周原全新世土壤剖面木炭屑与野火活动的关系研究

研究陕西周原全新世黄土剖面磁化率曲线、总有机碳曲线、木炭屑曲线和野火活动及其与生态环境演变的关系结果表明,马兰黄土堆积时期气候干旱,在当时半荒漠草原上当地时常有自然野火发生;全新世大暖时期(85 0 0～310 0aB .P)气候湿润,生物成壤作用强度大,呈现森林或森林草原自然景观,野火活动极少发生;先周人迁居到周原地区(310 0aB .P)开始,人类用火及其放火烧荒开垦农田等活动,加之气候变得干旱,生物化学成壤作用减弱,致使生态环境发生重大变化,自然生态景观向半自然、半人工景观演替;15 0 0aB .P开始可耕种土地几乎开垦殆尽,生态景观完全被人工农田生态景观所代替;而近几百年来随着人口密度和聚落的增加,人类生活用火和垃圾随之加大,人类对土壤环境的干扰进一步增强     

山东中部全新世环境演变与人类文化发展

全新世环境演变及其气候事件对古文化发展的影响是目前环境考古研究的热点。根据山东中部龙山镇山城村全新世黄土-古土壤及埋藏文化层的关系,利用色度、磁化率、粒度、碳酸钙含量等气候替代指标,揭示了全新世气候演变,早期(11500 a B.P.～8500 a B.P.)变暖,中期暖湿(8500 a B.P.～3100 a B.P.)和后期(3100 a B.P.以来)逐渐转凉,其中大暖期记录了3次气候寒冷事件。通过分析全新世气候阶段性、气候事件与古文化时空的耦合关系发现:在全新世最为暖湿的阶段(8500 aB.P.～4000 a B.P.),依次发展了后李文化、北辛文化、大汶口文化和龙山文化。其中,8200 a B.P.、5500 a B.P.气候事件没有对文化发展产生明显负面影响,反而对文化发展起了一定催化剂的作用。4000 a B.P.气候事件在剖面中表现明显,来自北部、东北部的大量风沙使淄博、潍坊等地龙山人的生存环境急剧恶化,进而使喜暖湿的稻作农业受到极大摧毁,人地资源矛盾突出,导致优秀的龙山文化被古朴的岳石文化所取代。     

豫中黄土地区全新世土壤剖面成壤环境变化研究

通过对河南新郑黄土-土壤剖面的野外考察及室内的磁化率、烧失量、碳酸钙及粒度分析研究,认为:豫西山地山前丘陵台地的完整黄土-土壤剖面,是在气候波动变化的条件下形成的。全新世气候的变化,导致了以风尘堆积为主的成黄土期与以风化成壤作用为主的成壤期互相更迭。在全新世早期,风尘堆积旺盛,形成了过渡性黄土层(Lt),在8500aB.P.～3100aB.P.的全新世大暖期,发育了浊红棕色古土壤(S0)。这一时期降水丰沛,土壤水分充足,导致了古土壤层(S0)及其以下的过渡层(Lt)、马兰黄土层(L1)顶部都受到了明显的淋溶作用影响,而完全脱钙。3100a B.P.之后,气候恶化,沙尘暴活动显著增强,加之黄河下游人类活动影响不断加剧,黄泛平原风沙活动十分强烈,风尘堆积形成了沙质黄土(L0)。1500aB.P.以来,近代黄土持续堆积,由于气候的转暖与人类农业耕作影响在持续堆积的近代黄土L0表层形成了现代土壤(TS)。     

史前关中盆地土壤剖面的黑碳与炭屑记录

参照OSL测年和考古与历史学断代,利用黄土—土壤剖面沉积物中炭屑和黑碳(焦炭和烟炱)记录,结合磁化率、有机碳等古环境指标,揭示过去12000年火灾历史演变过程。炭屑和黑碳浓度研究结果表明:全新世早期区域野火活动频繁发生,中期火灾很少,晚期本地火灾频率呈现增长态势。黑碳(烟炱和焦炭)和炭屑分析呈现不平行变化趋势,可能是生物质燃烧的物质排放方式和传输过程的区域差异引起。距今3500~2800年间,黑碳和炭屑颗粒浓度峰值与全新世短尺度恶化气候事件具有明显同步性;同期,先周人部落大规模土地开垦发展旱作农业活动加剧。黄土高原千年尺度火灾变化与季风气候变化之间的关系表明:全新世以来,野火频率变化取决于区域气候有效湿度和人类土地利用及其对气候变化的响应。     

