辽东山地冰缘地貌表层土壤粒度特征
2016-06-18刘剑刚张华朱岩朱夏夏何红刘玉国王颖马明军
刘剑刚, 张华†, 朱岩, 朱夏夏, 何红, 刘玉国, 王颖, 马明军
(1.辽宁师范大学城市与环境学院, 116029, 辽宁大连; 2. 辽宁老秃顶子国家级自然保护区管理局, 117218,辽宁桓仁)
辽东山地冰缘地貌表层土壤粒度特征
刘剑刚1, 张华1†, 朱岩1, 朱夏夏1, 何红1, 刘玉国1, 王颖2, 马明军2
(1.辽宁师范大学城市与环境学院, 116029, 辽宁大连; 2. 辽宁老秃顶子国家级自然保护区管理局, 117218,辽宁桓仁)
摘要:为探究辽东山区冰缘地貌表层土壤的质地特征及侵蚀强度,对48个典型冰缘地貌的土壤样品进行粒度测试分析,结果表明:研究区土壤级配良好,且径级跨度较大,质地以黏土质粉砂为主,粉砂其次,偶见砂质粉砂。土壤粒度整体较细(粒度参数平均粒径Mz的φ值约6.45),分选差(标准偏差σI约1.89),以正偏居多(约占58%),峰态多为很窄峰(约占83%);粒度频率分布包括单峰(25%)、双峰(50%)和多峰(25%);结合萨胡判据和南北坡土壤粒度不对称等特征,初步推测早期土壤沉积组分来自近源浅表风化和远源风成沉降,其混合组分经冰缘流水搬运改造后形成土壤沉积。根据分维值(约2.28)、级配比例及敏感组分的提取可知,沉积水动力不强,地表植被覆盖越优良,对流水侵蚀能力的消耗和抑制则越显著。供试样品的粒度特征反映流水侵蚀强度不大,植被覆盖发挥了重要的水土保持功能。
关键词:冰缘地貌; 土壤; 粒度; 萨胡判别; 分维值; 环境敏感组分; 辽东山地
土壤粒度是土壤的重要属性特征之一,其粒径大小、级配组合、分布状况与沉积介质动力强弱、土壤抗侵蚀能力关系密切。良好的土壤质地,不仅支撑植被的涵水保土作用,更是稳固生态系统、降低山地灾害的关键[1-4]。有关粒度的土壤侵蚀、水土流失、环境演变等研究已多有报道。例如:闫玉春等[5]对白音锡勒牧场土壤的粒度分析,探讨了草原土壤的风蚀特征;J. Poesen等[6]对亚欧大范围的坡面砾石堆积进行研究,认为砾石分布特征能够反映坡面土壤的侵蚀状况;李柏等[7]研究了沟坝地泥石流颗粒,得到上游侵蚀、下游堆积的水土流失模式;汤萃文等[8]根据土壤粒度特征,并应用水土流失方程USLE,估算了土壤侵蚀状况;许炯心[9]对长江上游观测站的悬移质泥沙粒度研究,得到水土保持措施能够影响泥沙粒度;孔祥淮等[10]依据粒度特征提取环境敏感组分,对南黄海西部陆架第四纪沉积环境进行研究,反演了古环境的沉积过程;Song X.Y.等[11]、刘淼等[12]、Su Y.Z.等[13]等在不同的土壤过程研究中,应用分形理论,将复杂的土壤结构进行量化、简化,实现了精准描述土壤的微特征。应用粒度分析已在许多土壤学问题的研究中,取得了丰硕成果,但大量的土壤粒度研究多是针对沙丘、湖泊、河流和沟谷等环境,对冰缘地貌的研究成果并不多见。辽东山区冰缘地貌具有特殊的土壤发育过程,同时,也面临着水土流失问题;然而,目前有关本区的研究多涉及生态服务、生物多样性和山地小气候等方面[14-15],缺乏对土壤粒度、侵蚀动力等方面的研究。本文通过对典型冰缘地貌土壤的粒度分析,探究其分布特征及沉积环境变化规律,尝试解释粒度特征所反应的土壤过程及侵蚀强度,为本区相关研究提供基础数据资料,也为水土保持及林业管护等工作提供有益参考。
