Water-Resources Investigations Report 03-4191

Nutrient and Chlorophyll Relations in 

Selected Streams of the New England Coastal 

Basins in Massachusetts and New Hampshire, 

June-September 2001

U.S. Department of the Interior

U.S. Geological Survey

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM
Nutrient and Chlorophyll Relations in 

Selected Streams of the New England Coastal 

Basins in Massachusetts and New Hampshire, 

June-September 2001

By Melissa L. Riskin, Jeffrey R. Deacon, Matthew L. Liebman, and Keith W. Robinson

Pembroke, New Hampshire

2003

Water-Resources Investigations Report 03-4191

U.S. GEOLOGICAL SURVEY

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

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not imply endorsement by the U.S. Government.

For additional information write to:

District Chief

U.S. Geological Survey

New Hampshire/Vermont District

361 Commerce Way

Pembroke, NH 03275-3718

http://nh.water.usgs.gov

Copies of this report can be purchased from:

U.S. Geological Survey

Information Services

Building 810

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FOREWORD

The U.S. Geological Survey (USGS) is 

committed to serve the Nation with accurate and 

timely scientific information that helps enhance 

and protect the overall quality of life, and 

facilitates effective management of water, 

biological, energy, and mineral resources. 

(http://www.usgs.gov/). Information on the quality 

of the Nation’s water resources is of critical interest 

to the USGS because it is so integrally linked to the 

long-term availability of water that is clean and 

safe for drinking and recreation and that is suitable 

for industry, irrigation, and habitat for fish and 

wildlife. Escalating population growth and 

increasing demands for the multiple water uses 

make water availability, now measured in terms of 

quantity and quality, even more critical to the longterm sustainability of our communities and 

ecosystems.

The USGS implemented the National WaterQuality Assessment (NAWQA) Program to support 

national, regional, and local information needs and 

decisions related to water-quality management and 

policy. (http://water.usgs.gov/nawqa/). Shaped by 

and coordinated with ongoing efforts of other 

Federal, State, and local agencies, the NAWQA 

Program is designed to answer: What is the 

condition of our Nation’s streams and ground 

water? How are the conditions changing over time? 

How do natural features and human activities affect 

the quality of streams and ground water, and where 

are those effects most pronounced? By combining 

information on water chemistry, physical 

characteristics, stream habitat, and aquatic life, the 

NAWQA Program aims to provide science-based 

insights for current and emerging water issues and 

priorities. NAWQA results can contribute to 

informed decisions that result in practical and 

effective water-resource management and 

strategies that protect and restore water quality.

Since 1991, the NAWQA Program has 

implemented interdisciplinary assessments in more 

than 50 of the Nation’s most important river basins 

and aquifers, referred to as Study Units. 

(http://water.usgs.gov/nawqa/nawqamap.html). 

Collectively, these Study Units account for more 

than 60 percent of the overall water use and 

population served by public water supply, and are 

representative of the Nation’s major hydrologic 

landscapes, priority ecological resources, and 

agricultural, urban, and natural sources of 

contamination. 

Each assessment is guided by a nationally 

consistent study design and methods of sampling 

and analysis. The assessments thereby build local 

knowledge about water-quality issues and trends in 

a particular stream or aquifer while providing an 

understanding of how and why water quality varies 

regionally and nationally. The consistent, multiscale approach helps to determine if certain types 

of water-quality issues are isolated or pervasive, 

and allows direct comparisons of how human 

activities and natural processes affect water quality 

and ecological health in the Nation’s diverse 

geographic and environmental settings. 

Comprehensive assessments on pesticides, 

nutrients, volatile organic compounds, trace 

metals, and aquatic ecology are developed at the 

national scale through comparative analysis of the 

Study-Unit findings. 

(http://water.usgs.gov/nawqa/natsyn.html). 

The USGS places high value on the 

communication and dissemination of credible, 

timely, and relevant science so that the most recent 

and available knowledge about water resources can 

be applied in management and policy decisions. 

We hope this NAWQA publication will provide 

you the needed insights and information to meet 

your needs, and thereby foster increased awareness 

and involvement in the protection and restoration 

of our Nation’s waters. 

The NAWQA Program recognizes that a 

national assessment by a single program cannot 

address all water-resource issues of interest. 

External coordination at all levels is critical for a 

fully integrated understanding of watersheds and 

for cost-effective management, regulation, and 

conservation of our Nation’s water resources. The 

Program, therefore, depends extensively on the 

advice, cooperation, and information from other 

Federal, State, interstate, Tribal, and local 

agencies, non-government organizations, industry, 

academia, and other stakeholder groups. The 

assistance and suggestions of all are greatly 

appreciated.

Robert M. Hirsch

Associate Director for Water
iv Contents

CONTENTS

Abstract ................................................................................................................................................................. 1

Introduction ........................................................................................................................................................... 2

Purpose and Scope ....................................................................................................................................... 3

Description of Study Area ............................................................................................................................ 3

Acknowledgments ........................................................................................................................................ 5

Data-Collection and Analysis ................................................................................................................................ 6

Sample Collection ................................................................................................................................................. 6

Quality Assurance ................................................................................................................................................. 6

Statistical Methods ....................................................................................................................................... 6

Characterization of Nutrients and Chlorophyll ..................................................................................................... 7

Nutrients ....................................................................................................................................................... 7

Chlorophyll .................................................................................................................................................. 7

Application of Nutrient and Chlorophyll a Data to In-Stream Criteria Development by

Water-Resources Managers ................................................................................................................................12

Summary and Conclusions ....................................................................................................................................14

References Cited ...................................................................................................................................................15
Figures v

FIGURES

Figure 1. Map showing sampling sites, site-identification numbers, and site types in the

New England Coastal Basins study area in Massachusetts and New Hampshire................................ 4

Figure 2. Graph showing total nitrogen concentrations among site types in the New England

Coastal Basins study area ................................................................................................................... 9

Figure 3. Graph showing total phosphorus concentrations among site types in the New England

Coastal Basins study area ................................................................................................................... 10

Figure 4. Graph showing chlorophyll a from periphyton samples among site types at the

open-canopy locations in the New England Coastal Basins study area .............................................. 10

Figure 5. Graph showing chlorophyll a from periphyton samples among site types at the

closed-canopy locations in the New England Coastal Basins study area ........................................... 11

Figure 6. Graph showing chlorophyll a from periphyton samples among site types at the six sites

with open- and closed-canopy sampling locations in the New England Coastal Basins

study area ............................................................................................................................................ 11

Figure 7. Graph showing relation between total nitrogen and periphyton chlorophyll a

concentrations for the six open-canopy sites sampled five times from June through

September 2001 in the New England Coastal Basins study area in Massachusetts and

New Hampshire .................................................................................................................................. 13

