邱 璐,姚 鵬,張婷婷,王金鵬,潘慧慧,高立蒙,趙 彬

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黃河下游顆粒有機(jī)碳的來(lái)源,降解與輸運(yùn)特征

邱 璐1,2,姚 鵬1*,張婷婷1,2,王金鵬1,2,潘慧慧1,2,高立蒙1,2,趙 彬1,2

(1.中國(guó)海洋大學(xué)海洋化學(xué)理論與工程技術(shù)教育部重點(diǎn)實(shí)驗(yàn)室,山東青島 266100；2.中國(guó)海洋大學(xué)化學(xué)化工學(xué)院,山東青島 266100)

2012年在黃河利津逐月采集懸浮顆粒物(SPM),通過(guò)分析粒度組成,顆粒有機(jī)碳(POC)及其穩(wěn)定同位素豐度(δ13C),木質(zhì)素等參數(shù),討論了黃河下游POC的來(lái)源,分布,降解狀態(tài)和輸運(yùn)的季節(jié)變化特點(diǎn).結(jié)果表明,2012年黃河利津徑流量,SPM濃度和中值粒徑(MGS)均有明顯的季節(jié)變化,且變化規(guī)律基本一致.春季降水較少,且下游灌溉較多,導(dǎo)致徑流量較小(300m3/s左右),較粗的顆粒物更容易沉降到河床上,而且不易再懸浮,使得SPM較低(平均0.44kg/m3),MGS較小(平均7.77 μm);夏秋季黃河流域降水較多,徑流量較大(1000m3/s以上),使得河床上較粗的顆粒物容易被帶入懸移質(zhì)中,因此SPM較高(0.67kg/m3),MGS較大(10.6 μm).POC及δ13C的結(jié)果表明了不同來(lái)源有機(jī)碳貢獻(xiàn)的季節(jié)變化,春季POC含量較高,δ13C較負(fù).顆粒物中木質(zhì)素含量季節(jié)規(guī)律變化與流量較為一致,春季木質(zhì)素含量較高,秋季較低.木質(zhì)素參數(shù)C/V(0.21~0.34)和S/V(0.83~1.28)表明黃河SPM中木質(zhì)素為被子植物草本和木本組織混合來(lái)源,降解參數(shù)(Ad/Al)v(0.33~ 0.52),3,5-Bd/ V(0.03~0.12)和P/(S+V)(0.20~0.36)均表明黃河SPM中木質(zhì)素存在一定程度的降解,且秋季降解程度較大,與流量和有機(jī)碳來(lái)源變化有關(guān).

黃河；懸浮顆粒物；顆粒有機(jī)碳；穩(wěn)定碳同位素；木質(zhì)素

據(jù)估計(jì),全球河流每年向海洋輸運(yùn)的顆粒物達(dá)1.8×1010t[1-2],其攜帶的顆粒有機(jī)碳(POC)約占河流輸送有機(jī)碳的一半[3].對(duì)河流顆粒有機(jī)碳輸運(yùn)特征(包括來(lái)源,組成和季節(jié)變化等)的認(rèn)識(shí)是全球碳循環(huán)研究的重要方面,有助于深入了解河流本身,乃至受其影響的河口和邊緣海中有機(jī)碳的源匯過(guò)程.

有機(jī)地球化學(xué)相關(guān)指標(biāo)是研究有機(jī)碳源匯過(guò)程的有力手段,最常見的方法為:有機(jī)質(zhì)來(lái)源的整體指標(biāo)法(如有機(jī)碳含量,碳氮元素比值(C/N)和穩(wěn)定碳同位素豐度(δ13C)等)和分子標(biāo)志物法.由于陸地生物和海洋生物所利用的碳的來(lái)源和途徑不同,使得δ13C在區(qū)分顆粒物有機(jī)碳來(lái)源方面具有重要的作用.例如,陸源有機(jī)物和海源有機(jī)物的δ13C有明顯差異,陸地C3植物δ13C值相對(duì)偏負(fù),為-28‰~-25‰,陸地C4植物δ13C值相對(duì)偏正,約為-12‰[4],而淡水浮游生物的δ13C值范圍一般為-25.5‰~-32‰[5],海洋浮游生物為-22‰~ -19‰[4,6].δ13C已被廣泛的應(yīng)用于顆粒有機(jī)碳來(lái)源的研究中[7].但有機(jī)碳的總體性質(zhì)也有其應(yīng)用的局限性[6,8].分子標(biāo)志物相比于總體性質(zhì)更加具體和敏感,被廣泛的應(yīng)用在有機(jī)物的來(lái)源分析上[9-10].木質(zhì)素是一類來(lái)源于陸地高等植物的生物標(biāo)志物[6],含量?jī)H次于纖維素.由于木質(zhì)素來(lái)源的唯一性和相對(duì)抗降解性,被廣泛的應(yīng)用于河流輸運(yùn)的陸源有機(jī)物來(lái)源及過(guò)程研究[11-15].

