閆金龍,吳文麗,江 韜,魏世強(qiáng)

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土壤組分對(duì)磷形態(tài)和磷吸附-解吸的影響——基于三峽庫(kù)區(qū)消落帶落干期土壤

閆金龍1,2*,吳文麗1,江 韜2,魏世強(qiáng)2

(1.重慶理工大學(xué)藥學(xué)與生物工程學(xué)院,重慶 400054；2.西南大學(xué)資源環(huán)境學(xué)院,重慶 4000716)

通過(guò)選擇性去除土壤組分的方法,探討了三峽庫(kù)區(qū)消落帶落干期3種典型土壤中有機(jī)質(zhì)、鐵氧化物組分對(duì)磷形態(tài)和磷吸附-解吸的影響.結(jié)果發(fā)現(xiàn),三峽庫(kù)區(qū)消落帶落干期3種典型土壤去除的有機(jī)質(zhì)以易氧化組分為主,去除有機(jī)質(zhì)后,土壤中各種磷形態(tài)的含量變化較小.然而,去除游離鐵氧化物后,土壤中各種磷形態(tài)的含量均發(fā)生明顯降低.同時(shí),去除有機(jī)質(zhì)、游離鐵氧化物組分后并未改變土壤中各種磷形態(tài)的相對(duì)大小順序,均為:鈣結(jié)合磷(Ca-P)>有機(jī)磷(OP)>鐵/鋁結(jié)合磷(Fe/Al-P).此外,黃壤(FJ)、紫色潮土(KX)和灰棕紫泥(FL)去除有機(jī)質(zhì)后對(duì)磷的吸附能力較原始土壤僅分別降低0.5%、2.3%、6.5%(=0.017<0.05,顯著性差異),表明3種土壤中有機(jī)質(zhì)組分對(duì)磷吸附的影響較小;而去除游離鐵氧化物后對(duì)磷的吸附能力分別降低45.6%、51.7%、43.9%(=0.004<0.05,顯著性差異),表明土壤中游離鐵氧化物組分是決定磷吸附大小的重要因素.另外,3種土壤去除游離鐵氧化物后較原始土壤吸附磷的解吸能力明顯增加,表明游離鐵氧化物組分是控制3種土壤吸附磷的解吸的重要因素.FL土壤去除有機(jī)質(zhì)組分后較原始土壤吸附磷的解吸能力略有降低,而KX和FJ土壤去除有機(jī)質(zhì)組分后較原始土壤吸附磷的解吸能力無(wú)明顯差異,表明有機(jī)質(zhì)組分對(duì)土壤吸附磷的解吸的影響與土壤類型有關(guān).

三峽庫(kù)區(qū)消落帶；落干期土壤；磷；有機(jī)質(zhì)；鐵氧化物

三峽庫(kù)區(qū)消落帶作為典型的陸地和水體過(guò)渡地帶,是陸地和水體物質(zhì)和能量的重要交換通道、生態(tài)敏感區(qū),其健康和穩(wěn)定程度直接影響著三峽庫(kù)區(qū)的生態(tài)安全.水體富營(yíng)養(yǎng)化已經(jīng)成為庫(kù)區(qū)核心的生態(tài)環(huán)境問(wèn)題,而磷作為限制性營(yíng)養(yǎng)元素是控制水體富營(yíng)養(yǎng)形成的關(guān)鍵因素,消落帶土壤同時(shí)扮演著磷“匯”和“源”的雙重角色,影響著庫(kù)區(qū)水體環(huán)境安全[1].因此,深入研究三峽庫(kù)區(qū)消落帶土壤磷形態(tài)變化及其吸附解吸行為十分重要.

