Effects of Urbanization on Benthic Macroinvertebrate 

Communities in Streams, Anchorage, Alaska

Water-Resources Investigations Report 01ñ4278

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

Oblique aerial view of downtown Anchorage and Cook Inlet, Alaska (photograph taken in 2001 by author)
Effects of Urbanization on Benthic Macroinvertebrate 

Communities in Streams, Anchorage, Alaska

By Robert T. Ourso

U.S. GEOLOGICAL SURVEY

Anchorage, Alaska

2001

Water-Resources Investigations Report 01ñ4278
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

CHARLES G. GROAT, Director

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

For additional information, contact:

District Chief

U.S. Geological Survey

4230 University Drive, Suite 201

Anchorage, AK 99508ñ4664

URL: <http://ak.water.usgs.gov>
The U.S. Geological Survey (USGS) is committed to serve the Nation with accurate and timely scientific information that 

helps enhance and protect the overall quality of life and facilitates effective management of water, biological, energy, and 

mineral resources. (URL: <http://www.usgs.gov/>). Information on the quality of the Nation’s water resources is of critical 

interest to the USGS because it is so integrally linked to the long-term availability of water that is clean and safe for drinking 

and recreation and that is suitable for industry, irrigation, and habitat for fish and wildlife. Escalating population growth and 

increasing demands for the multiple water uses make water availability, now measured in terms of quantity and quality, even 

more critical to the long-term sustainability of our communities and ecosystems.

The USGS implemented the National Water-Quality Assessment (NAWQA) program to support national, regional, and local 

information needs and decisions related to water-quality management and policy. (URL: <http://water.usgs.gov/nawqa>). 

Shaped by and coordinated with ongoing efforts of other Federal, State, and local agencies, the NAWQA program is 

designed to answer: What is the condition of our Nation’s streams and ground water? How are the conditions changing over 

time? How do natural features and human activities affect the quality of streams and ground water, and where are those 

effects most pronounced? By combining information on water chemistry, physical characteristics, stream habitat, and aquatic 

life, the NAWQA program aims to provide science-based insights for current and emerging water issues and priorities. 

NAWQA results can contribute to informed decisions that result in practical and effective water-resources management and 

strategies that protect and restore water quality.

Since 1991, the NAWQA program has implemented interdisciplinary assessments in more than 50 of the Nation’s most 

important river basins and aquifers, referred to as study units. (URL: <http://water.usgs.gov/nawqa/nawqamap.html>). 

Collectively, these study units account for more than 60 percent of the overall water use and population served by public 

water supply and are representative of the Nation’s major hydrologic landscapes, priority ecological resources, and 

agricultural, urban, and natural sources of contamination. 

Each assessment is guided by a nationally consistent study design and methods of sampling and analysis. The assessments 

thereby build local knowledge about water-quality issues and trends in a particular stream or aquifer while providing an 

understanding of how and why water quality varies regionally and nationally. The consistent, multiscale approach helps

to determine if certain types of water-quality issues are isolated or pervasive, and allows direct comparisons of how 

human activities and natural processes affect water quality and ecological health in the Nation’s diverse geographic and 

environmental settings. Comprehensive assessments on pesticides, nutrients, volatile organic compounds, trace metals, 

and aquatic ecology are developed at the national scale through comparative analysis of the study-unit findings. (URL: 

<http://water.usgs.gov/nawqa/natsyn.html>). 

The USGS places high value on the communication and dissemination of credible, timely, and relevant science so that the 

most recent and available knowledge about water resources can be applied in management and policy decisions. We hope 

this NAWQA publication will provide you the needed insights and information to meet your needs, and thereby foster 

increased awareness and involvement in the protection and restoration of our Nation’s waters. 

The NAWQA program recognizes that a national assessment by a single program cannot address all water-resources 

issues of interest. External coordination at all levels is critical for a fully integrated understanding of watersheds and for 

cost-effective management, regulation, and conservation of our Nation’s water resources. The program, therefore, depends 

extensively on the advice, cooperation, and information from other Federal, State, interstate, Tribal, and local agencies, 

nongovernment organizations, industry, academia, and other stakeholder groups. The assistance and suggestions of all

are greatly appreciated.

FOREWORD

Robert M. Hirsch

Associate Director for Water
CONTENTS

Abstract.................................................................................................................................................................................. 7

Introduction............................................................................................................................................................................ 7

Basin Characterization........................................................................................................................................................... 8

Study Sites ............................................................................................................................................................................. 8

Field Methods ........................................................................................................................................................................ 12

Analysis ................................................................................................................................................................................. 12

Results.................................................................................................................................................................................... 16

Discussion.............................................................................................................................................................................. 19

Conclusions............................................................................................................................................................................ 26

References Cited.................................................................................................................................................................... 27

Appendixes ............................................................................................................................................................................ 28

FIGURES

1. Location map of Anchorage area, showing stream basins and sampling sites ...................................................... 9

2. Three-dimensional representation of Anchorage area and sampling sites............................................................. 10

3. Cluster analysis using arithmetic means of macroinvertebrate presence–absence data ........................................ 14

4. Ratio of population density to road density, comparing group 1 sites (urban impacted) with groups 2 and 3

sites (nonimpacted and anomalous, respectively).................................................................................................. 16

5–8. Graphs showing variable-span bivariate smoothed scatterplots:

5. Three significant biological variables, showing threshold response against population density ............ 17

6. Four significant water-chemistry variables, showing threshold response against population density .... 18

7. Four significant trace-elements-in-bed-sediments variables, showing threshold response against

population density.................................................................................................................................... 20

8. Seven other significant biological and chemical variables, showing linear response against

population density.................................................................................................................................... 22

TABLES

1. Description of sites................................................................................................................................................. 11

2. Biological metrics and expected response of macroinvertebrates to perturbation................................................. 13

3. Coefficients of correlation between each metric or constituent or field property and population density ............ 15

4. Coefficients of determination (r

2) as calculated by linear and local regression analysis and significance (p)...... 21

APPENDIXES

1. Cook Inlet Basin National Water-Quality Assessment site-numbering system..................................................... 29

2. Abundance and distribution of benthic macroinvertebrates collected at 14 sites in Anchorage in 1999 .............. 31

3. Biological metrics calculated from macroinvertebrate data collected at 14 sites in Anchorage in 1999 .............. 36

4. Nutrient and major-ion concentrations in water samples from 14 sites in Anchorage in 1999 ............................. 37

5. Trace-element concentrations in streambed sediments collected from 14 sites in Anchorage in 1999................. 38
CONVERSION FACTORS, WATER-QUALITY AND OTHER METRIC UNITS, and VERTICAL DATUM

Multiply by To obtain

inch (in.) 25.4 millimeter

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

square mile (mi2

) 2.590 square kilometer

mile per square mile (mi/mi2

) 0.6212 kilometer per square kilometer

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

In this report, water temperature is reported in degrees Celsius (°C), which can be converted to degrees Fahrenheit (°F) by the equation

°F = 1.8 (°C) + 32

and ambient (air) temperature is reported in degrees Fahrenheit(°F), which can be converted to degrees Celsius (°C) by the equation

°C = (°F – 32) / 1.8

Abbreviated water-quality and other metric units used in this report: Chemical concentration in water, or solute mass per unit volume 

(liter) of water, is given in milligrams per liter (mg/L) or micrograms per liter (μg/L). (A concentration of 1,000 μg/L is equivalent to a 

concentration of 1 mg/L. For concentrations less than 7,000 mg/L, the numerical value is about the same as for concentrations in parts per 

million.) Specific conductance is given in microsiemens per centimeter (μS/cm) at 25 degrees Celsius. Other metric units used are micron 

(μm), centimeter (cm), and square meter (m2). The unit used for algal standing crop is milligram per square meter (mg/m2). Standard units 

are used for pH.

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929, formerly called “Sea-Level 

Datum of 1929”), which is derived from a general adjustment of the first-order leveling networks of the United States and Canada.
Effects of Urbanization on Benthic Macroinvertebrate 

Communities in Streams, Anchorage, Alaska

By Robert T. Ourso

Abstract

The effect of urbanization on stream macroinvertebrate communities was examined by using data 

gathered during a 1999 reconnaissance of 14 sites in the Municipality of Anchorage, Alaska. Data 

collected included macroinvertebrate abundance, water chemistry, and trace elements in bed sediments. 

Macroinvertebrate relative-abundance data were edited and used in metric and index calculations. 

Population density was used as a surrogate for urbanization. Cluster analysis (unweighted-pairedgrouping method) using arithmetic means of macroinvertebrate presence–absence data showed a 

well-defined separation between urbanized and nonurbanized sites as well as extracted sites that did not 

cleanly fall into either category. Water quality in Anchorage generally declined with increasing 

urbanization (population density). Of 59 variables examined, 31 correlated with urbanization. Local 

regression analysis extracted 11 variables that showed a significant impairment threshold response 

and 6 that showed a significant linear response. Significant biological variables for determining the 

impairment threshold in this study were the Margalef diversity index, Ephemeroptera–Plecoptera–

Trichoptera taxa richness, and total taxa richness. Significant thresholds were observed in the waterchemistry variables conductivity, dissolved organic carbon, potassium, and total dissolved solids. 

Significant thresholds in trace elements in bed sediments included arsenic, iron, manganese, and lead. 

Results suggest that sites in Anchorage that have ratios of population density to road density greater than 

70, storm-drain densities greater than 0.45 miles per square mile, road densities greater than 4 miles per 

square mile, or population densities greater than 125–150 persons per square mile may require further 

monitoring to determine if the stream has become impaired. This population density is far less than the 

1,000 persons per square mile used by the U.S. Census Bureau to define an urban area.

INTRODUCTION

The U.S. Geological Survey’s (USGS) National Water-Quality Assessment (NAWQA) program began 

studies in the Cook Inlet Basin (COOK) study unit in 1997. The goal of the COOK study is to describe the status 

and trends in the quality of water in the basin and to relate that to an understanding of the natural and human 

factors controlling water quality.

