河口陸基養(yǎng)蝦塘沉積物鐵的含量和形態(tài)

朱愛(ài)菊,仝 川,3,4,羅 敏,黃佳芳,3,4,譚 季,胡啟凱,李 敬

河口陸基養(yǎng)蝦塘沉積物鐵的含量和形態(tài)

朱愛(ài)菊1,2,仝 川1,2,3,4,羅 敏4,5*,黃佳芳1,2,3,4,譚 季1,2,胡啟凱5,李 敬1,2

(1.福建師范大學(xué),濕潤(rùn)亞熱帶生態(tài)地理過(guò)程教育部重點(diǎn)實(shí)驗(yàn)室,福建 福州 350007；2.福建師范大學(xué)地理科學(xué)學(xué)院,福建福州 350007；3.福建師范大學(xué)地理研究所,福建 福州 350007；4.閩江河口濕地生態(tài)系統(tǒng)國(guó)家定位觀測(cè)研究站(國(guó)家林業(yè)和草原局),福建 福州 350007；5.福州大學(xué)環(huán)境與資源學(xué)院,福建 福州 350116)

為研究河口陸基養(yǎng)殖塘底泥中鐵的遷移和轉(zhuǎn)化機(jī)制,本文測(cè)定了福建省3個(gè)河口養(yǎng)蝦塘養(yǎng)殖期表層和亞表層底泥沉積物中活性鐵含量及間隙水的常見(jiàn)組分.結(jié)果表明,不同站點(diǎn)間晶質(zhì)Fe(III)、非硫Fe(II)、有機(jī)鐵、鐵硫化物含量存在顯著差異.間隙水SO42–和Cl–可能是影響不同站點(diǎn)間Fe的形態(tài)和分布存在異質(zhì)性的主要環(huán)境影響因子之一.鹽度較高的養(yǎng)蝦塘,鐵的硫化物含量較高,有機(jī)鐵和晶質(zhì)Fe(III)含量較少.陸基養(yǎng)蝦塘底泥沉積物中活性鐵含量按固相Fe(III)>鐵硫化物>非硫Fe(II)>有機(jī)鐵的順序排列.養(yǎng)蝦塘亞表層沉積物鐵硫化物(FeS和FeS2)含量高于表層沉積物,而表層沉積物有機(jī)鐵含量與間隙水SO42–和NH4+濃度高于亞表層沉積物.鐵硫化物的生成一定程度上降低河口陸基養(yǎng)蝦塘沉積物營(yíng)養(yǎng)鹽污染的潛在風(fēng)險(xiǎn).

鐵形態(tài)；無(wú)定形Fe(III)；晶質(zhì)Fe(III)；鐵硫化物；非硫Fe(II)；有機(jī)碳代謝；陸基養(yǎng)蝦塘

近年來(lái)隨著人們對(duì)水產(chǎn)品需求的劇增,全球養(yǎng)殖業(yè)以每年8.3%的速率高速增長(zhǎng)[1-2].養(yǎng)殖業(yè)的高速發(fā)展使得對(duì)河口濕地的圍墾和開(kāi)發(fā)強(qiáng)度越來(lái)越大.目前我國(guó)濱海陸基養(yǎng)殖塘面積已經(jīng)位于世界首位(1370km2)[3].而大部分陸基養(yǎng)殖塘存在過(guò)量放養(yǎng)、餌料過(guò)剩等突出問(wèn)題,導(dǎo)致河口陸基養(yǎng)殖塘水體富營(yíng)養(yǎng)化問(wèn)題十分嚴(yán)重.與河口陸基養(yǎng)殖塘碳氮循環(huán)相關(guān)的元素生物地球化學(xué)循環(huán)成為了水產(chǎn)養(yǎng)殖業(yè)關(guān)注的重點(diǎn).

鐵(Fe)是地殼中豐度最高的氧化還原敏感性金屬元素,也是養(yǎng)殖水體中最重要的生源要素之一[4]. Fe的氧化還原反應(yīng)耦合有機(jī)碳代謝、營(yíng)養(yǎng)鹽的循環(huán)以及痕量金屬元素和污染物的吸附和解吸等,在水域生態(tài)系統(tǒng)中發(fā)揮著重要作用[5-6].目前,國(guó)內(nèi)外養(yǎng)殖塘生態(tài)系統(tǒng)Fe的相關(guān)報(bào)道多局限于總量分析和價(jià)態(tài)分析.事實(shí)上,沉積物中大部分的Fe并不會(huì)參與到鐵的生物地球化學(xué)循環(huán)過(guò)程中,只有不同形態(tài)的“活性”Fe才能表征濕地鐵的遷移和轉(zhuǎn)化規(guī)律.養(yǎng)殖塘沉積物中富含固相的三價(jià)氧化物或氫氧化物水合物,它們能成為鐵還原微生物的潛在營(yíng)養(yǎng)源[7],這個(gè)過(guò)程被稱(chēng)為鐵異化還原[8-9].鐵異化還原伴隨著有機(jī)碳的礦化,產(chǎn)生間隙水Fe2+或Fe(II)化合物(如菱鐵礦或藍(lán)鐵礦)[10].在養(yǎng)殖塘沉積物中,Fe(III)還可能發(fā)生化學(xué)還原,尤其是被硫酸鹽異化還原的產(chǎn)物H2S還原形成鐵的硫化物[11-12].因此,養(yǎng)殖塘沉積物中與Fe生物地球化學(xué)循環(huán)最密切相關(guān)的各形態(tài)Fe,包括間隙水Fe2+、非硫Fe(II)、無(wú)定形Fe(III)、晶質(zhì)Fe(III)、FeS和FeS2.在其他淺水水域生態(tài)系統(tǒng)(濕地、湖泊)中,已有不少針對(duì)上述不同形態(tài)Fe之間遷移和轉(zhuǎn)化的相關(guān)研究.例如Alongi等[13]對(duì)越南養(yǎng)蝦池的研究發(fā)現(xiàn)不同蝦池在0~15cm處Fe的含量差異顯著,且FeS2對(duì)總Fe的相對(duì)貢獻(xiàn)率隨著沉積物深度增加而增加.中,楊文斌等[14]發(fā)現(xiàn)中國(guó)太湖表層沉積物中鐵形態(tài)大部分以高活性鐵形式存在,Fe(III)的還原性溶解及再氧化生成自生Fe(III)氧化物是沉積物中Fe循環(huán)的主要路徑.Luo等[15]在中國(guó)閩江河口潮汐濕地沉積物中發(fā)現(xiàn)無(wú)定形Fe(III)和晶質(zhì)Fe(III)在漲潮帶表面積累,間隙水Cl–濃度對(duì)不同形態(tài)Fe的分布影響深遠(yuǎn).由上述研究可知,沉積物中Fe的空間分布受沉積物深度和間隙水常見(jiàn)組分影響深遠(yuǎn).

