检索项 检索词
  土壤学报  2024, Vol. 61 Issue (3): 746-756  DOI: 10.11766/trxb202207070375
0

引用本文  

尚月婷, 张加琼, 白茹茹. 不同形态河谷沉积物中稀土元素的粒径分布特征. 土壤学报, 2024, 61(3): 746-756.
SHANG Yueting, ZHANG Jiaqiong, BAI Ruru. Particle Size Distribution Characteristics of the Rare Earth Elements in Sediment from Different Shapes of River Valleys. Acta Pedologica Sinica, 2024, 61(3): 746-756.

基金项目

国家自然科学基金项目(42077068)资助

通讯作者Corresponding author

张加琼, E-mail:jqzhang@nwsuaf.edu.cn

作者简介

尚月婷(1997—),女,硕士研究生,主要从事土壤侵蚀研究。E-mail:YTS@nwafu.edu.cn
不同形态河谷沉积物中稀土元素的粒径分布特征
尚月婷1, 张加琼1,2, 白茹茹1    
1. 西北农林科技大学黄土高原土壤侵蚀与旱地农业国家重点实验室, 陕西杨凌 712100;
2. 中国科学院水利部水土保持研究所, 陕西杨凌 712100
摘要:稀土元素(REE)作为一种重要的土壤侵蚀示踪元素,明确其含量随土壤颗粒粒径的变化特征,对准确量化土壤侵蚀速率具有重要意义。本研究基于Samonova等采样测定的不同粒径范围(< 1、1~10、10~50、50~250和250~1 000 μm)土壤/沉积物颗粒中的REE含量,分析了俄罗斯普罗特瓦河左岸河谷形态(“U”和“V”形谷)、地貌部位(坡面、沟坡/沟壁、沟道底部和洪积扇)、侵蚀(坡面、沟坡/沟壁)和沉积(沟道底部和洪积扇)环境对土壤/沉积物REE含量、富集系数等的影响。结果表明:(1)“U”和“V”形谷四类地貌下,轻稀土(LREE)、重稀土(HREE)和总稀土(ΣREE)含量均随颗粒粒径变粗呈降低趋势。在相同地貌部位,“U”形谷细颗粒中(< 50 μm)中LREE、HREE和ΣREE含量较“V”形谷分别低14.6%~24.7%、10.0%~33.5%和14.2%~21.1%。(2)无论河谷形态和地貌部位,LREE和HREE均明显富集在细颗粒中,尤其是“V”形谷,LREE和HREE主要富集在 < 10 μm的颗粒中。(3)对比侵蚀和沉积区,“U”和“V”形谷沉积区细颗粒中LREE和HREE的富集程度均显著(P < 0.05)大于侵蚀区。可见,无论河谷形态、地貌部位和侵蚀沉积区,REE均主要富集在细颗粒中;但河谷形态和侵蚀、沉积对REE含量的粒径分布有重要影响。
关键词侵蚀区域    沉积区域    地貌部位    轻稀土元素    重稀土元素    富集    
Particle Size Distribution Characteristics of the Rare Earth Elements in Sediment from Different Shapes of River Valleys
SHANG Yueting1, ZHANG Jiaqiong1,2, BAI Ruru1    
1. State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest A&F University, Yangling, Shaanxi 712100, China;
2. Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources, Yangling, Shaanxi 712100, China
Abstract: 【Objective】Rare earth elements(REE) are one of the most important tracers in soil erosion study. Understanding the content variation of REEs alongside particle size ranges is significant to accurately quantify soil erosion rates.【Method】Based on the REE contents in different particle size ranges(< 1, 1-10, 10-50, 50-250 and 250-1000 μm) of soil/sediment samples measured by Samonova et al.(2020), this study analyzed the effects of valley morphology, landforms, erosional and depositional areas on the contents and enrichment coefficient of REE in soil/sediment at the left bank of the Protva River in Russia. Landform types including hillslope, gully slope/wall, valley bottom and alluvial fan, were separately selected from a "U" and a "V" shape valley, respectively. These four landforms were further classified into erosional (i.e., hillslope and gully slope/wall) and depositional areas (i.e., valley bottom and alluvial fan).【Result】The results showed that: (1) The contents of light rare earth elements (LREE), heavy rare earth elements (HREE) and total rare earth elements (ΣREE) were all decreased with the increase of particle size ranges under the four landform types of "U" and "V" shape valleys. Under the condition of the same landform types, the contents of LREE, HREE and ΣREE in fine particles (< 50 μm) of the "U" shaped valley were 14.6%-24.7%, 10.0%-33.5% and 14.2%-21.1% lower than those of the "V" shaped valley, respectively. (2) Both LREE and HREE were enriched in fine particles at all landform types for both "U" and "V" shape valleys. Particularly for the "V" shape valley, LREE and HREE were significantly enriched in < 10 μm particles. (3) Comparing the erosional and depositional areas, the enrichment degree of LREE and HREE in the fine particles of the depositional areas in both "U" and "V" shape valleys was significantly (P < 0.05) higher than that of the erosional area.【Conclusion】Accordingly, REE were enriched in fine particles regardless of river valley shapes, landforms, and erosional or depositional areas. However, both valley shape and erosion-deposition processes had important impacts on the REE content variation in different particle size ranges.
Key words: Erosional area    Depositional area    Landforms    Light rare earth elements    Heavy rare earth elements    Enrichment    