黃河含沙量高[16],輸送的有機(jī)碳以顆粒態(tài)為主,占有機(jī)碳輸送量的80%[17].黃河的水沙特征一方面受氣候等自然環(huán)境的控制[18-20],另一方面還受到人為活動(dòng),如調(diào)水調(diào)沙的影響,具有明顯的季節(jié)變化特征[21-24].針對(duì)黃河POC的輸運(yùn)已經(jīng)開展了大量研究,取得了豐富的研究成果[17,20,25-28].然而,目前對(duì)黃河POC輸運(yùn)的季節(jié)變化規(guī)律了解還不多,生物標(biāo)志物的手段應(yīng)用還很少,缺少對(duì)輸運(yùn)的POC來(lái)源和降解狀態(tài)等的認(rèn)識(shí),制約了對(duì)黃河POC源匯過(guò)程的深入理解.本研究于2012年每月在黃河利津河段采集懸浮顆粒物樣品,通過(guò)分析其中POC含量及其穩(wěn)定碳同位素豐度(δ13C),木質(zhì)素等參數(shù),討論黃河下游懸浮顆粒物中有機(jī)碳的來(lái)源,分布和降解狀態(tài)的季節(jié)變化特點(diǎn),并通過(guò)與2012年調(diào)水調(diào)沙期間的結(jié)果[28]比較,旨在認(rèn)識(shí)黃河POC的輸運(yùn)規(guī)律及對(duì)河口、邊緣海有機(jī)碳循環(huán)的影響.

1 材料與方法

1.1 樣品采集

采樣點(diǎn)位于黃河下游的利津水文站(37.52°N, 118.31°E),距黃河入?？?04km.2012年每月20日左右(2月份樣品量較少,只分析了SPM;8月份因故未采樣),在利津水文站取表層水樣500mL,用預(yù)先稱重的0.45μm孔徑的醋酸纖維濾膜(直徑47mm)過(guò)濾,濾膜于-20℃冷凍保存,帶回實(shí)驗(yàn)室用于懸浮顆粒物濃度(SPM)分析.另取表層水樣500mL,裝入潔凈聚乙烯瓶,帶回實(shí)驗(yàn)室用于激光粒度組成分析.取表層水樣500mL左右,用預(yù)先灼燒并稱重的玻璃纖維濾膜(GF/F,直徑25mm,孔徑0.7μm左右)過(guò)濾,濾膜于-20℃冷凍保存,帶回實(shí)驗(yàn)室用于POC含量及其穩(wěn)定碳同位素分析.取表層水樣2.5L左右,用0.45μm孔徑的醋酸纖維濾膜(直徑150mm)過(guò)濾,濾膜于-20℃冷凍保存,帶回實(shí)驗(yàn)室用于顆粒物樣品的木質(zhì)素分析.采樣當(dāng)日的利津水文站徑流量由水利部水文局水利信息中心提供(http://xxfb. hydroinfo.gov.cn).2012年調(diào)水調(diào)沙自6月19日9:00開始,7月9日8:00結(jié)束.因?yàn)樾±说姿畮?kù)放水需5d左右才能影響到下游,故2012年6月和7月的取樣均不受調(diào)水調(diào)沙影響,代表了自然條件下的狀態(tài).調(diào)水調(diào)沙期間為逐日采樣,采樣內(nèi)容和處理方式同上[29].

1.2 樣品分析

SPM濃度分析采用重量法,將濾膜冷凍干燥后稱重,與濾膜本身的質(zhì)量差減,然后除以過(guò)濾體積后得到.顆粒物粒度組成使用激光粒度儀(Mastersizer 2000,英國(guó)馬爾文)進(jìn)行分析[30],共分為3個(gè)粒級(jí),按顆粒粒徑從小到大依次為:黏土(<4μm),粉砂(4~63μm)和砂(>63μm).沉積物的分類按照三角分類法進(jìn)行[31].采用福克—沃德體系[32]計(jì)算粒度參數(shù).按體積百分比計(jì)算粒度組成,其多次測(cè)定的相對(duì)標(biāo)準(zhǔn)偏差<3%(= 6)[33].

