基于指纹识别技术的小流域泥沙来源研究进展

泥沙来源判别是小流域土壤侵蚀研究的重点,也是难点。复合指纹识别技术因其结果直接、准确度高、作业快等特点,在国内外泥沙来源研究中得到大量应用,并迅速发展。复合指纹识别技术是在划分潜在侵蚀区的基础上,采集侵蚀区土壤样和流域出口泥沙样,室内分析土壤样和泥沙样指纹因子,利用相关统计检验方法筛选最佳指纹因子组合,利用数值转换模型将最佳指纹因子浓度转换为各侵蚀区产沙比例。主要通过阐述指纹识别技术泥沙来源研究步骤,总结现有可靠性检验方法,归纳研究对象等方面,综述基于复合指纹识别技术的泥沙来源研究进展。重点介绍了复合指纹识别技术最佳指纹因子组合筛选和数值转换模型,并指出复合指纹识别技术存在的问题。     

森林火灾对贵州喀斯特山区土壤理化性质的影响

通过比较贵州喀斯特山区森林火烧迹地不同坡位表层土壤和未受火灾区域表层土壤的理化性质可以看出,较大森林火灾、重大森林火灾以及特别重大森林火灾下的土壤含水量、田间持水量、毛管孔隙度以及土壤通气度均降低,土壤容重和非毛管孔隙度增加,而火灾后土壤化学性质的改变因火灾等级的不同而有所不同,总体上火烧迹地土壤有机质和全氮含量均显著低于未受火灾区域,而在重大森林火灾和特别重大森林火灾下,火烧迹地的速效磷含量大幅增加。     

安溪县茶园小流域泥沙来源分析——以双岐溪为例

福建省茶园地处山丘地区加之缺乏水土保持措施,水土流失严重。指纹分析法利用泥沙特有的物理和生物化学性质作为示踪因子,用于区别不同泥沙来源地。本研究在安溪县山地茶园采集不同高程土壤样品及小流域中侵蚀泥沙样品,测定样品的8种土壤理化性质作为指纹识别因子,利用Kruskal-Wall检验筛选适合的指纹识别因子,运用组合指纹法与Isosource多元混合模型分析流域中侵蚀泥沙的来源及各潜在泥沙源地对侵蚀泥沙的贡献率。结果表明:茶园土壤中筛选出4种适用于山地茶园指纹因子:Ca、K、Zn、Mg,其中,K、Ca可作为判别泥沙来源的指纹因子组合。侵蚀泥沙超过70%来源于未治理茶园,且74%来源于未治理茶园山脚。组合指纹法在山地茶园的应用不仅能定量分析福建山地茶园水土流失、侵蚀泥沙的输移规律,进一步丰富了小流域侵蚀理论,也为茶园水土流失治理措施合理布设提供科学基础。     

指纹技术识别泥沙来源:不确定性研究进展

泥沙指纹技术是近年来研究流域泥沙来源与动态变化的一项重要技术方法,其主要局限性在于诸多的前提假设与实践条件的差异带入了一系列不确定性。泥沙从源到汇的迁移过程受自然环境和人为干扰的影响,其源地特征、迁移路径以及泥沙性质的潜在变化等均是指纹技术应用的不确定性因素,而采样方案设计、指纹选择方法、混合模型应用的一些主观因素进一步增加了不确定性的来源。不确定性分析是泥沙指纹技术的重要组成部分,是评估泥沙来源指纹识别结果可靠性的主要依据。本文综述了泥沙指纹技术的诸多不确定性问题以及主要应对方法的研究进展,总结了当前不确定性定量评估的研究现状并提出了未来的研究展望。     

指纹技术识别泥沙来源:进展与展望

泥沙来源信息有助于研究流域土壤侵蚀、泥沙输移与沉积特征,对于制定流域泥沙及非点源污染控制战略具有重要意义。泥沙指纹技术是识别泥沙来源的一个可靠方法被广泛应用于世界各地不同流域,最近20多年在指纹因子选择和混合模型优化等技术方法上以及不同时空尺度和源地分类等应用类型上都得到了快速发展,正在从一种研究工具逐步发展为一种管理工具。综述了国内外指纹技术识别泥沙来源在研究尺度、指纹因子筛选、源地贡献分配、不确定性分析等方面开展的研究,并对泥沙指纹技术研究当前存在的问题及今后研究趋势作了分析展望。     

