High expressions of eutrophic conditions are exhibited in 44

estuaries of the coterminous United States, representing

approximately 40% of the national estuarine surface area. An

additional 40 estuaries exhibit moderate conditions. When

considered together, the estuaries with moderate to high eutrophic

conditions represent approximately 65% of the nation's estuarine

surface area. High conditions, determined by assessing the extent

of primary and secondary symptoms of eutrophication, occur in

estuaries along all coasts, but are most prevalent in estuaries along

the Gulf of Mexico and Middle Atlantic coasts. A high level of

human influence is associated with 36 of the 44 estuaries with high

eutrophic conditions. While high levels of primary symptoms, such

as elevated levels of chlorophyll a, are strong indicators of the

onset of eutrophication, secondary symptoms such as depleted

dissolved oxygen, indicate more serious or highly developed

eutrophication. Moderate to high expressions of at least one of the

secondary symptoms are exhibited in 82 estuaries, representing

67% of the estuarine surface area studied.

To cite this material. This material has been produced by the

Government of the United States of America and holds no

copyright.

The following reference format is suggested:

Clement, Chris, S. B. Bricker and D.E. Pirhalla. 2001 (on-line).

Eutrophic Conditions in Estuarine Waters. In: NOAA's State of the

Coast Report. Silver Spring, MD: National Oceanic and

Atmospheric Administration.

URL: http://state-of-coast.noaa.gov/bulletins/html/eut_18/eut.html
Photo 2. Fish kills are symptoms of

highly eutrophic conditions. They can

result from low dissolved oxygen

caused by the decomposition of excess

amounts of algae.

Eutrophication is a natural process in which there is "an

increase in the rate of supply of organic matter" to a water

body (Nixon 1995). This usually refers to an increase in the

rate of algal production which, under natural conditions, is

influenced by a gradual buildup of plant nutrients in

ecosystems over long periods of time, and generally leads to

productive and healthy estuarine and marine environments.

However, in recent years, human activities have substantially

increased the rate of delivery of plant nutrients to many

estuarine and marine areas (National Research Council 2000,

Peierls et al. 1991, Turner and Rabalais 1991). As a result,

algal production in many estuaries has increased much faster

than would occur under natural circumstances. This accelerated

algal production is referred to as "cultural" or "anthropogenic"

eutrophication, and often results in a host of undesirable

conditions in estuarine and marine environments.

These conditions, which include low dissolved oxygen

concentrations, declining sea grasses, and harmful algal

blooms, may impact the uses of estuarine and coastal resources

by reducing the success of commercial and sport fisheries,

fouling swimming beaches, and causing odor problems from

the decay of excess amounts of algae (National Research

Council 2000, Duda 1982). Despite much research, however,

the link between coastal eutrophication and effects on living

marine resources and fisheries is not well understood or

quantified (National Research Council 2000, Boesch et. al.

2001).

Photo 1. Accelerated growth of nuisance algae, as

shown here, can be stimulated by high levels of plant

nutrients and leads to undesirable conditions, such as

low dissolved oxygen.

Assessing Symptoms of Eutrophication

Between 1992 and 1998, NOAA conducted a survey and series

of regional workshops to synthesize the best available

information on eutrophication-related symptoms in 138

estuaries, comprising over 90 percent of the estuarine surface

area of the coterminous United States. The Mississippi River

Plume in the Gulf of Mexico was also assessed; while "the

plume" is not an estuary, it is an important offshore marine

area that experiences eutrophic conditions. The information,

collected from more than 300 scientists and environmental

managers, was organized in a common spatial framework

(salinity zones representing tidal fresh, mixing, and saltwater

environments), and predefined data categories were used to

consistently characterize the information so that comparisons

could be made among all of the estuaries. The data characterize

the spatial domain, severity, duration, frequency and past

trends of 16 eutrophication-related symptoms in estuaries of

the coterminous United States (Figure 1) (NOAA 1996, 1997a,

1997b, 1997c, 1998).

To help interpret the eutrophication survey results, a simple

eutrophication model was employed (Figure 2). Of the 16

symptoms, survey data for three primary symptoms

(chlorophyll a, epiphyte abundance, and macroalgal

abundance) and for three secondary symptoms (depleted

dissolved oxygen, decline of submerged aquatic vegetation,

and nuisance/toxic algal blooms) were used to make an overall

assessment of the expression of eutrophic conditions.

In order to understand the overall extent of eutrophic

conditions in a given estuary, a determination was made of the

"level of expression" of each symptom based primarily on the

concentration, spatial coverage, and frequency of occurrence.

A single value for each of the primary symptoms and

secondary symptoms was then determined. The primary and

secondary values were then compared in a matrix to assign an

overall level of expression of eutrophic conditions in each

estuary (Figure 3).). For instance, estuaries having high scores

for both primary and secondary symptoms were considered to

have an overall "high" level of expression of eutrophic

conditions. Conversely, estuaries with low primary and

secondary values were assigned an overall "low" level of

eutrophication.

Due to many factors, susceptibility to nutrient inputs varies

widely from estuary to estuary. In some estuaries, large

quantities of nutrient inputs have seemingly little effect, while

in others, only moderate inputs appear to cause extensive

expressions of eutrophic conditions. Furthermore, the

expression of symptoms does not necessarily result from

nutrient inputs; many other factors may be involved. In an

effort to determine the level of human influence on the

expression of eutrophic conditions, the overall eutrophic

condition was considered with respect to the level of nutrient

inputs and an estuary's susceptibility to retain nutrients.

Nitrogen values were used as the primary estimates of nutrient

inputs, while information on population density and land use

was used as a general indicator of nutrient pressure to help

account for the presence of phosphorus and to corroborate the

nitrogen estimates. Nitrogen input estimates were based on

watershed monitoring data from the U.S. Geological Survey, as

produced by the SPARROW model (Smith et al. 1997). While

the human influence assessment was not as rigorously

performed as the Eutrophication Survey, it provides valuable

insight into the role that human activities play in the expression

of eutrophic conditions in estuaries.

Photo 3. Livestock feedlots are among the numerous

sources of excess nutrients to estuarine waters.

Following the data collection and preliminary assessment,

NOAA conducted a National Eutrophication Assessment

Workshop in which experts analyzed and interpreted the

preliminary conditions and human influences, finalized the

assessments, and assigned confidence ratings to each

assessment. These final national assessment results provide a

snapshot of eutrophic conditions (circa 1995) and are the

primary source of information for this essay (Bricker et al,

1999).

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Status of Eutrophic Conditions

The National Eutrophication Assessment Workshop

participants concluded that the expression of overall eutrophic

conditions ranked as high in 44 estuaries, representing 40% of

the total estuarine surface area studied. In these estuaries, one

or more symptoms generally occurred at problem levels every

year, or persistently, across a major part of the estuary. These

estuaries are concentrated in the Gulf of Mexico and Middle

Atlantic regions; however, all regions contained estuaries with

high eutrophic conditions. An additional 40 estuaries exhibited

moderate eutrophic conditions. When considered together, the

84 estuaries with moderate to high conditions represent 65% of

the estuarine surface area studied. The remaining 38 estuaries

exhibited low levels of eutrophic conditions, meaning that

symptoms were not observed at problem levels or that problem

conditions occurred infrequently or only under specific and

unusual circumstances. About half of these latter estuaries were

located in the South Atlantic and Pacific regions. Figure 4 and

Figure 5 summarize the national picture of overall eutrophic

conditions. Appendix A lists all of the estuaries in the

Eutrophication Survey and Assessment and their eutrophic

conditions.

Photo 4. The Mississippi River plume (above right)

was assessed for eutrophic conditions in addition to

138 estuaries. The Plume exhibits high eutrophic

conditions with the symptoms of low dissolved

oxygen, high chlorophyll a concentrations, and

nuisance algae blooms.

In more than 80 percent of estuaries with high and moderate

levels of eutrophic conditions, the assessment confidence was

high; conversely, confidence was high in fewer than half of the

systems assessed as having low eutrophic conditions. Most of

the estuaries with low confidence are located in the Pacific and

South Atlantic regions. Despite all of the monitoring and

research done to date, information and knowledge is still

inadequate in 48 of the nation's 138 best known estuaries (low

confidence or inadequate data for assessment). These estuaries

represent approximately 25% of the estuarine surface area

studied. The data for 17 estuaries were too sparse to provide

even a speculative overall view of eutrophic conditions,

although limited data existed for certain symptoms in some of

the estuaries.

Symptoms: Common Signs of Eutrophication

Primary Symptoms. The primary symptoms of increased

nutrient inputs to estuarine waters are high levels of

chlorophyll a, epiphytes, and/or macroalgae. It is thought that

once primary symptoms are observed at high levels, an estuary

is in the first stages of displaying undesirable eutrophic

conditions.

High expressions of chlorophyll a, macroalgal abundance, and

epiphyte abundance occurred in 39, 24, and 11 estuaries,

respectively. Overall, at least one of these primary symptoms

was expressed at high levels in 58 estuaries. This finding

indicates that 40 percent of the estuaries studied are probably in

the first stages of developing problems associated with

eutrophication. Figure 6 summarizes the number of estuaries

with primary symptoms.

Photo 5. An algae bloom on the tidal Potomac River, a

major tributary of the Chesapeake Bay.

