基于輸出系數(shù)法的農(nóng)業(yè)面源氮磷排放特征分析

茍 婷,裴德富,2,梁榮昌,佘 磊,楊 珺,馬千里,趙學敏,趙 瑞,姚玲愛*

基于輸出系數(shù)法的農(nóng)業(yè)面源氮磷排放特征分析

茍 婷1,裴德富1,2,梁榮昌1,佘 磊1,楊 珺3,馬千里1,趙學敏1,趙 瑞1,姚玲愛1*

(1.生態(tài)環(huán)境部華南環(huán)境科學研究所(生態(tài)環(huán)境部生態(tài)環(huán)境應急研究所),廣東 廣州 510535；2.沈陽建筑大學市政與環(huán)境工程學院,遼寧 沈陽 110168；3.太原師范學院經(jīng)濟與管理學院,山西 晉中 030619)

為研究東江源頭區(qū)農(nóng)業(yè)面源氮磷負荷情況,利用改進的輸出系數(shù)模型(ECM)對2020年東江源頭區(qū)農(nóng)業(yè)面源氮磷排放特征進行了探討.結(jié)果表明:(1)東江源頭區(qū)農(nóng)業(yè)面源污染物總氮(TN)和總磷(TP)負荷量分別是4884.23t/a和591.85t/a, TN污染負荷是TP污染負荷的8.25倍,其中高于源頭區(qū)TN平均負荷量的鄉(xiāng)鎮(zhèn)依次為留車鎮(zhèn)?文峰鄉(xiāng)?晨光鎮(zhèn)?南橋鎮(zhèn)?吉潭鎮(zhèn)?丹溪鄉(xiāng)和澄江鎮(zhèn),高于源頭區(qū)TP平均負荷量的鄉(xiāng)鎮(zhèn)依次為晨光鎮(zhèn)?留車鎮(zhèn)?南橋鎮(zhèn)?文峰鄉(xiāng)、丹溪鄉(xiāng)?菖蒲鄉(xiāng)和吉潭鎮(zhèn).(2)氮磷污染負荷強度與負荷量不同,且表現(xiàn)出一定的空間差異性.污染負荷量較高分別為留車鎮(zhèn)和晨光鎮(zhèn),但負荷強度最高分別為南橋鎮(zhèn)和菖蒲鄉(xiāng).TN負荷強度較高的依次為南橋鎮(zhèn)?菖蒲鄉(xiāng)?晨光鎮(zhèn)?留車鎮(zhèn)和項山鄉(xiāng),均高于源頭區(qū)TN平均負荷強度2.88t/(km2×a);TP負荷強度較高的依次為菖蒲鄉(xiāng)?南橋鎮(zhèn)?晨光鎮(zhèn)?丹溪鄉(xiāng)?留車鎮(zhèn)和羅珊鄉(xiāng),均高于源頭區(qū)TP平均負荷強度0.36t/(km2×a).(3)不同污染源類型對氮磷排放的貢獻率不一致,TN污染表現(xiàn)為土地利用>農(nóng)村生活>畜禽養(yǎng)殖,TP污染表現(xiàn)為畜禽養(yǎng)殖>土地利用>農(nóng)村生活.其中氮源中土地利用污染占比為37.67%～80.29%,主要分布在長寧鎮(zhèn)?桂竹帽鎮(zhèn)?三標鄉(xiāng)?水源鄉(xiāng)?文峰鄉(xiāng)等;磷源中畜禽養(yǎng)殖污染占比44.75%～70.71%,主要分布在菖蒲鄉(xiāng)?晨光鎮(zhèn)?羅珊鄉(xiāng)?南橋鎮(zhèn)?丹溪鄉(xiāng)?龍廷鄉(xiāng)和留車鎮(zhèn).東江源頭區(qū)各鄉(xiāng)鎮(zhèn)氮磷面源污染特征不同,其治理手段和目標也不盡相同,對于菖蒲鄉(xiāng)?晨光鎮(zhèn)?南橋鎮(zhèn)等需切實解決畜禽養(yǎng)殖規(guī)劃性不強,部分養(yǎng)殖戶選址不合理,糞污治理設施普及率和資源化利用水平低等問題;對于留車鎮(zhèn)?澄江鎮(zhèn)?吉潭鎮(zhèn)等應大力推進小型農(nóng)村污水處理設施建設,完善生活污水處理措施;對于文峰鄉(xiāng)?三標鄉(xiāng)?水源鄉(xiāng)等鄉(xiāng)鎮(zhèn)需制定合理的施肥方案,避免化肥過量施用及利用率低的問題.