稀土元素(Rare Earth Elements,REE)包括镧系元素与钇元素,可分为轻稀土(Light Rare Earth Elements,LREE,包括:La、Ce、Pr、Nd、Pm、Sm和Eu)和重稀土元素(Heavy Rare Earth Elements,HREE,包括:Y、Gd、Tb、Dy、Ho、Er、Tm、Yb和Lu)[1]。稀土元素具有易与土壤颗粒紧密吸附、难溶于水、不易淋溶、植物吸收利用率低、生态环境友好、测试分析快捷等优势,是较理想的示踪元素之一[2-3],在土壤侵蚀量估算、泥沙来源示踪等方面发挥着重要作用[4-6]

REE示踪法通过模型,将REE在土壤中的背景含量与其在侵蚀沉积物中含量的差异转换为土壤侵蚀速率或泥沙源地贡献[7-9]。由于自然界土壤中REE含量较低,前人常以人工拌施、喷淋等方法按照断面、条带、点穴等方式将REE均匀施放于小区、小流域。土壤侵蚀研究中,多个REE配合使用,可区分不同土地利用类型、地貌类型、侵蚀类型等的侵蚀速率,辨别坡面侵蚀时空演变过程[10-12]。REE作为指纹因子通过复合指纹识别法也可量化泥沙来源,辨析地貌、土壤、土地利用类型等对泥沙来源的影响[13-15]。然而,前人研究发现,REE与大多地球化学元素类似,在不同粒径范围颗粒的含量往往具有明显差异[16-17]。REE易选择性地吸附在较细颗粒内,这对其示踪土壤侵蚀和泥沙来源结果的准确性有重要影响[18-20]。因此,明确REE的粒径分布特征,对提高REE示踪土壤侵蚀和泥沙来源的准确性具有重要意义。

前人对REE在不同土壤颗粒或团聚体粒径中的分布特征相关研究较少,现有研究的一致结果是REE主要吸附在较细颗粒内;但不同的研究发现REE富集的颗粒粒径范围不同。紫色土(湖北省)中REE主要富集在≤75 μm的颗粒中;黄土(新疆)中REE主要吸附在 < 20 μm的颗粒中[8-9];而53~250 μm红壤(湖北省)颗粒中的REE含量明显高于其他粒径范围[21]。此外,在不同的环境条件下,即使土壤类型相同,REE的富集特征也有变化。例如伊犁盆地的昭苏、可克达拉等地区的黄土中REE明显富集在 < 2 μm的颗粒内;而黄土高原的黄土中REE主要富集在 < 63 μm的颗粒中[22-24]。风化、成土母质差异等环境条件可通过影响REE的释放量与过程、有机碳的粒径分布等方式,进而影响REE在不同颗粒中的含量变化[25-27]。可见,土壤类型和环境条件及其演变过程对REE粒径分布有明显的影响。

此外,土壤/沉积物侵蚀过程中的分选作用也对REE的粒径分布有重要影响。由于土壤颗粒在侵蚀、搬运和沉积过程中的分选作用,导致附着在不同粒径范围的地球化学元素(包括REE)、污染物等也会随之发生选择性迁移。在土壤颗粒的侵蚀搬运过程中,分选作用导致侵蚀区土壤和沉积区沉积物相同粒径范围内的REE含量发生明显变化。白茹茹[28]通过逐步稀释法将La、Y和Ce分别释放至红壤(江西德安)、黑土(黑龙江宾县)和风沙土(陕西榆林)中,模拟降雨前后虽各元素均主要富集在 < 63 μm的颗粒中,但模拟降雨后(雨强120 mm·h–1,坡度15°),< 63 μm泥沙中不同REE的富集特征却发生了明显变化。泥沙中La和Y的富集程度较释放对应元素的红壤和黑土均显著(P < 0.05)减小;而Ce的富集程度较风沙土却显著(P < 0.05)增大。这与侵蚀过程中的颗粒分选密切相关,可见,侵蚀沉积过程对REE粒径分布有重要影响。

综上,影响REE粒径分布的因素复杂,土壤类型、环境条件及其演变、侵蚀沉积过程中的颗粒分选等均可能影响REE的粒径分布。在土壤侵蚀和泥沙来源研究中,侵蚀过程中团聚体/颗粒的分选作用对REE的影响尤为突出。因此,明确侵蚀过程中,侵蚀、沉积过程/区域对REE含量粒径变化的影响对揭示其迁移机理,提高REE示踪侵蚀和泥沙来源研究的可靠性尤为重要。据此,本研究基于Samonova等[29]发表于Data in Brief的原始数据(数据未分析),分析处于不同发育阶段的河谷(“V”形谷和“U”形谷)的典型地貌部位中轻稀土和重稀土的粒径分布特征,探讨侵蚀和沉积对REE粒径分布的影响。研究结果有益于加深侵蚀沉积过程对REE粒径分布特征的认识,为REE示踪土壤侵蚀和泥沙来源研究中的颗粒校正提供依据。

1 材料与方法 1.1 数据来源与研究区概况

本研究数据来源于Samonova等[29]发表于Data in Brief的文章,该文章仅发表了不同粒径范围REE含量的测定原数据,未对数据进行任何分析。因此本文不存在数据重复使用分析的问题。研究选取的“V”形谷和“U”形谷是该区域典型的河谷形态,位于斯摩棱斯克-莫斯科高地(Smolensk-Moscow upland)东南部的普罗特瓦河(Protva river)左岸,距莫斯科西南约100 km。该区域是混交林与落叶林的过渡区域。“V”形谷形成于全新世,较形成于更新世的“U”形谷小[30]。“V”形谷在下切过程中穿透不同的母质,因而流域内土壤组成复杂。主要为形成于森林群落下的网状土(Retisols)(世界土壤资源参比基础,WRB);上游主要为晚更新世黄土状壤土(loessial loam),下游主要为泥砾沉积物;洪积扇草本植被茂密,主要为富含腐殖质的疏松岩性土(Regosols);沟道底部几乎裸露,有少量剖面结构难以辨认的疏松岩性土。“U”形谷的成土母质较均一,土壤主要为晚更新世黄土状壤土和中更新世冰川沉积物,沟道底部主要为壤质沉积物,坡面和沟坡/沟壁为疏松岩性土[30]

