植被在大氣汞收支中作用的研究進(jìn)展與展望

牛振川，張曉山，陳進(jìn)生，王森，王章瑋，慈志佳

1. 中國科學(xué)院地球環(huán)境研究所，黃土與第四紀(jì)地質(zhì)國家重點(diǎn)實(shí)驗(yàn)室，西安 710075 2. 中國科學(xué)院生態(tài)環(huán)境研究中心，北京 100085 3. 中國科學(xué)院城市環(huán)境研究所，廈門 361021 4. 國家加速器質(zhì)譜中心(西安)，西安 710054 5. 西北大學(xué)，城市與環(huán)境學(xué)院，西安 710127

植被在大氣汞收支中作用的研究進(jìn)展與展望

牛振川1,2,3,4,*，張曉山2，陳進(jìn)生3，王森5，王章瑋2，慈志佳2

1. 中國科學(xué)院地球環(huán)境研究所，黃土與第四紀(jì)地質(zhì)國家重點(diǎn)實(shí)驗(yàn)室，西安 710075 2. 中國科學(xué)院生態(tài)環(huán)境研究中心，北京 100085 3. 中國科學(xué)院城市環(huán)境研究所，廈門 361021 4. 國家加速器質(zhì)譜中心(西安)，西安 710054 5. 西北大學(xué)，城市與環(huán)境學(xué)院，西安 710127

在汞的生物地球化學(xué)循環(huán)中，對(duì)于“源”和“匯”的認(rèn)識(shí)還存在許多不確定性。大氣汞收支不平衡的問題使得植被在汞循環(huán)中的作用日益凸現(xiàn)；開展植被在大氣汞收支中作用的研究有助于為全球汞減排政策的制定提供參考。本文首先概述了植被中汞的來源和影響因素及其與大氣汞的源匯關(guān)系；進(jìn)而重點(diǎn)論述了植被參與大氣汞收支的主要方式：凋落物沉降、生物質(zhì)燃燒和植被表面與大氣汞的動(dòng)態(tài)交換，并闡述了植被在大氣汞污染監(jiān)測中的應(yīng)用；最后在總結(jié)我國相關(guān)研究的基礎(chǔ)上展望了未來的發(fā)展方向。

植被；大氣汞收支；交換過程；生物質(zhì)燃燒；凋落物沉降

汞是一種全球性污染物，會(huì)隨大氣傳輸擴(kuò)散到世界各地，甚至引起偏遠(yuǎn)地區(qū)環(huán)境介質(zhì)和生物體內(nèi)汞濃度的升高，對(duì)人類健康和生態(tài)系統(tǒng)安全造成潛在威脅[1,2]。針對(duì)全球汞污染問題，聯(lián)合國環(huán)境規(guī)劃署已于2013年1月正式通過了旨在全球范圍內(nèi)控制和減少汞排放的國際公約《水俁公約》，并在當(dāng)年10月由87個(gè)國家正式簽約。我國是世界上汞排放量較大的國家，人為源每年的汞排放量約為609.1 t[3,4]，這給我國的環(huán)境保護(hù)和環(huán)境外交帶來巨大壓力。排放到大氣的汞通過干濕沉降過程進(jìn)入植被系統(tǒng)，而植被系統(tǒng)又可通過復(fù)雜的物理、化學(xué)及生物過程釋放汞。因此，開展植被在大氣汞收支中作用的研究不僅有助于正確地評(píng)價(jià)自然排放源在大氣汞循環(huán)中的作用，而且能為全球汞減排政策的制定提供參考[5-7]。

在汞的生物地球化學(xué)循環(huán)過程中，對(duì)于“源”和“匯”的認(rèn)識(shí)仍存在很多的不確定性。主要表現(xiàn)在目前研究所認(rèn)識(shí)到的大氣汞排放源要遠(yuǎn)多于所認(rèn)識(shí)到的匯，產(chǎn)生大氣汞收支的不平衡問題[8]；其中的一個(gè)重要原因是忽視了植被在大氣汞收支中的重要作用。近年來，植被在汞循環(huán)中的重要作用得到了足夠的重視；本文對(duì)植被中汞的來源、與大氣汞的源匯關(guān)系、參與大氣汞收支的方式以及植被在大氣汞污染監(jiān)測中的應(yīng)用等方面的研究進(jìn)展進(jìn)行系統(tǒng)綜述，并對(duì)未來的發(fā)展方向進(jìn)行展望。