斋堂盆地的河谷地貌结构及近万年以来的水土流失概况

根据斋堂盆地的河谷地貌结构,估算出10000aB.P.～8500aB.P.的河流年平均侵蚀量为158.0×10³t/a,8500aB.P.～4000aB.P.的河流年平均堆积量为3.31×10³t/a,4000aB.P.以来的河流年平均侵蚀量为96.3×10³t/a。经比较得出,该区近万年以来的水土流失,受自然条件影响大。但随着人类活动作用的加强,人为因素逐渐成为水土流失的主导因素,现今的土地受人为破坏严重。     

渭河流域全新世古洪水滞流沉积物地球化学特征

对渭河流域野外实地详细调查,在渭河中游发现了具有典型古洪水滞流沉积物(SWD)的全新世黄土-古土壤沉积剖面。根据地层学对比和OSL测年,确定渭河流域在3200-2800aB.P.发生了特大古洪水事件。对沉积物地球化学特征分析表明,SWD为典型的古洪水滞流沉积物,各化学元素和氧化物的变异系数大,元素数据分布较为分散;Fe2O3、Al2O3、Ba、Cr、Cu、V、Rb含量高于S0和L0,SiO2、Zr含量低于S0和L0;化学元素粒度效应表明,SWD粒径小、粘粒强,是在滞流环境的水动力条件下沉积而成;通过气候指标Rb/Sr和Ba/Sr分析,认为古洪水滞流沉积物(SWD)记录的3200-2800aB.P.的特大古洪水事件,是在全新世大暖期结束之际,因夏季风减弱、气候系统不稳定、降水变率较大所导致的。     

洞庭湖的形成、演变与洪涝灾害

洞庭湖是由构造运动奠定基本格局,又叠加了江河作用以及人类活动的多因素的混成湖.以全新世开始为界,洞庭湖演变分为两个阶段:自然演变阶段;人类活动—自然复合作用演变阶段.洞庭湖区的洪涝灾害的时空分布是有一定规律的,荆江北岸大堤堵口是导致洞庭湖洪涝灾害频繁的根源,人类围垦是洪灾加剧的重要因素.     

周原全新世复合古土壤和成壤环境的微形态学研究

通过对陕西周原黄土剖面的微形态研究 ,结合微量元素、粒度及磁化率分析 ,探讨了黄土风化成壤的特征 ;揭示出该剖面的全新世古土壤S0 是温暖湿润的环境下形成的具有强烈粘化特征的复合土壤 ,是 60 0 0～ 5 0 0 0aB .P .出现的区域性干旱气候事件造成风尘加速堆积的结果。关中盆地在 85 0 0～60 0 0aB .P .风化成壤最为强烈 ,气候最为暖湿。在 5 0 0 0～ 3 1 0 0aB .P .又出现了一个比较强烈的成壤时期。而最近 3 1 0 0年以来是一个风尘堆积较强的相对干旱期。     

西安地区全新世气候变化与土壤侵蚀研究

为了揭示西安地区全新世环境变化和黄土地层的侵蚀期,利用野外调查和化学分析等方法,研究了西安地区全新世黄土与古土壤发育时的气候变化和不同气候阶段的土壤侵蚀。通过野外调查,在西安白鹿塬区发现了在黄土塬区很少见到全新世中期古土壤分为3个层次,整个全新世黄土剖面可分为5层,表明黄土塬区全新世气候变化与沙尘暴活动与河谷地区一样可分为5个阶段。土层氧化物、微量元素、CaCO3含量和磁化率测定结果显示,西安白鹿塬区全新世8 500~6 000年和5 000~3 100年古土壤发育时较10 000~8 500年、6 000~5 000年和3 100年以来的黄土发育时夏季风活动强,降水量多,气候湿润,沙尘暴活动弱。中全新世8 500~6 000年间发育的S02古土壤中Fe2O3和Al2O3有一定富集,该层土壤类型相当于黄棕壤,指示当时年平均降水量较现今多150 mm左右。虽然沙尘暴活动很弱的间冰期是黄土地层理论上的侵蚀期,但是实际上这一时期的土壤侵蚀很弱。全新世黄土的侵蚀主要发生在气候冷干时期,不是发生在温湿时期。全新世中期6 000~5 000年间的黄土侵蚀率一般大于堆积率,使得广大地区全新世中期的薄层黄土在绝大多数地区受到侵蚀而消失。全新世中期薄层黄土发育时气候变冷干引起的植被退化是当时土壤侵蚀加强和出现侵蚀期的原因。     

