Environmental Encyclopedia

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Environmental Encyclopedia 3

Double-crested cormorants

Ecologists have developed a number of quantitative

indices to describe the dominance of species within commu-

nities. One of these is known as the community dominance

index (CDI). It is calculated as the percentage of the total

abundance of all species in the community that is contributed

by the two most abundant species, as in:

CDI=100x(y

)/Y

where y

is the abundance of the most abundant spe-

cies, y

is that of the second-most abundant species, and Y

is the total of the abundances of all species in the community.

For these purposes, abundance may be estimated by

bio-

mass

, density, cover, productivity, or another suitable mea-

surement. In general, communities with high values of CDI

have relatively little community-level diversity. This rela-

tionship is being actively explored by ecologists who are

interested in the environmental factors that control the levels

biodiversity

in natural and managed ecosystems.

[Bill Freedman Ph.D.]

ESOURCES

OOKS

Begon, M., Harper, J.L., and Townsend, C.R. Ecology. Individuals, Popula-

tions and Communities. 3rd ed. London: Blackwell Sci. Pub., 1996.

Ricklefs, R.E. Ecology. New York: W.H. Freeman and Co., 1990.

Dose response

Dose response is the relationship between the effect on living

things and a stimulus from a physical, chemical, or biological

source. Examples of stimuli include therapeutic drugs, pesti-

cides, pathogens, and radiation. A quantal response occurs

when the living thing either responds or does not respond

to a stimulus of a given dose. Graded responses proportional

to the size of the stimulus are also found in environmental

applications. Some types of responses have a significant time

effect. The Effective Dose for affecting 50% of a population

of test subjects, ED

, and the Lethal Dose for killing 50%

of a population of test subjects,

, are commonly used

parameters for reporting the toxicity of an environmental

pollutant. See also Pollution; Radiation exposure; Toxic sub-

stance

Double-crested cormorants

The double-crested cormorant (Phalacrocorax auritus)isa

large (30–36 in; 73–90 cm), blackish water bird that eats fish

and crustaceans. The double-crested cormorant population

around the

Great Lakes

(but not in other areas) was once

in serious decline. It has now has recovered. In fact, some

377

fishermen feel that there are too many double-crested cor-

morants. These fishermen believe that an abundance of dou-

ble-crested cormorants is responsible for a decline in fish

populations in the Great Lakes. The

conservation

of this

bird entails weighing the interests of the fishing industry

against the interests of a now-abundant bird whose range

is expanding.

The double-crested cormorant is a large migratory

water bird native to North and Central America. The bird

is found along the West Coast as far north as southern

Alaska, wintering in Southern California and Baja Califor-

nia. On the East Coast it breeds from Maryland to New-

foundland, wintering along the southern coast to Florida,

the Bahamas, and Cuba. Inland, double-crested cormorants

breed along the upper Mississippi Valley and in the Great

Lakes and winter on the Gulf Coast.

The first double-crested cormorant in the great Lakes

region were sighted on the western shore of Lake Superior

in 1913. By the 1940s, the population around the Great

Lakes had increased to about 1,000 nesting pairs. Subse-

quently, the cormorant population began to decline. By 1973

a survey found only 100 pairs in the region.

In the early 1970s, cormorants were not the only water

bird whose population was declining. Around this time,

the United States Congress enacted several laws to protect

cormorants and other waterfowl. For example, the

pesticide

DDT was banned in 1972. This chemical had entered lakes

and rivers in run-off water and was implicated in reducing

the birth rate of fish-eating birds, including the

bald eagle

Congress also amended the Migratory Bird Treaty Act, first

passed in 1917, to make it illegal to harm or kill cormorants

and other migrating water fowl.

The double-crested cormorant populations around the

Great Lakes began to increase in the 1980s, and the birds

expanded their range eastward to

Lake Erie

and Lake On-

tario. The return of the double-crested cormorant seemed

to some conservationists to signal that the Great Lakes, once

seriously polluted, were recovering. However, one reason the

cormorant population may have increased around the Great

Lakes is that

overfishing

during this time seriously depleted

the number of large fish in the lakes. This led to an increase

in the number of smaller fish such has smelt (Osmerus mor-

dax) and alewife (Alosa pseudoharengus). Cormorants eat

these small fish. An increase in their food supply may have

contributed to an increase in the cormorant population.

Another ecological problem, the

zebra mussel

, may

also have helped the cormorant. The zebra mussel is an

exotic (non-native) invasive mussel that competes with native

mussels for food resources. It is a voracious feeder and can

clean lakes of green

plankton

, leaving the water particularly

clear. Clear water may have helped the cormorant, which

hunts fish by sight, find food more easily.

Environmental Encyclopedia 3

Marjory Stoneman Douglas

By the 1990s, some local cormorant populations had

grown to unprecedented proportions, and at the same time,

sport fish populations had declined. As a result, some Great

Lakes fishermen, refusing to consider the role of overfishing

in the decline of fish populations, blamed double-crested

cormorants for steep drops in populations of fish such as

smallmouth bass (Micropterus dolomieui), rock bass (Am-

bloplites rupestris), and brown bullheads (Ameiurus nebulosus).

An adult cormorant weighs about four pounds, and eats

about one pound of fish a day. Some areas hosted flocks of

thousands of cormorants. A 1991 study of cormorants in

Lake Ontario estimated that the birds had consumed about

five million pounds of fish. In addition, cormorants tend to

eat smaller fish, and if enough fish are eaten before they can

reproduce,

future generations

of fish are threatened.

Although fishermen have blamed the cormorant for

declining fish populations, conservationists have insisted on

scientific studies to determine if these birds are indeed caus-

ing a decline in fish populations. A 1998 study of cormorants

on Galloo Island in Lake Ontario found that the smallmouth

bass, a popular sport fish, made up just 1.5% of the cormo-

rant’s diet. Yet because the cormorants ate small bass that

had not yet grown to reproductive maturity, the bird was

considered linked to the smallmouth’s decline.

