U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2007–5022

Prepared in cooperation with the 

Massachusetts Department of Environmental Protection, Division of Watershed Management

Assessment of Data for Use in the Development of 

Nutrient Criteria for Massachusetts Rivers and Streams 
Assessment of Data for Use in the Development of 

Nutrient Criteria for Massachusetts Rivers and Streams

By Marc J. Zimmerman and Kimberly W. Campo

Prepared in cooperation with the 

Massachusetts Department of Environmental Protection, 

Division of Watershed Management

Scientific Investigations Report 2007–5022

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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Suggested citation:

Zimmerman, M.J., and Campo, K.W., 2007, Assessment of data for use in the development of nutrient criteria for 

Massachusetts rivers and streams: U.S. Geological Survey Scientific Investigations Report 2007–5022, 44 p.

For more information, contact:

U.S. Geological Survey

Massachusetts-Rhode Island Water Science Center

10 Bearfoot Road

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iii

Contents

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

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

Sampling Sites and Categories ...................................................................................................................2

Sampling-Site Selection ......................................................................................................................4

Sampling-Site Categories....................................................................................................................4

Sample Collection and Water-Quality Analyses.......................................................................................5

Assessment of Data.......................................................................................................................................8

Characterization of Water-Quality Data............................................................................................8

Nutrients and Turbidity..............................................................................................................14

Color............................................................................................................................................20

Field Parameters........................................................................................................................20

Chlorophyll a Concentrations and Plant Densities...............................................................20

Categorical Descriptions of Data.....................................................................................................20

U.S. Environmental Protection Agency Nutrient Ecoregions.............................................20

Drainage-Basin Size..................................................................................................................20

Massachusetts Nutrient Ecoregions......................................................................................21

Effects of Dischargers on Water Quality ..............................................................................21

Canopy Openness......................................................................................................................21

Relations Among Categorical Data ........................................................................................23

Correlations among Water-Quality Variables ................................................................................23

Relations among Chlorophyll a, Nitrogen, Phosphorus, and Canopy Openness .....................24

Stream-Velocity Effects .....................................................................................................................24

Effect of Antecedent Flows......................................................................................................24

Effect of Slope ............................................................................................................................26

Summary and Conclusions.........................................................................................................................27

Acknowledgments.......................................................................................................................................28

References Cited................................................................................................................................... 28–29

Figures

1. Map of Massachusetts showing sampling sites, presence of upstream National

Pollutant Discharge Elimination System permitted dischargers, U.S. Environmental

Protection Agency ecoregions, and Massachusetts nutrient ecoregions.........................3

2–17. Graphs showing—

 2. Distribution of median (A) total phosphorus, (B) total nitrogen, (C) total dissolved

nitrogen, and (D) chlorophyll a concentrations at all sampling sites by year in

Massachusetts............................................................................................................................10

 3. Distribution of median (A) total phosphorus, (B) total nitrogen, (C) total dissolved

nitrogen, and (D) chlorophyll a concentrations at 12 sampling sites by year in

Massachusetts............................................................................................................................11

 4. Distribution of median (A) total phosphorus, (B) total nitrogen, (C) total dissolved

nitrogen, and (D) chlorophyll a concentrations at all sampling sites by ecoregion in

Massachusetts............................................................................................................................15
iv

 5. Distribution of median (A) total phosphorus, (B) total nitrogen, (C) total 

dissolved nitrogen, and (D) chlorophyll a concentrations at all sampling sites 

by Massachusetts nutrient ecoregion ....................................................................................16

6. Distribution of median (A) total phosphorus, (B) total nitrogen, (C) total 

dissolved nitrogen, and (D) chlorophyll a concentrations at all sampling sites 

by drainage-basin-size class in Massachusetts...................................................................22

 7. Distribution of median (A) total phosphorus, (B) total nitrogen, (C) total dissolved 

nitrogen, and (D) chlorophyll a concentrations at all sampling sites by National 

Pollutant Discharge Elimination System discharger category in Massachusetts ..........30

 8. Distribution of median periphyton chlorophyll a concentrations at (A) closedand (B) open-canopy sampling sites by Massachusetts nutrient ecoregion...................31

 9. Distribution of median periphyton chlorophyll a concentrations at (A) closedand (B) open-canopy sampling sites for U.S. Environmental Protection Agency 

ecoregions VIII and XIV in Massachusetts............................................................................32

 10. Distribution of median periphyton chlorophyll a concentrations at (A) closed- and 

(B) open-canopy sampling sites by drainage-basin-size class in Massachusetts .........33

 11. Distribution of median periphyton chlorophyll a concentrations at (A) closedand (B) open-canopy sampling sites by National Pollutant Discharge Elimination 

System discharger category in Massachusetts....................................................................34

 12. Density of (A) filamentous periphyton, (B) periphyton film, (C) aquatic plants, 

(D) aquatic moss, and (E) periphyton floc as a function of median total phosphorus 

concentrations and the percentage of canopy openness at all sampling sites ..............35

 13. Density of (A) filamentous periphyton, (B) periphyton film, (C) aquatic plants, 

(D) aquatic moss, and (E) periphyton floc as a function of median total nitrogen 

concentrations and the percentage of canopy openness at all sampling sites ..............36

 14. Median (A) total phosphorus and (B) total nitrogen concentrations as a function 

of median chlorophyll a concentrations by Massachusetts nutrient ecoregion and 

National Pollutant Discharge Elimination System discharger category .................... 37–38

 15. Median (A, B) total phosphorus and (C, D) total nitrogen concentrations as 

a function of median chlorophyll a concentrations at (A, C) closed- and (B, D) 

open-canopy sites by Massachusetts nutrient ecoregion and National Pollutant 

Discharge Elimination System discharger category ..................................................... 39–42

 16. Median (A) total phosphorus concentrations, (B) total nitrogen concentrations, 

and (C) ratio of total nitrogen to total phosphorus as a function of median 

chlorophyll a concentrations and percentage of canopy openness in 

Massachusetts............................................................................................................................43

 17. Median (A) total phosphorus, (B) total nitrogen, (C) total dissolved nitrogen, 

and (D) chlorophyll a concentrations at all sampling sites as a function of slope in 

Massachusetts............................................................................................................................44
Tables

1. U.S. Geological Survey water-quality stations, station identifiers, and ancillary 

information ............................................................................................................................... 6–7

2. Summary statistics for median values of all water-quality parameters measured at

sampling stations .........................................................................................................................9

3. Annual median water-quality data at sites that were sampled in 2001, 2003, and 2004 ... 12–13

4. Twenty-fifth-percentile values for total phosphorus and total nitrogen concentrations 

and turbidity measured in U.S. Environmental Protection Agency ecoregions 

compared to values measured in this study and in Massachusetts low-, 

intermediate-, and high-nutrient ecoregions ........................................................................14

5. Median values of representative data for stations in this report ......................................... 17–19

6. Correlation coefficients among major water-quality parameters and percentage of 

open canopy and drainage area..............................................................................................24

7. Correlation coefficients among water-quality parameters, percentage of open canopy, 

and drainage area based on Massachusetts nutrient ecoregions ...................................25

8. Regression coefficients for chlorophyll a versus total phosphorus, total nitrogen, 

the ratio of total nitrogen to total phosphorus, and percentage of open canopy 

for all sites, closed-canopy sites, and open-canopy sites .................................................26
vi

Conversion Factors, Horizontal Datum, and Abbreviations

SI to Inch/Pound

Multiply By To obtain

centimeter (cm) 0.3937 inch (in.)

cubic meter per second (m3/s) 70.07 acre-foot per day (acre-ft/d)

gram (g) 0.03527 ounce, avoirdupois (oz)

kilometer (km) 0.6214 mile (mi)

liter (L) 0.2642 gallon (gal)

meter per second (m/s) 3.281 foot per second (ft/s)

square centimeter (cm2) 0.1550 square inch (in2)

square meter (m2) 10.76 square foot (ft2)

square kilometer (km2) 0.3861 square mile (mi2)

Inch/Pound to SI

Multiply By To obtain

acre-foot per day (acre-ft/d) 0.01427 cubic meter per second (m3/s)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

foot per second (ft/s) 0.3048 meter per second (m/s)

gallon (gal) 0.003785 cubic meter (m3) 

gallon (gal) 3.785 liter (L) 

million gallons per day (Mgal/d) 0.04381 cubic meters per second (m3/s)

inch (in.) 2.54 centimeter (cm)

mile (mi) 1.609 kilometer (km)

ounce, avoirdupois (oz) 28.35 gram (g) 

square foot (ft2) 0.09290 square meter (m2)

square inch (in2) 6.452 square centimeter (cm2)

square mile (mi2) 2.590 square kilometer (km2) 

Horizontal coordinate information is referenced to the North American 

Datum of 1983 (NAD 83).

Specific conductance is given in microsiemens per centimeter at 

25 degrees Celsius (μS/cm at 25°C).

Concentrations of chemical constituents in water are given in milligrams per liter (mg/L).

Abbreviations

DO Dissolved oxygen

DWM Division of Watershed Management

MassDEP Massachusetts Department of Environmental Protection

NPDES National Pollutant Discharge Elimination System

NTU Nephelometric turbidity units

NWQL National Water Quality Laboratory

PCU Platinum-cobalt units

RPD Relative percent difference

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey
Abstract

The U.S. Geological Survey synthesized, reviewed, 

and assessed Massachusetts water-quality data for use in the 

development of either numerical nutrient criteria for rivers 

and streams or a science-based framework for interpreting 

narrative criterial for nutrients. Water-quality data collected 

from 65 Massachusetts locations were selected to represent 

a wide range, but not a statistical selection, of drainage 

basins and high-, intermediate-, and low-nutrient ecoregions. 

Additional sites were selected at some locations to provide 

data to compare open- and closed-canopy effects on 

periphyton chlorophyll a concentrations. Nutrient and 

chlorophyll a concentrations are the primary focus of this 

study. Data for turbidity, color, dissolved oxygen, specific 

conductance, pH, and measures of aquatic-plant density also 

were examined. Water-quality data were analyzed by categories of year, ecoregion, drainage-basin size, Massachusetts 

nutrient ecoregion, presence of upstream wastewater dischargers, and canopy openness. Graphs and statistical analyses were 

used to evaluate data. 

The U.S. Environmental Protection Agency (USEPA)

recommends the 25th-percentile value of a waterquality constituent as the numerical nutrient criterion when 

using all available data for the constituent. In this study of 

Massachusetts waters, the 25th percentiles of median values at 

all sampling stations were: total phosphorus, 0.019 milligram 

per liter (mg/L); total nitrogen, 0.44 mg/L; and turbidity, 

1.2 nephelometric turbidity units (NTU). When the data are 

sorted by the two USEPA nutrient ecoregions in Massachusetts 

(VIII and XIV), the new values are: for Ecoregion VIII, total 

phosphorus, 0.009 mg/L; total nitrogen, 0.289 mg/L; and 

turbidity, 1.7 NTU; for Ecoregion XIV, total phosphorus, 

0.028 mg/L; total nitrogen, 0.583 mg/L; and turbidity, 

3.1 NTU. For the three Massachusetts lake-based nutrient 

ecoregions, the values are: high-nutrient ecoregion, total phosphorus, 0.030 mg/L; total nitrogen, 0.642 mg/L; and turbidity, 

1.5 NTU; intermediate-nutrient ecoregion, total phosphorus, 

0.016 mg/L; total nitrogen, 0.419 mg/L; and turbidity, 1.1 

NTU; and low-nutrient ecoregion, total phosphorus, 0.011 

mg/L; total nitrogen, 0.289 mg/L; and turbidity, 0.7 NTU. 

In general, median nutrient concentrations were found 

to be higher in the three following categories of analysis 

than in their complementary groups: sites in USEPA nutrient Ecoregion XIV, sites downstream from major National 

Pollutant Discharge Elimination System-permitted wastewater 

dischargers, and sites in the Massachusetts high-nutrient 

ecoregion. The largest drainage-basin size class had higher 

median nitrogen (total and dissolved) concentrations than the 

smallest, but total median phosphorus concentrations were not 

significantly different. Median chlorophyll a concentrations 

did not vary significantly among the categories analyzed. The 

effects of open and closed canopies on median chlorophyll 

a concentrations were greater within groups defined by 

the categories used in this study than between the groups; 

open-canopy sites generally had higher median chlorophyll a

concentrations than closed-canopy sites. More than 40 percent 

of the sampling stations were located downstream from 

major wastewater dischargers, and these dischargers were 

disproportionately located in USEPA Ecoregion XIV and the 

Massachusetts high-nutrient ecoregion and thus may constitute 

the same effect on water quality.

A number of expected relations among parameters 

analyzed did not materialize. Chlorophyll a did not correlate 

well with any other parameters. No strong relations among 

the categories and nutrient concentrations or canopy openness 

were apparent. The occurrence of antecedent flows exceeding 

mean annual discharges by 300 percent within 28 days of 

sample collection did not correlate with decreases in chlorophyll a concentrations that might have resulted from scouring 

associated with increasing velocities. No relation was apparent 

between a measure of stream slope (another surrogate for 

velocity) and nutrient or chlorophyll a concentrations.

The relatively small number of sites in some of the 

categories analyzed and the presence of wastewater-treatment facilities on many of the streams made it difficult to 

definitively interpret the effects of the different groups within 

descriptive categories. A long-term sampling program providing representative data from a wider variety of streams than 

were sampled for this study, could yield a more robust dataset 

for analysis.

Assessment of Data for Use in the Development of 

Nutrient Criteria for Massachusetts Rivers and Streams

By Marc J. Zimmerman and Kimberly W. Campo
Introduction

The U.S. Environmental Protection Agency (USEPA) has 

the responsibility for ensuring that water-quality standards are 

met in the Nation’s waterways and other bodies of water. The 

USEPA may also be responsible for enforcement actions when 

these standards are not met. Individual States are responsible 

for establishing water-quality standards, evaluating water 

quality, and reporting violations of particular standards to the 

USEPA. The USEPA has promulgated guidance water-quality 

criteria for States to use as starting points in the establishment 

of their own criteria that protect designated uses of rivers and 

streams and that reflect local conditions (U.S. Environmental 

Protection Agency, 2000, 2001). The standards serve the 

dual purpose of controlling pollutant release or discharge and 

of defining the maximum level of a pollutant or condition 

allowable to protect designated uses of ambient waters. For 

nutrients, the USEPA hopes to help States establish quantified, 

numerical criteria for causal variables, such as nitrogen and 

phosphorus, and response variables, such as chlorophyll a

and turbidity. The establishment of these criteria could protect 

local uses and maintain downstream uses. To adopt these 

criteria, the USEPA has recommended three possible 

approaches: (1) develop criteria that reflect local conditions 

and protect designated uses; (2) adopt the USEPA’s guidance 

water-quality criteria for nutrients; or (3) develop protective 

criteria using appropriate methods and data. As an example 

of the third option, Robertson and others (2001) provide an 

alternative, regional approach to determining nutrient criteria 

in rivers and streams.

The Massachusetts Department of Environmental 

Protection (MassDEP) Division of Watershed Management 

(DWM) is responsible for developing water-quality criteria for 

nutrients and other water-quality parameters for water bodies 

throughout the State of Massachusetts. The MassDEP did not 

feel that the criteria developed by the USEPA for Ecoregions 

VIII (Nutrient Poor, Largely Glaciated, Upper Midwest and 

Northeast) and XIV (Eastern Coastal Plain), the ecoregions in 

which Massachusetts lies, appropriately represented the 

water-quality conditions in the State (Dennis R. Dunn, 

Massachusetts Department of Environmental Protection, oral 

commun., 2006). That is, much of the data included in the 

USEPA’s criteria were obtained from areas where nutrient 

concentrations were not representative of conditions in 

Massachusetts, and using those data to derive nutrient criteria 

would result in concentrations inappropriate for Massachusetts 

rivers and streams. Therefore, the MassDEP decided to obtain 

new data that adequately reflected conditions in the State. 