1 植被中汞的來源及影響因素

汞循環(huán)中的一個(gè)中心問題是植被中的汞是來自土壤還是大氣。植物體內(nèi)的汞主要來源于以下途徑：(1)氣孔對(duì)大氣Hg0的吸收[9]；(2)葉對(duì)干濕沉降的大氣Hg0、Hg2+以及與顆粒物結(jié)合汞的吸附[10]；(3)根通過蒸騰作用對(duì)土壤中可溶性汞的吸收。大量研究結(jié)果表明，根部的汞主要來自土壤吸收，木本、灌木以及大部分草本植物地上部分的汞主要來自大氣吸收[11-15]；而對(duì)于部分草本植物，由于其獨(dú)特的生理和生長方式，葉中很大一部分的汞來自土壤吸收。例如，Deschampsiaflexuosa L和Calamagrostisvillosa(Chaix ex Vill.)這兩種草本植物葉中的汞來自土壤汞的比例分別為30%和93%[16]。

植物體內(nèi)汞濃度受環(huán)境汞濃度和生長時(shí)期的共同影響。隨著大氣汞濃度的增加，葉汞濃度也隨之線性增加，而其它器官汞濃度變化不明顯；同樣，當(dāng)土壤汞濃度增加時(shí)，根汞濃度也隨之增加，而其它器官汞濃度變化不明顯[11-15]。總體而言，植物葉汞濃度隨生長時(shí)期的延長而增加[14,17,18]。但對(duì)于一些草本植物，葉汞濃度在整個(gè)生長時(shí)期內(nèi)波動(dòng)[15,19]。Dunagan等對(duì)菠菜53 d試驗(yàn)結(jié)果表明，葉汞濃度在整個(gè)生長時(shí)期內(nèi)變動(dòng)較大，在28 d時(shí)濃度最高[19]。

2 植被與大氣汞的源匯關(guān)系

植被通過氣孔吸收Hg0和葉表面吸附干濕沉降的大氣汞而成為大氣汞的匯。然而，在一定條件下，植被富集的汞可通過以下方式向大氣排放而成為大氣汞的源：(1) 沉降在葉片表面的Hg2+在紫外線的照射下會(huì)還原為Hg0重新排放到大氣中[20]；(2) 植被隨呼吸作用向大氣排放汞[21,22]；(3) 植被以生物質(zhì)燃燒的方式向大氣釋放汞[33-35]。但總體而言，植被是大氣汞的凈匯(net sink)[13]，其富集的大氣汞進(jìn)而以凋落物沉降的方式釋放到地表系統(tǒng)。因此，植被通過凋落物沉降、生物質(zhì)燃燒和表面與大氣汞的交換這些方式參與大氣汞收支。此外，植被還通過影響土壤汞的排放來間接影響大氣汞的收支。

3 植被參與大氣汞收支的方式

3.1 凋落物沉降中汞的輸入通量

植被富集的大氣汞會(huì)以凋落物沉降的方式輸送到地表，可以作為估算森林系統(tǒng)富集大氣汞通量的一種粗略研究方法。凋落物沉降是植被參與大氣汞收支的重要方式，Lindberg 等估計(jì)全球凋落物沉降中汞的年輸入量可達(dá)2 400～6 000 t[23]。溫帶地區(qū)凋落物沉降中汞的輸入通量為8～25 μg·(m2·y)-1[24-27]；熱帶地區(qū)由于凋落物較大的生物量，汞的輸入通量可達(dá)30～122 μg·(m2·y)-1 [28-30]。在中國西南某些地區(qū)，凋落物沉降中汞的輸入通量也較高，云南哀牢山為119.5 μg·(m2·y)-1[31]，貴州雷公山為119.5 μg·(m2·y)-1，重慶鐵山坪為291.2 μg·(m2·y)-1[32]。

3.2 生物質(zhì)燃燒中汞的釋放通量

植被富集的大氣汞還可以以生物質(zhì)燃燒的方式參與大氣汞收支，全球生物質(zhì)燃燒釋放的汞通量每年可達(dá)數(shù)百t。通常，可以通過 Hg/CO、Hg/CO2和Hg/fuel等排放因子來估算生物質(zhì)燃燒過程中釋放的汞量。Weiss-Penzias等以排放因子△TAM/△CO估計(jì)全球生物質(zhì)燃燒釋放的汞量為670±330 t·y-1，其中北方針葉林燃燒釋放汞168±75 t·y-1[33]。Brunke等以排放因子Hg/CO (2.10±0.21)×10-7mol·mol-1和Hg/CO2(1.19±0.30)×10-8mol·mol-1分別估算全球生物質(zhì)燃燒釋放的汞量為930 t·y-1(510～1 140 t·y-1)和590 t·y-1(380～1 330 t·y-1)[34]。Friedli等將世界劃分為不同區(qū)域，并采用不同的排放因子17～312 gHg·(kg fuel)-1，估計(jì)全球生物質(zhì)燃燒釋放的汞通量為675±240 t·y-1[35]。