鐵氧化物作為土壤中的重要組成組分,具有可變電荷表面,有較大的比表面積,有較高的活性,是決定土壤物理化學(xué)性質(zhì)的重要因素,同時(shí)對(duì)土壤中磷素的遷移和轉(zhuǎn)化、固定發(fā)揮著重要作用[2-3], Zhang等[4]研究發(fā)現(xiàn),土壤對(duì)磷的吸附量與無(wú)定形鐵氧化物、結(jié)晶態(tài)鐵氧化物含量之間呈線性關(guān)系.此外,三峽庫(kù)區(qū)消落帶因水位漲落將周期性的經(jīng)歷落干和淹水過(guò)程,消落帶土壤中變價(jià)金屬氧化物如鐵氧化物等隨之將周期性經(jīng)歷氧化和還原過(guò)程[5].因此,一些學(xué)者通過(guò)室內(nèi)模擬淹水-落干過(guò)程或野外監(jiān)測(cè)等手段分析了鐵氧化物在周期性氧化還原過(guò)程中的形態(tài)變化及其對(duì)磷形態(tài)的影響[6-7].上述實(shí)驗(yàn)手段能很好地反應(yīng)消落帶土壤鐵氧化物與磷形態(tài)的關(guān)系,但有關(guān)鐵氧化物與磷形態(tài)的關(guān)系研究結(jié)果也多建立在相關(guān)性分析上,未直接給出土壤中鐵氧化物對(duì)磷形態(tài)和磷吸附-解吸的影響.另一方面,有機(jī)質(zhì)作為土壤中的重要組成成分,其對(duì)土壤中磷素的地球化學(xué)行為也有著重要影響,目前研究多著眼于有機(jī)質(zhì)與磷酸鹽在鐵氧化物表面的競(jìng)爭(zhēng)吸附,但也存在一些爭(zhēng)議.Borggaard等[8]發(fā)現(xiàn)腐殖酸(HA)或富里酸(FA)與磷酸鹽共存時(shí)對(duì)針鐵礦、水鐵礦吸附磷的影響很小.然而,Antelo等[9]發(fā)現(xiàn)土壤腐殖酸存在下,針鐵礦對(duì)磷酸鹽的吸附減少45%.針對(duì)三峽庫(kù)區(qū)消落帶,僅有部分研究發(fā)現(xiàn)土壤的部分磷形態(tài)與有機(jī)質(zhì)存在顯著相關(guān)關(guān)系[7,10],未對(duì)三峽庫(kù)區(qū)消落帶土壤中有機(jī)質(zhì)如何影響磷的環(huán)境化學(xué)行為做進(jìn)一步研究.

基于以上,本研究選擇三峽庫(kù)區(qū)消落帶土壤作為研究對(duì)象,以目前國(guó)內(nèi)外較常用的選擇性去除土壤組分的方法[11-12],分別去除土壤中有機(jī)質(zhì)、鐵氧化物組分,以期探討土壤有機(jī)質(zhì)、鐵氧化物組分對(duì)磷形態(tài)和磷吸附-解吸的直接影響.

1 材料與方法

1.1 土壤樣品和預(yù)處理

在三峽庫(kù)區(qū)重慶境內(nèi)奉節(jié)(109°24′25″E, 31°01′08″N)、開(kāi)縣(108°27′21″E,31°11′26″N)和涪陵(107°31′37″E,29°51′30″N)消落帶分別采集落干期原始表層土壤(0~10cm)樣品(先去除表層沉積物后再采集原始土壤),3種土壤分別為黃壤(FJ)、紫色潮土(KX)和灰棕紫泥(FL).紫色土和黃壤分別是三峽庫(kù)區(qū)第一和第二大類土壤[13].土壤樣品運(yùn)回實(shí)驗(yàn)室后自然風(fēng)干,過(guò)60目篩后室溫保存.

有機(jī)質(zhì)去除的處理:土壤去除有機(jī)質(zhì)的方法參照文獻(xiàn)[14].具體步驟如下:稱取10g土壤于100mL離心管中,加入30mL,pH=8.5的6%次氯酸鈉(NaClO),于25℃下振蕩16h,后在4000r/min下離心10min,去除上清液,重復(fù)上述操作3次,后用去離子水洗3次,得到去除有機(jī)質(zhì)的土壤,冷凍干燥后過(guò)60目篩,室溫下儲(chǔ)存待進(jìn)一步分析.

