中國(guó)近海營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡與磷消耗問(wèn)題及其生態(tài)環(huán)境效應(yīng)的研究進(jìn)展

冉祥濱, 韋欽勝, 于志剛

中國(guó)近海營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡與磷消耗問(wèn)題及其生態(tài)環(huán)境效應(yīng)的研究進(jìn)展

冉祥濱1, 韋欽勝1, 于志剛2

(1. 自然資源部第一海洋研究所海洋生態(tài)研究中心和自然資源部海洋生態(tài)環(huán)境科學(xué)與技術(shù)重點(diǎn)實(shí)驗(yàn)室, 山東 青島 266061; 2. 中國(guó)海洋大學(xué) 深海圈層與地球系統(tǒng)前沿科學(xué)中心和海洋化學(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)

近海的生態(tài)環(huán)境問(wèn)題態(tài)勢(shì)嚴(yán)峻。在機(jī)制上, 普遍認(rèn)為富營(yíng)養(yǎng)化是導(dǎo)致近海環(huán)境惡化的主導(dǎo)因子, 但實(shí)際上, 營(yíng)養(yǎng)鹽的結(jié)構(gòu)失衡對(duì)近海生態(tài)環(huán)境問(wèn)題的產(chǎn)生可能起到了更重要的作用。目前關(guān)于營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡的主導(dǎo)因素和機(jī)制尚缺乏全面系統(tǒng)的研究。本文基于對(duì)已有數(shù)據(jù)和文獻(xiàn)資料的整合分析發(fā)現(xiàn), 由于存在強(qiáng)烈的人類活動(dòng)影響, 中國(guó)近海營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡問(wèn)題較過(guò)去更為突出, 且可能引發(fā)潛在“磷消耗”問(wèn)題, 其影響在某種程度上較傳統(tǒng)意義上的磷限制要強(qiáng), 并進(jìn)而產(chǎn)生深遠(yuǎn)的生態(tài)環(huán)境效應(yīng)。據(jù)此提出, 今后相關(guān)的研究應(yīng)該特別關(guān)注河流流域-近海環(huán)境變化和它們之間的內(nèi)在關(guān)聯(lián), 闡明控制近海營(yíng)養(yǎng)鹽濃度、形態(tài)、分布和結(jié)構(gòu)的關(guān)鍵生物地球化學(xué)過(guò)程, 量化近海氮與磷的滯留機(jī)制與效率, 揭示浮游植物群落結(jié)構(gòu)變化與營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡和磷消耗的耦合關(guān)系及其生態(tài)效應(yīng)等, 最終制定中國(guó)入海河流與近海氮磷協(xié)同控制的適應(yīng)性管理措施。

近海; 生物地球化學(xué)過(guò)程; 環(huán)境變化; 關(guān)鍵過(guò)程; 營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡; 磷消耗

在人類活動(dòng)增強(qiáng)和氣候變化的多重影響下, 全球范圍內(nèi)的近海生態(tài)環(huán)境發(fā)生了明顯的變化, 導(dǎo)致赤潮、缺氧與酸化等生態(tài)災(zāi)害和環(huán)境問(wèn)題頻發(fā)[1-5], 嚴(yán)重影響了海洋的資源與環(huán)境價(jià)值。近海是海上經(jīng)濟(jì)活動(dòng)的主要區(qū)域, 事關(guān)人類的生存與可持續(xù)發(fā)展, 且在海洋環(huán)境上具有獨(dú)特的屬性。因此, 近海環(huán)境問(wèn)題已成為人們關(guān)注的重要議題, 相關(guān)研究也是海洋科學(xué)和環(huán)境科學(xué)研究的熱點(diǎn)。由于受到多重環(huán)境壓力的影響, 再加之與全球氣候變化相疊加, 近海海洋環(huán)境變化、驅(qū)動(dòng)機(jī)制和生態(tài)環(huán)境效應(yīng)紛繁復(fù)雜, 特別是在近些年呈現(xiàn)出新的變化模態(tài), 科學(xué)認(rèn)知近海環(huán)境已成為全球海洋治理的難點(diǎn)和焦點(diǎn)。

氮(N)與磷(P)營(yíng)養(yǎng)鹽作為水體重要的生源要素, 不僅是生態(tài)系統(tǒng)物質(zhì)與能量流動(dòng)的基礎(chǔ), 其生物地球化學(xué)過(guò)程也是影響碳循環(huán)和氣候變化的重要一環(huán)[6-7], 并在海洋環(huán)境演變過(guò)程中扮演著至關(guān)重要的角色。人類活動(dòng)強(qiáng)度的增加導(dǎo)致全球河流氮和磷的通量在20世紀(jì)分別增加了90%和75%[8-9], 特別是近幾十年來(lái)河流排放至近海的氮與磷的通量大為提升, 而活性硅(為硅藻等硅質(zhì)生物生長(zhǎng)所必需的一種重要的生源要素)的通量略有減少[10]; 與此同時(shí), 地下水中營(yíng)養(yǎng)鹽由陸向海的輸送量也有所增加[8], 且具有較Redfield比值[11]更高的氮與磷(N/P)比值[12], 這便造成了氮與磷的進(jìn)一步失衡[8]以及二者與硅的化學(xué)計(jì)量學(xué)關(guān)系的顯著變化[2, 13-14]等營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡問(wèn)題(N/P偏離Redfield比值的現(xiàn)象[11])。營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡除導(dǎo)致近海非硅藻類浮游植物生物量(主要是甲藻)的增加[1, 15], 影響海洋生態(tài)系統(tǒng)的穩(wěn)定[16-18]與碳循環(huán)過(guò)程[19]外, 還可能在化學(xué)計(jì)量學(xué)上產(chǎn)生磷相對(duì)于氮的過(guò)度消耗[20], 即近海富營(yíng)養(yǎng)化現(xiàn)象以及與之相關(guān)聯(lián)的環(huán)境問(wèn)題。盡管營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡并非海洋環(huán)境學(xué)家和生物學(xué)家關(guān)注的新的熱點(diǎn)問(wèn)題, 相關(guān)科學(xué)問(wèn)題在近幾十年來(lái)已得到國(guó)內(nèi)外科學(xué)家較為廣泛和系統(tǒng)的研究, 然而人們對(duì)于浮游植物生物量增加和結(jié)構(gòu)變化所可能導(dǎo)致的磷消耗(phosphorus depletion)[21](生物地球化學(xué)過(guò)程所導(dǎo)致, 具有非穩(wěn)態(tài)的特征, 直觀的表現(xiàn)為輸出大于輸入)的現(xiàn)象和機(jī)制的認(rèn)識(shí)依然不足。

中國(guó)近海海域深受人類活動(dòng)的影響, 是全球陸海相互作用中極為典型的陸架海, 也是全球海洋環(huán)境變化的典型海域[22-23], 其生態(tài)系統(tǒng)結(jié)構(gòu)和功能發(fā)生了顯著變化[2, 24]。特別是近些年來(lái), 中國(guó)近海生態(tài)環(huán)境急劇變化, 出現(xiàn)赤潮[2]、綠潮[25]、低氧和酸化[26]等諸多環(huán)境問(wèn)題, 成為世界上生態(tài)環(huán)境較為脆弱的海域之一; 在大多海域, 尤其是黃河口、長(zhǎng)江口和珠江口等海域, 氮的含量處于較高水平, 且顯著高于中國(guó)其他區(qū)域[27-28], 是近海生態(tài)環(huán)境保護(hù)與修復(fù)中亟需重點(diǎn)關(guān)注的污染物之一。近年來(lái), 國(guó)家采取系列舉措, 旨在解決中國(guó)近海突出的污染問(wèn)題, 改善其生態(tài)環(huán)境; 如針對(duì)渤海, 國(guó)家多部委聯(lián)合印發(fā)了《渤海綜合治理攻堅(jiān)戰(zhàn)行動(dòng)計(jì)劃》(環(huán)海洋〔2018〕158號(hào))等系列文件, 以應(yīng)對(duì)渤海嚴(yán)峻的環(huán)境問(wèn)題。然而, 在中國(guó)部分海域氮磷比居高不下的局面并沒(méi)有得到實(shí)質(zhì)性的改變, 部分海域還呈現(xiàn)比值持續(xù)升高的趨勢(shì), 如渤海[29-30]、黃海[31-32]和長(zhǎng)江口等海域[22]。

中國(guó)近海鮮明的區(qū)域特色和嚴(yán)峻的環(huán)境問(wèn)題賦予了其生態(tài)環(huán)境控制機(jī)制研究的典型意義, 相關(guān)環(huán)境問(wèn)題的研究對(duì)于海洋可持續(xù)發(fā)展與適應(yīng)性管理亦具有重要價(jià)值。然而, 長(zhǎng)期以來(lái)對(duì)近海生態(tài)環(huán)境問(wèn)題的研究大多圍繞污染物通量展開(kāi), 缺少陸海一體化視角下控制機(jī)制—響應(yīng)方面的綜合、系統(tǒng)性研究, 既不利于揭示近海海洋環(huán)境變異的驅(qū)動(dòng)機(jī)制, 也不利于制定科學(xué)的可持續(xù)發(fā)展的海洋戰(zhàn)略。在前人研究的基礎(chǔ)上, 本文以陸海相互作用為出發(fā)點(diǎn), 緊扣公眾關(guān)切的近海生態(tài)環(huán)境問(wèn)題, 深入探究近海營(yíng)養(yǎng)鹽結(jié)構(gòu)的失衡及其機(jī)制和生態(tài)環(huán)境效應(yīng), 相關(guān)工作有望為海洋管理和綜合治理等提供新的視角。

1 營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡問(wèn)題的研究現(xiàn)狀

當(dāng)近海環(huán)境系統(tǒng)的營(yíng)養(yǎng)鹽輸入大于輸出時(shí), 其在近海的累積便產(chǎn)生了富營(yíng)養(yǎng)化, 直觀地表現(xiàn)為水體氮與磷濃度普遍升高、生態(tài)災(zāi)害頻發(fā)等。無(wú)疑, 入海的陸源污染物負(fù)荷增加與結(jié)構(gòu)變化[8-9]是導(dǎo)致近海環(huán)境問(wèn)題的主控因素, 尤其是那些人類活動(dòng)比較集中且水交換能力相對(duì)較弱的近海海域, 在其中富營(yíng)養(yǎng)化又是諸多海洋環(huán)境問(wèn)題產(chǎn)生的根本所在[5]。

不斷增強(qiáng)的人類活動(dòng)是導(dǎo)致水體富營(yíng)養(yǎng)化加劇的主要驅(qū)動(dòng)力[6]; 氮與磷肥料在陸地上的大量使用和污水排放量的顯著增加, 使得人類活動(dòng)產(chǎn)生的氮與磷營(yíng)養(yǎng)鹽負(fù)荷較過(guò)去明顯升高, 導(dǎo)致富營(yíng)養(yǎng)化由河流、湖泊以及地下水傳遞到近海, 并對(duì)近海環(huán)境造成極大的影響。目前, 關(guān)于富營(yíng)養(yǎng)化現(xiàn)象、驅(qū)動(dòng)機(jī)制及其環(huán)境效應(yīng)的探討較為深入[6, 33-34], 特別是對(duì)陸源輸入的貢獻(xiàn)認(rèn)識(shí)尤為深入, 但缺少近海氮磷循環(huán)與營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡之間的量化關(guān)系, 關(guān)于營(yíng)養(yǎng)鹽由陸向海輸送及其近海環(huán)境響應(yīng)方面的陸海一體化的系統(tǒng)研究則更少[35-36], 這使得我們?nèi)鄙訇懞＝y(tǒng)籌的理論支撐, 無(wú)法有效地識(shí)別驅(qū)動(dòng)近海環(huán)境演變的關(guān)鍵過(guò)程, 進(jìn)而影響了開(kāi)展近海環(huán)境管理與修復(fù)工作的時(shí)效。概括而言, 國(guó)內(nèi)外開(kāi)展近海富營(yíng)養(yǎng)化、營(yíng)養(yǎng)鹽結(jié)構(gòu)及其環(huán)境效應(yīng)的研究主要集中在以下3個(gè)方面。

