Importance of allochthonous and autochthonous dissolved organic matter in Fe(II) oxidation: A case study in Shizugawa Bay watershed, Japan

Ying Ping Lee; Manabu Fujii; Tetsuro Kikuchi; Masafumi Natsuike; Hiroaki Ito; Toru Watanabe; Chihiro Yoshimura

doi:10.1016/j.chemosphere.2017.04.008

Importance of allochthonous and autochthonous dissolved organic matter in Fe(II) oxidation: A case study in Shizugawa Bay watershed, Japan

Chemosphere. 2017 Aug:180:221-228. doi: 10.1016/j.chemosphere.2017.04.008. Epub 2017 Apr 5.

Authors

Ying Ping Lee¹, Manabu Fujii², Tetsuro Kikuchi³, Masafumi Natsuike¹, Hiroaki Ito⁴, Toru Watanabe⁵, Chihiro Yoshimura¹

Affiliations

¹ Department of Civil and Environmental Engineering, School of Environment and Society, Tokyo Institute of Technology, 2-12-1-M1-4, Ookayama, Meguro-ku, Tokyo, 152-8552, Japan.
² Department of Civil and Environmental Engineering, School of Environment and Society, Tokyo Institute of Technology, 2-12-1-M1-4, Ookayama, Meguro-ku, Tokyo, 152-8552, Japan. Electronic address: fujii.m.ah@m.titech.ac.jp.
³ Department of Civil and Environmental Engineering, School of Environment and Society, Tokyo Institute of Technology, 2-12-1-M1-4, Ookayama, Meguro-ku, Tokyo, 152-8552, Japan; Ibaraki Kasumigaura Environmental Science Center, 1853 Okijyuku-machi, Tsuchiura, Ibaraki, 300-0023, Japan.
⁴ Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Chuou, Kumamoto, 860-8555, Japan.
⁵ Faculty of Agriculture, Yamagata University, 1-23 Wakaba-machi, Tsuruoka, Yamagata, 997-8555, Japan.

PMID: 28410502
DOI: 10.1016/j.chemosphere.2017.04.008

Abstract

Ferrous iron (Fe[II]) oxidation by dissolved oxygen was investigated in the Shizugawa Bay watershed with particular attention given to the effect of dissolved organic matter (DOM) properties on Fe(II) oxidation. To cover a wide spectrum of DOM composition, water samples were collected from various water sources including freshwater (e.g., river water and wastewater effluent) and coastal seawater. Measurement of nanomolar Fe(II) oxidation by using luminol chemiluminescence under dark, air-saturated conditions at 25 °C indicated that spatio-temporal variation of the second-order rate constant (6.7-74.5 M^-1 s^-1) was partially explained by the variation of the sample pH (7.5-8.6). However, at comparable pH values, the oxidation rates for freshwater were generally greater than those for coastal seawater. The substantial decline in oxidation rate constant after the removal of humic-type (allochthonous) DOM suggested that this hydrophobic DOM is a key factor that accelerates the Fe(II) oxidation in the freshwater samples. Observed lower oxidation rates for coastal seawater compared with freshwater and organic ligand-free seawater were likely associated with microbially derived autochthonous DOM, and the variation of Fe(II) oxidation at a fixed pH was best described by fluorescence index that represents the proportion of autochthonous and allochthonous DOM in natural waters. Consistently, Fe(II) oxidation was found to be slower in the presence of cellular exudates from phytoplankton. The present study highlighted the significant effect of DOM composition on the Fe(II) oxidation in inland and coastal waters.

Keywords: Allochthonous and autochthonous DOM; Coastal seawater; Dissolved organic matter; Fe(II) oxidation; Fluorescence index (FI); Freshwater.

MeSH terms

Bays / chemistry
Environmental Monitoring*
Ferrous Compounds / analysis*
Fresh Water / chemistry
Iron / chemistry
Japan
Oxidation-Reduction
Seawater
Water / chemistry
Water Pollutants / analysis*

Substances

Ferrous Compounds
Water Pollutants
Water
Iron