游離鐵氧化物去除的處理:土壤游離鐵氧化物的去除采用連二亞硫酸鈉-檸檬酸鈉-碳酸氫鈉法(DCB法)[15].具體步驟如下:稱取1g土壤于100mL離心管中,加入20mL 0.3mol/L的檸檬酸鈉和2.5mL 1mol/L的碳酸氫鈉,置于85℃的恒溫水浴鍋中,后加入0.5g連二亞硫酸鈉并持續(xù)攪拌15min后取出,于4000r/min下離心10min,棄去上清液,重復(fù)上述操作2次,后用1mol/L的氯化鈉溶液洗2次,得到去除游離鐵氧化物的土壤,冷凍干燥后過(guò)60目篩,室溫下儲(chǔ)存待進(jìn)一步分析.

1.2 土壤磷形態(tài)測(cè)定

基于歐共體提出的SMT磷形態(tài)分級(jí)方法[16],原始土壤和去除不同組分的土壤均測(cè)定了磷的形態(tài).SMT方法中,土壤磷形態(tài)被分成以下5個(gè)組分:總磷(TP),土壤樣品在450℃的馬弗爐中灼燒3h后,采用3.5mol/L的HCl在25℃下振蕩16h提取得到;無(wú)機(jī)磷(IP),土壤樣品直接采用1.0mol/L的HCl在25 ℃下振蕩16h提取得到;有機(jī)磷(OP),土壤提取無(wú)機(jī)磷后的殘?jiān)萌ルx子水洗2次后,烘干并在450℃的馬弗爐中灼燒3h,后用1.0mol/L的HCl在25℃下振蕩16h提取得到;鐵/鋁結(jié)合磷(Fe/Al-P),土壤樣品直接采用1.0mol/L的NaOH在25℃下振蕩16h提取得到;鈣結(jié)合磷(Ca-P),土壤提取Fe/Al-P后的殘?jiān)萌ルx子水洗2次后,用1.0mol/L的NaOH在25 ℃下振蕩16h提取得到.

1.3 土壤對(duì)磷的吸附-解吸

稱取0.5g土壤原樣和去除不同組分的土壤樣品分別置于100mL離心管中,加入25mL濃度為1,2,5,10,15,20,25mg/L的KH2PO4溶液(以P計(jì)),控制體系pH=7±0.1,=0.01mol/L KNO3.轉(zhuǎn)數(shù)220r/min下,25℃恒溫振蕩24h,過(guò)0.45 μm濾膜后,測(cè)定濾液中磷含量.土壤殘?jiān)Ａ舸馕鼘?shí)驗(yàn)使用.解吸劑為pH=7±0.1,=0.01mol/L KNO3溶液25mL,解吸步驟同吸附過(guò)程.所有處理均設(shè)置3個(gè)平行和空白處理.

1.4 化學(xué)分析和數(shù)據(jù)處理

本研究中,所有化學(xué)試劑均為分析純.土壤原樣和去除不同組分的土壤樣品均分析以下基本性質(zhì):pH值,采用PB-10型pH計(jì)(Sartorius, 德國(guó))設(shè)置土水比為1:2.5進(jìn)行測(cè)定;BET比表面積測(cè)試采用美國(guó)麥克ASAP 2020V4.00N2吸附測(cè)定;有機(jī)質(zhì),采用重鉻酸鉀氧化法測(cè)定[17];鐵全量(TFe)和游離態(tài)鐵氧化物含量(Fed)參照張甘霖等的提取方法[18],采用原子吸收光譜法(北京普析通用TAS-990,中國(guó))測(cè)定;磷含量,土壤磷形態(tài)測(cè)定參照鮑士旦的測(cè)定方法[17],吸附解吸實(shí)驗(yàn)磷含量測(cè)定參照文獻(xiàn)[19]的測(cè)定方法.實(shí)驗(yàn)結(jié)果數(shù)據(jù)均為平均值,相關(guān)數(shù)據(jù)處理采用Orgin 8.5和Microsoft Office 2013、SPSS 17進(jìn)行.

