BUIEJQ

PUB aujd >|98J3 3 BURBJ ^O 8LJ1 Ol 

junoyv 'IS sua|9H 

UO

 ; - v&, 
Multiply

METRIC CONVERSION FACTORS

By To obtain

foot (ft) 0.3048

cubic yard (yd3 ) 0.7646

mile (mi) 1.609

square mile (mi2 ) 2.590

cubic foot per second (ft3 /sec) .02832

meter (m) 

cubic meter (m3 ) 

kilometer (km) 

square kilometer (km2 ) 

Cubic meter per second (m3 /s)

120°

-L .__.

Seattle Spokanec

WASHINGTON

 Mount St Helens \

105°

110°

TT

\

MONTANA

Helena

Portland

o

Salem

..1

OREGON , Boise

IDAHO

200

_I

300 MILES

100 200 300 KILOMETERS

COVER: North Fork Toutle River, June 30, 1980. Volcanic mud How breccia 

and debris from the May 18, 1980 eruption of Mount St. Helens (in upper 

right) are as much as several hundred feet thick in the reach shown. 

Photograph by Austin Post, U.S. Geological Survey.
Effects of the Mount St. Helens Eruption 

on the Benthic Fauna of the Toutle River, 

Muddy River, and Pine Creek Drainage 

Basins, Washington

By Luis A. Fuste'

Hydrologic Effects of the Eruptions

of Mount St. Helens, Washington, 1980

GEOLOGICAL SURVEY CIRCULAR 850-H

1981
United States Department of the Interior

JAMES G. WATT, Secretary

Geological Survey

Doyle G. Frederick, Acting Director

Library of Congress catalog-card No. 81-600042

Free on application to Distribution Branch, Text Products Section, 

U. S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304
FOREWORD

On May 18, 1980, after more than a month of earthquakes and eruptions, Mount St. 

Helens, in southwestern Washington, exploded in a volcanic eruption more violent than 

any in the conterminous United States during the 20th century. A lateral blast of hot gas 

and rock particles devastated an area of about 150 square miles on the northern side 

of the mountain knocking down trees to a distance of 15 miles. Several minutes later, a 

giant ash cloud rose to about 60,000 feet. Winds then carried the ash cloud across the 

United States, with heavy fallout and deposition in eastern Washington and parts of 

Idaho and Montana. Earlier, smaller eruptions deposited ash in western Washington 

and parts of Oregon and Canada.

The hydrologic effects of the May 18 eruption have been both widespread and intense. 

During the eruption, a massive debris avalanche moved down the north flank of the 

volcano depositing about 3 billion cubic yards of rock, ice, and other materials in the 

upper 17 miles of the North Folk Toutle River valley. The debris deposits are about 

600 feet thick in the upper reaches of the valley. Following the avalanche, runoff from 

the melted glaciers and snow, and possible outflow from Spirit Lake, caused an extraordinary mudflow in the North Fork Toutle River. The mudflow shattered and uprooted 

thousands of trees, destroyed most of the local bridges, and deposited an estimated 

25,000 acre-feet of sediment in the Cowlitz River channel. A considerable amount of 

additional sediment was conveyed through the lower Cowlitz into the Columbia River 

where it was deposited and formed a shoal that blocked the shipping channel. Mudflows 

also occurred in the South Fork Toutle River and in tributaries on the east flank of 

Mount St. Helens which enter Swift Reservoir.

As part of a concerted Geological Survey effort to study the volcanic event and to 

identify potential hazards, Survey hydrologists have mounted an intensive program to 

document the hydrologic effects of the eruptions. The major initial hydrologic findings 

are reported in this circular series. Quick, useful assessment was made possible only 

because the Survey has long conducted extensive water-resources investigations in the 

affected areas of Washington, Oregon, and Idaho. Hence, there was a well-defined basis 

for identification and documentation of the types and magnitudes of hydrologic changes.

The Geological Survey Circular 850, "Hydrologic Effects of the Eruptions of Mount 

St. Helens, Washington, 1980," consists of individually published short chapters that 

emphasize data collection activities, field observations, and initial comparisons of preand post-eruption conditions. The series will cover hydrologic events occurring on 

May 18 in the Toutle and Cowlitz River; physical alteration of the Toutle River system; 

the chemical and physical quality of precipitation, streams, and lakes affected by volcanic ash fall; ash-leaching studies; and Mount St. Helens glaciers.

Doyle G. Frederick 

Acting Director

III

CONTENTS

Page

Abstract -------------------------------- HI

 __ 1

._ __ __ 2

._ _ 4

._ __ __ 4

Introduction ----------

Description of study areas 

Methods -------------

Results and discussion

Results and discussion Continued 

Pre-eruption ------------

Post-eruption ------------

Miscellaneous sites --------

Summary -----------------

References cited -------------

Page

H4 

9 

11 

13 

13

ILLUSTRATIONS

FIGURE 1. Map showing sampling locations on the North and South Forks Toutle River 

and selected tributaries, and on selected lakes in the vicinity of Mount 

St. Helens _________________________________________

2. Map showing sampling sites on the Muddy River and Pine Creek drainage 

basins ____________________________________________

3. Photograph of Castle Creek, showing the damage caused by the mudflow_

Page

H2

3

5

TABLES

TABLE 1. Taxa and numbers of benthic invertebrates at sampling sites near Mount St. 