1.1 陸源氮與磷污染物向海輸送與營(yíng)養(yǎng)鹽比值變化

陸源物質(zhì)通過(guò)河流向海洋的輸送及其對(duì)近海環(huán)境的影響是環(huán)境科學(xué)和海洋科學(xué)領(lǐng)域的重點(diǎn)研究?jī)?nèi)容。盡管從區(qū)域到全球尺度海洋系統(tǒng)中內(nèi)部的循環(huán)與再生作用是維持海洋系統(tǒng)初級(jí)生產(chǎn)的主要氮磷物質(zhì)來(lái)源, 但海洋外部穩(wěn)定的輸入是保持這個(gè)系統(tǒng)可持續(xù)性的重要方面。在氮和磷等生源要素向海洋的輸送中, 河流的輸送通量最高, 其次是地下水、大氣輸送等[2, 37]。在全球尺度上, 河流是海洋中磷的主要外部輸入源, 占海洋外源總輸入量的75%～94%[38-40]; 除固氮作用外, 河流向海洋輸送的氮也是海洋獲得外源性氮的主要途徑[8, 41]。在中國(guó)近海, 河流占海洋外部輸入的氮磷比例均高達(dá)90%以上[2], 成為控制近海環(huán)境演變的主要外部驅(qū)動(dòng)機(jī)制。相比過(guò)去, 社會(huì)經(jīng)濟(jì)的發(fā)展改變了流域的土地利用、河流的形態(tài)、水力停留時(shí)間等重要過(guò)程, 進(jìn)而影響了河流原有的生物地球化學(xué)過(guò)程[9, 42-43]。在當(dāng)前, 我們大多關(guān)注陸地向海輸送的營(yíng)養(yǎng)鹽通量的變化, 對(duì)于其比值的變化關(guān)注相對(duì)前者要少; 地球上近300個(gè)大河系統(tǒng)中超過(guò)半數(shù)的河流在不同程度上受到了持續(xù)增強(qiáng)的人類活動(dòng)的影響[44-45], 大多水體呈現(xiàn)出氮磷比升高的趨勢(shì)[8, 46], 而其中的中國(guó)河流則是當(dāng)今世界受人類活動(dòng)影響最顯著的典型河流體系[42], 如長(zhǎng)江氮與磷輸送通量在過(guò)去100年間分別增加了17倍和6.6倍[9], 氮磷比相比過(guò)去顯著升高。此外, 大氣沉降的氮也較過(guò)去大為增加[37], 進(jìn)一步加劇了陸地水體氮磷比失衡的態(tài)勢(shì)[47]。由此可見(jiàn), 陸源氮與磷污染物向海輸送通量的增加、比例變化成為當(dāng)前河流的主要特征, 其對(duì)近海海洋生源要素生物地球化學(xué)過(guò)程及相關(guān)水生態(tài)環(huán)境的影響正得到國(guó)內(nèi)外科學(xué)家越來(lái)越多的重視[48]。

盡管同為富營(yíng)養(yǎng)化的關(guān)鍵因子, 但氮與磷營(yíng)養(yǎng)鹽在來(lái)源、循環(huán)以及從陸到海的輸送過(guò)程中存在明顯的差異, 使得陸地生態(tài)系統(tǒng)存在差異化的氮或者磷營(yíng)養(yǎng)鹽限制情況[46]。陸地水體中溶解態(tài)的氮與磷濃度主要由流域水-土/水-巖作用、生態(tài)系統(tǒng)構(gòu)成以及流域特性控制, 特別是受到流域日益增強(qiáng)的農(nóng)業(yè)活動(dòng)的極大影響。流域化肥施用量逐年增加是導(dǎo)致水體中氮濃度升高的主要原因; 大多情況下, 肥料中的氮元素非常容易溶解于水和順?biāo)斔? 當(dāng)?shù)实氖褂昧砍^(guò)了生物生長(zhǎng)所需要的量時(shí), 多余的氮肥會(huì)在土地中累積、流向地表水體、滲透到地下水或揮發(fā)到大氣中, 并通過(guò)河流、地下水和干/濕沉降等方式影響陸地或海洋的生態(tài)系統(tǒng)[49-50]。而對(duì)于環(huán)境中的磷而言, 由于其存在強(qiáng)的顆粒物-水界面作用(通常由吸附-解吸過(guò)程控制), 水體搬運(yùn)作用對(duì)它的影響稍低[51]。上述控制過(guò)程的差異是產(chǎn)生高氮磷比的重要因素。

污水排放也是水體中氮與磷濃度升高的重要原因[52], 大約占河流輸送負(fù)荷的12%(全球尺度)[8], 從土壤流失或由廢水?dāng)y帶而增加的氮與磷提高了全球流向海洋的營(yíng)養(yǎng)鹽通量[8]。在中國(guó)長(zhǎng)江, 污水排放的氮與磷占陸源向海輸送的比例與全球河流大致相當(dāng), 在10%左右(氮與磷分別為9%和11%), 低于全國(guó)河流的平均值[2, 9]。不過(guò), 流域內(nèi)不同的區(qū)域?qū)Φc磷污染的貢獻(xiàn)也不相同, 即存在多樣化的熱點(diǎn)源區(qū)(hotspot, 指對(duì)入海負(fù)荷的貢獻(xiàn)量占比較多的源或單位面積輸出氮與磷通量較高的區(qū)域); 如在長(zhǎng)江流域, 中游來(lái)自農(nóng)田中化肥流失的氮與磷貢獻(xiàn)比例較高, 而下游污水的份額占比較大[9], 這也使得河流輸送的氮磷比在通量增加的同時(shí)顯著升高。

人類活動(dòng), 如化肥使用和污水排放, 也提高了陸地地下水中營(yíng)養(yǎng)鹽由陸向海的輸送通量, 尤其是氮的通量[53], 使之成為近海乃至全球海洋營(yíng)養(yǎng)鹽收支計(jì)算中重要的輸入項(xiàng)之一[54]。不過(guò), 在入海營(yíng)養(yǎng)鹽通量估算中數(shù)值模型的估算與同位素的結(jié)果存在較大的差別[8, 55]。盡管地下水入海的營(yíng)養(yǎng)鹽通量在數(shù)值上存在一定的不確定性, 然而大量的觀測(cè)顯示地下水中具有較高的氮磷比[12, 54], 對(duì)近海富營(yíng)養(yǎng)化加劇及氮磷比失衡的貢獻(xiàn)不可忽略。此外, 人類活動(dòng)強(qiáng)度的增加也影響了大氣沉降向海輸送的營(yíng)養(yǎng)鹽通量和組成[56]; 其中, 氮的通量增加較快, 其相比工業(yè)革命前增加了400%[57], 而磷僅為5%～15%[58]; 不過(guò),在全球尺度上, 大氣沉降輸送入海的營(yíng)養(yǎng)鹽對(duì)海洋初級(jí)生產(chǎn)的貢獻(xiàn)相對(duì)其他外源輸入以及大氣向海洋貢獻(xiàn)的鐵而言較低[56, 59]。

淡水[60]與海水[61]養(yǎng)殖作為人類活動(dòng)影響海洋環(huán)境的另一形式, 也在某種程度上增加了氮與磷的入海負(fù)荷, 加劇了近海水體富營(yíng)養(yǎng)化及營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡的趨勢(shì)。這一過(guò)程中氮與磷來(lái)源的貢獻(xiàn)及其相關(guān)的生物地球化學(xué)過(guò)程在近些年開(kāi)始被納入到近海物質(zhì)循環(huán)研究中[9, 61]。不過(guò), 相比于其他界面過(guò)程, 這一過(guò)程對(duì)近海氮與磷負(fù)荷的貢獻(xiàn)并不大[2]。相比于其他外源輸入, 固氮作用對(duì)近海氮來(lái)源的貢獻(xiàn)似乎也不大[62-64]。

正是由于氮與磷來(lái)源不同及生物地球化學(xué)循環(huán)模式的不同特點(diǎn), 在控制富營(yíng)養(yǎng)化和削減陸源氮與磷污染向海排放的應(yīng)用實(shí)踐過(guò)程中, 產(chǎn)生了限制氮[2, 65-66](部分研究是基于河口或近海的氮磷比值及其生態(tài)學(xué)效應(yīng), 海洋學(xué)家普遍支持此觀點(diǎn), 如王修林等提出削減渤海入海氮的負(fù)荷[67])或限制磷[68-69], 亦或氮與磷協(xié)同限制[70-73]等多種觀點(diǎn)和模式, 并在學(xué)界爭(zhēng)論不休。在中國(guó), 最近的研究開(kāi)始呼吁限制氮[74]。究竟是哪一種營(yíng)養(yǎng)元素或者二者均應(yīng)受到限制, 這取決于當(dāng)?shù)氐娜祟惢顒?dòng)和地理背景, 以及不同區(qū)域的實(shí)際情況, 不可一概而論。當(dāng)然, 這一爭(zhēng)論問(wèn)題的出現(xiàn)恰恰說(shuō)明了陸海一體化研究的必要性和緊迫性, 其過(guò)程與機(jī)理的深入研究理應(yīng)成為陸海統(tǒng)籌等管理實(shí)踐的關(guān)鍵科學(xué)依據(jù)。

1.2 近海富營(yíng)養(yǎng)化、氮磷滯留與初級(jí)生產(chǎn)變化

富營(yíng)養(yǎng)化是全球性的環(huán)境問(wèn)題。由于人類活動(dòng)影響的程度不同, 世界各地近海富營(yíng)養(yǎng)化呈現(xiàn)了從輕度到重度等不同的富營(yíng)養(yǎng)水平, 這些富營(yíng)養(yǎng)化水平的不同往往產(chǎn)生多樣化的生態(tài)學(xué)效應(yīng)[75]。大量的研究顯示, 富營(yíng)養(yǎng)化會(huì)提高近海初級(jí)生產(chǎn)水平; 如, 全球代表性的河流、海灣的數(shù)據(jù)顯示富營(yíng)養(yǎng)化不同程度上提高了河口、近岸的初級(jí)生產(chǎn)力[76-77]。當(dāng)然, 營(yíng)養(yǎng)鹽濃度變化(部分區(qū)域?yàn)楦粻I(yíng)養(yǎng)化)對(duì)初級(jí)生產(chǎn)的影響也存在明顯的區(qū)域性差異; 在低緯度區(qū)域, 初級(jí)生產(chǎn)因營(yíng)養(yǎng)鹽濃度變化而提高的幅度較低, 如南海大約升高了2%～4%[78]; 對(duì)于高緯度區(qū)域, 如北極, 這個(gè)升高幅度接近60%[79](受極區(qū)升高的海洋溫度和營(yíng)養(yǎng)鹽輸入共同作用); 在渤海, 初級(jí)生產(chǎn)升高的幅度大約為10%[80]。需關(guān)注的是, 初級(jí)生產(chǎn)的提高潛在影響海洋生物地球化學(xué)過(guò)程, 持續(xù)變化的生物地球化學(xué)過(guò)程協(xié)同海洋氣候變化又可能反作用于生物過(guò)程, 使得將來(lái)初級(jí)生產(chǎn)發(fā)生不確定性的變化; 盡管這一過(guò)程對(duì)于未來(lái)海洋環(huán)境變化的研究很重要, 但目前的關(guān)注還很少; 如, 基于地球系統(tǒng)模式的研究顯示未來(lái)全球海洋初級(jí)生產(chǎn)可能降低3%～10%[81], 這一初級(jí)生產(chǎn)先升高后降低的曲線變化過(guò)程主要受生物地球化學(xué)循環(huán)過(guò)程變化的驅(qū)動(dòng)。

