The National Ocean Service: Working for America’s Coasts

More information or access to data, products, and services can be obtained from our Web sites:

Special Projects Officehttp://spo.nos.noaa.gov

National Centers for Coastal Ocean Sciencehttp://www.nccos.noaa.gov

The National Ocean Service (NOS) approaches the 21st century with a clear vision–that our coasts and oceansenjoy robust health, provide a rich bounty of resources, and are wisely managed to endure competing uses. Asthe nation's principal advocate for coastal and ocean stewardship, the National Ocean Service develops thenational foundation for coastal and ocean science, management, response, restoration, and navigation. Thisreport, developed by the NOS Special Projects Office and the National Centers for Coastal Ocean Science, strength-ens this foundation, helping to bridge the gap between science, management, and public policy.

The Special Projects Office works to increase the effectiveness of coastal management in the United States, therebyensuring continued economic prosperity and environmental well-being throughout the nation's coastal regions.A main objective of the Special Projects Office is to provide expertise, products, and services that assist the NOSin designing and implementing an effective program of coastal stewardship throughout the agency. This effortincludes exploring ways to leverage the agency's considerable expertise into a force that more directly supportsand influences the sound management and protection of coastal areas. Special Projects is in a unique position tobridge the gap between NOS scientific efforts and coastal management policy issues.

The National Centers for Coastal Ocean Science (NCCOS) works to understand the ocean and coastal environ-ment, and the influences of human activities, by conducting research, monitoring, and assessments of thesedelicate and important areas. NCCOS activities include understanding and predicting impacts of pollution andcoastal development on sensitive habitats and resources; helping to protect coastal property and residents fromstorms and other natural hazards; understanding the causes and consequences of harmful algal blooms, such asred tides and toxic Pfiesteria piscicida; understanding how climate change may affect our lives; and determiningthe complex factors that affect fish populations.

To receive copies of this report, contact:

Pam RubinNOS Special Projects Officepam.rubin@noaa.gov301-713-3000, ext. 121

1305 East-West Highway, 9th FloorSilver Spring, MD 20910-3281

This report should be cited as: 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.

National Estuarine Eutrophication Assessment

Effects of Nutrient Enrichment in the Nation’s Estuaries

Special Projects Officeand the

National Centers for Coastal Ocean Science

National Ocean ServiceNational Oceanic and Atmospheric Administration

1305 East-West HighwaySilver Spring, MD 20910

September 1999

Suzanne B. Bricker, Christopher G. Clement, Douglas E. Pirhalla, S. Paul Orlando, Daniel R.G. Farrow

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Richard Alexander U.S. Geological SurveyWalter Boynton University of MarylandDavid Brock Texas Water Development BoardDarell Brown U.S. Environmental Protection AgencyDavid Chestnut South Carolina Department of Health and Environmental ControlDavid Flemer U.S. Environmental Protection AgencyHolly Greening Tampa Bay National Estuary ProgramThomas Malone University of MarylandGregory McMurray Oregon Department of Environmental QualityJan Newton Washington Department of EcologyJonathan Pennock University of Alabama/Dauphin Island Sea LabAndrew Robertson National Oceanic and Atmospheric AdministrationDonald Stanley East Carolina UniversityJ. Kevin Summers U.S. Environmental Protection AgencyTerry Whitledge University of Alaska

National Assessment Core Group

National Assessment Workshop ParticipantsMerryl Alber University of GeorgiaDonald Boesch University of MarylandThomas Brosnan National Oceanic and Atmospheric AdministrationBrian Cole U.S. Geological SurveyElizabeth Cosper Cosper Environmental Services, Inc.Christopher D’Elia State University of New York at AlbanyErnest Estevez Mote Marine LaboratoryPeggy Fong University of CaliforniaFred Holland South Carolina Department of Wildlife and Marine ResourcesRenee Karrh Maryland Department of Natural ResourcesJack Kelly U.S. Environmental Protection AgencyPeter Larsen Bigelow Laboratory for Ocean ScienceTheodore Loder University of New HampshireRobert Magnien Maryland Department of Natural ResourcesMichael Mallin University of North CarolinaHank McKellar University of South CarolinaGary Powell Texas Water Development BoardRandy Shuman Metropolitan King County, WashingtonRichard Smith U.S. Geological SurveyRonald Thom Battelle Marine Science LaboratoryDavid Tomasko Southwest Florida Water Management DistrictRichard Valigura National Oceanic and Atmospheric AdministrationPeter Verity Skidaway Institute of OceanographyRichard Wetzel Virginia Institute of Marine Science

We would like to thank all of the estuarine research scientists and coastal resource managers whose contribu-tions of data, information, and expertise were the key to making this report possible (Appendix C). The CoreGroup was instrumental in developing methods for aggregating the data and, along with the other participantsin the National Assessment Workshop, reviewed and analyzed the results and made recommendations for anational-level response to eutrophication problems in the nation’s estuaries.

This report is the result of the dedication and cooperation of many individuals who remained committed dur-ing the long duration of the project. Special thanks go to Daniel J. Basta, Director of NOS Special Projects, for hisvision and unflagging support, and to Richard Alexander and Richard Smith of the U.S. Geological Survey foruse of their SPARROW model results prior to publication. We also thank our NOS colleagues Charles Alexanderand C. John Klein for technical advice; Alison Hammer, John Hayes, Percy Pacheco, and Scot Frew for invalu-able support provided for the National Assessment Workshop; Denise Yver for designing the report cover; andPam Rubin for reviewing and editing the manuscript.

ii

Acknowledgments

Foreword.......................................................................................................................... ivExecutive Summary ........................................................................................................ vEutrophication Diagram ............................................................................................... ix

Introduction ..................................................................................................................... 1Estuarine Eutrophication: Background to the Problem ....................................................... 1The Nation’s First Comprehensive Estuarine Eutrophication Assessment ...................... 3The National Report: A Challenge to Interpret the Data ..................................................... 3Extending the Assessment: Toward a National Strategy ..................................................... 6Organizing the Results: Seven Key Questions ...................................................................... 8Using this Report and the Data ............................................................................................... 8

National Overview ......................................................................................................... 9Eutrophic Conditions ................................................................................................................ 9Completing the Picture ........................................................................................................... 13

Regional Summaries .................................................................................................... 19North Atlantic .......................................................................................................................... 20Middle Atlantic ........................................................................................................................ 24South Atlantic ........................................................................................................................... 28Gulf of Mexico.......................................................................................................................... 32Pacific ........................................................................................................................................ 36

Conclusions.................................................................................................................... 41

Toward A National Strategy ....................................................................................... 45

Data Sources .................................................................................................................. 47

AppendicesA. Methods ................................................................................................................... 49B. Table of Results ......................................................................................................... 63C. Participants ............................................................................................................... 67

iii

Table of Contents

Nancy Foster, Ph.D.Assistant Administrator for Ocean Services

and Coastal Zone ManagementNational Ocean Service, NOAA

This report is the culmination of almost seven years of effort to assess compre-hensively the scale, scope, and characteristics of nutrient enrichment andeutrophic conditions in the nation’s estuaries. It provides the most compre-hensive assessment of this issue ever assembled for our nation’s estuaries,and the results represent a significant contribution to the development of anational strategy to control nutrient enrichment problems affecting U.S. coastalwaters. With this information, we have the opportunity to make a real differ-ence in the actions this nation takes to address this important issue.

These results provide a valuable context for a host of ongoing and plannedactivities addressing estuarine eutrophication, including reauthorization ofthe Coastal Zone Management Act, particularly section 6217; reauthorizationof the Clean Water Act; the states’ development of Unified Watershed Assess-ments and Watershed Restoration Priorities as part of the Clean Water ActionPlan; the Report on the Status of the Nation’s Ecosystems; the Committee onEnvironment and Natural Resources Gulf of Mexico Hypoxia Study; andNOAA’s National Dialogues on Coastal Stewardship.

As important as the results themselves is the process used to acquire this in-formation. The approach explicitly recognized that much of what is knownabout these problems resides within the knowledge and experience of expertsaround the nation. Hence, a process was developed to systematically obtaininformation from more than 300 experts on estuarine eutrophication. Thoseinterested in this innovative approach to information synthesis can review theAppendices to learn more about these methods and how to apply them.