Another 2000 study of the Beaver Islands area in Lake

Michigan concluded that it likely the large cormorant popu-

lation was a factor in the declining numbers of smallmouth

bass and other fish. Yet the biologist who led the study was

unable to conclude that cormorants were entirely responsible

for the decline in the fish population. However,

wildlife

officials took action to manage this cormorant population.

Cormorants also have made themselves unpopular be-

cause they nest in large colonies, where thick layers of their

droppings can kill off underlying vegetation and leave the

area denuded of all but a few trees. Cormorant colonies have

endangered some sensitive woodland habitats and contrib-

uted to

soil erosion

by killing shoreline plants.

Because federal law protects double-crested cormo-

rants, people cannot legally harass or kill these birds. In

1999, nine men were convicted of slaughtering 2,000 cormo-

rants on Little Galloo Island in Lake Ontario. These men

had illegally tried to reduce the cormorant colony by shooting

adult birds. Soon after the incident, however, the New York

Department of Environmental Conservation enacted a plan

to reduce the Galloo colony from 7,500 to 1,500 birds over

five years by spraying vegetable oil on cormorant eggs. The

oil-coated eggs do not hatch. This method of thinning the

flock was considered less disruptive to other wildlife and

more humane than killing adult birds.

The New York program generated controversy, as not

all scientists who had studied the birds believed that double-

crested cormorants were responsible for the decline of the

378

fish population, and some conservationists feared similar

programs would be enacted against other fish-eating birds.

Ironically, success in protecting the double-crested cormo-

rant in the 1970s resulted in controversy two decades later.

Even though the population of double-crested cormorants

substantially increased, the bird is still under federal protec-

tion. Any action to manage the cormorant population must

be carefully developed, implemented, and evaluated.

[Angela Woodward]

ESOURCES

OOKS

Johnsgard, Paul A. Cormorants, Darters, and Pelicans of the World. Washing-

ton: Smithsonian Institution Press, 1993.

ERIODICALS

Farquar III, James F. “Balancing Act: Managing Cormorants in Upstate

New York.” New York State Conservation 56, no. 1 (August 2001): 26.

Kloor, Keith. “Killing All Cormorants?” Audubon (July/August 1999): 16.

Sharp, Eric. “Controversy Surrounds Cormorants.” Outdoor Life (August

2000): 119.

“State Studies Show Cormorants’ Toll on Fish.” New York Times (December

20, 1998): 64.

Wallace, Scott. “Who Killed the Cormorants?” Sports Afield 222, no. 3

(September 1999): 72.

Marjory Stoneman Douglas (1890 –

1998)

American environmentalist and writer

A newspaper reporter, writer, and environmentalist re-

nowned for her crusade to preserve Florida’s

everglades

Marjory Stoneman Douglas was part of the committee that

first advocated formation of the Everglades

National Park

in 1927, and she has been an active advocate of the area’s

preservation ever since. Born In 1890 in Minneapolis and

raised in Taunton, Massachusetts, Marjory Stoneman

Douglas graduated from Wellesley College in 1912. After

a brief marriage to Kenneth Douglas, a newspaper editor,

she moved south to Florida in 1915 to join her father. She

soon began to work as a reporter, columnist, and editor for

the Miami Herald, founded by her father, Judge Frank Bryant

Stoneman. During World War I, she left Miami to become

the first female enlistee for the Naval Reserves, then joined

the Red Cross, for which she worked and traveled in Europe

during and after the war. Returning to Coconut Grove in

1920, Douglas remained there for over 75 years.

Douglas was involved very early in efforts to preserve

the everglades from agricultural and residential development,

as was her father before her. Her book, The Everglades:

River of Grass was one of the most important statements

publicizing the ecological importance and uniqueness of the

Environmental Encyclopedia 3

Drainage

area, as well as its plight in the face of

drainage

, filling,

and water diversion. Her framing of the region as a “river

of grass” effectively instilled in the general public an idea of

the interconnectedness of the land, water, plants, and ani-

mals of the area, helping to raise public awareness of the

urgency of preserving the entire

ecosystem

, not just isolated

components of it.

Douglas did not start out as a full-time environmental

advocate. She wrote The River of Grass because she loved

the history and the natural history of the area, and she was

a long-time supporter of preserving the ecosystem, but she

did not become deeply involved in the movement to save

the everglades until the l970s. Friends of Douglas’ in the

National Audubon Society

, confronted in 1969 by propos-

als to build an airport in the everglades, enlisted her aid

and she helped organize the Friends of the Everglades, an

organization that continues to defend the Park and related

south Florida ecosystems.

Douglas proved to be an eloquent and forceful speaker

and writer in the cause to save the everglades from develop-

ment, and since the 1970s the everglades has become her

single cause for celebrity. However she had also written

poetry, short stories, histories, natural histories and novels,

nearly all based in Florida. Initially her writing was popular

at least in part because Florida and its history were little

known, and rarely written about, when she began her literary

career. Among her other publications are Road to the Sun

(1951), Hurricane (1958), Florida: the Long Frontier (1967),

and Nine Florida Stories (1990). She also wrote an autobiog-

raphy, co-authored by J. Rothchild, Marjory Stoneman Doug-

las: Voice of the River.