值得注意的是, 氮與磷在水體中的循環(huán)過(guò)程也明顯不同[51], 這也使得河口生態(tài)系統(tǒng)中的氮與磷在向外輸送的過(guò)程中呈現(xiàn)出不同的變化趨勢(shì)[82], 近海的其他區(qū)域同樣如此。營(yíng)養(yǎng)鹽滯留(nutrient retention)在刻畫營(yíng)養(yǎng)鹽跨區(qū)域輸送的主要手段, 其是指水體中發(fā)生的物理、化學(xué)與生物的過(guò)程, 將營(yíng)養(yǎng)鹽永久地去除或者臨時(shí)地存儲(chǔ)、延緩營(yíng)養(yǎng)鹽在跨區(qū)域輸運(yùn)的過(guò)程; 這一概念被廣泛用于量化河流、湖泊和水庫(kù)的營(yíng)養(yǎng)鹽輸送過(guò)程, 近些年開(kāi)始應(yīng)用到近海, 如歐洲的波羅的海[83]。一般而言, 河口、陸架對(duì)營(yíng)養(yǎng)鹽的滯留效率滿足磷大于氮[51, 84]。氮與磷滯留效率的差異實(shí)質(zhì)上是由于其滯留機(jī)理不同造成的。對(duì)于氮而言, 近海的滯留率一般在20%～30%之間不等[84-85], 主要滯留機(jī)制是脫氮反應(yīng)和生物轉(zhuǎn)化利用; 脫氮反應(yīng)受到水體溶氧水平、水體停留時(shí)間、磷負(fù)荷等因素的影響, 尤其是水體停留時(shí)間; 總體而言, 在近海水體氮循環(huán)過(guò)程中脫氮反應(yīng)總量巨大[64, 86], 是氮去除/滯留的主要過(guò)程。對(duì)于磷而言, 滯留率在50%～70%之間不等[84-85], 主要的滯留機(jī)制為顆粒態(tài)磷的沉降和生物利用, 這主要是由于顆粒態(tài)磷通常是水體磷的主要形式, 而顆粒物輸送則受到水動(dòng)力的顯著影響; 在磷限制的水體中, 生物的吸收轉(zhuǎn)化作用對(duì)磷酸鹽的滯留極為顯著[38], 并提高其他賦存形態(tài)磷(如多聚磷酸鹽[20]和有機(jī)磷[87])參與生物地球化學(xué)循環(huán)的能力, 有機(jī)磷的生物可利用性增加以及快速的周轉(zhuǎn)也可在一定程度上補(bǔ)償磷的限制作用, 特別是遠(yuǎn)離近岸的開(kāi)闊海域。在中國(guó)近海, 磷是水體主要的限制性因子[14, 88-89], 上述提到的近海初級(jí)生產(chǎn)升高的趨勢(shì)將可能提高磷向沉積物的埋藏通量, 使得河口-近海體系磷限制進(jìn)一步加強(qiáng), 甚至是磷耗竭, 后者將可能導(dǎo)致高的浮游生物數(shù)量難以維持。最近有關(guān)黃渤海氮與磷收支的模式研究顯示, 氮在水體中呈積累趨勢(shì), 而磷的外部輸入?yún)s低于輸出(即呈現(xiàn)“消耗/耗竭”的特征)[64], 這一現(xiàn)象也被最近的研究所證實(shí)[90]; 黃河口沉積物中由表至下逐漸變小的有機(jī)氮和總磷、有機(jī)氮和有機(jī)磷的物質(zhì)的量的比或許可以從一個(gè)側(cè)面支持了上述磷消耗的猜想(圖1), 值得進(jìn)一步的關(guān)注。盡管目前有關(guān)富營(yíng)養(yǎng)化趨勢(shì)下近海氮與磷滯留、累積與耦合循環(huán)的機(jī)制研究在逐漸地增多, 但缺少氮與磷不同滯留機(jī)制的研究, 對(duì)近海磷埋藏與浮游植物種群變動(dòng)響應(yīng)機(jī)制機(jī)理及其生態(tài)環(huán)境效應(yīng)方面的研究則更少, 這一研究的不足在中國(guó)近海尤為突出。

圖1 黃河口沉積物中有機(jī)氮與總磷和有機(jī)磷的物質(zhì)的量的比變化[91]

氮與磷在水體中之所以存在不同的滯留效率, 主要是由于二者的化學(xué)活性/特性與生物利用機(jī)制不同造成的[38, 92]。如中國(guó)近海多呈現(xiàn)磷限制的特點(diǎn), 這在一定程度上應(yīng)與磷易吸附在顆粒物表面及其沉積作用有關(guān)。在維持浮游植物生長(zhǎng)的過(guò)程中, 相對(duì)于氮在水體中的易獲取性, 磷往往表現(xiàn)出“吝嗇”的一面, 氮與磷這種不同的生物地球化學(xué)循環(huán)特性實(shí)際上維持了初級(jí)生產(chǎn)的相對(duì)穩(wěn)定, 減少了浮游藻類旺發(fā)的可能性, 即有利于維持生態(tài)系統(tǒng)的穩(wěn)定。富營(yíng)養(yǎng)化, 尤其是氮在水體中的積累在一定程度上打破了由磷“吝嗇”維持的這種“平衡”, 從而導(dǎo)致磷消耗甚至耗竭的現(xiàn)象出現(xiàn)。需說(shuō)明的是, 本文所指的磷消耗在表觀上是一種磷限制, 其產(chǎn)生既是過(guò)量營(yíng)養(yǎng)鹽(尤其是氮)輸入及與之相關(guān)的富營(yíng)養(yǎng)化共同作用的結(jié)果, 也在一定程度上受近海生物地球化學(xué)循環(huán)過(guò)程變化的驅(qū)動(dòng)(主要是浮游植物生物量和種群結(jié)構(gòu)的變化), 可能為富營(yíng)養(yǎng)化條件下磷限制的新模態(tài), 理應(yīng)成為當(dāng)前海洋環(huán)境需要關(guān)注的問(wèn)題之一。

1.3 營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡與浮游植物種群變動(dòng)

營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡(偏離Redfield比值)是海洋環(huán)境和生態(tài)學(xué)研究的熱點(diǎn)問(wèn)題, 其往往導(dǎo)致河口、近海生態(tài)系統(tǒng)的轉(zhuǎn)變[93], 這在世界上許多中緯度的近海海域均有出現(xiàn)[94], 特別是人口較為集中的區(qū)域。大多情況下, 我們關(guān)注河流對(duì)于近海營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡的貢獻(xiàn), 如, 多瑙河等河流入海營(yíng)養(yǎng)鹽結(jié)構(gòu)變化導(dǎo)致了黑海浮游植物優(yōu)勢(shì)種由硅藻向非硅藻(鞭毛藻和顆石藻)轉(zhuǎn)變, 藻類還呈現(xiàn)了小型化的趨勢(shì)[95]。類似群落變動(dòng)的情況在人類活動(dòng)深度影響的圣華金河口(美國(guó)加州)[96]、尼羅河(埃及)[97]、科羅拉多河(美國(guó))[98]、長(zhǎng)江[99]、黃河[100]等主要河流的河口區(qū)都有出現(xiàn), 并且從河口擴(kuò)展到了河口以外的近海。又如, 研究顯示近30 a來(lái), 渤海三個(gè)海灣和中部的營(yíng)養(yǎng)鹽濃度和結(jié)構(gòu)(N/P比)均發(fā)生了顯著的變化(表現(xiàn)為N/P比值升高(圖2))[29-30], 渤海生態(tài)系統(tǒng)也較過(guò)去[101]發(fā)生了較為明顯的變化, 在近些年甲藻在生物量中的占比甚至超過(guò)了硅藻[15, 30], 占到了生物量的60%[15], 同時(shí)出現(xiàn)了抑食金球藻()的褐潮, 這顯然與包括黃河在內(nèi)的環(huán)渤海流域所輸送營(yíng)養(yǎng)鹽的結(jié)構(gòu)變化[102]有關(guān), 還可能驅(qū)動(dòng)渤海中部低氧[103]和酸化[14, 104]的產(chǎn)生?？梢?jiàn), 浮游植物群落結(jié)構(gòu)轉(zhuǎn)變的特征在中國(guó)近海海域是十分獨(dú)特和鮮明的。由于生物有機(jī)體內(nèi)氮、磷循環(huán)機(jī)制的不同, 浮游植物結(jié)構(gòu)與生物量的變化很可能會(huì)進(jìn)一步加劇營(yíng)養(yǎng)鹽失衡問(wèn)題。然而, 這一過(guò)程的驅(qū)動(dòng)機(jī)制及其生態(tài)效應(yīng)還需要更多的研究來(lái)揭示。

圖2 渤海營(yíng)養(yǎng)鹽濃度、比值長(zhǎng)期變化與有害赤潮(HABs)爆發(fā)頻率的關(guān)系[64, 91, 102, 105]

浮游植物群落結(jié)構(gòu)變化在一定程度上可認(rèn)為是對(duì)低磷和高氮磷比的水環(huán)境采取的適應(yīng)策略, 且不同的區(qū)域呈現(xiàn)出較為顯著的差異。近些年來(lái), 河流輸入到近海的營(yíng)養(yǎng)鹽通量和組成較過(guò)去發(fā)生了顯著的變化[8], 一旦近海絕對(duì)的營(yíng)養(yǎng)鹽濃度限制狀況被日益變化的陸源輸入所打破, 無(wú)疑會(huì)引起河口和近岸海域生物量及其組成的顯著變化。中國(guó)近海硅藻和甲藻是主要的類群[106], 而硅藻在低磷和高氮磷比環(huán)境中不占優(yōu)勢(shì)[87, 107]。因此, 營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡必然引起浮游植物群落結(jié)構(gòu)向有利于甲藻生物量增加的趨勢(shì)發(fā)展, 由此改變水體氮磷的循環(huán)過(guò)程。一個(gè)針對(duì)渤海變化合理的解釋是: 渤海生態(tài)系統(tǒng)的轉(zhuǎn)變不僅僅受陸源輸送的營(yíng)養(yǎng)鹽通量升高的影響, 還受到水體內(nèi)部營(yíng)養(yǎng)鹽結(jié)構(gòu)相對(duì)外部輸入失衡的脅迫, 導(dǎo)致浮游植物生物量和群落結(jié)構(gòu)響應(yīng)陸源輸入變化的同時(shí)甲藻不斷增加, 這一過(guò)程提高了水體向沉積物中磷的埋藏量(圖1), 并進(jìn)一步加劇了營(yíng)養(yǎng)鹽的失衡。相比于黃河(升高大約12倍)、海河(相對(duì)穩(wěn)定)等主要環(huán)渤海河流, 渤海氮磷比升高(升高約15倍)的幅度要大些[30], 也可以說(shuō)明磷埋藏量相對(duì)于氮在比例上是增加的。同樣, 最新的研究還顯示類似磷消耗的情況在黃海和東海都存在[90], 即中國(guó)近海可能存在普遍的磷消耗問(wèn)題, 值得關(guān)注。

