U.S. GEOLOGICAL SURVEY

Open-File Report

Water-Quality Characteristics of the

Slate and East Rivers, Colorado,

During the Winter Recreational Season,

December 1996

By Norman E. Spahr and Jeffrey R. Deacon

Denver, Colorado

1998

98–279
U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Thomas J. Casadevall, Acting Director

The use of firm, trade, and brand names in this report is for identification purposes only and does

not constitute endorsement by the U.S. Geological Survey.

For additional information write to: Copies of this report can be purchased

U.S. Geological Survey

Information Services

Box 25286

Federal Center

Denver, CO 80225

from:

District Chief

U.S. Geological Survey

Box 25046, Mail Stop 415

Denver Federal Center

Denver, CO 80225–0046
FOREWORD

The mission of the U.S. Geological Survey

(USGS) is to assess the quantity and quality of the

earth resources of the Nation and to provide information that will assist resource managers and policymakers at Federal, State, and local levels in making sound

decisions. Assessment of water-quality conditions and

trends is an important part of this overall mission.

One of the greatest challenges faced by waterresources scientists is acquiring reliable information

that will guide the use and protection of the Nation’s

water resources. That challenge is being addressed by

Federal, State, interstate, and local water-resource

agencies and by many academic institutions. These

organizations are collecting water-quality data for a

host of purposes that include: compliance with permits

and water-supply standards; development of remediation plans for specific contamination problems; operational decisions on industrial, wastewater, or watersupply facilities; and research on factors that affect

water quality. An additional need for water-quality

information is to provide a basis on which regionaland national-level policy decisions can be based. Wise

decisions must be based on sound information. As a

society we need to know whether certain types of

water-quality problems are isolated or ubiquitous,

whether there are significant differences in conditions

among regions, whether the conditions are changing

over time, and why these conditions change from

place to place and over time. The information can be

used to help determine the efficacy of existing waterquality policies and to help analysts determine the

need for and likely consequences of new policies.

To address these needs, the U.S. Congress appropriated funds in 1986 for the USGS to begin a pilot program in seven project areas to develop and refine the

National Water-Quality Assessment (NAWQA) Program. In 1991, the USGS began full implementation of

the program. The NAWQA Program builds upon an

existing base of water-quality studies of the USGS, as

well as those of other Federal, State, and local agencies.

The objectives of the NAWQA Program are to:

• Describe current water-quality conditions for a

large part of the Nation’s freshwater streams,

rivers, and aquifers.

• Describe how water quality is changing over

time.

• Improve understanding of the primary natural

and human factors that affect water-quality

conditions.

This information will help support the development

and evaluation of management, regulatory, and monitoring decisions by other Federal, State, and local

agencies to protect, use, and enhance water resources.

The goals of the NAWQA Program are being

achieved through ongoing and proposed investigations

of 59 of the Nation’s most important river basins and

aquifer systems, which are referred to as study units.

These study units are distributed throughout the

Nation and cover a diversity of hydrogeologic settings.

More than two-thirds of the Nation’s freshwater use

occurs within the 59 study units and more than twothirds of the people served by public water-supply systems live within their boundaries.

National synthesis of data analysis, based on

aggregation of comparable information obtained from

the study units, is a major component of the program.

This effort focuses on selected water-quality topics

using nationally consistent information. Comparative

studies will explain differences and similarities in

observed water-quality conditions among study areas

and will identify changes and trends and their causes.

The first topics addressed by the national synthesis are

pesticides, nutrients, volatile organic compounds, and

aquatic biology. Discussions on these and other waterquality topics will be published in periodic summaries

of the quality of the Nation’s ground and surface water

as the information becomes available.

This report is an element of the comprehensive

body of information developed as part of the NAWQA

Program. The program depends heavily on the advice,

cooperation, and information from many Federal,

State, interstate, Tribal, and local agencies and the

public. The assistance and suggestions of all are

greatly appreciated.