Helens, Wash., March 28-30, 1980 _________________________

2. Relative abundance of benthic invertebrate populations before and after the 

eruption of May 18, 1980 _______________________________

3. Stream classification based on functional attributes of benthos samples, 

March 28-30, 1980 ___ __ __ ______ __ _ __ __ _ _____ _

4. Taxa and numbers of benthic invertebrates at sites near Mount St. Helens, 

Wash., July 27-29, 1980 ________________________

5. Stream benthos from miscellaneous sampling sites near Mount St. Helens, 

Wash _________________________________

Page 

H6

8

9

10

12

HYDROLOGIC EFFECTS OF THE ERUPTIONS OF 

MOUNT ST. HELENS, WASHINGTON, 1980

EFFECTS OF THE MOUNT ST. HELENS ERUPTION

ON THE BENTHIC FAUNA OF THE TOUTLE RIVER,

MUDDY RIVER, AND PINE CREEK DRAINAGE BASINS,

WASHINGTON

By Luis A. FUST'E

ABSTRACT

Benthic invertebrate samples were collected in the Toutle 

River, Muddy River, and Pine Creek drainage basins on March 

28-30,1980, to document pre-eruption conditions in watersheds 

surrounding Mount St. Helens, in the event of a major eruption. 

A highly diverse fauna was present at all sampling sites. 

Mayfly and midge (chironomid) larvae were the most numerous 

organisms. The mayflies were most common in the third-order 

streams, and the chironomid larvae were most common in firstand second-order streams. An attempt was made to classify the 

streams studied according to the functional role of organisms 

in the processing of organic matter. It was hypothesized that 

many of the organisms exhibiting multiple functional roles in 

processing of organic matter were predominantly detritivores. 

This classification was then compared to a conceptual stream 

ecosystem model.

The volcanic eruption of May 18 destroyed most, if not all, 

of the benthic fauna present at the sites sampled. The cataclysmic events that took place during the explosion modified 

the topography to the point of eliminating some of the watersheds, while in others the riparian vegetation was scoured out, 

along with the natural substrate of the streams. Of the remaining sites, a very simplified community was found in July, 

composed primarily of midges and blackfly larvae (98-100 

percent of the total number of organisms collected).

The potential for recolonization of stream benthos appears 

to be relatively high because of the creation of new habitats 

near backwaters and pools from springs that were exposed by 

the scouring action of the mudflows. These environments are 

very stable and provide ideal conditions for algal growth and 

for chironomid larvae to thrive.

It is believed that these "seed habitats," in conjunction with 

downstream drift from unaffected tributaries and aerial oviposition by winged adults of aquatic insects, will be the principal sources of stream benthos for the affected streams in the 

coming years. However, successful recolonization will be dependent mainly on substratum and channel stability, with 

some improvement of the chemical quality of the stream 

water.

Several lakes and Coldwater Creek, north of the volcano, as 

well as some lakes formed on top of the mudflow that went 

down the North Fork Toutle River valley, were visited in July 

to document survival of stream and lake benthos and to 

determine whether the new lakes had indications of colonization by stream benthos. Of the lakes visited, Spirit Lake, 

Lake St. Helens, and Tradedollar Lake, the latter had the 

greatest variety of lake benthos. Mosquito larvae (Culex sp.) 

were the only organisms found in Spirit Lake. Coldwater 

Creek contained rat-tailed maggots (Tubifera, sp. (?)) in 

areas of decaying organic matter. Numerous chironomids 

(midges) and blackfly larvae were found on some of the lakes 

on the mudflow area.

INTRODUCTION

On March 28-30,1980, stream benthos (bottomdwelling organisms) and water-quality characteristics were sampled along the main stem and 

various tributaries of the North and South Forks 

of the Toutle River, Muddy River, and Pine Creek. 

These samples were taken to document preeruption conditions in watersheds surrounding

HI
Mount St. Helens, Wash., in the event of a major 

eruption.

Three days after the first signs of volcanic activity (March 27, 1980), volcanic ash had been dispersed onto the northeast, east, and southeast 

flanks of the mountain, on the vegetation and 

snow-covered areas. As a result of the major eruption on May 18 and the cataclysmic events that 

occurred following the eruption, such as pyroclastic flows, ash fallout, and mudflows, the benthic fauna in most of the streams draining from 

Mount St. Helens were decimated or destroyed.

The purpose of this report is to present and discuss the biological data collected on March 28-30 

and compare them with similar information obtained on July 27-29, after the major eruption.

The water-quality data collected are presented in 

another report in this circular series.

DESCRIPTION OF STUDY AREAS

Samples of stream benthos were collected from 

five locations on the main stem of the North and 

South Forks Toutle River and from seven streams 

on the northwest and southeast sides of Mount St. 

