西南黄壤和西北黄土坡面侵蚀产沙规律比较研究

陈美淇,张卓栋,王晓岚,张科利†,陈月红

(1.北京师范大学,地理学与遥感科学学院,100875,北京;2.中国水利水电科学研究院,100048,北京)

西南黄壤和西北黄土坡面侵蚀产沙规律比较研究

陈美淇1,张卓栋1,王晓岚1,张科利1†,陈月红2

(1.北京师范大学,地理学与遥感科学学院,100875,北京;2.中国水利水电科学研究院,100048,北京)

喀斯特地区是我国主要生态脆弱地区之一,黄壤是该地区主要土壤类型,本文基于贵州省毕节市与陕西安塞径流小区观测资料,对比分析降雨与坡面径流深、产沙模数等关系,研究次降雨坡面侵蚀规律。结果表明:黄壤坡面产流产沙主要来源于大雨及暴雨,受降雨量影响最大,数量上小于黄土坡面;黄壤坡面产流与降雨量相关性大于与其与时段降雨强度相关性,黄土坡面反之;随降雨级别增大,黄壤坡面产流与降雨特征关系由无规律变为线性;时段降雨强度与黄壤坡面产沙呈指数关系,与黄土坡面呈幂函数关系;缺乏过程资料时,可采用M=0.54e0.11p预测黄壤坡面次降雨侵蚀量;降雨侵蚀力与产流产沙呈线性关系,单位降雨侵蚀力引起的产流产沙量黄壤坡面均小于黄土坡面;坡面产流与产沙均呈良好线性关系,产流量相近时,黄壤坡面产沙量略小于黄土坡面。研究结果表明黄壤坡面侵蚀量小于黄土坡面,但由于其土层薄,侵蚀程度仍十分严重,区域水土流失防治工作仍需加强。

黄壤;坡面侵蚀;径流;产沙;黄土

根据第1次全国水利普查结果,我国水土流失面积达129.32万km2,其中有27.93%分布在西南石质山区[1]。由于特殊的喀斯特地貌、土壤、水文过程和土地利用方式,西南喀斯特地区是我国因水土流失导致生态问题最为严重的地区,该地区土壤侵蚀和泥沙过程不同于全国其他地区,因此在实施水土保持及效益评价时不能照搬其他地区的研究成果。黄壤是西南喀斯特地区分布最广的土壤类型,为了有效地控制侵蚀和恢复生态,开展西南黄壤坡面产流产沙规律研究十分必要。近10多年来,有许多学者在西南喀斯特地区开展过土壤侵蚀和水土流失研究,为认识喀斯特地区水土流失规律做出了重要贡献;但这些研究多集中于对区域总体水土流失特征[2]、水土流失强度分级分区[3],水土流失现状与石漠化关系[4]等方面,且多采用人工模拟降雨、径流冲刷[56]等试验方法,以及运用RS、GIS[7]等技术进行区域尺度监测研究,而在坡面侵蚀方面的研究还较少。陈旭晖等[8]通过径流小区观测比较了不同水土保持措施的效益,也未研究坡面侵蚀规律。我国针对土壤坡面产流产沙的规律研究多集中于黄土高原区,张科利等[9]研究降雨单因子与坡面侵蚀模数关系,刘宝元等[10]提出适用于我国的土壤流失预报模型(CSLE),而西南喀斯特地区区域土壤侵蚀预报模型的研究尚有欠缺。笔者利用布设在贵州毕节和江忠善设在黄土高原安塞的径流小区资料,通过对比研究坡面侵蚀产沙过程,旨在揭示西南黄壤坡面侵蚀规律,获取基于研究区实际情况的区域土壤侵蚀预报模型因子参数,为西南喀斯特地区坡面土壤侵蚀预报模型建立和水保规划制定提供理论依据。