在生物質(zhì)燃燒中，汞主要以氣態(tài)元素汞(Hg0)和顆粒汞(Hgp)的形式釋放。燃料濕度是控制燃燒過程中汞形態(tài)的主要因素，在濕度較低的情況下，Hg0是主要的形態(tài)，可占95%以上；而在鮮樣中，顆粒汞會(huì)占相當(dāng)?shù)谋壤?，最多可達(dá)50%[36]。此外，燃燒方式對(duì)汞的形態(tài)也有影響，熏燒中顆粒汞的比例較高；而火焰比較明顯時(shí)，顆粒汞的比例不顯著[36]。

在森林大火中，不僅生物質(zhì)燃燒會(huì)釋放大量的汞，而且土壤受熱也會(huì)釋放一定量的汞來參與大氣汞的收支。實(shí)驗(yàn)室測得的排放因子為14～71×10-6gHg·(kg fuel)-1，而野外森林大火中測得的排放因子略高，為112 × 10-6gHg·(kg fuel)-1，F(xiàn)riedli等認(rèn)為差值來自土壤受熱釋放的汞[37]。在森林大火中，土壤釋放的大量汞主要來自表層土壤[38]，占土壤總汞的79%左右[39]。

生物質(zhì)燃燒會(huì)增加大氣汞的沉降而影響大氣汞的收支，對(duì)生態(tài)系統(tǒng)的汞循環(huán)造成一定影響。Witt等發(fā)現(xiàn)森林大火之后，美國北明尼蘇達(dá)州降水中總汞和甲基汞的濃度均增加1.7～8倍[40]。而Kelly等報(bào)道森林大火引起虹鱒魚(Oncorhynchusmykiss)體內(nèi)的汞濃度增加了5倍，其它種類魚肌肉中的汞濃度也有一定增加，這可能與大火使?fàn)I養(yǎng)元素輸入增加而導(dǎo)致食物鏈的重建，以及大火中瞬時(shí)釋放出大量的汞有關(guān)[41]。

3.3 植被表面與大氣汞的交換過程

植被表面與大氣汞的交換過程是其參與大氣汞收支的基本形式。Obrist估計(jì)全球植被的地上部分每年大約富集1 000 t的大氣汞，甚至可以引起春夏之際大氣汞濃度的降低，其認(rèn)為植被是大氣汞“丟失的匯”(missing sink)[42]。因此，植被生物量的增加將能富集更多的大氣汞從而降低國際減排壓力。植被表面存在富集和排放大氣汞的動(dòng)態(tài)雙向交換過程，據(jù)此，Shetty 等[43]和Quan等[44]分別通過模型的方法估計(jì)東亞和我國陸地植被每年向大氣排放630 t和79～177 t的汞。

研究植被表面與大氣汞交換過程的方法有動(dòng)態(tài)通量袋法(dynamic flux bags, DFB)和微氣象法(micrometeorological method)兩類。微氣象法包括修正波文比法(MBR)、氣體動(dòng)力學(xué)法(AER)和弛豫渦旋積累法(REA)，其對(duì)地表無干擾，可長期大面積連續(xù)監(jiān)測，但對(duì)儀器要求較高，采樣復(fù)雜。微氣象法是在冠層尺度上認(rèn)識(shí)植被與大氣汞的交換過程，其不僅包括植被與大氣汞的交換通量，還包括植被覆蓋土壤與大氣汞的交換通量。動(dòng)態(tài)通量袋法更適于在葉片尺度上認(rèn)識(shí)葉汞交換的動(dòng)態(tài)過程，簡單方便，但也存在改變袋內(nèi)氣象條件[45]和夜晚有水汽冷凝[46]的缺點(diǎn)。動(dòng)態(tài)通量袋法的影響因素包括袋體材料、體積、進(jìn)出口位置和氣體流速，其中氣體流速的影響最大，最佳氣體流速為保持出氣口與進(jìn)氣口汞濃度之差(ΔC)為恒定值的最小流速[45]。

植被與大氣汞的交換通量存在一個(gè)補(bǔ)償點(diǎn)，當(dāng)大氣汞濃度高于此補(bǔ)償點(diǎn)時(shí)，大氣汞被葉片表面所富集，此時(shí)交換通量數(shù)據(jù)為負(fù)；低于補(bǔ)償點(diǎn)時(shí)，植被向大氣排放汞，此時(shí)交換通量數(shù)據(jù)為正[47]。補(bǔ)償點(diǎn)因植物種類的不同而異，范圍為2～33 ng·m-3[11,12,47]。補(bǔ)償點(diǎn)也因環(huán)境而異，通常白天略高于夜晚[12]。因此，確立植被表面與大氣汞交換通量的補(bǔ)償點(diǎn)有助于揭示其與大氣汞的源匯關(guān)系。

影響植被表面與大氣汞交換通量的因素很多，主要包括植物的種類、生長環(huán)境及其生理活動(dòng)。對(duì)于旱生植物，交換通量隨溫度(20～40°C)和大氣汞濃度的增加而增加，太陽輻射(尤其紫外線)和氣孔導(dǎo)度是控制葉汞交換通量的重要因素[10,12,20,48]；而對(duì)于水生植物，交換通量與植物蒸騰作用所產(chǎn)生的水汽通量顯著相關(guān)[22]。

