黃土高原水蝕風(fēng)蝕交錯(cuò)帶六道溝小流域坡面表土鈣質(zhì)結(jié)核分布

鞏鐵雄，朱元駿,3?

(1.中國(guó)科學(xué)院 水利部 水土保持研究所，712100，陜西楊凌；2.中國(guó)科學(xué)院大學(xué)，100049，北京；3.西北農(nóng)林科技大學(xué) 黃土高原土壤侵蝕與旱地農(nóng)業(yè)國(guó)家重點(diǎn)實(shí)驗(yàn)室，712100，陜西楊凌)

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黃土高原水蝕風(fēng)蝕交錯(cuò)帶六道溝小流域坡面表土鈣質(zhì)結(jié)核分布

鞏鐵雄1,2，朱元駿1,2,3?

(1.中國(guó)科學(xué)院 水利部 水土保持研究所，712100，陜西楊凌；2.中國(guó)科學(xué)院大學(xué)，100049，北京；3.西北農(nóng)林科技大學(xué) 黃土高原土壤侵蝕與旱地農(nóng)業(yè)國(guó)家重點(diǎn)實(shí)驗(yàn)室，712100，陜西楊凌)

量化坡面鈣質(zhì)結(jié)核分布，有助于深化對(duì)黃土高原水蝕風(fēng)蝕交錯(cuò)帶特定土壤類(lèi)型(含鈣質(zhì)結(jié)核土壤)中水土過(guò)程的認(rèn)識(shí)。本研究通過(guò)對(duì)坡面不同部位的表層土壤(0～20 cm)顆粒組成、鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)和植被地上生物量、蓋度、豐富度及多樣性指數(shù)的測(cè)定和分析，研究了坡面鈣質(zhì)結(jié)核的分布及影響因素。結(jié)果表明：土壤黏粒體積分?jǐn)?shù)沿坡面呈逐漸降低趨勢(shì)；鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)沿坡面呈單峰曲線(xiàn)分布，在坡面1/4～1/3的位置(距離坡頂20～30 m)處，達(dá)到峰值(10%～15%)。鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)與坡度呈線(xiàn)性正相關(guān)，與植被地上生物量(蓋度)呈單峰曲線(xiàn)關(guān)系，峰值即為植被影響鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)的臨界點(diǎn)，臨界點(diǎn)處的植被蓋度在11%～16%之間。影響坡面鈣質(zhì)結(jié)核分布的最主要因素為坡度和植被；小尺寸的鈣質(zhì)結(jié)核在坡面分布范圍最廣、數(shù)量最多，起決定作用的鈣質(zhì)結(jié)核尺寸在5～15 mm之間。坡面鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)及分布反映了徑流、植被和鈣質(zhì)結(jié)核之間的相互作用關(guān)系，鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)可以用來(lái)指示坡面的土壤侵蝕狀況。

黃土高原水蝕風(fēng)蝕交錯(cuò)帶； 鈣質(zhì)結(jié)核； 土壤侵蝕； 坡度； 植被

黃土高原水蝕風(fēng)蝕交錯(cuò)帶地處干旱半干旱地區(qū)，歷史上的氣候干濕交替，導(dǎo)致黃土中的鈣質(zhì)成分在土層中淀積形成鈣質(zhì)層[1-3]。由于強(qiáng)烈土壤侵蝕和人類(lèi)活動(dòng)的干擾，鈣質(zhì)層逐漸露出地表，并在風(fēng)化和人類(lèi)活動(dòng)的作用下，破碎形成鈣質(zhì)結(jié)核(直徑>2 mm)，并露出地表，成為土壤物理性質(zhì)退化的一種標(biāo)志[4]。鈣質(zhì)結(jié)核直徑大于土壤顆粒，能改變土壤的結(jié)構(gòu)和物理特質(zhì)，影響土壤入滲[5-12]、蒸發(fā)[13-16]、地表產(chǎn)流產(chǎn)沙等水土過(guò)程[17-18]；同時(shí)徑流的影響，導(dǎo)致鈣質(zhì)結(jié)核在坡面形成特定的分布格局；此外，植被也能通過(guò)消減徑流動(dòng)能和其自身的攔截作用，來(lái)影響鈣質(zhì)結(jié)核在坡面的分布。