In 1990, Douglas was honored on her one hundredth

birthday with book signings, interviews, and banquets, and

in 1992, she was back in action. That year, Douglas spoke

out against President George Bush’s proposal to modify the

definition of “wetlands,” a move that critics pointed out

could open the door to future development. President Bill

Clinton in 1993 called to wish her a happy birthday as

she turned 103, and a few months later, awarded her the

Presidential Medal of Freedom. In 1994, Florida state law-

makers passed the Everglades Forever Act, and also in the

1990s the federal government committed hundreds of mil-

lions of dollars to restore and protect the area. In 1996,

Florida voters passed an amendment to their state’s constitu-

tion that makes Everglades polluters, particularly sugar farm-

ers, pay for clean-up costs, and more plans to save the

wet-

lands

were expected. However, voters did not pass a law to

tax sugar at a penny a pound to assist with the effort; sugar

producers had successfully argued that the ruling would cost

many jobs.

Douglas received a bevy of honors in her lifetime,

including Floridian of the Year in 1983 and a number of

379

buildings, schools, and parks named after her. The building

in Florida’s capitol of Tallahassee that is home to the state

Department of Natural Resources also bears her name, as

does a special

conservation

award. Douglas died in her

sleep at home on May 14, 1998.

On October 7, 2000, Douglas was inducted into the

National Women’s Hall of Fame in Seneca Falls, New York.

[Mary Ann Cunningham Ph.D.]

ESOURCES

OOKS

Douglas, M. S. The Everglades: River of Grass. New York: Reinhart, 1947.

ERIODICALS

Chusmir, J. “The Time and Possibilities of Marjory Stoneman Douglas.”

Miami Herald, April 6, 1975.

Soba, D. “Still Fighting the Good Fight.” Audubon 93 (1991): 30–39.

THER

Newsmakers 1998. Issue 4. Farmington Hills, MI: The Gale Group. 2002.

Drainage

The

hydrologic cycle

encompasses all movements of water

molecules through the

atmosphere

, hydrosphere, and

groundwater

zones. One key part is the drainage of surface

waters and groundwater back to the ocean. Natural drainage

systems are well-adjusted to their

climate

, vegetation, and

geology. Hydrologists and fluvial geomorphologists have

studied these systems in great detail; human disturbances

are readily apparent. Three impacts are considered here:

wetland drainage and

irrigation

; dam construction and min-

ing alterations; and urbanization.

Robert E. Horton identified many drainage character-

istics during the 1930s and 1940s. Later researchers added

other useful quantitative parameters. All of these show the

predictable patterns found in natural drainage systems. Best

known are stream order and drainage density. Although

influenced by the detail of the maps used (commonly

1:24,000 or 1:62,500 topographic maps), stream order pro-

vides a simple system for ranking tributaries. The smallest

ones are labeled first order, second-order streams have at

least two first-order tributaries, third-order streams have at

least two second-order tributaries, and so forth. The Missis-

sippi River is ranked as a tenth- or twelfth-order stream,

depending on the map scale used. Horton also developed a

bifurcation ration between stream orders, which is generally

around three; that is, on average there are three second-

order streams for each third-order one.

Drainage density is a measure of channel length per

unit area. This varies widely depending on the nature of the

vegetation cover and

soil

. Badlands and deserts have high

Environmental Encyclopedia 3

Dredging

drainage densities compared to well-vegetated basins with

permeable

soils.

Stream channels are finely adjusted to their drainage

requirements, and attain a state of quasi-equilibrium. Hu-

man activities disrupt this equilibrium, forcing channel ad-

justments. This disruption is so pervasive that essentially all

channels within settled areas have been impacted.

The earliest human intrusions are wetland drainage

and irrigation of

arid

lands for agriculture. Recent litigation

has involved decisions by federal officials to deny irrigation

water to farmers in order to maintain needed supplies for

endangered aquatic organisms. Only recently has the ten-

dency to drain

wetlands

been reversed. With the comeback

of the beaver from near

extinction

, wetland proponents now

have an efficient ally.

Many large rivers have been dammed, with direct im-

pact on the downstream riparian

environment

. To counter-

act this, in 1996, an experimental flood was produced on

the

Colorado River

through the Grand Canyon, with the

desired goal of improving

habitat

for

endangered species

there. Even farm ponds, through their sheer numbers, are

major drainage interrupters. Another strong impact has

come from mining, through the creation of huge holes,

massive

sedimentation

, or increased

runoff

Urbanization has had the greatest local impact on

drainage. Channels are altered, permeable areas are covered

with impervious materials, and storm drains deliver runoff

more rapidly to the overwhelmed drainage network. The

effect is to deliver much more water in substantial less time,

a sure formula for

flooding

Tulsa, Oklahoma, is a case study in urban flooding

and costly

remediation

. A computerized system now evalu-

ates rain and stream-gage data in real time, and issues flood

warning via sirens throughout the city. Construction is

banned within the 100-year flood, and valuable land has

been set aside for detention ponds so that runoff does not

exceed natural conditions up to the level of a 100-year flood.

Though costly, these steps have been essential in order to

protect lives and reduce property damage.

Changes in the drainage network are prime indicators

of human impact. If we are to work with nature rather than

fight her, we must understand and reckon with the impacts

of our development on this fragile and finely tuned system.

[Nathan Meleen]

URTHER

EADING

Cooke, R.U., and J.C. Doornkamp. Geomorphology in Environmental Man-

agement. London: Oxford University Press, 1974.

Leopold, L.B., M.G. Wolman, and J.P. Miller. Fluvial Processes in Geopmor-

phology. San Francisco: W.H. Freeman, 1964.

380

Strahler, A.N., and A.H. Strahler. Modern Physical Geography 2nd ed. New

York: John Wiley & Sons, 1983.