植被表面與大氣汞存在復(fù)雜的交換過程，不僅有氣孔的吸收和排放過程，還存在大氣汞在葉片表面的沉降和光致還原等引起的再排放的非氣孔過程[9,10,20]。其中，氣孔的數(shù)量是氣孔過程的控制因素[9]，紫外線是非氣孔過程的控制因素[20]。目前，氣孔和非氣孔的微觀過程機(jī)制及相關(guān)控制因素是植被與大氣汞交換過程的研究熱點(diǎn)。

3.4 植被對(duì)土壤汞排放的影響

此外，植被還通過影響土壤汞的排放來間接影響大氣汞的收支。隨著植物冠層的發(fā)育，使照射到土壤的紫外線減少，土壤中Hg2+的光致還原作用減弱，土壤汞的排放通量逐漸降低[49-53]。據(jù)報(bào)道，有森林覆蓋的土壤汞排放通量為1.4±0.3～2.4±1.0 ng·(m2·h)-1，裸地土壤汞的排放通量則高達(dá)7.6±1.7 ng·(m2·h)-1[53]。植被的存在還會(huì)影響森林土壤汞排放通量的季節(jié)變化，如在美國東部森林的觀測結(jié)果表明冬春季土壤汞的排放通量高于夏秋季[50]。

4 植物監(jiān)測在大氣汞污染中的應(yīng)用

葉汞濃度與大氣汞濃度的線性關(guān)系表明葉片可以用于大氣汞污染的植物監(jiān)測。與傳統(tǒng)的儀器監(jiān)測相比，大氣污染的植物監(jiān)測具有分布廣泛、采樣便利、監(jiān)測時(shí)間長、維護(hù)費(fèi)用低且能直接反應(yīng)污染物對(duì)生態(tài)系統(tǒng)的影響等優(yōu)點(diǎn)。自1886年Nylander用地衣的豐度來反應(yīng)大氣污染程度起[54]，大氣污染的植物監(jiān)測已有100多年的歷史了。隨后，苔蘚、樹皮、樹木的年輪、植物葉片以及蕨類植物都顯示出大氣污染的植物監(jiān)測能力[55]。

苔蘚是目前應(yīng)用最廣泛的監(jiān)測大氣污染的植物材料，它主要從大氣沉降中吸收水分和營養(yǎng)物質(zhì)，具有積累大氣污染物的能力[56]。苔蘚不僅已用于監(jiān)測市政固廢焚燒廠[57]、氯堿廠[58]、熱電廠[59]、溫度計(jì)廠[60]周邊大氣汞污染情況，而且用于區(qū)域大氣汞的植物監(jiān)測，例如整個(gè)歐洲大陸[61]?？諝怿P梨屬(Tillandsia genus)植物，既非苔蘚又非地衣，而是一類空中附生鳳梨科植物，平常纏繞在樹枝上，直接從大氣中吸收水分和營養(yǎng)物質(zhì)。常見的鳳梨屬植物西班牙苔蘚(Tillandsiausneoides L.)已用于監(jiān)測巴西氯堿廠[62]和亞馬遜金礦區(qū)[63]周圍大氣汞的污染狀況。

關(guān)于高等植物葉片監(jiān)測大氣汞污染的研究目前也有不少報(bào)道。Kono和Tomiyasu報(bào)道日本鹿兒島市蕨類植物瓦韋(Lepisorusthunbergianus (kaulf.) Ching)的葉汞濃度與大氣汞濃度有線性關(guān)系，可以用來原位估計(jì)大氣汞濃度[64]。草類植物的葉片在大氣污染的植物監(jiān)測中具有廣泛的應(yīng)用前景，是目前大氣汞污染植物監(jiān)測的研究熱點(diǎn)。多年生黑麥草(Loliumperenne L.)和意大利黑麥草(Loliummultiflorum Lam.)是目前研究較多的兩種植物材料，其葉片已用于德國和比利時(shí)大氣汞污染的植物監(jiān)測[65,66]。此外，松針[67]和一些葉菜類蔬菜的葉片[15,68]也顯示了大氣汞污染的植物監(jiān)測能力。Laacouri等探討了樹葉用于大氣汞污染被動(dòng)監(jiān)測的不確定性因素，如葉的生長日期和位置[9]。