對(duì)這類(lèi)特定土壤類(lèi)型的研究起于20世紀(jì)60年代[6,10,19-20]。有學(xué)者在極地和冰川地區(qū)發(fā)現(xiàn)，大顆粒礫石常常在地表聚集，并呈一定的分布格局。有研究發(fā)現(xiàn)，在干旱半干旱地區(qū)，坡度與地表礫石蓋度密切相關(guān)[21]，礫石粒徑大小分布與坡度有顯著關(guān)系[22-23]。Chen Hongsong等[24]發(fā)現(xiàn)在西南喀斯特地區(qū)，只有特定粒徑范圍的礫石才與坡度有一定相關(guān)性，礫石的空間分布受坡形影響較大。礫石在坡面的分布還與礫石類(lèi)型有關(guān)。玄武巖巖性礫石蓋度與坡度間表現(xiàn)出無(wú)相關(guān)性，礫石主要出現(xiàn)在3.40～22.8°的坡面上，5～20 mm石灰?guī)r性礫石的蓋度隨坡度增加呈對(duì)數(shù)增加[25]。人類(lèi)活動(dòng)如踩踏，也是導(dǎo)致土壤中礫石運(yùn)移的主要原因，而且礫石的垂直運(yùn)動(dòng)和水平運(yùn)動(dòng)共同影響著礫石空間分布[25-26]。鈣質(zhì)結(jié)核是含鈣質(zhì)土壤中常見(jiàn)的大顆粒成分，其廣泛分布在黃土高原、印度南部和東非地區(qū)[27-29]。由于鈣質(zhì)結(jié)核通常被認(rèn)為是土壤的組成部分，因而很少有人關(guān)注，而且，近些年因退耕還林還草政策的實(shí)施，黃土高原植被蓋度明顯增加，以往的研究較少考慮植被的影響；因此，研究鈣質(zhì)結(jié)核在坡面的分布，有助于理解特定土壤類(lèi)型中的水土過(guò)程及鈣質(zhì)結(jié)核的指示作用。

本研究通過(guò)對(duì)黃土高原水蝕風(fēng)蝕交錯(cuò)帶小流域坡面表層土壤中鈣質(zhì)結(jié)核的取樣，結(jié)合對(duì)植被、坡度、坡形和鈣質(zhì)結(jié)核尺寸的測(cè)定，研究表土中鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)沿坡面的變化、影響因素及其與植被的關(guān)系。

1　研究區(qū)概況

試驗(yàn)在地處黃土高原水蝕風(fēng)蝕交錯(cuò)帶的陜西省神木縣六道溝小流域(E110°21′23″～110°21′25″，N38°48′8″～38°48′10″)。該流域北依長(zhǎng)城，與毛烏素沙地邊緣地帶接壤，面積6.89 km2，海拔1 081～1 274 m，年平均溫度8.4 ℃，年均降水量408 mm，其中6—8月降水量占全年81%以上，年均強(qiáng)風(fēng)時(shí)間3.8～87.2 d，年沙塵時(shí)間多在4 d以上。流域土壤侵蝕模數(shù)為1萬(wàn)5 040 t/(km2·a)，水土流失面積占流域總面積的79%。劇烈的土壤侵蝕使流域地表出現(xiàn)大量侵蝕溝，溝道密度(>100 m)為6.45 km/km2，溝道面積占流域面積的38%。地貌類(lèi)型以丘陵和溝道為主，主要土壤類(lèi)型有綿沙土、紅土、風(fēng)沙土和硬質(zhì)黃土。流域表層黃土為馬蘭黃土，富含碳酸鈣，由于歷史氣候干濕交替，土層中鈣質(zhì)層發(fā)育充分[30]。在長(zhǎng)期水蝕和風(fēng)蝕的影響下，表層黃土被逐漸侵蝕，鈣質(zhì)層露出地表，并在風(fēng)化作用下破碎，導(dǎo)致鈣質(zhì)結(jié)核在坡頂和侵蝕劇烈的地方大量出現(xiàn)。流域植被以灌叢和草本為主，建群植物均為針茅(Stipa capillata Linn.)。

