Emerging role of dissolved organic nitrogen in supporting algal bloom persistence in Lake Taihu, China: Emphasis on internal transformations

Xiaolong Yao; Yunlin Zhang; Lu Zhang; Guangwei Zhu; Boqiang Qin; Yongqiang Zhou; Jingya Xue

doi:10.1016/j.scitotenv.2020.139497

Emerging role of dissolved organic nitrogen in supporting algal bloom persistence in Lake Taihu, China: Emphasis on internal transformations

Sci Total Environ. 2020 Sep 20:736:139497. doi: 10.1016/j.scitotenv.2020.139497. Epub 2020 May 17.

Authors

Xiaolong Yao¹, Yunlin Zhang², Lu Zhang¹, Guangwei Zhu¹, Boqiang Qin¹, Yongqiang Zhou¹, Jingya Xue³

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.
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. Electronic address: ylzhang@niglas.ac.cn.
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; University of Chinese Academy of Sciences, Beijing 100049, China.

PMID: 32502780
DOI: 10.1016/j.scitotenv.2020.139497

Abstract

Dissolved organic nitrogen (DON) accounts for a significant fraction of the dissolved nitrogen (N) pool in eutrophic lakes, and substantial components of DON are available for phytoplankton. However, long-term changes in DON concentrations in eutrophic lakes have been poorly documented, and the particulate-related internal cycling of DON at the molecular level remains unclear. In this study, changes in the concentration of DON during the past 14 years of Lake Taihu, China were analyzed. Algae and sediment suspensions were incubated under summer sunlight to examine transformations of DON (e.g., photodissolution) at the bulk concentration and molecular level. Concentrations of DON in Lake Taihu ranged from 0 to 4.59 mg L^-1, with a mean of 0.82 ± 0.60 mg L^-1 (n = 3360). Although annual averages of the concentration of DON (n = 240) showed no significant linear variation from 2005 to 2018, the percentage of DON in total dissolved nitrogen (TDN) increased linearly (p < .05) and was maintained at >50% after 2015. Seasonally, DON concentrations were highest in spring (1.10 ± 0.56 mg L^-1), followed by winter (0.87 ± 0.58 mg L^-1) and summer (0.54 ± 0.37 mg L^-1) concentrations, and lowest in autumn (0.44 ± 0.38 mg L^-1). Outdoor incubation experiments suggest that both algae and sediment suspensions contribute to significant increases of DON concentrations but contribute to decreases of inorganic N concentrations at the end of incubations. Moreover, the production of DON by algae suspensions differed from that of sediment suspensions, with more labile components released from algae (e.g., proteins and amino acids), while more refractory components were released from sediment suspensions (e.g., lignin with low H/C and O/C). Taken together, these results emphasize the increasing percentage of DON in TDN during 2009-2018 and the different patterns of algae- and sediment-dominated internal DON transformations in Lake Taihu.

Keywords: Algae-derived; Algal bloom; Concentrations; Dissolved organic nitrogen (DON); Lake Taihu; Sediment-derived.

MeSH terms

China
Environmental Monitoring
Eutrophication
Lakes*
Nitrogen / analysis*
Phosphorus / analysis

Substances

Phosphorus
Nitrogen