increasing numbers of manufactured chemicals and products introduced into the environment (EPA 2011a); and increased food and water demand and concomitant changes in land use (NRC 2011). Those demographic, consumption, and production changes contribute to the challenge of addressing environmental problems and health outcomes as increasing amounts of land and resources are demanded to meet human wants and needs.

Changes in Land Use

Land use is a major factor driving environmental quality. Land use strongly influences water quality through runoff, water quantity through influence on the hydrologic cycle, air quality through emissions and deposition and carbon storage in terrestrial landscapes, and biologic diversity through habitat loss, disturbance, and resource availability. In the United States, changes in land use result largely from expansion of urban and agricultural areas, energy development, and changes in forestry practices.

Population growth and demographic transitions have increased the requirement of land area for residential, commercial, and transportation activities (Squires 2002). In the conterminous United States, it has been estimated that up to 45.5 million acres (2.4%) of land is characterized by impervious surfaces (including roads, building, sidewalks, and parking lots) (Nowak and Greenfield 2012). Impervious surfaces change the hydrology and ecology of rivers (higher peak flows and scouring of habitat) and reduce the availability of groundwater for agriculture and other human use. In addition, the interconnected effects of urban sprawl are numerous and complex—greater automobile use in less-densely populated communities can lead to increased air pollution and more sedentary lifestyles, both of which are risk factors for heart disease. Less dense housing also increases energy use per capita and contributes to increased air pollution and climate change and potentially to such adverse health effects as increased asthmatic attacks (Frumkin 2002; Younger et al. 2008; Brownstone and Golob 2009).

Despite increased demand for food and fuel, the land area dedicated to agriculture has not increased substantially over the last few decades. In the United States, acreage devoted to corn has increased over the last 10 years, but total agricultural acreage has been largely unchanged. Agricultural productivity has increased as a result of major investments in research by both the public and private sectors, but there is still uncertainty as to whether the increase can be maintained and, if so, whether it would have associated environmental costs. For example, without substantially increased nutrient-use efficiency, increased amounts of fertilizers will be applied per acre of agricultural land, and therefore increased amounts of those nutrients will be lost to the environment. If increased productivity is not maintained, more acres will need to be devoted to agriculture, probably at the expense of marginally productive lands and natural ecosystems.



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