Robert M. Hirsch

Chief Hydrologist

FOREWORD III
CONTENTS V

CONTENTS

Foreword.............................................................................................................................................................. III

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

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

Approach...................................................................................................................................................................... 3

Acknowledgments ....................................................................................................................................................... 4

Characterization of Water Quality ......................................................................................................................................... 4

Quality-Assurance Results........................................................................................................................................... 4

Physical Characteristics ............................................................................................................................................... 4

Chemical Characteristics ............................................................................................................................................. 6

Benthic Algae .............................................................................................................................................................. 6

Summary and Conclusions .................................................................................................................................................... 8

References.............................................................................................................................................................................. 8

FIGURES

1. Map showing study area and sampling sites...................................................................................................................... 2

2. Graph showing nitrite plus nitrate concentrations in samples collected at East River below Cement Creek and

Colorado River below Baker Gulch......................................................................................................................... 3

3–4. Photographs showing:

3. Typical ice-free center of flow, Slate River, December 1996 .................................................................................. 4

4. Complete ice and snow cover on Slate River at site S3, December 1996 ............................................................... 4

5–6. Graphs showing:

5. Discharge and specific-conductance measurements and concentrations of selected chemical constituents ........... 5

6. Load computations and concentrations of ash-free dry mass and chlorophyll a and b........................................... 7

TABLES

1. Synoptic sites on the Slate and East Rivers ....................................................................................................................... 3
Abstract 1

Abstract

Periods of population influxes during

winter recreation occur simultaneously with

periods of extreme low flow in many Rocky

Mountain areas. The ability of streams to assimilate additional nutrient loading is reduced by the

low-flow conditions. Low-flow water-quality

characteristics of the Slate and East Rivers, which

drain the Crested Butte area, were investigated in

December 1996. Six sites were chosen for evaluation—four on the Slate River and two on the

East River—to assess water-quality conditions,

including nutrient (nitrogen and phosphorus)

concentrations and algal biomass, during a

24-hour period. Discharge in the Slate River

ranged from about 18 to 30 cubic feet per second,

and discharge in the East River downstream from

the mouth of the Slate River was about 80 cubic

feet per second. Chemical concentrations in

water in the Slate and East Rivers generally were

dilute with specific-conductance values of 175 to

300 microsiemens per centimeter and alkalinity

values of 40 to 110 milligrams per liter during

low-flow conditions.

Dissolved oxygen was at or near saturation

at all measurements sites. Ammonia nitrogen

concentrations increased downstream from

Crested Butte and Mount Crested Butte in the

Slate River and then returned to background

concentrations in the East River. Concentrations

of nitrite plus nitrate nitrogen increased downstream from the Crested Butte area, probably

associated with the nitrification of the ammonia to

nitrate, and concentrations then were diluted in

the East River downstream from the confluence of

the Slate River. Phosphorus concentrations also

increased slightly in the reach downstream from

Crested Butte and Mount Crested Butte.

Algal biomass values increased downstream from the Crested Butte area, decreased to

low values in a subsequent reach, and then

returned to higher values downstream. Biomass

values were similar to those found in unenriched

to moderately enriched streams. The lower

biomass and higher phosphorus values occurred

in a reach that was covered completely with ice

and snow. Algal biomass in this reach was

extremely low, probably due to the absence of

light. The biomass values upstream and downstream from this reach were moderately high

and probably resulted in the lower phosphorus

and possibly somewhat lower nitrogen, which

suggests that benthic algae may be partially

controlling the nutrient levels through assimilation and uptake. When light conditions restrict

algal growth and subsequent loading occurs,

the concentrations of phosphorus increase

slightly. Once the physical limitation (absence of

light) is removed, the biomass responds with a

corresponding decrease in phosphorus.

The nutrient concentrations were low and

well below stream standards. Nutrient increases

were measured downstream from Crested Butte

and Mount Crested Butte, and these increases

resulted in an increase of algal biomass. Overall

results indicate that, at the present time, the Slate

and East Rivers can assimilate winter low-flow

nutrient loads.