5 我國相關(guān)的研究進(jìn)展與展望

鑒于植被在大氣汞循環(huán)中的重要作用，我國開展了農(nóng)作物中汞的來源與影響因素[14,15]、農(nóng)田植被與大氣汞的雙向動(dòng)態(tài)交換過程[69]、凋落物沉降中汞的通量[26,31,32,70]以及森林植被對(duì)土壤汞揮發(fā)的影響[52]等方面的研究，但對(duì)于大氣汞在植物體內(nèi)的遷移轉(zhuǎn)化、植被與大氣汞交換的微觀過程以及植被削減我國大氣汞濃度的宏觀作用還認(rèn)識(shí)不足。植被圈上下聯(lián)系著大氣圈和土壤圈，在今后的研究中，微觀上應(yīng)重視植被表面富集和排放大氣汞的動(dòng)態(tài)機(jī)制和植被富集的大氣汞在葉表面、表皮和葉肉組織中的分布與轉(zhuǎn)化過程；宏觀上應(yīng)重視我國植被對(duì)較高且還在上升的大氣汞濃度的降低作用和植樹造林、退耕還林導(dǎo)致的生物量增加對(duì)汞匯的增加作用；并將植被表面與大氣汞交換的微觀過程與大氣汞長距離遷移的宏觀過程相結(jié)合來研究植被在我國大氣汞跨區(qū)域傳輸中的捕集作用；而在大氣汞污染防治上應(yīng)重視大氣汞污染儀器監(jiān)測與植物監(jiān)測的結(jié)合。

[1] Weiss H V, Koide M, Goldberg E D. Mercury in a Greenland ice sheet: evidence of recent input by man[J]. Science, 1971, 174: 692-694

[2] Dietz R, Outridge P M, Hobson K A. Anthropogenic contributions to mercury levels in present-day Arctic animals a review [J]. Science of the total Environment, 2009, 407: 6120-6131

[3] Feng X, Streets D, Hao J, et al. Mercury Emissions from Industrial Sources in China [M]. Springer, New York, 2009, chap. 3: pp. 67-79

[4] Streets D G, Hao J, Wang S, et al. Mercury Emissions from Coal Combustion in China [M]. Springer, New York, 2009, chap. 2: 51-65

[5] 馮新斌, 付學(xué)吾, Sommar J, 等. 地表自然過程排汞研究進(jìn)展及展望[J]. 生態(tài)學(xué)雜志, 2011, 30(5): 845-856.

Feng X B, Fu X W, Sommar J, et al. Earth surface natural mercury emission: Research progress and perspective [J]. Chinese Journal of Ecology, 2011, 30(5): 845-856 (in Chinese)

[6] 付學(xué)吾, 馮新斌, 王少鋒, 等. 植物中汞的研究進(jìn)展[J]. 礦物巖石地球化學(xué)通報(bào), 2005, 24(3): 232-238

Fu X W, Feng X B, Wang S F, et al. Advances of research on mercury in plants [J]. Bulletin of Mineralogy, Petrology and Geochemistry, 2005, 24(3): 232-238 (in Chinese)

[7] Lindberg S, Bullock R, Ebinghaus R, et al. A synthesis of progress and uncertainties in attributing the sources of mercury in deposition [J]. Ambio, 2007, 36: 19-32

[8] Gustin M S, Lindberg S E. Terrestrial mercury fluxes: Is the net exchange up, down, or neither? [A]// Dynamics of Mercury Pollution on Regional and Global Scales: Atmospheric Processes and Human Exposures around the World [M]. Springer, New York, 2005, 241-259

[9] Laacouri A, Nater E A, Kolka R K. Distribution and uptake dynamics of mercury in leaves of common deciduous tree species in Minnesota, U.S.A [J]. Environmental Science &Technology, 2013, 47, 10462-10470

[10] Stamenkovic J, Gustin M S. Nonstomatal versus stomatal uptake of atmospheric mercury [J]. Environmental Science & Technology, 2009, 43: 1367-1372

[11] Ericksen J A, Gustin M S, Schorran D E, et al. Accumulation of atmospheric mercury in forest foliage [J]. Atmospheric Environment, 2003, 37: 1613-1622

[12] Ericksen J A, Gustin M S. Foliar exchange of mercury as a function of soil and air mercury concentrations [J]. Science of the Total Environment, 2004, 324: 271-279

[13] Millhollen A G, Gustin M S, Obrist D. Foliar mercury accumulation and exchange for three tree species [J]. Environmental Science & Technology, 2006, 40: 6001-6006

[14] Niu Z C, Zhang X S, Wang Z W, et al. Field controlled experiments of mercury accumulation in crops from air and soil [J]. Environmental Pollution, 2011a, 159(10): 2684-2689

[15] Niu Z C, Zhang X S, Wang S, et al. The linear accumulation of atmospheric mercury by vegetable and grass leaves: Potential biomonitors for atmospheric mercury pollution [J]. Environmental Science and Pollution Research, 2013, 20: 6337-6343

[16] Schwesig D, Krebs O. The role of ground vegetation in the uptake of mercury and methylmercury in a forest ecosystem [J]. Plant and Soil, 2003, 253: 445-455

