Destruction of the nitrogen cycle.
Nitrogen is essential for plants and animals, but it is fairly unreactive, making it hard to use in nature. Through fertilizers and pollution mankind is putting out enormous amounts of reactive nitrogen which can be used extremely easily by plants. One way we can see this changing the environment now is in increasing fertility throughout most of the world.
"In the Netherlands, for example, extreme reactive nitrogen levels
have changed the Dutch countryside’s characteristic heathlands to
This doesn't sound too bad, but when this reactive nitrogen hits the oceans it is disastrous. The influx of phosphors and nitrogen causes algae blooms, which choke out most other life in the area. This has caused dead zones along the Gulf Coast and other areas that stretch for hundreds of square miles. If this goes on the most productive parts of the oceans will be algae filled muck.
In their summary of water quality impacts of fertilizers, FAO/ECE
(1991) cited the following problems:
· Fertilization of surface waters (eutrophication) results in, for
example, explosive growth of algae which causes disruptive changes to
the biological equilibrium [including fish kills]. This is true both
for inland waters (ditches, river, lakes) and coastal waters. ·
Groundwater is being polluted mainly by nitrates. In all countries
groundwater is an important source of drinking water. In several areas
the groundwater is polluted to an extent that it is no longer fit to
be used as drinking water according to present standards.
Also plants can only absorb a limited amount of nitrates. Once they take their maximum limit the remaining nitrate doesn't remain in the topsoil.
As with water and air, reactive nitrogen builds up in soil. There’s a
limit, however, to how much nitrogen plants can use. When soil reaches
a point at which plants can’t use additional nitrogen, it’s said to be
“saturated.” And saturated soil, in theory at least, will shed any
additional nitrogen introduced to it. But that nitrogen doesn’t leave
unaccompanied. “When it leaches out of the system,” says Townsend, “it
takes other nutrients with it, so it ends up acidifying the soil, and
it takes things like magnesium and calcium out into the water. And you
end up with a very unbalanced system.”
Another problem is that reactive nitrogen causes a whole cascade of problems in the atmosphere.
But as nitrogen levels continue to rise, Townsend says, the net health
effects become increasingly negative. Furthermore, says Galloway,
reactive nitrogen can not only impact many different ecosystems, but a
single atom also can make mischief repeatedly, unlike most better
recognized pollutants. “If you put a molecule of NOx in the atmosphere
from fossil fuel combustion or a molecule of ammonium on an
agricultural field as a fertilizer,” he explains, “you have a whole
series, or cascade, of effects that goes from acid rain to particle
formation in the atmosphere, decreasing visibility and causing impacts
on human health, acid rain, soil and stream acidification, coastal
eutrophication, decreasing biodiversity, human health issues in
groundwater, and nitrous oxide [N2O] emissions to the atmosphere,
which impact the greenhouse effect and stratospheric ozone.”
Even better, nitrogen damages the ozone layer at lower levels, and in the stratosphere it destroys the ozone layer. So on top of acid rain, increasing acidity in the soil and water, a cloudier sky and algae blooms, UV rays will be killing plants and animals.
So while it is a greenhouse gas, and far worse than CO2, changing the climate a degree or two is the least of the problems of an out of control nitrogen cycle. The earth will survive, but the food chain will be in tatters, plants will have to deal with intense UV rays, acidic soil and water, and agriculture will be very difficult but not impossible.