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3CIENTIFIC)NVESTIGATIONS2EPORT

Effects of Urbanization on Stream Quality 

at Selected Sites in the Seacoast Region in 

New Hampshire, 2001–03

By Jeffrey R. Deacon, Sally A. Soule, and Thor E. Smith

In cooperation with the New Hampshire Department of Environmental Services

Scientific Investigations Report 2005-5103

U.S. Department of the Interior

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

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2005

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested Citation:

Deacon, J.R., Soule, S.A., and Smith, T.E., 2005, Effects of urbanization on stream quality at selected sites in the 

Seacoast region in New Hampshire, 2001-03: U.S. Geological Survey Scientific Investigations Report 2005-5103, 

18 p.
Contents

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

Introduction.............................................................................................................................. 1

Purpose and Scope ............................................................................................................... 2

Description of Study Area ...................................................................................................... 2

Data Collection and Analysis ......................................................................................................... 2

Site Selection ..................................................................................................................... 2

Sample Collection ............................................................................................................... 2

Data Analysis ..................................................................................................................... 5

Characterization of Physical Measurements, Water Quality, Macroinvertebrates, and Habitat at Selected Sites......... 6

Physical Measurements and Water Quality ................................................................................. 7

Macroinvertebrates and Habitat ................................................................................................ 7

Effects of Urbanization on Stream Quality at Selected Sites ..................................................................... 12

Impervious Surface and Stream-Quality Measures ........................................................................ 13

Radial Buffers and Stream-Quality Measures................................................................................. 13

Stream Buffers and Stream-Quality Measures .............................................................................. 14

Water-Quality and Habitat Conditions Score and the Biological Condition Score ....................................... 15

Summary and Conclusions ............................................................................................................ 16

Acknowledgments ..................................................................................................................... 16

Literature Cited ........................................................................................................................ 17

Figures

1. Map showing sampling sites, site-identification numbers, and land use in the Seacoast region in 

New Hampshire ............................................................................................................ 3

2. Schematic showing (A) 0.5-kilometer, 1-kilometer, and 2-kilometer radial buffers upstream of a 

sampling site; and (B) a 100-meter stream buffer along the stream corridor, upstream of a sampling site 

for the Seacoast region in New Hampshire .............................................................................. 6

 3. Graph showing mean annual streamflow for historical and study period years from the Oyster River at 

Durham, N.H. ............................................................................................................... 9

4. Hydrograph of mean daily streamflow for water years 2001–03 from the Oyster River at Durham, N.H. ......... 9

 5-11. Graphs showing—

5. Mean Escherichia coli concentrations among sampling sites, predominant land use, and percentage 

of impervious surface at study sites in the Seacoast region of New Hampshire .............................. 10

 6. Mean nitrite plus nitrate yields among sampling sites, predominant land use, and percentage of 

impervious surface at study sites in the Seacoast region of New Hampshire ................................. 10

7. Mean value for Ephemeroptera, Plecoptera, and Trichoptera taxa richness among sampling sites, 

predominant land use, and percentage of impervious surface at study sites in the Seacoast region 

of New Hampshire...................................................................................................... 11

8. Relation between the percent of impervious surface in the watershed and the (A) water-quality 

and habitat conditions score, (B) biological condition score, and (C) mean Ephemeroptera, 

Plecoptera, and Trichoptera taxa richness at the study sites in the Seacoast region in New Hampshire... 13

iii
 9. Relation between the percent of urban land in a 1-kilometer radial buffer and the (A) water-quality and 

habitat conditions score, (B) biological condition score, and (C) mean Ephemeroptera, Plecoptera, and 

Trichoptera taxa richness at the study sites in the Seacoast region in New Hampshire ..................... 14

10. Relation between the percent of urban land in a 25-meter stream buffer and the (A) water-quality and 

habitat conditions score, (B) biological condition score, and (C) mean Ephemeroptera, Plecoptera, and 

Trichoptera taxa richness at the study sites in the Seacoast region in New Hampshire ..................... 15

11. Relation between the water-quality and habitat conditions score and the biological condition score at 

the study sites in the Seacoast region in New Hampshire......................................................... 16

Tables

 1. Selected characteristics for the study sites in the Seacoast region in New Hampshire ........................... 4

 2. Summary statistics of physical measurements for the study sites in the Seacoast region in

New Hampshire ............................................................................................................ 8

 3. Summary statistics of Escherichia coli, nitrite plus nitrate, total phosphorus, and number of pesticide 

detections from water samples collected at the study sites in the Seacoast region in New Hampshire......... 8

 4. Mean values of selected macroinvertebrate metrics for samples collected at each of the study 

sites in the Seacoast region in New Hampshire ........................................................................ 11

 5. Summary of Spearman rank correlations between watershed characteristics and stream-quality variables 

at the study sites in the Seacoast region in New Hampshire ......................................................... 12

iv
Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 0.004047 square kilometer (km2)

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2) 

Flow rate

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

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

 °F = (1.8 × °C) + 32

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Abbreviated water-quality units used in this report: 

Chemical concentrations in water are reported in milligrams per liter (mg/L). Milligrams per liter is a unit expressing the 

concentration of chemical constituents as weight (milligrams) of chemical per unit volume (liter) of water.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 25 °C).

Turbidity is reported in Nephelometric Turbidity Units (NTUs).

Concentrations of bacteria in water: 

Bacteria concentrations in water are reported in colony counts per 100 mL (col/100mL).

Conversion Factors, Abbreviated Water-Quality Units, and Datums

v

Abstract

A study of selected water-quality and macroinvertebrate 

community data was conducted at 10 stream sites in the Seacoast region of New Hampshire to determine if a relation is 

present between stream quality and the extent of urbanization 

in a watershed. Watersheds with similar characteristics, but 

varying in their degree of urban development, were studied. 

The percent of impervious surface, the percent of urban land 

use in a watershed, and the percent of urban land use in two 

types of stream buffers were compared and correlated with 

stream-quality variables. 

Specific conductance, turbidity, nitrite plus nitrate 

yields, and selected macroinvertebrate community data were 

significantly correlated with most measures of urbanization 

used in this study; however, Escherichia coli concentrations 

and total phosphorus yields were not statistically correlated 

with most measures of urbanization in this study. The 

measures of urbanization that had the highest correlations 

with stream-quality variables were those measures that were 

associated with the percent of urban land in buffer zones near 

and upstream of a sampling site. A water-quality and habitat 

conditions score was negatively correlated with the percent of 

urban land in a 1-kilometer radial buffer of the sampling site 

(rho (r) = -0.86; p < 0.001), the percent of impervious surface 

(r = -0.70; p < 0.05), and the percent of urban land in the 

watershed (r = -0.67; p < 0.05). A biological condition score 

also was negatively correlated with the percent of urban land 

in a 1-kilometer radial buffer of the sampling site (r = -0.95; 

p < 0.0001), the percent of impervious surface (r = -0.75; 

p < 0.05), and the percent of urban land in the watershed 

(r = -0.79; p < 0.01). The percent of urban land in a 25-meter 

stream buffer along the stream corridor also had negative 

correlations with a water-quality and habitat conditions 

score (r = -0.80; p < 0.01) and a biological condition score 

(r = -0.86; p < 0.01). Mean Ephemeroptera, Plecoptera, 

and Trichoptera (EPT) taxa richness showed a response to 

urbanization in a watershed, indicating that EPT taxa richness 

may be an appropriate metric to evaluate the effects of urban 

land use on small streams in this region. Results from this 

study indicate that the percent of urban land use in buffer 

zones and the percent of impervious surface in a watershed 

can be used as indicators of stream quality. 

