太湖沉积物的磁性特征及其环境意义

本文以太湖沉积物为研究对象,试图在磁性测量的基础上,对太湖湖区四个样芯进行分层,建立芯间层位对应联系,并结合孢粉,粒度,地球化学和有机质含量等分析测定,从沉积物样芯的磁参数曲线变化中提取该地区的环境变化信息,研究结果表明,由于该方法具快速简便,经济易行,无破坏等优点,从而可能对样芯作连续测量,以提取分辨率的环境变化信息,在湖泊沉积物的研究中有着独的作用,可作为地球化学,孢粉,微体古生物,粒度等分析     

洪湖沉积物的磁性特征及其环境意义

以洪湖沉积物为研究对象,通过对Hh01-2(B)孔岩芯磁参数的测量发现在岩芯所代表的时间段内洪湖沉积物磁化率呈现了明显的四个主阶段变化;频率磁化率变化与磁化率变化具有较好的相关性,亚铁磁性矿物的变化主导了沉积物磁化率的变化.同时结合年代、孢粉分析以及参考相关历史记载资料,发现磁化率高值段对应湖水动力强、湖面较宽、气候较湿润,而磁化率低值段对应湖水动力弱、湖面较小、气候偏干旱.从而得出了洪湖沉积物磁参数曲线波峰和波谷分别对应洪湖在历史上曾经历了扩张和收缩、气候温湿和冷干的旋回.     

贵州省麦岗水库沉积物磁性特征及其与粒度的关系

对贵州省麦岗水库沉积物环境磁性特征的研究表明,亚铁磁性矿物主导了沉积物矿物磁性特征,但同时也存在反铁磁性矿物等其他矿物,超顺磁颗粒在沉积物中广泛存在.在所选矿物磁性参数中,χlf、χfd、SOFT与粒度不相关;χARM、SIRM、F300与粒度相关,但相关系数不高;χARM/χlf、χARM/SIRM和粒度显著相关,可以作为粒度的代用指标.研究结果显示,磁性参数确实可以作为粒度的代用指标.但对比研究表明,在不同沉积环境,甚至相似沉积环境的沉积物中,矿物磁性参数和粒度的关系可能不同,在特定沉积环境中,利用磁性参数作为粒度的代用指标应该在充分研究的基础上进行,使研究结果更为可靠.     

长江口潮滩沉积物氧化铁与磁性特征的关系

通过对长江口潮滩沉积物以连二亚硫酸钠－柠檬酸纳－重碳酸钠（DCB）、避光草酸铵（AOD）提取方法进行的氧化铁分析以及磁性测量，探讨了氧化铁与磁性参数的关系，提出了不同类型氧化铁含量估算方法，并分析了DCB提取对全样及分粒级样品磁性特征的影响。结果显示，磁化率及饱和等温剩磁与游离氧化铁和无定形铁含量之间存在显著的相关性。对不同类型氧化铁含量的半定量估算显示，长江口潮滩沉积物中以无定形铁占绝对优势，磁铁矿仅占游离氧化铁的12％左右。DCB提取对磁性特征的影响依赖于磁性矿物晶粒大小和含量。DCB试剂不仅能提取小于2μm粒级中的细晶粒氧化铁，还能溶解相当一部分粗晶粒磁铁矿。此外，根据DCB提取前后S－100及硬剩磁的变化，表明粘土中更富集不完整反铁磁性氧化铁。     

贵州红枫湖沉积物磷赋存形态的空间变化特征

选取贵州省红枫湖这一典型的亚深水型人工湖泊作为对象,研究了6个代表性湖区沉积物柱芯磷的赋存形态,结合水体温度和溶解氧现场监测结果,探讨了该类型湖泊沉积物内源磷释放风险.研究结果表明,红枫湖沉积物总磷含量普遍较高,表层沉积物总磷含量均值大于1500 mg/kg,明显高于下部沉积物.NaOH-SRP和rest-P是沉积物磷的主要赋存形态.NH4Cl-P和BD-P含量表层最高,随深度增加明显降低,rest-P含量在垂向上变化不大.人为活动是造成沉积物总磷及赋存形态空间分布差异的主要原因,工业废水和网箱养鱼活动等大大增加了沉积物NaOH-SRP含量.红枫湖深水湖区底部水温多在14.5～23.5℃之间,随季节变化底部水温差异明显,溶解氧含量通常不高于1.5 mg/L,整体处于季节性缺氧或厌氧状态.以NaOH-SRP为主的沉积物磷赋存形态和深水缺氧环境大大增加了红枫湖沉积物内源磷释放的风险,在未来的研究中亟待加强对该类型湖泊沉积物内源磷释放机制、控制因素及治理措施的研究.     