2　研究方法

在流域范圍內(nèi)，選取2個(gè)鈣質(zhì)結(jié)核廣泛分布的坡面S1和S2(圖1)，坡長(zhǎng)分別為87和68 m；坡面S1坡度沿坡面呈先增大后減小的趨勢(shì)，而坡面S2前2/3坡長(zhǎng)的坡度均保持在17°左右，之后出現(xiàn)減小的趨勢(shì)(圖2)。沿坡頂—坡底方向，每隔5 m，做2個(gè)50 cm×50 cm的樣方，調(diào)查坡面植被的物種數(shù)、蓋度和地上生物量(干質(zhì)量)；同時(shí)，沿坡面每隔5 m，取2個(gè)點(diǎn)土層(0～20 cm)的土樣，帶回室內(nèi)，過(guò)2 mm篩，把土壤和鈣質(zhì)結(jié)核分開(kāi)；然后，將鈣質(zhì)結(jié)核顆粒洗凈、烘干稱(chēng)量，分別過(guò)5、10、15、20 和25 mm土篩；最后，利用激光粒度儀MS2000，測(cè)定土壤樣品的顆粒組成(美國(guó)農(nóng)業(yè)部土壤分類(lèi)系統(tǒng)，黏粒為<0.002 mm、粉粒為0.05～0.002 mm、砂粒為2～0.05 mm)。

圖2　坡度沿坡面變化Fig.2　Changes of slope gradient along the hillslopes

3　結(jié)果與分析

3.1坡面土壤顆粒組成與鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)

坡面S1和S2采樣點(diǎn)的土壤顆粒組成沿坡面的變化趨勢(shì)見(jiàn)圖3。坡面S1的土壤黏粒和粉粒沿坡面有逐漸降低的趨勢(shì)，砂粒有逐漸增加的趨勢(shì)；坡面S2的土壤黏粒和砂粒沿坡面稍有降低趨勢(shì)，粉粒稍有增加。坡面S1的黏粒、粉粒和砂粒的平均質(zhì)量分?jǐn)?shù)分別為14.1%、52.0%和33.9%，而坡面S2的分別為10.7%、51.9%和37.4%。坡面S1的平均坡度為12.3°，坡面S2的為14.7°。

圖3　土壤顆粒組成沿坡面變化Fig.3　Changes of soil particle composition along the hillslopes

圖4　鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)沿坡面的變化Fig.4　Changes of caliche nodule content along the hillslopes

坡面S1和S2表土中，鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)沿坡面的變化見(jiàn)圖4。2個(gè)坡面的鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)都是在沿坡頂向下的方向上先增加，在距離坡頂20～30 m(坡面1/4～1/3的位置)左右的地方，鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)達(dá)到最大；然后，又沿著坡面逐漸降低。坡面鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)呈單峰曲線(xiàn)分布，坡面礫石質(zhì)量分?jǐn)?shù)最大在15%左右。坡面S1和S2的平均鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)分別為4.6%和6.9%。對(duì)比2個(gè)坡面的剖面圖和坡度變化圖(圖1b和圖2)可知，2個(gè)坡面在距離坡頂約20～30 m的位置坡度最大(分別為19°、20 m和19°、30 m)；因而，此處的侵蝕也最強(qiáng)，土壤流失會(huì)更多，導(dǎo)致鈣質(zhì)結(jié)核在此處聚集。