Water-Quality Characteristics of the Slate and

East Rivers, Colorado, During the Winter

Recreational Season, December 1996

By Norman E. Spahr and Jeffrey R. Deacon
2 Water-Quality Characteristics of the Slate and East Rivers, Colorado, During the Winter Recreational Season, December 1996

INTRODUCTION

The Upper Colorado River (UCOL) study unit

is 1 of 59 National Water-Quality Assessment

(NAWQA) study units. Hydrologic and water-quality

assessments of the UCOL study unit began in 1994 by

the U.S. Geological Survey (USGS). The environmental setting of the UCOL is described by Apodaca

and others (1996). One of the high-priority waterquality issues in the UCOL study is the effect of

increasing urban and recreational land uses in such

areas as Crested Butte (Driver, 1994), which is drained

by the Slate and East Rivers. A network of 14 surfacewater monitoring stations was established in the

UCOL (Spahr and others, 1996). The East River below

Cement Creek (site E2, fig. 1) is one of these stations

and was established to monitor water quality in an area

of increasing urban and recreational land use.

Many areas within the Rocky Mountains experience large influxes of people during winter and

summer periods for recreational pursuits. For example,

skier visits to Crested Butte Ski area during the 1996–

97 season were about 519,000 (Colorado Ski Country,

written commun., 1997), whereas, the estimated 1996

population for Crested Butte and Mount Crested Butte

was about 1,400 (Colorado State Demography, written

commun., 1997). Although skier visits are not broken

down by shorter periods, the common perception is

that holiday periods have larger influxes of people. In

the winter, during low-flow conditions, the ability of

rivers to assimilate additional nutrient loading may be

reduced. Effects within the stream could include

increases in nutrient levels (nitrogen and phosphorus)

and algal productivity. Although moderate stream

eutrophication can increase the productivity of sport

fisheries, excessive benthic-algal growth in streams

thought to be pristine is visible evidence of waterquality contamination to recreational users.

Although water-quality information has been

collected during several studies in the Slate and East

River Basins during the last 20 years, there is a lack of

water-quality data for streams in the Crested Butte

area during the low-flow winter season. In 1995,

several local entities, in cooperation with the Upper

Gunnison Water Conservancy District and the USGS

NAWQA program, established the East River below

Cement Creek station to develop long-term baseline

water-quality data in an area of increasing urbanization. Using data from the UCOL NAWQA program, a

comparison of nitrite plus nitrate concentrations in

samples from the East River below Cement Creek and

from a site in Rocky Mountain National Park (Colorado River below Baker Gulch) indicated that concentrations in the East River generally are greater,

particularly during winter periods (fig. 2). The Colorado River below Baker Gulch is a site chosen to

represent background (minimally impacted) conditions with respect to land-use effects on water quality.

To further investigate water-quality conditions in the

basin upstream from the East River below Cement

Creek site, a winter low-flow synoptic was designed

and implemented by the UCOL NAWQA during

December 1996.

The Slate River is the major tributary to the East

River. It originates in the mountains northwest of

Crested Butte and directly, or by tributary input, drains

Crested Butte, Mount Crested Butte, and the Crested

Butte Ski Area. The Slate River empties into the East

River about 9 river miles downstream from Crested

Butte. The East River continues downstream for about

Figure 1. Study area and sampling sites (numbers refer to

table 1).
INTRODUCTION 3

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

0.26

10/01/95 01/01/96 04/01/96 07/01/96 10/01/96 01/01/97

East River below

Cement Creek

Colorado River

below Baker Gulch

NITRITE PLUS NITRATE, IN MILLIGRAMS PER LITER

Date

Smooth Line

MInimum Reporting Level

13 river miles to the confluence with the Taylor River

to form the Gunnison River. This report presents

nutrient and general chemistry characteristics of the

Slate and East Rivers in the Crested Butte area and the

relations between nutrients and algal biomass during

low-flow, cold-temperature conditions. Six sites were

chosen to characterize water-quality conditions in the

Slate and East River Basins (fig. 1). Measurements

were made during the December 1996 low-flow highrecreation-use period.

 Approach

Water-quality and algae samples were collected

at four sites on the Slate River and two sites on the

East River (fig. 1 and table 1). Site S1 was the most

upstream site on the Slate River and was upstream

from point-source inputs. Site S1 was assumed to

represent background conditions for the synoptic.

Site S2 on the Slate River was located downstream

from the Crested Butte Wastewater Treatment Facility.

