金春潔,張傳松,王麗莎*,石曉勇,3,韓秀榮,唐洪杰

黃海溶解無(wú)機(jī)氮時(shí)空變化及其水團(tuán)對(duì)DIN總量的影響

金春潔1,2,張傳松1,2,王麗莎1,2*,石曉勇1,2,3,韓秀榮1,2,唐洪杰1,2

(1.中國(guó)海洋大學(xué)化學(xué)化工學(xué)院,山東 青島 266100；2.中國(guó)海洋大學(xué)海洋化學(xué)理論與技術(shù)教育部重點(diǎn)實(shí)驗(yàn)室,山東 青島 266100；3.自然資源部海洋減災(zāi)中心,北京 100194)

本文根據(jù)2013~2016年4個(gè)航次調(diào)查資料,研究了黃海水體中溶解無(wú)機(jī)氮(DIN)的時(shí)空變化及其總量影響因素.結(jié)果表明:春、夏、秋和冬季黃海調(diào)查海域DIN平均濃度分別為(5.43±4.02),(4.47±3.16),(7.46±3.56)和(5.09±2.59)μmol/L.其中,秋季濃度最高,夏季最低;黃海調(diào)查海域各季節(jié)DIN的分布呈現(xiàn)近岸高、外海低的變化規(guī)律,近岸高值點(diǎn)多集中在長(zhǎng)江口以北、山東半島和遼東半島等處.春~秋季影響DIN分布的因素主要是陸源輸入和浮游植物的生長(zhǎng)繁殖,冬季則主要是河流輸入和沉積物再懸浮作用.四季在中央海域底層還存在一個(gè)高值區(qū)(>6μmol/L),主要受黃海冷水團(tuán)和黃海暖流等共同影響;通過(guò)聚類分析法對(duì)黃海四季水團(tuán)進(jìn)行了基本劃分,調(diào)查海域主要包括5個(gè)水團(tuán):黃?；旌纤畧F(tuán)、黃海冷水團(tuán)、黃海暖流水、沿岸水團(tuán)和黃東海混合水團(tuán),除黃?；旌纤畧F(tuán)終年存在外,其他水團(tuán)均為季節(jié)性存在;調(diào)查海域DIN總量四季差異不大,整體含量介于1.0×106~1.5×106t,春、夏、秋和冬季DIN總量分別約為1.2×106,1.0×106,1.5×106和1.3×106t.春季和夏季受浮游植物吸收影響,DIN總量略低,從水團(tuán)對(duì)DIN總量的貢獻(xiàn)上來(lái)看,春季以黃海暖流為主,夏季以黃海冷水團(tuán)為主,秋、冬季以黃海混合水團(tuán)為主.

DIN；黃海；季節(jié)；分布；總量

黃海是典型的半封閉陸架邊緣海,長(zhǎng)期受人類活動(dòng)和自然環(huán)境的雙重影響,現(xiàn)已成為世界上近海研究中具有典型意義的研究對(duì)象之一.黃海終年存在著復(fù)雜的水團(tuán),對(duì)于營(yíng)養(yǎng)鹽的來(lái)源、分布和運(yùn)移有重要作用[1-2].有研究表明,黃海環(huán)流、水體內(nèi)部循環(huán)都會(huì)影響著黃海營(yíng)養(yǎng)鹽時(shí)空分布[2-8].

