耿潤哲，王曉燕,2,*，趙雪松，陳永娟

(1. 首都師范大學(xué)資源環(huán)境與旅游學(xué)院，北京 100048; 2. 首都圈水環(huán)境研究中心，北京 100048；3. 河北省豐寧滿族自治縣統(tǒng)計(jì)局，豐寧 068350)

基于模型的農(nóng)業(yè)非點(diǎn)源污染最佳管理措施效率評(píng)估研究進(jìn)展

耿潤哲1，王曉燕1,2,*，趙雪松3，陳永娟1

(1. 首都師范大學(xué)資源環(huán)境與旅游學(xué)院，北京 100048; 2. 首都圈水環(huán)境研究中心，北京 100048；3. 河北省豐寧滿族自治縣統(tǒng)計(jì)局，豐寧 068350)

隨著點(diǎn)源污染的逐步控制，農(nóng)業(yè)非點(diǎn)源污染已成為世界范圍內(nèi)關(guān)注的熱點(diǎn)，由于其特有的時(shí)空異質(zhì)性特點(diǎn)導(dǎo)致對(duì)其進(jìn)行有效控制較為困難，最佳管理措施(BMPs，Best Management Practices)是實(shí)現(xiàn)流域農(nóng)業(yè)非點(diǎn)源污染控制的有效手段，對(duì)擬實(shí)施的BMPs效率進(jìn)行評(píng)估是實(shí)施流域非點(diǎn)源污染BMPs配置的前提。通過模型模擬的方法可對(duì)擬采用的不同措施的削減效率及經(jīng)濟(jì)成本進(jìn)行評(píng)估以獲取最具成本-效益的BMPs空間配置方案，為措施有效選擇提供依據(jù)。通過對(duì)多種模型在工程型和管理型BMPs評(píng)估方面的研究進(jìn)行論述表明，通常概念化模型多用于對(duì)污染源控制類措施進(jìn)行評(píng)估，而機(jī)制類模型則可用于對(duì)不同時(shí)空尺度下的過程控制類BMPs進(jìn)行評(píng)估；措施效率發(fā)揮的時(shí)間滯后性及模型模擬不確定性是模型模擬過程中需要重點(diǎn)考慮的問題，可通過增加野外監(jiān)測(cè)點(diǎn)數(shù)量、監(jiān)測(cè)頻率、優(yōu)化監(jiān)測(cè)點(diǎn)位置并選擇合適的評(píng)估指標(biāo)以降低模型評(píng)估BMPs過程中滯后效應(yīng)的影響；此外BMPs實(shí)施時(shí)間與空間位置的不匹配、時(shí)空尺度異質(zhì)性、污染物形態(tài)及生態(tài)系統(tǒng)服務(wù)功能轉(zhuǎn)換風(fēng)險(xiǎn)均需在BMPs評(píng)估過程中加以考慮。模型模擬是BMPs效率評(píng)估(包括非點(diǎn)源污染關(guān)鍵源區(qū)的時(shí)空識(shí)別)、污染物遷移轉(zhuǎn)化以及成本效益分析的有效工具，同時(shí)對(duì)于流域非點(diǎn)源污染管理控制及BMPs實(shí)施利益相關(guān)者有效參與問題的分析也具有重要意義。

最佳管理措施(BMPs)；削減效率；模型；非點(diǎn)源污染

在中國、歐盟以及美國的大部分水體中均存在藻類的過量繁殖和溶解氧含量過低等問題[1- 3]，其中農(nóng)業(yè)非點(diǎn)源污染的貢獻(xiàn)量達(dá)到了污染負(fù)荷總量的半數(shù)以上[4- 5]。雖然已采取大量的控制措施，但受限于普遍存在的措施可執(zhí)行性、效率滯后性[6- 7]、配置方案和實(shí)施時(shí)間的合理性以及時(shí)空尺度轉(zhuǎn)換等因素的影響導(dǎo)致河流水體的整體水質(zhì)狀況并未達(dá)到預(yù)期的治理目標(biāo)[4]。

BMPs的有效實(shí)施能夠提高其污染物削減效率及經(jīng)濟(jì)效益，同時(shí)還可減少土地占用。因此BMPs 削減效率的準(zhǔn)確評(píng)估是決定措施是否適用的關(guān)鍵步驟[8]。美國農(nóng)業(yè)部自20世紀(jì)80年代起提出采用BMPs對(duì)全國范圍內(nèi)的農(nóng)業(yè)非點(diǎn)源污染進(jìn)行控制，并制定了相應(yīng)的評(píng)估方案，如切薩皮克海灣BMPs控制計(jì)劃(Chesapeake Bay Program)就采用了小尺度代表流域監(jiān)測(cè)與大尺度模型模擬相結(jié)合的方式來對(duì)該流域內(nèi)的BMPs效率進(jìn)行評(píng)估，并以此為實(shí)施藍(lán)本在美國其他流域內(nèi)進(jìn)行評(píng)估方法的推廣；在歐洲，BMPs也得到了廣泛的應(yīng)用，如希臘Arachtos 河流域保護(hù)規(guī)劃中的BMPs模型評(píng)估工作、德國Ems河流域所采用的與GIS技術(shù)相結(jié)合的基于可視化評(píng)估平臺(tái)的BMPs配置及效果評(píng)估工作等；在我國，隨著政府對(duì)農(nóng)業(yè)非點(diǎn)源污染控制逐步重視，在BMPs研究方面也逐步深入，代表性工作如長江三峽流域的BMPs評(píng)估及優(yōu)化方案的提出、長春石頭口門水庫流域的BMPs配置方案的實(shí)地監(jiān)測(cè)及模型評(píng)估以及北京密云水庫流域BMPs空間配置方案的優(yōu)選以及BMPs評(píng)估工具箱的構(gòu)建。目前流域BMPs的配置研究已經(jīng)發(fā)展到采用多尺度控制技術(shù)同優(yōu)化模擬算法相結(jié)合的綜合控制階段，但是BMPs效率評(píng)估作為流域整體配置的基礎(chǔ)仍具有不可忽視的重要作用，以上這些研究均可對(duì)BMPs評(píng)估工作提供一定的借鑒意義。