1.2 样品采集与处理

按地貌部位和侵蚀沉积差异,Samonova等[29]在“V”形谷和“U”形谷流域的上游、中游和下游分别选取代表性横断面,采集坡面(c)、沟坡/沟壁(s)、沟道底部(b)和洪积扇(f)表层(0~10 cm)的土壤样品。在“V”形谷的c、f、b和s区分别采集4、3、3和1个土壤样品;“U”形谷的c、f、b和s区分别采集3、3、4和1个土壤样品(图 1)。

注:“V”形谷和“U”形谷分别用“G”和“B”表示,坡面、沟坡/沟壁、沟道底部和洪积扇分别用“c”,“s”,“b”和“f”表示。  Note: The "V" and "U" shape valleys were represented using "G" and "B", respectively. Hillslope, gully slope/wall, valley bottom and diluvial fan of the "V" and "U" shape valleys were represented using "c", "s", "b" and "f", respectively. 图 1 “V”形谷和“U”形谷地形与采样点分布(该图基于Samonova等文中的图 1修改)[29] Fig. 1 The distribution of topography and sampling sites in the "V" and "U" shape valleys(This figure was revised based on the Figure 1 in the study of Samonova et al.)[29]

所有土样经风干、去除杂质并过筛(1000 μm)后,依据俄罗斯分级标准分为黏粒(< 1 μm)、细粉粒(1~10 μm)、粗粉粒(10~50 μm)、细砂(50~250 μm)、中砂和粗砂(250~1000 μm)[31]。其中细颗粒(黏粒和粉粒)采用沉降法分离,> 50 μm的粗颗粒通过湿筛分离。粒径分级后的110个样品经酸混合物(NSAM-499AES/MS方法)消解后,采用电感耦合等离子体质谱仪(ICP-MS)(Elan-6100)测定La、Ce、Nd、Pr、Eu、Sm、Gd、Tb、Dy、Ho、Er、Tm、Yb和Lu的含量,采用电感耦合等离子体原子发射光谱仪(ICP-AES)(Optima-4300)测定Fe和Mn的含量。

1.3 数据分析

本研究将测定的14个REE分为轻稀土和重稀土两类。其中轻稀土元素包括La、Ce、Nd、Pr、Eu和Sm,重稀土元素包括Gd、Tb、Dy、Ho、Er、Tm、Yb和Lu。根据不同粒径范围中稀土元素的含量,计算REE的富集系数和14种REE的总含量[32]

$ {E_r} = \frac{{{\text{RE}}{{\text{E}}_x} -{\text{RE}}{{\text{E}}_{{\text{bulk}}}}}}{{{\text{RE}}{{\text{E}}_{{\text{bulk}}}}}} $ (1)
$ \Sigma \mathrm{REE}=\Sigma \mathrm{LREE}+\Sigma \mathrm{HREE} $ (2)

式中,Er为REE富集系数,REEx为各粒径(x)土壤颗粒(< 1,1~10,10~50,50~250和250~1 000 μm)中REE的含量(μg·g–1),REEbulk为全样(< 1 000 μm)中REE的含量(μg·g–1)。当Er > 0时,则说明REE发生富集,若Er < 0时,REE则发生贫化;ΣREE为14种REE的总含量(μg·g–1),ΣLREE表示各轻稀土元素的含量之和(μg·g–1),ΣHREE表示各重稀土元素的含量之和(μg·g–1)。

2 结果 2.1 不同河谷形态与地貌下REE含量的粒径分布特征

无论“U”形谷还是“V”形谷,LREE、HREE和ΣREE含量均随土壤/沉积物粒径变粗总体表现逐渐减小的趋势。当土壤/沉积物粒径从 < 1 μm增大至250~1 000 μm,LREE、HREE和ΣREE含量在“U”形谷不同地貌部位分别减小了36.7%~58.4%、52.8%~65.6%和34.1%~54.5%;三者在“V”形谷不同地貌部位下分别减小了75.0%~80.3%、76.0%~81.8%和75.2%~81.5%。在相同地貌下“U”形谷细颗粒中(< 50 μm)中LREE、HREE和ΣREE含量较“V”形谷平均分别低14.6%~24.7%、10.0%~33.5%和14.2%~21.1%,而在粗颗粒中(50~1000 μm)却较“V”形谷平均分别高29.9%~73.8%、15.0%~68.6%和27.7%~101.5%。对比“U”形谷和“V”形谷,“U”形谷土壤/沉积物中LREE、HREE富集较“V”形谷聚集在更细的颗粒中,但“U”形谷细颗粒中REE的富集程度更大。“V”形谷不同地貌部位土壤/沉积物中,< 50 μm颗粒(黏粒和粉粒)中LREE和HREE含量较全样平均分别高48.3%和53.3%。而“U”形谷不同地貌部位土壤/沉积物中,< 10 μm颗粒(黏粒)中LREE和HREE含量较全样平均分别高16.2%和12.7%,而10~50 μm颗粒(粉粒)中LREE和HREE含量较全样平均分别低24.3%和27.2%。此外,在粗颗粒中,“U”形谷和“V”形谷不同地貌部位土壤/沉积物中的LREE和HREE含量均低于全样,但二者随粒径变粗表现出相反的变化趋势。亦表明“V”形谷LREE和HREE含量随粒径变粗逐渐减小,而在“U”形谷三者的含量随粒径变粗在不同的地貌部位呈现不同程度的增大趋势(图 2图 3图 4)。可见,地貌部位和河谷形态对LREE和HREE含量的粒径分布均有重要影响。

