南漪湖上覆水溶解性有機(jī)質(zhì)的光譜特征

李海斌,謝發(fā)之*,李國蓮,翟紅俠,龔 雪,劉 站,羅 錕,袁志偉

南漪湖上覆水溶解性有機(jī)質(zhì)的光譜特征

李海斌1,2,3,謝發(fā)之1,2,3*,李國蓮2,翟紅俠1,3,龔 雪1,3,劉 站1,3,羅 錕1,3,袁志偉2

(1.安徽建筑大學(xué)材料與化學(xué)工程學(xué)院,安徽 合肥 230601；2.水污染控制與廢水資源化安徽省重點(diǎn)實(shí)驗(yàn)室,安徽 合肥 230601；3.安徽省先進(jìn)建筑材料國際聯(lián)合研究中心,安徽 合肥 230601)

為考察南漪湖上覆水中溶解性有機(jī)質(zhì)(DOM)的光譜特征與來源,采用紫外-可見光吸收光譜(UV-Vis)與三維熒光光譜(EEMs)為工具,并結(jié)合平行因子分析(PARAFAC)、熒光區(qū)域積分分析(FRI)、相關(guān)性分析、主成分分析與聚類分析對DOM進(jìn)行定性與定量分析.結(jié)果顯示,UV-Vis參數(shù)(440)、2/3、3/4、R表明DOM具有腐殖化特征與自生源特征,且2/3、3/4與(440)呈顯著正相關(guān)關(guān)系(<0.01,<0.05),R與(440)無顯著相關(guān)關(guān)系(>0.05),說明腐殖酸濃度越高則DOM相對分子量越大,但無法依據(jù)腐殖酸濃度大小判斷DOM來源.根據(jù)(440)計算獲得溶解性有機(jī)碳(DOC)平均濃度為26.79mg/L,且該湖泊出口附近DOC濃度為10.15mg/L.熒光指數(shù)(:、FI、BIX、HIX、Fn(280)、Fn(355))顯示該湖泊DOM具有腐殖化程度較低及強(qiáng)自生源特征,類蛋白組分(Fn(280))相對濃度的空間分布上由西向東逐漸增大,而腐殖酸類組分(Fn(355))相對濃度峰值出現(xiàn)在入湖口與出湖口.通過PARAFAC解析出3種組分,分別為類富里酸(C1)、類色氨酸(C2)和類腐殖酸(C3),且C1、C2、C3含量分別占總組分強(qiáng)度21.96%、13.36%、84.21%.FRI法分析顯示類蛋白物質(zhì)所占比例之和(區(qū)域I + II)為49.65%,該結(jié)果說明水體已受到了人為因素影響.通過相關(guān)性分析結(jié)果顯示,C1、C3與、BIX呈顯著負(fù)相關(guān)系(<0.001),C2與:、BIX、Fn(355)呈正相關(guān)系(<0.001).通過主成分分析與聚類分析,南漪湖上覆水中DOM在16個位點(diǎn)間呈現(xiàn)不同特征,但整體上水體中DOM來源受內(nèi)源輸入影響較為顯著,應(yīng)加強(qiáng)該湖泊內(nèi)源釋放污染物控制與管理.

溶解性有機(jī)質(zhì)；紫外-可見吸收光譜；三維熒光光譜；平行因子分析(PARAFAC)；熒光區(qū)域積分分析(FRI)；聚類分析

南漪湖位于宣城市宣州區(qū)與郎溪縣交界,其屬于泥沙長期封淤積水而成的淺水湖泊[1].該湖泊作為長江下游南岸外流淡水湖,其水源主要來自新、舊郎川河,且水源經(jīng)過新河莊匯入水陽江后直達(dá)長江[2].由于該湖泊受人為活動影響,其生物化學(xué)參數(shù)(浮游植物組成、葉綠素濃度、總氮磷濃度)表明該湖泊已由富營養(yǎng)化初級階段向中級階段過渡[3].另外,溶解性有機(jī)質(zhì)(DOM)作為非均質(zhì)高分子化合物,其容易影響水體中各種污染物的遷移與轉(zhuǎn)化[4].南漪湖水體中DOM不僅影響其自身生態(tài)功能,而且對長江流域生態(tài)系統(tǒng)也會構(gòu)成重要影響.為此,揭示南漪湖上覆水DOM組成、空間分布及來源具有重要意義.