改進輸出系數(shù)法；農(nóng)業(yè)面源污染負荷；畜禽養(yǎng)殖源；農(nóng)村生活源；土地利用類型

隨著人口快速增長及經(jīng)濟、工業(yè)迅猛發(fā)展,面源污染已成為水污染的重要來源,其中氮磷污染是面源污染的重要組成部分.同時,氮磷也是水生態(tài)系統(tǒng)必需的生源要素,過量的氮磷污染會導致水體富營養(yǎng)化加劇和藻類水華頻發(fā),威脅流域水生態(tài)安全.據(jù)報道,美國的面源污染占污染總量的2/3,其中農(nóng)業(yè)面源污染貢獻率占68%～83%[1].荷蘭的農(nóng)業(yè)面源污染產(chǎn)生的氮、磷污染分別占水污染總負荷的60%和40%～50%[2].在我國,氮?磷污染占水污染的比例已分別達到81%和93%[3].2020年《第二次全國污染源普查公報》顯示,農(nóng)業(yè)面源對水體氮?磷的貢獻率分別高達46.5%和67.2%,且農(nóng)業(yè)面源污染沒有固定的排污口,具有分散性?隱蔽性?累積性和模糊性等特性[4].因此,準確掌握氮磷污染空間分布特征及污染物來源成為治理面源污染的關鍵技術難題[5].

目前研究面源污染最普遍的方法是Johnes[6]等提出的輸出系數(shù)模型法(ECM),它是通過一種“黑箱”的方法來對污染物輸入輸出進行模擬,模型主要利用區(qū)域水文氣象參數(shù),通過多元線性相關分析建立土地利用類型與污染輸出負荷之間的關系,再基于污染物輸出系數(shù),將不同類型污染源的污染負荷相加,估算流域面源污染負荷總量.但該模型僅適用于降雨均勻的平原地區(qū),具有使用范圍局限的弊端,需要對該模型進行改進.利用引入降雨因子和流域損失系數(shù)、以及坡度對徑流流量和流速的影響的方法改進輸出系數(shù)模型可以成功提高了污染負荷結(jié)果的精度[7-9].引入降雨?地形因子(,)估算西南喀斯特山區(qū)的北盤江流域的農(nóng)業(yè)面源污染,結(jié)果顯示北盤江流域農(nóng)業(yè)面源氮、磷污染負荷呈現(xiàn)分布不均的特質(zhì),污染負荷局部集中,坡度較高和人口密度大的區(qū)域負荷量較高[10].利用改進的輸出系數(shù)模型對媯水河流域農(nóng)業(yè)面源污染負荷進行估算,并且通過分區(qū)、分類、分期的三分法對結(jié)果進行闡釋,表明改進輸出系數(shù)模型精確度較高[11].以上研究通過對ECM的有效改進,推進了其在農(nóng)業(yè)面源污染負荷估算方面的應用,同時也為其他地區(qū)更好的采用ECM核算農(nóng)業(yè)面源污染負荷奠定了基礎.

東江是廣州、深圳、香港及惠州等粵港澳大灣區(qū)的重要供水水源,保障了約4600萬人的飲水安全.東江源頭區(qū)地處江西省贛州市尋烏縣,以農(nóng)業(yè)活動為主,源頭區(qū)排水直接流入東江,不僅影響東江流域水質(zhì),而且威脅東江的供水安全.因此無論是從保障東江供水安全的重要性,還是從東江源頭區(qū)農(nóng)業(yè)發(fā)展的生態(tài)經(jīng)濟性角度考慮,開展東江源頭區(qū)的面源污染問題研究均顯得尤為必要.但目前關于東江源頭區(qū)面源污染仍沒有相關的研究.因此,本研究通過收集東江源頭區(qū)各鄉(xiāng)鎮(zhèn)的人口、畜禽養(yǎng)殖、土地利用和降雨量等數(shù)據(jù),采用改進的ECM模型研究東江源頭區(qū)氮磷污染問題,有助于準確掌握該地區(qū)氮磷面源污染分布特征,進而提出有效的面源污染防治對策.本研究對合理調(diào)整東江源頭區(qū)農(nóng)業(yè)結(jié)構(gòu)布局、保障東江供水安全及促進粵港澳大灣區(qū)的經(jīng)濟繁榮與民生穩(wěn)定具有重要的科學意義和社會價值.

1 材料與方法

1.1 研究區(qū)域概況

東江源頭區(qū)位于江西省東南端尋烏縣(115°21′222～115°54′252E,24°30′402～25°12′102N),居贛、閩、粵三省交界處.境內(nèi)最大的水系是東江水系,流域面積1974km2,占全縣流域總面積的83.7%.尋烏水是尋烏縣唯一的主河,全長113.4km,流域面積1744km2,占全縣總面積的72.1%,流經(jīng)三標鄉(xiāng)、水源鄉(xiāng)、澄江鎮(zhèn)、吉潭鎮(zhèn)、文峰鄉(xiāng)、南橋鎮(zhèn)、留車鎮(zhèn)、龍廷鄉(xiāng)8個鄉(xiāng)(鎮(zhèn)).尋烏縣東北?西北與東南部地勢高,且向西南部傾斜,地形以山地丘陵為主,僅沿河兩岸呈狹小谷地,境內(nèi)以山地為主,山地占總面積的75.62%.該地屬于亞熱帶季風氣候,溫暖濕潤,多年平均氣溫19.1℃,歷年平均降雨量1605.7mm.土壤主要是亞熱帶紅壤區(qū),土地肥力較好.土地利用類型主要有園地和耕地,園地以果園為主;耕地利用方式主要包括水田和旱地.