1 研究区概况

黄壤研究区位于贵州省毕节市石桥小流域,流域面积35.93 km2,属亚热带湿润季风气候区,海拔1 400～1 742 m,基岩种类为石灰岩,年均气温14.03℃,多年平均降雨量863 mm,7—9月降雨量占全年总降雨的52.4%,主要植被类型为常绿落叶针阔混交林。陕西安塞水土保持综合实验站位于黄土高原中部,属典型黄土丘陵沟壑区,属暖温带半湿润半干旱气候过渡区,海拔1 040～1 425 m,年均气温8.8℃,年均降雨量549.1 mm,7—9月降雨量占全年降水61.1%。在2个研究区内各布设一个坡长设20 m,坡度15°的标准裸露径流小区[11],其中黄壤径流小区坡向北偏西15°,土壤类型为黄壤,土层厚度21 cm,粘粒22.2%、粉粒32.5%以及砂粒45.3%[12],水稳性团聚体(＞0.25 mm)质量分数61.6%,土壤密度0.94 kg/cm3,总孔隙度44.31%,稳渗速率7.75 mm/min,黄土径流小区土壤类型为黄绵土,其中4.3%粘粒、54.1%粉粒以及41.6%砂粒,水稳性团聚体(＞0.25 mm)质量分数29.6%,土壤密度1.1 kg/cm3[13],稳渗速率0.67 mm/min[14]。

2 材料与方法

2.1 数据来源

所有降雨中只有部分发生地表径流进而引起土壤侵蚀,发生真正意义上的土壤流失,将这部分降雨称为侵蚀性降雨[15],本文将降雨后产流产沙的降雨定义为侵蚀性降雨。每次侵蚀性降雨后,记录集流桶及分流桶水位,由此计算径流总量;分别取悬移质和推移质样品,采用烘干法测定。用自记雨量计记录降雨过程,计算降雨动能和次降雨侵蚀力。黄壤坡面所用数据为2012—2014年3年间43场侵蚀性降雨的径流泥沙资料;黄土坡面所用数据为1985—1989年5年间38场侵蚀性降雨产流产沙资料。

2.2 数据处理及分析

统计方法采用SPSS 18.0软件中的相关分析模块,做双变量相关分析并进行显著性检验,进一步利用回归分析模块,对数据进行线性、指数等回归分析,研究降雨、径流与泥沙之间关系。

3 结果与讨论

3.1 次降雨产流产沙特征

对西南黄壤与北方黄土坡面径流小区观测数据进行统计分析(表1),发现黄壤区降雨与产流产沙统计特征值均小于黄土区,平均次降雨量为黄土地区的66.8%,平均次降雨产流量为黄土区的57.8%,平均次降雨产沙量仅为黄土区的40.6%;除径流系数外,黄壤区降雨量、坡面径流深以及产沙模数的变异系数均大于黄土区,数据更为离散程度,表明黄壤坡面发生产流产沙的降雨较黄土坡面更为分散。

表1 西南黄壤与北方黄土坡面次降雨及产流产沙对比Tab.1 Basic characteristics of rainfall,runoff and sediment yield on yellow soil slope and loess slope

采用气象学降雨分级方法[16],以降雨量P为指标——分为小雨(P＜10 mm)、中雨(10≤P＜25 mm)、大雨(25≤P＜50 mm)、暴雨(50≤P＜100 mm)、大暴雨(100 mm≤P)5级。将黄壤区2012—2014年43次和黄土区1985—1989年38次侵蚀性降雨进行分级得到表2。对黄壤坡面而言,小雨和中雨型降雨占总降雨次数的74.4%,累计降雨量占总降雨量的21.1%,大雨和暴雨累计径流深占总径流深的89.7%。对黄土坡面而言,小雨和中雨型降雨占总降雨次数的57.9%,累计降雨量占总降雨量的10.7%,大雨和暴雨累计径流深要占总径流深的85.4%。相比而言,黄壤区降雨以小雨和中雨型为主,而黄土区降雨以中到暴雨为主,2地区大雨及暴雨降雨量均占年降雨量的绝大部分。随降雨级别增大,黄壤区产流产沙逐渐增加,超过一定范围,增幅明显,可超过10倍,黄土区产流产沙随降雨则平稳增长。