Figure 8. Graph showing relation between total phosphorus and periphyton chlorophyll a

concentrations for the six open-canopy sites sampled five times from June through

September 2001 in the New England Coastal Basins study area in Massachusetts and

New Hampshire .................................................................................................................................. 13
vi Tables

TABLES

Table 1. Selected characteristics for the study sites in the New England Coastal Basins

study area in Massachusetts and New Hampshire .............................................................................. 5

Table 2. Summary of selected nutrient and chlorophyll a concentrations (open- and closedcanopy sites) for the study site types in the New England Coastal Basins study area in

Massachusetts and New Hampshire .................................................................................................... 8

Table 3. Percentile statistics of total nitrogen, total phosphorus, and periphyton chlorophyll a

concentrations for the study sites in the New England Coastal Basins study area in

Massachusetts and New Hampshire .................................................................................................... 9

Table 4. Summary of total nitrogen and total phosphorus concentrations for potential methods

of nutrient criteria development in the Northeastern Coastal Zone in Massachusetts and

New Hampshire .................................................................................................................................. 14
Conversion Factors and Abbreviations vii

CONVERSION FACTORS AND ABBREVIATIONS

CONVERSION FACTORS

Temperature in degrees Celsius (oC) may be converted to degrees Fahrenheit (oF) as follows:

oF=1.8 oC+32.

Concentrations of nutrients are reported in milligrams per liter (mg/L).

Concentrations of phytoplankton are reported in micrograms of chlorophyll a per liter (μg/L). 

Concentrations of periphyton are reported in milligrams of chlorophyll a per square meter (mg/m2).

Water volumes are reported in milliliters (mL).

ABBREVIATIONS USED IN REPORT

EWI Equal Width Increment

NAWQA National Water-Quality Assessment Program

NECB New England Coastal Basins

NWIS National Water Information System

NWQL National Water-Quality Laboratory

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

Multiply By To obtain

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

square mile (mi2) 2.590 square kilometer (km2)

Abstract 1

Nutrient and Chlorophyll Relations in Selected Streams 

of the New England Coastal Basins in Massachusetts 

and New Hampshire, June-September 2001

By Melissa L. Riskin1, Jeffrey R. Deacon1, Matthew L. Liebman2, and Keith W. Robinson1

ABSTRACT

The U.S. Environmental Protection Agency 

is developing guidance to assist states with defining nutrient criteria for rivers and streams and to 

better describe nutrient-algal relations. As part of 

this effort, 13 wadeable stream sites were selected, 

primarily in eastern Massachusetts, for a nutrientassessment study during the summer of 2001. The 

sites represent a range of water-quality impairment 

conditions (reference, moderately impaired, 

impaired) based on state regulatory agency assessments and previously assessed nitrogen, phosphorus, and dissolved-oxygen data. In addition, a 

combination of open- and closed- canopy locations 

were sampled at six of the sites to investigate the 

effect of sunlight on algal growth. Samples for 

nutrients and for chlorophyll a from phytoplankton 

and periphyton were collected at all stream sites.

Total nitrogen (dissolved nitrite + nitrate + 

total ammonia + organic nitrogen) and total 

phosphorus (phosphorus in an unfiltered water 

sample) concentrations were lowest at reference 

sites and highest at impaired sites. There were 

statistically significant differences (p < 0.05) 

among reference, moderately impaired, and 

impaired sites for total nitrogen and total phosphorus. Chlorophyll a concentrations from 

phytoplankton were not significantly different 

among site impairment designations. Concentrations of chlorophyll a from periphyton were highest at nutrient-impaired open-canopy sites. 

Chlorophyll a concentrations from periphyton 

samples were positively correlated with total nitrogen and total phosphorus at the open- and closedcanopy sites. Correlations were higher at opencanopy sites (p < 0.05, rho = 0.64 to 0.71) than at 

closed-canopy sites (p < 0.05, rho = 0.36 to 0.40). 

Statistically significant differences in the median 

concentrations of chlorophyll a from periphyton 

samples were observed between the open- and 

closed-canopy sites (p < 0.05). 

Total nitrogen and total phosphorus data 

from moderately impaired and impaired sites in 

this study exceeded the preliminary U.S. 

Environmental Protection Agency nutrient criteria 

values for the coastal region of New England. In 

an effort to establish more appropriate nutrient 

and chlorophyll criteria for streams in the New 

England coastal region, relations between total 

nitrogen and total phosphorus to periphyton 

chlorophyll a in wadeable streams from this study 

were quantified to present potential techniques for 

determining nutrient concentrations. Linear 

regression was used to estimate the total nitrogen 

and total phosphorus concentrations that 

corresponded to various chlorophyll a 

concentrations. On the basis of this relation, a 

median concentration for moderately enriched 

streams of 21 milligrams per square meter 

1U.S. Geological Survey.

2U.S. Environmental Protection Agency.
2 Nutrient and Chlorophyll Relations in Selected Streams of the New England Coastal Basins in Massachusetts and New Hampshire, June-September 2001

(mg/m2) of periphyton chlorophyll a from the literature corresponded to estimated concentrations 

of 1.3 milligrams per liter (mg/L) for total nitrogen 

and 0.12 mg/L for total phosphorus. The median 

concentration for periphyton chlorophyll a from 

the literature is similar to the 50th-percentile concentration of periphyton chlorophyll a (17 mg/m2) 

calculated with the data from open-canopy sites in 

this study. The 25th-percentile concentration for 

periphyton chlorophyll a of all open-canopy sites

(5.2 mg/m2) and the 75th-percentile concentration 

for periphyton chlorophyll a of open-canopy reference sites (16 mg/m2) also were plotted to provide 

additional estimates and methods for developing 

total nitrogen and total phosphorus criteria.

 The 25th-percentile concentrations of total 

nitrogen and total phosphorus were calculated 

based on all sites in this study and were used as 

another potential criteria estimation. A 

concentration of 0.64 mg/L for total nitrogen and 

0.030 mg/L for total phosphorus were calculated. 

As another possible method to develop threshold 

concentrations, the 10th-percentile concentrations 

of total nitrogen and total phosphorus were 

calculated based on all the impaired sites in this 

study. A concentration threshold of 0.73 mg/L 

for total nitrogen and 0.036 mg/L for total 

phosphorus were calculated. Ultimately, a 

combination of these techniques may be 

appropriate for water-resources managers to use 

to set regional nutrient criteria to limit undesirable 

levels of algal growth in streams.

NTRODUCTION

Nutrients are essential to the health and diversity 

of surface waters. In excessive amounts, however, 

they can be harmful. Chronic symptoms of excessive 

nutrient enrichment include algal blooms, low 

dissolved oxygen, fish kills, turbid water, and loss of 

desirable flora and fauna. Human activities that may 

affect levels of algal biomass include (1) discharge of 

nutrient-rich wastewater; (2) development that 

increases impervious surfaces in the drainage basin;

(3) reduction of flows; (4) removal of streamside vegetation, which increases light and the flux of nutrients 

and sediment from riparian zones because of reduced 

uptake from plants; and (5) construction of residential 

development with individual septic systems (U.S. 

