Environmental Engineering Reference
In-Depth Information
wastewater treatment plants. The weakness of these systems is the loss of nutrients that are
taken from limited supplies (ores or Haber-Bosch process) and then discharged into rivers and
oceans.
Another example is the feedlot practice used to finish beef cattle before slaughter. Feedlots
are operations generally separated by long distances from where feed is produced, so the
waste produced by the animals is rarely economical to be returned to the field where the feed
was produced. Considering that bovines have a low-feed conversion efficiency, they create
huge amounts of waste (manure), which that creates not only environmental issues but also
does not get recycled into the fields to close the nutrients cycles.
An additional weakness of man-made agricultural ecosystems is the lack of regulation.
Therefore, to maintain the system balance in a direction that is profitable, competition
from weeds and insects is controlled by application of herbicides and pesticides. And to
maintain a high productivity, besides the energy from the sun, man-made agricultural
ecosystems need to use input of mechanical energy, which in most cases comes from
burning fossil fuels.
Ecological footprint and Earth's carrying capacity
Ecological footprint
Even when human ingenuity finds ways to accelerate many of the natural processes to
satisfy human needs by using fossil fuels and nonrenewable resources, in the end, the Earth
is the ultimate support system that provides the services we need, such as water, oxygen,
waste removal, shelter, and food. The ecological footprint is a measure that indicates the
area of productive land along with natural ecosystems needed per capita to support a certain
lifestyle. In addition to land to produce food, water, and treat wastes, land is used to build
houses, to obtain lumber from forests as construction materials, to build roads, and to have
forests to absorb carbon dioxide from fossil fuels. Eventually, if humans ever move to a
biobased supply of energy and materials, land is going to be for that purpose, too (McKinney
et al., 2007).
Ecological footprints are connected to lifestyle with more affluent societies having larger
footprints. The global ecological footprint is about 2.2 hectares per person and different values
for selected footprints for different countries are shown in Table 2.4 (Global Footprint
Network, 2010). Ecological footprints are not tied just to individuals; they can be calculated
for organizations, cities, states, and countries.
Earth's carrying capacity
The Earth's carrying capacity is the maximum number of people the planet can support
indefinitely while providing food, water, shelter, and other necessities. Carrying capacity is
linked to biocapacity, which is a measure of biological productivity of the land, which is not
evenly distributed around the world. Half (50 percent) of the global biocapacity is contained
in eight countries: the United States, Brazil, Russia, China, Canada, India, Argentina, and
Australia. The ecological footprint of some countries exceeds by far their biocapacity, and so
facilitated by the current global conditions, they become importers of biocapacity. From the
eight countries mentioned, the United States, China, and India are net importers whereas the
rest are exporters (World Wildlife Fund [WWF], 2008). According to the Global Footprint
Network, if the global ecological footprint of 2.7 hectares per person is subtracted from the