Site S3 was located downstream from Washington

Gulch (a tributary to the Slate River), which receives

point-source inputs from the Mount Crested Butte

area. Site S4 was located on the Slate River just

upstream from the mouth. Sites on the East River

included site E1, upstream from the mouth of the Slate

River and site E2, the East River below Cement Creek

UCOL NAWQA site. From five to six water-quality

samples were collected at each site during a 24-hour

period beginning on December 28, 1996, at about

11:00 am.

Field measurements for each sample included

dissolved oxygen, water temperature, specific conductance, pH, and alkalinity. Discharge was measured or

estimated by using stage values for each sample. A

monitor for hourly measurements of dissolved oxygen

was operated at site S2 for the 24-hour period. Water

samples were collected using an equal-width-increment method and were processed onsite for preparation for shipping to the USGS National Water-Quality

Laboratory. Laboratory analysis of the samples

consisted of determination of concentrations of major

ions, ammonia nitrogen, organic plus ammonia

nitrogen (dissolved and total), nitrite nitrogen, nitrite

plus nitrate nitrogen, phosphorus (total and dissolved),

orthophosphate phosphorus, and dissolved and

suspended organic carbon. All constituents, unless

specifically designated as total, were analyzed for the

dissolved phase, which is defined operationally as

water that has been filtered through a 0.45-micrometer

filter. At each site, one sample was collected for

analysis of algal biomass and chlorophyll a and b.

Algae samples were collected from the stream reach

Figure 2. Nitrite plus nitrate concentrations in samples

collected at East River below Cement Creek and Colorado

River below Baker Gulch [smooth line, locally weighted

scatterplot smoothing (LOWESS)].

Table 1. Synoptic sites on the Slate and East Rivers

Site

number

USGS station

number Site name

River miles

upstream

from mouth

of East River

Number

of waterquality

samples

S1 385237106583300 Slate River at Crested Butte 21.6 5

S2 09111500 Slate River near Crested Butte 20.8 6

S3 385106106571000 Slate River above Baxter Gulch 17.5 6

S4 384853106541500 Slate River near mouth 12.8 6

E1 09110500 East River near Crested Butte 16.6 6

E2 09112200 East River below Cement Creek 9.5 6
4 Water-Quality Characteristics of the Slate and East Rivers, Colorado, During the Winter Recreational Season, December 1996

by brushing the entire surface of five representative

rocks and determining the surface area by the foil

template method (Porter and others, 1993). Three

field blank samples were processed for concentrations

of chemical and nutrient constituents. One replicate

sample was collected for concentrations of chemical

and nutrient constituents, algal biomass, and chlorophyll a and b.

Acknowledgments

The authors express their thanks to Bob

Boulger, Jeff Foster, Dennis Smits, Cory Stephens,

Rick Szmajter, and Kirby Wynn for assistance with

data collection during the 1996 Christmas holiday

season. We also would like to thank Alene Brogan for

manuscript preparation, John Evans for graphics

assistance, and Carol Anderson for the editorial effort.

CHARACTERIZATION OF WATER

QUALITY

Quality-Assurance Results

Three field blank samples, one by each

measurement team, were processed during the 24-hour

synoptic. Field blank samples provide information on

bias or the potential for contamination of analytical

results by sample collection, processing, shipping, and

analysis. A field blank sample is processed using water

that is free of the analytes of interest (blank water).

The blank water is passed through all the sampling

equipment and then processed as a typical waterquality sample. Analytical results from the field blank

samples showed that concentrations for all constituents discussed in this report were at the minimum

laboratory reporting level. Based upon these results,

sample collection, processing, shipping, and analysis

did not appear to contaminate samples or produce bias

in the results.

One replicate sample was collected at site S4 for

chemical analysis, and one replicate sample was

collected at site E2 for ash-free dry mass (AFDM) and

chlorophyll a and b. Replicate samples provide information on the variability of analytical results due to

sample collection, processing, shipping, and analysis.

Results of the replicate sample for nutrients showed

that the differences in concentrations between the

environmental and replicate samples were about

0.01 mg/L (milligram per liter). Computed AFDM

values for the replicate samples differed by 2 g/m2

(grams per square meter). The chlorophyll a and b

replicates had identical concentrations. The variability

as determined by differences between the environmental and replicate samples is low and does not affect

results presented in this report.