1.2 數(shù)據(jù)來源

本研究數(shù)據(jù)主要來自尋烏縣數(shù)字高程模型(DEM)、2013～2020年的氣象數(shù)據(jù)?2020年的土地利用和社會經(jīng)濟數(shù)據(jù),如表1所列.

表1 研究數(shù)據(jù)及其來源

1.3 研究方法

1.3.1 輸出系數(shù)模型 (1)改進的ECM模型綜合考慮降雨和地形的影響對東江源頭區(qū)面源氮磷輸出進行模擬,具體公式如下:

式中:L為第種污染物的輸出量,kg/(hm2·a);為降雨因子;為地形影響因子;E為第種污染物第個污染源的輸出系數(shù),kg/(hm2·a),kg/(人·a)或kg/(只·a);A為流域中第種土地利用類型的面積(hm2)、畜禽養(yǎng)殖數(shù)量(頭)或人口數(shù)量(人).

(2)降雨因子取值主要通過降水的年際分布差異與空間分布差異共同確定,且流域年降雨量與面源污染氮磷負荷存在一定的相關關系[12-13],可表達為:

考慮到缺少流域內(nèi)污染物入河的監(jiān)測數(shù)據(jù),參考高田田等[14]在巢湖烔煬河流域的研究成果,建立東江源頭區(qū)降雨量與污染負荷之間的關系:

L

TN

=0.0993

r

2

+9.503

r

+216.8,(

R

2

=0.86;

P

<0.05) (3)

L

TP

=0.01146

r

2

+0.3498

r

-16.69,(

R

2

=0.98;

P

<0.05) (4)

根據(jù)2013～2020年降雨數(shù)據(jù)得到東江源頭區(qū)多年平均降雨量為562.0mm,由式(2)～(4)計算分析可以得出東江流域2020年TN的降雨影響因子為4.52、TP降水影響因子為4.54.

(3)地形影響因子主要是通過影響徑流量的大小來改變面源TN和TP污染的輸出量[8],其計算公式如下:

通過計算得到東江源頭區(qū)地形影響因子為0.68～1.32.如圖1所示.整體呈現(xiàn)流域坡度四周高中間低的趨勢,這與流域四周多以山地丘陵為主地勢較高,僅沿河兩岸呈狹小谷地的現(xiàn)狀吻合.

圖1 東江源頭區(qū)DEM(a)和土地利用圖(b)

1.3.2 模型參數(shù)的確定 (1)基礎數(shù)據(jù)的獲取.由于東江源頭區(qū)尋烏水流域面積占全縣總面積的72.1%,考慮到數(shù)據(jù)資料的限制,本文在計算尋烏縣的氮磷面源污染負荷基礎上,使用面積修正法得到東江源頭區(qū)流域內(nèi)的氮磷面源污染負荷.本次研究中農(nóng)業(yè)面源污染源分為農(nóng)村生活污染源、畜禽養(yǎng)殖污染源及土地利用污染源.具體結(jié)果如表2所示.

表2 東江源頭區(qū)流域農(nóng)村人口?牲畜數(shù)量及土地利用

(2)土地利用輸出系數(shù)的確定一般可采用研究試驗或文獻調(diào)研的方法確定[14-15].Beaulac等[16]和Frink[17]通過調(diào)查不同土地利用方式下氮磷輸出系數(shù)的變化范圍,取其平均值作為所研究流域的輸出系數(shù).由于缺乏研究區(qū)域的輸出系數(shù)試驗數(shù)據(jù),因此本文中尋烏縣各種土地利用類型的輸出系數(shù),參考國內(nèi)相似自然條件下的其他地區(qū)的研究結(jié)果而取其平均值確定[10,13,18-26].不同土地利用類型的參考輸出系數(shù)和取值結(jié)果見表3.

表3 不同土地利用類型的輸出系數(shù)取值[kg/(hm2×a)]

注:“-”表示無數(shù)據(jù)

(3)畜禽養(yǎng)殖和農(nóng)村生活面源污染物輸出系數(shù)分別采用生態(tài)環(huán)境部發(fā)布的排泄系數(shù)和人口輸出系數(shù),畜禽養(yǎng)殖業(yè)的總氮和總磷輸出系數(shù)分別取為各自排泄系數(shù)的10%[2].其取值分別見表4.

表4 東江源頭區(qū)流域畜禽養(yǎng)殖和農(nóng)村生活污染輸出系數(shù)

