Environmental Engineering Reference
In-Depth Information
methane hydrates
Recently discovered sources of methane (natural gas) that are locked in ice formed at low
temperatures and high pressures, found in the tundra beneath the permafrost or deep in the oceans.
mid-ocean ridge
An opening in the Earth's crust beneath an ocean where magma emerges and creates new, el-
evated sea floor. A mid-ocean ridge appears as a scar along the crust of an ocean bottom.
mobile source pollution
Pollution emitted from a moving source such as a car, truck, train, boat, or plane.
monoculture
The planting of only one crop over a farmed area.
mountaintop removal
A form of mining in which the tops of mountains are blasted off in order to access nat-
ural resources.
municipal waste
Waste from homes, businesses, schools, hospitals, and other institutions.
mutagen
A toxin that causes mutations in the DNA of organisms.
mutualism
A species interaction in which all engaged species benefit.
natural gas
A gaseous combustible fossil fuel used in the production of electricity and home uses (heating,
water heaters, and cooking).
natural selection
The process by which genetic traits that strengthen an organism's chance of survival and re-
production are passed on from generation to generation, eventually dominating less successful genetic traits.
neurotoxin
A toxin that affects the nervous system, including motor control and brain function.
niche
An organism's specific ecosystem position, described by its resources, role in the community, habitat
use, food consumption, interactions with other species, shelter, and other factors.
nitrification
The stage of the nitrogen cycle during which NH
4
+
is converted into nitrite ions (NO
2
-
), and then
into nitrate ions (NO
3
-
).
nitrifying bacteria
Bacteria that conduct nitrification as part of the nitrogen cycle.
nitrogen dioxide (NO
2
)
A reddish-brown gas with a strong odor created from combustion processes at high
temperatures, most commonly in vehicles and electric utilities.
nitrogen-fixing bacteria
A type of bacteria that "fixes" atmospheric nitrogen to a form that can be absorbed
by plants. Nitrogen-fixing bacteria live in the soil and in nodules on the roots of legumes.
nitrous oxide (NO
x
)
Gases containing nitrogen and oxygen that play a role in photochemical smog; they in-
clude nitrogen oxide (NO) and nitrogen dioxide (NO
2
).
noise pollution
Any unwanted, disturbing, or harmful sound that causes irritation or harm to humans.
nonmarket effect
A result for which a fixed dollar amount cannot be attached.
nonnative species
A species that migrates into an ecosystem or is deliberately or accidentally introduced into
an ecosystem by humans.
non-point-source pollution
Pollution for which it is difficult to identify the main source and that may come
from a multitude of smaller sources.