營(yíng)養(yǎng)鹽是海水中最基礎(chǔ)的要素,同時(shí)也是維持海洋生物生命活動(dòng)的重要生源要素[9],在一定條件下,營(yíng)養(yǎng)鹽的濃度、組成及分布的變化是導(dǎo)致藻華暴發(fā)的重要基礎(chǔ)[10-13].其含量和比例的改變會(huì)影響浮游植物和藻類的群落結(jié)構(gòu)及生長(zhǎng)[14-15],現(xiàn)場(chǎng)調(diào)查結(jié)果顯示營(yíng)養(yǎng)鹽的輸入為大型藻類生長(zhǎng)和暴發(fā)提供物質(zhì)基礎(chǔ)[16],而營(yíng)養(yǎng)鹽分布受環(huán)流、陸源輸入和浮游植物消耗共同影響.氮是海洋中營(yíng)養(yǎng)鹽主要組成元素之一,海洋中總?cè)芙獾?TDN)由溶解無(wú)機(jī)氮(DIN)和溶解有機(jī)氮(DON)組成,他們占總氮庫(kù)的絕大部分[17].DIN作為溶解態(tài)氮的重要賦存形態(tài),在藻類植物生命活動(dòng)中占據(jù)重要地位,近年來(lái)黃海大面積暴發(fā)的滸苔綠潮災(zāi)害,與DIN濃度逐年上升有關(guān)[18-24].黃海滸苔綠潮藻類更傾向于吸收無(wú)機(jī)態(tài)氮鹽,尤其是硝酸鹽[25-26],DIN為綠潮發(fā)展提供了近87%的氮支撐[27],在綠潮暴發(fā)期間DIN濃度呈降低趨勢(shì)[28].所以,DIN是支撐滸苔生長(zhǎng)最重要的營(yíng)養(yǎng)鹽[29-33].因此,研究氮營(yíng)養(yǎng)鹽的變化規(guī)律并厘清其來(lái)源,對(duì)了解海洋氮循環(huán)、碳循環(huán)、生態(tài)系統(tǒng)變化以及海洋環(huán)境狀況評(píng)估具有重要意義.

目前對(duì)黃海營(yíng)養(yǎng)鹽的研究多局限于南黃?；虮秉S海的討論,且多以季節(jié)或短期變化為主.針對(duì)整個(gè)黃海DIN的較長(zhǎng)期變化趨勢(shì)及黃海環(huán)流和水團(tuán)對(duì)其含量的貢獻(xiàn)尚未見(jiàn)報(bào)道.本文以整個(gè)黃海DIN為研究對(duì)象,2013~2016年在黃海海域進(jìn)行的4個(gè)航次調(diào)查數(shù)據(jù)為依據(jù),闡述了近年來(lái)黃海海域DIN的分布特征和季節(jié)變化,并結(jié)合歷史數(shù)據(jù)分析了DIN近40a的年際變化,探討黃海DIN發(fā)生變化的原因和黃海環(huán)流及水團(tuán)對(duì)DIN總量貢獻(xiàn)的調(diào)控作用,為厘清黃海DIN來(lái)源、氮的地球化學(xué)循環(huán)和滸苔綠潮的防治提供一定的科學(xué)依據(jù)和理論支撐.

1 研究區(qū)域及分析方法

1.1 研究區(qū)域和站位

2013年6月22日~7月6日、11月6~21日、2014年4月28日~5月18日、2016年1月15~30日搭載“東方紅2”號(hào)科考船對(duì)黃海進(jìn)行綜合性大面站調(diào)查,采樣站位基本涵蓋整個(gè)黃海125°E以西海域.各航次采樣站位如圖1所示.

圖1 黃海研究區(qū)域調(diào)查站位

◆為采樣站位

1.2 采樣及分析方法

現(xiàn)場(chǎng)調(diào)查采用直讀式溫鹽深儀(Seabird 911-plus CTD)對(duì)溫度和鹽度進(jìn)行測(cè)定.使用12L Niskin采水器分別采集標(biāo)準(zhǔn)層水樣(表層,10m,20m, 30m,中層一般取10m層,底層離海底2m).水樣經(jīng)GF/F濾膜(預(yù)先450℃溫度下灼燒4h)過(guò)濾用聚乙烯瓶貯存,-20℃冷凍保存.使用SEAL-AA3流動(dòng)分析儀測(cè)定,NO3--N,NO2--N,NH4+-N均按照海洋調(diào)查規(guī)范方法(GB/T 12763.6-2007)[34]測(cè)定,其中NO3--N (銅-鎘還原)和NO2--N采用重氮-偶氮法,NH4+-N使用靛酚藍(lán)法,檢出限分別為0.02,0.02,0.04μmol/L,其測(cè)量精度分別是:99.41%、99.05%和99.69%;DIN= NO3--N+NO2--N+NH4+-N.