元素和穩(wěn)定碳同位素分析參照文獻(xiàn)[34]的方法,將凍干的GF/F濾膜稱重,計(jì)算收集的顆粒物質(zhì)量,然后將濾膜放入加有濃鹽酸的干燥器中熏蒸12h以去除無(wú)機(jī)碳,熏蒸結(jié)束后將樣品置于烘箱內(nèi)于55℃下烘干至恒重,然后將濾膜放入錫囊,使用元素分析儀-穩(wěn)定同位素比值質(zhì)譜聯(lián)用儀(vario MICRO cube EA + Isoprime IRMS,德國(guó))測(cè)定有機(jī)碳,總氮含量及穩(wěn)定碳同位素豐度.有機(jī)碳和總氮多次測(cè)量的標(biāo)準(zhǔn)偏差分別為±0.02%和±0.01 %(=10).同位素豐度的計(jì)算方法為:

δ13C(‰)=(樣品/標(biāo)準(zhǔn)-1)×1000 (1)

式中:樣品和標(biāo)準(zhǔn)分別是樣品和標(biāo)準(zhǔn) (VPDB)的13C/12C比值.分析精度優(yōu)于±0.1‰(=10).

木質(zhì)素的測(cè)定采用堿性CuO氧化法[35-36].將濾膜上的顆粒物凍干,準(zhǔn)確稱重樣品(約含有機(jī)碳3.1~5.8mg)和CuO(330±4mg),加入不銹鋼反應(yīng)器中.在N2氛圍中加入2mol/L NaOH溶液,然后在150℃下消化3h.向反應(yīng)器內(nèi)加入內(nèi)標(biāo)3-乙氧基-4-羥基苯甲醛(EVAL),用去除氧化劑的無(wú)水乙醚萃取木質(zhì)酚后,在N2條件下吹干,用吡啶再溶解吹干的木質(zhì)酚,加入雙(三甲基硅烷)三氟乙酰胺(BSTFA),在70℃下加熱1h將木質(zhì)酚衍生化.衍生化結(jié)束后,立即將BSTFA衍生物用氣相色譜(Agilent 7890A GC)進(jìn)行檢測(cè).在每組樣品中加入1~2個(gè)沉積物標(biāo)準(zhǔn)(NIST-1944)來(lái)檢測(cè)每次操作的偏差,對(duì)于沉積物標(biāo)準(zhǔn)的單個(gè)木質(zhì)素氧化產(chǎn)物多次測(cè)量的精密度在2%~10%之間.

木質(zhì)素被氧化后產(chǎn)生12種單體:香草基酚類3種(V系列:香草醛,香草酮和香草酸);紫丁香基酚類3種(S系列:丁香醛,丁香酮和丁香酸);肉桂基酚類2種(C系列:香豆酸和阿魏酸);對(duì)羥基酚類3種(P系列:對(duì)羥基苯甲醛,對(duì)羥基苯乙酮和對(duì)羥基苯甲酸)以及3,5-二羥基苯甲酸[37-38].∑8和Λ8分別表示V,S和C系列8種單體之和相對(duì)于樣品干重和100mg有機(jī)碳含量的結(jié)果.

2 結(jié)果與分析

2.1 黃河下游2012年水沙季節(jié)變化

2012年黃河利津徑流量和SPM濃度均有明顯的季節(jié)變化.利津徑流量171~1020m3/s,平均為565m3/s,春季(3月~5月)徑流量較低(平均281m3/s左右),夏秋季徑流量處在較高水平(6月~ 11月,平均754m3/s),冬季(12月~2月)流量高于春季(平均473m3/s左右)(圖1a).SPM濃度變化規(guī)律與徑流量基本一致,其范圍為0.24~1.28kg/m3(圖1b),春季SPM濃度較低(平均0.44kg/m3),夏秋季相對(duì)較高(平均0.76kg/m3),冬季SPM濃度相對(duì)于春季略高(平均0.55kg/m3).