Increasing urban populations, and the urban sprawl associated with the increase in population, are known 

to alter drainage basins and the streams that drain these urbanized catchments. Point sources of pollution in the 

U.S. and most developed countries have been studied intensely and regulated more closely since the passage of 

the Clean Water Act. The understanding of point-source pollution and its effects has shown that other factors 

contribute to the degradation of urban water quality as streams still show impairment. Many prior studies 

describe the effects of nonpoint-source pollution on water quality, especially in urban areas (Klein, 1979; Milner 

and Oswood, 1989; Wear and others, 1998; Winter and Duthie, 1998). Nonpoint-source pollution factors that 

are commonly cited as detrimental to water quality are increases in conductivity due to road deicing, organic 

pollution from high-density livestock facilities, nutrient enrichment from fertilizers, and petroleum byproducts 

from the use of vehicles, among many others.
Associated with increases in population is increased impervious area, which leads to elevated runoff and 

streamflows over short time periods. As water in the catchment exits the system more rapidly owing to increases 

in impervious cover, low flows tend to decrease, and the overall habitat availability for stream-dwelling organisms correspondingly decreases. Increases in pollutants, which also are attributed to increasing populations and 

impervious areas, exacerbate the problems associated with lowered discharges: Because less water is available 

for dilution of pollutants, resident organisms are subjected to increasing stress. Macroinvertebrate-community 

structures have shifted from greater numbers of specialist feeders in undisturbed areas to greater numbers of 

generalists in less-diverse disturbed areas (Whiting and Clifford, 1983; Garie and McIntosh, 1986).

Anchorage presents a unique opportunity to study the effects of urbanization on benthic macroinvertebrates. Streams in Anchorage originate in undisturbed catchments and then course through areas having different 

population densities before emptying into Cook Inlet. This report generally describes the results of site reconnaissance for a study examining the changes in water quality along an urban gradient and specifically examines 

the response of benthic macroinvertebrates to changes in water quality along a gradient of urbanization in five 

stream basins within the Municipality of Anchorage, Alaska.

BASIN CHARACTERIZATION

The hydrology of Anchorage is dominated by five stream basins, all having headwaters in the Chugach 

Mountains, which border the municipality on the east side. Each stream courses through the city on the way to its 

mouth along the Cook Inlet. Anchorage, the most populated city in the State, is located within the Cook Inlet 

Basin in south-central Alaska. More than one-third of Alaska’s population lives in Anchorage. Estimated population of the municipality as of 1996 was approximately 254,000 (Municipality of Anchorage, 1996). The mean 

annual precipitation is 20 to 25 in. and average temperature is about 27°F (Brabets and others, 1999).

Streams are affected by ice cover for a significant part of the year. Ice typically forms over the streams in 

late November to early December and open water reappears around the beginning of April. The time of ice cover 

varies according to the elevation of a particular segment of the stream.

The geology consists primarily of unconsolidated Quaternary alluvial or glacial deposits in the lower elevations and Mesozoic metamorphic, volcanic, and igneous rock in the Chugach Mountains on the east side (Brabets 

and others, 1999).

Land cover is dominated by moist herbaceous and shrub tundra. Open and closed spruce forest, low and 

tall shrub, and alpine tundra and barrens cover smaller areas (Brabets and others, 1999). Within the area under 

investigation in this study, land use is principally forest (military lands and State parklands) and urban (residential 

and commercial).

STUDY SITES

The five stream basins within the Municipality of Anchorage (fig. 1, fig. 2, table 1) that were chosen for the 

study were, from north to south, Ship Creek, Chester Creek, Campbell Creek, Rabbit Creek, and Little Rabbit 

Creek. During August–September 1999, 14 stream sites (appendix 1) were selected to represent these 5 basins—

2 sites in the Ship Creek Basin and 3 in each of the other 4 basins. Total basin areas range from 125 mi2

 (Ship 

Creek) to 6.4 mi2 (Little Rabbit Creek). Snowmelt from the Chugach Mountains is the primary contributor to 

surface-water flow within the five basins studied.
Figure 1. Anchorage area, showing stream basins and sampling sites. Site numbers (appendix 1) correspond to 

those introduced by Brabets and others (1999) in their National Water-Quality Assessment environmental-setting 

study.

62

59

63 69

61

60

65

64 23

67 66

27

29

68

 	




 
 	


 	



	 	



 	


 


Knik Arm

Turnagain Arm

Cook

Inlet

N





29

 !"#!$

%"&$

%"

 !" $

'

' #

#

' ()

' )

(

*"	
Figure 2. Three-dimensional representation of Anchorage area and sampling sites. (See fig. 1 and appendix 1 regarding 

sampling sites.)

Knik Arm

Turnagain Arm

N

Sites initially were selected on the basis of their position along a gradient of urbanization as represented by 

road density (miles of road per square mile of drainage area) upstream from each sample site. The South Fork 

of Campbell Creek (site 23, fig. 1) and Chester Creek at Arctic Boulevard (site 27) were gaged sites and were 

planned as upper and lower (respectively) endpoints of the gradient. Upstream sites were chosen on the basis of 

level of development and access. Upstream sites had road densities that ranged from 0 to 2.1 mi/mi2 (table 1). 

Intermediately positioned sites had a greater degree of development (road-density range, 0.9 to 4.2 mi/mi2). 

The farthest downstream sites were the most highly developed sites within their respective basins and had road 

densities ranging from 0.57 to 9.2 mi/mi2. Ship Creek skewed the road-density calculations at its upstream and 

downstream sites owing to the overall size of the contributing area of the basin upstream from each site. The most 

current land-use and population information, used to calculate urbanization metrics, was assembled from landuse maps, satellite images, aerial photography, and geographic information systems databases.
Table 1. Description of sites

[Site no.: Number used in this report (see figs. 1 and 2 for site locations); corresponds to site number assigned by Brabets and others (1999) in earlier National Water-Quality Assessment report. Sites are ordered from least to greatest population density]

Site

no.

U.S. Geological Survey station 

Elevation

(feet above

sea

level)

Upstream

watershed

area

(square

miles)

Discharge

(cubic

feet

per

second)

Specific

conductance

(microsiemens

per

centimeter

at 25°C)

pH

(standard

units)

Water

temperature

(degrees

Celsius)

Dissolved

oxygen

(milligrams

per

liter)

Road

density

(miles

per

square

mile)

Population

density

(persons

per

square

mile)

Stormdrain

density

(miles of

storm

sewers

per

square

mile)

Ratio

of

population

density

to

road

density

Station

number Name

66 15274796 South Branch of South Fork Chester 

Creek at Tank Trail

358 4.3 3.4 113 8.2 4.5 11.4 0 0 0 0

68 15276200 Ship Creek at Glenn Highway 286 103.4 148 156 7.5 7 11.8 .1 0 .00 023 15274000 South Fork Campbell Creek 233 29.2 58 72 7.7 4 12.7 .33 9 0 29.4229 15276570 Ship Creek below powerplant at 

Elmendorf Air Force Base

47 113.3 224 169 7.6 9.5 10.7 .6 28 .08 48.28

59 15273020 Rabbit Creek at Hillside Drive 876 9.8 30 86 7.3 3.5 12.2 .98 32 0 32.6862 15273090 Little Rabbit Creek at Nickleen 

Street

1,230 2.6 6.2 109 7.7 1 12.6 2.12 60 0 28.36

63 15273097 Little Rabbit Creek at Goldenview 

Drive

590 5.6 15 128 7.9 2.5 12.8 4.2 125 0 29.86

60 15273030 Rabbit Creek at East 140th Avenue 436 11.3 28 90 7.6 6 12.5 2.97 136 0 45.9264 15274395 Campbell Creek at New Seward 

Highway

98 45.9 78 84 7.6 5 11.6 .89 176 .45 198.48

69 15273100 Little Rabbit Creek 92 6.4 15 137 7.9 3 12.4 4.77 182 0 38.3961 15273040 Rabbit Creek at Porcupine Trail 121 13.3 34 96 7.6 6 12.2 4.04 262 0 64.9365 15274557 Campbell Creek at C Street 52 65.7 89 92 7.9 8 8.9 3.55 662 1.59 186.5267 15274830 South Branch of South Fork Chester 

Creek at Boniface Parkway

197 14.8 12 168 7.7 8 11.7 4.14 1,222 3.22 295.1

27 15275100 Chester Creek at Arctic Boulevard 16 27.3 31 242 8.1 11.5 10.4 9.24 2,736 6.95 296.2
FIELD METHODS

Water-chemistry data (major ions, nutrients, dissolved and suspended organic carbon), field properties 

(stream discharge, specific conductance, dissolved oxygen, pH, and water temperature), concentrations of trace 

elements in streambed sediments, macroinvertebrate relative abundances, and chlorophyll-a data were collected 

to assess water quality along the urban gradient. For most sites, data were collected during August 23 to September 23, 1999; for the South Fork of Campbell Creek (site 23), data collected in late July 1999 as part of the 

NAWQA basic fixed-site sampling regime was used.

Water samples for major ions and nutrients and streambed-sediment samples for trace elements were 

collected according to NAWQA protocols (Shelton, 1994; Shelton and Capel, 1994) and sent to the USGS 

National Water-Quality Laboratory (NWQL) for constituent analysis. Major ions and trace elements addressed 

in this report include calcium, magnesium, sodium, potassium, sulfate, chloride, phosphorus, iron, manganese, 

aluminum, arsenic, cadmium, cobalt, copper, chromium, lead, mercury, molybdenum, nickel, selenium, silver, 

sulfur, and zinc.

Epilithic periphyton (algae attached to rocks) was collected using quantitative methods described by Porter 

and others (1993) and fluorometrically analyzed for chlorophyll-a concentrations at the University of Alaska at 

Fairbanks. Three algae samples comprising five rocks each were collected in each reach. These concentrations 

were averaged to measure algal standing crop in milligrams per square meter.

Macroinvertebrate samples were collected according to NAWQA protocols (Cuffney and others, 1993). 

The richest targeted habitat (RTH or semiquantitative) method was designed to provide identification and 

enumeration of species within a given area. Riffles, which are known to support a taxonomically rich macroinvertebrate community (Hynes, 1970), were targeted for semiquantitative sampling. Five samples, each 

representing a sampling area of 0.25 m2

, were collected in riffles within each reach by using a 425-μm mesh 

Slack sampler. Bed sediment within the sample area was disturbed to a depth of approximately 10 cm for 

approximately one minute. Large rocks were scrubbed to remove any adhering organisms. The five samples 

then were composited and packaged for shipment. The samples were submitted to the Biological Unit of the 

NWQL for taxonomic determination. The resulting data was entered into a database for further manipulation 

(see appendix 2 for raw data). Macroinvertebrate metrics were calculated and categorized according to richness, 

composition, tolerance, and feeding measures (table 2).

