sand plain ecosystems where fire regimes include a mix of surface and crown fires. Using standard techniques for the analysis of charcoal from lake sediments, we compiled 1000- to 4000-yr-long records of charcoal accumulation and charcoal peak frequencies from 10 small lakes across a sand plain in northwestern Wisconsin. We used cluster analysis to identify six types of charcoal signatures that differ in their charcoal influx rates, amount of grass charcoal, and frequency and magnitude of charcoal peaks. The charcoal records demonstrate that while fire histories vary among sites, there are regional patterns in the occurrence of charcoal signature types that are consistent with expected differences in fire regimes based on regional climate and vegetation reconstructions. The fire histories also show periods of regional change in charcoal signatures occurring during times of regional climate changes at ~ 700, 1000, and 3500 cal yr BP.     

活性炭测量系统的最佳条件选择和影响因素

活性灰吸附器测氡法在铀矿勘探中得到了较广泛的应用。作者根据实验室内活性炭吸附器测氡的试验结果,选择了测量系统中装置参数的最佳条件,包括吸附剂类型,干燥剂的性质,吸附系统的灵敏度,吸附器的埋置时间,装置的容积、吸附容量与氧浓度的关系。另外,还研究了活性炭的解吸温度和时间以及温度对活性炭吸附能力的影响。文中详细给出了实验数据。     

Permineralization process promotes preservation of Holocene macrofossil charcoal in soils

The use of macrofossil soil charcoal as a palaeoecological tool to reconstruct past vegetation, climate or fire history has gained much interest in recent years. Yet little is known about taphonomy of charcoal in soils. Here we assessed the putative loss of palaeoecological information due to charcoal fragmentation after burial. We found no significant loss of charcoal mass with time. Instead, we found a significant positive relationship between the mass of charcoal particles and their age. Permineralization of charcoal particles older than ca. 5200 a explained the increased charcoal mass with time in mineral soils. The permineralization process increased the density of charcoal particles (resulting in a twofold particles mass increase) and thus offers a protection against subsequent degradation. Our results suggest high stability of palaeoecological information from charcoal macrofossils buried in mineral soils at least over the Holocene timescale. Copyright © 2011 John Wiley & Sons, Ltd.     

Understanding the origin and analysis of sediment-charcoal records with a simulation model

Interpreting sediment-charcoal records is challenging because there is little information linking charcoal production from fires to charcoal accumulation in lakes. We present a numerical model simulating the major processes involved in this pathway. The model incorporates the size, location, and frequency of fires, primary and secondary charcoal transport, sediment mixing, and sediment sampling. We use the model as a tool to evaluate assumptions of charcoal dispersal and taphonomy and to assess the merits of inferring local and regional fire history by decomposing charcoal records into low-frequency (‘background’) and high-frequency (‘peak’) components. Under specific dispersal scenarios, the model generates records similar in appearance to sediment-charcoal records from Alaskan boreal forests. These scenarios require long-distance dispersal (e.g. 10⁰–10¹ km), consistent with observations from wildfires but longer than previously inferred from experimental dispersal data. More generally, charcoal accumulation in simulated records mainly reflects area burned within the charcoal source area. Variability in charcoal peak heights is primarily explained by the size of charcoal source areas relative to the size of simulated fires, with an increase in this ratio resulting in increased variability in peak heights. Mixing and multi-year sampling add noise to charcoal records, obscuring the relationship between area burned and charcoal accumulation. This noise highlights the need for statistical treatments of charcoal records. Using simulated records we demonstrate that long-term averages of charcoal accumulation (>10×mean fire return interval) correlate well with area burned within the entire charcoal source area. We further demonstrate how decomposing simulated records to isolate the peak component emphasizes fire occurrence at smaller spatial scales (<1 km radius), despite the importance of long-distance charcoal dispersal in simulating charcoal records similar to observations. Together, these results provide theoretical support for the analysis of charcoal records using the decomposition approach.     

Treatment of secondary effluents by infiltration-percolation process using sand fortified with activated charcoal

The main purpose of this study was to investigate the ability of sand/granular activated charcoal mixture medium to treat urban wastewater effluents. Several laboratory experiments were conducted to determine the best combination ratio of sand/activated charcoal which would allow the optimum water purification. A comparative study was undertaken to evaluate the effect of the addition of activated charcoal on infiltration-percolation efficiency. Experiments demonstrated that fortifying sand medium with granular activated charcoal improved the pollutants removal efficiencies. Results showed that a combination ratio of 3:1 (by volume) of sand and granular activated charcoal gave the best depuration efficiency regarding organic matter, nitrogen and orthophosphorous. The mean removal rates of COD, NH₄–N and PO₄–P were 83.29, 95.85 and 65.21%, respectively. Furthermore, experiments demonstrated that a mixture of sand/activated charcoal in a 3:1 ratio resulted in the optimum oxidation capacity.     