The MassDEP DWM is considering the development of 

not only numerical nutrient criteria, but also an alternative, 

science-based framework for interpreting narrative criteria 

for nutrients. These narrative criteria would limit nutrients to 

concentrations that do not produce noxious conditions (Mark 

Mattson and Russell Isaac, Massachusetts Department of 

Environmental Protection, Division of Watershed 

Management, written commun., 2006).

The U.S. Geological Survey (USGS), in cooperation with 

the MassDEP DWM, collected water-quality and ancillary 

data in 2003 and 2004 for the MassDEP DWM to use in 

establishing these criteria or in developing a framework for 

interpreting the narrative criteria. Samples were collected 

in June, July, August, and September of each year. To avoid 

effects of storm-runoff high flows, samples were not collected 

until summer low-flow conditions were re-established 

after storms.

This report describes the review, synthesis, and assessment of water-quality data collected in 2003 and 2004 by 

the USGS for the development of nutrient criteria by the 

MassDEP; data collected by another USGS study in 2001 

(Riskin and others, 2003) are also included, as recommended 

by the USEPA (U.S. Environmental Protection Agency, 

2000, 2001). The analyses described in the report were those 

determined by the MassDEP as being most useful to its efforts 

to establish nutrient criteria.

Water-quality and related parameters described in this 

report include the nutrients, phosphorus and nitrogen, periphyton chlorophyll a, turbidity, aquatic-plant density, dissolved 

oxygen concentration, color, and specific conductance. The 

report also considers yearly differences, the effects of some 

geographical, or landscape, characteristics on water quality, 

the presence or absence of upstream licensed dischargers (in 

general, this refers to wastewater-treatment plants), the degree 

of canopy openness, and antecedent flow conditions. 

Data were from 76 sites distributed throughout the 

Massachusetts mainland; no sites were chosen on islands, such 

as Martha’s Vineyard or Nantucket. The sites were selected 

to provide a wide range of representative samples of various 

types of surface waters, not to obtain a statistical sample. 

Sixty-five of the sites had unique USGS station identifiers 

associated with them (fig. 1). At 11 of these locations, there 

were 2 closely colocated sites, which were differentiated by 

their extent of canopy openness where one site was described 

as open canopy and the other as closed canopy; identical 

USGS station identifiers were used for these sites. 

Sampling Sites and Categories

Sampling sites were selected by the DWM based 

primarily on prior knowledge and experience from state-wide 

investigations. Specific sites were included to obtain data 

representing predetermined categories of data analyses, 

such as basin area, nutrient ecoregion, canopy openness; the 

number of sites does not necessarily represent the proportion 

of streams in each category. Dodds and Welch (2000) recommend that the full range of stream categories be sampled in 

proportion to their occurrence when developing models for 

setting nutrient criteria.

 Assessment of Data for Use in the Development of Nutrient Criteria
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SAMPLING SITE AND IDENTIFIER—Color indicatespresence and type of National Pollutant DischargeElimination System discharger. (See table 1 for corresponding USGS station identification) 

10 Major

MinorNone

MASSACHUSETTS NUTRIENT ECOREGION

EXPLANATION

LowIntermediateHigh

STATE BOUNDARY

U.S. ENVIRONMENTAL PROTECTION AGENCY ECOREGIONS

ECOREGION VIII—Nutrient Poor, Largely Glaciated, Upper Midwest and NortheastECOREGION XIV—Eastern Coastal Plain

0 20 MILES 10

0 20 KILOMETERS 10

Base from U.S. Geological Survey digital data, 1:25,000, 1991Lambert conformal conic projection. 1983 North American datumMassachusetts coordinate system mainland zone

73°30' 70°

41°30'

43°

Figure 1. Map of Massachusetts showing sampling sites, presence of upstream National Pollutant Discharge Elimination System permitted dischargers, U.S. Environmental Protection Agency ecoregions, and Massachusetts nutrient ecoregions.

Sampling Sites and Categories 
Sampling-Site Selection

Forty-three streams were selected for sampling by the 

DWM in 2003, representing free-flowing reaches located in 

each of three lake-based nutrient ecoregions in Massachusetts 

(Rohm and others, 1995; fig. 1). The streams included headwater streams, major tributaries, and mainstem rivers (Steven 

Halterman, Massachusetts Department of Environmental 

Protection, Division of Watershed Management, written 

commun., 2006). In order to ensure the inclusion of streams 

characterized by a wide range of nutrient concentrations and 

environmental conditions, sampling stations were selected 

on the basis of historical phosphorus data and field observations of algal blooms or extensive periphyton growth. To 

minimize the effects of light on periphyton distribution and 

density wherever possible, closed-canopy sites were preferred 

for periphyton sampling. Streams in each size category and 

nutrient ecoregion, with water-quality conditions ranging from 

near-pristine to highly eutrophic, were represented in the sites 

selected (fig. 1; table 1). 

In order to test the effect of stream shading on nutrientrelated effects, the 2004 sampling design included stations 

where open and closed canopy sites in close proximity could 

be sampled (Steven Halterman, Massachusetts Department 

of Environmental Protection, Division of Watershed 

Management, written commun., 2006). In addition, 13 sites 

sampled in 2003 were resampled in 2004 to test for year-toyear differences. To gain insights into variability within 

1 sampling season, samples were collected 3 times at 

12 stations in 2004.

Data from a 2001 investigation (Riskin and others, 2003) 

were incorporated to enlarge the water-quality dataset used 

in this study. In the combined water-quality dataset of data 

collected for the DWM and the data from the 2001 study, color 

was the only parameter not in the 2001 data. The study by 

Riskin and others (2003) selected sites to represent impaired 

and moderately impaired water-quality conditions and sites for 

reference. The 12 Massachusetts sampling sites in that study 

also were used in the 2003 and 2004 field studies; however, 

the sites are all located in eastern Massachusetts and do not 

represent conditions throughout the State.

Some of the water-quality data were collected from multiple sites on the same streams: the Assabet River, with three 

sites, is a tributary to the Concord River, one site; the Charles 

River, four sites; the Millers River, two sites; the Nashua 

River, two sites; and the French River, two sites. Furthermore, 

the East Branch of the Neponset River, with one site, is also a 

major tributary of the Neponset River, which also has one site. 

Possible similarities in data from these rivers with multiple 

sites may weight their effects on the analyses.

Sampling-Site Categories

Rohm and others (1995) described nutrient ecoregions for 

the northeastern United States based on measured concentrations of phosphorus in lakes. In Massachusetts, three 

phosphorus-based nutrient ecoregions were defined, and 

the DWM used these ecoregions to guide the selection of 

stream-sampling sites (fig. 1). The high phosphorus-concentration nutrient ecoregion was in the northeastern part 

of Massachusetts and along the Connecticut River, and the 

low phosphorus-concentration nutrient ecoregion primarily 

comprised the southeastern part of the State, including Cape 

Cod, and the central part of western Massachusetts. The 

intermediate phosphorus-concentration nutrient ecoregion 

included the Housatonic River Basin, central Massachusetts 

east of the Connecticut River, and about half of southeastern 

Massachusetts. Thirty stations were chosen in the high 

phosphorus-concentration nutrient ecoregion of the State, 

22 stations in the intermediate phosphorus-concentration 

nutrient ecoregion, and 13 stations in the low phosphorus-concentration nutrient ecoregion. The unequal distribution of sites 

among the three nutrient ecoregions may have the effect of 

weighting the data more strongly toward reflecting conditions 

in the high phosphorus-concentration nutrient ecoregion.

The MassDEP DWM selected basins for sampling 

ranging in size from watersheds of less than 10 mi2 (25.9 km2) 

(second-order streams, in general), 10 to approximately 

100 mi2 (25.9 to approximately 259 km2) (third- and fourthorder streams, in general), and 100 to approximately 350 mi2

(259 to approximately 900 km2)(fifth order, in general) (Steven 

Halterman, Massachusetts Department of Environmental 

Protection, Division of Watershed Management, written 

commun., 2006). In this study’s analyses, the sites were sorted 

among basins that were divided into 3 size groups: (1) 22 sites 

with drainage basins less than 10 mi2; (2) 31 sites with drainage basins from 10 to 90 mi2

 (233 km2); and (3) 12 sites with 

drainage basins from 90 to 350 mi2. (As noted above, some 

of the sites are located in the same basin, a potential source 

of autocorrelation in the data analyses.) While this distribution of basins may reflect the distribution of stream basins in 

the State, the small number of large basins may exaggerate 

differences among the size categories and may affect statistical 

interpretations of these data.

Twenty-six of the sampling locations are located downstream from major NPDES-permitted dischargers; 25 of these 

locations are downstream from wastewater-treatment plants 

and one location is downstream from a nuclear power plant. 

(Major NPDES-permitted dischargers release more than 

1 Mgal/d; minor NPDES-permitted dischargers release less 

than 1 Mgal/d.) Six of these locations have both open- and 

 Assessment of Data for Use in the Development of Nutrient Criteria
closed-canopy sampling sites; thus, 42 percent of all sites 

are downstream from major NPDES dischargers. Eleven 

locations, including 2 with open- and closed-canopy sites, 

are downstream from minor NPDES-permitted dischargers, and the remaining 28 locations (including 3 with both 

open- and closed-canopy sites) have no dischargers in their 

upstream catchments. Thus, about 57 percent of the sites are 

downstream from major or minor dischargers. A substantial 

majority of the NPDES-permitted major and minor dischargers 

upstream from sampling stations are located in the intermediate- and high-nutrient ecoregions (fig. 1); the numbers of 

dischargers in these two ecoregions are approximately equal. 

The low-nutrient ecoregion only has one major NPDESpermitted discharger. Thus, relations between water-quality 

data in this study and lake-based nutrient ecoregions may be 

more strongly affected by NPDES-permitted dischargers than 

by the nutrient ecoregions. Or there may be other explanatory 

variables, such as population, which were not investigated 

during this study. 

Although USEPA ecoregions (Omernik, 1987) were 

not used to select sites, they were used to examine data. 

Massachusetts lies in two of these geographic ecoregions 

(fig. 1): the Northeastern Coastal Zone (Ecoregion XIV, 

Eastern Coastal Plain) that covers about 60 percent of the State 

and the Northeastern Highlands (Ecoregion VIII, Nutrient 

Poor, Largely Glaciated Upper Midwest and Northeast) that 

includes the remainder of the State (U.S. Environmental 

Protection Agency, 2000, 2001). Forty-four sampling 

stations were in Ecoregion XIV and 21 were in Ecoregion 

VIII. The unequal distribution of sites, although not part of the 

original field study design, may weight interpretations toward 

Ecoregion XIV conditions.

In light of the findings of Riskin and others (2003) that 

shading affected the concentrations of periphyton chlorophyll 

a, sampling sites were selected in 2004 to include opencanopy sites rather than exclusively choosing closed-canopy 

sites. Eleven of the stations had both open- and closed-canopy 

sites, 34 had only closed-canopy sites, and 20 had only opencanopy sites. 

Sample Collection and Water-Quality 

Analyses

Water-quality sample collection followed USGS 

guidelines for collecting grab samples (Webb and others, 

1999). Because the streams were generally small, shallow, 

and well-mixed, integrated sampling using equal-width- or 

equal-depth-increment procedures were not needed. Samples 

were collected from the centroid of flow in 3-L Teflon bottles. 

After collection, water-quality samples were processed and 

stored on ice prior to shipment to the USGS National Water 

Quality Laboratory (NWQL) for analysis (Patten and Truitt, 

1992, 2000). Samples for determination of turbidity were 

stored on ice and returned to the USGS Massachusetts-Rhode 

Island Water Science Center for analysis using a Hach 

2100N turbidimeter (Wilde and Gibs, 1998). Water color was 

determined in the field using a Hach Color Test Kit (Hach 

Company, 1984; Mark Mattson, Massachusetts Department 

of Environmental Protection, Division of Watershed 

Management, written commun., 2003). Field-parameter data 

(temperature, specific conductance, pH, and dissolved oxygen 

concentration) were collected with each water-quality sample 

(Wilde and Gibs, 1998).

Chlorophyll a was measured in samples collected from 

periphyton attached to submerged rocks (Moulton and others, 

2002). Algae from a section of each rock were completely 

removed by scraping and rinsing, and a foil template was 

made of the scraped area for use in calculating the area. A 

5-mL aliquot of the scraped algae-containing rinsate was 

filtered. The filter was stored and shipped on dry ice to the 

NWQL for analysis (Arar and Collins, 1997). 

 A number of semiquantitative and qualitative observations were made when samples were collected. Stream 

velocity was visually estimated in ranges of: (1) less than 

1 ft/s (0.3 m/s); (2) 1 to 3 ft/s (0.3 to 0.9 m/s); and (3) greater 

than 3 ft/s (0.9 m/s), following DWM standard procedures for 

the collection of ancillary information during water-quality 

sampling. The percentage of open canopy was calculated from 

measurements made with an inclinometer (Fitzpatrick and 

others, 1998). The densities (as percentage of streambed substrate covered) of several categories of aquatic plant life were 

estimated visually in classes defined as not observed (none), 

sparse (1 to 25 percent), moderate (26 to 50 percent), dense 

(51 to 75 percent), and very dense (76 to 100 percent). The 

categories included aquatic plants, filamentous periphyton, 

periphyton film, periphyton floc, and aquatic moss. While the 

values reported seem amenable to semiquantitative analysis, 

the subjective (qualitative) nature of their determination calls 

for caution in any data interpretation.

During the 2003 and 2004 field studies, 5 field-blank and 

13 split-sample-replicate samples were collected for quality 

control. Blank samples provide information on contamination that may occur during sample processing and affect the 

resulting data. One blank sample had a single detection (total 

phosphorus at an estimated concentration of 0.003 mg/L, 

which is less than the reporting level of 0.004 mg/L). Splitsample replicates help define the variability in environmental 

data associated with sample processing. Relative percent 

differences (RPD) were calculated for turbidity and for nutrient and chlorophyll a concentrations. Two pairs of turbidity 

samples and replicates had RPD values that exceeded 10 

percent, as did one of the chlorophyll a sample pairs. None of 

the RPD values for the paired nutrient samples and replicates 

exceeded 10 percent. 

Sample Collection and Water-Quality Analyses 
Table 1. U.S. Geological Survey water-quality stations, station identifiers, and ancillary information used in this report.—Continued

[Map identifier is shown in fig. 1. USGS, U.S. Geological Survey; NPDES, National Pollutant Discharge Elimination System; USEPA, U.S. Environmental Protection Agency]

Map 

identifier 

USGS station 

identification 

number 

Station name Year(s) sampled Canopy type

Category of 

NPDES dischargers 

upstream

USEPA 

ecoregion

Massachusetts nutrient 

ecoregion

Drainage 

area (square 

kilometers)

1 01332350 Paul Brook at Galvin Road at North Adams, Mass. 2004 Closed None VIII Intermediate 5.72 01331630 Hoosic River near North Adams, Mass. 2004 Open Major VIII Intermediate 1753 01331870 North Branch Hoosic River near Clarksburg, Mass. 2004 Closed None VIII Intermediate 74.64 01168160 Deerfield River at Florida Bridge near Zoar, Mass. 2003 Open Major VIII Low 1925 01168921 Tissdell Brook near Adamsville, Mass. 2003 Closed/Open None VIII Low 4.16 01170100 Green River near Colrain, Mass. 2003 Closed None VIII Low 1077 01197000 East Branch Housatonic River at Coltsville, Mass. 2003 Open Major VIII Intermediate 1498 01178215 Westfield River at Route 9 Bridge near Cummington, Mass. 2003 Open None VIII Low 1089 01170905 Roaring Brook near Conway, Mass. 2003 Closed None VIII Low 8.8

10 01197440 Housatonic River below Mohawk Brook near Glendale, Mass. 2003 Open Major VIII Intermediate 72311 01198011 Green River Route 23 near Great Barrington, Mass. 2003 Open None VIII Intermediate 13612 01197225 Hop Brook at Tyringham Center, Tyringham, Mass. 2003 Closed None VIII Low 40.913 1184820 West Branch Farmington River at Otis, Mass. 2003 Closed None VIII Low 59.314 01181000 West Branch Westfield River at Huntington, Mass. 2003 Open None VIII Low 24415 01183070 Dickinson Brook upstream from Water Street at Granville, Mass. 2003 Closed None VIII Low 9.316 01183290 Powdermill Brook near Westfield, Mass. 2003 Closed None XIV High 6.517 01166600 Mormon Hollow Brook near Farley, Mass. 2003 Closed None VIII Intermediate 1018 01165450 Millers River at Route 2, near Wendell Depot, Mass. 2004 Open Major VIII Intermediate 87219 01164000 Millers River at South Royalston, Mass. 2003 Open Major VIII Intermediate 49020 01163820 Beaver Brook above Hoyt Brook near Phillipston, Mass. 2003, 2004 Closed Major VIII Intermediate 1721 01163200 Otter River at Otter River, Mass. 2004 Closed Major VIII Intermediate 87.522 01174560 West Branch Swift River at Cooleyville, Mass. 2003 Closed None VIII Intermediate 1823 01173005 Ware River Site 6 near Barre, Mass. 2003 Closed None XIV Intermediate 24924 01123120 West Brook at Route 20 near Brimfield, Mass. 2004 Open None XIV Intermediate 3.125 01123110 Sherman Pond Outlet at Route 20 at Brimfield, Mass. 2004 Open Minor XIV Intermediate 1526 01123360 Quinebaug River below East Brimfield Dam at Fiskdale, Mass. 2003 Open Minor XIV Intermediate 16227 01123730 Cady Brook at Charlton, Mass. 2003 Closed Major XIV Intermediate 2428 01124275 Burncoat Brook, Pine Street, near Leicester, Mass. 2004 Closed None XIV Intermediate 9.829 01124395 Little River downstream from Turner Road near Charlton, Mass. 2004 Closed Minor XIV Intermediate 26.930 01124292 French River, downstream from Clara Barton Road near 

Oxford, Mass.

