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Estimating Sediment Denitrification Rates Using Cores and N2O Microsensors
Published on: December 6, 2018
Nitrous oxide, dinitrogen and methane emission in a subsurface flow constructed wetland
U Mander1, V Kuusemets, K Lõhmus
1Institute of Geography, University of Tartu, 46 Vanemuise St, 51014 Tartu, Estonia. mander@ut.ee
Summary
Greenhouse gas emissions, including nitrous oxide (N2O), nitrogen (N2), and methane (CH4), were measured from a constructed wetland. Nutrient content and water table significantly influenced these gas fluxes, impacting the wetland
Area of Science:
- Environmental Science
- Water Treatment Engineering
- Soil Science
Background:
- Constructed wetlands (CWs) are increasingly used for wastewater treatment.
- Understanding greenhouse gas (GHG) emissions from CWs is crucial for climate change mitigation.
- Horizontal subsurface flow (HSSF) CWs present unique conditions for gas flux dynamics.
Purpose of the Study:
- To quantify nitrous oxide (N2O), nitrogen (N2), and methane (CH4) fluxes from an HSSF CW in Estonia.
- To investigate the influence of environmental factors (e.g., groundwater table, temperature) and nutrient content on GHG emissions.
- To assess the nitrogen removal efficiency and global warming potential of the CW.
Main Methods:
- Field measurements using the closed chamber method.
- Laboratory analyses of intact soil cores (He-O method).
- Continuous monitoring from October 2001 to June 2002.
Main Results:
- Average fluxes varied significantly across microsites: N2O-N (0.1-59 mg m(-2) d(-1)), N2-N (4.1-1,458 mg m(-2) d(-1)), and CH4-C (-0.04 to 2,094 mg m(-2) d(-1)).
- Higher N2O flux observed near inlet pipes; higher CH4 flux in wetter inlet areas.
- Groundwater table significantly correlated with all gas emissions; N2 emission increased with wastewater temperature.
- Phosphate (PO4(3-)) and ammonium (NH4+) enhanced N2O and CH4 fluxes, while nitrite (NO2-) and nitrate (NO3-) inhibited them.
- Ammonium (NH4+) showed a negative correlation with N2 flux.
- Nitrification and denitrification accounted for 42.9% of nitrogen removal.
- Specific global warming potential was highest in wet conditions and lowest in dry conditions.
Conclusions:
- Wastewater characteristics and hydrological conditions within HSSF CWs significantly control GHG emissions.
- Optimizing CW design and operation, particularly water table management, can mitigate climate impact.
- Nitrification and denitrification are key N removal processes, but associated GHG fluxes require careful management.
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