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      撫仙湖秋、冬季光衰減特征及其與有色可溶性有機(jī)物的關(guān)系?

      2016-11-24 09:31:43周起超張運林周永強(qiáng)陳毅良聶菊芬
      湖泊科學(xué) 2016年6期
      關(guān)鍵詞:撫仙湖衰減系數(shù)湖泊

      周起超,張運林,周永強(qiáng),陳毅良,秦 江,聶菊芬

      (1:云南省環(huán)境科學(xué)研究院(中國昆明高原湖泊國際研究中心)高原湖泊流域污染過程與管理云南省重點實驗室,昆明650034)(2:中國科學(xué)院南京地理與湖泊研究所湖泊與環(huán)境國家重點實驗室,南京210008)(3:中國科學(xué)院大學(xué),北京100049)

      撫仙湖秋、冬季光衰減特征及其與有色可溶性有機(jī)物的關(guān)系?

      周起超1,2,張運林2??,周永強(qiáng)2,3,陳毅良1,秦 江1,聶菊芬1

      (1:云南省環(huán)境科學(xué)研究院(中國昆明高原湖泊國際研究中心)高原湖泊流域污染過程與管理云南省重點實驗室,昆明650034)(2:中國科學(xué)院南京地理與湖泊研究所湖泊與環(huán)境國家重點實驗室,南京210008)(3:中國科學(xué)院大學(xué),北京100049)

      為了研究撫仙湖紫外輻射(UVR)和光合有效輻射(PAR)衰減的時空特征及其與有色可溶性有機(jī)物(CDOM)、懸浮物(SS)、浮游植物(葉綠素a表征)等因子的關(guān)系,于2014年10月(秋季)、2015年1月(冬季)開展現(xiàn)場調(diào)查,結(jié)果顯示:秋季不同波長(段)的漫射衰減系數(shù)Kd(305)、Kd(340)和Kd(PAR)分別為1.27±0.12、0.68±0.11和0.32±0.13 m-1,冬季分別為1.13±0.10、0.63±0.07和0.36±0.07 m-1;秋季CDOM的不同波長吸收系數(shù)ag(254)、ag(305)和ag(340)分別為4.09±0.26、1.18±0.09和0.57±0.05 m-1,冬季分別為2.95±0.24、0.61±0.11和0.11±0.07 m-1,秋季ag(254)、ag(305)和ag(340)顯著高于冬季;秋季Kd(305)顯著大于冬季,這與秋季(雨季)較高的CDOM豐度、浮游植物生物量(及SS濃度)有關(guān).秋季ag(305)/Kd(305)、ag(340)/Kd(340)均顯著高于冬季;秋季及秋冬季整體而言,ag(254)與Kd(305)、Kd(340)呈顯著正相關(guān),各多元逐步回歸方程中均包含ag(254),說明CDOM吸收對UVR的衰減有重要貢獻(xiàn).空間差異方面,秋季北部的ag(254)、Kd(305)和Kd(340)顯著高于南部,冬季南北部無明顯差異,或與雨旱季北岸河流輸入的CDOM和SS的情況有關(guān).此外,浮游植物對UV-B衰減的影響和SS(與CDOM的交互作用)對UV-A衰減的影響更在于季節(jié)變化方面,而影響UVR、PAR衰減的各因子的相對貢獻(xiàn)有待進(jìn)一步量化.

      漫射衰減系數(shù);紫外輻射;真光層;有色可溶性有機(jī)物;時空分布;撫仙湖

      spectively in autumn,which were 2.95±0.24 m-1,0.61±0.11 m-1,0.11±0.07 m-1,respectively in winter.The values of of ag(254),ag(305)and ag(340)in autumn were significantly higher than in winter.The values of of Kd(305)in autumn were significantly higher than in winter,which was related with higher CDOM abundance,phytoplankton biomass(and SS concentration)in autumn(rainy season).Furthermore,the values of ag(305)/Kd(305)and ag(340)/Kd(340)in autumn were significantly higher than which in winter;there were significant positive correlations between ag(254)and Kd(305),Kd(340),and the ag(254)included in all stepwise regression equations both in autumn and autumn-winter,indicated that the absorption of CDOM was an important factor affecting on the diffuse attenuation of UVR.Moreover,there were obvious differences depend on spatial distribution of ag(254),Kd(305)and Kd(340)in autumn,the values of ag(254),Kd(305)and Kd(340)in the north region of the lake was significantly higher than in the south region,whereas there were no significant differences between the north and south regions of ag(254),Kd(305)and Kd(340)in winter,which might be related with the different river input scenarios of CDOM and SS from the northern shore between autumn(rainy season)and winter(dry season).In addition,the influences of phytoplankton on UV-B attenuation,the interaction between SS and CDOM on UV-A attenuation were reflected in seasonal changes.However,the relative contribution of pure water,CDOM,phytoplankton and tripton to spectral attenuation(including UVR and PAR)should be quantized in future.