Palaeobotanical evidence of wildfires in the Late Palaeozoic of South America – Early Permian, Rio Bonito Formation, Paraná Basin, Rio Grande do Sul, Brazil

Fossil charcoal, as direct evidence of palaeowildfires, has repeatedly been reported from several plant-bearing deposits from the Late Palaeozoic of the Northern Hemisphere. In contrast charcoal reports from the Late Palaeozoic deposits of the Southern Hemisphere are relatively rare in comparison to the Northern Hemisphere. Although the presence of pyrogenic coal macerals has repeatedly been reported from Late Palaeozoic coals from South America, no detailed anatomical investigations of such material have been published so far. Here is presented an anatomical analysis of charcoal originating from Early Permian sediments of the Quitéria Outcrop, Rio Bonito Formation, Paraná Basin, located in the central-eastern portion of Rio Grande do Sul, Brazil. This charcoal comes from two different coaly facies, and it was possible to scrutinize between three types, based on anatomical characters of the charcoal. Two of these charcoal types can be correlated to gymnosperm woods, and the other type corresponds to strongly permineralized bark with characteristic features of lycopsids. The presence of charcoal in different facies, ranging from parautochtonous to allochtonous origin, indicates that different vegetation types, i.e. plants which grew under wet conditions in the lowland as well as in the more dry hinterland, have experienced wildfires. Taking into account previous petrographic and lithological analyses from the facies in which the charcoal occurs and from the conditions of the wood and bark fragments, it was possible to speculate that the intensity of such wildfires most probably corresponds to forest-crown fires. Moreover, it is possible to state that wildfires have been a more or less common element in distinct Late Palaeozoic terrestrial ecosystems in the South American part of Gondwana. The data support previous assumptions on the occurrence of wildfires in the Early Permian of the Paraná Basin which were based solely on coal-petrographic data.     

甘肃东海金矿床地质特征及开发利用

东海金矿床位于甘肃北山重要的Au,Ag多金属成矿带上,为一含伴生Ag的多金属金矿床.具长期活动特征的花牛山-察客尔呼都格压扭性断裂横贯成矿带,成矿的有利位置为大断裂及次一级断层、层间裂隙,断裂控矿十分明显.主要矿石类型为破碎蚀变岩型(据氧化程度不同,又分为氧化矿和原生矿)、石英脉型.目前黄金生产只对氧化矿采用堆浸法提金,贵液吸附工艺由原来的活性炭吸附法,改用锌粉置换沉淀法后,使贵液中的Au和Ag得到了充分的回收利用,对原生矿的开发利用则需要进一步的研究.     

Soil charcoal stability over the Holocene across boreal northeastern North America

The analysis of macroscopic wood charcoal fragments extracted from soils is frequently used as a palaeoecological tool for reconstructing stand-scale forest composition and fire history. Here we explored the putative loss of palaeoecological information due to charcoal degradation through time and in different biogeographical settings. We compared the relationship between charcoal mass and abundance for soil samples from five biogeographical regions of boreal northeastern North America spanning most of the Holocene period. We verified whether charcoal (Ø ≥ 2 mm) conservation differed as a consequence of different taphonomical processes between organic and mineral soil types. We also assessed the mass/abundance relationship as a function of charcoal residence time in soil. Overall, the slope of the regression between charcoal particles mass (g) and abundance (number of particles) was 0.0042. The slope was not significantly different in samples from organic and mineral soil, and all biogeographical regions had similar slope values except one (higher charcoal fragmentation, probably due to high colluvial activity). Charcoal conservation also did not vary according to residence time in soil. This study shows that macroscopic soil charcoal particles resist fragmentation over millennia in different biogeographical settings and under the influence of various taphonomical processes.     

晚冰期月亮湖炭屑记录反映的古气候演化

位于大兴安岭中段的月亮湖地处季风/非季风影响过渡地带,其沉积岩心下部886～546 cm的炭屑记录揭示了末次冰期晚期到全新世早期(20.9～10.8 cal.ka B.P.)的古气候演化历史,反映了东亚季风对研究区气候的影响。研究区炭屑浓度的变化主要由可供燃烧的生物量决定,生长在气候温暖时期的森林草原能够提供更多可供燃烧的生物量。在同一植被类型的条件下,气候寒冷湿润时炭屑浓度低,气候温暖干旱时炭屑浓度高。20.9～18.0 cal.ka B.P.炭屑浓度较低, 气候寒冷偏干,18.0～15.3 cal.ka B.P.炭屑浓度最低,气候寒冷湿润,15.3～14.4 cal.ka B.P.炭屑浓度增高,气候开始向温暖的方向发展,14.4～11.8 cal.ka B.P.炭屑浓度快速变化,气候也经历了一系列的快速变化,11.8～10.8 cal.ka B.P.炭屑浓度总体较高,气候温暖湿润。<50 μm的炭屑浓度指示了区域火演化的历史, >50 μm的炭屑则反映了当地野火发生的状况。     

