saltwater intrusion
The inflow of ocean (salt) water into a freshwater aquifer that happens when an aquifer has lost some of its freshwater stores. (Chapter 14)
sanitary landfills
Disposal sites that seal in trash at the top and bottom to prevent its release into the atmosphere; the sites are lined on the bottom, and trash is dumped in and covered with soil daily. (Chapter 7)
science
A body of knowledge (facts and explanations) about the natural world and the process used to get that knowledge. (Chapter 2)
scientific method
The procedure scientists use to empirically test a hypothesis. (Chapter 2)
secondary air pollutants
Air pollutants formed when primary air pollutants react with one another or with other chemicals in the air. (Chapter 20)
secondary sources
Sources that present and interpret information solely from primary sources. (Chapter 3)
secondary succession
Ecological succession that occurs in an ecosystem that has been disturbed; occurs more quickly than primary succession because soil is present. (Chapter 10)
seed banks
Places where seeds are stored in order to protect the genetic diversity of the world’s crops. (Chapter 17)
selective pressure
A nonrandom influence that affects who survives or reproduces. (Chapter 11)
service economy
A business model whose focus is on leasing and caring for a product in the customer’s possession rather than on selling the product itself (that is, selling the service that the product provides). (Chapter 6)
sex ratio
The relative number of males to females in a population; calculated by dividing the number of males by the number of females. (Chapter 4)
single-species conservation
A management strategy that focuses on protecting one particular species. (Chapter 13)
sliding reinforcer
Actions that are beneficial at first but that change conditions such that their benefit declines over time. (Chapter 1)
smart growth
Strategies that help create walkable communities with lower ecological footprints. (Chapter 25)
smog
Hazy air pollution that contains a variety of pollutants including sulfur dioxide, nitrogen oxides, tropospheric ozone, and particulates. (Chapter 20)
social trap
Decisions by individuals or groups that seem good at the time and produce a short-term benefit but that hurt society in the long run. (Chapter 1)
solar energy
Energy harnessed from the Sun in the form of heat or light. (Chapter 23)
solar thermal system
An active technology that captures solar energy for heating. (Chapter 23)
solubility
The ability of a substance to dissolve in a liquid or gas. (Chapter 3)
species
A group of plants or animals that have a high degree of similarity and can generally only interbreed among themselves. (Chapter 8)
species diversity
The variety of species, including how many are present (richness) and their abundance relative to each other (evenness). (Chapter 10, 12)
species evenness
The relative abundance of each species in a community. (Chapter 10)
species richness
The total number of different species in a community. (Chapter 10)
statistics
The mathematical evaluation of experimental data to determine how likely it is that any difference observed is due to the variable being tested. (Chapter 2)
stormwater runoff
Water from precipitation that flows over the surface of the land. (Chapter 15)
stratosphere
The region of the atmosphere that starts at the top of the troposphere and extends up to about 31 miles; contains the ozone layer. (Chapter 2)
strip cropping
Alternating different crops in adjacent strips, several rows wide; helps keep pest populations low. (Chapter 17)
subsidies
Financial assistance given by the government or other party in support of actions that are expected to benefit the public good. (Chapter 20, 24)
subsurface mines
Sites where tunnels are dug underground to access mineral resources. (Chapter 18)
suburban sprawl
Low-population-density developments that are built outside of a city. (Chapter 25)
surface mining
A form of mining that involves removing soil and rock that overlays a mineral deposit close to the surface in order to access that deposit.
surface water
Any body of water found above ground, such as oceans, rivers, and lakes. (Chapter 14)
sustainable
Capable of being continued without degrading the environment. (Chapter 1, 6)
sustainable agriculture
Farming methods that can be used indefinitely because they do not deplete resources, such as soil and water, faster than they are replaced. (Chapter 17)
sustainable development
Economic and social development that meets present needs without compromising the ability of future generations to do the same. (Chapter 1, 6)
sustainable energy
Energy from sources that are renewable and have a low environmental impact. (Chapter 23)
symbiosis
A close biological or ecological relationship between two species. (Chapter 10)
synergistic effects
Exposure to two or more chemicals that has a greater effect than the sum of their individual effects would predict. (Chapter 3)