2 結(jié)果與討論

2.1 土壤去除不同組分前后的基本性質(zhì)

如表1所示,3種供試土壤處理前均為弱堿性,處理后的土壤樣品均用去離子水洗滌數(shù)次,以降低化學(xué)試劑對(duì)土壤pH值的影響,3種土壤去除游離鐵氧化物和有機(jī)質(zhì)后,供試土壤的pH值均增加.FJ,KX和FL土壤采用NaClO去除有機(jī)質(zhì)的效率分別達(dá)到66.8%、61.5%和67.5%,同時(shí)對(duì)土壤樣品中TFe和Fed損失較小,這與文獻(xiàn)報(bào)道[14]結(jié)果一致.另一方面,FJ,KX和FL土壤采用DCB法去除Fed的效率分別達(dá)到93.9%、91.9%和87.2%,且TFe分別去除43.9%、43.8%和43.4%.結(jié)果表明,3種土壤中游離鐵氧化物是土壤中鐵的主要成分.此外,土壤比表面積作為一個(gè)重要的基本指標(biāo),能反應(yīng)土壤吸附能力的大小,鐵氧化物是土壤中比表面積的重要貢獻(xiàn)組分[20].當(dāng)游離鐵氧化物去除后,FJ,KX和FL土壤的比表面積分別降低39.6%、40.9%和35.1%.FJ,KX和FL土壤去除有機(jī)質(zhì)后,比表面積分別降低15.2%、19.5%和23.7%,去除有機(jī)質(zhì)的過(guò)程中伴隨著部分鐵氧化物的去除,這可能是造成土壤比表面積降低的原因.

表1 供試土壤去除不同組分前后的基本性質(zhì)Table 1 Basic characteristics of the soils with and without different treatments

注:T1代表未作任何處理的土壤樣品,T2代表去除游離鐵氧化物的土壤樣品,T3代表去除有機(jī)質(zhì)的土壤樣品;* 處理過(guò)(+)和沒(méi)有處理過(guò) (-);# 采用連二亞硫酸鈉-檸檬酸鈉-碳酸氫鈉處理;ζ 有機(jī)質(zhì);€ 比表面積;& 游離鐵氧化物采用DCB提取;數(shù)據(jù)為3個(gè)平行處理的均值±標(biāo)準(zhǔn)偏差.

2.2 土壤去除不同組分前后的磷形態(tài)

由表2可知,土壤不同磷形態(tài)的質(zhì)量回收率較高,與文獻(xiàn)報(bào)道結(jié)果相似[21],表明本研究采用SMT法提取土壤各種磷形態(tài)是可行的.由圖1和表2可知,供試土壤去除不同組分前后,IP均為土壤中TP的主要成分,3種土壤原樣IP占TP的比例為53.0%~65.2%.去除有機(jī)質(zhì)后,3種土壤IP占TP的比例為52.8%~64.5%,而去除游離鐵氧化物后,3種土壤IP占TP的比例為52.4%~61.9%.其中,Ca-P又是IP的主要組成部分,3種土壤原樣Ca-P占IP的比例為58.4%~74.5%.去除有機(jī)質(zhì)后,3種土壤Ca-P占IP的比例為56.3%~76.1%,而去除游離鐵氧化物后,3種土壤Ca-P占IP的比例為74.2%~82.4%.土壤去除不同組分前后磷形態(tài)分布的相對(duì)大小順序均為:Ca-P>OP>Fe/Al-P,這與以往研究三峽庫(kù)區(qū)消落帶土壤中磷形態(tài)分布的結(jié)果一致[22].本研究中土壤磷形態(tài)分布大小與土壤類型無(wú)關(guān),但3種土壤中不同磷形態(tài)的絕對(duì)含量有差異,不同磷形態(tài)均表現(xiàn)出FJ土壤值最大,其次是KX土壤,最小的是FL土壤.此外,去除有機(jī)質(zhì)組分后,3種土壤中不同磷形態(tài)含量均略微減少,除FL-T3土壤中OP減少11.7%,其余土壤中各形態(tài)磷減少量均低于10.0%.然而,當(dāng)去除游離鐵氧化后,3種土壤中Fe/Al-P含量均降低約75.0%,其余各形態(tài)磷含量也有不同程度的降低,可知,鐵氧化物在土壤中對(duì)其他組分能起到一個(gè)基質(zhì)作用,因此去除游離鐵氧化物后,土壤中各種磷形態(tài)含量均有不同程度降低.報(bào)道稱,SMT方法中Fe/Al-P和OP被稱為生物可利用磷(BAP)[13].當(dāng)供試土壤去除有機(jī)質(zhì)后,FJ、KX和FL土壤的BAP含量?jī)H分別降低6.6%、8.3%、10.0%,而當(dāng)去除游離鐵氧化物后,FJ、KX和FL土壤的BAP含量分別降低36.4%、41.1%、60.0%.綜上可知,游離鐵氧化物是影響三峽庫(kù)區(qū)消落帶土壤中磷形態(tài)變化的重要因素,而有機(jī)質(zhì)的作用較小.