福建省地處我國(guó)東南沿海,據(jù)估算其濱海河口陸基水產(chǎn)養(yǎng)殖塘面積占我國(guó)濱海河口陸基水產(chǎn)養(yǎng)殖塘總面積的45%[3].各類(lèi)養(yǎng)殖產(chǎn)品,尤其是南美白對(duì)蝦()的養(yǎng)殖已經(jīng)成為福建省河口地區(qū)的重要產(chǎn)業(yè)之一.目前,已經(jīng)開(kāi)展對(duì)福建省河口陸基養(yǎng)殖塘有機(jī)質(zhì)代謝潛勢(shì)[16]、溫室氣體排放通量[17]、營(yíng)養(yǎng)鹽的遷移轉(zhuǎn)化機(jī)制[18]等研究,而對(duì)養(yǎng)殖塘底泥沉積物中Fe元素的形態(tài)組成及其遷移轉(zhuǎn)化特征等目前尚不清楚,開(kāi)展相關(guān)研究對(duì)于揭示養(yǎng)殖塘的Fe生物地球化學(xué)循環(huán)特征具有重要意義.基于此,本研究以福建省河口陸基水產(chǎn)養(yǎng)蝦塘為研究對(duì)象,研究養(yǎng)蝦塘表層和亞表層沉積物“活性鐵”的形態(tài)和組成,并以此為基礎(chǔ)探索養(yǎng)蝦塘沉積物中鐵的遷移轉(zhuǎn)化規(guī)律,為進(jìn)一步探索沿海地區(qū)水產(chǎn)養(yǎng)殖塘的環(huán)境效應(yīng)提供科學(xué)依據(jù).

1 材料與方法

1.1 研究區(qū)概況

本研究中的河口陸基養(yǎng)蝦塘分別位于福建省閩江河口區(qū)蝙蝠洲(FB)(119°33′09.53″E, 26°03′28.43″N)及粗蘆島(FC)(119°37′47.56″E, 26°08′39.52″N)、木蘭溪河口區(qū)(PE)(119°07′10.57″E, 25°24′24.09″N)和九龍江河口區(qū)(ZG)(117°46'28.19"E, 24°29'15.35"N)(圖1).閩江、木蘭溪和九龍江3個(gè)河口所在區(qū)域均屬于亞熱帶海洋性季風(fēng)氣候,氣候暖熱濕潤(rùn),年均氣溫19.6~21.0℃,年均降雨量均為1300mm以上,多集中在3~9月[19-21].

圖1 福建省河口陸基養(yǎng)蝦塘樣地位置

4個(gè)養(yǎng)蝦塘均由河口短葉茳芏沼澤濕地圍墾而成,土地利用轉(zhuǎn)化年限相近(7~9a),且均為泥質(zhì)塘坡和塘底.養(yǎng)蝦塘內(nèi)的產(chǎn)品均為南美白對(duì)蝦(),每年5月底投放蝦苗,10月中下旬將蝦全部收獲后養(yǎng)殖結(jié)束.養(yǎng)殖規(guī)模和管理模式如表1所示.養(yǎng)蝦塘以相鄰河口附近水作為養(yǎng)殖水源,鹽度跨度范圍為1.89‰~20.03‰.每個(gè)養(yǎng)蝦塘均配置2臺(tái)功率為1.5kW的葉輪式增氧機(jī),開(kāi)機(jī)時(shí)間約為20:00~次日02:00,白天增氧機(jī)開(kāi)關(guān)情況視天氣、魚(yú)蝦生長(zhǎng)情況以及水質(zhì)情況而定.養(yǎng)殖密度約為80~90萬(wàn)尾/hm2,每天07:00和17:00投餌兩次,投餌量按常規(guī)要求.4個(gè)養(yǎng)蝦塘基本特征如表1所示.

表1 河口陸基養(yǎng)蝦塘基本特征

1.2 樣品采集與前處理

采樣時(shí)間為2017年7月23~28日(養(yǎng)殖中期),使用PVC管采集4個(gè)養(yǎng)蝦塘的沉積物柱樣,每個(gè)塘設(shè)置3個(gè)重復(fù).取樣后將裝有沉積物柱樣的PVC管兩端塞上硅膠墊并加蓋密封.采集后的樣品均放置在裝有冰袋的泡沫保溫箱中冷藏帶回實(shí)驗(yàn)室.返回實(shí)驗(yàn)室后,在YQX-II厭氧培養(yǎng)箱(上海躍進(jìn)醫(yī)療器械廠公司生產(chǎn))中用塑料刀將沉積物柱樣品表層黑色的塘泥(深度范圍約為0~8cm)及亞表層黑褐色的沉積物(深度范圍約8~15cm)分層切割.利用改進(jìn)后的間隙水采樣器[22]采集養(yǎng)蝦塘沉積物間隙水.與傳統(tǒng)的離心法或壓榨法取間隙水相比,該裝置能保證間隙水采集過(guò)程中不與空氣接觸,隨后利用孔徑為0.45μm濾膜的針頭過(guò)濾器過(guò)濾后注入西林瓶中.用于間隙水NH4+、NO3?和DOC分析的西林瓶中事先加入10μL 6mol/L的HCl,最后,將上述沉積物和間隙水樣品置于4℃冷藏保存,并在一周內(nèi)完成所有測(cè)定分析.