Environmental Protection Agency, 2000a). 

Factors that control the response of algal biomass to nutrient inputs include hydrologic disturbance, 

days of algal accrual (Biggs, 2000), light availability 

(Spahr and Deacon, 1998), turbidity, consumption of 

algae by invertebrate grazers

(Deacon and Spahr, 1998), and possible toxic 

responses associated with herbicides and other organic 

contaminants. The importance of any one or any combination of these factors in limiting the growth of algae 

appears to vary among streams. Nutrient concentrations and light availability, however, often are regarded 

as the most important factors affecting the primary production in streams that may result in excessive algal 

growth (Mosisch and others, 1999). Light can be a limiting factor in small streams where there is dense riparian cover. Kjeldsen (1996) found that differences in 

algal growth between a shaded stream reach and an 

unshaded stream reach were highly significant (p < 

0.05) if the sampling reaches differed only with respect 

to light availability but the water chemistry and other 

physical factors remained the same. Welch and others 

(1992) found that lower than expected algal biomass 

levels were associated with riparian shading and high 

macroinvertebrate-grazer densities. 

Approaches for assessing the effects of nutrients 

on algae in streams and rivers are not as well developed 

as the approaches for lakes. For lakes and reservoirs, a 

strong quantitative framework has been developed over 

the past three decades that allows prediction of algal 

biomass and other water-quality parameters from nutrient loading and nutrient concentrations; however, there 

is no generally accepted system for classifying streams 

and rivers (Reckhow, 1979). The U.S. Environmental 

Protection Agency (USEPA) has developed guidance 

to assist states in developing nutrient and algal criteria 

for rivers and streams to protect water quality for designated uses from impairment (U.S. Environmental 

Protection Agency, 2000a).

Nutrient concentrations that lead to waterquality degradation and impairment of designated use 

(for example, recreation and aquatic life) differ because 

of regional variations in geology, climate, and 
INTRODUCTION 3

soil types. To be most effective, therefore, water-quality criteria need to take into account ecoregional variations (U.S. Environmental Protection Agency, 2000a). 

Currently (2003), most states use qualitative criteria 

based on “best professional judgment” to assess 

impairment. To control nutrient loading to streams 

more effectively, however, quantitative nutrient criteria would be valuable to water-resources managers. 

The numerical criteria could translate qualitative criteria into quantitative endpoints and range along the transition from a desirable mesotrophic (moderately 

enriched) condition to an undesirable eutrophic condition.

The USEPA has established preliminary recommendations for reference concentrations of total nitrogen and total phosphorus in rivers and streams for 

ecoregions of the country. These concentrations represent the 25th-percentile concentrations of nitrogen and 

phosphorus for all sites, which are expected to prevent 

nuisance algal growths. Concentration thresholds 

based on the 25th percentile from all sites for USEPA 

subecoregion 59 (the region of this study) are 0.57 milligram per liter (mg/L) for total nitrogen (dissolved 

nitrite + nitrate + total ammonia + organic nitrogen) 

and 0.024 mg/L for total phosphorus (phosphorus in an 

unfiltered water sample) (U.S. Environmental Protection Agency, 2000b). Another method is to choose the 

75th percentile of concentrations of total nitrogen and 

total phosphorus from a reference population of 

streams that are minimally affected. Analyses of 

national nutrient data to date indicate that the 25th percentile from an entire population roughly approximates 

the 75th percentile for a reference population (U.S. 

Environmental Protection Agency, 2000b). Although 

the USEPA did not publish preliminary recommendations for concentrations of periphyton chlorophyll a to 

maintain suitable levels of algal growth in streams, 

according to Biggs (1996), streams with chlorophyll a

concentrations of 100 milligrams per square meter 

(mg/m2

) or greater for periphyton are generally characterized as eutrophic.

Currently, because of the lack of nutrient and 

algal data for New England streams, it is difficult to 

define a precise range of nitrogen and phosphorus concentrations that would promote excessive algal growth 

and result in water-quality impairments. In an effort to 

define such a range for the New England Coastal 

Basins (fig. 1), the U.S. Geological Survey (USGS) 

National Water-Quality Assessment Program 

(NAWQA) performed a study from June through 

September 2001 to derive more quantitative relations 

between total nitrogen and total phosphorus to 

periphyton chlorophyll a in wadeable streams in the 

Northeastern Coastal Zone (fig. 1). 

Purpose and Scope

The objective of this report is to develop 

potential methods that could guide water-resource 

managers in the development of nutrient criteria for 

New England streams on the basis of water-quality data 

collected at sites in the New England Coastal Basins 

study area. This report (1) summarizes

water-quality data at selected wadeable streams,

(2) examines the response of algae to nutrients and 

incident light (as measured by tree canopy) from June 

through September 2001, and (3) provides potential 

methods for nutrient-criteria development. The results 

presented are relevant only to the data analysis performed in this study. However, examples are presented 

in this report of how nutrient criteria could be developed by water-resource managers for the Northeastern 

Coastal Zone.

Description of Study Area

The New England Coastal Basins (NECB) study 

area is a 23,000 square mile (mi2) area that encompasses central Maine, eastern New Hampshire, eastern 

Massachusetts, and Rhode Island. Major rivers in the 

NECB study area include the Kennebec, Androscoggin, Saco, Merrimack, Charles, and Blackstone Rivers. 

Land use in the NECB study area consists of 74 percent 

forest, 11 percent urban development, 8 percent surface-water bodies, and 6 percent agriculture (Flanagan 

and others, 1999). A more detailed description of the 

physical and cultural settings of the NECB study area 

is found in Flanagan and others (1999). All sites for 

this specific investigation were in subecoregion 59 of 

the NECB, which is the Northeastern Coastal Zone 

(fig. 1).

Thirteen wadeable stream sites, primarily in 

eastern Massachusetts, were selected on the basis of 

previous nitrogen, phosphorus, and dissolved oxygen 

data. Six of the 13 sites were classified as impaired 

because of existing nutrient problems, low levels of 

dissolved oxygen, or extensive algal growth. Five of
4 Nutrient and Chlorophyll Relations in Selected Streams of the New England Coastal Basins in Massachusetts and New Hampshire, June-September 2001

Figure 1. Sampling sites, site-identification numbers, and site types in the New England Coastal Basins study area in Massachusetts and New 

Hampshire. (Site identification numbers are show in table1.)