ANALYSIS

Macroinvertebrate identification and presence–absence data were entered into a database and sorted for 

further analysis. An unweighted-paired-grouping-method (UPGM) cluster analysis using arithmetic means was 

applied to Bray–Curtis distance matrices and was performed by using lowest identifiable taxa data. Dendrograms 

were generated to aid in relating clusters of sites. UPGM clustering refers to the measurement of the distance 

between two clusters as measured by the average of all sampling units within each group (Pielou, 1984; Ludwig 

and Reynolds, 1988). The resultant dendrogram grouped the sites on the basis of dissimilarities (fig. 3). 

Groupings that have larger Bray–Curtis dissimilarity values (approaching 1) are more dissimilar.
Table 2. Biological metrics and expected response of macroinvertebrates to perturbation

[Data modified from Kerans and Karr (1994); Barbour and others (1996); and Fore and others (1996). EPT, insect orders Ephemeroptera, Plecoptera, and Trichoptera]

Biological metric Definition and remarks

Expected 

response to 

increasing 

perturbation

Abundance category

EPT abundance Number of EPT individuals Decrease

Composition category

Margalef diversity index (lowest practical 

taxonomic level of identification)

Measure of species richness (measured to the lowest practical

taxonomic level of identification).

Decrease

Margalef diversity index (family level) Measure of species richness (measured to the family level of

identification).

Decrease

Shannon diversity index Index that uses richness and evenness to measure general diversity

and composition.

Decrease

Percentage Chironomidae Percentage midge larvae Increase

Percentage Ephemeroptera Percentage mayfly nymphs Decrease

Percentage Plecoptera Percentage stonefly nymphs Decrease

Percentage Trichoptera Percentage caddisfly larvae Decrease

Percentage Oligochaeta Percentage aquatic worms Variable

Ratio of EPT to Chironomidae abundances Measure of balance between two indicator groups Decrease

Feeding category

Percentage filterers Percentage of macrobenthos that filter from water column or sediment Variable

Percentage collectors (gatherers) Percentage of macrobenthos that feed by gathering Variable

Percentage predators Percentage of macrobenthos that feed upon other organisms Variable

Percentage scrapers Percentage of macrobenthos that scrape or graze on periphyton Decrease

Percentage shredders Percentage of macrobenthos that shred leaf material Decrease

Richness category

Total taxa richness (lowest practical taxonomic 

level of identification)

Measure of overall variety of macroinvertebrates at lowest taxa identified Decrease

Total taxa richness (family level) Measure of overall variety of macroinvertebrates at family level of

identification.

Decrease

EPT taxa richness Number of EPT taxa represented Decrease

Tolerance category

Hilsenhoff family-level biotic index Index that uses tolerance values to weight family-level identifications

to evaluate organic pollution.

Increase

Percentage two dominant taxa Percentage composition of the two most abundant taxa Increase

Ratio of Baetidae to Ephemeroptera abundances Relative abundance of pollution-tolerant mayflies Increase
Variables for water chemistry (major ions and nutrients) and bed-sediment chemistry (trace elements) that 

were below detection limits were removed from analysis because of the limited number of sites in the data set. 

A correlation table of the significant variables (p < 0.05, r > |0.7|) against population density was generated to 

determine those variables associated with urbanization for further analysis (table 3).

Population, road, and storm-drain densities were calculated by using data provided by the Municipality of 

Anchorage. Population density was defined as number of persons/mi2 of basin; road density was defined as linear 

miles of road per square mile of basin; storm-drain density was defined as miles of storm drains per square mile 

of basin. The ratio of population density to road density, or PDRD ratio, was calculated as the number of persons 

per mile of road. Each of these calculations incorporates all basin area upstream from each site.

Local regression analysis, performed by using the statistical package S-Plus 2000 (Mathsoft, Inc., 2000), 

was used to examine the variables associated with urbanization (measured as population density in this study) 

for the presence of a threshold response or of a linear response. Threshold responses, visually identified by a 

breakpoint in or change in slope of a smooth-fit line, suggest a point at which further increases in population 

density could have a significant effect on stream condition with respect to the particular constituent or metric. 

Scatterplot smoothing was used to remove noise (that is, extraneous information that reduces our ability to see 

patterns in the data) from a data set and to produce a more easily interpreted fit. After the threshold had been 

identified visually on the plot, the breakpoint was tested by determining if the slopes of the two lines converging 

at the breakpoint differed significantly. A t-test (Zar, 1996) was used to check the equality of two population 

regression coefficients; a linear response indicates that any increase in population density (the independent 

variable, x) relates to an increase or decrease (depending on the variable) in the dependent variable (y) in a linear 

fashion without a significant change in the slope of the line at a breakpoint.

Figure 3. Cluster analysis (unweighted-paired-grouping method) using arithmetic means 

of macroinvertebrate presenceñabsence data. Values approaching 1 are more dissimilar. Nodes (13, 11, 10, 12, and others) represent clusters and facilitate assessment of 

dissimilarity. Group 1 sites are considered ìurban impactedî; group 2 sites are ìnonimpactedî; group 3 sites are considered to be possibly anomalous compared to other 

two groups. (See fig. 1 and appendix 1 regarding sampling sites.)

      



	





























 


 


 















	












 
Table 3. Coefficients of correlation between each metric or constituent or 

field property and population density

[Blue shading indicates that correlation is significant at p < 0.05, n =14. EPT, insect orders 

Ephemeroptera, Plecoptera, and Trichoptera]

Biological metric or constituent Coefficient of correlation

with population density

Biological variables

Margalef diversity index (lowest practical taxonomic level of identification) -0.78

Margalef diversity index (family level) -.36

Shannon diversity index (lowest practical taxonomic level of identification) -.81

Total abundance -.18

EPT abundance -.33

Hilsenhoff family-level biotic index .78

Percentage Chironomidae -.23

Percentage Ephemeroptera -.38

Percentage Plecoptera -.43

Percentage Trichoptera -.36

Percentage Oligochaeta .71

Percentage filterers -.34

Percentage collectors .1

Percentage predators -.56

Percentage scrapers -.63

Percentage shredders -.37

Total taxa richness (lowest practical taxonomic level of identification) -.73

Total taxa richness (family level) -.56

Percentage two dominant taxa .82

Percentage EPT -.62

EPT taxa richness -.85

Ratio of EPT to Chironomidae abundances -.34

Ratio of Baetidae to Ephemeroptera abundances .65

Chlorophyll-a .35

Water chemistry and field properties

Silica .66

Calcium .61

Chloride .97

Sodium .92

Potassium .95

Magnesium .84

Sulfate .27

Total dissolved solids .76

Organic carbon, dissolved .74

Discharge -.15

Specific conductance .76

pH -.04

Temperature .36

Oxygen, dissolved -.17

Mercury -.26

Copper .64

Sulfur .64

Cobalt .41

Chromium .55

Bed-sediment chemistry

Phosphorus .15

Sodium .01

Magnesium .25

Potassium -.27

Iron .85

Calcium .04

Aluminum -.15

Selenium -.27

Arsenic .86

Cadmium .97

Silver .81

Zinc .98

Lead .98

Nickel .5

Molybdenum .05

Manganese .84
Correlation coefficients between chosen metrics or constituents and population density are shown in table 3

(p < 0.05, n = 14). Of these variables, 12 biological variables (appendix 2 and appendix 3), 12 water-chemistry 

variables (appendix 4), and 7 trace-element-in-bed-sediments variables (appendix 5) were shown to be 

significant (p < 0.05).

The PDRD ratio was greatest for those sites rated as urban impacted (table 1, fig. 4). The ratios for sites 27, 

67, 65, and 64 (members of group 1 in the cluster analysis, fig. 3) were an order of magnitude higher than for all 

other sites, which had PDRD ratios of less than 70. No difference with respect to the PDRD ratio was evident 

between UPGM cluster groupings 2 and 3.

Locally weighted regression analysis was performed on 31 macroinvertebrate metrics, water-chemistry 

variables, field properties, and bed-sediment variables that correlated significantly (p < 0.05) with population 

density (table 3). Of these 31 variables, 11 showed a threshold response of the constituent to population densities 

when plotted and tested for significance (fig. 5, fig. 6, fig. 7, table 4), and 7 exhibited a linear response (no 

significant breakpoint in the line) (fig. 8, table 4).

RESULTS

A UPGM cluster analysis of macroinvertebrate-species abundance data using Bray–Curtis distance matrices 

is shown in figure 3. The sites separated into three primary groupings based on cluster analysis. These groupings 

illustrate a delineation between urban-impacted (group 1) and nonimpacted sites (group 2), as well as substantiate 

the differences between Ship Creek (group 3) and the rest of the basins in the Anchorage Bowl. The South Fork 

of Campbell Creek site (site 23, group 3) appears anomalous, possibly due to a different sampling time compared 

to the other sites. The PDRD ratio appears to support the separation of sites in group 1 from those in groups 2 and 

3 but does not distinguish group 3 from group 2 (table 1, fig. 3, fig. 4). Storm-drain density also supports the 

separation of group 1 from groups 2 and 3. All group 1 sites had storm-drain densities ≥0.45.

Figure 4. Ratio of population density to road density, comparing group 1 sites (green), 

which are urban impacted, with groups 2 and 3 sites (yellow), which are nonimpacted 

and anomalous, respectively. (See fig. 1 and appendix 1 regarding sampling sites.)

         	  
 



 





	

	








  
 



  

66

68

23

29

59

62

63

60

64

69 61

65

67

66

68

23

29

59

62

63

60

64

69

61

65

67

27

66

68

23

29

59

62

63

60

64

69

61

65

67

27

MARGALEF DIVERSITY INDEX TOTAL TAXA RICHNESS

5.5

5.0

4.5

4.0

3.5

3.0

40

35

30

25

EPT TAXA RICHNESS

9

7

5

20

45

13

11

0 500 1,000 1,500 2,000 2,500 3,000

POPULATION DENSITY, IN PERSONS PER SQUARE MILE

27

Figure 5. Variable-span bivariate 

smoothed scatterplot of three significant biological variables (p < 0.05, 

n = 14), showing threshold response 

against population density. Total taxa 

richness and Margalef diversity index: 

both at lowest practical taxonomic 

level of identification. EPT, insect 

orders Ephemeroptera, Plecoptera, 

and Trichoptera. (See fig. 1 and 

appendix 1 regarding sampling sites.)




