Helens (figs. 1 and 2). Prior to the eruptions, all the 

sampling stations had gravel-armored streambeds 

with fairly stable banks. The stream gradient of 

the sampling sites ranged from low gradient (stations 1, 2, 6, 11, 12, and 13) and medium gradient 

(stations 4, 7, 9, and 10) to a very steep gradient 

(stations 3, 5, and 8). Low gradient streams are

122°22'30"' 122°15'. 122°07'30"

KID VALLEY 

(About 5 miles 

downstream) Index map of Washington 

showing study area

DEVASTATION AREA

St Helens Lake

Jackson Creek 

Lake

Spotted Buck 

Mountain

:;v; :£i; '' Mount 

: ::W St Helens *

FIGURE 1. Locations of sampling sites on the North and South Forks Toutle River and selected tributaries, and on selected lakes 

in the vicinity of Mount St. Helens. Stream locations shown are those that existed prior to the May 18, 1980, eruption.

H2
122°00'

FIGURE 2. Location of sampling sites on the Muddy River and Pine Creek drainage basins. Stream locations shown are those that

existed prior to the May 18, 1980, eruption.

defined here as those within a range of 0.014 ft/ft 

to 0.24 ft/ft. Medium gradients are those with a 

slope between 0.038 ft/ft and 0.049 ft/ft, and steep

gradients are those with a slope between 0.067 

ft/ft and 0.075 ft/ft. With the exception of the 

South Fork Toutle River and Pine Creek, the riparH3
ian (riverbank) vegetation was a dense coniferous 

forest. The South Fork Toutle River had a sparse 

riparian vegetation because of extensive logging 

operations over the past 10 years. Pine Creek had 

mainly deciduous vegetation along the streambanks in the sampled reach. The unnamed tributary of the North Fork Toutle (station 3) and 

Studebaker Creek (station 5) had the greatest canopy covers of all sampling sites.

Many of the tributaries of the North Fork Toutle 

River provided several miles of good spawning 

gravel for chinook, chum, and coho salmon (State 

of Washington, Department of Fisheries, 1973). 

The South Fork Toutle River valley is narrow, and 

the tributaries have steep gradients that generally 

limited upstream migration of adult salmon from 

the main stem of the South Fork.

All the sampling stations from which benthic 

invertebrate samples were collected were on first 

(stations 2, 3, and 10), second (stations 4, 5, and 7), 

or third order (stations 6,9,11,12, and 13) streams 

(Strahler, 1957). The stream order was determined 

by using 1:62,500 scale maps.

As a result of the major and subsequent eruptions, all the sampling sites visited in March received mudflows, pyroclastic flows, ash falls, or a 

combination of these. The North Fork Toutle River 

downstream from Spirit Lake was plugged by a 

mudflow which obliterated stations 1-7 (fig. 1). 

Part of the hot mudflow went down the Castle 

Creek drainage basin, uprooting and felling trees 

and thus creating an impoundment close to its 

original confluence with the North Fork Toutle 

River. The entire basin was stripped of all vegetation (fig. 3). Similar mudflows occurred in Pine 

Creek, Smith Creek, and the Muddy River drainage basins (fig. 2).

A mudflow on the South Fork Toutle River destroyed sampling sites 8 and 9 (fig. 1). The river's 

main stem was divided into two channels, one having turbid water resulting from a large amount of 

suspended sediment being transported downstream and the other having virtually no suspended sediment.

A reconnaissance visit was made on July 28 to 

the main stem of the North Fork Toutle River near 

Kid Valley and to Coldwater Creek (fig. 1). The 

North Fork carried a heavy load of sediment from 

natural sources and sediment brought into suspension by dredging operations. In the Coldwater 

Creek valley, two lakes near the confluence with 

the North Fork Toutle River were formed by

mudflow impoundment. Farther upstream, an impoundment similar to the one at Castle Creek was 

created from piles of trees stripped from the 

drainage basin by the force of the volcanic blast 

and washed down into the channel.

METHODS

With the exception of stations 1, 8, and 9, replicate samples of benthic invertebrates were collected with a Surber sampler (0.210-mm mesh 

openings) at every sampling station. Each pair of 

replicate samples was then combined, preserved 

with 70-percent ethanol, and brought to the U.S. 

Geological Survey laboratory in Tacoma, Wash., 

for processing, sorting, and identification. Synoptic or reconnaissance samples were collected from 

stations 1, 8, and 9. For these samples, benthic 

organisms were collected either with a dip net or 

by examining all the types of habitat present 

(wood, leaves, pools, riffles, etc.) and sampling randomly from each. The majority of the organisms in 

the samples were identified to the genus level and, 

in many cases, to the species level when adult 

specimens were collected from the snowbanks next 

to the streams.

RESULTS AND DISCUSSION

PRE-ERUPTION

A total of 87 taxonomic groups (taxa) were 

identified from all sampling stations (table 1). The 

most abundant organisms were two genera of 

mayfly, Baetis and Iron, and chironomid (midge) 

larvae. Nearly all the sampling sites had a rich 

faunal community when sampled in March. Biological samples collected at stations 1, 8, and 9 

were considered to be nonrepresentative for comparative purposes because they were only reconnaissance samples. Station 7, Castle Creek, had 

the richest faunal assemblage, with a total of 53 

taxa. Station 3, the unnamed tributary of the 

North Fork Toutle River, had the least fauna, with 

12 taxa.

