Ammonium Photoproduction from Aquatic Humic and Colloidal Matter |
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| Authors: | Weiwei Wang Matthew A Tarr Thomas S Bianchi Erika Engelhaupt |
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| Institution: | (1) Department of Chemistry, University of New Orleans, New Orleans, LA, 70148;(2) Institute for Earth and Ecosystem Sciences, Department of EEO Biology, Tulane University, New Orleans, LA, 70118-5698 |
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| Abstract: | It has recently been shown thatnitrogen contained in humic substances can be releasedas low molecular weight species through photochemicalprocesses or reactions. Nitrogen released in thismanner may then become available for biological useand chemical reactivity. This report providesadditional kinetic data for nitrogen photochemistry oforganic matter in natural waters from Louisiana andfor Suwannee River humic and fulvic acids. Naturalwater samples were fractionated into colloidal(>0.2  m, <1000 Dalton) and dissolved (>1000Dalton) fractions and the kinetics of these fractionsas well as 0.2 m filtered water samples weremeasured. For irradiations of less than 10 hours ofsimulated noon-time sun, samples showed linearproduction of ammonium and first-order fading at350 nm. Ammonium photoproduction was enhanced asmuch as three-fold by lowering pH, but linear kineticswere maintained. Light-dark cycling showed continuedrelease of ammonium immediately after irradiation,followed by uptake at longer post irradiation times.A two step mechanism was proposed to explain theobserved kinetics. Calculated net daytime release ofammonium from natural surface waters ranged from 0.33to 1.9 M h-1 in the samples studied,corresponding to a photic zone conversion rate of9–20% of the total organic nitrogen per day intoammonium. |
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| Keywords: | ammonium colloids dissolved organic nitrogen humics nitrogen cycling photochemistry |
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