巢湖沉积物磁性特征及其对沉积动力的响应

对巢湖西部柱样以及杭埠河流域土壤的环境磁学研究表明,磁铁矿是决定磁性特征的主要磁性矿物,杭埠河流域是巢湖西部沉积物的主要来源．靠近巢湖西岸的柱样AC1砂含量较高,X、SIRM值较大而xARM／SIRM较低,说明磁铁矿含量较高、颗粒较粗．距岸稍远的柱样AC2砂含量较低,X、SIRM值也较低,其变化与XARM较相似,与粘土含量变化也有一定程度的相似,AC2沉积物X、SIRM值较ACI小,但XARM／SIRM较高,说明磁铁矿含量较低且颗粒较细．杭埠河流域土壤的磁性测量结果表明,砂、砾含量高的粗骨土磁性最强,富含粗颗粒磁铁矿．巢湖柱样沉积物砂的含量随踞岸远近而不同, 反映了沉积环境的水动力不同,由此产生明显的磁性特征差异,实质是对沉积动力的响应．研究表明磁性参数XARM／SIRM 可以间接反映沉积物中粘土含量的高低变化．     

湖泊沉积物的矿物磁性测量及其环境应用

本文结合太湖沉积物的磁性研究，简要地阐述了湖泊沉积物磁性测量的方法与磁信息的环境应用，通过分析太湖沉积样芯的磁参数曲线所内含的环境信息，揭示了磁测方法在古湖沼学研究中的应用前景。     

贵州红枫湖沉积物生物可利用磷分布特征及其与粒径的关系

应用化学提取法分析了红枫湖主要出入湖河口及湖心沉积物生物可利用磷(BAP)的含量,并探讨了BAP空间分布与总磷(TP)和粒度组成之间的关系.研究结果表明,各形态BAP含量顺序为:藻类可利用磷(AAP)NaHCO3可提取磷(Olsen-P)水溶性磷(WSP)易解吸磷(RDP).沉积物柱芯中BAP迅速降低,剖面变化比TP更为明显.各形态BAP与TP显著相关,除RDP与AAP外,其它形态BAP之间也显著相关.Olsen-P是评价红枫湖沉积物磷的生物有效性的最佳指标.红枫湖沉积物颗粒组成以粘土及粉砂为主,湖心沉积物比河口粒度小.表层(0-5cm)沉积物中Olsen-P和AAP的含量与细组分(粘土)的比例呈正相关,而RDP、WSP与细组分呈负相关性,表明沉积物细组分对深水湖泊富营养化的重要性.     

中国东部红土的磁性及其环境意义

通过中国东部红土剖面的环境磁学参数（磁化率、频率磁化率、非磁滞剩磁、饱和等温剩磁等）测量,获得了红土剖面磁性矿物浓度、粒度和类型等特性随深度的变化曲线以及红土经连二亚硫酸钠一柠檬酸钠一重碳酸钠溶液（ＤＣＢ）处理后的磁性参数变化．根据红土剖面环境磁学参数及其磁参数比值的变化可将红土分为３个层段,各层段的磁性矿物特征存在明显的差异．证实了红土剖面中的磁性载体主要是磁赤铁矿、赤铁矿和针铁矿,并分离出了球粒状磁颗粒．认为红土磁性矿物的数量、粒度、类型等的变异指示了其形成时的环境特征,其频率磁化率和ＤＣＢ处理的磁化率损失量指示了红土成壤化作用的强弱,可作为在红壤区研究过去全球变化的一种新途径．     

中国东部红土的磁性及其环境意义

通过中国东部红土剖面的环境磁学参数（磁化率、频率磁化率、非磁滞剩磁、饱和等温剩磁等）测量,获得了红土剖面磁性矿物浓度、粒度和类型等特性随深度的变化曲线以及红土经连二亚硫酸钠一柠檬酸钠一重碳酸钠溶液（ＤＣＢ）处理后的磁性参数变化．根据红土剖面环境磁学参数及其磁参数比值的变化可将红土分为３个层段,各层段的磁性矿物特征存在明显的差异．证实了红土剖面中的磁性载体主要是磁赤铁矿、赤铁矿和针铁矿,并分离出了球粒状磁颗粒．认为红土磁性矿物的数量、粒度、类型等的变异指示了其形成时的环境特征,其频率磁化率和ＤＣＢ处理的磁化率损失量指示了红土成壤化作用的强弱,可作为在红壤区研究过去全球变化的一种新途径．     

