EPA 822-B-00-023

 

 AMBIENT WATER QUALITY CRITERIA RECOMMENDATIONS

INFORMATION SUPPORTING THE DEVELOPMENT OF STATE AND TRIBAL

NUTRIENT CRITERIA

FOR

WETLANDS IN NUTRIENT ECOREGION XIII

Southern Florida Coastal Plain

including all or parts of the State of:

Florida

and the authorized Tribes within the Ecoregion

U.S. ENVIRONMENTAL PROTECTION AGENCY

OFFICE OF WATER

OFFICE OF SCIENCE AND TECHNOLOGY

HEALTH AND ECOLOGICAL CRITERIA DIVISION

WASHINGTON, D.C.

DECEMBER 2000
ii

FOREWORD

This document presents EPA’s nutrient criteria for Wetlands in Nutrient Ecoregion

XIII. These criteria provide EPA’s recommendations to States and authorized Tribes for use in

establishing their water quality standards consistent with section 303(c) of CWA. Under section

303(c) of the CWA, States and authorized Tribes have the primary responsibility for adopting

water quality standards as State or Tribal law or regulation. The standards must contain

scientifically defensible water quality criteria that are protective of designated uses. EPA’s

recommended section 304(a) criteria are not laws or regulations – they are guidance that States

and Tribes may use as a starting point for the criteria for their water quality standards. 

The term “water quality criteria” is used in two sections of the Clean Water Act, Section

304(a)(1) and Section 303(c)(2). The term has a different impact in each section. In Section 304,

the term represents a scientific assessment of ecological and human health effects that EPA

recommends to States and authorized Tribes for establishing water quality standards that

ultimately provide a basis for controlling discharges or releases of pollutants or related

parameters. Ambient water quality criteria associated with specific waterbody uses when

adopted as State or Tribal water quality standards under Section 303 define the level of a

pollutant (or, in the case of nutrients, a condition) necessary to protect designated uses in ambient

waters. Quantified water quality criteria contained within State or Tribal water quality standards

are essential to a water quality-based approach to pollution control. Whether expressed as

numeric criteria or quantified translations of narrative criteria within State or Tribal water quality

standards, quantified criteria serve as a critical basis for assessing attainment of designated uses

and measuring progress toward meeting the water quality goals of the Clean Water Act.

EPA is developing section 304(a) water quality criteria for nutrients because States and

Tribes consistently identify excessive levels of nutrients are a major reason why as much as half of

the surface waters surveyed in this country do not meet water quality objectives, such as full

support of aquatic life. EPA expects to develop nutrient criteria that cover four major types of

waterbodies – lakes and reservoirs, rivers and streams, estuarine and coastal areas, and wetlands –

across fourteen major ecoregions of the United States. EPA’s section 304(a) criteria are

intended to provide for the protection and propagation of aquatic life and recreation. To support

the development of nutrient criteria, EPA is publishing Technical Guidance Manuals that describe

a process for assessing nutrient conditions in the four waterbody types. 

EPA’s section 304(a) water quality criteria for nutrients provide numeric water quality

criteria, as well as procedures by which to translate narrative criteria within State or Tribal water

quality standards. In the case of nutrients, EPA section 304(a) criteria establish values for causal

variables (e.g., total nitrogen and total phosphorus) and response variables (e.g., turbidity and

chlorophyll a). EPA believes that State and Tribal water quality standards need to include

quantified endpoints for causal and response variables to provide sufficient protection of uses and

to maintain downstream uses. These quantified endpoints will most often be expressed as

numeric water quality criteria or as procedures to translate a State or Tribal narrative criterion

into a quantified endpoint.

EPA will work with States and authorized Tribes as they adopt water quality

criteria for nutrients into their water quality standards. EPA recognizes that States and authorized

Tribes require flexibility in adopting numeric nutrient criteria into State and Tribal water quality

standards. States and authorized Tribes have several options available to them. EPA

recommends the following approaches, in order of preference:
iii

(1) Wherever possible, develop nutrient criteria that fully reflect localized conditions and

protect specific designated uses using the process described in EPA’s Technical Guidance

Manuals for nutrient criteria development. Such criteria may be expressed either as

numeric criteria or as procedures to translate a State or Tribal narrative criterion into a

quantified endpoint in State or Tribal water quality standards.

(2) Adopt EPA’s section 304(a) water quality criteria for nutrients, either as numeric

criteria or as procedures to translate a State or Tribal narrative nutrient criterion into a

quantified endpoint.

(3) Develop nutrient criteria protective of designated uses using other scientifically

defensible methods and appropriate water quality data.

 

Geoffrey H. Grubbs, Director

Office of Science and Technology
iv

DISCLAIMER

This document provides technical guidance and recommendations to States, authorized

Tribes, and other authorized jurisdictions to develop water quality criteria and water quality

standards under the Clean Water Act (CWA) to protect against the adverse effects of nutrient

overenrichment. Under the CWA, States and authorized Tribes are to establish water quality

criteria to protect designated uses. State and Tribal decision-makers retain the discretion to adopt

approaches on a case-by-case basis that differ from this guidance when appropriate and

scientifically defensible. While this document contains EPA’s scientific recommendations

regarding ambient concentrations of nutrients that protect aquatic resource quality, it does not

substitute for the CWA or EPA regulations; nor is it a regulation itself. Thus it cannot impose

legally binding requirements on EPA, States, authorized Tribes, or the regulated community, and

it might not apply to a particular situation or circumstance. EPA may change this guidance in the

future.
v

EXECUTIVE SUMMARY

Nutrient Program Goals

EPA developed the National Strategy for the Development of Regional Nutrient Criteria

(National Strategy) in June 1998. The strategy presents EPA=s intentions to develop technical

guidance manuals for four types of waters (lakes and reservoirs, rivers and streams, estuaries and

coastal waters, and wetlands) and produce section 304(a) criteria for specific nutrient ecoregions

by the end of 2000. In addition, the Agency formed Regional Technical Assistance Groups

(RTAGs) which include State and Tribal representatives working to develop more refined and

more localized nutrient criteria based on approaches described in the waterbody guidance

manuals. This document presents EPA=s current recommended criteria for total phosphorus for

wetlands in Nutrient Ecoregion XIII - Southern Florida Coastal Plain which were derived using

peer-reviewed publications of research conducted in the Everglades and the findings and

information associated with the EPA approval of the Miccosukee Tribe of Indians of Florida

standard for phosphorus for the Federal Reservation within the Everglades.

EPA’s ecoregional nutrient criteria are intended to address cultural eutrophication – the

adverse effects of excess inputs of nutrients. The criteria are empirically derived to represent

conditions of surface waters that are minimally impacted by human activities and are protective of

aquatic life and recreational uses. The information contained in this document represent starting

points for States and Tribes to develop (with assistance from EPA) more refined nutrient criteria.

In developing these criteria recommendations, EPA followed a process which included, to

the extent they were readily available, the following elements critical to criterion derivation: 

! Historical and recent nutrient data in Nutrient Ecoregion XIII.

Historical and recent data used in the development of the nutrient criteria for this

ecoregion include information from more than 300 scientific publications and reports were

reviewed and summarized; the Everglades Interim Report (1999) published by the South

Florida Water Management District; Phosphorus Biogeochemistry in Subtropical

Ecosystems (1999) a compilation of papers from a symposium, and a comparison of soil

phosphorus concentrations in 1990 and 1998 by DeBusk et al. (1994) and DeBusk et al.

(in press). 

! Reference sites/reference conditions in Nutrient Ecoregion XIII. 

Reference conditions presented in this document were summarized from peer-reviewed

literature and the primary source documents listed above. The water column phosphorus

number for reference condition and criteria recommendations is based on long-term (at

least three months) average values. Hydrologic variability can result in variable

concentrations of water column total phosphorus, therefore, a long-term or rolling

average, or geometric mean (as required by the Everglades Forever Act; Section 373.4592

Florida Statutes) is most appropriate to identify reference conditions and evaluate

excursions from numeric criteria in this system. In developing reference conditions, the

natural, seasonal/annual hydrologic variability should be considered. Periphyton reference

condition and criterion recommendations are based on relative species abundance, which

has been found to be an integrative measure of nutrient condition. for the previous three

months. The oligotrophic Everglades marsh system contains a mosaic of wetland

community types, such as sloughs, wet prairies and sawgrass marshes, all of which are

adapted to low nutrient conditions. The mosaic character of the South Florida Coastal

Plain Nutrient Ecoregion, which provides a diverse array of habitats for animals, is an

important defining characteristic of the Everglades and was recognized in developing

reference conditions for the ecoregion. States and Tribes are urged to determine their

own reference sites for wetlands within the ecoregion at different geographic scales and to
vi

compare them to EPA’s reference conditions.

! Models employed for prediction or validation. 

Several models have been developed for the Everglades. Summaries and detailed

descriptions of models developed for the Everglades can be found in McCormick et al.

(1999) and Phosphorus Biogeochemistry in Subtropical Ecosystems (1999), respectively. 

States and Tribes are encouraged to identify and apply appropriate models to support

nutrient criteria development. 

! RTAG expert review and consensus.

EPA recommends that when States and Tribes prepare their nutrient criteria, they obtain 

the expert review and consent of the RTAG.

! Downstream effects of criteria. 

EPA encourages the RTAG to assess the potential effects of the proposed criteria on

downstream water quality and uses.

A summary of reference conditions for the Aggregate nutrient ecoregion for water column

TP and vegetation are presented below. These were chosen because they constitute early warning

indicators of eutrophication within the Everglades systems. 

BASED ON LITERATURE VALUES

Aggregate Ecoregion XIIISouthern Florida Coastal PlainReference Conditions

Total Water Column Phosphorus

(μg/L)

10

Periphyton No significant change in relative

species abundance

EPA also recommends that States and Tribes develop reference conditions and criteria for

soil phosphorus levels since it is considered a necessary indicator of eutrophication and

phosphorus condition within the Everglades. Studies have indicated that 300-600 mg P/kg soil is

the preferred range for organic soils. However, these same levels may not be appropriate for

mineral soils in some regions of the Everglades. 
vii

NOTICE OF DOCUMENT AVAILABILITY

This document is available electronically to the public through the INTERNET at:

(http://www.epa.gov/OST/standards/nutrient.html). Requests for hard copies of the document

should be made to EPA’s National Service Center for Environmental Publications (NSCEP),

11029 Kenwood Road, Cincinnati, OH 45242 or (513) 489-8190, or toll free (800) 490-9198. 

Please refer to EPA document number EPA-822-B-00-023.
viii

ACKNOWLEDGMENTS

The authors thankfully acknowledge the contributions of the following State and Federal

reviewers: Amanda Parker (Warnell School of Forest Resources, University of Georgia); EPA

Region 4; the State of Florida; the Tribes within the Ecoregion; EPA Headquarters personnel

from the Office of Wetlands, Oceans and Watersheds, Office of Wastewater Management, Office

of General Counsel, Office of Research and Development, and the Office of Science and

Technology. EPA also acknowledges the external peer review efforts of Paul McCormick (The

Nature Conservancy), Ramesh Reddy (University of Florida), and Jan Stevenson (Michigan State

University). 
ix

LISTS OF FIGURES AND TABLES

 

Figures 

 

Figure 1 Aggregate Ecoregion XIII .............................. 6

 

Figure 2 Aggregate ecoregion XIII with level III ecoregions shown ..... 7

Tables

Table 1 Reference conditions for Aggregate Ecoregion XIII– Southern 

Florida Coastal Plain ................................. 11

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
x

TABLE OF CONTENTS

 

Foreword ................................................................. ii

Disclaimer ............................................................... iv

Executive Summary .......................................................... v

Notice of Document Availability ............................................... vii

Acknowledgments ........................................................ viii

List of Tables and Figures .................................................... ix

Table of Contents ........................................................... x

1.0 Introduction ............................................................ 1

2.0 Best Use of this Information ............................................... 3

 

3.0 Area Covered by This Document (waterbody type and ecoregion) .................. 5

 3.1 Description of Aggregate Ecoregion XIII --Southern Florida Coastal Plain .... 5

 3.2 Geographical Boundaries of Aggregate Ecoregion XIII ................... 6

 3.3 Level III Ecoregions within Aggregate Ecoregion XIII ................... 6

4.0 Data Review for Wetlands in Aggregate Ecoregion XIII .......................... 7

 4.1 Data Sources ................................................... 7

 4.2 Historical Data from Aggregate Ecoregion XIII (TP, Soil P, and Vegetation) . . 8

 4.3 Data for all Wetlands within Aggregate Ecoregion XIII .. .................. 9

 4.4 Classification of Wetland Type ...................................... 9

 

5.0 Reference Sites and Conditions for Wetlands in Aggregate Ecoregion XIII ............ 9

6.0 Models Used to Predict or Verify Response Parameters .......................... 11

 

7.0 Framework for Refining Recommended Nutrient Criteria for Wetlands in Aggregate 

 Ecoregion XIII ................................................. 11

 7.1 Example Worksheet for Developing Aggregate Ecoregion and Subecoregion 

 Nutrient Criteria ............................................... 12

 7.2 Setting Seasonal Criteria ......................................... 13

 7.3 Site-specific Criteria Development .................................. 13

 

8.0 Literature Cited ........................................................ 13

 

9.0 Appendices ........................................................... 14
1

1.0 INTRODUCTION

Background

Nutrients are essential to the health and diversity of our surface waters. However, in

excessive amounts, nutrients cause hypereutrophication, which results in overgrowth of plant life

and decline of the biological community. Excessive nutrients can also result in potential human

health risks, such as the growth of harmful algal blooms - most recently manifested in the

Pfiesteria outbreaks of the Gulf and East Coasts. Chronic nutrient overenrichment of a

waterbody can lead to the following consequences: low dissolved oxygen, fish kills, algal blooms,

overabundance of macrophytes, likely increased sediment accumulation rates, and species shifts of

both flora and fauna. 

Historically, National Water Quality Inventories have repeatedly shown that nutrients are a

major cause of ambient water quality use impairments. EPA’s 1996 National Water Quality

Inventory report identifies excessive nutrients as the leading cause of impairment in lakes and the

second leading cause of impairment in rivers (behind siltation). In addition, nutrients were the

second leading cause of impairments reported by the States in their 1998 lists of impaired waters. 

Where use impairment is documented, nutrients contribute roughly 25-50% of the impairment

nationally. The Clean Water Act establishes a national goal to achieve, wherever attainable, water

quality which provides for the protection and propagation of fish, shellfish, and wildlife and

recreation in and on the water. In adopting water quality standards, States and Tribes designate

uses for their waters in consideration of the Clean Water Act goals, and establish water quality

criteria that contain sufficient parameters to protect those uses. To date, EPA has not published

information and recommendations under section 304(a) for nutrients to assist States and Tribes in

establishing numeric nutrient criteria to protect uses when adopting water quality standards.