During the past year, the National Ocean Service (NOS) has undergone a reor-ganization, and is emerging with a new focus on coastal stewardship. One ofthe new roles for NOS is as a catalyst to ensure that scientific results are tar-geted to providing solutions to environmental problems and to preservingthe nation’s coastal and ocean resources. This report is also an example of thetype of activity that is needed to better bridge the gap between scientists andresource managers. I encourage you to use this work to stimulate further ef-forts to protect our natural resources.

iv

Foreword

Eutrophication is the accelerated productionof organic matter, particularly algae, in a wa-ter body. It is usually caused by an increasein the amount of nutrients being dischargedto the water body. As a result of acceleratedalgal production, a variety of impacts mayoccur, including nuisance and toxic algalblooms, depleted dissolved oxygen, and lossof submerged aquatic vegetation. These im-pacts are interrelated and usually viewed ashaving a negative effect on water quality andecosystem health. Eutrophication has beenrecognized as a problem in freshwater sys-tems for many years, but only in the pastthree decades has concern grown about thewidespread occurrence of eutrophic condi-tions in estuarine systems. Due to the com-plexity of the phenomena and the lack ofconsistent national data sets, the severity andextent of the problem had never been ad-equately characterized at the national scale.

What are the severity and extent ofeutrophic conditions exhibited withinthe estuaries of the United States?

To what extent are eutrophic conditionsin the nation’s estuaries caused by hu-man activities?

To what extent do eutrophic conditionsimpair the use of estuarine resources,and what are the important impaireduses?

Where should management efforts betargeted to achieve the greatest benefittoward remediation and protection fromdegradation?

v

The National AssessmentThis report presents the results of a NationalAssessment Workshop held in August 1998to address the problem of estuarineeutrophication. The assessment was basedprimarily on the results of the National Es-tuarine Eutrophication Survey, conductedby NOAA from 1992 to 1997, but wassupplemented by information on nutrientinputs, population projections, and land usedrawn from a variety of sources. It covers138 estuaries, representing over 90 percentof the estuarine surface area of the cotermi-nous United States, plus the MississippiRiver Plume. The final assessment pre-sented here was undertaken at the NationalAssessment Workshop by a select group ofexperts, all of whom participated in theeutrophication survey. The Workshop wasstructured around answering seven keyquestions regarding the severity and extentof eutrophication in the nation’s estuaries.All results presented in this report were re-viewed by the Workshop participants.

About Estuarine Eutrophication

To what extent can the severity and ex-tent of eutrophic conditions be expectedto increase by the year 2020, given thenatural susceptibility of estuaries and thepotential for increasing nutrient inputs?

Which data gaps and research and moni-toring needs are most critical in terms ofimproving the ability to assess and re-spond to eutrophication symptoms?

How can the results of this assessmentbe translated into a national strategy?

1.

2.

3.

4.

5.

6.

7.

Key Questions

Executive Summary

vi

Executive Summary

Eutrophication Severity and Extent

Human Influence on Eutrophication

High expressions of eutrophic conditions are ex-hibited in 44 estuaries, representing 40% of thetotal estuarine surface area studied. An additional40 estuaries exhibit moderate conditions. Whenconsidered together, the estuaries with moderateto high conditions represent 65% of estuarine sur-face area in the study.

High conditions occur in estuaries along all coasts,but are most prevalent in estuaries along the Gulfof Mexico and Middle Atlantic coasts.

82 estuaries, representing 67% of estuarine sur-face area, exhibit moderate to high expressions ofat least one of the following symptoms: depleteddissolved oxygen, loss of submerged vegetation,and nuisance/toxic algal blooms.

A high level of human influence is associated witha majority (36) of the 44 estuaries with higheutrophic conditions.

Only six (14%) of the 44 estuaries with high-leveleutrophic conditions have corresponding high-level nitrogen inputs. An additional 22 of the 44estuaries have moderate-level nitrogen inputs.

Of the 44 estuaries with high-level eutrophic con-ditions, more than half (25) exhibit a high suscep-tibility to retaining nutrients.

Human influence on the expression of eutrophic conditions is substantial.

Symptoms of eutrophication are prevalent in the nation’s estuaries.

Assessment Data: National Estuarine Eutrophication Survey

Description: rigorous multi-year effort to synthesize the bestavailable information about eutrophic conditions

Characteristics:consistent and comparable national data set was producedthrough survey of over 300 estuarine scientists and managers

includes spatial and temporal information about eutrophi-cation symptoms, including chlorophyll a, macroalgae, epi-phytes, dissolved oxygen, submerged aquatic vegetation,and nuisance/toxic algae

survey data aggregated by estuary and final results re-viewed by experts at the Assessment Workshop

collection, evaluation, and review of the survey data was mostrigorous of all evaluations in the National Assessment

•

•

•

•

Watershed monitoring data from the U.S. Geological Sur-vey provided first-order estimates of nitrogen inputs.

U.S. Census Bureau population estimates and Depart-ment of Agriculture Agricultural Census data were usedas potential nutrient pressure indicators.

Estuarine susceptibility was determined using NOAAdata on freshwater inflow, tide, and estuarine geometry.

Characteristics: assessment based on data less rigorouslyevaluated and reviewed than for eutrophic conditions

Description: provides estimates of human-related nutri-ent inputs, estuarine susceptibility, and human influence

Assessment Data:•

•

•

1

2

Assessment Data: expert evaluations at Workshop

Description: Experts identified impaired uses they judgedto be related to estuarine eutrophic conditions.

Characteristics: Although the information is not supportedby a comprehensive national data set, it does provide arough insight into the extent of problems stemming fromeutrophic conditions.

69 estuaries were identified by workshop partici-pants as having human-use impairments relatedto eutrophication.

Compared to other impaired uses, commercial/recreational fishing and shellfisheries were iden-tified as impaired for human use in the greatestnumber of estuaries, 43 and 46, respectively.

Impaired Uses of Estuaries3

Impairments to estuarine resources, and fisheries in particular, are of great concern.

Key Findings

vii

Executive Summary

Eutrophic conditions will most likely worsen in86 estuaries by the year 2020.

Of the 86 estuaries expected to worsen, 43 exhibitonly low to moderate eutrophic conditions.

The 10 estuaries that exhibit low eutrophic con-ditions and have high susceptibility are most atrisk of future degradation if human-related nu-trient inputs increase.

The 23 estuaries with high expressions of eutrophicconditions and high susceptibility are likely to requiregreater management effort and longer response timefor results than those estuaries with low susceptibil-ity. These estuaries represent approximately 10% ofthe national estuarine surface area.

There are 10 estuaries that have low eutrophic condi-tions and high susceptibility; accordingly, they shouldbe priorities for preventive management. These estu-aries represent approximately 3% of the national es-tuarine surface area.

All of the typical point and nonpoint pollution sourceswere identified at the Workshop as important to tar-get in order to manage nutrient problems. However,there are some important regional differences in nu-trient sources, such as combined sewer overflows inthe North Atlantic.

Potential Management Concerns

Management requirements are dependent on eutrophic conditions and susceptibility.

4

Assessment Data: NOAA susceptibility and Eutrophica-tion Survey data plus expert evaluations at Workshop

Description: In addition to evaluating eutrophic condi-tions and susceptibility (see numbers 1 and 2), expertsidentified pollution sources important for managingnutrient inputs in each watershed.

Characteristics: Although the pollutant source informa-tion is not based on a comprehensive national data set,the expert evaluation of important point and nonpointsources is useful for gaining a first-order understandingat the national level of the types of actions, and the levelof effort, that will be required to address the problem.

Future Eutrophic Conditions5

Without preventive efforts, eutrophic conditions can be expected to continually worsen.

Assessment Data: projected population growth estimatesadapted from the U.S. Census Bureau and NOAA sus-ceptibility data

Description: Experts at the National Workshop usedpopulation growth and estuarine susceptibility esti-mates, along with their knowledge of the estuarine wa-tersheds, to project the direction and magnitude ofchange in current eutrophic conditions.