	





























	










 


 

 
 


 	

	

		





  
 


	











	























	









 
 

  
 


	

	





	

	



  	 	   

 
  
 
  
 


Figure 6. Variable-span bivariate 

smoothed scatterplot of four 

significant water-chemistry 

variables (p < 0.05, n = 14), 

showing threshold response 

against population density.

(See fig. 1 and appendix 1

regarding sampling sites.)
      

	

 
 
   	 

































 
 


 



  



 

 

 

 



 

 

 

 

 

Figure 6.óContinued

DISCUSSION

The Bray–Curtis distance measures revealed three distinguishable groupings. Group 1 or the “urbanimpacted” group is under the 12th node (dissimilarity index, 0.510). These sites (27, 67, 65, and 64) have the 

relatively high population densities, road densities, and storm-drain densities (≥0.45). Each of these sites also 

had PDRD ratios greater than 185. The separation of these sites is due primarily to the presence of oligochaetes 

(worms) and mayflies of the family Baetidae, both of which commonly are associated with diminished water 

quality. This is supported further by the metric percentage composition of the two most common taxa (PDT2), 

higher values of which commonly are associated with impaired water quality (Barbour and others, 1999). 

Because all the group 1 sites had higher PDT2 values than all other sites, these sites were considered to be urbanimpacted sites. At these sites, we observed higher levels of fine sediments in the bed materials, which make better 

oligochaete habitat (Thorp and Covich, 1991). The two major families, Naididae and Tubificidae, continuously 

feed on the sediments through which they burrow. Algae and other periphytic materials are the primary food 

source for most naidids, whereas bacteria are the preferred food source for most tubificids (Brinkhurst and 

Gelder, 1991). Both these food sources are found in abundance at urban-impacted sites. Epiphytic algal blooms 

can be related to an increase in nutrients (lawn fertilizers, etc.) entering the stream after a storm event via storm 

drains, and bacteria in streams are most commonly associated with sewage or other organic pollution (such as 

from a large population of waterfowl, livestock, etc.). Both of these nutrient sources are common at or near the 

group 1 sites.

Sites in group 2 or the “nonimpacted” group (63, 61, 60, 59, 62, 69, 66), which is beneath the ninth node 

(dissimilarity index, 0.421), generally have considerably lower population, road, and storm-drain densities than 

sites have in the urban-impacted group. Two sites in the group (61 and 69) do have relatively high population 

densities, but this is offset by the lower PDRD ratio when compared to the urban-impacted sites. The primary 

macroinvertebrate groups driving this separation in the cluster analysis are those sensitive to perturbation—

the mayflies (Ephemeroptera), stoneflies (Plecoptera), and caddisflies (Trichoptera).


















	













 





















	









	
















   
    



	



  	 	   

 
  
 
 
 












 





	










   
 

	





	





Figure 7. Variable-span bivariate 

smoothed scatterplot of four 

significant trace-elements-inbed-sediments variables 

(p < 0.05, n = 14), showing 

threshold response against 

population density. (See fig. 1

and appendix 1 regarding 

sampling sites.)
      

	

 
 
   	 







































 
 
  











Figure 7.óContinued

1Lowest practical taxonomic identification.

Table 4. Coefficients of determination (r 2) as calculated by linear and local regression 

analysis and significance (p)

[Threshold population-density range: Range of values that includes breakpoint. EPT, insect orders Ephemeroptera, Plecoptera, 

and Trichoptera. <, less than; —, not applicable]

Biological metric

or constituent

Linearregression

model,

coefficient of

determination,

r 2

Significance,

p

Localregression

model,

coefficient of

determination,

r 2

Threshold

population-density

range

(persons per

square mile)

Type of

response

Biological metrics

Margalef diversity index1 0.62 0.0008 0.78 125–137 Threshold

Hilsenhoff family biotic index .61 .001 .57 — Linear

Percentage Oligochaetes .52 .003 .63 — Linear

Percentage dominant two taxa .68 .0002 .27 — Linear

EPT taxa richness .72 .001 .8 262–662 Threshold

Total taxa richness1 .54 .002 .26 125–137 Threshold

Water chemistry (major ions)

Chloride .94 <.0001 .98 — Linear

Potassium .9 <.0001 .91 177–183 Threshold

Magnesium .7 .002 .79 — Linear

Sodium .84 <.0001 .93 — Linear

Conductivity .55 .002 .68 125–137 Threshold

Dissolved organic carbon .55 .002 .66 125–137 Threshold

Total dissolved solids .58 .001 .6 177–183 Threshold

Bed-sediment chemistry (trace elements)

Lead .96 <.0001 .99 177–183 Threshold

Zinc .95 <.0001 .99 — Linear

Arsenic .75 <.0001 .92 32–60 Threshold

Iron .73 <.0001 .81 137–177 Threshold

Manganese .72 .0001 .89 125–137 Threshold




















	

 





  	 	   



   
   







 
    































	


















 ! "
 











 









	







 










#
$  












	

Figure 8. Variable-span bivariate 

smoothed scatterplot of seven other 

significant biological and chemical 

variables (p < 0.05, n = 14), showing 

linear response against population 

density. (See fig. 1 and appendix 1

regarding sampling sites.)








 

	

	






 










  

  








      


      

















 







	

	








  
























 

	

	












  

  


	







	












Figure 8.óContinued
The last group in the cluster analysis is made up of the two Ship Creek sites (29 and 68) and the reference 

site for Campbell Creek (site 23). The Ship Creek sites are considered anomalous because of the size of the basin 

compared to the other basins in the study and the fact that the creek has been regulated through the building of 

two small dams. Salmon are no longer able to pass to the upper site (68) because of obstructions. Therefore, the 

replenishment of instream nutrients from salmon carcasses no longer occurs, depriving many macroinvertebrates 

of an important food source and thereby limiting occurrence and abundance. Another confounding factor relates 

to the drying of the streambed at the upper site (29) during winter low flows in some years. Discharge for the Ship 

Creek sites is also considerably greater than the other sites. The South Fork of Campbell Creek site (23) grouped 

with the Ship Creek sites, probably because of a shift in macroinvertebrate-community structure influenced by 

the date at which the sample was collected compared to the other sites. Food-type availability could be a driving 

factor in the separation of this site from group 2. This site was sampled in July and would not have had the 

abundance of leaf litter found during the later sampling period when all other sites were sampled. That a shift 

from a feeding regime dominated by grazing (of algae) to one dominated by shredding (of leaf litter) probably 

had not yet taken place is shown by the relative percentages of scrapers and shredders. We predict that an 

upstream site having few known urban factors would fit into group 2 if sampled during the same time period.

The PDRD ratio and storm-drain density appear useful for separation of urban-impacted from nonimpacted 

sites. High PDRD ratios (>70) are associated with areas that have a high percentage impervious cover. As population densities increase, more roads, parking, and housing are required to meet basic needs. Accumulation of 

pollutants (deicing salts, petroleum products, combustion byproducts, etc.) on road and parking surfaces has been 

modeled for small watersheds and was shown to have a potentially negative impact on the quality of water in 

streams when runoff events occur (Novotny and others, 1985). The potentially greater input of pollutants into 

streams in areas of increased population density and hence high road density may have a significant role in the 

separation of urban-impacted from nonimpacted areas. Group 1 sites had storm-drain densities ≥0.45. Increased 

storm-drain density adds to the number of artificial channels that in turn rapidly pass water to the streams, thereby 

circumventing the natural hydrologic cycle (May and others, 1997). This rapid channeling diminishes infiltration 

and storage of water in shallow aquifers and hence reduces baseflows during periods of reduced precipitation. 

Reduced baseflows have the effect of reducing habitat suitable for aquatic species, thereby negatively impacting 

the “natural state” of the stream.

      

	

 
 
   	 









 




















 
 
  

















Figure 8.óContinued
Regression analysis of the most significant variables, with respect to population density, revealed that the 

majority exhibited a threshold response to urbanization (table 4, fig. 5, fig. 6, fig. 7). This finding suggests that 

streams in the Anchorage Bowl are able to accommodate the effects of urbanization only up to a point; beyond 

that, stream structure and function are impaired.

Three of the six biologically significant variables (p < 0.05, r

2

 >0.5) showed threshold responses (table 4). 

Two variables (EPT taxa richness and total taxa richness) are richness measures, and one (Margalef diversity) is 

an index of the macroinvertebrate community. These biological variables tend to support the separation of urbanimpacted from nonimpacted sites revealed by the cluster analysis, especially when related to the PDRD ratio 

rather than exclusively to population density. Both taxa richness and macroinvertebrate diversity decrease in a 

downstream direction. In contrast, the percentage oligochaetes, the Hilsenhoff family-level biotic index (FBI) 

(Hilsenhoff, 1988), and the PDT2 increase downstream; all three exhibit linear responses to population density 

(fig. 8, table 4). Oligochaetes were generally one of the major components making up the PDT2 at the urbanimpacted sites. The FBI, which is a measure of organic pollution and the subsequent response by macroinvertebrates based on tolerance values, also increased downstream. FBI values greater than 5 suggest the probability 

of organic pollution. Sites that had PDRD ratios greater than 50 had FBI values greater than 5. Urban-impacted 

sites tended to have fewer species of more-tolerant, generalist organisms, whereas nonimpacted sites had greater 

numbers of more-sensitive species. Negative impact in general, with respect to the biological variables exhibiting 

a threshold response, appears to occur near population densities of 140 persons/mi2. EPT taxa richness shows a 

break in slope between 262 and 662 persons/mi2

, but this threshold is due in part to the occurrence of the 

generally perturbation-tolerant Baetid family of mayflies (Ephemeroptera). Removal of this group from the 

metric calculations increases the sensitivity of the measure and brings it in line with the other two threshold 

variables.

The major ions (inorganic constituents in water samples) found to be significant with respect to population 

density include magnesium, sodium, potassium, and chloride (table 4). Magnesium, sodium, and chloride are 

found in low concentrations in natural streams. The elevated levels found in the urban-impacted sites are probably a result of the application of deicing salts and subsequent runoff and possibly also a result of leakage of 

domestic wastewater. The linear trends in the fitted curves of the analyses for these three constituents (fig. 8, 

table 4) suggest that any increase in population density would result in a corresponding increase in the concentration of these constituents in water in Anchorage. Potassium, which showed a threshold response (fig. 6), is an 

essential element for growth in both plants and animals. Elevated levels in urban areas are generally attributed to 

nonpoint-source pollution due to the application of fertilizers. The variables conductivity, total dissolved solids, 

and dissolved organic carbon also showed threshold responses (fig. 6, table 4). The breakpoints for waterchemistry variables reflect the threshold range for the biological metrics (table 4).