2.2 黃河下游2012年顆粒物粒度組成的季節(jié)變化

2012年黃河懸浮顆粒物主要以粉砂為主(51.6%~79.8%,平均為72.2%),其次為黏土(14.4%~28.2%,平均為22.7%),砂的貢獻(xiàn)最小,平均只有5.1%(0.4%~33.8%).2月份砂的含量最高,達(dá)33.8%,其次是7月份,但只有6.8%,其余月份均低于5%.中值粒徑范圍在7.5~14.9μm之間,平均為9.8μm,夏季顆粒物中值粒徑相對(duì)較高(平均為13.6μm),春季顆粒物中值粒徑較低(平均為7.8μm)(圖2).2月份顆粒物樣品的中值粒徑最大,達(dá)30.0μm,其次是7月份,為14.8μm.

2.3 黃河下游2012年P(guān)OC含量和d13C的季節(jié)變化

2012年黃河利津POC質(zhì)量含量(1%代表 0.01g/gdw)的范圍0.50%~0.66%,平均為0.55%,季節(jié)周期變化總體表現(xiàn)為春季POC含量較高(3~5月,平均0.61%),夏季較低(6~8月,平均0.52%),其它季節(jié)浮動(dòng)較小(平均0.53%左右)(圖1c).利津POC體積含量(單位體積水體中的含量)的范圍2.5~5.3mg/L,平均為3.4mg/L,與SPM濃度變化趨勢(shì)較為一致,春季POC體積含量相對(duì)較小(平均為2.6mg/L),夏季較高(平均為4.1mg/L),冬季略高于秋季(平均為3.7mg/L)(圖1d).黃河懸浮顆粒物C/N摩爾比在5.3~8.3之間,平均為6.5,季節(jié)周期變化呈現(xiàn)冬季較高(平均為7.7),秋季低(平均為5.3),春夏浮動(dòng)較小的特點(diǎn)(圖1e).利津POC的δ13C在-24.2%~-26.4‰之間(平均為-24.7‰±0.6‰),夏季較低(如7月份δ13C為-26.4‰),秋冬季相對(duì)較高且較為穩(wěn)定(平均為-24.4‰)(圖1f).

2.4 黃河下游2012年顆粒物中木質(zhì)素含量的季節(jié)變化

2012年黃河利津懸浮顆粒物的Σ8范圍在21.7~39.3μg/g之間,平均為32.0μg/g,季節(jié)周期變化總體表現(xiàn)為春,冬季較高(平均分別為37.8μg/g和34.9μg/g,夏,秋季較低(平均分別為25.6μg/g和28.5μg/g (圖1g).Λ8值范圍在0.39~0.70mg/100mg,平均為0.59±0.11mg/100mg.季節(jié)周期變化與Σ8相似,春,冬季較高(平均分別為0.63mg/100mg和0.66mg/100mg),夏秋季較低(平均分別為0.50mg/ 100mg和0.55mg/100mg).

3 討論

3.1 黃河下游水沙輸運(yùn)特征

2012年黃河SPM與徑流量變化規(guī)律是一致的,兩者呈現(xiàn)顯著的相關(guān)性(=0.001,2=0.81),表明在不考慮調(diào)水調(diào)沙的情況下[29],黃河水沙季節(jié)輸運(yùn)是同步的(圖3).

如果不考慮調(diào)水調(diào)沙期間大量泥沙在短時(shí)間內(nèi)入海,黃河2012年年均含沙量約為0.58kg/ m3,雖然遠(yuǎn)低于同年調(diào)水調(diào)沙時(shí)期(3.06kg/m3)[39],但仍遠(yuǎn)高于長(zhǎng)江(0.07kg/m3)[40]和密西西比河(0.15kg/m3)[41]等世界大河,仍是世界上含沙量最高的河流.黃河下游徑流量春季較小,夏秋季較多與降水和農(nóng)業(yè)灌溉的季節(jié)性特點(diǎn)有關(guān).黃河在春季降水較少,且下游農(nóng)業(yè)灌溉用水增多,導(dǎo)致徑流量較低,夏秋季黃河流域降水較多,水資源較豐富[42-44].

中值粒徑與流量和SPM濃度的變化規(guī)律也是基本一致的(=0.001,2=0.79)(圖3).春季徑流量較小時(shí),較粗的顆粒物更容易沉降到河床上,而且不易再懸浮,使得SPM濃度降低,中值粒徑減小;而在徑流量較大的夏秋季,河床上較粗的顆粒物容易被帶入懸移質(zhì)中,使得SPM濃度增大,中值粒徑也隨之增大.