Introduction

The Seacoast region of New Hampshire, like many other 

coastal areas in the United States, is experiencing an increase 

in population and urban development. Urban land use typically 

expands the area of impermeable surfaces, such as roads, parking lots, sidewalks, and rooftops, which results in increased 

watershed runoff (Wang and others, 1997). The primary effect 

of urban development is an increase in impervious surface and 

the corresponding loss of riparian areas and natural vegetation. Development within a watershed is often quantified in 

terms of the proportion of the basin area covered by impervious surfaces (Schueler, 1994). Although impervious surfaces 

do not generate contamination, these surfaces are a major 

contributing factor leading to physical changes of a watershed 

that affect stream quality. In other studies, measures of the 

impervious surface area of about 10 percent have been identified as the level at which stream quality decreases (Klein, 

1979; Schueler, 1994; Booth and Reinelt, 1993). In developed 

watersheds, the chemical composition of runoff often differs 

from pre-development conditions (Booth and Reinelt, 1993). 

Increases of up to one order of magnitude may be typical for 

some contaminant classes, including nutrients and bacteria. 

A study of coastal New England streams in August 2000 

indicated that the greatest change in aquatic communities may 

occur between low and moderate levels of urban intensity 

(Coles and others, 2004). 

State and local agencies in New Hampshire are concerned 

about the effects of increasing urban development on water 

quality and stream biota in the Seacoast region. The combined 

effects to stream quality of increased development, nonpoint 

source contamination, and loss of natural vegetation along 

stream corridors have not been documented in this region. 

To assess these potential effects, the U.S. Geological Survey 

(USGS), in cooperation with New Hampshire Department of 

Environmental Services (NHDES) Coastal Program, designed 

and operated a surface water-quality monitoring network 

during 2001–03 to collect water-quality and stream-biota data 

and to use these data to determine if stream-quality degradation can be observed at a defined level of development and to 

determine which measures of urbanization may be appropriate 

indicators of stream quality in a watershed.

Effects of Urbanization on Stream Quality at Selected 

Sites in the Seacoast Region in New Hampshire, 2001–03 

By Jeffrey R. Deacon, Sally A. Soule, and Thor E. Smith
Purpose and Scope

This report (1) summarizes water-quality and macroinvertebrate data at 10 stream sites, (2) determines the relation 

between water-quality concentrations and habitat conditions 

with macroinvertebrate community data and measures of 

urbanization in a watershed, and (3) determines which measures of urbanization may serve as appropriate indicators of 

stream quality.

The data discussed were collected from 10 stream sites 

in subwatersheds of the major coastal tributaries. Five of the 

10 stream sites were sampled for 3 years (2001–03). The 

other five sites were sampled for 2 years (2002–03). Physical 

measurements (discharge, specific conductance, pH, dissolved 

oxygen, and turbidity), nutrients, bacteria, macroinvertebrates, 

qualitative habitat, and pesticide data are presented.

Description of Study Area

The Seacoast region is a coastal watershed encompassing 1,087 mi2

 in southeastern New Hampshire and southern 

Maine (fig. 1). The region includes diverse ecosystems such 

as coastal bays, tidal rivers and estuaries, salt marshes, and 

freshwater rivers, lakes, and ponds. Major rivers include the 

Oyster, Piscataqua, Lamprey, and Exeter Rivers. The watershed topography ranges from forested, hilly uplands in the 

north and west, to coastal plains and salt marshes in the east 

near the Atlantic coast (Stevens and Anderson, 1997). Geology consists of grey marine clays in the flat coastal plain in the 

lower reaches of the watershed, and in the upper reaches, the 

geology is composed of a combination of bedrock outcropping 

at the surface, mixed glacial materials (sand, gravel, silts, and 

clays), and hardened, dried soils (Short, 1992). Air temperatures range from -29o to 35o C, and precipitation averages 

about 44 inches per year, with most falling during the winter 

season. Slightly less than half of the annual precipitation falling on the coastal watershed is lost through evaporation, with 

the remainder divided between surface runoff and groundwater discharge (David Brown, University of New Hampshire, 

written commun., 2005).

Many areas in the Seacoast region are experiencing 

increased population growth and development. Coincident 

with population increase is the increasing development of 

new impervious surfaces from roads, parking lots, commercial buildings, homes, and other developments which can 

increase runoff to streams. Between 1990 and 2000, impervious surfaces covering 11,154 acres were created in the coastal 

watershed (New Hampshire Estuaries Project, 2003). Land use 

in the watershed consists of highly urbanized regions in the 

easternmost section of the watershed along the coast to rural 

and residential regions (urban) in the northern and western 

areas (fig. 1). Forty-three municipalities are located in the New 

Hampshire part of the coastal watershed including cities such 

as Portsmouth, Dover, Durham, Exeter, and Hampton and rural 

communities such as Chester, Sandown, and Raymond (fig. 1). 

Data Collection and Analysis

The sampling program for this study was designed to 

compare selected stream-quality measures to measures of 

urbanization in a watershed. This study collected data on 

physical measurements, bacteria, nitrogen, and phosphorus 

concentrations and macroinvertebrate communities and correlated these data to the extent of urbanization in a watershed. 

Site Selection

Approximately 40 stream sites were initially categorized 

by stream size, percent of land use types, and population 

density in the watershed. The selection of 10 sites utilized 

a process which included topographic map inspection and 

field reconnaissance. Generally, sites were selected to 

determine if streams draining watersheds with similar physical 

characteristics (basin size, geology, geographical location, and 

instream features), but varied in degrees of urban land in the 

watershed, would indicate decreasing quality as the amount 

and extent of urbanization increased. Five sites were selected 

in populated areas where the predominant land use near and 

upstream of the sampling site is urban (table 1, fig. 1). The 

additional five sites were selected in rural areas where the 

predominant land use near and upstream of the sampling site is 

forest (table 1, fig. 1). A geographic information system (GIS) 

was then used to determine other watershed characteristics 

(the percent impervious surface and the percent of urban land 

use within stream buffers) of these sites. The sites in this 

study ranged from 1.8 to 38 percent impervious surface in the 

watershed. The five sites having urban as the predominant 

land use near and upstream of the sampling site had between 

15 and 38 percent impervious surface in the watershed. The 

five sites having forest as the predominant land use near and 

upstream of the sampling site had between 1.8 and 6.5 percent 

impervious surface in the watershed. 

Sample Collection

Water-column samples were collected using standard 

surface-water protocols (Wilde and Radtke, 1998a and b). 

Physical measurements consisted of streamflow, specific conductance, pH, dissolved oxygen, and turbidity. Instantaneous 

streamflow (discharge) was measured using streamflowgaging methods described by Rantz and others (1982). Water 

samples were analyzed for Escherichia coli (E. coli), nitrite 

plus nitrate, and total phosphorus concentrations. Water 

samples were analyzed once for a suite of 61 pesticide compounds, predominantly consisting of organochlorine, polycyclic aromatic hydrocarbons (PAHs), and thalates, during the 

study to determine their occurrence and distribution. 

