By Sybil P. Seitzinger and Leigh Phillips
Nitrogen compounds, mainly from agriculture and sewage, are causing widespread eutrophication of estu- aries and coastal waters (1). Rapid growth of algal blooms can deprive cosystems of oxygen when the algae
decay, with sometimes extensive ecological and economic effects. Nitrogen oxides
from fossil fuel combustion also contribute
to eutrophication, and nitrous oxide, N2O,
is an extremely powerful greenhouse gas
(GHG). On page 405 of this issue, Sinha et
al. confirm that climate change is worsening nitrogen pollution, notably coastal eutrophication (2). The results highlight the
urgent need to control nitrogen pollution.
Solutions may be found by drawing on decarbonization efforts in the energy sector.
Increased precipitation and greater fre-
quency and intensity of extreme rainfall
events will see increased leaching and run-
off—or nitrogen loading—in many agricul-
tural areas in the United States. Sinha et al.
show that, in the Mississippi-Atchafalaya
River Basin, a business-as-usual emission
scenario leads to an 18% increase in nitro-
gen loading by the end of the 21st century,
driven by projected increases in both total
and extreme precipitation. To counter this,
a 30% reduction in anthropogenic nitrogen
inputs in the region would be required.
Farmers here already are trying to achieve
a 20% loading reduction target imposed by
the U.S. Environmental Protection Agency
(EPA), requiring a 32% reduction in nitro-
gen inputs to the land. To offset the climate-
induced boost to nitrogen pollution in
addition to meeting this target would thus
require a 62% reduction in nitrogen inputs,
a colossal challenge for any farmer.
As Sinha et al. show, regions with historically substantial rainfall, high nitrogen
inputs, and projected robust increases in
rainfall are most likely to experience increased coastal nitrogen loading (2). This
includes great swaths of east, south, and
southeast Asia, India, and China—regions
where coastal eutrophication already occurs.
Solutions to coastal eutrophication and climate change are closely intertwined. To stay
below a 2°C increase in global average temperature will require attaining net zero GHG
emissions soon after mid-century (3). To
achieve this goal, fossil fuel combustion must
plummet, thus also reducing production, deposition, and consequent eutrophication due
to nitrogen oxides associated with fossil fuel
combustion. However, nitrogen and carbon
Nitrogen stewardship in the Anthropocene
How can nitrogen emissions be reduced and reused to reduce pressure on ecosystems?