Can wetlands designed for flood attenuation efficiently remove nitrogen from agricultural runoff?

Area of Science:

• Environmental Science
• Ecology
• Agricultural Science

Background:

• Eutrophication from agricultural nitrogen (N) runoff and increased flood risk due to climate change are significant ecological and societal challenges.
• Created wetlands offer dual benefits: nutrient removal and flood attenuation, but their combined efficacy in agricultural landscapes is not well understood.
• Understanding the interplay between water flow buffering and N removal in wetlands is crucial for sustainable land management.

Purpose of the Study:

• To investigate how water flow buffering in created wetlands influences nitrogen removal and greenhouse gas (GHG) emissions.
• To compare the N removal and GHG emissions of wetlands with different designs (depth, size) and flooding regimes (intermittent vs. permanent).

Main Methods:

• Experimental wetlands of varying designs and flooding regimes (intermittent vs. permanent) were established.
• Nitrogen removal rates and concentrations of N2O and CH4 were measured under different hydrological conditions.
• Water storage capacity and flow buffering effects were analyzed in relation to N removal and GHG emissions.

Main Results:

• Intermittently flooded wetlands exhibited lower N removal than permanently flooded ones, particularly during non-flow periods.
• Deep, intermittently flooded wetlands showed significantly reduced N removal (25%) compared to deep, permanently flooded wetlands (38%).
• No significant differences in N2O or CH4 concentrations were observed between wetlands with high and low water storage, suggesting similar GHG emissions.

Conclusions:

• Created wetlands designed for flood attenuation may compromise nitrogen removal efficiency.
• Intermittent flooding, while beneficial for flood control, can decrease the effectiveness of wetlands as nutrient sinks.
• Optimizing created wetlands for both flood attenuation and nutrient removal requires careful consideration of design and hydrological management to avoid trade-offs.