Recovery Patterns i n
Stream Communitie s
Impacted by th e
Mt . St . Helens Eruptio n
by
Peggy Wilzbac h
Thomas L . Dudle y
James D . Hal l
Water Resources Research Institut e
Oregon State Universit y
Corvallis, Orego n
WRRI-83
August 1983
RECOVERY PATTERNS IN STREAM COMMUNITIE S
IMPACTED BY THE MT . ST . HELENS ERUPTIO N
by
Peggy Wilzbach, Thomas L . Dudley and James D . Hal l
Fisheries and Wildlife Department, Oregon State Universit y
Final Technical Completion Repor t
for Project No . A-059-OR E
to
United States Department of the Interio r
Washington, D .C . 2024 0
Project Sponsored by :
Water Resources Research Institut e
Oregon State University
Corvallis, Oregon 9733 1
The research upon which this report is based was financed in part by the U .S .
Department of the Interior, Washington, D .C . (Project No . A-059-ORE), a s
authorized by the Water Research and Development Act of 1978, P .L . 95-467 .
Contents of this publication do not necessarily reflect the views an d
policies of the U .S . Department of the Interior, nor does mention of trad e
names or commercial products constitute their endorsement or recommendatio n
for use by the United States Government .
WRRI-83
August 1983
ABSTRAC T
Recovery patterns of benthic communities in seven small streams impacted t o
varying degrees by the eruption of Mt . St . Helens were examined in winte r
1981-82, particularly in relation to habitat constraints . Overall abundance an d
diversity of the communities were low, and instability of channel banks an d
bottom appears to severely limit re-establishment of biota . Communities appea r
to be undergoing cycles of establishment and denudation in concert with change s
in landscape geomorphology . Disturbance events of varying frequencies were als o
simulated in experimental stream channels to more closely evaluate the respons e
of benthic communities to periodic, non-catastrophic disturbances and to compar e
this with tie response observed to catastrophic perturbation associated wit h
volcanic eruption . Results of simulations suggest that non-catastrophi c
disturances may not play a major role in determining stream community ove r
ecological time because the predictability of these events may have enable d
evolution in species of adaptive responses to cope with disturbance .
Catastrophes appear to have different consequences on stream communities fro m
other disturbances, and should be distinguished from them .
t
FOREWOR D
The Water Resources Research Institute, located on the Oregon State _
.
University campus, serves the St:a.te of Oregon . The, Institute foters ,
encourages andrfa•cilitates water resources research and education inyo .l . viig al l
aspects of the quality and quantity of water available for beneficial use . Th e
Institute administers and coordinates statewide and regional progpmms o f
multidisciplinary research in water and related land resources . The Institut e
provides a necessary communications and coordination link between . the'agencie s
of local, state and federal government, as well as the private sector, and-M e
- broad research community , at universities in the state on matters of water related research . The Institute also coordinates the . inter-disciplinary program
of graduate education in water resources at Oregon State University .
It is Institute policy to wake available the results of significant water= related research conducted in Oregon's universities and colleges . The Instirtut e
neither endorses nor rejects the findings of the authors of such research . I t
does recommend careful consideration of the accumulated facts by those concerned with the solution of water-related problems .
ACKNOWLEDGEMENT S
We thank the U .S .G .S . Cascades Volcano Observatory, Vancouver subdistrict ,
for providing access to and field assistance in sampling sites within th e
restricted area surrounding the volcano . The Weyerhaeuser Company (Tacoma ,
Washington) generously donated use of the Kalama Springs research facilities .
P . Bisson is especially thanked for his assistance in logistical matters .
K .W . Cummins made helpful comments on the manuscript . N .H . Anderson an d
C .P . Hawkins are thanked for use of their data .
ii
TABLE OF CONTENT S
I
1
INTRODUCTION
N
II METHODS
"3
3
Mt . St . Helens
Sites
3
Biological Sampling
3
Habitat Characterization
6- •
6
Kalama Springs
6
Site Description
.
Experimental,Manipulations 7
9
III RESULTS
Recovery Patterns Of Streams Impacted By Mt . St . Helens
Habitat Constraints
9
9
'
:
Biological Properties 13
16
Experimental Simulations of Disturbance
16.
Benthic Invertebrates Periphyton
IV
DISCUSSION
V
LITERATURE CITED
VI
APPENDICES
27
r
29
31
1.
Channel Stability Evaluation
2.
Invertebrate Taxa Collected From. Streams Impacted By
Mt . St . Helens, winter 1981-82 32
33
'rJ
111
LIST OF ' FIGURE S
Figure
Pag e
1.
Map showing location of study sites .
2.
Substrate stability indexed by mean particle size an d
the coefficient of variation .
14
3.
M croinvertebrate density in Ape Canyon since the eruptio n
May 1980) of Mt . St . Helens .
17
4.
Taxonomic richness of macroinvertebrates in Ape Canyon an d
an unimpacted stream since the eruption of Mt . St . Helens .
18
5.
Abundance of macroinvertebrate taxa at Kalama Spring s
three months after disturbance simulations .
19
Proportional biomass of invertebrate functional groups a t
Kalama Springs three months after disturbance simulations .
15
6.
4
LIST OF TABLE S
Table
Page
1.
Impact experienced and physical characteristics of strea m
sites near Mt . St . Helens .
2.
Habitat characterization of the study sites,
winter 1981-82 .
3.
Channel stability evaluation of study sites nea r
Mt . St . Helens, winter 1981-82 .
12
4.
Biological parameters of benthic assemblages in streams
near Mt . St . Helens, winter 1981-82 .
15
5.
Community composition parameters of benthic invertebrate s
prior to and after disturbance simulations at Kalama Springs .
23
6.
Similarity of invertebrate assemblages among channels prio r
to and after three months of disturbance simulations a t
Kalama Springs .