1研究区概况
老秃顶子国家级自然保护区(E 124°41′13″~125°5′15″;N 41°11′11″~41°21′34″)位于辽宁省东部桓仁、新宾两县交界处,主峰海拔1 367.3 m,为辽宁最高峰,末次冰期形成了一定规模的冰缘地貌。区内基岩以花岗岩为主,变质岩和混合岩均有出露;土壤类型以棕壤、暗棕壤为典型代表,多由花岗岩残积母质发育而成;境内气候类型属温带大陆性季风湿润气候,年平均气温6.0 ℃,年降雨量651~1 315 mm,平均相对湿度72%,无霜期139 d;地带性植被为温性落叶阔叶林,森林覆盖率达97%,植物多样性丰富,且垂直带谱明显,属典型的北温带中山山地森林生态系统[16]。
2材料与方法
2.1样品采集
于2013年6—7月,随海拔梯度选取48处典型冰缘地貌样地,囿于上覆土壤沉积厚度普通很薄,无法做剖面取样,且颗粒无明显粘连,故各取表层土壤0~20 cm不等,并记录相应地形、地貌、植被和土壤等样地特征参数,海拔由1∶5万DEM(2008)提取、经纬度由易测宝T2 GIS采集器测定,详见表1。
表1 调查样地基本情况
表1(续)
2.2实验方法
粒度测试使用美国贝克曼LS13 320激光衍射粒度分析仪(量程0.04~2 000 μm)。土样经自然风干、碾碎和去渣,过2 mm筛,电子秤(精度0.1 mg)称取样品0.1~0.3 g,倒入烧杯,注入20 mL体积分数为30%的H2O2溶液,静置48 h(若有气泡,则继续添加,确保充分去除有机质),注入10 mL体积分数为10%的HCl溶液,搅匀后在电热板上逐渐加热煮沸,使其充分反应、冷却至常温后,加入蒸馏水30 mL静置72 h,除去悬浮液,加入5 mL浓度为0.05 mol/L的六偏磷酸钠(NaPO3)6溶液以备测试之用。测试过程中,各样品均采用超声波震荡30 s。使用日本Rigaku ZSX Primus Ⅱ型X射线荧光光谱仪获取土样化学元素体积分数,并计算化学蚀变指数CIA。依据测试数据,完成土样的颗粒组成、级配比例、频率分布类型、粒度参数特征、沉积动力环境特征、粒度分形维数、敏感组分提取等分析。
3结果与分析
3.1粒级级配与频率分布
土壤颗粒组成包括粉砂级(69.64%)、黏土级(20.74%)和砂级(9.62%)。其中,黏土级颗粒体积分数介于10.52%~26.85%,粉砂和砂体积分数各介于56.32%~82.35%、1.40%~30.89%,变幅稍大。对不均匀系数(Cu)和曲率系数(Cs)(详见文献[18])的计算结果(表2)表明,供试土样级配良好,粒径分布范围广且分布不均。由三角图解(图1)可知,供试样品以黏土质粉砂为主,其次为粉砂,偶见砂质粉砂。
粒度频率分布存在3种类型(图2):单峰(25%,φ值集中在4.98~6.73),均分布在北、东两坡的石河、石流坡地貌;不对称双峰(50%,主峰φ值集中在4.85~6.74,次峰φ值为2~2.5),其中,粉砂级占主体,分布最为广泛;多峰(25%,包括三峰、四峰,主峰不确定,多在粗粒端),形成于坡度稍缓的山顶附近,且南坡比例高于北坡。缘于向阳坡风化强度更大,植被覆盖也相对稀疏[19],且坡度较缓(北坡22.4°、南坡11.3°、山顶7.2°),成壤颗粒在外营力搬运下,容易混合多种组分;而单峰(和部分双峰)均在北坡和东坡,则暗示南北坡土壤沉积组分可能存在差异,或物源提供和沉积动力有所不同。