2 結(jié)果與分析

2.1 東江源頭區(qū)氮磷負荷量

根據(jù)東江源頭區(qū)15個鄉(xiāng)鎮(zhèn)的土地利用、畜禽養(yǎng)殖和農(nóng)村生活3大類面源數(shù)據(jù),計算得出TN和TP污染負荷量,結(jié)果見圖2所示.源頭區(qū)TN負荷量為4884.23t/a,TP負荷量為591.85t/a,TN負荷量是TP負荷量的8.25倍.TN和TP負荷量分布呈現(xiàn)較大的空間差異性,其中TN負荷量最高的鄉(xiāng)鎮(zhèn)為留車鎮(zhèn)771.43t/a,貢獻率為11.39%,其次為文峰鄉(xiāng)TN負荷量為759.97t/a,貢獻率為11.22%,此外TN負荷量較高的鄉(xiāng)鎮(zhèn)依次為晨光鎮(zhèn)、南橋鎮(zhèn)、吉潭鎮(zhèn)、丹溪鄉(xiāng)和澄江鎮(zhèn),均高于源頭區(qū)TN的平均負荷量451.62t/a;其他鄉(xiāng)鎮(zhèn)TN負荷量相對較低,長寧鎮(zhèn)負荷量最低為41.80t/a,貢獻率為0.62%.TP負荷量最高的鄉(xiāng)鎮(zhèn)為晨光鎮(zhèn)119.38t/a,貢獻率為14.54%;其次為留車鎮(zhèn)TP負荷量為96.56t/a,貢獻率為11.76%,TP負荷量較高的鄉(xiāng)鎮(zhèn)依次為南橋鎮(zhèn)、文峰鄉(xiāng)、丹溪鄉(xiāng)、菖蒲鄉(xiāng)和吉潭鎮(zhèn),均高于源頭區(qū)TP負荷量的均值54.72t/a,其他鄉(xiāng)鎮(zhèn)TP負荷量相對較低,負荷量最低為長寧鎮(zhèn)4.38t/a,貢獻率為0.53%.

圖2 東江源頭區(qū)農(nóng)業(yè)面源污染輸出負荷量分布

2.2 東江源頭區(qū)氮磷負荷強度

根據(jù)東江源頭區(qū)TN和TP污染負荷強度的數(shù)據(jù)分析,農(nóng)業(yè)面源污染的TN負荷強度大于TP負荷強度,前者是后者的8.87倍.各鄉(xiāng)鎮(zhèn)TN和TP負荷強度存在明顯的空間差異性(圖3).TN負荷強度最高的鄉(xiāng)鎮(zhèn)為南橋鎮(zhèn),負荷強度為5.03t/(km2·a),其他較高鄉(xiāng)鎮(zhèn)依次為菖蒲鄉(xiāng)(4.38t/(km2·a))、晨光鎮(zhèn)(3.52t/ (km2·a))、留車鎮(zhèn)(3.34t/(km2·a))和項山鄉(xiāng)(3.02t/ (km2·a)),均高于源頭區(qū)TN平均負荷強度2.88t/ (km2·a),其他鄉(xiāng)鎮(zhèn)均低于源頭區(qū)平均負荷強度,桂竹帽鎮(zhèn)排放負荷強度最低為1.82t/(km2·a).不同污染源類型中除菖蒲鄉(xiāng)呈現(xiàn)畜禽養(yǎng)殖負荷強度最高外,其他鄉(xiāng)鎮(zhèn)均呈現(xiàn)土地利用排放強度最高.

TP負荷強度最高的鄉(xiāng)鎮(zhèn)為菖蒲鄉(xiāng),負荷強度為0.81t/(km2·a),其他負荷強度較高的鄉(xiāng)鎮(zhèn)依次為南橋鎮(zhèn)(0.63t/(km2·a))、晨光鎮(zhèn)(0.57t/(km2·a))、丹溪鄉(xiāng)(0.42t/(km2·a))、留車鎮(zhèn)(0.42t/(km2·a))和羅珊鄉(xiāng)(0.39t/(km2·a)),均高于源頭區(qū)TP平均負荷強度0.36t/(km2·a),其他鄉(xiāng)鎮(zhèn)均低于源頭區(qū)平均負荷強度,負荷強度最低的為桂竹帽鎮(zhèn),負荷強度為0.16t/ (km2·a).不同污染源類型呈現(xiàn)部分鄉(xiāng)鎮(zhèn)的畜禽養(yǎng)殖強度較高,依次包括菖蒲鄉(xiāng)、南橋鎮(zhèn)、晨光鎮(zhèn)、羅珊鄉(xiāng)、丹溪鄉(xiāng)和留車鎮(zhèn),其他鄉(xiāng)鎮(zhèn)則土地利用排放較高(圖4).

圖3 東江源頭區(qū)各鄉(xiāng)鎮(zhèn)農(nóng)業(yè)面源污染物總氮?總磷負荷強度

圖4 東江源頭區(qū)各鄉(xiāng)鎮(zhèn)不同污染類型的總氮、總磷負荷強度

2.3 不同污染源類型對氮磷污染的貢獻率

東江源頭區(qū)不同污染源類型對TN和TP負荷量的貢獻情況如圖5所示.污染源類型對TN的貢獻率整體呈現(xiàn)土地利用>農(nóng)村生活>畜禽養(yǎng)殖,且土地利用以耕地和林地為主.各鄉(xiāng)鎮(zhèn)污染源類型TN貢獻率中,除菖蒲鄉(xiāng)呈現(xiàn)為畜禽養(yǎng)殖(37.18%)>土地利用(35.56%)>農(nóng)村生活(27.26%),其他鄉(xiāng)鎮(zhèn)均呈現(xiàn)為土地利用貢獻率最大,占比在37.67%～ 80.29%,其中南橋鎮(zhèn)(36.06%)、晨光鎮(zhèn)(31.10%)、羅珊鄉(xiāng)(24.16%)和丹溪鄉(xiāng)(21.32%)的畜禽養(yǎng)殖>農(nóng)村生活,且南橋鎮(zhèn)畜禽養(yǎng)殖以牛為主,其他鄉(xiāng)鎮(zhèn)以豬為主;其余10個鄉(xiāng)鎮(zhèn)則表現(xiàn)為農(nóng)村生活>畜禽養(yǎng)殖,其中農(nóng)村生活污染較嚴重的鄉(xiāng)鎮(zhèn)有澄江鎮(zhèn)(38.53%)、水源鄉(xiāng)(31.30%)、吉潭鎮(zhèn)(29.74%)和留車鎮(zhèn)(28.64%).