The extent of soil erosion in upland England and Wales

Following recommendations by the 19th Royal Commission on Environmental Pollution, the area, causes and rates of upland soil erosion in England and Wales were investigated between 1997 and 1999. This paper describes the methods and results of the field survey of 1999 in which the extent of eroded ground was determined. 2. The area of degraded soil and the volume of eroded material were both determined from the dimensions of individual erosion features at 399 field sites located on an orthogonal grid across the uplands. Using measurements of individual erosion features, degraded soil extent in upland England and Wales was estimated at almost 25 000 ha, 2·46 per cent of the total upland area surveyed. Half this eroded area was revegetated and no longer subject to continued accelerated soil loss in 1999. The total volume of eroded material was estimated at 0·284 km³. Although deposition of eroded material occurred within 20 per cent of eroded field sites, the total volume of redeposited material was less than 1 per cent of the total volume of eroded soil. 3. Erosion was more extensive on peat soils than on dry, wet mineral or wet peaty mineral soils. In addition, the higher incidence of erosion at high altitudes and on low slopes reinforced the relationship between erosion and areas of peat formation. Copyright © 2002 John Wiley & Sons, Ltd.     

贵州红枫湖近10年来(2009—2018年)水质变化及影响因素

为更好地研究贵州红枫湖的水质变化情况,本文利用贵阳市两湖一库环境保护监测站2009 2018年对红枫湖7个代表性监测点的营养盐、叶绿素a(Chl.a)浓度和水温、气温、透明度、降雨量等水文气象条件逐月监测数据,分析红枫湖10年间水体营养盐和Chl.a浓度以及部分水文气象条件的变化趋势.运用综合营养状态指数(TLI)对红枫湖营养状态进行评价,采用Pearson相关系数法统计分析10年内Chl.a浓度与总磷(TP)、总氮(TN)等水化学组成及水位、气温等水文气象条件的相关性.结果表明,2009—2018年红枫湖水体逐月TN浓度有较大波动(0.56～2.80 mg/L),春、夏季高于秋、冬季;水体逐月TP浓度为0.016～0.103 mg/L,夏季略高于冬季;逐月氨氮(NH3-N)浓度为0.007～0.71 mg/L,春季>冬季>秋季>夏季;水体逐月Chl.a浓度呈季节性波动(0.8～38.9 mg/m3),夏季>春季>秋季>冬季,年内先上升后下降.TP、NH3-N、Chl.a浓度整体呈下降趋势,10年间水质有很大改善.经计算红枫湖在这10年间处于中营养状...     

Rapid decrease of soil erosion rates with soil formation and vegetation development in periglacial areas

High mountainous areas are geomorphologically active environments which are strongly shaped by redistribution of sediments and soils. With the projected climate warming in the twenty-first century and the continued retreat of glaciers, the area of newly exposed, highly erodible sediments and soils will increase. This presents a need to better understand and quantify erosion processes in young mountainous soils, as an increase in erodibility could threaten human infrastructure (i.e. hydroelectric power, tourist installations and settlements). While soil development is increasingly well understood and quantified, a coupling to soil erosion rates is still missing. The aim of this study was, therefore, to assess how soil erosion rates change with surface age. We investigated two moraine chronosequences in the Swiss Alps: one in the siliceous periglacial area of Steingletscher (Sustenpass), with soils ranging from 30 a to 10 ka, and the other in the calcareous periglacial area of Griessgletscher (Klausenpass) with surfaces ranging from age of 110 a to 13.5 ka. We quantified the erosion rates using the ^239+240Pu fallout radionuclides and compared them to physical and chemical soil properties and the vegetation coverage. We found no significant differences between the two parent materials. At both chronosequences, the erosion rates were highest in the young soils (on average 5−10 t ha^-1 a^-1 soil loss). Erosion rates decreased markedly after 3−5 ka of soil development (on average 1−2.5 t ha^-1 a^-1 soil loss) to reach a more or less stable situation after 10−14 ka (on average 0.3–2 t ha^-1 a^-1). Climate change not only causes glacier retreat, but also increased sediment dynamics. Depending on the relief and vegetational development, it takes up to at least 10 ka to reach soil stability. The establishment of a closed vegetation cover with dense root networks seems to be the controlling factor in the reduction of soil erodibility. © 2020 John Wiley & Sons, Ltd.     