BMPs在所實(shí)施區(qū)域的本地化效應(yīng)可以通過地塊尺度的實(shí)驗(yàn)監(jiān)測(cè)工作來實(shí)現(xiàn)，但是對(duì)大尺度流域內(nèi)BMPs的評(píng)估工作卻很難以通過有效實(shí)地監(jiān)測(cè)實(shí)驗(yàn)來完成。目前來看模型模擬是應(yīng)用最為廣泛的非點(diǎn)源污染最佳管理措施的評(píng)估技術(shù)，在流域綜合管理方案的設(shè)計(jì)執(zhí)行過程中扮演著非常重要角色，尤其是對(duì)于擬實(shí)施措施的選擇和本地化應(yīng)用、環(huán)境效益以及實(shí)現(xiàn)河流水質(zhì)物理化學(xué)及生態(tài)質(zhì)量明顯提升所需的時(shí)間等預(yù)測(cè)方面具有重要的用途。如：歐盟WFD計(jì)劃的初始階段，就將模型模擬技術(shù)作為擬實(shí)施BMPs潛在效率評(píng)估的首選方法。Cherry等基于不同的評(píng)估目標(biāo)和研究尺度對(duì)不同的BMPs評(píng)估方法進(jìn)行劃分，建議采用實(shí)地監(jiān)測(cè)、模型模擬、風(fēng)險(xiǎn)評(píng)估以及養(yǎng)分平衡法相結(jié)合的耦合模型系統(tǒng)來對(duì)擬實(shí)施的BMPs進(jìn)行評(píng)估，且在措施的設(shè)計(jì)和配置階段也多通過模型模擬與實(shí)地監(jiān)測(cè)網(wǎng)絡(luò)構(gòu)建相結(jié)合的方式來進(jìn)行必要的決策支持[9]。但是受限于多模型數(shù)據(jù)采集以及模型操作人員技術(shù)程度等因素的限制，耦合模型在實(shí)際操作方面還存在一定的困難。

本文通過對(duì)國內(nèi)外BMPs模型評(píng)估方面的相關(guān)研究進(jìn)行總結(jié)，分析不同模型在BMPs評(píng)估方面的適用性，及存在的問題，以對(duì)流域綜合管理中模型評(píng)估BMPs工作研究提供理論支持和建議。

1 BMPs模型評(píng)估

按照模型運(yùn)行復(fù)雜程度、適用的時(shí)空尺度，可將BMPs削減效率評(píng)估模型劃分為經(jīng)驗(yàn)?zāi)Ｐ汀⒏拍罨Ｐ图皺C(jī)制型模型[9]。在本文中按照以下兩種不同層次對(duì)模型進(jìn)行劃分；1)根據(jù)模型運(yùn)行機(jī)制的不同將模型分為經(jīng)驗(yàn)?zāi)Ｐ?、概念化模型以及物理機(jī)制模型，包括不同復(fù)雜程度的實(shí)際模擬過程；2)根據(jù)可模擬BMPs運(yùn)行機(jī)制的不同將模型劃分為源頭控制類措施模型和過程控制類措施模型。具體劃分情況見圖1。

圖1 BMPs (Best Management Practices)評(píng)估模型分級(jí)圖Fig.1 Classification map of modelsSWAT: Soil and Water Assessment Tool; HSPF: Hydrological Simulation Program-Fortran; AGNPS: Annualized Agricultural Non-Point Source Pollution;HBV-N/HYPE: Hydrological Predictions for the Environment; STICS-MODCOU: Simulateur Multidiscplinaire pour les Cultures Standard; EPICgird: Erosion Productivity Impact Calculator; MONERIS: Modelling Nutrient Emissions in River Systems; GREEN: Geospatial Regression Equation for European Nutrient losses; MITERRA: A tool for integrated assessment of N emissions from agriculture at regional; ECM: Export Coefficient Model; PI: Phosphorus Index

1.1 經(jīng)驗(yàn)-概念化模型

經(jīng)驗(yàn)?zāi)Ｐ陀址Q為“黑箱模型”，其不涉及復(fù)雜函數(shù)運(yùn)算過程(即不考慮污染物的遷移轉(zhuǎn)化過程)，僅以污染物輸入輸出間的量化關(guān)系為基礎(chǔ)進(jìn)行模擬。具有工作原理及操作簡單且所需數(shù)據(jù)量少的特點(diǎn)。但經(jīng)驗(yàn)?zāi)Ｐ蛯?duì)異常值和極端事件的預(yù)測(cè)可能會(huì)產(chǎn)生較大的誤差。概念化模型相對(duì)而言要比經(jīng)驗(yàn)?zāi)Ｐ蛷?fù)雜一些，能夠?qū)Σ糠趾唵蔚奈廴疚飩鬏斶^程進(jìn)行表征，因此所需的數(shù)據(jù)量相比經(jīng)驗(yàn)?zāi)Ｐ鸵哺唷?/p>