E. coli has been identified by the U.S. Environmental 

Protection Agency (USEPA) as the preferred and most useful 

fecal indicator of the freshwater quality of recreational waters 

   Effects of Urbanization on Stream Quality in the Seacoast Region, New Hampshire
Figure 1. Sampling sites, site-identification numbers, and land use in the Seacoast region in New Hampshire. (Site identification 

numbers and names are shown in table 1.)

Data Collection and Analysis   

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for body contact (Dufour, 1984). Algae and aquatic vegetation 

depend on nitrogen and phosphorus compounds for nutrient supply (Hem, 1992). However, excessive concentrations 

of nutrients may lead to an overabundance of aquatic plants 

resulting in decreased dissolved oxygen levels, loss of available habitat for macroinvertebrates, and decreased aesthetics. 

Samples were collected at sites 1 through 5 in 2001-03 

and sites 6 through 10 in 2002-03 (table 1). Water-column 

samples were collected monthly between June and November 

in 2001, and between March and October in 2002 and 2003. 

The monthly sampling represents various weather conditions 

that may effect water-sample concentrations during the study 

as a result of increased runoff during rain or snowmelt events. 

All water-column samples were analyzed at the NHDES Laboratory in Concord, N.H. Results of the physical and the waterquality data for all sampling sites are in the USGS National 

Water Information System (NWIS).

Quality-control procedures included analysis of field 

blank and replicate samples. Field blanks provide information 

on bias or the potential for contamination of analytical results 

by sample collection, processing, and analysis. Analytical 

results from the field blank samples showed that concentrations for all constituents discussed in this report were less 

than the laboratory reporting level. Replicate samples provide 

information on the variability of analytical results caused by 

sample collection, processing, and analysis. Differences in 

concentrations between environmental and replicate samples 

for E. coli colonies per 100 mL were generally less than 20 

percent. Differences in concentrations in environmental and 

replicate samples for nitrite plus nitrate and total phosphorus 

were generally less than 0.01 and 0.005 mg/L, respectively. 

It was concluded that sample processing and analysis did not 

introduce enough variation in the environmental data to affect 

interpretation of results.

A number of studies have shown that macroinvertebrate 

community data can be used as indicators of stream quality 

(Benke and others, 1981; Shaver and others, 1994; Schueler 

and Galli, 1992; Pederson and Perkins, 1986; Garie and 

McIntosh, 1986). These data can be useful in evaluating 

stream quality because macroinvertebrate habitat preference 

and their low motility cause them to be affected directly 

by water quality and habitat conditions. Macroinvertebrate 

samples were collected once each year in July during the 

low-flow summer period using a Surber square-foot sampler. 

Samples were collected from five representative areas of 

riffle habitat containing primarily rock substrates (Cuffney 

and others, 1993). The five subsamples were composited into 

one sample for each site. The samples were preserved with 

70-percent ethanol. Macroinvertebrate samples were analyzed 

for species composition and abundance and were identified to 

genus/species level and enumerated at EcoAnalysts, 

Moscow, Idaho.

Table 1. Selected characteristics for the study sites in the Seacoast region in New Hampshire.

[USGS, U.S. Geological Survey; Latitude and longitude are given in degrees°, minutes ́, and seconds ̋; mi2, square miles; km/km2, kilometers per square 

kilometer]

Site 

number 

(fig. 1)

Site name

USGS

station 

number

Latitude Longitude

Drainage 

area 

(mi2)

Impervious 

surface 

area1

(percent)

Road 

density 

(km/km2)

Population 

density 

(people/

mi2)

Predominant 

land use

1 Fordway Brook at Lane Rd., 

near Raymond, N.H.

01073572 43°01 ́00 ̋ 71°13 ́15 ̋ 5.79 2.2 1.8 206 Forest

2 Towle Brook at Towle Rd., 

near Chester, N.H.

01073562 42°58 ́06 ̋ 71°12 ́55 ̋ 5.52 2.7 1.8 153 Forest

3 Exeter River at Wells Rd., 

near Sandown, N.H.

01073554 42°56 ́10 ̋ 71°12 ́49 ̋ 6.52 1.8 1.7 229 Forest

4 Parkman Brook at Route 108, 

near Stratham, N.H.

01073690 42°59 ́42 ̋ 70°55 ́33 ̋ 1.91 6.5 2.4 393 Forest

5 Parting Brook at Route 85, 

near Newfields, N.H.

01073720 43°01 ́53 ̋ 70°56 ́38 ̋ 1.30 3.4 3.0 229 Forest

6 Hodgson Brook at Cate St., 

at Portsmouth, N.H.

01073800 43°04 ́12 ̋ 70°46 ́34 ̋ 3.53 32 5.9 445 Urban

7 Paul Brook at Woodbury Ave., 

near Newington, N.H.

01073798 43°06 ́03 ̋ 70°48 ́03 ̋ .75 38 3.7 62 Urban

8 College Brook at Mill Pond Rd., 

at Durham, N.H.

01073040 43°07 ́48 ̋ 70°55 ́27 ̋ .88 23 4.6 2,216 Urban

9 Reservoir Brook at Madbury Rd., 

at Durham, N.H.

01073050 43°08 ́06 ̋ 70°55 ́32 ̋ 1.00 15 4.0 1,810 Urban

10 Berry Brook at 6th St., at 

Dover, N.H.

010728802 43°12 ́13 ̋ 70°52 ́54 ̋ 0.50 30 10 3,372 Urban

1

Rubin and Justice, 2001.

 Effects of Urbanization on Stream Quality in the Seacoast Region, New Hampshire
One important aspect of relating biological communities 

to water quality is the assessment of available habitat for 

aquatic organisms. Habitat-assessment data were collected 

according to the USEPA’s Rapid Bioassessment Protocols 

(RBPs) (Barbour and others, 1999). This process involves 

rating 10 habitat parameters as optimal, suboptimal, marginal, 

or poor. RBPs provide a qualitative assessment of stream 

habitat features such as substrate and instream cover, riffle/

run/pool ratio, channel morphology, bank features, and 

riparian vegetation. A total score is calculated based on 

individual scores of the dominant habitat features. Each habitat 

variable was categorized, and a total score of the variables 

provided a qualitative assessment of each site. 

Data Analysis

For purposes of this study, the percent of impervious 

surface, urban land use in the entire watershed and urban land 

use within two types of stream buffers were selected for use 

in correlating the extent of watershed urbanization to stream 

quality. Impervious surface area was calculated using 30-m 

Landstat 5 thematic mapper satellite image data with subpixel 

classification (Rubin and Justice, 2001). The national land 

cover data (NLCD) with 30-m pixels was used to calculate 

urban land-use statistics in each watershed (U.S. Geological Survey, 1992). Stream buffers were calculated using the 

1:24,000 digital line graph data (U.S. Geological Survey, 

1995). Two types of stream-buffer variables, each with various distances in relation to the sampling site, were used for 

data analysis. The first stream-buffer variable and the various 

distances of the buffer that were selected for data analysis was 

the percent of urban land within a 0.5-km, 1-km, and 2-km 

radius of the sampling site, termed radial buffer in this report 

(fig. 2). The second stream-buffer variable and the various 

distances of the buffer that were selected for data analysis was 

the percent of urban land within a 25-m, 100-m, and 250-m 

corridor upstream of the sampling site, termed stream buffer in 

this report (fig. 2). 