Mayflies were dominant (greater than 50 percent) in the third-order streams (stations 6,11,12, 

and 13), and the chironomid larvae (table 2) were 

dominant (greater than 46 percent) in the firstand second-order streams (stations 2, 3, 4, 5, and 

10). The only exception was Castle Creek (station 

7), a second-order stream in which mayflies were 

dominant (62 percent).

The streams visited may be classified (Vannote 

and others, 1980) on the basis of the functional role 

benthic invertebrates have in processing organic

H4
FIGURE 3. Castle Creek, showing the damage caused by the mudflow.

matter (table 3) from terrestrial and instream 

sources. Theoretically, stream ecosystems follow a 

transition from headwaters to higher stream orders in the utilization of organic matter to sustain 

the benthic invertebrate communities. Headwaters are typically more dependent upon terrestrial 

inputs of particulate organic matter, especially 

coarse particles (CPOM) such as leaf litter, with 

little or no photosynthetic production of organic 

matter in the stream. CPOM-feeding invertebrates, or shredders, and detritivores feeding 

on fine particulate organic matter (FPOM, generally less than 1 mm in diameter), or collectors, are 

the dominant macroconsumers. In the higher 

order streams there is more dependency upon organic production by photosynthesizing algae and 

aquatic plants, along with input of FPOM from 

upstream. This conceptual idea of stream ecosystems is imperfect, because factors such as 

channel shape, watershed slope, discharge, terrestrial input characteristics, and the light and thermal regimes of the streams introduce variations 

into the model (Cummins, 1975). In spite of these 

watershed influences, this continuum concept

H5
TABLE l. Taxa and numbers ofbenthic invertebrates at sampling sites near Mount St. Helens, Wash., March 28-30, 1980

Station _np. 1* 2 3 4 5 6 7 8* 9* 10 11 12 13 

Taxonomic 

category

Phylum Arthropoda 

fClass Insecta

Order Ephemenoptera 

Family Siphlonuridae

Ameletus sp. 9 1 1 

Family Ephpmerel1idae

Ephemerella delantala 21 1

E. hystrix~ 15 1

T. heterocaudata heterocaudata 2 8 9 12 1 3

t. subaenus DruneTTa1

T. flavilinel 48 38 46 41 28 229 2 11 46 17

F. subgenus Ephemerella 1 ? 7 25 149

T. inermis 2 

Family Leptophlebiidae

Paraleptophlebia sp. 1 11 1 

Family Baetidae

Baetis sp. 100 217 353 85 314 2,459 95 108 209 604 355 

Family Heptageniidae

Iron sp. 118 47 254 7 165 157 3 23 74 216

Irpnpdes sp. 2

Rhithrogena sp. 6

CinygmulaTp. 1 51 28 2 35 86 1 18 132 93 

f Order plecoptera

Family Peltoperlidae

Yoraperla brevis 1 1 

Family Taeniopterygidae

Taenionema sp. ' 54 85 1 46 31 3 48 42 

Family Nemouridae

Malenka sp. 1 1 2

R. coloradensis 61 5

F. calI ifornica 2

loycdina potteri 1

Prostoia sp. 23 12 1 25 22 2 49 19

Ostrpcerca sp. 1

Zapada coTombiana 1

Tapada oregonensis group sp. 9 

Family Capniidae

Capnia elongata 3

Capnia complex sp. 

Family Leuctridae *

Paraleuctra occidental is #1 2

Paralcuctra occidental is 92 I

Despaxia sp. 1 3 

Family Chloroperlidae 1 ^

Alloperla sp. 2 1 11 39 162 

Family Perlodidae

Kogotus sp. 311 1 i

Megarcys sp. 21 ^ ^

Skwala sp. 2 39 6 2 21 1 65

Order Trichoptera

Family Hydropsychldae j

Hydropsyche sp. 1 2

Parapsyche sp. 1 1

Arctopsyche sp. ^ 

Family Glossosomatidae I

Glosspsoma sp. ^

Family Rhyacophilidae 11 1 ?0 2? 56 15 

( Rhyacophila spp. 15 5 24 24 216 <-.

FanTiV Brachycentridae ^

Micrasena sp. ^ 3 

Family Limnephilidae

Dicosmpecus sp. 1 15 1 57

(Higophlebiodes sp. 11 219

ITIostoeca sp. 1

Ps.ychoql'ypha sp. * \ 

v Nepphylax sp. ^ 

MDrder Diptera

Family Tipulidae 2

Antocha sp. zos 22

Hesperoconopa sp. 4 125

Dic'ranota sp. * 22

Pedicia "sp. 2

Mo1 ophi 1 us sp. 

Family Tlephariceridae 2 1

Bibiocephala SP. A I 4 l 

Family Deuterophlebiidae 1

Deuterophlebia sp.

H6
TABLE 1. Taxa and numbers ofbenthic invertebrates at sampling sites near Mount St. Helens, Wash., March 28-30,1980 Continued

Station no.

Mosquitoes,

Konomic 

ategory

1 Family Dixidae 

Dixa sp. 

FamTTy Simulildae 

Simulium sp. 

Prosimul ium sp.