Physical Characteristics

Shore and anchor ice was prevalent throughout

streams in the study area; however, the center of flow

was open to the atmosphere for most of the sites

(fig. 3). The Slate River was covered completely with

ice and snow for about 2 miles upstream and downstream from site S3 (fig. 4). A cross section from bank

to bank was cut through the snow and ice to allow

sampling at site S3. Streamwater temperature ranged

Figure 3. Typical ice-free center of flow, Slate River,

December 1996.

Figure 4. Complete ice and snow cover on Slate River at

site S3, December 1996.
CHARACTERIZATION OF WATER QUALITY 5

10

20

30

40

50

60

70

80

90

22 20 18 16 14 12 10 8

125

150

175

200

225

250

275

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325

350

22 20 18 16 14 12 10 8

30

50

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90

110

130

22 20 18 16 14 12 10 8

7.0

7.5

8.0

8.5

9.0

22 20 18 16 14 12 10 8

7

8

9

10

11

12

22 20 18 16 14 12 10 8

 0

0.05

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0.30

22 20 18 16 14 12 10 8

 0

0.05

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22 20 18 16 14 12 10 8

0.005

0.010

0.015

0.020

0.025

0.030

0.035

22 20 18 16 14 12 10 8

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

22 20 18 16 14 12 10 8

 0

0.2

0.4

0.6

0.8

1.0

1.2

22 20 18 16 14 12 10 8

MRL

MRL

MRL

MRL

SITE NUMBER

RIVER MILES UPSTREAM FROM MOUTH OF EAST RIVER RIVER MILES UPSTREAM FROM MOUTH OF EAST RIVER MOUTH OF SLATE RIVER

SITE NUMBER

SI S2 S3 E1 S4 E2 SI S2 S3 E1 S4 E2

Slate

East

MRL

Maximum

Median

Minimum

Minimum Laboratory

Reporting Level

Maximum

Median

Minimum

MEDIAN BELOW MRL

MEDIAN BELOW MRL

DISCHARGE, IN CUBIC FEET PER SECOND CONDUCTIVITY, IN MICROSIEMENS PER

CENTIMETER AT 25 DEGREES CELSIUS

ALKALINITY, IN MILLIGRAMS PER LITERPHOSPHORUS, IN MILLIGRAMS PER LITER TOTAL PHOSPHORUS, IN MILLIGRAMS

 PER LITER

DISSOLVED ORGANIC CARBON, 

IN MILLIGRAMS PER LITER

AMMONIA, IN MILLIGRAMS PER LITER NITRITE PLUS NITRATE, 

IN MILLIGRAMS PER LITER

pH, IN STANDARD UNITS DISSOLVED OXYGEN, IN MILLIGRAMS

PER LITER

from 0 to 3 degrees Celsius. With the frigid night-air

temperatures and subsequent warming during the day,

water moved into and out of ice storage making estimation of stage-discharge relations difficult and

requiring the estimation of some discharge values

during the 24-hour period. Discharge values ranged

from about 18 ft3/sec (cubic feet per second) at the

upstream site (site S1) to about 80 ft3

/sec at the downstream site (site E2). Results of discharge estimates

and measurements are presented in figure 5.

Figure 5. Discharge and specific-conductance measurements and concentrations of selected

chemical constituents.
6 Water-Quality Characteristics of the Slate and East Rivers, Colorado, During the Winter Recreational Season, December 1996

Chemical Characteristics

Results of chemical analyses are presented in

figure 5. Specific conductance and alkalinity values

reflect the dilute nature of the water and tend to be

lower in the Slate River than the East River (fig. 5),

probably due to different geology. Measurements of

pH ranged from 7.2 to 8.8 and also are slightly greater

in the East than the Slate River. Dissolved oxygen

was at or near saturation at all sites during the 24 hours

of sampling. All dissolved-oxygen values were greater

than the 6-mg/L instream standard (Colorado Department of Public Health and Environment, 1995).

Concentrations of ammonia nitrogen are low

(near the laboratory reporting limit of 0.015 mg/L) in

the East River. Concentrations in the Slate River

increase downstream from Crested Butte and then

gradually decrease at subsequent sites downstream.