In 1995, EPA gathered a set of national experts and asked the experts how to best deal

with the national nutrient problem. The experts recommended that the Agency not develop single

criteria values for phosphorus or nitrogen applicable to all water bodies and regions of the

country. Rather, the experts recommended that EPA put a premium on regionalization, develop

guidance (assessment tools and control measures) for specific waterbodies and ecological regions

across the country, and use reference conditions (conditions that reflect pristine or minimally

impacted waters) as a basis for developing nutrient criteria.

With these suggestions as starting points, EPA developed the National Strategy for the

Development of Regional Nutrient Criteria (National Strategy), published in June 1998. This

strategy presented EPA’s intentions to develop technical guidance manuals for four types of

waters (lakes and reservoirs, rivers and streams, estuaries and coastal waters, and wetlands) and,

thereafter, to publish section 304(a) criteria recommendations for specific nutrient ecoregions. 

Technical guidance manuals for lakes/reservoirs and rivers/streams were published in April 2000

and July 2000, respectively. The technical guidance manual for estuaries/coastal waters will be

published in spring 2000 and the draft wetlands technical guidance manual will be published by

December 2001. Each manual presents EPA’s recommended approach for developing nutrient

criteria values for a specific waterbody type. In addition, EPA is committed to working with

States and Tribes to develop more refined and more localized nutrient criteria based on

approaches described in the waterbody guidance manuals and this document. 

Overview of the Nutrient Criteria Development Process

For each Nutrient Ecoregion, EPA developed a set of recommendations for two causal

variables (total nitrogen and total phosphorus) and two early indicator response variables

(chlorophyll a and some measure of turbidity). Other indicators such as dissolved oxygen and

macrophyte growth or speciation, and other fauna and flora changes are also deemed useful. 

However, the first four are considered to be the best suited for protecting designated uses. This
2

basic set ofindicators clearly must be modified for wetlandsto accommodate the complexityofthese

aquatic environments. The parameters of concern for the Southern Florida Coastal Plain are water

column totalphosphorus(TP) concentration; soil phosphorus concentration, and change in vegetation

communities. Parameters of concern for the Everglades will also be used in other wetland systems,

if appropriate. 

The technical guidance manuals describe a process for developing nutrient criteria that

involves consideration of five factors. The first of these is the Regional Technical Assistance Group

(RTAG), which is a body of qualified regional specialists able to objectively evaluate all of the

available evidence and select the value(s) appropriate to nutrient control in the water bodies of

concern. These specialists may come from such disciplines as limnology, biology, natural resources

management-- especiallywater resource management, chemistry, and ecology. The RTAG evaluates

and recommends appropriate classification techniques for criteria determination, usually physical

within an ecoregional construct.

The second factor is the historical information available to establish a perspective of the

resource base. This is usually data and anecdotal information available within the past ten to twentyfive years. This information gives evidence about the background and enrichment trend of the

resource.

The third factor is the present reference condition. A selection of reference sites chosen to

represent the least culturally impacted waters ofthe class existing at the present time. The data from

these sites are combined and a value from the distribution of these observations is selected to

represent the reference condition, or best attainable, most natural condition of the resource base at

this time.

A fourth factor often employed is theoretical or empirical models of the historical and

reference condition data to better understand the condition of the resource. It is recognized that,

distinct fromambient monitoring or empirical efforts, field and laboratory experiments can elucidate

specific processes and establish cause and effect. These studies (such as field nutrient dosing studies,

mesocosm studies, or laboratory mesocosm or microcosm experiments) can facilitate causal

interpretation of data. (Lean, et al., 1992; Hopkinson, et la., 1998).

The RTAG comprehensively evaluates the other three elements to propose a candidate

criterion (initially one each for TP, TN, chl a, and some measure of turbidity).

The last and final element ofthe criteria development process isthe assessment by the RTAG

of the likely downstream effects of the criterion. Will there be a negative, positive, or neutral effect

on the downstreamwaterbody? If the RTAG judges that a negative effect is likely, then the proposed

State/Tribal water quality criteria should be revised to ameliorate the potential for any adverse

downstream effects.

While States and authorized Tribes would not necessarily need to incorporate allfive elements

into their water quality criteria setting process (e.g., modeling may be significant in only some

instances), the best assurance of a representative and effective criterion for nutrient management

decision making is the balanced incorporation of all five elements, or at least all elements except

modeling.

Because some parts of the country have naturally higher soil and parent material enrichment,

and different precipitation regimes, the application of the criterion development process has to be

adjusted by region. Therefore, an ecoregional approach was chosen to develop nutrient criteria

appropriate to each of the different geographical and climatological areas of the country. Initially,

the continental U.S. was divided into 14 separate ecoregions ofsimilar geographical characteristics.

Ecoregions are defined as regions of relative homogeneity in ecological systems; they depict areas

within which the mosaic of ecosystem components (biotic and abiotic as well as terrestrial and
3

aquatic) is different than adjacent areas in a holistic sense. Geographic phenomena such as soils,

vegetation, climate, geology, land cover, and physiology that are associated with spatial differences

in the quantity and quality of ecosystem components are relatively similar within each ecoregion. 

The Nutrient ecoregions are aggregates of U.S. EPA=s hierarchal level III ecoregions

(Omernik, 1995, 1998). As such, they are more generalized and less defined than level III

ecoregions. EPA determined that setting ecoregional criteria for the large scale aggregates is not

without itsdrawbacks- variabilityis high due to the lumping ofmanywaterbody classes,seasons, and

years worth of multipurpose data over a large geographic area. For these reasons, the Agency

recommends that States and Tribes develop nutrient criteria at the level III ecoregional scale and at

the waterbody classscale where those data are readily available. Data analyses and recommendations

on both the large aggregate ecoregion scale as well as more refined scales (level III ecoregions and

waterbody classes), where data were available to make such assessments, are presented for

comparison purposes and completeness of analysis. 

Relationship of Nutrient Criteria to Biological Criteria

Biological criteria are quantitative expressions of the desired condition of the aquatic

community. Such criteria can be based on an aggregation of data from sites that represent the leastimpacted and attainable condition for a particular waterbody type in an ecoregion, subecoregion, or

watershed. EPA’s nutrient criteria recommendations and biological criteria recommendations have

many similarities in the basic approach to their development and data requirements. Both are

empirically derived from statistical analysis of field collected data and expert evaluation of current

reference conditions and historical information. Both utilize direct measurements from the

environment to integrate the effects of complex processes that vary according to type and location

of waterbody. The resulting criteria recommendations, in both cases, are efficient and holistic

indicators of water quality necessary to protect uses.

States and authorized Tribes can develop and apply nutrient criteria and biological criteria in

tandem, with each providing important and useful information to interpret both the nutrient

enrichment levels and the biological condition ofsampled waterbodies. For example, using the same

reference sites for both types of criteria can lead to efficiencies in both sample design and data

analysis. In one effort, environmental managers can obtain information to support assessment of

biological and nutrient condition, either through evaluating existing data sets or through designing

and conducting a common sampling program. The traditional biological criteria variables of benthic

invertebrate and fish sampling can be readily incorporated to supplement a nutrient assessment. To

demonstrate the effectiveness of this tandem approach, EPA has initiated pilot projects in both

freshwater and marine environmentsto investigate the relationship between nutrient overenrichment

and apparent declines in diversity indices of benthic invertebrates and fish.

2.0 BEST USE OF THIS INFORMATION

EPA recommendations published under section 304(a) of the CWA serve several purposes,

including providing guidance to States and Tribes in adopting water quality standards for nutrients

that ultimately provide a basis for controlling discharges or releases of pollutants. The

recommendations also provide guidance to EPA when promulgating Federalwater qualitystandards

under section 303(c) when such action is necessary. Other uses include identification of

overenrichment problems, management planning, project evaluation, and determination ofstatus and

trends of water resources. 

State water quality inventories and listings of impaired waters consistently rank nutrient

overenrichment as a top contributor to use impairments. EPA’s water quality standards regulations

at 40 CFR §131.11(a) require States and Tribes to adopt criteria that contain sufficient parameters

and constituents to protect the designated uses of their waters. In addition, States and Tribes need

quantifiable targetsfor nutrientsin theirstandardsto assess attainment ofuses, developwater quality-
4

based permit limits and source control plans, and establish targets for total maximum daily loads

(TMDLs).

EPA expects States and Tribes to address nutrient overenrichment in their water quality

standards, and to build on existing State and Tribalinitiated effortswhere possible. States and Tribes

can address nutrient overenrichment through establishment of numerical criteria or through use of

new or existing narrative criteria statements(e.g., free fromexcess nutrientsthat cause or contribute

to undesirable or nuisance aquatic life or produce adverse physiologicalresponse in humans, animals,

or plants). In the case of narrative criteria, EPA expects that States and Tribes establish procedures

to quantitatively translate these statements for both assessment and source control purposes. 

The intent of developing ecoregional nutrient criteria is to represent conditions of surface

waters that are minimally impacted by human activities and thus protect against the adverse effects

ofnutrient overenrichment from cultural eutrophication. EPA’s recommended process for developing

such criteria includes physical classification of waterbodies, determination of current reference

conditions, evaluation of historical data and other information (such as published literature), use of

models to simulate physical and ecological processes or determine empirical relationships among

causal and response variables(if necessary), expert judgement, and evaluation ofdownstreameffects.

To the extent allowed by the information available, EPA has used elements ofthis processto produce

the information contained in this document. The values for both causal (total nitrogen, total

phosphorus) and biological and physicalresponse (chlorophyll a, turbidity) variables represent a set

ofstarting pointsfor States and Tribesto use in establishing their own criteria in standards to protect

uses.

In its water quality standards regulations, EPA recommends that States and Tribes establish

numerical criteria based on section 304(a) guidance,section 304(a) guidance modified to reflect sitespecific conditions, or other scientifically defensible methods. For many pollutants, such as toxic

chemicals, EPA expectsthat section 304(a) guidance will provide an appropriate level of protection

without further modification in most cases. EPA has also published methods for modifying 304(a)

criteria on a site-specific basis, such as the water effect ratio, where site-specific conditions warrant

modification to achieve the intended level of protection. For nutrients, however, EPA expects that,

in most cases, it will be necessary for States and authorized Tribes to identify with greater precision

the nutrient levels that protect aquatic life and recreational uses. This can be achieved through

development of criteria modified to reflect conditions at a smaller geographic scale than an ecoregion

such as a subecoregion, the State or Tribe level, or specific class of waterbodies. Criteria refinement

can occur by grouping data or performing data analyses at these smaller geographic scales.

Refinement can also occur through further consideration of other elements of criteria development,

such as published literature or models.

The values presented in this document generally represent nutrient levels that protect against

the adverse effects of nutrient overenrichment and are based on information available to the Agency

at the time ofthis publication. However, States and Tribes should critically evaluate this information

in light of the specific designated uses that need to be protected. For example, more sensitive uses

may require more stringent values as criteria to ensure adequate protection. On the other hand,

overly stringent levels ofprotection against the adverse effectsof cultural eutrophicationmayactually

fall below levels that represent the natural load of nutrientsfor certain waterbodies. In cases such as

these, the level of nutrients specified may not be sufficient to support a productive fishery. In the

criteria derivation process, it is important to distinguish between the natural load associated with a

specific waterbody and current reference conditions, using historical data and expert judgement.

These elementsofthe nutrient criteria derivation process are best addressed byStates and Tribes with

accessto information and local expertise. Therefore, EPA strongly encourages States and Tribes to

use the information contained in this document and to develop more refined criteria according to the

methods described in EPA’s technical guidance manuals for specific waterbody types.

To assist in the process of further refinement of nutrient criteria, EPA has established ten
5

RegionalTechnicalAdvisoryGroups(expertsfromEPA Regional Offices and States/Tribes). In the

process of refining criteria, States and authorized Tribes need to provide documentation of data and

analyses, along witha defensible rationale, for any new or revised nutrient criteria they submit to EPA

forreview and approval. As part of EPA’s review of State and Tribal standards, EPA intends to seek

assurance from the RTAG that proposed criteria are sufficient to protect uses.

In the process of using the information and recommendations contained in this document, as

well as additional information, to develop numerical criteria or procedures to translate narrative

criteria, EPA encourages States and Tribes to:

C Address both chemical causal variables and early indicator response variables. Causal

variables are necessary to provide sufficient protection of uses before impairment occurs and

to maintain downstream uses. Early response variables are necessary to provide warning

signs of possible impairment and to integrate the effects of variable and potentially

unmeasured nutrient loads.

C Include variables that can be measured to determine if standards are met, and variables that

can be related to the ultimate sources of excess nutrients.

C Identify appropriate periods of duration (i.e., how long) and frequency (i.e., how often) of

occurrence in addition to magnitude (i.e., how much). EPA does not recommend identifying

nutrient concentrations that must be met at all times, rather a seasonal or annual averaging

period (e.g.,based on weekly measurements) is considered appropriate. However, these

seasonal or annual central tendency measures (i.e., geometric mean or median) should apply

each season or each year, except under the most extraordinary of conditions (e.g., a 100 year

flood).

3.0 AREA COVERED BY THIS DOCUMENT

The following sections provide a general description of the aggregate ecoregion and its

geographical boundaries. A descriptions of the level III ecoregion contained within the aggregate

ecoregion is also provided.

3.1 Description of Aggregate Ecoregion XIII – Southern Florida Coastal Plain

The Southern Florida Coastal Plain is nearly level and subtropical to tropical (U.S. EPA,

2000). It is characterized by wildlife-rich fresh water marshes, wet prairies, sloughs, swamps, and

coastal wetlands; only about 10% is used as cropland. Canals, ditches, and broad, poorly-defined

stream channels are common. Lakes are generally rare but one large, shallow, regulated lake is

found in the region, Lake Okeechobee; it links the waters of the Kissimmee Basin to the

Everglades. Elevations are low and range from sea level to less than 50 feet; only hummocks,

limestone ridges, beach ridges, and dunes relieve the flatness of the region. Poorly- and very

poorly-drained, organic soils (peat and muck) are common and overlie carbonate-rich bedrock. 

Much of the Southern Florida Coastal Plain (XIII) has been set aside as parks, game refuges,

water conservation areas, and Indian reservations. However, extensive areas have also been

urbanized or drained for agriculture, resulting in the widespread alteration of hydrological and

biological systems, depletion of peat deposits, and reduction of regional water quality. Canals

draining developed areas generally have higher nutrient concentrations than those flowing through

undeveloped areas. Lake Okeechobee is one of the largest lakes in the United States and has been

significantly impacted by agricultural runoff. Cattle and dairy farms have contributed a large

amount of phosphorus to the lake and the Everglades Agricultural Area has pumped nitrogen-rich

water into the lake to control flooding. During the 1970s, lake concentrations of phosphorus and

nitrogen more than doubled and bottom sediments accumulated a massive quantity of phosphorus. 