Dredging

Dredging is a process to remove

sediment

. Dredging sedi-

ment to construct new ports and navigational waterways or

maintain existing ones is essential for vessels to be able to

enter shallow areas. Maintenance dredging is required be-

cause sediment suspended in the water eventually settles out,

gradually accumulating on the bottom. If dredging were not

done, harbors would eventually fill in and marine

transpor-

tation

would be severely limited. Dredging is also used to

collect sediment (usually sand and gravel) for construction

and other commercial uses. Hundreds of millions of cubic

feet of sediment are dredged from marine bottoms annually

in the United States and throughout the world.

One of the oldest types of dredging is agitation dredg-

ing, which uses a combination of mechanical and hydraulic

processes and dates back over 2,000 years. An object is

dragged along the bottom with the prevailing current; this

suspends the sediment and the current carries the suspended

material away from the area. Technology currently used to

dredge sediment from a harbor, bay, or other marine bottom

consists of hydraulic or mechanical devices. Hydraulic dredg-

ing involves suspending the sediment, which mixes with

water to form a

slurry

, and pumping it to a

discharge

site. Mechanical dredging is typically used to dredge small

amounts of material. It lifts sediment from the bottom by

metal clamshells or buckets without adding significant

amounts of water, and the dredged material is usually trans-

ferred to a barge for disposal at a particular site.

Most of the dredging that occurs in the United States is

hydraulic dredging. Hopper dredges are vessels that employ

hydraulic dredging, and they are often used in the open

ocean or in areas where there is vessel traffic. The ship’s

hull is filled with dredged material and the ship moves the

material to a designated disposal site where it is dumped

through doors in the hull. Pipeline dredges use hydraulic

dredging to remove sediment in nearshore areas, and the

dredged material is discharged through a pipeline leading

to a beach or diked area. Approximately 550 million wet

metric tons of sediment are dredged from the waters of

the United States each year, and an estimated one-third is

disposed in the marine

environment

, accounting for the

greatest amount of waste material dumped in the ocean. Of

the dredged material dumped in the marine environment,

66% is disposed in estuaries. Two dozen marine disposal

sites in the United States receive approximately 95% of all

of the dredged material disposed at sea.

Dredged material is typically composed of

silt

, clay,

and sand, and can sometimes include gravel, boulders, or-

Environmental Encyclopedia 3

Dredging

ganic matter, as well as chemical compounds such as sulfides,

hydrous oxides, and metal and organic contaminants. The

grain size of the dredged sediment will determine the condi-

tions under which the sediment will be deposited or resus-

pended if disposed in the marine environment.

The choice of where the dredged material should be

placed depends on whether it is uncontaminated or contami-

nated by pollutants. If contaminated, the level of pollutants

in the dredged material can also play a role in the decision of

the type and location of disposal. Because many navigational

channels and ports are located in industrialized areas, and

because sediments are a sink for many pollutants, dredged

material may be contaminated with toxic metals, organoha-

logens,

petrochemical

by-products, or other pollutants.

Dredged material can also contain contaminants from ag-

ricultural and urban sources.

Dredged material with very little contaminants can be

placed in a variety of locations and beneficially reused for

beach restoration, construction aggregate, fill material, cover

for sanitary landfills, and

soil

supplementation on agricul-

tural land. The primary concerns over the disposal of uncon-

taminated dredged material in the marine environment are

the physical impacts it can have, such as high turbidity in

the water column, changes in grain size, and the smothering

of bottom dwelling organisms. The ensuing alterations to

the bottom

habitat

can lead to changes in the benthic com-

munity. Deposited dredged sediment is usually recolonized

by different organisms than were present prior to the disposal

of the dredged material. For example, disposal of sediment

from a dredging project in Narragansett Bay, Rhode Island

changed the bottom

topography

and sediment type, and

this change in benthic habitat led to a subsequent decline

in the clam and finfish fishery at the site and an increase in

the lobster fishery. If the dredged material is similar to the

sediment on which it is dumped, the area may be recolonized

by the same

species

that were present prior to any dumping.

If dredged material is dumped in an area that has less

than 197 ft (60 m) of water, most of the material will rapidly

descend to the bottom as a high-density mass. A radial

gradation of large-to-fine grained sediment usually occurs

from the impact area of the deposition outward. Fine-

grained material spreads outward from the disposal site, in

some cases up to 328 ft (100 m), in the form of a fluid mud.

It can range in thickness up to 3.9 in (1 dm). From one to

five% of the sediment remains suspended in the water as

plume

; this sediment plume is transient in

nature

and

eventually dissipates by dispersion and gravitational settling.

The long-term fate of dredged material dumped in the ma-

rine environment depends on the location of the dumping

site, its physical characteristics such as bottom topography

and currents, and the nature of the sediment. Deep-ocean

dumping of dredged material results in wider dispersal of

381

the sediment in the water column. The deposition of the

dredged material becomes more widely distributed over the

ocean bottom than in nearshore areas.

Dredging contaminated sediment poses a much more

severe problem for disposal. Disposing contaminated

dredged material in the marine environment can result in

long-term degradation to the

ecosystem

. Sublethal effects,

biomagnification

of pollutants, and genetic disorders of

organisms are some examples of possible long-term effects

from toxic pollutants in contaminated dredged material en-

tering the food chain. However, attributing effects from

placement of contaminated dredged material at a marine

site to a specific cause can be very difficult if other sources

of contaminants are present.

Dredged material must be tested to determine contam-

ination levels and the best method of disposal. These tests

include bulk chemical analysis, the elutriate test, selective

chemical

leaching

, and bioassays. Bulk chemical analysis

involves measurements of volatile solids,

chemical oxygen

demand

, oil and grease,

nitrogen

mercury

, lead, and zinc.

But this chemical analysis does not necessarily provide an

adequate assessment of the potential environmental impact

on bottom dwelling organisms from disposal of the dredged

material. The elutriate test is designed to measure the poten-

tial release of chemical contaminants from suspended sedi-

ment caused by dredging and disposal activities. However,

the test does not take into account some chemical factors

governing sediment-water interactions such as complex-

ation,

sorption

, redox, and acid-base reactions.

