ing off fields ends up in lakes and coastal
areas, causing algal blooms that kill marine
life. Airborne nitrogen can also harm eco-
systems. One source is nitrogen oxides,
mostly from power plants and engine ex-
haust. In the Netherlands, even more comes
from the ammonia vapors from livestock
urine and manure. Both kinds of nitrogen re-
act to form aerosols that cause smog, damage
foliage, and acidify the soil, hindering roots’
absorption of nutrients. (Dutch farmers must
add lime to their fields to fight acidity.)
The Netherlands is a nitrogen hot spot
partly because it is a dense, urbanized na-
tion, although controls on power plants and
catalytic converters in autos have helped
curb nitrogen oxide emissions. The bigger
problem is ammonia emissions from con-
centrated livestock operations. Dutch farms
contain four times more animals biomass
per hectare than the EU average. Practices
such as injecting liquid manure in the soil
and installing air scrubbers on pig and poul-
try facilities have reduced ammonia emis-
sions 60% since the 1980s, but they have
risen slightly since 2014 because of expand-
ing dairy operations. Dutch agriculture is
responsible for nearly half of nitrogen pollu-
tion that falls in the country.
In 118 of 162 Dutch nature reserves, ni-
trogen deposits now exceed ecological risk
thresholds by an average of 50%. In dunes,
bogs, and heathlands, home to species
adapted to a lack of nitrogen, plant diversity
has decreased as nitrogen-loving grasses,
shrubs, and trees move in. Heathlands are
turning green-gray as invasive grasses over-
whelm the purple heather and yellows and
blues of small herbaceous flowering plants,
says Eva Remke, an ecologist at B-WARE
Research Centre in Nijmegen. “The grasseswill win, and the herbs will lose.” These
losses cascade through the ecosystem, con-
tributing to the decline of insect and bird
diversity, she says.
To control emissions, in 2015 the Nether-
lands introduced a nitrogen permit system
that allows construction if, for example, re-
gional governments reduce nitrogen from
other sectors, such as farming. The system
relies on a model developed by the Dutch
National Institute for Public Health and
the Environment (RIVM) to calculate how
much nitrogen is emitted by various activi-
ties and how much they contribute to pollu-
tion in natural areas.
The system was not enough to satisfy en-
vironmental groups. They sued the Dutch
government in 2016, demanding that it
deny construction permits for expanded
animal operations near two nature reserves.
The cases ended up in the Court of Justice
of the European Union, which last year
ruled against the government and criticized
the permit system for not ensuring immedi-
ate nitrogen reductions.
The Dutch high court implemented the
ruling in May, halting all permit applica-
tions. It said the government needed to
come up with a better system and a long-
term plan to reduce nitrogen emissions. In
September, a high-level commission sug-
gested some short-term fixes, which the gov-
ernment has asked the high court to review.
One idea is to lower the daytime speed limit
from 130 to 100 kilometers per hour, which
would reduce emissions enough to restart
some home building. (The entire construc-
tion sector contributes just 0.6% of nitrogen
emissions.) The government also wants to
require changes in animal feed that would
reduce nitrogen levels in manure and to buyout some farms near nature reserves. But
the commission warned that deeper emis-
sions cuts would require hard choices.
Some scientists and environmental groups
say the Netherlands should move to circu-
lar agriculture: Farms should only produce
as much manure as they can use to fertil-
ize nearby fields; cows should graze rather
than be fed nitrogen-rich, imported soy; and
pigs and poultry should eat food waste. That
would mean 50% fewer animals, says Natasja
Oerlemans, head of agriculture for the World
Wildlife Fund–Netherlands in Zeist. “We
should use this crisis to transform agricul-
ture,” she says, adding that it will require sev-
eral decades and billions of euros to reduce
the number of animals.
LTO Netherlands in The Hague, which
represents 35,000 farmers, endorses the con-
cept of circular agriculture, but cautioned
against “hasty measures.” One new grass-
roots group, the Farmers Defence Force,
contests the RIVM model’s calculations of
how much nitrogen from farms is deposited
on nature reserves. RIVM has defended its
model, which was peer reviewed before its
2015 launch. But it will ask an external com-
mittee to review both the model and the na-
tional nitrogen monitoring network.
Candel thinks EU courts might impose
similar decisions on other European nations
in the future. But for now, Dutch farmers
will likely face tougher nitrogen restrictions
than those in neighboring countries. That
will rankle, especially because cross-border
pollution is part of the problem, says Wim
de Vries, who studies nitrogen impacts at
Wageningen. About one-third of the nitro-
gen pollution deposited in the Netherlands
comes from other countries, he says. “Nitro-
gen spreads everywhere.” jSCIENCE sciencemag.org 6 DECEMBER 2019 • VOL 366 ISSUE 6470 1181PHOTO: VINCENT JANNINK/ANP/AFP/GETTY IMAGES
Dutch farmers have protested a ruling that curtails the expansion of livestock operations because of the nitrogen pollution they produce.Published by AAASon December 12, 2019^http://science.sciencemag.org/Downloaded from