黄壤区产沙模数大于100 t/km2的降雨共5次,其中大雨1次,暴雨4次,其产沙之和占总产沙量的97.49%,径流量占总产流量的64%;黄土地区产沙模数大于1 000 t/km2的降雨共6次,其中中雨与大暴雨各1次,大雨及暴雨4次,其产沙之和占总产沙量的78.2%,径流量占总产流量的66.3%。说明两地区坡面侵蚀产流产沙均主要来自大雨及暴雨。

3.2 次降雨特征与产流关系

为进一步分析产流产沙与降雨特征之间的关系,将降雨等级合并为小雨及中雨(0＜P≤25 mm,简称A型)和大雨及暴雨(P＞25 mm),简称B型。不同类型降雨次降雨特征与径流深、径流系数进行相关分析,如表3。不同降雨特征与黄壤坡面径流深相关性大小依次为P＞I60＞I30＞I15＞I5＞I10,与黄土坡面径流深相关性依次为I60＞I30＞I15＞I10＞I5＞P;除降雨量外,黄壤坡面径流与降雨特征相关性均小于黄土坡面,黄壤坡面产流主要受降雨量影响,黄土坡面产流则主要受时段降雨强度影响,降雨特征对黄壤坡面产流影响小于黄土坡面。A型降雨时,黄壤坡面径流与降雨特征相关性极低,随降雨级别增大,降雨特征与径流相关性均有所增加,增幅明显大于黄土坡面。

对A型与B型降雨分别作次降雨特征与径流深回归分析,结果如图1所示。可知:A型降雨时,黄壤坡面产流与降雨特征无明显规律;而黄土坡面产流与时段降雨强度It呈线性关系,与降雨量无明显定量关系。B型降雨时,黄壤坡面产流与降雨特征回归关系明显好于A型降雨,产流与降雨特征均呈良好线性关系。地表产流主要与降雨和下垫面2个因素有关,下垫面特征是由地形、土壤、地表覆盖等决定的[17]。黄壤黏粒质量分数高,土壤吸水性好。发生A型降雨时,其坡面产流主要受下垫面土壤影响,与降雨关系不明显;黄土坡面土质相对均一,产流与降雨关系密切。发生B型降雨时,坡面产流与降雨关系密切;径流深与降雨量回归方程斜率黄壤坡面大于黄土坡面(图1(d)),前期黄壤吸收水分多,降雨更易下渗,而黄土砂粒含量高,持水性差,降雨直接产流,随着降雨继续进行,黄土坡面下渗增多,产流速率反而降低;由(e)、(f)知,黄壤坡面开始产流的时段降雨强度明显大于黄土地区,斜率明显小于黄土坡面,主要由于2地区产流方式不同,崔泰昌等[18]在其研究中有相应论述。黄土砂粒含量高,土壤吸水性差,稳渗速率小,降雨极易超过土壤水分入渗速率,且位于我国干旱地区,降雨多历时短降雨强度大,坡面产流常为超渗产流,反之黄壤黏粒质量分数大,稳渗速率大,处于我国湿润地区,坡面产流多为蓄满产流。

3.3 次降雨特征与产沙关系

对降雨与产沙进行相关性分析如表4所示。黄壤坡面产沙与降雨特征相关性大小为I60＞P＞I30,黄土坡面为I60＞I30＞P,黄壤坡面产沙与降雨相关性均小于黄土坡面。降雨特征与产沙量之间的定量关系如图2所示。随降雨强度增大,黄壤坡面侵蚀量呈指数函数增加,张赫斯等[19]在研究红壤坡面侵蚀规律时得出与本文一致结论;黄土坡面侵蚀量呈幂函数增加,与张科利等[11]在黄土丘陵区研究结论类似。降雨强度增量相同时,黄壤坡面侵蚀增量明显小于黄土坡面,其粘粒、水稳性团聚体质量分数高,土壤黏结力强,不易被侵蚀是主要原因。黄壤坡面产沙与降雨量为指数关系,图2(c)所示,与顾礼斌等[20]在黔西高原研究结论相似。拟合方程为