Selective chemical leaching divides the total concen-

tration of an element in a sediment into identified phases.

This test is better than the bulk chemical analysis for provid-

ing information that will predict the impact of contaminants

on the environment after the disposal of dredged material.

Bioassay

tests commonly use sensitive aquatic organisms

to measure directly the effects of contaminants in dredged

material as well as other waste materials. Different concen-

trations of wastes are measured by determining the waste

dilution that results in 50%

mortality

of the test organisms.

Permissible concentrations of contaminants can be identified

using bioassay tests.

If dredged material is considered contaminated, special

management and long-term maintenance are required to

isolate it from the rest of the environment. Special manage-

ment techniques can include capping dredged material dis-

posed in water with an uncontaminated layer of sediment,

a technique which is recommended in relatively quiescent,

shallow water environments. Other management strategies

to dispose contaminated dredged material include the use

of upland containment areas and containment islands. The

use of submarine burrow pits has also been examined as a

possible means to contain contaminated dredged material.

Environmental Encyclopedia 3

Drift nets

There is more than one law in the United States gov-

erning dredging and disposal operations. The General Sur-

vey Act of 1824 delegates responsibility to the

Army Corps

of Engineers

(ACOE) for the improvement and mainte-

nance of harbors and navigation. The ACOE is required to

issue permits for any work in navigable waters, according to

the Rivers and Harbors Act of 1899. The Marine Protection,

Research, and Sanctuaries Act (MPRSA) of 1972 requires

the ACOE to evaluate the transportation and

ocean dump-

ing

of dredged material based on criteria developed by the

Environmental Protection Agency

(EPA), and to issue

permits for approved non-federal dredging projects. Desig-

nating ocean disposal sites for dredged material is the respon-

sibility of EPA. The discharge of dredged material through

a pipeline is controlled by the Federal

Water Pollution

Control Act, as amended by the

Clean Water Act

(1977).

This act requires the ACOE to regulate ocean discharges

of dredged material and evaluate projects based on criteria

developed by the EPA in consultation with the ACOE.

Other Federal agencies such as the U. S.

Fish and Wildlife

Service

and the National Marine Fisheries Service can pro-

vide comments and recommendations on any project, but

the EPA has the power to veto the use of proposed disposal

sites. See also Agricultural pollution; Contaminated soil;

Hazardous waste; LD50; Runoff; Sedimentation; Syner-

gism; Toxic substance; Urban runoff

[Marci L. Bortman Ph.D.]

URTHER

EADING

Bokunwiewicz, H. J. “Submarine Borrow Pits as Containment Sites for

Dredged Sediment.” Wastes in the Ocean. Volume 2, Dredged Material

Disposal in the Ocean, edited by D. R. Kester, et al. New York: Wiley, 1983.

Engler, R. M. “Managing Dredged Materials.” Oceanus 33 (1990): 63-9.

Kamlet, K. S. “Dredge-Material Ocean Dumping: Perspectives on Legal

and Environmental Impacts.” Wastes in the Ocean. Volume 2, Dredged

Material Disposal in the Ocean, edited by D. R. Kester, et al. New York:

Wiley, 1983.

Kester, D. R., et al. “The Problem of Dredged-Material Disposal.” Wastes

in the Ocean. Volume 2, Dredged Material Disposal in the Ocean, edited by

D. R. Kester, et al. New York: Wiley, 1983.

Kester, D. R., et al. “Have the Questions Concerning Dredged-Material

Disposal Been Answered?” Wastes in the Ocean. Volume 2, Dredged Material

Disposal in the Ocean, edited by D. R. Kester, et al. New York: Wiley, 1983.

Office of Technology Assessment. Wastes in Marine Environments. OTA-

O-334. Washington, DC: U.S. Government Printing Office, 1987.

Dreissena polymorpha

see

Zebra mussel

382

Drift nets

Drift nets are used in large-scale

commercial fishing

opera-

tions. Miles-long in length, nets are suspended from floats

at various depths and set adrift in open oceans to capture

fish or squid. Drift nets are constructed of a light, plastic

monofilament that resists rotting. These nets are generally

of a type known as gill nets, because fish usually become

entangled in them by their bony gill plates. The fishing

industry has found these nets to be cost-effective, but their

use has become increasingly controversial. They pose a

severe threat to many forms of marine life, and they have

long been the object of protests and direct action from a

range of environmental groups. National and international

policies concerning their use have only recently begun to

change.

Drift nets are not selective; there is no way to use

them to target a particular species of fish. Drift nets can

catch almost everything in their path, and there are few

protections for species that were never intended to be caught.

Although some nets can be quite efficient in capturing only

certain species, the

bycatch

from drift nets can include not

only non-commercial fish, but sea turtles, seabirds, seals and

sea lions,

sharks

, porpoises,

dolphins

, and large whales.

Nets that are set adrift from fishing vessels in the open ocean

and never recovered pose an even more severe hazard to the

marine environment. Lost nets can drift and kill animals for

long periods of time, becoming what environmentalists have

called “ghost nets.”

Drift nets are favored by fishing industries in many

countries because of their economic advantages. The equip-

ment itself is relatively inexpensive; it is also less labor inten-

sive than other alternatives, and it supplies larger yields

because of its ability to capture fish over such broad areas.

Drift-net fisheries can vary considerably, according to the

target species and the type of fishing environment. In coastal

areas, short nets can be set and recovered in an hour. The

nets do not drift very far in this time and the environmental

damage can be limited. But in the open ocean, where the

target species may be widely dispersed, nets in excess of 31

mi (50 km) in length may be set and allowed to drift for 24

hours before they are recovered and stripped. The primary

targets for drift netting include squid in the northern Pacific,

salmon in the northeastern Pacific, tuna in the southern

Pacific and eastern Atlantic, and swordfish in the Mediter-

ranean.