不同污染源類型對TP貢獻率與TN的規(guī)律不一致,呈現(xiàn)畜禽養(yǎng)殖>土地利用>農(nóng)村生活的特點,其中菖蒲鄉(xiāng)、晨光鎮(zhèn)、羅珊鄉(xiāng)、南橋鎮(zhèn)、丹溪鄉(xiāng)、龍廷鄉(xiāng)和留車鎮(zhèn)7個鄉(xiāng)鎮(zhèn)呈現(xiàn)為畜禽養(yǎng)殖污染占主導,占比在44.75%～70.71%,但三標鄉(xiāng)和水源鄉(xiāng)無畜禽養(yǎng)殖污染.土地利用TP貢獻率較大的鄉(xiāng)鎮(zhèn)有8個,依次為桂竹帽鎮(zhèn)、三標鄉(xiāng)、水源鄉(xiāng)、長寧鎮(zhèn)、吉潭鎮(zhèn)、文峰鄉(xiāng)、項山鄉(xiāng)和澄江鎮(zhèn),占比在40.43%～ 71.75%,另外TP農(nóng)村生活污染較嚴重的鄉(xiāng)鎮(zhèn)有澄江鎮(zhèn)(38.89%)、水源鄉(xiāng)(37.70%)、吉潭鎮(zhèn)(33.18%)和三標鄉(xiāng)(29.60%).

圖5 東江源頭區(qū)不同污染源的氮磷輸出空間分布

3 討論

3.1 流域氮磷污染負荷來源解析

不同區(qū)域因其發(fā)展方式的差異,面源污染源類型的貢獻率會呈現(xiàn)顯著的時空異質(zhì)性.已有研究顯示,洱海流域[27]農(nóng)業(yè)面源污染中土地利用對面源污染的貢獻率影響最顯著,TN和TP的排放量均主要來自于種植業(yè);洞庭湖流域[1]面源污染負荷TN的排放負荷來自種植業(yè),而TP的排放負荷主要來自于畜禽養(yǎng)殖.伊通河流域[28]的面源污染不同土地利用類型污染物流失濃度呈現(xiàn)旱田>水田>草地>林地.沱江流域[29]TP污染主要是畜禽養(yǎng)殖,成為影響沱江水環(huán)境的首要污染源.此外宋曉明等[30]研究發(fā)現(xiàn)湖南省46個區(qū)縣TN污染的主要來源為農(nóng)村生活污水和畜禽養(yǎng)殖,TP污染的主要來源為農(nóng)村生活污水.

本研究東江源頭區(qū)氮磷面源污染負荷主要來源分別為土地利用和畜禽養(yǎng)殖,這與洞庭湖流域[1]、媯水河流域[11]?滇池流域[31]等的研究結(jié)果一致,農(nóng)業(yè)種植為農(nóng)業(yè)面源污染TN的主要污染源、畜禽養(yǎng)殖為農(nóng)業(yè)面源污染TP的主要污染源[32-33].究其原因東江源頭區(qū)尋烏縣作為農(nóng)業(yè)種植大縣,是我國重要的水果(尤其是柑橘和臍橙)生產(chǎn)基地,種植柑橘和臍橙是當?shù)剞r(nóng)民脫貧致富的途徑之一.果樹種植面積的迅速增加導致大量山體遭到開發(fā),坡度大于15°,甚至超過25°的山體用于種植果樹,山體水土流失嚴重,導致土壤中的氮、磷等營養(yǎng)鹽進入地表水體.尋烏縣農(nóng)區(qū)2020年化肥投入強度約為34kg[34],高于全國平均水平22kg[35],且主要以尿素為主,過高的氮素投入和低的作物吸收率導致農(nóng)田土壤氮的大量累積,土壤中累積的氮素會隨著降雨形成的地表徑流匯入流域中,導致農(nóng)業(yè)種植成為總氮污染的主要來源.另外,資料顯示[36]尋烏縣畜禽以生豬為主,2020年底全縣生豬出欄量為13.5 萬頭,占養(yǎng)殖總量的39.68%,雖已逐步引進大規(guī)模養(yǎng)豬場,但農(nóng)村散養(yǎng)畜禽亦呈加速發(fā)展的趨勢,且養(yǎng)殖戶主要位于農(nóng)村居住區(qū)周邊或臨河而建,環(huán)保設施不完善,其中28.2%養(yǎng)殖戶未設置污水處理設施,導致畜禽養(yǎng)殖產(chǎn)生的糞污水經(jīng)簡單處理后直排入河.而且由于豬禽飼料中,總磷的60%～70%是以植酸的形式存在[37],而豬等單胃動物體內(nèi)缺乏有效降解植酸的消化酶類,對植酸磷的利用率極低,不被消化的植酸磷排出體外導致水環(huán)境污染[38],因此畜禽養(yǎng)殖是導致總磷污染的主要來源.