Blackstone River

Providence River

Wading River

East Branch

Matfield River

Charles River

Charles River Assabet River

Stillwater River

Stony Brook

Mill River

Aberjona River Merrimack Riv er

Ipswich River

Saugus

River

M errimack River

Black Brook

Neponset

River

Atlantic Ocean

Boston Harbor

1

12

10

7 8

2

9

6

3

4

5

11

13

0

0

50 MILES

50 KILOMETERS

68 ̊

New

Hampshire

Massachusetts

Connecticut

Rhode

Island

Vermont

CANADA

Maine

New England

 Coastal Basins

Study area

70 ̊

46 ̊

72 ̊

44 ̊

42 ̊

EXPLANATION

Ecoregions (from Omernik, J.M., 1987)

 Northeastern Highlands

 Northeastern Coastal Zone

 (Sub-ecoregion 59)

 Atlantic Coastal Pine Barrens

 New England Coastal Basins 

 boundary

 Capital

 City

Sampling site, identification number, 

 and site type

 Reference

 Moderately impaired

 Impaired

1

4

3

0

0 20 KILOMETERS

10 20 MILES

10

NEW HAMPSHIRE

MASSACHUSETTS

CONNECTICUT

RHODE ISLAND

Providence

Boston

Taunton

Worcester

Lawrence

Marlborough

Nashua

Manchester Portsmouth

Base from U.S. Geological Survey digital data, 1:2,000,000

Albers Equal-Area Conic projection

Standard parallels 29 ̊30'N and 45 ̊30'N, central meridian 71 ̊W

MAINE

71 ̊ 72 ̊

43 ̊

42 ̊

these sites were considered impaired, or not meeting 

narrative standards, on the basis of the State’s 305(b) 

water-quality report or Clean Water Act 303(d) list 

(U.S. Environmental Protection Agency, 2002; Commonwealth of Massachusetts, 1999). The sixth site was 

classified as impaired because previous water samples 

collected at that site had nutrient concentrations that 

greatly exceeded preliminary standards. Five additional sites were selected on the basis of previous 

water-quality data (Karen Beaulieu, U.S. Geological 

Survey, written commun., 2002). Water samples collected at these sites were categorized as moderately 

impaired because their total nitrogen and total phosphorus concentrations slightly exceeded preliminary 

standards for subecoregion 59. Two additional sites 

were selected to represent reference conditions (table 1, 

fig. 1).

Riparian zones dominated by trees that provided 

substantial canopy cover (closed canopy) characterized 

all 13 sites. Additional locations with increased patchiness of riparian-tree cover provided an unshaded 

stream-sampling area (open canopy) at 6 of the 13 sites 

where supplementary periphyton samples were collected to compare with data from the closed-canopy 

sites.
INTRODUCTION 5

Table 1. Selected characteristics for the study sites in the New England Coastal Basins study area in Massachusetts and New Hampshire

[No., number; fig., figure; mi2, square mile; --, no impairment designation; latitude and longitude are given in degrees °, minutes ′, and seconds ′′]

Site 

No. 

(fig. 1)

Site name USGS station 

No. Site type Impairment justification Canopy Latitude Longitude

Drainage 

area 

(mi2

)

1 Black Brook, Dunbarton Road near 

Manchester, N.H.

01090477 Reference -- Open4

Closed5

43°01′31′′ 71°30′17′′ 20.72

2 Stillwater River near Sterling, Mass. 01095220 Reference -- Open

Closed

42°24′39′′ 71°47′30′′ 31.6

3 Charles River at Maple Street at 

North Bellingham, Mass.

011032058 Impaired 305b report1

303d list2

Closed 42°07′11′′ 71°27′10′′ 21.0

4 East Branch Neponset River at 

Canton, Mass.

01105504 Moderately

impaired

Nutrients exceed 

standards3

Closed 42°09′31′′ 71°09′17′′ 28.13

5 Matfield River at North Central 

Street at East Bridgewater, Mass.

01106468 Impaired Nutrients greatly 

exceed standards

Open

Closed

42°02′01′′ 71°58′21′′ 30.61

6 Mill River at Summer Street near 

Blackstone, Mass.

01112262 Moderately

impaired

Nutrients exceed 

standards

Open

Closed

42°02′27′′ 71°30′56′′ 28.46

7 Saugus River at Saugus Ironworks at 

Saugus, Mass.

01102345 Moderately

impaired

Nutrients exceed 

standards

Closed 42°28′05′′ 71°00′27′′ 23.3

8 Aberjona River (head of Mystic 

River) at Winchester, Mass.

01102500 Impaired 303d list Closed 42°26′50′′ 71°08′22′′ 24.1

9 Assabet River at Allen Street at 

Northborough, Mass.

01096710 Impaired 305b report

303d list

Open

Closed

42°19′46′′ 71°37′48′′ 29.5

10 Ipswich River at South 

Middleton, Mass.

01101500 Impaired 305b report

303d list

Closed 42°34′10′′ 71°01′39′′ 44.5

11 Neponset River at Norwood, Mass. 01105000 Impaired 305b report

303d list

Closed 42°10′39′′ 71°12′05′′ 34.7

12 Stony Brook at School Street at 

Chelmsford, Mass.

01096544 Moderately

impaired

Nutrients exceed 

standards

Open

Closed

42°37′04′′ 71°24′08′′ 41.6

13 Wading River (head of Threemile 

River) near Norton, Mass.

01109000 Moderately

impaired

Nutrients exceed 

standards

Closed 41°56′51′′ 71°10′38′′ 43.3

1 U.S. Environmental Protection Agency, 2002, Waterbody system database for the Clean Water Act for 305(b) reporting. 2 Commonwealth of Massachusetts, Final Massachusetts section 303(d) list of waters, 1998. 3 Previous data shows that site exceeded U.S. Environmental Protection Agency preliminary standards. 4 Sampling site located in an open-canopy section of the stream. 5 Sampling site located in a closed-canopy section of the stream.

Acknowledgments

The authors thank Karen Beaulieu,

Kimberly Campo, and Maureen Thomas for their assistance with field work. The authors also thank Stephen 

Porter, USGS Denver, Colo., and Jacob Gibs, USGS 

West Trenton, N.J., for their critical review of the 

manuscript. Appreciation is extended to the following 

USGS employees: Ann Marie Squillacci for manuscript preparation, Laura Hayes and Anita Cotton for 

graphics assistance, and Matthew Cooke and

Mary Ashman for editorial review of this report. 
6 Nutrient and Chlorophyll Relations in Selected Streams of the New England Coastal Basins in Massachusetts and New Hampshire, June-September 2001

DATA-COLLECTION AND ANALYSIS

This study was designed to measure nutrient and 

chlorophyll a concentrations for a range of wadeable 

sites from reference to nutrient-impaired conditions 

and to compare data from open- and closed-canopy 

sites in the same stream. Samples for nutrients and 

chlorophyll a from phytoplankton and periphyton were 

collected at all 13 sites. Seven field-blank and 10 fieldreplicate samples were collected throughout the sampling period for nutrients and chlorophyll a. Total 

nitrogen, total phosphorus, and periphyton chlorophyll 

a are the primary constituents discussed in this report. 