表2 供試土壤去除不同組分前后磷形態(tài)去除率,所占比例以及質(zhì)量回收率(%) Table 2 Recovery of phosphorus fractions and ratio of different phosphorus fractions, removal rate of different phosphorus fractions in the soils with and without treatment(%)

圖1 土壤去除不同組分前后的磷形態(tài)分布(SMT法提取) Fig.1 Phosphorus fractions extracted by the SMT method in the soils with and without different treatments

2.3 土壤去除不同組分前后對(duì)磷的吸附

由圖2可知,實(shí)驗(yàn)濃度范圍內(nèi),3種土壤去除不同組分前后對(duì)磷的吸附量均隨著初始磷濃度的增加而增加,未出現(xiàn)明顯的吸附平衡.與原始土壤對(duì)磷的吸附量相比,3種土壤去除游離鐵氧化物后對(duì)磷的吸附量明顯降低,其降低程度遠(yuǎn)大于土壤去除有機(jī)質(zhì)組分對(duì)磷的吸附量.為進(jìn)一步分析吸附結(jié)果,發(fā)現(xiàn)Freundlich等溫方程能較好的擬合吸附數(shù)據(jù)(2>0.982),方程如下:

e=′e1/n(1)

式中:e表示磷吸附量,mg/g;e表示吸附液中磷濃度,mg/L;表示Freundlich吸附系數(shù),反應(yīng)吸附能力和吸附親和力的大小,值越大表示吸附能力越強(qiáng);為常數(shù),與吸附劑表面均一性有關(guān).Freundlich方程擬合參數(shù)如表3所示.結(jié)果發(fā)現(xiàn),與原始土壤吸附能力相比(基于值比較),FJ、KX、FL土壤去除游離鐵氧化物后對(duì)磷的吸附能力分別降低67.2%、71.5%、63.6%,一些學(xué)者也發(fā)現(xiàn)相似的研究結(jié)果,土壤中鐵、鋁氧化物增加有利于土壤對(duì)磷的吸附[23].然而,FJ、KX、FL土壤去除有機(jī)質(zhì)后對(duì)磷的吸附能力較原始土壤僅分別降低15.6%、21.3%、28.6%.由于土壤有機(jī)質(zhì)的去除過(guò)程伴隨著部分鐵氧化物的損失,導(dǎo)致土壤比表面積降低,因此,對(duì)值進(jìn)行比表面積歸一化后得到SSA,通過(guò)SPSS對(duì)SSA配對(duì)兩樣本檢驗(yàn)得到,3種土壤去除有機(jī)質(zhì)或游離鐵氧化物后,值分別為0.017和0.004,均小于0.05,表明處理前后的土壤達(dá)到顯著性差異.FJ、KX、FL土壤去除有機(jī)質(zhì)后對(duì)磷的吸附能力(基于SSA值比較)較原始土壤僅分別降低0.5%、2.3%、6.5%,可知,消落帶3種土壤去除有機(jī)質(zhì)后造成的磷吸附差異主要是由于土壤比表面積的改變?cè)斐?其中有機(jī)質(zhì)所起作用較小,這和一些文獻(xiàn)報(bào)道結(jié)果相似,有機(jī)質(zhì)對(duì)土壤吸附磷的能力沒(méi)有影響或僅起到間接的作用[24-25],甚至有報(bào)道稱有機(jī)質(zhì)對(duì)金屬氧化物吸附磷沒(méi)有影響[8].然而,FJ、KX、FL土壤去除游離鐵氧化物后對(duì)磷的吸附能力(基于SSA值比較)較原始土壤仍分別降低45.6%、51.7%、43.9%,說(shuō)明游離鐵氧化物在消落帶3種土壤中對(duì)磷的吸附發(fā)揮著重要作用.