泥沙来源“指纹”示踪技术研究综述

泥沙来源"指纹"示踪技术是综合研究流域土壤侵蚀和泥沙输移的新方法。泥沙来源"指纹"示踪技术基于流域侵蚀产沙过程划分潜在物源类型,根据物源特性筛选具有诊断能力的"指纹"性质,通过定量转换模型建立流域出口泥沙与内部潜在物源间的"指纹"联系,定量描述各潜在物源对流域出口产沙的相对贡献;结合悬移质或沉积泥沙通量监测,定量分析各潜在物源对流域产沙的绝对贡献量及流域侵蚀产沙时、空变化特征。通过综述泥沙来源"指纹"示踪技术的理论基础及实施框架,流域尺度潜在物源类型,泥沙"指纹"因子类别、分布特点及诊断能力,泥沙来源复合"指纹"示踪技术的研究进展,指出泥沙来源"指纹"示踪技术的局限性,并对泥沙来源"指纹"示踪技术进行展望。     

基于泥沙指纹识别的小流域颗粒态磷来源解析

控制泥沙迁移一直是流域管理的重点,而泥沙携带污染物与养分(磷)对下游水体的影响愈发引起关注。研究泥沙来源的位置、特征及各来源对泥沙输出的贡献,有助于针对重点源区实施水土流失以及水污染治理措施。农业小流域中磷的输出以泥沙吸附的颗粒态磷为主,研究泥沙来源可为探讨颗粒态磷的来源提供重要基础。复合指纹技术是一种可靠的泥沙源解析方法,但在一些地表物质相对均一、输沙量较小、受人为因素影响较多的东部小流域,能否应用指纹识别法解析泥沙来源并探讨颗粒态磷来源还需要验证。该文以南京市九乡河上游小流域为研究区,尝试以指纹识别技术分析流域泥沙来源为基础,进而研究不同来源对颗粒态磷输出的相对贡献。研究结果表明,农田对泥沙输出的贡献为25.3%~65.2%,对颗粒态磷输出的贡献达52.2%~85.8%;矿山及道路施工用地对泥沙输出的贡献为34.8%~74.7%,但是对颗粒态磷输出的贡献仅为14.2%~47.7%;而来源于林地的泥沙与颗粒态磷总体上均不到0.1%。复合指纹技术不但能够有效识别泥沙来源,且以泥沙源解析来研究颗粒态磷来源,能够为基础资料缺乏地区提高颗粒态磷来源识别的合理性以及流域非点源磷污染控制提供一种思路和方法。     

火烧对土壤性质的影响

火烧以后 ,土壤的各种性质会发生较大变化 ,原因是火向土壤中施加了热量、灰烬 ,并且改变了土壤环境和微气候 ,土壤性质也可因植被和生物活性的改变而发生相应的变化。本文对火烧后土壤生态系统中养分的浓度、有效性、迁移性 ,土壤中的生物和酶活性 ,土壤有机碳库等的变化进行了综合评述 ,以期为森林火灾、草地烧荒后的土壤管理等提供理论参考。     

重度火烧迹地巨尾桉营造技术

解决火烧迹地的植被恢复，是火灾后人们面临的一个重要问题。有选择地种植适应性强、生态效益好、经济效益高且具有开发前景的造林树种，是火烧地人工更新、加速森林植被恢复的最佳选择。为了探索森林火灾后迹地的巨尾桉造林技术，使森林生态环境良性发展，针对淘溪小流域的调查资料进行分析论述，重点介绍了造林技术。     