注:不同粒径范围和全样中LREE的含量:Pr(10 mg·kg–1)、Sm(10 mg·kg–1)、Eu(100 mg·kg–1)。  Note: Units of LREE in different particle sizes and whole samples: Pr(10 mg·kg–1)、Sm(10 mg·kg–1)、Eu(100 mg·kg–1). 图 2 不同颗粒粒径及全样中LREE含量的变化(对“V”形谷的洪积扇,未筛分出足量 < 1 μm的颗粒供测试。该图依据Samonova等文中表2的数据绘制)[29] Fig. 2 Changes of LREE contents in different particle size ranges and bulk samples(the mass of < 1 μm particles from diluvial fan of "V" valleys was insufficient for testing. This figure was drawn based on data in Table 2 in the study of Samonova et al.)[29]

注:不同粒径范围和全样中HREE的含量:Tb(10 mg·kg–1)、Ho(10 mg·kg–1)、Tm(10 mg·kg–1)、Lu(10 mg·kg–1)。  Note: Units of HREE in different particle sizes and whole samples: Tb(10 mg·kg–1)、Ho(10 mg·kg–1)、Tm(10 mg·kg–1)、Lu(10 mg·kg–1). 图 3 不同颗粒粒径及全样中HREE含量的变化(对“V”形谷的洪积扇,未筛分出足量 < 1 μm的颗粒供测试。该图依据Samonova等文中表2的数据绘制)[29] Fig. 3 Changes of HREE contents in different particle size ranges and bulk samples(the mass of < 1 μm particles from diluvial fan of "V" valleys was insufficient for testing. This figure was drawn based on data in Table 2 in the study of Samonova et al.)[29]

图 4 不同颗粒粒径及全样中ΣREE含量的变化(对“V”形谷的洪积扇,未筛分出足量 < 1 μm的颗粒供测试。ΣREE依据Samonova等文中表2的数据计算)[29] Fig. 4 Changes of ΣREE contents in different particle size ranges and bulk samples(the mass of < 1 μm particles from diluvial fan of "V" valleys was insufficient for testing. ΣREE in this figure was calculated based on data in Table 2 in the study of Samonova et al.)[29]
2.2 侵蚀与沉积区稀土元素的粒径分布特征

根据“U”形谷和“V”形谷不同地貌部位(坡面、沟坡/沟壁、沟道底部和洪积扇)的侵蚀和沉积特性,将四个地貌部位划分为侵蚀区(坡面、沟坡/沟壁)和沉积区(沟道底部和洪积扇)。对比侵蚀与沉积区,LREE和HREE在“U”形谷和“V”形谷侵蚀与沉积区均表现出在细颗粒内富集,在粗颗粒内贫化的特征。具体地,对“U”形谷侵蚀与沉积区,LREE和HREE均在 < 10 μm颗粒内富集,在 > 10 μm颗粒内贫化;对“V”形谷侵蚀与沉积区,LREE和HREE均在 < 50 μm颗粒内富集,在 > 50 μm颗粒内贫化(图 5图 6)。可见,总体上无论是侵蚀或沉积区,“U”形谷土壤/沉积物中LREE和HREE较“V”形谷均富集在更细的土壤颗粒中。

图 5 侵蚀(坡面和沟坡/沟壁)和沉积区(沟道底部和洪积扇)LREE在不同粒径范围的富集特征(LREE的富集系数依据Samonova等文中表2的数据计算)[29] Fig. 5 Enrichment of LREE in different soil particle size ranges in erosional(hillslope and gully slope) and depositional areas(valley bottom and diluvial fan)(The enrichment factor of LREE in this figure was calculated based on data in Table 2 in the study of Samonova et al.)[29]

图 6 侵蚀(坡面和沟坡/沟壁)和沉积区(沟道底部和洪积扇)HREE在不同粒径范围的富集特征(HREE的富集系数依据Samonova等文中表2的数据计算)[29] Fig. 6 Enrichment of HREE in different soil particle size ranges in erosional(hillslope and gully slope) and depositional areas(valley bottom and diluvial fan)(The enrichment factor of HREE in this figure was calculated based on data in Table 2 in the study of Samonova et al.)[29]

相同粒径范围内,“U”形谷和“V”形谷沉积区细颗粒中LREE和HREE的富集程度显著(P < 0.05)高于侵蚀区,而在粗颗粒中LREE和HREE的贫化程度却显著(P < 0.05)低于侵蚀区。具体地,“U”形谷和“V”形谷沉积区细颗粒中LREE和HREE的富集系数分别较侵蚀区高32.6%~147.7%、3.9%~150.2%和80.75%~438.2%、2.5%~290.7%;而在粗颗粒中,LREE和HREE的富集系数在沉积区分别较侵蚀区低12.5%~80.7%、2.0%~17.0%和16.6%~22.1%、15.1%~21.3%。此外,虽然在细颗粒土壤/沉积物中,无论侵蚀还是沉积区,“U”形谷的LREE与HREE富集程度均极显著(P < 0.01)低于“V”形谷。但在粗颗粒中,侵蚀和沉积区LREE和HREE的富集变化特征存在差异。在50~250 μm中,“U”形谷侵蚀和沉积区LREE贫化程度均极显著(P < 0.01)高于“V”形谷,而HREE的贫化程度在侵蚀区显著(P < 0.05)低于“V”形谷,在沉积区与“V”形谷无显著差异。在250~1 000 μm中,HREE和LREE在“U”形谷侵蚀和沉积区的贫化程度均显著(P < 0.05)低于“V”形谷。可见,侵蚀、沉积对土壤/沉积物中的REE分布特征有重要影响,同时也进一步表明了河谷形态对REE粒径分布特征的影响。