1.3 沉積物和間隙水常見(jiàn)組分濃度

溶解性有機(jī)碳(DOC)濃度使用日本島津公司TOC-VCPH總有機(jī)碳分析儀測(cè)定分析,實(shí)驗(yàn)室內(nèi)配置KHP(鄰苯二甲酸氫鉀)(0.5~10)′10-6標(biāo)準(zhǔn)溶液進(jìn)行校準(zhǔn),檢測(cè)限為2μmol/L.間隙水SO42–和Cl–濃度利用孔徑0.22μm針頭式注射器過(guò)濾后進(jìn)樣,接著利用美國(guó)賽默飛世爾科技的ICS-2100離子色譜儀測(cè)定(SO42–和Cl–的檢測(cè)限分別為0.09mg/L和0.02mg/L).間隙水NH4+和NO3–濃度采用荷蘭SKALAR SAN++連續(xù)流動(dòng)分析儀測(cè)定(檢測(cè)限分別為1μmol/L和4μmol/L).間隙水中Fe2+的濃度采用1,10-鄰菲啰啉法[23],通過(guò)日本島津UV-2450型紫外可見(jiàn)分光光度計(jì)測(cè)定(檢測(cè)限為3 μmol/L).溶解性CH4采用頂空平衡法采樣[24],利用日本島津氣相色譜儀(GC-2010)進(jìn)行頂空氣體CH4濃度的測(cè)定.溶解性CH4濃度根據(jù)公式(1)計(jì)算.

= (H·H/22.4)/P(1)

式中:為溶解性CH4的濃度,μmol/L;H為玻璃瓶中頂空氣體CH4的濃度,μL/L;H為玻璃瓶中頂空氣體的體積,mL;P為玻璃瓶中間隙水的體積, mL.

固相Fe和S的含量均利用光度比色法通過(guò)日本島津公司UV-2450紫外可見(jiàn)分光光度計(jì)測(cè)定.固相Fe(III)與Fe(II)的含量采用改進(jìn)的連續(xù)浸提法[7]測(cè)定.利用0.5mol/L HCl溶液、0.5mol/L HCl與10mg/L羥胺的混合液,以及CBD溶液(0.35mol/L冰醋酸和0.2mol/L檸檬酸鈉混合液,再加上50mg/L連二亞硫酸鈉緩沖液)分別浸提得到沉積物中的非硫Fe(II)、無(wú)定形Fe(III)和晶質(zhì)Fe(III)[8,25].有機(jī)鐵含量利用1mol/L MgCl2(pH=5)以及0.1mol/L焦磷酸鈉進(jìn)行16h的萃取[26].

酸性揮發(fā)性硫(AVS)和鉻還原性硫(CRS)含量分別利用0.1mol/L抗壞血酸溶液+6mol/L HCl和酸性CrCl2溶液提取[27],提取后溶解硫的濃度(∑H2S=H2S(g)+HS–+S2–)利用亞甲基藍(lán)法測(cè)定(檢測(cè)限為1μmol/L)[28].鐵的硫化物FeS和FeS2的物質(zhì)的量濃度利用AVS和CRS的Fe和S化學(xué)計(jì)量比計(jì)算(AVS:Fe:S=1:1;CRS:Fe:S=1:2).本研究中各固相形態(tài)Fe的含量單位均為μmol Fe/g,即每g干土中含有多少μmol的Fe.

1.4 數(shù)理統(tǒng)計(jì)分析

在數(shù)據(jù)分析前,先進(jìn)行正態(tài)分布檢驗(yàn)和方差齊次性檢驗(yàn),不符合正態(tài)分布的數(shù)據(jù)采用log轉(zhuǎn)置后分析,采用SPSS 22.0軟件中雙因素方差分析(Two- way ANOVA)檢驗(yàn)不同深度和不同站點(diǎn)對(duì)各形態(tài)鐵含量的影響.利用Tukey事后檢驗(yàn)分析組間的差異性.各形態(tài)鐵與間隙水中常見(jiàn)組分濃度的相關(guān)性分析采用 Pearson相關(guān)分析法.以上數(shù)據(jù)統(tǒng)計(jì)分析顯著性水平均為0.05.文中圖表數(shù)值為平均值±標(biāo)準(zhǔn)差.

2 結(jié)果與分析

2.1 間隙水常見(jiàn)組分濃度

間隙水Cl–和SO42–濃度變化范圍分別為23.41~ 324.01mmol/L與0.19~29.36mmol/L(圖2a和2b).不同站點(diǎn)間Cl–和SO42–濃度差異顯著(< 0.001,表2),表現(xiàn)為閩江河口的FB和FC站點(diǎn)<木蘭溪站點(diǎn)PE<九龍江站點(diǎn)ZG(表3).表層和亞表層間隙水Cl–濃度變化不明顯(>0.05,表2),但表層沉積物間隙水SO42?濃度總體上高于亞表層(<0.05,表4),暗示亞表層間隙水SO42?的消耗較大,可能存在較高的硫酸鹽還原.

間隙水DOC濃度范圍為0.94~6.69mmol/ L(圖2c).4個(gè)站點(diǎn)之間間隙水DOC濃度差異顯著(0.001,表2),閩江河口站點(diǎn)FC和FB間隙水DOC的濃度要高于九龍江站點(diǎn)ZG和木蘭溪PE(表3).此外,不同站點(diǎn)間表層和亞表層的間隙水DOC濃度變化不一致(0.01,表2),站點(diǎn)FB和FC表層DOC含量高于亞表層沉積物,站點(diǎn)PE和ZG表層DOC含量低于亞表層沉積物(圖2c).DOC為有機(jī)碳礦化過(guò)程中的底物,以上結(jié)果表明各站點(diǎn)表層沉積物和亞表層有機(jī)碳礦化的潛力可能不一致.

溶解性CH4濃度范圍為13.4~528.13μmol/ L(圖2d).與間隙DOC濃度一致,閩江河口站點(diǎn)FC和FB溶解性CH4的濃度要顯著高于九龍江站點(diǎn)ZG和木蘭溪PE(0.01;表3).高鹽站點(diǎn)的溶解性CH4的濃度要低于低鹽站點(diǎn).表層溶解性CH4的濃度總體上高于亞表層(0.05;表4),但不同站點(diǎn)表層和亞表層的溶解性CH4濃度變化不一致(0.05;表2).站點(diǎn)FC表層溶解性CH4的濃度要遠(yuǎn)高于底層,其他站點(diǎn)溶解性CH4的濃度高于亞表層沉積物(圖2d).