[17] Frescholtz T F, Gustin M S, Schorran D E, et al. Assessing thesource of mercury in foliar tissue of quaking aspen [J]. Environmental Toxicologyand Chemistry, 2003, 22: 2114-2119

[18] Rea A W, Lindberg S E, Scherbatskoy T, et al. Mercury accumulationin foliage over time in two northern mixed-hardwood forests [J]. Water, Air, and Soil Pollution, 2002, 133: 49-67

[19] Dunagan S C, Gilmore M S, Varekamp J C. Effects of mercury on visible/near-infrared reflectance spectra of mustard spinach plants (Brassica rapa P.) [J]. Environmental Pollution, 2007, 148: 301-311

[20] Graydon J A, St Louis V L, Lindberg S E, et al. Investigation of mercury exchange between forest canopy vegetation and the atmosphere using a new dynamic chamber [J]. Environment Science and Technology, 2006, 40: 4680-4688

[21] Lindberg S E, Meyers T P. Development of an automated micrometeorological method for measuring the emission of mercury vapor from wetland vegetation [J]. Wetlands Ecology and Management, 2001, 9: 333-347

[22] Lindberg S E, Don W, Meyers T. Transpiration of gaseous elemental mercury through vegetation in a subtropical wetland in Florida[J]. Atmospheric Environment, 2002, 36: 5207-5219

[23] Lindberg S E, Porcella D, Prestbo E, et al. The problem with mercury: Too many sources, not enough sinks [J]. RMZ Materials and Geoenvironment, 2004, 52: 1172-1176

[24] Graydon J A, St. Louis V L, Hintelmann H, et al. Long-term wet and dry deposition of total and methyl mercury in the remote boreal ecoregion of Canada [J]. Environmental Science and Technology, 2008, 42(22): 8345-8351

[25] Iverfeldt ?. Mercury in forest canopy throughfall water and its relation to atmospheric deposition [J]. Water, Air, and Soil Pollution, 1991, 56: 553-564

[26] Niu Z C, Zhang X S, Wang Z W, et al. Mercury in leaf litter in typical suburban and urban broadleaf forests in China [J]. Journal of Environmental Sciences, 2011b, 23(12): 2042-2048

[27] Sheehan K D, Fernandez I J, Kahl J S, et al. Litterfall mercury in two forested watersheds at Acadia National Park, Maine, USA [J]. Water, Air, and Soil Pollution, 2006, 170: 249-265

[28] Fostier A H, Cecon K, Forti M C. Urban influence on litterfall trace metals fluxes in the Atlantic Forest of S?o Paulo (Brazil) [J]. Journal de Physique, 2003, IV: 491-494

[29] Silva-Filho E V, Machado W, Oliveira R R, et al. Mercury deposition through litterfall in an Atlantic Forest at Ilha Grande, Southeast Brazil[J]. Chemosphere, 2006, 65: 2477-2484

[30] Mélières M A, Pourchet M, Charles-Dominique P, et al. Mercury in canopy leaves of French Guiana in remote areas [J]. Science of the total Environment, 2003, 311(1 3): 261-267

[31] Zhou J, Feng X, Liu H, et al. Examination of total mercury inputs by precipitation and litterfall in a remote upland forest of Southwestern China[J]. Atmospheric Environment, 2013, 81: 364-372

[32] Wang Z W, Zhang X S, Xiao J S, et al. Mercury fluxes and pools in three subtropical forested catchments, southwest China [J]. Environmental Pollution, 2009, 157(3): 801-808

[33] Weiss-Penzias P, Jaffe D, Swartzendruber P, et al. Quantifying Asian and biomass burning sources of mercury using the Hg/CO ratio in pollution plumes observed at the Mount Bachelor observatory [J]. Atmospheric Environment, 2007, 41: 4366-4379

[34] Brunke E G, Labuschagne C, Slemr F. Gaseous mercury emissions from a fire in the Cape Peninsula, South Africa, during January 2000 [J]. Geophysical Research Letters, 2001, 28(8): 1483-1486

[35] Friedli H R, Arellano A F, Cinnirella S, et al. Initial estimates of mercury emissions to the atmosphere from global biomass burnin g[J]. Environment Science and Technology, 2009, 43: 3507-3513

[36] Obrist D, Moosmüller H, Schürmann R, et al. Particulate-phase and gaseous elemental mercury emissions during biomass combustion: controlling factors and correlation with particulate matter emissions [J].Environmental Science and Technology, 2008, 42: 721-727

[37] Friedli H R, Radke L F, Lu J Y, et al. Mercury emissions from burning of biomass from temperate North American forests: Laboratory and airborne measurements [J]. Atmospheric Environment, 2003, 37: 253-267

[38] Biwas A, Blum J D, Klaue B, et al. Release of mercury from rocky mountain forest fires [J]. Global Biogeochemical Cycles, 2007, 21: GB1002