2004 Closed/Open Major XIV Intermediate 40.7

31 01125000 French River at Webster, Mass. 2004 Open Major XIV Intermediate 77.432 01095220 Stillwater River near Sterling, Mass. 2001, 2003, 2004 Closed/Open None XIV High 74.933 42294207 North Nashua River near Lancaster, Mass. 2004 Open Major XIV High 284

 Assessment of Data for Use in the Development of Nutrient Criteria
Table 1. U.S. Geological Survey water-quality stations, station identifiers, and ancillary information used in this report.—Continued

[Map identifier is shown in fig. 1. USGS, U.S. Geological Survey; NPDES, National Pollutant Discharge Elimination System; USEPA, U.S. Environmental Protection Agency]

Map 

identifier 

USGS station 

identification 

number 

Station name Year(s) sampled Canopy type

Category of 

NPDES dischargers 

upstream

USEPA 

ecoregion

Massachusetts nutrient 

ecoregion

Drainage 

area (square 

kilometers)

34 01095529 Nashua River Tributary at Lancaster, Mass. 2003 Closed Major XIV High 28535 42331007 Bennetts Brook at Ayer, Mass. 2004 Closed None XIV High 8.536 01096544 Stony Brook at School Street at Chelmsford, Mass. 2001, 2003, 2004 Closed/Open Minor XIV High 10837 01099500 Concord River below River Meadow Brook, at Lowell, Mass. 2003 Open Major XIV High 79538 01100100 Richardson Brook near Lowell, Mass. 2004 Closed/Open None XIV High 1139 01100300 Fish Brook near Andover, Mass. 2004 Open Minor XIV High 1540 01100640 Bare Meadow Brook near Methuen, Mass. 2004 Closed None XIV High 1841 01100844 Powwow River off Mill Street at Amesbury, Mass. 2004 Closed Major XIV High 13042 01096710 Assabet River at Allen Street at Northborough, Mass. 2001, 2003, 2004 Closed/Open Major XIV High 76.443 01096630 Assabet River at School Street near Northborough, Mass. 2004 Closed Major XIV High 47.444 01097000 Assabet River at Maynard, Mass. 2004 Closed/Open Major XIV High 29645 01104615 Charles River above Watertown Dam at Watertown, Mass. 2004 Open Major XIV High 70346 01102500 Aberjona River at Winchester, Mass. 2001, 2003, 2004 Closed/Open Major XIV High 64.247 01101500 Ipswich River at South Middleton, Mass. 2001, 2003, 2004 Closed Minor XIV High 11548 01102345 Saugus River at Saugus Iron Works at Saugus, Mass. 2001, 2003, 2004 Closed Minor XIV High 65.049 01102063 Goldthwait Brook at Foster Street at Peabody, Mass. 2004 Open Minor XIV High 1650 01110500 Blackstone River at Northbridge, Mass. 2003 Closed Major XIV High 36551 01111149 West River upstream side Glen Avenue Bridge at Upton, Mass. 2003 Closed None XIV High 2052 01112160 Mill River at Route 16 at Spindleville, Mass. 2003 Closed None XIV High 28.053 01112170 Mill River at Spindleville, Mass. 2003 Closed None XIV High 29.854 01112262 Mill River at Summer Street near Blackstone, Mass. 2001, 2003, 2004 Closed/Open Major XIV High 73.855 011032058 Charles River at Maple Street at North Bellingham, Mass. 2001, 2003, 2004 Closed Major XIV High 54.456 01103280 Charles River at Medway, Mass. 2003 Open Major XIV High 17057 01103500 Charles River at Dover, Mass. 2004 Open Major XIV High 47358 01105000 Neponset River at Norwood, Mass. 2001, 2003, 2004 Closed Minor XIV High 90.159 01105504 East Branch Neponset River at Canton Junction, Mass. 2001, 2003, 2004 Closed Minor XIV High 72.860 01109000 Wading River near Norton, Mass. 2001, 2003, 2004 Closed/Open Minor XIV Intermediate 11361 01106468 Matfield River at North Central Street at East Bridgewater, Mass. 2001, 2003, 2004 Closed/Open Major XIV Intermediate 79.862 01105883720 Childs River, 2,200 feet north of Route 28, near Waquoit Village, 

Falmouth, Mass.

2003 Closed None XIV Low 4.1

63 0110588368 Quashnet River, 0.8 mile downstream from Route 151, near 

Waquoit Village, Falmouth, Mass.

2003 Closed None XIV Low 11

64 01105883595 Mashpee River upstream from Asher Path Bridge at 

Mashpee, Mass.

2003 Closed None XIV Low 74.9

65 01105880 Herring River at North Harwich, Mass. 2003 Closed None XIV Low 284

Sample Collection and Water-Quality Analyses 
Assessment of Data

USEPA guidelines recommend the use of all existing 

data to describe conditions at all sites selected to characterize 

a State’s water quality. To avoid biasing the data analysis and 

interpretation because of unequal distribution of data among 

sites, the USEPA further recommends the use of a median 

value for each parameter at each site. For example, in this 

study, some sites were sampled five times in 2001, once in 

2003, and three times in 2004, whereas almost all others were 

sampled only once in 2003 or 2004. One site was sampled 

once in both 2003 and 2004 (table 1). Without normalizing the 

data by using medians for each site, analyses would be biased 

toward the results of more frequently sampled sites (U.S. 

Environmental Protection Agency, 2000, 2001). This study 

used the median values as recommended by the USEPA.

To take account of the effects of seasonal differences in 

water quality, the USEPA recommends that medians should 

be determined after separating the data by seasons defined as 

winter (January through March), spring (April through June), 

summer (July through September), and fall (October through 

December). The USEPA recommends the use of either the 

25th-percentile value of median concentrations at all sampled 

sites for setting numerical nutrient criteria when using all 

available data or the 75th-percentile when only using 

reference-site data. In this study, neither seasonal data nor 

extensive reference-site data were available. The existing data 

were collected from June through September, with few data 

collected in June; therefore, median values were not differentiated seasonally. When determining distributions of concentrations among groups of data, median values for all data 

were used. Thus, a 25th-percentile value is actually the 25th 

percentile of the medians; the median value for all stations is 

the median of all station medians.

Natural and anthropogenic effects are considered in 

examining specific factors that may influence water quality. 

Thus, geographic differences, such as ecoregions and 

nutrient ecoregions; hydrologic differences, such as stream 

size and slope and antecedent flow; ecological differences, 

such as degree of canopy openness; and the presence and 

size of NPDES-permitted dischargers are included in this 

report’s analyses. 

Water-quality samples and field parameter data were only 

collected once at a sampling station on a sampling date, even 

if chlorophyll a samples were collected at open- and closedcanopy sites. Therefore, other than the chlorophyll a data, 

the water-quality data associated with co-located open- and 

closed-canopy sites on a given date are identical. 

The software package used for all graphical and statistical 

analyses was S-PLUS Professional version 6.1 (Insightful 

Corp.) Scatter plots, boxplots, and bubble plots were the 

graphical routines used to visually present the data. In most 

of these graphs, data were presented as log concentrations 

because the wide range of concentrations caused by outlier 

values would otherwise make it difficult to differentiate data 

points. Statistical analyses used in this study included summary statistics, correlation analysis, the Kruskal-Wallis Rank 

Sum Test (a=0.05), and linear regression analysis.

Total nitrogen was calculated as the sum of analytical 

results for nitrate plus nitrite, ammonia, and organic nitrogen. 

In calculating total nitrogen values in the raw data, there were 

rare instances of missing data because of analytical results 

for ammonia that were less than the reporting level. In order 

to maximize the number of total nitrogen values that could 

be used in analyses, some substitutions were made for the 

censored ammonia concentrations. If the ammonia reporting 

level was less than 20 percent of the other total nitrogen 

components, then the ammonia reporting level was substituted in the calculation. If the ammonia reporting level was 

greater than 20 percent, then the total nitrogen value was not 

calculated, and data were listed as not available (NA) in tables. 

These approaches were taken to minimize effects on data 

while adding useful data to the evaluations.

In order to describe the water-quality data that compose 

the results of this study, several different approaches are taken. 

These approaches involve splitting the completed dataset into 

categorical subsets that separate geographic (Massachusetts 

nutrient ecoregion, for example), environmental (type of 

upstream NPDES-permitted discharger), and temporal 

(year-to-year) differences for comparison. Subdividing these 

categories occasionally created sample sizes that were too 

small for robust statistical interpretation. Summary statistics 

are presented to describe the general characteristics of the 

data within categories. Then, graphical methods were used to 

enable visual comparisons among the data subsets. Finally, 

statistical analyses examined whether the distributions 

of medians among the data subsets differed significantly. 

Regression and correlation analyses were used to explore 

causal relations among some of the data.

Characterization of Water-Quality Data

Water-quality data at stations are characterized by 

medians (as described previously) that may represent one 

sample per station or multiple samples per station that were 

collected during 1, 2, or 3 years. This introduces variability 

into the dataset (and a different amount of variability per 

station) that is illustrated by summary statistics of water-quality data by year. Summary data (table 2; fig. 2) synthesizing 

the yearly median data indicate that the values vary somewhat 

from year to year but, because the sampling-site selection 

varied from year to year, inferences drawn from these annual 

summary data may not be dependable. Specifically, the 2001 

data in the table represent medians from 12 stations, whereas 

2003 and 2004 data represent more than 30 stations in each 

year. Another factor affecting comparisons of the variability 

among the year-to-year data is the absence of stream-discharge 

data. Measuring discharge was not part of the 2003 and 2004 

field studies, and differences in discharge, even under summer 

low-flow conditions, can cause considerable variations in 

 Assessment of Data for Use in the Development of Nutrient Criteria
Assessment of Data 

Table 2. Summary statistics for median values of all water-quality parameters measured at sampling stations.

[Parentheses enclose all chlorophyll a values, separating them from closed-canopy chlorophyll a values (not in parentheses). 2001, 2003, and 2004 indicate 

the years for which medians were determined]

CONCENTRATIONS OTHER PARAMETERS

Total phosphorus, in milligrams per liter, as P Color, in platinum-cobalt units

2001 2003 2004 All years 2003 2004 Both years

Minimum 0.021 0.004 0.002 0.002 18.6 17 18.5

25th percentile .037 .017 .027 .019 37.2 27 34.7

Median .048 .03 .043 .038 37.2 40 37.2

75th percentile .06 .052 .085 .065 55.8 65 58

Maximum .2 1.12 .51 1.12 112 160 160

Total nitrogen, in milligrams per liter, as N Turbidity, in nephelometric turbidity units

2001 2003 2004 All years 2001 2003 2004 All years

Minimum 0.44 0.214 0.179 0.179 1.2 0.29 0.49 0.29 

25th percentile .71 .369 .601 .44 2.275 .93 1.525 1.2

Median .83 .598 .842 .66 3.1 1.35 1.95 1.7

75th percentile 2.713 1.021 1.359 1.24 4.4 2 3.9 2.8

Maximum 4.15 13.96 8.4 8.32 6.8 7.1 10 10

Total dissolved nitrogen, in milligrams per liter, as N Specific conductance, in microsiemens 

per centimeter at 25° Celsius

2001 2003 2004 All years 2001 2003 2004 All years

Minimum 0.12 0.034 0.052 0.034 141 25 72 25

25th percentile .205 .154 .171 .154 258.5 110.5 235.25 134

Median .415 .284 .336 .32 359 274 346.5 277

75th percentile 2.183 .972 1.024 1.024 447.5 426 548.25 431

Maximum 3.41 14.66 7.47 7.47 732 729 921 892

Dissolved oxygen, in milligrams per liter pH, in standard units

2001 2003 2004 All years 2001 2003 2004 All years

Minimum 6.3 2.8 2.1 2.1 6.6 6 5.9 5.9

25th percentile 7.25 7.55 6.7 7.3 6.775 6.65 6.7 6.7

Median 7.8 8.2 7.5 8.1 7.1 7.0 7.0 7.0

75th percentile 8.475 8.7 8.2 8.7 7.425 7.25 7.25 7.3

Maximum 8.8 10.3 10.0 10.3 7.5 8.2 8.7 8.7

Chlorophyll a, in milligrams per square meter

Minimum 2.8 (2.8) 1.9 (1.9) 2.4 (2.4) 1.9 (1.9)

25th percentile 4.325 (4.725) 8.25 (8.75) 6.5 (7.8) 6.0 (7.2)

Median 6.1 (8.25) 18.65 (20.05) 11.7 (15.3) 15.5 (16.1)

75th percentile 13.0125 (19.425) 37.5 (42.45) 40.3 (44.625) 40.25 (40.875)

Maximum 43.2 (101) 216 (216) 85.5 (322) 216 (216)
2001 2003 2004

0.1

1

10

100

1,000

CHLOROPHYLL A, IN MILLIGRAMS PER SQUARE METER

D

x

(85) (47) (78)

2001 2003 2004

0.001

0.01

0.1

1

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER AS P

x

x

x

(12) (43) (35)

2001 2003 2004

YEAR

TOTAL NITROGEN, IN MILLIGRAMS PER LITER AS N

xx

x

x

x

x

(12) (42) (36)

0.1

0.5

10

5

1

2001 2003 2004

YEAR

0.1

1

10

TOTAL DISSOLVED NITROGEN, IN MILLIGRAMS 

PER LITER AS N

C

(12) (37) (33)

A B

Number of samples

0utlier between 1.5 and 3.0 times the 

interquartile range above the box

Highest data point within 1.5 times the 

interquartile range above the box

Lowest data point within 1.5 times the 

interquartile range below the box

Outlier between 1.5 and 3.0 times the 

interquartile range below the box

x

x

(35)

Third quartile

Median

First quartile

EXPLANATION

Figure 2. Distribution of median (A) total phosphorus, (B) total nitrogen, (C) total dissolved nitrogen, and (D) chlorophyll a

concentrations at all sampling sites by year in Massachusetts. N, nitrogen; P, phosphorus.