Because of their cost-effectiveness, the Food and Ag-

ricultural Organization (FAO) of the United Nations ac-

tively promoted the use of drift nets during the early 1980s.

Earthwatch

, Earth Island Institute, and other environmen-

tal groups instituted drift-net monitoring during this period

and founded public education programs to pressure drift-

Environmental Encyclopedia 3

Drift nets

Drift net. (Photograph by Dan Guravich. Photo Researchers Inc. Reproduced by permission.)

net fishing nations. The Sea Shepherd Conservation Society

and other direct action groups have actually intervened with

drift-net fishing operations on the high seas. Organizations

such as these led international awareness about the dangers

of drift nets, and their efforts have affected national and

international policy. In December of 1991, the United Na-

tions reversed its earlier endorsement of drift-net fishing

and adopted General Assembly Regulations 44-225, 45-

197, and 46-215 that totally banned high seas drift nets.

The regulations applied to all international waters and went

into effect on December 31, 1992. An agreement between

the United States and the South and Central American

countries of Costa Rica, Ecuador, Mexico, Nicaragua, Pan-

ama and Venezuela for a moratorium on drift nets was also

signed. In 1998, the European Union banned all drift nets

in its jurisdiction, with the exception of the Baltic Sea. The

ban took effect in 2002. The regulatory body for the Baltic

Sea is the International Baltic Sea Fishery Commission,

which sets more liberal restrictions on nets and catch limits

than the

European Union

(EU).

According to the United States National Marine Fish-

eries Service, enforcement of the drift net ban in the north

383

Pacific has been successful, and the U.S. salmon fishery

in these waters is no longer impacted by illegal drift nets.

Enforcement of this ban in other waters has so far proven

difficult, however, as drift net fishing is done in open oceans,

far from national jurisdictions. In reaching enforceable inter-

national agreements about drift net fishing, the primary

problem has been the large investment some nations have

in this technology. Japan had 457 fishing vessels using drift

nets in 1990, and Taiwan and Korea approximately 140

vessels each. France, Italy, and other nations own smaller

fleets.

Japan and many of these nations are primarily con-

cerned with protecting their investment, despite worldwide

protest. The United States and Canada have both expressed

concern about ecological integrity and the rate of unintended

catch in drift nets, particularly the bycatch of North Ameri-

can salmon. In the 1990s, bilateral negotiations were pur-

sued with Korea and Taiwan to control their drift net fleets.

The International North Pacific Fisheries Commission has

provided a forum for United States, Japan, and Canada to

examine and discuss the economic advantages and environ-

mental costs of drift net fishing. A special committee has

Environmental Encyclopedia 3

Drinking-water supply

analyzed bycatch from drift nets used in the northern Pacific.

Three avenues are currently being considered to control eco-

logical damage: the use of subsurface nets, research into the

construction of biodegradable nets, and alternative gear types

for capturing the same species. The Irish Sea Fisheries Board

has tested trawl nets as an alternative to drift nets, and

found that they are effective in catching tuna. However,

environmental groups have raised the concern that trawl nets

also capture significant numbers of marine mammals, and

have called for restrictions on their use after the Irish Sea

Fisheries Board study found that more than 140 whales and

dolphins were killed by trawlers during the two year study.

[Douglas Smith and Marie H. Bundy]

URTHER

EADING

ERIODICALS

Bowden, C. “At Sea With the Shepherd.” Buzzworm 3 (March-April

1991): 38-47.

McCloskey, W. and C. Wallace. “Casting Drift Nets with the Squidders.”

International Wildlife 21 (March-April 1991): 40-47.

“Net Losses.” Sierra 76 (March-April 1991): 48-54.

“U.S. Considers Ratification of Driftnet Fishing Treaty.” U. S. Department

of State Dispatch 2 (26 August 1991): 639-40.

Drinking-water supply

The

Safe Drinking Water Act

, passed in 1974, required

the

Environmental Protection Agency

(EPA) to develop

guidelines for the treatment and monitoring of public water

systems. In 1986, amendments to the act accelerated the

regulation of contaminants, banning the future use of lead

pipe, and requiring surface water from most sources to be

filtered and disinfected. The amendments also have provi-

sions for greater

groundwater

protection. Despite the im-

provement these regulations represent, only public and pri-

vate systems that serve a minimum of 25 people at least 60

days a year are covered by them. Millions obtain their drink-

ing water from privately owned

wells

that are not covered

under the act.

Drinking water comes from two primary sources: sur-

face water and groundwater. Surface water comes from a

river or lake, and groundwater, which is pumped from under-

ground sources, generally needs less treatment. Contami-

nants can originate either from the water source or from the

treatment process.

The most common contaminants found in the public

water supply are lead, nitrate, and radon–all of which pose

substantial health threats. Studies indicate that substances

such as

chlorine

and fluoride which are added to water

during the treatment process may also have adverse effects

on human health. Over 700 different contaminants have

384

been found in water supplies in the United States, yet the

EPA has only established maximum containment levels for

30 of them. Drinking water enforcement has been severely

limited at both the state and federal levels. In 1990, 38,000

public water systems committed over 100,000 violations of

the act, yet state governments only took legal enforcement

action against 1,000, and the federal government took action

against only 32. In only 6% of these cases were customers

informed of the violations.

Chlorinated water was first used in 1908 as a means

of reducing diseases in Chicago stockyards.