Secondary Symptoms. While high levels of primary symptoms

are strong indicators of the onset of eutrophic problems, the

secondary symptoms, which include low dissolved oxygen

concentrations, the loss of submerged aquatic vegetation, and

the occurrence of nuisance and toxic blooms, indicate more

serious problems, even at moderate levels. While there is a

direct causative link between nutrients and primary symptoms,

there are many other factors, both natural and human-related,

that might contribute to the occurrence of secondary

symptoms.

Depleted dissolved oxygen was expressed at moderate to high

levels in 42 estuaries. Twenty-seven estuaries had moderate to

high levels of submerged aquatic vegetation loss, and 51

estuaries exhibited moderate to high expressions of

nuisance/toxic algal blooms. Overall, moderate or high levels

of at least one secondary symptom were observed in 82

estuaries, representing 67% of the nation's estuarine surface

area. Figure 6 summarizes the number of estuaries with

secondary symptoms. Appendix A lists all of the estuaries and

their expressions of primary and secondary symptoms of

eutrophication.

Influencing Factors

Figure 7 shows the nitrogen input data and the estuarine

susceptibility data, which together provide a rough estimate of

the level of human influence on the overall expression of

eutrophic conditions in the study.

Of the 44 estuaries with high expressions of eutrophic

conditions, 36 appear to be highly influenced by human

activities, despite relatively low to moderate nutrient inputs

(only six had high-level nitrogen inputs). Most of these 44

estuaries (86 %) also had a moderate to high susceptibility to

retaining nutrient inputs; that is, their physical characteristics

made them vulnerable to developing the symptoms of

eutrophication. For instance, estuaries with very low tidal

exchange or low dilution with fresh water tend to retain

nutrients, and thus, are more susceptible to developing

eutrophic conditions. It follows that susceptibility is an

important factor in the expression of high eutrophic conditions,

especially when nutrient inputs are not extremely high.

Furthermore, of the 38 estuaries with a low expression of

eutrophic conditions, 10 had high susceptibility for retaining

nutrients. Appendix B lists all of the estuaries in the

Eutrophication Survey and Assessment and estimates of the

levels of human influence on the expression of eutrophic

conditions.

Photo 6. The nutrient-laden waters often discharged by

sewage treatment plants can be a significant factor in

the expression of eutrophic conditions in estuaries.

Six estuaries (mostly in the North Atlantic) with high levels of

eutrophic conditions had low human influence. The overall

eutrophic conditions in these estuaries were assessed as high

generally because of toxic algal blooms, which are believed to

originate naturally offshore and drift into the estuaries.

However, the role of land-based nutrients in maintaining or

enhancing these blooms in the estuaries is not entirely clear.

(top)
Photo 9. Ten of the 22 estuaries in the

Middle Atlantic, including the

Chesapeake Bay (above center), exhibit

high levels of eutrophic conditions.

Seven, including Delaware Bay (top

right), exhibit low conditions.

Photo 12. Low dissolved oxygen and

toxic algal blooms, two symptoms of

eutrophication, often result in

mortalities for fish and shellfish.

Photo 13. Galveston Bay (above) has

moderate levels of nutrient inputs and

is moderately susceptible to retaining

them. Despite this, it ranks high in

eutrophic conditions.

Photo 14. Substantially high levels of

human influence are associated with

many estuaries in the Gulf of Mexico.

Estuaries exhibiting high expressions of eutrophic conditions

were concentrated mainly in the Gulf of Mexico and Middle

Atlantic regions; however, all regions included at least a few

estuaries with high expressions of eutrophic conditions (Figure

8). About 45 percent of the estuaries in both the Gulf of

Mexico and Middle Atlantic regions exhibit a high level of

eutrophic conditions. In contrast, high levels of eutrophic

conditions are exhibited in about 18 percent of both South

Atlantic and Pacific estuaries. About 33 percent of North

Atlantic estuaries exhibited high expressions of eutrophic

conditions; however, the level of human influence attributed to

these conditions was estimated primarily as low. About half of

the estuaries with low eutrophic conditions were located in the

South Atlantic and Pacific regions. The Gulf of Mexico and

Middle Atlantic had the largest percentages of estuaries with

high eutrophic conditions and concurrent high levels of human

influence, 45% and 35%, respectively. In the Pacific, 18% of

estuaries had these conditions, while in the North Atlantic and

South Atlantic, very few had them. Although every region

includes estuaries for which conditions are predicted to worsen,

the Pacific and Gulf of Mexico regions contain the largest

numbers of estuaries with negative outlooks, primarily due to

estimates of increasing population and related nutrient supplies.

Most of the estuaries with low confidence in the assessment of

eutrophic conditions are located in the Pacific and South

Atlantic regions.

North Atlantic

The North Atlantic region (Figure 9), which extends from the

St. Croix River near the Canadian border south through Cape

Cod Bay, includes 18 estuarine systems, encompassing roughly

2,000 square miles of water surface area. In the northern part of

the region, the coastal shoreline consists mainly of drowned

river valleys characterized by numerous small embayments,

rocky shorelines, wave-cut cliffs, and large, rocky islands. The

southern part of the region contains more cobble, gravel, and

sand beaches, and tidal marshes are more extensive. A high

degree of tidal flushing and relatively low freshwater input are

characteristic of many of these systems. Major population

centers, including Portland and Boston, are located in the

southern portion.

Photo 7. Cobscook Bay, on the border between Maine

and Canada, shows high levels eutrophic conditions

primarily due to toxic algal blooms and the

overabundance of macroalgae. As with many North

Atlantic estuaries, the degree of human influence here

on the expression of eutrophic conditions is low.

Overall Conditions. Moderate or higher levels of eutrophic

conditions occurred in more than half of the 18 estuarine

systems, with six in the high category. Estuaries with these

conditions were located along the length of the coast, and were

interspersed with the five estuaries exhibiting low eutrophic

conditions.

Expression of Symptoms. Close to half of the estuaries

exhibited at least one of the six primary or secondary

symptoms at high levels. Chlorophyll a was expressed at

moderate levels in a majority of estuaries. Macroalgal

abundance problems occurred in almost half of the systems, but

epiphyte problems were minimal. With regard to secondary

symptoms, moderate to high levels of nuisance or toxic blooms

occurred in more than half of the systems; depleted dissolved

oxygen occurred at low levels in more than half; and losses of

submerged aquatic vegetation were minimal.

In general, for those systems with high eutrophic conditions,

nuisance or toxic algal blooms and overabundance of

macroalgae were the principal symptoms contributing to the

observed overall condition. Moderate expressions of

chlorophyll a and low expressions of depleted dissolved

oxygen were also observed in most of the systems with high

eutrophic conditions, although these symptoms tended to occur

regardless of overall eutrophic condition.

Photo 8. Toxic algal blooms such as red tides are

thought to be caused primarily by natural conditions.

This one (at left) in coastal Maine occurred after heavy

rains following a very dry summer. The same area is

shown (at right) six days later after the red tide has

cleared.

Influencing Factors. Nutrient inputs from human sources are

low in all but three North Atlantic estuarine systems, primarily

because freshwater inflow in the region is generally low and

drains from watersheds with sparse populations. Susceptibility

to nutrient inputs is low in most systems because tidal flushing

is very effective in this region. As a result of the low nutrient

inputs and low susceptibility, human influence is generally low

in the region.

Of the six estuaries exhibiting high eutrophic conditions, only

one, Boston Harbor, also had a high level of human influence.

Furthermore, according to expert consensus at the National and

Regional Assessment Workshops, offshore coastal waters are

the major nutrient source for most estuarine systems in this

region. Consequently, certain eutrophic symptoms, such as

toxic algal blooms, are thought to be primarily reflective of

natural conditions. Human-related nutrient inputs may or may

not exacerbate these natural conditions.

Middle Atlantic

The Middle Atlantic region (Figure 10), which extends from

Buzzards Bay, MA through Chesapeake Bay, includes 22

estuarine systems encompassing more than 7,790 square miles

of water surface area. Coastal areas are characterized by

irregular shorelines, wide, sandy beaches, numerous barrier

island formations, and extensive salt marshes. Tides range from

one to six feet but generally fall within the lower part of the

range. Tidal flushing is more important in the northern part of

the region, while freshwater inflow is more important in the

Chesapeake Bay systems. Land use is characterized by large

urban tracts and extensive agricultural areas. Major population

centers include Providence, Hartford, New York City,

Philadelphia, Baltimore, Washington, D.C., and Richmond.

Overall Conditions. Estuaries with moderate to high eutrophic

conditions were widespread and evenly spaced throughout the

region. Close to half of the 22 estuarine systems exhibit high

levels of eutrophic conditions, with an additional five

exhibiting moderate conditions. Seven estuaries in the region

exhibited low eutrophic conditions.

Expression of Symptoms. Well over half of the estuaries

exhibited at least one of the six eutrophic symptoms at high

levels. Of the primary symptoms, chlorophyll a had the most

pronounced expression, with high levels in half of the estuaries

and moderate levels in the rest. Macroalgal abundance

problems occurred in 10 estuaries, and in five of these at

moderate to high levels. Epiphyte abundance problems

occurred in more than one-quarter of the estuaries. Extensive

expressions of secondary symptoms were also noted in the

region. Depleted dissolved oxygen occurred in every estuary,

although it tended to be expressed at low levels. Both

submerged aquatic vegetation loss and nuisance or toxic algal

blooms were problems in more than half of the estuaries,

generally occurring at moderate to high levels.

