Environmental Engineering Reference
In-Depth Information
PRESSURES AND PACE OF ENVIRONMENTAL
CHANGE
Many advances in ecosystem science have been driven by the need to meet the
demands of a society wanting to understand and solve pressing environmental problems.
In the past, issues such as acid rain, the ozone hole, declining fisheries yields, and eutro-
phication have motivated considerable ecosystem research, and society has benefited from
discoveries of that science. Currently, Earth's system is experiencing an increasing number
of planetary-scale changes due to the consequences of human population and economic
growth. The conditions of the earth, and how ecosystems function, are being modified at
unprecedented rates (Schlesinger 1997). The potential severity of these global changes is
challenging to predict, and will motivate scientists worldwide to understand and mitigate
their socio-ecological consequences. In this section, we describe a number of components
of change that, due to their global significance, will draw the attention of ecosystem scien-
tists in the coming years.
Urbanization
In 2008, for the first time in history, half of the world's population lived in urban areas;
by 2050 it is expected that the urban population will double and more than 70% of the
world's population will live in urban regions. Although these areas occupy less than 0.5%
of Earth's total land area, urbanization and its associated changes in land use are
predicted to alter the properties of ecosystems at local, regional, and continental scales
( Grimm et al. 2008 ). As these changes occur, politicians and managers will be faced with
decisions about regional planning, conservation, and sustainability.
Over the last decade, scientists have overturned many of our assumptions about urban
areas such as the idea that concern about environmental quality is higher among the
wealthy, biodiversity is lower in urban areas, lawns are bad, or that urbanization decreases
water quality. Indeed, recent work has demonstrated that concern about air quality is
independent of socio-economic status, cities are not biological deserts, lawns have some
ecological value, and water quality is not always worse in urban areas ( Pickett et al. 2008 ).
Ecosystem scientists are now studying urban systems as they have studied “natural” ecosys-
tems. As examples,
two urban ecosystem research sites
(Baltimore and Central
Arizona
Phoenix) are part of the 26-site U.S. Long-Term Ecological Research Network
( http://www.lternet.edu/ ), Miami and New Orleans are part of more than 16 U.S. cities
participating in the Urban Long-Term Research Area Exploratory program (ULTRA-Ex),
and universities throughout the United States now offer courses in urban ecology. Thus,
ecosystem scientists now are using cities as model systems to understand how ecosystems
respond to perturbations such as warmer temperatures, increased CO 2 , higher nitrogen
deposition, or invasive species. They have also begun to realize how urban ecosystems func-
tion differently from their better-studied nonurban counterparts and that many of the tradi-
tional models and monitoring networks that were developed for either “natural” or
agricultural systems do not work well in urban systems because human effects on primary
drivers of biogeochemical cycles such as hydrology, atmospheric chemistry, nutrients, and
land use are fundamentally altered in urban areas. An example of this is what has been
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