By the mid-1980s, large algal blooms had occurred.
6

3.2 Geographic Boundaries of Aggregate Ecoregion XIII

Ecoregion XIII is small compared to the other ecoregions; encompassing only the southern

quarter of Florida (Figure 1).

3.3 Level III Ecoregion Within Aggregate Ecoregion XIII

76. Southern Florida Coastal Plain

The frost-free climate of the Southern Florida Coastal Plain makes it distinct from other

ecoregions in the conterminous United States (Figure 2). This region is characterized by flat plains

with wet soils, marshland and swamp land cover with Everglades and palmetto prairie vegetation

types. Although portions of this region are in parks, game refuges, and Indian reservations, a large

part of the region has undergone extensive hydrological and biological alteration.

Figure 1. Aggregate Ecoregion XIII
7

Figure 2. Aggregate Ecoregion XIII with level III ecoregion shown

4.0 DATA REVIEW FOR WETLANDS IN AGGREGATE ECOREGION XIII

The following section describes the nutrient data information that EPA reviewed for this

Ecoregion. They include data for the causal parameters-- total water column phosphorus and soil

phosphorus and the primary response variable-- periphyton- relative species abundance. These are

the parameterswhichEPAconsiders essentialto nutrient assessment inwetlands because the first two

are the measurements of the main causative agents of phosphorus enrichment and the response

variable is the early indicator of system enrichment for the Everglades ecosystem (Ecoregion XIII).

4.1 Data Sources 

Relevant scientific information used in determining the phosphorus criterion range in this

document has been summarized from the EPA finding in support of the criterion proposed for

Miccosukee triballandsin Nutrient EcoregionXIII (EPA 1999), fromthe EvergladesInterim Report

(SFWMD 1999), from Phosphorus Biogeochemistry in Subtropical Ecosystems (1999), and from

DeBusk et al., 1994, and DeBusk et al., in press. 
8

4.2 Historical Data from Aggregate Ecoregion XIII (water column TP, soil P and

vegetation):

EPA recommendsthat States/Tribes assesslong-termtrends observed over the past 50 years.

Thisinformationmay be obtained fromscientific literature or documentation of historicaltrends. To

gain additional perspective on more recent trends, it is recommended that States and Tribes assess

nutrient trends over the last 10 years (e.g., what do seasonal trends indicate?)

- long term trends over past 50 years.

Historical descriptions of the Everglades ecosystem are relatively scarce, and those that are

available are largely descriptive and qualitative, rather than quantitative in nature. Information on

historical large-scale vegetation patterns is available, but water quality information is sparse prior to

the 1970s (McCormick et al., 1999). Phosphorus inputs to the Everglades historically came largely

from atmospheric deposition. Current estimates indicate that the total phosphorus concentration in

rainfall istypically lessthan 10 μg/L and that total atmospheric inputs average between 22 and 36 mg

TP/m2/yr; it is assumed that historical inputs were not greater than current estimates (McCormick et

al, 1999). Historically, the Everglades also received periodic inflows from Lake Okeechobee, but

these inputs were likely small relative to atmospheric inputs. The more remote interior areas of the

Everglades still exhibit the low P concentrations that once prevailed throughout the Everglades

system. Measurements of soluble reactive phosphorus (SRP) and orthophosphate in some interior

marsh sites in the 1970s and 1980s indicate that background concentrations of 2 to 5 ppb were not

uncommon (Scheidt 1999). More recent studies in the Everglades National Park (ENP) note the low

concentrations of phosphorus in the interior sites. Scheidt, et al. (1989) summarized water quality

characteristics of the ENP from 1984-1986, and found typical orthophosphate concentrations of 4

ppb in the interior marsh sites, with P concentration values from 10 to 35 times higher from sites in

and around the Everglades Agricultural Area (EAA) and Lake Okeechobee. 

The majority ofsoils data collected from the Everglades in the early 1900s were descriptive.

The few soil data from the 1900s that are quantitative are summarized in McCormick et al. (1999),

and indicate that soil P concentrations near Okeechobee weremuch higherthan those in more interior

Everglades sites. Early studies found that soil P concentrations in the top 30 cm of organic soil at

sites adjacent to Lake Okeechobee (in what is now the EAA) averaged (1,800 to 2,000 mg P/kg), and

soil P concentrations at interior Everglades sites near Tamiami trail averaged (~400 mg P/kg)

(McCormick et al. 1999). More recent studies of soil P have indicated an increase in surficial soil

phosphorus concentrations of up to three-fold since the 1970s (Davis 1989; Reddy et al. 1991;

DeBusk et al. 1994; Reddy et al. 1998; DeBusk et al., in press) in those areas receiving inflowsfrom

canals draining the EAA. 

Periphyton is the most widely distributed plant community in the Everglades. Periphyton

exhibits three growth forms in the Everglades: benthic (growing on the soil surface), epiphytic

(growing attached to rooted vegetation) and floating (growing on the water surface sometimes in

association with other floating vegetation such as Utricularia purpurea) (McCormick et al., 1999).

Periphyton mat communities are found throughout the unimpacted Everglades marsh, especially in

open water areas, sloughs and wet prairies, and are particularly well adapted to the low P conditions

historically found in the Everglades ecosystem. The first visible changes caused by P enrichment are

seen in the periphyton mat communities. As the P-limited areas of the Everglades are enriched, the

calcareous blue-green algae and diatoms are replaced by soft-bodied green and blue-green algae, and

the soft-water periphyton communities show increased relative abundance of pollution-tolerant

species. Swift (1984) found that marsh water TP was the controlling factor regulating periphyton

growth. Elevated water TP increased periphyton biomass, increased periphyton phosphorus content,

and altered community species composition toward pollution-tolerant species. The continued flow

of nutrient enriched waters into the Everglades from the EAA has also resulted in more profound

changes in the vegetation community. Increased macrophyte growth has decreased periphyton

productivity due to reduced light availability, and has caused a change in macrophyte community
9

composition. The historically dominant marsh macrophyte, Cladium jamaicense, is being displaced

with the high P-adapted species, Typha domingensis, in those areas enriched by EAA outflows

(McCormick et al. 1999; Bechtel et al. 1999; DeBusk, et al., in press). This also includes the loss

of open water wet prairies plant communities. 

-trends over the last 10 years

Recent trends in the Everglades reflect the continued enrichment of the Everglades. 

Phosphorus concentrations in those areas closest to the Everglades Agricultural Area (EAA)

outflows show the greatest levels of enrichment in both the water column and soil phosphorus

concentrations. The increasing loss of native periphyton, and continued spread of Typha latifolia

into the more interior areas of the Everglades further support the conclusion that nutrient

enrichment is affecting the Everglades ecosystem. 

Water column total phosphorus concentrations in remote interior sites currently average

between 4 and 10 μg/L (McCormick et al. 1999); contemporary measurements of soil porewater

concentrations are consistently below 50 μg/L soluble reactive phosphorus (SRP), and are often at

or below 4 μg/L, and total phosphorus concentrations in surface soils range between 200 and

500mg/kg (McCormick et al. 1999). Chronic inputs of P from the EAA has lead to increased P in

the water and soil in areas receiving inflows from canals draining the EAA, and a forward moving

front of P-enriched surficial soil (McCormick et al. 1999; DeBusk et al, in press). 

Water column phosphorus concentrations within the Everglades fluctuate naturally with

water conditions. Marsh phosphorus concentrations have been shown to vary with water depth,

with higher concentration excursions occurring during periods of low water or marsh drying

(McCormick, et al. 1999). McCormick et al. (1999) summarized the impact of increased P

loading to the Everglades on microbial and biogeochemical processes. P loading has been shown

to affect the quality and quantity of organic matter, rates of nutrient accumulation, microbial

biomass and community composition, and biogeochemical cycling. Moreover, P enrichment has

been shown to initiate a series of effects on the cycling of carbon and nitrogen, as well as a shift in

the system from an aerobic environment where oxygen is readily available to an anaerobic

environment where oxygen is lacking.

4.3 Data for all Wetlands Within Aggregate Ecoregion XIII 

The Everglades predominate in Ecoregion XIII. The information presented in this document

is from studies performed in the Everglades.

4.4. Classification of Wetland Type:

The Everglades ecosystem is a large, unique wetland mosaic in the tropical and sub-tropical

southern peninsula of Florida. Classification of the Everglades system into sub-types based on

chemical, physical and biological differences can help decrease variability in monitoring data. In

addition, nutrient gradients are evident in the Everglades system, and comparisons of data along the

spatial gradient may be of use in further refining nutrient criteria for this system. 

5.0 REFERENCE SITES AND CONDITIONS IN AGGREGATE ECOREGION XIII

The Everglades is a nutrient poor (oligotrophic) wetland, with natural populations of

plants and animals adapted to extremely low nutrient conditions. Scheidt (1999) summarized and

reviewed approximately 300 scientific journal articles, state, and federal reports relevant to

nutrients in the Everglades. The literature summarized indicate long-term average water column

phosphorus concentrations of less than 10 μg/L. Data supporting this number span three decades

and were analyzed by independent laboratories (see Appendix A). For the purposes of reducing
10

these data to a single value which represents an appropriate characterization of reference

condition, EPA recommends a central tendency value such as the long-term geometric mean or

median because of the large amount of data available, the relatively long length of time

represented by the data, and the effects of hydrologic variability on water column concentration of

phosphorus in this system.

Unenriched portions of the Everglades are reported to have some of the lowest rates of

phosphorus accumulation in peatlands in North America. Increased surface water phosphorus

from EAA canal inflows has caused elevated soil phosphorus concentrations. Studies conducted

in the last decade by DeBusk et al. (1994; in press) indicate that chronic dosing has lead to

increased soil P in Water Conservation Area 2A (WCA2A), the primary recipient of EAA inflows,

and the front of P-enriched soils is moving south and encompassing increasingly larger areas.

Periphyton mat communities are found throughout the unimpacted Everglades marsh,

especially in open water areas, sloughs and wet prairies. These mats, often referred to as

calcareous mats, are known to be extremely sensitive to P enrichment. The calcareous algal mats

in the hardwater calcium rich portions of the Everglades exhibit the first visible changes as a result

of increased phosphorus when the dominant periphyton, calcareous blue-green algae, is replaced

by soft-bodied green and blue-green algae (McCormick et al. 1999). The soft-water habitats of

the Everglades also have periphyton adapted to low-nutrient conditions. These periphyton

communities are comprised primarily of a type of green algae (desmids) and diatoms. Shifts in

relative species abundance and an increase in pollution-tolerant species also occur as a response to

nutrient enrichment in the soft-water periphyton community (McCormick et al 1999). 

 Reference conditions in the Everglades are defined by the native periphyton and

macrophyte communities. Everglades periphyton provides multiple functions in the ecosystem. 

These functions include: accounts for much of the primary productivity in wet prairies and

sloughs; provides habitat for aquatic animals such as invertebrates; along with macrophyte

detritus, forms forming the base of the Everglades aquatic food web; is the major source of

oxygenating the water for fish and other animal life in sloughs and wet prairies; maintaining low

water TP concentrations; plays a role in cycling of nitrogen, phosphorus, carbon and oxygen; and

contributes to the formation of marl soils.

The oligotrophic Everglades marsh system contains a mosaic of macrophyte communities,

such as sloughs, wet prairies and sawgrass marshes, all of which are adapted to low nutrient

conditions. This mosaic, which provides a diverse array of habitats for animals, is an important

defining characteristic of the Everglades. Wet prairies encompass a group of plant communities

generally described by soil type and dominant plant species. Wet prairies on peat soil are

generally characterized by spikerush (Eleocharis cellulosa), beak rush (Rhynchospora tracyi), or

maidencane (Panicum hemitomon), although dozens of plant species exist. Sloughs generally

refer to deeper water areas, often dominated by white water lily (Nymphaea odorata), floating

hearts (Nymphoides aquatica), and spatterdock. Bladderworts (Utricularia purpurea or

Utricularia foliosa) are common submerged aquatic plants that provide a substrate for dense

periphyton mats. Wet prairies and sloughs in particular provide critical habitat for animals and

provide cover, nesting, and feeding sites for all animal groups. The wet prairie/slough habitat is

also the major feeding area in the Everglades for both wintering and nesting wading birds,

especially during the dry season when fish concentrations provide food for their nestlings (Scheidt

1999). 

An important characteristic of unimpacted wet prairies and sloughs is their diversity and

the large number of native plant species (Scheidt 1999). Multiple factors are responsible for the

alteration and maintenance of plant community structure in the Everglades, including nutrients,

fire, disturbance, and hydroperiod. Elevated water phosphorus concentrations or elevated soil

phosphorus concentrations in the Everglades are associated with elimination of submerged

vegetation species including the Utricularia-periphyton complex and expansion of nutrient-
11

tolerant macrophytes such as cattail or Sagittaria lancifolia (Arrowhead) into areas previously

dominated by sawgrass, sloughs or wet prairies. Historically, cattail was a minor component of

the Everglades landscape.

The table below (Table 1) shows the reference condition recommendations for the

Aggregate nutrient ecoregion for water column TP and vegetation. The recommendations are

based on literature values. 

Table 1: Reference Conditions for Aggregate Ecoregion XIII.

Aggregate Ecoregion XIIISouthern Florida Coastal PlainReference Conditions

Total Water Column Phosphorus

(μg/L)

10

Periphyton No significant change in relative

species abundance

These recommendations were derived based on data from the over 300 peer-reviewed

publications from Everglades research. They may not be appropriate for all the wetlands within

the Everglades because the mosaic character of the system may result in site-specific conditions

that do not reflect the characteristics were used to derive these reference values. EPA encourages

the State and Tribes of Florida to apply this approach in other wetlands within the ecoregion. 

EPA also recommends that States and Tribes develop reference conditions and criteria for

soil phosphorus levels since it is considered a necessary indicator of eutrophication and

phosphorus condition within the Everglades. Studies have indicated that 300-600 mg P/kg soil is

the preferred range for organic soils. However, these same levels may not be appropriate for

mineral soils in other parts of the Everglades. 

6.0 MODELS USED

No models were directly used in the preparation of this document. However, many

models have been produced to model nutrient effects in the Everglades. An overview of the

models used in the Everglades is provided in the Everglades Interim Report (1999). Summaries

and detailed descriptions of models developed for the Everglades can be found in McCormick et

al. (1999) and Phosphorus Biogeochemistry in Subtropical Ecosystems (1999), respectively.

It is recognized that, distinct from ambient monitoring or empirical efforts, field and

laboratory experiments can elucidate specific processes and establish cause and effect. These

studies (such as field nutrient dosing studies, mesocosm studies, or laboratory mesocosm or

microcosm experiments) can facilitate causal interpretation of data. (Lean, et al., 1992;

Hopkinson, et la., 1998). 