3.2 黃河下游顆粒有機(jī)碳的輸運(yùn)特征

黃河下游2012年P(guān)OC季節(jié)變化總體表現(xiàn)為春季較高,夏秋季偏低(圖1c).這可能主要與顆粒物來(lái)源有關(guān).在低流量的春季,SPM濃度較小,中值粒徑也較小,顆粒物以細(xì)顆粒為主,吸附的有機(jī)物較多導(dǎo)致有機(jī)碳含量增加;而在流量較高的夏季,SPM濃度較高,顆粒物以粗顆粒為主,造成其POC含量較低.

從黃河POC季節(jié)變化的已有研究來(lái)看,黃河POC含量在不同年份受不同來(lái)源變化的影響,其季節(jié)變化并不一致.Zhang等[45]研究結(jié)果表明黃河POC含量冬季較高,其他季節(jié)浮動(dòng)較小,這可能是由于生源有機(jī)碳的貢獻(xiàn)較高導(dǎo)致的.Ran等[19]研究表明黃河POC含量季節(jié)變化并不明顯.顯然,對(duì)黃河下游POC輸運(yùn)特征,需要根據(jù)具體情況具體分析,也有必要開展長(zhǎng)期連續(xù)觀測(cè)以進(jìn)一步明確其變化規(guī)律.

綜合本研究數(shù)據(jù)和前人研究結(jié)果,可以看出黃河利津POC與SPM之間的關(guān)系符合全球河流經(jīng)典模式,即POC含量(%)隨著SPM濃度增加而逐漸減小,呈現(xiàn)指數(shù)變化關(guān)系,這實(shí)際上與顆粒物粒度隨SPM增大而變粗有關(guān)(圖4a);而POC體積含量(mg/L)隨著SPM濃度的增加而逐漸增大,表明POC體積含量主要受控于SPM濃度(圖4b).

與2012年調(diào)水調(diào)沙時(shí)期相比,黃河顆粒物的POC含量(%)要略高于調(diào)水調(diào)沙時(shí)期,POC體積含量(mg/L)受到水沙量的限制要明顯低于調(diào)水調(diào)沙時(shí)期[28].調(diào)水調(diào)沙期間黃河懸浮顆粒物主要來(lái)源于黃河河床再懸浮泥沙以及水庫(kù)中的泥沙,以有機(jī)碳含量低的粗顆粒物為主,而非調(diào)水調(diào)沙時(shí)期由于流量和含沙量相對(duì)較小,表層水體以細(xì)顆粒物為主,有機(jī)碳含量相應(yīng)較高[29].

從已有結(jié)果來(lái)看,黃河下游POC的δ13C季節(jié)變化十分復(fù)雜,不同的研究得出的結(jié)論并不一致.在本研究中,黃河POC的δ13C呈現(xiàn)夏季較低,秋冬季相對(duì)偏高且較穩(wěn)定,春季較秋冬季偏低的特點(diǎn)(圖5),與Wang等[41]及薛躍君等[47]的研究結(jié)果相符.寧有豐等[35],蔡德陵等[30]和Liu等[41]的研究結(jié)果均表明黃河POC的δ13C呈現(xiàn)夏季偏高冬季偏低的季節(jié)周期變化,并認(rèn)為可能反映了流域內(nèi)植被組成狀況(如C3和C4植被群落結(jié)構(gòu)季節(jié)性更替)的季節(jié)性變化.陶舒琴等[48]的研究則表明黃河下游POC的δ13C無(wú)明顯季節(jié)周期變化,認(rèn)為這主要是由于周轉(zhuǎn)周期較慢(千年尺度)的土壤有機(jī)質(zhì)的貢獻(xiàn)較高造成的.造成黃河下游POC的δ13C季節(jié)變化規(guī)律不清晰的原因,一方面可能與黃河流域每年降水,黃河下游流量和輸沙量本身變化較大有關(guān),另一方面也可能與黃河攜帶的POC主要來(lái)自黃河流域的預(yù)陳化土壤和沉積巖等一些不易降解或者降解完全的較老碳(年齡在4000~8000a)有關(guān),在含沙量較高的月份,水生浮游植物的生長(zhǎng)也會(huì)受到限制,導(dǎo)致其他來(lái)源貢獻(xiàn)和季節(jié)更替信號(hào)會(huì)被掩蓋[41,49].