3 讨论 3.1 河谷形态对REE粒径分布的影响

“U”形谷和“V”形谷不同地貌部位(坡面、沟坡/沟壁、沟道底部和洪积扇)土壤/沉积物中REE含量存在明显差异,这与处于不同的发育阶段的“U”形谷和“V”形谷河谷形态、土壤/沉积物性质变化均有关。首先,“U”形谷一般处于河谷发育的壮年期,河床宽阔平坦;而“V”形谷处于河谷发育的青年期,河床狭窄且仍在下切和拓宽中,河床纵比降通常较“U”形谷大[33]。因此,在相同流量、流速等侵蚀动力条件下,土壤/沉积物更容易沉积在较平坦的“U”形谷底。这也是“V”形谷底部几乎没有沉积物,而“U”形谷底部覆盖壤质土壤/沉积物的原因[30]。其次,不同形态河谷中,形成于不同时期的土壤/沉积物在土壤类型、颗粒粒径、有机质含量等方面均存在差异,尤其是颗粒粒径[34],对REE含量变化有重要影响。当土壤中细颗粒含量较高时,细颗粒中大量黏土矿物对REE的吸附、黏结等作用导致REE在细颗粒明显富集。“U”形谷和“V”形谷不同地貌部位土壤/沉积物的颗粒粒径差异显示,“U”形谷不同地貌部位土壤/沉积物均以细颗粒为主(85.5%~96.7%),而“V”形谷除坡面细颗粒含量达到81.2%外,其余地貌部位细颗粒含量仅为44.9%~58.8%(图 7)。这正是不同地貌部位“U”形谷土壤/沉积物中LREE、HREE和ΣREE含量较“V”形谷分布在更细的颗粒中的原因。

图 7 “U”形谷和“V”形谷坡面、沟坡/沟壁、沟底和洪积扇的颗粒组成(该图依据Samonova等文中表1数据绘制)[29] Fig. 7 Soil particle fraction in soil/sediment samples collected from hillslope, gully slope/wall, valley bottom and diluvial fan of "U" and "V" valley(This figure was drawn based on data in Table 1 in the study of Samonova et al.)[29]
3.2 侵蚀和沉积对不同粒径范围REE富集与贫化的影响

“U”形谷和“V”形谷侵蚀区(坡面和沟坡)和沉积区(沟道底部和洪积扇)土壤/沉积物中LREE和HREE在细颗粒和粗颗粒中的富集和贫化差异表明侵蚀和沉积对REE的粒径分布有重要的影响。本研究“U”形谷和“V”形谷土壤/沉积物种类多、沉积结构复杂,侵蚀、搬运和沉积中不同来源土壤/沉积物混合、分选等过程复杂,从而导致REE在侵蚀和沉积主导的区域发生粒径分布变化[35]。在侵蚀区,分选作用导致 < 125 μm的颗粒,尤其是 < 50 μm的颗粒优先搬运,从而导致与之黏附的REE也随之优先搬运[36-37]。此外,侵蚀区长期风化、淋溶、生物地球化学等作用导致REE活化、迁移能力增强,改变土壤pH,增加土壤胶体的含量,使土壤吸附较多REE[3638]。在沉积区,土壤细颗粒的富集促进了土壤团聚体的形成,增强了对REE的吸附[39],同时,细颗粒中含量较高的黏土矿物、有机质、微生物等形成的胶体物质也加强了对REE的吸附[2740]。此外,由于Fe-Mn氧化物是REE等元素的良好吸附剂[41-42],其含量与REE含量通常存在明显的正相关关系[1843]。本研究中,“U”形谷和“V”形谷沉积区细颗粒中Fe-Mn氧化物的含量均显著(P < 0.05)高于侵蚀区,而粗颗粒中Fe-Mn含量均极显著(P < 0.01)低于侵蚀区(表 1)。这也表明了侵蚀和沉积对REE粒径变化的影响。

表 1 “U”形谷与“V”形谷侵蚀区和沉积区不同颗粒粒径中Fe-Mn氧化物的含量变化(该表依据Samonova等文中表2修改)[29] Table 1 The content variation of Fe-Mn oxides in different particle size ranges in the erosional and depositional areas of the "U" and "V" valleys(This table was edited based on Table 2 in the study of Samonova et al.)[29]
4 结论

