Nitrogen mineralization/immobilization dynamics across the river-estuary-sea continuum: Effects of organic matter and microorganisms

Hengchen Wei; Peiyi Wang; Jing Li; Qingyan Wang; Fengwei Zhang; Dongyao Sun; Dengzhou Gao; Zhuhong Ding; Wei Du; Guoling Zhang; Xianbiao Lin

doi:10.1016/j.marpolbul.2024.117241

Nitrogen mineralization/immobilization dynamics across the river-estuary-sea continuum: Effects of organic matter and microorganisms

Mar Pollut Bull. 2024 Nov 13;209(Pt B):117241. doi: 10.1016/j.marpolbul.2024.117241. Online ahead of print.

Authors

Hengchen Wei¹, Peiyi Wang¹, Jing Li², Qingyan Wang², Fengwei Zhang², Dongyao Sun³, Dengzhou Gao⁴, Zhuhong Ding¹, Wei Du⁵, Guoling Zhang², Xianbiao Lin⁶

Affiliations

¹ School of Environmental Science and Technology, Nanjing Tech University, Nanjing 210008, China.
² Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, and College of Chemistry & Chemical Engineering, Ocean University of China, Qingdao 266100, China.
³ School of Geography Science and Geomatics Engineering, Suzhou University of Science and Technology, Suzhou 215009, China.
⁴ Key Laboratory for Humid Subtropical Eco-Geographical Processes of the Ministry of Education, School of Geographical Sciences, Fujian Normal University, Fuzhou 350117, China.
⁵ Yunnan Provincial Key Laboratory of Soil Carbon Sequestration and Pollution Control, Faculty of Environmental Science & Engineering, Kunming University of Science & Technology, Kunming 650500, China.
⁶ Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, and College of Chemistry & Chemical Engineering, Ocean University of China, Qingdao 266100, China. Electronic address: [email protected].

PMID: 39541660
DOI: 10.1016/j.marpolbul.2024.117241

Abstract

N mineralization and immobilization are important N cycling pathways. While they are widely studied in individual coastal habitats, they are rarely compared across different habitats along the river-estuary-sea continuum. We addressed this gap by investigating gross nitrogen mineralization (GNM) and gross ammonium immobilization (GAI) in urban rivers, estuary, and adjacent sea of the Yangtze River-Estuary-East China Sea system. We sampled 30 stations during winter and summer, quantifying GNM and GAI rates using enriched ¹⁵N stable isotopes. We observed a 65 % decrease in total organic C concentrations and a three-fold increase in fungi/bacteria ratios from river to sea. Along the gradient, GNM decreased from 5.41 to 2.41 μg N g^-1 d^-1 and GAI decreased from 6.08 to 3.27, with their ratios generally >1, indicating nitrogen limitation. Redundant analyses identified temperature and Fe as significant environmental variables. This study highlights the importance of cross-habitat comparisons to N cycling studies in coastal systems.

Keywords: China; N cycling; N immobilization; N mineralization; River-estuary-sea continuum; Sediment.