3.2不同尺寸的鈣質(zhì)結(jié)核在坡面的分布

試驗(yàn)對(duì)6個(gè)尺寸范圍(2～5，5～10，10～15，15～20，20～25和>25 mm)的鈣質(zhì)結(jié)核數(shù)量在坡面的分布，進(jìn)行了分析(圖5)。在2～15 mm之間，鈣質(zhì)結(jié)核的數(shù)量占到2個(gè)坡面鈣質(zhì)結(jié)核總數(shù)量的80%以上。直徑15 mm的鈣質(zhì)結(jié)核，除了在S1坡面25 m處和S2坡面10和30 m處的數(shù)量占到10%以上外，在2個(gè)坡面的其他位置均很少出現(xiàn)。不同尺寸的鈣質(zhì)結(jié)核在坡面不同位置的數(shù)量變化，反映了徑流對(duì)鈣質(zhì)結(jié)核尺寸的分選作用，小尺寸的鈣質(zhì)結(jié)核更容易受到徑流的影響，而在坡面廣泛分布。

3.3鈣質(zhì)結(jié)核分布與坡度和植被的關(guān)系

對(duì)坡面S1和S2上鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)和坡度二者關(guān)系的分析表明，隨著坡度的增加，鈣質(zhì)結(jié)核的蓋度也是逐漸增加的，二者存在很好的線(xiàn)性正相關(guān)關(guān)系(圖6)。當(dāng)坡度增大時(shí)，土壤侵蝕會(huì)更加劇烈，更多土壤顆粒被徑流帶走，使得鈣質(zhì)結(jié)核大量出現(xiàn)在表土而發(fā)生聚集，造成鈣質(zhì)結(jié)核的質(zhì)量分?jǐn)?shù)增加。

圖5　不同粒徑范圍鈣結(jié)核數(shù)量比例Fig.5　Numerical percentages of caliche nodules at different ranges of particle size

圖6　鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)與坡度的關(guān)系Fig.6　Relationship between caliche nodule content and slope gradient

植被在消減徑流動(dòng)能的同時(shí)，還具有攔截作用；因此，試驗(yàn)對(duì)植被地上生物量和蓋度進(jìn)行了測(cè)定，以分析鈣質(zhì)結(jié)核與植被之間的關(guān)系。坡面S1和S2的建群植物均為針茅，植被蓋度和地上生物量在沿坡頂向下的方向上逐漸增加。其中：植被蓋度變化范圍為7%～90%；植被的豐富度和多樣性指數(shù)在S1坡面分別為5±2.373 8、1.301 6±0.312 8，S2坡面分別為5.269 2±2.215 5、1.39±0.584，其沿坡面沒(méi)有明顯的變化趨勢(shì)，說(shuō)明坡面植被蓋度增大，主要是由于地上生物量的增加而導(dǎo)致的。鈣質(zhì)結(jié)核和植物地上生物量的關(guān)系與鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)沿坡面的變化一樣，呈單峰曲線(xiàn)關(guān)系(圖7)。當(dāng)植被地上生物量在22 g左右，也就是蓋度在11%～16%之間時(shí)，鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)達(dá)到最大。

圖7　鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)與植被地上生物量的關(guān)系Fig.7　Relationship between caliche nodule content and vegetation above-ground biomass

3.4影響鈣質(zhì)結(jié)核分布的因素

試驗(yàn)計(jì)算了與鈣質(zhì)結(jié)核在坡面分布有關(guān)的7個(gè)因素(植被地上生物量、黏粒、粉粒、砂粒、植被蓋度、豐富度和多樣性指數(shù))之間的相關(guān)關(guān)系(表1)。從相關(guān)矩陣可以看出，坡度、植被蓋度、地上生物量、豐富度和多樣性指數(shù)顯著影響坡面鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)，土壤顆粒組成與鈣質(zhì)結(jié)核無(wú)顯著相關(guān)性。也就是說(shuō)，在坡面尺度上，植被(包括地上生物量、蓋度和結(jié)構(gòu))和坡度是影響坡面鈣質(zhì)結(jié)核分布的最主要因素。其中，坡度、豐富度和多樣性指數(shù)與鈣質(zhì)結(jié)核之間存在極顯著的正相關(guān)(P<0.01，R2>0.5)，植被蓋度與鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)之間存在極顯著的負(fù)相關(guān)關(guān)系(P<0.01，R2>0.5)，植被地上生物量與鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)之間存在顯著的負(fù)相關(guān)關(guān)系(P<0.05，R2>0.4)。