      ?國家自然科學(xué)基金項目(41601208,41325001)、湖泊與環(huán)境國家重點實驗室開放基金項目(2016SKL007)、云南省科技計劃項目(2016RA081)和云南省應(yīng)用基礎(chǔ)研究計劃項目聯(lián)合資助.2015-11-10收稿;2016-01-02收修改稿.周起超(1985~),男,博士,副研究員/博士后;E-mail:qchzhou@gmail.com.

      ??通信作者;E-mail:ylzhang@niglas.ac.cn.

      紫外輻射(ultraviolet radiation,UVR)是日光的必有成分,UV-C(200~280 nm)通常被臭氧層和大氣層完全吸收,到達(dá)地面的主要為UV-B(280~320 nm)和UV-A(320~400 nm);UVR與光合有效輻射(photosynthetically active radiation,PAR,400~700 nm)共同影響著湖泊生態(tài)系統(tǒng)的熱力學(xué)結(jié)構(gòu)、生物地球化學(xué)循環(huán)、光合作用與初級生產(chǎn)力、種群動態(tài)和群落結(jié)構(gòu)等層面的發(fā)展與變化[1-3].光輻射在水體中的傳輸分布主要受純水、有色可溶性有機(jī)物(chromophoric dissolved organic matter,CDOM)、浮游植物和非色素顆粒物的影響[1];其中,CDOM普遍存在于自然水體,是重要的光化學(xué)、光生物學(xué)和生物地球化學(xué)物質(zhì),對UVR有強(qiáng)烈的吸收[1,4].高海拔清澈型湖泊中,溶解性有機(jī)質(zhì)(含CDOM)、浮游植物對UVR衰減的貢獻(xiàn)大[5-8],加之二者含量低,使其光輻射對流域環(huán)境的變化更加敏感;同時,海拔高致使所接受的UVR強(qiáng)[9],較深的UVR穿透深度或使其對湖泊生態(tài)系統(tǒng)的影響進(jìn)一步放大.

      撫仙湖是高原深水貧營養(yǎng)湖泊的典型代表,主導(dǎo)功能為飲用水源地,保持著良好水質(zhì)(Ⅰ~Ⅱ類)[10].然而,歷史數(shù)據(jù)已表明,撫仙湖富營養(yǎng)化和有機(jī)污染水平及浮游植物生物量有所升高,透明度下降,水質(zhì)有惡化趨勢[11-12],浮游植物功能群[13]、底棲動物[14]和魚類[15]群落結(jié)構(gòu)等亦已發(fā)生變化.鑒于光對湖泊生態(tài)過程的驅(qū)動作用,要更好地實現(xiàn)對撫仙湖生態(tài)環(huán)境的保護(hù),對其光學(xué)特征的深入了解是難以回避的.目前,涉及撫仙湖光學(xué)特征(含CDOM)的研究并不多[16-18],且未涉及時空差異及其影響因子等方面的分析;秋、冬季不僅是太陽輻射與溫度變化、湖泊熱分層變化的重要時期,還是撫仙湖雨季、旱季的不同代表,亦是浮游植物增殖或衰退的關(guān)鍵時期,以上均可能對CDOM的來源、降解以及湖泊光場等產(chǎn)生重要影響.因此,本文基于新近開展的野外調(diào)查,研究了撫仙湖秋、冬兩季UV-B、UV-A、PAR的衰減特征及其與CDOM、懸浮物(suspended solids,SS)、浮游植物等的關(guān)系,結(jié)果既能為撫仙湖積累有關(guān)歷史數(shù)據(jù),又能為基于湖沼學(xué)原理的高原清澈型深水湖泊的生態(tài)環(huán)境保護(hù)提供支撐.