3.2 流域氮磷污染負荷空間解析

雖然東江源頭區(qū)農(nóng)業(yè)面源污染以土地利用和畜禽養(yǎng)殖為主,但各鄉(xiāng)鎮(zhèn)氮磷污染負荷存在明顯的空間異質(zhì)性.其中TN污染負荷高值區(qū)主要集中分布在南部的留車鎮(zhèn)、晨光鎮(zhèn)和中部的文峰鄉(xiāng),TP污染負荷最高值區(qū)分布在南部的晨光鎮(zhèn),其次主要集中在留車鎮(zhèn)、南橋鎮(zhèn)和文峰鄉(xiāng),而兩者污染的低值區(qū)均零散的分布在中部的長寧鎮(zhèn)、北部的水源鄉(xiāng)、南部的龍廷鄉(xiāng)和東部的項山鄉(xiāng).污染負荷高值區(qū)由于農(nóng)業(yè)活動密集導致污染負荷隨之增加[11],但不同鄉(xiāng)鎮(zhèn)的污染類型的貢獻率有所差異.其中留車鎮(zhèn)、澄江鎮(zhèn)、吉潭鎮(zhèn)、水源鄉(xiāng)和丹溪鄉(xiāng)農(nóng)村生活污染面源污染較嚴重,主要原因是鄉(xiāng)鎮(zhèn)的農(nóng)村人口數(shù)龐大,且對于農(nóng)村生活污水無集中處理;而菖蒲鄉(xiāng)、晨光鎮(zhèn)、南橋鎮(zhèn)、羅珊鄉(xiāng)和龍廷鄉(xiāng)的畜禽養(yǎng)殖數(shù)量較多,由此產(chǎn)生的污染源貢獻率較大,且畜禽養(yǎng)殖結(jié)構(gòu)以大牲畜牛、豬為主;文峰鄉(xiāng)、三標鄉(xiāng)、水源鄉(xiāng)、長寧鎮(zhèn)、桂竹帽鎮(zhèn)由土地利用引起的氮磷負荷最高,主要原因是農(nóng)業(yè)種植面積尤其是耕地面積較大,而土地利用類型中耕地的固氮磷能力較差,耕地化肥利用率不高[39-40],是氮磷流失最主要的土地利用類型,且耕地的氮磷輸出系數(shù)為林地的3～4倍.盡管留車鎮(zhèn)的TN污染負荷量和晨光鎮(zhèn)的TP污染負荷量分別呈現(xiàn)最大,但污染強度并不是最高,TN負荷強度最高為南橋鎮(zhèn),而TP負荷強度最高為菖蒲鄉(xiāng).因此,在污染防控上,需綜合考慮污染負荷量和負荷強度來進行面源整治.

3.3 流域農(nóng)業(yè)面源污染源控制措施探討

東江源頭區(qū)各鄉(xiāng)鎮(zhèn)的污染特征不同,其治理手段和目標有所側(cè)重,對于畜禽養(yǎng)殖大鎮(zhèn)菖蒲鄉(xiāng)、晨光鎮(zhèn)、南橋鎮(zhèn)等實施以源頭防控與重點治理相結(jié)合,著力改善現(xiàn)有農(nóng)業(yè)生態(tài)環(huán)境,切實解決畜禽養(yǎng)殖規(guī)劃性不強,部分養(yǎng)殖戶選址不合理,污染防治技術體系薄弱,糞污治理設施普及率和資源化利用水平低等問題.資料顯示[37]尋烏縣規(guī)模養(yǎng)殖場均采用干清糞方式處理,但養(yǎng)殖戶中僅10%采用干清糞方式,90%采用水沖糞方式處理,而水沖糞的方式存在耗水量大、污水產(chǎn)生量大、舍內(nèi)有害氣體含量高、產(chǎn)生的污水有機污染物濃度高等問題[41-42],因此改變養(yǎng)殖戶糞肥處理方式,鼓勵養(yǎng)殖戶采用干清糞、機械清糞方式,逐步淘汰水沖糞清糞方式,減少養(yǎng)殖過程中用水量和污水排放壓力的有效途徑.另外由于尋烏縣的畜禽養(yǎng)殖結(jié)構(gòu)以牛和豬為主,建設規(guī)?；笄蒺B(yǎng)殖場可推廣生物發(fā)酵床養(yǎng)殖技術[43],不僅可以提高畜禽的免疫力,降低養(yǎng)殖成本,還可有效的處理畜禽糞污,同時結(jié)合源頭區(qū)域“柑桔種植優(yōu)勢區(qū)”的特點,建設畜禽養(yǎng)殖-果業(yè)開發(fā)生態(tài)經(jīng)濟循環(huán)圈,按照“資源化?無害化?生態(tài)化”的原則,利用資源化治理工程和配套措施處理規(guī)模化畜禽養(yǎng)殖有機污染,實現(xiàn)畜禽糞便資源化無害化利用和種植與養(yǎng)殖的良性循環(huán).

