Fluorescence peak integration ratio IC:IT as a new potential indicator tracing the compositional changes in chromophoric dissolved organic matter

Yongqiang Zhou; Kun Shi; Yunlin Zhang; Erik Jeppesen; Xiaohan Liu; Qichao Zhou; Huawu Wu; Xiangming Tang; Guangwei Zhu

doi:10.1016/j.scitotenv.2016.08.196

Fluorescence peak integration ratio I_C:I_T as a new potential indicator tracing the compositional changes in chromophoric dissolved organic matter

Sci Total Environ. 2017 Jan 1:574:1588-1598. doi: 10.1016/j.scitotenv.2016.08.196. Epub 2016 Sep 6.

Authors

Yongqiang Zhou¹, Kun Shi², Yunlin Zhang³, Erik Jeppesen⁴, Xiaohan Liu², Qichao Zhou⁵, Huawu Wu², Xiangming Tang², Guangwei Zhu²

Affiliations

¹ Taihu Laboratory for Lake Ecosystem Research, State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100049, China; Sino-Danish Centre for Education and Research, Beijing 100190, China.
² Taihu Laboratory for Lake Ecosystem Research, State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China.
³ Taihu Laboratory for Lake Ecosystem Research, State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China. Electronic address: ylzhang@niglas.ac.cn.
⁴ Sino-Danish Centre for Education and Research, Beijing 100190, China; Department of Bioscience and Arctic Research Centre, Aarhus University, Vejlsøvej 25, DK-8600 Silkeborg, Denmark.
⁵ Taihu Laboratory for Lake Ecosystem Research, State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; Yunnan Key Laboratory of Pollution Process and Management of Plateau Lake-Watershed, Yunnan Institute of Environmental Science, Kunming 650034, China.

PMID: 27613668
DOI: 10.1016/j.scitotenv.2016.08.196

Abstract

The present study demonstrates that the ratio of fluorescence integration of peak C to peak T (I_C:I_T) can be used as an indicator tracing the compositional dynamics of chromophoric dissolved organic matter (CDOM). CDOM absorption and fluorescence spectroscopy and stable isotope δ¹³C were determined on a seasonal basis in seventeen Chinese inland waters as well as in a series of mixing and photodegradation experiments in the lab. A strong positive linear correlation was recorded between I_C:I_T and the ratio of terrestrial humic-like C1 to tryptophan-like C4 (C1:C4) derived by parallel factor analysis. The r² for the linear fitting between I_C:I_T and C1:C4 (r²=0.80) was notably higher than between C1:C4 and other indices tested, including the ratio of CDOM absorption at 250nm to 365nm, i.e. a(250):a(365) (r²=0.09), spectral slope (S_275-295) (r²=0.26), spectral slope ratio (S_R) (r²=0.31), the humification index (HIX) (r²=0.47), the recent autochthonous biological contribution index (BIX) (r²=0.27), and a fluorescence index (FI₃₇₀) (r²=0.07). I_C:I_T exhibited larger variability than the remaining six indices and a closer correlation with stable isotope δ¹³C than that observed for a(250):a(365), S_275-295, S_R, FI₃₇₀, and BIX during field campaigns. Confirming our field observations, significant correlations were recorded between I_C:I_T and the remaining six indices, and I_C:I_T also demonstrated notably larger variability than the six other indices during our wastewater addition experiment. Compared with HIX, eutrophic water addition and photobleaching substantially decreased I_C:I_T but had no pronounced effect on a(250):a(365), S_275-297, S_R, FI₃₇₀, and BIX, further suggesting that I_C:I_T is the most efficient indicator of the CDOM compositional dynamics.

Keywords: Chromophoric dissolved organic matter (CDOM); Fluorescence peak integration; Parallel factor (PARAFAC) analysis; Photobleaching.