本文選用文獻(xiàn)[35-36]提出的系統(tǒng)聚類法對(duì)整個(gè)黃海水團(tuán)進(jìn)行劃分,采用歐氏平方距離——重心法作為劃分水團(tuán)的依據(jù).采用SPSS 18.0軟件,對(duì)2013~ 2016年4個(gè)航次的所有水層(2m/層)CTD實(shí)測(cè)溫鹽值進(jìn)行標(biāo)準(zhǔn)化處理,并根據(jù)T-S點(diǎn)聚圖結(jié)合水團(tuán)“內(nèi)同性和外異性”的原則[37],對(duì)水團(tuán)劃分的結(jié)果進(jìn)行調(diào)整,并將調(diào)整后結(jié)果與參考文獻(xiàn)相對(duì)比.

1.2.1 數(shù)據(jù)標(biāo)準(zhǔn)化處理

1.2.2 聚類參數(shù)和方法 本文以溫度和鹽度作為參數(shù)指標(biāo)對(duì)觀測(cè)站位的所有水層樣品進(jìn)行聚類分析,以歐幾里德平方和距離為計(jì)算各樣本之間的距離,采用此距離可以使誤差縮減到最小.其歐式平方距離(2個(gè)指標(biāo)值)的計(jì)算公式如下:

式中:,=1,2,3,…,,≠代表樣品數(shù);=1,2,3,…,代表變量個(gè)數(shù);ZX為標(biāo)準(zhǔn)化后的數(shù)據(jù).

最后,選擇計(jì)算結(jié)果與T-S點(diǎn)聚圖最相近的質(zhì)心法(也叫重心法)作為劃分水團(tuán)的聚類方法.

式中:n=n+n,即類和類合并為類,n為該類的站數(shù).

類與類的類間距離為:

類與類合并后的重心為:

為指標(biāo)值,溫度鹽度兩個(gè)指標(biāo)值分別為:

在計(jì)算中,*為臨界值,當(dāng)<*時(shí)繼續(xù)合并,檢驗(yàn)值計(jì)算公式:

水團(tuán)體積通過(guò)克里格-網(wǎng)格化法,采用Surfer 8.0軟件進(jìn)行計(jì)算[38],其中 1 °E=91.1km,1 °N=111.2km.假設(shè)各水團(tuán)在相應(yīng)季節(jié)DIN濃度基本不變,各水團(tuán)DIN含量計(jì)算公式如下:

(t)=摩爾質(zhì)量(g/mol)×濃度(μmol/L)

×水團(tuán)體積(km3)(9)

2 結(jié)果與討論

2.1 黃海DIN分布特征及組成

2.1.1 黃海DIN分布特征 春、夏、秋和冬季整個(gè)調(diào)查海域DIN濃度在0.24~18.01mmol/L之間,平均濃度分別為(5.43±4.02),(4.47±3.16),(7.46±3.56), (5.09± 2.59)μmol/L.從平面分布來(lái)看(圖2),表、中層海水中DIN的分布在4個(gè)航次中均呈現(xiàn)近岸高、外海低的分布趨勢(shì),這與文獻(xiàn)[2,39-43]結(jié)論一致.底層水體DIN分布特征與表層不同,在黃海近岸和中央海區(qū)存在2個(gè)高值區(qū)(>6μmol/L),與王保棟等[3,28,44-46]分析結(jié)果一致.表、中層水體DIN高值區(qū)分布在黃海近岸,主要集中在長(zhǎng)江口以北、蘇北沿岸、山東半島和遼東半島附近[2,39],結(jié)合鹽度分布特征可知其主要受陸源輸入的影響[31,47-48];其中2014年4月調(diào)查海區(qū)長(zhǎng)江口以北和山東半島以南海區(qū)高值區(qū)DIN濃度高于15μmol/L,超過(guò)了國(guó)家一類海水水質(zhì)標(biāo)準(zhǔn)(DIN=14.29μmol/L),已成為南黃海近岸水質(zhì)的污染物之一.春、夏季表中層水體中央海區(qū)DIN濃度較低的主要原因是浮游植物生長(zhǎng)旺盛消耗所致[16];底層近岸和中央海域兩個(gè)高值區(qū)結(jié)合鹽度分布特征推測(cè)分別受河流輸入和黃海暖流及黃海冷水團(tuán)的影響[3,44-46].