對于農(nóng)村生活污染較嚴重的留車鎮(zhèn)、澄江鎮(zhèn)、吉潭鎮(zhèn)等大力推進小型農(nóng)村污水處理設施建設,完善生活污水處理措施[31,44-45],如建立沼氣池、垃圾分類站等,杜絕污染物直接進入水體.另外對于山區(qū)邊遠鄉(xiāng)鎮(zhèn)如丹溪鄉(xiāng)、三標鄉(xiāng)、桂竹帽鎮(zhèn)等基于人口較少、社會活動水平較低、山地丘陵地形為主的特點,可采取戶用化糞池、沼氣池等進行分散治理,建設污水儲存罐用于冬季儲存,結(jié)合農(nóng)業(yè)化肥減量增效、水肥一體化等,引導林果種植?農(nóng)業(yè)合作社、家庭農(nóng)場等現(xiàn)代農(nóng)業(yè)經(jīng)營主體將治理后的污水作為有機肥水使用,實現(xiàn)無害化處理、資源化利用.

對于農(nóng)業(yè)種植污染較嚴重的文峰鄉(xiāng)、三標鄉(xiāng)、水源鄉(xiāng)等鄉(xiāng)鎮(zhèn)需制定合理的施肥方案,避免化肥過量施用以及利用率低的問題[46-48],控制旱地總氮徑流流失應側(cè)重于降低徑流量和土壤氮含量,而水田則應同時減低徑流量和施氮量,加大推廣節(jié)水灌溉技術和循環(huán)灌溉方法,將土壤氮作為作物生產(chǎn)的潛在氮源予以再利用,并進一步推廣應用測土配方施肥技術,減少土壤氮過量積累及流失.另外需在深入了解各鄉(xiāng)鎮(zhèn)施肥習慣的基礎上,科學計算化肥施用量,實行以產(chǎn)定肥,平衡施用有機肥?新型肥料以及無機肥[44].提倡應用新型肥料,同時對農(nóng)藥進行減量控制,優(yōu)先選擇生物措施或物理措施,合理輪作,減緩污染.

4 結(jié)論

4.1 研究期間,東江源頭區(qū)農(nóng)業(yè)面源污染物TN和TP負荷量分別是4884.23和591.85t/a,TN負荷量是TP負荷量的8.25倍,不同鄉(xiāng)鎮(zhèn)的污染負荷量呈現(xiàn)較大的空間異質(zhì)性.TN負荷量較高的鄉(xiāng)鎮(zhèn)依次為留車鎮(zhèn)、文峰鄉(xiāng)、晨光鎮(zhèn)、南橋鎮(zhèn)、吉潭鎮(zhèn)、丹溪鄉(xiāng)和澄江鎮(zhèn);TP負荷量較高的鄉(xiāng)鎮(zhèn)依次為晨光鎮(zhèn)、留車鎮(zhèn)、南橋鎮(zhèn)、文峰鄉(xiāng)、丹溪鄉(xiāng)、菖蒲鄉(xiāng)和吉潭鎮(zhèn).

4.2 源頭區(qū)氮磷負荷強度與負荷量表現(xiàn)出一定的空間差異性.TN和TP污染負荷量較高分別為留車鎮(zhèn)和晨光鎮(zhèn),但負荷強度最高分別為南橋鎮(zhèn)和菖蒲鄉(xiāng).其中TN負荷強度高于源頭區(qū)TN平均負荷強度的依次為南橋鎮(zhèn)、菖蒲鄉(xiāng)、晨光鎮(zhèn)、留車鎮(zhèn)和項山鄉(xiāng);TP負荷強度高于源頭區(qū)TP負荷強度均值的依次為菖蒲鄉(xiāng)、南橋鎮(zhèn)、晨光鎮(zhèn)、丹溪鄉(xiāng)、留車鎮(zhèn)和羅珊鄉(xiāng).

4.3 不同農(nóng)業(yè)面源污染源類型對TN和TP污染負荷的貢獻率不同,其中TN負荷量主要受土地利用影響,且土地利用污染占比為37.67%～80.29%,主要分布在長寧鎮(zhèn)、桂竹帽鎮(zhèn)、三標鄉(xiāng)、水源鄉(xiāng)、文峰鄉(xiāng)等;而TP負荷量主要受畜禽養(yǎng)殖影響,畜禽養(yǎng)殖污染占比44.75%～70.71%,主要分布在菖蒲鄉(xiāng)、晨光鎮(zhèn)、羅珊鄉(xiāng)、南橋鎮(zhèn)、丹溪鄉(xiāng)、龍廷鄉(xiāng)和留車鎮(zhèn).