There did not appear to be a single symptom dominating the

overall expression of high eutrophic conditions. Rather, there

was a wide and varied array of symptoms contributing to the

overall conditions observed. The 10 estuaries exhibiting high

eutrophic conditions had varying combinations of low

dissolved oxygen, submerged aquatic vegetation loss, and

nuisance or toxic algal blooms. In most of these estuaries,

secondary symptoms coincided with high expressions of

primary symptoms. The five estuaries exhibiting moderate

eutrophic conditions displayed similar symptoms, except that

the secondary symptoms were somewhat less severe.

Photo 10. Nonpoint sources of nutrients from fertilizer

applications are a significant human influence on the

expression of eutrophic conditions in estuaries.

Influencing Factors. The expression of severe eutrophic

conditions was more pervasive in enclosed or river-dominated

estuaries, such as the Chesapeake Bay and its tributaries and

the Delaware Inland Bays. Ocean-influenced systems, such as

Buzzards Bay and Delaware Bay, exhibited fewer impacts

(although these systems had small, more localized areas of high

symptoms). Nitrogen inputs were moderate to high in 15

estuaries, and susceptibility was moderate to high in all

systems. Accordingly, human influence was considered strong

in this region. Of the 15 estuaries with moderate to high

eutrophic conditions, 12 also exhibited high human influence.

Conversely, several systems displayed minimal eutrophic

conditions despite a substantial level of human influence. It is

possible that some of these systems are close to developing

full-scale eutrophic symptoms.

South Atlantic

The South Atlantic region (Figure 11) includes 22 estuaries,

encompassing more than 4,440 square miles of water surface

area. The region, which extends from the Outer Banks in North

Carolina south through Biscayne Bay in Florida, is comprised

of extensive barrier and sea islands that parallel the shoreline.

The coastal environment consists of shallow lagoonal estuaries,

extensive tidal marshes and drowned river valleys. Estuarine

circulation patterns are dominated mainly by wind and seasonal

freshwater inflow in North Carolina, and mainly by freshwater

inflow and tides in South Carolina and Georgia. Estuarine

circulation along the Florida coast is dominated by wind

forcing and human engineering. Tidal range throughout the

region is moderately low to high (1.5-7.0 feet) and influences

mixing in the water column, primarily near the inlets. The

predominant land uses are agriculture and industry, and, to a

lesser extent, forestry. Major population centers include Miami,

Jacksonville, and Savannah.

Photo 11. Satellite view of Charleston Harbor estuary

in South Carolina. This estuary exhibits moderate

eutrophic conditions.

Overall Conditions. The South Atlantic region contains only

four estuarine systems with high overall levels of expression of

eutrophic conditions: the Neuse River, Pamlico/Pungo Rivers,

and New River of North Carolina, and the St. John's River in

northern Florida. Five additional systems exhibited moderate

levels of eutrophic conditions. The other 13 systems, mostly in

South Carolina and Georgia, are relatively unaffected by

eutrophic symptoms.

Expression of Symptoms. In five estuaries, at least one of the

six eutrophic symptoms was expressed at high levels. Of the

primary symptoms, chlorophyll a had the most pronounced

expression in five estuaries located in North Carolina and

Florida. Of the secondary symptoms, depleted dissolved

oxygen was considered high in only one North Carolina

system, the Neuse River. Nuisance/toxic algal blooms occurred

at high to moderate levels in the Pamlico/Pungo Rivers of

North Carolina. The loss of submerged aquatic vegetation was

a problem in almost half of the estuaries, but mainly at low to

moderate levels.

Influencing Factors. The overall level of human influence was

low in half of the region's estuaries, especially in South

Carolina and Georgia, and moderate in most of the remaining

estuaries. Human influence was most pronounced in the North

Carolina estuaries of Pamlico/Pungo Rivers, the Neuse River,

and the New River.

Many factors influence the expression of eutrophic conditions

in South Atlantic estuaries. The limited number of systems in

which eutrophic conditions were high generally had restricted

circulation, low tidal exchange, and moderate to high nitrogen

inputs. In most of the other estuaries, which were relatively

unaffected by eutrophication, the influence of tidal marshes

(which act as a nutrient filtering mechanism), strong tides, and

low nitrogen inputs combined to keep eutrophic conditions at

low levels.

Gulf of Mexico

The Gulf of Mexico region (Figure 12) includes 37 estuaries,

covering 11,000 square miles of water surface area. The region

also contains the Mississippi River Plume, an offshore area

stretching from Louisiana to Texas. The plume roughly

encompasses an additional 12,000 square miles of water

surface area. The region is comprised of a gently sloping,

lowland area as part of the Gulf Coastal Plain. Estuarine and

coastal environments are highly diverse, consisting of

unrestricted open bays, semi-enclosed lagoons, tidal marshes

and delta complexes. The fresh water that flows naturally into

estuaries can fluctuate greatly in the Gulf, and depends on

seasonal rainfall patterns. Estuarine circulation patterns are

generally wind driven, and coastal waters are usually warmer

than in other regions due to the subtropical climate. Estuaries

have fairly low tidal energy (0.5-3.5 ft. tide range), and water

depths are typically shallow as compared to estuaries in other

regions. Land-use activity in the watersheds is typically

dominated by agricultural practices. Major population centers

include Houston, New Orleans and Tampa.

Overall Conditions. The Gulf of Mexico was significantly

affected by elevated expressions of eutrophication. Almost half

of the 37 estuaries in the region had high levels of eutrophic

conditions. Estuaries noted as having the highest-level

conditions were Florida Bay, Lake Pontchartrain, Calcasieu

Lake, Corpus Christi Bay and the Laguna Madre system. The

Mississippi River Plume off the coast also was noted to have

very high overall expressions of eutrophic conditions. Fourteen

estuaries had moderate levels of eutrophic conditions, and only

six had low levels.

Expression of Symptoms. In 20 estuaries, at least one of the six

individual symptoms was expressed at high levels. Of the

primary symptoms, chlorophyll a was expressed at high levels

in 12 estuaries, which were located mainly on the coasts of

western Florida, Louisiana and lower Texas. In eight estuaries,

epiphytes were considered moderate to high; in seven estuaries,

magroalgal abundance was considered moderate to high. Of the

secondary symptoms, depleted dissolved oxygen was

expressed at high levels in four estuaries, mainly along the

Florida coast and in the Mississippi River Plume. The loss of

submerged aquatic vegetation was a problem in almost half of

the estuaries, but usually at low to moderate levels. Nuisance or

toxic algal blooms also tended to be pervasive, occurring in 28

estuaries, eight of which exhibited high levels of expression.

In the systems with high overall eutrophic conditions, the

symptoms that generally contributed the most to the observed

overall eutrophic condition were the loss of submerged aquatic

vegetation, high expressions of chlorophyll a concentration,

and depleted dissolved oxygen concentrations. Moderate to

high levels of nuisance or toxic algal blooms and epiphyte

abundance were also major factors in systems with pronounced

expressions of eutrophication.

Overall Human Influence. The overall level of human

influence was high in more than half of all Gulf systems and

corresponded well with high levels of eutrophic conditions.

Human influence was considered prominent in the Mississippi

River Plume, Lake Pontchartrain, Upper and Lower Laguna

Madre, and Baffin Bay. Noted for having relatively low human

influence were Rookery Bay, Suwannee River, Apalachee Bay,

and Breton/Chandeleur Sounds.

Many factors influenced the expression of eutrophication in

Gulf estuaries. The following factors were generally associated

with moderate to pronounced levels of expression: low tidal

energy, low flushing rates with high nutrient inputs, and low

dissolved oxygen levels, generally due to warmer waters and a

long growing season. These factors, coupled with substantial

levels of human influence in many Gulf estuaries, resulted in

pronounced eutrophic conditions, even though nitrogen inputs

were generally moderate. For example, although population

density was relatively low in the Baffin Bay and Upper Laguna

Madre watersheds, human influence was magnified due to high

estuarine susceptibility.

Pacific Coast

The Pacific region (Figure 13) includes 39 estuaries,

encompassing more than 2,750 square miles of water surface

area. The region consists of a relatively straight and

uninterrupted shoreline with rocky shores, sandy beaches and

occasional river outlets. Limited areas of flat, lowland

environments support estuaries, bays and lagoons. Estuaries are

typically small and separated by large distances. Estuarine

circulation patterns are dominated mainly by seasonal

freshwater inflow in Southern California and by freshwater

inflow and tides in the larger estuaries of central California and

Washington state. The tidal range is moderately high (5.0-7.5

feet). Forestry, agriculture and industry are the predominant

land uses in the region's watersheds. Some of the major

population centers include Los Angeles, San Diego, San

Francisco, Portland, and Seattle.

Photo 15. Very high levels of

chlorophyll and nuisance algae plus

loss of submerged aquatic vegetation,

give San Francisco Bay a high overall

eutrophic condition.

Overall Conditions. High levels of expression of overall

eutrophic conditions occurred in seven estuaries, mainly in the

northern and southern sections of the region. Among these

were Tijuana Estuary, Newport Bay, and San Francisco Bay.

Eleven estuaries were characterized as in the moderate range;

these were interspersed throughout California and the Pacific

Northwest. Nine estuaries appeared relatively unaffected by

eutrophic conditions. There was insufficient data to determine

eutrophic conditions in the remaining 12 estuaries.

Expression of Symptoms. In 19 estuaries, at least one of the six

individual eutrophic symptoms was expressed at high levels.

Of the primary symptoms, chlorophyll a was expressed at high

levels in 11 systems, most of them in Southern California and

northern Washington. Macroalgal abundance was observed at

moderate to high levels in 13 estuaries, most of them also in

Southern California and Washington. Epiphyte abundance was

minimal. Eight estuaries exhibited losses in submerged aquatic

vegetation, two at high levels. Nuisance or toxic algal blooms

occurred in 21 estuaries, 12 of which were in the moderate to

high range.

