Characteristics and sources analysis of riverine chromophoric dissolved organic matter in Liaohe River, China Tiantian Shao, Kaishan Song, Pierre-Andre Jacinthe, Jia Du, Ying Zhao, Zhi Ding, Ying Guan and Zhang Bai ABSTRACT Chromophoric dissolved organic matter (CDOM) in riverine systems can be affected by environmental conditions and land-use, and thus could provide important information regarding human activities in surrounding landscapes. The optical properties of water samples collected at 42 locations across the Liaohe River (LHR, China) watershed were examined using UV-Vis and fluorescence spectroscopy to determine CDOM characteristics, composition and sources. Total nitrogen (TN) and total phosphorus (TP) concentrations at all sampling sites exceeded the GB3838- 2002 (national quality standards for surface waters, China) standard for Class V waters of 2.0 mg N/L and 0.4 mg P/L respectively, while trophic state index (TSI M ) indicated that all the sites investigated were mesotrophic, 64% of which were eutrophic at the same time. Redundancy analysis showed that total suspended matter (TSM), dissolved organic carbon (DOC), and turbidity had a strong correlation with CDOM, while the other parameters (Chl a, TN, TP and TSI M ) exhibited weak correlations with CDOM absorption. High spectral slope values and low SUVA254 (the specific UV absorption) values indicated that CDOM in the LHR was primarily comprised of low molecular weight organic substances. Analysis of excitation-emission matrices contour plots showed that CDOM in water samples collected from upstream locations exhibited fulvic-acid-like characteristics whereas protein- like substances were most likely predominant in samples collected in estuarine areas and downstream from large cities. These patterns were interpreted as indicative of water pollution from urban and industrial activities in several downstream sections of the LHR watershed. Tiantian Shao Kaishan Song (corresponding author) Jia Du Ying Zhao Zhi Ding Ying Guan Zhang Bai Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, No. 85 Minglun Road, Shunhe Hui District, Kaifeng, Changchun 475001, China E-mail: songks1106@163.com Tiantian Shao Key Research Institute of Yellow River Civilization and Sustainable Development & Collaborative Innovation Center on Yellow River Civilization of Henan Province, Henan University, Kaifeng, Henan, China Pierre-Andre Jacinthe Department of Earth Sciences, Indiana University-Purdue University, Indianapolis, IN, USA Key words | CDOM, DOC, fluorescence intensity, spectral slope, water pollution INTRODUCTION Dissolved organic matter (DOM), which includes humic substances, carbohydrates, and proteinaceous material, plays a multifaceted role in the biology, the flow of energy and elements cycling in aquatic ecosystems (Benner ; Spencer et al. ; Zhang et al. ; Bre- zonik et al. ). Chromophoric dissolved organic matter (CDOM), the colored fraction of DOM, possesses unique chemical properties that affect ultraviolet radiation pen- etration through the water column, and determine the inherent optical properties of water, thus facilitating remote sensing application to hydrochemical studies of surface waters (Cory et al. ; Zhu et al. ). Several previous studies (Sobek et al. ; Webster et al. ) have suggested links between CDOM concentration and nutrient status of lake waters. It has also been proposed (Huang & Chen ; Zhang et al. ) that CDOM could be used as indicator of river ecosystem responses to disturbances such as agricultural tillage, acid precipi- tation and global warming. Although DOM is involved in a wide array of biogeochemical processes (Landry & Tremblay ), determination of its source, composition and transformation in large natural systems poses meth- odological challenges (Spencer et al. , ). The combination of spectroscopic analysis and remote sen- sing can be an effective approach for regional-scale characterization of DOM, and thus could help resolve 2843 © IWA Publishing 2016 Water Science & Technology | 74.12 | 2016 doi: 10.2166/wst.2016.457 Downloaded from https://iwaponline.com/wst/article-pdf/74/12/2843/456090/wst074122843.pdf by guest on 03 July 2020