Microscopic charcoal in sediments: Quaternary fire history of the grassland and savanna regions in South Africa

The microscopic charcoal content of several Quaternary pollen sequences is used to investigate fire history in South Africa both during the Holocene and the Late Pleistocene. Although fluctuations in charcoal composition are recorded, it is difficult to link them directly to either human‐made or natural fires. Strong long‐term variations in microscopic charcoal of Middle and Upper Pleistocene layers are independent of pollen indications of past temperature and moisture conditions. Holocene charcoal sequences from different areas show no correlation, so no phases of regional burning are found. Some fluctuations in charcoal probably are the result of local burning in the various regions. The arrival of Iron Age people some 2000 yr ago apparently did not coincide with widespread wild fires, as these events do not consistently appear in regional microscopic charcoal records. The only exception appears to be the Wonderkrater spring deposit. Relatively open savanna environments, which are implied by pollen analysis at some sites during this period and the generally low microscopic charcoal contents, were either caused by climate change or controlled burning by Iron Age people. Copyright © 2002 John Wiley & Sons, Ltd.     

古炭屑与古森林火?

森林火普遍发生在地质历史时期中，它对自然植被系统的演替起着重要作用。不同强度和频率的森林火培育出不同类型的植被：频繁的森林火导致草甸的形成，而热带雨林形成的原因之一是森林火的缺乏。古炭屑作为古森林火的遗迹，具有分布广泛、细胞结构保存完好以及原地埋藏等特点，为研究古森林火发生的强度和频率提供了宝贵的材料。古炭屑的出现与当时的气候因素、植被类型和地理状况有密切关系：干旱、少雨的气候常常伴随高频率森林火的发生，表现出古炭屑的数量增多；易燃物种组成的植被易发生森林火，古炭屑的出现也会增多，而耐火树种会降低森林火的强度，古炭屑则出现少。因此，从古炭屑的数量和种类的变化，可探讨古森林火的发生规律，进而推断长期地质历史时期的气候、植被、地理状况的演变。     

Tracking recorded fires using charcoal morphology from the sedimentary sequence of Prosser Lake, British Columbia (Canada)

Quantitative analyses of variations in morphological features of charcoal were undertaken in a ²¹⁰Pb-dated sediment core from Prosser Lake (British Columbia, Canada). Seven morphological types of charcoal were defined by particle shape, major-minor axis ratio, apparent porosity and progradation to unburned material. The distribution of morphotypes and total charcoal abundances were assessed as a proxy for fire events recorded between 1919 and 2000 and to subsequent mechanisms of transportation-sedimentation to lake sediments. Charcoal morphotypes showed distinct relationships to recorded area burned by fires. Fragile charcoal fragments with highly irregular porosity (termed Type M) displayed the strongest correlation to burned area (r² = 0.51; P = 0.0001) and did not produce any false-positive signal for fires recorded within a radius of 20 km around the lake. We infer that high porosity and low density Type M fragments are aerially transported and directly deposited on the lake, and that the fragility of Type M charcoal prevents significant quantities from being secondarily transported and incorporated into the sedimentary record. We propose that charcoal morphology is an important but underutilized technique that can yield important insights into fire type, proximity and transportation-sedimentation processes.     

Charcoal records from thermokarst deposits in central Yakutia, eastern Siberia: Implications for forest fire history and thermokarst development

Macroscopic charcoal records from a thermokarst lake deposit in central Yakutia, eastern Siberia, were used to reconstruct the history of forest fires and investigate its relationship to thermokarst initiation. High accumulation rates of charcoal and pollen were coincident in the basal deposits of the thermokarst lake, which suggests that both were initially deposited on the forest floor and subsequently reworked and accumulated in the thermokarst depression. High charcoal and pollen accumulation rates in the basal deposits, dating to 11,000-9000 cal yr BP, also indicate that the thermokarst topography developed during the early Holocene. A lower charcoal accumulation rate after ca. 9000 cal yr BP suggests that thermokarst development has been inhibited since this time. It also indicates that a surface-fire regime has been predominant at least since ca. 9000 cal yr BP in central Yakutia.     