Characteristics: The reliability of this information is in-herently vulnerable to unforeseen changes in input lev-els from nutrient pollution sources.

Data Gaps and Research Needs6

Much remains to be done to better characterize and understand estuarine eutrophication.

Assessment Data: expert experience and knowledge, incombination with data completeness and reliabilityanalysis of the Eutrophication Survey results

Description: Experts at the National Assessment Work-shop identified data gaps and research needed to im-prove the assessment of the severity, human influence,impacts, and appropriate responses to eutrophicationproblems in estuaries.

Given all of the monitoring and research done todate, information and knowledge is still inad-equate in 48 estuaries (low confidence or inad-equate data for assessment). These estuaries rep-resent approximately 25% of the nation’s estua-rine surface area.

All participants in the National Assessment pro-cess agreed that research is needed to clarify thelinkages between eutrophication and impacts onestuarine resources, including fisheries, recreationand tourism, and risks to human health.

viii

Executive Summary

A national strategy, which incorporates the resultsof this assessment, should be developed to helpset priorities and support decision-making at thenational level.

The strategy should focus on management, moni-toring, and research, and should effectively inte-grate with regional, state, and local programs.

For estuaries in serious condition, prioritiesshould focus on management action; for those inless serious condition but at risk, the focus shouldbe on monitoring and prevention.

Estuaries for which there is insufficient informa-tion for evaluation should undergo basic moni-toring and assessment activities.

Data Gaps and Research Needs, continued6

Toward A National Strategy7

Assessment results will be valuable in setting national priorities.

Assessment Data: expert experience and knowledge base

Description: These recommendations were developedat the National Assessment Workshop from facilitateddiscussions with the participating estuarine eutrophi-cation experts.

The National Assessment process confirms thatmuch remains to be done to adequately charac-terize nutrient pressure on estuaries. Better quan-tification is needed of total nutrient inputs, inputsby source, and estimators of nutrient pressure(e.g., population, land use). Atmospheric andgroundwater inputs are least well quantified.

Better characterization of physical factors isneeded, including basic circulation patterns, ef-fects of weather patterns, climate change, chang-ing land use, and resultant effects on nutrient de-livery, circulation, and eutrophic conditions.

Other research needs include defining the relation-ship between nutrient inputs and toxic blooms, bet-ter characterization of assimilative capacity, andcharacterization of the effects of seasonal popula-tion changes.

Key Findings, continued

Estuarine Eutrophication: Nutrient Sources and Effects in EstuariesEutrophication is a process in which the addition of nutrients to water bodies stimulates algal growth. Under natural conditions, this is usually a slowprocess that results in healthy and productive ecosystems. In recent decades, however, a variety of human activities has greatly acceleratednutrient inputs to estuarine systems, causing excessive growth of algae and leading to degraded environmental conditions.

Eutrophication Diagram

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1

Estuarine Eutrophication: Background tothe ProblemEutrophication refers to a process in which the ad-dition of nutrients to water bodies, primarily nitro-gen and phosphorus, stimulates algal growth. Thisis a natural process, but it has been greatly acceler-ated by human activities. Estuaries have always re-ceived nutrients from natural sources in the water-shed and from the ocean. In recent decades, how-ever, population growth and related activities, suchas various agricultural practices, wastewater treat-ment plants, urban runoff, and the burning of fossilfuels, have increased nutrient inputs by many timesthe levels that occur naturally.

Increased nutrient inputs promote a complex arrayof symptoms, beginning with the excessive growthof algae, which, in turn, may lead to other, more se-rious symptoms. In addition to the rate of algalgrowth, nutrient inputs may also affect which algalspecies are favored. This process is poorly under-stood, but some unfavorable species (e.g., Pfiesteria)appear to be linked to nutrient inputs.

This report presents the results of a comprehensive National Assessment to address the problem of estuarine eutrophication.The assessment includes evaluations of eutrophic conditions, human influence, impaired estuarine uses, future conditions,data gaps and research needs, and recommendations for a national strategy to respond to the problem.

Eutrophication refers to a process inwhich the addition of nutrients towater bodies stimulates algal growth.In recent decades, human activitieshave greatly accelerated nutrient in-puts, causing the excessive growth ofalgae and leading to degraded waterquality and associated impairments ofestuarine resources for human use.

Introduction

In recent decades, eutrophication problems havebeen reported globally, from the Baltic, Adriatic, andBlack Seas, to the estuaries and coastal waters of Ja-pan, China, and Australia. Eutrophic symptomshave also been observed in the United States, includ-ing the Chesapeake Bay, Long Island Sound, and thenorthern Gulf of Mexico. More recently, it has be-come clear that nearly all U.S. estuaries exhibit somelevel of eutrophic symptoms, although the scale, in-tensity and impacts vary widely, as do the levels ofnutrient inputs that produce these symptoms.

Whether nutrient additions result in degraded wa-ter quality depends on the extent of additional in-put and on natural characteristics that affect estua-rine susceptibility to nutrients. In some estuaries, nu-trients cause dense algal blooms to occur for monthsat a time, blocking sunlight to submerged aquaticvegetation. Decaying algae from the blooms usesoxygen that was once available to fish and shellfish.In other estuaries, these or other symptoms may oc-cur, but less frequently, for shorter periods of time,or over smaller spatial areas. In still other estuaries,the assimilative capacity, or ability to absorb nutri-ents, may be greatly reduced, though no other symp-toms are apparent. These eutrophic symptoms areindicative of degraded water quality conditions thatcan adversely affect the use of estuarine resources,including commercial and recreational fishing, boat-ing, swimming, and tourism. Eutrophic symptomsmay also cause risks to human health, including se-rious illness and death, that result from the consump-tion of shellfish contaminated with algal toxins, orfrom direct exposure to waterborne or airborne tox-ins.

It should be noted that although nutrients causeeutrophic symptoms, other human and natural in-fluences may cause or affect the expression of such

A red tide causes a fish kill.Photo courtesy of Woods Hole Oceanographic Institution

2

Introduction

symptoms. These influences include engineeredwater flow, which decreases estuarine flushing rates;and development, dredging, and disease, whichchange nutrient assimilative capacity through lossesof wetlands, sea grasses, oysters, and other filterfeeders. In addition to nitrogen and phosphorus,there are other nutrients (e.g., silica) and trace ele-ments that may be important under certain condi-tions, but their role is less understood.

Climate changes may also be significant for futureconditions. Global warming may result in increasedwater temperatures, causing lower dissolved oxy-gen with no changes in nutrient inputs. At the sametime, flushing times and exchange rates might in-crease with rising sea levels, which could possiblyoffset these effects.

For more than 40 years, scientists and natural re-source managers have worked to understand, docu-ment, and resolve the complex issues associated witheutrophication in the nation’s estuaries. Nonetheless,information concerning algal blooms, low dissolvedoxygen, and other eutrophic symptoms was slow tocapture the attention of the public, administrators,and legislators. Recently, the consequences of thesesymptoms have become more apparent, helping toraise awareness of nutrient-related environmentalproblems. For instance, extensive losses of sub-merged aquatic vegetation and the associated lossof fish habitat have occurred, many coastal waterbodies have suffered worsening episodes of low dis-

solved oxygen, and blooms of nuisance and toxicalgae have been occurring in new areas. For example,Pfiesteria was first identified as a major fish-killingagent in the Neuse and Pamlico River estuaries ofNorth Carolina in 1992; in 1997, outbreaks occurredin tributaries of the Chesapeake Bay, where they hadpreviously not been observed.

Given the rising concern of the scientific commu-nity and the public at large, NOAA began to inves-tigate and evaluate the need for a more deliberatenational response to the problem of estuarineeutrophication. In order to determine the nationalextent of this problem and to provide a basis for anappropriate and effective national response, it wasnecessary to survey the overall symptoms ofeutrophication within the nation’s estuaries. Histori-cal information and ongoing field programs offeredthe raw materials, but the task remained to constructa comprehensive and consistent characterization ofthe symptoms of eutrophication. In addition, it wasessential to present the results of the survey withinthe context of everyday use impairments (e.g., swim-ming, fish consumption) that are important to theAmerican public. In fact, the population of U.S.coastal and upstream areas is projected to increaseby more than 13 percent by 2010, suggesting thatnutrient-related problems are likely to get worse.This underscores the need to stimulate additionalpublic involvement by presenting and publicizingthe best available information to concerned citizens,resource managers, and policy makers alike.