Significant trace elements in bed sediments (arsenic, lead, iron, manganese) (fig. 7, table 4), displayed a 

threshold-response curve with respect to population density (fig. 7). Although Klein (1979) considered the 

constituents lead and zinc to be good urban-signature constituents with respect to impervious area, zinc exhibited 

a linear response to population density in this study (fig. 8, table 4). The primary sources for both metals are 

vehicles, piping, and commercial and industrial nonpoint-source activity. Arsenic, iron, and manganese were 

more likely from natural sources, but because of organic pollution and the reducing (anaerobic) environment it 

helps to create in the sediments, they were more readily detected in the highly urbanized areas. The breakpoint 

for lead, at a population density between 60 and 125 persons/mi2

, suggests that it is a potentially sensitive 

urbanization variable. Iron and arsenic levels were probably at background levels at upstream sites; changes in 

concentration were noted at urban-impacted site 65 and increased in a downstream direction. Manganese was in 

line with the biological metrics; its regression shows a breakpoint at a population density between 125 and 137 

persons/mi2

 (fig. 7).
CONCLUSIONS

Site-based reconnaissance data allowed us to visualize the effect of urbanization on stream macroinvertebrates in Anchorage. Population density appears to be a reasonable surrogate of urbanization, but further testing 

of the PDRD ratio as a rapid urbanization variable is needed. A threshold effect was observed for most of the 

significant variables. Adversely impacted sites typically had higher human population, road, and storm-drain 

densities. As trace-element and salt concentrations increased with increasing population, road, and storm-drain 

densities, macroinvertebrate diversity decreased. PDRD ratios greater than 70, road densities greater than 4.0 mi/

mi2, and(or) population densities of 125–150 persons/mi2 (a conservative approximation) can be used to warn of 

the heightened potential of urbanization-induced degradation of streams in Anchorage. Exceptions to this are the 

Ship Creek sites, which may have skewed the data. Contributing factors may include disproportionate basin size 

and relative lack of development normally associated with urbanization over much of its area, localized industrialization, impoundments, and cessation of flow during winter months. Incremental areas between sites also 

should be examined for integration into calculations to determine if a more robust explanation can be generated.

The U.S. Census Bureau (1990) defines urban areas as having minimum population densities of 1,000 

persons/mi2

; this criterion is met by only two of the sites in this study, though many of the other sites meet criteria 

to be designated “urban fringe”. Wear and others (1998) suggested that two main areas along an urban–rural 

gradient may significantly impact water quality—at the edge of urban expansion and at the most undeveloped 

parts of the basin. According to results of our study, stream impairment appears to begin within the urban fringe. 

Areas having population densities of 125–150 persons/mi2 appear to be the first to start showing signs of stream 

impairment. We readily could see evidence of changes in the streams and surrounding riparian areas at those sites 

near or at this threshold. For example, channels had been modified, the riparian zones were altered, manmade 

litter was observed, and the distance between roads and streams had decreased. The PDRD ratio complemented 

the results of the cluster analysis, at least with respect to differentiating urban-impacted and nonimpacted sites. 

Further study of this ratio as a rapid assessment of potential urban impact is warranted.
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for biological criteria for Florida streams using benthic macroinvertbrates: Journal of the North American Benthological 

Society, v. 15, no. 2, p. 185–211.

Barbour, M.T., Gerritsen, J., Snyder, B.D., and Stribling, J.B., 1999, Rapid bioassessment protocols for use in streams and 

wadeable rivers—Periphyton, benthic macroinvertebrates, and fish (2d ed.): U.S. Environmental Protection Agency EPA 

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Brabets, T.P., Nelson, G.L., Dorava, J.M., and Milner, A.M., 1999, Water-quality assessment of the Cook Inlet Basin, 

Alaska—Environmental setting: U.S. Geological Survey Water-Resources Investigations Report 99–4025, 65 p.

Brinkhurst, R.O., and Gelder, S.R., 1991, Annelida—Oligochaeta and Branchiobdellida, in Thorp, J.H., and Covich, A.P., 

eds., Ecology and classification of North American freshwater invertebrates: Academic Press, p. 401–435.

Cuffney, T.F., Gurtz, M.E., and Meador, M.R., 1993, Methods for collecting benthic invertebrate samples as part of the 

National Water-Quality Assessment program: U.S. Geological Survey Open-File Report 93–406, 66 p.

Fore, L.S., Karr, J.R., and Wisseman, R.W., 1996, Assessing invertebrate responses to human activities—Evaluating 

alternative approaches: Journal of the North American Benthological Society, v. 15, no. 2, p. 212–231.

Garie, H.L., and McIntosh, A., 1986, Distribution of benthic macroinvertebrates in a stream exposed to urban runoff: Water 

Resources Bulletin, v. 22, no. 3, p. 447–451.

Hilsenhoff, W.H., 1988, Rapid field assessment of organic pollution with a family-level biotic index: Journal of the North 

American Benthological Society, v. 20, no. 1, p. 65–68.

Hynes, H.B.N., 1970, The ecology of running waters: University of Toronto Press, Toronto, 555 p.

Kerans, B.L., and Karr, J.R., 1994, A benthic index of biotic integrity (B-IBI) for rivers of the Tennessee Valley: Ecological 

Applications, v. 4, p. 768–785.

Klein, R.D., 1979, Urbanization and stream quality impairment: Water Resources Bulletin, v. 15, no. 4, p. 948–963.

Ludwig, J.A., and Reynolds, J.F., 1988, Statistical ecology—A primer on methods and computing: Wiley, 337 p.

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May, C.W., Welch, E.B., Horner, R.R., Karr, J.R., and Mar, B.W., 1997, Quality indices for urbanization effects in Puget 

Sound lowland streams: Department of Civil Engineering, University of Washington, Water Resources Series Technical 

Report no. 154, 229 p.

Milner, A.M., and Oswood, M.W., 1989, Macroinvertebrate distribution and water quality in Anchorage streams: Institute of 

Arctic Biology, University of Alaska at Fairbanks, 48 p.

Municipality of Anchorage, 1996, Population and housing sampling frame—By census tracts: Municipality of Anchorage 

Community Planning and Development, 6 p.

Novotny, V., Sung, H.M., Bannerman, R., and Baum, K., 1985, Estimating nonpoint pollution from small urban watersheds: 

Journal of the Water Pollution Control Federation, v. 57, no. 4, p. 339–348.

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APPENDIXES
Appendix 1. Cook Inlet Basin National Water-Quality Assessment site-numbering system

[Site numbers used in this report (shown in bold and shaded blue; see fig. 1 and fig. 2 for site locations) follow numbering system for stream-gaging 

stations that was introduced in National Water-Quality Assessment Cook Inlet Basin environmental-setting report (Brabets and others, 1999). Total 

number of sites listed reflects assignments as of this writing. Sequence of site numbers generally parallels order used in U.S. Geological Survey datastation identification]

Site

number

U.S. Geological Survey station

Number Name

1 15238820 Barabara Creek near Seldovia

2 15239500 Fritz Creek near Homer

3 15239000 Bradley River near Homer

4 15239050 Middle Fork Bradley River near Homer

5 15239900 Anchor River near Anchor Point

6 15240000 Anchor River at Anchor Point

7 15241600 Ninilchik River at Ninilchik

8 15242000 Kasilof River near Kasilof

9 15244000 Ptarmigan Creek at Lawing

10 15246000 Grant Creek near Moose Pass

11 15248000 Trail River near Lawing

12 15254000 Crescent Creek near Cooper Landing

13 15258000 Kenai River at Cooper Landing

14 15260000 Cooper Creek near Cooper Landing

15 15264000 Russian River near Cooper Landing

16 15266300 Kenai River at Soldotna

17 15266500 Beaver Creek near Kenai

18 15267900 Resurrection Creek near Hope

19 15271000 Sixmile Creek near Hope

20 15272280 Portage Creek at Portage Lake outlet near Whittier

21 15272550 Glacier Creek at Girdwood

22 15273900 South Fork Campbell Creek at Canyon Mouth near Anchorage

23 15274000 South Fork Campbell Creek near Anchorage

24 15274300 North Fork Campbell Creek near Anchorage

25 15274600 Campbell Creek near Spenard

26 15275000 Chester Creek at Anchorage

27 15275100 Chester Creek at Arctic Boulevard at Anchorage

28 15276000 Ship Creek near Anchorage

29 15276570 Ship Creek below powerplant at Elmendorf Air Force Base

30 15277100 Eagle River at Eagle River

31 15277410 Peters Creek near Birchwood

32 15281000 Knik River near Palmer

33 15282000 Caribou Creek near Sutton

34 15284000 Matanuska River near Palmer

35 15290000 Little Susitna River near Palmer

36 15291000 Susitna River near Denali

37 15291200 Maclaren River near Paxson

38 15291500 Susitna River near Cantwell

39 15292000 Susitna River at Gold Creek

40 15292400 Chulitna River near Talkeetna

41 15292700 Talkeetna River near Talkeetna

42 15294005 Willow Creek near Willow

43 15294010 Deception Creek near Willow

44 15294100 Deshka River near Willow

45 15294300 Skwentna River near Skwentna

46 15294350 Susitna River at Susitna Station

47 15294410 Capps Creek below North Capps Creek near Tyonek

48 15294450 Chuitna River near Tyonek

49 15294500 Chakachatna River near Tyonek

50 15283700 Moose Creek near Palmer

51 585750154101100 Kamishak River near Kamishak

52 15294700 Johnson River above Lateral Glacier near Tuxedni Bay

53 15266010 Kenai River below Russian River near Cooper Landing

54 15266020 Kenai River at Jims Landing near Cooper Landing

55 15266110 Kenai River below Skilak Lake outlet near Sterling

56 15267160 Swanson River near Kenai

57 631629149352000 Colorado Creek near Colorado

58 631018149323700 Costello Creek near Colorado

59 15273020 Rabbit Creek at Hillside Drive near Anchorage

60 15273030 Rabbit Creek at East 140th Avenue near Anchorage
Appendix 1. Cook Inlet Basin National Water-Quality Assessment site-numbering systemóContinued