目前在BMPs評(píng)估方面應(yīng)用較為廣泛的經(jīng)驗(yàn)-概念化模型主要有輸出系數(shù)模型(ECM，Export Coefficient Model)[10]、GREEN模型(Geospatial Regression Equation for European Nutrient losses)[11]、MONERIS模型(Modelling Nutrient Emissions in River Systems)[7]、磷指數(shù)法(Phosphorus Index，PI)[12- 13]以及MITERRA模型(A tool for integrated assessment of N emissions from agriculture at regional)[14]等。

1.2 機(jī)制模型

機(jī)制模型能夠?qū)ξ廴疚锏漠a(chǎn)生機(jī)理、遷移轉(zhuǎn)化過程以及較為復(fù)雜的時(shí)空傳輸過程進(jìn)行詳盡的模擬，因此這類模型一般較為復(fù)雜，能夠?qū)Ψ屈c(diǎn)源污染“源—匯”過程及與之相關(guān)的控制措施進(jìn)行模擬。在BMPs評(píng)估研究中有兩類機(jī)制模型應(yīng)用較為廣泛。第一類由一維營養(yǎng)物循環(huán)模型、水文模型以及河道過程模擬模塊組合所構(gòu)成的綜合模型；第二類為耦合的流域尺度模型，在這類模型中營養(yǎng)物質(zhì)陸地循環(huán)與河道循環(huán)過程均可通過水文模擬模塊形成反饋回路流動(dòng)系統(tǒng)。常見的BMPs評(píng)估機(jī)制型模型包括HYPE(Hydrological Predictions for the Environment)[15- 16]、SWAT(Soil and Water Assessment Tool)[17]、AGNPS(Annualized Agricultural Non-Point Source Pollution)[18]、SUSTAIN(System for Urban Stormwater Treatment and Analysis Integration Model)[19]、HSPF(Hydrological Simulation Program-Fortran)[20]等。相關(guān)模型模擬BMPs削減效率的研究案例及模型適用性和局限性分析見表1。

表1 模型及BMPs評(píng)估工作案例分析

2 BMPs效率模型評(píng)估中存在的問題

2.1 污染物滯留及流域響應(yīng)時(shí)間

BMPs實(shí)施后水質(zhì)顯著改善的響應(yīng)時(shí)間主要受到措施類型、配置時(shí)間、空間位置、氣候條件以及當(dāng)?shù)氐淖匀坏乩頎顩r等因素的共同影響。農(nóng)業(yè)流域內(nèi)營養(yǎng)物質(zhì)主要通過地表徑流、壤中流以及地下水傳輸?shù)冗^程到達(dá)受納水體。而壤中流和地下水流動(dòng)傳輸受不同空間土壤亞層性質(zhì)差異、含水層復(fù)雜動(dòng)態(tài)效應(yīng)的影響，措施作用的發(fā)揮可能需要一定的時(shí)間。另外，在營養(yǎng)物質(zhì)的傳輸過程中可能還會(huì)受到反硝化作用(氮)、土壤吸附所導(dǎo)致的臨時(shí)儲(chǔ)存效應(yīng)植物和微生物的吸附作用等的影響而延遲到達(dá)受納水體時(shí)間[40]。如河岸帶和濕地系統(tǒng)對(duì)于氮、磷等營養(yǎng)物質(zhì)均具有較高的儲(chǔ)存效率，但是卻很難在流域尺度上對(duì)其效應(yīng)進(jìn)行評(píng)估。氣候條件、水動(dòng)力環(huán)境(水土比、水力停留時(shí)間)以及化學(xué)物理特性(如：水體、沉積物以及水土界面中溶解氧濃度和光照等)均會(huì)使其對(duì)流域尺度營養(yǎng)物質(zhì)的滯留效應(yīng)產(chǎn)生較大的不確定性和復(fù)雜性。

通過實(shí)地監(jiān)測(cè)對(duì)流域尺度營養(yǎng)物質(zhì)傳輸和滯留效應(yīng)進(jìn)行研究具有一定難度，而模型模擬和養(yǎng)分平衡法更適用于這類研究。Meals等研究發(fā)現(xiàn)時(shí)間滯后性主要由3部分組成[41]：1)措施效用發(fā)揮所需的時(shí)間，如植被緩沖帶需要在措施完全設(shè)置完畢3a后才能夠發(fā)揮效用；2)BMPs所發(fā)揮的效用轉(zhuǎn)變?yōu)閷?duì)水質(zhì)的改善效用也需要一定時(shí)間；3)河流水體生態(tài)系統(tǒng)對(duì)于BMPs效用的響應(yīng)所需要的時(shí)間。因此，在模型校準(zhǔn)的過程中需考慮時(shí)間滯后性影響，在對(duì)模型校準(zhǔn)時(shí)一定要明確所測(cè)得數(shù)據(jù)可能是措施實(shí)施后多年?duì)I養(yǎng)物濃度的混合值，并且長期的監(jiān)測(cè)數(shù)據(jù)相比于臨時(shí)監(jiān)測(cè)數(shù)據(jù)受時(shí)間滯后性的影響更大[41]。有學(xué)者采用模型模擬的方法對(duì)流域水質(zhì)狀況對(duì)措施實(shí)施后效應(yīng)的響應(yīng)時(shí)間進(jìn)行了評(píng)估。Behrendt等應(yīng)用MONERIS模型對(duì)德國境內(nèi)所實(shí)施的河岸帶非點(diǎn)源污染管理措施的評(píng)估結(jié)果表明，流域水質(zhì)改善對(duì)措施效益的響應(yīng)時(shí)間為10—30a不等[7]。Sohier等應(yīng)用EPICgrid模型發(fā)現(xiàn)比利時(shí)Walloon流域在實(shí)施改善地下水水質(zhì)的BMPs后由于受到蓄水層水力傳輸時(shí)間滯后性的影響，流域水質(zhì)對(duì)BMPs效應(yīng)的響應(yīng)時(shí)間達(dá)到了15a之久[32]。 Fenton等所進(jìn)行的研究表明措施實(shí)施后的流域響應(yīng)時(shí)間最多可達(dá)到21a[42]。以上這些研究成果均表明應(yīng)用模型對(duì)BMPs效率進(jìn)行評(píng)估時(shí)應(yīng)當(dāng)考慮較長的河流水質(zhì)響應(yīng)滯后期，同時(shí)也可采用短期穩(wěn)態(tài)模型以弱化時(shí)間滯后性的影響。