1* 2 3

1

67 20 1.228 

1 5 45

« 5 6 7 8* 9* 10 11 1? 13

3 1 1 

5 42 134

Gymnopais sp. 

Family Ceratopoqonldae 

Family Chironomidae 

Family Psychodldae

Haruina sp. 

F ami ly Taban i dae 

Family Empidldae 

CIinocera sp. 

ChelifeFa sp. 

i Hemerodromia sp. 

Beetles / Ordei7 Coleoptera 

^ Family Elmidae 

Vorder Collembola

SpMngtalls < f"11. 1/ Hypoqastryridae

j Family Entomobrydae

V Family Sminthruridae

23 391 505 578 161

2

1

295 1,037

3

30

2

10

1

2,277 609

1

159 356

1

289

23

5

3

Class Crustacea 

Scuds /Order Amphipoda

\ Family Gammarldae 

Seed Shrimp Order Ostracoda 

Order Copepoda 

Suborder Cyclopolda 

Suborder Harpacticoida 

n s" Order Cladocera 

/Class Arachnoidea 

Subclass Arachnida 

Order Acarina**

Family Hydraphantidae 

Subfamily Protziinae 

Protzia subgenus Calonyx sp. 

Family Torrenticolidae 

Subfamily Torrenticolinae 

Torrenticol a sp. 

Subfamily Testudinacarinae

Testudacarus sp. 

Family Lebertiidae

Lebertia sp. 

Family Sperchontii dae 

Subfamily Sperchontiinae 

Sperchon sp. 

Family Momoniidae

Stygomomonia subgenus ATIomomonia sp. 

Family Hygrobatidae

Atractides sp. 

/Phylum Platyhelminthes 

Flatworms/ C1ass jurbellaria 

v Order Tricladida 

'hylum Annelida 

Class Clitellata

Subclass Oligochaeta 

[Phylum Mollusca 

Class Gastropoda

Family Pleuroceridae

Goniobasis sp. 

Family Planorbiidae sp. II 

sp. f2 

Phylum Nematoda

1 1

5 1

8

Aquatic 

Earthworms

Snails*

11

1

5

21

4

4

3

2

104

10 3

12

5

Roundworms

2 1 82

Total number of taxa 

Total number of organisms

9 26 12 23 25 20 53

118 862 820 2,666 380 996 4,890

1 8 21 25 26 35

2 2,420 795 509 1,41« 1,358

Explanation:

 Samples collected at stations 1, 8, and 9 are synoptic surveys and by no 

means intended to be used as representative samples.

**Susan Hahn, written commun., 1980. 

Menlo Park CA

U.S. Geological Survey, WRD,

H7
TABLE 2. Relative abundance (percent) ofbenthic invertebrate populations before and after the eruption of May 18, 1980

PRE-ERUPTION (March 28-30, 1980) 

STATION NO. 2 3 4 5 6 7 10 11 12 13

ORDER

EPHEMENOPTERA 37.2 36.8 25.7 37.4 56.0 61.7 14.2 50.9 61.0 51.1

PLECOPTERA 13.7 .4 4.0 .3 8.6 2.6 .6 10.2 7.6 2.3

TRICHOPTERA 2.0 .1 .2 .7 2.6 5.1 .6 4.3 4.1 5.7

DIPTERA 45.6 62.2 69.5 47.3 31.4 27.2 76.9 32.6 26.0 33.3

ACARI .1 .8 .2 .6 1.0 1.3

Others 1.3 .5 .7 .5 .1 .3 .1 1.4 .3 6.3

POST-ERUPTION (July 27-29, 1980)

STATION NO. 2 3 4 5 6 7 10 11 12 13

ORDER

EPHEMENOPTERA ~ 2 z 1.1

LU UJ

PLECOPTERA g _ £ £

US UJ UJ

TRICHOPTERA ~g E^ ^

DIPTERA g^ 99.1 100.0 ^ " 98.6

^ o o

ACARI

Others .9 -- .7

H8
TABLE 3. Stream classification based an functional attributes of benthos samples, March 28-30, 1980

STATION NO.

TROPHIC

CATEGORY

Shredders

Scrapers

Engulfers

Piercers

Collectors

General ists**

Carnivorous

parasitic

2

2.7

6.4

4.3

--

3.8

82.8

.1

3

0.1

--

--

1.0

98.8

--

4

0.5

3.2

.3

--

48.4

47.9

--

5

0.6

.6

4.1

_-

6.0

88.6

--

6

2.5

6.0

.4

__

3.0

88.1

--

7

0.7

.8

1.2

.04

8.6

88.0

.8

10

__

0.5

1.1

-_

1.3

96.4

1.5

11

0.6

9.4

.2

__

2.6

86.2

.6

12

3.6

3.1

.9

__

.3

90.5

.1

13

1.

.

10.

_

6.

79.

1.

4

2

4

_

8

9

3

1. *Merritt and Cummins, 1978

2. **"Generalists" are those organisms having multiple functions in the 

stream benthos by being processors of organic matter drifting from upstream 

sources, consuming attached algae, having predatory behavior, or a combination 

of these depending on the amount of canopy cover and availability of upstream 

food sources.