7.0 FRAMEWORK FOR REFINING RECOMMENDED NUTRIENT CRITERIA

FOR AGGREGATE ECOREGION XIII

Information on each of the following six weight of evidence factors is important to refine

the criteria presented in this document. All elements should be addressed in developing criteria. It

is our expectation that EPA Regions and States (as RTAGs) will consider these information

elements as States/Tribes develop their criteria. This section should be viewed as a work sheet to

assist in the completion of the nutrient criteria assessment. For example, States and Tribes should

address factors that have the potential to impact downstream receiving waters, particularly
12

Florida Bay and the Keys. If these elements are ultimately unaddressed, EPA may rely on the

proposed reference conditions and criteria recommendations presented in this document, and

other literature and information readily available to the HQ nutrient team to develop nutrient

water quality recommendations for this ecoregion.

7.1 Example Worksheet for Developing Aggregate Ecoregion and Subecoregion

Nutrient Criteria 

C Literature sources

C Historical data and trends

C Reference condition

C Models

C RTAG expert review and consensus

C Downstream effects
13

7.2 Setting Seasonal Criteria

 States/Tribes may choose to develop criteria which reflect each particular season or a

given year when there is significant variability between seasons/years or designated uses that are

specifically tied to one or more seasons of the year (e.g., recreation, fishing). Obviously, this

option is season-specific and would also require increased monitoring within each season to assess

compliance. 

7.3 Site-specific Criteria Development 

Criteria may be refined in a number of ways. The best way to refine criteria is to follow

the critical elements of criteria development as well as to refer to the Wetlands technical guidance

manual (due out for publication in 2001).

The Technical Guidance Manual presents sections on each of the following factors to

consider in setting criteria

Ç refinements to ecoregions

Ç classification of waterbodies

Ç setting seasonal criteria to reflect major seasonal climate differences

Ç accounting for significant or cyclical rainfall events - high flow/low flow conditions

Ç Wetland types

8.0 LITERATURE CITED

Bechtel, Timothy, Steven Hill, Nenad Iricanin, Kimberly Jacobs, Cheol Mo, Victor Mullen,

Richard Pfeuffer, David Rudnick and Stuart Van Horn. 1999. Status of Compliance with

Water Quality Criteria in the Everglades Protection Area and tributary waters. Chapter 4

in Everglades Interim Report. South Florida Water Management District. West Palm

Beach, Florida. 

Davis, Steven M. 1989. Sawgrass and Cattail Production in Relation to Nutrient Supply in the

Everglades. pp. 325-341 in "Freshwater Wetlands and Wildlife", CONF-860301, DOE

Symposium Series No. 61, R. R. Scharitz and J. W. Gibbons (eds.), USDOE Office of

Scientific and Technical Information, Oak Ridge, Tennessee.

DeBusk, W. F., K. R. Reddy, M. S. Koch, and Y. Wang. 1994. Spatial distribution of soil

nutrients in a northern Everglades marsh: Water Conservation Area 2A. Soil Sci. Soc.

Am. J. 58:543-552.

DeBusk, W. F., S. Newman, and K. R. Reddy. (in press). Spatio-temporal patterns of soil

phosphorus enrichment in Everglades WCA-2A. Journal of Environmental Quality. 

Everglades Interim Report. 1999. South Florida Water Management District.

Hopkinson, Charles Jr., Patrick Mulholland, Lawrence Pomeroy, Robert Twilley and Dennis

Whigham. 1998. External panel report to the Florida Department of Environmental

Protection. Overview and evaluation of Everglades nutrient threshold research for the

period October 1996 to October 1997. 47 p.

Lean, David, Kenneth Reckhow, William Walker and Robert Wetzel. 1992. Everglades nutrient

threshold research plan. July 3, 1992. 12 p.
14

McCormick, Paul, Susan Newman, Shili Miao, Ramesh Reddy, Dale Gawlick, Carl Fitz, Tom

Fontaine and Darlene Marley. 1999. Ecological needs of the Everglades. Chapter 3 in

Everglades Interim Report. South Florida Water Management District. West Palm

Beach, Florida. 

Omernik, J. A. 1995. Ecoregions: A Spatial Framework for Environmental Management. In: Biological

Assessment and Criteria: Tools for Water Resource Planning and Decision Making, Wayne S.

Davis and Thomas P. Simon (editors), pp. 49-66. Lewis Publishers an imprint of CRC Press,

Boca Raton, FL.

Omernik, J. A. 1998. Draft Aggregations of Level III Ecoregions for the National Nutrient Strategy.

[http://www.epa.gov/ost/standards/ecomap.html].

Reddy, K. R., G. A. O’Connor, and C. L. Schelske, 1999. Phosphorus Biogeochemistry in

Subtropical Ecosystems. eds. Lewis Publishers, Boca Raton, FL. 

Reddy, K. R., Y. Wang, W. F. DeBusk, M. M. Fisher and S. Newman. 1998. Forms of Soil

Phosphorus in selected hydrologic units of the Florida Everglades. Soil Sci. Soc. Am J.

62:1134-1147.

Scheidt, D. J., M.D. Flora, and D. R. Walker. 1989. Water Quality Management for Everglades

National Park. P. 377-390. In: “Wetlands: Concerns and Success”. American Water

Resources Association, Bethesda, MD. USA.

Scheidt, D. J. 1999. EPA Memorandum. Numeric phosphorus water quality criterion for the

Everglades as adopted by the Miccosukee Tribe of Indians of Florida for Class III-A

Waters. May 20, 1999.

Swift, D. R.1984. Periphyton and water quality relationships in the Everglades Water

Conservation Areas. Pp. 97-117 in "Environments of South Florida: Present and Past II" 

Miami Geological Society, Coral Gables, Florida. 551 pp.

U.S. EPA. April 2000, Nutrient Criteria Technical Guidance Manual: Lakes and Reservoirs,

EPA-822-B00-001.

9.0 APPENDICES

Appendix A: Scheidt, D. J. 1999. EPA Memorandum. Numeric phosphorus water quality

criterion for the Everglades as adopted by the Miccosukee Tribe of Indians of

Florida for Class III-A Waters. May 20, 1999.

Appendix B: EVERGLADES NUTRIENT-RELEVANT REFERENCES. Compiled by D.

Scheidt, USEPA, May 1999. 
APPENDIX A
Memorandum

To: Robert F. McGhee

Director, Water Management Division

Through: Richard Harvey

Director, South Florida Office

From: Dan Scheidt

Senior Scientist

South Florida Initiative

Subject: Numeric phosphorus water quality criterion for the Everglades as adopted by the

Miccosukee Tribe of Indians of Florida for Class III-A Waters

Date: May 20, 1999

The Miccosukee Tribe of Indians of Florida (the Tribe) has submitted to the United States

Environmental Protection Agency (USEPA) a numeric criterion for total phosphorus of 10 parts

per billion (ppb, or micrograms per liter). The Tribe adopted this numeric criterion for Class IIIA waters of the Miccosukee Tribe’s Federal Reservation in the Everglades on December 19,

1997. The Tribe has defined Class III-A waters within the Federal Reservation as: "Those Tribal

water bodies which are used for fishing, frogging, recreation (including airboating), and the

propagation and maintenance of a healthy, well-balanced population of fish and other aquatic life

and wildlife. These waters have been primarily designated for preservation of native plants and

animals of the natural Everglades ecosystem." (page 23 of the Final Miccosukee Environmental

Protection Code, Subtitle B, dated December 19,1997). The Tribal water quality standard for

nutrients includes the narrative statement: “In no case shall nutrient concentrations of Tribal Class

I or Class III-A surface waters be altered so as to cause an imbalance in natural populations of

aquatic flora or fauna.” (page 11). The areas which the Tribe has designated as Class III-A

waters include the north grass, south grass and gap areas (Everglades habitat within western

Water Conservation Area 3A) (Figures 1 and 2).

PROBLEM STATEMENT

The determination that USEPA must make in approving or disapproving the Miccosukee

10 ppb phosphorus criterion is whether it is protective of the Class III-A designated use. 

The Everglades marsh is extremely oligotrophic (nutrient poor). The mosaic of native

plant communities and associated animals developed under, and are adapted to, very low

phosphorus conditions. Phosphorus enrichment in the Everglades has caused a series of welldocumented impacts (see below) such as loss of water column dissolved oxygen, loss of native

plant life (periphyton (micro-algae) and macrophytes), and loss of preferred foraging habitat for

wading birds. 
2

As summarized by the external peer-review panel to the Florida Department of

Environmental Protection (Hopkinson et al. 1998), in phosphorus-limited aquatic systems such as

the Everglades, concentrations of total phosphorus in the water column are very low, and a small

pool of dissolved phosphorus cycles or turns over very rapidly. 

Added phosphorus is assimilated rapidly into biomass or adsorbed by particulate

matter. Phosphorus concentrations in the water will begin to increase only when a

number of other living and non-living pools begin to saturate with excess P. For

this reason, measurements of the standing stocks of total P in Everglades water are

a relatively insensitive measure of significant changes of the system. By the time

the concentration of total P in water has increased significantly, the system has

already begun to approach P saturation in other components of the system

(periphyton, macrophytes, sediments) and species succession may well be

underway. In terms of time, the microbial components will be the first to change,

followed much later by changes in macro-organisms, such as sawgrass to cattails. 

The stages in this succession can be seen in the present-day Everglades.

 (Hopkinson et al.1998, page 11).

Phosphorus condition in the “Natural Everglades Ecosystem” is depicted in Figure 3. In

contrast, Figure 4 depicts the phosphorus-impacted Everglades system. Figure 5, “Cultural

Eutrophication”, depicts the succession of changes caused by phosphorus enrichment in the

Everglades, proceeding from those that are not visible to the naked eye (such as decreased

alkaline phosphatase activity or increased soil phosphorus content) to those that are visible (such

as changes in periphyton communities and macrophyte species composition). 

Ultimately, determining whether a numeric TP criterion will protect Class III-A

Everglades plant and animal communities appears to revolve around three issues: 1) selecting

appropriate indicators of some change in the marsh ecosystem (sensitive indicators such as

alkaline phosphatase activity or periphyton species versus less sensitive indicators such as

macrophyte species); 2) determining what constitutes an imbalance in natural populations of

aquatic flora or fauna: 3) determining what spatial extent of phosphorus impact, if any, is

acceptable. These issues are not solely scientific ones.

The numeric phosphorus water quality criterion adopted by the Tribe must be sufficiently

stringent to protect the Class III-A designated use, including preservation of native plants

(periphyton and macrophytes) and animals of the natural oligotrophic Everglades ecosystem for

decades or centuries. “This issue, obviously, is what amount of input of phosphorus to the

Everglades will result in system change after several decades or a century...” (Hopkinson et 

al.1998, page 14). Phosphorus impacts in the Everglades are well-documented. This

documentation includes observational studies as well as controlled experimental manipulations. 

Some of the observed phosphorus impacts have been based on short-term phosphorus addition or

dosing experiments, with the nutrient addition taking place for a duration of a few weeks up to a

few (less than five) years. With this type of study although it is possible to observe the

phosphorus impacts that occur within the short-term duration of dosing, it is not possible to

observe or infer what other indirect effects may occur later as the added phosphorus continues to
3

cycle. Nor is it possible to infer what effects may have occurred later had dosing at the same

concentration continued for a much longer period of time, such as decades or even centuries. It is

not possible to identify all final long-term direct and indirect ecological impacts from short-term

nutrient addition studies. Thus, there is a risk that a numeric criterion based solely on short-term

(less than 5 years) dosing without also considering long-term observational studies would not be

protective of the Class III-A designated use.

SUMMARY 

Extent of the Review

A very extensive body of peer-reviewed scientific literature and data has been assembled

during the last three decades concerning Everglades water quality, periphyton communities,

macrophyte communities, and the impacts of phosphorus enrichment on Everglades plants and

animals. USEPA received 110 documents from the Tribe in support of their adoption of the

numeric phosphorus criterion. These documents have been reviewed by USEPA. In addition, an

effort was made to identify and review other equally relevant scientific literature specific to the

Everglades. A listing (attached) of the published reports identified numbers about 300 scientific

documents. All of this literature is specific to the Everglades and is relevant to eutrophication. No

other wetland system and few, if any, other bodies of water in the world have been the subject of so

much scientific information concerning phosphorus conditions and the ecological impacts of

phosphorus enrichment.

A brief review is presented of the scientific documentation about Everglades natural

background phosphorus conditions and the impacts of phosphorus enrichment. This review relied 

on published scientific literature (peer-reviewed publications in scientific journals as well as 

technical publications by agencies such as the South Florida Water Management District, United

States Geological Survey or USEPA). The reviewed literature included publications about

Everglades:

C phosphorus conditions including the Everglades Agricultural Area,

C periphyton communities,

C macrophyte communities,

C cycling of oxygen, carbon, sulfur, and nitrogen, and

C wading bird foraging habitat.

The literature review excluded hundreds of additional scientific publications that primarily concern

Everglades:

C hydrology, 

C Phase II phosphorus treatment technology, 

C water management, 

C mercury contamination, 

• pesticides, 

• botany, and

C soils. 
4

An extensive additional body of scientific information and opinion exists that was not included:

published abstracts, memoranda, depositions, various legal documents, court exhibits, and public

meetings and conferences.

Summary of conclusions

Based on the best available scientific information and the review that follows, the Tribe’s 10

ppb criterion for phosphorus meets the requirements of 40 CFR §131.11 as it is protective of the

Class III-A designated use, and review of published available information and data shows that the

value is scientifically defensible.

This review has identified the following major points, which are expanded upon in the text that

follows: 

C The Everglades marsh system is naturally extremely oligotrophic. Un-impacted

interior portions of the Everglades marsh have long-term average water column

phosphorus concentrations of approximately 10 ppb or even less. 

C The native plant and animal communities in the Everglades marsh developed under

and are adapted to these very low phosphorus conditions.

C Phosphorus is the primary limiting nutrient in the oligotrophic Everglades marsh

system.

C Microbial processes are important in controlling nutrient cycling in wetlands and

they play an important role in determining water quality and maintaining an

ecosystem’s normal productivity. Elevated water column or soil phosphorus

concentrations in the Everglades have been implicated as cause for disruption of

various microbial processes.

C Periphyton communities are an important defining characteristic of the Everglades

marsh ecosystem. According to the scientific literature, Everglades periphyton 

accounts for much of marsh primary productivity in wet prairies and sloughs;

provides habitat for aquatic animals such as invertebrates; along with macrophyte

detritus, forms the base of the Everglades aquatic food web; is the major source of

oxygen for fish and other animal life in sloughs and wet prairies; maintains low water

TP concentrations; plays a role in cycling of nitrogen, phosphorus, carbon and

oxygen; and affects formation of marl soils. Periphyton communities are extremely

sensitive to phosphorus enrichment. Phosphorus enrichment at levels above 10 ppb

TP has been shown to cause a loss of Everglades native periphyton communities. 
5

C Surface water dissolved oxygen in pristine Everglades wet prairie and slough

communities often exhibits a strong diel cycle, with concentration at a particular

location ranging from 0 mg/l in early morning to over 12 mg/l in late afternoon. 