图1 次降雨特征与坡面径流深的关系Fig.1 Relationship between rainfall characteristics and runoff depths

图2 次降雨特征与坡面产沙模数的关系Fig.2 Relationship between sediment yields and rainfall characteristics

式中:M为产沙模数,t/km2;P为降雨量,mm。在缺乏过程资料的地区,可用该方程进行坡面土壤流失预报。黄土坡面产沙量与降雨量为线性关系,与杨占彪等[21]研究结果类似。由于土壤性质以及降雨类型差异,降雨量相同时,黄壤坡面侵蚀量明显小于黄土坡面侵蚀量。虽根据模拟函数,雨量超过一定范围后,黄壤坡面侵蚀量将大于黄土坡面,而实际中该情况较少出现,一是黄壤区降雨分布中大暴雨较

少,二是黄壤较黄土更不易被侵蚀。

表4 次降雨特征与产沙模数相关性Tab.4 Correlation of rainfall characteristics and sediment yields

我国学者在研究降雨侵蚀力指标时多采用动能En和时段雨强In的乘积EnIn结构[22],其经典指标为Wischmeier所提出的EI30值。本文根据实测径流资料,对降雨侵蚀力作回归拟合分析,结果如图3。降雨侵蚀力与径流深、产沙模数均呈线性关系,黄壤坡面单位降雨侵蚀力下产流产沙量均明显小于黄土坡面,说明黄土比黄壤更容易发生侵蚀,降雨侵蚀力越大,产流产沙的差异越大。EI30与黄壤坡面产沙模数回归方程决定系数明显小于黄土坡面产沙模数回归方程决定系数。黄壤坡面产流方式以与降雨量密切相关,与降雨动能和降雨强度关系较弱的蓄满产流为主,而径流是坡面产沙的直接动力;因此以EI30作为降雨动能与降雨强度复合指标,不能有效反应降雨与黄壤侵蚀的关系。

图3 降雨侵蚀力与产流产沙的关系Fig.3 Relationship among sediment yield,runoff and rainfall erosivity

3.4 坡面侵蚀泥沙与径流关系

径流是引起土壤侵蚀的重要因子,土壤侵蚀与径流量之间一般都存在良好关系。为此,根据小区实测资料,对径流深与产沙模数进行回归分析(图4)。结果表明:不论是黄壤坡面还是黄土坡面,径流与泥沙之间均呈良好的线性关系,用次降雨产流量都能较好预测两地区次降雨坡面产沙量。回归方程中黄壤坡面斜率要略小于黄土坡面,表明在径流量相近时,黄土坡面产沙量略大于黄壤坡面。此外由于西南喀斯特地区土壤资源匮乏,黄壤坡面侵蚀对土壤资源的破坏程度要远大于黄土地区。

图4 径流深与产沙模数的关系Fig.4 Relationship between sediment yields and runoff depths

4 结论

1)坡面径流泥沙均主要来自大雨及暴雨,黄壤区侵蚀性降雨及产流产沙量均小于黄土区。

2)黄壤坡面产流与降雨量相关性最大,黄土坡面产流与降雨强度I60相关性最大;降雨级别增大,黄壤坡面产流与降雨特征由无规律变为线性关系,黄土坡面产流与时段雨强It呈线性关系。

3)降雨侵蚀力(EI30)作为反应降雨与坡面侵蚀量指标,在黄土坡面更为适用。在没有过程资料时,直接采用降雨量,M=0.54e0.11p预测黄壤坡面次降雨侵蚀量也能满足实践需要。