After the Slate River empties into the East River, the

concentrations return to low (about 0.015 mg/L)

levels. Un-ionized ammonia concentrations as

computed using the method described by Willingham

(1976) are less than 0.001 mg/L, which is less than the

0.02 mg/L instream standard (Colorado Department of

Public Health and Environment, 1995), at all synoptic

sites. Nitrite plus nitrate concentrations peak at site S3,

probably as a result of the ammonia nitrogen being

converted to nitrate. Concentrations of nitrite plus

nitrate at site S4 are similar to those at site S3, and

concentrations are diluted downstream from site S4 in

the East River (site E2). Concentrations in the East

River upstream from the Slate River (site E1) are low

(about 0.09 mg/L) and similar to the background

concentrations in the Slate River (site S1). Measured

concentrations are less than the 10 mg/L instream

standard (Colorado Department of Public Health and

Environment, 1995) for nitrate. Phosphorus concentrations, which are low (0.01 to 0.03 mg/L) in the Crested

Butte area, are largest at site S3 and then return to

concentrations similar to background downstream in

the study area. Dissolved organic carbon (DOC)

concentrations increase slightly in the Slate River

below Crested Butte before returning to lower concentrations in the East River. Minimum DOC values for

small watersheds are reported to be on the order of

0.5 to 1 mg/L (Meybeck, 1982; Meybeck and others,

1989), and concentrations from this synoptic were

within this minimum range.

Loads of nitrogen and total phosphorus were

estimated for each site using constituent concentrations and measured (or estimated) discharge (fig. 6).

Inorganic nitrogen loads were calculated using the

sum of ammonia plus nitrite plus nitrate nitrogen

concentrations. Inorganic nitrogen load is low [4.5 and

8.4 kilograms per day, (kg/d)] at the upstream sites S1

and E1. Inorganic nitrogen load increases to about

21 kg/d at site S3 probably as a result of point sources

discharging to the Slate River and tributaries. The load

decreases slightly between sites S3 and S4. Downstream from site S4, the Slate River enters the East

River. Inorganic nitrogen load in the East River downstream reflects the load in the Slate River plus the load

contributed from the upper East River, site E1

(upstream from the Slate River) plus additional loads

from unmeasured tributaries.

 Phosphorus loads were calculated using the

concentrations of total phosphorus. When the total

phosphorus concentration was less than the laboratory

reporting limit (a less-than value), a value of one-half

the reporting limit was used in the load computations.

Phosphorus loads are low (about 0.2 kg/d) at site S1.

The load increases slightly between sites S1 and

S2 and increases again between sites S2 and S3. These

increases probably are the result of point-source

discharges. Phosphorus load decreases between

sites S3 and S4. The load in the East River downstream from the Slate River (E2) is the result of loads

in the Slate River, upstream loads in the East River,

and loads in unmeasured tributaries.

Benthic Algae

Algae that are attached to submerged surfaces

(benthic algae or periphyton) are affected by waterquality conditions at a specific location. Algae integrate water-quality conditions that occurred at a site

during the previous several weeks to months,

depending on antecedent hydrologic conditions. The

abundance of algae increases when nutrient concentrations, light conditions, velocity, and other factors are

favorable, but decreases because of hydrologic disturbance (scouring and washout during periodic high

flows), chemical toxicity, and biological factors such

as grazing by invertebrates and fish (Porter and others,

1993).

Benthic algal biomass is the mass of algal

organic matter that has accumulated on an area of

substratum over time. Many methods of measurement

are used to estimate algal biomass, and each have rela-
CHARACTERIZATION OF WATER QUALITY 7