10 Assessment of Data for Use in the Development of Nutrient Criteria
2001 2003 2004

2001 2003 2004

YEAR YEAR

0.5

10

5

1

TOTAL NITROGEN, IN MILLIGRAMS PER LITER AS N

B

D

x

o (12) (12) (12)

2001 2003 2004

0.01

0.02

0.03

0.04

0.05

0.1

0.2

0.3

 TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER AS P

A

x x

x

(12) (12) (12)

2001 2003 2004

0.1

1

10

TOTAL DISSOLVED NITROGEN, IN MILLIGRAMS 

PER LITER AS N

C

x

(12) (12) (12)

(12)

o

Number of samples

Outlier greater than 3.0 times the 

interquartile range above the box

0utlier between 1.5 and 3.0 times the 

interquartile range above the box

Highest data point within 1.5 times the 

interquartile range above the box

Lowest data point within 1.5 times the 

interquartile range below the box

Outlier between 1.5 and 3.0 times the 

interquartile range below the box

x

x

Third quartile

Median

First quartile

EXPLANATION

10

5

4

3

2

20

30

40

50

CHLOROPHYLL A, IN MILLIGRAMS PER SQUARE METER

x

(12) (10) (12)

Figure 3. Distribution of median (A) total phosphorus, (B) total nitrogen, (C) total dissolved nitrogen, and (D) chlorophyll a

concentrations at 12 sampling sites by year in Massachusetts.

Assessment of Data 11
Table 3. Annual median water-quality data at sites that were sampled in 2001, 2003, and 2004.—Continued

[Map identifier is shown in fig. 1. Values for total phosphorus, total nitrogen, total dissolved nitrogen, chlorophyll a, and dissolved oxygen are concentrations. 2001, 2003, and 2004 indicate the years for which medians were determined. Specific conductance is in microsiemens per centimeter at 25° Celsius. mg/L, milligrams per liter; mg/m2, milligrams per square meter; NA, not available]

Map 

identifier Station name

Total phosphorus (mg/L) Total nitrogen (mg/L) Total dissolved nitrogen (mg/L)

2001 2003 2004 2001 2003 2004 2001 2003 2004

46 Aberjona River at Winchester, Mass. 0.058 0.03 0.043 3.07 6.03 2.41 2.46 5.21 1.8342 Assabet River at Allen Street at Northborough, Mass. .198 .2 .21 2.69 2.04 4.55 2.16 1.608 3.9655 Charles River at Maple Street at North Bellingham, 

Mass.

.045 .09 .035 2.78 .772 2.42 2.25 .072 1.974

59 East Branch Neponset River at Canton Junction, Mass. .039 .041 .035 .78 .741 .867 .26 .32 .409

47 Ipswich River at South Middleton, Mass. .052 .052 .061 .84 1.06 1.001 .12 .225 .20161 Matfield River at North Central Street at 

East Bridgewater, Mass.

.2 .22 .27 4.15 13.96 8.4 3.41 14.66 7.47

54 Mill River at Summer Street near Blackstone, Mass. .05 .048 .045 .82 .865 1.273 .81 .474 .954

58 Neponset River at Norwood, Mass. .044 .042 .036 .73 .798 .701 .28 .284 .24248 Saugus River at Saugus Iron Works at Saugus, Mass. .065 .057 .059 1.02 .902 1.003 .55 .344 .543

32 Stillwater River near Sterling, Mass. .021 .015 .016 .44 .456 .437 .16 .244 .17136 Stony Brook at School Street at Chelmsford, Mass. .028 .022 .019 .64 .599 .502 .21 .242 .16 

60 Wading River near Norton, Mass. .031 .028 .025 .65 .681 .657 .19 .208 .222

Chlorophyll a (mg/m2

)

Closed-canopy sites Open-canopy sites Color, in platinumcobalt units Turbidity, in nephelometric turbidity units

2001 2003 2004 2001 2003 2004 2003 2004 2001 2003 2004

46 Aberjona River at Winchester, Mass. 18 34 24.8 15.2 42.6 44.1 74 54 6.8 7.1 4.9

42 Assabet River at Allen Street at Northborough, Mass. 19.9 12.9 8.1 20.2 NA 60.7 37 17 2.4 1.2 1.655 Charles River at Maple Street at North Bellingham, 

Mass.

3.8 12.8 12.5 NA NA NA 74 18 2.8 1.6 1.7

59 East Branch Neponset River at Canton Junction, Mass. 2.9 3.5 6.5 NA NA NA 55.8 37 4.7 3.1 4

47 Ipswich River at South Middleton, Mass. 10 12.5 12.7 NA NA NA 55.8 74 3.1 2.3 4.261 Matfield River at North Central Street at East Bridgewater, Mass. 43.2 NA 40.3 101 168 322 37.2 18 3.1 1.2 1.7

54 Mill River at Summer Street near Blackstone, Mass. 11.35 24.1 14.6 41.2 NA 29.6 37.2 28 1.9 1.5 258 Neponset River at Norwood, Mass. 6.5 16.5 7.7 NA NA NA 55.8 26 3.2 1.9 2.5

48 Saugus River at Saugus Iron Works at Saugus, Mass. 2.8 1.9 4.5 NA NA NA 74.4 60 4.8 4.4 5.3

32 Stillwater River near Sterling, Mass. 4.5 7.9 16.4 NA NA NA 37.2 24 1.2 1.1 1.536 Stony Brook at School Street at Chelmsford, Mass. 5.7 14.7 4.1 5.1 84.2 27.1 55.8 24 4.3 1.9 1.5

60 Wading River near Norton, Mass. 4.6 NA 55.9 NA 14.1 NA 55.8 52 1.9 1.6 1.7

12  Assessment of Data for Use in the Development of Nutrient Criteria
Table 3. Annual median water-quality data at sites that were sampled in 2001, 2003, and 2004.—Continued

[Map identifier is shown in fig. 1. Values for total phosphorus, total nitrogen, total dissolved nitrogen, chlorophyll a, and dissolved oxygen are concentrations. 2001, 2003, and 2004 indicate the years for which medians were determined. Specific conductance is in microsiemens per centimeter at 25° Celsius. mg/L, milligrams per liter; mg/m2, milligrams per square meter; NA, not available]

Specific conductance Dissolved oxygen (mg/L) pH, in standard units

2001 2003 2004 2001 2003 2004 2001 2003 2004

46 Aberjona River at Winchester, Mass. 429 569 666 6.8 7.5 6.3 7.5 7.2 7.142 Assabet River at Allen Street at Northborough, Mass. 732 647 921 8.8 8.3 8 7.5 7.2 755 Charles River at Maple Street at North Bellingham, 

Mass.

587 494 525 6.7 5.1 6.6 7 6.6 7.1

59 East Branch Neponset River at Canton Junction, Mass. 192 274 281 8.1 7.8 8.4 7.1 7.1 7.647 Ipswich River at South Middleton, Mass. 335 368 356 7.4 6.5 6.8 7.1 6.8 6.7

61 Matfield River at North Central Street at East Bridgewater, Mass. 494 686 638 6.3 2.8 6.3 6.8 7.1 7.254 Mill River at Summer Street near Blackstone, Mass. 227 360 337 8.4 7.2 8.6 6.6 6.5 6.9

58 Neponset River at Norwood, Mass. 287 330 332 8.7 7.2 8 7.2 6.9 7.5

48 Saugus River at Saugus Iron Works at Saugus, Mass. 432 533 575 7.5 8.4 8.1 7.4 7.4 7.432 Stillwater River near Sterling, Mass. 141 262 223 8.7 7 8.1 6.7 6.4 6.5

36 Stony Brook at School Street at Chelmsford, Mass. 383 475 471 8.4 8.7 8.1 7.5 7.2 7.3

60 Wading River near Norton, Mass. 269 281 NA 7.5 7.9 7.3 6.7 6.6 6.9

Assessment of Data 13
concentrations due to dilution effects. Comparisons based on 

geographical and hydrological differences may prove more 

meaningful than yearly differences. Also, a general overview 

of the values for individual parameters should be useful for 

understanding sources of data variability. The 25th-percentile 

values for all Massachusetts stream data in this study are 

0.019 mg/L for total phosphorus, 0.44 mg/L for total nitrogen 

and 1.2 NTU for turbidity (table 2).

While comparisons of the variability among the medians 

for the 12 stations for which there are 3 years of collected data 

(table 3; fig. 3) may be more valid on the basis of consistent 

use of stations than comparisons among the varying array of 

all stations sampled, the differences in numbers of samples 

and the uncertain stream-discharge conditions among years 

for the 12 stations are possible causes for the changing values 

from year to year (for example, figs. 2 and 3). Some of the 

values for the stations sampled in 2001, 2003, and 2004 

may remain approximately the same over the 3 years (total 

phosphorus at a number of stations, for example), and others 

may have a high value as great as 30 times the low value 

(total dissolved nitrogen at the Charles River at Maple Street 

at North Bellingham, Mass.). Using medians for all years 

combined to represent individual stations may minimize datavariability issues associated with those stations; however, most 

of the stations have only one sampling date that provides the 

representative data, and that circumstance probably contributes 

to data variability among the stations.

Nutrients and Turbidity

USEPA standards relevant to this study are limited 

to total phosphorus, total nitrogen, and turbidity (U.S. 

Environmental Protection Agency, 2000, 2001). The USEPA 

provides values for phytoplankton, but not for periphyton 

chlorophyll a. On the basis of the 25th percentile of concentration data from reference sites aggregated by ecoregion, the 

USEPA established recommended water-quality critera for 

total phosphorus, total nitrogen, and turbidity for the two 

ecoregions in Massachusetts. For Ecoregion VIII (western 

Massachusetts), the USEPA values are 0.010 mg/L for total 

phosphorus, 0.380 mg/L for total nitrogen, and 0.81 for 

turbidity. For Ecoregion XIV (eastern Massachusetts), the corresponding values are 0.031 mg/L for total phosphorus, 0.710 

mg/L for total nitrogen, and 1.94 NTU for turbidity.

These values were compared to the 25th-percentile values 

from this study for the ecoregions (table 4; figs. 4A and 4B). 

The 25th-percentile values for Ecoregion VIII are 0.009 mg/L 

for total phosphorus, 0.289 mg/L for total nitrogen, and 

1.7 NTU for turbidity. The 25th-percentile values for 

Ecoregion XIV are 0.028 mg/L for total phosphorus, 

0.583 mg/L for total nitrogen, and 3.1 NTU for turbidity. 

Thus, on the basis of samples collected for this study, the 

25th-percentile values for median total phosphorus and total 

nitrogen concentrations are less than the USEPA values for 

both ecoregions, and the 25th-percentile values for median 

turbidity exceeded the USEPA values for both ecoregions.

The 25th-percentile values for these three constituents 

also were examined by Massachusetts nutrient ecoregion 

(table 4; figs. 5A and 5B). The 25th-percentile values for the 

Massachusetts low-nutrient ecoregion are 0.011 mg/L for total 

phosphorus, 0.289 mg/L for total nitrogen, and 0.7 NTU for 

turbidity. The 25th-percentile values for the Massachusetts 

intermediate-nutrient ecoregion are 0.016 mg/L for total 

phosphorus, 0.419 mg/L for total nitrogen, and 1.1 NTU for 

turbidity. The 25th-percentile values for the Massachusetts 

high-nutrient ecoregion are 0.030 mg/L for total phosphorus, 

0.642 mg/L for total nitrogen, and 1.5 NTU for turbidity. 

As would be expected from the field studies designed 

to analyze a variety of stream-water-quality conditions, the 

ranges of nutrient concentrations were wide (table 5). Total 

phosphorus ranged from 0.002 mg/L (North Branch Hoosic 

River near Clarksburg, Mass.) to 1,120 mg/L (Blackstone 

River at Northbridge, Mass.). Total dissolved nitrogen ranged 

from 0.034 mg/L (West Branch Swift River at Cooleyville, 

Mass.) to 7.47 mg/L (Assabet River at School Street near 

Northborough, Mass.); total nitrogen ranged from 0.179 mg/L 

(North Branch Hoosic River near Clarksburg, Mass.) to 

8.32 mg/L (Assabet River at School Street near 

Northborough, Mass.). 

Turbidity readings were generally quite low. The highest 

value was 10 NTU (at the Sherman Pond Outlet at Route 20 

at Brimfield, Mass.) and the lowest value was 0.29 (at Green 

River Rt. 23 near Great Barrington, Mass.). 

Table 4. The twenty-fifth-percentile values for total phosphorus and total nitrogen concentrations and turbidity measured 

in U.S. Environmental Protection Agency ecoregions compared to values measured in this study and in Massachusetts low-, 

intermediate-, and high-nutrient ecoregions. 

[USEPA, U.S. Environmental Protection Agency; mg/L, milligrams per liter; NTU, nephelometric turbidity units]

Constituent

ECOREGION VIII ECOREGION XIV Massachusetts nutrient ecoregion

USEPA This Study USEPA This Study Low Intermediate High

Total phosphorus (mg/L) 0.010 0.009 0.031 0.028 0.011 0.016 0.030

Total nitrogen (mg/L) .380 .289 .710 .583 .289 .419 .642

Turbidity (NTU) .81 1.7 1.94 3.1 .7 1.1 1.5

14  Assessment of Data for Use in the Development of Nutrient Criteria
Figure 4. Distribution of median (A) total phosphorus, (B) total nitrogen, (C) total dissolved nitrogen, and (D) chlorophyll 

a concentrations at all sampling sites by ecoregion in Massachusetts. The results of the Kruskal-Wallis rank sum test are 

represented as letters. Distributions of groups of data with at least one letter in common do not differ significantly.

0.05

0.1

0.5

1

5

10

TOTAL DISSOLVED NITROGEN, N MILLIGRAMS 

PER LITER AS N

(16) (41)

A

A

C

A B

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER AS P

xx

x

(21) (44)

A

B

VIII XIV

VIII XIV VIII XIV

VIII XIV

TOTAL NITROGEN, IN MILLIGRAMS PER LITER AS N

x

(21) (44)

A

B

10

5

1

50

100

CHLOROPHYLL A, IN MILLIGRAMS PER SQUARE METER

(22) (53)

A

A

0.001

0.01

0.1

1

0.1

0.2

0.3

0.4

0.5

1

2

3

4

5

0

D

Number of samples

0utlier between 1.5 and 3.0 times the 

interquartile range above the box

Highest data point within 1.5 times the 

interquartile range above the box

Lowest data point within 1.5 times the 

interquartile range below the box

x

(41)

Third quartile

Median

First quartile

EXPLANATION

ECOREGION ECOREGION

Assessment of Data 15
16  Assessment of Data for Use in the Development of Nutrient Criteria

Figure 5. Distribution of median (A) total phosphorus, (B) total nitrogen, (C) total dissolved nitrogen, and (D) chlorophyll a 

concentrations at all sampling sites by Massachusetts nutrient ecoregion. The results of the Kruskal-Wallis rank sum test are 

represented as letters. Distributions of groups of data with at least one letter in common do not differ significantly. 

Number of samples

0utlier between 1.5 and 3.0 times the 

interquartile range above the box

Highest data point within 1.5 times the 

interquartile range above the box

Lowest data point within 1.5 times the 

interquartile range below the box

x

(9)

Third quartile

Median

First quartile

EXPLANATION

Low Medium High

Low Medium High

Low Medium High

Low Medium High

0.001

0.01

0.1

1

TOTAL PHOSPHORUS, IN MILLIGRAMS 

PER LITER AS P

xx

x

(13) (22) (30)

B

B

A

A

C D

B

0.1

0.2

0.3

0.4

0.5

1

2

3

4

5

10

TOTAL NITROGEN, IN MILLIGRAMS PER LITER AS N

(13) (22) (30)

C

A

B

MASSACHUSETTS NUTRIENT ECOREGION MASSACHUSETTS NUTRIENT ECOREGION

0.05

0.1

0.5

1

5

10

TOTAL DISSOLVED NITROGEN, IN 

MILLIGRAMS PER LITER AS N

(9) (19) (29)

A A

A

10

5

1

50

100

CHLOROPHYLL

A, IN MILLIGRAMS 

PER SQUARE METER

(14) (24) (37)

A

A

A
Table 5. Median values of representative data for stations in this report. —Continued

[Values for aquatic plant life approximate median values. Map identifier is shown in fig. 1. TDN, total dissolved nitrogen, in milligrams per liter, as N; TN, total nitrogen, in milligrams per liter, as N; TP, total phosphorus in milligrams per liter, as P; Chl a, chlorophyll a in milligrams per square meter; SC, specific conductance in microsiemens per centimeter at 25° Celsius; DO, dissolved oxygen in milligrams per liter; ND, no data]

Map 

identifier 

Station name Aquatic plant life

Closed-canopy sites TDN TN TP TN:TP Chl a Color Turbid- ity SC DO pH Rooted aquatic plants Filamentous periphyton Periphyton film Periphyton floc Aquatic moss

1 Paul Brook at Galvin Road at North Adams, 

Mass.