Statistical analyses were completed on the nutrient and 

algal data.

Sample Collection

Each of the 13 sites was sampled on 5 occasions 

between June through September 2001. Streams were 

sampled during the summer in an effort to capture 

changes in biomass throughout the “growing season.” 

The equal-width increment (EWI) technique was used 

to obtain a representative water sample at each site. 

The samples were then processed in the field according 

to standard surface-water-collection protocols

(Shelton, 1994). Samples were packed on ice and sent 

to the USGS National Water-Quality Laboratory 

(NWQL) in Denver, Colo., for analysis. Inorganic constituents were analyzed using methods cited in Fishman (1993) and Fishman and Friedman (1989). Field 

measurements for each sample included water temperature, dissolved oxygen, pH, specific conductance, and 

stream discharge. Field measurements, nutrients, and 

major ion data are stored in the USGS National Water 

Information System (NWIS) and published in the 

USGS Annual Water Data Report (Coakley and others, 

2001; and Socolow and others, 2001).

Chlorophyll a was measured in phytoplankton 

and periphyton samples to estimate the algal biomass at 

the sampling sites. Phytoplankton measurements were 

determined by filtering 500 mL of water through a 

glass-fiber filter. The filter was then wrapped in foil, 

placed in a petri dish, and immediately put on dry ice 

for shipment to the USGS NWQL for chlorophyll a

determination (Porter and others, 1993). Chlorophyll a 

in phytoplankton was analyzed by methods in Arar and 

Collins (1997). Periphyton samples were collected 

from five representative rocks in riffle areas by scraping the algae from the rock surface. The scraped area 

was estimated by fitting an equivalent area of aluminum foil to the scraped section, using the foil-template 

method (Porter and others, 1993). Two subsamples of 

algal slurry were filtered, stored on dry ice, and sent to 

the USGS NWQL for chlorophyll a and ash-free drymass determinations (Arar and Collins, 1997). 

At each site, the open-canopy angle was used to 

assess the amount of direct sunlight reaching the 

stream. The left and right canopy angles were measured with a handheld clinometer and the percentage of 

open canopy was calculated (Fitzpatrick and others, 

1998).

Quality Assurance

Field blanks provide information on the potential 

for bias due to contamination of analytical results by 

sample collection, processing, shipping, and analysis. 

A field-blank sample is processed with water free of 

the analytes of interest. The blank water is passed 

through all the sampling equipment, processed as a regular water-quality sample, and analyzed for all waterquality constituents. Analytical results from the seven 

field-blank samples indicated that concentrations for 

constituents discussed in this report were less than the 

laboratory reporting level.

Replicate samples provide information on the 

variability of analytical results caused by sample collection, processing, shipping, and analysis. Differences in concentrations between environmental and 

replicate samples for nutrients were generally less than 

0.01 mg/L. Differences in concentrations between 

environmental and replicate samples for periphyton 

chlorophyll a were less than 2 mg/m2. 

Statistical Methods

A Spearman rho correlation test was used to 

determine relations between nutrient concentrations in 

the water column to chlorophyll a concentrations in 

phytoplankton and periphyton. Correlations were considered significant if the probability was less than

5 percent (p < 0.05). The Kruskal-Wallis statistical test 

(Helsel and Hirsch, 1992) with an alpha value of

0.05 was performed on nutrient concentrations and 

chlorophyll a concentrations to determine if there were 
CHARACTERIZATION OF NUTRIENTS AND CHLOROPHYLL 7

significant differences among the groups of data for 

each of the three site types. If results from the KruskalWallis test indicated significant differences, a Tukey’s 

multiple comparison test (Helsel and Hirsch, 1992) was 

used to determine which site types differed significantly. Linear regression analysis was used to determine the relation between total nitrogen or total 

phosphorus and chlorophyll a concentrations. All statistical analyses were performed using Statview Statistical Software (SAS Institute, Inc., 1998).

CHARACTERIZATION OF NUTRIENTS AND CHLOROPHYLL

Median concentrations of total nitrogen and total 

phosphorus exceeded the preliminary recommended 

criteria set by the USEPA for subecoregion 59 at 11 of 

the 13 sites. Periphyton chlorophyll a data from the six 

open-canopy sites were selected to determine the association between total nitrogen and total phosphorus 

concentrations and chlorophyll a concentrations 

because these sites represented areas of greatest nutrient and algal concentrations. 

Nutrients

Summary statistics for nutrients are listed in 

table 2. Selected percentile statistics for total nitrogen 

and total phosphorus are summarized in table 3. The 

two reference sites were the only streams with median 

nutrient concentrations less than the USEPA preliminary recommendations for total nitrogen and total 

phosphorus (figs. 2 and 3). Median total nitrogen and 

total phosphorus concentrations were significantly different (p < 0.05) among all three site types (figs. 2 and

3). Among the streams sampled, concentrations of 

total nitrogen and total phosphorus were highest at the 

Matfield and Assabet Rivers. It is well documented 

that point sources are the major impact to the Assabet 

River especially during the summer low flow (ENSR 

International, 2000). In addition, a wastewater-treatment plant upstream of the Matfield River site may be 

the primary source of nutrient loading to this water 

body. Nutrient concentrations were also high at the 

Aberjona River, which may be a result of the heavily 

urbanized drainage basin. Eleven of the sites were 

nitrogen and phosphorus limited and two sites were 

only phosphorus limited based on ratios of dissolved 

nutrient concentrations.

Chlorophyll

Summary statistics for chlorophyll a from phytoplankton and periphyton samples and ash-free-dry 

mass are listed in table 2. Selected percentile statistics 

for periphyton chlorophyll a are summarized in table 3. 

Chlorophyll a concentrations were higher at the opencanopy sites than the closed-canopy sites (table 3). 

There were no significant relations between chlorophyll a in phytoplankton and total nitrogen and total 

phosphorus. However, chlorophyll a concen-trations 

from periphyton samples increased significantly with 

total nitrogen and total phosphorus concentrations at 

the open- and closed-canopy sites. Correlation coefficients were higher at the open-canopy sites (rho = 0.64 

to 0.71) than at the closed-canopy sites (rho = 0.36 to 

0.40). This indicates that light affected the algal biomass and the relation between nutrient and chlorophyll a

concentrations. There was no significant temporal 

variation in phytoplankton or periphyton samples collected throughout the sampling period.

Median concentrations of periphyton chlorophyll a were highest at nutrient-impaired sites (table 2). 

There were significant differences (p < 0.05) in median 

periphyton chlorophyll a concentrations among all 

three site types for open-canopy sampling sites (fig. 4). 