In general, the symptoms contributing most to high eutrophic

conditions were elevated levels of chlorophyll a, coupled with

various combinations of macroalgal abundance, nuisance or

toxic algal blooms, and low dissolved oxygen concentrations.

High chlorophyll a concentrations were also a common natural

condition in some North Pacific estuaries due to tidal import of

seasonal algal blooms.

Photo 16. An algal bloom in estuarine waters of

Washington.

Overall Human Influence. In general, estuaries with high-level

eutrophic conditions also had high levels of human influence.

Human influence on the expression of eutrophic symptoms was

most pronounced in the Tijuana Estuary, Newport Bay, San

Pedro Bay, Anaheim Bay and San Francisco Bay. Three of

these —Newport, Newport, Anaheim and San Pedro—are are

among the top 10 U.S. estuaries with respect to watershed

population density. The Tijuana Estuary is also notable because

three-quarters of the watershed is located in Mexico, making

management an international challenge. The Tijuana River is

the primary source of fresh water to the estuary; it is also a

source of untreated sewage from the city of Tijuana. In general,

restricted circulation and moderate to high levels of nutrient

inputs were noted as the principal factors contributing to

elevated eutrophic symptoms in Pacific Coast systems.

(top)
Photo 18. Sediment particles,

particularly from agricultural fields, can

carry phosphorus, a nutrient that

stimulates the growth of nuisance algae

in parts of some estuaries. Groundwater

is the primary source of the nutrient

nitrogen.

Chesapeake Bay: The Classic Case of Estuarine

Eutrophication

The largest estuarine system in the U.S., the Chesapeake Bay,

is perhaps the best known example of human activities leading

to accelerated estuarine eutrophication and its associated

negative affects. During the last 50 to 100 years, nutrient

additions to the Chesapeake accelerated rapidly as chemical

fertilizers came into widespread use. Also, the population

density of the watershed continually increased, creating the

need for numerous wastewater treatment plants and generating

increasing emissions of nitrogen oxides from automobiles.

Human activities, such as the filling in of wetlands and

deforestation for agricultural and urban development,

concurrently reduced the ability of natural ecosystem processes

to remove or trap nutrients, thereby further accelerating

nutrient delivery to the bay. In addition, natural diseases and

over harvesting led to a dramatic decline of the once highly

abundant eastern oyster, seriously reducing the natural filtering

of algae and other organic matter from the water column. As a

result, eutrophic symptoms intensified greatly in the

Chesapeake from the mid-1950s to the mid-1980s. The most

apparent symptoms were the extremely high production of

algae, increasingly turbid water, major declines in submerged

aquatic vegetation abundance and species, and increasingly

worsening anoxia and hypoxia (Boesch et. al. 2001).

Photo 17. Underwater beds of Ruppia

maritima, known commonly as

widgeon grass, and other submerged

aquatic grasses were once found

extensively throughout Chesapeake

Bay. Excessive concentrations of algae

in the water column and on the leaves

of the grass itself, as well as in

suspended sediments, reduce the

amount of light needed for these

grasses to thrive.

Concentrations of chlorophyll a in the surface mixed layer have

increased tenfold in the seaward regions of the bay and

one-and-one-half- to twofold elsewhere, paralleling estimates

of increased loading of nitrogen and phosphorus to the bay

since 1945 (Harding and Perry 1997).

Submerged aquatic vegetation (SAV) began to decline as a

result of nutrient enrichment during the mid-1960s,

disappearing entirely from the Patuxent and lower Potomac

Rivers. By 1980, many areas of the bay that once contained

abundant SAV beds had none or only very small remnants left

(Orth and Moore 1984). Research indicated that the major

driving factor in the decline of SAV was nutrient enrichment,

which was causing excessive growth of algae in the water

column and on SAV leaf blades (epiphytic algae). This algal

growth decreased light availability to the submerged plants to

the point that they simply could not survive (Kemp et. al. 1983,

Twilley et. al. 1985).

Seasonal hypoxia (very low dissolved oxygen) has been a

feature of the Chesapeake Bay since deforestation during the

colonial period (Cooper and Brush, 1991), but evidence

suggests an aggravation of the problem in more recent decades

(Taft et al. 1980, Officer et al. 1984, Malone 1991). The annual

cycle of oxygen depletion in the Chesapeake Bay begins as the

water starts to warm and accelerates during and following the

spring freshet. The spring accumulation of algal biomass is

more than sufficient to create conditions for oxygen depletion

and summer anoxia (Malone 1991, 1992). Hypoxia and anoxia

generally occur from May through September, with the most

severe conditions observed in mid-summer (see the Oxygen

Depletion in Coastal Waters essay for a more detailed

description).

The Chesapeake Bay is the object of an ambitious nutrient

management program. In 1983, the U.S. Environmental

Protection Agency, District of Columbia, and states of

Virginia, Maryland, and Pennsylvania signed the first

Chesapeake Bay Agreement, which established the Chesapeake

Bay Program--a voluntary government partnership that directs

and manages bay cleanup efforts. An executive council was

established to assess and oversee the implementation of

coordinated plans to improve and protect the bay's water

quality and living resources. Scientific findings from the

program led to the signing of the second Chesapeake Bay

Agreement in 1987, in which it was agreed to reduce by 40%

the nitrogen and phosphorus entering the Chesapeake Bay by

the year 2000.

The Chesapeake Bay Program has continued to push for

meeting the overall nutrient-reduction goal by implementing

several strategies, including tributary nutrient goals, living

resources restoration (e.g., SAV replanting and oyster bar

restoration), and riparian forest buffer restoration. Point source

reductions have been most successful, especially for

phosphorus. Between 1985 and 1996, phosphorus point sources

were reduced by 58% and nitrogen by 15%. Nonpoint source

reductions have been slower, and have proven more difficult to

control. Nonpoint sources of nitrogen and phosphorus have

been reduced by only 7% and 9%, respectively. Challenges to

the effective reduction of nonpoint source nutrients include the

adoption of better agricultural practices, the reduction of

atmospheric nitrogen deposition, enhancement of wetlands and

other nutrient sinks, and the control of urban sprawl (Boesch et

al. 2001)

Tampa Bay: Reversing Anthropogenic Eutrophication

Prior to the 1930s, seagrass meadows covered about 31,000

hectares of Tampa Bay. However, the area's growing

population and subsequent development resulted in increased

nitrogen loading, high chlorophyll concentrations, and the

subsequent loss of seagrasses. By 1982, only 8,800 hectares of

seagrass remained, a loss of 72%. Since the early 1990s,

however, seagrass coverage has been increasing due to

effective management actions.

Photo 19. The recovery of seagrasses in

Tampa Bay is attributed to management

efforts in the watershed, including a

nearly 50% reduction in nitrogen

loading from domestic wastewater

treatment plants since the early 1980s.

Monitoring programs in Tampa Bay show that, since 1985,

chlorophyll concentrations have returned to levels observed in

1950, and since 1988, the trend of seagrass loss has been

reversed. Bay-wide seagrass coverage in 1996 was estimated at

10,930 hectares, a 25% increase since 1982. Recovery is

attributed to a nearly 50% reduction in nitrogen loading from

domestic wastewater treatment plants since the early 1980s.

To maintain these improvements, the Tampa Bay National

Estuary Program adopted nitrogen loading targets based on the

water quality requirements to restore turtle grass, a type of sea

grass. A nitrogen management consortium consisting of a local

electric utility, industries, agricultural interests, local

governments, and regulatory agencies, was established to

develop and implement a plan to reduce nitrogen loads by 140

tons per year by the year 2000. The results in Tampa Bay

demonstrate that eutrophication impacts can be reduced and

reversed (Greening et al. 1997, Johansson and Greening, in

press, Tomasko and Ries 1997).

Honokowai, Hawaii: Eutrophic Symptoms in a Coral Reef

System

In 1988, corals of Honokowai were healthy and abundant. At

that time, Honokowai was rated among the top snorkeling spots

on the island of Maui. A garden of low coral growth extended

all along the coastline from Honokowai Park up to the S-Bend

at a depth of about 17 feet. Today, large sections of these coral

garden are dead or degraded, due, in large measure, to massive

algal blooms and sedimentation. Concrete erosion-control

channels without catch basins deliver runoff to this coastal area

from adjacent agricultural areas and from sewage treatment

plants.

Photo 20. Nuisance algae blanketing

coral.

In the summer of 1989, West Maui was plagued by a massive

algal bloom in its near-shore waters. Large tracts of the coral

reefs were blanketed with the nuisance green macroalgae,

Cladophora sericea. The green algae that did not snag on the

corals collected in large pads in the depressions and valleys

between the reefs. By 1990, after a single season of these

unusual algal blooms, much of the coral at Honokowai had

died. In 1991, another large algae bloom wreaked havoc. At

low tide, thick ropes of Cladophora became entangled with

Hypnea musciformis, another nuisance algae. These

accumulated on the beach, attracting flies and causing

unpleasant odors of decay. Again, pads of Cladophora up to 3

feet deep collected in the depressions between reefs, and huge

"rafts" of the algae drifted on the surface. By 1992, various

macroalgae--primarily red Hypnea--had become a permanent

feature of the area.

