Anthropogenic nitrate attenuation versus nitrous oxide release from a woodchip bioreactor

• Nitrogen loss via overland flow from agricultural land use is a global threat to waterways. On-farm denitrifying woodchip bioreactors can mitigate NO3− exports by increasing denitrification capacity. However, denitrification in sub-optimal conditions releases the greenhouse gas nitrous oxide (N2O), swapping the pollution from aquatic to atmospheric reservoirs. Here, we assess NO3−-N removal and N2O emissions from a new edge-of-field surface-flow bioreactor during ten rain events on intensive farming land. Nitrate removal rates (NRR) varied between 5.4 and 76.2 g NO3−-N m−3 wetted woodchip d−1 with a mean of 30.3 ± 7.3 g NO3−-N m−3. The nitrate removal efficiency (NRE) was ∼73% in ideal hydrological conditions and ∼18% in non-ideal conditions. The fraction of NO3−-N converted to N2O (rN2O) in the bioreactor was ∼3.3 fold lower than the expected 0.75% IPCC emission factor. We update the global bioreactor estimated Q10 (NRR increase every 10 °C) from a recent meta-analysis with previously unavailable data to >20 °C, yielding a new global Q10 factor of 3.1. Mean N2O CO2-eq emissions (431.9 ± 125.4 g CO2-eq emissions day−1) indicate that the bioreactor was not significantly swapping aquatic NO3− for N2O pollution. Our estimated NO3−-N removal from the bioreactor (9.9 kg NO3−-N ha−1 yr−1) costs US$13.14 per kg NO3−-N removed and represents ∼30% NO3−-N removal when incorporating all flow and overflow events. Overall, edge-of-field surface-flow bioreactors seem to be a cost-effective solution to reduce NO3−-N runoff with minor pollution swapping to N2O. © 2022

Subject headings

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Environmental Sciences (hsv//eng)

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Oceanografi, hydrologi och vattenresurser (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Oceanography, Hydrology and Water Resources (hsv//eng)

Keyword

Climate change

Greenhouse gases

Horticulture

Remediation

Water quality

Agriculture

Bioconversion

Bioreactors

Carbon dioxide

Cost effectiveness

Denitrification

Land use

Nitrogen oxides

Anthropogenics

Greenhouses gas

N removal

Nitrates removal

Nitrogen loss

Nitrous oxide

Overland flow

Removal rate

Surface flow

Wood chip

Nitrates

nitrate

nitrogen

rain

agricultural land

Article

carbon dioxide equivalent

controlled study

cost effectiveness analysis

ecosystem restoration

human impact (environment)

hydrology

nitrous oxide emission

surface runoff

water sampling

Publication and Content Type

ref (subject category)

art (subject category)