Site

number

U.S. Geological Survey station

Number Name

61 15273040 Rabbit Creek at Porcupine Trail Road near Anchorage

62 15273090 Little Rabbit Creek at Nickleen Street near Anchorage

63 15273097 Little Rabbit Creek at Goldenview Drive near Anchorage

64 15274395 Campbell Creek at New Seward Highway near Anchorage

65 15274557 Campbell Creek at C Street near Anchorage

66 15274796 South Branch of South Fork Chester Creek at tank trail near Anchorage

67 15274830 South Branch of South Fork Chester Creek at Boniface Parkway near Anchorage

68 15276200 Ship Creek at Glenn Highway near Anchorage

69 15273100 Little Rabbit Creek near Anchorage

70 15239070 Bradley River near tidewater near Homer

71 594507151290000 Beaver Creek 2 miles above mouth near Bald Mountain near Homer

72 594734151142900 Anchor River near Bald Mountain near Homer

73 15239840 Anchor River above Twitter Creek near Honmer

74 595126151391000 Chakok River 7.5 miles above mouth near Anchor Point

75 595506152403300 Stariski Creek 2 miles below unnamed tributary near Ninilchik

76 15240300 Stariski Creek near Anchor Point

77 600107151112800 North Fork Deep Creek 4 miles above mouth near Ninilchik

78 600047151383100 Deep Creek 0.4 mile above Clam Creek near Ninilchik

79 600204151401800 Deep Creek 0.6 mile above Sterling Highway near Ninilchik

80 600945151210900 Ninilchik River 1.5 miles below tributary 1 near Ninilchik

81 600321151325000 Ninilchik River below tributary 3 near Ninilchik

82 601100151000000 Nikolai Creek near Kasilof

83 613430150255000 Susitna River above Yentna River near Susitna Station

84 15281500 Camp Creek near Sheep Mountain Lodge

85 15292780 Susitna River at Sunshine

86 622302150083000 Susitna River 5 miles above Talkeetna River near Talkeetna

87 623705150005000 Susitna River at Curry

88 623850147225000 Oshetna River near Cantwell

89 623840147260000 Goose Creek near Cantwell

90 624658147562000 Kosina River near Cantwell

91 624953148151500 Watana Creek near Cantwell

92 625000149223500 Portage Creek near Gold Creek

93 624718149393600 Indian River near Gold Creek

94 15283550 Moose Creek above Wishbone Hill near Sutton

95 15292302 Camp Creek at mouth near Colorado

96 15292304 Costello Creek below Camp Creek near Colorado

97 625012150182700 Crystal Creek at mouth near Talkeetna

98 625014150183200 Coffee River above Crystal Creek near Talkeetna

99 623834150543300 Bear Creek near Talkeetna

100 623920150540300 Wildhorse Creek near Talkeetna

101 623510150450400 Long Creek near Talkeetna

102 623501151112900 Hidden Creek near Talkeeetna

103 623324151321600 Snowslide Creek at mouth near Talkeetna

104 623325151321800 Cripple Creek above Snowslide Creek near Talkeetna

105 622522151592200 Cascade Creek at mouth near Talkeetna

106 621936151582700 Fourth of July Creek at mouth near Talkeetna

107 621759152410500 Morris Creek at mouth near Talkeetna

108 621800152410600 Kichatna River above Morris Creek near Talkeetna

109 15294345 Yentna River near Susitna Station

110 600826152554400 Kona Creek 3 miles above mouth above Lateral Glacier near Tuxedni Bay

111 600803152552400 Kona Creek 2.5 miles above mouth above Lateral Glacier near Tuxedni Bay

112 600635152550900 Kona Creek tributary above Lateral Glacier near Tuxedni Bay

113 600636152551400 Kona Creek 0.8 mile above mouth above Lateral Glacier near Tuxedni Bay

114 600739152570701 Spring 1 near Johnson Glacier near Tuxedni Bay

115 600715152572800 North Fork Ore Creek near mouth near Johnson Glacier near Tuxedni Bay

116 600713152574000 East Fork Ore Creek near mouth near Johnson Glacier near Tuxedni Bay

117 600658152581400 Ore Creek near mouth near Johnson Glacier near Tuxedni Bay

118 600609152561100 Johnson River tributary above Lateral Glacier near Tuxedni Bay
Appendix 2. Abundance and distribution of benthic macroinvertebrates collected at 14 sites in Anchorage in 1999

[Taxon: Phyla are shown in bold. Site number: See fig. 1, fig. 2, and appendix 1 regarding site locations and numbering; sites are ordered from least to greatest population density.

L, larvae; P, pupae; A, adults]

Taxon

Site number

66 68 23 29 59 62 63 60 64 69 61 65 67 27

Platyhelminthes

Turbellaria 84 18 25 25 302 70 20 158 52 12 36 23 0 0

Nematoda 9 0 0 0 14 14 0 11 0 0 14 0 11 0

Cnidaria

Hydridae

Hydra sp. 0 0 0 0 0 0 0 0 0 0 0 0 11 0

Mollusca

Gastropoda

Hydrobiidae 0 0 0 0 0 0 0 11 0 4 0 0 0 4

Planorbidae 5 0 0 8 00 0 0 0 4 0 3 0 0

Valvatidae 0 0 0 0 00 0 0 0 0 0 0 0 8

Bivalvia

Sphaeriidae 0 0 0 0 0 0 0 0 0 0 0 0 137 28

Annelida 0 0 109 0 0 0 0 0 0 0 0 0 0 0

Oligochaeta 0 0 0 34 0 0 2 0 2 0 0 1 2 8

Enchytraeidae 0 0 0 67 0 14 4 0 6 16 24 5 21 36

Lumbriculidae 79 84 0 512 58 29 20 53 0 20 0 0 0 0

Naididae 0 534 0 294 0 0 4 0 320 28 240 97 305 904

Tubificidae 5 0 0 34 0 0 0 0 2 76 66 4 63 208

Arthropoda

Arachnida 14 36 269 76 158 112 24 42 12 72 72 25 126 48

Insecta

Collembola 0 0 0 0 0 0 4 0 0 24 54 0 11 0

Ephemeroptera 0 0 8L 0 0 0 0 0 0 0 0 0 0 0

Ameletidae

Ameletus sp. 0 12L 0 0 0 0 0 0 0 0 0 0 0 0

Baetidae 196L 84L 8L 622L 72L

14A

546L 228L 84L 16L 12L 12L 1L 1691L 28L

Acentrella sp. 5L 0 0 0 00 0 0 0 0 0 0 0 0

Acentrella turbida 0 0 168L 8L 0 0 0 0 0 0 0 1L 0 0

Baetis bicaudatus 5L 12L 25L 0 30L 14L 0 1L 0 4L 0 0 0 0

Baetis tricaudatus 0 0 0 18L 0 0 0 0 0 0 0 0 0 0
Appendix 2. Abundance and distribution of benthic macroinvertebrates collected at 14 sites in Anchorage in 1999óContinued

[Taxon: Phyla are shown in bold. Site number: See fig. 1, fig. 2, and appendix 1 regarding site locations and numbering; sites are ordered from least to greatest population density.

L, larvae; P, pupae; A, adults]

Taxon

Site number

66 68 23 29 59 62 63 60 64 69 61 65 67 27

Arthropoda—Continued

Insecta—Continued

Ephemeroptera—Continued

Heptageniidae 140L

5A

186L 17L 8L 101L 392L 92L 168L 6L 8L 42L 0 0 0

Cinygmula sp. 5L 0 202L 0 158L 0 0 189L 0 4L 42L 0 0 0

Epeorus sp. 159L 3L 302L 0 763L 420L 308L 420L 2L 108L 222L 0 0 0

Ephemerellidae

Drunella doddsi 93L 354L 386L 60L 202L 210L 60L 117L 18L 9L 78L 0 0 0

Ephemerella aurivillii 0 30L 1L 0 0 0 0 0 0 0 0 0 0 0

Plecoptera

Taeniopterygidae

Taenionema sp. 0 12L 0 8L 29L 0 12L 105L 32L 0 6L 3L 0 0

Nemouridae

Zapada sp. 75L 24L 42L 17L 144L 420L 40L 263L 3L 0 48L 0 11L 0

Zapada cinctipes 9L 48L 8L 42L 43L 70L 28L 53L 2L 52L 42L 1L 210L

11A

24L

Leuctridae

Despaxia augusta 5L 0 0 0 43L 57L 4L 0 0 0 0 0 0 0

Capniidae 5L 6L 0 17L 0 14L 4L 21L 4L 4L 0 3L 63L 0

Eucapnopsis brevicauda 0 18L 0 0 0 0 0 0 0 0 0 0 0 0

Perlodidae 5L 1A 8L 0 14L 0 0 32L 8L 4L 0 1L 53L 4L

Isoperla sp. 0 12L 1L 68L 0 84L 8L 0 0 0 0 0 0 1L

Chloroperlidae 0 102L 25L 34L 72L 84L 17L 42L 38L 0 12L 15L 0 16L

Suwallia sp. 44L 0 25L 0 187L 29L 44L 85L 0 40L 1L 0 0 0

Coleoptera

Staphylinidae 0 0 0 0 14A 0 0 0 0 0 0 0 0 0
Appendix 2. Abundance and distribution of benthic macroinvertebrates collected at 14 sites in Anchorage in 1999óContinued

[Taxon: Phyla are shown in bold. Site number: See fig. 1, fig. 2, and appendix 1 regarding site locations and numbering; sites are ordered from least to greatest population density.