Everglades fish are adapted to these conditions. In contrast, oxygen levels in

nutrient-rich locations within WCA2A have been shown to often be undetectable and

rarely exceed 2 mg/l, with protracted periods of oxygen depletion.

C Unenriched portions of the Everglades are reported to have some of the lowest rates

of phosphorus accumulation in peatlands in North America. Increased surface water

phosphorus has caused elevated soil phosphorus concentrations. Over 51% of

WCA2A has been reported as having increased soil phosphorus. 

C The oligotrophic Everglades marsh system contains a mosaic of macrophyte

communities, such as sloughs, wet prairies and sawgrass marshes, all of which are

adapted to low nutrient conditions. This mosaic is an important defining

characteristic of the Everglades. Wet prairies and sloughs in particular provide

critical habitat for animals and provide cover, nesting, and feeding sites for all animal

groups. Elevated water phosphorus concentrations or elevated soil phosphorus

concentrations in the Everglades are associated with elimination of submerged

vegetation species including the important Utricularia-periphyton complex and

expansion of nutrient-tolerant macrophytes such as cattail or Sagittaria into areas

previously dominated by sawgrass, sloughs or wet prairies. 

C Shallow, open water areas with scattered to moderately dense emergent

macrophytes are the preferred foraging habitat for Everglades wading birds.

Conversion of these areas to dense emergent macrophytes due to phosphorus

enrichment constitutes a loss of wading bird foraging habitat.

C Phosphorus enrichment initiates a succession of changes within the marsh system. 

Initial changes, such as those that occur at the microbial level, are not visible. 

Visible impacts eventually occur, such as loss of native flora or fauna. 

C The oligotrophic Everglades marsh system has very low assimilative capacity, or

tolerance, for phosphorus before changes in ecosystem structure and function occur.

C The well-documented phosphorus impacts in WCA2A have taken place since the

discharge of phosphorus-rich water through the S-10 structures beginning about

1960 (a period of about four decades). There is no information available concerning

low-level additions of excess phosphorus for a century or more.

• The nutrient dosing studies and observational studies described below indicate that

total phosphorus concentrations above 10 ppb have been shown to cause impacts to

native Everglades periphyton and macrophytes such as Utricularia purpurea that are

adapted to low phosphorus conditions. The best available scientific information 

indicates that average TP concentrations greater than 10 ppb, in general, can be
6

expected to be inadequate for long-term protection of the Class III-A designated

use. Therefore the Tribe’s adopted numeric phosphorus criterion of 10 ppb is not

overly protective.

• Currently available scientific information reviewed also indicates that the Tribe’s

proposed numeric criterion of 10 ppb is protective of the Class III-A use and the

native Everglades periphyton and macrophytes. Although some data have identified

long-term phosphorus concentrations within the Everglades as low as 5.0 ppb,

EPA’s review identified no currently available published scientific information

documenting changes in the natural flora or fauna resulting from total phosphorus

concentrations in the 5 ppb to 10 ppb range. If new data or information are 

presented in the future that demonstrate that 10 ppb is not protective of the Class

III-A use, the Tribe should revise the criterion accordingly.

Therefore, USEPA has determined that the 10 ppb total phosphorus criterion is protective

of the Class III-A designated use, is reasonable, and is scientifically defensible.

REVIEW OF RELEVANT SCIENTIFIC INFORMATION

Phosphorus is a nutrient that is essential to the growth of organisms and is often the nutrient

that limits primary productivity in a water body. Phosphorus can exist in a water body as organic

and inorganic forms. Phosphorus cycles in aquatic environments from the organic and inorganic

state, and vice versa, with microorganisms playing a key role (Jones, 1996). Phosphorus data from

water bodies is typically reported as total phosphorus and inorganic soluble phosphate

(orthophosphate). The citations that follow include mention of these two forms. Phosphate is the

form that is considered to be readily available for biological uptake. 

In the summary that follows, the term “Everglades” is used to refer to the freshwater marsh

habitats, such as sawgrass marsh, wet prairies and sloughs, in the greater Everglades system. The

geographic area includes Loxahatchee National Wildlife Refuge (the Refuge), Everglades National

Park (the Park), the Holeyland, the Rotenberger Tract, and all of the Water Conservation Areas

(2A, 2B, 3A and 3B). The water quality and ecology of the Tribe’s Class III-A waters are

generally consistent with the water quality and ecology found in the greater Everglades system.

1- Reference conditions in the Everglades marsh ecosystem.

The Everglades is a nutrient poor (oligotrophic) wetland, with natural populations of plants

and animals adapted to extremely low nutrient conditions. A reasonable approximation of longterm average surface water total phosphorus concentration is 10 ppb. The smallest but most widely

distributed plant community in the Everglades is an assemblage of micro-algae referred to

collectively as periphyton. Everglades periphyton generally is comprised of three major divisions or

groups: diatoms, blue-green algae and green algae (Browder et al., 1994). Periphyton exhibits

three growth forms in the Everglades: benthic (growing on the soil surface), epiphytic (growing

attached to rooted vegetation) and floating (growing on the water surface sometimes in association

with other floating vegetation such as Utricularia purpurea) (McCormick et al. 1999). These
7

periphyton mat communities are found throughout the unimpacted Everglades marsh, especially in

open water areas, sloughs and wet prairies. These mats, often referred to as calcareous mats, are

known to be extremely sensitive to phosphorus enrichment. The widespread distribution of

floating periphyton mats throughout the Everglades as observed during 1995-1996 is presented by

Stober et al. (1998). 

Periphyton provides multiple functions in the marsh ecosystem. These have been

summarized by Browder et al. (1994), McCormick et al. (1998) and McCormick et al. (1999). 

Everglades periphyton: accounts for much of marsh primary productivity in wet prairies and

sloughs; provides habitat for aquatic animals such as invertebrates; along with macrophyte detritus,

forms the base of the Everglades aquatic food web; is the major source of oxygen for fish and other

animal life in sloughs and wet prairies; maintains low water TP concentrations; plays a role in

cycling of nitrogen, phosphorus, carbon and oxygen; and affects formation of marl soils.

Everglades plant communities, along with the factors contributing to plant community

distribution and change, have been studied extensively. Recent vegetation classification maps have

been published for Loxahatchee National Wildlife Refuge, WCA2A, and the Shark River Slough

portion of Everglades National Park. The oligotrophic Everglades marsh system contains a mosaic

of macrophyte communities, such as sloughs, wet prairies and sawgrass marshes, all of which are

adapted to low nutrient conditions. This mosaic, which provides a diverse array of habitats for

animals, is an important defining characteristic of the Everglades. Wet prairies encompass a group

of plant communities generally described by soil type and dominant plant species. Wet prairies on

peat soil are generally characterized by spikerush (Eleocharis cellulosa), beak rush (Rhynchospora

tracyi), or maidencane (Panicum hemitomon), although dozens of plant species exist. Sloughs

generally refer to deeper water areas, often dominated by white water lilly (Nymphaea odorata),

floating hearts (Nymphoides aquatica), and spatterdock. Bladderwort (Utricularia purpurea or

Utricularia foliosa) are common submerged aquatic plants that provide a substrate for dense

periphyton mats. Wet prairies and sloughs in particular provide critical habitat for animals and

provide cover, nesting, and feeding sites for all animal groups. The wet prairie/slough habitat is

also the major feeding area in the Everglades for both wintering and nesting wading birds, especially

during the dry season when fish concentrations provide food for their nestlings (Gunderson and

Loftus, 1993). An important characteristic of unimpacted wet prairies and sloughs is their diversity

and the large number of native plant species (Olmstead et al, 1980; Olmstead and Loope, 1984;

Goodrick, 1974; Gunderson and Loftus, 1993). Multiple factors are responsible for the alteration

and maintenance of plant community structure in the Everglades, including nutrients, fire,

disturbance, and hydroperiod. Elevated water phosphorus concentrations or elevated soil

phosphorus concentrations in the Everglades are associated with elimination of submerged

vegetation species including the Utricularia-periphyton complex and expansion of nutrient-tolerant

macrophytes such as cattail or Sagittaria lancifolia (Arrowhead) into areas previously dominated

by sawgrass, sloughs or wet prairies. Historically, cattail was a minor component of the

Everglades landscape.

The following discussion of Everglades animals is taken largely from McCormick et al.

(1999). Aquatic invertebrates such as insects, snails and crayfish play an important role in the

Everglades food web. Most invertebrates feed directly on periphyton and/or plant detritus and are

then consumed by other animals. Invertebrates tend to be concentrated in periphyton-rich habitats
8

such as sloughs or wet prairies where dissolved oxygen is plentiful and food is more readily

available. Fish are a key link between invertebrates and predators, such the wading birds for

which the Everglades is widely renown. Fish biomass in the natural (oligotrophic) Everglades is

low relative to other wetlands. Turner et al. (in press) report that the natural condition in the

oligotrophic Everglades is one of a high periphyton standing stock, but low invertebrate and fish

standing stock.

The conditions described above are representative of unimpaired Miccosukee Tribal Waters. 

SFWMD has produced a classified vegetation map of northern WCA3A dated 1 July 1997. This

map was based on September 1994 and June 1995 color infrared aerial photographs, and involved

extensive ground-truthing (see Doren et al., 1999 for methods). The vegetation communities

within the Tribal Waters indicative of unimpaired conditions include a mosaic of sawgrass marsh

and wet prairies dominated by maidencane or spikerush. In addition, USEPA made visual

observations of the Tribal Waters by airboat on July 30, 1998 and by helicopter on November 13,

1998. 

2- The Everglades marsh system is extremely oligotrophic. Un-impacted interior portions

of the Everglades marsh have long-term average water column phosphorus concentrations of

approximately 10 ppb or less. 

Relevant scientific literature: Gleason et al., 1974b; Gleason et al., 1975a; Millar, 1981; Swift and

Nicholas, 1987; Flora et al., 1988; Scheidt et al., 1989; Davis, 1991; Walker, 1991; SFWMD, 1992;

Reddy et al., 1993; Richardson et al., 1994; Walker, 1995; McCormick et al., 1996; Walker, 1997a;

Richardson et al., 1997; Vaithiyanathan et al., 1997; Stober et al., 1998; McCormick et al., 1999. 

Long-term average concentrations of 10 ppb or less have been documented repeatedly

throughout the Everglades system, including Loxahatchee National Wildlife Refuge, Water

Conservation Area 2 (WCA2), Water Conservation Area 3 (WCA3), and Everglades National

Park. These complementary and corroborative data come from several independent studies

conducted by different investigators spanning a time-frame of three decades. These data come from

several independent analytical laboratories, including South Florida Water Management District

(SFWMD), Florida Department of Environmental Protection (FDEP), Duke University, the 

National Park Service, and the Florida International University Southeast Environmental Research

Program (FIU SERP).

Surface water phosphorus concentrations within the Everglades fluctuate naturally with

water conditions. Marsh phosphorus concentrations have been shown to vary with water depth,

with higher concentration excursions occurring during periods of low water or marsh drying

(Walker, 1997a; McCormick et al., 1999). McCormick et al. (1999) reported that occasional high

P concentrations at Everglades reference stations can be attributed to difficulty in collecting water

samples that are not contaminated by flocculent sediment when water depths are low (a few inches),

P released as a result of oxidation of exposed soils, or mobilization of P with fires. This represents

recycling within the marsh internal phosphorus pool, as opposed to marsh exposure to additional

phosphorus from external sources. In spite of this internal cycling, 10 ppb is a reasonable

approximation of long-term average or median phosphorus concentrations at Everglades reference

stations. 
9

Some water samples from the Everglades marsh that are analyzed for phosphorus are below

the limits of analytical detection. For example, the phosphorus analytical limit is 4 ppb for the

SFWMD laboratory and varies across laboratories. In these cases, the low end of the distribution

of phosphorus concentration at a sampling location is artificially truncated, and the actual median or

average phosphorus concentration at a location would in reality be even lower than the reported

median or average.

In a study of nutrient uptake and rates of nutrient deposition in WCA2A from 1973-1974,

Gleason et al. (1974b) documented phosphorus gradients downstream of the S-10 structures, with

background orthophosphate concentrations of 2 ppb.

During 1974 Gleason et al. (1975a) studied the effect of agricultural runoff on algal

communities at 5 wet prairie marsh stations within the Loxahatchee National Wildlife Refuge. The

orthophosphate phosphorus concentration reported for all of the 57 water samples collected was

less than 2 ppb. 

Swift and Nicholas (1987) summarized 1977-1983 water quality throughout LNWR,

WCA2A and WCA3A interior marsh sites. They reported mean total phosphate concentrations of

14 ppb for LNWR, 11 ppb for WCA2A and 9 ppb for WCA3A, with a grand mean of 11 ppb. 

Swift (1981) summarized average total dissolved phosphate concentration at these same

interior marsh sites from 1978-1979. The average total dissolved phosphate concentration at

interior marsh sites within LNWR, WCA2A and WCA3A was 2 to 5 ppb.

Walker (1995, figure 1) presented surface water mean TP concentration at water control

structures and marsh locations throughout the Everglades system. Mean TP concentration at

remote marsh stations away from alligator ponds within Everglades National Park ranged from

5.2 ppb at P-37 to 10.8 ppb at P-35 (statistical summary used for preparation of Figure 1 received

from the author). The grand mean of the eight station means was 8.3 ppb.

Grimshaw et al. (1997) reported 8 ppb as the 1994-1995 mean surface water TP

concentration at an unenriched slough site within WCA2A.

In a 1991-1996 study of WCA2A sloughs, Vaithiyanathan et al. (1997) found an average

water column dissolved phosphate concentration of 5 ppb (n=2557) and total phosphorus (TP)

concentration of 9 ppb (n=1659), with individual TP concentration measurements ranging from 2 to

20 ppb.

In a summary of a 1992-1996 nutrient dosing study in WCA2A, Richardson et al. (1997,

pages 15-32 and 15-44) reported mean 1993-1996 surface water TP concentrations at 16 locations

in the control area ranging from 8.8 ppb to 12.1 ppb, with a grand median of 9.1 ppb and a grand

mean of 10.9 ppb.

Walker (website:“http://www2.shore.net/~wwwalker/clearwtr/maps/sld010.htm, 04/04/98)

depicted TP in marsh surface water sites and water control structures throughout the Everglades
10

from 1992-1996. Geometric mean TP concentration for 1992-1996 was 10 ppb or less at all 14

marsh stations within LNWR, all 9 marsh stations within ENP, and all 12 marsh stations within

WCA2A or WCA3A that are away from sources of phosphorus enrichment.

McCormick et al. (1999) summarized surface water TP at interior marsh locations

throughout LNWR, WCA2A, WCA3A, and ENP. The median for each of the eight stations ranged

from about 4 to 10 ppb. The lowest median of about 5 ppb (n=100) was for WCA3A station CA3-

15.

