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Estimating Sediment Denitrification Rates Using Cores and N2O Microsensors
Published on: December 6, 2018
Nitrous oxide emission from denitrification in stream and river networks
Jake J Beaulieu1, Jennifer L Tank, Stephen K Hamilton
1Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA. beaulieu.jake@epa.gov
Summary
Rivers are significant sources of nitrous oxide (N2O), a potent greenhouse gas. Studies show that while nitrogen pollution boosts N2O production in streams, the N2O yield remains low, with most nitrogen converting to dinitrogen gas.
Area of Science:
- Environmental Science
- Geochemistry
- Ecology
Background:
- Nitrous oxide (N2O) is a major greenhouse gas and ozone-depleting substance.
- Anthropogenic nitrogen (N) loading into river networks is a potential N2O source through microbial denitrification.
- The N2O yield, the fraction of denitrified N converted to N2O, is crucial for understanding riverine N2O production but is poorly understood in flowing waters.
Purpose of the Study:
- To investigate the N2O yield of denitrification in headwater streams across various land-use types in the United States.
- To determine the relationship between stream water nitrate concentrations and N2O production and yield.
- To estimate the global contribution of river networks to anthropogenic N2O emissions.
Main Methods:
- Whole-stream (15)N-tracer additions were conducted in 72 headwater streams.
- Stream water nitrate concentrations and N2O production rates were measured.
- A global river network model was used to estimate N2O emissions.
Main Results:
- Denitrification rates increased with stream water nitrate (NO3-) concentrations.
- Less than 1% of denitrified nitrogen was converted to N2O, indicating a low N2O yield.
- No relationship was found between N2O yield and stream water NO3- concentrations.
- Most streams emitted N2O, with highest rates observed in urban-draining basins.
- Microbial N transformations in river networks convert at least 0.68 Tg·y(-1) of anthropogenic N to N2O, a 10% global emission rate.
Conclusions:
- Increased stream nitrate loading stimulates denitrification and N2O production but does not increase the N2O yield.
- River networks are significant sources of N2O, emitting three times more than previously estimated by the IPCC.
- These findings highlight the critical role of riverine N-transformations in global N2O budgets and climate change.
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