In July 1993, Tropical Storm Dora, a hundred-year storm,

struck West Maui. Heavy runoff flowed from the West Maui

mountains and pineapple fields. Silt-laden fresh water flowed

through the two concrete channels at Honokowai. Red soils

from upland were directly flushed into the shallows of the reef.

The red silt covered corals and rubble, mixed with the sand,

and even coated the backs of sea turtles. In deeper waters

(33-50 feet), red silt piled up four inches thick and accumulated

between reefs. Then, yet another (unidentified) species of algae

bloomed in 1994 and 1995, growing throughout the sandy

bottom. In the summer of 1995, red Hypnea once again

plagued the area. The Cladophora and other nuisance algal

blooms have continued yearly at varying intensities through the

summer of 1999 (Bennett and Bennett 1999 on-line).

(top)
The individuals below are experts in the topic of eutrophic

conditions in estuarine waters. Here they voice their opinions on

two questions relevant to that topic.

Question 1. Given the difficulty in establishing clear and

quantifiable linkages between eutrophic conditions and

degradation of estuarine resources (e.g. commercial fishery

declines), should eutrophication be as high of a management

priority as over-harvesting, invasive species, and other more

tangible problems? What steps should be taken to elevate

eutrophication into a priority problem in the public eye?

Question 2. The NOAA assessment predicts serious future

degradation of water quality for the nation over the next 20

years, based on estuarine susceptibility and expected

population growth in the coastal zone. Is this a fair

assessment of future conditions, or are there other important

factors to consider? What should be done to reduce, mitigate,

or prevent nutrient enrichment and its associated effects on

the nation's estuaries, and will the costs and effort associated

with these actions benefit the nation in the long run?

Experts

Tom Malone Holly Greening Jan Newton Michael Mallin

Thomas Malone

Director

Center for Environmental

Science

Horn Point Laboratory

University of Maryland

Dr. Thomas Malone is the Director of the University of

Maryland's Center for Environmental Science Horn Point

Laboratory on the Chesapeake Bay. His research expertise centers

on the dynamics of coastal ecosystems, phytoplankton ecology

and coastal eutrophication. He has held numerous positions on

government and university panels and commissions related to

ocean and coastal environmental quality and monitoring and has

published extensively in the scientific literature. 

Response to Question 1

Response to Question 2

(top)

Question 1. Given the difficulty in establishing clear and

quantifiable linkages between eutrophic conditions and

degradation of estuarine resources (e.g. commercial fishery

declines), should eutrophication be as high of a management

priority as over-harvesting, invasive species, and other more

tangible problems? What steps should be taken to elevate

eutrophication into a priority problem in the public eye?

No audio response is availalbe.

Given the concentration of resources in coastal ecosystems, the

rapid increase in the number of people living, working and

playing in the coastal zone should not come as a surprise. The

pressures on these ecosystems to provide living space, resources,

recreation, and commerce and to receive, process, and dilute the

effluents of human society will continue to grow. At the same

time, coastal ecosystems are experiencing unprecedented changes

that affect their capacity to provide these services and support

valuable resources. The resulting conflicts between these uses

will become increasingly contentious, politically charged, and

expensive.

Environmental changes in coastal ecosystems include habitat loss

(coral reefs, sea grass beds, tidal wetlands), loss of biodiversity,

oxygen depletion of bottom waters (hypoxia), harmful algal

events, fish kills, declining fish stocks, and beach closures. These

are occurring despite antipollution laws that have greatly reduced

discharges of toxic substances into coastal waters over the last 40

years. At the same time, nutrient loading to coastal waters has

increased dramatically from both point and diffuse (line) sources

as the number of people living, working and playing in the coastal

zone has increased. This has resulted in the loss of critical habitat

and increases in the extent of hypoxia in the nation's coastal

waters. There is also evidence that nutrient over-enrichment

increases the probability of harmful algal events and associated

fish kills and may be related to losses of biodiversity and

declining fish stocks. Given the systemic effects of nutrient

enrichment, high priority must be placed on controlling both point

and diffuse sources of nitrogen and phosphorus into coastal

aquatic ecosystems.

(top)

Question 2. The NOAA assessment predicts serious future

degradation of water quality for the nation over the next 20

years, based on estuarine susceptibility and expected

population growth in the coastal zone. Is this a fair

assessment of future conditions, or are there other important

factors to consider? What should be done to reduce, mitigate,

or prevent nutrient enrichment and its associated effects on

the nation's estuaries, and will the costs and effort associated

with these actions benefit the nation in the long run?

No audio response is availalbe.

Over 60% of coastal rivers, estuaries and bays are moderately to

severely degraded by over-enrichment, a problem that is

particularly acute in the mid-Atlantic, the southeast, and the

northern Gulf of Mexico. Given the susceptibility of these

ecosystems and projected human demographics, their capacity to

provide services and support valuable resources is likely to

continue to deteriorate rapidly in the absence of a major

commitment to control nutrient inputs. As called for by a recent

NRC report, the minimum goal should be a 10% reduction in the

number of degraded coastal ecosystems by 2010 and a 25%

reduction by 2020. No systems that are currently categorized as

"healthy" should be allowed to develop the symptoms of

over-enrichment. Highest priority should be placed on tertiary

sewage treatment (to remove nitrogen) for those coastal

watershed subject to rapid population growth, to the control of

diffuse inputs from animal wastes and fertilizers, and to the

control of nitrogenemissions from the combustion of fossil fuels.

The costs of taking immediate action control inputs pale in the

face of the costs of mitigation and restoration once the damage is

done.

(top)

Holly S. Greening

Senior Scientist

Tampa Bay Estuary Program

St. Petersburg, Florida

Ms. Greening is a senior scientist with the Tampa Bay National

Estuary Program where she designs, conducts, and manages

projects related to aquatic ecology, watershed management, water

quality, information management, and atmospheric deposition

and toxic materials management. Her academic training involved

extensive food web studies in North Florida estuaries. She has an

M.S. in Marine Ecology from Florida State University in 1980.

Ms. Greening recently served as a member of the National

Academy of Sciences, National Research Council's Committee on

the Causes and Management of Coastal Eutrophication. 

Response to Question 1

Response to Question 2

(top)

Question 1. Given the difficulty in establishing clear and

quantifiable linkages between eutrophic conditions and

degradation of estuarine resources (e.g. commercial fishery

declines), should eutrophication be as high of a management

priority as over-harvesting, invasive species, and other more

tangible problems? What steps should be taken to elevate

eutrophication into a priority problem in the public eye?

Click here for audio response

The National Research Council established the Committee on the

Causes and Management of Coastal Eutrophication (Clean

Coastal Waters: Understanding and Reducing the Effects of

Nutrient Pollution; NRC 2000) to provide broad advice on

effective control of nutrient pollution and eutrophication.

Eutrophication can lead to excess, and sometimes toxic,

production of algal biomass (including red and brown tides); loss

of important nearshore habitat such as seagrass beds (caused by

light reduction); changes in marine biodiversity and species

distribution; increased sedimentation of organic particles; and

depletion of dissolved oxygen (hypoxia and anoxia). Recognizing

eutrophication as a significant coastal problem and high

management priority, the committee concluded that one of the

first steps needed to spark improved nutrient management is

setting challenging but attainable goals. It recommended the

following as national goals to address coastal eutrophication

(measured in relation to the benchmarks determined by NOAA's

National Estuarine Eutrophication Assessment (Bricker et al.

1999)):

•Reduce the number of coastal water bodies

demonstrating severe impacts of nutrient

over-enrichment by at least 10 percent by 2010 (5

estuaries);

•Further reduce the number of coastal water bodies

demonstrating severe impacts of nutrient

over-enrichment by at least 25 percent by 2020 (11

estuaries); and

•Ensure that no coastal area now ranked as "healthy"

(showing no or low/infrequent nutrient-related

symptoms) develop symptoms related to nutrient

over-enrichment over the next 20 years.

(top)

Question 2. The NOAA assessment predicts serious future

degradation of water quality for the nation over the next 20

years, based on estuarine susceptibility and expected

population growth in the coastal zone. Is this a fair

assessment of future conditions, or are there other important

factors to consider? What should be done to reduce, mitigate,

or prevent nutrient enrichment and its associated effects on

the nation's estuaries, and will the costs and effort associated

with these actions benefit the nation in the long run?

Click here for audio response

Although U.S. coastal counties account for only 17 percent of the

U.S. landmass, population in these counties exceeds 141 million.

This means that over half of the U.S. population lives in less than

one fifth of its total area, and this pattern is expected to continue.

Nearly 14,000 housing units are built in coastal counties every

week. With this pattern of increased population in coastal areas

comes additional nutrient loading to coastal waters. The National

Research Council committee found that the key to addressing

coastal nutrient problems is understanding that nutrient inputs to

coastal waters are affected directly and significantly by activities

in the watersheds and airsheds that feed coastal streams and

rivers, and building this recognition into planning as well as

implementation of management solutions. It recommended that a

national coastal nutrient management strategy be developed and

implemented by local, state, and federal entities, working with

academia and the private sector to provide information and

assistance with the development and implementation of effective

management at all levels, as a means for meeting the goals listed

in response to the first question (NRC 2000).

Watershed-specific sources (such as urban stormwater runoff or

excess nutrients from farms) can be addressed most effectively at

the local or state level. Federal leadership is essential to support

and coordinate the research and development needed to provide

new approaches and technologies that can be used by local and

state agencies charged with reducing and reversing the effects of

nutrient over-enrichment. Federal leadership is also critical for

dealing with nutrient sources in large watersheds that span

multiple states or sources distant from the coast, particularly

atmospheric sources. Costs are unknown (no doubt large on a

national level), but several examples (e.g., Tampa Bay) show

reversal of eutrophication symptoms with reduction in nutrient

loading, where multiple benefits have been realized.