There were significant differences between reference 

and impaired sites and between moderately impaired 

and impaired sites at the closed-canopy sampling locations, but not between reference and moderately 

impaired sites (fig. 5). Concentrations of chlorophyll a 

from periphyton were significantly higher (p < 0.05) at 

open-canopy sites than at closed-canopy sites. Chlorophyll a concentrations from phytoplankton were not 

significantly different among site designations. This 

suggests that periphyton may be a better indicator of 

eutrophication than phytoplankton in wadeable NECB 

streams, regardless of canopy conditions.

Comparison of periphyton chlorophyll a

concentrations from the six sampling sites that had 

open- and closed-canopies indicated that open-canopy 

sites had higher concentrations of chlorophyll a among 

all three site types (fig. 6). Periphyton chlorophyll a

concentrations from samples collected at closed-
8 Nutrient and Chlorophyll Relations in Selected Streams of the New England Coastal Basins in Massachusetts and New Hampshire, June-September 2001 Table 2. Summary of selected nutrient and chlorophyll a concentrations (open- and closed-canopy sites) for the study site types in the New England Coastal Basins 

Hampshire [Sites sampled five times between June 1 and September 30, 2001; mg/L, milligrams per liter; Min, minimum; Max, maximum; μg/L, micrograms per liter; mg/m2, milligrams per square 

than] Site type Total nitrogen (dissolved nitrite + nitrate + total ammonia + organic nitrogen) (mg/L) Dissolved inorganic nitrogen (dissolved nitrite + nitrate + dissolved ammonia) (mg/L) Total phosphorus (phosphorus in an unfiltered water sample) (mg/L) Dissolved phosphorus (mg/L) 

Min Median Max Min Median Max Min Median Max Min Median Max 

Reference 0.32 0.44 0.54 0.07 0.13 0.22 0.006 0.019 0.043 < 0.006 0.009 0.013 Moderately impaired .49 .78 2.2 .12 .26 1.5 .016 .039 .072 .009 .017 .041 Impaired .64 2.2 10 .08 1.5 9.2 .024 .055 .905 < .006 .025 .899 

Site type Dissolved nitrite + nitrate (mg/L) Dissolved nitrite (mg/L) Orthophosphate (mg/L) Nitrogen ammonia + organic tota

(mg/L) 

Min Median Max Min Median Max Min Median Max Min Median Max 

Reference <0.047 0.090 0.202 < 0.006 < 0.006 < 0.006 < 0.020 < 0.020 < 0.020 0.23 0.34 0.41 Moderately impaired .086 .231 1.4 < .006 < .006 .056 < .020 < .020 < .020 .28 .49 2.0 Impaired .055 .921 6.7 < .006 .014 .436 < .020 < .020 .812 .35 .66 3.8 

Site type Chlorophyll a from phytoplankton 

(μg/L)

Chlorophyll a from periphyton 

(mg/m2

)

Min Median Max Min Median Max Min 

Reference 0.40 1.3 5.5 1.4 5.4 22 1.6 Moderately 

impaired

.30 1.2 16 .50 5.2 59 2.7 

Impaired .30 1.4 22 .30 17 166 2.4 
CHARACTERIZATION OF NUTRIENTS AND CHLOROPHYLL 9

Table 3. Percentile statistics of total nitrogen, total phosphorus, and periphyton chlorophyll a concentrations for the study sites in the 

New England Coastal Basins study area in Massachusetts and New Hampshire

[n, number of samples; mg/L, milligrams per liter; mg/m2, milligrams per square meter]

Minimum 25th percentile 50th percentile 75th percentile Maximum n

Total nitrogen (mg/L) 0.32 0.64 0.90 2.1 10 65

Total phosphorus (mg/L) .006 .030 .044 .065 .905 65

Periphyton chlorophyll a1 (mg/m2) 2.2 5.2 17 41 166 30

Periphyton chlorophyll a2 (mg/m2) .30 3.3 6.0 15 52 65

1 Open-canopy sites.

2 Closed-canopy sites.

canopy reference and moderately impaired sites were 

less than the median literature value for moderately 

enriched streams (21 mg/m2) (Biggs, 1996). 

Chlorophyll a concentrations from most samples 

collected at closed-canopy impaired sites had 

concentrations greater than the median literature value 

for moderately enriched streams. Chlorophyll a 

concentrations from samples collected at open-canopy 

sites had higher ranges of chlorophyll a concentrations 

than those at closed-canopy sites for all three site 

types. Generally, most of the chlorophyll a

concentrations from open-canopy reference and 

moderately impaired sites had concentrations less than 

the median literature value for moderately enriched 

streams (fig. 6). Chlorophyll a concentrations from 

open-canopy impaired sites, however, were generally 

between the median literature value for moderately 

enriched and enriched streams (fig. 6). Nutrient 

concentrations, types of substrate, and stream 

velocities were similar between the closed- and opencanopy sampling locations at the same site, indicating 

that light is affecting algal biomass as measured by 

chlorophyll a.

Figure 2. Total nitrogen concentrations among site types in New England Coastal Basins study area. [Result of Tukey’s multiplecomparison test [Helsel and Hirsch, 1992] among groups are presented as letters, and concentrations with at least one letter in comon do not 

differ significantly; for example, concentrations among all three groups differ significantly.

EXPLANATION

 Number of samples

 (five samples per site)

 Outlier-data value

 90th percentile

 75th percentile

 50th percentile (median)

 25th percentile

 10th percentile

 USEPA preliminary recommendation 

 for total nitrogen in subecoregion 59

(30)

0.1

1

10

100

 TOTAL NITROGEN,

IN MILLIGRAMS PER LITER

SITE TYPES

A

B

C

(10)

(30)

(25)

Reference Moderately impaired Impaired
10 Nutrient and Chlorophyll Relations in Selected Streams of the New England Coastal Basins in Massachusetts and New Hampshire, June-September 2001

Figure 3. Graph showing Total phosphorus concentrations among site types in the New England Coastal Basins study area. (Results of Tukey’s 

multiple-comparison test [Helsel and Hirsch, 1992] among groups are presented as letters, and concentrations with at least one letter in common do not 

differ significantly; for example, concentrations among all three groups differ significantly.)

EXPLANATION

 Number of samples

 (five samples per site)

 Outlier-data value

 90th percentile

 75th percentile

 50th percentile (median)

 25th percentile

 10th percentile

 USEPA preliminary recommendation 

 for total nitrogen in subecoregion 59

(30)

0.1

0.01

1

10

 TOTAL PHOSPHORUS,

IN MILLIGRAMS PER LITER

SITE TYPES

A

B

(10) C

(30)

(25)

Reference Moderately impaired Impaired

0.001

Figure 4. Graph showing Chlorophyll a from periphyton samples among site types at the open-canopy locations in the New England 

Coastal Basins study area. (Results of Tukey’s multiple-comparison test [Helsel and Hirsch, 1992] among sites are presented as letters, and 

concentrations with at least one letter in common do not differ significantly; for example, concentrations among all three groups differ 

significantly.)