本研究通过在不同河谷形态小流域分析地貌部位和侵蚀、沉积区域土壤/沉积物中REE含量和富集特征的变化,发现河谷形态、地貌部位、侵蚀/沉积均对LREE和HREE的粒径分布有明显的影响。总体上,土壤/沉积物中的LREE、HREE和ΣREE含量在不同河谷形态、地貌部位、侵蚀/沉积区均随颗粒粒径变粗总体呈现降低趋势。LREE和HREE均主要富集在细颗粒中(< 50 μm),且二者在“V”形谷不同地貌部位均富集在更细的颗粒中(< 10 μm),但“U”形谷细颗粒中REE的富集程度更大,这与河谷形态对侵蚀沉积过程的影响和土壤/沉积物性质的差异有关。可见,侵蚀和沉积对土壤/沉积物中REE的粒径分布的影响尤为显著。“U”形谷和“V”形谷沉积区细颗粒中LREE和HREE的富集程度均显著(P < 0.05)高于侵蚀区。“U”形谷沉积区细颗粒中LREE和HREE的富集系数较侵蚀区分别高32.6%~147.7%和3.9%~150.2%;“V”形谷沉积区细颗粒中二者的富集系数较侵蚀区分别高80.75%~438.2%和2.5%~290.7%。这与侵蚀和沉积区颗粒分选、侵蚀沉积过程影响REE释放、迁移、吸附等相关。可见,REE粒径分布的影响因素复杂,未来应加强REE与不同颗粒粒径结合的机理研究,为正确运用REE准确示踪土壤侵蚀和泥沙来源服务。