基于文献计量学分析泥沙来源研究进展与热点

明确流域或区域泥沙来源对水土保持措施科学布局有重要意义。为了更好地掌握泥沙来源研究的发展动态,研究借助文献计量方法与可视化工具——CiteSpace软件,对中国知网(CNKI)总库和Web of Science数据库迄今关于泥沙来源的所有文献进行收集分析,探寻当前该领域的研究热点,为未来的发展研究提供参考。对检索获取的6 000余篇中文和英文文献的分析发现,当前泥沙来源研究的主要对象包括淤地坝、小流域、河流与盆地。研究热点主题主要包括泥沙输移、泥沙形态和土壤侵蚀; 热点研究内容注重对环境效应、影响因素等进行综合研究; 热点研究手段是复合指纹识别技术。关键词突现图和时区图展现的前沿研究趋势显示,在重点研究区要重建流域泥沙来源历史的演变规律; 指纹识别法作为热点研究手段则亟需科学的试验设计来验证该方法的准确性; 将来的研究则侧重于形成类似“复合指纹系统工具”的工具,服务于流域管理、侵蚀泥沙产生的环境风险预测等方面。     

Comparison of sampling designs for sediment source fingerprinting in an agricultural watershed in Atlantic Canada

Purpose

Sediment fingerprinting is increasingly being used to improve the understanding of sediment dynamics within the critical zone and provide information that can help guide management decisions at the watershed scale. The objectives of this study were to investigate both the implications of different sediment fingerprinting sampling designs and spatial scales on the characterization of sediment dynamics in a predominantly agricultural watershed in northwestern New Brunswick, Canada.

Materials and methods

Color and radionuclide fingerprints were used to discriminate between three potential sediment sources: agricultural topsoil, agricultural streambanks, and forested areas (topsoil and streambanks). Suspended sediment was collected seasonally, between 2008 and 2014, at five sites with drainage areas ranging from 3.0 to 13.4 km². Using the same source and sediment data set, multiple-, nested-, and local-location fingerprinting sampling designs were employed to investigate the influence of scale of observation, geomorphic connectivity, land use, and the heterogeneity of source fingerprints on apportionment results.

Results and discussion

Sediment collected in the headwaters was primarily derived from forested areas while the sediment collected at the outlet of the watershed was primarily from agricultural topsoil. When comparing the multiple- and nested-location designs, it was found that accounting for the spatial variability in the fingerprint properties of each source had a small difference in the sediment apportionment results. Furthermore, the local-location design demonstrated that the sediment collected at each location was composed of predominately local sources as opposed to upstream sediment entering the local catchment.

Conclusions

Assessment of the sources of sediment at a range of spatial scales better accounts for both geomorphic connectivity and differences in land use throughout the watershed. Overall, each of the three fingerprinting sampling designs provided different information that can be used to guide soil and water conservation management.

     

Investigating the role of connectivity and scale in assessing the sources of sediment in an agricultural watershed in the Canadian prairies using sediment source fingerprinting

Purpose

Sediments adversely impact the quality of surface waters and are a significant source of contaminants, such as nutrients and pesticides, in agricultural watersheds. The development of effective beneficial management practices (BMPs) to minimize these impacts requires a sound understanding of the sources of sediments. The objectives of this study were: (1) to determine the sources of sediment in an agricultural watershed in the Canadian prairies using sediment source fingerprinting and; (2) to assess the results of the sediment fingerprinting study within the context of the scale of observation and the hydro-geomorphic connectivity of the watershed.

Materials and methods

Geochemical and radionuclide fingerprints were used to discriminate between the three potential sediment sources identified: topsoil, streambanks, and shale bedrock. Suspended and bed sediment samples were collected over the course of 3 years at six locations along the main stem of the creek, ranging from 3rd- (48 ha) to 7th-order (7441 ha) drainage basins. Four sediment fingerprint properties were selected that met statistical- and process-based selection criteria and the Stable Isotope Analysis in R model was used to estimate the proportion of sediment derived from each source at each sampling location in the watershed.