(top)

Jan Newton

Senior Oceanographer

Washington State Department

of Ecology and

Affiliate Assistant Professor

School of Oceanography

University of Washington

Dr. Newton has a Ph.D. in Oceanography (1989) and has focused

her research on understanding marine systems, including the

dynamics of phytoplankton blooms and global carbon cycle

fluxes. Since 1994, she has focused on assessing water quality of

Puget Sound and Pacific Coast estuaries. This entails deciphering

human impacts, the role of climate variation, and natural

variability. Dr. Newton is on the board of the Estuarine Research

Federation and is president of the Pacific Estuarine Research

Society. 

Response to Question 1

Response to Question 2

(top)

Question 1. Given the difficulty in establishing clear and

quantifiable linkages between eutrophic conditions and

degradation of estuarine resources (e.g. commercial fishery

declines), should eutrophication be as high of a management

priority as over-harvesting, invasive species, and other more

tangible problems? What steps should be taken to elevate

eutrophication into a priority problem in the public eye?

Click here for audio response

Certainly, I do think eutrophication should be a high priority

management issue. Just because a problem is not straightforward

does not mean we can ignore it. The difficulty is that our

"eutrophication indicators" are found in aquatic systems naturally.

For instance, chlorophyll is high when phytoplankton bloom

seasonally, oxygen can be low when productive waters have

naturally slow flushing rates, and nutrient concentrations can be

high from intrusions of deep ocean water. So you cannot simply

measure a high or low concentration of these indicators and know

that it is bad or good, like you can with many toxic or

contaminant chemicals. Thus, the eutrophication indicator data

must be interpreted relative to the region, to typical or historical

values, and in consideration of climate variation. Assessing the

degree of eutrophication being affected by humans in a particular

area can be very difficult unless you have good documentation of

historical conditions, which clearly does not exist for much of the

country.

Although assessing eutrophication is difficult, its consequences, if

unchecked, are profound. Impacts of eutrophication are pervasive,

not just on commercial fisheries. Eutrophication to the point

where oxygen is depleted is essentially like strangling an aquatic

ecosystem. Species shifts and alteration of habitat can result. Both

of these have far-reaching implications for ecosystem integrity.

Because the impacts from eutrophication are serious, it must be a

management priority. Establishing good scientific procedures for

assessing eutrophication and for collecting time-series data are

important. But the key to bringing this awareness to the public

eye is education. And this education must be aimed at all levels of

our citizenry: in schools, in media, on the web. Eutrophication,

the process, is relatively easy to explain. Although the

eutrophication status of a given area may be difficult to assess,

with good presentation of the important factors and

considerations, the public can grasp the issue. It is not that

different from other familiar environmental problems. We need to

help people better realize that what goes down their drains and

sewers and runs off of their lawns reaches the coastal waters. I

think our society is very unaware of where its wastes go and what

these substances can do.

(top)

Question 2. The NOAA assessment predicts serious future

degradation of water quality for the nation over the next 20

years, based on estuarine susceptibility and expected

population growth in the coastal zone. Is this a fair

assessment of future conditions, or are there other important

factors to consider? What should be done to reduce, mitigate,

or prevent nutrient enrichment and its associated effects on

the nation's estuaries, and will the costs and effort associated

with these actions benefit the nation in the long run?

Click here for audio response

Regarding future conditions, I think there are some truths that we

must be aware of. First, some systems respond to nutrient

enrichment, some do not. NOAA asked the local scientists for

help in determining these. Next, the capacity of an estuary to

absorb nitrogen is a fixed number. It cannot increase with time.

Finally, the amount of nitrogen delivered to an estuary by humans

will increase as human and livestock populations increase, unless

significant efforts are made to reduce the loads. So, accepting

these, it follows that as human populations and development

increase and nitrogen loads are delivered to coastal waters

unchecked, eventually some estuaries will have eutrophication

problems. I think that point is inarguable. What we can argue

over is where and when this will or will not occur. However, as a

national problem, it certainly does need focus.

The regional approach NOAA took is exactly right. Estuarine

systems of the East coast, Gulf coast, Pacific coast are all

different naturally in terms of nutrient loads, responses, and

mechanisms. I think there should be nationally mandated

attention that is implemented by local regions and sub-regions on

how to best focus on what makes the most sense for nutrient

over-enrichment control. First, we need a clear understanding of

the systems' sensitivity (not cheap or easy to assess, in some

cases), then effective measures to best control the

nutrient-enrichment impact (also not cheap or easy). Both steps

need to be conducted in scientifically rigorous and publicly open

forums. Ignoring this is not a viable option if coastal ecosystem

health and sustainability are of societal importance.

(top)

Michael E. Mallin

Research Associate Professor

Center for Marine Science

The University of North

Carolina at Wilmington

Wilmington, North Carolina

Dr. Michael Mallin is an aquatic

ecologist at the University of North

Carolina at Wilmington where he has

worked since1992. He oversees several

comprehensive water quality programs

in urban and rural watersheds. His

research interests include the impacts of

nutrient loading on estuaries and

streams, environmental effects of

catastrophic weather events, impact

analysis of land use practices on water

quality, and water quality management

issues. He has authored or co-authored

over one hundred publications on the

ecology and pollution of freshwater,

estuarine, and coastal marine systems.

Response to Question 1

Response to Question 2

(top)

Question 1. Given the difficulty in

establishing clear and quantifiable

linkages between eutrophic

conditions and degradation of

estuarine resources (e.g. commercial

fishery declines), should

eutrophication be as high of a

management priority as

over-harvesting, invasive species, and

other more tangible problems? What

steps should be taken to elevate

eutrophication into a priority

problem in the public eye?

Click

here for audio response

There are clear and quantifiable

linkages between eutrophic conditions

and degradation of aquatic resources.

Numerous field and experimental

studies have demonstrated that nutrient

loading causes phytoplankton and

macroalgal blooms. Both nitrogen and

phosphorus have been shown to be

important in causing estuarine

eutrophication, with nitrogen the most

problematic during summer and

phosphorus in spring. Also, in some

systems phosphorus impacts are most

notable in upper estuarine areas in

lower salinity waters, while nitrogen

becomes the most critical nutrient in

mid-estuarine to marine conditions.

Nutrient-caused algal blooms

eventually die, causing increased

biochemical oxygen demand (BOD),

which leads to bottom water hypoxia or

anoxia. These conditions result in

habitat loss for finfish and shellfish, and

occasionally death to less mobile

bottom fauna. It has also been

demonstrated that nitrogen loading

through the coastal eutrophication

process can cause physiological

disruption and death to seagrass, which

is important fish and shellfish habitat.

Phosphorus loading has recently been

shown to directly cause increased BOD

concentrations in coastal plain

blackwater streams, leading to reduced

dissolved oxygen in these abundant

ecosystems. Eutrophication also causes

the increase of certain toxic

dinoflagellates including Pfiesteria,

which has caused large-scale fish kills

along the U.S. eastern seaboard, and

more recently, overseas. Levels of

nutrients causing the above problems

have been experimentally quantified;

thus, the results can, in many instances,

be predicted. Eutrophication leads to

outright fish death, loss of habitat for

fish and shellfish, disruption of food

chains, and occasionally human health

problems. Clearly, control of

eutrophication should be a high priority

management effort.

Question 2. The NOAA assessment

predicts serious future degradation of

water quality for the nation over the

next 20 years, based on estuarine

susceptibility and expected

population growth in the coastal

zone. Is this a fair assessment of

future conditions, or are there other

important factors to consider? What

should be done to reduce, mitigate, or

prevent nutrient enrichment and its

associated effects on the nation's

estuaries, and will the costs and effort

associated with these actions benefit

the nation in the long run?

Click

here for audio response

Population growth is an important

factor that increases eutrophication of

coastal waters. Population growth leads

to urbanization, which is the conversion

of natural or rural landscapes to heavy

use areas such as subdivisions and

commercial areas. Urbanization leads to

dramatic increases in impervious

surface coverage (roads, parking lots,

rooftops, driveways, and sidewalks) at

the expense of undeveloped natural

landscapes, or "green space". Green

space naturally cleanses rainfall-driven

runoff of pollutants that cause

eutrophication and other environmental

problems, because pollutants are

absorbed or adsorbed to soil particles or

taken up by vegetation. In contrast,

impervious surfaces concentrate

nutrients, bacteria, metals, pesticides,

and other pollutants. When it rains, the

runoff flushes the accumulated

pollutants into the nearest stream, creek,

canal or lake, often without the benefit

of any kind of treatment.

Strong evidence links impervious

surface coverage with increased

flooding, degraded fisheries,

impairment of the benthic community,

and bacterial contamination of

shellfishing beds. To avoid these

problems, advance planning to

minimize impervious surface coverage

and maximize green space is essential.

Another useful technique is to require

streamside buffer zones consisting of a

mixture of grass, shrubs, and trees to

adsorb surface and subsurface nutrients

and other pollutants associated with

runoff. Above all, natural wetlands

should be protected and new wetlands

created where possible. In some

circumstances wetlands can be

incorporated into the runoff treatment

process. By utilizing these techniques to

prevent inputs of pollutants to coastal

waters it saves much cost and effort

later when agencies and municipalities

try to repair already-damaged aquatic

resources. The most cost-effective

means of reducing estuarine

eutrophication is to prevent it in the first

place.