Chlorination

which kills some disease-causing

microbes

, is now used to

disinfect approximately 75% of the water supply in the

United States. Numerous studies conducted over the past

20 years have found that chlorine reacts with organic prod-

ucts such as farm

runoff

or decaying leaves to form by-

products that increase the risk of certain kinds of

cancer

These by-products of chlorination are associated with cancer

of the bladder and of the colon, probably because both

store concentrated waste products. Research released by the

Medical College of Wisconsin suggests that drinking chlori-

nated water increases the risk of bladder cancer by 20% and

the risk of rectal cancer by 38%. Despite the correlation

between chlorination by-products and these types of cancer,

many still believe that the benefits of chlorine disinfection

outweigh the risks. Some hope this study will prompt those

in charge of public water systems to investigate other meth-

ods of disinfection, such as the use of

ozone

or exposure to

ultraviolet light, both of which are currently used in Europe.

The effectiveness of fluoridated water in reducing den-

tal cavities was first noted in communities with a naturally

occurring source of fluoride in their drinking water, and

controlled studies of communities where fluoride was added

to the water confirmed the results. As of 1989, residents in

70% of all cities with populations greater than 100,000 were

drinking fluoridated water. The EPA limit for fluoride in

water is 4

parts per million

(ppm), and most cities add

only one ppm to their water. Fluoridated water also has

adverse effects, and these may include immune system sup-

pression, tooth discoloration, undesirable bone growth,

en-

zyme

inhibition, and carcinogenesis.

The EPA has set the acceptable level of lead in drink-

ing water at 15

parts per billion

(ppb), yet according to

tests the agency has done, drinking water in almost 20% of

cities in the United States exceeds that limit. The EPA has

estimated that 25% of a child’s lead intake comes from

drinking water, and it cautions that the percentage could

be much higher if the water contains high levels of lead.

Depending on exposure, lead

poisoning

can cause perma-

nent learning disabilities, behavioral and nervous system dis-

orders, as well as severe brain damage and death. Service

pipes made of lead and leaded solder used on

copper

plumb-

Environmental Encyclopedia 3

Drinking-water supply

ing and brass faucets are the main sources of lead in water.

Acidic or soft water increases the danger of lead contamina-

tion, because it corrodes the plumbing and leeches out the

lead. About 80% of homes have water that is moderately to

highly acidic. As of January 1, 1993, EPA regulations require

all large public water companies to reduce the corrosiveness

of water by adding calcium oxide or other hardening agents.

Chlorination and government standards for drinking

water quality

have virtually eliminated the outbreak of the

classic water-borne diseases such as

cholera

, typhoid, and

malaria

. According to The American Journal of Public Health,

however, recent studies have shown that water that meets

current drinking water standards can still contain organisms

which cause gastrointestinal (GI) disease. In a 15-month

study conducted by the University of Quebec in Montreal,

researchers equipped 299 homes with reverse-osmosis water

filters

, which remove bacterial and chemical contaminants.

Over 600 families participated in the study, about half with

the filters and half without them, and they were asked to

keep records of all GI illnesses among household members.

During this 15 month period, the households equipped with

the water filters had 35% fewer incidents of GI illness and

diarrhea. In 1992, The New England Journal of Medicine

published a study showing that drinking water can harbor the

bacterium that causes Legionnaire’s disease. Some patients

diagnosed with Legionnaire’s disease were infected with the

same type of Legionella pneumophila that was found in sam-

ples of their drinking water.

Vegetables, drinking water, and meat preservatives are

the main sources of

nitrates and nitrites

in our diet. There

is a definite link between nitrate and gastric cancer. Nitrate

is converted to nitrite by bacteria in the mouth and stomach,

and this is in turn converted into N-nitroso compounds,

which have been proven highly carcinogenic in laboratory

animals. Bottle-fed infants are at additional risk, because

once the nitrate is converted to nitrite in the stomach it

combines with fetal hemoglobin and converts to methaemo-

globin. When 10% of the hemoglobin has been converted,

cyanosis or

blue-baby syndrome

occurs; and when 70%

of the hemoglobin is in methaemoglobin form, death occurs.

According to a recent EPA report, half of the private wells

in the United States contain nitrate.

Radioactivity

occurs naturally and it can be present

in drinking water. Preliminary studies have linked it to in-

creased rates of

leukemia

and cancers of the bladder, breast,

and lungs. The EPA has established 5 picocuries per liter

(pCi/L) as the safe limit for radium in drinking water. An

estimated 100–1,800 deaths per year are attributed to

radon

in tap water. According to EPA estimates over eight million

people have excessively high radon levels in their water sup-

ply. Unlike most contaminants found in water, radon does

not have to be ingested to pose a health hazard; dish washing,

385

showering, or just running the faucet can agitate the water

and release the radon into the air. According to EPA esti-

mates, there are 10,000–40,000 lung-cancer deaths each year

from radon inhalation. Radon is most frequently a problem

in New England, North Carolina, and Arizona, and it is

most likely to be found in well water and small water systems.

Most large treatment facilities disperse radon during the

treatment process.

Most water-treatment plants in the United States use

chemical coagulation to remove impurities and contami-

nants.

Aluminum

sulfate is often added to the water, causing

some contaminants to coagulate with the aluminum and

precipitate out. The majority of the aluminum left in the

water is removed by subsequent treatment processes, but a

residual amount passes through the system to the consumer.

Aluminum in drinking water has been linked with neurotox-

icity, specifically Alzheimer’s disease.

The organic

chemicals

that are found most frequently

in drinking water are pesticides, trichloreothylene, and triha-

lomines. Pesticides usually make their way into drinking

water through

seepage

and runoff in agricultural areas, and

in high doses they can damage the liver, the kidney, and

the nervous system, as well as increase the risk of various

cancers. Trichloroethylene are industrial wastes and the pop-

ulations at highest risk from this chemical have a water

supply located near

hazardous waste

sites. The health

risks associated with trichloroethylene are nervous system

damage and cancer. Chlorination of water that is contami-

nated with organic matter is responsible for the formation

trihalomethanes

in water, and preliminary studies sug-

gest that it may increase cancer rates.