贵州红枫湖沉积物磷赋存形态及沉积历史

采集了云贵高原深水湖泊红枫湖现代沉积物未受扰动的柱状样品,通过分析不同形态沉积磷在沉积剖面上的分布特征,并结合沉积物样品柱的210Pb、137Cs年代学研究结果,揭示了红枫湖现代沉积过程中不同形态沉积磷的早期成岩改造的时间变化序列,以及沉积磷外源输入负荷的历史变化.采用Ruttenberg法分析沉积磷的地球化学赋存形态,研究表明,红枫湖沉积物中有机磷和铁结合态磷是沉积磷的主要赋存形态,分别占沉积全磷的60%和28%.沉积磷在垂直剖面上的分布特征显示,红枫湖现代沉积过程中,沉积磷在最终埋藏前可能发生非常剧烈的形态转化和再迁移,尤其是有机磷和铁结合态磷的成岩改造可能是湖泊系统磷循环质量平衡的重要方面.年代学数据同时表明,近年的人为活动导致湖泊系统(包括沉积物)磷负荷的显著增加.     

Rainfall and land management effects on erosion and soil properties in traditional Brazilian tobacco plantations

No-tillage and inter-crops have been progressively introduced into traditional Brazilian tobacco plantations. However, there is a lack of information about their impact on soil erosion rates and soil properties. We studied 10 experimental plots in Paraná (Brazil) that rotated from no-tillage tobacco to two different inter-crop types (black beans and oats) and conventionally tilled tobacco to quantify erosion rates from September 2014 to February 2016. The results show that soil loss (18 Mg ha^?1) and runoff coefficient (8.3%) were higher under conventional tillage tobacco than under no-tillage tobacco (3.4 Mg ha^?1 and 0.6%). Bulk density was higher at the end of the cropping cycle than at the beginning. We concluded that conventional crops increased soil erosion, and the use of inter-crops and no-tillage is highly recommended for soil and water conservation. The findings should be valid for other regions that have similar cropping systems and environmental conditions.     

Monitoring soil erosion on agricultural land: results and implications for the Rother valley,West Sussex,UK

Monitoring has played a key role in understanding the rates, extent and frequency of erosion on agricultural land and this includes projects in Switzerland, Germany and the UK. In this case we focus on highly erodible soils in the Rother valley, West Sussex, southern England on which grow a range of arable crops throughout the year. Erosion rates and extent are high, particularly in response to exceptionally wet periods in the early winter. In the monitored period, rates on summer crops were relatively low due to an absence of intense summer storms. In the years 2015–2020, erosion was localized to where limited areas of bare ground coincided with heavy winter rainfall. Issues of river pollution, associated with excessive sedimentation, off-site flooding and a high degree of connectivity between arable fields and the river, are of increasing concern. Mitigation measures need to be expanded to protect freshwater systems and properties. This study has implications for similar programmes in intensely farmed regions. © 2020 John Wiley & Sons, Ltd.     

Magnetic enhancement in wildfire‐affected soil and its potential for sediment‐source ascription

Intense rainfall following wildfire can cause substantial soil and sediment redistribution. With concern for the increasing magnitude and frequency of wildfire events, research needs to focus on hydrogeomorphological impacts of fire, particularly downstream fluxes of sediment and nutrients. Here, we investigate variation in magnetic enhancement of soil by fire in burnt eucalypt forest slopes to explore its potential as a post‐fire sediment tracer. Low‐frequency magnetic susceptibility values (χ_lf) of <10 µm material sourced from burnt slopes (c. 8·0–10·4 × 10^?6 m³ kg^?1) are an order of magnitude greater than those of <10 µm material derived from long‐unburnt areas (0·8 × 10^?6 m³ kg^?1). Susceptibility of anhysteretic remanent magnetization (χARM) and saturation isothermal remanent magnetization (SIRM) values are similarly enhanced. Signatures are strongly influenced by soil and sediment particle size and storage of previously burnt material in footslope areas. Whilst observations indicate that signatures based on magnetic enhancement show promise for post‐fire sediment tracing, problems arise with the lack of dimensionality in such data. Magnetic grain size indicators χ_fd%, χARM/SIRM and χ_fd/χARM offer further discrimination of source material but cannot be included in numerical unmixing models owing to non‐linear additivity. This leads to complications in quantitatively ascribing downstream sediment to source areas of contrasting burn severity since sources represent numerical multiples of each other, indicating the need to involve additional indicators, such as geochemical evidence, to allow a more robust discrimination. Copyright © 2005 John Wiley & Sons, Ltd.     