表2 样品粒径不均匀系数与曲率系数
图1 粒度组成三角图Fig.1 Ternary diagram of the grain composition
图2 频率分布曲线Fig.2 Frequency-distribution curves
3.2粒度参数与环境判别
应用矩值法计算粒度参数平均粒径(Mz)、标准偏差(σI)、偏度(Sk)和峰态(Kg)[20]。本区土壤颗粒细致,平均粒径φ值为6.45(5.41~6.95);标准偏差1.89,分选差;偏度多为正偏,细粒度端形成长尾,反映细颗粒过剩,且分布更分散;峰态值介于2.41~4.04,多为很窄峰(占83%),少数极窄峰,都不属常态峰。由于偏度和峰态最能反映沉积动力的微弱变化,由样本的偏度特征(58%正偏;6%负偏;36%趋于0且均属混合组分)及频率分布可知,土壤沉积以双组分混合为显著,异常峰态值则暗示沉积颗粒中,包含早期经历过良好分选后,进入本区的沉积组分[20]。
萨胡环境判别是判断沉积作用和沉积环境的有效方法[21-22]。基于粒度参数逐级判断:
Y(风成<-2.741 1<海滩)=
Y=-0.831 1(海滩)→Y(海滩<65.365 0<浅海)=
Y=389.856 7(浅海)→Y(河流<-7.419 0<浅海)=
Y=-30.162 6(河流)→Y(浊流<9.843 3<冲积)=
Y=17.625 7(冲积)
结果表明,土壤沉积环境为河流冲积。粒度参数特征也恰好契合了沉积分选差、多为双峰、多正偏、峰态不正常,且掺有黏土、粉砂等悬移质的河流沉积特征[20]。
3.3粒度分维与敏感组分
分维值可配合传统粒度参数,共同反映介质动力和土壤沉积特征[23-25]。本区土壤分维值约为2.28(2.11~2.39),且不同条件下分维值各异(表3)。对比可知,海拔较低、植被覆盖较好,尤其拥有良好林冠遮蔽的条件,土壤分维值更低,对应水动力也较弱,指示良好植被条件对地表水动力具有抑制作用。
表3 不同地貌、坡向和植被类型下土壤的分维值
对不同颗粒与分维值的线性拟合结果(图3)表明:黏土组分比例越大,分维值越大;粉砂比例越大分维值则越小;砂粒比例越大,分维值则随之增大(含砾石)。此缘于粉砂颗粒易于搬运,黏土和细粉砂与更粗颗粒同步沉积时,会因粘连效应很难再呈悬移状态进行搬运,即使能够再次启动,所需的势能也更大,而砂粒或砾石因自身重力更大,对搬运介质动能要求也更高。结合级配比例,粉砂组分近于70%,指示地表水动力不强。
图3 不同颗粒类型与分维值Fig.3 Relationship between different types of grain-size and fractal dimension values
图4 粒级-标准偏差曲线Fig.4 Standard deviation curve of different particle size fraction