0.161 0.251 0.008 31.4 5.6 ND 1.70 245 9.0 7.9 Sparse Not observed Not observed Not observed Not observed

3 North Branch Hoosic River near 

Clarksburg, Mass.

.099 .179 .002 89.5 6.2 ND .49 72.0 8.9 7.0 Not observed Moderate Moderate Not observed Moderate

5 Tissdell Brook near Adamsville, Mass. .149 .214 .008 26.8 4.9 ND .3 97.0 8.8 7.7 Not observed Not observed Not observed Not observed Not observed

6 Green River near Colrain, Mass. ND .372 .015 24.8 17.6 37.2 1.20 72.0 8.8 7.5 Sparse Not observed Moderate Not observed Not observed

9 Roaring Brook near Conway, Mass. .114 .366 .017 21.5 7 37.2 1.70 105 7.7 7.2 Not observed Not observed Sparse Not observed Sparse

12 Hop Brook at Tyringham Center, 

Tyringham, Mass.

.101 .366 .016 22.9 24.4 18.6 1.30 180 8.4 7.8 Not observed Sparse Not observed Not observed Moderate

13 West Branch Farmington River at Otis, Mass. ND .484 .016 30.3 55.5 37.2 1.30 198 8.2 7.0 ND ND ND ND ND15 Dickinson Brook upstream from Water Street 

at Granville, Mass.

.101 .346 .017 20.4 1.9 37.2 .47 48.0 8.9 6.8 Not observed Not observed Not observed Not observed Moderate

16 Powdermill Brook near Westfield, Mass. .348 .503 .034 14.8 27.7 37.2 .9 155 8.3 7.2 Not observed Not observed Moderate Not observed Moderate

17 Mormon Hollow Brook near Farley, Mass. ND .323 .012 26.9 6.4 37.2 .6 25.0 8.7 6.2 Not observed Not observed Sparse Not observed Sparse20 Beaver Brook above Hoyt Brook near 

Phillipston, Mass.

.203 .778 .195 4.0 28.8 69 2.45 287 6.3 5.9 Sparse Not observed Sparse Not observed Moderate

21 Otter River at Otter River, Mass. 4.44 5.21 .13 40.1 9.9 160 8.60 408 7.4 6.3 Sparse Not observed Sparse Not observed Moderate22 West Branch Swift River at Cooleyville, Mass. .034 .334 .014 23.9 28.3 55.8 .94 29.0 9.3 6.1 Not observed Not observed Sparse Not observed Sparse

23 Ware River Site 6 near Barre, Mass. .045 .368 .028 13.1 9 37.2 4.40 131 7.8 6.2 Not observed Not observed Moderate Not observed Moderate

27 Cady Brook at Charlton, Mass. 4.685 5.37 .108 49.7 53.6 37 1.00 729 9.6 7.6 Not observed Not observed Moderate Not observed Sparse28 Burncoat Brook, Pine Street, near 

Leicester, Mass.

.336 1.615 .148 10.9 4.3 40 8.50 232 8.1 8.7 Sparse Not observed Not observed Not observed Not observed

29 Little River downstream from Turner Road 

near Charlton, Mass.

.054 .603 .028 21.5 4.9 54 1.50 277 6.3 6.5 Not observed Not observed Not observed Not observed Not observed

30 French River, downstream from Clara Barton 

Road near Oxford, Mass.

.118 .535 .026 20.6 11.7 42 1.00 189 8.3 7.2 Not observed Not observed Sparse Not observed Not observed

32 Stillwater River near Sterling, Mass. .16 .44 .02 22.0 7.4 30 1.20 189 8.4 6.6 Sparse Sparse Sparse Sparse Moderate

34 Nashua River Tributary at Lancaster, Mass. 2.856 3.13 .042 74.5 24.9 37.2 1.30 274 8.7 7.1 Not observed Not observed Moderate Not observed Not observed35 Bennetts Brook at Ayer, Mass. .77 .791 .049 1.6 11.2 130 5.20 314 6.9 6.7 ND Not observed Very dense Moderate Sparse

36 Stony Brook at School Street at 

Chelmsford, Mass.

.21 .63 .028 22.5 5.7 30.6 4.20 415 8.4 7.3 Sparse Not observed Sparse Not observed Not observed

38 Richardson Brook near Lowell, Mass. .076 .575 .021 27.4 8.8 59 2.00 332 7.0 6.8 Sparse Not observed dense Not observed Not observed40 Bare Meadow Brook near Methuen, Mass. .247 .816 .029 28.1 64.5 71 3.10 392 5.8 6.7 Not observed Moderate Moderate Not observed Sparse

41 Powwow River off Mill Street at 

Amesbury, Mass.

.052 .595 .017 35.0 10.3 ND 1.90 167 8.6 7.4 Not observed Not observed Not observed Not observed Sparse

42 Assabet River at Allen Street at 

Northborough, Mass.

2.39 2.9 .2 14.5 16.9 18.6 2.30 755 8.3 7.4 Sparse Not observed Sparse Not observed Dense

Assessment of Data 17
Table 5. Median values of representative data for stations in this report. —Continued

[Values for aquatic plant life approximate median values. Map identifier is shown in fig. 1. TDN, total dissolved nitrogen, in milligrams per liter, as N; TN, total nitrogen, in milligrams per liter, as N; TP, total phosphorus in milligrams per liter, as P; Chl a, chlorophyll a in milligrams per square meter; SC, specific conductance in microsiemens per centimeter at 25° Celsius; DO, dissolved oxygen in milligrams per liter; ND, no data]

Map 

identifier 

Station name Aquatic plant life

Closed-canopy sites TDN TN TP TN:TP Chl a Color Turbid- ity SC DO pH Rooted aquatic plants Filamentous periphyton Periphyton film Periphyton floc Aquatic moss

43 Assabet River at School Sreet near 

Northborough, Mass.

7.47 8.32 0.51 16.3 6.5 30 1.60 892 6.5 6.4 Not observed Not observed Sparse Not observed Moderate

44 Assabet River at Maynard, Mass. 1.345 1.83 .065 28.2 54.8 ND 1.00 701 7.3 7.2 Sparse Sparse Dense Not observed Not observed46 Aberjona River at Winchester, Mass. 2.46 3.07 .043 71.4 24.8 57 5.80 569 6.8 7.3 Sparse Not observed Sparse Sparse Moderate

47 Ipswich River at South Middleton, Mass. .195 .96 .052 18.5 12.5 73.2 3.10 341 7.3 6.9 Sparse Not observed Sparse Not observed Moderate

48 Saugus River at Saugus Iron Works at 

Saugus, Mass.

.543 1.003 .059 17.0 3.3 63.6 4.80 536 7.6 7.4 Not observed Not observed Sparse Not observed Sparse

50 Blackstone River at Northbridge, Mass. 5.231 6.28 1.120 5.6 72.2 37 2.40 670 7.2 7.0 Not observed Not observed Moderate Not observed Not observed

51 West River upstream side Glen Avenue Bridge 

at Upton, Mass.

.052 .597 .038 15.7 16.1 37.2 1.30 295 9.6 7.0 Not observed Not observed Sparse Not observed Moderate

52 Mill River at Route 16 at Spindleville, Mass. .122 .487 .019 25.6 12.5 74.4 2.00 431 7.4 6.6 Sparse Not observed Sparse Not observed Sparse53 Mill River at Spindleville, Mass. 2.873 3.39 .042 80.7 42.4 37.2 1.50 597 8.6 7.3 Not observed Moderate Moderate Not observed Sparse

54 Mill River at Summer Street near 

Blackstone, Mass.

.917 1.24 .05 24.8 15.45 32.4 1.90 291 8.4 6.6 Sparse Sparse Not observed Not observed Moderate

55 Charles River at Maple Street at North 

Bellingham, Mass.

1.974 2.42 .04 60.5 5.7 18.6 1.80 552 6.6 7.0 Not observed Not observed Not observed Not observed Moderate

58 Neponset River at Norwood, Mass. .28 .73 .04 18.3 7.6 31.8 2.50 318 8.0 7.2 Not observed Not observed Not observed Not observed Not observed

59 East Branch Neponset River at Canton 

Junction, Mass.

.32 .8 .039 20.5 3.2 46.5 4.00 267 8.1 7.1 Not observed Not observed Sparse Not observed Not observed

60 Wading River near Norton, Mass. .208 .654 .025 26.2 6.6 53.7 1.70 287 7.5 6.7 Sparse Moderate Not observed Not observed Sparse

61 Matfield River at North Central Street at 

East Bridgewater, Mass.

7.3 8.13 .22 37.0 41.75 18.5 1.80 583 6.3 6.9 Sparse Not observed Sparse Not observed Dense

62 Childs River, 2,200 feet north of Route 28, 

near Waquoit Village, Falmouth, Mass.

.747 .842 .051 16.5 216 37.2 .71 99.0 7.6 6.7 Sparse Sparse Sparse Not observed Not observed

63 Quashnet River, 0.8 mile downstream from 

Route 151, near Waquoit Village, Falmouth, Mass.

.194 .349 .045 7.8 37.2 37.2 1.70 83 8.1 6.7 Moderate Not observed Sparse Not observed Not observed

64 Mashpee River upstream from Asher Path 

Bridge at Mashpee, Mass.

.33 .46 .022 20.9 4.1 37.2 .7 96.0 8.1 6.8 Moderate Sparse Sparse Not observed Moderate

65 Herring River at North Harwich, Mass. .332 .586 .029 20.2 5.6 18.6 .9 116 7.8 6.3 Moderate Not observed Moderate Not observed Moderate

Open-canopy sites

2 Hoosic River near North Adams, Mass. 1.024 1.17 .101 11.6 46.1 20 1.70 445 10 8.1 Not observed Sparse Moderate Not observed Not observed

4 Deerfield River at Florida Bridge near 

Zoar, Mass.

.161 .276 .004 69.0 5.5 37.2 .43 48 10.3 6.8 Not observed Not observed Sparse Not observed Sparse

5 Tissdell Brook near Adamsville, Mass. .149 .214 .008 26.8 3.9 ND .3 97.0 8.8 7.7 Not observed Not observed Sparse Not observed Not observed7 East Branch Housatonic River at 

Coltsville, Mass.

.198 .66 .026 25.4 37.1 37.2 2.80 237 8.7 8.1 Sparse Moderate Moderate Not observed Not observed

8 Westfield River at Route 9 bridge near 

Cummington, Mass.

ND .283 .011 25.7 19.7 18.6 .7 81.0 8.3 7.6 Sparse Not observed Sparse Not observed Not observed

10 Housatonic River below Mohawk Brook near 

Glendale, Mass.

1.1 1.58 .05 31.6 66.5 37.2 1.40 421 9.7 8.2 Moderate Not observed Moderate Not observed Moderate

18  Assessment of Data for Use in the Development of Nutrient Criteria
Table 5. Median values of representative data for stations used in this report.—Continued

[Values for aquatic plant life approximate median values. Map identifier is shown in fig. 1. TDN, total dissolved nitrogen, in milligrams per liter, as N; TN, total nitrogen, in milligrams per liter, as N; TP, total phosphorus in milligrams per liter, as P; Chl a, chlorophyll a in milligrams per square meter; SC, specific conductance in microsiemens per centimeter at 25° Celsius; DO, dissolved oxygen in milligrams per liter; ND, no data]

Map 

identifier 

Station name Aquatic plant life

Closed-canopy sites TDN TN TP TN:TP Chl a Color Turbid- ity SC DO pH Rooted aquatic plants Filamentous periphyton Periphyton film Periphyton floc Aquatic moss

11 Green River Route 23 near Great Barrington, 

Mass.

0.463 0.548 0.005 109.6 48.8 ND 0.29 247 8.9 7.9 Not observed Moderate Moderate Not observed Sparse

14 West Branch Westfield River at Huntington, 

Mass.

ND .289 .009 32.1 8 37.2 .8 119 8.7 7.1 Not observed Not observed Moderate Not observed Not observed

18 Millers River at Route 2 near Wendell Depot, 

Mass.

.447 .835 .047 17.8 6.7 70 1.40 190 9.3 7.5 Sparse Not observed Sparse Not observed Not observed

19 Millers River at South Royalston, Mass. .972 1.477 .076 19.4 40 74.4 2.80 290 8.2 6.6 Sparse Not observed Sparse Not observed Sparse

24 West Brook at Route 20 near Brimfield, Mass. .172 .44 .015 29.3 72.1 30 2.50 114 7.3 6.9 Moderate Not observed Moderate Moderate Not observed25 Sherman Pond Outlet at Route 20 at 

Brimfield, Mass.

.113 .81 .09 9.0 30.3 160 10.00 180 3.5 6.5 Sparse Not observed Not observed Dense Sparse

26 Quinebaug River below East Brimfield Dam at 

Fiskdale, Mass.

ND .412 .019 21.7 ND 74.4 1.60 134 7.0 6.7 Moderate Dense Not observed Not observed Not observed

30 French River, downstream from Clara Barton 

Road near Oxford, Mass.

.118 .535 .026 20.6 16 42 1.00 189 8.3 7.2 ND ND ND ND ND

31 French River at Webster, Mass. ND .503 .04 12.6 15.1 72 1.40 204 8.3 7.0 Dense Moderate Not observed Not observed Sparse

32 Stillwater River near Sterling, Mass. .16 .44 .021 21.0 9.9 30 1.10 150 8.6 6.6 Moderate Moderate Not observed Sparse Sparse33 North Nashua River near Lancaster, Mass. 4.28 5.68 .167 34.0 85.5 28 2.80 556 7.7 6.8 Sparse Sparse Dense Not observed Sparse

36 Stony Brook at School Street at 

Chelmsford, Mass.

.21 .63 .028 22.5 10.7 30.6 4.20 415 8.4 7.3 Sparse Sparse Sparse Not observed Not observed

37 Concord River below River Meadow Brook, 

at Lowell, Mass.

1.16 1.87 .15 12.5 37.6 37.2 3.00 582 8.3 7.4 Not observed Not observed Moderate Not observed Sparse

38 Richardson Brook near Lowell, Mass. .076 .575 .21 2.7 34.1 59 2.00 332 7.0 6.8 Moderate Moderate Not observed Not observed Moderate

39 Fish Brook near Andover, Mass. ND .636 .033 19.3 101 84 1.30 673 2.1 6.2 Sparse Sparse Sparse Not observed Moderate42 Assabet River at Allen Street at 

Northborough, Mass.

2.95 2.9 .2 14.5 21.75 18.6 2.35 760 8.4 7.4 Dense Moderate Not observed Sparse Dense

44 Assabet River at Maynard, Mass. 1.345 1.83 .065 28.2 59 ND 1.00 701 7.3 7.2 Sparse Moderate Dense Not observed Not observed

45 Charles River above Watertown Dam at 

Watertown, Mass.

.228 1.016 .076 13.4 48.7 48 5.40 472 6.3 7.2 Sparse Sparse Sparse Not observed Sparse

46 Aberjona River at Winchester, Mass. 2.46 3.07 .04 76.8 42.6 57 5.10 666 6.8 6.9 Sparse Not observed Sparse Sparse Sparse

49 Goldthwait Brook at Foster Street at 

Peabody, Mass.

.355 .664 .029 22.9 44.8 23 1.30 579 7.5 7.0 Sparse Not observed Sparse Not observed Sparse

54 Mill River at Summer Street near 

Blackstone, Mass.