2.2 模型模擬的不確定性

很多學(xué)者在應(yīng)用模型方法對(duì)流域BMPs進(jìn)行評(píng)估時(shí)發(fā)現(xiàn)措施效率會(huì)受到特定區(qū)域氣候條件的影響，因此，沒有任何一種模型能夠具有普適性。各種不同的模型在特定區(qū)域使用時(shí)由于研究目的不同均會(huì)體現(xiàn)出一定的優(yōu)勢(shì)和不足，同時(shí)不同的區(qū)域特征及數(shù)據(jù)的可獲取性也會(huì)對(duì)模型的不確定性產(chǎn)生影響，如歐盟WFD計(jì)劃中各成員國所采用的BMPs評(píng)估模型在歐洲南部區(qū)域使用時(shí)的不確定性要高于其他區(qū)域[40]。歐洲多國的研究表明由于模型模擬主要是以流域出口的實(shí)測(cè)數(shù)據(jù)為基準(zhǔn)，而不是以營養(yǎng)物滯留過程及非點(diǎn)源污染物的排放為基準(zhǔn)，因此在目標(biāo)流域內(nèi)建立合適的營養(yǎng)物滯留與排放過程模擬模型是較為困難的。實(shí)際上，在模型模擬過程中如果對(duì)營養(yǎng)物滯留與排放過程同時(shí)出現(xiàn)高估或低估的現(xiàn)象，那么模擬結(jié)果也可能是合理的。模型模擬過程中不同參數(shù)的組合也可能會(huì)出現(xiàn)相同的模擬結(jié)果，也即“異參同效”效應(yīng)[9]。對(duì)模型的校準(zhǔn)和營養(yǎng)物傳輸模擬過程的調(diào)整會(huì)對(duì)模型有效評(píng)估起到重要的控制作用。通過對(duì)基礎(chǔ)情景模擬結(jié)果和措施實(shí)施后模擬值之間均方根誤差進(jìn)行比較，將有助于識(shí)別和降低措施實(shí)施后模型評(píng)估校準(zhǔn)和驗(yàn)證過程導(dǎo)致的污染物負(fù)荷量的變化隊(duì)評(píng)估結(jié)果的影響[43]。

2.3 措施實(shí)施的時(shí)間和位置

在BMPs的實(shí)際配置工作中首先需要采用模型模擬或風(fēng)險(xiǎn)評(píng)估的方法來對(duì)目標(biāo)流域內(nèi)非點(diǎn)源污染的關(guān)鍵源區(qū)(CSAs，Critical Source Areas)進(jìn)行識(shí)別，這有助于提高措施配置目的性并獲得較高的成本效益比[9]。Vagstad等分別采用7種復(fù)雜程度不同的模型對(duì)恩扎河流域(意大利)和Zelivka河(捷克)流域內(nèi)的BMPs評(píng)估結(jié)果的一致性及對(duì)流域出口水質(zhì)狀況的影響進(jìn)行評(píng)估。結(jié)果表明，不同類型措施對(duì)于不同模型工具的反映存在一定的差異，但是在兩個(gè)流域內(nèi)組合實(shí)施的BMPs卻產(chǎn)生了相似的削減效果[44]。究其原因可能是由不同模型對(duì)不同類型措施進(jìn)行模擬時(shí)內(nèi)部參數(shù)設(shè)置差異所致。另外其研究結(jié)果還表明措施空間配置不同也會(huì)產(chǎn)生不同的效果(如土地利用變化措施中所需實(shí)施變化的土地利用的位置不同)。因此，在運(yùn)用模型對(duì)措施進(jìn)行評(píng)估時(shí)(如增加林地覆蓋面積或改變農(nóng)作物種植類型)，模型的參數(shù)化、對(duì)時(shí)空變化的敏感性等都會(huì)對(duì)措施效果的模擬結(jié)果產(chǎn)生影響[44]。部分學(xué)者還針對(duì)BMPs配置前進(jìn)行CSAs識(shí)別的必要性以及哪些模型適用于CSAs識(shí)別進(jìn)行了討論[45- 47]。Panagopoulos等就如何在有限的實(shí)測(cè)數(shù)據(jù)條件下運(yùn)用SWAT模型進(jìn)行流域非點(diǎn)源污染CSAs識(shí)別進(jìn)而配置合適的BMPs問題進(jìn)行了討論[36]?，F(xiàn)有關(guān)于模型的研究大多僅關(guān)注單一措施實(shí)施后的效果的評(píng)估，但實(shí)際監(jiān)測(cè)發(fā)現(xiàn)流域非點(diǎn)源污染治理目標(biāo)的實(shí)現(xiàn)只有通過在合理的時(shí)空節(jié)點(diǎn)上進(jìn)行BMPs的組合配置才能夠?qū)崿F(xiàn)。