EXPLANATION

 Number of samples

 (five samples per site)

 Outlier-data value

 90th percentile

 75th percentile

 50th percentile (median)

 25th percentile

 10th percentile

(10)

1

10

100

1,000

 CHLOROPHYLL a,

IN MILLIGRAMS PER SQUARE METER

SITE TYPES

A

B

C

(10)

(10)

(10)

Reference Moderately impaired Impaired
CHARACTERIZATION OF NUTRIENTS AND CHLOROPHYLL 11

Figure 5. Graph showing Chlorophyll a from periphyton samples among site types at the closed-canopy locations in the New England 

Coastal Basins study area. (Results of Tukey’s multiple-comparison test [Helsel and Hirsch, 1992] among sites are presented as letters, 

and concentrations with at least one letter in common do not differ significantly; for example, concentrations between the reference and 

moderately impaired sites do not differ significantly.)

EXPLANATION

 Number of samples

 (five samples per site)

 Outlier-data value

 90th percentile

 75th percentile

 50th percentile (median)

 25th percentile

 10th percentile

(30)

0.1

1

10

100

 CHLOROPHYLL a,

IN MILLIGRAMS PER SQUARE METER

SITE TYPES

A A

(10) B

(30)

(25)

Reference Moderately impaired Impaired

Figure 6. Graph showing Chlorophyll a from periphyton samples among site types at the six sites with open- and closed-canopy sampling 

locations in the New England Coastal Basins study area.

EXPLANATION

 Open-canopy samples

 Closed-canopy samples

 Number of samples

 (five samples per site)

 90th percentile

 75th percentile

 50th percentile (median)

 25th percentile

 10th percentile

 Median literature value for 

 enriched streams (Biggs, 1996)

 Median literature value for 

 moderately enriched streams 

 (Biggs, 1996)

(10)

1

10

100

1,000

 CHLOROPHYLL a,

IN MILLIGRAMS PER SQUARE METER

SITE TYPES

(10)

Reference Moderately impaired Impaired

(10) (10)

(10) (10)

(10)
12 Nutrient and Chlorophyll Relations in Selected Streams of the New England Coastal Basins in Massachusetts and New Hampshire, June-September 2001

APPLICATION OF NUTRIENT AND 

CHLOROPHYLL a DATA TO IN-STREAM 

CRITERIA DEVELOPMENT BY WATERRESOURCES MANAGERS

The nutrient and chlorophyll data collected for 

this study can provide information useful for nutrientcriteria development. One approach is to use linear 

regression to estimate the total nitrogen and total phosphorus concentrations that corresponded to various 

chlorophyll a concentrations at open-canopy sites (figs. 

7 and 8). The periphyton chlorophyll a concentration 

at which a stream is considered mesotrophic can be 

identified on the regression line, and the corresponding 

nutrient concentrations may be applicable as estimates 

for setting nutrient criteria. The mesotrophic concentration should be used rather than the eutrophic concentration because this criterion is intended to prevent the 

adverse effects of nutrient enrichment. Biomass data 

from multiple studies including Lock (1981), Horner 

and others (1983),Bott and others (1985), and Biggs 

and Price (1987) were summarized by Biggs (1996) to 

determine typical algal biomass concentrations for different site types according to levels of nutrient enrichment. On the basis of these data, the median 

concentration of periphyton chlorophyll a from moderately enriched streams (mesotrophic) was determined 

to be 21 mg/m2, which is similar to the 50th-percentile 

concentration of periphyton chlorophyll a (17 mg/m2

) 

calculated with the data from all open-canopy sites in 

this study. An estimated concentration of 1.3 mg/L for 

total nitrogen and 0.12 mg/L for total phosphorus corresponded to the periphyton chlorophyll a concentration (21 mg/m2) for moderately enriched streams (figs. 

7 and 8).

The allowable or desired concentrations of nutrients and chlorophyll a may depend on the designated 

use or existing quality of a water body. Lines representing the 25th percentile of periphyton chlorophyll a 

from all open-canopy sites in this study (5.2 mg/m2

) 

and the 75th percentile value for open-canopy reference 

sites (16 mg/m2

) also were plotted on figures 7 and 8 to 

provide additional total nitrogen and total phosphorus 

concentrations. An estimated concentration of 0.45 

mg/L for total nitrogen and 0.027 mg/L for total phosphorus corresponded to the periphyton chlorophyll a 

concentration of 5.2 mg/m2 (25th percentile from the 

open-canopy sites) and an estimated concentration of 

0.90 mg/L for total nitrogen and 0.075 mg/L for total 

phosphorus corresponded to the periphyton chlorophyll a concentration of 16 mg/m2 (75th percentile 

value for open-canopy reference sites). It is reasonable 

to assume that the data for impaired open-canopy sites 

would represent conditions most favorable for the 

growth of nuisance algae. If nutrient criteria were 

established from data collected under these conditions, 

it could also be applied to other conditions (closed-canopy sites) that are less favorable for the growth of nuisance algae because of light limitation, and could be 

considered a conservative limit.

The concentrations of total nitrogen and total 

phosphorus obtained using several potential methods 

for nutrient criteria development using data in this 

study are summarized in table 4. These methods are 

some of the possible techniques that can be used by 

water-resources managers; depending on the designated use of a specific area, other calculated percentiles 

or estimates might be more appropriate.

The resulting total nitrogen and total phosphorus 

concentrations are generally similar for the various 

approaches. The lowest total nitrogen and total phosphorus concentrations were the subecoregion 59 preliminary criteria developed by the USEPA

(0.57 mg/L for total nitrogen and 0.024 mg/L for total 

phosphorus) and the estimated total nitrogen and total 

phosphorus concentrations that corresponded to the 

25th percentile of chlorophyll a from all open-canopy 

sites in this study (0.45 mg/L for total nitrogen and 

0.027 mg/L for total phosphorus). The highest total 

nitrogen (1.3 mg/L) and total phosphorus

(0.120 mg/L) concentrations corresponded to the estimated concentration from the median literature concentration of chlorophyll a from moderately enriched 

streams (21 mg/m2

). A combination of these methods 

may aid in the selection of an appropriate range of total 

nitrogen and total phosphorus concentrations to be 

used for nutrient criteria development in wadeable 

New England Coastal streams.
APPLICATION OF NUTRIENT AND CHLOROPHYLL a DATA TO IN-STREAM CRITERIA DEVELOPMENT BY WATER-RESOURCES MANAGERS 13

Figure 7. Graph showing Relation between total nitrogen and periphyton chlorophyll a concentrations for the six open-canopy sites sampled 

five times from June through September 2001 in the New England Coastal Basins study area in Massachusetts and New Hampshire.

