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Major Processes Shaping Mangroves as Inorganic Nitrogen Sources or Sinks: Insights From a Multidisciplinary Study
Author(s) -
Wang Fenfang,
Chen Nengwang,
Yan Jing,
Lin Jingjie,
Guo Weidong,
Cheng Peng,
Liu Qian,
Huang Bangqin,
Tian Yun
Publication year - 2019
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1029/2018jg004875
Subject(s) - mangrove , environmental science , denitrification , wetland , nitrogen cycle , estuary , nitrate , environmental chemistry , sink (geography) , nutrient cycle , sediment , nutrient , ecosystem , carbon sink , carbon cycle , nitrification , biota , biogeochemical cycle , oceanography , ecology , nitrogen , chemistry , geology , biology , paleontology , cartography , organic chemistry , geography
Mangrove wetlands support numerous ecosystem services including nutrient cycling and carbon sequestration and storage (blue carbon). Mangrove sediments may serve as a nitrogen source or sink to the hydrosphere and atmosphere at both regional and global scales. However, major mechanisms controlling the connection between the mangrove and the adjacent tidal creek (nitrogen cycling in sediments and outfluxing) remain unclear. A multidisciplinary study based on intensive investigation, incorporating detailed sediment profiling, multi‐isotopes analysis, sediment incubation, and microbiological identification was conducted in the Yunxiao mangrove reserve and Zhangjiang Estuary in southeast China. Here we show that mineralization and denitrification are major processes shaping mangroves as an ammonium source and nitrate sink. Enrichment of ammonium in pore water (10–40 cm in depth) likely resulted from strong ammonification with limited nitrification in the anaerobic sediments. Denitrification played a key role in nitrate removal from pore waters while producing N 2 O and N 2 . Decreasing δ 15 N‐N 2 O and associated δ 15 N:δ 18 O ratio suggested that most of the outgassing N 2 O was derived from incomplete denitrification in sediment pore water. Overall, there was a net export of dissolved inorganic nitrogen from mangroves toward the estuary in winter and spring but a net import to mangroves in summer and fall, mainly driven by tidal pumping with seasonal variation of bio‐uptake. These findings highlight the role of mangrove wetlands in regulating nutrient status and carbon budget in coastal areas.