2.4 模型模擬的時(shí)空尺度

目前多數(shù)學(xué)者都對(duì)BMPs評(píng)估中的空間(如地塊、景觀、流域、區(qū)域)及時(shí)間尺度問題進(jìn)行了討論[48- 50]。有研究表明措施設(shè)置的空間尺度(地塊尺度)與水質(zhì)評(píng)價(jià)(河道水質(zhì)狀況)之間本身就存在一定的尺度差異性[51]。通常情況下措施是在地塊尺度上實(shí)施，但卻以流域整體的水質(zhì)狀況是否達(dá)標(biāo)作為評(píng)價(jià)標(biāo)準(zhǔn)，同時(shí)在不同的空間尺度內(nèi)還可能涉及不同的利益相關(guān)者。正如2.1節(jié)中所提到響應(yīng)的時(shí)間滯后性，氣候變化等因素均會(huì)對(duì)不同時(shí)空尺度內(nèi)的措施效果產(chǎn)生影響?？臻g尺度的差異也會(huì)對(duì)措施實(shí)施后所導(dǎo)致的污染物轉(zhuǎn)換風(fēng)險(xiǎn)產(chǎn)生影響[52- 53]。

通常根據(jù)研究區(qū)的空間尺度大小來選擇合適的BMPs評(píng)估模型，機(jī)制型模型適用于小尺度到大中尺度流域BMPs的評(píng)估，而區(qū)域尺度BMPs的評(píng)估則主要通過經(jīng)驗(yàn)型模型來完成，如GREEN、MONERIS、MITERRA、PI以及輸出系數(shù)模型等。隨著近年來全球環(huán)境基礎(chǔ)數(shù)據(jù)庫構(gòu)建的不斷完善，也有部分學(xué)者采用機(jī)制型模型對(duì)區(qū)域或國家尺度上的非點(diǎn)源污染進(jìn)行研究[54]。適用于大尺度農(nóng)業(yè)系統(tǒng)中作物生長、土壤侵蝕以及營養(yǎng)物流失過程模擬的機(jī)制型模型(如EPIC、MITERRA模型等)也逐漸受到了較多的關(guān)注，但是這些模型對(duì)地下水及匯水區(qū)污染物對(duì)河流營養(yǎng)物負(fù)荷總量貢獻(xiàn)率的相關(guān)研究在大尺度區(qū)域內(nèi)卻仍然存在一定的限制。

不同空間尺度流域內(nèi)實(shí)測(cè)/調(diào)查數(shù)據(jù)(如：BMPs相關(guān)信息、基礎(chǔ)情景下營養(yǎng)物質(zhì)輸入量、氣候環(huán)境特征以及用于模型校準(zhǔn)的水質(zhì)流量數(shù)據(jù)的時(shí)間序列)的可用性也會(huì)對(duì)模型模擬結(jié)果產(chǎn)生較大的影響。非點(diǎn)源污染模型可以對(duì)BMPs實(shí)施后對(duì)目標(biāo)流域內(nèi)污染物的遷移、轉(zhuǎn)化、緩沖以及滯留等過程進(jìn)行模擬，但其模擬精度卻受到實(shí)測(cè)數(shù)據(jù)的可用性的影響而產(chǎn)生較大的差異。因此，精確模擬結(jié)果的獲取應(yīng)當(dāng)以構(gòu)建完善的監(jiān)測(cè)網(wǎng)絡(luò)及數(shù)據(jù)庫為基礎(chǔ)。然而，目前來看世界各地均存在多尺度水質(zhì)監(jiān)測(cè)網(wǎng)絡(luò)不足以支撐各類BMPs評(píng)估的問題[6]，同時(shí)監(jiān)測(cè)數(shù)據(jù)的可靠性還受到采樣頻率及實(shí)驗(yàn)計(jì)算方法不同的影響[55]。即使是在監(jiān)測(cè)數(shù)據(jù)缺乏的條件下，模型法在BMPs評(píng)估工作中仍然會(huì)發(fā)揮較大的作用，如Panagopoulos等和Maringanti等的研究中就是在有限的監(jiān)測(cè)數(shù)據(jù)條件下實(shí)現(xiàn)了對(duì)CSAs的識(shí)別以及污染物不同季節(jié)變化趨勢(shì)的合理解釋，但是這些研究也僅僅是對(duì)措施實(shí)施后污染物負(fù)荷量及關(guān)鍵源區(qū)的整體變化趨勢(shì)進(jìn)行了評(píng)估，并沒有獲得較為可靠的量化環(huán)境評(píng)估結(jié)果[35,36]。

2.5 污染物形態(tài)及生態(tài)系統(tǒng)服務(wù)功能轉(zhuǎn)換風(fēng)險(xiǎn)