参考文献
[1]
Kabata-Pendias A. Trace elements in soils and plants . 4th ed[M]. Boca Raton, Florida: CRC Press, 2000. (0)
[2]
Tian J L, Peng Y L. Soil geochemistry in the Loess Plateau (In Chinese). Beijing: Science Press, 1994: 73-87. [田均良, 彭译林. 黄土高原土壤地球化学[M]. 北京: 科学出版社, 1994: 73-87.] (0)
[3]
Shi H, Tian J L, Liu P L, et al. Study on sediment source in small watershed by tracer method (In Chinese)[J]. Scientia Sinica(Technologica), 1996, 26(5): 474-480. [石辉, 田均良, 刘普灵, 等. 利用REE示踪法研究小流域泥沙来源[J]. 中国科学(技术科学), 1996, 26(5): 474-480.] (0)
[4]
Song W, Liu P L, Yang M Y, et al. Using REE tracers to measure sheet erosion changing to rill erosion[J]. Journal of Rare Earths, 2003, 21(5): 587-590, 500. (0)
[5]
Zhang X C, Nearing M A, Garbrecht J D. Gaining insights into interrill erosion processes using rare earth element tracers[J]. Geoderma, 2017, 299: 63-72. DOI:10.1016/j.geoderma.2017.04.004 (0)
[6]
Zhang X C, Liu G, Zheng F L. Understanding erosion processes using rare earth element tracers in a preformed interrill-rill system[J]. Science of the Total Environment, 2018, 625: 920-927. DOI:10.1016/j.scitotenv.2017.12.345 (0)
[7]
Mahler B J, Bennett P C, Zimmerman M. Lanthanide-labeled clay: A new method for tracing sediment transport in Karst[J]. Groundwater, 1998, 36(5): 835-843. DOI:10.1111/j.1745-6584.1998.tb02202.x (0)
[8]
Liu G, Xiao H, Liu P L, et al. An improved method for tracing soil erosion using rare earth elements[J]. Journal of Soils and Sediments, 2016, 16(5): 1670-1679. DOI:10.1007/s11368-016-1356-y (0)
[9]
Li X J, et al. Grain-size-dependent geochemical characteristics of Middle and Upper Pleistocene loess sequences from the Junggar Basin: Implications for the provenance of Chinese eolian deposits[J]. Palaeogeography, Palaeoclimatology, Palaeoecology, 2020, 538: 109458. DOI:10.1016/j.palaeo.2019.109458 (0)
[10]
Li Y Q, Wu P T, Liu P L, et al. Simulation experiments to study soil erosion by REE tracer method (In Chinese)[J]. Research of Soil and Water Conservation, 1997, 4(2): 26-33. [李雅琦, 吴普特, 刘普灵, 等. REE示踪法研究土壤侵蚀的室内模拟试验[J]. 水土保持研究, 1997, 4(2): 26-33.] (0)
[11]
Zhu Z Z, Liu C Q, Wang Z L, et al. Rare earth element for tracing the source of suspended particulate matter of Lake Chaohu (In Chinese)[J]. Journal of Lake Sciences, 2006, 18(3): 267-272. DOI:10.3321/j.issn:1003-5427.2006.03.012 [朱兆洲, 刘丛强, 王中良, 等. 巢湖悬浮物中稀土元素(REE)的物源精确示踪作用[J]. 湖泊科学, 2006, 18(3): 267-272.] (0)
[12]
Tang Z Q, Liu G, Xu W N. REE tracing method and application in soil erosion (In Chinese)[J]. Journal of the Chinese Society of Rare Earths, 2011, 29(5): 515-522. [汤振权, 刘刚, 许文年. 稀土元素示踪技术及其在土壤侵蚀研究中的应用[J]. 中国稀土学报, 2011, 29(5): 515-522.] (0)
[13]
Lei S, Wei X P. Quantitative tracing of sediment sources in small watersheds in southwestern Karst depressions by composite fingerprinting (In Chinese)[J]. Research of Soil and Water Conservation, 2021, 28(1): 44-49. [雷珊, 魏兴萍. 复合指纹法定量示踪西南岩溶洼地小流域泥沙来源[J]. 水土保持研究, 2021, 28(1): 44-49.] (0)
[14]
Wang X, Shang B X, Li Z B, et al. Evolution of rill erosion by rare earth element tracer method[C]. China Association for Science and Technology, 2007, 1585-1589.[王瑄, 尚佰晓, 李占斌, 等. 利用REE示踪法研究细沟侵蚀的演变过程[C]. 中国科学技术协会, 2007, 1585-1589.] (0)
[15]
Xiao H, Liu G, Xu W N, et al. Using REE to trace sediment source from simulated watershed in Three Gorges reservoir region (In Chinese)[J]. Journal of Soil and Water Conservation, 2014, 28(1): 47-52. DOI:10.3969/j.issn.1009-2242.2014.01.009 [肖海, 刘刚, 许文年, 等. 利用稀土元素示踪三峡库区小流域模型泥沙来源[J]. 水土保持学报, 2014, 28(1): 47-52.] (0)
[16]
Li B, Sun G H, Zhong H X, et al. Rare earth element characteristics of surface sediments in the Fujian coastal area and their implications for provenance (In Chinese)[J]. Marine Geology Frontiers, 2017, 33(8): 47-56. [李波, 孙桂华, 钟和贤, 等. 福建近岸海域表层沉积物稀土元素地球化学特征及其物源指示意义[J]. 海洋地质前沿, 2017, 33(8): 47-56.] (0)
[17]
Liu N N, Wang H B, Zuo H J, et al. Geochemical analysis of different particle sizes on the surface of sand and gravel (In Chinese)[J]. Environmental Science & Technology, 2020, 43(2): 21-26. [刘娜娜, 王海兵, 左合君, 等. 砂砾质地表不同粒径颗粒地球化学特征分析[J]. 环境科学与技术, 2020, 43(2): 21-26.] (0)
[18]
Li Y, Li X S, Han Z Y, et al. The distribution of REE in different particle size fractions of loess and restraining factors (In Chinese)[J]. Acta Pedologica Sinica, 2016, 53(4): 972-984. [李洋, 李徐生, 韩志勇, 等. 黄土不同粒级稀土元素分布特征及其制约因素[J]. 土壤学报, 2016, 53(4): 972-984.] (0)
[19]
Wu K K, Liu S F, Kandasamy S, et al. Grain-size effect on rare earth elements in Pahang River and Kelantan River, Peninsular Malaysia: Implications for sediment provenance in the southern South China Sea[J]. Continental Shelf Research, 2019, 189: 103977. DOI:10.1016/j.csr.2019.103977 (0)
[20]
Xiao H, Liu G, Xu W N, et al. Effects of soil particle composition on REE adsorption capacity and erosion tracing precision (In Chinese)[J]. Journal of the Chinese Society of Rare Earths, 2013, 31(5): 627-635. [肖海, 刘刚, 许文年, 等. 土壤颗粒组成对REE吸附量及侵蚀示踪精度的影响[J]. 中国稀土学报, 2013, 31(5): 627-635.] (0)
[21]
Wu W X. Rare earth element tracer method to explore the turnover path of soil aggregates in the process of splash erosion[D]. Wuhan: Huazhong Agricultural University, 2021.[吴文枭. 稀土元素示踪法探究团聚体在溅蚀过程中的周转路径[D]. 武汉: 华中农业大学, 2021.] (0)
[22]
Chen X L, Song Y G, Li J C, et al. Size-differentiated REE characteristics and environmental significance of aeolian sediments in the Ili Basin of Xinjiang, NW China[J]. Journal of Asian Earth Sciences, 2017, 143: 30-38. DOI:10.1016/j.jseaes.2017.03.030 (0)
[23]