(top)
Text References

On-line References

Text References

Bennett, U. K. and P. Bennett. 1999 on-line. An underwater

history of Honokowai (1988-1995): Algae blooms, coral heads,

and sea turtles. Turtle Trax Web site.

www.turtles.org/honohist.htm

Boesch, D.F., R.B. Brinsfield, and R.E. Magnien. 2001.

Chesapeake Bay eutrophication: Scientific understanding,

ecosystem restoration, and challenges for agriculture. Journal of

Environmental Quality 30: 303-320.

Bricker, S.B., C.G. Clement, D.E. Pirhalla, S.P. Orlando, and

D.R.G. Farrow. 1999. National Estuarine Eutrophication

Assessment: Effects of nutrient enrichment in the nation's

estuaries. NOAA, National Ocean Service, Special Projects

Office and the National Centers for Coastal Ocean Science.

Silver Spring, MD: 71 pp.

Cooper, S.R. and G.S. Brush. 1991. Long-term history of

Chesapeake Bay anoxia. Science 254:992-996.

Duda, A.M. 1982. Municipal point source and agricultural

nonpoint source contributions to coastal eutrophication. Water

Resources Bulletin 18: 397-407.

Harding Jr., L.W. and E.S. Perry. 1997. Long-term increase of

phytoplankton biomass in Chesapeake Bay, 1950-1994. Marine

Ecology Progress Series 157:39-52.

Greening, H.S., G. Morrison, R.M. Eckenrod, and M.J. Perry.

1997. The Tampa Bay resource-based management approach. In:

Treat, S.F. (ed.), Proceedings, Tampa Bay Area Scientific

Information Symposium 3. Tampa, FL: pp. 349-355.

Johansson, J.O.R. and H.S. Greening. In press. Seagrass

Restoration in Tampa Bay: A Resource-Based Approach to

Estuarine Management. In: Bortone, S.A. (ed.), Subtropical and

Tropical Seagrass Management Ecology, Boca Raton, FL: CRC

Publication.

Kemp, W. M., R. R. Twilley, J. C. Stevenson, W. R. Boynton,

and J. C. Means. 1983. The decline of submerged vascular plants

in upper Chesapeake Bay: Summary of results concerning

possible causes. Marine Technology Society Journal 17: 78-89.

National Oceanic and Atmospheric Administration (NOAA).

1998. NOAA's Estuarine Eutrophication Survey, vol. 5: Pacific

Coast region. Silver Spring, MD: National Ocean Service, Office

of Ocean Resources Conservation and Assessment. 75 pp.

NOAA. 1997a. NOAA's Estuarine Eutrophication Survey, vol. 2:

Mid-Atlantic region. Silver Spring, MD: National Ocean

Service, Office of Ocean Resources Conservation and

Assessment. 50 pp.

NOAA. 1997b. NOAA's Estuarine Eutrophication Survey, vol.

3: North Atlantic region. Silver Spring, MD: National Ocean

Service, Office of Ocean Resources Conservation and

Assessment. 45 pp.

NOAA. 1997c. NOAA's Estuarine Eutrophication Survey, vol. 4:

Gulf of Mexico region. Silver Spring, MD: National Ocean

Service, Office of Ocean Resources Conservation and

Assessment. 78 pp.

NOAA. 1996. NOAA's Estuarine Eutrophication Survey, vol. 1:

South Atlantic region. Silver Spring, MD: National Ocean

Service, Office of Ocean Resources Conservation and

Assessment. 50 pp.

National Research Council. 2000. Clean Coastal Waters:

Understanding and reducing the effects of nutrient pollution.

National Academy Press, Washington, DC. 405 pp.

Malone, T.C. 1992. Effects of water column processes on

dissolved oxygen, nutrients, phytoplankton and zooplankton. In:

Smith, D.E., M. Leffler, and G. Makiernan (eds.), Oxygen

dynamics in Chesapeake Bay: A synthesis of recent research.

College Park, MD: Maryland Sea Grant College Program. pp.

61-112.

Malone, T.C. 1991. River flow, phytoplankton production and

oxygen depletion in Chesapeake Bay. In: Tyson, R.V. and T.H.

Pearson (eds.), Modern and ancient continentintal shelf anoxia.

Geological Society special publication no. 58. London: The

Geological Society. pp. 83-93.

Nixon, S. W. 1995. Coastal marine eutrophication: A definition,

social causes, and future concerns. Ophelia 41: 199-219.

Officer, C. B., R.B. Biggs, J.L. Taft, L.E. Cronin, M. Tyler, and

W.R. Boynton. 1984. Chesapeake Bay anoxia: Origin,

development, and significance. Science 223:22-27.

Orth, R. J. and K. A. Moore. 1984. Distribution and abundance

of submerged aquatic vegetation in Chesapeake Bay: An

historical perspective. Estuaries 7: 531-540.

Peierls, B.L., N.F. Caraco, M.L. Pace, and J.J. Cole. 1991.

Human influence on river nitrogen. Nature 350: 386-387.

Smith, R.A., G.E. Schwarz, and R.B. Alexander. 1997. Regional

interpretation of water-quality monitoring data. Water Resources

Research 33: 2781-2798.

Taft, J.L., E.O. Hartwig, and R. Loftus. 1980. Seasonal oxygen

depletion in Chesapeake Bay. Estuaries 3:242-247.

Tomasko, D.A. and T.F. Ries. 1997. Responses of Tampa Bay

and Sarasota Bay seagrass meadows to nitrogen loading

reductions. Estuarine Research Federation Newsletter 23(1):1,

19.

Turner, R.E. and N.N. Rabalais. 1991. Changes in Mississippi

River water quality this century. Implications for coastal food

webs. BioScience 41:140-147.

Twilley, R. R., W. M. Kemp, K. W. Staver, J. C. Stevenson, and

W. R. Boynton. 1985. Nutrient enrichment of estuarine

submersed vascular plant communities. 1. Algal growth and

effects on production of plants and associated communities.

Marine Ecology Progress Series 23: 179-191.

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On-line References

The following references were accessed on the World Wide Web

during 2000.

General

Nixon, Scott W., Enriching the Sea to Death.

http://www.sciam.com/specialissues/0898oceans/0898nixon.html

A feature article in Scientific American on-line. This in-depth

article explores the history, causes, and consequences of

estuarine eutrophication.

Special Projects Office, NOAA. CADS Make a Map and Digital

Data.

http://cads.nos.noaa.gov/

Provides access to all National Estuarine Eutrophication

Assessment data. The Publications link provides access to PDF

files of the five regional reports and the national report.

Symptoms of Eutrophication

Submerged Aquatic Vegetation (SAV) Loss

Virginia Institute of Marine Science. SAV in Chesapeake Bay.

http://www.vims.edu/bio/sav/index.html

Includes a brief primer on SAV in Chesapeake Bay, recent and

historical SAV distribution information with continual updating,

and a full bibliography of papers published about SAV in

Chesapeake Bay.

US Fish and Wildlife Service, Chesapeake Bay Field Office.

Submerged Aquatic Vegetation: Where have all the grasses

gone?

http://www.fws.gov/r5cbfo/CBSAV.HTM

Explains the role SAV plays in the Chesapeake Bay ecosystems,

describes the nature and causes of widespread decline of bay

grasses, and what is being done to restore them. Includes

photographs of common bay SAV.

Maryland Department of Natural Resources. Chesapeake Bay

Grasses.

http://www.dnr.state.md.us/bay/sav/

Comprehensive site provides information on past and present

distribution, the importance of SAV, factors affecting growth,

and SAV varieties and identification, and detailed information on

restoration efforts. Also includes information on bay grass

regulations in Maryland.

Chesapeake Bay Program. Bay Grasses.

http://www.chesapeakebay.net/info/baygras.cfm

Provides information on the ecological role of SAV, SAV

Species and Distribution, SAV decline in the Chesapeake, SAV

as habitat, SAV habitat requirements, and restoration of

Chesapeake Bay grasses.

Nuisance/Toxic Algal Blooms

Woods Hole Oceanographic Institution. The Harmful Algae

Page.

http://habserv1.whoi.edu/hab/

Contains maps of current HAB locations and trends. Also

provides information on HAB's including introductory material

on what algal blooms are and how they form, characteristics of

different harmful species, and the adverse impacts of blooms.

Recent news coverage about current HAB outbreaks is also

included.

Low Dissolved Oxygen

U.S. Environmental Protection Agency. Long Island Sound

Study.

http://www.epa.gov/region01/eco/lis/hypox.html

Describes the extent of hypoxic conditions and explains the

chemical, physical, and biological synergisms leading to hypoxic

conditions in Long Island Sound. Also, documents how two- and

three-dimensional models of the Sound's dynamics are being

used to better understand the causes of, and solutions to,

hypoxia. Presents efforts by The Management Conference to

ameliorate the current effects of human activities on the Sound

and future plans to continue improvements.

Case Studies

Chesapeake Bay Program. Overview of the Bay Program.

http://www.chesapeakebay.net/overview.htm

Provides information about the bay program, including PDF files

of the 1983 and 1985 Chesapeake Bay Agreement documents

and the 1992 Amendments. The site also provides a wealth of

information pertaining to nutrient enrichment and eutrophication

of the Chesapeake Bay.

Tampa Bay Estuary Program. The State of the Bay: Special

Report! Making Strides in Saving Tampa Bay.

http://www.tbep.org/baystate/progress899.html

Outlines management efforts underway to further improve

nitrogen management and submerged aquatic vegetation in

Tampa Bay.

