Effects of long-term nitrogen addition on dissolved organic matter characteristics in a temperate wetland of Northeast China

Yi-Dong Ding; Chang-Chun Song; Guang-Jiao Chen; Xin-Hou Zhang; Rong Mao

doi:10.1016/j.ecoenv.2021.112822

Effects of long-term nitrogen addition on dissolved organic matter characteristics in a temperate wetland of Northeast China

Ecotoxicol Environ Saf. 2021 Dec 15:226:112822. doi: 10.1016/j.ecoenv.2021.112822. Epub 2021 Sep 24.

Authors

Yi-Dong Ding¹, Chang-Chun Song², Guang-Jiao Chen¹, Xin-Hou Zhang³, Rong Mao⁴

Affiliations

¹ Key Laboratory of National Forestry and Grassland Administration on Forest Ecosystem Protection and Restoration of Poyang Lake Watershed, College of Forestry, Jiangxi Agricultural University, Nanchang 330045, China.
² Key Laboratory of Wetland Ecology and Environment, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130102, China.
³ Key Laboratory of Wetland Ecology and Environment, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130102, China; School of Environment, Nanjing Normal University, Nanjing 210046, China.
⁴ Key Laboratory of National Forestry and Grassland Administration on Forest Ecosystem Protection and Restoration of Poyang Lake Watershed, College of Forestry, Jiangxi Agricultural University, Nanchang 330045, China; Key Laboratory of Wetland Ecology and Environment, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130102, China. Electronic address: maorong@jxau.edu.cn.

PMID: 34571419
DOI: 10.1016/j.ecoenv.2021.112822

Abstract

Dissolved organic matter (DOM) plays an indispensable role in ecosystem services and functions in wetlands. While most wetlands have undergone increased nitrogen (N) loading due to intensive human activities, the response of DOM characteristics to long-term N addition remains unexplored. In this study, we assessed the changes in dissolved organic carbon (DOC), NH₄⁺, NO₃^-, dissolved organic N (DON), dissolved total N (DTN), and dissolved total phosphorus (DTP) in surface water and soil pore water at 15 cm depth after 10 years of N addition at four levels (0, 60, 120, and 240 kg N hm^-2 year^-1) in a freshwater marsh of Northeast China. We also examined the effect of N addition on DOM aromaticity and humification by measuring the specific UV absorbance at 254 nm (SUVA₂₅₄), the color per C unit (C/C ratio), and the fulvic acid/humic acid ratio (E4/E6 ratio). Our results showed that N addition significantly altered DOM properties, but the direction and magnitude of these changes generally did not vary with the N addition level. During the growing season, DOC, NH₄⁺, NO₃^-, DON, and DTN concentrations in both surface water and soil pore water were increased by N addition. Accordingly, N addition increased the DOC/DTP and DTN/DTP ratios but decreased the DOC/DTN ratio in surface water and soil pore water. In addition, the SUVA₂₅₄ value and C/C ratio increased, while the E4/E6 ratio reduced after N addition in surface water and soil pore water, indicating increases in DOM aromaticity and humification. These observations suggest that long-term N addition changes DOM characteristics by causing stoichiometric imbalances and increasing recalcitrant compounds in temperate freshwater wetlands, which may then deteriorate water quality, alter microbial-mediated ecological processes, and impact downstream aquatic ecosystem structures.

Keywords: Aromaticity; Dissolved organic carbon; Humification; N saturation; Optical properties; Stoichiometry.

MeSH terms

Carbon / analysis
China
Ecosystem
Humans
Nitrogen* / analysis
Soil
Wetlands*

Substances

Soil
Carbon
Nitrogen