間隙水NO3–和NH4+濃度變化范圍分別為2.97~84.15μmol/L與0.25~1.6mmol/L(圖2e和2f).四個(gè)站點(diǎn)之間間隙水NO3–和NH4+濃度均無(wú)顯著差異(0.05,表2),但表層和亞表層間隙水NO3–和NH4+濃度差異顯著(0.01,表2).表層沉積物間隙水NO3–濃度要顯著低于亞表層沉積物,但表層沉積物NH4+濃度卻顯著高于亞表層沉積物(0.01,表4).

圖2 福建省河口陸基養(yǎng)蝦塘間隙水常見(jiàn)組分濃度 Fig.2 Concentrations of each porewater constituent of wetland-based shrimp ponds in the estuaries of Fujian province, southeast China 表2 鹽分和深度影響下間隙水常見(jiàn)組分濃度和不同形態(tài)鐵的含量的雙因素方差分析 Table 2 Two-way ANOVA analysis of concentrations of porewater constituents and iron species under the effect of sites and depth 指標(biāo)站點(diǎn)(df =3)深度(df =1)站點(diǎn)′深度(df=3) FPFPFP 間隙水 §Cl?160.471<0.0011.8910.1880.5820.636 §SO42?36.847<0.0017.2600.0164.7030.015 DOC5.480<0.0010.2500.6248.6060.001 §溶解性CH424.967<0.0014.9650.0415.1620.011 §NH4+1.2230.33425.974<0.0011.2070.339 §NO3?3.1240.05514.2420.0027.2670.003 不同形態(tài)鐵 §非硫Fe(II)10.362<0.0014.5390.0490.2740.843 有機(jī)鐵21.093<0.00114.4100.0021.3230.302 §Fe(III)-HCl2.4920.0970.4150.5291.2580.322 §Fe(III)-CBD122.640<0.0013.5450.0783.5140.060 §FeS3.2630.04835.629<0.0011.3770.286 §FeS223.369<0.0016.3240.0230.8100.507 注:§表示數(shù)據(jù)在分析前經(jīng)過(guò)log轉(zhuǎn)置. 2.2 沉積物中的各形態(tài)固相鐵的含量 如圖3所示,非硫Fe(II)含量范圍為2.12~ 36.77μmol Fe/g(圖3a).不同站點(diǎn)之間沉積物中非硫Fe(II)含量最高值出現(xiàn)在站點(diǎn)ZG,最低值出現(xiàn)在站點(diǎn)FB(P<0.05,表3).各站點(diǎn)表層沉積物的非硫Fe(II)含量顯著低于亞表層沉積物(表4).有機(jī)鐵含量范圍為0.23~0.61μmol Fe/g(圖3b).對(duì)比不同站點(diǎn)發(fā)現(xiàn),站點(diǎn)FB和FC的有機(jī)鐵含量顯著高于站點(diǎn)PE和ZG(P< 0.05,表3).與非硫(II)含量不同,各站點(diǎn)表層沉積物有機(jī)鐵的含量顯著高于亞表層沉積物(P<0.01,表4). 無(wú)定形Fe(III)含量范圍為19.91~45.66μmol Fe/g(圖3c),晶質(zhì)Fe(III)含量范圍為31.79~ 106.88μmol Fe/g(圖3d).不同站點(diǎn)間無(wú)定形Fe(III)含量差異不顯著(P>0.05,表2),但晶質(zhì)Fe(III)含量差異顯著(P<0.001,表2).站點(diǎn)FB和PE的晶質(zhì)Fe(III)含量顯著高于站點(diǎn)FC和ZG.各站點(diǎn)表層和亞表層沉積物無(wú)定形Fe(III)和晶質(zhì)Fe(III)均無(wú)顯著差異性(P>0.05),該結(jié)果說(shuō)明沉積深度對(duì)固相Fe(III)的影響并不顯著. FeS含量變化范圍為3.12~61.86μmol Fe/g(圖3e),FeS2含量范圍為3.62~49.97μmol Fe/g(圖3f).不同站點(diǎn)之間FeS和FeS2含量存在顯著差異(P<0.05,表2).FeS含量最大值出現(xiàn)在站點(diǎn)PE,而最小值出現(xiàn)在站點(diǎn)FB(P<0.001,表3),站點(diǎn)FC的FeS2含量顯著高于其他3個(gè)站點(diǎn)(P<0.05,表3).各站點(diǎn)亞表層沉積物的FeS和FeS2含量均顯著高于表層沉積物(P<0.05;表4),說(shuō)明亞表層沉積物中Fe的化學(xué)還原潛勢(shì)要高于表層沉積物. 鄒磊表示，良好的產(chǎn)品功效可以直觀地改變農(nóng)民原有的認(rèn)知，使其認(rèn)可并接受新型肥料產(chǎn)品，這也是目前液體肥等產(chǎn)品集中在種植周期短、見(jiàn)效快的蔬菜種植區(qū)推廣的原因所在。新型肥料的推廣更需要服務(wù)支持，傳統(tǒng)經(jīng)銷(xiāo)商技術(shù)的缺乏導(dǎo)致新型肥料產(chǎn)品在推廣中出現(xiàn)服務(wù)滯后或缺失，需要廠商打造出優(yōu)秀的技術(shù)服務(wù)團(tuán)隊(duì)，構(gòu)建起產(chǎn)品與服務(wù)的雙核驅(qū)動(dòng)。鄒磊表示，隨著液體肥等新型肥料市場(chǎng)的完善以及推廣成本的下降，產(chǎn)品價(jià)格會(huì)逐漸下降并趨于理性，將形成更加健全的市場(chǎng)機(jī)制。 圖3 福建省河口陸基養(yǎng)蝦塘不同形態(tài)鐵的含量 Fig.3 Iron species in the sediments of land-based shrimp ponds in the estuaries of Fujian province, southeast China 表3 河口陸基養(yǎng)蝦塘不同站點(diǎn)間隙水常見(jiàn)組分濃度和不同形態(tài)鐵的含量 Table 3 Concentrations of iron species and porewater constituents among four study sites of land-based shrimp ponds in the estuaries of Fujian province, southeast China 項(xiàng)目指標(biāo)站點(diǎn) FBFCPEZG 間隙水Cl?(mmol/L)*35.93±8.12c61.62±9.01c151.43±18.62b267.86±33.48a SO42?