三維熒光光譜(EEMs)與紫外-可見光吸收光譜(UV-Vis)是表征DOM分子結(jié)構(gòu)、組成與來源的重要技術(shù),尤其在開展湖泊DOM溯源方面已存在諸多報道.Wang等[5]以EEMs研究了呼倫湖水體中DOM組成與來源,該湖泊DOM濃度達(dá)到6.46～42.87mg/L,且濃度變化表現(xiàn)為夏季最高、冬季最低,冬季受結(jié)冰使得DOM空間分布呈顯著差異,湖岸周圍濃度高于湖中心,該湖泊DOM主要由類腐殖質(zhì)與類蛋白組成,陸源是該湖泊DOM主要來源.Lü等[6]采用EEMs解析了太湖DOM與顆粒有機(jī)物(POM)中熒光組分及來源,其熒光指數(shù)的時空分布表明POM主要來自內(nèi)源, POM夏、秋季以類蛋白為主,冬、春季以類腐殖質(zhì)為主,類色氨酸對POM成分貢獻(xiàn)最大,河口處POM與其它區(qū)域相比表現(xiàn)出更多外源性特征,而湖泊中DOM則主要表現(xiàn)為內(nèi)源特征.由于UV-Vis可提取DOM特征光譜參數(shù),進(jìn)而獲取DOM類型、相對濃度、芳香性強(qiáng)弱、疏水性組分含量等信息,將該光譜與EEMs相結(jié)合有其必要性.Wang等[7]將EEMs與UV-Vis結(jié)合剖析太湖水華暴發(fā)早期上覆水體DOM,其DOM主要由酪氨酸、類色氨酸與類腐殖質(zhì)組成,有色DOM在波長280,350nm處的紫外吸收系數(shù)分別為6.63～29.87,1.84～10.41m-1,全湖DOM濃度為2.86～11.83mg/L,且濃度從東南向西北呈上升趨勢,水華早期上覆水中DOM主要來自藻類活動及代謝.Ren等[8]采用EEMs與UV-Vis考察不同水文條件下南四湖水體DOM分布特征,該湖泊中DOM主要來自內(nèi)源釋放,空間尺度上湖底腐殖質(zhì)含量與腐殖化程度比湖面低,時間尺度上DOM貢獻(xiàn)表現(xiàn)為類腐殖質(zhì)比類蛋白強(qiáng),該結(jié)果可能與南水北調(diào)及沉水植物衰亡有關(guān).由于南漪湖點(diǎn)源污染及農(nóng)業(yè)面源污染負(fù)荷增加,圍欄養(yǎng)殖過程也未采取較好控制措施,其生態(tài)系統(tǒng)功能已呈退化現(xiàn)象.該湖泊中DOM信息尚不明確,采用EEMs與UV-Vis結(jié)合考察該湖泊上覆水DOM光譜特征,有利于從定性與定量角度揭示DOM性質(zhì)、濃度、分布特征等,理論方面能系統(tǒng)闡釋各光譜參數(shù)間相關(guān)性,實(shí)踐方面可為長江中下游湖泊群水質(zhì)數(shù)據(jù)完善、環(huán)境治理及風(fēng)險防控等提供參考.

通過采集南漪湖不同位點(diǎn)水面(上覆水)水樣,利用UV-Vis與EEMs考察該湖泊上覆水DOM光譜特征,并結(jié)合平行因子分析(PARAFAC)、熒光區(qū)域積分分析(FRI)、相關(guān)性分析、主成分分析與聚類分析對該湖泊DOM組成、分布與來源等情況予以解析,以期為南漪湖水生態(tài)環(huán)境決策與保護(hù)提供科學(xué)依據(jù).