同時(shí),1/越接近于0,說(shuō)明吸附劑表面異質(zhì)性越強(qiáng),且1/值在0.1~0.5之間表明吸附劑有較強(qiáng)的吸附能力[26].由表3可知,Freundlich方程對(duì)三峽庫(kù)區(qū)消落帶3種土壤去除不同組分前后吸附磷數(shù)據(jù)擬合得到的1/值大小順序均為:原始土壤<去除有機(jī)質(zhì)土壤<去除游離鐵氧化物土壤,結(jié)果同樣表明原始土壤表面異質(zhì)性更強(qiáng),較去除不同組分的土壤有更強(qiáng)的磷吸附能力.此外,反應(yīng)吸附能力大小的值與供試土壤基本性質(zhì)的相關(guān)性結(jié)果也進(jìn)一步說(shuō)明上述結(jié)果(圖3).值與TFe、SSA呈顯著正相關(guān)關(guān)系,與Fed呈極顯著正相關(guān)關(guān)系,但與有機(jī)質(zhì)未發(fā)現(xiàn)有顯著的相關(guān)關(guān)系.綜上可知,三峽庫(kù)區(qū)消落帶3種土壤中有機(jī)質(zhì)組分對(duì)磷吸附的影響較小,而土壤中游離鐵氧化物組分是決定磷吸附大小的重要因素.

表3 Freundlich模型擬合參數(shù) Table 3 Fitting parameters of Freundlich model

注:SSA=/SSA.

圖3 Freundlich方程k值與土壤基本性質(zhì)的相關(guān)性風(fēng)玫瑰 Fig.3 Wind-rose diagrams of the correlations between k of Freundlich model and different soil constituents

2.4 土壤去除不同組分前后對(duì)磷的解吸

土壤磷解吸過(guò)程是磷吸附的逆過(guò)程,決定磷在土壤中的生物有效性,因此磷解吸過(guò)程較吸附過(guò)程更為重要[27-28].三峽庫(kù)區(qū)消落帶3種土壤去除不同組分前后的磷解吸過(guò)程如圖4所示,所有供試土壤吸附的磷均出現(xiàn)部分解吸,且磷解吸量均隨吸附量的增加而增加,與文獻(xiàn)報(bào)道的其他研究區(qū)域結(jié)果一致[29-30].表4顯示所有供試土壤的磷解吸量和磷吸附量均存在極顯著的正相關(guān)關(guān)系(> 0.988,<0.01).同時(shí)發(fā)現(xiàn)線性方程能較好地對(duì)磷解吸量和磷吸附量數(shù)據(jù)進(jìn)行擬合(2>0.977)(圖4,表5),線性方程如下:

=′+(2)