垂直方向上(圖2),除冬季外,DIN濃度均表現(xiàn)為底層>表層>中層.冬季調(diào)查海區(qū)受強(qiáng)烈的垂直混合擾動(dòng)影響[49],導(dǎo)致淺水區(qū)上、下水體中DIN濃度相近.DIN實(shí)際水平將取決于DIN的補(bǔ)充與生物活動(dòng)消耗過(guò)程的消長(zhǎng)和平衡[50],春季~秋季底層海水中存在一個(gè)DIN含量較高的黃海冷水團(tuán),為DIN的儲(chǔ)庫(kù)[3];表層海水既有浮游植物的生命活動(dòng)消耗,又有富含高DIN的沖淡水和大氣沉降補(bǔ)充[51],而中層水樣處于真光層,該層浮游植物生長(zhǎng)繁殖消耗了大量的DIN,加之調(diào)查期間溫躍層的存在[52],致使底層高濃度的DIN無(wú)法上升至表中層水體[2,52],因此該層DIN濃度比表層低.冬季在中央深水區(qū)濃度稍高,推測(cè)其原因是底層受冬季強(qiáng)風(fēng)垂直擾動(dòng)影響較小且有黃海暖流的補(bǔ)充所致[3,44,46].

S:表層, M:中層, B:底層

季節(jié)變化上(圖2),DIN濃度整體表現(xiàn)為秋季最高、夏季最低,秋、冬季高于春、夏季的變化規(guī)律,這與蔣昊等[53]研究一致.秋季DIN濃度最高可能是該季浮游植物消耗減少,加之河流輸入和水團(tuán)環(huán)流等外源輸入的補(bǔ)充作用所致[7];夏季DIN濃度最低可能是浮游植物大量繁殖消耗增加,加之近年來(lái)滸苔綠潮頻發(fā),且水體層化現(xiàn)象顯著[52],水體底層的DIN無(wú)法對(duì)表層水體進(jìn)行補(bǔ)充所致[2,52,54].

圖3 黃海DIN形態(tài)組成的季節(jié)變化

2.1.2 黃海DIN形態(tài)組成 調(diào)查海域春、夏、秋和冬季DIN的主要存在形態(tài)均為NO3--N,分別占DIN總量的比例為58.10%、60.01%、80.70%和86.47%,其次為NH4+-N分別占37.64%、33.71%、12.96%和9.92%,最少的是NO2--N分別占4.26%、6.28%、6.34%和2.85%(圖3).從春季到冬季,NO3--N占DIN的比例逐漸升高;NH4+-N所占比例逐漸降低;NO2--N所占比例相對(duì)穩(wěn)定,均小于7%.有研究表明滸苔在硝酸鹽和銨鹽同時(shí)存在時(shí),會(huì)優(yōu)先吸收NH4+-N[55].NH4+-N可以被海藻直接吸收利用,NH4+- N的吸收效率遠(yuǎn)遠(yuǎn)大于NO3--N[56-57],且NH4+-N對(duì)NO3--N的吸收有抑制作用[58-61].黃海調(diào)查海域NH4+-N在春、夏季所占比例高達(dá)37.64%和33.71%,較高比例的NH4+-N可能為黃海滸苔綠潮暴發(fā)提供物質(zhì)保證[58].

2.2 黃海DIN的年際變化

圖4 1980~2010年黃海春季表層DIN的年際變化特征

根據(jù)歷史資料對(duì)春季表層海水中DIN的年際變化進(jìn)行分析[3-4,62-63],近40a春季整個(gè)黃海表層水體中DIN濃度呈現(xiàn)波動(dòng)式的變化特征(圖4),在2005年之前,DIN呈現(xiàn)逐漸增長(zhǎng)的變化特征,2006~2007年略有下降, 2009年急劇上升達(dá)到近40a來(lái)最大值12.40μmol/L,2009年以后呈現(xiàn)波動(dòng)式下降的變化趨勢(shì),2010年濃度水平降至1984年濃度水平.實(shí)驗(yàn)室培養(yǎng)結(jié)果表明,DIN的濃度水平是制約滸苔生長(zhǎng)的主要因素[64-65],2009年DIN的峰值恰逢滸苔綠潮在黃海近岸大面積暴發(fā),最大分布面積達(dá)58000km2[66],推測(cè)DIN輸入的逐年增加是導(dǎo)致滸苔綠潮大面積暴發(fā)的重要因素,這與Keesing等[19]、Lin等[18]和Li等[25]的研究結(jié)果一致.隨著國(guó)家對(duì)海洋環(huán)境污染的重視與治理,2009年以后,DIN開(kāi)始波動(dòng)式下降,使氮營(yíng)養(yǎng)鹽的輸入得以控制.