.936 1.24 .048 25.8 35.4 32.4 1.95 267 8.5 6.7 Sparse Moderate Sparse Not observed Moderate

56 Charles River at Medway, Mass. .154 .849 .077 11.0 20.4 112 2.80 351 7.8 7.1 Sparse Sparse Sparse Not observed Sparse

57 Charles River at Dover, Mass. .55 1.183 .046 25.7 12.8 37 3.60 403 7.6 6.8 Sparse Sparse Moderate Not observed Very dense60 Wading River near Norton, Mass. .208 .654 .028 23.4 14.1 53.7 1.60 281 7.9 6.7 Not observed Not observed Sparse Not observed Not observed

61 Matfield River at North Central Street at 

East Bridgewater, Mass.

7.3 8.13 .22 37.0 108 18.5 1.80 583 6.3 6.9 Dense Dense Sparse Not observed Very dense

Assessment of Data 19
Color

Median color values ranged from 18.5 to 160 

platinum-cobalt units (PCU), with an overall median of 

37.2 PCU, for the 2003 and 2004 data (table 2). The DWM 

has suggested that 70 PCU may be the value used in the future 

to differentiate colored from clear water (Mark Mattson, 

Massachusetts Department of Environmental Protection, 

Division of Watershed Management, written commun., 2006). 

On the basis of median color values, 12 stations had waters 

that equaled or exceeded the 70-PCU criterion (table 5). 

The USEPA did not include color as a characteristic nutrient 

criterion, but in the future it could be a factor considered by 

the State in aquatic-use criteria.

Field Parameters

The field parameters of dissolved oxygen and pH can 

reflect local watershed conditions, but they also can change 

considerably during the day at any given site. Variations 

among these parameters, therefore, may not be directly linked 

to nutrient conditions in streams. For example, dissolved 

oxygen concentration varies with temperature and may drop 

below the saturation level if the amount of organic matter 

being oxidized is sufficient; dissolved oxygen concentrations 

also can rise above saturation level when photosynthesis 

releases oxygen. Photosynthesis can also cause pH to vary. 

Elevated specific conductance may indicate upstream wastewater releases or the presence of salts from urban runoff. 

Dissolved oxygen values for all data ranged from 2.1 to 

10.3 mg/L with a median of 8.1 mg/L (table 2). The lowest 

pH value was 5.9 and the highest was 8.7 with an overall 

median of 7.0. Specific conductance ranged from 25 to 

892 μS/cm at 25°C, with a median of 277 μS/cm at 25°C; 

the minimum value is indicative of a reference site (Mormon 

Hollow Brook; map identifier number 17), and the maximum 

value represents the conditions at an Assabet River site 

(map-identifier number 43) downstream from a wastewatertreatment plant (table 5). 

Chlorophyll a Concentrations and Plant Densities

Concentrations of chlorophyll a and plant densities 

are presumed to reflect nutrient concentrations in surface 

water, light conditions, topography, and hydrology. Dodds 

and Welch (2000) did not find any published reports relating water-column nutrient concentrations and macrophyte 

biomass; the authors further noted that macrophytes can 

derive nutrition from sediments, and therefore do not rely on 

surface water to supply nutrients. Relations between nutrients 

and benthic algal biomass were found to be weak. In this 

study, concentrations and densities vary widely (table 5). The 

highest chlorophyll a concentration, 216 mg/m2, was found at 

the Childs River (map-identifier number 62), and the lowest 

concentration, 1.9 mg/m2, was found at Dickinson Brook 

(map-identifier number 15). As stated previously, the visual 

determination of levels of plant density provides subjective, 

semiquantitative data that do not yield to simple interpretation; additionally, there are large numbers of “not observed” 

values. For example, periphyton floc was observed too rarely 

to make any interpretation about its occurrence. 

Categorical Descriptions of Data

In order to consider the effects of geographic (landscape), anthropogenic, and other natural factors on water 

quality, data were sorted into a number of categories. These 

categories include large areal considerations such as USEPA 

ecoregion, Massachusetts nutrient ecoregion, drainage-basin 

size, and site-specific considerations such as the presence of 

upstream wastewater dischargers, and canopy openness. The 

number of categories and sub-categories occasionally resulted 

in small sample sizes for statistical interpretation. 

U.S. Environmental Protection Agency 

Ecoregions

According to the USEPA’s ecoregion descriptions, 

Massachusetts is a part of two of the 14 National ecoregions: 

the western part of the State is in the Nutrient Poor, Largely 

Glaciated Upper Midwest and Northeast (Ecoregion VIII), 

and the eastern part of the State is in the Eastern Coastal Plain 

(Ecoregion XIV, fig. 1). The median values for total phosphorus, total nitrogen, and total dissolved nitrogen are higher in 

Ecoregion XIV than in Ecoregion VIII; however, the values 

for total dissolved nitrogen are almost the same in the two 

Ecoregions (fig. 4). With many of the Ecoregion XIV stations 

located in the Massachusetts high-nutrient ecoregion and 

downstream from major and minor dischargers, these differences are not unexpected. Chlorophyll a concentrations in the 

two ecoregions are similar and do not reflect the differences in 

the median nutrient concentrations (fig. 4D). 

Drainage-Basin Size

Drainage-basin size, in square miles, possibly has an 

effect on water-quality conditions. Larger basins are assumed 

to have higher nutrient concentrations than smaller basins 

because the water quality of the larger basins probably is 

affected by larger cities and wastewater-treatment plant effluent. The data seem to support this assumption. Streams with 

the largest drainage basin areas (greater than 90 mi2) have 

20 Assessment of Data for Use in the Development of Nutrient Criteria
Assessment of Data  21

higher nutrient concentrations than the basins smaller than 90 

mi2, which are characterized by approximately equal nutrient 

concentrations (fig. 6). Periphyton chlorophyll a concentrations, in contrast, do not necessarily increase with increasing 

basin area. Some of the relatively small numbers of sampling 

sites in basins larger than 90 mi2 are on the same river, 

however, which may affect how well the dataset represents 

these large rivers statewide.

Massachusetts Nutrient Ecoregions

Relatively high nutrient concentrations at sites sampled in 

this study that were located in the Massachusetts high-nutrient 

ecoregion indicate that the lake-based phosphorus nutrient 

ecoregions are consistent with stream-water nutrient concentrations. The median total concentration in the high-nutrient 

ecoregion is the highest, but is only slightly higher than in the 

intermediate-nutrient ecoregion. Median dissolved nitrogen 

concentrations show a similar pattern, and median total 

nitrogen concentrations seem to show the clearest differences 

among the three Massachusetts nutrient ecoregions. However, 

the interquartile ranges for the intermediate- and high-nutrient 

ecoregions overlap considerably, suggesting that these two 

nutrient ecoregions do not differ much. Median chlorophyll 

a concentrations follow the trend of increasing concentration 

with nutrient ecoregion, but the medians and interquartile 

ranges for the intermediate- and high-nutrient ecoregions 

are almost identical. The unequal distribution of sites among 

ecoregions and the high proportion of major and minor 

dischargers in the intermediate- and high-nutrient ecoregions 

may affect the interpretations of the nutrient and chlorophyll a

data, however.

Effects of Dischargers on Water Quality 

In Massachusetts, with numerous small towns and 

cities distributed throughout the state, many streams serve as 

receiving waters for much of the treated wastewater. Because 

26 of the sampling stations in this study are downstream from 

major NPDES-permitted dischargers and an additional 11 are 

downstream from minor NPDES-permitted dischargers, it is 

expected that the effluent from these facilities would have 

a substantial effect on the downstream nutrient concentrations. The median concentrations of total phosphorus and 

total nitrogen demonstrate that the presence of dischargers 

increases nutrient concentrations (fig. 7, at end of report). 

The trend in median dissolved nitrogen concentrations is 

similar; however, the interquartile ranges overlap more than 

for total phosphorus or total nitrogen. The median periphyton 

chlorophyll a concentration is highest downstream from major 

NPDES-permitted dischargers but interquartile ranges and all 

data, in general, overlap. 

Canopy Openness

Riskin and others (2003) found higher periphyton

chlorophyll a concentrations in samples collected from 

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

sampling locations when the sites were sorted among three 

categories of nutrient impairment, or enrichment. When comparing the distribution of periphyton chlorophyll a concentrations across the Massachusetts nutrient ecoregions used in 

this study (fig. 5D), the interquartile ranges of the medians are 

similar (not significantly different), but the median chlorophyll 

a concentration for the low-nutrient ecoregion is lower than 

the other two nutrient ecoregions. If these same data are 

divided into open- or closed-canopy categories, the chlorophyll a concentration boxplots are similar for closed-canopy 

sites among the three nutrient ecoregions 

(fig. 8, at end of report). For the open-canopy sites, the median 

chlorophyll a concentrations (approximately 40 mg/m2) in 

the intermediate- and high-nutrient ecoregions are higher 

than in the low-nutrient ecoregion (approximately 7 mg/m2) 

and higher than the median chlorophyll a concentrations at 

closed-canopy sites (approximately 10 mg/m2). Only four 

open-canopy sites are in the low-nutrient ecoregion; however, 

four may be too small a number for drawing inferences.

Median chlorophyll a values at open- and closed-canopy 

sites do not differ substantially between Ecoregions VIII and 

XIV. The open-canopy sites do exhibit approximately 4 times 

higher median values than the closed-canopy sites overall 

(fig. 9, at end of report).

When closed-canopy sites are compared based on basin 

size, the median chlorophyll a concentration is highest in the 

largest basins (greater than 90 mi2) at closed-canopy sites 

(fig. 10, at end of report), but only four basins are included in 

that class. The median chlorophyll a concentrations open- and 

closed-canopy sites in basins larger than 90 mi2 are about the 

same. In basins smaller than 90 mi2, the closed-canopy sites 

have lower median chlorophyll a concentrations than the opencanopy sites. For open-canopy sites, basins larger than 90 mi2

and basins smaller than 10 mi2 have approximately 

the same median chlorophyll a concentrations. Physical 

factors, such as water depth and turbidity, likely greater in 

basins larger than 90 mi2 than in smaller basins, probably 

influence light penetration and may have site-specific effects 

on periphyton growth.

Among the sites downstream from NPDES-permitted 

dischargers, the differences between open- and closed-canopy 

sites are not substantial. The only exception is in the minor 

discharger category where open-canopy sites have a higher 

chlorophyll a median concentration than closed-canopy 

sites (fig. 11, at end of report). The numbers of sites in each 

category, however, are unequal and this distribution of sites 

may affect the interpretation of the data.
22  Assessment of Data for Use in the Development of Nutrient Criteria

Number of samples

0utlier between 1.5 and 3.0 times the 

interquartile range above the box

Highest data point within 1.5 times the 

interquartile range above the box

Lowest data point within 1.5 times the 

interquartile range below the box

Outlier between 1.5 and 3.0 times the 

interquartile range below the box

x

x

(18)

Third quartile

Median

First quartile

EXPLANATION

0.001

0.01

0.1

1

 TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER AS P

x x

x

x

x

(22) (31) (12)

A

A

A

A

0.1

0.2

0.3

0.4

0.5

TOTAL NITROGEN, IN MILLIGRAMS PER LITER AS N

x

xx

x

(22) (31) (12)

AB

B

A

1

2

3

4

5

10

B

C D

DRAINAGE-BASIN SIZE CLASS, IN SQUARE MILES

0.05

<10 10–90 90–350

DRAINAGE-BASIN SIZE CLASS, IN SQUARE MILES

<10 10–90 90–350

0.1

0.5

TOTAL DISSOLVED NITROGEN, IN MILLIGRAMS 

PER LITER AS N

x

(20) (26) (11)

A

AB

B

1

5

10

<10 10–90 90–350 <10 10–90 90–350

10

5

1

50

100

TOTAL CHLOROPHYLL A, IN MILLIGRAMS 

PER SQUARE METER

(18) (23) (4)

A

A A

Figure 6. Distribution of median (A) total phosphorus, (B) total nitrogen, (C) total dissolved nitrogen, and (D) chlorophyll 

a concentrations at all sampling sites by drainage-basin size class in Massachusetts. The results of the Kruskal-Wallis 

rank sum test are represented as letters. Distributions of groups of data with at least one letter in common do not differ 

significantly.
Assessment of Data  23

The effect of canopy openness on plant-density data was 

evaluated in conjunction with the relations of plant density 

and nutrient concentrations (figs. 12 and 13, at end of report). 

Strong relations are not apparent. As stated previously, 

however, the observed plant-density data are subjective and 

do not seem to be related to nutrient concentrations. Canopy 

openness does not seem to have a substantial effect on the 

density of filamentous algae and aquatic plants. Filamentous 

algae and aquatic plants were commonly not observed at sites 

with closed canopies, but they were also not observed at sites 

with open canopies. Other categories of plant-density data 

also were ambiguous; for example, there may be a weak 

relation between moderate densities of aquatic moss and less 

canopy openness.

Differences and variability in benthic (periphyton) 

chlorophyll a concentrations and plant densities in streams 

generally do not correlate well with measured nutrient concentrations (Dodds and Welch, 2000). The comparisons examined 

here, however, do show a relation between median chlorophyll 

a concentrations and canopy openness. The median values 

for all stations in the categories seem to be higher for opencanopy sites than for closed-canopy sites. 

Relations Among Categorical Data 

Comparison of nutrient and chlorophyll a concentrations 

with the distribution of NPDES-permitted dischargers among 

Massachusetts nutrient ecoregions reveals that the distribution of major NPDES-permitted dischargers upstream from 

sampling stations appears to be related to the lake-based phosphorus nutrient ecoregions (fig. 1 and 14, at end of report); 

and other landscape factors, such as geology and soils, also 

may affect water quality, but are not examined in this report. 

In general, the highest concentrations of total phosphorus and 

total nitrogen are present at stations downstream from major 

NPDES-permitted dischargers that are in high-nutrient ecoregions. The lowest nutrient concentrations generally appear 

at stations with no upstream NPDES-permitted dischargers 

in low-nutrient ecoregions. Stations downstream from minor 

NPDES-permitted dischargers (red-colored symbols) usually 

are characterized by intermediate nutrient concentrations and 

are found in the intermediate- and high-nutrient ecoregions; no 

minor NPDES-permitted dischargers are in the low-nutrient 

ecoregion. Increases in chlorophyll a concentrations do not 

appear to be associated with increases in nutrient concentrations, regardless of nutrient ecoregion or the presence of 

upstream NPDES-permitted dischargers. The inclusion of 

open- and closed-canopy data with the nutrient ecoregions or 

dischargers similarly does not reveal any relations with median 

chlorophyll a concentrations (fig. 15, at end of report).

Using the New England SPARROW model, Moore and 

others (2004) found that relatively high nutrient concentrations 

may be associated with permitted wastewater dischargers, 

agricultural land area, and urbanized land area. They also 

found that streamflows less than 2.83 m3/s and the existence 

of small (surface area less than 10 km2) impoundments were 

associated with losses in phosphorus. Although the present 

study did not explicitly examine land-use relations, urban 

areas with relatively high incidences of treatment plants have 

data similar to data from the intermediate- and high-nutrient 

ecoregions in Massachusetts. 

Correlations Among Water-Quality Variables

Correlation analysis serves to determine how two 

parameters covary. The results of such analyses can be 

presented in the form of correlation matrices that show the 

relations among any number of parameters (tables 6 and 7). 

By matching the values in the matrices (correlation coefficients) to their associated parameters heading the rows 

and columns, it is possible to determine the fraction of the 

variation in one parameter that is correlated with the other. A 

negative value indicates an inverse relation. When considering 

all the data, very few of the parameters seem to be correlated. 

The strongest correlations, in general, are among the nutrients 

and specific conductance (table 6): total nitrogen and total 

phosphorus (0.610); total nitrogen and specific conductance 

(0.704); total phosphorus and specific conductance (0.485). 