式中:為磷解吸量,mg;為磷吸附量,mg;為斜率,反映解吸能力的大小,其值越大表示解吸能力越強(qiáng);為截距,反應(yīng)土壤本底釋放磷的能力[23].線性擬合結(jié)果發(fā)現(xiàn),消落帶3種土壤去除游離鐵氧化物后解吸磷的能力在3種處理中均最強(qiáng)(通過(guò)比較斜率得出),這可能是土壤中游離鐵氧化物的去除導(dǎo)致磷酸鹽與土壤的化學(xué)作用過(guò)程較少造成[31].另一方面,FL土壤去除有機(jī)質(zhì)組分后較原始土壤的磷解吸能力略有降低,說(shuō)明FL土壤中有機(jī)質(zhì)含量越多有利于磷的解吸,這與一些學(xué)者的報(bào)道結(jié)果相似[32-33].然而,KX和FJ土壤去除有機(jī)質(zhì)組分后較原始土壤的磷解吸能力無(wú)明顯差異,說(shuō)明KX和FJ土壤中有機(jī)質(zhì)組分對(duì)磷解吸無(wú)影響.同時(shí),由表5可知,值均為負(fù)數(shù),而值能反應(yīng)土壤本底釋放磷的能力,表明不同處理的消落帶3種土壤均有一定的磷吸附能力,3種土壤去除游離態(tài)鐵氧化物后對(duì)磷的吸附能力最弱,3種土壤去除有機(jī)質(zhì)后與原始土壤吸附磷的能力差異不大.綜上,三峽庫(kù)區(qū)消落帶3種土壤中游離鐵氧化物組分是控制磷解吸的重要因素,而土壤中有機(jī)質(zhì)組分對(duì)磷解吸的影響與土壤類型有關(guān).

表4 供試土壤的磷解吸量和磷吸附量的相關(guān)關(guān)系 Table 4 Correlation results of sorbed phosphorus and phosphorus desorption in all original soils and subsamples with different pretreatments

注:**<0.01.

表5 供試土壤磷解吸量和磷吸附量的線性擬合參數(shù)結(jié)果 Table 5 The linear fitting results between sorbed phosphorus and phosphorus desorption in all original soils and subsamples with different pretreatments

2.5 環(huán)境意義

三峽庫(kù)區(qū)消落帶由于水位漲落將周期性的經(jīng)歷淹水和落干,消落帶土壤每年將有3個(gè)月時(shí)間處于落干期.因此,部分距離人類活動(dòng)近的落干土壤常被用于作物耕作,為提高作物的產(chǎn)量常施用有機(jī)肥,同時(shí),部分作物秸稈也存在滯留土地的情況,此外,落干期消落帶土壤還會(huì)生長(zhǎng)出各種草類,以上過(guò)程都將導(dǎo)致消落帶土壤有機(jī)質(zhì)的輸入.報(bào)道稱,有機(jī)質(zhì)(如生物質(zhì)炭、枯枝落葉、城市堆肥等)的輸入將降低土壤對(duì)磷的吸附,促使土壤中磷的釋放[34-36].然而,本研究結(jié)果發(fā)現(xiàn),三峽庫(kù)區(qū)消落帶土壤易氧化的有機(jī)質(zhì)對(duì)土壤吸附和解吸磷的影響較小.另一方面,消落帶土壤去除游離鐵氧化物的過(guò)程在一定程度上能模擬鐵氧化物由落干到淹水的還原溶解過(guò)程.結(jié)果表明,一旦三峽庫(kù)區(qū)消落帶土壤中鐵錳等變價(jià)金屬氧化物發(fā)生還原溶解,土壤中各種磷形態(tài)都將隨著釋放,尤其是Fe/Al-P,土壤對(duì)磷的吸附能力將大大降低.綜上,本研究結(jié)果能較好地反應(yīng)鐵氧化物、有機(jī)質(zhì)組分對(duì)三峽庫(kù)區(qū)消落帶土壤中磷吸附解吸的影響,進(jìn)一步驗(yàn)證了消落帶土壤由落干到淹水過(guò)程將導(dǎo)致活性磷的釋放,增加庫(kù)區(qū)水環(huán)境安全的風(fēng)險(xiǎn).