敏感组分的表达基于粒度参数,能够反映不同粒级所对应的介质动力或沉积环境变化大小[26]。根据不同地貌和植被覆盖提取到3组环境敏感粒度组分(图4):组分Ⅰ(4.66~27.39 μm)最为敏感;组分Ⅱ(30.07~57.77 μm)对应粉砂-细砂混合组分,敏感度较低;组分Ⅲ(110.98~176.93 μm)颗粒稍粗,对应细砂。粒度细(<100 μm)、分选差的组分Ⅰ,更倾向于悬浮搬运,指示水流速度慢、扰动小;粒度稍大的组分Ⅲ(>100 μm),则更倾向于跃移搬运,指示水动力稍强[22]。植被覆盖更好的条件下,组分Ⅱ、Ⅲ也表现出较高的敏感度,表明此时该植被条件能够影响水流动能,相反,植被覆盖较差则对水动力敏感度低,对水流动能的消耗很小,暗示地表植被覆盖越好,越能减缓水流速度,从而降低流水侵蚀能力。
4讨论
末次冰期白头山冰川发育(距今70 ka),东北大部分地区进入冰缘环境,辽东山地地处冰缘区边缘,冰缘地貌广泛发育[27]。随着温度的显著降低,风蚀、流水、冻融和坍塌等冰缘作用加剧,浅表岩体崩解分离,风化碎屑遍布坡谷,森林面积显著萎缩,大量风化物被强劲的外营力搬运至远处低地,直至冰后期气温回升,植被覆盖渐好,地貌活动趋于稳定,土壤沉积才得以保存,此为本区土壤厚度很薄的原因所在。颗粒细致、多双峰,且南、北坡存在差异的粒度分布,暗示早期土壤过程经历过风成沉降。对比辽西地区自南向北,兴城、朝阳和义县一线,土壤颗粒由粗变细[28-30](φ值分别为2.5、3.56~5.70和4~6),辽东地区南部七顶山、大莲泡至北部老秃顶子,也呈现颗粒逐渐变细的特征[31-32](φ值分别为4.55;5.89;6.45)。通过对比南、北两坡土壤沉积特征参数(表4),可知南坡土壤颗粒稍粗,分选稍差,风化程度更高(CIA[33]=68.02),黏土质沉积物成熟度也稍高(Al2O3/Na2O=5.82)。指示在大尺度上,存在由西向东、由低纬向高纬的风力搬运。晚冰期极盛期(距今约18 ka),曾发生大范围海退,海平面下降约140 m,古海岸线向外退出500~600 km[34],整个渤海出露成陆,海滩砂受蚀严重,砂粒在强劲的冰缘季风吹扬下输入本区,并沉降在各个山间谷地,后经流水改造搬运至他处。另外,供试样品的CIA平均值为64.29(36.57~70.44),介于55~70的样品占93.75%,对照前人成果,本区成土母质应属于黄土和更新世冰川黏土[35],故推测早期土壤组分应包括远源风成沉降(不排除夹杂有内陆黄土的可能)和近源浅表岩石的成熟风化物。
另一方面,粒度特征及分维值、敏感组分,都反映了弱水动力环境受地表植被覆盖的影响。结合粒径与地表状况的相关分析可知(表5),粒径大小与风化程度关系密切,说明沉积颗粒仍继承物源的粒度特征,且受沉积后化学风化活动的影响;灌木密度虽未与其达到显著相关,但仍保持了较高的负相关性,说明耐冷湿的低矮植被覆盖良好,粒度趋于细致的可能性更大,对应水动力可能越弱。
表4 不同坡向土壤沉积的特征值
Note:Mz: mean grain size;σI: standard deviation;Sk: skewness;Kp: kurtosis; CIA: chemical index of alteration.
表5 粒径与地表状况的关系
注:*P= 0.05 时,显著相关. Note: * indicates significantly correlated atP= 0.05.