Simply stated, high concentrations of one nutrient can be 

expected in the presence of another. Because high nutrient 

concentrations may be associated with urban settings, high 

concentrations of other dissolved materials, such as salts, 

also may be expected, and these concentrations tend to 

increase specific-conductance measurements. Chlorophyll a

concentrations are only weakly correlated with concentrations 

of any of the nutrients. When the data are categorized on the 

basis of open or closed canopy, the correlation between total 

nitrogen and chlorophyll a becomes stronger at open-canopy 

sites (0.381) than at closed-canopy sites (0.023); on the other 

hand, the correlation between percentage of open canopy and 

chlorophyll a at open-canopy sites (0.003) is not as strong as it 

is at closed-canopy sites (0.259) (table 8).

Stronger correlations can be made by dividing the data 

on the basis of Massachusetts nutrient ecoregion (table 7). 

In these views of the data, relatively strong correlations 

(correlation coefficients greater than 0.500) can be seen among 

total phosphorus, total dissolved nitrogen, and chlorophyll a in 

the low-nutrient ecoregion. The correlation becomes weaker 

for total phosphorus in the intermediate-nutrient ecoregion, 

and is generally weakest in the high-nutrient ecoregion. The 

correlations among nutrients and specific conductance are 

weakest in the low-nutrient ecoregion and strongest in the 

intermediate-nutrient ecoregion. In the low-nutrient ecoregion, 

there are also strong negative correlations: (1) of total nitrogen 

and total phosphorus with dissolved oxygen; (2) of specific 

conductance with color; (3) of DO or percentage of openness 

with both total nitrogen and total phosphorus concentrations; 

and (4) of drainage basin area with both total phosphorus 

and total nitrogen. These correlations are not as strongly 

negative, or are slightly positive, in the intermediate- or highnutrient ecoregions. 
Relations Among Chlorophyll a, Nitrogen, 

Phosphorus, and Canopy Openness

Individual relations between chlorophyll a and the 

principal parameters (total nitrogen, total phosphorus, their 

ratios, and canopy openness) that might be expected to affect 

its concentration were examined graphically and by performing linear regression analysis. Increasing median chlorophyll a 

concentrations only seem weakly related to increasing canopy 

openness, regardless of nutrient concentration or the ratio of 

total nitrogen to total phosphorus (fig. 16, at end of report). 

The regression coefficients among these variables are quite 

low (table 8).

Although separating the stations on the basis of open or 

closed canopies generally increases the regression coefficients 

somewhat, these regression coefficients remain low, indicating 

weak relations between chlorophyll a and the various 

independent variables (table 8). In the closed-canopy 

category, the correlation coefficient of 0.259 indicates 

that the median total nitrogen concentration explains about 

26 percent of the variation in median chlorophyll a. Among 

open-canopy sites, total nitrogen explains about 38 percent of 

the variation. The other regressions explain generally less than 

5 percent of the variation.

Stream-Velocity Effects

Stream velocity was considered as a factor possibly 

affecting periphyton chlorophyll a concentrations. Because 

stream velocity was estimated visually, and not measured 

directly, continuously varying data were unavailable. 

Surrogate data, such as antecedent high discharges and stream 

slope, were used instead to estimate stream velocity. 

Effect of Antecedent Flows

One factor that can affect periphyton density and 

hence the chlorophyll a concentration is the occurrence of 

antecedent stormflows that can scour the periphyton from 

rocks. To study the effect of antecedent flow conditions on 

chlorophyll a, the MassDEP DWM selected the 28-day time 

period preceding periphyton sampling (Steven Halterman, 

Massachusetts Department of Environmental Protection, 

Division of Watershed Management, written commun., 2006). 

If streamflow exceeded 300 percent of the annual median 

discharge, the chlorophyll a data were examined to determine 

whether a scouring effect could be observed (Biggs, 2000); 

that is, if chlorophyll a concentrations routinely declined 

after such a storm between sampling dates, then the decline 

24  Assessment of Data for Use in the Development of Nutrient Criteria

Table 6. Correlation coefficients among major water-quality parameters and percentage of open canopy and drainage area. 

[Only values above the diagonal values of 1.000 are presented. The values below the diagonal mirror values above the diagonal and have been replaced by 

“–” to simplify the table. Coefficients (except for diagonal values=1.000) that represent relatively high correlations greater than 0.500 or less than -0.500 are 

shaded. Negative correlation coefficients indicate inverse relations]

Percentage of 

open 

canopy

Drainage 

area

Total 

dissolved 

nitrogen

Total 

nitrogen

Total 

phosphorus

Chlorophyll a

Color Turbidity

Specific 

conductance

Dissolved 

oxygen

Percentage of open canopy 1.000 0.543 0.021 0.037 0.026 0.496 -0.014 -0.047 0.088 0.188

Drainage area – 1.000 .013 .037 .130 .195 -.024 .014 .101 .202

Total dissolved nitrogen – – 1.000 .993 .590 .446 -.148 -.003 .697 -.189

Total nitrogen – – – 1.000 .610 .460 -.124 .050 .704 -.225

Total phosphorus – – – – 1.000 .326 -.073 .029 .485 -.205

Chlorophyll a – – – – – 1.000 -.168 -.075 .317 -.145

Color – – – – – – 1.000 .608 -.166 -.427

Turbidity – – – – – – – 1.000 .097 -.505

Specific conductance – – – – – – – – 1.000 -.211

Dissolved oxygen – – – – – – – – – 1.000
Assessment of Data  25

Table 7. Correlation coefficients among water-quality parameters, percentage of open canopy, and drainage area based on 

Massachusetts nutrient ecoregions.

[Only values above the diagonal values of 1.000 are presented. The values below the diagonal mirror values above the diagonal and have been replaced by “–” 

to simplify the table. Coefficients (except for diagonal values=1.000) that represent relatively high correlations greater than 0.500 or less than -0.500 are shaded. 

Negative correlation coefficients indicate inverse relations]

Percentage 

of open 

canopy

Drainage 

area

Total 

dissolved 

nitrogen

Total 

nitrogen

Total 

phosphorus

Chlorophyll aColor Turbidity Specific 

conductance

Dissolved 

oxygen

Low-nutrient ecoregion

Percentage of open canopy 1.000 0.887 0.057 -0.716 -0.640 -0.152 -0.367 -0.577 0.054 0.819

Drainage area – 1.000 .302 -.931 -.617 -.300 .081 -.596 -.316 .899

Total dissolved nitrogen – – 1.000 -.446 .541 .542 .447 .191 -.380 .183

Total nitrogen – – – 1.000 .465 .341 -.381 .691 .627 -.935

Total phosphorus – – – – 1.000 .805 .140 .653 .067 -.608

Chlorophyll a – – – – – 1.000 -.342 .655 .463 -.428

Color – – – – – – 1.000 -.159 -.895 .156

Turbidity – – – – – – – 1.000 .559 -.870 

Specific conductance – – – – – – – – 1.000 -.516

Dissolved oxygen – – – – – – – – – 1.000

Intermediate-nutrient ecoregion

Percentage of open canopy 1.000 0.561 -0.001 -0.036 -0.090 0.463 -0.012 -0.175 0.121 0.287

Drainage area – 1.000 -.112 -.131 -.189 .025 -.013 -.196 -.013 .431

Total dissolved nitrogen – – 1.000 .996 .737 .543 -.126 -.027 .818 -.134

Total nitrogen – – – 1.000 .767 .516 -.102 .031 .814 -.165

Total phosphorus – – – – 1.000 .391 -.012 .246 .641 -.339

Chlorophyll a – – – – – 1.000 -.346 -.237 .494 -.016

Color – – – – – – 1.000 .708 -.213 -.456

Turbidity – – – – – – – 1.000 -.152 -.504

Specific conductance – – – – – – – – 1.000 .077

Dissolved oxygen – – – – – – – – – 1.000

High-nutrient ecoregion

Percentage of open canopy 1.000 0.526 0.009 0.061 0.043 0.576 -0.040 0.055 0.046 0.089

Drainage area – 1.000 .086 .145 .224 .338 -.112 .254 .145 -.044

Total dissolved nitrogen – – 1.000 .991 .681 .319 -.278 -.098 .728 -.199

Total nitrogen – – – 1.000 .698 .375 -.264 -.065 .728 -.231

Total phosphorus – – – – 1.000 .378 -.134 -.105 .491 -.199

Chlorophyll a – – – – – 1.000 -.071 .013 .241 -.227

Color – – – – – – 1.000 .422 -.220 -.393

Turbidity – – – – – – – 1.000 .182 -.411

Specific conductance – – – – – – – – 1.000 -.351

Dissolved oxygen – – – – – – – – – 1.000
could be ascribed to the scouring effect. Twelve stations 

had sufficient data for inclusion, and some had open- and 

closed-canopy sites. Data from 2001 and 2004 were included. 

Where no USGS continuous-monitoring station existed, the 

change in streamflow was estimated by selecting the nearest 

gaged stream of comparable drainage area as a surrogate. 

When applying these criteria to the data, no relation between 

antecedent storms and chlorophyll a concentration changes 

was found; approximately equal numbers of increases (13) and 

decreases (14) were detected in chlorophyll a concentrations 

in the 28 days following antecedent storms. Samples collected 

when there were no qualifying antecedent storms between 

sampling dates also had approximately equal numbers of 

increases (25) and decreases (24). 

Effect of Slope

Although stream discharge and velocity were not 

measured as part of the field studies, in retrospect, the effect of 

velocity on the concentration of chlorophyll a was determined 

by using channel slope. In lieu of velocity measurements, 

average upstream channel slope was used as a surrogate for 

velocity because streams with relatively high average slopes 

are assumed to have relatively high velocities at sampling 

sites. This assumption implies that increasing average velocities would be associated with increasing scour and diminishing chlorophyll a concentrations. Average slopes for each 

catchment associated with a sampling station were obtained 

by the DWM (Mark Mattson, Massachusetts Department 

of Environmental Protection, Division of Watershed 

Management, oral commun., 2006) from the New England 

SPARROW model (Moore and others, 2004). Because Moore 

and others (2004) suggest that steep slopes may increase 

loadings of nutrients to streams, the relations of nutrients to 

slope also are examined here. Comparing the median nutrient 

and chlorophyll a concentrations with stream slopes appears 

to show that with the exception of some elevated median 

concentrations of total nitrogen in streams with slopes less 

than 10 percent, no obvious relations with slope exist (fig. 17, 

at end of report).

26  Assessment of Data for Use in the Development of Nutrient Criteria

Table 8. Regression coefficients for chlorophyll a versus total phosphorus, total nitrogen, the ratio of total nitrogen 

to total phosphorus, and percentage of open canopy for all sites, closed-canopy sites, and open-canopy sites. 

[TP, total phosphorus; TN, total nitrogen; R2, regression coefficient]

All sites R2

Chlorophyll a versus TP 0.040

Chlorophyll a versus TN .077

Chlorophyll a versus TN:TP .001

Chlorophyll a versus percentage of open canopy .090 

Closed-canopy sites

Chlorophyll a versus TP 0.039

Chlorophyll a versus TN .023

Chlorophyll a versus TN:TP .001

Chlorophyll a versus percentage of open canopy .259

Open-canopy sites

Chlorophyll a versus TP 0.154

Chlorophyll a versus TN .381

Chlorophyll a versus TN:TP .013

Chlorophyll a versus percentage of open canopy .003
Summary and Conclusions

The U.S. Geological Survey (USGS) assessed 

Massachusetts water quality for developing nutrient criteria 

or a science-based framework for interpreting narrative 

criteria for nutrients. The USGS collected the water-quality 

data using a deterministic sampling design developed by 

the Massachusetts Department of Environmental Protection, 

Division of Watershed Management. The numbers of sites and 

numbers of samples collected at some sites varied each year. 

To avoid biasing study results toward conditions at sites that 

were sampled relatively frequently, median values of waterquality parameters were used to represent each sampling site. 

Data were classified into categories for analysis by year, 

USEPA ecoregion, Massachusetts nutrient ecoregion, drainage-basin size, presence and type of upstream dischargers, 

and canopy openness. While the relations among nutrients 

and periphyton chlorophyll a were the focus of this study, 

other water-quality characteristics, such as dissolved oxygen, 

specific conductance, pH, and plant density also 

were examined. 

More than half the sampling locations were downstream 

from NPDES-permitted wastewater-treatment plants. The 

majority of these treatment plants are located in Ecoregion 

XIV and the Massachusetts high-nutrient ecoregion. Major 

NPDES-permitted wastewater-treatment plants also tend to be 

located in large river basins. 

Yearly differences in water-quality conditions were not 

substantial. Median total nitrogen and median total phosphorus 

concentrations were higher in USEPA Ecoregion XIV than 

in USEPA Ecoregion VIII. For USEPA Ecoregions VIII and 

XIV, the data analyzed here indicate that the 25th-percentile 

median nutrient concentrations of total phosphorus and total 

nitrogen are lower than those recommended by the USEPA. 

Median turbidity values are somewhat higher than the USEPA 

recommendations. On the basis of drainage-basin size, only 

median nitrogen (total and dissolved) concentrations differed 

significantly, and the concentrations differed only between 

the largest and smallest basin-size classes. The presence or 

absence of major or minor NPDES-permitted dischargers 

upstream from sampling stations had the most obvious effect 

on median total phosphorus and nitrogen concentrations. The 

stations with no upstream dischargers had the lowest nutrient 

concentrations, followed by stations with minor dischargers; 

stations with major dischargers upstream had the highest 

median total phosphorus and nitrogen concentrations.

Among the categories of USEPA ecoregion, drainagebasin size, Massachusetts (lake-based) nutrient ecoregion, 

and presence of upstream dischargers, the median chlorophyll 

a concentrations were not found to differ. For the categories 

of USEPA ecoregion, Massachusetts nutrient ecoregion, 

and presence of upstream dischargers, at least one of the 

distributions of total phosphorus and total nitrogen median 

values was found to differ. Median total phosphorus values 

among the drainage-basin-size classes were not found to 

differ, but at least one of the median total nitrogen values 

did differ. Further statistical testing indicated that, among 

drainage-basin-size classes, median total dissolved nitrogen 

and total nitrogen values did not differ between the smallest 

and intermediate basins or between the intermediate and 

largest basins; however, the values for the smallest basins 

were different from values for the largest basins. Among the 

Massachusetts nutrient ecoregions, median total phosphorus 

values for the intermediate- and high-nutrient ecoregions did 

not differ, but were significantly greater than in the low-nutrient ecoregion. Median total dissolved nitrogen concentrations 

did not differ among the three nutrient ecoregions, but the 

distributions of median total nitrogen values differed among 

all nutrient ecoregions. In the categories defined by NPDESpermitted dischargers, median total phosphorus and median 

total nitrogen had significantly different distributions in all 

three nutrient ecoregions. Median total dissolved nitrogen 

distributions did not differ between the stations that had either 

minor or no upstream dischargers, but both of these categories 

differed from the major discharger category. 

Differences were observed when open- and closed-canopy sites were compared either at the same sampling location 

or among categorical groups. Open-canopy sites tended to 

have higher median periphyton chlorophyll a concentrations 

than co-located closed-canopy sites.

No strong correlations could be determined for median 

periphyton chlorophyll a concentrations with other waterquality characteristics. Nutrients correlated relatively strongly 

with each other and with specific conductance. These correlations further support the relations of the data with the presence of wastewater-treatment plants and other urban land-use 

effects. The possible effects of antecedent flows and stream 

slope on the median periphyton-chlorophyll a concentrations 

were examined. No relations were determined.

Summary and Conclusions  27
Acknowledgments

Environmental analysts Joan L. Beskenis and Mark 

D. Mattson and environmental engineers Dennis R. Dunn, 

Steven G. Halterman, and Russell A. Isaac, Massachusetts 

Department of Environmental Protection, Division of 

Watershed Management, designed the field studies and 

provided guidance for making this interpretive study relevant 

to the requirements for their development of water-quality 

criteria. The authors thank U.S. Geological Survey staff 

Timothy R. Driskell, Domenic Murino, Jr., Britt O. Stock, and 

Jason R. Sorenson for their work in collecting the field data 

on which much of this report’s analysis is based. Virginia L. 

McGuire, hydrologist, U.S. Geological Survey, has provided 

this and other projects with invaluable technical support in 

applications of the S-PLUS data-analysis software package. 