除種群變化外, 浮游植物還往往通過(guò)調(diào)整它的生化組成來(lái)適應(yīng)低磷和高氮磷比的環(huán)境[20, 108], 使得它們體內(nèi)的元素組成偏離Redfield比值(106C/16N/ 1P[11, 109-110]); 如中國(guó)常見(jiàn)的兩種微微型浮游植物聚球藻()和原綠球藻()在磷限制下可以出現(xiàn)N/P比介于(59～109)/1的高值情況[110]。此外, 水體磷限制(主要是無(wú)機(jī)磷酸鹽)情況下其他賦存形態(tài)的磷參與物質(zhì)循環(huán)的程度可能提高, 這在前面已經(jīng)提到。不過(guò), 由于有機(jī)磷形態(tài)和組成復(fù)雜多樣, 目前對(duì)于其參與生物地球化學(xué)循環(huán)的主要過(guò)程的量化還較少?？梢?jiàn), 浮游植物對(duì)于水環(huán)境的自我調(diào)整和適應(yīng)機(jī)制無(wú)疑將影響磷的生物地球化學(xué)過(guò)程[111], 進(jìn)而改變其在水體中循環(huán)和沉積物內(nèi)埋藏的規(guī)律等。

諸多研究還顯示, 營(yíng)養(yǎng)鹽失衡還會(huì)導(dǎo)致有害赤潮暴發(fā)頻率與面積的增加[2, 112], 以及優(yōu)勢(shì)種的變遷。Wang等[2]的研究顯示, 營(yíng)養(yǎng)鹽輸送通量居高不下的當(dāng)前, 當(dāng)河流輸送的氮與磷營(yíng)養(yǎng)鹽比值(總氮與總磷的摩爾比)高于25～30的閾值時(shí)(其中, 渤海和黃海為25, 東海和南海為30), 中國(guó)近海赤潮暴發(fā)的頻率和面積將大為增加。與過(guò)去相比, 當(dāng)前中國(guó)河流輸送的營(yíng)養(yǎng)鹽的氮磷比明顯高于這一閾值, 這無(wú)疑增加了近海赤潮發(fā)生的風(fēng)險(xiǎn)。與此同時(shí), 世界范圍內(nèi)許多區(qū)域河流輸送的氮磷比都有升高的趨勢(shì)[113], 而低磷和高氮磷比的海洋環(huán)境更適合甲藻的快速生長(zhǎng)[114]。上述營(yíng)養(yǎng)鹽輸入與比值的變化還可能導(dǎo)致浮游植物優(yōu)勢(shì)種的改變; 再以渤海為例, 其優(yōu)勢(shì)種由1990年前硅藻門的角毛藻()和中肋骨條藻()等轉(zhuǎn)變?yōu)?000年后的硅藻門的舟形藻()、具槽帕拉藻()與海線藻()和甲藻門的角藻()等聯(lián)合占優(yōu)[15], 即“硅藻占優(yōu)”至“硅甲藻聯(lián)合為主”的轉(zhuǎn)變; 同時(shí), 赤潮發(fā)生特征也由偶發(fā)發(fā)展到多發(fā)與有毒階段, 且種類隨時(shí)間變化明顯[115]。這表明渤海的浮游植物群落組成、優(yōu)勢(shì)種變化等可能與富營(yíng)養(yǎng)化程度特別是營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡等密切相關(guān), 其響應(yīng)過(guò)程還將不斷催生磷消耗的問(wèn)題。圖2顯示有害赤潮暴發(fā)頻率與N/P比值存在正相關(guān)關(guān)系, 這也從側(cè)面證實(shí)上述假設(shè)。當(dāng)然, 除營(yíng)養(yǎng)鹽比值外, 營(yíng)養(yǎng)鹽的形態(tài)也可能影響上述種群變化, 如氨氮相對(duì)于其他無(wú)機(jī)氮比例的變化以及有機(jī)氮、有機(jī)磷相對(duì)于總氮、總磷比例的變化也是推動(dòng)近海浮游植物種群變化的“推手”, 如在東海, 持續(xù)暴發(fā)的東海原甲藻()赤潮還可能與水體有機(jī)磷濃度升高有關(guān)[116]。然而, 相關(guān)的研究主要是依據(jù)培養(yǎng)實(shí)驗(yàn)[93], 還需要更多的現(xiàn)場(chǎng)數(shù)據(jù)來(lái)驗(yàn)證。同樣, 在南海近岸赤潮的優(yōu)勢(shì)種也從束毛藻()轉(zhuǎn)變?yōu)榍蛐巫啬以?)[117], 后者可能與水體氨氮、尿素等含量變化有關(guān)。除近岸水域外, 南海營(yíng)養(yǎng)鹽的供給還受到多尺度物理過(guò)程的影響[118], 其營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡與浮游植物種群變動(dòng)的相關(guān)研究較中國(guó)其他海域少。

可見(jiàn), 水文、水化學(xué)環(huán)境背景場(chǎng)是影響環(huán)境質(zhì)量狀況和水生生態(tài)的重要因素, 其變化將首要對(duì)近海浮游植物的結(jié)構(gòu)和功能產(chǎn)生長(zhǎng)期的生態(tài)學(xué)效應(yīng), 并對(duì)水體生態(tài)系統(tǒng)產(chǎn)生深遠(yuǎn)影響, 特別是由此導(dǎo)致生態(tài)災(zāi)害事件頻發(fā), 將對(duì)近海資源產(chǎn)生不利的影響。如前所述, 氮、磷有著不同的生物地球化學(xué)循環(huán)過(guò)程, 近海浮游植物響應(yīng)陸源輸入變化及其相關(guān)聯(lián)的生物地球化學(xué)過(guò)程是產(chǎn)生磷消耗這一環(huán)境問(wèn)題的重要因素(圖3)。因此, 開(kāi)展以氮與磷營(yíng)養(yǎng)鹽由陸向海輸送及其海洋過(guò)程響應(yīng)為基礎(chǔ)的研究, 特別是導(dǎo)致近海氮磷營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡加劇的生物地球化學(xué)機(jī)制的研究, 將為近海環(huán)境變化和重要生物資源保護(hù)等提供重要科學(xué)依據(jù), 豐富和提升人們對(duì)環(huán)境變化的系統(tǒng)認(rèn)知。

2 中國(guó)近海相關(guān)工作的切入點(diǎn)

近海環(huán)境的演變最終將引起與之相關(guān)的氮與磷埋藏的變化以及浮游植物種群變動(dòng)。中國(guó)近海海洋環(huán)境與浮游植物群落結(jié)構(gòu)變化現(xiàn)象是十分獨(dú)特的, 顯著區(qū)別于鄰近的韓國(guó)和日本[119]; 受人類活動(dòng)的影響, 流域-近海的氮與磷物質(zhì)輸送過(guò)程-循環(huán)正在發(fā)生改變, 而作為物質(zhì)之“匯”的邊緣海必將通過(guò)調(diào)節(jié)系統(tǒng)的狀態(tài)以響應(yīng)這種變化, 從而對(duì)近海氮與磷埋藏格局產(chǎn)生影響, 如近海磷消耗乃至耗竭的現(xiàn)象。以上這些過(guò)程變化將導(dǎo)致近海磷的沉積環(huán)境發(fā)生怎樣的變化, 以及以何種方式、在多大程度上影響近海環(huán)境健康與穩(wěn)定正在成為一個(gè)廣受關(guān)注的科學(xué)問(wèn)題, 但相關(guān)研究仍較匱乏, 亟待加強(qiáng)。因此, 從海洋環(huán)境演變的角度, 陸地對(duì)緊鄰的海洋影響不容忽視, 應(yīng)加強(qiáng)陸海一體化研究, 做出科學(xué)合理的“以海統(tǒng)陸”的決策, 科學(xué)規(guī)劃流域污染物入海通量和組成[120]。這便要求沿海省份和大河流域各行政單元盡可能通過(guò)優(yōu)化化肥使用、改進(jìn)污水處理、優(yōu)化養(yǎng)殖活動(dòng)等有效措施降低陸源污染物入海通量。不過(guò), 當(dāng)前近乎于“一刀切”的減排舉措可能無(wú)法改變氮磷比失衡的環(huán)境問(wèn)題。由此不難理解, 在過(guò)去20 a, 盡管渤海的環(huán)境治理行動(dòng)取得了階段性的進(jìn)展, 但渤海生態(tài)環(huán)境惡化的趨勢(shì)依舊嚴(yán)峻(如, 近海富營(yíng)養(yǎng)化海域面積和程度繼續(xù)擴(kuò)大, 氮磷比持續(xù)升高[121]), 且有新的環(huán)境問(wèn)題出現(xiàn)(由2000年前的氮限制向當(dāng)前的磷限制轉(zhuǎn)變, 出現(xiàn)了抑食金球藻()褐潮[102, 122])。類似美國(guó)切薩皮克灣(Chesapeake Bay, 世界上富營(yíng)養(yǎng)化程度最高的海灣[6])差異化的陸源氮與磷削減實(shí)踐[123-124]或可為氮與磷減排量提供參考。同樣, 歐洲的陸地營(yíng)養(yǎng)鹽管理策略降低了河流營(yíng)養(yǎng)鹽輸送通量, 改善了其近海海洋環(huán)境, 使得波羅的海浮游植物的優(yōu)勢(shì)種出現(xiàn)了從硅藻到甲藻再到硅藻的轉(zhuǎn)變[125]。從目前有限的數(shù)據(jù)分析來(lái)看, 應(yīng)優(yōu)先削減輸入到近海的氮營(yíng)養(yǎng)鹽通量, 以減少其生態(tài)災(zāi)害發(fā)生的頻率和面積。不過(guò), 上述問(wèn)題的科學(xué)回答需要明確氮與磷驅(qū)動(dòng)近海環(huán)境演變的機(jī)制以及陸地氮與磷的熱點(diǎn)源區(qū)、組成與輸送路徑等, 因地制宜地制定不同區(qū)域差異化的“氮與磷配額”, 有針對(duì)性地開(kāi)展氮與磷減排工作。值得說(shuō)明的是, 最新的基于網(wǎng)格化的環(huán)境評(píng)估模型-營(yíng)養(yǎng)鹽數(shù)值模式 (integrated model to assess the global environment - global nutrient model, IMAGE-GNM)[9]對(duì)長(zhǎng)江氮與磷的溯源研究, 對(duì)于污染物來(lái)源的源地解析、管控和陸海統(tǒng)籌等具有很好的借鑒意義; 同時(shí), 最近Wang等[102]基于IMAGE-GNM與海洋3D模式(D-flow flexible mesh)的耦合是一次新的嘗試, 初步揭示了中國(guó)近海赤潮發(fā)生的新模態(tài), 給出了削減陸源氮和磷的比例, 初步回答了中國(guó)海洋環(huán)境治理應(yīng)該限制氮、還是限制磷抑或協(xié)同限制氮和磷排放的問(wèn)題, 為今后相關(guān)研究提供了重要手段。