Figure 1. Data characteristics of NOAA’s Estuarine Eutrophication Survey

*See Appendix A for detailed descriptions of the symptoms.

DATA SHEETS COMPILED FOR 138 ESTUARIES REGIONAL DATA SUMMARIES COMPILED

Between 120 - 1,200 Data Values per Estuary

Chlorophyll a

Turbidity

Suspended Solids Problems

Nuisance Algae Problems

Toxic Algae Problems

Macroalgae Problems

Epiphyte Problems

Total Dissolved Nitrogen

Total Dissolved Phosphorus

Anoxia

Hypoxia

Biological Stress

Primary Productivity Dominance

Pelagic Community Dominance

Benthic Community Dominance

Submerged Aquatic Vegetation (SAV)

Eutrophication Symptoms*

Existing Conditions

Concentrations

Presence/Absence of Conditions

Spatial Coverage

Months of Occurrence

Frequency of Occurrence

Duration of event

Trends in Conditions (1970 - 1995)

Direction and Magnitude of Change

Frequency

Duration

Spatial coverage

Dominance Shifts

Contributing Factors to Change

Reliability of Information

Symptom Information Collected for Each Salinity Zone

North Atlantic

Middle Atlantic

South Atlantic

Gulf of Mexico

Pacific

Eutrophication

Survey Data

Summary

3

Introduction

The Nation’s First ComprehensiveEstuarine Eutrophication AssessmentSince its inception in 1992, NOAA’s National Estua-rine Eutrophication Survey has synthesized the bestavailable information on eutrophication-relatedsymptoms from more than 300 scientists and envi-ronmental managers. Recently published in five re-gional reports, the data characterize the spatial do-main, severity, duration, frequency and past trendsof 16 eutrophication related conditions in estuariesof the coterminous United States (NOAA 1996,1997a, 1997b, 1997c, 1998).

The 138 estuaries characterized in this study repre-sent more than 90 percent of both the total estuarinewater surface area and the total number of majorU.S. estuaries. Although not an estuary, the Missis-sippi River Plume is also included because of its im-

portance to the Gulf of Mexico and associated estu-aries to the west. Alaska, Hawaii and U.S. territo-ries were not included in this assessment due to lim-ited resources.

A common spatial framework (salinity zones repre-senting tidal fresh, mixing, and saltwater environ-ments) and predefined data categories were used toconsistently characterize the information on condi-

tions and trends for each estuary. In all, this surveyproduced an array of data containing more than40,000 data values (120 to 1,200 per estuary; Figure1). While providing the best possible information onthe problem, this array of data was also challengingto interpret.

The National Report: A Challenge toInterpret the DataNOAA worked with a “Core Group” of 15 scientistsand resource managers (see Acknowledgments) todevelop and apply methods that would best inte-grate the survey data for each estuary. It seemed rea-sonable that eutrophication symptoms and theirtime/space characteristics could be combined in away that provided a single value to represent thestatus of eutrophication symptoms in each estuary.Moreover, this index would allow comparisons,

ranking, and priority-setting amongestuaries, as well as facilitate sum-maries of national and regional re-sults. To accomplish this, two ob-stacles—data quality and a lack ofmethodology for combining numer-ous parameters into a single value—would have to be overcome.

Data Quality. An analysis of datacompleteness and the reliability ofsymptom data was performed forall estuaries so that confidence lev-els could be estimated for the data.For 17 estuaries, symptom datawere so limited that an assessmentof overall eutrophic conditionscould not be made. Most of thesewere on the Pacific Coast. For 31other systems, some of the symp-tom data provided by the expertswas rated as “speculative” becauseit was based on spatially or tempo-rally limited field observations. Theoverall confidence levels for theseestuaries was therefore assessed aslow. The evaluations for each symp-tom were carried through the as-sessment process to provide a basis

for assigning a confidence rating to the overall as-sessment of eutrophic conditions. This confidenceevaluation is important, because incomplete or un-certain data were sometimes included in the overallassessment because it was the best information avail-able.

Developing a Methodology to Aggregate Symptom Data.There was no method available for combining symp-

Experts interpret survey results at the National Assessment Workshop.

4

Introduction

tom data into a single assessment for each estuary;therefore, the Core Group had to address severalquestions while determining the best way to inte-grate the existing data:

Are all eutrophic symptoms and their character-istics equally important? Should all 16 symptomsbe considered in the national assessment? Do cer-tain symptoms logically group or occur in a linearsequence?

Do all eutrophic symptoms have the potential toexist in all estuaries?

Is the threshold for symptoms the same in all es-tuaries? For example, does a given concentrationof chlorophyll a represent “high” eutrophic symp-toms in all estuaries?

The Eutrophication Model. To help overcome theseobstacles and properly interpret the information, theCore Group participated in two work sessions to de-velop and test several analytical and numericalmethods. Ultimately, a single model was developedthat made maximum use of the survey data. Whilethis model does not account entirely for the com-plexity of this issue, it uses available information tobest describe the sequence and severity of eutrophicconditions (Figure 2). The model used six symptomsthat were most directly related to nutrient inputs.Three primary symptoms, algal abundance (usingchlorophyll a as an indicator), epiphyte abundance,and macroalgae, represent the first possible stage ofwater-quality degradation associated with eutrophi-cation. Although nitrogen and phosphorus concen-trations in the water column are related to nutrientinputs, they are also influenced by other biologicaland chemical processes. As a result, elevated con-centrations do not necessarily indicate that eutrophic

symptoms are present, nor dolow concentrations necessarilyindicate that eutrophication isnot present. As an example,chlorophyll a concentrationsmay be very high while dis-solved nutrient concentrationsare low. This scenario is com-mon during peak phytoplank-ton production because theseorganisms assimilate the nutri-ents very efficiently. Thus, nu-trient concentrations in the wa-ter column were not included asprimary symptoms in themodel.

In many estuaries, the primarysymptoms lead to secondarysymptoms, such as submergedaquatic vegetation loss, nui-sance and toxic algal blooms (al-though for toxic forms the link-age is not well established), andlow dissolved oxygen. In somecases, secondary symptoms canexist in the estuary withoutoriginating from the primarysymptoms. This occurs, for in-stance, in many North Atlanticestuaries where toxic algalblooms are transported from thecoastal ocean. In other places,disease or suspended sedimentshave contributed to declines insubmerged aquatic vegetation.

Nitrogen and Phosphorus

Extreme Chl-a Concentrations

Problematic Epiphytic Growth

SAV Spatial Coverage

Diatoms to Flagellates

Benthic Dominance to Pelagic Dominance

AnoxiaHypoxiaBiological Stress

Nuisance Bloom Problems

Toxic Bloom Problems

Primary Symptoms

Secondary Symptoms

Extreme Chl-a Concentrations

Problematic MacroalgalGrowth

Problematic MacroalgalGrowth

Loss of Submerged Aquatic Vegetation

SAV Spatial Coverage Trends

Decreased Light Availability

Algal Dominance Changes Harmful Algae

Increased Organic MatterDecomposition

Low Dissolved Oxygen

External Nutrient Inputs

Figure 2. The simplified eutrophication model used for the National Assessment

•

•

•

5

Introduction

Determining Overall Eutrophic Conditions. A nu-merical scoring system was developed to integrateinformation from all six primary and secondarysymptoms to determine the overall status ofeutrophic symptoms in each estuary. This scoringsystem was implemented in three phases accordingto the methods described in Figure 3 (see AppendixA for a detailed description).

First, a single index value was computed from allprimary symptoms. The scoring system gave equalweight to all three symptoms and considered thespatial and temporal characteristics of each. Thescores for the three symptoms were then averaged,resulting in the highest values being assigned to es-tuaries having multiple primary symptoms that oc-cur with great frequency, over large spatial areas of

the estuary, and for extended periods of time. Like-wise, the lowest scores indicate estuaries that exhibitfew, if any, characteristics of the primary symptoms.