1 材料與方法

1.1 樣品采集

圖1 采樣點(diǎn)示意

根據(jù)南漪湖水源入口與出口位置選取16個典型采樣點(diǎn),于2020年11月28～29日對南漪湖上覆水進(jìn)行采樣,具體位置如圖1所示.采樣時通過GPS定位器定位,在租賃漁船上通過有機(jī)玻璃水質(zhì)采樣器采集水面最上層水,采集水樣裝入已清洗的不透明聚四氟乙烯瓶中保存,并及時運(yùn)至實(shí)驗(yàn)室處理.水樣用0.45μm濾膜過濾獲得待測液,并將待測液及時進(jìn)行光譜檢測,其pH值、電導(dǎo)率、溶解氧濃度采用便攜式水質(zhì)測定儀現(xiàn)場測定.

1.2 光譜分析

采用UV-5500PC紫外可見分光光度計(上海元析儀器有限公司)測定UV-Vis,以超純水作為空白樣品,室溫條件下在1cm光程石英比色皿中測試,掃描波長為200～700nm.吸收系數(shù)采用公式(1)、(2)計算[9],2/3值、3/4值分別通過250與365nm、300與400nm處吸光度之比計算[10],光譜斜率R計算為275～295nm與350～450nm區(qū)域光譜斜率之比.EEMs測定采用F-4700熒光分光光度計(日立高新技術(shù)公司),基本參數(shù)為:光電倍增管(PMT)電壓為700V;激發(fā)與發(fā)射狹縫寬度均為5nm;響應(yīng)時間為自動;掃描速度為12000nm/min,設(shè)置激發(fā)波長(x)為220～ 450nm, 發(fā)射波長(m)為280～550nm.新鮮度指數(shù)(:)為x=310nm時,m在380nm熒光強(qiáng)度與420～ 435nm波段最大熒光強(qiáng)度比值;熒光指數(shù)(FI)為x= 370nm時,m在450nm與500nm處熒光強(qiáng)度比值[11];生物源指數(shù)(BIX)為x=310nm時,m在380nm與430nm處熒光強(qiáng)度比值;腐殖化指數(shù)(HIX)為x= 254nm時,m=435～480nm與m=300～345nm的熒光強(qiáng)度積分值的比值;Fn(280)、Fn(355)分別為x= 280nm處m=340～360nm間最大熒光強(qiáng)度、x= 355nm處m=440～470nm間最大熒光強(qiáng)度[12-14].

式中:為波長,nm;*()為條件下未去除誤差的吸收系數(shù),m-1;()為條件下去除誤差的吸收系數(shù), m-1;()為條件下吸光度;為光程路徑,0.01m.

1.3 數(shù)據(jù)處理與繪圖

采用Matlab 2019b軟件對EEMs進(jìn)行PARAFAC與FRI分析,采用Origin 2021b軟件進(jìn)行相關(guān)性分析、主成分分析與聚類分析,繪圖工具為軟件Origin 2021b與Sufer 8.0.

2 結(jié)果與討論

2.1 水體理化性質(zhì)

南漪湖上覆水理化性質(zhì)如表1所示,上覆水平均pH值為7.58,標(biāo)準(zhǔn)偏差為0.13,水質(zhì)呈弱堿性.水體平均電導(dǎo)率為380.56mS/cm,其數(shù)值較大,且其最大值與最小值差距較大.水體平均溶解氧濃度為9.26mg/L,水體呈現(xiàn)好氧狀態(tài).

表1 上覆水理化性質(zhì)