圖3 營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡與磷消耗示意圖

值得注意的是渤海水體磷的濃度持續(xù)走低[29](圖2), 沉積物中磷的埋藏卻呈升高的趨勢(shì)[126], 這應(yīng)與環(huán)渤海陸源氮與磷輸送變化及其不同的生物地球化學(xué)過(guò)程直接相關(guān), 這也從多個(gè)側(cè)面支持了上述“磷消耗(耗竭)”的猜想。同樣有限的數(shù)據(jù)[25, 31-32, 90, 127]也顯示磷消耗的問(wèn)題在黃海與東海等中國(guó)近海都存在, 特別是南黃海在近些年因滸苔綠潮的頻發(fā)其營(yíng)養(yǎng)鹽結(jié)構(gòu)變化備受關(guān)注[25, 127-128]。因此應(yīng)高度重視“磷消耗/耗竭”所可能引發(fā)的潛在生態(tài)災(zāi)害和環(huán)境問(wèn)題。此外, 近海的水動(dòng)力結(jié)構(gòu)極為復(fù)雜[129], 地球化學(xué)背景場(chǎng)的區(qū)域性差異顯著, 不同區(qū)域的生態(tài)環(huán)境演變規(guī)律和磷消耗的變率并不完全一致[30, 104], 在其中近海區(qū)域內(nèi)物質(zhì)通量的急劇變化、結(jié)構(gòu)失衡及其環(huán)境效應(yīng)最為引人注目[14, 80], 是開(kāi)展海洋環(huán)境管理有效的切入點(diǎn)。

不過(guò), 面對(duì)如此廣闊的區(qū)域, 僅僅依靠沿海省市的努力, 中國(guó)近海的生態(tài)環(huán)境無(wú)法得到根本的改善, 急需陸地(通過(guò)流域延深的區(qū)域)-海洋的“一體化聯(lián)動(dòng)”。目前針對(duì)近海生態(tài)環(huán)境的研究多關(guān)注于大河[27, 130-131]及其河口區(qū)和典型海灣等子區(qū)域或子系統(tǒng), 很少涉及到陸-海區(qū)域的綜合研究, 陸海一體化的營(yíng)養(yǎng)鹽輸送、循環(huán)等過(guò)程的綜合研究更為有限, 亦缺乏以此為基礎(chǔ)的適應(yīng)性管理對(duì)策的探討。2021年3月12日, 《中華人民共和國(guó)國(guó)民經(jīng)濟(jì)和社會(huì)發(fā)展第十四個(gè)五年規(guī)劃和2035年遠(yuǎn)景目標(biāo)綱要》[132](簡(jiǎn)稱“綱要”)對(duì)外公布, “綱要”明確提出加快推進(jìn)重點(diǎn)海域綜合治理, 構(gòu)建流域–河口–近岸海域污染防治聯(lián)動(dòng)機(jī)制。可見(jiàn), 開(kāi)展陸海一體化的研究正是“綱要”提出的“打造可持續(xù)海洋生態(tài)環(huán)境”所亟需的。

綜上所述, 人類活動(dòng)深刻影響著近海的生態(tài)環(huán)境。入海營(yíng)養(yǎng)鹽的大量排放以及營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡已導(dǎo)致近海生態(tài)系統(tǒng)結(jié)構(gòu)和功能發(fā)生了明顯的變化, 也產(chǎn)生了“磷消耗”的環(huán)境問(wèn)題, 從而造成了近海水體營(yíng)養(yǎng)鹽結(jié)構(gòu)的進(jìn)一步失衡, 并可能引發(fā)近海生態(tài)環(huán)境不確定性或?yàn)?zāi)難性的變化, 需要進(jìn)一步深入研究。在上述問(wèn)題中, 對(duì)入海河流流域內(nèi)氮與磷產(chǎn)生的熱點(diǎn)區(qū)域進(jìn)行溯源, 定量估算流域-近海系統(tǒng)的物質(zhì)輸送通量、循環(huán)與收支, 揭示其生態(tài)響應(yīng), 對(duì)于準(zhǔn)確和深入認(rèn)識(shí)近海生態(tài)環(huán)境變化是十分必要的。相關(guān)研究工作的深入開(kāi)展將有助于深入闡釋人類活動(dòng)對(duì)近海環(huán)境的影響及其生態(tài)效應(yīng), 為實(shí)現(xiàn)可持續(xù)的海洋生態(tài)環(huán)境提供科學(xué)基礎(chǔ)。需要指出的是, 前述三方面的主要研究?jī)?nèi)容并未涉及到全球變化的影響。實(shí)事上, 氣候變化也可能通過(guò)影響近海環(huán)流從而進(jìn)一步影響區(qū)域的富營(yíng)養(yǎng)化進(jìn)程, 或通過(guò)水體升溫加劇富營(yíng)養(yǎng)化過(guò)程[106, 114]。不過(guò), 對(duì)于近海這一緊鄰陸地的淺海而言, 人類活動(dòng)應(yīng)該是影響其環(huán)境變化的主要控制因素, 這也恰恰是《渤海綜合治理攻堅(jiān)戰(zhàn)行動(dòng)計(jì)劃》等系列治理文件出臺(tái)的根本原因。

3 結(jié)語(yǔ)和展望

人類活動(dòng)深刻影響近海的生態(tài)環(huán)境。中國(guó)近海營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡較過(guò)去更為突出, 可能引發(fā)潛在的磷消耗問(wèn)題, 而這一問(wèn)題不能簡(jiǎn)單地視作磷限制; 入海營(yíng)養(yǎng)鹽通量和結(jié)構(gòu)的變化是導(dǎo)致近海營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡的外部因素, 近海浮游植物對(duì)陸源輸入變化的響應(yīng)及其相關(guān)聯(lián)的生物地球化學(xué)過(guò)程是產(chǎn)生磷消耗這一環(huán)境問(wèn)題的內(nèi)部因素, 從而造成近海水體營(yíng)養(yǎng)鹽結(jié)構(gòu)的進(jìn)一步失衡, 并可能帶來(lái)近海生態(tài)環(huán)境不確定性或?yàn)?zāi)難性的變化, 需要進(jìn)一步深入研究。在上述問(wèn)題中, 對(duì)入海河流流域氮與磷產(chǎn)生的熱點(diǎn)區(qū)進(jìn)行溯源, 定量評(píng)估河流流域-近海系統(tǒng)的物質(zhì)輸送、循環(huán)與收支及其生態(tài)學(xué)響應(yīng), 對(duì)于準(zhǔn)確和深入認(rèn)識(shí)近海營(yíng)養(yǎng)鹽結(jié)構(gòu)失衡等生態(tài)環(huán)境變化是十分必要的。

毫無(wú)疑問(wèn), 人類活動(dòng)導(dǎo)致的氮磷失衡是全球性的生態(tài)環(huán)境問(wèn)題[133-134], 勢(shì)必會(huì)對(duì)海洋物質(zhì)循環(huán)和生態(tài)系統(tǒng)穩(wěn)定產(chǎn)生深遠(yuǎn)的影響, 其中近海磷消耗及其生態(tài)系統(tǒng)響應(yīng)應(yīng)該得到重視。長(zhǎng)期以來(lái), 中國(guó)學(xué)科劃分過(guò)細(xì), 陸地與海洋學(xué)科間的交叉融合不足。但地球系統(tǒng)科學(xué)下的海洋環(huán)境問(wèn)題是一個(gè)“大科學(xué)”, 環(huán)境問(wèn)題的復(fù)雜性使其無(wú)法通過(guò)單一學(xué)科的觀測(cè)與研究或有限區(qū)域的觀測(cè)與研究得以解決, 而是需要多學(xué)科、不同領(lǐng)域間的深度交叉。近年來(lái), 隨著科技投入的增大、科研條件的改善和對(duì)外合作交流的加強(qiáng), 中國(guó)海洋科學(xué)的觀測(cè)與研究正在走向深入, 但不同學(xué)科間的深度融合依然不足, 也缺少應(yīng)對(duì)海洋環(huán)境問(wèn)題的國(guó)家戰(zhàn)略。在全球變化大環(huán)境下, 中國(guó)需要及早布局, 有效應(yīng)對(duì); 這就要求海洋科學(xué)觀測(cè)與研究必須創(chuàng)新模式, 通過(guò)跨領(lǐng)域、跨學(xué)科的交叉, 力爭(zhēng)在陸海耦合機(jī)制和環(huán)境演變方面取得理論上的突破。同時(shí), 我們也應(yīng)該注意到中國(guó)海域廣闊, 不同海區(qū)存在顯著不同的生態(tài)環(huán)境特征。統(tǒng)一的入海河流氮、磷協(xié)同控制或許并不合適, 無(wú)法適用于不同的海域。因此, 建議在綜合考慮這些典型近海區(qū)域背景和環(huán)境演變的基礎(chǔ)上, 開(kāi)展“因地制宜”的入海河流氮磷協(xié)同控制, 建立近海水質(zhì)、入海氮磷通量、生態(tài)系統(tǒng)穩(wěn)定等多控制目標(biāo)。今后, 應(yīng)堅(jiān)持“陸海統(tǒng)籌”和“陸海協(xié)作”, 整體提升陸地-海洋聯(lián)合觀測(cè)監(jiān)測(cè)體系的水平和綜合研究的能力。基于地球系統(tǒng)多圈層相互作用的理念, 以陸地-近海海洋為體系, 將歷史記錄、現(xiàn)代過(guò)程和預(yù)測(cè)預(yù)報(bào)相結(jié)合, 開(kāi)展陸地-河流-近海的耦合研究, 將為維持海洋生態(tài)系統(tǒng)健康與穩(wěn)定、促進(jìn)國(guó)家經(jīng)濟(jì)社會(huì)可持續(xù)發(fā)展提供有力的科學(xué)依據(jù)。

[1] JENNY J P, FRANCUS P, NORMANDEAU A, et al. Global spread of hypoxia in freshwater ecosystems during the last three centuries is caused by rising local human pressure[J]. Global Change Biology, 2016, 22(4): 1481-1489.

[2] WANG J, BOUWMAN A F, LIU X, et al. Harmful algal blooms in Chinese coastal waters will persist due to perturbed nutrient ratios[J]. Environmental Science & Technology Letters, 2021, 8(3): 276-284.

[3] HEISLER J, GLIBERT P M, BURKHOLDER J M, et al. Eutrophication and harmful algal blooms: a scientific consensus[J]. Harmful Algae, 2008, 8(1): 3-13.

[4] KEYS M, TILSTONE G, FINDLAY H S, et al. Effects of elevated CO2and temperature on phytoplankton com-munity biomass, species composition and photosynthesis during an experimentally induced autumn bloom in the western English Channel[J]. Biogeosciences, 2018, 15(10): 3203-3222.

[5] WALLACE R B, BAUMANN H, GREAR J S, et al. Coastal ocean acidification: The other eutrophication problem[J]. Estuarine, Coastal and Shelf Science, 2014, 148: 1-13.