L, larvae; P, pupae; A, adults]

Taxon

Site number

66 68 23 29 59 62 63 60 64 69 61 65 67 27

Arthropoda—Continued

Insecta—Continued

Diptera

Ceratopogonidae

Ceratopogoninae 5L 6L 0 0 0 0 0 11L 0 0 0 0 0 0

Chironomidae 0 6P 42P

25L

0 14P

130A

0 4A 11L

21P

0 8P

24A

66P

6L

1P

4A

0 0

Tanypodinae

Macropelopiini

Macropelopia sp. 0 0 0 0 0 14L 0 0 0 0 0 0 0 0

Pentaneurini 0 0 0 0 0 0 0 0 0 0 0 1L 105L 16L

Diamesinae 0 0 0 8P 0 0 0 0 0 0 0 0 0 0

Diamesini

Diamesa sp. 0 0 0 25L 0 0 0 0 0 0 0 0 0 0

Pagastia sp. 42L 318L 160L 185L 230L 140L 4L 63L 20L 12L 60L 109L 74L 16L

Potthastia sp. 0 0 0 25L 0 0 0 0 0 20L

12P

0 5L 32L 40L

Prodiamesinae

Prodiamesa sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 4L

Orthocladiinae 23L

5P

30L 210L

59P

151L

25P

403L

101P

28L 0 85L

53P

2P

2L

0 120L

108P

0 420L 0

Corynoneura sp. 0 0 8L 0 0 0 0 11L 0 0 0 0 0 0

Thienemanniella sp. 0 0 25L 0 0 0 0 0 0 0 0 0 0 0

Brillia sp. 23L 0 0 17L 274L 140L 20L 420L 2L 36L 276L 6L 105L 0

Cricotopus sp. 0 0 0 0 0 0 0 0 0 0 0 0 11L 0

Eukiefferiella sp. 5L 0 50L 17L 130L 504L 4L 32L 0 4L 48L 0 32L 0

Heleniella sp. 9L 0 0 0 0 0 0 0 22L 0 6L 4L 0 0

Orthocladius sp. 0 0 8L 0 14L 14L 0 11L 0 0 6L 0 0 0

Parakiefferiella sp. 0 0 0 0 14L 14L 0 0 0 0 0 0 0 0

Paraphaenocladius sp. 5L 0 25L 0 0 0 0 0 0 0 0 0 0 0

Parorthocladius sp. 0 0 0 0 101L 0 0 0 0 0 12L 0 0 0

Rheocricotopus sp. 5L 6L 0 0 14L 14L 0 11L 0 0 0 0 0 0

Rheosmittia sp. 0 0 0 0 0 0 0 0 2L 0 0 0 0 0

Synorthocladius sp. 0 0 0 0 0 0 0 21L 0 0 0 0 0 0

Tvetenia sp. 5L 6L 17L 25L 72L 0 0 21L 0 24L 0 0 0 0
Appendix 2. Abundance and distribution of benthic macroinvertebrates collected at 14 sites in Anchorage in 1999óContinued

[Taxon: Phyla are shown in bold. Site number: See fig. 1, fig. 2, and appendix 1 regarding site locations and numbering; sites are ordered from least to greatest population density.

L, larvae; P, pupae; A, adults]

Taxon

Site number

66 68 23 29 59 62 63 60 64 69 61 65 67 27

Arthropoda—Continued

Insecta—Continued

Diptera—Continued

Chironomidae—Continued

Chironominae 0 0 25P 0 0 0 0 0 0 0 0 0 0 0

Chironomini 0 0 0 0 0 0 0 0 0 0 0 0 11L 0

Parachironomus sp. 0 0 0 0 0 0 0 147L 0 0 6L 0 0 0

Polypedilum sp. 0 6L 0 8L 0 0 0 0 0 4L 0 0 0 0

Tanytarsini 0 0 0 0 0 0 0 11L 0 0 0 0 0 0

Micropsectra sp. 65L 0 0 17L 144L 154L 16L 462L 0 60L 192L 0 0 0

Rheotanytarsus sp. 0 0 0 0 0 0 0 0 6L 0 0 11L 84L 0

Stempellina sp. 5L 0 25L 0 0 0 0 0 0 0 0 0 0 0

Psychodidae 5L 0 8L 0 14L 28L 0 0 2L 24L 48L 0 0 4L

Simuliidae 84L

5P

0 101L 0 0 840L 172L 0 2L 4L 6L

6P

0 00

Simulium sp. 0 6L 17L

34P

8L 1L 0 0 0 0 0 0 0 0 0

Tipulidae

Tipula sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 1L

Dicranota sp. 6L 6L 0 25L 30L 14L 0 11L 6L 4L 0 9L 43L 4L

Hesperoconopa sp. 0 6L 0 0 0 0 0 0 14L 12L 6L 1L 0 0

Pedicia sp. 0 0 0 0 0 0 4L 0 0 0 0 1L 0 0

Empididae 0 0 0 34L 14P 0 0 0 0 0 0 0 0 0

Clinocera sp. 0 0 8L 0 0 28L 0 0 0 24L 6L 0 0 0

Oreogeton sp. 1L 0 0 0 43L 0 0 0 0 6L 0 0 0

Hemerodromiinae 23L 36L 8L 0 72L 14L 0 21L 2L 16L 12L 6L 32L 0

Stratiomyidae 0 0 0 0 0 0 0 0 0 0 6L 0 0 0

Sciomyzidae 0 0 0 0 0 0 0 0 0 0 0 0 32L 0
Appendix 2. Abundance and distribution of benthic macroinvertebrates collected at 14 sites in Anchorage in 1999óContinued

[Taxon: Phyla are shown in bold. Site number: See fig. 1, fig. 2, and appendix 1 regarding site locations and numbering; sites are ordered from least to greatest population density.

L, larvae; P, pupae; A, adults]

Taxon

Site number

66 68 23 29 59 62 63 60 64 69 61 65 67 27

Arthropoda—Continued

Insecta—Continued

Trichoptera

Hydropsychidae

Ceratopsyche sp. 0 0 0 0 0 0 0 0 0 0 0 0 11L 4L

Rhyacophilidae

Rhyacophila sp. 23L 0 0 0 15L 280L 24L 43L 0 44L 37L 0 0 0

Glossosomatidae 0 0 0 0 0 0 100L 0 0 0 0 0 0 0

Glossosoma sp. 271L 204L 168L 126L 43L 112L 0 42L 60L 380L 6L 52L

4P

33L

11P

0

Brachycentridae

Brachycentrus sp. 0 42L 0 0 0 0 0 0 0 0 0 0 63L 0

Brachycentrus americanus 0 1L 8L 314L 0 0 0 0 4L 0 0 0 13L 0

Limnephilidae 23L 36L 0 84L 29L 98L 16L 63L 2L 108L 78L 6L 11L 8L

Apatania sp. 0 0 0 8L 0 0 0 0 0 0 0 0 11L 0

Ecclisomyia sp. 0 15L 9L 3L 45L 0 8L 63L 2L 0 6L 0 0 0

Ecclisocosmoecus scylla 1L 0 0 0 0 17L 4L 11L 0 0 0 0 0 0

Hesperophylax sp. 0 0 0 0 0 0 0 0 0 0 0 0 0 1L

Onocosmoecus unicolor 0 0 1L 1L 0 0 0 0 0 0 6P 0 0 0

Psychoglypha subborealis 0 0 1L 0 0 0 0 0 0 0 0 0 0 1P

Lepidoptera

Pyralidae

Crambus sp. 9L 0 0 0 0 0 4L 0 0 0 0 0 0 0
Appendix 3. Biological metrics calculated from macroinvertebrate data collected at 14 sites in Anchorage in 1999

[Site number: See fig. 1, fig. 2, and appendix 1 regarding site locations and numbering; sites are ordered from least to greatest population density. EPT, insect orders Ephemeroptera, Plecoptera, and Trichoptera]

Biological metric

Site number

66 68 23 29 59 62 63 60 64 69 61 65 67 27

Margalef diversity index (lowest practical taxonomic level of identification) 5.42 4.52 5.19 4.73 4.65 3.99 4.32 4.78 4.76 5.01 5.06 4.33 3.87 3.17Margalef’s diversity index (family level) 3.12 2.58 2.28 2.87 2.39 2.35 3.07 2.33 3.22 3.2 2.73 2.83 2.54 2.21Shannon diversity index 2.93 2.59 3.06 2.79 3.18 2.86 2.56 3.10 2.16 2.85 3.16 2.33 2.34 1.46Hilsenhoff family-level biotic index 3.54 4.33 3.53 4.66 4.32 3.96 3.43 4.30 5.34 3.11 5.14 4.77 4.48 7.30Percentage Chironomidae 12.0 16.1 25.2 16.4 37.6 20.3 3.7 39.4 8.3 15.4 44.3 35.0 22.6 5.4Percentage Ephemeroptera 37.9 29.5 41.4 23.4 30.7 31.4 52.8 28.0 6.2 11.0 17.9 .5 43.8 2.0Percentage Plecoptera 9.5 9.7 4.0 6.1 12.2 15.1 12.0 17.2 12.9 7.6 4.9 5.7 9.0 3.2Percentage Trichoptera 19.8 12.9 6.9 17.5 3.0 10.1 11.7 6.3 10.1 40.3 6.0 15.4 4.0 1.0Percentage Oligochaeta 5.2 26.8 4.0 30.8 1.3 .9 2.3 1.5 49.0 10.6 14.9 26.6 10.1 81.6Percentage filterers 17.5 18.3 31.4 27.0 37.6 37.0 16.9 39.4 9.2 15.7 44.8 35.0 28.4 7.6Percentage collectors 24.2 24.5 22.1 42.1 8.9 16.4 23.6 7.3 5.9 11.0 9.2 1.7 45.5 17.5Percentage predators 5.4 5.2 2.5 3.3 7.9 10.0 7.1 6.1 6.8 8.5 3.3 4.0 2.2 1.5Percentage scrapers 41.4 17.8 26.5 5.2 31.3 19.8 38.4 27.9 17.8 38.8 15.7 19.6 1.1 .0Percentage shredders 8.0 5.9 2.3 5.6 7.7 13.4 8.0 13.3 4.3 13.3 8.4 4.5 7.4 2.5Total taxa richness (lowest practical

taxonomic level of identification)

41 36 42 39 40 35 32 40 32 37 40 27 33 24

Total taxa richness (family level) 24 21 19 24 21 21 23 20 22 24 22 18 22 17Percentage two dominant taxa 29.1 38.5 25.5 37.1 25.7 27.5 41.1 25.2 56.5 36.9 23.3 51.1 53.1 78.5Percentage EPT 67.2 52.1 52.4 47.0 45.9 56.6 76.5 51.5 29.3 58.8 28.9 21.6 56.8 6.1EPT taxa richness 11 12 10 12 11 11 12 11 11 10 9 8 9 6Ratio of EPT to Chironomidae abundances 85 76 68 74 55 74 95 57 78 79 39 38 71 53Ratio of Baetidae to Ephemeroptera abundances 34 14 18 91 9 35 33 9 38 11 3 100 100 100
Appendix 4. Nutrient and major-Ion concentrations in water samples from 14 sites in Anchorage in 1999

[Site number: See fig. 1, fig. 2, and appendix 1 regarding site locations and numbering; sites are ordered from least to greatest population density. E, estimated value. —, none]