3 結(jié)論

3.1 三峽庫(kù)區(qū)消落帶FJ、KX和FL土壤去除的有機(jī)質(zhì)以易氧化的組分為主,去除有機(jī)質(zhì)組分后,土壤中各種磷形態(tài)的含量變化較小,有機(jī)質(zhì)含量與各種磷形態(tài)之間無(wú)顯著相關(guān)關(guān)系.然而,3種土壤去除游離鐵氧化物后,土壤中各種磷形態(tài)的含量均發(fā)生明顯的降低.3種土壤去除有機(jī)質(zhì)、游離鐵氧化物組分后并未改變土壤中各種磷形態(tài)的相對(duì)大小順序,均為:Ca-P>OP>Fe/Al-P.

3.2 FJ、KX、FL3種土壤去除有機(jī)質(zhì)組分后對(duì)磷吸附的影響較小,而土壤去除游離鐵氧化物組分后對(duì)磷的吸附能力明顯降低,表明游離鐵氧化物是決定土壤吸附磷的重要因素.

3.3 FJ、KX、FL3種土壤去除游離鐵氧化物后較原始土壤吸附磷的解吸能力明顯增加,表明游離鐵氧化物組分是控制3種土壤吸附磷的解吸的重要因素.

3.4 FL土壤去除有機(jī)質(zhì)組分后較原始土壤吸附磷的解吸能力略有降低,而KX和FJ土壤去除有機(jī)質(zhì)組分后較原始土壤吸附磷的解吸能力無(wú)明顯差異,表明有機(jī)質(zhì)組分對(duì)土壤吸附磷的解吸的影響與土壤類型有關(guān).

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Effect of organic matter and iron oxides on phosphorus forms and adsorption-desorption on dry-period soils in the water- level-fluctuating zone of the Three Gorges Reservoir.

YAN Jin-long1,2*, WU Wen-li1, JIANG Tao2, WEI Shi-qiang2

(1.College of Pharmacy and Biological Engineering, Chongqing University of Technology, Chongqing 400054, China；2.College of Resources and Environment, Southwest University, Chongqing 400716, China)., 2019,39(3)：1124~1131

Selective removal of organic matter or iron oxide from three typical dry-period soils were explored to investigate its direct effect on P fractions and adsorption-desorption behavior in the water-level-fluctuating zone (WLFZ) of the Three Gorges Reservoir (TGR). The data showed that kinds of P fractions in three dry-period soils were not significant decreased with removal of readily oxidizable organic matter. However, kinds of P fractions were significantly decreased with removal of free iron oxides in the three soils. Notably, different P fractions were both in the order as follows: Ca-P > OP > Fe/Al-P, before and after removal of organic matter or free iron oxides in the three soils. Moreover, after removal of organic matter, the adsorption capacity of yellow soil (FJ), purple alluvial soil (KX), grey brown purple soil (FL) for P was only decreased by 0.5%, 2.3%, 6.5%(=0.017<0.05, significant difference), respectively, which indicated that P adsorbed on the three soils were little influenced by organic matter. In addition, after removal of free iron oxides, the adsorption capacity of FJ, KX, FL soil for P was significantly decreased by 45.6%, 51.7%, 43.9%(=0.004<0.05, significant difference), respectively, which revealed that P adsorbed on the three soils were dominated by free iron oxides. More importantly, the desorption capacity of three soils for P was increased after removal of free iron oxides, which presented that free iron oxides were also the predominant factor to control desorption behavior of freshly sorbed P. Then, the desorption capacity of FL for P was little decreased after removal of organic mater, and there were no distinction for it before and after removal of organic matter in KX and FJ soils, which showed that the desorption capacity of three soils for P were influenced by organic matter related to soil category.

water-level-fluctuating zone (WLFZ) of the Three Gorges Reservoir (TGR)；dry-period soil；phosphorus；organic matter；iron oxide

X142

A

1000-6923(2019)03-1124-08

閆金龍(1989-),男,四川渠縣人,博士,講師,主要研究方向?yàn)榄h(huán)境污染化學(xué).發(fā)表論文20余篇.

2018-08-13

國(guó)家自然科學(xué)基金資助項(xiàng)目(41171198,41403079);重慶理工大學(xué)科研啟動(dòng)基金(0110170340)

* 責(zé)任作者, 講師, yanjinlong6439@126.com