In 1991 the best available surface water TP data (data source: SFWMD) were used to

determine the surface water TP condition that existed from 1979-1988 at water structures

discharging into Everglades National Park and at interior marsh stations within Loxahatchee

National Wildlife Refuge. These data became the basis for phosphorus limits or levels intended to

maintain the water quality condition that existed from 1979-1988 in order to protect the

oligotrophic marsh system including the associated plants and animals within the Refuge and the

Park. The development of and scientific basis for these water column phosphorus limits or levels is

described in SFWMD (1992) and Walker (1997), and is summarized in the next two paragraphs.

Phosphorus limits for inflows to Everglades National Park were derived in 1991. Attaining

these concentrations would continue to provide the Park with the quality of water that existed from

1979-1988. These apply to the annual flow-weighted mean TP concentration of inflows

composited across the five water delivery structures to Shark River Slough (the S-12 structures and

S-333). Although the required phosphorus limits vary from a flow-weighted mean of about 13 ppb

during dry years to about 8 ppb during wet years, if attained these limits would provide Shark

River Slough a long-term average flow-weighted mean inflow TP concentration of approximately 8

ppb. Phosphorus limits were also established for water delivered to the Taylor Slough and Coastal

Basin portion of the Park. Attaining these limits is expected to provide these portions of the Park

with a long-term average flow-weighted mean inflow TP concentration of 6 ppb.

In addition, separate marsh water column phosphorus levels were derived in 1991 for

Loxahatchee National Wildlife Refuge based on historic data from SFWMD at 14 interior marsh

stations. To account for the observed correlation between marsh total phosphorus concentration

and water depth (as determined by stage) the phosphorus concentration levels (determined monthly)

vary with the average interior water level on the date of sample collection. Although the required

phosphorus levels vary from 17 ppb at low water depth to 7 ppb at high water depth, attaining these

concentrations would be expected to provide the Refuge with a long-term geometric mean

concentration of approximately 7 ppb TP at the 14 interior marsh stations.

3- Phosphorus is the primary limiting nutrient in the oligotrophic Everglades marsh

system.

Relevant scientific literature: Stewart and Ornes, 1975; Stewart and Ornes, 1983; Swift, 1984;

Swift and Nicholas, 1987; Flora et al., 1988; Hall and Rice, 1990; Davis, 1991; Koch and Reddy,

1992; Grimshaw et al., 1993; Vymazal et al., 1994; Craft et al., 1995; Craft and Richardson, 1997;

Vymazal and Richardson, 1995; McCormick and O’Dell, 1996; Vaithiyanathan et al., 1997a;

Daoust and Childers, 1999.
11

Investigators have used two approaches to conclude that phosphorus is the limiting nutrient

in unenriched portions of the marsh system. The first approach is identifying nutrient ratios within

water, periphyton tissue and macrophyte tissue (Swift, 1984; Swift and Nicholas, 1987; Davis,

1991; Koch and Reddy, 1992; Grimshaw et al., 1993; Daoust and Childers, 1999). For example, in

a 1991-1996 study of WCA2A sloughs, Vaithiyanathan et al. (1997a) concluded that nutrient ratios

in surface water and in the periphyton and macrophyte tissues suggest strong P-limitation in the

Everglades sloughs. (Page 5-21).

Daoust and Childers (1999) studied the relationships between tissue nutrient content,

species productivity, and species abundance for seven plant species in sawgrass marsh or wet

prairies. They found that the dominant plants in both communities (Cladium jamaicense in the

sawgrass community, and Eleocharis spp. and Sagittaria lancifolia in the wet prairie) are strongly

limited by phosphorus availability. They concluded that although no single environmental factor is

responsible for controlling all species that occur, a majority of the plant species within this system

are limited by phosphorus availability.

The second approach is nutrient dosing experiments (Stewart and Ornes, 1975; Stewart and

Ornes, 1983; Flora et al., 1988; Hall and Rice, 1990; McCormick and O’Dell, 1996). In a 1983-

1984 nutrient dosing study in an Everglades National Park wet prairie dominated by Eleocharis

spp. and Utricularia spp. (Flora et al., 1988; Hall and Rice, 1990), one flow-through channel was

dosed with phosphate only for one year at an average concentration of 27 ppb while a second

channel was dosed with nitrate only at an average of 85 ppb. The background concentrations in the

adjacent reference sites averaged 6 ppb phosphate and 11 ppb nitrate. In the phosphate only

channel, plant tissue phosphorus was increased, Utricularia was eliminated, Panicum and

Sagittaria became the dominant macrophytes, plant biomass was increased, periphyton phosphorus

content changed and the native periphyton community was lost. These changes were not observed

in the channel dosed with nitrate only or the reference sites. All treatments and the reference site

were exposed to the same hydroperiod and water depth. 

4- Impacts of phosphorus enrichment: microbial processes.

Relevant scientific literature: Maltby, 1985; Amador et al., 1992; Lean et al., 1992; Amador and

Jones, 1993; Koch-Rose et al., 1994; Stober et al., 1996; Stober et al., 1998; McCormick et al.,

1999; Newman et al., in press.

McCormick et al. (1999 page 3-13) summarized the importance of microbes in wetland

systems as follows: “Wetlands host complex microbial communities including bacteria, fungi,

protozoa and viruses. The size and diversity of microbial communities are related directly to the

quality and quantity of the resources (i.e., nutrients, energy sources) available in the system. 

Microbial biomass and activity is highest in habitats where these resources are concentrated,

including periphyton mats, plant litter, and surface soils. Microbial processes regulate major

nutrient cycles in wetlands and, therefore, play an important role in determining water quality and

ecosystem productivity.” Microbial populations regulate the decomposition of organic matter and

the cycling of nutrients, including carbon, nitrogen, and phosphorus. Increasing water column

phosphorus or soil phosphorus has been implicated as cause for the disruption of various microbial
12

processes within the Everglades system. Lean et al. (1992) in an Everglades nutrient threshold

research plan, stated that “Sufficient data from the Everglades and other wetland ecosystems exist

to indicate that microorganisms (algae, bacteria) and their metabolic influences on organic detrital

and soil components are critical to the retention, cycling, and biological impacts of phosphorus. 

Organisms with the fastest turnover rates respond most rapidly to P enrichments. Their growth

rates and composition provide initial indicators of imbalance.” (page 7).

In a nutrient dosing study performed in a wet prairie within Everglades National Park during

1983 and 1984, Maltby (1985) deployed cellulose strips to observe the effects of nutrient loadings

on decomposition profiles in the water column and peat. He observed that cellulose decomposition

within the water column was accelerated by nitrate and phosphate dosed together and by phosphate

alone but not by nitrate alone, and that the decomposition profile increased sharply in the peat

within areas where P had been added. He stated that nutrient addition “may elicit marked

acceleration of decomposition not only of litter but also of organic matter stored in the sedimentary

peat system. It is impossible to be certain that this will not result in further release of nutrients

previously fixed by the peat and a progressive instability developed in the ecosystem” (page 457).

In studies of phosphate and phosphorus removal by peat soils from Everglades National

Park, Amador et al. (1992), Jones and Amador (1992), and Amador and Jones (1992) found that

microbial processes play a role in determining how much phosphorus Everglades peat can store,

continued exposure to water containing high P concentrations significantly decreased the available P

storage capacity of Everglades soils, these soils have a finite ability to remove and store

phosphorus, and P pollution may have a marked, long-term effect on microbial respiration in

organic soils with low P content.

Phosphatase enzymes, such as alkaline phosphatase, have been used as a sensitive indicator

of phosphorus enrichment in aquatic systems (Jones, 1996; Newman et al., in press). Stober et al.

(1998) used alkaline phosphatase activity in surface water as a sensitive indicator of phosphorus

condition. During 1995 and 1996 marked gradients were observed throughout the Everglades

marsh, with the interior of LNWR and ENP having the highest alkaline phosphatase activity

(indicative of a condition void of readily available phosphorus). The area that consistently had the

lowest alkaline phosphatase activity (indicating that phosphorus within the water column was in a 

readily available form) was the northern portion of WCA3A and WCA2A adjacent to canals

delivering water of high phosphorus content. 

McCormick et al. (1999) summarized the impact of increased P loading to the Everglades

on microbial and biogeochemical processes. P loading has been shown to affect the quality and

quantity of organic matter, rates of nutrient accumulation, microbial biomass and community

composition, and biogeochemical cycling. Moreover, P enrichment has been shown to initiate a

series of effects on the cycling of carbon and nitrogen, as well as a shift in the system from an

aerobic environment where oxygen is readily available to an anaerobic environment where oxygen is

lacking. 

5- Impacts of phosphorus enrichment: periphyton community impacts. 

Scientific literature describing Everglades periphyton communities, their function and the impacts of
13

phosphorus include the following: Hunt, 1961; Brock, 1970; Gleason and Spackman, 1974; 

Wilson, 1974; Wood and Maynard, 1974; Gleason et al., 1975b; Swift and Nicholas, 1987; Flora et

al., 1988; Hall and Rice, 1989; Belanger et al., 1989; Grimshaw et al., 1993; Raschke, 1993; 

Browder et al., 1994; Craft and Richardson, 1994; Craft et al., 1995; McCormick et al., 1996; 

McCormick and O'Dell, 1996; McCormick et al., 1997; Vaithiyanathan et al., 1997; Vaithiyanithan

and Richardson, 1998; McCormick et al., 1999.

Periphyton is an important defining characteristic of the Everglades ecosystem. 

The smallest but most widely distributed plant community in the Everglades is an

assemblage of micro-algae referred to collectively as periphyton. Everglades periphyton generally is

comprised of three major divisions or groups: diatoms, blue-green algae and green algae (Browder

et al., 1994). Periphyton exhibits three growth forms in the Everglades: benthic (growing on the

soil surface), epiphytic (growing attached to rooted vegetation) and floating (growing on the water

surface sometimes in association with other floating vegetation such as Utricularia purpurea) 

(McCormick et al., 1999). These periphyton mat communities are found throughout the

unimpacted Everglades marsh, especially in open water areas, sloughs and wet prairies. The

widespread distribution of floating periphyton mats throughout the Everglades as observed during

1995-1996 is presented by Stober et al. (1998). 

The designated use for Class III-A Waters of the Tribe is “preservation of native plants and

animals of the natural Everglades ecosystem”. This clearly includes preservation of natural

periphyton communities, in so far as periphyton are native plants.

Periphyton provides multiple functions in the marsh ecosystem. These have been

summarized by Browder et al. (1994), McCormick et al. (1998) and McCormick et al. (1999). 

Everglades periphyton: accounts for much of marsh primary productivity in wet prairies and

sloughs; provides habitat for aquatic animals such as invertebrates; along with macrophyte detritus,

forms the base of the Everglades aquatic food web; is the major source of oxygen for fish and other 

animal life in sloughs and wet prairies; maintains low water TP concentrations; plays a role in

cycling of nitrogen, phosphorus, carbon and oxygen; and affects formation of marl soils.

Periphyton photosynthesis and respiration play an important role in controlling surface water

dissolved oxygen concentrations. (Hunt, 1961; Gleason and Spackman, 1974, Wilson, 1974,

Belanger et al., 1989; McCormick et al., 1997; Vaithiyanathan et al., 1997).

Vymazal et al. (1994) stated that “Highly calcified periphyton, dominated by blue-green

algae, is the primary source of oxygen in open water habitats and for most of the Everglades

ecosystem” (page 76). 

Vaithiyanathan et al. (1997a) in a 1991-1996 study of WCA2A sloughs found that the

dissolved oxygen concentration on the surface of the periphyton mat was substantially higher than

the water column concentration, reflecting the intense photosynthetic activity of the Utriculariaperiphyton complex. They concluded that: periphyton photosynthesis is a major source of oxygen

production in Everglades sloughs, periphyton regulate water column TP concentrations, nutrient
14

ratios in surface water and in the periphyton and macrophyte tissues suggest strong P-limitation,

and “preservation of the Everglades sloughs is strongly related to the integrity of the periphyton

mat” (page 5-22).

Belanger et al. (1989) described a 1985 oxygen budget study in enriched and unenriched

marsh habitats with WCA2A. They found strong surface water diurnal oxygen variations in slough

and sawgrass areas, with extremely low surface water dissolved oxygen and frequent anoxia in the

enriched cattail area. The periphyton mat was the major source of oxygen at the slough site. They

stated that pristine slough areas are essential for oxygen production, and loss of these areas due to

phosphorus enrichment could have serious ecological consequences, such as lost feeding areas for

fishes and birds.

Numerous scientists have stated that periphyton is an integral component of the oligotrophic

marsh system. In their external panel peer-review report to FDEP, Hopkinson et al. (1998, page

20) stated that “The periphyton community is a particularly important component of sloughs in the

Everglades, and is often associated closely with floating macrophytes (e. g., Utricularia spp.) which

serve as physical substrata for growth. Periphyton contributes a substantial portion of the primary

production in the Everglades and appears to be the primary food resource for many

macroinvertebrates. Periphyton may be of higher importance in Everglades food webs than

macrophytes because of its high rate of production and turnover. While organic matter derived

from sawgrass and other macrophytes is consumed primarily after it dies and becomes the basis of a

relatively inefficient detritus-based food web, periphyton is consumed while living, providing a

richer, more direct, and probably more efficient, transfer of organic matter and energy to

invertebrate and vertebrate consumers. Loss of periphyton or shifts in species composition toward

forms that are less palatable to consumers are likely to create a significant change in Everglades

food webs”.

Vaithiyanathan et al. (1997, page 5-1) summarized the multiple functions of periphyton and

concluded that “The integrity of the periphyton mat is crucial to the protection of the Everglades

slough community”. 

Richardson et al. (1997, page 17-28) stated that “Any changes in Eleocharis spp. may be

the most significant ecological change in the slough community since it is the dominant plant and an

important substrate for periphyton.” 

Grimshaw et al. (1997, page 19) stated that “Periphyton communities are critical structural

and functional components of the Florida Everglade wetland ecosystem.”

McCormick and Stevenson (1998, page 730) stated that “...the loss of the oligotrophic

periphyton assemblage represents a significant ecological change because periphyton represents a

habitat and food source for other species as well as an important part of major biogeochemical

cycles.” 

The South Florida Ecosystem Restoration Task Force adopted a series of success indices in

order to define ecosystem restoration goals, track ecosystem health, and measure the effectiveness

of restoration efforts. The Science Sub-Group of the Task Force (1997) established 14 ecologic or
15

precursor success criteria for ecosystem protection and restoration. These specific success criteria

were selected based on several years of collaborative scientific effort, representing the distillation of

the best professional judgement of dozens of scientists. One of the adopted ecologic success

criteria is “restored natural taxonomic composition of periphyton communities”. 