David L. Lorenz, hydrologist, U.S. Geological Survey, assisted 

with advice on statistical analyses.

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the development of State and Tribal nutrient criteria for 

rivers and streams in Nutrient Ecoregion XIV: U.S Environmental Agency, EPA 822-B-00-022, variously paged. 

U.S. Environmental Protection Agency, 2001, Ambient water 

quality criteria recommendations, information supporting 

the development of State and Tribal nutrient criteria for 

rivers and streams in Nutrient Ecoregion VIII: U.S Environmental Agency, EPA 822-B-01-015, variously paged.

Webb, W.E., Radtke, D.B., and Iwatsubo, R.T., 1999, Surfacewater sampling—Collection methods at flowing-water and 

still-water sites, in Wilde, F.D., Radtke, D.B., Gibs, Jacob, 

and Iwatsubo, R.T., eds., National field manual for the 

collection of water-quality data: U.S. Geological Survey 

Techniques of Water-Resources Investigations, book 9, 

chap. A4, section 4.1.1A, variously paged.

Wilde, F.D. and Gibs, Jacob, 1998, Turbidity, in Wilde, 

F.D., Radtke, D.B., Gibs, Jacob, and Iwatsubo, R.T., eds., 

National field manual for the collection of waterquality data: U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 9, chap. A6, 

variously paged.
30 Assessment of Data for Use in the Development of Nutrient Criteria

Major Minor None

0.001

0.01

0.1

1

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER AS P

x

x

x

o

x

(26) (11) (28)

B

A

A

C

Major Minor None

0.1

0.2

0.3

0.4

0.5

5

10

TOTAL NITROGEN, IN MILLIGRAMS PER LITER AS N

x

x

o

(26) (11) (28)

B

B

D

C

A 1

2

3

4

Major Minor None

0.05

0.1

0.5

1

5

10

TOTAL DISSOLVED NITROGEN, IN MILLIGRAMS 

PER LITER AS N

(25) (9) (23)

C

NATIONAL POLLUTANT DISCHARGER ELIMINATION SYSTEM

DISCHARGER CATEGORY

x

x

A B

B

Major Minor None

50

1

5

10

100

CHLOROPHYLL A, IN MILLIGRAMS PER SQUARE METER

(32) (12) (31)

A A

A

NATIONAL POLLUTANT DISCHARGER ELIMINATION SYSTEM

DISCHARGER CATEGORY

(12)

o

Number of samples

Outlier greater than 3.0 times the 

interquartile range above the box

0utlier between 1.5 and 3.0 times the 

interquartile range above the box

Highest data point within 1.5 times the 

interquartile range above the box

Lowest data point within 1.5 times the 

interquartile range below the box

Outlier between 1.5 and 3.0 times the 

interquartile range below the box

x

x

Third quartile

Median

First quartile

EXPLANATION

Figure 7. Distribution of median (A) total phosphorus, (B) total nitrogen, (C) total dissolved nitrogen, and (D) chlorophyll a

concentrations at all sampling sites by National Pollutant Discharge Elimination System discharger category in Massachusetts. 

The results of the Kruskal-Wallis rank sum test are represented as letters. Distributions of groups of data with at least one letter 

in common do not differ significantly.
Number of samples

Highest data point within 1.5 times the 

interquartile range above the box

Lowest data point within 1.5 times the 

interquartile range below the box

(22)

Third quartile

Median

First quartile

EXPLANATION

A

MASSACHUSETTS NUTRIENT ECOREGION

10

50

100

CHLOROPHYLL A, IN MILLIGRAMS PER SQUARE METER

(10) (13) (22)

5

1

Low Intermediate High Low Intermediate High

MASSACHUSETTS NUTRIENT ECOREGION

100

(4) (11) (15)

50

10

5

CHLOROPHYLL A, IN MILLIGRAMS PER SQUARE METER

B

Figure 8. Distribution of median periphyton chlorophyll a concentrations at (A) closed- and (B) open-canopy sampling sites 

by Massachusetts nutrient ecoregion.

Additional Figures  31
32  Assessment of Data for Use in the Development of Nutrient Criteria

VIII XIV VIII XIV

ECOREGION

10

5

1

50

100

CHLOROPHYLL A, IN MILLIGRAMS PER SQUARE METER

(12) (33)

A

ECOREGION

CHLOROPHYLL A, IN MILLIGRAMS PER SQUARE METER

(10) (20)

10

5

50

100

B

Number of samples

Highest data point within 1.5 times the 

interquartile range above the box

Lowest data point within 1.5 times the 

interquartile range below the box

(10)

Third quartile

Median

First quartile

EXPLANATION

Figure 9. Distribution of median periphyton chlorophyll a concentrations at (A) closed- and (B) open-canopy sampling 

sites for U.S. Environmental Protection Agency ecoregions VIII and XIV in Massachusetts.
10

5

1

50

100

CHLOROPHYLL A , IN MILLIGRAMS PER SQUARE METER

(18) (23)

(23)

(4)

100

50

10

5

CHLOROPHYLL A, IN MILLIGRAMS PER SQUARE METER

x

(6) (15) (9)

A B

Number of samples

Highest data point within 1.5 times the 

interquartile range above the box

Lowest data point within 1.5 times the 

interquartile range below the box

Outlier between 1.5 and 3.0 times the 

interquartile range below the box

x

Third quartile

Median

First quartile

EXPLANATION

DRAINAGE-BASIN-SIZE CLASS, IN SQUARE MILES DRAINAGE-BASIN-SIZE CLASS, IN SQUARE MILES

<10 10–90 90–350 <10 10–90 90–350

Figure 10. Distribution of median periphyton chlorophyll a concentrations at (A) closed- and (B) open-canopy sampling 

sites by drainage-basin-size class in Massachusetts.

Additional Figures  33
34  Assessment of Data for Use in the Development of Nutrient Criteria

Major Minor None

10

5

1

50

100

CHLOROPHYLL A, IN MILLIGRAMS PER SQUARE METER

(14) (7)

(7)

(24)

A

Major Minor None

100

50

10

5

CHLOROPHYLL A, IN MILLIGRAMS PER SQUARE METER

(18) (5) (7)

B

Number of samples

Highest data point within 1.5 times the 

interquartile range above the box

Lowest data point within 1.5 times the 

interquartile range below the box

Third quartile

Median

First quartile

EXPLANATION

NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM

DISCHARGER CATEGORY

NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM

DISCHARGER CATEGORY

Figure 11. Distribution of median periphyton chlorophyll a concentrations at (A) closed- and (B) open-canopy sampling 

sites by National Pollutant Discharge Elimination System discharger category in Massachusetts.
0.001 0.010 0.100 1.000

0

1

2

3

FILAMENTOUS PERIPHYTON DENSITY

0.001 0.010 0.100 1.000

0

1

2

3

4

PERIPHYTON FILM DENSITY

A B

D

E

C

0.001 0.010 0.100 1.000

0

1

2

3

ROOTED AQUATIC PLANT DENSITY

EXPLANATION

DENSITY SCALE ON Y AXIS, IN PERCENT 

OF COVER

 0 Not observed

 1 Sparse (0–25)

 2 Moderate (26–50)

 3 Dense (51–75)

 4 Very Dense (76–100)

0.001 0.010 0.100 1.000

0

1

2

3

4

AQUATIC MOSS DENSITY

0.001 0.010 0.100 1.000

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER AS P

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER AS P

0

1

2

3

PERIPHYTON FLOC DENSITY

Figure 12. Density of (A) filamentous periphyton, (B) periphyton film, (C) aquatic plants, (D) aquatic moss, and (E) periphyton floc as 

a function of median total phosphorus concentrations and the percentage of canopy openness at all sampling sites in Massachusetts. 

Circle size is proportional to canopy openness.

Additional Figures  35
36  Assessment of Data for Use in the Development of Nutrient Criteria

0.10 1.00 10.00

0

1

2

3

FILAMENTOUS PERIPHYTON DENSITY

0.10 1.00 10.00

0

1

2

3

4

PERIPHYTON FILM DENSITY

0.10 1.00 10.00

TOTAL NITROGEN, IN MILLIGRAMS PER LITER AS N 

TOTAL NITROGEN, IN MILLIGRAMS PER LITER AS N 

0

1

2

3

ROOTED AQUATIC PLANT DENSITY

EXPLANATION

DENSITY SCALE ON Y AXIS, IN PERCENT

OF COVER

 0 Not observed

 1 Sparse (0–25)

 2 Moderate (26–50)

 3 Dense (51–75)

 4 Very Dense (76–100)

0.10 1.00 10.00

0

1

2

3

4

AQUATIC MOSS DENSITY

0.10 1.00 10.00

0

1

2

3

PERIPHYTON FLOC DENSITY

A

D

B

E

C

Figure 13. Density of (A) filamentous periphyton, (B) periphyton film, (C) aquatic plants, (D) aquatic moss, and (E) periphyton floc as a 

function of median total nitrogen concentrations and the percentage of canopy openness at all sampling sites in Massachusetts. Circle 

size is proportional to canopy openness.
1.0 10.0 100.0

CHLOROPHYLL A, IN MILLIGRAMS PER SQUARE METER 

0.001

0.01

0.1

1

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER AS P

EXPLANATION

Major Minor None

Low

Intermediate

High

A

SYMBOL REPRESENTS MASSACHUSETTS NUTRIENT ECOREGION, AND COLOR 

REPRESENTS TYPE OF NATIONAL POLLUTANT DISCHARGE ELIMINATION 

SYSTEM DISCHARGER

Figure 14. Median (A) total phosphorus and (B) total nitrogen concentrations as a function of median chlorophyll a concentrations 

by Massachusetts nutrient ecoregion and National Pollutant Discharge Elimination System discharger category.

Additional Figures  37
38  Assessment of Data for Use in the Development of Nutrient Criteria

1.0 10.0 100.0

CHLOROPHYLL A, IN MILLIGRAMS PER SQUARE METER 

0.1

1.0

10.0

TOTAL NITROGEN, IN MILLIGRAMS PER LITER AS N

B

EXPLANATION

Major Minor None

Low

Intermediate

High

SYMBOL REPRESENTS MASSACHUSETTS NUTRIENT ECOREGION, AND COLOR 

REPRESENTS TYPE OF NATIONAL POLLUTANT DISCHARGE ELIMINATION 

SYSTEM DISCHARGER

Figure 14. Median (A) total phosphorus and (B) total nitrogen concentrations as a function of median chlorophyll a

concentrations by Massachusetts nutrient ecoregion and National Pollutant Discharge Elimination System discharger 

category.—Continued
1.0 10.0 100.0

CHLOROPHYLL A, IN MILLIGRAMS PER SQUARE METER 

0.001

0.010

0.100

1.000

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER AS P

A

EXPLANATION

Major Minor None

Low

Intermediate

High

SYMBOL REPRESENTS MASSACHUSETTS NUTRIENT ECOREGION, AND COLOR 

REPRESENTS TYPE OF NATIONAL POLLUTANT DISCHARGE ELIMINATION 

SYSTEM DISCHARGER

Figure 15. Median (A, B) total phosphorus and (C, D) total nitrogen concentrations as a function of median chlorophyll a

concentrations at (A, C) closed- and (B, D) open-canopy sites by Massachusetts nutrient ecoregion and National Pollutant 

Discharge Elimination System discharger category. 

Additional Figures  39
40 Assessment of Data for Use in the Development of Nutrient Criteria

1.0 10.0 100.0

CHLOROPHYLL A, IN MILLIGRAMS PER SQUARE METER 

0.001

0.010

0.100

1.000

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER AS P

B

EXPLANATION

Major Minor None

Low

Intermediate

High

SYMBOL REPRESENTS MASSACHUSETTS NUTRIENT ECOREGION, AND COLOR 

REPRESENTS TYPE OF NATIONAL POLLUTANT DISCHARGE ELIMINATION 

SYSTEM DISCHARGER

Figure 15. Median (A, B) total phosphorus and (C, D) total nitrogen concentrations as a function of median chlorophyll a

concentrations at (A,C) closed- and (B, D) open-canopy sites by Massachusetts nutrient ecoregion and National Pollutant 

Discharge Elimination System discharger category. —Continued
Figure 15. Median (A, B) total phosphorus and (C, D) total nitrogen concentrations as a function of median 

chlorophyll a concentrations at (A, C) closed- and (B, D) open-canopy sites by Massachusetts nutrient ecoregion 

and National Pollutant Discharge Elimination System discharger category. —Continued

Additional Figures  41

CHLOROPHYLL A, IN MILLIGRAMS PER SQUARE METER 

0.1

1.0

10.0

TOTAL NITROGEN, IN MILLIGRAMS PER LITER AS N

1.0 10.0 100.0

C

EXPLANATION

Major Minor None

Low

Intermediate

High

SYMBOL REPRESENTS MASSACHUSETTS NUTRIENT ECOREGION, AND COLOR 

REPRESENTS TYPE OF NATIONAL POLLUTANT DISCHARGE ELIMINATION 

SYSTEM DISCHARGER
42  Assessment of Data for Use in the Development of Nutrient Criteria

1.0 10.0 100.0

0.1

1.0

10.0

CHLOROPHYLL A, IN MILLIGRAMS PER SQUARE METER 

TOTAL NITROGEN, IN MILLIGRAMS PER LITER AS N

D

EXPLANATION

Major Minor None

Low

Intermediate

High

SYMBOL REPRESENTS MASSACHUSETTS NUTRIENT ECOREGION, AND COLOR 

REPRESENTS TYPE OF NATIONAL POLLUTANT DISCHARGE ELIMINATION 

SYSTEM DISCHARGER

Figure 15. Median (A, B) total phosphorus and (C, D) total nitrogen concentrations as a function of median 

chlorophyll a concentrations at (A, C) closed- and (B, D) open-canopy sites by Massachusetts nutrient ecoregion 

and National Pollutant Discharge Elimination System discharger category. —Continued
CHLOROPHYLL A, IN MILLIGRAMS PER SQUARE METER

1

10

100

TOTAL NITROGEN TO TOTAL 

PHOSPHORUS RATIO

CHLOROPHYLL A, IN MILLIGRAMS PER SQUARE METER

0.1

1

10

TOTAL NITROGEN, IN MILLIGRAMS 

PER LITER AS N

0.01

0.1

1

TOTAL PHOSPHORUS, IN MILLIGRAMS 

PER LITER AS P

A B

C

1 10 100 1 10 100

1 10 100

Figure 16. Median (A) total phosphorus concentrations, (B) total nitrogen concentrations, and (C) ratio of total nitrogen to total 

phosphorus as a function of median chlorophyll a concentrations and percentage of canopy openness in Massachusetts. Circle 

size is proportional to canopy openness.

Additional Figures  43
44  Assessment of Data for Use in the Development of Nutrient Criteria

44  Assessment of Data for Use in the Development of Nutrient Criteria

A B

C D

0 10 15 20 25 30

0

0.2

0.4

0.6

0.8

1.0

TOTAL PHOSPHORUS, IN MILLIGRAMS 

PER LITER AS P 

0 5 10 15 20 25 30

SLOPE, IN PERCENT SLOPE, IN PERCENT

0

2

4

6

8

TOTAL DISSOLVED NITROGEN, IN MILLIGRAMS

PER LITER AS N

10 15 20 25 30

0

2

4

6

8

TOTAL NITROGEN, IN MILLIGRAMS 

PER LITER AS N

0 5

0 5

5

10 15 20 25 30

0

50

100

150

200

CHLOROPHYLL A, IN MILLIGRAMS PER

 SQUARE METER

Figure 17. Median (A) total phosphorus, (B) total nitrogen, (C) total dissolved nitrogen, and (D) chlorophyll a concentrations 

at all sampling sites as a function of slope in Massachusetts.
For additional information write to:

Director

USGS Massachusetts–Rhode Island Water Science Center

10 Bearfoot Road

Northborough, MA 01532

or visit our Web site at

http://ma.water.usgs.gov
Zimmerman and Campo—Assessment of Data for Use in the Development of Nutrient Criteria for Massachusetts Rivers and Streams—SIR 2007–5022

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