流域水環(huán)境治理目標(biāo)的實(shí)現(xiàn)需要對(duì)不同形態(tài)或類型的污染物同時(shí)進(jìn)行有效控制，但是目前還沒有任何一種BMP能夠?qū)崿F(xiàn)多種污染物的同時(shí)有效調(diào)控[52]。反而在BMPs的配置過程中可能會(huì)使得一種BMPs的實(shí)施可能會(huì)對(duì)某一種污染物起到控制削減作用，但同時(shí)可能會(huì)使得另一種或多種的污染物濃度或負(fù)荷量得到增加，或者是在對(duì)某種污染物的一種形態(tài)進(jìn)行削減，但是導(dǎo)致污染物其他形態(tài)之間出現(xiàn)化學(xué)成分轉(zhuǎn)換或增加[52]。例如，在流域內(nèi)設(shè)置以提高氮的反硝化作用為工作機(jī)制的BMPs后可能會(huì)使得水體中的硝酸鹽氮負(fù)荷量降低，但同時(shí)會(huì)使得排入大氣層中的亞硝態(tài)氮的負(fù)荷量增加，這會(huì)使得溫室氣體的效應(yīng)風(fēng)險(xiǎn)得到增加。

應(yīng)用模型對(duì)BMPs進(jìn)行評(píng)估時(shí)的污染物形態(tài)轉(zhuǎn)換風(fēng)險(xiǎn)可以通過多模型耦合的方法來解決。這對(duì)于BMPs配置過程中的多目標(biāo)優(yōu)化決策問題具有重要的意義。然而，由于污染物形態(tài)轉(zhuǎn)換風(fēng)險(xiǎn)所涉及的多種污染物或同種污染物多種形態(tài)所導(dǎo)致對(duì)其進(jìn)行準(zhǔn)確模擬具有一定的復(fù)雜性和難度，目前關(guān)于BMPs配置過程中的污染物形態(tài)轉(zhuǎn)換風(fēng)險(xiǎn)的研究案例還不多[56]。僅有的研究來自Velthof等應(yīng)用MITERRA模型對(duì)歐盟27國所采用的BMPs對(duì)氮的排放對(duì)地下水和大氣層的影響的削減效果進(jìn)行了評(píng)估[14]。

另外，在進(jìn)行流域非點(diǎn)源污染BMPs多目標(biāo)配置工作中還應(yīng)當(dāng)考慮措施的實(shí)施對(duì)流域內(nèi)不同生態(tài)系統(tǒng)服務(wù)功能的影響。因此，在今后的研究中，需要進(jìn)一步建立能夠?qū)ι鷳B(tài)系統(tǒng)服務(wù)功能轉(zhuǎn)換風(fēng)險(xiǎn)進(jìn)行評(píng)估的模型[57]。多種措施的集成實(shí)施以及多學(xué)科模型研究的交叉應(yīng)用也應(yīng)當(dāng)成為未來BMPs評(píng)估模型研究的方向。

2.6 成本-效益分析和優(yōu)化

通過BMPs效率的評(píng)估已經(jīng)不能夠在有限的資金資源條件下解決BMPs的有效配置問題，因此，成本-效益分析在BMPs配置工作中受到了越來越多的關(guān)注。目前來看成本-效益分析多通過非點(diǎn)源污染模型與經(jīng)濟(jì)評(píng)估模型相結(jié)合構(gòu)建成本-效益分析模擬系統(tǒng)的途徑來解決，如自然環(huán)境-經(jīng)濟(jì)模型就是通過基于自然環(huán)境模擬機(jī)制的非點(diǎn)源污染模型與經(jīng)濟(jì)評(píng)估模型組合而成，其所采用的經(jīng)濟(jì)評(píng)估模型還能夠?qū)Σ煌胧?shí)施后的環(huán)境效益進(jìn)行貨幣化轉(zhuǎn)換[58- 59]。如：Ledoux等應(yīng)用STICS模型對(duì)法國東北部小流域內(nèi)所設(shè)置的不同BMPs組合的成本-效益進(jìn)行分析[31]；Volk等采用包括SWAT模型在內(nèi)的4種不同的生物-物理機(jī)制模型建立了空間決策支持系統(tǒng)以評(píng)估不同的土地利用管理政策對(duì)德國埃姆斯河上游流域內(nèi)污染物的削減情況進(jìn)行成本-效益分析[49]；Cools等將SWAT模型與經(jīng)濟(jì)優(yōu)化模型相結(jié)合來獲取成本-效益比較高的措施組合以對(duì)比利時(shí)境內(nèi)的非點(diǎn)源污染負(fù)荷量進(jìn)行削減[60]。以上這些研究都較好的提供了在不同的空間尺度下所適用的成本-效益分析耦合模型系統(tǒng)。

耦合模型是BMPs成本-效益分析過程中的空間尺度、氣候變化以及污染物形態(tài)轉(zhuǎn)換風(fēng)險(xiǎn)進(jìn)行評(píng)估的有效途徑，但是該方法對(duì)于數(shù)據(jù)量及精度要求較高，同時(shí)還需要包括自然科學(xué)、社會(huì)科學(xué)、經(jīng)濟(jì)科學(xué)以及利益相關(guān)者共同參與建立模型優(yōu)化所需的環(huán)境和社會(huì)經(jīng)濟(jì)目標(biāo)。另外，由于自然邊界和行政邊界的不匹配性，在進(jìn)行成本-效益分析時(shí)措施實(shí)施后的短期及長期環(huán)境效益的量化、空間分布等問題也會(huì)對(duì)BMPs的成本-效益分析工作及措施的最終實(shí)施帶來很大的影響。[54,61]。

