Nitrogen purification potential limited by nitrite reduction process in coastal eutrophic wetlands

Area of Science:

• Environmental Science
• Ecology
• Biogeochemistry

Background:

• Coastal wetlands act as crucial nitrogen sinks due to their unique land-sea interface position.
• High nitrogen accumulation in wetlands can lead to coastal eutrophication, necessitating efficient nitrogen removal mechanisms.
• Empirical studies quantifying wetland nitrogen purification and identifying removal pathways remain scarce.

Purpose of the Study:

• To empirically measure nitrogen (N) purification potential and enzyme activities in subtropical wetlands.
• To identify the primary nitrogen removal pathways, focusing on denitrification and anammox.
• To assess the influence of environmental factors and habitat types on N purification in Daya Bay, China.

Main Methods:

• Quantified nitrogen purification rates and N2 production via denitrification and anammox.
• Measured enzyme activities related to denitrification, including nitrate reductase (Nar) and nitrite reductase (Nir).
• Assessed variations in N purification across different seasons, tidal zones, and wetland habitats (mangrove, estuary, barren).

Main Results:

• The average N purification rate was 11.4 μmol N·kg-1·h-1, with denitrification contributing 84.2%-100% of N2 production.
• Higher N purification potential was observed in the wet season, subtidal areas, and mangrove forests.
• Nitrite reductase (Nir) activity correlated positively with denitrification, indicating it as a rate-limiting step; mangroves enhanced N removal by 48.0%.

Conclusions:

• Denitrification is the dominant nitrogen removal pathway in Daya Bay wetlands, with nitrite reduction being the rate-limiting step.
• Mangrove ecosystems exhibit superior nitrogen removal capacity compared to other wetland types.
• Protecting and restoring mangrove wetlands is a critical strategy for mitigating coastal eutrophication.