55

Appendix
56 ■ HYPOXIA IN THE NORTHERN GULF OF MEXICO

algae: a group of chiefly aquatic

plants (e.g., seaweed, pond scum,

stonewort, phytoplankton) that

contain chlorophyll and may passively drift, weakly swim, grow on

a substrate, or establish root-like

anchors (steadfasts) in a water

body.

anoxia: the absence of dissolved

oxygen.

benthic organisms: organisms living

in association with the bottom of

aquatic environments (e.g., polychaetes, clams, snails).

chlorophyll: pigment found in plant

cells that are active in harnessing

energy during photosynthesis.

copepod: zooplankton whose bodies are covered with a hard shell

or crust; order of crustacea.

cyanobacteria: formerly known as

blue-green algae. 

demersal organisms: organisms that

are, at times, associated with the

bottom of aquatic environments,

but capable of moving away from

it (e.g., blue crabs, shrimp, red

drum).

denitrification: nitrogen transformations in water and soil that make

nitrogen effectively unavailable

for plant uptake, usually returning

it to the atmosphere as nitrogen

gas.

diatom: a major phytoplankton

group characterized by cells

enclosed in silicon frustules, or

shells.

edge-of-field nitrogen loss: a term

that refers to the nitrogen that is

lost or exported from fields in

agricultural production.

eutrophic: waters, soils, or habitats

that are high in nutrients; in

aquatic systems, associated with

wide swings in dissolved oxygen

concentrations and frequent algal

blooms.

eutrophication: an increase in the

rate of supply of organic matter to

an ecosystem.

hydrogen sulfide: a chemical, toxic

to oxygen-dependent organisms,

that diffuses into the water as the

oxygen levels above the seabed

sediments become zero.

hypoxia: very low dissolved oxygen concentrations, generally less

than 2 milligrams per liter.

mesotrophic: intermediate between

oligotrophic (low-nutrient) and

eutrophic (high-nutrient) systems. 

nitrate: inorganic form of nitrogen;

chemically NO3.

nonpoint: a diffuse source of chemical and/or nutrient inputs not

attributable to any single discharge (e.g., agricultural runoff,

urban runoff, atmospheric deposition).

nutrients: inorganic chemicals

(particularly nitrogen, phosphorus, and silicon) required for the

growth of plants, including crops

and phytoplankton.

oligotrophic: waters or soils that

have low concentrations of nutrients and have low primary productivity.

pelagic: living or growing in the

water column or at the surface of

the ocean near shore.

phytoplankton: plant life (e.g.,

algae), usually containing chlorophyll, that passively drifts in a

water body.

plankton: organisms living suspended in the water column, incapable of moving against currents.

productivity: the conversion of

light energy and carbon dioxide

into living organic material.

pycnocline: the region of the water

column characterized by the

strongest vertical gradient in density, attributable to temperature,

salinity, or both.

recruitment: the influx, initial survival, and establishment of new

members into a population by

reproduction or immigration.

respiration: the consumption of

oxygen during energy utilization

by cells and organisms.

riparian areas: area adjacent to a

river or other body of water.

senescence: the aging process in

mature individuals; in plants, the

process that occurs before the

shedding of leaves.

stratification: a multilayered water

column, delineated by pycnoclines.

zooplankton: animal life that drifts

or weakly swims in a water body,

often feeding on phytoplankton.

Glossary
Appendix ■ 57

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Conversion Table

Multiply . . . . . . . . . . . . . . . . . . . . . . . . . . . By . . . . . . . . . . . . . . To Obtain

meter (m) 3.281 foot

kilometer (km) 0.6214 mile

square kilometer (km2) 0.3861 square mile

square kilometer (km2) 100 hectare

hectare (ha) 2.471 acre

kilogram (kg) 2.205 pound

metric ton (t) 1,000 kilogram

cubic meters (m3) per second 35.31 cubic feet per second

kilogram per sq. kilometer (kg/km2) 0.008924 pounds per acre

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Proper citation of this document is as follows:

CENR. 2000. Integrated Assessment of Hypoxia in the Northern Gulf of Mexico.

National Science and Technology Council Committee on Environment and

Natural Resources, Washington, DC.

For additional copies or information, please contact:

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