仰韶村遗址黏土矿物组成特征及古气候演变

在仰韶村遗址内分别选取受到古人类活动干扰的土壤剖面(简称文化剖面)和未受到古人类活动干扰的土壤剖面(简称自然剖面),通过两剖面的黏土矿物类型以及测年数据,还原该遗址全新世以来的气候变化,并对古人类活动内容进行了推测。根据自然剖面的黏土矿物类型判断,该遗址10～6.9 ka B. P.增温增湿至稳定,6.9～5.6 ka B. P.气候出现波动,总体向干旱转折,5.6～4 ka B. P.气候变为干冷,4 ka B. P.之后气候进一步变干冷。通过比较,受古人类活动干扰,黏土矿物类型变得简单,并在某一文化时期出现高岭石,推测古人类用黏粒含量高的土壤进行地面铺设,便于塑性和硬化以作为居住地面。     

Carbon sequestration,vegetation dynamics and soil development in the Boreal Transition ecoregion of Saskatchewan during the Holocene

Boreal forest soils have the potential to sequester large amounts of carbon by accumulating charcoal from fire. Some suggest that sequestration rates could be large enough to account for some of the missing sink in the global CO₂ budget, but further data on soil charcoal pools are necessary to adequately develop boreal carbon budgets under a changing climate and fire regime. The primary objective of this study was to determine the amount of charred wood in surface mineral soil horizons (Ah) of the Boreal Transition of Saskatchewan, a fire-prone grassland forest ecotone region of western Canada. A second objective was to use the charcoal data to infer vegetation dynamics and the development of these Ah horizons as a function of parent material type, i.e. glacio-fluvial, glacio-lacustrine and glacial till. The latter objective served to provide information in regards to future vegetation shifts and ecosystem C budgets of Boreal Plain ecosystems under climatic warming. The carbon fraction measured as charcoal is an important component of organic matter in Ah horizons of Chernozemic soils in Saskatchewan and differs from the classical model of humus fractions in Chernozems which suggests that it is a system created from microbial degradation of root litter only. The carbon sequestered as charcoal within the whole ecoregion was estimated at 36.1 Tg, which is the lower limit of the global annual rate of charcoal accumulation in terrestrial environments estimated from experimental fires. Charcoal pools were consistently lower in the fluvial soils relative to the lacustrine and till soils. We suggest a model where dry conditions and low water availability prevailing under the coarser fluvial soils during the Holocene favoured the dominance of low productivity herbaceous vegetation that led to a high ash to charcoal production ratio from fire and to the development of relatively thick Ah horizons through below ground additions of organic matter from root decay. We propose that the more available water in lacustrine and till soils favoured the growth of trembling aspen which, through less frequent/intense fires relative to grasslands and incomplete burning of the woody material, led to high charcoal accumulation rates in soil. The development of thick Ah horizons in lacustrine soils likely occurred during a warm and dry period of the early Holocene (i.e. the hypsithermal) when herbaceous vegetation invaded forested land or during dry spells in the mid to late Holocene (e.g. the Medieval Warm Period) when opening of forest canopies occurred, thus augmenting light transmission to the forest floor and favouring the growth of herbaceous vegetation in the understory. Such events did not create deep Ah horizons in the tills soils as a consistent rock impediment near the surface limited the penetration of understory roots at greater depth. These results suggest that fluvial sites my be the first shifting to herbaceous vegetation in the future due to climatic warming, followed by till sites and then lacustrine sites.     

基于MODIS数据的内蒙古野火时空变化特征

野火是陆地生态系统的重要干扰因子,影响生态系统的演替和更新。研究基于MCD45A1火烧迹地和MCD12Q1土地利用数据,提取2002—2014年内蒙古不同生态分区、土地利用类型的过火面积及火点分布,分析该区域野火的时空分布格局,同时结合降水数据,探讨野火年际变化对降水的响应特性。结果表明:1)2002—2014年内蒙古野火火点空间分布格局表现为由东北向西南逐渐减少,高密度火点主要分布在中蒙边境区域、森林-草原区以及平原典型农耕区。2)内蒙古野火过火面积2003年最大,2006年次之,2010年最小,分析表明过火面积的年际变动与火灾高发月降水异常有关。过火面积的季节变化表现为春秋多,冬夏少,尤其是3月、4月、5月和9月灾情严重。在7大生态分区中,90%的过火面积集中在兴安岭山地丘陵区、呼伦贝尔高平原丘陵区和锡林郭勒高平原区,过火面积占比分别为52%、28%和10%。3)野火干扰最严重的土地利用类型为草地,火点主要集中分布于草甸草原和典型草原,其次为农业用地和林地,对其他类型干扰程度最小。充分认识野火时空分布格局有利于深入了解其发生规律,为区域火灾预警监测提供科学依据。     