辽东山区土温稳定、降水丰沛、森林结构比较完整[16,36],其构成的植物群落系统可通过根系改善土壤质地、创造抗冲型土壤结构,依靠木本植物垂直根系的锚固作用、水平根系的支撑作用和草本植物根系的加筋作用以稳固土壤。而且,植物体还具备蒸腾排水特性,林冠也具有截流、减速效果,地被物也能够调节湿度、削弱溅蚀和抑制径流等,都极大的降低了流水侵蚀强度。本区土壤的粒度特征,反映流水侵蚀并不显著,有利于土壤累积及植物群落的演替。
5结论
1)土壤颗粒组分包括粉砂(69.64%)、黏土(20.74%)和砂(9.62%)。不均匀系数和曲率系数表明,粒级级配良好且跨度大、分布不均。依据海洋地质调查规范中的分类命名原则,本区土壤以黏土质粉砂为主,粉砂其次,偶见砂质粉砂。粒度频率分布表现为单峰、双峰(居多)和多峰。
2)应用矩值法求得粒度参数:平均粒径φ值为6.45,标准偏差为1.89,偏度多为正偏,峰态以很窄峰为主,反映沉积颗粒整体细致、分选差、细粒过剩、沉积组分主要为双组分混合。基于所得粒度参数完成萨胡环境判别,并提取环境敏感组分,结果显示沉积环境属河流冲积,敏感粒度组分3类:4.66~27.39 μm(最敏感)、30.07~57.77 μm、110.98 ~176.93 μm。
3)供试样品分维值介于2.11~2.39(平均值2.28),结合级配比例共同指示水动力不强。不同植被条件下,分维值与敏感粒度组分同样反映了地表植被覆盖状况越好,对流水侵蚀能力的消耗和抑制越显著。
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(责任编辑:程云郭雪芳)
Grain size characteristics of overlying soil onperiglacial landforms in mountainous region of eastern Liaoning
Liu Jiangang1, Zhang Hua1, Zhu Yan1, Zhu Xiaxia1, He Hong1, Liu Yuguo1, Wang Ying2, Ma Mingjun2
(1.School of Urban and Environmental, Liaoning Normal University, 116029, Dalian, Liaoning, China 2. Administration of Laotudingzi National Nature Reserve, 117218, Huanren, Liaoning, China)
Abstract:[Background] As typical and representative periglacial landforms in the Mt. Laotudingzi in the center of Nature Reserve in eastern Liaoning, the characteristics of the surface ground and the changes in the natural environment are concerned by the geographers. More researches associated with it were done. However, the specific research on the mechanical analysis of soil here has been rarely published. [Methods] In order to fill the blank of the research on this area and provide the reference data for the soil and water conservation specialist or forestry specialist, based on the investigation and fieldwork, the undisturbed soil samples were returned and pretreated, the grain size characteristics of the overlying soil in 48 sample plots were analyzed. [Results] The most of the soil particles were fine (average on about φ value is 6.45), and the soil texture was mainly dominated by clayey silt. Additionally, the soil texture also had other presentation by consisting of silt or sandy silt that was rarely discovered. The soil of the study area was mainly positive skew distribution (about 58%), and the sorting feature of grain size was “Not good” (σI about 1.89), as for leptokurtosis, most of the soil samples were showed by “Very narrow” (83%). The frequency curves of sediment-size distribution of 48 samples presented in 3 forms by test data showing: unimodal (25%), bimodal (50%) and multimodal (25%). The sedimentary environment was categorized as fluvial according to the calculation by Sahu discriminant. Considering the grain-size characteristic parameter, sediment-size frequency distribution and the asymmetrical sedimentary features in southern and northern slope, it was preliminarily inferred that the incipient sediment source should be including the weathered material of local rock fragments formed by frost weathering and the sand long-distance deposit by wind from the area of Yellow Sea and Bohai Sea in late glacial; and the multi-component removed and deposited by periglacial stream during a long process, and settled on the surface ground. The fractal dimension of grain size was between 2.11 to 2.39 and average on about 2.28, taking the ratio of clay and fine silt into consideration, it could be deduced that the water dynamics here was not strong. [Conclusions] And the fractal dimension, together with the environmentally sensitive grain size component, reflected that the better the land surface vegetation covered, the more significant the depletion and suppression of water erosion were. The characteristic of grain size here indicated that the intensity of water erosion was low and vegetation coverage played the vital role in the the water and soil conversation.
Keywords:periglacial landform; soil; grain size; Sahu discriminant; fractal dimension; environmentally sensitive grain size component; Mt. Laotudingzi
收稿日期:2015-05-21修回日期: 2016-01-12
第一作者简介:刘剑刚(1986—),男,博士研究生。主要研究方向:区域生态与环境。E-mail:ljgemail@126.com †通信 张华(1965—),女,教授,博士生导师。主要研究方向:植物地理和生态恢复. E-mail:zhanghua0323@sina.com
中图分类号:P931.4
文献标志码:A
文章编号:1672-3007(2016)01-0036-10
DOI:10.16843/j.sswc.2016.01.005
项目名称: 国家自然科学基金“辽东山地老秃顶子冰缘地貌植物群落稳定性研究”(41271064)