Ursula Keuper-Bennett and Peter Bennett. An Underwater

History of Honokowai (1988-1995), Algae Blooms, Coral

Heads, and Sea Turtles. Turtle Trax.

http://www.turtles.org/honohist.htm

A chronology of the condition of algal blooms, corals and sea

turtles in nearshore Hawaiian waters between 1988 and 1995.

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Appendix A. Expression of Eutrophic Condition and Symptoms

in the Nation's Estuaries

A1. North Atlantic

A2. Middle Atlantic

A3. South Atlantic

A4. Gulf of Mexico

A5. Pacific

Appendix B. Overall Human Influence on Expression of

Eutrophic Conditions in the Nation's Estuaries

B1. North Atlantic

B2. Middle Atlantic

B3. South Atlantic

B4. Gulf of Mexico

B5. Pacific
algae: a diverse group of chiefly aquatic plants (e.g., seaweed,

pond scum, stonewort) that contain chlorophyll but lack roots,

stems, leaves, and vascular tissues, and may passively drift,

weakly swim, grow on a substrate, or take root in a water body.

See also epiphytes, macroalgae, nuisance algae, toxic algae.

anoxia: the absense of dissolved oxygen. May occur as a result

of large algal blooms that sink to the bottom of the water

column where bacteria break down the algae, using oxygen

during the process.

chlorophyll a: a pigment found in microscopic algae, called

phytoplankton. Measurements of chlorophyll a levels are used

to indicate the amount of phytoplankton growing in a water

body. High concentrations are indicative of problems related to

the overproduction of algae.

epiphytes: algae that grow on the surfaces of plants or other

objects. They can cause losses of submerged aquatic vegetation

by encrusting leaf surfaces and thereby reducing the light

available to the plant leaves.

eutrophication: a process in which the addition of nutrients

(primarily nitrogen and phosphorus) to water bodies stimulates

algal growth. This is a natural process, but it can be greatly

accelerated by human activities.

hypoxia: very low dissolved oxygen concentrations, usually

ranging between 0 and 2 milligrams per liter. May occur as a

result of large algal blooms that sink to the bottom of the water

column where bacteria break down the algae, using oxygen

during the process.

macroalgae: are large algae, commonly referred to as

"sea-weed." Blooms can cause losses of submerged aquatic

vegetation by blocking sunlight. Additionally, blooms may also

smother immobile shellfish, corals, or other habitat. The

unsightly nature of some blooms may impact tourism due to

the declining value of swimming, fishing, and boating

opportunities.

nuisance algae: any type of algae that bloom in sufficient

quantity to cause low dissolved oxygen (anoxia or hypoxia),

create unaesthetic conditions (unsightly blooms and/or foul

odors), or other undesirable conditions. Nuisance and toxic

algal blooms are often reffered to as harmful algal blooms

(HABs).

nutrient enrichment: an increase in the amount of nutrients

added to an ecosystem, above normal (naturally expected)

levels.

submerged aquatic vegetation (SAV): rooted plants that

grow entirely underwater, often in large beds or meadows.

Loss of SAV is indicative of accelerated eutrophication. SAV

beds serve as important habitat in many estuaries. Also called

seagrasses and submerged macrophytes.

toxic algae: algae that produce toxins that are considered

harmful because they are capable of causing fish kills and may

also be hazardous to avians and mammals. Related

human-health problems are caused by the consumption of

seafood that has accumulated algal toxins, or from the

inhalation of airborne toxins. Nuisance and toxic algal blooms

are often reffered to as harmful algal blooms (HABs).

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Acknowledgments

Photo Credits

About the Authors

Acknowledgments

We would like to thank all of the estuarine research scientists

and coastal resource managers whose contributions of data,

information, and expertise were the key to making this report

possible. Special thanks go to Daniel J. Basta, Director of the

Special Projects Office at the National Ocean Service (NOS),

for his vision and unflagging support. We also thank our other

NOS colleagues, Charles Alexander and C. John Klein for

technical advice; Alison Hammer, John Hayes, Percy Pacheco,

and Scot Frew for invaluable support provided for the National

Estuarine Eutrophication Assessment; and Pam Rubin for

reviewing and editing the manuscript.

Thanks also to Gregory McMurray, Oregon Department of

Environmental Quality and Walter Boynton, University of

Maryland Chesapeake Biological Laboratory, for providing

critical reviews of the draft document.

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Photo Credits

Many of the photos were gathered from NOAA archives or

were generously provided from the personal collections of

NOAA staff members. Others were contributed from outside of

NOAA, and we gratefully thank the following institutions and

individuals:

Photo 4. Louisiana State University

Photo 5. W. Bennett, U.S. Geological Survey

Photo 7. Cobscook Bay Resource Center Web Site

Photo 8. Maureen Keller, Bigelow Laboratory for Ocean

Sciences

Photo 17. Chesapeake Bay Program Web Site

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About the Authors

Christopher Clement is a physical scientist with the

Special Projects Office in NOAA's National Ocean

Service where he has worked since 1990. He has a BS

in Natural Resources Management from the University

of Maryland and a Masters degree in Environmental

Science and Policy from Johns Hopkins University. Mr.

Clement has been actively involved in conducting the

national estuarine eutophication survey and assessment

since the start of the survey in 1992. He has also worked

on assessments of classified shellfish growing waters,

and developed information management systems for

projects such as the Sustainable Seas Expeditions in the

nation's marine sanctuaries.

Suzanne B. Bricker is a Physical

Scientist at NOAA's Special Projects

Office where she has been since 1990.

She earned a Ph.D. in Oceanography

from the University of Rhode Island's

Graduate School of Oceanography in

1990 and a B.A. in Biology from

Northwestern University in 1981. Dr.

Bricker is the Project Manager for

NOAA's National Estuarine

Eutrophication Assessment, an 8 year

effort completed in 1999, to characterize

the extent and severity of nutrient

pollution and eutrophication-related

impacts on the nation's coastal waters

including hypoxia, occurrences of

harmful and toxic algal blooms, and

losses of submerged aquatic vegetation.

Her research interests include the cause

and effect linkages between land-based

contaminants and water quality

degradation and the role of physical

processes within estuaries, the role of

wetlands in mitigating the effects of

land-based contaminant sources, and the

atmospheric contribution to

eutrophication.

 

Douglas Pirhalla is an environmental scientist with the

Center for Coastal Monitoring and Assessment in

NOAA's National Ocean Service where he has worked

since 1990. He has a Masters degree in Environmental

Science and Policy from Johns Hopkins University and

a BS degree from Frostburg State University in

Geography. Mr. Pirhalla has been actively involved in

conducting the National Estuarine Eutrophication

Survey and Assessment since its inception in 1992. He

has also worked on numerous NOAA supported remote

sensing studies classifying benthic habitats in coastal

waters, and has been intimately involved in

watershed-based biological assessment and monitoring

activities supported by Maryland's Department of

Natural Resources.

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Return to National Picture

Figure 4. National summary of eutrophic condition in 138 estuaries

and the Mississippi River Plume.

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Figure 5. Estuaries with a high level of eutrophic conditions.

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Figure 6. Number of estuaries with primary and secondary symptoms of eutrophication.

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Figure 7. Nitrogen input, estuarine susceptibility, and level of human influence on the

overall expression of eutrophic conditions in the nation's estuaries.

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Figure 8. Regional distribution of estuaries with high, moderate,

and low eutrophic conditions.

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Figure 9. Summary of eutrophication and future outlook for estuaries of the North

Atlantic region.

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Figure 10. Summary of eutrophication and future outlook for estuaries of the Middle

Atlantic region.

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Figure 11. Summary of eutrophication and future outlook for estuaries of the South

Atlantic region.

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Figure 12. Summary of eutrophication and future outlook for estuaries of the Gulf of

Mexico region.

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Figure 13. Summary of eutrophication and future outlook for estuaries of the Pacific

region.

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Appendix A1. Expression of

Eutrophic Condition and

Symptoms in the Nation's

Estuaries: North Atlantic

Region

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Appendix A2. Expression of

Eutrophic Condition and

Symptoms in the Nation's

Estuaries: Middle Atlantic

Region

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Appendix A3. Expression of

Eutrophic Condition and

Symptoms in the Nation's

Estuaries: South Atlantic

Region

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Appendix A4. Expression of

Eutrophic Condition and

Symptoms in the Nation's

Estuaries: Gulf of Mexico

Region

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Appendix A5. Expression of

Eutrophic Condition and

Symptoms in the Nation's

Estuaries: Pacific

Region

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Appendix B1. Overall Human

Influence on Expression

of Eutrophic Conditions: North

Atlantic Region

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Appendix B2. Overall Human

Influence on Expression

of Eutrophic Conditions: Middle

Atlantic Region

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Appendix B3. Overall Human

Influence on Expression

of Eutrophic Conditions: South

Atlantic Region

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Appendix B4. Overall Human

Influence on Expression

of Eutrophic Conditions: Gulf of

Mexico Region

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Appendix B5. Overall Human

Influence on Expression

of Eutrophic Conditions: Pacific

Region

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Return to Introduction

Figure 1. Data parameters for survey of eutrophication-related symptoms in 138 estuaries of the

coterminous United States collected between 1992 and 1998.

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Figure 2. Simple model used to interpret eutrophication

survey of 138 estuaries and the Mississippi River Plume.

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Figure 3. Matrix used to assign overall level of expression of eutrophic

conditions in an estuary.

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