A Spearman rank correlation test (Helsel and Hirsch, 

1992) was used to determine the strength of association 

between two variables, such as the percent of impervious 

surface and a biological condition score, and to identify 

stream-quality measures that might be useful in monitoring 

urban effects. Correlations were considered significant if the 

probability was less than 5 percent (p < 0.05). 

To compare water-quality and habitat conditions to 

macroinvertebrate data and to the measures of urbanization at each site, a water-quality and habitat conditions score 

(WQHS) was developed, on the basis of data from this study, 

that includes five water-quality parameters and one habitat 

parameter. The six parameters, which are assumed to be 

independent of each other, were E. coli concentrations, nitrite 

plus nitrate yields, specific conductance, turbidity, the number 

of pesticide detections, and a qualitative habitat score. Median 

values were used in the analysis for four of the parameters (E. 

coli concentrations, nitrite plus nitrate yields, specific conductance, turbidity). Median values are used to represent typical 

water-quality conditions at each site to eliminate the effect of 

outlying concentrations from varying stream conditions during 

a sampling event. Single values were used in the analysis for 

two of the parameters (the number of pesticide detections and 

a qualitative habitat score). Sampling for pesticide occurrence 

and assessing the habitat was conducted once at each stream 

site during stable streamflow and weather conditions.

Nitrite plus nitrate yields were calculated based on nitrite 

plus nitrate concentrations, stream discharge, and basin area 

and are expressed in kilograms per day per square mile 

(kg/day/mi2). Each site was ranked in the same way with a 

score from 1 to 10 that represented the quality of that measurement at that site relative to all the other sites. The five waterquality parameters were ranked high to low corresponding to 

the lowest to highest concentrations or values of each of the 

five parameters at all sites. The habitat parameter was ranked 

high to low corresponding to the highest to lowest values at 

all sites. Individual site WQHS rankings for each of the six 

parameters were summed to arrive at a final WQHS for a 

particular site. These scores represent the overall water-quality 

and habitat conditions and were used to examine differences 

among sites in this study. 

To compare macroinvertebrate data to the WQHS and to 

measures of urbanization at each site, single- and multi-metric 

approaches were used. Single metrics, such as richness and 

composition measures, were used in evaluating the macroinvertebrate community. Total taxa richness and Ephemeroptera, 

Plecoptera, and Trichoptera (EPT) richness, or the number of 

distinct taxa, represents the diversity within a sample and measures the overall variety of the macroinvertebrate assemblage 

(Barbour and others, 1999). Composition measures, such as 

the percent dominant taxa is a simple measure of redundancy. 

A high level of redundancy is equated with the dominance 

of contaminant tolerant organisms and a decreased diversity 

(Barbour and others, 1999). The mean value from the macroinvertebrate samples collected during the study was used in the 

analysis of the macroinvertebrate data. 

The overall biological condition of the macroinvertebrate community was expressed in terms of a multi-metric 

approach based on the macroinvertebrate community structure, 

group tolerances, and functional feeding groups at that site, 

and was determined for all sites using a biological condition score (BCS) (Rosenberg and Resh, 1993). The BCS is 

an index that is determined by ranking biotic metrics that are 

commonly used in bioassessment studies. The metrics used 

to determine a BCS at sites in this study are taxa richness, the 

Hilsenhoff biotic index, the ratio of scraper to collector-filterer 

abundances, the ratio of EPT to chironomid abundances, the 

percent of dominant taxon, number of EPT taxa, and the ratio 

of shredders to total abundance of all macroinvertebrates at 

a site (Rosenberg and Resh, 1993). Except for the dominant 

taxon and the Hilsenhoff Index, all metrics were ranked from 

high to low, corresponding to the highest to lowest numbers or 

percentages of each of the metrics at all sites. In other words, 

Data Collection and Analysis 
the numbers and percentages of these metrics decrease in 

response to increasing disturbance. According to Barbour and 

others (1999), percent of dominant taxon and the values of the 

Hilsenhoff Index increase in response to increasing disturbance; therefore, these two metrics were ranked from high to 

low based on lowest to highest numbers or percentages. 

The WQHS and the BCS were used to examine differences in these scores among study sites, the relation between 

water-quality and habitat conditions and macroinvertebrate 

communities to measures of urbanization in a watershed, and 

the relation between water-quality and habitat conditions and 

macroinvertebrate communities. All statistical analyses were 

performed using Statview and SAS statistical software (SAS 

Institute Inc., 1998, 2000).

Characterization of Physical 

Measurements, Water Quality, 

Macroinvertebrates, and Habitat at 

Selected Sites

Physical measurements, E. coli, nitrite plus nitrate, total 

phosphorus, and macroinvertebrate data collected from 2001 

to 2003 were used to characterize the spatial distribution of 

these parameters at sampling sites. Data were examined in 

relation to watershed characteristics to determine if correlations were present between measures of urbanization and 

stream quality (physical measurements, water quality, habitat, 

and macroinvertebrates). 

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Figure 2. Schematic showing (A) 0.5-kilometer, 1-kilometer, and 2-kilometer radial buffers upstream of a sampling site; 

and (B) a 100-meter stream buffer along the stream corridor, upstream of a sampling site for the Seacoast region in 

New Hampshire. (Also calculated, but not shown are 25-meter and 250-meter stream buffers.).

 Effects of Urbanization on Stream Quality in the Seacoast Region, New Hampshire
Physical Measurements and Water Quality

Summary statistics from physical measurements for the 

study period are in table 2. Median instantaneous discharge 

ranged from 0.37 to 4.2 ft3/s. Continuous streamflow data are 

available at USGS gaging stations in the Seacoast region; however, the sites selected in this study did not contain USGS stations. The Oyster River at Durham, N.H., was used as an index 

gaging station to assist in characterizing streamflow conditions in the Seacoast region during the study. A comparison 

of the study data-collection-period streamflow to the historical data-collection period streamflow indicates that the study 

data-collection streamflow had below normal runoff (fig. 3). A 

comparison between daily mean streamflow for 2001–03 and 

the time during which water-quality samples were collected 

shows that most samples represent low-flow conditions, with 

some samples collected during spring snowmelt or rains, especially in 2002 and 2003 (fig. 4). 

Median values of specific conductance ranged from 159 

to 1,920 μS/cm. Median pH ranged from 6.7 to 7.6 standard 

units and were within the water-quality criteria for pH (New 

Hampshire Department of Environmental Services, 2004). 

Median dissolved oxygen values ranged from 7.1 to 9.7 mg/L 

and were within water-quality criteria for dissolved oxygen 

(New Hampshire Department of Environmental Services, 

2004). Measurements of pH and dissolved oxygen at the study 

sites did not exceed the magnitude of exceedances criteria 

(New Hampshire Department of Environmental Services, 

2004). Median turbidity ranged from 1 to 8 NTUs at study 

sites during the study period. Median values of specific conductance (an indication of the dissolved ionic concentration) 

and turbidity (an indication of sediment or particulates) were 

elevated at sites with increased percentages of impervious surface in the watershed compared to sites with low percentages 

of impervious surface in the watershed, potentially indicating increased runoff from paved areas. The highest specific 

conductance (4,060 μS/cm) and turbidity (45 NTUs) values 

were found at site 7 (Paul Brook) and site 10 (Berry Brook), 

respectively (table 2). 