2.2 紫外-可見吸收光譜

圖2(a)為DOM的UV-Vis曲線.由于受環(huán)境因子、水動力作用、光化學(xué)催化、生物化學(xué)等過程影響,各位點(diǎn)間UV-Vis曲線強(qiáng)度存在明顯差異[15].吸光度均隨波長增加呈減小趨勢,且226～250、250～280nm處吸收峰分別由無機(jī)陰離子、木質(zhì)素磺酸及其衍生物組分所引起[16-17].如圖2(b)為不同位點(diǎn)(440)變化圖,在位點(diǎn)16處(440)達(dá)到最大值8.19m-1,即說明位點(diǎn)16處腐殖酸濃度最高[18].由于地理位置顯示該處遠(yuǎn)離河流入口,水動力條件不足會使水體復(fù)氧能力衰退,此外水溫增高會加快微生物及藻類殘體分解有機(jī)物速度,從而增大水體腐殖化程度.如圖2(c)為(440)、2/3、3/4、R變化,其值波動分別為0.66～8.19、2.85～7.40、1.37～7.57、0.01～4.32,均值分別為(2.37±1.12)、(4.66±1.34)、(3.92±1.24)、(1.48± 0.46).DOM分子量與2/3值呈負(fù)相關(guān)性,南漪湖2/3值與Erlandsson等[19]報道的湖泊2/3平均值4.70高度接近,說明兩湖泊間水體DOM分子量相似.腐殖化程度與3/4值呈負(fù)相關(guān)性,南漪湖3/4平均值顯然高于3.50,但56%位點(diǎn)要低于3.50,說明南漪湖腐殖質(zhì)主要以類腐殖酸為主[20].南漪湖81%樣品R值均大于1,說明南漪湖上覆水DOM主要來自內(nèi)源釋放,其釋放途徑主要為水生物代謝與生物殘骸腐化等作用[21].圖2(d)顯示(440)與2/3、3/4呈顯著正相關(guān)系(<0.01,<0.05),即說明腐殖酸濃度高則DOM分子量相對較大.其可能是在自然環(huán)境或在光譜檢測過程中,光照條件會使大分子量DOM發(fā)生降解形成了小分子量DOM,且降解過程中DOM濃度會發(fā)生降低[22].由于(440)反映腐殖酸濃度高低,而R反映DOM來源,(440)與R無顯著相關(guān)性(>0.05),說明在統(tǒng)計學(xué)角度無法從腐殖酸濃度判斷DOM來源,該結(jié)果正好與實(shí)際情況相吻合,即無法單純從腐殖酸濃度明確DOM來源.根據(jù)文獻(xiàn)[23]中方法可定量計算溶解性有機(jī)碳(DOC)濃度,計算的平均DOC濃度為26.79mg/L,該湖泊出口附近DOC濃度為10.15mg/L,此結(jié)果用于評估南漪湖上覆水DOM對長江水質(zhì)的影響.

2.3 三維熒光光譜

2.3.1 熒光參數(shù) 為考察DOM的EEMs特征,選取熒光參數(shù)(:、FI、BIX 、HIX、Fn(280)、Fn(355))進(jìn)行分析,結(jié)果如圖3所示.:變化為0.92～1.68,其平均值為(1.06±0.10),說明水體中新生DOM較多,且水體生物活性較高,內(nèi)源特征較為明顯.FI變化為1.71～2.49,其平均值為(1.95±0.14).當(dāng)FI<1.20、FI>1.80、1.20

2.3.2 熒光組分 利用PARAFAC對DOM的EEMs進(jìn)行分析,核心一致度評價最優(yōu)主成分為3,即解析獲得主要熒光組分為3種,其相應(yīng)激發(fā)與發(fā)射光譜圖如圖4所示.組分主要為2個類腐殖質(zhì)組分(C1,C3)和1個類蛋白組分(C2),且3種熒光組的光譜特征如表3所示.C1組分在天然水體中廣泛存在,屬于陸源性短波小分子類微生物腐殖質(zhì),其不易光降解及生物降解,主要來源為森林地區(qū)、濕地、地表徑流、土壤滲濾液等,與細(xì)菌以及藻類細(xì)胞釋放的胞外腐殖質(zhì)類似[37].C2組分最大波峰特征顯示其主要來源為水體內(nèi)部產(chǎn)生的低激發(fā)態(tài)類色氨酸物質(zhì),屬于游離或結(jié)合在蛋白質(zhì)中的微生物代謝產(chǎn)物.C3組分為與富里酸相似的大分子疏水性長波類陸源UVA類腐殖質(zhì), 其主要來源為陸源,該組分可光降解及生物降解,但生物降解、生物活動是其潛在的二次來源.