0

5

10

15

20

25

30

22 20 18 16 14 12 10 8

 0

0.5

1.0

1.5

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0

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0

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18

22 20 18 16 14 12 10 8

0

2

4

6

8

10

22 20 18 16 14 12 10 8

RIVER MILES UPSTREAM FROM MOUTH OF EAST RIVER

RIVER MILES UPSTREAM FROM MOUTH OF EAST RIVER MOUTH OF SLATE RIVER

SITE NUMBER

SI S2 S3 E1 S4 E2

SITE NUMBER

SI S2 S3 E1 S4 E2

Slate

East

AMMONIA PLUS NITRITE

PLUS NITRATE NITROGEN LOAD,

IN KILOGRAMS PER DAY

TOTAL PHOSPHORUS LOAD,

IN KILOGRAMS PER DAY

ASH FREE DRY MASS,

IN GRAMS PER SQUARE METER

CHLOROPHYLL a, IN MILLIGRAMS

PER SQUARE METER

CHLOROPHYLL b, IN MILLIGRAMS

PER SQUARE METER

tive advantages and disadvantages (Stevenson and

others, 1996). AFDM and chlorophyll a and b values

are used in this report to estimate algal biomass and its

relation to nutrients. AFDM (weight of the algae) is

the portion of the sample that is organic or contains

carbon. When detritus (for example, leaves) and

heterotrophic organisms (invertebrates) are not prevalent, AFDM can be a good estimate of algal biomass.

Chlorophyll a is the portion of the sample that represents all algae (for example, green, blue-green,

diatoms), whereas chlorophyll b is the portion of the

sample that represents only green algae.

AFDM and chlorophyll a and b measurements

followed similar patterns among sites (fig. 6). AFDM

ranged from 0.5 to 7.9 g/m2

; chlorophyll a ranged

from 0.1 to 17 milligrams per square meter (mg/m2);

and chlorophyll b ranged from 0.1 to 8.2 mg/m2

.

Typical median biomass values for unenriched,

moderately enriched, and enriched streams for AFDM

are 1.5, 4.8, and 15 g/m2

, respectively (Biggs, 1996).

Typical median biomass values for unenriched,

moderately enriched, and enriched streams for chlorophyll a are 1.7, 21, and 84 mg/m2

, respectively (Biggs,

1996). Sites S1 and E1, which represent background

conditions for this study, were characterized by low

algal biomass and low concentrations and loads of

nutrients. Nutrient loads increase from sites S1 to S2

and again from sites S2 to S3, because of inputs to the

stream between these sites. Site S2 is located just

downstream from a point-source discharge in Crested

Butte. Increases in AFDM and chlorophyll a and b

concentrations at site S2 may be a response to the

nutrient discharges. Values for AFDM and chlorophyll

a and b at site S3 were low and similar to background

Figure 6. Load computations and concentrations of ash-free dry mass and Chlorophyll a and b.
8 Water-Quality Characteristics of the Slate and East Rivers, Colorado, During the Winter Recreational Season, December 1996

conditions at site S1. Site S3 was completely iced over

prior to the synoptic study. The ice cover limited availability of sunlight for the algae. Although nutrient

loads were highest at this site, algal biomass did not

increase with nutrient concentrations, probably

because of insufficient light to sustain algal growth.

The low (0.5 g/m2) algal biomass at site S3 may be

associated with the higher dissolved nutrients concentrations. If the stream reach at site S3 were exposed to

light, higher algal productivity would be expected,

resulting in higher rates of nutrient uptake, and thus

relatively lower concentrations of dissolved nutrients.

Once the streamflow opened back to the atmosphere,

increases in AFDM and chlorophyll a and b were

observed at site S4 (mouth of Slate River) with a

corresponding decrease in dissolved nutrients. Algal

uptake may be a major factor for the decrease in the

dissolved nutrient load at this site. When comparing

site S4 to site E2, decreases were observed in AFDM

and chlorophyll a and b. Nitrogen and phosphorus at

site E2 reflect the combined loads of the Slate and East

Rivers (fig. 6) and any algal uptake. A decrease in

chlorophyll a and an increase in chlorophyll b from

site S2 to S4 (fig. 6) may indicate that the composition

of the algal community shifts and contains a larger

abundance of green algal species. Cursory identification of this sample indicated an abundance of Ulothrix,

a green algal taxon (Dev Niyogi and Stephen Porter,

USGS, oral commun., 1997). Studies have shown that

growth of Ulothrix is stimulated by phosphorus, and

higher densities of Ulothrix can effectively remove

phosphorus from the system (Tate and others, 1991;

Tate and others, 1995).