Next, a single index value was computed from allsecondary symptoms. The scoring system again gaveequal weight to all symptoms and their spatial andtemporal characteristics. The highest score of any ofthe three symptoms was then chosen as the overallsecondary value for the estuary. This weights the sec-ondary symptoms higher than the primary symp-toms, because the secondary symptoms take longerto develop, thereby indicating a more chronic prob-lem, and being more indicative of actual impacts tothe estuary.

Finally, the range of numeric scores assigned to pri-mary and secondary symptoms was dividedinto categories of high, moderate, and low. Pri-mary and secondary scores were then com-pared in a matrix so that overall categoriescould be assigned to the estuaries (Figure 3).Estuaries having high scores for both primaryand secondary conditions were considered tohave an overall “high” level of eutrophication.Likewise, estuaries with low primary and sec-ondary values were assigned an overall “low”level of eutrophication. The Core Group mem-bers, using the matrix as a guide, then assignedscores to the remaining estuaries based on theirinterpretations of each estuary’s combinedvalues.

Interpreting the Model Results. While themodel offered a potentially wide scale overwhich to define the severity of the problem,few of the 138 estuaries or the Mississippi RiverPlume actually fell at either extreme of this con-tinuum, where the numerical scoring systemsare more easily interpreted. Logically, estuar-ies with few primary symptoms and low nu-meric scores were considered to be relativelyunaffected by nutrient-related conditions whencompared to estuaries with both primary andsecondary symptoms and higher numericscores.

Most estuaries showed varying degrees of bothprimary and secondary symptoms, so that themeaning of these scores was more difficult todetermine. This was particularly true for twoconditions, for which these general guidelinesfor interpretation were offered:

High or moderate primary symptoms and low sec-ondary symptoms. These estuaries have rela-

Primary and Secondary Symptom Index values are ranked and split into categories as follows:

Category AssignedScore Range

2

1 Individual scores are determined for the primary symptoms and combined into a single primary symptom index. Individual scores are determined for the secondary symptoms and combined into a single secondary symptom index.

3Primary and Secondary Symptom Categories are cross compared in a matrix to determine the overall level of expression of eutrophic conditions.

OVERALL LEVEL OF EXPRESSION OF EUTROPHIC CONDITIONS

LOW

MODERATE

MODERATE LOW MODERATE HIGH

Moderate secondary symptoms indicate substantial eutrophic conditions, but low primary symptoms indicate other factors may be involved in causing the conditions.

Level of expression of eutrophic conditions is minimal.

High secondary symptoms indicate serious problems, but low primary symptoms indicate other factors may also be involved in causing the conditions.

Primary symptoms beginning to indicate possible problems but still very few secondary symptoms expressed.

Primary symptoms high but problems with more serious secondary symptoms still not being expressed.

Level of expression of eutrophic condtions is substantial.

Substantial levels of eutrophic conditions occurring with secondary symptoms indicating serious problems.

Primary symptoms high and substantial secondary symptoms becoming more expressed, indicating potentially serious problems.

High primary and secondary symptom levels indicate serious eutrophication problems.

MODERATE LOW HIGH

MODERATE MODERATE HIGH HIGH

Secondary Symptoms

Pri

mar

y S

ymp

tom

s

Low Moderate High0 0.3 0.6 1

Low

Mod

erat

eH

igh

0.3

0.6

1

In This Report:LOW and MODERATE LOW are grouped together as LOW.HIGH and MODERATE HIGH are grouped together as HIGH.

Low> < Moderate

10.6 High

Figure 3. Steps followed in determining the overall level of expression ofeutrophic conditions in estuaries

6

Introduction

tively well developed conditions associated with al-gal blooms, epiphytes, and/or macroalgae, whichsuggests that they are in the early stages of eutrophi-cation and may be on the edge of developing moreserious conditions. These systems may be suscep-tible to additional nutrient inputs and could beginto develop secondary symptoms of eutrophication.

High or moderate secondary symptoms and low primarysymptoms. For these estuaries, advanced secondarysymptoms exist, even though the “prerequisite” pri-mary symptoms (as suggested by the model) maynot be well developed. Three possible interpretationsare offered to describe these conditions. For someestuaries, the secondary conditions were transportedfrom offshore coastal areas, rather than originatingwithin the estuary. This occurs, for example, withtoxic bloom conditions in North Atlantic estuaries.Alternatively, it is possible that nutrient-related wa-ter quality conditions have recently improved, butthe response time to reduce secondary symptoms islonger than it is for primary symptoms. The second-ary symptoms that remain may be residual condi-tions that also may improve as nutrient concentra-tions continue to decrease. Finally, it is possible thatsecondary conditions in an estuary are related onlypartially, or not at all, to nutrient enrichment. Forexample, submerged aquatic vegetation losses in LongIsland Sound have been attributed to both disease andnutrient enrichment.

Through the use of a simple model, a frameworkwas established to help understand the sequence,processes, and symptoms associated with nutrientenrichment. Despite its limitations (e.g., the modeldoes not account for changes in assimilative capac-ity from losses of wetlands), the model representsthe first attempt to synthesize large volumes of dataand to derive a single value for eutrophication ineach estuary. With this foundation, the next stepsare to (1) expand understanding of the relationshipbetween eutrophication and nutrient sources, and(2) evaluate appropriate responses to the problem.

Extending the Assessment: Toward aNational StrategyThis National Assessment focuses on the data inNOAA’s Estuarine Eutrophication Survey, the fun-damental goal of which was to describe the scale,scope, and severity of nutrient enrichment condi-tions nationwide, and to compare the various ex-pressions of eutrophic symptoms in individual es-tuaries. In a sense, the model represents a form ofenvironmental triage—separating estuaries that arein serious condition, but could potentially improve,from those that presently do not experience many

symptoms, but are seemingly at risk. In turn, thisrepresents a starting point for understanding whythese conditions exist, how and why conditions dif-fer across estuaries, whether certain problematic con-ditions may respond to remedial actions, and whichof these actions would best protect estuaries fromfurther degradation.

To do so means to go beyond the survey data. At thevery least, more information is needed about themagnitude and sources of nutrient inputs, the natu-ral ability of estuaries to flush or assimilate incom-ing nutrients, and the relative influence of both ofthese factors on the expression of eutrophication.Moreover, these results need to be associated withuse impairment and public health issues that bringthe message to the public and help to set prioritiesfor management and research activities. With theguidance of the Core Group, the National Assess-ment was expanded to include additional data setsthat begin to examine these linkages.

Expanding the Model. To accommodate the addi-tional analyses, the original eutrophication modelwas expanded (Figure 4) so that eutrophic symp-toms could be compared with other national datasets, specifically estuarine transport (i.e., flushing,also referred to as susceptibility), nutrient inputs andsources, and eutrophication-related estuarine useimpairments. The data for these assessments werederived from a variety of sources, described below.These assessments were intended to allow generalobservations about the linkages between symptoms,nutrient loading and susceptibility, and betweeneutrophic conditions and use impairments. Recom-mendations for potential responses to the problemwere developed from conclusions based on theseobservations.

Susceptibility. Estimates were made of the naturaltendency of an estuary to retain or export nutrients.The rate at which water moves through the estuarywas determined by examining tidal action and thevolume of freshwater flowing in from rivers. In gen-eral, if the water (and nutrients) are flushed quickly,there is not sufficient time for problems to developand the estuary is not particularly susceptible. If theestuary acts more like a bathtub, with nutrient-richwater sitting in the system for a long time, then thereis time for nutrients to be taken up by algae. Theseestuaries are more susceptible to developingeutrophic symptoms.

Although only dilution and flushing were includedin this susceptibility estimate, biological processesmay also affect susceptibility. For instance, filter feed-ers raise an estuary’s capacity to assimilate more

7

Introduction

nutrients before showing symptoms. Wetlands,which retain nutrients that might otherwise enterestuarine waters, also improve an estuary’s abilityto fend off eutrophic symptoms.

Nutrient Inputs. The level of nutrients entering es-tuaries is a critical factor in determining the level towhich they will develop symptoms. Excess nutrientinputs are mainly human-related and are due to highcoastal population density, various agricultural prac-tices (e.g., fertilizer applications, animal feedlot op-erations), the burning of fossil fuels, and sewagetreatment effluents.