(Vannote and others, 1980) is useful in understanding the biological processes taking place in 

flowing water.

The sampling sites around Mount St. Helens 

would represent, with some limitations, the headwaters of this conceptual model. On the basis of 

the available literature summarized by Merritt 

and Cummins (1978) and the taxonomic level of 

identification used in this study, many of the benthic invertebrates found appear to exhibit multiple functional roles in the benthic community as 

shredders, engulfers, scrapers, collectors, or piercers. This role will be dependent on food availability, stream habitat conditions, and the season 

of the year. One can hypothesize that these "generalists" (table 3) are composed predominantly of 

detritivores feeding on fine particulate organic 

matter resulting from CPOM-feeding invertebrates in the fall and winter seasons. According to 

this stream ecosystem model, shredders play an 

important role in processing the CPOM. Sampling 

took place during the spring snowmelt and very 

little leaf fall was present in the streams, suggesting that most, if not all, of the leaf fall was 

degraded into fine particulate organic matter in

the fall when these shredders were probably more 

abundant.

Other than suspended sediment introduced into 

the streams from old logging operations on the 

South Fork Toutle River, there was no evidence, 

based on the biological data collected, of any maninduced effects on any of the other sampling sites 

prior to the May 18 eruption.

POST-ERUPTION

Nineteen taxa were identified from the four 

sites remaining after the eruption of May 18 (table 

4). The benthic fauna at stations 7, 9, 10, and 13 

shows a simplified community structure composed 

predominantly of blackflies and chironomids 

(midge larvae; table 2). It was impossible to obtain 

samples from stations 11 and 12 because of the 

excessive amount of fine suspended sediment. The 

stream channel at station 9 in the South Fork 

Toutle River was divided into two channels. One of 

the channels carried virtually no sediment in suspension, while the other carried a high suspendedsediment load. The decrease in abundance of organisms at the remaining sites may be due in part 

to a seasonal change in numbers and kinds of orH9
ganisms, as well as to the effects of the blast such 

as modifications of the streambed substrate and 

alteration of the stream water quality. The survival of several forms of midge larvae (some genera from the subfamily Diamesinae) in the Castle 

Creek drainage basin despite the high temperatures from the mudflow is unusual, because 

they are known to be particularly sensitive to increases in temperature (W. CofFman, Dept. of Biology, University of Pittsburgh, oral commun.,

1980). These larvae are apparently characteristic 

of streams and did not come from nearby Spirit 

Lake. How they survived is presently unknown. 

The mudflows and pyroclastic flows left the 

headwaters devoid of living vegetation. Any algae 

or mosses growing on the rocks were also scoured 

away. The absence of tree canopy may have modified the thermal regime of the water, although the 

higher temperatures found in July were normal 

for that time of the year (Collings and Hill, 1973).

TABLE 4. Taxa and numbers ofbenthic invertebrates at sites near Mount St. Helens, Wash., July 27-29, 1980

Clear Muddy

Station No.__________________12345678 9 9_____10 11 12 13 

Taxonomic 

category

Phylum Arthropoda 

Class Insecta

Order Ephemenoptera 

Family Ephemerel1idae

Ephemerrella subgenus Ephemerella 1 

Family Baetidae

Baetis sp. 31 3 

Family Heptagenii dae

Iron sp. 1 

Rhithroqena sp. 1 

Cinygmula sp. 1

Order Diptera

Family Tipulidae , /> v / ~ ^ 

Dicranota sp. 1

Ormosia sp. 1 £ 

Family Simuliidae t t; {3

Simulium sp. £ £ 6 ^19 

Family Ceratopogonidae iC i2 o 

Atrichopogon sp. 2 X 1 ~° 

Family Chironomidae ± 103 z 17 7 7 J2 249 

Family Empididae § §1 s"

Chelifera sp. § 1 

Family Dolichopodidae ^ 

Family Muscidae 1 2 \ 

Order Coleoptera "^ ^ ' 

Family Hydrophilidae

Subfamily Hydrobiinae (Crenitis sp.?) 1 

Family Elmidae 

Order Hemiptera 

Family Corixidae

Subfamily Corixinae 

Order Hymenoptera 

Class Arachnoidea 

Subclass Arachnida 

Order Acarina

Family Sperchontiidae 

Subfamily Sperchonti i nae

Sperchon sp. 1 

Acari IT 1

Phylum Nematoda 2

Total number of taxa 

Total number of organisms

3 

105

13 

37

2 

8

2 

8

6 

274

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Before the eruption, there was a normal succession of pools and riffles at sample sites. After the 

cataclysmic event, riffles predominated, with a 

high suspended-sediment concentration (more 

than 3,000 milligrams per liter) and considerable 

bed material being transported downstream (average thickness of 3-9 inches in the Muddy River 

in July), making the stream-bottom substrate extremely unstable for a person to stand in the middle of the stream. These conditions created an unsuitable environment for the survival of stream 

benthos, owing to the scouring action of the sediment. The excessive turbidities prevented algae 

from growing on rocks; thus, instream food 

sources were absent also. As of July, there were no 

mechanical means of holding back the suspended 

sediment. It will probably take years for the 

affected streambeds to reach equilibrium again. It 

is also highly probable that removing trees that 

have fallen across the riverbeds may affect the 

natural process.