2.7 BMPs利益相關(guān)者參與及可行性

在BMPs的適用性評(píng)估中，利益相關(guān)者對(duì)措施的可接受度評(píng)價(jià)是最重要的一部分內(nèi)容。利益相關(guān)者包括決策者、農(nóng)戶、河流管理機(jī)構(gòu)、用水企業(yè)等。非點(diǎn)源污染模型能夠?yàn)槠涮峁┐胧?shí)施前后的水質(zhì)改善信息、增加對(duì)相關(guān)措施的了解并獲取可視化評(píng)估結(jié)果以提高不同涉益群體對(duì)擬實(shí)施BMPs的接受度。許多研究發(fā)現(xiàn)模型對(duì)BMPs評(píng)估結(jié)果的可靠性、利益相關(guān)者之間的信任度、社會(huì)屬性以及模擬結(jié)果的表達(dá)方式等都會(huì)對(duì)BMPs的可接受度產(chǎn)生影響[62- 65]。不同部門的利益相關(guān)者可以參與到流域BMPs配置工作的各個(gè)階段包括：問題識(shí)別、模型設(shè)置及調(diào)校、BMPs情景制定以及模型預(yù)測(cè)結(jié)果討論等[64]。在BMPs模型評(píng)估工作中引入利益相關(guān)者參與機(jī)制具有以下幾方面優(yōu)勢(shì)：1)縮短模擬工作準(zhǔn)備時(shí)間：利益相關(guān)者參與有助于模型模擬者更好的獲取和理解所模擬流域的基本狀況；2)不確定性：利益相關(guān)者能夠?qū)δM結(jié)果提供反饋和相關(guān)信息，以降低模型模擬工作的不確定性；3)措施篩選：利益相關(guān)者參與有助于更快的識(shí)別當(dāng)前的措施并選擇合適的模型以對(duì)措施的時(shí)間和空間過程進(jìn)行評(píng)估；4)尺度方面：由于流域非點(diǎn)源污染評(píng)估的利益相關(guān)者均來自流域內(nèi)不同的空間尺度單元，使其參與其中有助于模型操作者更快的獲取多尺度模擬方法以對(duì)不同措施的削減效率進(jìn)行評(píng)估；5)污染物形態(tài)轉(zhuǎn)換風(fēng)險(xiǎn)：利益相關(guān)者參與是識(shí)別BMPs在特定區(qū)域所具有的特定控制效果、環(huán)境目標(biāo)以及生態(tài)系統(tǒng)服務(wù)功能的基礎(chǔ)，因此有助于更加準(zhǔn)確的獲取合適的BMPs配置方案；6)成本-效益分析：不同利益相關(guān)者對(duì)水資源或生態(tài)系統(tǒng)的價(jià)值具有不同的看法和觀點(diǎn)。因此，使其參與BMPs的模擬評(píng)估過程對(duì)于BMPs配置情景的成本分析及不同措施的可行性的評(píng)估具有重要的作用。

3 研究展望

BMPs削減效率的評(píng)估是順利實(shí)現(xiàn)高效的流域整體配置方案的基礎(chǔ)，模型技術(shù)是進(jìn)行多尺度復(fù)雜條件下BMPs有效評(píng)估的重要手段。采用模型模擬法對(duì)BMPs進(jìn)行評(píng)估應(yīng)對(duì)措施實(shí)施時(shí)間和位置、成本效益、污染物形態(tài)以及生態(tài)系統(tǒng)服務(wù)功能轉(zhuǎn)換風(fēng)險(xiǎn)、利益相關(guān)者參與問題等加以考慮，以增加模擬結(jié)果的可靠性和措施的可接受度。模型的合理應(yīng)用對(duì)于構(gòu)建最具成本-效益的BMPs控制規(guī)劃、降低潛在的經(jīng)濟(jì)社會(huì)成本、提高措施的可執(zhí)行性具有重要的意義。

(1)BMPs削減效率的滯后性問題是模擬過程中非常重要的影響因素，在今后的研究中可在以下方面進(jìn)行改進(jìn)：1)提高流域特征識(shí)別的準(zhǔn)確性(水文傳輸過程、自然地理過程以及污染源空間位置)以降低模型選擇以及措施配置失當(dāng)所導(dǎo)致的滯后性；2)BMPs的合理選擇、優(yōu)化空間配置方案以減少由于措施的不合理配置所導(dǎo)致的削減效率響應(yīng)的滯后性；3)通過增加野外監(jiān)測(cè)點(diǎn)的數(shù)量、監(jiān)測(cè)頻率并優(yōu)化監(jiān)測(cè)位置(如：通過地表徑流監(jiān)測(cè)可能會(huì)比河道監(jiān)測(cè)更快的獲取作物輪作及化肥減施等措施的污染物削減效應(yīng))[66]，并選擇合適的評(píng)估指標(biāo)以降低滯后效應(yīng)的影響[41]。

(2)模型的評(píng)估和驗(yàn)證是降低模型應(yīng)用過程中不確定性非常重要的步驟，在今后的研究中應(yīng)通過完善監(jiān)測(cè)網(wǎng)絡(luò)增加流域內(nèi)的實(shí)測(cè)數(shù)據(jù)點(diǎn)以及對(duì)利益相關(guān)者進(jìn)行調(diào)查以獲取相關(guān)參數(shù)對(duì)模型進(jìn)行校準(zhǔn)和驗(yàn)證是提高模型對(duì)污染物傳輸機(jī)制進(jìn)行合理模擬并實(shí)現(xiàn)模型參數(shù)化和本地化的良好途徑[40,44,67]。

