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09:03
Assessment of Methane and Nitrous Oxide Fluxes from Paddy Field by Means of Static Closed Chambers Maintaining Plants Within Headspace
Published on: September 6, 2018
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Methane and nitrous oxide temporal and spatial variability in two midwestern USA streams containing high nitrate
1U.S. Geological Survey, Boulder, CO 80303, USA.
The Science of the Total Environment
|June 11, 2019
Summary
Greenhouse gases like methane (CH4) and nitrous oxide (N2O) co-occur in streams, impacting climate change. Their emissions vary with stream flow and nitrate levels, influenced by seasonal and daily cycles.
Area of Science:
- Environmental Science
- Biogeochemistry
- Climate Change Research
Background:
- Greenhouse gases (GHGs) like carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are often studied individually in aquatic environments.
- Their combined presence and interactions in rivers (fluvial settings) offer crucial insights into biogeochemical processes and contributions to global climate change.
- Agricultural land drainage can significantly influence GHG dynamics in streams.
Purpose of the Study:
- To investigate the spatial and temporal variability of CH4, N2O, and CO2 concentrations and emissions in two agriculturally impacted streams.
- To compare seasonal, diel, and reach-scale sampling approaches for assessing GHG dynamics.
- To understand the relationship between GHG emissions, stream flow, and nitrate concentrations.
Main Methods:
- Conducted spatial and temporal measurements of dissolved CH4, N2O, and CO2 concentrations from June 1999 to September 2003.
- Utilized seasonal (biweekly), diel (hourly), and transport-oriented (reach-scale) sampling strategies.
- Analyzed GHG concentrations, emissions, and isotopic compositions in relation to stream flow and nitrate levels.
Main Results:
- Dissolved CH4 and N2O concentrations frequently exceeded atmospheric equilibrium values.
- CH4 emissions were higher in summer/fall, negatively correlated with flow and nitrate; N2O emissions were higher in winter/spring, positively correlated with flow and nitrate.
- The larger stream exhibited higher mean GHG concentrations and a greater total reach-scale emission rate (including CO2) compared to the smaller stream.
- Methane contributed 9-28% to the total flux, suggesting groundwater or sediment sources despite high nitrate and oxygen levels.
Conclusions:
- The co-occurrence and dynamic interactions of CH4, N2O, and CO2 in streams are critical for understanding their biogeochemical cycling and climate impact.
- Stream flow and nitrate concentrations are key factors modulating CH4 and N2O emissions.
- Agricultural streams can be significant sources of greenhouse gases, with CH4 potentially originating from groundwater or sediments.
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