土壤氡析出率活性炭累积吸附法

为解决大面积多点快速土壤氡析出率测量问题, 设计开发并进行了土壤氡析出率活性炭累积吸附法的方法技术研究.在参考氡析出率装置和野外实验数据的基础上, 进行了测量装置及材料的选择、装置刻度、野外累积暴露时间、活性炭盒吸附氡有效衰变常数等研究.通过2002-2003年22次重复观测, 北京西北郊区粘土类土壤氡析出率平均值为20.15mBq.m-2.s-1, 最大值和最小值分别为26.75和13.49mBq.m-2.s-1, 标准偏差为3.55mBq.m-2.s-1.与仪器静电收集法比对结果表明, 两种方法的相对误差小于±10%.实验结果表明: 活性炭方法测量结果稳定可靠, 简便易行, 适用于全国大面积土壤氡析出率调查.      

阴离子交换树脂-活性炭动态吸附无火焰原子吸收法测定矿石中的微量金铂钯

采用717阴离子交换树脂-活性炭分离富集矿石中的微量Au、Pt、Pd。40μg待测元素富集结果表明,Au、Pt、Pd的回收率分别为100%、95.3%和96.3%。以HC l为介质在无火焰原子吸收仪上测定。方法经对国家一级标准物质GBW 07291、GBW 07292分析检验,结果与标准值相符。对GBW 07291国家一级标准物质测定7次,其精密度(RSD)分别为:Au 9.4%、Pt 11.2%、Pd 3.0%。方法适用于矿石中10-6~10-9量级Au、Pt、Pd的测定。     

The impact of decentralised forest management on charcoal production practices in Eastern Senegal

In accordance with Senegal’s decentralisation policy, important forest management tasks, including the right to allocate charcoal production rights, have been transferred to rural councils. This paper investigates the impact of these institutional reforms on charcoal production practices using the environmental entitlement framework developed by Leach et al. [Environmental entitlements: dynamics and institutions in community-based natural resource management. World Development 27 (2) (1999) 225]. The councils have not been able to turn their new endowments into entitlements because they lack sufficient strength and legitimacy. Informal institutions, notably the coalition between merchants, state agents and village chiefs, continue to run the charcoal business and are hardly affected by decentralisation efforts. Most rural people, especially those relying solely on agriculture for sustenance, do not benefit at all from the charcoal trade. They do suffer from the environmental costs it brings with it, however. Although tensions between pro-exploitation actors and pro-conservation actors are evident, the pro-exploitation actors’ firm grip on the informal institutions will probably lead to a prolonged subversion of the laws that seek to enhance local control and to sustain the forest.     

块金成因新见及其分级

本文描述了块金的形成新机制。在热液中呈金氢化物、金羰基化合物及纳料金粒子、纳米金合金粒子活化迁移。在表生条件下,金硫代硫酸盐配合物、金粒子、金合金粒子是金迁移的主要形式。块金是地质的、化学的、物理的、生物化学的综合作用的结果。按块金成因分为内生块金和次生块金。按单块块金质量分为４级。     

吸附丝法吸附量的影响因素

探讨了影响吸附丝法吸附量的一些因素,认为活性炭的黑度、湿度对吸附量产生重要的影响,水分是影响吸附量的主要因素。因此,选用一定黑度的活性炭作为吸附剂,同时测试样品必须干燥才能取得较好的效果。     

Variability in oxidative degradation of charcoal: Influence of production conditions and environmental exposure

Charcoal is a key component of the Black Carbon (BC) continuum, where BC is characterized as a recalcitrant, fire-derived, polyaromatic material. Charcoal is an important source of palaeoenvironmental data, and of great interest as a potential carbon sink, due to its high apparent environmental stability. However, at least some forms of charcoal are clearly susceptible to environmental alteration and degradation over relatively short timescales. Although these processes have importance for the role of charcoal in global biogeochemistry, they remain poorly understood.Here we present results of an investigation into the susceptibility of a range of charcoal samples to oxidative degradation in acidified potassium dichromate. The study examines both freshly-produced charcoal, and charcoal exposed to environmental conditions for up to 50,000 years. We compare the proportion of carbon present in different forms between the samples, specifically with respect to the relative chemical resistance of these forms. This was undertaken in order to improve understanding of the post-depositional diagenetic changes affecting charcoal within environmental deposits.A wide range in chemical compositions are apparent both within and between the sample groups. In freshly-produced charcoal, material produced at 300 °C contains carbon with more labile forms than charcoal produced at ?400 °C, signifying a key chemical change over the 300-400 °C temperature range. Charcoal exposed to environmental depositional conditions is frequently composed of a highly carboxylated aromatic structure and contains a range of carbon fractions of varying oxidative resistance. These findings suggest that a significant number of the environmental charcoals have undergone post-depositional diagenetic alteration. Further, the data highlight the potential for the use of controlled progressive oxidative degradation as a method to characterize chemical differences between individual charcoal samples.