      1 材料與方法

      1.1 撫仙湖概況

      撫仙湖(24°21′~24°38′N,102°49′~102°57′E),斷陷型湖泊,地跨云南省玉溪市澄江、江川、華寧三縣,屬中亞熱帶高原半濕潤季風(fēng)氣候,湖泊面積216.6 km2,最大水深158.9 m,平均水深95.2 m,是我國第二深內(nèi)陸淡水湖泊;運行水位1720.8~1722.5 m,蓄水量206.2×108m3,占云南九大高原湖泊總蓄水量的67.9%,屬貧營養(yǎng)湖泊[10].

      1.2 樣品采集與指標(biāo)測定

      在撫仙湖設(shè)置16個點位(圖1,1?!?#代表北部,10#~16#代表南部),于2014年10月下旬(秋季)和

      2015年1月下旬(冬季)開展調(diào)查工作.各點位均用PUV-2500水下剖面輻射儀(Biospherical Instruments Inc.,USA)測定不同深度不同波長(段)的光強(qiáng),測定的深度范圍為0~3.3 m,再根據(jù)指數(shù)擬合計算UV-B(305 nm)、UV-A(340 nm)與PAR(400~700 nm)衰減系數(shù)(Kd),并計算1%輻射深度(Z1%)[16];用多參數(shù)水質(zhì)監(jiān)測儀YSI 6600(Yellow Springs Instruments,USA)測定水柱水溫(WT)、電導(dǎo)率(EC)、pH和溶解氧(DO),由此計算熱分層期的溫躍層相關(guān)指標(biāo)[19];與此同時,采集各點位水下0.5 m水樣,測定其它相關(guān)指標(biāo).

      CDOM光譜吸收系數(shù):采用經(jīng)孔徑0.22 μm的Millopore膜過濾的水樣在帶積分球的UV-2550 PC型分光光度計(SHIMADZU,Japan)下測定200~800 nm波長范圍的吸光度,然后進(jìn)行計算、校正得到各波長的吸收系數(shù)[18],以254 nm的吸收系數(shù)(ag(254))表征CDOM豐度[20];ag(λ)/Kd(λ)為λ波長時CDOM吸收系數(shù)與漫射衰減系數(shù)的比例[16].溶解性有機(jī)碳(dissolved organic carbon,DOC)濃度:水樣經(jīng)GF/F濾膜過濾后,用TOC-VCPN儀(SHIMADZU,Japan)通過高溫燃燒法測定.總氮(TN)、總磷(TP)、化學(xué)耗氧量(CODMn)、SS、葉綠素a(Chl.a)濃度的測定參照文獻(xiàn)[21].

      圖1 撫仙湖采樣點位置Fig.1 Location of sampling sites in Lake Fuxian

      1.3 統(tǒng)計分析

      兩獨立樣本T檢驗、Pearson相關(guān)性分析及一元線性回歸和多元逐步回歸均采用SPSS 22.0軟件完成,P<0.05表示顯著,P<0.01表示極顯著.

      2 結(jié)果

      2.1 撫仙湖水柱表層理化參數(shù)與湖泊熱分層

      調(diào)查期間,撫仙湖秋季水柱表層WT、EC、TP濃度、CODMn、DOC濃度、Chl.a濃度顯著大于冬季,而TN濃度顯著小于冬季,秋、冬季pH、DO、SS無顯著差異(表1).秋季有明顯的熱分層現(xiàn)象,其溫躍層上界深度為28.64±1.98 m、溫躍層下界深度為34.07±2.19 m、溫躍層厚度為5.56±1.92 m、溫躍層強(qiáng)度為0.79±0.20℃/m;冬季水溫相對均一,無明顯熱分層.由于秋季溫躍層的深度高達(dá)28.64±1.98 m,因此在表層的3.3 m范圍內(nèi)進(jìn)行水下光輻射垂直剖面測定不會受湖泊分層的影響,混合層水柱垂直上相對均一.