試驗(yàn)還分析了不同尺寸鈣質(zhì)結(jié)核影響坡面鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)的程度，也就是坡面上決定鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)的主要鈣質(zhì)結(jié)核尺寸范圍。利用因子分析，計(jì)算坡面總的鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)(Crock)與6個(gè)尺寸(2～5 mm(MR1)，5～10 mm(MR2)，10～15 mm(MR3)，15～20 mm(MR4)，20～25 mm(MR5)和>25 mm(MR6))的鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)的相關(guān)性，并給出主成分荷載圖(圖8)。2個(gè)坡面上，在5～10 mm(MR2)和10～15 m(MR3)2個(gè)尺寸范圍，鈣質(zhì)結(jié)核與坡面總的鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)的相關(guān)性最高(也就是MR2和MR3最靠近Crock)，相關(guān)性達(dá)到極顯著水平(P<0.01)，決定系數(shù)R2均>0.7。這表明在坡面上，5～15 mm是坡面鈣質(zhì)結(jié)核的最主要組分，其多少?zèng)Q定了坡面鈣質(zhì)結(jié)核的質(zhì)量分?jǐn)?shù)。

表1　鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)與影響因子之間的相關(guān)矩陣

注：*—顯著相關(guān)(P<0.05)，**—極顯著相關(guān)(P<0.01)。Note:* refers to significant correlation (P<0.05) and ** refers to extremely significant correlation (P<0.01).VC:vegetation coverage; AD:abundance; DI:diversity index; CNC:caliche nodule content.

Crock represents the total caliche nodule contents on slope.MR1,MR2,MR3,MR4,MR5 and MR6 represent particle size range of caliche nodule,which are 2-5,5-10,10-15,15-20,20-25 mm respecively.圖8　總鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)與不同粒徑鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)的關(guān)系Fig.8　Relationship between total caliche nodule content and the caliche nodule content in different size

4　討論

2個(gè)坡面的土壤黏粒質(zhì)量分?jǐn)?shù)在沿坡頂向下的方向上，均有降低的趨勢(shì)(圖3)。其原因在于黏粒最容易被徑流帶走，而且沿著坡面向下的方向，徑流會(huì)越來(lái)越強(qiáng)，其攜帶能力逐漸增強(qiáng)，更多的黏粒會(huì)被帶走，導(dǎo)致黏粒質(zhì)量分?jǐn)?shù)沿坡面逐漸降低。由于黏粒最容易受到侵蝕的影響，因此，坡面黏粒的平均質(zhì)量分?jǐn)?shù)可以反映坡面的侵蝕狀況。坡面S1的土壤黏粒平均質(zhì)量分?jǐn)?shù)高于坡面S2，表明S2受到的土壤侵蝕要強(qiáng)于S1；而強(qiáng)烈的土壤侵蝕又會(huì)使得坡面變得更陡，導(dǎo)致坡面S2的平均坡度大于S1。侵蝕帶走土壤顆粒，使得鈣質(zhì)結(jié)核露出地表并聚集。顯然侵蝕越劇烈，表土鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)就會(huì)增加。