(mmol/L)*3.29±1.26c0.42±0.37c8.32±2.53b17.09±7.55a DOC(mmol/L)*4.01±1.98ab5.22±1.01a3.16±1.63b3.19±1.03b 溶解性CH4(μmol/L)*246.50±76.42a268.50±162.53a24.50±11.00b19.67±11.54b NH4+(mmol/L)0.81±0.5a0.62±0.22a0.93±0.41a0.85±0.54a NO3?(μmol/L)33.84±34.9a33.33±16.33a17.5±7.58a18.33±9.83a 不同形態(tài)鐵非硫Fe(II)(μmol Fe/g)*7.33±5.01b27.83±6.37a16.00±9.01ab28.17±10.21a 有機(jī)鐵(μmol Fe/g)*0.50±0.13a0.48±0.08a0.28±0.09b0.25±0.04b Fe(III)-HCl(μmol Fe/g)33.83±5.74a42.17±4.79a26.67±18.22a34.17±1.47a Fe(III)-CBD(μmol Fe/g)*94.67±13.56a45.50±4.89c78.67±4.13b33.50±3.62d FeS(μmol Fe/g)*10.92±9.15b22.6±24.81ab34.62±26.43a26.81±24.63ab FeS2(μmol Fe/g)*10.02±3.06b33.42±8.81a7.09±3.88b11.49±9.14b 注:* 表示該指標(biāo)不同站點(diǎn)之間存在顯著差異P<0.05,小寫(xiě)字母順序表示四個(gè)站點(diǎn)均值的大小. 表4 河口陸基養(yǎng)蝦塘表層和亞表層間隙水常見(jiàn)組分濃度和不同形態(tài)鐵的含量 Table 4 Porewater constituents and iron species between surface and subsurface layers of land-based shrimp ponds in the estuaries of Fujian province, southeast China 項(xiàng)目指標(biāo)深度 表層沉積物亞表層沉積物 間隙水Cl?(mmol/L)134.90±101.90123.52±90.96 SO42?(mmol/L)*8.90±9.405.66±4.79 DOC(mmol/L)4.00±1.953.79±1.28 溶解性CH4(μmol/L)*170.17±178.45109.42±106.24 NO3–(mmol/L)*16.08±11.8935.42±23.11 NH4+(μmol/L)*1.10±0.390.50±0.17 不同形態(tài)鐵非硫Fe(II)(μmol Fe/g)*16.50±11.1623.17±11.46 有機(jī)鐵(μmol Fe/g)*0.43±0.160.32±0.11 Fe(III)-HCl(μmol Fe/g)32.92±9.5435.50±12.18 Fe(III)-CBD(μmol Fe/g)60.67±22.8965.5±29.90 FeS(μmol Fe/g)*7.40±4.6740.07±21.61 §FeS2(μmol Fe/g)*16.50±11.1623.17±11.46 注:* 表示該指標(biāo)不同站點(diǎn)之間存在顯著差異P<0.05. 2.3 不同形態(tài)鐵和間隙水常見(jiàn)組分之間的關(guān)系 表5 不同形態(tài)鐵的含量和間隙水常見(jiàn)組分濃度之間的關(guān)系 Table 5 Relationship between contents of different iron species and concentrations of porewater constituents 指標(biāo)SO42?Cl?DOCNO3–NH4+CH4 非硫Fe(II)0.1940.3430.1050.009?0.301?0.195 有機(jī)鐵?0.558*?0.724**0.410*?0.0280.1920.317 無(wú)定形Fe(III)?0.247?0.1950.3490.017?0.2210.306 晶質(zhì)Fe(III)?0.384*?0.380?0.1040.214?0.0180.240 FeS?0.0770.197?0.0060.177?0.427*?0.372 FeS20.487*?0.3590.444*0216?0.492*0.358 注:**表示在0.01水平上顯著相關(guān),*表示在0.05水平上顯著相關(guān). 如表5所示,晶質(zhì)Fe(III)含量與間隙水SO42?濃度呈中度負(fù)相關(guān)關(guān)系,FeS2含量和間隙水SO42?濃度呈中度正相關(guān)關(guān)系.有機(jī)鐵與間隙水Cl?和SO42?濃度分別呈強(qiáng)和中度負(fù)相關(guān)關(guān)系,與DOC含量呈中度正相關(guān)關(guān)系.FeS2含量與間隙水DOC濃度存在中度正相關(guān)關(guān)系,FeS和FeS2含量與間隙水NH4+濃度呈現(xiàn)中度負(fù)相關(guān)關(guān)系. 3 討論 3.1 養(yǎng)蝦塘與其他生態(tài)系統(tǒng)鐵的形態(tài)和含量的比較 當(dāng)河口潮汐沼澤濕地轉(zhuǎn)換為養(yǎng)蝦塘后,淹水狀態(tài)由潮汐周期性浸沒(méi)轉(zhuǎn)變?yōu)殚L(zhǎng)期淹水,有機(jī)質(zhì)輸入方式也從沼澤植物輸入,轉(zhuǎn)化為餌料、魚(yú)蝦糞便和殘?bào)w等高氮有機(jī)質(zhì)輸入[29-30].大部分時(shí)間養(yǎng)蝦塘是一個(gè)相對(duì)獨(dú)立的生態(tài)系統(tǒng),與外界最大的物質(zhì)和能量交換為養(yǎng)蝦塘水定期(通常為每月大潮時(shí))與外界河水進(jìn)行置換.在本研究中,發(fā)現(xiàn)間隙水中Fe2+低于檢測(cè)限.因此,大部分“活性鐵”的遷移和轉(zhuǎn)化存在于養(yǎng)蝦塘的固相形態(tài)鐵之間.福建省河口陸基養(yǎng)蝦塘“活性鐵”主要由固相Fe(III)、鐵硫化物、非硫Fe(II)組成,有機(jī)鐵的含量相對(duì)較少(圖4).在表層和亞表層沉積物中,Fe(III)均為所有活性鐵中含量最高的組分,約占(63%±16%);其次為鐵的硫化物(FeS和FeS2),約占(23%±12%);最后為非硫Fe(II),約占(13%±8%);有機(jī)鐵的含量最低,不到1%. 