[6] MALONE T C, NEWTON A. The globalization of cultural Eutrophication in the coastal ocean: Causes and consequences[J]. Frontiers in Marine Science, 2020, 7(670): 1-30.

[7] HOUGHTON R A, NASSIKAS A A. Global and regional fluxes of carbon from land use and land-cover change 1850-2015[J]. Global Biogeochemical Cycles, 2017, 31: 456-472.

[8] BEUSEN A H W, BOUWMAN A F, VAN BEEK L P H, et al. Global riverine N and P transport to ocean increased during the 20th century despite increased retention along the aquatic continuum[J]. Biogeo-sciences, 2016, 13(8): 2441-2451.

[9] LIU X, BEUSEN A H W, VAN BEEK L P H, et al. Exploring spatiotemporal changes of the Yangtze River (Changjiang) nitrogen and phosphorus sources, retention and export to the East China Sea and Yellow Sea[J]. Water Research, 2018, 142: 246-255.

[10] MAAVARA T, D RR H H, VAN CAPPELLEN P. Worldwide retention of nutrient silicon by river damming: From sparse data set to global estimate[J]. Global Biogeochemical Cycles, 2014, 28(8): 842-855.

[11] REDFIELD A C. The biological control of chemical factors in the environment[J]. American Scientist 1958, 46: 205-221.

[12] LIU J, DU J, WU Y, et al. Nutrient input through submarine groundwater discharge in two major Chinese estuaries: the Pearl River Estuary and the Changjiang River Estuary[J]. Estuarine, Coastal and Shelf Science, 2018, 203: 17-28.

[13] RAN X, BOUWMAN A F, YU Z, et al. Implications of eutrophication for biogeochemical processes in the Three Gorges Reservoir, China[J]. Regional Environ-mental Change, 2019, 19(1): 55-63.

[14] ZHAI W D, ZHENG L W, LI C L, et al. Changing nutrients, dissolved oxygen and carbonate system in the Bohai and Yellow Seas, China[M]//CHEN C T A, GUO X. Changing Asia-Pacific Marginal Seas. Singapore; Springer Singapore, 2020: 121-137.

[15] LIU D, SHEN X, DI B, et al. Palaeoecological analysis of phytoplankton regime shifts in response to coastal eutrophication[J]. Marine Ecology Progress Series, 2013, 475: 1-14.

[16] LAUFK TTER C, VOGT M, GRUBER N, et al. Drivers and uncertainties of future global marine primary production in marine ecosystem models[J]. Biogeos-ciences, 2015, 12(23): 6955-6984.

[17] XING L, ZHAO M, ZHANG T, et al. Ecosystem responses to anthropogenic and natural forcing over the last 100 years in the coastal areas of the East China Sea[J]. The Holocene, 2016, 26: 669-677.

[18] GLIBERT P M, ICARUS A J, ARTIOLI Y, et al. Vulnerability of coastal ecosystems to changes in harmful algal bloom distribution in response to climate change: Projections based on model analysis[J]. Global Change Biology, 2014, 20(12): 3845-3858.

[19] BAUER J E, CAI W J, RAYMOND P A, et al. The changing carbon cycle of the coastal ocean[J]. Nature, 2013, 504(7478): 61-70.

[20] MARTIN P, DYHRMAN S T, LOMAS M W, et al. Accumulation and enhanced cycling of polyphosphate by Sargasso Sea plankton in response to low phosphorus[J]. Proceedings of the National Academy of Sciences, 2014, 111(22): 8089-8094.

[21] WU J, SUNDA W, BOYLE E, et al. Phosphate depletion in the western North Atlantic Ocean[J]. Science, 2000, 289: 759-762.

[22] WANG B, XIN M, WEI Q, et al. A historical overview of coastal eutrophication in the China Seas[J]. Marine Pollution Bulletin, 2018, 136: 394-400.

[23] BOUWMAN L, BEUSEN A M, GLIBERT P M, et al. Mariculture: significant and expanding cause of coastal nutrient enrichment[J]. Environmental Research Letters, 2013, 8(4): 044026.

[24] ZHOU M J, SHEN Z L, YU R C. Responses of a coastal phytoplankton community to increased nutrient input from the Changjiang (Yangtze) River[J]. Continental Shelf Research, 2008, 28(12): 1483-1489.

[25] ZHANG Y, HE P, LI H, et al. Ulva prolifera green-tide outbreaks and their environmental impact in the Yellow Sea, China[J]. National Science Review, 2019, 6(4): 825-838.

[26] WEI Q, WANG B, YU Z, et al. Mechanisms leading to the frequent occurrences of hypoxia and a preliminary analysis of the associated acidification off the Changjiang estuary in summer[J]. Science China Earth Sciences, 2017, 60(2): 360.

[27] 宋金明, 李學(xué)剛, 袁華茂, 等. 渤黃東海生源要素的生物地球化學(xué)[M]. 北京: 科學(xué)出版社, 2019. SONG Jinming, LI Xuegang, YUAN Huamao, et al. Biogeochemistry of biogenic elements in the Bohai Sea, the Yellow Sea and the East China Sea[M]. Beijing: Science Press, 2019.

[28] 俞志明, 沈志良, 陳亞瞿, 等. 長(zhǎng)江口水域富營(yíng)養(yǎng)化[M]. 北京: 科學(xué)出版社, 2011. YU Zhiming, SHEN Zhiliang, CHEN Yaqu, et al. Eutrop-hication in the Changjiang estuary[M]. Beijing: Science Press, 2011.

[29] WANG J, YU Z, WEI Q, et al. Long-term nutrient variations in the Bohai Sea over the past 40 years[J]. Journal of Geophysical Research: Oceans, 2019, 124(1): 703-722.

[30] XIN M, WANG B, XIE L, et al. Long-term changes in nutrient regimes and their ecological effects in the Bohai Sea, China[J]. Marine Pollution Bulletin, 2019, 146: 562-573.

[31] YANG F, WEI Q, CHEN H, et al. Long-term variations and influence factors of nutrients in the western North Yellow Sea, China[J]. Marine Pollution Bulletin, 2018, 135: 1026-1034.

[32] WEI Q, YAO Q, WANG B, et al. Long-term variation of nutrients in the southern Yellow Sea[J]. Continental Shelf Research, 2015, 111: 184-196.

[33] JESSEN C, BEDNARZ V, RIX L, et al. Marine eutrop-hication[M]// ARMON R, H?NNINEN O. Environmental indicators. Dordrecht: Springer, 2015: 177-203.

[34] RABALAIS N N, TURNER R E, D AZ R J, et al. Global change and eutrophication of coastal waters[J]. ICES Journal of Marine Science, 2009, 66: 1528-1537.

[35] LIU Y, LU M, YANG H, et al. Land–atmosphere–ocean coupling associated with the Tibetan Plateau and its climate impacts[J]. National Science Review, 2020, 7(3): 534-552.

[36] BOUWMAN A F, BIERKENS M F P, GRIFFIOEN J, et al. Nutrient dynamics, transfer and retention along the aquatic continuum from land to ocean: towards integ-ration of ecological and biogeochemical models[J]. Biogeosciences, 2013, 10(1): 1-22.

[37] GAO Y, ZHOU F, CIAIS P, et al. Human activities aggravate nitrogen-deposition pollution to inland water over China[J]. National Science Review, 2019, 7(2): 430-440.

[38] RUTTENBERG K C. Phosphorus Cycle[M]//COCHRAN J K, BOKUNIEWICZ H J, YAGER P L. Encyclopedia of Ocean Sciences (Third Edition). Oxford: Academic Press, 2019: 447-460.

[39] BENITEZ-NELSON C R. The biogeochemical cycling of phosphorus in marine systems[J]. Earth-Science Reviews, 2000, 51(1): 109-135.

[40] TYRRELL T. The relative influences of nitrogen and phosphorus on oceanic primary production[J]. Nature, 1999, 400(6744): 525-531.

[41] YAN W, MAYORGA E, LI X, et al. Increasing anthropogenic nitrogen inputs and riverine DIN exports from the Changjiang River basin under changing human pressures[J]. Global Biogeochemical Cycles, 2010, 24(4): GB0A06.

[42] LI L, NI J, CHANG F, et al. Global trends in water and sediment fluxes of the world’s large rivers[J]. Science Bulletin, 2019, 65(1): 62-69.

[43] MAAVARA T, LAUERWALD R, REGNIER P, et al. Global perturbation of organic carbon cycling by river damming[J]. Nature Communications, 2017, 8: 15347.

[44] LEHNER B, LIERMANN C R, REVENGA C, et al. High-resolution mapping of the world's reservoirs and dams for sustainable river-flow management[J]. Frontiers in Ecology and the Environment, 2011, 9(9): 494-502.

[45] HOWARTH R, SWANEY D, BILLEN G, et al. Nitrogen fluxes from the landscape are controlled by net anthropogenic nitrogen inputs and by climate[J]. Frontiers in Ecology and the Environment, 2012, 10(1): 37-43.

[46] DU E, TERRER C, PELLEGRINI A F A, et al. Global patterns of terrestrial nitrogen and phosphorus limitation[J]. Nature Geoscience, 2020, 13(3): 221-226.

[47] ZHU J, WANG Q, HE N, et al. Imbalanced atmospheric nitrogen and phosphorus depositions in China: Implications for nutrient limitation[J]. Journal of Geophysical Research: Biogeosciences, 2016, 121(6): 1605-1616.

[48] BENNEKOM A J, SALOMONS W. Pathways of nutrients and organic matter from land to ocean through rivers[M]. 1980: 33-51.

[49] MAHOWALD N, JICKELLS T D, BAKER A R, et al. Global distribution of atmospheric phosphorus sources, concentrations and deposition rates, and anthropogenic impacts[J]. Global Biogeochemical Cycles, 2008, 22(4): GB4026.

[50] KANAKIDOU M, DUCE R A, PROSPERO J M, et al. Atmospheric fluxes of organic N and P to the global ocean[J]. Global Biogeochemical Cycles, 2012, 26(3): GB3026.

[51] BURSON A, STOMP M, AKIL L, et al. Unbalanced reduction of nutrient loads has created an offshore gradient from phosphorus to nitrogen limitation in the North Sea[J]. Limnology and Oceanography, 2016, 61: 869-888.

[52] VAN METER K J, BASU N B, VEENSTRA J J, et al. The nitrogen legacy: emerging evidence of nitrogen accumulation in anthropogenic landscapes[J]. Environ-mental Research Letters, 2016, 11(3): 035014.

[53] BEUSEN A H W, SLOMP C P, BOUWMAN A F. Global land–ocean linkage: direct inputs of nitrogen to coastal waters via submarine groundwater discharge[J]. Environmental Research Letters, 2013, 8(3): 034035.

[54] SANTOS I R, CHEN X, LECHER A L, et al. Submarine groundwater discharge impacts on coastal nutrient biogeochemistry[J]. Nature Reviews Earth & Environment, 2021, 2(5): 307-323.

[55] CHO H-M, KIM G, KWON E Y, et al. Radium tracing nutrient inputs through submarine groundwater discharge in the global ocean[J]. Scientific Reports, 2018, 8(1): 2439.

[56] MYRIOKEFALITAKIS S, GR GER M, HIERONYMUS J, et al. An explicit estimate of the atmospheric nutrient impact on global oceanic productivity[J]. Ocean Science, 2020, 16(5): 1183-1205.