Summary statistics for E. coli, nitrite plus nitrate, and 

total phosphorus, and the number of pesticide detections at 

study sites are listed in table 3. Median E. coli concentrations 

ranged from 20 to 210 col/100 mL, with maximum concentrations exceeding 2,000 col/100 mL at some sites. With the 

exception of site 5 (Parting Brook), at least one sample from 

all study sites exceeded the single sample maximum criteria 

for primary contact (swimming) for E. coli (New Hampshire 

Department of Environmental Services, 2004). However, 

median concentrations of E. coli at all sites were below the 

single sample maximum criteria. Median nitrite plus nitrate 

concentrations generally were low and ranged from 0.05 to 

1.0 mg/L. The highest nitrite plus nitrate concentration 

(1.7 mg/L) was found at site 8 (College Brook) (table 3). 

Median total phosphorus concentrations generally were low 

and ranged from 0.013 to 0.040 mg/L. The highest total phosphorus concentration (0.132 mg/L) was found at site 5 (Parting 

Brook) (table 3). The number of pesticide detections ranged 

from 0 to 13 detections. The highest number of pesticide 

detections (11 and 13) were found at site 8 (College Brook) 

and site 9 (Reservoir Brook), respectively (table 3). 

Generally, the lowest E. coli concentrations and nitrite 

plus nitrate yields were observed at sites with forest as the 

predominant land use in the watershed (figs. 5 and 6, respectively). Sampling sites having urban as the predominant land 

use in the watershed generally had elevated mean E. coli concentrations and nitrite plus nitrate yields. Other measurements, 

such as specific conductance and turbidity, showed similar 

patterns (table 2).

Macroinvertebrates and Habitat

Mean values for selected macroinvertebrate metrics are 

shown in table 4. Total abundance at the sampling sites ranged 

from 885 to 6,321 organisms per 0.45 m2 and EPT abundance 

at the sampling sites ranged 62 to 1,499 organisms per 0.45 

m2. Total taxa richness and EPT taxa richness at the sampling 

sites ranged from 11 to 25 and from 2 to 15, respectively. 

Dominant taxon ranged from 38 to 60 percent at the sampling 

sites. The percent of one dominant taxon was greater at sites 

with urban as the predominant land use compared to sites with 

forest as the predominant land use (table 4). With the exception of percent dominant taxon, the selected macroinvertebrate 

community metrics generally decreased at sites with urban as 

the predominant land use compared to sites with forest as the 

predominant land use. 

Generally, the highest EPT taxa richness values (from 6 

to 15) were observed at sites with forest as the predominant 

land use in the watershed (fig. 7). Site 2 (Towle Brook) had the 

highest EPT taxa richness (table 4). Sampling sites with urban 

as the predominant land use in the watershed had lower mean 

EPT taxa richness (from 2 to 4) compared to the predominantly forested sites (fig. 7). Site 10 (Berry Brook) had the 

lowest EPT taxa richness (table 4).

General habitat quality was scored at each site using 

RBPs (Barbour and others, 1999). Eight of the study sites 

were rated as having optimal/suboptimal habitat, site 9 (Reservoir Brook) was rated as marginal habitat and site 4 (Parkman Brook) was rated as poor habitat (table 4) primarily as a 

result of modifications to the stream channel. Optimal/suboptimal habitat was considered suitable conditions for biological communities at sampled sites. Marginal and poor habitat 

was considered less than desirable conditions for biological 

communities at sampled sites. The habitat scores were used to 

represent the qualitative habitat conditions at sampling sites 

and are reflected in the WQHS. 

Characterization of Physical Measurements, Water Quality, Macroinvertebrates, and Habitat at Selected Sites 
Table 2. Summary statistics of physical measurements for the study sites in the Seacoast region in New Hampshire.

[ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter, mg/L, milligrams per liter; NTUs, nephelometric turbidity units; Min, minimum; Max, maximum] 

Site number 

(table 1,

fig. 1)

Discharge 

(ft3/s)

Specific conductance 

(μS/cm) pH Dissolved oxygen (mg/L) Turbidity (NTUs)

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

1 0.43 3.2 51 87 162 450 6.2 6.7 7.1 4.2 7.1 13.4 1 2 62 .03 4.2 53 98 159 248 6.3 7.1 8.0 7.4 8.8 13.5 1 1 113 .01 2.3 56 115 174 327 6.7 7.1 7.5 5.0 8.6 12.7 1 1 34 .01 .85 12 202 565 1,170 6.8 7.4 7.9 5.5 8.5 13.0 1 2 165 .03 .52 12 187 300 573 6.8 7.1 7.6 6.7 7.5 13.3 1 3 166 .21 2.0 59 329 1,014 1,770 7.2 7.4 7.9 5.6 7.5 12.8 3 6 267 .08 .37 9 296 1,920 4,060 7.2 7.3 7.9 4.3 7.5 12.5 2 3 218 .05 .38 7.0 490 1,232 2,130 7.0 7.6 7.9 5.7 9.7 13.0 4 7 289 .09 .49 10 350 1,245 3,050 7.0 7.5 7.9 6.6 8.8 13.5 2 4 38

10 .16 .37 1.8 269 582 786 7.1 7.3 7.7 8.9 9.5 12.5 5 8 45

Table 3. Summary statistics of Escherichia coli, nitrite plus nitrate, total phosphorus, and number of pesticide detections from water samples collected at the study sites in the Seacoast region in New Hampshire.[mL, milliliter; col/100 mL = colony counts per 100 mL; mg/L, milligrams per liter; kg/day/mi2, kilograms per day per square mile; Min, minimum; Max, maximum; <, less than; >, greater than]

Site

 number 

(table 1, 

fig. 1)

Number of 

samples

Escherichia coli

(col/100 mL)

Nitrogen, 

(dissolved nitrite + nitrate) 

(mg/L)

Nitrite plus nitrate yield, 

(kg/day/mi2

)

Total phosphorus 

(phosphorus in an unfiltered water 

sample) (mg/L)

Number of 

pesticides 

detected1

Min Mean Median Max Min Mean Median Max Min Mean Median Max Min Mean Median Max

1 18 < 10 162 50 1,890 < 0.05 0.06 0.05 0.16 < 0.05 0.28 0.07 3.4 0.006 0.016 0.018 0.028 02 18 < 10 159 60 1,390 < .05 .08 .05 .22 < .05 .78 .13 11 .006 .017 .013 .050 03 18 < 10 226 45 > 2,000 < .05 .08 .05 .39 <.05 .51 .05 8.2 .009 .018 .014 .060 04 18 < 10 172 30 > 2,000 < .05 .28 .24 .57 <.05 .67 .21 8.1 .007 .027 .021 .110 55 18 < 10 35 20 180 < .05 .15 .12 .36 <.05 .41 .07 6.5 .012 .035 .022 .132 06 14 < 10 505 210 > 2,000 < .05 .21 .16 .54 <.05 1.6 .19 8.2 .016 .031 .028 .061 27 14 < 10 168 60 800 .12 .24 .19 .82 .05 1.3 .21 11 .014 .025 .022 .057 28 14 < 10 421 185 > 2,000 .52 1.1 1.0 1.7 .12 3.1 1.0 25 .023 .045 .037 .088 119 14 < 10 336 180 > 2,000 .34 .62 .64 .89 .20 1.8 .53 17 .019 .043 .040 .096 13

10 14 < 10 209 40 > 2,000 .20 .48 .32 1.3 .16 1.9 .64 8.1 .007 .020 .014 .068 1

1One sample collected and analyzed for pesticides at each site in June 2002.