3.3 黃河下游不同粒級(jí)顆粒物木質(zhì)素的輸運(yùn)特征

木質(zhì)素絕對(duì)和相對(duì)含量的季節(jié)變化規(guī)律均為春冬季較高,夏秋季較低(圖1g).在春季,黃河下游POC中木質(zhì)素相對(duì)貢獻(xiàn)較多,秋末較少,隨著時(shí)間增加逐漸增大(圖1g).這可能與夏秋季黃河流量較大,河床再懸浮的泥沙增多有關(guān).

利用木質(zhì)素特征參數(shù)S/V和C/V可以大致判斷木質(zhì)素的植被來(lái)源[51-53].由于V系列單體存在于所有維管植物木質(zhì)素中,而S系列單體主要存在于被子植物木質(zhì)素中,所以S/V可以區(qū)分被子植物和裸子植物.C系列單體主要存在于木本植物的葉或草本植物的木質(zhì)素中,所以根據(jù)C/V可以判斷木質(zhì)素來(lái)自植物的草本組織還是木本組織.

如圖7所示,黃河懸浮顆粒物中木質(zhì)素C/V值在0.21~0.34之間,S/V值在0.83~1.28之間,表明黃河懸浮顆粒物中木質(zhì)素為被子植物的草本和木本的混合來(lái)源,更偏向于被子植物草本來(lái)源.這與2012年黃河調(diào)水調(diào)沙期間的結(jié)果很接近[38].如圖6所示,從黃河干流土壤到下游顆粒物,再到渤海表層沉積物,可以清楚地看到S/V和C/V值逐漸增大的變化過(guò)程,即在土壤中顯示木質(zhì)素是被子植物和裸子植物的共同貢獻(xiàn),而到了渤海表層沉積物中則顯示木質(zhì)素主要來(lái)自被子植物草本組織,下游顆粒物中的木質(zhì)素則處在兩者之間,這可能體現(xiàn)了草本植物來(lái)源木質(zhì)素的選擇性輸運(yùn),也可能是在輸運(yùn)過(guò)程中V系列木質(zhì)素的選擇性降解.

木質(zhì)素參數(shù)(Ad/Al)v,3,5-Bd/V和P/(S+V)常用來(lái)指示陸源有機(jī)碳的降解狀態(tài)[54-55].(Ad/Al)v是指木質(zhì)素V系列單體中香草酸與香草醛的比值,可用來(lái)指示木質(zhì)素受白腐菌降解程度.新鮮植物組織的(Ad/Al)v為0.1~0.3,而高度降解的木質(zhì)素的(Ad/Al)v高于0.6[56].3,5-Bd是土壤有機(jī)物的降解產(chǎn)物,3,5-Bd/V是3,5-對(duì)羥基苯甲酸與V系列單體總量的比值,可以表征土壤腐殖化程度和陸源有機(jī)物的降解程度.3,5-Bd/V比值越高,土壤腐殖化程度越高,陸源有機(jī)物的降解程度越高.P/(S+V)是木質(zhì)素中P系列單體與S和V系列單體總和的比值,可以用來(lái)評(píng)估木質(zhì)素受真菌(棕腐菌)去甲基/去甲氧基降解的程度,比值隨著降解的增強(qiáng)而增大[56-57].

黃河懸浮顆粒物中木質(zhì)素(Ad/Al)v的值在0.33~0.52之間,平均為0.43±0.04(圖7b).3,5-Bd/V的值在0.03~0.12之間,平均為0.09±0.03(圖7c), P/(S+V)的值在0.20~0.36之間,平均為0.27±0.05 (圖7d).綜合(Ad/Al)v, 3,5-Bd/V和P/(S+V) 3個(gè)降解參數(shù)來(lái)看,黃河顆粒物木質(zhì)素存在一定程度的降解.3,5-Bd/V和P/(S+V)比值夏季較低,說(shuō)明木質(zhì)素降解程度相對(duì)較小.(Ad/Al)v,3,5-Bd/V和P/(S+V) 3個(gè)降解參數(shù)均在秋季較高,說(shuō)明秋季黃河懸浮顆粒物木質(zhì)素降解程度較大.這可能是由于夏季初級(jí)生產(chǎn)較高,淡水浮游生物和陸源植物對(duì)有機(jī)碳有一定的貢獻(xiàn)造成的.Wang等[25]通過(guò)分析黃河POC的14C年齡也發(fā)現(xiàn),夏季黃河POC較為新鮮.而黃河秋季流量較大,使得沉積在河床上的顆粒物進(jìn)入懸移質(zhì)中.有研究表明,黃河河道沉積物上的有機(jī)碳年齡較高,多是“老碳”,降解程度較大[58].