(3)通過模型模擬的方法對(duì)不同措施及其組合實(shí)施后的協(xié)同效應(yīng)、不同景觀特征之間關(guān)系以及合理的措施設(shè)置時(shí)間進(jìn)行評(píng)估是下一步流域BMPs優(yōu)化配置研究中的重點(diǎn)[68]。主要包括采用適用于不同運(yùn)行機(jī)制、不同空間尺度的多模型相結(jié)合的方式來對(duì)BMPs進(jìn)行評(píng)估[9]，或是通過多步驟模擬相結(jié)合的方式開展BMPs評(píng)估工作。同時(shí)多模型耦合法也是應(yīng)對(duì)污染物形態(tài)轉(zhuǎn)換風(fēng)險(xiǎn)的有效手段。

(4)流域BMPs配置研究涉及多學(xué)科、多目標(biāo)以及多尺度條件下的綜合研究，因此僅考慮BMPs削減效率評(píng)估還不能夠滿足流域綜合管理研究的需求，需要將BMPs的環(huán)境效益同經(jīng)濟(jì)評(píng)估相結(jié)合并考慮利益相關(guān)者參與以有效的解決BMPs優(yōu)化配置過程中的滯后效應(yīng)、多尺度條件下的BMPs時(shí)空配置問題、模型的不確定性以及污染物形態(tài)轉(zhuǎn)換風(fēng)險(xiǎn)等問題，實(shí)現(xiàn)成本-效益最優(yōu)化的BMPs配置方案。

致謝：感謝中國科學(xué)院東北地理與農(nóng)業(yè)生態(tài)研究所歐洋博士對(duì)寫作給予的幫助。

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A review: model estimations on effectiveness of best management practices for agricultural non-point source pollution control

GENG Runzhe1, WANG Xiaoyan1,2,*，ZHAO Xuesong3，CHEN Yongjuan1

1CollegeofResources,Environment&Tourism,CapitalNormalUniversity,Beijing100048,China2ResearchCenterofAquaticEovironmentintheCapitalRegion,Beijing100048,China3BureauofStatisticsofFengningManchuAutonomousCounty,Fengning068350,China

With the development of point source pollution control, Agricultural Non-point Source Pollution (AGNPS) issues have become increasingly prominent worldwide. Non-point source pollution is difficult to control because it comes from the everyday activities of many different people, such as fertilizing a lawn, using a pesticide, or constructing a road or building. Recently, the agricultural non-point source pollution control has become a hotspot in the water research. As a common tool used to reduce non-point source pollution, Best management practices (BMPs) have been widely adopted to improve water quality problems associated with agricultural nonpoint source pollution, however, there have been few realistic efforts to assess their effectiveness in reducing AGNPS pollution. The effectiveness of BMPs must be evaluated at various spatial and temporal scales before adoption. Models are more comprehensive that can reflect choice of mitigation at a widely range of scales and then to achieve the best cost-effectiveness selection and placement of BMPs for non-point source pollution control. In this paper, we review some models used to assess the effectiveness of BMPs for agricultural non-point source pollution control, including non-structure practices and structure practices. The conceptual models mostly used to evaluate the impact of source control measures, while the physically-based models used to evaluate the BMPs that through control the timing and location, the response time and the transport and transformation of pollutants. The lag time between adoption of management changes and the detection of measurable improvement in water quality in the target water body are extremely important for the BMPs estimation as well as the model evaluation and validation. Models can be served as an effective tool to identify timing and critical non-point source pollution areas for target actions at different spatial scales. Other issues of critical importance include minimizing pollution swapping and assessing the cost-effectiveness of the measures within multi-objectives, as well as the acceptance of the these measures by the stakeholders involved before performing an integrated assessment of BMPs implementation. These issues are all relevant and challenging for the implementation of water and environmental policies. For future research, approaches to deal with the inevitable lag time between implementation of management practices and water quality response lies in appropriately characterizing the watershed, considering lag time in selection, location, and monitoring of management measures including the selection of appropriate indicators and designing an effective monitoring programs to detect water quality response. Understanding of NPS model uncertainty has become a front edge topic, and future studies should focus on improvement of parameter calibration, optimization of data acquisition solutions, and uncertainty analysis. Regarding to the timing and location of measures, pollution and ecosystem service swapping, and optimization and placement of BMPs in watershed, the integration of NPS models with 3S technology (GPS, RS, GIS) should be proposed. Stakeholders may play important role in developing the mitigation plan and enhancing the communication, reciprocal understanding, trust and acceptance of modelling results.

BMPs; effectiveness estimation; models; non-point source pollution

國家自然科學(xué)基金項(xiàng)目(40971258,41271495,41201534)；高等學(xué)校博士學(xué)科點(diǎn)專項(xiàng)科研基金聯(lián)合資助項(xiàng)目(20121108110006)

2013- 12- 31;

2014- 06- 16

10.5846/stxb201312313081

*通訊作者Corresponding author.E-mail: cnuwxy@gmail.com

耿潤哲，王曉燕,趙雪松,陳永娟.基于模型的農(nóng)業(yè)非點(diǎn)源污染最佳管理措施效率評(píng)估研究進(jìn)展.生態(tài)學(xué)報(bào),2014,34(22):6397- 6408.

Geng R Z, Wang X Y,Zhao X S，Chen Y J.A review: model estimations on effectiveness of best management practices for agricultural non-point source pollution control.Acta Ecologica Sinica,2014,34(22):6397- 6408.