      2.2 撫仙湖漫射衰減系數(shù)與1%輻射深度

      秋季UV-B、UV-A和PAR的衰減系數(shù)分別為1.27±0.12、0.68±0.11和0.32±0.13 m-1,冬季UV-B、UV-A和PAR的衰減系數(shù)分別為1.13±0.10、0.63±0.07和0.36±0.07 m-1,秋季UV-B衰減系數(shù)顯著高于冬季(P<0.01,表1),秋、冬季UV-A(P=0.110)、PAR(P=0.138)衰減系數(shù)的差異則不顯著(表1);相應(yīng)的,冬季UV-B

      的1%輻射深度顯著高于秋季(P<0.01),UV-A、PAR的1%輻射深度則無明顯差異.空間差異方面(圖2~4),秋季北部UV-B(P<0.01)、UV-A(P<0.05)的衰減系數(shù)顯著高于南部,對應(yīng)的,1%輻射深度則為北部顯著低于南部,南部PAR的1%輻射深度略高于北部,但無顯著性差異;冬季UV-B、UV-A的1%輻射深度南北部無明顯差異且UV-B的1%輻射深度最深處為湖心附近,南部PAR的1%輻射深度顯著高于北部(P<0.05).

      表1 撫仙湖水柱表層有關(guān)參數(shù)Tab.1 Some parameters in the surface of water column in Lake Fuxian

      2.3 撫仙湖CDOM吸收光譜特征與時空分布

      秋、冬季水柱表層CDOM吸收光譜表明,200~225 nm時,冬季的吸收系數(shù)高于秋季,冬季各點位間的差異大于秋季;225~250 nm時,冬季的吸收系數(shù)高于秋季(圖5).秋季CDOM在254、305和340 nm處的吸收系數(shù)分別為4.09±0.26、1.18±0.09和0.57±0.05 m-1,冬季CDOM在254、305和340 nm處的吸收系數(shù)分別為2.95± 0.24、0.61±0.11和0.11±0.07m-1,秋季CDOM 3個波長的吸收系數(shù)均顯著高于冬季(P<0.01,表1).秋季ag(305)/Kd(305)、ag(340)/Kd(340)分別為92.85%±6.57%、85.27%±13.28%,冬季分別為54.31%±10.62%、18.01%±10.87%,秋季的比值均顯著高于冬季的比值,UV-B的比值顯著高于UV-A的比值(P<0.01,表1). CDOM豐度水平空間分布表明(圖6),秋季北部顯著高于南部(P<0.01),冬季南北部無顯著差異,但中部最低.

      2.4 輻射衰減與各參數(shù)相關(guān)性

      UV-B、UV-A、PAR的漫射衰減系數(shù)與各參數(shù)相關(guān)性分析表明,秋季,Kd(305)與CODMn、ag(254)、ag(305)均呈顯著正相關(guān),Kd(340)與ag(254)、ag(305)均呈顯著正相關(guān),Kd(PAR)與ag(305)呈顯著正相關(guān).冬季,僅Kd(340)與TN呈顯著負(fù)相關(guān),其余均無顯著相關(guān)性(表2).若以秋、冬季為整體進(jìn)行分析,Kd(305)與TN呈顯著負(fù)相關(guān),與TP、CODMn、SS、DOC、Chl.a、ag(254)、ag(305)、ag(340)均呈顯著正相關(guān);Kd(340)與TN呈顯著負(fù)相關(guān),與ag(254)、ag(305)均呈顯著正相關(guān).對UV-A、UV-B、PAR的漫射衰減系數(shù)與CDOM豐度、Chl.a、SS及各參數(shù)的交互因子做了多元逐步回歸,結(jié)果表明,秋季UV-B衰減主要與CDOM豐度及其SS

      的交互效應(yīng)有關(guān),UV-A衰減主要與CDOM豐度有關(guān);秋冬季整體而言,UV-B衰減與CDOM豐度及其與Chl. a和SS的交互效應(yīng)有關(guān),UV-A衰減與CDOM和SS的交互效應(yīng)有關(guān);冬季,UV-B、UV-A衰減與檢測因子均無明顯關(guān)系;不論秋季、冬季或秋冬季為整體,PAR衰減與檢測因子均無明顯相關(guān)性(表3).