Results and discussion

The suspended sediments in the upper reaches were dominated by topsoil sources (64%–85%), whereas the suspended sediments moving through the lower reaches and being exported from the watershed had a higher proportion of sediment coming from streambank (32%–51%) and shale bedrock (29%–40%) sources. The switch in the sources of sediment between the headwaters and the watershed outlet are due to: (1) changes in sediment storage and connectivity; (2) a transition in the dominant erosion processes from topsoil to streambank erosion; and (3) the incision of the stream through the shale bedrock as it crosses the Manitoba Escarpment.

Conclusions

The results of this sediment fingerprinting study demonstrated that there was a switch in sediment sources between the headwaters and the outlet of the watershed. This research highlights the importance of the sampling location, in relation to the scale and geomorphic connectivity of the watershed, on the interpretation of results derived from the sediment fingerprinting technique, particularly in terms of developing suitable watershed BMPs to protect surface waters.     

西南喀斯特小流域地表、地下河流细粒泥沙来源的137Cs和磁化率双指纹示踪研究

在黔中喀斯特高原农林复合生态系统峰丛谷地小流域,利用¹³⁷Cs和磁化率双指纹因子对碳酸盐岩表层土壤(坡地和坝地)、深层土壤(沟道和洞穴/裂隙)以及碎屑岩夹层岩屑3类来源开展指纹特征分析,通过多元混合模型对流域暴雨过程侵蚀悬移质泥沙进行指纹复合示踪,并计算小流域地表及地下出口输出泥沙的主要来源及相对贡献率。结果表明:¹³⁷Cs和磁化率在碳酸盐岩表层土壤、深层土壤以及碎屑岩夹层岩屑3类来源存在显著差异,流域内表层土壤、深层土壤和碎屑岩夹层岩屑的¹³⁷Cs和磁化率平均含量分别为3.39 Bq/kg和310.07×10^-8 m^3/kg、0.50 Bq/kg和180.69×10^-8 m^3/kg、0 Bq/kg和7.02×10^-8 m^3/kg。表层土壤、深层土壤和碎屑岩夹层岩屑对流域地表出口泥沙的相对贡献分别为16.2%,4.3%和79.5%,拟合优度为99.97%;表层土壤、深层土壤和碎屑岩夹层岩屑对流域地下出口泥沙的相对贡献分别为<0.1%,37.9%和62.1%,拟合优度为83.80%。喀斯特流域泥沙来源区别于其他碎屑岩流域具有的特点为:(1)碳酸盐岩风化表层土壤来源少,对河流泥沙贡献小,主要贡献于地表河流。(2)无论流域地表出口还是地下出口,河流泥沙来源主要为流域中碳酸盐岩所夹的少量(地面物质组成<10%)的碎屑岩夹层岩屑。(3)深层土壤略有贡献,地下河流贡献比例高于地表河流。另外,¹³⁷Cs和磁化率可作为双指纹示踪物较好地示踪喀斯特小流域地表、地下河流泥沙来源和确定相对贡献率。     

复合指纹法分析红壤区强度开发小流域泥沙来源

南方红壤区人口密集,土地资源开发利用强度大,水土流失类型多样。为研究不同土地利用类型下红壤区强度开发小流域侵蚀泥沙来源,选取感德镇红壤强度开发小流域为研究区,分析了流域内潜在泥沙源地和泥沙的41个地球化学特征,利用Kruskal-Wallis H检验及逐步判别分析确认最佳指纹因子组合,并通过多元混合模型计算各泥沙源地泥沙贡献率。结果表明:共有速效P、Cu、P、Y、Ca、Ga、Sn、Nd 8种因子通过检验被确认为最佳指纹因子组合,累计贡献率达90%以上,拟合优度均大于0.80。多元混合模型结果显示,锋面雨季流域泥沙主要来源于林地、茶园与矿区,贡献率分别为28.59%,28.20%,27.59%;在台风雨季,4种土地利用类型泥沙相对贡献率为茶园>林地>矿区>耕地。通过对不同降雨特征下各土地利用类型泥沙贡献百分比数据进一步分析,结果显示矿区单位面积泥沙贡献百分比均值分别是耕地、林地与茶园单位面积泥沙贡献百分比均值的8,10,10倍,即单位面积下矿区土壤侵蚀强度最大。     

Toward generalizable sediment fingerprinting with tracers that are conservative and nonconservative over sediment routing timescales

Purpose

The science of sediment fingerprinting has been evolving rapidly over the past decade and is well poised to improve our understanding, not only of sediment sources, but also the routing of sediment through watersheds. Here, we discuss channel–floodplain processes that may convolute or modify the sediment fingerprinting signature of alluvial bank/floodplain sources and explore the use of nonconservative tracers for differentiating sediment derived from surface soil erosion from that of near-channel fluvial erosion.