2.3 水團(tuán)對(duì)DIN含量的貢獻(xiàn)分析

通過(guò)聚類分析和T-S點(diǎn)聚圖(圖6)對(duì)調(diào)查海域四季水團(tuán)進(jìn)行劃分(圖5),黃海主要存在黃?；旌纤畧F(tuán)(Y)、黃海冷水團(tuán)(YC)、黃海暖流水(YW)、沿岸水團(tuán)(CW)和黃東?；旌纤畧F(tuán)(YE)5個(gè)水團(tuán)(臺(tái)灣暖流TW并非黃海特征水團(tuán),故本文不作討論),結(jié)果與邱道立等[35]和劉樹(shù)勛等[67]水團(tuán)劃分較為一致.邱道立等[35]提出除了Y終年存在外,其它均是季節(jié)性水團(tuán).各水團(tuán)水文特征如表1所示, Y溫度、鹽度均存在明顯的季節(jié)變化,從溫鹽特性上看,具備中鹽的特征[68],溫度在6.1~23.3℃之間,鹽度在29.91~33.37之間.YC溫度鹽度特性是低溫中鹽,溫度在3.8~13.2℃之間,鹽度在30.75~33.30之間,是溫度最低的水團(tuán). YW溫度鹽度特性為中溫高鹽,溫度在8.3~17.2℃之間,鹽度在31.72~33.85之間. CW最大的溫度鹽度特性是低鹽,溫度在11.0~23.0℃之間,鹽度在28.71~ 30.85之間,均<31.YE水文特性是中溫中鹽,溫度在9.0~23.8℃之間,鹽度在31.19~33.42之間.

表1 黃海各水團(tuán)的水文特征

注: /表示該水團(tuán)在該季節(jié)不明顯或者影響很小.

圖5 四季黃海表、底層水團(tuán)分布

由于4個(gè)調(diào)查航次站位不完全相同,因此本文只討論125°E以西調(diào)查海域,根據(jù)上述已劃分的水團(tuán),采用Surfer 8.0軟件克里格-網(wǎng)格化法對(duì)水團(tuán)體積進(jìn)行計(jì)算,并根據(jù)式9分別計(jì)算各水團(tuán)中DIN含量,其結(jié)果如表2所示.各季節(jié)不同水團(tuán)對(duì)DIN總量的貢獻(xiàn)大小如圖7所示.

Y由進(jìn)入黃海的沿岸水和外海水混合而成,常年占據(jù)調(diào)查海區(qū)表、中層絕大部分海域,底層面積較小,多集中于南黃海西側(cè)(圖5). Y是四季體積最大且DIN濃度最低的非季節(jié)性水團(tuán),春、夏、秋和冬季Y水團(tuán)體積分別約為6.8×103,6.0×103,9.1×103,9.2× 103km3;DIN平均濃度約為(4.36±3.60),(3.17±2.38), (6.84±3.37),(4.71±1.87)μmol/L;對(duì)DIN總量的貢獻(xiàn)比例分別為33.6%,26.4%,57.7%,78.8%(圖7),由此可知,秋、冬季以Y對(duì)DIN總量的貢獻(xiàn)為主.春季Y多分布于表中層水體;夏季Y的范圍縮小至四季最小(圖5),春季~夏季DIN濃度隨著浮游植物生長(zhǎng)繁殖的消耗越來(lái)越低[16],且因溫躍層的存在,底層水體高濃度DIN無(wú)法對(duì)表中層水體進(jìn)行補(bǔ)充[2,52,54],因此Y在春、夏季對(duì)DIN總量的貢獻(xiàn)較小.而秋季浮游植物活動(dòng)開(kāi)始減弱,伴隨著降溫和大風(fēng)的垂直擾動(dòng)影響,Y占據(jù)調(diào)查海區(qū)大部分海域(圖5),由于溫躍層的逐漸消失和垂直擾動(dòng)作用的影響,底層高濃度DIN對(duì)表層水體進(jìn)行補(bǔ)充,使得DIN濃度達(dá)到全年最高,因此,秋季Y對(duì)DIN總量貢獻(xiàn)最大.冬季隨著垂直混合作用加強(qiáng)和YW、YE北上,Y整體向北擴(kuò)展,體積增至最大,因而對(duì)調(diào)查海域該季節(jié)DIN總量貢獻(xiàn)最大.