      表2 漫射衰減系數(shù)與各參數(shù)相關(guān)性Tab.2 Pearson correlations between Kd(λ)and other parameters in the surface of water column

      表3 Kd(λ)與ag(254)、Chl.a、SS及其交互因子的多元逐步回歸Tab.3 Stepwise regression between Kd(λ)and ag(254),Chl.a,SS and their interactive factors

      3 討論

      光輻射在水體中的傳輸分布主要受純水、CDOM、浮游植物和非色素顆粒物的影響,各因子權(quán)重變化直接影響著水下光場結(jié)構(gòu)[1].Laurion等[7]的研究表明,CDOM在很大程度上解釋了阿爾卑斯山和庇里牛斯山26個湖泊間(海拔422~2799 m,Chl.a濃度0.25~3.61 μg/L,DOC濃度0.21~3.50 mg/L)UVR衰減的變化;張運林等[5]于2005年夏季對云南高原34個湖泊開展了調(diào)查,認(rèn)為透明度大于1 m的清澈型湖泊中CDOM吸收很大程度上決定了UVR的影響深度.2006-2007年長江中下游平原湖泊的調(diào)查結(jié)果顯示,其ag(320)/Kd(320)、ag(360)/Kd(360)分別為50.7%±11.6%、38.6%±12.5%,Zhang等[16]認(rèn)為這預(yù)示著CDOM吸收是影響UVR衰減的重要因子之一.本研究中,秋季的ag(305)/Kd(305)、ag(340)/Kd(340)與之相當(dāng)或更高,且秋季和秋冬季整體的UVR衰減系數(shù)與CDOM豐度顯著正相關(guān),各逐步回歸方程中均包括ag(254),說明CDOM吸收在撫仙湖UVR的衰減中扮演著重要角色.基于CDOM的吸收光譜可知,其對UV-B的吸收要高于UV-A,而不論秋季或冬季,ag(305)/Kd(305)均大于ag(340)/Kd(340),與撫仙湖夏季及云南高原、長江中下游平原湖泊之前的研究結(jié)果一致[16,18];不論秋季或秋冬季整體,Kd(305)與ag(305)均呈極顯著正相關(guān),Kd(340)與ag(340)則無顯著相關(guān)性,說明CDOM吸收對UV-B衰減的影響大于UV-A.秋季Kd(305)與ag(254)、ag(305)均呈顯著正相關(guān),Kd(340)與ag(254)呈顯著正相關(guān),冬季Kd(305)、Kd(340)與ag(254)、ag(305)、ag(340)均無顯著相關(guān)性,且未建立相應(yīng)的逐步回歸方程,說明CDOM吸收對秋季UVR衰減的影響大于冬季.

      圖2 撫仙湖秋、冬季UV-B(305 nm)衰減系數(shù)與1%輻射深度空間分布Fig.2 Spatial distributions of Kdand Z1%of UV-B(305 nm)in autumn and winter in Lake Fuxian

      CDOM的吸收光譜特征與水體類型有關(guān)[4],如湖泊所處的地理位置、營養(yǎng)狀態(tài)等均可能對其產(chǎn)生影響[16,22],有研究表明云南高原湖泊CDOM的吸收整體上小于長江中下游湖泊[16],同處云南高原[18]或長江中下游平原[22-23]的湖泊之間同樣存在差異,而同一水體的CDOM吸收的時空差異已有許多報道[24-28],這也在本研究中得以體現(xiàn).CDOM的來源可分為外源的河流輸入、降水和內(nèi)源的沉水植物死亡降解以及沉積物間隙水的釋放[1],浮游植物的降解[27]、分泌[29]以及細(xì)菌和水生動物[30]等均會產(chǎn)生CDOM.本研究中,ag(254)與Chl.a的回歸關(guān)系(Slope=0.724,R2=0.387,P<0.001,N=32)表明,撫仙湖浮游植物對CDOM有所貢獻(xiàn),ag(254)與CODMn的回歸關(guān)系(Slope=1.802,R2=0.186,P<0.05,N=32)表明,CDOM是撫仙湖有機(jī)污染的重要組分.雖然原位產(chǎn)生的CDOM會影響其季節(jié)變化[26],但這并不排除河流輸入的主要貢獻(xiàn)[1];雖然降水自身攜帶的CDOM對湖體CDOM輸入的貢獻(xiàn)較低[20],但雨季的河流輸入會攜帶大量的陸源CDOM[24-25,31]和SS[32]入湖.撫仙湖北部的澄江縣是非點源污染最嚴(yán)重的區(qū)域,其河道徑流量占63.7%,TN、 TP輸入量分別占57.5%、49.9%,且雨季(6-11月)遠(yuǎn)高于旱季(12月、1-5月)[33].撫仙湖較深且秋季(10