Have you checked for charcoal? Assessment of soil condition using soil organic carbon

Soil condition is commonly assessed by using soil organic carbon (SOC) as an indicator; however, a large proportion of the world's soils can contain charcoal, a biologically‐inert form of organic carbon. We investigated whether the presence of charcoal in soil could lead to an inaccurate assessment of soil condition when using SOC as an indicator. We sampled topsoil in a south‐east Australian catchment affected by severe fires in 2003. Samples (n = 100) were analysed for two SOC fractions: (i) total SOC (t‐SOC, loss on ignition), which included charcoal, and (ii) biologically‐active SOC (a‐SOC, persulphate‐oxidation), which did not contain charcoal. Using novel (boosted regression trees) and traditional (linear regression) modelling methods we compared the relative importance of abiotic (slope, aspect, elevation and soil texture) and biotic (land use and vegetation structure) factors as predictors of t‐SOC and a‐SOC concentration. A major difference between the two response variables was less relative importance of land use as a predictor when using t‐SOC as a response variable. Therefore, ignoring the presence of charcoal would have led to an under‐estimation of the effect of land‐use conversion on the biologically‐available SOC fraction. The presence of charcoal has important ramifications for routine assessments of soil condition given that (i) SOC is a commonly used indicator and charcoal and biologically‐active SOC differ in their effects on soil properties, (ii) fires historically occur on a large area of land, (iii) charcoal is a long‐lasting consequence of fires and (iv) charcoal can account for a large proportion of SOC and yet be unnoticed during sample preparation.     

Soil microbial response following wildfires in thermic oak-pine forests

The ecosystem response to wildfire is often linked to fire severity, with potentially large consequences for belowground biogeochemistry and microbial processes. While the impacts of wildfire on belowground processes are generally well documented, it remains unclear how fire affects the fine-scale composition of microbial communities. Here, we investigate the composition of soil bacterial and fungal communities in burned and unburned forests in an attempt to better understand how these diverse communities respond to wildfire. We explored the belowground responses to three wildfires in Linville Gorge, NC, USA. Wildfires generally increased soil carbon content while simultaneously reducing soil respiration. We employed amplicon sequencing to describe soil microbial communities and found that fires decreased both bacterial and fungal diversity. In addition, wildfires resulted in significant shifts in both bacterial and fungal community composition. Bacterial phylum-level distributions in response to fire were mixed without clear patterns, with members of Acidobacteria being representative of both burned and unburned sites. Fungal communities showed consistent increases in Ascomycota dominance and concurrent decreases in Basidiomycota and Zygomycota dominance in response to burning. Indicator species analysis confirmed shift to Ascomycota in burned sites. These shifts in microbial communities may reflect differences in the quality and quantity of soil organic matter following wildfires.     

Wildfire effects on the properties and microbial community structure of organic horizon soils in the New Jersey Pinelands

The frequency and intensity of wildfires are expected to increase in the coming years due to the changing climate, particularly in areas of high net primary production. Wildfires represent severe perturbations to terrestrial ecosystems and may have lasting effects. The objective of this study was to characterize the impacts of wildfire on an ecologically and economically important ecosystem by linking soil properties to shifts in microbial community structure in organic horizon soils. The study was conducted after a severe wildfire burned over 7000 ha of the New Jersey Pinelands, a low nutrient system with a historical incidence of fires. Soil properties in burned and non-burned soils were measured periodically up to two years after the fire occurred, in conjunction with molecular analysis of the soil bacterial, fungal and archaeal communities to determine the extent and duration of the ecosystem responses. The results of our study indicate that the wildfire resulted in significant changes in the soil physical and chemical characteristics in the organic horizon, including declines in soil organic matter, moisture content and total Kjeldahl nitrogen. These changes persisted for up to 25 months post-fire and were linked to shifts in the composition of soil bacterial, fungal and archaeal communities in the organic horizon. Of particular interest is the fact that the bacterial, fungal and archaeal communities in the severely burned soils all changed most dramatically during the first year after fire, changed more slowly during the second year after the fire, and were still distinct from communities in the non-burned soils 25 months post-fire. This slow recovery in soil physical, chemical and biological properties could have long term consequences for the soil ecosystem. These results highlight the importance of relating the response of the soil microbial communities to changing soil properties after a naturally occurring wildfire.     

