Photooxidation and Its Effects on the Carboxyl Content of Dissolved Organic Matter in Two Coastal Rivers in the Southeastern United States

Huixiang Xie; Oliver C.Zafiriou; Wei-Jun CaiRichard G.ZeppYongchen Wang

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Photooxidation and Its Effects on the Carboxyl Content of Dissolved Organic Matter in Two Coastal Rivers in the Southeastern United States

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Photodecarboxylation (often stoichiornetrically expressed as RCOOH + 1/2O_2 - ROM + CO_2)has long been postulated to be principally responsible for generating C0_2 from photooxidation of dissolved organic matter (DOM).In this study,the quantitative relationships were investigated among O_2 consumption,C0_2 production,and variation of carboxyl content resulting from photooxidation of DOM in natural water samples obtained from the freshwater reaches of the Satilla River and Altamaha River in the southeastern United States.In terms of loss of dissolved organic carbon (DOC),loss of optical absorbance,and production of CO_2,the rate of photooxidation of DOM was increased in the presence of Fe redox chemistry and with increasing O_2 content.The ratio of photochemical O_2 consumption to CO_2 photoproduction ranged from -0.8 to 2.5,depending on the O_2 content,the extent of involvement of Fe,and probably the initial oxidation state of DOM as well.The absolute concentration of carboxyl groups (-COOH)on DOM only slightly decreased or increased over the course of irradiation,possibly depending on the stages of photooxidation,while the DOC-normalized carboxyl content substantially increased in the presence of Fe redox chemistry and sufficient O_2.Both the initial -COOH and the apparent loss of this quantity over the course of irradiation was too small to account for the much larger production of C0_2,suggesting that carboxyl groups were photochemically regenerated or that the major production pathway for C0_2 did not involve photodecarboxylation.The results from this study can be chemically rationalized by a reaction scheme of (a)photodecarboxylation/ regeneration of carboxyl:C_xH_yO_z(COOH)_m + aO_2 + (metals,hv)-> bC0_2 + cH_20_2 + C_(x-b)H_1/O_z'(COOH)__(m-b)r(COOH)_b or of (b)nondecarboxylation photooxidation:+ aO_2 + (metals,hv)-> bC0_2 + cH_2O2 + C_(x-b)H_1/0_Z'(COOH)_m.

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《Environmental Science & Technology: ES&T》 |2004年第15期|4113-4119|共7页
作者
Huixiang Xie; Oliver C.Zafiriou; Wei-Jun CaiRichard G.ZeppYongchen Wang;
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Institut des Sciences de la Mer de Rimouski,Universite du Quebec a Rimouski,Quebec,Canada G5L 3A1,Department of Marine Chemistry and Geochemistry,Woods Hole Oceanographic Institution,Woods Hole,Massachusetts 02543,Department of Marine Sciences,Univer;

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正文语种英语
中图分类环境化学;
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Photooxidation and Its Effects on the Carboxyl Content of Dissolved Organic Matter in Two Coastal Rivers in the Southeastern United States

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