Nutrient, major ion, or physical property

Site number

66 68 23 29 59 62 63 60 64 69 61 65 67 27

Water temperature, in degrees Celsius 7.5 7 9.5 9.5 6 8.5 9.5 7.5 11.5 9.5 7.5 9 10 10Discharge, in cubic feet per second 6.2 148 44 224 18 4.4 6.3 18 71 7 23 99 8.9 31Specific conductance (laboratory), in microsiemens per centimeter at 25°C 109 156 76 169 68 87 116 60 103 136 86 111 217 242

Oxygen, dissolved, in milligrams per liter 11 11.8 11 10.7 12 11 11.1 12 10.2 11.8 11.6 10.5 10.2 11.3Field pH, in standard units 7.7 7.5 7.7 7.6 7.4 7.8 7.6 7 7.9 7.9 7.6 7.4 7.3 7.7Laboratory pH, in standard units 7.8 7.8 7.7 7.8 7.7 7.7 7.9 7.7 7.7 7.9 7.5 7.4 7.3 7.6Ammonia as nitrogen, in milligrams per liter as N .002 .003 .009 .004 <.002 .002 .003 .002 .004 <.002 .003 .005 .012 .024Nitrite as nitrogen, in milligrams per liter as N .001 <.001 .001 .002 <.001 <.001 .001 <.001 .001 .001 <.001 .001 <.001 .009Ammonia as nitrogen plus organic nitrogen, in milligrams per liter as N .14 E .10 <.10 E .10 E .10 .11 .11 E .10 E .10 .17 E .10 <.10 .18 .17Ammonia plus organic nitrogen, in milligrams per liter as N .23 E .09 E .07 E .09 E .09 .14 .19 E .09 .1 .15 .16 .14 .26 .22Nitrite and nitrate, dissolved, in milligrams per liter as N .412 .106 .064 .356 .282 .194 .437 .287 .098 .505 .318 .228 .462 .629Total phosphorous, dissolved, in milligrams per liter as P .022 <.004 <.004 .009 .004 .008 .008 <.004 .008 .009 .014 .012 .026 .022Phosphorous, dissolved, in milligrams per liter as P <.004 <.004 <.004 <.004 <.004 <.004 .005 <.004 <.004 <.004 <.004 <.004 .004 .008Orthophosphorus, in milligrams per liter as P .004 <.001 .001 <.001 <.001 .002 <.001 <.001 .002 .002 .001 <.001 <.001 .004Organic carbon, dissolved, in milligrams per liter as C 1.9 .9 .9 1.3 .6 1.4 2.8 .8 1.2 3.1 1.4 1.9 3.9 4Organic carbon, suspended, in milligrams per liter as C .2 <.20 .2 <.20 — — <.20 <.20 .2 — .2 <.20 — .4Calcium, dissolved, in milligrams per liter as Ca 17 24 13 25 9.6 12 17 11 14 20 12 16 25 29Magnesium, dissolved, in milligrams per liter as Mg 3.2 3.4 1.7 3.9 1.6 2.1 2.9 1.9 2 3.3 2.1 2.7 5.3 6.8Sodium, dissolved, in milligrams per liter as Na 1.7 2.2 1.1 2.6 1.2 1.5 2.1 1.4 1.3 2.7 1.9 1.8 5.9 7.5Potassium, dissolved, in milligrams per liter as K .21 .28 .21 .36 .15 .17 .32 .21 <.10 .35 .28 .32 .58 1.1Chloride, dissolved, in milligrams per liter as Cl .46 .34 .2 1.4 .33 .37 1.3 .96 <.10 2.8 2 1.7 9.6 15Sulfate, dissolved, in milligrams per liter as SO4 11 29 13 25 8.9 14 13 7.9 14 16 8.9 14 17 22

Fluoride, dissolved, in milligrams per liter as F <.10 <.10 <.10 <.10 <.10 <.10 <.10 <.10 <.10 <.10 <.10 <.10 <.10 <.10Silica, dissolved, in milligrams per liter as SiO2 10 5.7 6 6.8 7.3 7.3 8.5 7.7 6 8.7 7.8 6.7 11 11

Iron, dissolved, in micrograms per liter as Fe <10 <10 <10 E 7.5 <10 <10 13 <10 28 12 E 5.8 46 200 160Manganese, dissolved, in micrograms per liter as Mn <3.0 <3.0 <3.0 22 <3.0 3.9 3.4 <3.0 5.6 E 2.1 <3.0 16 70 67Dissolved-solids residue at 180°C, in milligrams per liter 87 96 53 99 49 62 78 53 68 99 55 74 129 151

Specific conductance (field), in microsiemens per centimeter 129 164 87 177 74 96 124 82 101 151 93 120 206 251
Appendix 5. Trace-element concentrations in streambed sediments collected from 14 sites in Anchorage in 1999

[Site number: See fig. 1, fig. 2, and appendix 1 regarding site locations and numbering; sites are ordered from least to greatest population density. <, below detection limit]

Trace element

Site number

66 68 23 29 59 62 63 60 64 69 61 65 67 27

Aluminum, in percent 4.6 6.8 6.5 7.1 6.5 6.3 6.1 5.7 6.3 6.4 5.7 6.3 6.3 5.8

Antimony, in micrograms per gram .6 1.2 1 1.2 1.4 1 1 1.2 .9 .9 1.2 1 1.4 2.4

Arsenic, in micrograms per gram 15 10 10 11 7.7 6.2 8.8 7.9 9.6 7.6 7.6 9.1 15 26

Barium, in micrograms per gram 410 660 720 650 650 670 660 600 610 670 580 610 550 600

Beryllium, in micrograms per gram 1 2 1 2 1 1 1 1 1 1 1 1 1 1

Bismuth, in micrograms per gram <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1

Cadmium, in micrograms per gram .2 .2 .2 .2 .2 .2 .3 .2 .2 .2 .2 .3 .7 1

Calcium, in percent 2.8 1.7 2.1 1.8 2 1.9 2 1.9 2 1.9 2 2 2.2 2

Cerium, in micrograms per gram 29 49 46 49 41 44 42 44 45 43 45 44 43 32

Cobalt, in micrograms per gram 14 19 21 20 18 15 16 16 17 15 16 18 20 20

Chromium, in micrograms per gram 81 95 110 110 72 62 63 85 99 64 91 110 110 120

Copper, in micrograms per gram 38 48 50 61 47 44 41 43 40 37 45 49 53 64

Europium, in micrograms per gram <1 1 1 1 1 1 1 1 1 1 1 1 1 1

Gallium, in micrograms per gram 9 16 14 16 13 12 12 12 13 12 13 14 12 13

Gold, in micrograms per gram <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1

Holmium, in micrograms per gram <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1

Iron, in percent 3.5 4.2 4.2 4.4 3.9 3.5 3.8 3.4 4 3.6 3.5 4 4.9 5.9

Lanthanum, in micrograms per gram 14 24 22 24 20 22 21 23 21 21 23 22 20 18

Lead, in micrograms per gram 10 11 11 15 10 10 10 10 11 10 11 17 61 110

Lithium, in micrograms per gram 21 40 32 40 31 30 31 28 28 31 28 30 29 27

Magnesium, in percent .9 1.2 1.2 1.4 1 .94 .96 .98 1.1 .99 1 1.2 1.1 1.2

Manganese, in micrograms per gram 1,300 870 970 1,300 1,000 1,200 1,500 1,100 860 1,300 1,100 970 1,400 2,600

Mercury, in micrograms per gram .16 .18 .81 .16 .34 .21 .25 .29 .61 .22 .36 .33 .17 .17

Molybdenum, in micrograms per gram 2 1 2 1 1 3 2 1 1 2 1 1 1 2

Neodymium, in micrograms per gram 15 23 21 24 20 21 21 22 20 21 22 21 19 17

Nickel, in micrograms per gram 29 43 44 46 32 28 30 35 40 31 36 62 47 50

Niobium, in micrograms per gram <4 6 6 7 5 6 6 6 6 6 6 6 5 8

Phosphorus, in percent .22 .12 .14 .13 .16 .13 .14 .12 .13 .12 .12 .12 .18 .15

Scandium, in micrograms per gram 11 17 17 18 15 14 15 15 16 15 15 17 15 16

Selenium, in micrograms per gram 5.8 .9 2.2 .8 2.1 2.1 2.1 1.5 1.4 1.6 1.5 1.1 1.4 1.1

Silver, in micrograms per gram .2 .2 .3 .2 .2 .2 .2 .2 .2 .2 .2 .2 .2 .5

Sodium, in percent 1.2 1.7 1.6 1.8 1.6 1.8 1.7 1.7 1.8 1.8 1.7 1.7 1.8 1.6

Strontium, in micrograms per gram 270 270 240 270 240 270 250 250 250 260 250 240 240 250

Sulfur, in percent .2 .06 .1 .06 .09 .1 .12 .06 .1 .08 .07 .1 .18 .2

Tantalum, in micrograms per gram <1 1 <1 1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1

Thorium, in micrograms per gram 2 4 4 4 3 3 3 4 4 4 4 4 4 3

Tin, in micrograms per gram <1 1 1 2 <1 1 <1 <1 1 <1 <1 1 2 4

Titanium, in percent .33 .43 .52 .47 .47 .48 .4 .36 .49 .41 .41 .4 .37 .39

Uranium, in micrograms per gram 2.4 1.6 2.1 1.6 1.5 1.5 1.5 1.4 1.7 1.4 1.5 1.7 1.4 1.3

Vanadium, in micrograms per gram 100 140 140 150 120 110 110 120 120 110 120 130 120 130

Ytterbium, in micrograms per gram 1 2 2 2 2 2 2 2 2 2 2 2 2 2

Yttrium, in micrograms per gram 15 20 20 22 20 18 19 20 19 19 20 20 18 20

Zinc, in micrograms per gram 82 100 100 120 110 110 140 110 92 160 120 180 420 590

Organic carbon, in percent 16 3.16 6.32 2.9 7.26 5.51 6.74 5.07 4.99 4.3 5.71 4.63 6.93 6.04

Inorganic carbon, in percent .13 .02 .03 .02 .03 .03 .06 .02 .02 .03 .03 .02 .04 .05

Total, organic plus inorganic carbon,

in percent

16.2 3.18 6.35 2.92 7.29 5.54 6.8 5.09 5.01 4.33 5.74 4.65 6.97 6.09