The implications of bias correction methods and climate model ensembles on soil erosion projections under climate change

Climate change will most likely cause an increase in extreme precipitation and consequently an increase in soil erosion in many locations worldwide. In most cases, climate model output is used to assess the impact of climate change on soil erosion; however, there is little knowledge of the implications of bias correction methods and climate model ensembles on projected soil erosion rates. Using a soil erosion model, we evaluated the implications of three bias correction methods (delta change, quantile mapping and scaled distribution mapping) and climate model selection on regional soil erosion projections in two contrasting Mediterranean catchments. Depending on the bias correction method, soil erosion is projected to decrease or increase. Scaled distribution mapping best projects the changes in extreme precipitation. While an increase in extreme precipitation does not always result in increased soil loss, it is an important soil erosion indicator. We suggest first establishing the deviation of the bias-corrected climate signal with respect to the raw climate signal, in particular for extreme precipitation. Furthermore, individual climate models may project opposite changes with respect to the ensemble average; hence climate model ensembles are essential in soil erosion impact assessments to account for climate model uncertainty. We conclude that the impact of climate change on soil erosion can only accurately be assessed with a bias correction method that best reproduces the projected climate change signal, in combination with a representative ensemble of climate models. © 2018 John Wiley & Sons, Ltd.     

Laboratory soil piping and internal erosion experiments: evaluation of a soil piping model for low‐compacted soils

Mechanistic models have been proposed for soil piping and internal erosion on well‐compacted levees and dams, but limited research has evaluated these models in less compacted (more erodible) soils typical of hillslopes and streambanks. This study utilized a soil box (50 cm long, 50 cm wide and 20 cm tall) to conduct constant‐head, soil pipe and internal erosion experiments for two soils (clay loam from Dry Creek and sandy loam from Cow Creek streambanks) packed at uniform bulk densities. Initial gravimetric moisture contents prior to packing were 10, 12 and 14% for Dry Creek soil and 8, 12, and 14% for Cow Creek soil. A 1‐cm diameter rod was placed horizontally along the length of the soil bed during packing and carefully removed after packing to create a continuous soil pipe. A constant head was maintained at the inflow end. Flow rates and sediment concentrations were measured from the pipe outlet. Replicate submerged jet erosion tests (JETs) were conducted to derive erodibility parameters for repacked samples at the same moisture contents. Flow rates from the box experiments were used to calibrate the mechanistic model. The influence of the initial moisture content was apparent, with some pipes (8% moisture content) expanding so fast that limited data was collected. The mechanistic model was able to estimate equivalent flow rates to those observed in the experiments, but had difficulty matching observed sediment concentrations when the pipes rapidly expanded. The JETs predicted similar erodibility coefficients compared to the mechanistic model for the more erodible cases but not for the less erodible cases (14% moisture content). Improved models are needed that better define the changing soil pipe cross‐section during supply‐ and transport‐limited internal erosion, especially for piping through lower compacted (more erodible) soils as opposed to more well‐compacted soils resulting from constructing levees and dams. Copyright © 2013 John Wiley & Sons, Ltd.     

Response of soil aggregate disintegration to the different content of organic carbon and its fractions during splash erosion

Aggregate disintegration is a critical process in soil splash erosion. However, the effect of soil organic carbon (SOC) and its fractions on soil aggregates disintegration is still not clear. In this study, five soils with similar clay contents and different contents of SOC have been used. The effects of slaking and mechanical striking on splash erosion were distinguished by using deionized water and 95% ethanol as raindrops. The simulated rainfall experiments were carried out in four heights (0.5, 1.0, 1.5 and 2.0 m). The result indicated that the soil aggregate stability increased with the increases of SOC and light fraction organic carbon (LFOC). The relative slaking and the mechanical striking index increased with the decreases of SOC and LFOC. The reduction of macroaggregates in eroded soil gradually decreased with the increase of SOC and LFOC, especially in alcohol test. The amount of macroaggregates (>0.25 mm) in deionized water tests were significantly less than that in alcohol tests under the same rainfall heights. The contribution of slaking to splash erosion increased with the decrease of heavy fractions organic carbon. The contribution of mechanical striking was dominant when the rainfall kinetic energy increased to a range of threshold between 9 J m⁻² mm⁻¹ and 12 m⁻² mm⁻¹. This study could provide the scientific basis for deeply understanding the mechanism of soil aggregates disintegration and splash erosion.