 Effects of Urbanization on Stream Quality in the Seacoast Region, New Hampshire
Figure 3. Mean annual streamflow for historical and study period years from the Oyster River at Durham, N.H. 

(used as an index gaging station for the study area).

Figure 4. Hydrograph of mean daily streamflow for water years 2001–03 from the Oyster River at Durham, N.H. (used 

as an index gaging station for the study area). The blue bars represent the general streamflow characteristics in the 

Seacoast region during the water-quality sampling period.

Characterization of Physical Measurements, Water Quality, Macroinvertebrates, and Habitat at Selected Sites 













     

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Figure 5. Mean Escherichia coli (E. coli) concentrations among sampling 

sites, predominant land use, and percentage of impervious surface at study 

sites in the Seacoast region of New Hampshire. (Refer to table 1 and figure 

1 for site numbers and locations of sampling sites.)

Figure 6. Mean nitrite plus nitrate yields among sampling sites, predominant land use, and percentage of impervious surface at study sites in the 

Seacoast region of New Hampshire. (Refer to table 1 and figure 1 for site 

numbers and locations of sampling sites).

10 Effects of Urbanization on Stream Quality in the Seacoast Region, New Hampshire















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Figure 7. Mean value for Ephemeroptera, Plecoptera, and Trichoptera taxa 

richness among sampling sites, predominant land use, and percentage of 

impervious surface at study sites in the Seacoast region of New Hampshire. 

(Refer to table 1 and figure 1 for site numbers and locations of sampling sites).

Table 4. Mean values of selected macroinvertebrate metrics for samples collected at each of the study 

sites in the Seacoast region in New Hampshire. 

[EPT, Ephemeroptera, Plecoptera, Tichoptera; m2, square meters]

Site number 

(table 1; fig. 1)

Total 

abundance1

EPT 

abundance1

Total taxa 

richness2

EPT taxa 

richness2

Percent 

dominant taxon

Habitat 

score3

Forest sites

1 3,503 1,499 19 10 42 150

2 4,922 818 25 15 42 147

3 1,786 444 18 10 41 154

4 6,321 567 21 6 40 45

5 3,762 1,074 21 8 38 105

Mean 4,059 4,402 21 10 41 120

Urban sites

6 1,143 602 16 4 57 101

7 2,204 371 14 3 55 112

8 3,515 666 13 3 56 131

9 5,294 680 11 3 60 64

10 885 62 13 2 59 112

Mean 2,608 476 13 3 57 104

1 Number of organisms per 0.45 m2

.

2 Number of taxa per 0.45 m2

.

3 Habitat scores of 0–50, poor habitat rating; 51–100, marginal habitat rating; 101–150, suboptimal habitat rating; 151–200, 

optimal habitat rating. 

Characterization of Physical Measurements, Water Quality, Macroinvertebrates, and Habitat at Selected Sites 11

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Table 5. Summary of Spearman rank correlations between watershed characteristics and stream-quality variables at the study sites 

in the Seacoast region in New Hampshire.

[E. coli, Escherichia coli; col/100 ml, colony counts per 100 milliliters; kg/day/mi2, kilograms per day per square mile; EPT, Ephemeroptera, Plecoptera, 

Trichoptera; WQHS, water-quality and habitat conditions score; BCS, biological condition score; NS, is not statistically significant at α = 0.05, all other 

relations were statistically significant; km, kilometers; m, meters]

Watershed

characteristics

Specific 

conductanceTurbidity E. coli

(col/100mL)

Nitrite plus 

nitrate yield

(kg/day/mi2)

Total phosphorus yield

(kg/day/mi2)

Species 

richness

EPT 

richness

Percent 

dominant 

taxon

WQHS BCS

Infrastructure variables1

Impervious surface 0.84 0.78 NS 0.74 NS NS -0.75 NS -0.70 -0.75

Road density .70 .95 NS .81 NS -0.68 -.81 0.72 -.82 -.88

Population density NS .72 NS .64 NS NS -.66 NS -.75 -.77

Land-cover variables2

Urban 0.71 0.85 NS 0.74 NS NS -0.74 NS -0.68 -0.79

Forest -.67 -.70 NS -.67 NS NS .70 -0.66 .64 .74

Radial-buffer variables3

Urban-0.5 km 0.70 0.87 NS 0.90 NS -0.70 -0.88 0.73 -0.85 -0.92

Urban-1 km .76 .95 NS .92 NS -.78 -.89 .76 -.86 -.94

Urban-2 km .72 .94 NS .85 NS -.70 -.80 .73 -.75 -.85

Forest-0.5 km -.70 -.87 NS -.90 NS .70 .89 -.73 .88 .92

Forest-1 km -.74 -.92 NS -.94 NS .74 .89 -.74 .89 .93

Forest-2 km -.68 -.90 NS -.87 NS .68 .76 -.77 .72 .81

Stream-buffer variables4

Urban-25 m 0.65 0.92 0.35 0.86 NS -0.68 -0.80 0.73 -0.80 -0.86

Urban-100 m .66 .90 NS .82 NS -.69 -.77 .83 -.77 -.82

Urban-250 m .67 .89 NS .81 NS -.65 -.74 .78 -.71 -.79

Forest-25 m NS -.66 NS -.68 NS NS NS -.78 .67 .68

Forest-100 m NS -.79 NS -.72 NS NS .66 -.79 .70 .73

Forest-250 m -.65 -.85 NS -.79 NS .71 .76 -.86 .75 .80

1

Impervious surface, the percent of impervious surface in the watershed; Road density, road density in watershed [road length (kilometer)/watershed area 

(square kilometer)]; Population density, population density, 2000 [people per square mile]. 

2

Urban, the percent of urban land in the entire watershed; Forest, the percent of forest land in the entire watershed..

3

Urban-0.5 km, the percent of urban land within a 0.5-km radius of the sampling site; Urban-1 km, the percent of urban land within a 1-km radius of the 

sampling site; Urban-2 km, the percent of urban land within a 2-km radius of the sampling site; Forest-0.5 km, the percent of forest land within a 

0.5-km radius of the sampling site; Forest-1 km, the percent of forest land within a 1-km radius of the sampling site; Forest-2 km, the percent of forest land 

within a 2-km radius of the sampling site.

4

Urban-25 m, the percent of stream buffer (25 m) area in urban land use; Urban-100 m, the percent of stream buffer (100 m) area in urban land use; Urban250 m, the percent of stream buffer (250 m) area in urban land use; Forest-25 m, the percent of stream buffer (25 m) area in forest land use; Forest-100 m, the 

percent of stream buffer (100 m) area in forest land use; Forest-250 m, the percent of stream buffer (250 m) area in forest land use.

Effects of Urbanization on Stream 

Quality at Selected Sites

The degraded character of streams typically does not 

result from any single factor, but rather from the interaction 

of various effects (Klein, 1979). Although the exact point at 

which stream quality and macroinvertebrate communities 

shift from good to poor is not known with precision, increased 

urbanization within a watershed does result in degraded water 

quality and a less diverse macroinvertebrate community 

(Schueler, 1994; Jones and Clark, 1987). 