圖4 河口陸基養(yǎng)蝦塘表層和亞表層沉積物中不同形態(tài)鐵的百分比堆積 Fig.4 Accumulation percent bar charts of different iron species in the sediments of wetland-based shrimp ponds in the estuaries of Fujian province, southeast China 養(yǎng)蝦塘沉積物中無(wú)定形Fe(III)和晶質(zhì)Fe(III)含量與近海以及淡水湖泊沉積物相近(表6),但與河口潮汐淡水以及半咸水沼澤濕地生態(tài)系統(tǒng)相比,養(yǎng)蝦塘沉積物中無(wú)定形和晶質(zhì)Fe(III)含量相對(duì)偏低,尤其是無(wú)定形Fe(III)的含量(表6).以閩江河口潮汐沼澤濕地為例,淡水沼澤濕地晶質(zhì)Fe(III)/無(wú)定形Fe(III)的比值約為1.05,半咸水沼澤濕地晶質(zhì)Fe(III)/無(wú)定形Fe(III)的比值約為1.56,但河口陸基養(yǎng)蝦塘晶質(zhì)Fe(III)/無(wú)定形Fe(III)的比值約為1.85(表6).河口潮汐沼澤濕地沉積物富含無(wú)定形Fe(III),大部分無(wú)定形Fe(III)礦物的形成主要是由于植物沼澤植物根系泌氧、底棲動(dòng)物擾動(dòng)或者潮汐作用帶來(lái)的O2氧化沉積物中的Fe(II)[31].這些無(wú)定形Fe(III)沉積時(shí)間短,還未來(lái)得及形成完整的晶質(zhì)結(jié)構(gòu),具有比表面積大、生物可利用性好以及化學(xué)性質(zhì)比較活潑等特征 [25,32].以上結(jié)果表明,當(dāng)河口潮汐濕地轉(zhuǎn)換為河口陸基養(yǎng)蝦塘后,無(wú)定形Fe(III)被大量消耗. 表6 福建省河口陸基養(yǎng)蝦塘沉積物鐵的形態(tài)和含量與其他生態(tài)系統(tǒng)的比較 Table 6 Comparison of iron speciation and abundance in sediments of land-based shrimp ponds in estuaries of Fujian, southeast China with other ecosystems 研究區(qū)生態(tài)系統(tǒng)采樣深度(cm)無(wú)定形Fe(III)(μmol/g)晶質(zhì)Fe(III)(μmol/g)FeS(μmol/g)FeS2(μmol/g)參考文獻(xiàn) 中國(guó)東海大陸架0~432.231.9~131NA5.88[39] 美國(guó)特拉華州河口濕地0~2.5279.6NA31.7315.20[40] 德國(guó)易北河口河口濕地0~564.14±0.18NA1.0723.14±0.06[41] 閩江河口河口濕地0~30104.8109.41.1914.04[42] 閩江河口河口濕地0~12048±2475±3239±657±25[15] 巴西塞阿臘州河口濕地0~30NANA43.755.5~17.7[43] 中國(guó)膠州灣海灣0~412.0±7.2118.7±21.40.924.74±3.6[44] 中國(guó)黃海海洋0~10NANA0.01~25.020.61~113.1[45] 丹麥海岸海岸0~2NANA0.513.25[46] 美國(guó)明尼蘇達(dá)州湖泊0~15NANA<0.1~9.8NA[47] 中國(guó)太湖東太湖湖泊1~520NA2117[48] 越南湄公河三角洲養(yǎng)殖塘0~40NANANA32~280[13] 福建省河口養(yǎng)蝦塘0~1534.21±9.3163.17±26.4023.74±22.6315.50±12.43本研究 注:NA代表未檢測(cè). 與固相Fe(III)相比,鐵的二價(jià)化合物(包括非硫Fe(II)化合物與鐵的硫化物)顯著高于其他河口、沿海與濕地沉積物(表6).鐵的還原反應(yīng)耦合沉積物有機(jī)碳厭氧礦化和鐵的硫化物生成,其中非硫Fe(II)是活性Fe(III)在鐵異化還原微生物作用下的還原產(chǎn)物 [33].在本研究中,無(wú)定形Fe(III)的含量與非硫Fe(II)的含量呈正比(r=0.497,P<0.01),說(shuō)明當(dāng)土地利用類(lèi)型從河口潮汐沼澤濕地轉(zhuǎn)化為養(yǎng)蝦塘底泥之后,非硫Fe(II)的生成與無(wú)定形Fe(III)的消耗相關(guān).類(lèi)似結(jié)果在越南湄公河三角洲也發(fā)現(xiàn)當(dāng)紅樹(shù)林轉(zhuǎn)化為養(yǎng)殖塘后,鐵異化還原的潛勢(shì)增加,促進(jìn)無(wú)定形Fe(III)的分解[13].硫酸鹽異化還原也是水生生態(tài)系統(tǒng)中常見(jiàn)的厭氧有機(jī)質(zhì)礦化途徑之一,沉積物中無(wú)定形Fe(III)還將被硫酸鹽還原的產(chǎn)物H2S還原而生成FeS.FeS是活性Fe(III)被H2S還原后得到的中間產(chǎn)物[27].在較豐富的H2S存在的前提下,FeS將與H2S反應(yīng)生成更加穩(wěn)定的FeS2[34].FeS2是黃鐵礦的主要成分,在我國(guó)近海沉積物和其他河口鹽沼濕地的土壤均發(fā)現(xiàn)大量FeS2(表6).在本研究中,發(fā)現(xiàn)養(yǎng)蝦塘沉積物和間隙水中游離狀態(tài)的H2S均低于檢測(cè)限.游離態(tài)的H2S毒性強(qiáng),可刺激和腐蝕養(yǎng)殖魚(yú)蝦的鰓組織,造成呼吸困難[35].HS–還能與魚(yú)蝦的血紅蛋白結(jié)合,進(jìn)而產(chǎn)生硫血紅蛋白,降低機(jī)體的攜氧能力同時(shí)抑制某些酶化反應(yīng)過(guò)程[36].游離態(tài)的H2S還能影響大多數(shù)需氧微生物和藻類(lèi)的正常新陳代謝,弱化水體自?xún)裟芰?因此,H2S被養(yǎng)蝦塘底泥中的Fe(III)捕獲后,生成的鐵的硫化物無(wú)毒且不被生命體利用,可暫時(shí)緩沖土壤利用類(lèi)型發(fā)生轉(zhuǎn)變后H2S累積對(duì)養(yǎng)蝦塘產(chǎn)生的危害[37],對(duì)水產(chǎn)養(yǎng)殖業(yè)具有重要的環(huán)境意義[38].同時(shí),發(fā)現(xiàn)養(yǎng)殖塘沉積物中鐵的硫化物含量要大于淡水沼澤濕地土壤,但是要低于河口半咸水沼澤濕地,這可能是由于河口養(yǎng)蝦塘站點(diǎn)PE和ZG中間隙水SO42?濃度高于河口淡水沼澤濕地,但是低于河口半咸水沼澤濕地,后者受海水咸潮影響能夠源源不斷地補(bǔ)充電子受體SO42?. 3.2 不同站點(diǎn)間養(yǎng)蝦塘沉積物鐵的含量和形態(tài)分析 高鹽站點(diǎn)PE和ZG與低鹽站點(diǎn)FB和FC之間,晶質(zhì)Fe(III)、非硫Fe(II)、有機(jī)鐵、FeS和FeS2有顯著差異.