表2 不同水體中DOM光譜參數(shù)對比結(jié)果

根據(jù)Zhou等[43]方法將DOM熒光區(qū)域分成5個區(qū)域,其劃分情況如表4所示.由于FRI法是將定量分析與光譜學(xué)相結(jié)合的有效方法之一,可以較為細(xì)致闡明DOM組成與熒光光譜變化規(guī)律[44].圖5(a)為南漪湖上覆水區(qū)域積分面積百分比堆積圖,溶解性微生物代謝副產(chǎn)物在湖入口位點(diǎn)6處濃度最高,在湖入口位點(diǎn)4處濃度最低,該結(jié)果應(yīng)是生物活動與水動力相互作用結(jié)果.色氨酸類蛋白濃度在湖入口位點(diǎn)7處最高,說明此處受到人為活動影響最大.圖5(b)為積分體積與百分比平均值圖,區(qū)域II平均百分含量最高為34.29%,其在26.18%～47.21%波動變化,芳香類蛋白物質(zhì)濃度較高則說明水體容易受到污水排放影響.區(qū)域III平均百分含量(29.61%)次于區(qū)域II,說明紫外光區(qū)類富里酸濃度較高,DOM受到沉積物與河流中陸源腐殖質(zhì)影響.區(qū)域 IV與V平均百分含量分別為14.17%、6.57%,而類蛋白物質(zhì)所占比例之和(區(qū)域I +II)為49.65%,進(jìn)一步說明水體已受到人為活動影響.

表3 熒光組分特征

表4 5個積分區(qū)域劃分

圖5 FRI分析結(jié)果

2.4 來源解析

為考察DOM熒光組分與光譜參數(shù)間關(guān)系,采用Pearson相關(guān)性分析與主成分分析(PCA)對DOM進(jìn)行解析.圖6(a)為相關(guān)性分析結(jié)果,:、BIX、Fn(355)與C2呈正相關(guān)系(<0.001),:、BIX與C1、C3呈顯著負(fù)相關(guān)系(<0.001).PCA分析結(jié)果如圖6(b)所示,PCA1與PCA2分別解釋了48.30%、28.00%(共解釋76.30%變化).PCA顯示采樣點(diǎn)分布相對較為分散,表明不同位點(diǎn)間DOM存在顯著差異.圖7為南漪湖上覆水DOM研究思路,通過熒光區(qū)域積分面積百分比數(shù)據(jù)進(jìn)行聚類,結(jié)果顯示位點(diǎn)分布相對分散.南漪湖上覆水DOM可以聚為4類,第一類主要是郎川河支流附近的樣品,第二類主要是距支流較遠(yuǎn)樣品,第三類主要為飛鯉河支流附近樣品,第四類為前面三類所剩余樣品,說明該湖泊中DOM具有不同來源,其存在差異原因主要受地理位置、環(huán)境因素及人為因素影響.

綜上所述,由于南漪湖屬于淺水湖泊,水體流動性強(qiáng)使得DOM腐殖化程度低. 陸源與自生源共同作用是DOM來源,但主要以內(nèi)源輸入為主.目前,湖泊DOM主要是內(nèi)源輸入有南四湖[8]、五里湖[45]、蠡湖[46]等.然而,南漪湖上覆水中DOM內(nèi)源輸入與該湖泊中蘆葦、菱角、蓮藕等植物殘體腐解及生物代謝密切相關(guān).

3 結(jié)論

3.1 南漪湖上覆水UV-Vis參數(shù)(440)為0.66～ 8.19m-1,2/3與3/4值顯示南漪湖腐殖質(zhì)主要以類腐殖酸為主,且(440)與2/3、3/4呈顯著正相關(guān)關(guān)系(P<0.01,<0.05).R表明其DOM內(nèi)源釋放作用較強(qiáng),且R與(440)與無顯著相關(guān)性(>0.05).上述參數(shù)相關(guān)性說明腐殖酸濃度越高則DOM相對分子量越大,而在統(tǒng)計學(xué)角度無法從腐殖酸濃度判斷DOM來源.

3.2 熒光指數(shù)(、FI、BIX 、HIX、Fn(280)、Fn(355))表明DOM來源受外源輸入與內(nèi)源釋放共同作用,且腐殖酸類組分(Fn(355))相對濃度在入湖口與出湖口呈現(xiàn)最大值.由于南漪湖為典型淺水湖泊,其DOM腐殖化程度相對較低. PARAFAC分析鑒別獲得3種熒光組分,C1為類富里酸、C2為類色氨酸、C3類腐殖酸.FRI法分析結(jié)果顯示類蛋白物質(zhì)所占比例之和(區(qū)域I + II)為49.65%,說明水體已受到了人為因素影響.

