Environmental Engineering Reference
In-Depth Information
In response to growing alarm, the EPA and other federal and state agencies drafted
a plan to shrink the Gulf's dead zone to 1,930 square miles by 2015. The EPA calls the
plan “urgent.” Yet, funding and political will seem to have dissipated. “It's so much talk
and not enough action,” Rabalais complained to the NewYorkTimes. “Because you're
not just going up against the agribusiness lobby, but also the livelihood of farmers. It is
not exactly popular in the Midwest.”
Economists have suggested using a cap-and-trade system for nitrogen polluters,
based on that used for carbon—an approach to control pollution by setting limits, or a
cap, on how much pollution can be emitted by factories. Companies that are big pol-
luters can buy additional pollution credits from those that pollute less; in effect, buyers
pay to pollute and the sellers are rewarded for reducing emissions.
Some nations are exploring so-called geoengineering solutions: large-scale human
intervention into natural systems, such as bubbling air into bays, to stir up the hypoxic
water. Biotech companies are trying to engineer technologies to keep nitrogen fixed in
the soil. Others are trying to develop nitrogen-use efficiency (NUE) technology, which
allows plant roots to absorb more nitrogen before it gets washed away.
One option that Bob Hirsch favors is the imposition of strict TMDLs , or total max-
imum daily loads. A TMDL is a pollution budget: if a body of water remains polluted
even after point sources, such as sewage plants and factories, have been cleaned up, then
regulators allocate the maximum load of pollution that comes from each part of the
watershed, allowing quality standards to be met. TMDLs are a provision of the Clean
Water Act; many of them have been calculated and put into place, but they remain only
goals with no easy way to enforce them. If it were granted authority, the EPA would
oversee TMDLs and be able to fine polluters who flout the standards.
But no hydrologists, biologists, activists, or politicians really know whether such
measures will solve the dead zone puzzle. Humans have put nutrients into the soil for
centuries, and by now they have penetrated deep into groundwater and sediments. Even
if new sources of nitrogen are removed, the old stores will continue to be released over
time. Since 1950, the amount of nitrogen applied to the land in the Mississippi River
Basin has grown by more than a factor of ten . “If you stopped applying nitrogen to the
land surface today—magically put an end to all of the pesticides and fertilizers, which
you can't—it would still take decades before you'd see significant reductions of nitrogen
in Chesapeake Bay or in the Gulf of Mexico,” said Hirsch.
But he finds room for cautious optimism. “Seven million metric tons of nitrogen
is applied to the land in the Mississippi Basin every year. But the amount that flows
into the Gulf is only about one to one and a half million metric tons,” he says. “What
happened to the rest of it? Clearly, there's a lot of natural processing occurring along the
way, such as storage or denitrification. These numbers suggest there's something we can
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