YC是黃海最保守的季節(jié)性水團(tuán),主要盤踞在黃海中央底層水體(圖5),其形成與黃海海底地形、溫躍層和深度相關(guān)[69]. YC在春、夏和秋季體積分別約為3.7×103,9.3×103,2.0×103km3;DIN濃度分別約為(5.52 ± 3.39),(5.57 ± 2.91),(10.50 ± 4.00) μmol/L;對(duì)DIN總量的貢獻(xiàn)比例分別為23.4%,71.5%,19.6%.因此,夏季以YC對(duì)DIN總量的貢獻(xiàn)最大,其DIN含量為7.24×105t. YC于春季黃海北部開(kāi)始形成,前一年冬季冷水有助于春季YC的形成[70],雖然DIN濃度高于Y,但是規(guī)模尚小,體積約為Y的1/2,因而貢獻(xiàn)也相對(duì)Y較小.夏季YC規(guī)模最大[2],受南風(fēng)作用南下[70]延伸至濟(jì)州島附近,幾乎覆蓋整個(gè)南北黃海中央底層區(qū)域.此時(shí),底層浮游植物殘?bào)w被分解成DIN重新回到水體中,加之水體的層化作用使得YC中高濃度DIN無(wú)法擴(kuò)散進(jìn)入上層水體[2,52,54],YC中DIN濃度在該季最高,體積較其他季節(jié)也最大,因此,對(duì)DIN總量貢獻(xiàn)最高,進(jìn)而YC成為整個(gè)黃海DIN的主儲(chǔ)備庫(kù),這與王保棟等[3]研究結(jié)論一致.秋季隨著降溫和垂直擾動(dòng)作用的增強(qiáng),YC向西北方向回縮至黃海中央海域[70],貢獻(xiàn)比例與春季接近.冬季隨著降溫和垂直混合作用的進(jìn)一步加強(qiáng),YC消失.

YW是由黃海暖流與黃海水混合而成,受北風(fēng)作用驅(qū)動(dòng)形成[72-77],多分布于底層水體(圖5), YW在秋、冬和春季體積分別約為0.5×103,0.2×103,4.7× 103km3;DIN濃度分別約為(9.98±5.92),(12.19± 1.76), (8.01±3.83) μmol/L;對(duì)DIN總量的貢獻(xiàn)比例分別為4.3%,3.6%,42.8%.由此可知,春季以YW對(duì)DIN總量的貢獻(xiàn)最為突出,其DIN含量為5.3×105t,且YW所攜帶的DIN濃度較高,這與Jin等[44]、Fu等[46]和Guo等[78]研究結(jié)論一致.秋季隨著降溫和季風(fēng)作用的加強(qiáng)YW攜帶高濃度DIN從黃海東南端開(kāi)始入侵,冬季隨著季風(fēng)作用進(jìn)一步加強(qiáng),YW進(jìn)一步向西北方向迅速擴(kuò)展[73,79-81],延伸至黃海中部海域,強(qiáng)度達(dá)到全年最高,雖然DIN濃度較高,體積卻較小.因此,秋、冬季YW對(duì)DIN總量貢獻(xiàn)不大.春季YW繼續(xù)北上擴(kuò)張至36.5°N[82-83],影響范圍全年最大[84],且在34°N以南123.5°E以東海域表層呈舌狀向西北方向擴(kuò)張,體積達(dá)四季最大,加上攜帶較高濃度DIN,因而對(duì)春季DIN總量貢獻(xiàn)最大.夏季YW消失.