Estuarine Use Impairments. Impaired resources (interms of human use) were evaluated to gain a basicunderstanding of the level of negative impacts oc-curring in the nation’s estuaries. These include im-pacts to recreational activities, such as swimmingand boating, as well as to commercial operations,such as fishing and shellfishing.

Potential Management Concerns. Evaluations werealso made of the most important sources to target inorder to manage nutrient inputs into estuaries.

Data Sets and Data Quality. NOAA had access tonational data sets that were used for characteriza-tions; however, the assessments were largely basedon the knowledge and experience of the Core Groupand other Workshop participants.

For nutrient-loading estimates, NOAA providedcomparative data for 1987 (adapted from the U.S.Geological Survey’s SPARROW model; Smith et al.,1997) for five major sources: fertilizer, livestockwastes, point sources, atmospheric deposition, andnonagricultural sources. In addition, NOAA pro-vided information on coastal population and landusage, which were used as comparative estimatorsof loading. Estuarine susceptibility estimates werebased on an estuary’s dilution potential and flush-ing potential, which are calculated from freshwater

Nitrogen and Phosphorus

USGS SPARROW MODEL, NOAA CA&DS DATA, CORE GROUP EUTROPHICATION SURVEY DATA CORE GROUP

Potential Effects and Use Impairments

Decreased Light Availability

Loss of Submerged Aquatic

Vegetation

Algal Dominance Changes

Nuisance/Toxic Algal Blooms

Increased Organic Matter

Production

Low Dissolved Oxygen

Secondary Symptoms

Primary Symptoms

External Nutrient Inputs and Susceptibility

Loss of Habitat

Commercial Fishing Recreational FishingTourism

Offensive Odors

Aesthetic ValuesTourism

Fish Kills

Commercial Fishing Recreational FishingAesthetic ValuesTourism

Commercial Fishing Recreational FishingHuman Health ProblemsSwimmingTourism

Increase of Algal Toxins

Loss of Habitat

Commercial Fishing Recreational FishingTourism

Influence of Physical and

Biological Processes

(i.e. freshwater inflow, flushing,

wetlands uptake, filter feeders)

Figure 4. The expanded eutrophication model

8

Introduction

inflow, tidal prism, and estuary geometry (NOAA’sCoastal Assessment & Data Synthesis System, 1998).These data sets were synthesized and interpreted lessrigorously than the symptom data, and thus, weremore speculative than the data for eutrophic symp-toms.

The assessment of estuarine-use impairments andmanagement targets was not based on hard data;rather, it was derived from the expert knowledge ofparticipants at the National Assessment Workshop.Despite the speculative nature of these assessments,the information was still very useful, providing in-sight into the consequences of eutrophic symptomsin estuaries, and into the most effective managementactions for reducing them.

See Appendix A for details on the methods and in-formation sources used in the assessment.

Organizing the Results: Seven KeyQuestionsSeven questions, which follow the logic sequence ofthe expanded eutrophication model, were developedto help organize results for the National Assessment.Question 1 examines the results of the model. Ques-tions 2 through 4 examine linkages between thesesymptoms, pollution sources, and coastal use im-pairments. Questions 5 through 7 identify prioritymanagement, monitoring, and research needs.

1. What are the severity and extent of eutrophic con-ditions exhibited within the estuaries of the UnitedStates?This analysis is based on the eutrophication data setand its interpretation using the eutrophicationmodel.

2. To what extent are eutrophic conditions in U.S.estuaries caused by human activities?The U.S. Geological Survey SPARROW model pro-vided first-order estimates of nutrient loads for 1987from five major sources. Population estimates andAgricultural Census data also were used to repre-sent the potential for nutrient sources. In addition,an indicator of estuarine flushing potential was de-veloped based on freshwater inflow, tide, and es-tuarine geometry.

3. To what extent do eutrophic conditions impairthe use of estuarine resources, and what are the im-portant impaired uses?Core Group members selected from a list of sevenuse impairments for each estuary. This list includedrecreational and commercial fishing, fish consump-tion, shellfishing, swimming, boating, aesthetics, andtourism.

4. Where should management efforts be targeted toachieve the greatest benefit toward remediation andprotection from future degradation, and what arethe most important sources to target?Core Group members selected from a list of 10 pointand nonpoint nutrient source targets.

5. To what extent can the severity and extent ofeutrophic conditions be expected to increase by theyear 2020, given the natural susceptibility of estu-aries and the potential for increasing nutrient in-puts?Projected population growth estimates were usedto represent the potential for future nutrient inputsand thus, changes in eutrophic conditions. Suscep-tibility was used to determine the expected severityof change.

6. Which data gaps and research and monitoringneeds are most critical in terms of improving theability to assess and respond to eutrophic condi-tions?Core Group members listed these, based on their ex-perience and the findings of Questions 1 through 5above.

7. How can the results of this assessment be trans-lated into a national strategy?Recommendations were developed from discussionsbetween members of the Core Group.

Using this Report and the DataThis report contains five sections that are organizedaccording to the seven questions listed above. Thereport emphasizes the results from the eutrophicsymptoms model (i.e., Question 1) as they representthe culmination of the multi-year survey work andprovide an unprecedented classification for thenation’s estuaries. The results of the expanded as-sessment model (i.e., Questions 2 through 7) are alsoprovided, but at a more general level consistent withthe less rigorous methods of data collection. Themost direct responses to the seven questions are pro-vided in the Executive Summary, while the NationalOverview and Regional Summaries sections aresupplemented by mapped and tabular displays ofthe synthesized results. The Conclusions and Rec-ommendations sections propose next steps, as sug-gested by the Core Group and other Workshop par-ticipants. The data and methods used in this Na-tional Assessment are described in the Appendices.The digital data can be accessed on-line at:http://cads.nos.noaa.gov

9

National Overview

The expression of overall eutrophic con-ditions is high in 44 U.S. estuaries. Theseestuaries are located mainly in the Gulfof Mexico and Middle Atlantic regions;however, certain estuaries along allcoastlines exhibit high levels ofeutrophic conditions.

This assessment characterizes the overall eutrophic conditions and the water-quality problems associated with nutrientenrichment for 138 U.S. estuaries. A Core Group of eutrophication experts collaborated with NOAA and was instrumentalin developing methods to assess the results of the National Eutrophication Survey. At a National Assessment Workshop,the Core Group and additional experts reviewed and interpreted the Survey results, and analyzed the factors that influencethe development of problematic conditions. They also reported on impairments in estuarine uses, potential managementconcerns, and the future outlook to the year 2020. Note that the Mississippi River Plume was also characterized, and iscounted as an additional “estuary” in the figures, but is not included in surface area statistics.

Eutrophic ConditionsThe assessment of overall eutrophic conditions isbased on the combined level of expression of sixsymptoms: chlorophyll a, epiphyte abundance,macroalgal abundance, depleted dissolved oxygen,submerged aquatic vegetation loss, and nuisance/toxic algal blooms. The level of expression of each isdetermined by the concentration, spatial coverage,frequency of occurrence, and/or other factors (referto Figure 3, page 5).

For each symptom assessment, an evaluation of thelevel of confidence was made based on the tempo-ral and spatial representativeness of the data. Theconfidence evaluation is important, because in somecases the data were incomplete or uncertain, but stillprovided the best information available and the onlymeans of presenting a national picture. These symp-tom confidence ratings provided the basis for evalu-ating the confidence of overall eutrophic conditions.

The data for 17 estuaries were too sparse to providean overall view of eutrophic conditions althoughlimited data existed for certain symptoms in someof these estuaries (see page 18 for list). For an addi-tional 38 estuaries, the overall assessment confidencewas rated as low (see Appendix B).