[39] Mailman M, Bodaly R A. Total mercury, methyl mercury, and carbon in fresh and burned plants and soil in Northwestern Ontario [J]. Environmental Pollution, 2005, 138: 161-166

[40] Witt E L, Kolka R K, Nater E A, et al. Forest fire effects on mercury deposition in the boreal forest [J]. Environmental Science and Technology, 2009, 43: 1776-1782

[41] Kelly E N, Schindler D W, St. Louis V L, et al. Forest fire increases mercury accumulation by fishes via food web restructuring and increased mercury inputs [J]. Proceedings of the National Academy of Sciences, 2006, 103(51): 19380-19385

[42] Obrist D. Atmospheric mercury pollution due to losses of terrestrial carbon pools? [J]. Biogeochemistry, 2007, 85: 119-123

[43] Shetty S K, Lin C J, Streets D G, et al. Model estimate of mercury emission from natural sources in East Asia[J]. Atmospheric Environment, 2008, 42: 8674-8685

[44] Quan J N, Zhang X S, Shim S G. Estimation of vegetative mercury emissions in China [J]. Journal of Environmental Sciences, 2008, 20: 1070-1074

[45] Eckley C S, Gustin M, Lin C J, et al. The influence of dynamic chamber design and operating parameters on calculated surface-to-air mercury fluxes [J]. Atmospheric Environment, 2010, 44: 194-203

[46] Zhang H H, Poissant L, Xu X, et al. Explorative and innovative dynamic flux bag method development and testing for mercury air-vegetation gas exchange fluxes [J]. Atmospheric Environment, 2005, 39: 7481-7493

[47] Hanson P J, Lindberg S E, Tabberer T A, et al. Foliar exchange of mercury vapor: Evidence for a compensation point [J]. Water, Air, and Soil Pollution, 1995, 80: 373-382

[48] Leonard T L, Taylor Jr G E, Gustin M S, et al. Mercury and plants in contaminated soils: 2. Environmental and physiological factors governing mercury flux to the atmosphere [J]. Environmental Toxicology and Chemistry, 1998, 17: 2072-2079

[49] Gustin M S, Ericksen J A, Schorran D E, et al. Application of controlled mesocosms for understanding mercury air-soil-plant exchange[J]. Environmental Science & Technology, 2004, 38: 6044-6050

[50] Kuiken T, Gustin M S, Zhang H, et al. Mercury emission from terrestrial background surfaces in the eastern USA. Part I: Air/surface exchange of mercury within a southeastern deciduous forest (Tennessee) over one year [J]. Applied Geochemistry, 2008, 23: 345-355

[51] Lindberg S E, Jackson D R, Huckabee J W, et al. Atmospheric emission andplant uptake of mercury from agricultural soils near theAlmaden mercury mine [J]. Journal of Environmental Quality, 1979, 8: 572-578

[52] Ma M, Wang D, Sun R, et al. Gaseous mercury emissions from subtropical forested and open field soils in a national nature reserve, southwest China [J]. Atmospheric Environment, 2013, 64: 116-123

[53] Zhang H, Lindberg S E, Marsik F J, et al. Mercury air/surface exchange kinetics of background soils of the Tahquamenon River watershed in the Michigan Upper Peninsula [J]. Water, Air, and Soil Pollution, 2001, 126: 151-169

[54] Nylander W. Les lichens du Jardin de Luxembourg [J]. The Bulletin of the Botanical Society of France, 1886, 13: 364-371

[55] De Bruin M. Applying biomonitors and neutron activation analysis in studies of heavy metal air pollution [J]. IAEA, 1990, Bull. 4

[56] Rühling ?, Tyler G. An ecological approach to the lead problem [J]. BotaniskaNotiser, 1968, 121: 321-342

[57] Carpi A, Weinstein L H, Ditz D W. Bioaccumulation of mercury by Sphagnum moss near a municipal solid waste incinerator [J]. Journal of the Air Waste Management, 1994, 44: 669-672

[58] Fernández J A, Aboal J R, Carballeira A. Use of native and transplanted mosses as complementary techniques for biomonitoring mercury around an industrial facility[J]. Science of the Total Environment, 2000, 256: 151-161

[59] Carballeira A, Fernández J A. Bioconcentration of metals in the moss Scleropodiumpurum in the area surrounding a power plant Ageotopographical predictive model for mercury [J]. Chemosphere, 2002, 47: 1041-1048

[60] Balarama Krishna M V, Karunasagar D, Arunachalam J. Study of mercury pollution near a thermometer factory using lichens and mosses [J]. Environmental Pollution, 2003, 124: 357-360

[61] Harmens H, Norris D A, Georgia R. et al. Temporal trends (1990-2000) in the concentration of cadmium, lead and mercury in mosses across Europe [J]. Environmental Pollution, 2008, 151: 368-376