The bottled water industry is not sufficiently regulated,

and it does not guarantee water purity. Despite the image

portrayed by advertising, studies indicate that bottled water

is not any safer in most cases than tap water. Home treatment

units carry labels which frequently claim they are EPA-

approved, but these are not regulated either. Different types

of water filters are capable of removing different contami-

nants, so most experts recommend that anyone planning to

install a treatment system have their water tested first.

Though scientific evidence clearly demonstrates that

drinking water can be a health hazard, some of the most

effective measures are also the easiest to implement. Studies

have found that letting tap water run for several minutes

reduces the lead content of the water by up to 70%. Compa-

nies that supply drinking water can be monitored by re-

questing copies of their test results and reporting any viola-

tions to the EPA. Lobbying for more stringent regulations is

widely considered an effective tool for ensuring safe drinking

water. Reduction of

pesticide

use and additional measures

implemented for the protection of groundwater and surface

water would also greatly reduce many of these health risks.

Environmental Encyclopedia 3

Drip irrigation

See also Carcinogen; Communicable diseases; Filtration;

Groundwater pollution; Hazardous waste siting; Neuro-

toxin; Toxic substance; Water pollution; Water quality stan-

dards; Water resources; Water treatment

[Debra Glidden]

ESOURCES

ERIODICALS

Felsenfield, A., and M. A. Roberts. “A Report of Fluorosis in the United

States Secondary to Drinking Well Water.” Journal of the American Medical

Association 265 (23/30 January 1991): 486-8.

Stout, J., et al. “Potable Water as a Cause of Sporadic Cases of Community-

Acquired Legionnaires’ Disease.” New England Journal of Medicine 326 (16

January 1992): 151-5.

THER

Packham, R. F. “Chemical Aspects of Water Quality and Health.” Annual

Symposium of the Institution of Water and Environmental Management. Lon-

don, England: IWEM, 1990.

Drinking-water treatment

see

Water treatment

Drip irrigation

Drip

irrigation

maximizes scarce resources by delivering

water exactly where it is needed. The

percolation plume

from drip sources follows the bulb shape of the root zone,

wasting little water. This also better controls

fertilizer

inputs

by applying nutrients with the water application. Though

expensive to install, and best-suited to perennials or high-

value crops, this system overcomes or minimizes problems

from traditional irrigation methods. Spray irrigation maxi-

mizes evaporation; while gravity-fed systems contribute to

seepage

losses,

waterlogging

, and

salinization

. Through

water budget analyses and weed control, growers can main-

tain the exact moisture and nutritional levels needed for

optimum plant growth.

Drought

Of all natural disasters, drought is the most subtle. Often,

farmers cannot tell there is going to be a drought until it is

too late. Unlike flash floods, drought is slow to develop.

Unlike earthquakes, with destruction to the exterior

envi-

ronment

, drought does its damage underground long before

dust storms rage across the plains.

Technically, drought is measured by the decrease in

the amount of

subsoil

moisture that causes crops to die or

yield less (agricultural drought) or by a drop in the water

level in surface reservoirs and below ground aquifers, causing

386

wells

to go dry (hydrological drought). Agricultural plus

hydrological drought can lead to sociological drought. In

this condition, drought effects food and water supplies to

the extent that people have to rely on relief donations or are

forced to migrate to another area.

Droughts are worldwide, repetitive, and unpredictable.

Scientists believe there is a drought somewhere on the earth

at any time. Nor are droughts recent developments; analysis

of rock cores, glacial ice cores, and tree rings reveal prehistor-

ical and historical droughts, some of which lasted for several

decades. Tree rings in California, for example, record a 40-

year-drought 300 years ago.

The direct cause of drought is a continued decrease

in optimal rainfall. But what causes clouds not to form over

an area, or the winds to carry rain-bearing clouds elsewhere,

is complex.

Climate

change will alter the location of in-

creased and reduced rainfall, so that some places that have

always been well-watered will experience drought.

Some scientists believe that El Nin

o-La Nin

a events

in the western Pacific Ocean are main drivers in the cause

of droughts around the world.

El Nin

, an eastward flow of

warm surface waters, creates a high pressure zone over the

equator that results in a change in the high and low pressure

zones in other parts of the world. This affects the flow of

the jet stream and results in a disturbed rainfall pattern,

causing, for example, excessive rain in California and drought

in southwestern Africa, among other places. The

La Nin

which usually follows El Nin

o, is an upwelling of cold deep

waters in the western Pacific Ocean. It causes disturbed

pressure zones that result in droughts in the Midwest, among

other places.

Drought prediction is still in its infancy. Although

scientists know that El Nin

o-La Nin

a events cause droughts

in specific areas, they cannot yet predict when El Nin

o will

occur. Weather satellites can measure subsoil moisture, a

good indicator of incipient drought, but other factors also

contribute to drought.

Lack of rain, for example, in the

Sahel

, is exacerbated

by man-made environmental problems, such as cutting down

trees for fuel and not allowing the

soil

to lie fallow, which

conserves soil moisture.

Overgrazing

by animals such as

cattle, goats, and sheep also contributes to the denuding of

topsoil

, which blows away in the wind, a condition known

desertification

. Drought then becomes a cycle that feeds

on itself: lack of trees reduces the amount of water vapor

given off into the

atmosphere

; lack of topsoil reduces water

retention. The result is that local rainfall is reduced, and the

rain that does fall runs off and is not absorbed. Lack of rain

has been the reason for five years of consecutive drought in

Texas. The total amount of profit loss from 1998 until 2002

is estimated at $3.7 billion dollars.