3.3、BIX與C1、C3呈顯著負(fù)相關(guān)系(< 0.001),、BIX、Fn(355)與C2呈正相關(guān)系(<0.001). PCA分析與聚類分析顯示采樣點(diǎn)分布相對分散,說明不同位點(diǎn)間DOM存在顯著差異,但DOM來源主要是以內(nèi)源輸入為主.

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Spectral characteristics of dissolved organic matter in the overlying water from Nanyi Lake.

LI Hai-bin1,2,3, XIE Fa-zhi1,2,3*, LI Guo-lian2, ZHAI Hong-xia1,3, GONG Xue1,3, LIU Zhan1,3,LUO Kun1,3, YUAN Zhi-wei2

(1.School of Materials and Chemical Engineering, Anhui Jianzhu University, Hefei 230601, China；2.Anhui Key Laboratory of Water Pollution Control and Wastewater Resource, Hefei 230601, China；3.Anhui Province International Research Center on Advanced Building Materials, Hefei 230601, China)., 2022,42(7)：3306～3315

In order to investigate the spectral characteristics and the sources of dissolved organic matter (DOM) in the overlying water of the Nanyi Lake. Herein, ultraviolet-visible (UV-Vis) absorption and three-dimensional fluorescence excitation-emission matrix (EEMs) were utilized to characterize the DOM. Parallel factor analysis (PARAFAC), fluorescence regional integration, correlation analysis, principal component analysis, and cluster analysis were applied to qualitative and quantitative analysis on the DOM. Based on the absorption parameters of(440),2/3,3/4,Rof UV-Vis spectrum, it was found that DOM has humification and autogenesis characteristics. Moreover,2/3,3/4and(440) had positively correlation (<0.01,<0.05), and there was no significant correlation betweenRand(440) (>0.05). The relative molecular weight of DOM increased with increasing the humic acid concentration, but the humic acid concentration cannot be used to determine the sources of dissolved organic matter (DOM). According to the(440) values, the average concentration of dissolved organic carbon (DOC) in the water was calculated to be 26.79mg/L, and the DOC value in the outlet area of the lake was 10.15mg/L. From the analysis of fluorescence indices (:, FI, BIX, HIX, Fn(280), Fn(355)), the DOM exhibited low humification and highly autochthonous characteristics. The spatial distribution of the relative concentration of protein-like components (Fn(280)) was gradually increased from west to east, but the peak values of the relative concentration of humic-like components (Fn(355)) were observed in the estuary and lake outlet. Three fluorescence components of fulvic-like, tryptophan-like and humic-like identified by PARAFAC model were named as C1, C2, C3, and the contribution of C1, C2, C3 to the total fluorescence intensity were 21.96%, 13.36%, 84.21%, respectively. The results of the FRI method showed that the sum of the proportions of protein-like substances (region I +II) was as large as 49.65%, and it was mainly related to anthropogenic activities. Certain correlation was observed between the fluorescence components and the spectral parameters, and it was found that the C1, C3 and:, BIX were significantly negative correlated (<0.001). C3 and:, BIX, Fn (355) were positive correlated (<0.001). Based on the principal components analysis and cluster analysis, the DOM presented different characteristics between the 16sites in the Nanyi Lake. Overall, the DOM was significantly affected by endogenous input, and the control and management of pollutants released from the lake should be strengthened.

DOM；ultraviolet-visible spectrum；fluorescence spectroscopy；PARAFAC；FRI；cluster analysis

X524

李海斌(1989-),男,安徽省安慶人,講師,碩士,主要從事研究方向?yàn)樗w富營養(yǎng)化與水污染控制研究.發(fā)表論文7篇.

2021-12-15

國家自然科學(xué)基金資助項目(21777001);安徽省重點(diǎn)研發(fā)計劃(202004i07020006);安徽省高校省級自然科學(xué)研究項目(KJ2020JD13);安徽省先進(jìn)建筑材料國際聯(lián)合研究中心主任基金(JZCL014ZZ)

* 責(zé)任作者, 教授, fzxie@ahjzu.edu.cn

A

1000-6923(2022)07-3306-10