Specific conductance, turbidity, nitrite plus nitrate 

yields, and selected macroinvertebrate community data were 

significantly correlated with most measures of urbanization 

used in this study (table 5). E. coli concentrations and total 

phosphorus yields were not statistically correlated with most 

measures of urbanization in this study (table 5). Measures of 

urbanization that generally had the highest correlations with 

stream-quality variables were associated with the percent of 

urban land in buffer zones upstream of the sampling site 

(table 5). Specifically, the percent of urban land use in a 

1-km radial buffer and the percent of urban land use in a 25-m 

stream buffer generally had higher correlation coefficients 

with stream-quality variables than other urban stream-buffer 

variables and stream-quality variables (table 5). 

12 Effects of Urbanization on Stream Quality in the Seacoast Region, New Hampshire
Effects of Urbanization on Stream Quality at Selected Sites 13

Impervious Surface and Stream-Quality 

Measures

There appears to be a level (between 7 and 14 percent 

impervious surface) at which water-quality and habitat site 

rankings become affected by urban characteristics such as 

impervious surface. This result is similar to other studies, 

where measures of the impervious surface area of about 

10 percent have been identified as the level at which stream 

quality decreases (Klein, 1979; Schueler, 1994; Booth and 

Reinelt, 1993). In this study, a negative correlation was found 

between the WQHS and the percent of impervious surface 

in the upstream watershed of the sampled sites (r = -0.70; 

p < 0.05). The WQHS decreased with increased percent of 

impervious surface (fig. 8a).

The biological condition score also appears to be affected 

by the level of impervious surface area in the watershed. A 

negative correlation was found between the BCS and the 

percent of impervious surface in the upstream watershed of the 

sampled sites (r = -0.75; p < 0.05). The BCS decreased with 

increased percent of impervious surface in the watershed at 

sampled sites (fig. 8b). These results are similar to the relation 

between the WQHS and the percent of impervious surface in a 

watershed in that there appears to be a level (between 7 and 14 

percent impervious surface) at which the biological condition 

of a site becomes affected by urban characteristics. 

To determine the response of EPT taxa richness to measures of urbanization, mean EPT taxa richness was plotted 

against the percent of impervious surface (fig. 8c). A negative correlation was found between EPT taxa richness and the 

percent of impervious surface (r = -0.75; p < 0.01) (table 5). 

The response of this single metric to the percent of impervious surface in a watershed is similar to the response of the 

multi-metric (BCS) to the percent of impervious surface in 

the watershed. This similarity indicates that EPT taxa richness 

may be used to evaluate effects of urban land use on small 

streams in this region. Other studies also have reported that 

EPT taxa were responsive to the intensity of urbanization in a 

watershed (Ourso and Frenzel, 2003; Coles and others, 2004).

Radial Buffers and Stream-Quality Measures

Stream quality, when measured by the WQHS, the BCS, 

and EPT taxa richness, decreased as the percent of urban land 

use increased in a 1-km radial buffer of the sampling site 

(fig. 9). The highest correlation coefficients between the 

radial-buffer variables and the WQHS and BCS were for the 

percent of urban land in a 1-km radial buffer. The percent of 

urban land in a 1-km radial buffer was negatively correlated 

with the WQHS (r = -0.86; p < 0.001) and this correlation 

was higher than correlations between the percent of impervious surface and the WQHS (r = -0.70; p < 0.05) and between 

the percent of urban land use in the entire watershed and the 

WQHS (r = -0.68; p < 0.05) (table 5).



















        

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Figure 8. Relation between the percent of impervious surface 

in the watershed and the (A) water-quality and habitat conditions 

score, (B) biological condition score, and (C) mean Ephemeroptera, Plecoptera, and Trichoptera taxa richness at the study sites 

in the Seacoast region in New Hampshire. [smooth line, locally 

weighted scatterplot smoothing]


















        

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Figure 9. Relation between the percent of urban land in a 

1-kilometer radial buffer and the (A) water-quality and habitat 

conditions score, (B) biological condition score, and (C) mean 

Ephemeroptera, Plecoptera, and Trichoptera taxa richness at the 

study sites in the Seacoast region in New Hampshire [smooth line, 

locally weighted scatterplot smoothing

14  Effects of Urbanization on Stream Quality in the Seacoast Region, New Hampshire

The WQHS decreased with increased percent of urban 

land in the 1-km radial buffer (fig. 9a). The relation between 

these two variables indicates a change in water-quality and 

habitat conditions at sites with increased percent of urban land 

in the 1-km radial buffer. In contrast, a positive correlation 

was found between the percent of forest land in the 1-km 

radial buffer and the WQHS (r = 0.89; p < 0.001). The percent 

of forest land in other radial-buffer variables and the entire 

watershed also showed positive correlations with the WQHS 

(table 5). Forest land use typically reduces runoff of water, 

sediments, nutrients, and other constituents and provides more 

organic material and debris to the stream as food supply for 

aquatic life (Wang and other, 1997). The positive correlations 

between the forested characteristics in the upstream watershed 

and the WQHS indicates that forested riparian areas may be 

important in maintaining water-quality and habitat conditions. 

The percent of urban land in a 1-km radial buffer of 

the sampling site was negatively correlated with the BCS 

(r = -0.94; p < 0.0001) and this correlation was higher than 

correlations between the percent of impervious surface and the 

BCS (r = -0.75; p < 0.05) and between the percent of urban 

land use in the entire watershed and the BCS (r = -0.79; 

p < 0.01) (table 5). The BCS decreased with increased percent 

of urban land in the 1-km radial buffer (fig. 9b). The relation 

between these two variables indicates a change in the macroinvertebrate community structure at sites with increased percent 

of urban land in the 1-km radial buffer. Various other studies 

have also shown that urban development affects macroinvertebrate communities (Benke and others, 1981; Garie and McIntosh, 1986; Coles and others, 2004). In contrast, a positive 

correlation was found between the percent of forest land in 

the 1-km radial buffer and the BCS (r = 0.93; p < 0.0001). The 

percent of forest land in other radial- and stream-buffer variables and the entire watershed also showed significant positive 

correlations with the BCS (table 5). These correlations indicate that the macroinvertebrate community may be affected by 

the percent and type of vegetation near the sampling site and 

that these data appear to discriminate urbanization effects on 

stream quality at sampled sites in this study. These results are 

in agreement with those of previous studies (Coles and others, 

2004; Jones and Clark, 1987; Lenat and Crawford, 1994).

To determine the response of EPT taxa richness to 

urbanization, mean EPT taxa richness was plotted against the 

percent of urban land in the 1-km radial buffer (fig. 9c). The 

response of this single metric to the percent of urban land in 

the 1-km radial buffer is similar to the response of the multimetric (BCS) to the percent of urban land in the 1-km radial 

buffer. 

Stream Buffers and Stream-Quality Measures

Stream quality, when measured by the WQHS, the BCS, 

and EPT taxa richness, decreased as the percent of urban land 

use increased in a stream buffer along the stream corridor, 

upstream of a sampling site (fig. 10). The percent of urban 


















       

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Figure 10. Relation between the percent of urban land in a 

25-meter stream buffer and the (A) water-quality and habitat 

conditions score, (B) biological condition score, and (C) mean 

Ephemeroptera, Plecoptera, and Trichoptera taxa richness at the 

study sites in the Seacoast region in New Hampshire [smooth line, 

locally weighted scatterplot smoothing].