表2 研究海域不同季節(jié)各水團(tuán)體積、DIN濃度和含量

注:1./代表可以忽略不計(jì).2.*代表冬季補(bǔ)足缺失部分后總量.

圖7 各水團(tuán)對(duì)DIN含量貢獻(xiàn)比例的季節(jié)變化

CW是由黃海沿岸徑流與黃海水混合而成,分布于黃海沿岸區(qū)域(圖5).因本研究近岸調(diào)查站位較少,故根據(jù)實(shí)際站位進(jìn)行討論,本研究CW存在于春、夏季.春季CW分布在長(zhǎng)江口以北的表底層和鴨綠江口附近表層海域,夏季隨著河流徑流量的增大, CW在長(zhǎng)江口明顯呈舌狀向東北方向擴(kuò)展,在山東半島和遼東半島表層水體也開(kāi)始向外擴(kuò)展,其分布面積達(dá)到最大.秋季隨著徑流量減少僅分布在鴨綠江口附近,冬季隨著河流枯水期的到來(lái),CW消失. CW在春、夏季體積分別約為0.01×103,0.2×103km3; DIN濃度分別約為(14.13±4.70),(5.28±4.26)μmol/L;對(duì)DIN總量的貢獻(xiàn)比例分別為0.2%,1.8%,貢獻(xiàn)較小,幾乎可忽略不計(jì).

YE是由東海水北上與黃海水混合而成,主要分布于研究海域南部(圖5),存在于夏、冬季, YE在夏、冬季體積分別約為0.3×103,1.0×103km3;DIN濃度分別約為(0.62±0.10),(5.20±2.77)μmol/L;對(duì)DIN總量的貢獻(xiàn)比例分別為0.3%,9.2%.由此可見(jiàn),YE對(duì)DIN總量的貢獻(xiàn)冬季比夏季高.夏季YE分布于34°N以北123.5°E以東小部分海域,水團(tuán)體積和DIN濃度均較小,其貢獻(xiàn)可忽略不計(jì).冬季表層分布于34°N以南海域,底層移至33.5°N以南海域,水團(tuán)體積和DIN濃度較夏季均增大,因而對(duì)DIN總量貢獻(xiàn)較夏季大.

綜上所述,調(diào)查海域春季~冬季黃海各水團(tuán)DIN總量分別為1.2×106,1.0×106,1.5×106和0.8× 106t.由于各個(gè)航次調(diào)查海域的區(qū)域性差別(冬季航次東至124°E以西,北至39°N;其他季節(jié)東至125°E,北約至40°N),為了更好的比較DIN總量的季節(jié)變化,本文估算了冬季航次缺失部分的DIN總量,冬季航次水體體積為1.6×104km3,冬季DIN總量為1.3×106t.由此可以看出,夏季DIN總量略低,受浮游植物消耗作用較為明顯.從不同季節(jié)水團(tuán)對(duì)DIN含量貢獻(xiàn)比例來(lái)看,春季以YW為主,高達(dá)42.8%;夏季以YC為主,高達(dá)71.5%;秋冬季以Y為主,貢獻(xiàn)比例分別為57.7%和78.8%.

3 結(jié)論

3.1 2013~2016年黃海DIN的濃度在0.24~ 18.01μmol/L之間,平均值在4.47~7.46μmol/L之間,春、夏、秋和冬季DIN平均值分別為(5.43±4.02), (4.47±3.16),(7.46±3.56)和(5.09±2.59)μmol/L.DIN濃度平均值季節(jié)變化整體表現(xiàn)為秋季最高、夏季最低,秋、冬季高于春、夏季.其平面分布規(guī)律基本上呈現(xiàn)近岸高、外海低的分布特征.表層水體DIN濃度高值區(qū)主要集中在遼東半島、山東半島、蘇北沿岸及長(zhǎng)江口以北近岸海區(qū),底層水體高值區(qū)多集中在中央海域;垂直方向上,除冬季外,黃海DIN濃度均表現(xiàn)為底層>表層>中層.