Materials and methods

We use a mathematical model to demonstrate the theoretical effects of channel–floodplain exchange on conservative and nonconservative tracers. Then, we present flow, sediment gauging data, and geochemical measurements of long- (meteoric beryllium-10, ¹⁰Be) and short-lived (excess lead-210 and cesium-137, ²¹⁰Pb_ex and ¹³⁷Cs, respectively) radionuclide tracers from two study locations: one above, and the other below, a rapidly incising knick zone within the Maple River watershed, southern Minnesota.

Results and discussion

We demonstrate that measurements of ¹⁰Be, ²¹⁰Pb_ex, and ¹³⁷Cs associated with suspended sediment can be used to distinguish between the three primary sediment sources (agricultural uplands, bluffs, and banks) and estimate channel–floodplain exchange. We observe how the sediment sources systematically vary by location and change over the course of a single storm hydrograph. While sediment dynamics for any given event are not necessarily indicative of longer-term trends, the results are consistent with our geomorphic understanding of the system and longer-term observations of sediment dynamics. We advocate for future sediment fingerprinting studies to develop a geomorphic rationale to explain the distribution of the fingerprinting properties for any given study area, with the intent of developing a more generalizable, process-based fingerprinting approach.

Conclusions

We show that measurements of conservative and nonconservative tracers (e.g., long- and short-lived radionuclides) can provide spatially integrated, yet temporally discrete, insights to constrain sediment sources and channel–floodplain exchange at the river network-scale. Fingerprinting that utilizes nonconservative tracers requires that the nonconservative behavior is predictable and verifiable.     

Drill and crop performances as affected by different drill configurations for no-till seeding

The stable rare earth element (REE) tracer method was evaluated in this study as a new method for studying soil erosion. Erosion and sedimentation amounts for a slope section can be estimated for each rainfall event using multiple tracers. The REE tracer method can be used for quantitative estimates of the distribution of soil erosion from specific areas and for determining sources of sediment in a small watershed.     

Fire and Tillage as Degrading Factors of Soil Structure in Northern Zagros Oak Forest,West Iran

The effects of fire and the conversion to vineyard on soil organic carbon (SOC), and soil aggregate size distribution and stability were studied in a forest of Iran. For this purpose, topsoil was sampled in an unburned area, a portion of the forest burned three years earlier, and a vineyard, all three contiguous and showing similar topographic features. In the burned forest, soil was sampled in areas undergone high, moderate, or low severity. Air‐dried soil samples were sieved to obtain four aggregate size classes, which were subsequently wet sieved. Soil aggregate distribution index, mean weight diameter, geometric mean diameter, and aggregate stability index were determined on both dry and wet specimens. No significant differences in SOC between burned and unburned forest were found, most probably because of the supply of charred biomass to soil, while in the vineyard thirty years of cultivation had removed half of initial SOC. Both severe fire and cultivation had decreased the stability of aggregates and the relative amount of the biggest ones (8 to 2‐cm diameter). However, aggregate stability was significantly lower in the vineyard than in the burned forest, which points out to a stronger impact of prolonged cultivation than a single fire, although severe. Cultivation and severe fire had decreased the proportion of C in macroaggregates, to the advantage of meso (1 to 0.25 mm) and micro (<0.25 mm) aggregates. A hierarchical cluster analysis of all investigated properties and indices demonstrated that cultivation and highly severe fire both were causes of soil degradation. Copyright © 2016 John Wiley & Sons, Ltd.