4 結(jié)論

4.1 黃河利津2012年水沙輸運(yùn)季節(jié)性變化顯著,夏秋季徑流量和含沙量較高,水沙同步.

4.2 春季POC含量較高,可能與陸地植物和浮游生物的貢獻(xiàn)有關(guān). δ13C春夏季偏負(fù),可能是由于春夏季河水中初級(jí)生產(chǎn)較高,浮游生物和陸地植物貢獻(xiàn)較大.δ13C與C/N比及Λ8等參數(shù)結(jié)合,可判斷黃河有機(jī)碳主要來(lái)源于干流土壤及高等植物貢獻(xiàn).

4.3 黃河懸浮顆粒物有機(jī)碳中春季木質(zhì)素相對(duì)貢獻(xiàn)較多,秋末木質(zhì)素貢獻(xiàn)較少,但降解程度較大,這可能與秋季徑流較大,河床再懸浮的泥沙增多有關(guān).顆粒物中木質(zhì)素從陸地向海洋輸送過(guò)程中,具有一定選擇性,被子植物的草本組織更容易被保存并輸運(yùn)到渤海中.

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Sources, decay status and transport of particulate organic carbon in the lower Yellow River.

QIU Lu1,2, YAO Peng1*, ZHANG Ting-ting1,2, WANG Jin-peng1,2, PAN Hui-hui1,2, GAO Li-meng1,2, ZHAO Bin1,2

(1.Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China；2.College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China).

Both natural processes and human activities in river basins have important impacts on the transport of riverine particulate organic carbon (POC). Knowledge of the sources, decay status and transport of POC in rivers is therefore critical for a better understanding of global carbon cycling. Suspended particulate matters (SPM) monthly collected from the Lijin Station in the lower Yellow River in 2012 were analyzed for grain size,POC contents and stable carbon isotopic ratios (δ13C), and lignin composition. The water discharge, SPM contents and median grain size (MGS) at Lijin Station in 2012 were characterized by strong seasonal variations, which were basically identical. In spring, lower water discharge of the Yellow River (300m3/s) was observed compared with other seasons, possibly due to less precipitation and more downstream irrigation activities, making coarser particles more easily to settle down to the river bed. As a result, the SPM contents and MGS were both very low in this season (avg. 0.44kg/m3and avg. 7.77μm, respectively). In summer and autumn, sediments on river bed were easily resuspended due to high water discharge (more than 1000m3/s), which resulted in high SPM contents (0.67kg/m3) and high MGS (10.6μm). The results of POC and δ13C showed that OC contributions from different sources varied among seasons. In spring, the concentration of POC was relatively high and the13C of POC was depleted. The seasonal variation of lignin contents was similar with that of water discharge. The C/V (0.21~0.34) and S/V (0.83~1.28) ratios of lignin phenols indicated that the vascular plant tissues in SPM of the lower Yellow River were a mixture of woody and non-woody angiosperms. Lignin decay parameters, such as (Ad/Al)v(0.33~0.52), 3,5-Bd/V(0.03~0.12) and P/(S+V) (0.20~0.36) all showed that there was a certain degree of degradation of lignin in SPM. Relatively high degree of lignin decay was observed in autumn, which is probably connected with the variations of water discharge and OC sources during this period.

Yellow River；suspended particulate matters；particulate organic carbon；stable carbon isotope；lignin

X143

A

1000-6923(2017)04-1483-09

2016-08-22

國(guó)家重點(diǎn)研發(fā)計(jì)劃“全球變化及應(yīng)對(duì)”重點(diǎn)專項(xiàng)課題(2016YFA0600902);國(guó)家自然科學(xué)基金創(chuàng)新群體研究項(xiàng)目(41521064)

邱 璐(1992-),女,吉林樺甸人,青島海洋大學(xué)碩士研究生,主要研究方向?yàn)楹Ｑ笥袡C(jī)地球化學(xué).

* 責(zé)任作者, 教授, yaopeng@ouc.edu.cn

, 2017,37(4)：1483~1491