[57] SHI Z, HERBERT R. The Importance of atmospheric nutrients in the earth system[J]. EOS Transactions of the American Geophysical Union, 2016, 97: EO044133.

[58] MAHOWALD N, JICKELLS T D, BAKER A R, et al. Global distribution of atmospheric phosphorus sources, concentrations and deposition rates, and anthropogenic impacts[J]. Global Biogeochemical Cycles, 2008, 22(4): GB4026.

[59] OKIN G S, BAKER A R, TEGEN I, et al. Impacts of atmospheric nutrient deposition on marine productivity: Roles of nitrogen, phosphorus, and iron[J]. Global Biogeochemical Cycles, 2011, 25(2): GB2022.

[60] WANG J, BOUWMAN A F, BEUSEN A H W, et al. Comment on “Multi-scale modeling of nutrient pollution in the rivers of China”[J]. Environmental Science & Technology, 2020, 54(3): 2043-2045.

[61] WU W, LIU J, BOUWMAN A F, et al. Exploring oxygen dynamics and depletion in an intensive bivalve production area in the coastal sea off Rushan Bay, China[J]. Marine Ecology Progress Series, 2020, 649: 53-65.

[62] WANG R, LI X, HOU L, et al. Nitrogen fixation in surface sediments of the East China Sea: Occurrence and environmental implications[J]. Marine Pollution Bulletin, 2018, 137: 542-548.

[63] LI D, JING H, ZHANG R, et al. Heterotrophic diazotrophs in a eutrophic temperate bay (Jiaozhou Bay) broadens the domain of N2 fixation in China's coastal waters[J]. Estuarine, Coastal and Shelf Science, 2020, 242: 106778.

[64] 趙晨英, 臧家業(yè), 劉軍, 等. 黃渤海氮磷營(yíng)養(yǎng)鹽的分布、收支與生態(tài)環(huán)境效應(yīng)[J]. 中國(guó)環(huán)境科學(xué), 2016, 36(7): 2115-2127. ZHAO Chenying, ZANG Jiaye, LIU Jun, et al. Distribution and budget of nitrogen and phosphorus and their influence on the ecosystem in the Bohai Sea and Yellow Sea[J]. China Environmental Science, 2016, 36(7): 2115-2127.

[65] HOWARTH R W, MARINO R. Nitrogen as the limiting nutrient for eutrophication in coastal marine ecosystems: Evolving views over three decades[J]. Limnology and Oceanography, 2006, 51(1, part2): 364-376.

[66] WOODLAND R J, THOMSON J R, MAC NALLY R, et al. Nitrogen loads explain primary productivity in estuaries at the ecosystem scale[J]. Limnology and Oceanography, 2015, 60(5): 1751-1762.

[67] 王修林, 崔正國(guó), 李克強(qiáng), 等. 環(huán)渤海三省一市溶解態(tài)無(wú)機(jī)氮容量總量控制[J]. 中國(guó)海洋大學(xué)學(xué)報(bào)(自然科學(xué)版), 2008(4): 109-112, 116. WANG Xiulin, CUI Zhengguo, LI Keqiang, et al. Study on the gross control of DIN environmental capacity in the peripheral zone of the Bohai Sea[J]. Periodical of Ocean University of China, 2008(4): 109-112, 116.

[68] SCHINDLER D W, CARPENTER S R, CHAPRA S C, et al. Reducing phosphorus to Curb Lake eutrophication is a success[J]. Environmental Science & Technology, 2016, 50(17): 8923-8929.

[69] SCHINDLER D W, HECKY R E, FINDLAY D L, et al. Eutrophication of lakes cannot be controlled by reducing nitrogen input: Results of a 37-year whole-ecosystem experiment[J]. Proceedings of the National Academy of Sciences, 2008, 105(32): 11254-11258.

[70] PAERL H W. Controlling eutrophication along the freshwater–marine continuum: dual nutrient (N and P) reductions are essential[J]. Estuaries and Coasts, 2009, 32(4): 593-601.

[71] CONLEY D J, PAERL H W, HOWARTH R W, et al. Controlling eutrophication: nitrogen and phosphorus[J]. Science, 2009, 323(5917): 1014-1015.

[72] DODDS W K, SMITH V H. Nitrogen, phosphorus, and eutrophication in streams[J]. Inland Waters, 2016, 6(2): 155-164.

[73] PAERL H W, SCOTT J T, MCCARTHY M J, et al. It takes two to tango: when and where dual nutrient (N & P) reductions are needed to protect lakes and downstream ecosystems[J]. Environmental Science & Technology, 2016, 50(20): 10805-10813.

[74] YU C, HUANG X, CHEN H, et al. Managing nitrogen to restore water quality in China[J]. Nature, 2019, 567(7749): 516-520.

[75] SCAVIA D, BRICKER S B. Coastal eutrophication assessment in the United States[M]//MARTINELLI L A, HOWARTH R W. Nitrogen cycling in the Americas: natural and anthropogenic influences and controls. Dordrecht: Springer Netherlands, 2006: 187-208.

[76] JUSTI? D, RABALAIS N N, TURNER R E. Stoichiometric nutrient balance and origin of coastal eutrophication[J]. Marine Pollution Bulletin, 1995, 30(1): 41-46.

[77] EVANS M A, SCAVIA D. Exploring estuarine eutrop-hication sensitivity to nutrient loading[J]. Limnology and Oceanography, 2013, 58(2): 569-578.

[78] LIN I, LIU W T, WU C C, et al. New evidence for enhanced ocean primary production triggered by tropical cyclone[J]. Geophysical Research Letters, 2003, 30(13): 1718.

[79] LEWIS K M, VAN DIJKEN G L, ARRIGO K R. Changes in phytoplankton concentration now drive increased Arctic Ocean primary production[J]. Science, 2020, 369(6500): 198-202.

[80] LIU J, ZANG J, WANG H, et al. Changes in the distribution and preservation of silica in the Bohai Sea due to changing terrestrial inputs[J]. Continental Shelf Research, 2018, 166: 1-9.

[81] MORA C, WEI C L, ROLLO A, et al. Biotic and human vulnerability to projected changes in ocean biogeochemistry over the 21st Century[J]. PLOS Biology, 2013, 11(10): e1001682.

[82] METSON G S, LIN J, HARRISON J A, et al. Where have all the nutrients gone? Long-term decoupling of inputs and outputs in the Willamette River watershed, Oregon, United States[J]. Journal of Geophysical Research: Biogeosciences, 2020, 125(10): e2020JG005792.

[83] ASMALA E, CARSTENSEN J, CONLEY D J, et al. Efficiency of the coastal filter: Nitrogen and phosp-horus removal in the Baltic Sea[J]. Limnology and Oceanography, 2017, 62(S1): S222-S238.

[84] LENHART H-J, MILLS D K, BARETTA-BEKKER H, et al. Predicting the consequences of nutrient reduction on the eutrophication status of the North Sea[J]. Journal of Marine Systems, 2010, 81(1): 148-170.

[85] PASSY P, GYPENS N, BILLEN G, et al. A model reconstruction of riverine nutrient fluxes and eutrophication in the Belgian Coastal Zone since 1984[J]. Journal of Marine Systems, 2013, 128: 106-122.

[86] WANG W, YU Z, WU Z, et al. Rates of nitrification and nitrate assimilation in the Changjiang River estuary and adjacent waters based on the nitrogen isotope dilution method[J]. Continental Shelf Research, 2018, 163: 35-43.

[87] LI J, GLIBERT P M, ZHOU M, et al. Relationships between nitrogen and phosphorus forms and ratios and the development of dinoflagellate blooms in the East China Sea[J]. Marine Ecology Progress Series, 2009, 383: 11-26.

[88] YANG B, SONG G D, LIU S M, et al. Phosphorus recycling and burial in core sediments of the East China Sea[J]. Marine Chemistry, 2017, 192: 59-72.

[89] LIU S M. Response of nutrient transports to water–sediment regulation events in the Huanghe basin and its impact on the biogeochemistry of the Bohai[J]. Journal of Marine Systems, 2015, 141: 59-70.

[90] MOON J Y, LEE K, LIM W A, et al. Anthropogenic nitrogen is changing the East China and Yellow seas from being N deficient to being P deficient[J]. Limnology and Oceanography, 2021, 66(3): 914-924.

[91] 李夢(mèng)露. 磷觀渤海: 由陸向海磷的分布與通量和收支及其海洋生態(tài)環(huán)境效應(yīng)研究[D]. 青島: 自然資源部第一海洋研究所, 2021. LI Menglu. Insighting into the Bohai Sea from the phosphorus dimension: A study of fluxes and budget of phosphorus from land to sea with implications for the marine environmental evolution[D]. Qingdao: First Institute of Oceanography, Ministry of Natural Resources, 2021.

[92] GRANTZ E M, HAGGARD B E, SCOTT J T. Stoichiometric imbalance in rates of nitrogen and phosphorus retention, storage, and recycling can perpetuate nitrogen deficiency in highly-productive reservoirs[J]. Limnology and Oceanography, 2014, 59(6): 2203-2216.

[93] MEYER J, L SCHER C R, NEULINGER S C, et al. Changing nutrient stoichiometry affects phytoplankton production, DOP accumulation and dinitrogen fixation – a mesocosm experiment in the eastern tropical North Atlantic[J]. Biogeosciences, 2016, 13(3): 781-794.

[94] ANDERSEN T, CARSTENSEN J, HERN NDEZ-GARC A E, et al. Ecological thresholds and regime shifts: approaches to identification[J]. Trends in Ecology & Evolution, 2009, 24(1): 49-57.

[95] LUDWIG W, DUMONT E, MEYBECK M, et al. River discharges of water and nutrients to the Mediterranean and Black Sea: Major drivers for ecosystem changes during past and future decades?[J]. Progress in Oceanography, 2009, 80(3/4): 199-217.

[96] GLIBERT P M. Long-term changes in nutrient loading and stoichiometry and their relationships with changes in the food web and dominant pelagic fish species in the San Francisco Estuary, California[J]. Reviews in Fisheries Science, 2010, 18(2): 211-232.

[97] RAM REZ-ROMERO E, MOLINERO J C, SOMMER U, et al. Phytoplankton size changes and diversity loss in the southwestern Mediterranean Sea in relation to long-term hydrographic variability[J]. Estuarine, Coastal and Shelf Science, 2020, 235: 106574.

[98] BRUSCA R C, áLVAREZ-BORREGO S, HASTINGS P A, et al. Colorado River flow and biological productivity in the Northern Gulf of California, Mexico[J]. Earth-Science Reviews, 2017, 164: 1-30.

[99] WANG Y, XU H, LI M. Long-term changes in phytoplankton communities in China's Yangtze Estuary driven by altered riverine fluxes and rising sea surface temperature[J]. Geomorphology, 2021, 376: 107566.

[100]ZHANG J, LI F, LV Q, et al. Impact of the Water–Sediment Regulation Scheme on the phytoplankton community in the Yellow River estuary[J]. Journal of Cleaner Production, 2021, 294: 126291.

[101]于志剛, 米鐵柱, 謝寶東, 等. 二十年來(lái)渤海生態(tài)環(huán)境參數(shù)的演化和相互關(guān)系[J]. 海洋環(huán)境科學(xué), 2000, 19(1): 15-19. YU Zhigang, MI Tiezhu, XIE Baodong, et al. Changes of the environmental parameters and their relationship in recent twenty years in the Bohai Sea[J]. Marine Environmental Science, 2000, 19(1): 15-19.