3.2 DIN的主要形態(tài)為NO3--N,春季~冬季, NO3--N所占DIN比例逐漸升高.NH4+-N所占DIN比例逐漸降低,其中春、夏季NH4+-N所占比例是秋、冬季的近3倍.

3.3 調(diào)查海域主要分布著5個(gè)水團(tuán):黃海混合水團(tuán)、黃海冷水團(tuán)、黃海暖流、沿岸水和黃東?；旌纤?其中黃?；旌纤畧F(tuán)終年存在,而黃海冷水團(tuán)和黃海暖流是典型的季節(jié)性水團(tuán).

3.4 黃海各水團(tuán)DIN含量和對(duì)DIN總量貢獻(xiàn)因季節(jié)而異,春、夏、秋和冬季黃海所有水團(tuán)中DIN總量分別為1.2×106,1.0×106,1.5×106和1.3×106t,夏季總量最低.從水團(tuán)對(duì)DIN總量的貢獻(xiàn)分析,春季以黃海暖流為主,夏季以黃海冷水團(tuán)為主,秋、冬季以黃?；旌纤畧F(tuán)為主.

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Spatial-temporal variation of dissolved inorganic nitrogen (DIN) and impacts of water mass on the reserves estimation of the total DIN content in the Yellow Sea.

JIN Chun-jie1,2, ZHANG Chuan-song1,2, WANG Li-sha1,2*, SHI Xiao-yong1,2,3, HAN Xiu-rong1,2, TANG Hong-jie1,2

(1.College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China；2.Key Laboratory of Marine Chemistry Theory and Technology,Ministry of Education, Ocean University of China, Qingdao 266100, China；3.National Marine Hazard Mitigation Service, Beijing 100194, China)., 2021,41(4)：1642~1654

Based on the data of 4 curies in 2013~2016, the distribution of DIN in the Yellow Sea、nitrogen pool and its influencing factors have been studied. Results showed that the average concentrations of DIN in the Yellow Sea were (5.43±4.02) μmol/L in spring, (4.47±3.16) μmol/L in summer, (7.46±3.56) μmol/L in autumn, and (5.09±2.59) μmol/L in winter, among which DIN contents reached maximum in autumn and minimum in summer, respectively. DIN concentrations declined from coastal zones to the offshore area. The DIN-rich sites near the coast were mostly centralized in the north of the Yangtze River estuary, Shandong Peninsula and Liaodong Peninsula. The main affecting factors all the year except winter were terrigenous input and the growth of phytoplankton, as the resuspension of the riverine input and sediment were the main factors affecting the distribution of DIN in winter. There was an area with high concentration of DIN(>6μmol/L) in the central area, which was co-influenced by the Yellow Sea warm current and the Yellow Sea Cold Water Mass. Cluster analysis has been used to classified the Yellow Sea water into 5 water masses, including the Yellow Sea water masses (Y), Yellow Sea cold water mass (YC), Yellow Sea warm current water (YW), Coastal water mass (CW) and Yellow Sea-East China Sea mixed water mass (YE), which was the main water mass in the researching sea area. All these water masses except for Y were seasonal. The total DIN content in the research field showed no obvious difference in all year, and their range was 1.0×106~1.5×106t. The DIN content was slightly lower in spring and summer under the influence of phytoplankton assimilation. The total DIN contents were about 1.2×106t in spring, 1.0×106t in summer, 1.5×106t in autumn, and 1.3×106t in winter, respectively. The contributions of water masses to the total DIN content were different in the varying season. In autumn and winter, Y was dominant, while in summer and spring, YW and YC played the dominant roles, respectively.

DIN；Yellow Sea；season；distribution；total content

X55

A

1000-6923(2021)04-1642-13

金春潔(1988-),女,山東青島人,中國(guó)海洋大學(xué)博士研究生,主要從事海洋污染生態(tài)化學(xué)研究.發(fā)表論文2篇.

2020-08-04

國(guó)家重點(diǎn)研發(fā)計(jì)劃項(xiàng)目(2016YFC1402101)

* 責(zé)任作者, 高級(jí)實(shí)驗(yàn)師, lishawang@ouc.edu.cn