[62] Calasans C F, Malm O. Elemental mercury contamination survey in chlor-alkali plant by the use of transplanted Spanish moss, Tillandsiausneoides (L.) [J]. Science of the total Environment, 1997, 208: 165-177

[63] Malm O, Fresitas Fonseca M, Hissnauer Miguel P, et al. Use of epiphyte plants as biomonitors to map atmospheric mercury in a gold grade center city, Amazon, Brazil [J]. Science of the Total Environment, 1998, 213: 57-64

[64] Kono Y, Tomiyasu T. Biomonitoring of atmospheric mercury levels with the epiphytic fern Lepisorusthunbergianus(Polypodiaceae) [J]. Chemosphere, 2009, 77(10): 1387-1392

[65] VDI 3957/2. Biological measuring techniques for the determination and evaluation of effects of air pollutants on plants (bioindication). Part 2. Method of standardized grass exposure [S]. VDI Guidelines., 2003, BeuthVerlag GmbH, Berlin

[66] De Temmerman L, Claeys N, Roekens E, et al. Biomonitoring of airborne mercury with perennial ryegrass cultures [J]. Environmental Pollution, 2007, 146: 458-462

[67] Barghigiani C, Ristori T, Bauleo R. Pinus as an atmospheric Hg biomonitor [J]. Environmental Technology, 1991, 12(12): 1175-1181

[68] De Temmerman L, Waegeneers N, Claeys N, et al. Comparison of concentrations of mercury in ambient air to its accumulation by leafy vegetables: An important step in terrestrial food chain analysis [J]. Environmental Pollution, 2009, 157: 1337-1341

[69] Sommar J, Zhu W, Shang L et al. A whole-air relaxed eddy accumulation measurement system for sampling vertical vapour exchange of elemental mercury[J].Tellus B, 2013, 65: 19940

[70] Fu X, Feng X, Zhu W et al. Elevated atmospheric deposition and dynamics of mercury in a remote upland forest of southwestern China[J]. Environmental Pollution, 2010, 158(6): 2324-2333

◆

TheRoleofVegetationinAtmosphericMercuryBudgets:ProgressesandPerspectives

Niu Zhenchuan1,2,3,4,*, Zhang Xiaoshan2, Chen Jinsheng3, Wang Sen5, Wang Zhangwei2, Ci Zhijia2

1. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China 2. Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China 3. Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China 4. National Center for Accelerator Mass Spectrometry in Xi'an 710054, China 5. College of Urban and Environmental Sciences, Northwest University, Xi'an 710027, China

15 May 2010accepted8 July 2010

There are some uncertainties on the sinks and sources of mercury (Hg) in the Hg biogeochemical cycle. The estimated Hg emissions to the atmosphere are significantly greater than the known sinks, resulting in the mass unbalance for atmospheric Hg. Therefore the role of vegetation in Hg biogeochemical cycle has attracted more and more attentions. The studies of the role of vegetation in atmospheric Hg budgets can provide important information for the global Hg-reduced strategies. In this paper, we briefly review the origination of Hg in vegetation and its controlling factors, as well as the source/sink relationship to atmospheric Hg. Then three main manners involved in the atmospheric Hg budgets were emphasized in detail, including litterfall, biomass burning and bi-directional exchange of Hg between the surfaces of vegetation and atmosphere. In addition, the application of vegetation as biomonitorsof atmospheric Hg pollution was discussed. Finally, the progresses of mercury in vegetationin China were presented and some suggestions on future research were put forward.

vegetation; atmospheric Hg budgets; exchange process; biomass burning; litterfall

國家自然科學(xué)基金(41303072)，中國科學(xué)院地球環(huán)境研究所青年人才項(xiàng)目(Y354011480)，福建省青年科學(xué)基金(2013J05063)，環(huán)境化學(xué)與生態(tài)毒理學(xué)國家重點(diǎn)實(shí)驗(yàn)室開放基金(KF2011-11)

牛振川(1982-)，男，環(huán)境科學(xué)博士，副研究員，研究方向?yàn)楣纳锏厍蚧瘜W(xué)循環(huán)和14C環(huán)境示蹤，E-mail: niuzc@ieecas.cn

10.7524/AJE.1673-5897-20140515011

2014-05-15錄用日期：2014-07-08

1673-5897(2014)5-843-07

： X171.5

： A

牛振川, 張曉山, 陳進(jìn)生, 等. 植被在大氣汞收支中作用的研究進(jìn)展與展望[J]. 生態(tài)毒理學(xué)報(bào)，2014, 9(5): 843-849

Niu Z C, Zhang X S, Chen J S, et al. The role of vegetation in atmospheric mercury budgets: Progresses and perspectives [J]. Asian Journal of Ecotoxicology, 2014, 9(5): 843-849 (in Chinese)