綜上所述，坡面S2的侵蝕強(qiáng)于坡面S1，那么坡面S2的鈣質(zhì)結(jié)核平均質(zhì)量分?jǐn)?shù)也應(yīng)高于S1。實(shí)際測(cè)定結(jié)果為坡面S2的鈣質(zhì)結(jié)核平均質(zhì)量分?jǐn)?shù)為6.9%，高于坡面S1的4.6%；因此，鈣質(zhì)結(jié)核可以指示坡面土壤侵蝕的強(qiáng)弱，這與礫石可以指示冰川剝蝕和沉積作用類(lèi)似(Poesen 和 Lavee ,1994)。此外，鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)與坡度呈正相關(guān)關(guān)系，這與J.R.Simanton等[29]、Zhu Yuanjun等[27]結(jié)果一致。試驗(yàn)中鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)與植被存在單峰曲線(xiàn)關(guān)系(圖4)，表明植被對(duì)侵蝕的影響存在一個(gè)臨界點(diǎn)(在11%～16%之間)。臨界點(diǎn)之下，由于植被蓋度小，對(duì)侵蝕的影響很小，侵蝕能夠同時(shí)帶走坡面的土壤顆粒和鈣質(zhì)結(jié)核；超過(guò)臨界點(diǎn)，植被能通過(guò)降低徑流動(dòng)能和攔截作用，顯著影響侵蝕，使得徑流攜帶土壤顆粒和鈣質(zhì)結(jié)核的作用顯著降低，其降低程度與植被地上生物量(蓋度)呈正相關(guān)。

試驗(yàn)還發(fā)現(xiàn)，鈣質(zhì)結(jié)核尺寸越小，其在坡面的數(shù)量越多，這與J.W.Poesen等[22]、Zhu Yuanjun等[27]的研究結(jié)果一致。可見(jiàn)侵蝕對(duì)鈣質(zhì)結(jié)核的影響存在尺寸效應(yīng)，也就是說(shuō)小的鈣質(zhì)結(jié)核更容易受到影響。通過(guò)對(duì)影響坡面鈣質(zhì)結(jié)核的主要因素進(jìn)行相關(guān)分析，進(jìn)一步揭示坡度和植被是影響坡面鈣質(zhì)結(jié)核分布的最主要因素；同時(shí)，草地植被影響侵蝕的作用，與植被的豐富度和多樣性指數(shù)呈負(fù)相關(guān)，也就是說(shuō)，單一植被和大的生物量(蓋度)更有效。試驗(yàn)還利用主成分分析，確定坡面鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)的鈣質(zhì)結(jié)核尺寸，發(fā)現(xiàn)坡面上5～15 mm的鈣質(zhì)結(jié)核是坡面鈣質(zhì)結(jié)核的最主要組分，決定著坡面鈣質(zhì)結(jié)核的質(zhì)量分?jǐn)?shù)。這一結(jié)果也印證了前述中對(duì)坡面不同尺寸鈣質(zhì)結(jié)核數(shù)量的研究結(jié)果，即尺寸小的鈣質(zhì)結(jié)核容易受到侵蝕的影響，在坡面的分布就越多，大尺寸的鈣質(zhì)結(jié)核不容易受到影響，相對(duì)就少。

5　結(jié)論

通過(guò)對(duì)黃土高原水蝕風(fēng)蝕交錯(cuò)帶六道溝小流域坡面鈣質(zhì)結(jié)核的分布特征，以及影響因素的分析，得出以下結(jié)論：

1)坡面土壤黏粒和鈣質(zhì)結(jié)核的平均質(zhì)量分?jǐn)?shù)，可以用于指示坡面的土壤侵蝕狀況，低的黏粒質(zhì)量分?jǐn)?shù)和高的鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)指示著更為強(qiáng)烈的土壤侵蝕。

2)坡面鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)沿坡面呈單峰曲線(xiàn)分布，鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)與坡度呈線(xiàn)性正相關(guān)。鈣質(zhì)結(jié)核與植被地上生物量(蓋度)呈單峰曲線(xiàn)關(guān)系，植被對(duì)鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)的影響存在一個(gè)臨界點(diǎn)。

3)坡面小尺寸的鈣質(zhì)結(jié)核分布范圍最廣、數(shù)量最多。決定坡面鈣質(zhì)結(jié)核質(zhì)量分?jǐn)?shù)的鈣質(zhì)結(jié)核尺寸為5～15 mm。