      月)存在明顯的熱分層,沉積物間隙水CDOM懸浮釋放可忽略,故北部CDOM豐度顯著高于南部,或與南部UVR的衰減系數(shù)顯著低于北部、1%輻射深度顯著高于北部有關(guān).冬季(1月,旱季)降水少,撫仙湖入湖河流徑流量?。?3],CDOM和SS的河流輸入減少,水溫低浮游植物生物量減少、生理活性降低,陸源和藻源CDOM均隨之減少,加之光降解作用[34],故冬季CDOM豐度顯著低于秋季,又因湖水的梯度稀釋作用[31],導(dǎo)致CDOM豐度南北部無明顯差異且湖心附近最低,或與UV-B的衰減系數(shù)最小值、1%輻深度最大值在湖心有關(guān).同時,相關(guān)性分析和多元逐步回歸結(jié)果表明,UV-B衰減的季節(jié)變化與CDOM、SS和浮游植物有關(guān),加之秋、冬季(雨旱季)的情景差異(如前所述),故秋季UV-B衰減系數(shù)顯著大于冬季.此外,本研究顯示撫仙湖SS濃度為1.45±0.61 mg/L、Chl.a濃度為1.90±0.54 μg/L、DOC濃度為1.71±0.37 mg/L,暗示清澈型湖泊由于SS濃度、DOC濃度(CDOM豐度)、浮游植物生物量的本底值低,光輻射特征易受流域有機(jī)質(zhì)輸入的影響,與有關(guān)結(jié)果一致[35-36].

      圖3 撫仙湖秋、冬季UV-A(340 nm)衰減系數(shù)與1%輻射深度空間分布Fig.3 Spatial distributions of Kdand Z1%of UV-A(340 nm)in autumn and winter in Lake Fuxian

      就輻射衰減的其它影響因子而言.高海拔清澈型湖泊中,浮游植物對UVR衰減的顯著影響主要表現(xiàn)在

      低DOC濃度條件下[7-8],如阿爾卑斯山Gossenk?llesee湖紫外穿透深度在時間尺度上的減小與浮游植物Chl.a濃度的上升顯著相關(guān)[8].本研究中,雖然Chl.a濃度與UV-B的衰減在整體上呈顯著正相關(guān),但同一季節(jié)內(nèi)并無明顯關(guān)系,說明浮游植物的作用主要體現(xiàn)在季節(jié)變化上,SS、DOC(不等同于CDOM)與之類似;根據(jù)回歸方程可知,SS、Chl.a對UV-B衰減的影響存在與CDOM的交互效應(yīng),SS與CDOM的交互效應(yīng)在一定程度上影響了UV-A衰減的季節(jié)變化.此外,遠(yuǎn)洋中純水對光衰減的貢獻(xiàn)在波長大于440 nm時超過了CDOM、浮游植物和非色素顆粒物的貢獻(xiàn),可達(dá)30%~95%以上[4],而撫仙湖秋冬季PAR的衰減與SS、DOC、Chl.a、CDOM豐度等均未表現(xiàn)出明顯關(guān)系,且現(xiàn)有數(shù)據(jù)難以解釋冬季PAR衰減的南北部差異,暗示著有必要通過測定非色素顆粒物、浮游植物等的吸收光譜并量化各組分的相對貢獻(xiàn).

      圖4 撫仙湖秋、冬季PAR(400~700 nm)衰減系數(shù)與1%輻射深度空間分布Fig.4 Spatial distributions of Kdand Z1%of PAR(400-700 nm)in autumn and winter in Lake Fuxian

      不論UVR還是PAR,在水柱中的衰減特征依湖泊而不同[37-38].撫仙湖是典型的高原清澈型深水湖泊,接受的UVR較長江中下游強(qiáng),DOC、CDOM、浮游植物和懸浮物(非色素顆粒物)等本底濃度低,光輻射穿透深度較深,光輻射特征與渾濁型湖泊明顯不同[16,37].需要注意的是,撫仙湖水質(zhì)的惡化趨勢如有機(jī)污染水平