Figure 5. Level of expression of eutrophic conditions Figure 6 . Eutrophic conditions by region

Overall Conditions. National Assessment Work-shop participants concluded that the expression ofoverall eutrophic conditions was high in 44 estuar-ies, representing 40% of the total estuarine surfacearea studied (Figure 5). These estuaries were locatedmainly in the Gulf of Mexico and Middle Atlanticregions; however, some estuaries along all coastlinesexhibited high levels of eutrophic conditions (Fig-ures 6 and 7). This means that in these estuaries, oneor more symptoms occurred at problem levels ev-ery year, or persistently, across a major part of eachestuary. An additional 40 estuaries exhibited mod-erate eutrophic conditions. When considered to-gether, the estuaries with moderate to high condi-tions represent 65% of the estuarine surface areastudied. The remaining 38 estuaries exhibited low

Moderate Moderate Low

5

10

15

20

25

30

35

High Moderate High Low

5

10

15

20

25

30

35

North Atlantic

Middle Atlantic

South Atlantic

Gulf of Mexico

Pacific

Num

ber

of E

stua

ries

Num

ber

of E

stua

ries

Eutrophic Condition

HighModerate High

Moderate

Moderate LowLow

Grouped as High in this Report Grouped as Low in this Report

0 High

0 Low

Low Confidence

Moderate to High Confidence

Moderate High to High Expression Moderate Expression

Moderate Low to Low Expression

Low Confidence

Moderate to High Confidence

Low Confidence

Moderate to High Confidence

Eutrophic Condition and Assessment Confidence

Grouped as High in this Report

Grouped as Low in this Report

National Overview

10

National Overview

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erce

ntag

es o

f est

uari

es w

ith

high

eut

roph

ic c

ondi

tion

s. T

he P

acifi

c an

d So

uth

Atl

anti

c re

gion

sco

ntai

n th

e hig

hest

per

cent

age o

f est

uari

es th

at la

ck su

ffici

ent i

nfor

mat

ion

to c

onfid

entl

y as

sess

eutr

ophi

c co

ndit

ions

. A

n ad

diti

onal

fort

y es

tuar

ies (

not

show

n) h

ave

mod

erat

e le

vels

of e

utro

phic

con

diti

ons.

Note: Conditions are not necessarily related in whole to human-related eutrophication; to various degrees natural causes and other human disturbancesmay also play a role. For instance, some estuaries in Maine are typified by natural occurrences of toxic algae, which drift in from the open ocean. Once in theestuary, however, these blooms may be sustained by human nutrient inputs.

Figure 7. Estuaries with high levels of expression of eutrophic conditions

Est

uarie

s in

thi

s ca

tego

ry e

xhib

it va

ryin

g co

mbi

natio

ns o

f eu

trop

hic

sym

p-to

ms,

incl

udin

g hi

gh e

xpre

ssio

ns o

f ch

loro

phyl

l a,

mac

roal

gal a

bund

ance

prob

lem

s, e

piph

yte

abun

danc

e pr

oble

ms,

low

dis

solv

ed o

xyge

n, n

uisa

nce

and

toxi

c al

gal

bloo

ms,

and

los

s of

sub

mer

ged

aqua

tic v

eget

atio

n. T

ypi-

cally

, thi

s m

eans

that

one

or

mor

e of

thes

e sy

mpt

oms

occu

r ov

er la

rge

ar-

eas

of th

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tuar

y, a

nnua

lly o

r pe

rsis

tent

ly, a

nd/o

r fo

r lo

ng d

urat

ions

.

11

National Overview

Chlorophyll a is a measure used to indicate the amount ofmicroscopic algae, called phytoplankton, growing in a wa-ter body. High concentrations are indicative of problemsrelated to the overproduction of algae.

Epiphytes are algae that grow on the surfaces of plants orother objects. They can cause losses of submerged aquaticvegetation by encrusting leaf surfaces and thereby reduc-ing the light available to the plant leaves.

Macroalgae are large algae, commonly referred to as “sea-weed.” Blooms can cause losses of submerged aquatic veg-etation by blocking sunlight. Additionally, blooms may alsosmother immobile shellfish, corals, or other habitat. Theunsightly nature of some blooms may impact tourism dueto the declining value of swimming, fishing, and boatingopportunities.

Low dissolved oxygen occurs as a result of large algalblooms that sink to the bottom and use oxygen during theprocess of decay. Low dissolved oxygen can cause fish kills,habitat loss, and degraded aesthetic values, resulting in theloss of tourism and recreational water use.

Losses of submerged aquatic vegetation (SAV) occur whenlight is decreased due to turbid water associated with over-growth of algae or as a result of epiphyte growth on leaves.The loss of SAV can have negative effects on the ecologicalfunctioning of an estuary and may impact some fisheriesbecause the SAV beds serve as important habitat.

Nuisance and toxic algal blooms are thought to be causedby a change in the natural mixture of nutrients that occurswhen nutrient inputs increase over a long period of time.These blooms may release toxins that kill fish and shellfish.Human-health problems may also occur due to the consump-tion of seafood that has accumulated algal toxins or from theinhalation of airborne toxins. Many toxic algal blooms occurnaturally; however, the role of nutrient enrichment is unclear.

Common Symptoms of Eutrophication

Figure 8. Level of expression of symptoms within each overall category of eutrophic condition

levels of eutrophic conditions, meaning that symp-toms were not observed at problem levels or thatproblem conditions occurred infrequently or onlyunder specific and unusual circumstances. Abouthalf of these estuaries were located in the South At-lantic and Pacific regions.

In more than 80 percent of estuaries with high andmoderate levels of eutrophic conditions, the assess-ment confidence was high; conversely, confidencewas high in fewer than half of the systems assessedas having low eutrophic conditions. Most of the es-tuaries with low confidence are located in the Pa-cific and South Atlantic regions.

Symptoms: Common Signs of Eutrophication. Theimmediate response to nutrient inputs is the over-growth of algae. The primary symptoms of increasednutrient concentrations in the water column are highlevels of chlorophyll a, epiphytes, and/ormacroalgae (see sidebar, right). It is thought that onceprimary symptoms are observed at high levels, anestuary is in the first stages of displaying undesir-able eutrophic conditions.

High expressions of chlorophyll a occurred in 39 es-tuaries, high expressions of macroalgal abundanceoccurred in 24 estuaries, and high expressions of epi-phyte abundance occurred in 11 estuaries (see Fig-ure 8 for an accounting of symptom expression bro-ken down by eutrophic condition category). Over-all, at least one of these primary symptoms was ex-pressed at high levels in 58 estuaries. In some cases,high levels may be natural, but this observation in-dicates that 40 percent of the nation’s estuaries maybe in the first stages of developing problems associ-ated with eutrophication. On a regional basis, epi-

10 20 30 40

Chlorophyll a

Epiphyte Abundance

Macroalgal Abundance

Low Dissolved Oxygen

Submerged Aquatic

Vegetation Loss

Nuisance/Toxic Algae

10 20 30 40 10 20 30 40

Prim

ary

Sym

ptom

sS

econ

dary

Sym

ptom

s

High Moderate Low

High Eutrophic Conditions(44 Estuaries)

Moderate Eutrophic Conditions(40 Estuaries)

Low Eutrophic Conditions(38 Estuaries)

50Number of Estuaries Number of Estuaries Number of Estuaries

Symptom Expression

12

National Overview

phyte problems occurred mainly in Gulf of Mexicoestuaries, while higher levels of chlorophyll a andmacroalgae were observed in estuaries of all regions(Figure 9).

While high levels of primary symptoms are strongindicators of the onset of eutrophication, the second-

Figure 9. Expression of eutrophic symptomsThese maps depict estuaries with moderate to high levels of expression of eutrophic symptoms, indicating areas of possibleconcern. Note that these symptoms are not necessarily related in whole to human-related nutrient inputs; natural causes andother human disturbances may also play a role, to various degrees, in the expression of symptoms.

ary symptoms, which include low dissolved oxygen,the loss of submerged aquatic vegetation, and theoccurrence of nuisance and toxic blooms, indicatemore serious problems, even at moderate levels.Note that while there is a direct causative link be-tween nutrients and primary symptoms, there aremany other factors, both natural and human related,

A

A A

A A

A

Primary Symptoms Secondary Symptoms

Chlorophyll a Low Dissolved Oxygen

MacroalgalAbundanceProblems

EpiphyteAbundanceProblems

Nuisance and/orToxic Algal Bloom

Problems

Submerged AquaticVegetation Loss

13

National Overview

More than half of U.S. estuaries havemoderate to high expressions of at leastone of the secondary symptoms. Thisfinding is important because these symp-toms can have serious consequences, in-cluding negative impacts on commercialfish yields, degraded recreational oppor-tunities, increased risks to human health,and adverse affects on tourism.

that may contribute to the occurrence of secondarysymptoms.