[102]WANG H, BOUWMAN A F, VAN GILS J, et al. Hindcasting harmful algal bloom risk due to land-based nutrient pollution in the Eastern Chinese coastal seas[J]. Water Research, 2023, 231: 119669.

[103]WEI Q, WANG B, YAO Q, et al. Spatiotemporal variations in the summer hypoxia in the Bohai Sea (China) and controlling mechanisms[J]. Marine Pollution Bulletin, 2019, 138: 125-134.

[104]ZHAI W D, ZHAO H D, SU J L, et al. Emergence of summertime hypoxia and concurrent carbonate mineral suppression in the central Bohai Sea, China[J]. Journal of Geophysical Research: Biogeosciences, 2019, 124(9): 2768-2785.

[105]WANG H, RAN X, BOUWMAN L, et al. Competitive advantages of HAB species under changing environmental conditions in the coastal waters of the Bohai Sea, Yellow Sea and East China Sea[J]. Continental Shelf Research, 2023, 259: 104991.

[106]XIAO X, AGUST S, PAN Y, et al. Warming amplifies the frequency of harmful algal blooms with eutrophication in Chinese coastal waters[J]. Environmental Science & Technology, 2019, 53(22): 13031-13041.

[107]LIANG Y, ZHANG G, WAN A, et al. Nutrient- limitation induced diatom-dinoflagellate shift of spring phytoplankton community in an offshore shellfish farming area[J]. Marine Pollution Bulletin, 2019, 141: 1-8.

[108]DEVRIES T. New directions for ocean nutrients[J]. Nature Geoscience, 2018, 11(1): 15-16.

[109]REDFIELD A C, KETCHUM B H, RICHARDS F A. The influence of organisms on the composition of sea-water[M]//HILLS M N. The sea. New York: Wiley and Sons, 1963: 12-37.

[110]BERTILSSON S, BERGLUND O, KARL D M, et al. Elemental composition of marine Prochlorococcus and Synechococcus: Implications for the ecological stoic-hiometry of the sea[J]. Limnology and Oceanography, 2003, 48(5): 1721-1731.

[111]WEBER T S, DEUTSCH C. Ocean nutrient ratios governed by plankton biogeography[J]. Nature, 2010, 467 (7315): 550-554.

[112]GLIBERT P, BURFORD M. Globally changing nutrient loads and harmful algal blooms: recent advances, new paradigms, and continuing challenges[J]. Oceanography (Washington DC), 2017, 30(1): 58-69.

[113]ROMERO E, LUDWIG W, SADAOUI M, et al. The Mediterranean region as a paradigm of the global decoupling of N and P between soils and freshwaters[J]. Global Biogeochemical Cycles, 2021, 35: e2020GB006874.

[114]XIAO W, LIU X, IRWIN A J, et al. Warming and eutrophication combine to restructure diatoms and dinoflagellates[J]. Water Research, 2018, 128: 206-216.

[115]宋南奇, 王諾, 吳暖, 等. 基于GIS的我國(guó)渤海1952～ 2016年赤潮時(shí)空分布[J]. 中國(guó)環(huán)境科學(xué), 2018, 38(3): 1142-1148. SONG Nanqi, WANG Nuo, WU Nuan, et al. Temporal and spatial distribution of harmful algal blooms in the Bohai Sea during 1952～2016 based on GIS[J]. China Environmental Sciencece, 2018, 38(3): 1142-1148.

[116]OU L, HUANG X, HUANG B, et al. Growth and competition for different forms of organic phosphorus by the dinoflagellate Prorocentrum donghaiense with the dinoflagellate Alexandrium catenella and the diatom Skeletonema costatum s.l[J]. Hydrobiologia, 2015, 754(1): 29-41.

[117]LIU C, TANG D. Spatial and temporal variations in algal blooms in the coastal waters of the western South China Sea[J]. Journal of Hydro-environment Research, 2012, 6(3): 239-247.

[118]LI Q P, WANG Y, DONG Y, et al. Modeling long-term change of planktonic ecosystems in the northern South China Sea and the upstream Kuroshio Current[J]. Journal of Geophysical Research: Oceans, 2015, 120(6): 3913-3936.

[119]SAKAMOTO S, LIM W A, LU D, et al. Harmful algal blooms and associated fisheries damage in East Asia: Current status and trends in China, Japan, Korea and Russia[J]. Harmful Algae, 2021, 102: 101787.

[120]LIU Y, ENGEL B A, FLANAGAN D C, et al. A review on effectiveness of best management practices in improving hydrology and water quality: Needs and opportunities[J]. Science of The Total Environment, 2017, 601/602: 580-593.

[121]WANG Y, LIU D, XIAO W, et al. Coastal eutrophication in China: Trend, sources, and ecological effects[J]. Harmful Algae, 2021, 107: 102058.

[122]OU L, CAI Y, JIN W, et al. Understanding the nitrogen uptake and assimilation of the Chinese strain of Aureococcus anophagefferens (Pelagophyceae)[J]. Algal Research, 2018, 34: 182-190.

[123]D’ELIA C F, BIDJERANO M, WHEELER T B. Chapter 17 - Population Growth, Nutrient Enrichment, and Science-Based Policy in the Chesapeake Bay Watershed[M]//WOLANSKI E, DAY J W, ELLIOTT M, et al. Coasts and Estuaries. Amsterdam: Elsevier, 2019: 293-310.

[124]LEFCHECK J S, ORTH R J, DENNISON W C, et al. Long-term nutrient reductions lead to the unprecedented recovery of a temperate coastal region[J]. Proceedings of the National Academy of Sciences, 2018, 115(14): 3658-3662.

[125]WASMUND N, TUIMALA J, SUIKKANEN S, et al. Long-term trends in phytoplankton composition in the western and central Baltic Sea[J]. Journal of Marine Systems, 2011, 87(2): 145-159.

[126]江輝煌, 劉素美. 渤海沉積物中磷的分布與埋藏通量[J]. 環(huán)境科學(xué)學(xué)報(bào), 2013, 33(1): 125-132.JIANG Huihuang, LIU Sumei. Distribution and burial flux of phosphorus in sediments of the Bohai Sea[J]. Acta Scientiae Circumstantiae, 2013, 33(1): 125-132.

[127]LI H, ZHANG Y, HAN X, et al. Growth responses of Ulva prolifera to inorganic and organic nutrients: Implications for macroalgal blooms in the southern Yellow Sea, China[J]. Scientific Reports, 2016, 6(1): 26498.

[128]ZHANG X, SONG Y, LIU D, et al. Macroalgal blooms favor heterotrophic diazotrophic bacteria in nitrogen- rich and phosphorus-limited coastal surface waters in the Yellow Sea[J]. Estuarine, Coastal and Shelf Science, 2015, 163: 75-81.

[129]WU D, WAN X, BAO X, et al. Comparison of summer thermohaline field and circulation structure of the Bohai Sea between 1958 and 2000[J]. Chinese Science Bulletin, 2004, 49(4): 363-369.

[130]谷文艷, 陳洪濤, 姚慶禎, 等. 黃河下游溶解態(tài)營(yíng)養(yǎng)鹽季節(jié)變化及入海通量研究[J]. 中國(guó)海洋大學(xué)學(xué)報(bào)(自然科學(xué)版), 2017, 47(3): 74-79, 86. GU Wenyan, CHEN Hongtao, YAO Qingzhen, et al. Seasonal variation and fluxes of dissolved nutrients in the lower reaches of the Huanghe[J]. Periodical of Ocean University of China, 2017, 47(3): 74-79, 86.

[131]吳念, 劉素美, 張桂玲. 黃河下游調(diào)水調(diào)沙與暴雨事件對(duì)營(yíng)養(yǎng)鹽輸出通量的影響[J]. 海洋學(xué)報(bào), 2017, 39(6): 114-128. WU Nian, LIU Sumei, ZHANG Guiling. Impacts of water-sediment regulation and rainstorm events on nutrient transports in the lower Huanghe River[J]. Haiyang Xuebao, 2017, 39(6): 114-128.

[132]中華人民共和國(guó)中央人民政府. 中華人民共和國(guó)國(guó)民經(jīng)濟(jì)和社會(huì)發(fā)展第十四個(gè)五年規(guī)劃和2035年遠(yuǎn)景目標(biāo)綱要[M]. 北京: 人民出版社, 2021. The State Council of the People’s Republic of China. The outline of the 14th Five-Year Plan (2021-2025) for national economic and social development and the long-range objectives through the year 2035[M]. Beijing: People Press, 2021.

[133]PE?UELAS J, POULTER B, SARDANS J, et al. Human-induced nitrogen–phosphorus imbalances alter natural and managed ecosystems across the globe[J]. Nature Com-munications, 2013, 4(1): 2934.

[134]DUHAMEL S, DIAZ J M, ADAMS J C, et al. Phosphorus as an integral component of global marine biogeochemistry[J]. Nature Geoscience, 2021, 14(6): 359-368.

Stoichiometric imbalance in the rates of nutrient and phosphorus depletion in coastal China with implications for the ecological environment

RAN Xiang-bin1, WEI Qin-sheng1, YU Zhi-gang2

(1. Research Center for Marine Ecology and Key Laboratory of Marine Eco-Environmental Science and Technology of Ministry of Natural Resources, First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China; 2. Frontiers Science Center for Deep Ocean Multispheres and Earth System, and Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China)

Recently, anthropogenic nitrogen (N) and phosphorus (P) loadings in coastal seas have significantly increased, seriously impacting the environmental evolution of coastal areas, thereby gaining the widespread attention of scientists and local governments. In addition to the elevated abundances of N and P in the coastal zones, the stoichiometric imbalance of these nutrients could play an important role in stimulating environmental changes. However, the detailed influence of terrestrial N and P and their unbalanced nutrient ratios on marine ecosystems has been poorly documented. In this study, terrestrial nutrient inputs were analyzed from rivers, submarine freshwater and groundwater discharge, atmospheric deposition, water–sediment benthic flux, and water exchange to coastal seas. We reviewed the key biogeochemical processes controlling N and P transport and retention in the coastal areas, highlighted the unbalanced nutrient and P depletion, and explored the ecological influence of imbalanced N and P structures on the ecosystem. In the future, a multiapproach strategy is required to identify the contributions of different interfaces on the N and P concentrations, forms, and distributions. Additionally, a theoretical framework for reducing N and P loadings should be developed based on the land–sea coordination. Within this context, studying the response of terrestrial N and P in the coastal sea would improve the understanding of regional ecological patterns and provide a scientific foundation for marine ecological research and management. Addressing these scientific problems would offer a key basis for preventing and controlling environmental issues in coastal seas.

marginal seas; biogeochemical process; environmental change; major process; nutrient stoichiometric imbalance; phosphorus depletion

Sep. 1, 2021

[National Natural Science Foundation of China, Nos. 42176048, 41930862, 42149902]

P734; P735

A

1000-3096(2023)8-0075-15

10.11759/hykx20210901001

2021-09-01;

2021-10-12

國(guó)家自然科學(xué)基金(42176048, 41930862, 42149902)

冉祥濱(1980—), 男, 山東夏津人, 研究員, 博士, 主要從事生物地球化學(xué)循環(huán)方面研究, E-mail: rxb@fio.org.cn

(本文編輯: 楊 悅)