Effects of Urbanization on Stream Quality at Selected Sites 15

land in this 25-m stream buffer area had higher correlations 

with the WQHS (r = -0.80; p < 0.01) than correlations between 

the percent of urban land in a 100-m and 250-m stream buffer, 

the percent of impervious surface, and the percent of urban 

land use in the entire watershed with the WQHS. The WQHS 

decreased with increased percent of urban land in a 25-m 

stream buffer (fig. 10a). 

When the percent of urban land increased in a 25-m 

stream buffer upstream the BCS decreased (fig. 10b). The 

percent of urban land in a 25-m stream buffer had higher 

correlations with the BCS (r = -0.86; p < 0.01) than correlations between the percent of urban land in a 100-m and 250-m 

stream buffer, the percent of impervious surface, and the percent of urban land use in the entire watershed with the BCS. 

The relation between these two variables indicates a change 

in the macroinvertebrate community structure at sites with 

increased percent of urban land in a 25-m stream buffer.

To determine the response of EPT taxa richness to measures of urbanization, mean EPT taxa richness was plotted 

against the percent of urban land in a 25-m stream buffer 

(fig. 10c). A negative correlation was found between EPT taxa 

richness and the percent of urban land in a 25-m stream buffer 

(r = -0.80; p < 0.01) (table 5).

In contrast to these results described above, the highest 

correlation between the percent of forest land use and 

the WQHS (r = 0.75; p < 0.05) and the BCS (r = 0.80; 

p < 0.05) was for a 250-m stream buffer, compared to the 

25-m or 100-m stream buffers (table 5). These results indicate 

that the increased width of a forested area along the stream 

corridor may result in improved stream quality. These results 

also indicate that watersheds with urban land along a stream 

corridor may be subject to greater stream-quality degradation 

than watersheds with forested land along a stream corridor. 

May and others (1997) report similar findings on small 

streams in the Puget Sound ecoregion where stream buffers 

are important and play a key role in mitigating effects from 

watershed development.

Water-Quality and Habitat Conditions Score 

and the Biological Condition Score

The WQHS and the BCS generally follow a similar 

relation to one another with the measures of urbanization 

in a watershed. The WQHS and the BCS were correlated 

(r = 0.89; p < 0.01). The relation between the WQHS and the 

BCS indicates that sampling sites with high scores for waterquality and habitat conditions also had high scores for the 

biological condition (fig. 11). The scores show that the ranks 

of general water-quality and habitat (WQHS) follow a similar 

pattern as the ranks of the biological metrics (BCS) and high 

scores indicate improved stream quality at a sampling site. 
Figure 11. Relation between the water-quality and habitat conditions score and the biological condition score at the study sites 

in the Seacoast region in New Hampshire [smooth line, locally 

weighted scatterplot smoothing].

Summary and Conclusions

Concentrations of selected chemical constituents and 

macroinvertebrate community data collected from small 

streams in the Seacoast region of New Hampshire were evaluated in relation to the intensity of urbanization in a watershed. 

Water-quality samples were collected from 10 stream sites 

during the spring, summer, and fall seasons from 2001 to 2003 

and analyzed for E. coli, nitrite plus nitrate, and total phosphorus. Macroinvertebrate samples were collected once each year 

during low-flow conditions and analyzed for identification and 

enumeration. The U.S. Geological Survey, in cooperation with 

the New Hampshire Department of Environmental Services 

Coastal Program, designed this study to determine the degree 

to which urbanization affects stream quality in the Seacoast 

region.

Concentrations of selected chemical constituents were 

found to be higher in watersheds with high percent of impervious surface than in watersheds with low percent of impervious 

surface. Chemical concentrations in watersheds with the lowest percentages of impervious surface had the lowest concentrations of all detectable constituents. Specific conductance, 

turbidity, nitrite plus nitrate yields, and selected macroinvertebrate community data were significantly correlated with 

most measures of urbanization used in this study, whereas 

E. coli concentrations and total phosphorus yields were not 

statistically correlated with most measures of urbanization 

in this study. Generally, the highest median and maximum 

values of the analyzed water-quality constituents were found 

at sites with a high percent of impervious surface and urban 

land in the watershed. The macroinvertebrate data also showed 

changes in relation to the percent of impervious surface and 

urban land use among sampling sites. Streams draining predominantly forested watersheds generally were characterized 

by higher abundance and taxa richness in the macroinvertebrate community than streams draining predominantly urban 

watersheds.

The correlations between the percent of urban land use in 

a 1-km radial buffer of the sampling site and the water-quality and habitat conditions score and the biological condition 

score were higher than correlations between other radial- and 

stream-buffer variables, the percent of impervious surface, and 

the percent of urban land in the entire watershed with these 

same indicators of stream quality. The measures of stream 

quality (water-quality and habitat conditions score, biological 

condition score, and EPT taxa richness) at sampled sites were 

negatively related to the percent of urban land and positively 

related to the percent of forest land upstream from a sampling 

site. Watershed urbanization appeared to have caused noticeable changes in the stream quality at sampled sites. Another 

key variable affecting stream quality was the quantity and 

quality of a stream buffer. Specifically, radial or stream buffers 

dominated by forested land appear to help maintain a better 

level of stream quality than radial or stream buffers dominated 

by urban land. 

In this study, sites with greater than 14-percent impervious surface in a watershed generally showed changes in stream 

quality as measured by a water-quality and habitat conditions 

score and a biological condition score. Results from this study 

also indicate that the percent of urban land use in streambuffer areas generally were valuable indicators of stream 

quality. Ongoing water-quality or stream-biota monitoring of 

these small streams in the Seacoast region will be important to 

assess the effects of continued urban development in southeastern New Hampshire.

Acknowledgments

The authors acknowledge the effort provided by 

Ted Diers, New Hampshire Department of Environmental 

Services Coastal Program, and Joanne McLaughlin (formerly 

of the New Hampshire Coastal Program) for their assistance 

in the collection of data and project development and support. 

Thanks are extended to Kenneth Gallagher, New Hampshire 

Office of Energy and Planning; Fay Rubin, University of 

New Hampshire; and Laura Hayes, U.S. Geological Survey, 

for their geographic information systems assistance. Thanks 

are also extended to Melissa Riskin, U.S. Geological Survey, 

for her assistance in collection of water-quality samples and 

streamflow measurements and Philip Trowbridge, New 

Hampshire Department of Environmental Services, and 

Tim Brabets, U.S. Geological Survey, for their critical review 













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16  Effects of Urbanization on Stream Quality in the Seacoast Region, New Hampshire
of this report. Appreciation is extended to Debra Foster for the 

editorial report review and manuscript and layout, and Anita 

Cotton for graphics. 

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18  Effects of Urbanization on Stream Quality in the Seacoast Region, New Hampshire
Prepared by the New Hampshire-Vermont Water Science Center 

Publications Unit

For more information concerning the research in this report, contact:

Brian Mrazik, Director,

U.S. Geological Survey

NH-VT Water Science Center

361 Commerce Way

Pembroke, NH 03275

dc_nh@usgs.gov

or visit our Web site at:

http://nh.water.usgs.gov