4)黄壤、黄土坡面侵蚀量与降雨强度分别呈指数、幂函数关系,与产沙均呈线性关系。

论文部分数据来自江忠善先生在陕西安塞布设的小区观测资料,在此表示衷心感谢。

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A comparison of slope erosion sediment yield characteristics of yellow soil in Southwest China and loess in Northwest China

Chen Meiqi1,Zhang Zhuodong1,Wang Xiaolan1,Zhang Keli1,Chen Yuehong2

(1.School of Geography,Beijing Normal University,100875,Beijing,China; 2.China Institute of Water Resources and Hydropower Research,100048,Beijing,China)

[Background]Karst region is one of the most vulnerable ecosystems in China,and the soil resources in this region are limited because of the slow pedogenesis processes of severe soil erosion influenced by the unique karst process.In recent decades,soil erosion resulted in large rocky desertification,reductions of agricultural productivity,and decreases of land fertility.Yellow soil is the major soil type in this region.It is essential to study sediment yield characteristics at slope scales for effective soil slope loss control,water and soil resources utilization and management.[Methods]Based on the data of field plots in Bijie of Guizhou Province in Southwest Cina and Ansai of Shaanxi Province in Northuest China,the characteristics and relationships of rainfall,runoff and sediment yield under natural rainfall events were investigated and analyzed by statistical methods,and the differences between two stations were compared and discussed.[Results]1)Runoff and sediment yield in the yellow soil slope of Bijie mainly resulted from heavy rains and storms,and they were smaller than those of loess slopes in Ansai,and more evenly distributed.2)Runoff was more relevant to precipitation than to rainfall intensity,which was contrary to the relationships on loess slope.As precipitation increased from Arainfall type(0＜P≤25 mm)to B type(P＞25 mm),the relationship between runoff and rainfall characteristics on yellow soil slopes changed from random to a linear function.While under the same change of rainfall type,the relationship between runoff and rainfall characteristics remained linear on loess slopes.The relationship of rainfall intensity and sediment yield on yellow soil slopes was in an exponential function,while it was in power on loess slopes.3)When lacking process data,the equation M=0.54e0.11pcan be used to predict soil loss on yellow soil slope for individual rainfall events.4) Rainfall erosivity was linear to both runoff and sediment yield on both yellow soil and loess slopes,and it was a proper indicator to predict runoff and sediment yields on loess slopes,while it was not that suitable for yellow soil slopes.Runoff and sediment yield caused by unit rainfall erosivity on yellow soil slopes were smaller than those on loess slopes.5)Sediment yield of both yellow soil and loess slopes were in linear function to the runoff.When runoff was similar,sediment yield on yellow soil slopes was smaller to that on loess slopes.[Conclusions]It is valuable to study soil erosion factors for quantitative estimation of soil erosion,especially in Karst region.Precipitation is a dominant factor that influences runoff and sediment yield on yellow soil slopes.The more precipitation,the more runoff and sediment yield.The amount of runoff and sediment yield on yellow soil slopes are smaller than those on loess slopes,however, the soil erosion situation in the Karst region is even severer due to the scarcity of soil resources here.

yellow soil;slope erosion;runoff;sediment yield;loess

S157.1

A

1672-3007(2016)06-0053-08

10.16843/j.sswc.2016.06.007

2016 04 28

2016 09 10

项目名称:国家自然科学基金“东北黑土区冻融作用与水蚀过程耦合机理研究”(41471224);水利部公益性行业科研专项“水土保持生态效应监测与评价技术研究”(201501045)

陈美淇(1992—),女,硕士研究生。主要研究方向:土壤资源利用与保护。Email:mqchen@mail.bnu.edu.cn

†通信作者简介:张科利(1962—),男,教授,博士生导师。主要研究方向:土壤侵蚀。Email:keli@bnu.edu.cn