The Need for Sustainable Food Production Systems - Agroecology: The Ecology of Sustainable Food Systems - page 11

The difference between the amount of water needed to
grow calorie-equivalent amounts of plant food and animal
food can be extreme. For example, it takes only 89 liters
of water to grow 500 calories of potatoes, but an aston-
ishing 55 times more, or 4902 liters, to raise 500 calories
of grain-fed beef (Postel and Vickers, 2004). If we look
at protein alone, the ratio is even more skewed: on average,
producing 1 kg of animal protein requires about 100 times
as much water as producing 1 kg of grain protein (Pimentel
and Pimentel, 2003).
In addition to using a large share of the world's fresh
water, conventional agriculture has an impact on
regional and global hydrological patterns and the
aquatic, riparian, and marine ecosystems dependent on
them. First, by drawing such large quantities of water
from natural reservoirs on land, agriculture has caused
a massive transfer of water from the continents to the
oceans. A 1994 study concluded that this transfer of
water involves about 190 billion m 3 of water annually
and has raised sea level by an estimated 1.1 cm
(Sahagian et al., 1994). Moreover, the amount of water
that agriculture causes to be moved from the land to the
oceans is only increasing; by one estimate the net flow
will increase by as much as 30% over present rates
(Sahagian, 2000). Second, where irrigation is practiced
on a large scale, agriculture brings about changes in
hydrology and microclimate. Water is transferred from
natural watercourses to fields and the soil below them,
and increased evaporation changes humidity levels and
may affect rainfall patterns. These changes in turn sig-
nificantly impact natural ecosystems and wildlife. Third,
the dams, aqueducts, and other infrastructure created to
make irrigation possible have dramatically altered many
of the world's rivers, causing enormous ecological dam-
age. Rivers that once provided valuable “ecosystem
services” to human society cannot do so anymore — their
wetland, aquatic, and floodplain ecosystems can no
longer absorb and filter out pollutants or provide habitat
for fish and waterfowl, and they can no longer deposit
the rich sediment so important for restoring the fertility
of agricultural soils in floodplain areas (Postel and
Richter, 2003).
If conventional agriculture continues to use water in
the same ways, our rivers will become increasingly crippled
and regional water crises will become increasingly com-
mon, either shortchanging the environment, marginalized
peoples, and future generations, or limiting irrigation-
dependent food production.

Pesticides and herbicides — applied in large quantities
on a regular basis, often from aircraft — are easily spread
beyond their targets, killing beneficial insects and wildlife
directly and poisoning farmers and farmworkers. The
pesticides that make their way into streams, rivers, and
lakes — and eventually the ocean — can have serious
deleterious effects on aquatic ecosystems. They can also
affect other ecosystems indirectly. Fish-eating raptors, for
example, may eat pesticide-laden fish, reducing their
reproductive capacity and thereby impacting terrestrial
ecosystems. Although persistent organochloride pesti-
cides such as DDT — known for their ability to remain
in ecosystems for many decades — are being used less in
many parts of the world, their less-persistent replacements
are often much more acutely toxic.
Pesticides also pose a significant human health hazard.
They spread throughout the environment by hydrological,
meteorological, and biological means, and so it is impos-
sible for humans to avoid exposure. In its 2003 edition
of Human Exposure to Environmental Chemicals , the
Centers for Disease Control reported that all of the 9282
people they tested had pesticides and their breakdown
products in their bodies, and the average person had
detectable amounts of 13 different pesticides (Schafer
et al., 2004). Pesticides enter our bodies through our food
and our drinking water. Pesticide contamination of
groundwater has occurred in at least 26 states, and an EPA
study in 1995 found that of 29 cities tested in the Midwest,
28 had herbicides present in their tap water. If all the
drinking water sources in the U.S. at risk for pesticide
contamination were properly monitored for the presence
of harmful agents, the cost would be well over U.S.$15
billion (Pimentel, 2005).
Fertilizer leached from fields is less directly toxic
than pesticides, but its effects can be equally damaging
ecologically. In aquatic and marine ecosystems it pro-
motes the overgrowth of algae, causing eutrophication and
the death of many types of organisms. Nitrates from
fertilizers are also a major contaminant of drinking water
in many areas. Rounding out the list of pollutants from
crop lands are salts and sediments, which in many locales
have degraded streams, helped destroy fisheries, and
rendered wetlands unfit for bird life.
Where factory farming has become the dominant
form of meat, milk, and egg production, animal waste has
become a huge pollution problem. Farm animals in the
U.S. produce far more waste than do humans (Marks and
Knuffke, 1998). The large size of feedlot and other factory
farming operations poses challenges for the treatment of
these wastes. As noted above, the wastes are typically
treated in large anaerobic lagoons not well suited to pro-
tection of the environment. Some of the nitrogen from the
wastes leaks out of the lagoons and into underlying aqui-
fers, adding large quantities of nitrates to the groundwater
and eventually to rivers. Even more nitrogen from the

P OLLUTION OF THE E NVIRONMENT

More water pollution comes from agriculture than from
any other single source. Agricultural pollutants include
pesticides, herbicides, other agrochemicals, fertilizer,
animal wastes, and salts.