1.3 mg/L (estimated)

 0.90 mg/L (estimated)

 0.45 mg/L (estimated)

21 mg/m2

16 mg/m2

5.2 mg/m2

EXPLANATION

Site type

 Reference

 Moderately impaired

 Impaired

 

Chlorophyll a

5.2 mg/m2 25th percentile from all open- 

 canopy sites

16 mg/m2 75th percentile from open- 

 canopy reference sites 

21 mg/m2 Median literature value for 

 moderately enriched streams 

 (Biggs, 1996)

1

10

100

 TOTAL NITROGEN,

IN MILLIGRAMS PER LITER (mg/L)

CHLOROPHYLL a,

IN MILLIGRAMS PER SQUARE METER (mg/m2)

0.1

1 10 100 1,000

Figure 8. Graph showing Relation between total phosphorus and periphyton chlorophyll a concentrations for the six open-canopy sites 

sampled five times from June through September 2001 in the New England Coastal Basins study area in Massachusetts and New Hampshire.

0.120 mg/L (estimated)

 0.075 mg/L (estimated)

21 mg/m2

16 mg/m2

5.2 mg/m2

0.1

1

10

 TOTAL PHOSPHORUS,

IN MILLIGRAMS PER LITER (mg/L)

CHLOROPHYLL a,

IN MILLIGRAMS PER SQUARE METER (mg/m2)

0.001

1 10 100 1,000

 0.027 mg/L (estimated)

0.01

EXPLANATION

Site type

 Reference

 Moderately impaired

 Impaired

 

Chlorophyll a

5.2 mg/m2 25th percentile from all open- 

 canopy sites

16 mg/m2 75th percentile from open- 

 canopy reference sites 

21 mg/m2 Median literature value for 

 moderately enriched streams 

 (Biggs, 1996)
14 Nutrient and Chlorophyll Relations in Selected Streams of the New England Coastal Basins in Massachusetts and New Hampshire, June-September 2001

SUMMARY AND CONCLUSIONS

The U.S. Environmental Protection Agency is 

currently developing guidance to assist state waterresources managers with establishing nutrient and algal 

criteria to prevent streams and rivers from becoming 

impaired and to preserve them for designated water 

uses (such as the protection of wildlife). Nutrient levels differ among regions because of variations in geology, climate, soil, and other physical factors. 

Therefore, for the criteria to be most effective, ecoregional variations need to be considered. 

Thirteen stream sites, primarily in eastern Massachusetts, were selected for a nutrient-chlorophyll 

assessment study. The sites represent a range of waterquality impairment conditions (reference, moderately 

impaired, impaired) based on state regulatory agency 

assessments and previously assessed nitrogen, phosphorus, and dissolved-oxygen data. In addition, a combination of open- and closed-canopy sections were 

sampled at six of the sites to investigate the effect of 

sunlight on algal growth. Among the sites sampled, 

median nutrient concentrations were lowest at the two 

reference sites and highest at the six impaired sites. 

When sites were grouped by site type, there were statistically significant differences (p < 0.05) among all 

site types for total nitrogen and total phosphorus. 

The chlorophyll a concentrations from periphyton samples were positively correlated with total nitrogen and total phosphorus concentrations at the openand closed-canopy sites. Correlations were higher at 

the open-canopy sites than at the closed-canopy sites 

because light stimulates the production of algal biomass and enhances algal-nutrient relations. Median concentrations of chlorophyll a from periphyton were 

highest at impaired sites and were significantly higher 

at open-canopy sites than at sites with closed canopies. 

Results of analysis of periphyton chlorophyll a concentrations from the six sites that had open- and closedcanopy sampling locations indicated that open-canopy 

sites had higher concentrations of chlorophyll a among 

all three site types. Nutrient concentrations, types of 

substrate, and stream velocities were similar between 

the closed- and open-canopy locations at the same site, 

indicating that light was affecting algal biomass as 

measured by chlorophyll a.

Linear regression was used to estimate the total 

nitrogen and total phosphorus concentrations that corresponded to various chlorophyll a thresholds. Nutrient concentrations were plotted as a function of 

chlorophyll a concentrations. A regression line was 

drawn and used to estimate concentrations of total 

nitrogen and total phosphorus from concentrations of 

chlorophyll a. On the basis of a median value in the literature for periphyton chlorophyll a of 21 mg/m2 for 

moderately enriched streams, total nitrogen and total 

phosphorus for this ecoregion (subecoregion 59) were 

estimated from a regression line using the literature 

value to yield concentration thresholds of 1.3 mg/L for 

total nitrogen and 0.12 mg/L for total phosphorus. 

Lines representing the 25th percentile of periphyton 

chlorophyll a concentrations for all of the open-canopy 

sites in this study (5.2 mg/m2

) and the

75th-percentile value for open-canopy reference sites 

(16 mg/m2) also were plotted to provide additional 

nutrient limits based on allowable levels of algae. The 

25th-percentile total nitrogen and total phosphorus concentrations were calculated with all of the study data as 

a possible additional threshold. From these data, concentrations of 0.64 mg/L for total nitrogen and 0.030 

mg/L for total phosphorus were obtained. As another 

possible method of threshold development, the 10thpercentile concentrations of total nitrogen and total 

Table 4. Summary of total nitrogen and total phosphorus concentrations 

for potential methods of nutrient criteria development in the Northeastern 

Coastal Zone in Massachusetts and New Hampshire

[mg/L, milligrams per liter]

Criteria method

Total 

nitrogen 

(mg/L)

Total 

phosphorus 

(mg/L)

Subecoregion 59 preliminary criteria. 0.57 0.024

25th percentile-all sites in this study. .64 .030

10th percentile-impaired sites in this 

study.

.73 .036

Estimated concentrations of total nitrogen and total phosphorus1

Estimated concentration at the 25th

percentile of chlorophyll a from all 

open-canopy sites.

.45 .027

Estimated concentration at the 75th

percentile of chlorophyll a from all 

open-canopy reference sites.

.90 .075

Estimated concentration at the median 

literature concentration for chlorophyll 

a for moderately enriched streams.

1.3 .120

1 Concentrations of total nitrogen and total phosphorus are 

estimated from chlorophyll a concentrations in this study (figs. 7 and 8).
REFERENCES CITED 15

phosphorus were calculated using all of the impaired 

sites in this study. Concentration thresholds of 0.73 

mg/L for total nitrogen and 0.036 mg/L for total phosphorus were obtained. These nutrient concentrations 

derived from current data (2001) may contribute to 

development of a potential set of regional nutrient criteria. The combination of these methods may aid in the 

selection of an appropriate range of total nitrogen and 

total phosphorus concentrations to be used by waterresources managers for nutrient criteria development.

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