而表層和亞表層的非硫Fe(II)、有機(jī)鐵、FeS和FeS2有顯著差異.不同站點(diǎn)和不同深度之間無(wú)定形Fe(III)、晶質(zhì)Fe(III)、非硫Fe(II)、有機(jī)鐵、FeS和FeS2含量的概念示意圖如圖5所示. 鹽度升高會(huì)增加鐵異化還原菌的鹽脅迫,除芽孢桿菌屬(Bacillus spp.)以外,絕大部分的鐵異化還原微生物不能適應(yīng)中、高鹽環(huán)境[44].由于可溶的SO42–比起固相Fe(III)更易被微生物利用[49],鹽度增加還會(huì)提高硫酸鹽電子受體的含量,從而抑制鐵異化還原速率[50].在本研究中,晶質(zhì)Fe(III)含量與間隙水SO42–濃度呈現(xiàn)負(fù)相關(guān)關(guān)系(表5),說(shuō)明當(dāng)上覆水中的SO42–濃度較高時(shí),將減少河口陸基養(yǎng)蝦塘沉積物中晶質(zhì)Fe(III)含量.鹽度升高也同時(shí)促進(jìn)鐵硫化物的沉積,研究發(fā)現(xiàn)FeS2的含量與間隙水SO42–濃度呈正相關(guān)關(guān)系(表5).此外,FeS2的含量與間隙水DOC濃度呈現(xiàn)正相關(guān)關(guān)系(表5),說(shuō)明養(yǎng)蝦塘底泥中FeS2沉積過(guò)程中伴隨著有機(jī)質(zhì)的礦化.在鹽度較低的養(yǎng)蝦塘中(站點(diǎn)FB和FC),FeS含量相對(duì)于其他2個(gè)站點(diǎn)PE和ZG較低,但FeS2的情況剛好完全相反,這可能是因?yàn)榛钚訤e(III)的含量影響FeS2和FeS含量之間的平衡[36,51],站點(diǎn)FB和FC的高Fe(III)含量限制了FeS向FeS2的轉(zhuǎn)化. 研發(fā)“Lumen”表盤(pán)時(shí)的技術(shù)難題，在于以光能為隱藏于表盤(pán)中的夜光物料“充能”。朗格專(zhuān)家的解決方案，便是在藍(lán)寶石水晶玻璃表盤(pán)，覆上有半透明物料，容許紫外線穿過(guò)。可見(jiàn)光的光波傳輸，因高對(duì)比度且清晰顯眼的表盤(pán)而減弱。相反，紫外線光波則可穿過(guò)。Zeitwerk “Luminous”、Grand Lange 1 “Lumen”、 Grand Lange 1 Moon Phase的表盤(pán)因而可在黑暗中發(fā)光數(shù)小時(shí)。 在河口養(yǎng)蝦塘土壤中,除了固相Fe(III),沉積物中還有有機(jī)鐵[52].這些有機(jī)鐵是Fe(III)異化還原的初級(jí)產(chǎn)物[53].在有機(jī)質(zhì)含量較高的地區(qū),Fe(III)在溶解或沉積時(shí)與間隙水中有機(jī)質(zhì)絡(luò)合產(chǎn)生膠體狀的有機(jī)鐵[54-55].因此,在本研究中,有機(jī)鐵的含量與間隙水DOC呈正相關(guān)關(guān)系(表5),說(shuō)明有機(jī)鐵的含量受可溶有機(jī)質(zhì)含量影響.另一方面,有機(jī)鐵含量與間隙水Cl–和SO42–呈顯著負(fù)相關(guān)關(guān)系(表5).在美國(guó)東南喬治亞州沿海平原沼澤Satilla河的調(diào)查研究,也發(fā)現(xiàn)有機(jī)鐵的含量與鹽分呈現(xiàn)負(fù)相關(guān)關(guān)系[56],這主要是因?yàn)樵诟啕}環(huán)境下,硫酸鹽會(huì)抑制Fe(III)還原溶解為有機(jī)鐵絡(luò)合物[52].Fe(III)與有機(jī)絡(luò)合物結(jié)合,進(jìn)一步證明在河口養(yǎng)殖塘沉積物中存在Fe-C-O耦合的生物地球化學(xué)循環(huán)[57]. 圖5 河口陸基養(yǎng)蝦塘鐵的含量和形態(tài)分布示意 Fig.5 Conceptual map of different forms of different iron species in the sediments of land-based shrimp ponds in the estuaries of Fujian province, southeast China 圖中化合物字體大小表征含量的高低 3.3 養(yǎng)蝦塘表層和亞表層沉積物鐵的含量和形態(tài)差異 由于高密度養(yǎng)殖,大量餌料和魚(yú)蝦糞便殘留在養(yǎng)蝦塘底泥,使得養(yǎng)蝦塘底泥表層呈現(xiàn)黑色,次表層沉積物為褐色,且含砂量偏高.亞表層沉積物中鐵的硫化物FeS和FeS2的含量均高于表層沉積物,亞表層沉積物中FeS和FeS2的含量分別為表層沉積物的5.5和1.4倍(表4),該結(jié)果說(shuō)明沉積深度對(duì)鐵的硫化物沉積造成的影響較大.高含量的FeS和FeS2同時(shí)也是表層塘泥的致黑物質(zhì)[34].FeS2的含量越高,表明硫酸鹽異化還原對(duì)鐵異化還原的抑制效果更強(qiáng).在水域生態(tài)系統(tǒng)中,鐵異化還原速率和間隙水NH4+含量的關(guān)系密切,鐵異化還原可間接促進(jìn)間隙水NH4+含量增加[58].養(yǎng)殖塘沉積物中間隙水NH4+的富集會(huì)造成上覆池塘水體的二次污染,導(dǎo)致水體中藻類(lèi)過(guò)量繁殖,這些藻類(lèi)在死亡后分解能夠快速消耗大量氧氣,導(dǎo)致季節(jié)性水體出現(xiàn)黑臭現(xiàn)象[59].本研究中,鐵硫化物FeS和FeS2的含量與間隙水NH4+的含量呈現(xiàn)顯著負(fù)相關(guān)關(guān)系(表5),這可能是由于硝酸鹽異化還原微生物無(wú)法在H2S濃度較高的情況下生存[60].以上研究結(jié)果表明,鐵硫化物的生成抑制間隙水中硝態(tài)氮向銨態(tài)氮的轉(zhuǎn)化,減少了沉積物中NH4+向上覆水體的擴(kuò)散,一定程度抑制內(nèi)源氮污染的發(fā)生[61]. 當(dāng)前的主要研究是在將地基視為彈性地基的基礎(chǔ)上開(kāi)展的，研究地基與基礎(chǔ)板的彎曲接觸作用。JIA等[1]采用Hankel逆變換分析了Winkler地基上的水泥混凝土路面的位移和應(yīng)力。Yas等[2]基于三維彈性理論研究了彈性地基上的矩形纖維增強(qiáng)板的振動(dòng)特性。王春玲等[3]、何芳社等[4]分別采用傅里葉變換和Fourier-Bessel級(jí)數(shù)研究了層狀彈性地基及橫觀各向同性彈性地基與板的相互作用問(wèn)題。Akavci[5]分析了彈性地基上簡(jiǎn)支功能梯度夾層板的自由振動(dòng)和失穩(wěn)特性。 4 結(jié)論 4.1 陸基養(yǎng)蝦塘活性鐵由固相Fe(III)、鐵的硫化物、非硫Fe(II)以及有機(jī)鐵組成,含量大小順序?yàn)?