The impact of fire on redistribution of soil organic matter on a mediterranean hillslope under maquia vegetation type

Soil organic matter (SOM) changes affect the CO₂ atmospheric levels and is a key factor on soil fertility and soil erodibility. Fire affects ecosystems and the soil properties due to heating and post‐fire soil erosion and degradation processes. In order to understand fire effects on soil organic carbon (SOC) balance research was undertaken on a fire‐prone ecosystem: the Mediterranean maquia . The spatial distribution of SOC was measured in a Burnt site 6 months after a wildfire and in a Control site. Samples were collected at two different depths (0–3 and 3–10 cm) and SOC was determined. The results show that 41·8 per cent of the SOC stock was lost. This is due to the removal of the burnt material by surface wash. No significant differences in SOC content were found for the subsurface samples between burnt and control plots. Those results show that ashes and charcoal are transported by runoff downslope and are subsequently deposited in the valley bottom and this is the key process that contributes the burial of SOC after a forest fire. SOC redistribution by water erosion is accelerated after forest fires and contribute to the degradation of soils located at the upper part of the hillslopes but causes the enrichment with SOM of the soils located at the valley bottom. Buried SOC in the bottoms valley terraces will contribute to the sequestration of carbon for longer. Conservation of abandoned terraces is a key policy to avoid land degradation and climate change. Copyright © 2010 John Wiley & Sons Ltd.     

A susceptibility model for post wildfire soil erosion in a temperate oceanic mountain area of Spain

In the North-West of the Cantabrian Range (North of Spain) the climate is oceanic and vegetation cover is continuous. In those areas where livestock farming prevails, wildfires are common, although small in size, their recurrence makes the phenomenon critical for the conservation of soils.In this study we propose that the structural stability of soil, associated with the type and size of the structural aggregates, may be a useful indicator to assess erosion susceptibility in burnt soils. We have chosen an area of approximately 485 km² over quartzitic lithologies where a high recurrence of wildfires has been noted and which displays several forms of erosion: gullying, rilling and erosion by overland flow. We have measured texture, percentage and degree of structural aggregate stability and the rate of infiltration in soils that have been burnt up to 3 times over the last 20 years and also in unburnt soils. The results obtained enable us to establish connections between wildfires, soil deterioration and macro-aggregate stability.We have used the stability of macro-aggregates as an indicator to elaborate a soil erosion susceptibility model for a large area of 10,600 km² with sharp relief and Atlantic climate. The model was constructed by combining three main factors: soil structural stability, fire intensity and relief. Variables related to soil structural stability and presence of basic cations have been derived from lithology (% Clay and % Silt + Fine Sand). The availability of humified organic material has also been taken into account as an additional variable in the formation of stable macro-aggregates. The expected fire intensity was calculated from the amount of inflammable material and the structure of the different vegetation types. Finally, the influence of relief was analyzed by considering the slope steepness.The resultant cartographic model presents five types of post wildfire soil erosion susceptibility. Those areas with the highest risk correspond to quartzite lithology regions, with long, steep hillsides covered with heaths. Those with the lowest risk correspond to limestone bedrock areas with gentle slopes and herbaceous vegetation. The accuracy of the model is determined by the scale of the original thematic cartography: 1:25000, and the cell size of the Digital Terrain Model is 50 × 50 m.     

黄土高原褐土和黑垆土剖面中Rb和Sr分布与全新世成土环境变化

对黄土高原 3个土壤剖面Rb和Sr分布规律的研究表明 ,全新世不同阶段的黄土和土壤中Rb和Sr分布存在明显的差异 ,Rb/Sr比值的变化反映了成土环境和成土作用强度的变化。全新世早期 ,气候比较温和干燥 ,风尘堆积速率降低 ,土壤发育表现为边沉积边成土 ;全新世中期 ,气候温暖湿润 ,沙尘暴很少发生 ,风尘堆积速率极低 ,生物风化成土作用达到最强 ,以至于在黄土高原面发育黑垆土 ,在关中盆地形成褐土。到了 3 10 0多年前 ,气候恶化变干 ,风尘堆积速率加快 ,土壤严重退化。从区域上看 ,冬季风对黄土高原南部的环境效应比夏季风对北部的环境效应要强 ;黄土高原南部季风场强的变化较北部大。     

离石黄土中的第五层古土壤及其古气候的意义

古土壤作为历史或地质时期自然景观中形成的土壤,不仅是古环境和古气候的一种良好的记录,而且对于研究土壤的发生、发展乃至退化的过程有重要意义。古土壤学成为土壤学、地质学、地理学、生物学和考古学等学科的边缘学科,它的深入研究特别需要上述学科工作者的大力协作和综合的研究。