Xiao H. Quantitative monitoring generation and development process of ephemeral gully erosion on hillslope using ree[D]. Yangling, Shaanxi: Northwest A&F University, 2017.[肖海. 稀土元素定量监测坡面浅沟产生及发育过程[D]. 陕西杨凌: 西北农林科技大学, 2017.] (0)
[24]
Zhang J, Meng X W, Fang X S, et al. Grain-size-dependent decoupling of REE and 143Nd/144Nd of the Yellow River sediments: Controlled by detrital minerals (In Chinese)[J]. Acta Mineralogica Sinica, 2022, 42(5): 618-630. [张俊, 孟宪伟, 方习生, 等. 黄河沉积物REE和143Nd/144Nd的粒度解耦: 碎屑矿物制约[J]. 矿物学报, 2022, 42(5): 618-630.] (0)
[25]
Wang J Y, Zhang F H. Distribution of soil aggregates and aggregate-associated organic carbon from typical halophyte community in arid region (In Chinese)[J]. Acta Ecologica Sinica, 2016, 36(3): 600-607. [王静娅, 张凤华. 干旱区典型盐生植物群落土壤团聚体组成及有机碳分布[J]. 生态学报, 2016, 36(3): 600-607.] (0)
[26]
Li Q, Qin F, Ji H B, et al. Geochemical characteristics of the rare-earth elements in the gold mine soil in the upstream area of the Miyun reservoir, Beijing (In Chinese)[J]. Earth and Environment, 2014, 42(6): 733-741. [李倩, 秦飞, 季宏兵, 等. 北京市密云水库上游金矿区土壤稀土元素的地球化学特征[J]. 地球与环境, 2014, 42(6): 733-741.] (0)
[27]
Zhang L J, Li X S, Li D C, et al. Rare earth elements distribution and its correlation with macro elements and particle-size of basalt-derived soils in Leizhou peninsula (In Chinese)[J]. Acta Pedologica Sinica, 2011, 48(1): 1-9. [张立娟, 李徐生, 李德成, 等. 雷州半岛玄武岩母质土壤剖面稀土元素分布及其与常量元素、粒度的关系[J]. 土壤学报, 2011, 48(1): 1-9.] (0)
[28]
Bai R R. Study on the accuracy of REE tracing soil erosion and sediment sources[D]. Yangling, Shaanxi: Northwest A&F University, 2022.[白茹茹. REE示踪土壤侵蚀与泥沙来源的准确性研究[D]. 陕西杨凌: 西北农林科技大学, 2022.] (0)
[29]
Samonova О A, Aseyeva E N, Chernitsova O V. Data on rare earth elements in different particle size fractions of topsoil for two small erosional landforms in central European Russia[J]. Data in Brief, 2020, 30: 105450. DOI:10.1016/j.dib.2020.105450 (0)
[30]
Panin A, Fuzeina Y, Karevskaya I, et al. Mid-Holocene gullying indicating extreme hydroclimatic events in the centre of the Russian Plain[J]. Geographia Polonica, 2011, 95-115. (0)
[31]
Arinushkina E. Handbook for chemical analysis of soils . Moscow in Russian: Chimiya Publishing House, 1992. (0)
[32]
Huang M, Shi X F, Yu M, et al. Distribution and enrichment principles of rare earth elements in surface sediments from the Central Indian Ocean Basin (In Chinese)[J]. Geochimica, 2022, 51(1): 70-82. [黄牧, 石学法, 于淼, 等. 中印度洋海盆表层沉积物稀土元素分布特征及富集规律[J]. 地球化学, 2022, 51(1): 70-82.] (0)
[33]
Yang C Q. A review of the controversy over the question of Moulin and pothole (In Chinese)[J]. Tropical Geography, 2001, 21(1): 86-93, 99. DOI:10.3969/j.issn.1001-5221.2001.01.018 [杨超群. 冰臼与壶穴之争述评[J]. 热带地理, 2001, 21(1): 86-93, 99.] (0)
[34]
Li X S, Han Z Y, Yang D Y, et al. Ree geochemistry of Xiashu loess in Zhenjiang, Jiangsu Province (In Chinese)[J]. Acta Pedologica Sinica, 2006, 43(1): 1-7. DOI:10.3321/j.issn:0564-3929.2006.01.001 [李徐生, 韩志勇, 杨达源, 等. 镇江下蜀黄土的稀土元素地球化学特征研究[J]. 土壤学报, 2006, 43(1): 1-7.] (0)
[35]
Shi Y, Gao J H, Liu Q, et al. Fine sediment transport in north-central of Yellow Sea: The role of continental shelf circulation (In Chinese)[J]. Acta Oceanologica Sinica, 2019, 41(4): 53-63. [石勇, 高建华, 刘强, 等. 陆架环流作用下的北黄海中北部细颗粒物质输运[J]. 海洋学报, 2019, 41(4): 53-63.] (0)
[36]
Sutherland R A, Wan Y, Lee C T, et al. Aggregate enrichment ratios for splash and wash transported sediment from an Oxisol[J]. Catena, 1996, 26(3/4): 187-208. (0)
[37]
Wang H B, Chen F H, Zhang J W. Environmental significance of grain size of loess-paleosol sequence in western part of Chinese loess plateau (In Chinese)[J]. Journal of Desert Research, 2002, 22(1): 21-26. DOI:10.3321/j.issn:1000-694X.2002.01.005 [汪海斌, 陈发虎, 张家武. 黄土高原西部地区黄土粒度的环境指示意义[J]. 中国沙漠, 2002, 22(1): 21-26.] (0)
[38]
Mei X, Zhang X H, Li R H. REE of DLC70-3 core sediments from mud areas in the central south Yellow Sea and its environmental significance (In Chinese)[J]. Geological Science and Technology Information, 2011, 30(4): 21-28. DOI:10.3969/j.issn.1000-7849.2011.04.003 [梅西, 张训华, 李日辉. 南黄海中部泥质沉积区DLC70-3孔稀土元素及环境意义[J]. 地质科技情报, 2011, 30(4): 21-28.] (0)
[39]
Huang C M, Wang C S. Geochemical features of rare earth elements in process of rock weathering and soil formation (In Chinese)[J]. Chinese Rare Earths, 2002, 23(5): 46-49. [黄成敏, 王成善. 风化成土过程中稀土元素地球化学特征[J]. 稀土, 2002, 23(5): 46-49.] (0)
[40]
Ma Y J, Huo R K, Xu Z F, et al. Ree behavior and influence factors during chemical weathering (In Chinese)[J]. Advance in Earth Sciences, 2004, 19(1): 87-94. [马英军, 霍润科, 徐志方, 等. 化学风化作用中的稀土元素行为及其影响因素[J]. 地球科学进展, 2004, 19(1): 87-94.] (0)
[41]
Sun W G, Gan Z T, Sun Z G, et al. Spatial distribution characteristics of Fe and Mn contents in the new-born coastal marshes in the Yellow River Estuary (In Chinese)[J]. Environmental Science, 2013, 34(11): 4411-4419. [孙文广, 甘卓亭, 孙志高, 等. 黄河口新生湿地土壤Fe和Mn元素的空间分布特征[J]. 环境科学, 2013, 34(11): 4411-4419.] (0)
[42]
Ding Z H, Liu J L, Li L Q, et al. Distribution of mercury in surficial sediments from main mangrove wetlans of China (In Chinese)[J]. Environmental Science, 2009, 30(8): 2210-2215. [丁振华, 刘金铃, 李柳强, 等. 中国主要红树林湿地沉积物中汞的分布特征[J]. 环境科学, 2009, 30(8): 2210-2215.] (0)
[43]
Zhang H C, Zhang W X, Chang F Q, et al. Geochemical fractionation of rare earth elements in Lacustrine Deposits from Qaidam Basin (In Chinese)[J]. Science in China(Earth Sciences), 2009, 39(8): 1160-1169. [张虎才, 张文翔, 常凤琴, 等. 稀土元素在湖相沉积中的地球化学分异——以柴达木盆地贝壳堤剖面为例[J]. 中国科学(地球科学), 2009, 39(8): 1160-1169.] (0)