4.4 東江源頭區(qū)各鄉(xiāng)鎮(zhèn)氮磷面源污染特征不同,其治理手段和目標也不盡相同.對于畜禽養(yǎng)殖大鎮(zhèn)菖蒲鄉(xiāng)、晨光鎮(zhèn)、南橋鎮(zhèn)等以源頭防控與重點治理相結(jié)合,切實解決畜禽養(yǎng)殖規(guī)劃性不強,部分養(yǎng)殖戶選址不合理,污染防治技術體系薄弱,糞污治理設施普及率和資源化利用水平低等問題;對于農(nóng)村生活污染較嚴重的留車鎮(zhèn)、澄江鎮(zhèn)、吉潭鎮(zhèn)等大力推進小型農(nóng)村污水處理設施建設,完善生活污水處理措施;對于農(nóng)業(yè)種植污染較嚴重的文峰鄉(xiāng)、三標鄉(xiāng)、水源鄉(xiāng)等鄉(xiāng)鎮(zhèn)需制定合理的施肥方案,盡量避免化肥過量施用以及利用率低的問題.

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GOU Ting1, PEI De-fu1,2, LIANG Rong-chang1, SHE Lei1, YANG Jun3, MA Qian-li1, ZHAO Xue-min1, ZHAO Rui1, YAO Ling-ai1*

(1.South China Institute of Environmental Sciences, Ministry of Ecology and Environment (Research Institute of Eco-environmental Emergency, Ministry of Ecology and Environment), Guangzhou 510535, China；2.School of Municipal and Environmental Engineering, Shenyang University of Architecture, Shenyang 110168, China；3.School of Economics and management, Taiyuan Normal University, Jinzhong 030619, China)., 2023,43(12)：6539～6550

To study the nitrogen and phosphorus loadings from agricultural surface sources in the source area of Dongjiang River, the characteristics of nitrogen and phosphorus emissions from agricultural surface sources in the source area of Dongjiang River in 2020 were explored using an improved output coefficient model (ECM). The results show that: (1) the loads of total nitrogen (TN) and total phosphorus (TP) of agricultural surface source pollutants in the source area of Dongjiang River were 4884.23t/a and 591.85t/a, respectively, and the TN pollution load was 8.25 times of the TP pollution load. Among the townships with higher than the average TN load were Liuche Township, Wenfeng Township, Chenguang Township, Nanqiao Township, Jitan Township, Danxi Township and Chengjiang Township, higher than the TP average load of the township were Chenguang, Liuche Township, Nanqiao Township, Wenfeng Township, Danxi Township, Calamus Township and Jitan Township. (2) Nitrogen and phosphorus pollution load intensity and load amount was different, and showed spatial variability. The higher pollution load was Liuche Township and Chenguang Township respectively, but the highest load intensity was Nanqiao Township and Calamus Township respectively. The higher TN load intensity was in the order of Nanqiao Township, Calamus Township, Chenguang Township, Liuche Township and Xiangshan Township, which all higher than the average TN load intensity of 2.88t/(km2×a) in the source area; the higher TP load intensity was in the order of Calamus Township, Nanqiao Township, Chenguang Township, Danxi Township, Liuche Township and Luoshan Township, which all higher than the source area TP average load intensity of 0.36t/(km2×a). (3) The contribution of different source types to nitrogen and phosphorus emissions was not consistent, TN pollution was manifested as land use > rural life > livestock breeding, TP pollution was manifested as livestock breeding > land use > rural life. Among the nitrogen sources, land use pollution accounted for 37.67%～80.29%, mainly distributed in Changning Township, Guizhumat Township, Sanbiao Township, Water Source Township, Wenfeng Township; phosphorus sources of livestock breeding pollution accounted for 44.75%～70.71%, mainly distributed in Calamus Township, Chenguang Township, Luoshan Township, Nanqiao Township, Danxi Township, Longting Township and Liuche Township. Based on different characteristics of nitrogen and phosphorus non-point source pollution in the source area of Dongjiang River, the treatment methods were also different. For the townships were seriously polluted by livestock breeding, which should to solve the problems of poor planning of livestock breeding, unreasonable site selection and low level of resource utilization. The townships were seriously polluted by rural living pollution which should vigorously promote the construction of small rural sewage treatment facilities and improve the living sewage treatment measures. Other townships need to develop a reasonable fertilizer application program to avoid excessive application of chemical fertilizers. This study has important practical significance for improving the continuous emission reduction of agricultural non-point source pollution and ensuring the safety of water supply in Dongjiang River.

improved output coefficient method；agricultural non-point source pollution；livestock breeding sources；rural living sources；land use types

X501

A

1000-6923(2023)12-6539-12

茍 婷,裴德富,梁榮昌,等.基于輸出系數(shù)法的農(nóng)業(yè)面源氮磷排放特征分析 [J]. 中國環(huán)境科學, 2023,43(12):6539-6550.

Gou T, Pei D F, Liang R C, et al. Analysis of nitrogen and phosphorus emissions from agricultural non-point sources based on improved output coefficient method [J]. China Environmental Science, 2023,43(12):6539-6550.

2023-04-19

廣東省重點領域研發(fā)計劃項目(2019B110205004);國家自然科學基金資助項目(41977353);中央級公益性科研院所基本科研業(yè)務專項 (PM-zx703-202204-075)

* 責任作者, 高級工程師, yaolingai@scies.org

茍 婷(1988-),女,甘肅白銀人,工程師,碩士,主要從事水污染防治研究.發(fā)表論文18篇.gouting@scies.org.