SUMMARY AND CONCLUSIONS

The Slate and East Rivers near Crested Butte,

Colorado, are affected by increasing urbanization and

recreational uses. Increases in population due to

winter-recreation activities can produce added nutrient

(nitrogen and phosphorus) loads to receiving waters

during low-flow periods. Slightly higher nitrite plus

nitrate concentrations were measured during low flow

in the East River as compared to a site with minimal

land-use effects on water quality (Colorado River

below Baker Gulch). Water-quality and algae samples

were collected at six sites within the Slate and East

River Basins to investigate potential increases in nutrients and algal biomass during peak winter-recreation

use. Dissolved oxygen was at or near saturation at all

sites. Nutrient concentrations and loads were low but

increased along the Slate and East Rivers. State

standards for concentrations of nitrate and un-ionized

ammonia were not exceeded during this study period

at any sites. The abundance of algae increases when

nutrient concentrations, light conditions, velocity, and

other factors are favorable. Biomass generally

responded to higher nutrient loads in the study area

with the exception of site S3. Ice cover at this site

limited availability of sunlight, which affected the

algal biomass. Algal-biomass values at the synoptic

sites reflected those of unenriched to moderately

enriched streams. Overall results of this study indicated that during 1996 peak winter-recreation use, the

streams were able to assimilate the nutrient loadings.

REFERENCES

Apodaca, L.E., Driver, N.E., Stephens, V.C., and

Spahr, N.E., 1996, Environmental setting and

implications on water quality, Upper Colorado River

Basin, Colorado and Utah: U.S. Geological Survey

Water-Resources Investigations Report 95–4263, 33 p.

Biggs, B.J.F., 1996, Patterns in benthic algae of streams,

chap. 2 of Stevenson, R.J., Bothwell, M.L., and

Lowe, R.L., Algal ecology—Freshwater benthic

ecosystems: San Diego, Harcourt Brace and Company,

Academic Press, p. 31–56.

Colorado Department of Public Health and Environment,

1995, Classifications and numeric standards for

Gunnison and lower Dolores River Basins 3.5.0:

Denver, Colorado Department of Public Health and

Environment Water Quality Control Commission,

35 p.

Driver, N.E., 1994, National Water-Quality Assessment

Program—Upper Colorado River Basin: U.S. Geological Survey Open-File Report 94–102, 2 p. [Water Fact

Sheet]

Meybeck, Michel, 1982, Carbon, nitrogen, and phosphorus

transport by world rivers: American Journal of

Science, v. 282, p. 401–450.

Meybeck, Michel, Chapman, D.V., and Helmer, Richard,

eds., 1989, Global environment monitoring system,

global freshwater quality, a first assessment: World

Health Organization, United Nations Environment

Programme, 306 p.

Porter, S.D., Cuffney, T.F., Gurtz, M.E., and Meador, M.R.,

1993, Methods for collecting algal samples as part

of the National Water-Quality Assessment Program:

U.S. Geological Survey Open-File Report 93–409,

39 p.
REFERENCES 9

Spahr, N.E., Driver, N.E., and Stephens, V.C., 1996,

The Upper Colorado River National Water-Quality

Assessment Program surface-water-monitoring

network: U.S. Geological Survey Fact Sheet

FS–191–96, 4 p.

Stevenson, R.J., Bothwell, M.L., and Lowe, R.L., 1996,

Algal ecology—Freshwater benthic ecosystems:

San Diego, Harcourt Brace and Company, Academic

Press, 753 p.

Tate, C.M., Broshears, R.E., and McKnight, D.M., 1995,

Phosphate dynamics in an acidic mountain stream—

Interactions involving algal uptake, sorption by iron

oxide, and photoreduction: Limnological Oceanography, v. 40, no. 5, p. 938–946.

Tate, C.M., McKnight, D.M., and Spaulding, S.A., 1991,

Phosphate uptake by algae in a stream contaminated by

acid mine drainage, St. Kevin Gulch, Leadville,

Colorado, in Mallard, G.E., and Aronson, D.A., eds.,

U.S. Geological Survey Toxic Substances Hydrology

Program—Proceedings of the technical meeting,

Monterey, Calif., March 11–15, 1991: U.S. Geological Survey Water-Resources Investigations

Report 91–4034, p. 387–391.

Willingham, W.T., 1976, Ammonia toxicity: U.S. Environmental Protection Agency Report EPA–908/3–76–001,

19 p. plus appendixes.