The most significant changes in the streamwater chemistry, following the eruption of May 18, 

were sharp increases in total constituents (predominantly the suspended fraction) of sulfate, 

chloride, aluminum, manganese, boron, and iron 

when compared with the stream-water chemistry 

in March, 37 days before the major eruption 

(Klein, U.S. Geological Survey, oral commun., 

1980).

The potential for recolonization of stream benthos appears to be relatively high because of the 

creation of new habitats near backwaters and 

pools from springs. Many of these springs were 

obscured by vegetation and topsoil, prior to the 

eruption of May 18. The scouring action of the 

mudflows exposed the source of many of the 

springs. These provide a stable environment for 

algal growth and bottom-dwelling organisms. 

Such "seed habitats" will probably be one of the 

major sources of stream benthos for the affected 

streams in the coming years. Therefore, successful 

recolonization of the stream benthos will depend 

principally on substratum stability followed by 

improvement of the chemical quality of the stream 

water.

MISCELLANEOUS SITES

A reconnaissance survey of benthic invertebrates was made at several miscellaneous sites on 

June 6 and July 27-29, 1980 (table 5). The sites 

included: (1) Tradedollar Lake, Spirit Lake, and 

Lake St. Helens; (2) Coldwater Creek; (3) one of the

newly formed ponds near Elk Rock Lake; (4) the 

two new channels of the North Fork Toutle River 

below the mud dam; and (5) the main stem of the 

North Fork Toutle River at Kid Valley.

All three lakes were within the blast area of the 

volcanic explosion; thus, most of the surrounding 

vegetation was killed. Logs from some larger trees 

remain in the drainage basins of the lakes. The 

presence of skunk cabbage and various fern species was evidence that new growth was occurring. 

Of the three lakes, Tradedollar Lake had the 

greatest variety of benthos. Spirit Lake and Lake 

St. Helens showed no evidence of zooplankton. 

Mosquito larvae (Culex sp.) were the only organisms found in Spirit Lake. Samples from Coldwater Creek were collected above the lowest wooddebris-mud impoundment. Rat-tailed maggots 

(Tubifera sp. (?)), generally found in areas with 

decaying organic matter, were the only benthic 

invertebrates collected at this site.

One of the newly formed lakes on top of the mud 

dam on the North Fork Toutle River was sampled 

for indications of colonization by stream benthos. 

Numerous chironomid (midge) and blackfly larvae 

were found.

The mudflow that went down the North Fork 

Toutle River and stopped a few miles upstream 

from Camp Baker, a logging camp, divided the 

main stem of the river into two channels, on the 

north and south sides of the mud dam. The benthic 

fauna found in the two channels was somewhat 

similar, in that at least 50 percent of the taxa were 

common to both. The north channel, containing 

clear water, appeared to originate from the southerly flowing tributaries. The south channel is further subdivided upstream into a clear side and a 

muddy side. Samples were collected from the 

"clear" channels, since the muddy water did not 

allow sampling with a Surber sampler. Synoptic 

sampling in the muddy channel did not yield any 

organisms. The muddy side received water from 

the main channel of the North Fork Toutle River, 

seeping from underneath the mud dam, whereas 

the clear south channel received water from Castle 

and Jackson Creek Lakes.

Although no numerical estimates are available, 

the fauna in the North Fork Toutle River near Kid 

Valley retained a higher degree of structural complexity than the other sites sampled in the posteruption surveys. Because of the presence of mature nymph stoneflies (Calineuria californica and 

Pteronarcys princeps), whose large bodies could

Hll
TABLE 5. Stream benthos from miscellaneous sampling sites near Mount St. Helens, Wash. (+=present)

_____Station (see explanation)_________A B C D E F G H ___ ______ 

Taxonomic 

category

Phylum Arthropoda 

Class Insecta 

Order Ephemenoptera 

Family Baetidae

Baetis sp. + + + 

Family Heptageniidae

Cinygmula sp. + 

Order Plecoptera 

Family Pteronarcidae

Pteronarcys princeps + 

Family Perlidae

Calineuria californica + 

Order Trichoptera

Family Hydropsychidae + 

Order Diptera

Family Tipulidae + + 

Dicranpta sp. + 

Family Dixidae

Dixa sp. + 

Family Simuliidae

Simulium sp. + + 

Family Chironomidae + + » » + + 

Family Psychodidae

Chelifera sp + 

Family Syrphidae

Tubifera sp.(?) + 

Family Culicidae

Culex sp. + + 

Family Muscidae » » + 

Order Coleoptera

Family Elmidae + + 

Family Dysticidae » 

Order Collembola

Family Entomobrydae + 

Order Hemiptera 

Family Corixidae

Subfamily Corixinae + + 

Order Homoptera » » 

Class Crustacea 

Order Copepoda

Suborder Cyclopoida » 

Order Dstracoda » + 

Class Arachnoida 

Order Acarina

Acarl II + 

Phylum Annelida 

Class Clitellata 

Subclass Oligochaeta +

Total number of taxa 4 1 242 10 88 

Explanation:

A. Tradedollar Lake - 7/28/80

B. Spirit Lake - 7/28/80

C. Lake St. Helens - 7/28/80

D. Coldwater Cr. above lowest impoundment - 7/28/80

E. Debris pile (red pond) next to Elk Rock Lake - 7/30/80

F. North Fork Toutle River below mud dam (right side) - 7/30/80

G. North Fork Toutle River below mud dam (left side) - 7/30/80

H. North Fork Toutle River near Kid Valley - 6/6/80 and 7/30/80

	(Cinygmula sp. and Calineuria californica were collected on 6/6/80)

H12
easily have been crushed by the exceedingly high 

bedload transported downstream, it is most likely 

that these organisms drifted downstream from 

tributaries outside the blast zone. This is supported by the fact that Pteronarcys normally takes 3 to 

4 years to reach the adult stage. The presence of 

the other organisms at the downstream stations is 

probably due to a combination of downstream 

drift and aerial oviposition (egg laying) by adult 

forms. Adults of aquatic insects were conspicuous 

at all sites visited in July.

It will be essential to assess the degree to which 

stream channel stability will be affected by increasing streamflow and tree salvage operations.

SUMMARY

A highly diverse benthic fauna was present at 

the sampling sites visited during March 27-29, 

1980. Mayflies (Baetis sp. and Iron sp.) and chironomid (midge) larvae were the most numerous organisms. In general, mayfly nymphs were most 

common in the third-order streams, and the chironomid larvae were most common in the firstand second-order streams. If the streams are 

classified on the basis of the role bottom-dwelling 

organisms have in processing organic matter, the 

benthic community found in March was composed 

of organisms exhibiting multiple functional roles 

as shredders, scrapers, engulfers, collectors, or 

piercers. According to the continuum concept, the 

benthic fauna in these first, second, and thirdorder streams are, in theory, composed of detritivores, which are the dominant macroconsumers. 

It is possible to speculate that the majority of 

these "generalists" are detritivores, since most of 

the leaf fall from the previous autumn had already 

disappeared and probably was being utilized as 

fine particulate organic matter. If these streams 

had been sampled in the fall, one might expect a 

higher percentage of shredders in the benthic community, since coarse particulate organic matter 

(leaves, twigs, and other material) would be more 

readily available.

The volcanic eruption of May 18,1980, destroyed 

most, if not all, of the benthic fauna at the sites 

sampled. After the eruption, a much simplified 

benthic community was found, composed principally of blackflies and chironomid larvae. The 

mudflows and pyroclastic flows scoured out the 

vegetation alo^ig with the natural substrate of the 

streams, virtually eliminating all allochthonous

and autochthonous sources of organic matter and 

destroying the diverse habitats found prior to May 

18.

Observations at miscellaneous sites after the 

May 18 eruption indicated that, of the three lakes 

visited (Spirit Lake, Lake St. Helens, and Tradedollar Lake), Tradedollar Lake had the greatest 

variety of lake benthos. A rat-tailed maggot, Tubifera sp., characteristic of environments with decaying organic matter, was found in Coldwater 

Creek.

A slightly higher level of structural complexity 

was observed in the benthic fauna farther downstream than in the upstream sites in the North 

Fork Toutle River. This was attributed mainly to 

downstream drift from the tributaries outside the 

blast zone.

The potential for recolonization of stream benthos appears to be relatively high because of the 

creation of new habitats near backwaters and 

pools from springs. Spring environments are generally stable and provide ideal conditions for algal 

growth and for chironomid larvae to thrive. These 

"seed habitats," downstream drift from unaffected 

tributaries, and winged adults of aquatic insects 

from other areas laying eggs on the water will be 

the principal sources of stream benthos for the 

affected streams in the coming years. Nevertheless, successful recolonization will be dependent mainly on substratum stability and 

further improvement of the chemical quality of 

the stream water.

REFERENCES CITED

Collings, M. R., and Hill, G. W., 1973, The hydrology of ten 

streams in western Washington as related to several Pacific salmon species: State of Washington Department of 

Fisheries Water-Resources Investigations 11-73, 149 p.

Cummins, K. W., 1975, The ecology of running waters: theory 

and practice: in Proceedings of the Sandusky River Basin 

Symposium, May 2-3,1975, Tiffin, Ohio, p. 277-293.

Merritt, R. W., and Cummins, K. W., 1978, An introduction to 

the aquatic insects of North America: Dubuque, Iowa, 

Kendall/Hunt Pub. Co., 441 p.

State of Washington, Department of Fisheries, 1973, Fisheries 

resources in southwest Washington: southwest Washington river basins study: Review Draft, Olympia, Washington, 154 p.

Strahler, A. N., 1957, Quantitative analysis of watershed geomorphology: American Geophysical Union Transactions, 

v. 38, p. 913-920.

Vannote, R. L., Minshall, G. W., Cummins, K. W., Sedell, J. R., 

and Gushing, C. E., 1980, The river continuum concept: 

Canadian Journal of Fisheries and Aquatic Sciences, v. 37, 

p. 130-137.

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U.S. GOVERNMENT PRINTING OFFICE: 1981 -34I-6U /I74