McCormick and O’Dell (1996, page 465) concluded: “Periphyton is an important biological

component of the Everglades ecosystem and may represent one of the most sensitive indicators of

eutrophication in the marsh. The periphyton assemblage that dominates oligotrophic areas of the

Everglades was replaced by a taxonomically distinct assemblage in response to relatively small

increases in water column phosphorus concentration above background levels, which ranged

between 5 and 10 ug/L in WCA2A during this and previous work (McCormick et al., 1996). 

Because of its ubiquity and significance to fundamental ecosystem processes (i.e., energy fixation,

nutrient cycling, and soils formation) in the Everglades, the native periphyton assemblage represents

an important indicator of ecosystem condition, and its loss has several implications for the success

of ecosystem restoration and management efforts in this wetland. Most importantly, our findings

indicate that restoration measures must reduce and maintain phosphorus concentrations in the

marsh close to background levels to preserve the oligotrophic characteristic of the Everglades.” 

McCormick et al. (1998) studied periphyton biomass and productivity in WCA2A during

1994-1995. They noted many functions that periphyton communities provide, and that periphyton

appears to play a critical role in sequestering phosphorus from the water column and maintaining

the oligotrophic status of this wetland. They noted that eutrophication has caused a decline in

Everglades periphyton biomass, productivity, and nutrient retention, and a shift in species

composition. They hypothesized that functional changes resulting from this decline may affect

other biotic and abiotic components of the marsh including changes in the food web, reduced

suitability of eutrophic habitats for some native species, and a reduction in the capacity of the marsh

to assimilate added phosphorus without causing further biological changes. They stated that (page

206) “...it is increasingly clear that the maintenance of the native periphyton assemblage is essential

to the normal functioning of the Everglades and, thus, is critical to the success of efforts to restore

and manage this wetland in a sustainable manner.” 

Vaithiyanithan and Richardson (1998) studied the biogeochemical characteristics of two

WCA-2A sloughs. They noted that the decline in periphyton mat cover reported in parts of the

Everglades subjected to eutrophication will result in a decrease in the water column dissolved

oxygen concentration and may also lead to other ecosystem changes by enhancing light availability

to the slough bottom. They stated that increased light availability may also lead to the establishment

of other macrophyte species uncharacteristic of the oligotrophic sloughs. They concluded (page

1449): “Preservation of the Everglades sloughs is thus strongly related to the integrity of the

periphyton mat”. 
16

Phosphorus enrichment changes or eliminates the native Everglades periphyton communities.

Increasing water column phosphorus has been repeatedly shown to cause numerous

changes to the periphyton community, including changed phosphorus content, changed biomass,

loss of native species such as diatoms that are indicators of oligotrophic conditions, or

establishment of a different community with changed spatial extent and species composition.

Gleason et al. (1975a) investigated the effect of agricultural runoff on the periphyton

communities observed at five Refuge wet prairie marsh sites during the spring of 1974. The two

marsh stations in contact with agricultural runoff were distinct from the other stations with respect

to diatoms, green algae, blue-green algae, and periphyton biomass and phosphorus content. They

stated that the “correlation between high biomass, high phosphorus and close proximity to the

peripheral canal suggests that the high biomass and high phosphorus concentrations are probably, in

part, a response to higher nutrient concentrations near the rim canal.” (page 63). 

Swift (1984) reported on water quality and periphyton relationships observed during 1978-

1979 throughout Loxahatchee National Wildlife Refuge and WCAs 2A and 3A. He found that

periphyton growth on glass slides was significantly affected by site differences in marsh water major

ion content, pH, alkalinity and phosphorus concentration. Marsh water TP was the controlling

factor regulating periphyton growth. Elevated water TP increased periphyton biomass, increased

periphyton phosphorus content, and altered community species composition toward pollutiontolerant species. 

In an analysis of periphyton data collected by Swift from 1978-1983 in WCA2A, WCA3A,

and WCA3B, Grimshaw et al. (1993) found strong statistically significant correlations between

mean dissolved phosphorus concentrations in the marsh water column and the mean phosphorus

content and mean relative abundance of eutrophic algae in periphyton communities within WCA2A. 

They also found statistically strong significant correlations between total, dissolved and inorganic

phosphorus in the water column with the mean phosphorus content of periphyton communities

when WCA3A and WCA3B were included.

A 1983-1984 nutrient dosing study in an Everglades National Park wet prairie (Flora et al.,

1988; Hall and Rice, 1990) documented changes in the algal community in response to phosphorus

enrichment. An average addition of 14 ppb phosphate over a 63-day period resulted in the

elimination of the native periphyton mat, which continued to remain at the adjacent reference sites

that were not subjected to nutrient addition. Continued dosing caused an increase in periphyton

biomass and a succession of changes in periphyton community composition. The average

background phosphate concentration for the study duration was 6 ppb.

Raschke (1993) reported the results of a 1990-1991 study of diatom community response

along a soil phosphorus gradient within Everglades National Park downstream of water control

structure S-12C. A strong correlation was found between sediment phosphorus concentration

and diatom community mean diversity. He concluded that the periphyton diatom community was

responding to sediment phosphorus increases as evidenced by changes in the number of diatom

species, mean diversity, and occurrence of periphyton species that are indicators of phosphorus

enrichment. The TP concentration of water discharged to the marsh through the S-12C structure
17

had an annual median ranging from 7 ppb to 14 ppb during the previous 12 years. From 1978 to

1989 water TP at S-12C had increased from about 7 ppb to 12 ppb. 

McCormick and O’Dell (1996) quantified periphyton responses to phosphorus in

WCA2A. During 1995 they sampled transect stations along a phosphorus gradient while

simultaneously performing a phosphorus enrichment experiment in a pristine slough. Phosphorus

content of periphyton mats was strongly correlated with surface water TP, and periphyton mat

species composition changed along the phosphorus gradient. They concluded that these changes

were caused by phosphorus concentrations. McCormick and O’Dell also stated that:

“The cyanobacterial-diatom assemblage characteristic of oligotrophic conditions in the

Everglades was replaced by filamentous green algae at marsh stations where water-column

phosphorus concentrations exceeded 10 ug/L TP.” (page 464).

“Our study provides strong experimental evidence to support previous evidence that

relatively small increases in marsh phosphorus concentration are associated with

substantial changes in the Everglades periphyton assemblage.” (page 464).

“The loss of the calcareous cyanobacterial mat in response to phosphorus enrichment has

ramifications for several ecosystem processes in the Everglades. This mat can account for

more than 50% of the vegetative biomass in sloughs (Wood and Maynard, 1974,

Browder, et al. 1982) and represents an important substrate for invertebrate populations in

the marsh (Reark, 1961).” (page 465).

McCormick and O’Dell also mentioned: the role that this periphyton mat plays in

maintaining surface water oxygen in the marsh, with mat absence associated with protracted periods

of low dissolved oxygen or anoxia; its role in affecting availability of phosphorus and nitrogen; and

its role in forming marl soils in portions of the Everglades. They stated that changes in the

periphyton assemblage may have important implications for the Everglades food web. 

Pan et al. (1997, page 2-13) sampled 32 sloughs in WCA2A along a phosphorus enrichment

gradient during 1995 and found that diatom species composition, periphyton biomass, and physicochemical structure of periphyton assemblages all shifted relative to native assemblages as P loading

increased. “Changes in periphyton assemblages along the P gradients were evident at the

community, functional, and population levels”. They also stated that changes in algal species

composition are much more sensitive and predictable than algal biomass (chlorophyll a and

biovolume) in response to P loading. Cluster analysis of data separated the 32 sites along the P

gradient into 3 groups based on diatom species composition. Periphyton biomass and ash weight

decreased and the TP content of periphyton increased as water column TP increased from group I

(surface water TP mean 11.54 ppb) to group II (surface water TP mean 16.37 ppb). 

McCormick and Stevenson (1998) reported data from an experiment in which several

different concentrations of phosphate were added to nutrient dosing flumes as described in

Richardson et al. (1994). They stated that calcareous periphyton was reduced in waters averaging 5

ug/l soluble reactive phosphorus (SRP) above the background concentration of about 4 ug/L SRP. 

They noted that the observed periphyton mat cover varied over time taxonomically and chemically,
18

and the common characteristic of the phosphorus environment in which the calcareous mat did not

exist was that SRP was at least 5 ug/L greater than the concentration in the control treatment. 

In their 1999 Everglades Interim Report, SFWMD (McCormick et al., 1999) found that

controlled dosing studies combined with sampling along marsh phosphorus gradients in WCA-2A

indicate that periphyton species changes begin to occur at water column total phosphorus

concentrations of about 10 ppb. 

6- Impacts of phosphorus enrichment: water column dissolved oxygen. 

Relevant scientific literature: Hunt, 1961; Gleason and Spackman, 1974; Gleason et al., 1975a; 

McPherson et al., 1976; Scheidt et al., 1985; Belanger and Platko, 1986; Belanger et al., 1989;

McCormick et al., 1997.

Dissolved oxygen in pristine Everglades wet prairie and slough communities often exhibits a

strong diel cycle, with concentration at a particular location ranging from 0 mg/l in early morning to

over 12 mg/l in late afternoon. In contrast, oxygen levels in nutrient-rich locations within WCA2A

have been shown to often be undetectable and rarely exceed 2 mg/l, with protracted periods of

oxygen depletion. Although wetland plant and animal species are well adapted to the natural diel

cycle of anoxia that often characterizes pristine marsh ecosystems, it is improbable that many native

Everglades fish species are tolerant of prolonged oxygen depletion.

McCormick et al. (1997) summarized marsh diel dissolved oxygen data at minimally

nutrient-impacted sites (reference sites) in WCA1, WCA2A, and WCA3A and at a phosphorusimpacted site in WCA2A. They found that all reference sites were characterized by a strong diel

variation in water column oxygen (0-12 mg/L) while oxygen concentration at the phosphorusimpacted site rarely exceeded 2 mg/L and were often undetectable. Rates of gross primary

productivity and aerobic respiration were higher, with average P/R ratios near unity (1.0) at

reference sites, as compared to the enriched site (P/R<0.5). Nutrient enrichment was associated

with reduced primary productivity, a shift towards increasing community heterotrophy and

protracted periods of oxygen depletion. They also state that the “intense photosynthetic activity of

the periphyton-Utricularia mats represents the major source of aquatic O2 production in the

Everglades,...”(page 124) and the “loss of the native periphyton-Utricularia mat from enriched

sloughs corresponds with a shift towards a heterotrophic system (P/R<1) and prolonged periods of

O2 depletion (<2 mg/L) in the water column.” (page 127).

7- Impacts of phosphorus enrichment: soil.

Relevant scientific literature: Koch, 1991; Reddy et al., 1991; Koch and Reddy, 1992; Jones and

Amador, 1992; Reddy et al., 1993; Craft and Richardson, 1993; Debusk et al., 1994; Qualls and

Richardson, 1995; Doren et al., 1996; Walker and Kadlec, 1996; Newman et al., 1997; Craft and

Richardson, 1997; Richardson et al., 1997; Vaithiyanithan and Richardson, 1997; Stober et al.,

1998; Reddy et al., 1998.

Increasing water column phosphorus concentration over sufficient duration has increased
19

Everglades soil phosphorus concentrations. Soil TP gradients have been documented throughout

the Everglades system with the highest concentrations observed at soils downstream of structures

discharging high phosphorus water. This soil enrichment phenomenon has been documented

within:

LNWR- [Richardson et al., 1990; Doren et al., 1996; Newman et al., 1997; Stober et al., 1998];

WCA2A- [Koch, 1991; Reddy et al., 1991; Koch and Reddy, 1992; Craft and Richardson, 1993;

Debusk et al., 1994; Qualls and Richardson, 1995; Doren et al., 1996; Craft and Richardson, 1997;

Richardson et al., 1997; Craft and Richardson, 1998; Vaithiyanithan and Richardson, 1997; Stober 

et al., 1998)]; WCA3A- [Doren et al., 1996; Stober et al., 1998]; and ENP- [Raschke, 1993;

Doren et al., 1996; Stober et al., 1998].

Craft and Richardson (1998) studied peat soil accretion and accumulation throughout the

Everglades. They found that unenriched areas of the Everglades possess some of the lowest rates

of P accumulation of peatlands in North America. In enriched areas of WCA2A, phosphorus

accumulation was eight times higher and soil accretion was three to five times higher than in

unenriched areas. They stated that even small anthropogenic P loadings may alter organic soil

accretion and nutrient accumulation. “Successful restoration of the Everglades will have to include

the elimination of anthropogenic nutrient loadings to limit the P enrichment zone from expanding

into existing unenriched interior areas and areas downstream of WCA2A.” (abstract)

Richardson et al. (1997) noted that the most nutrient-impacted area of the Everglades is

WCA2A, with 51% of the area showing increased soil P (page 14-3). 

Several investigators have documented a correlation between elevated soil TP and the

expansion of cattail into sawgrass or wet prairies (see below). Walker and Kadlec (1996)

developed a mass balance model to simulate phosphorus concentrations in waters and soils

downstream of Everglades Stormwater Treatment Areas. They proposed a soil threshold

phosphorus criteria of 540 to 990 milligrams per kilogram (mg/kg) as a surrogate for impacts on

ecosystem components which respond primarily to soil P, such as cattail expansion.

8- Impacts of phosphorus enrichment: macrophyte impacts.

Relevant scientific literature: Steward and Ornes, 1975a; Steward and Ornes, 1975b; Gleason et

al., 1975b; Davis, 1989; Flora et al., 1988; Walker et al., 1989; Richardson et al., 1990; Davis,

1991; Koch, 1992; Urban et al., 1993; Rutchey and Vilchek, 1994; Davis, 1994; DeBusk et al.,

1994; Jensen et al., 1995; Doren et al., 1996; Walker and Kadlec, 1996; Craft and Richardson,

1997; Newman et al., 1997; Stewart et al., 1997; Stober et al., 1998; Daoust and Childers, 1999.

The oligotrophic Everglades marsh system contains a mosaic of macrophyte communities,

such as sloughs, wet prairies and sawgrass marshes, all of which are adapted to low nutrient

conditions. This mosaic is an important defining characteristic of the Everglades. Wet prairies and

sloughs in particular provide critical habitat for animals and provide cover, nesting, and feeding sites

for all animal groups. The wet prairie/slough habitat is also the major feeding area in the

Everglades for both wintering and nesting wading birds, especially during the dry season when fish

concentrations provide food for their nestlings (Gunderson and Loftus, 1993). An important
20

characteristic of unimpacted wet prairies and sloughs is their diversity and the large number of

native plant species (Olmstead et al, 1980; Olmstead and Loope, 1984; Goodrick, 1974; Gunderson

and Loftus, 1993). Multiple factors are responsible for the alteration and maintenance of plant

community structure in the Everglades, including nutrients, fire, disturbance, and hydroperiod. 

Elevated water phosphorus concentrations or elevated soil phosphorus concentrations in the

Everglades are associated with elimination of submerged vegetation species including the

Utricularia-periphyton complex and expansion of nutrient-tolerant macrophytes such as cattail or

Sagittaria into areas previously dominated by sawgrass, sloughs or wet prairies. 