Depleted dissolved oxygen was expressed at mod-erate or high levels in 42 estuaries. Twenty-seven es-tuaries had moderate or high levels of submergedaquatic vegetation loss, and 51 estuaries exhibitedmoderate or high nuisance/toxic algal blooms (Fig-ures 8 and 9). Overall, moderate or high levels of atleast one secondary symptom was observed in 82estuaries, representing 67% of the nation’s estuarinesurface area—an indication that eutrophication iswell developed and is potentially causing seriousproblems in more than half of U.S. estuaries. Thesecondary symptoms were restricted regionally, withthe exception of nuisance and toxic blooms, whichwere observed in systems along all coasts. Losses ofsubmerged aquatic vegetation were mostly limitedto the Gulf of Mexico and Middle Atlantic regions,

This crab could not survive in the anoxic zone near the mouthof the Mississippi River. Photo courtesy of Nancy Rabalais,courtesy of the National Undersea Research Program.

and low dissolved oxygen was observed mainly inthe Gulf of Mexico, Middle Atlantic, and South At-lantic regions. These geographical differences maybe useful for developing regionally specific indica-tors that are more sensitive than the nationally ap-plied model used here.

Completing the PictureThese results provide a picture of the overalleutrophic conditions in the nation’s estuaries andthe specific symptoms that occur. Nevertheless,questions remain, such as: What factors influencethe development of these symptoms? What types ofuse impairments do these symptoms cause? Whatare the management implications? At the NationalAssessment Workshop, the Core Group used dataand information about estuarine susceptibility andhuman-related nutrient inputs, which, together, pro-vided the basis for evaluating the overall human in-fluence on these conditions. Participants reliedheavily on their experience and prior knowledge toevaluate estuarine-use impairments and potentialmanagement targets. The data for these ancillary as-sessments were not as robust, and were less rigor-ously reviewed, than the Eutrophication Surveydata, and some findings were inconclusive. This in-formation was included, however, because it helpedto complete the national picture.

Influencing Factors. In an effort to determine thelevel of human influence on the development ofeutrophication, workshop participants consideredthe overall eutrophic condition with respect to nu-trient inputs and estuarine susceptibility to retainnutrients. Figure 10 (next page) shows the input dataseparately from the susceptibility data, as well asthe aggregated results, which represent the overalllevel of human influence. Although both phospho-rus and nitrogen cause nutrient enrichment prob-lems in estuaries, at the time of the AssessmentWorkshop, national-level information was availableonly for nitrogen inputs. For this reason, nitrogenvalues were used as the primary estimates of nutri-ent inputs, and information on population densityand land use was used as a general indicator of nu-trient pressure to help account for phosphorus andcorroborate nitrogen estimates. The nitrogen inputestimates were based on watershed monitoring datafrom the U.S. Geological Survey, as produced by theSPARROW model (Smith et al., 1997).

While these data were variable and did not showdistinct groupings, some generalizations could bemade. Many estuaries assessed as having high lev-els of overall eutrophic conditions also had high sus-ceptibility and moderate to high levels of nutrient

14

National Overview

inputs. These estuaries are very sensitive to nutri-ent inputs, and as a result, many were assessed ashaving a high level of human-related influence onthe development of eutrophic conditions. The con-verse also seems to hold true; that is, most estuarieswith low susceptibility and low inputs of nutrientshad a low overall level of eutrophic conditions. Theseestuaries are less sensitive to development ofeutrophic conditions even with human related nu-trient inputs.

The assessment results highlight these generaliza-tions; of the 44 estuaries with high levels of eutrophicconditions, workshop participants assessed 36 ashaving a high level of human influence on the de-velopment of conditions. It is important to note thata common feature of these estuaries was high or

moderate susceptibility. It is also noteworthy thatmost of the 44 estuaries have moderate, not high (asin only six of the estuaries), levels of nutrient inputs.In estuaries with high or moderate susceptibility,even a moderate level of nutrient input may be suf-ficient to cause serious eutrophic symptoms. In thesesystems, natural estuarine characteristics, such aslow tidal exchange, enhance the expression of symp-toms. Most of these estuaries were located in theGulf, Middle Atlantic, and Pacific regions.

In contrast, 38 estuaries exhibited low overalleutrophic conditions. The common traits of theseestuaries were lower susceptibility and lower nitro-gen inputs; 31 of these estuaries had moderate orlow nitrogen inputs, and 28 had moderate or lowsusceptibility. In these systems, natural characteris-

Figure 10. Influencing factors on the expression of eutrophic conditions

Estuarine Susceptibility

The estuarine susceptibility estimates are based on estuarineflushing and dilution capacity - freshwater inflow, tidal flush-ing, and degree of stratification. These characteristics influ-ence the transport and fate of nutrients in coastal water bod-ies, and help to determine the susceptibility of an estuary toretain nutrients. These data were derived from national datasets contained in NOAA’s Coastal Assessment and Data Syn-thesis system.

Overall Human Influence

An estimation of the overall level of human influence on theexpression of eutrophic conditions was determined for eachestuary by combining estuarine susceptibility estimates withindicators of nutrient pressure. Although nitrogen input wasused as the primary indicator of nutrient pressure, workshopparticipants made appropriate modifications to the overallnutrient pressure assessment, based on analysis of popula-tion density and land use data as general nutrient pressureindicators.

Nitrogen Inputs

Nitrogen yield estimates, adapted from USGS’s SPARROWmodel, characterize the level of nitrogen inputs to estuariesfor five major nutrient source types: point sources, fertilizer,livestock, atmospheric deposition, and nonpoint/nonagricul-tural. These data provide a rough snapshot estimation of ni-trogen input conditions for 1987.

At the National Assessment Workshop, an attempt was made to characterize the natural conditions and human activities that influence theexpression of eutrophic conditions in the nation’s estuaries. The purpose was to develop an understanding of why eutrophic conditions differamong estuaries and to provide a basis for guiding management responses to problems. These figures indicate that the response to a givenlevel of nutrient is highly variable and is primarily due to differences among estuarine susceptibility to nutrients. Some estuaries are sosusceptible that only small amounts of additional nutrients will cause problems, while others can seemingly take in large quantities and stilldisplay few eutrophic symptoms (but may pass the nutrients on to other receiving bodies downstream).

9 85

19 19

13

1013

25

Susc

eptib

ility

Eutrophic Condition

Low Moderate High

High

Moderate

Low

Num

ber

of E

stua

ries

16

1213

15

22 22

4 36

Eutrophic Condition

Nitro

gen

Inpu

t

Low Moderate High

High

Moderate

LowNum

ber

of E

stua

ries

21(14)

10(2)

6(0)

7(4)

19(10)

2 (1)8(4)

11(2)

36(5)

Low Moderate High

Eutrophic ConditionOv

erall

Hum

an In

fluen

ce

High

Moderate

Low

Num

ber

of E

stua

ries

(paren

these

s ind

icate

fracti

on

of tot

al wi

th low

confi

denc

e)

15

National Overview

Most estuaries with high eutrophicconditions also have high levels of hu-man influence due to a combination ofmoderate to high nutrient inputs andnatural susceptibility.

tics appeared to suppress the expression of symp-toms. It should be noted, however, that 10 of the es-tuaries with low eutrophic conditions exhibited highsusceptibility.

It is important to note that although these generali-zations can be made, the relationships between nu-trient inputs and the expression of symptoms, orbetween susceptibility and the expression of symp-toms (Figure 10), are not entirely predictable. For in-stance, not all of the 44 estuaries with high eutrophicconditions had high nutrient inputs and high sus-ceptibility, though most did follow this general rule.There were exceptions, including six estuaries as-sessed with high levels of eutrophic conditions andlow human influence. Five of these are located inthe North Atlantic regi