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Spatial pattern of caliche nodule in surface soil of the hillslopes in Liudaogou catchment in the wind-water erosion crisscross zone of the Loess Plateau

Gong Tiexiong1,2,Zhu Yuanjun1,2,3

(1.Institute of Soil and Water Conservation,Chinese Academy of Sciences and Ministry of Water Resources,712100,Yangling,Shaanxi，China;2.University of Chinese Academy of Science,100049,Beijing,China;3.State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau,Northwest A&F University,712100,Yangling,Shaanxi,China)

[Background] Loess soil is rich of calcium carbonate.With climate alternations of wetting and drying in soil genesis process,the calcium carbonate happens leaching and deposition and forms caliche in soil layer.This caliche rises to ground surface due to intensive soil erosion and human activity in the wind-water erosion crisscross region of the Loess Plateau and then it breaks down to pieces by outside forces to form caliche nodules.Quantifying the distribution pattern of caliche nodule on hillslopes can improve the understanding of soil-water process in special soil type (soil containing caliche nodules) in this region.[Methods] This study aimed to investigate the spatial pattern of caliche nodule on hillslopes,its influencing factors and their interactions through taking soil and plant samples and analyzing surface soil (0-20 cm) particle compositions,caliche nodule mass fraction,vegetation above-ground biomasses,coverage,abundances and diversity indexes in the different positions of the hillslopes.The soil samples were firstly through 2 mm sieve to separate caliche nodules from fine soil.The caliche nodules were then cleaned,dried,and weighed.Finally they were classified by sieves of 5,10,15,20 and 25 mm,respectively.Soil particle composition was measured by MS2000 laser granulometer.[Results] The results indicated that soil clay particle decreased gradually along the hillslopes.Caliche nodule content had a distribution pattern of single peak along the hillslopes and it achieved peak value (10%-15%) at the position of 1/4-1/3 hillslopes (about 20-30 m distance from the top of the hillslopes).Caliche nodule content was positively correlated with slope gradient.It had single peak curve relationship with vegetation above-ground biomass.This peak value was the threshold point of vegetation affecting caliche nodule content and the vegetation coverage at the threshold point was among 11%-16%.Slope gradient and vegetation were two most important factors to control caliche nodule distribution on the hillslopes.Small size caliche nodules spread more widely on the hillslopes and meanwhile their numbers were the most.The dominant size of caliche nodule was 5-15 mm.[Conclusions] Caliche nodule content and pattern on the hillslopes reflected the interactions between runoff,vegetation and caliche nodule.Runoff tended to take caliche nodules from higher position to lower position and its carrying force was positively related to slope gradient.Vegetation can reduce the carrying force of runoff and at the same time can intercept caliche nodule.All of these led to caliche nodule content positively related to slope gradient,and on the other hand it showed a single peak pattern along the slopes.Caliche nodule content could be used as a slope erosion indicator.

wind-water erosion crisscross zone of the Loess Plateau; caliche nodule; soil erosion; slope gradient; vegetation

2016-02-29

2016-04-14

項(xiàng)目名稱(chēng)：國(guó)家自然科學(xué)基金“黃土區(qū)水蝕風(fēng)蝕交錯(cuò)帶礫石對(duì)坡面土壤水循環(huán)的影響及機(jī)制”(41371242)；中國(guó)科學(xué)院重點(diǎn)部署項(xiàng)目“黃土高原生態(tài)服務(wù)功能提升與果園水肥協(xié)同技術(shù)集成與示范”(KFZD-SW-306)

鞏鐵雄(1991—)，男，碩士研究生。主要研究方向：土壤水分運(yùn)動(dòng)。E-mail：gongtiexiong@126.com

簡(jiǎn)介：朱元駿(1978—)，男，博士，副研究員。主要研究方向：土壤水循環(huán)及坡面水土過(guò)程。E-mail：zhuyuanjun@foxmail.com

K903； S157.1

A

1672-3007(2016)04-0042-08

10.16843/j.sswc.2016.04.006