Ornes and Steward (1973) added phosphorus (10 milligrams per liter) and potassium to a

WCA3B sawgrass marsh for 22 weeks in order to simulate sewage effluent discharge. They

reported algal blooms and macrophyte community changes, including elimination of native 

submerged aquatic vegetation such as Utricularia spp. 

Gleason et al. (1975b) investigated the effect of agricultural runoff on the Everglades marsh. 

They looked at the effect of nutrient inputs on biomass and phosphorus concentrations in cattail and

sawgrass downstream of the S-10 structures within WCA2A. They noted that the two species

respond differently to added nutrients and concluded that “The differential growth response of the

two plant species to phosphorus enrichment offers an explanation for the invasion of sawgrass by

cattail in Area 2A below the S-10 structures.” (page 115).

A 1983-1984 nutrient dosing study in an Everglades National Park wet prairie (Flora et al.,

1988; Hall and Rice, 1990) documented changes in periphyton and emergent plant communities in

response to phosphorus enrichment. Within one year of phosphate addition at an average

concentration of 27 ppb the native Utricularia-periphyton assemblage had been eliminated and the

open water marsh which was previously dominated by Eleocharis spp. became dominated by dense

emergent stands of Sagittaria and Panicum. Plant tissue concentrations, biomass and community

composition were all changed within several months. The background phosphate concentration for

the study duration was 6 ppb.

From 1985 to 1990, Richardson et al. (1990) conducted a study of vegetation and habitats

within Loxahatchee National Wildlife Refuge and their relationships to water quality, quantity and

hydroperiod. Multi-variate analysis indicated that soil phosphorus rather than hydroperiod was the

primary factor controlling cattail distribution in the Refuge. 

Craft and Richardson (1997) studied relationships between soil nutrients and plant species

(sawgrass, cattail and other species) in WCA2A during 1989. They found that plant species

composition along a P enrichment gradient was highly correlated with soil P content, but not with

sodium or calcium. They concluded that “P, not Na, is the primary determinant of the observed

changes in macrophyte community composition in enriched areas of WCA2A” (page 231) and

“These findings support previous studies, which indicate that cattail encroachment into sawgrass

communities in northern WCA2A is caused, to a large extent, by P enrichment of the peat (Urban 

et al., 1993; DeBusk et al., 1994)” (page 232).
21

Newman et al. (1997) observed the spatial distribution of soil nutrients and plant species in

Loxahatchee National Wildlife Refuge during 1991. Of the 90 sites sampled, 66 sites consisted of

sloughs and sawgrass, while 24 were either cattail-dominated or had a significant cattail presence. 

“These 24 cattail sites were closest to the nutrient inflow areas and had the highest soil nutrient

concentrations” (page 1275).

From 1991-1993 Newman et al., (1996) studied the effects of nutrients (P and nitrate) and

hydroperiod on cattail, sawgrass and Eleocharis in controlled outdoor tanks. Their high treatment

consisted of nutrient additions to adjust ambient marsh water concentrations to 100 ppb phosphorus

and 1 milligram per liter (1000 ppb) nitrogen. Their low treatment increased the ambient P

concentration to 50 ppb with no adjustment made to the nitrate concentration. They observed that

cattail was enhanced by both elevated nutrient concentration and increased depth of flooding. 

Increased nutrients led to a significant dominance of cattail over sawgrass and Eleocharis, and this

dominance was further enhanced by increased flooding levels. They noted that the interaction

between nutrients and hydrology is important, and that restoration of Everglades vegetation

requires more natural hydroperiods as well as reduced nutrient inputs.

Grimshaw et al. (1997) compared the relative net primary productivity of periphyton

communities within WCA2A under emergent plant canopies typical of enriched and unenriched

Everglades habitats. The amount of photosynthetically active radiation reaching periphyton

communities was reduced only by 35% in sawgrass habitats but was reduced by 85% or more in

dense stands of cattail. The net primary productivity of periphyton in nutrient-rich cattail habitats

was severely reduced (by about 80%) as compared to open water habitats. The plant shading effect

suppressed periphyton photosynthesis. 

A 1990-1996 study of WCA2A found a significant positive correlation between cattail and

Sagittaria and several indicators of increased P, including soil TP (Richardson et al., 1997, page

14-28). They also found a significant negative correlation between sawgrass and soil TP as well as

surface water TP. As phosphorus enrichment increased, the number of macrophyte species typical

of the oligotrophic area showed a progressive decline, and nearly half of the macrophyte species

widespread throughout the unenriched Everglades were absent from the two most enriched sites

(page 14-44).

In a nutrient dosing study in WCA2A, Richardson et al (1997, chapter 17) found that:

Utricularia is generally not found at TP concentrations greater than 30 ppb; maximum densities of

Eleocharis elongata were reached in the un-walled control channel where TP averaged close to 10

ppb; a significant relationship was found between Eleocharis cellulosa and surface water TP

concentration with a significant decrease in density above 30 ppb after four years of P dosing;

“elevated TP concentrations above 20 ug/L demonstrates direct or indirect effects of elevated PO4

concentrations, which inhibits the survival of U. purpurea.” (Page 17-27); “Any changes in

Eleocharis spp. may be the most significant ecological change in the slough community since it is

the dominant plant and an important substrate for periphyton” (Page 17-28).

Walker and Kadlec (1996) developed a mass balance model to simulate phosphorus

concentrations in waters and soils downstream of Everglades Stormwater Treatment Areas. They

proposed a 0 to 10 centimeter soil threshold phosphorus criteria of 540 to 990 milligrams per
22

kilogram (mg/kg) as a surrogate for impacts on ecosystem components which respond primarily to

soil P, such as cattail expansion.

Wu et al. (1997) developed a probability model to test the effect of water depth and soil TP

concentration on the cattail invasion of WCA2A. They proposed a soil TP concentration of 650

milligrams per kilogram as a threshold above which accelerated cattail invasion occurs.

9- Impacts of phosphorus enrichment: food web changes and loss of wading bird foraging

habitat.

Relevant scientific literature: Bancroft et al., 1992; Hoffman, 1994; Gunderson and Loftus, 1993;

Fleming et al., 1994; Turner et al., in press.

Shallow, open water areas with low to moderate density emergent macrophytes are the

preferred foraging habitat for Everglades wading birds. Bancroft et al. (1992) documented the

importance of the Water Conservation Areas as foraging habitat for the wood stork, an endangered

species. They noted that the habitats used by wood storks generally are drying ponds, wet prairies,

and sloughs. The storks feed in these more open areas, where their foraging habitats are least

affected by submerged or emergent vegetation. 

Hoffman et al. (1994) studied wading bird foraging habitat in the Water Conservation Areas

from 1985-1988. They reported that great egrets, great blue herons, white ibises and wood storks

all avoided dense grass habitats, defined as continuous coverage of sawgrass, cattail, sedges, reeds

or grasses. They noted the importance of perpetuating slough and wet prairie habitats for wading

birds. Conversion of these open water or wet prairie plant communities to dense stands of

emergent nutrient-tolerant macrophyte species such as cattail constitutes a loss of preferred wading

bird foraging habitat.

Turner et al. (in press) reported that the natural condition in the Everglades is one of high

periphyton standing stock, but low standing stocks of invertebrates and fish. They also reported

that: enriched areas have a higher fish standing stock; “The data we present also suggest the

possibility of a trophic cascade that may lead to unanticipated changes in community structure

where nutrients are added” (page 20); and “Anthropogenic eutrophication in Everglades marshes

will lead to the loss of distinctive ecosystem features.” (abstract). 

Gunderson and Loftus (1993) presented food web diagrams for known trophic relationships

among the characteristic Everglades animals with a macrophyte base (Utricularia, Eleocharis,

sawgrass, beak rush, and Panicum) and a detritus/periphyton base. Macrophytes, periphyton and

detritus are at the bottom or base of both food webs. Invertebrates, insects, fish, birds, amphibians,

reptiles and mammals are found at higher trophic levels. Everglades phosphorus enrichment has

been shown to change detrital formation processes, and change periphyton and macrophyte

communities. Such changes at the food web base can be expected to change inter-relationships

among species across higher trophic levels. 
23

CONCLUSION

The Tribe has defined Class III-A waters within the Federal Reservation as "Those Tribal

water bodies which are used for fishing, frogging, recreation (including airboating), and the

propagation and maintenance of a healthy, well-balanced population of fish and other aquatic life

and wildlife. These waters have been primarily designated for preservation of native plants and

animals of the natural Everglades ecosystem." (page 19 of the Final Miccosukee Environmental

Protection Code, Subtitle B, dated December 19, 1997). In the section on water quality standards

for nutrients the Tribe states: “Nutrients: In no case shall nutrient concentrations of Tribal Class I or

Class III-A surface waters be altered so as to cause an imbalance in natural populations of aquatic

flora or fauna.” (page 9).

There is no single scientific study or publication that provides a complete synthesis of the

data and information regarding background Everglades phosphorus conditions and phosphorus

enrichment impacts. Rather, a great number of scientific publications and efforts provide relevant

pieces of information, which when considered collectively, provide a generally consistent and more

complete understanding.

The scientific information summarized above has been independently developed by different

scientists, in different studies, over different time frames, using different methods, in different areas

of the Everglades system. These scientists include consultants and individuals employed by but not

limited to SFWMD, USDA, NPS, USFWS, USEPA, USGS, Florida International University,

University of Florida, and Duke University. Generally, the results are complementary and

corroborative. There is no question that phosphorus enrichment in the Everglades causes direct and

indirect changes within this marsh ecosystem. Taken as a whole, these collective changes must be

reasonably viewed as systemic. That is, phosphorus enrichment at a marsh location changes not

only surface water phosphorus concentrations, but eventually also impacts plants and animals at that

location. The natural structure and function of the Everglades system becomes lost. Such changes

are directly contrary to the intent of the Class III-A designated use adopted by the Tribe.

The nutrient dosing studies and observational studies reviewed indicate that total

phosphorus concentrations above 10 ppb have been shown to cause impacts to native Everglades

periphyton and macrophytes such as Utricularia purpurea that are adapted to low phosphorus

conditions. The best available scientific information indicates that average TP concentrations

greater than 10 ppb, in general, can be expected to be inadequate for long-term protection of the

designated use defined by the Tribe. Therefore the Tribe’s adopted numeric phosphorus criterion of

10 ppb is not overly protective. 

The currently available data and information also indicates that the Tribe’s adopted numeric

phosphorus criterion of 10 ppb is protective of the Class III-A designated use. While in certain

portions of the Everglades system, long-term phosphorus concentrations are less than 10 ppb, the

scientific information reviewed did not demonstrate that a numeric phosphorus criterion of 10 ppb

would not be protective of the Class III-A designated use. For example, as summarized by Walker

(1995), the long-term phosphorus concentration at wet prairie marsh station P-37 with Everglades

National Park was 5.2 ppb. For WCA-3A, the SFWMD identified a total phosphorus median

concentration of 5 ppb of phosphorus (McCormick et al., 1999). However, EPA’s review
24

identified no currently available published scientific information documenting changes in the natural

flora or fauna of the Everglades System as a result of changes in the phosphorus concentrations in

the 5 ppb to 10 ppb range. If new data or scientific information are presented that demonstrate that

10 ppb is not protective of the Class III-A designated use, then the Tribe should revise the 10 ppb

standard accordingly.

In conclusion, the Miccosukee Tribe’s 10 ppb criterion for phosphorus meets the

requirements of 40 CFR §131.11 as it is protective of the Class III-A designated use and review of

available data shows that this value is scientifically defensible.
APPENDIX B
1

EVERGLADES NUTRIENT-RELEVANT REFERENCES

Compiled by D. Scheidt, USEPA, May 1999

Abtew, Wossenu. 1996. Evapotranspiration measurements and modeling for three wetland systems in

South Florida. Water Resources Bulletin, 32(3):465-473.

Abtew, Wossenu. 1997. Lysimeter study of evapotranspiration from a wetland. South Florida Water

Management District Department of Research Publication #274. West Palm Beach, Florida. 7 pp.

Abtew, W. and J. Obeysekera. 1994. Evapotranspiration of cattails (Typha domingensis). South

Florida Water Management District Water Department of Research Publication #147. West Palm Beach,

Florida. 21 pp. plus figures.

Abtew, Wossenu, and Nagendra Khanal. 1994. Water Budget Analysis for the Everglades Agricultural

Area Drainage Basin. Water Resources Bulletin 30:429-439.

Abtew, W., M. Chimney, T. Kosier, M. Guardo and J. Obeysekera. 1995. The Everglades Nutrient

Removal Project: A Constructed wetland designed to treat agricultural runoff/drainage. pp. 45-56 in

“Versatility of wetlands in the agricultural landscape”, Kenneth Campbell, editor. Published by the

American Society of Agricultural Engineers. 

Abtew, W., S. Newman, K. Pietro, and T. Kosier. 1995. Canopy Resistance Studies of Cattails. 

Transactions of the American Society of Agricultural Engineers 38(1):113-119.

Abtew, W., M. Chimney, and T. D. Fontaine. 1996. Particulate Phosphorus Fraction and Total

Suspended Solids Role in P Removal Strategy in the Inflow Waters of the Everglades. Paper No. 962128

written for presentation at the 1996 ASAE Annual International meeting, July 14-18, 1998, Phoenix,

Arizona. South Florida Water Management District. 12 pp.

Abtew, W., L. J. Lindstrom, and T. Bechtel. 1997. A Comparison of methods for estimating the mean and

variance of censored total phosphorus concentrations in South Florida rain. South Florida Water

Management District Technical Manuscript #352. West Palm Beach, Florida 33 pp.

Abtew, W., A. Cadogan, A. Ali, T. Kosier, G. Germain and D. Wilkins. 1998. Hydrologic Performance

of an Everglades Stormwater Treatment Area- STA6: A Constructed Wetland. South Florida Water

Management District Water Resources Evaluation Publication #362. West Palm Beach, Florida. 12 pp.

Ahn, Hosung. 1998. Estimating the mean and variance of censored phosphorus concentrations in Florida

rainfall. Journal of the American Water Resources Association 34(3):583-593.

Ahn, Hosung. 1998. Statistical Modeling of Total Phosphorus Concentrations measured in South Florida

Rainfall. South Florida Water Management District Technical Manuscript #358. West Palm Beach,

Florida. 20 pp. plus figures.

Ahn, Hosung. 1998. Outlier detection in total phosphorus concentration data from South Florida rainfall. 

 South Florida Water Management District Technical Manuscript #359. West Palm Beach, Florida. 18 pp.

plus figures
2

Alexander, Taylor and Alan Crook. 1984. Recent vegetational changes in southern Florida. pp. 199-210

in “Environments of South Florida: Present and Past II”. Patrick Gleason, editor. Miami Geological

Society, Coral Gables, Florida. 551 pp.

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