Changes of dissolved organic matter following salinity invasion in different seasons in a nitrogen rich tidal reach

Rongrong Xie; Jiabin Qi; Chengchun Shi; Peng Zhang; Rulin Wu; Jiabing Li; Joanna J Waniek

doi:10.1016/j.scitotenv.2023.163251

Changes of dissolved organic matter following salinity invasion in different seasons in a nitrogen rich tidal reach

Sci Total Environ. 2023 Jul 1:880:163251. doi: 10.1016/j.scitotenv.2023.163251. Epub 2023 Apr 5.

Authors

Rongrong Xie¹, Jiabin Qi², Chengchun Shi³, Peng Zhang⁴, Rulin Wu², Jiabing Li⁵, Joanna J Waniek⁶

Affiliations

¹ College of Environmental Science and Engineering, Fujian Normal University, Fuzhou 350007, China; Key Laboratory of Pollution Control and Resource Recycling of Fujian Province, Fujian Normal University, Fuzhou 350007, China; Digital Fujian Environmental Monitoring Internet of Things Laboratory, Fujian Normal University, Fuzhou 350007, China. Electronic address: xierr1118@163.com.
² College of Environmental Science and Engineering, Fujian Normal University, Fuzhou 350007, China.
³ Fujian Provincial Academy of Environmental Sciences, Fuzhou 350013, China.
⁴ School of Environmental and Municipal Engineering, North China University of Water Resources and Electric Power, Zhengzhou 450046, China.
⁵ College of Environmental Science and Engineering, Fujian Normal University, Fuzhou 350007, China; Key Laboratory of Pollution Control and Resource Recycling of Fujian Province, Fujian Normal University, Fuzhou 350007, China; Digital Fujian Environmental Monitoring Internet of Things Laboratory, Fujian Normal University, Fuzhou 350007, China.
⁶ Leibniz Institute for Baltic Sea Research, Warnemünde, Rostock 18119, Germany. Electronic address: joanna.waniek@io-warnemuende.de.

PMID: 37023805
DOI: 10.1016/j.scitotenv.2023.163251

Abstract

Dissolved organic matter (DOM) is a heterogeneous mixture of dissolved material found ubiquitously in aquatic systems and dissolved organic nitrogen is one of its most important components. We hypothesised nitrogen species and salinity intrusions affect the DOM changes. Here, using the nitrogen rich Minjiang River as an easily accessible natural laboratory 3 field surveys with 9 sampling sites (S1-S9) were conducted in November 2018, April and August 2019. The excitation emission matrices (EEMs) of DOM were explored with parallel factor (PARAFAC) and cosine-histogram similarity analysis. Four indices including fluorescence index (FI), biological index (BIX), humification index (HIX) and the fluorescent DOM (FDOM) were calculated and the impact of physicochemical properties was assessed. The results suggested that the highest salinities of 6.15, 2.98 and 10.10, during each campaign corresponded to DTN concentrations of 119.29-240.71, 149.12-262.42 and 88.27-155.29 μmol·L^-1, respectively. PARAFAC analysis revealed the presence of tyrosine-like proteins (C1), tryptophan-like proteins or a combination of the peak N and tryptophan-like fluorophore (C2) and the humic-like material (C3). The EEMs in the upstream reach (i.e. S1-S3) were complex with larger spectra ranges, higher intensities and similar similarity. Subsequently, the fluorescence intensity of three components decreased significantly with low similarity of EEMs (i.e. S4-S7). At the downstream, the fluorescence levels dispersed significantly and no obvious peaks were seen except in August. In addition, FI and HIX increased, while BIX and FDOM decreased from upstream to downstream. The salinity positively correlated with FI and HIX, and negatively related to BIX and FDOM. Besides, the elevated DTN had a significant effect on the DOM fluorescence indices. Altogether, salinity intrusion and elevated nitrogen are relevant for the distribution of the DOM, which is helpful for the water management tracing the DOM source according to the on-line monitoring of salinity and nitrogen in estuaries.

Keywords: Cosine-histogram similarity; DOM; EEMs; PARAFAC; Tidal reach.