      升高、浮游植物生物量升高、透明度降低等[11-12],意味著輻射穿透深度有進(jìn)一步減小的可能,而真光層深度的減小會影響到淺水區(qū)沉水植物的生長,真光層與混合層深度比的變化亦會對浮游植物初級生產(chǎn)力、生長與分布等產(chǎn)生重要影響[2];雖然本次調(diào)查對撫仙湖光輻射等特征有了初步了解,但仍缺乏對其光熱特征全面系統(tǒng)的認(rèn)識.此外,高海拔、清澈型湖泊對環(huán)境變化極為敏感[6,39-40],而UVR增強(qiáng)、氣候變暖、流域土地利用、污染物輸入等的變化,勢必會對湖泊生態(tài)系統(tǒng)的光熱特征、生物地球化學(xué)循環(huán)、水生生物等方面產(chǎn)生重要影響[3].因此,有必要針對以上方面開展深入研究,且需注意不同季節(jié)(及雨季和旱季)的北部河流的物質(zhì)輸入情況.

      圖5 撫仙湖秋、冬季水柱表層CDOM吸收光譜Fig.5 The absorption spectra of CDOM in the surface water column in autumn and winter in Lake Fuxian

      圖6 撫仙湖秋(a)、冬(b)季ag(254)空間分布Fig.6 Spatial distributions of ag(254)of CDOM in autumn(a)and winter(b)in Lake Fuxian

      4 結(jié)論

      于2014年秋季和2015年冬季現(xiàn)場獲取撫仙湖的光輻射、CDOM及其它理化數(shù)據(jù),分析UV-B、UV-A、PAR的衰減特征及其與CDOM、SS、Chl.a等因子的關(guān)系,主要結(jié)論為:CDOM吸收對UVR衰減具有重要影響,對UV-B的影響大于UV-A,秋季的影響大于冬季;秋季UV-B的衰減系數(shù)顯著高于冬季,與秋季(雨季)較高的CDOM豐度、浮游植物生物量(及懸浮物濃度)有關(guān);秋季北部UVR的衰減系數(shù)顯著高于南部而冬季南北部無明顯差異,或與雨旱季北部河流CDOM和SS的輸入情況有關(guān);此外,浮游植物對UV-B衰減的影響主要體現(xiàn)在季節(jié)變化方面,UV-A衰減的季節(jié)變化亦受SS與CDOM交互作用的影響,而影響UVR、PAR衰減的各因子的相對貢獻(xiàn)有待進(jìn)一步量化.

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      Spectral attenuation of ultraviolet and visible radiation and its relationship with chromo?phoric dissolved organic matter in autumn/winter in Lake Fuxian,China

      ZHOU Qichao1,2,ZHANG Yunlin2??,ZHOU Yongqiang2,3,CHEN Yiliang1,QIN Jiang1&NIE Jufen1
      (1:Yunnan Key Laboratory of Pollution Process and Management of Plateau Lake?Watershed,Yunnan Institute of Environmen?tal Science(Kunming China International Research Center for Plateau Lake),Kunming 650034,P.R.China)(2:State Key Laboratory of Lake Science and Environment,Nanjing Institute of Geography and Limnology,Chinese Academy of Sciences,Nanjing 210008,P.R.China)(3:University of Chinese Academy of Sciences,Beijing 100049,P.R.China)

      To understand the temporal-spatial characteristics of the diffuse attenuation of ultraviolet radiation(UVR)and photosynthetically active radiation(PAR)and its relationship with chromophoric dissolved organic matter(CDOM),suspended solids(SS),chlorophyll-a(Chl.a)and other factors in Lake Fuxian,an oligotrophic deep lake in Yunnan Plateau,we carried out an investigation based on field work in October 2014(autumn)and January 2015(winter).The results showed that the values of diffuse attenuation coefficient that Kd(305),Kd(340)and Kd(PAR)were 1.27±0.12 m-1,0.68±0.11 m-1and 0.32±0.13 m-1,respectively in autumn,which were 1.13±0.10 m-1,0.63±0.07 m-1and 0.36±0.07 m-1,respectively in winter.Meanwhile,the values of absorption coefficient of CDOM that ag(254),ag(305)and ag(340)were 4.09±0.26 m-1,1.18±0.09 m-1,0.57±0.05 m-1,re-

      Diffuse attenuation coefficient;ultraviolet radiation;euphotic;chromophoric dissolved organic matter;temporalspatial distribution;Lake Fuxian

      J.Lake Sci.(湖泊科學(xué)),2016,28(6):1316-1327

      DOI 10.18307/2016.0617

      ?2016 by Journal of Lake Sciences

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