Contribution of ferric iron to light absorption by chromophoric dissolved organic matter

Limnology and Oceanography - Tập 58 Số 2 - Trang 653-662 - 2013
Yihua Xiao1, Timo Sara-Aho2, Helinä Hartikainen3, Anssi V. Vähätalo4
1Department of Environmental Sciences, University of Helsinki, Helsinki, Finland
2Finnish Environment Institute, Environmental Testing and Measurement Laboratory, Helsinki, Finland
3Department of Food and Environmental Sciences, University of Helsinki, Helsinki, Finland
4Aronia Research and Development Institute, Novia University of Applied Sciences and Åbo Akademi University, Ekenäs, Finland

Tóm tắt

This study experimentally determined the contribution of ferric iron (Fe(III)) associated with humic substances (HS) to light absorption by chromophoric dissolved organic matter (CDOM). The associations between Fe(III) and HS (HS‐Fe) were generated by mixing HS standards with Fe(III) in acidic conditions and adjusting pH to 8. HS‐associated Fe was separated from total Fe by filtering (0.7 µm and 0.2 µm filters) and by removing the free Fe ions by cation exchange chromatography. The maximum Fe‐binding capacities (at pH 8) of Suwannee River humic acid, Suwannee River fulvic acid, and Pony Lake (Antarctica) fulvic acid were 13.0, 13.5, and 7.64 µmol Fe [mg C]−1, respectively, indicating that wetland‐derived HS had a higher Fe‐binding capacity than plankton‐derived HS. HS‐associated Fe increased the absorption coefficient of CDOM by up to several fold in the visible range of the spectrum and reduced the spectral slope coefficient of CDOM. The Fe‐induced increase in light absorption was spectrally similar among different HS examined. The Fe‐specific absorption coefficient spectrum for HS‐associated Fe (aλ,Fe*) was calculated from the Fe‐induced increase in light absorption by normalizing it with the concentration of Fe in the HS pool. The aλ,Fe* was adopted in estimation of the contribution of HS‐associated Fe to light absorption by CDOM in 13 circum‐neutral natural waters collected from a spring, 10 major rivers, a lake, and a coastal area. HS‐associated Fe was calculated to be responsible for from 0.6% (Mississippi River) to 56.4% (Löytynlähde spring) of light absorption by CDOM at a wavelength of 410 nm. This study shows that HS‐associated Fe can be an important component in light absorption by CDOM and also influence the spectral slope coefficient of CDOM.

Từ khóa


Tài liệu tham khảo

Thông tin
Thông tin xuất bản

Limnology and Oceanography

Tập 58 Số 2

653-662

Thông tin tác giả