固相Fe(III)>鐵的硫化物>非硫Fe(II)>有機(jī)鐵. 4.2 間隙水SO42–和Cl–可能是影響?zhàn)B蝦塘不同站點(diǎn)間Fe的形態(tài)和分布的環(huán)境影響因子之一.鹽度較高的養(yǎng)蝦塘,鐵的硫化物含量較高,有機(jī)鐵含量和晶質(zhì)Fe(III)含量較少.同時(shí)有機(jī)鐵和FeS2還受到間隙水DOC濃度的影響,說(shuō)明硫酸鹽異化還原及鐵的化學(xué)還原與有機(jī)碳礦化代謝密切相關(guān). 4.3 養(yǎng)蝦塘亞表層沉積物中鐵的硫化物(FeS和FeS2)均高于表層沉積物,鐵的硫化物生成一定程度會(huì)降低養(yǎng)蝦塘沉積物中營(yíng)養(yǎng)鹽污染的潛在風(fēng)險(xiǎn). 參考文獻(xiàn)： [1] Naylor R L, Goldburg R J, Primavera J H, et al. 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ZHU Ai-ju1,2, TONG Chuan1,2,3,4, LUO Min4,5*, HUANG Jia-fang1,2,3,4, TAN Ji1,2, HU Qi-kai5, LI Jing1,2 (1.Key Laboratory of Humid Subtropical Eco-geographical Process, Ministry of Education, Fujian Normal University, Fuzhou 350007, China；2.School of Geographical Sciences, Fujian Normal University, Fuzhou 350007, China；3.Institute of Geographical Research, Fuzhou University, Fuzhou 350116, China；4.Wetland Ecosystem Research Station of Minjiang Estuary, State Forestry and Grassland Administration, Fuzhou 350007, China；5.School of Environment and Resource, Fuzhou University, Fuzhou 350116, China). China Environmental Science, 2019,39(11)：4785~4795 Abstract：To research the mechanisms of Fe transport and cycling in wetland-based aquaculture ponds. In this study, the abundance and speciation of reactive Fe in sediments of four wetland-based shrimp ponds in three estuaries of Fujian Province, southeast China, were investigated during the intensive culture period. Significant differences of crystalline Fe(III), non-sulfidic Fe(II), organic Fe-complex, and Fe sulfides were observed among the four shrimp ponds. Porewater Cl- and SO42- were key factors affecting the abundance and speciation of Fe among different shrimp ponds. Along with increasing salinity, the contents of Fe sulfides increased, whereas those of organic Fe-complexes and crystalline Fe(III) decreased. The contents of reactive Fe were in the following order: solid-phase Fe (III) > Fe sulfides > non-sulfidic Fe (II) > organic Fe complexes. The contents of FeS and FeS2 were higher in the subsurface sediments of the shrimp ponds than those in the surface sediments.However,the contents of organic Fe complexes and concentrations of porewater SO42- and NH4+ were higher in the surface sediments than those in the subsurface sediments. The precipitation of Fe sulfides could partially reduce the potential risk of nutrient contamination in sediments of wetland-based shrimp ponds. Key words：iron species；amorphous Fe(III)；crystalline Fe(III)；iron sulfides；non-sulfidic Fe(II)；organic carbon metabolism；wetland-based shrimp ponds 中圖分類(lèi)號(hào)：X131 文獻(xiàn)標(biāo)識(shí)碼：A 文章編號(hào)：1000-6923(2019)11-4785-11 作者簡(jiǎn)介：朱愛(ài)菊(1995-),女,安徽六安人,福建師范大學(xué)碩士研究生,主要研究方向?yàn)闈竦厣锏厍蚧瘜W(xué)循環(huán).發(fā)表論文1篇. 收稿日期：2019-04-29 基金項(xiàng)目：國(guó)家自然科學(xué)基金資助項(xiàng)目(41671088);濕潤(rùn)亞熱帶生態(tài)-地理過(guò)程教育部重點(diǎn)實(shí)驗(yàn)室基金資助項(xiàng)目(2017KFJJ02);中國(guó)科學(xué)院海岸帶環(huán)境過(guò)程與生態(tài)修復(fù)重點(diǎn)實(shí)驗(yàn)室開(kāi)放基金資助項(xiàng)目(2018KFJJ10) * 責(zé)任作者, 副教授, luomin@fzu.edu.cn