24
iv
5
-
10
I . INTRODUCTIO N
Life cycles of organisms are adapted to the stability of the habitat i n
which they occur, and organisms may evolve a dependency on the disturbance `
regime that regulates habitat persistence . When the ratio of disturbanc e
interval to generation time becomes too large, or when disturbances are extreme ,
organisms are not capable of an adaptive response and cannot persist in, an are a
(Paine 1979) . For this reason, Harper (1977) suggests that catastrophes (large ,
extreme events destroying large portions of the population) should b e
distinguished from disasters (more frequent, locally disruptive influences) eve n
though they form a continuum, because of the different consequences these event s
have on community structure .
The effects on the biota and habitat of small streams near Mt . St . Helen s
from the May 1980 eruption were certainly of catastrophic proportion . Impact s
on stream channels associated with their eruption varied from light to hep y
tephra deposits to pyroclastic flows, mudflows, flooding, and landslides . Th e
effects realized by the biota included tissue abrasion, injury by impact wit h
rock, smothering, burial, and incineration .
Rates-and patterns of recovery of the impacted stream commumities ar e
dependent on the type and intensity of the impact received, and on its spatia l
scale . The areal extent of the damage affects the distance from a source o f
potential colonists, and this may determine the life history and behaviora l
attributes of the initial colonizing species . The type and intensity of th e
impact affects the extent of mortality in the community from the disturbance ,
and may also affect susceptibility of the stream channels to disruption fro m
further perturbation .
Rates of recovery will vary inversely with disturbance intensity, an d
recovery will be faster in streams with refugia than in streams in which al l
internal sources of colonists were destroyed . Return to pre-eruption state s
should occur most quickly in streams in which damage was slight and patchy . Th e
mechanisms and course of succession in this situation may be similar to thos e
occurring an a small spatial scale in 'typical' streams experiencing patch y
disturbance from periodic, non-catastrophic floods .
1
Little is known, however, of the role non-catastrophic disturbances play i n
determining stream community structure . For this reason, evaluation o f
recovery to prior equilibria) conditions is difficult . Periodic disturbance s
- may prevent the attainment of local equilibria, and the species composition of
a
stream community may be continually changing .
The objectives of this study were to examine recovery of benthi c
communities in small streams impacted to varying degrees by the eruption of Mt .
St . Helens, particularly in relation to habitat constraints, and to compare thi s
with the response of benthic communities to periodic, non-catastrophi c
disturbances . The latter was evaluated by simulating disturbance events i n
artificial outdoor channels and monitoring colonization patterns .o f
invertebrates and algae . Use of the Weyerhaeuser's Kalama Springs researc h
facility for this purpose enabled us to examine response of a species sourc e
pool that is similar to that potentially available for recolonization o f
streams impacted by the eruption of Mt . St .-Helens .
II . METHODS
•
Mt . ' St . Helens:,
Sites :
Seven sites, in small streams impacted to varying degrees byavalanc .he-s acme( '
mudflows from the May 1980 and subsequent eruptions of Mt . St . He]•erns, wer e
selected for biological sampling . These were chosen to coincide with sites
.,
established by the U .S . Geological Surve y ' s Cascades Volcano Observatory and the .
U .S . Forest Service for studies of erosion and sediment routing . Site locati-€is.
are shown in Figure 1 and a description of impacts experienced and physica l
characteristics of the streams is listed in Table 1 . One of the sites, on th e
upper Kalama River, received only minor mudflow from the eruption, and it wa s
selected to serve as a control . Biological sampling and habitat swrveys- wer e
conducted one to two times at each site from late October 1981 to early,Febru a .ry~
1982 . Winter access to the sites was limited'to helicopter travel, an d
unfavorable flying weather prevented more frequent sampling . Additional data
from Ape Canyon are provided from short-term intensive "Pulse" studies (funded _
by the National Science Foundation and the U .S . Forest Service) during the '
summers of 1980 and 1981, and from subsequent studies of N . Anderson, and C .
Hawkins (Oregon State University) .
Biological Sampling :
Benthic invertebrates were sampled with a modified Hess, sampler . Three t o
six samples were taken at each site and the substrate type associated•with eac h
sample was noted . Qualitative samples of the invertebrates attached to larg e
woody debris were collected . Samples were preserved in 70% alcabQl, and sorted
-
in the lab . Invertebrate biomass was estimated from length-weight regression s
(Rogers et al . 1976, K .W . Cummins, unpubl . data) . Standing crop of chlorophyll= _
a and phaeophytin was estimated from rock scrapings to provide an indexof al
l
biomass and photosynthetic capacity of the stream sites . Twenty rocks, eac h
8-12 cm in diameter, were collected from each site, and chlorophyll levels fro m
these were measured by acetone extraction (Wetzel and Likens 4.9{7) .
to
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Habitat . Characterization :
Ten line transects were established at b-m meter intervals at each site .
.At each transect3 width of the wetted channel, average depth, water velocit y
(measured at 0 .6 water depth), and substrate type were recorded . Substrate '
categories were broken down into the following : sand (< 1cm), fine gravel (1-2 '
cm), coarse gravel (3-4 cm), pebble (5-8 cm), rubble (9-16 cm), cobble (17-3 2
cm), small boulder (33-64 cm), large. boulder (> 64 cm) and bedrock . Pebbl e
counts (measurement of the length of the longest linear dimension of 10 0
randomly selected sediment particles) were taken at each site to-Provide
estimates of mean particle size . Cherrn.el stability of each site • was evaluate d
with the Pfankuch rating scheme (1975, Appendix 1) . Drainage areas, eleva•tion , , '
and stream length of the sites were estimated from U .S .G .S . topographic maps .
Stream gradients were measured with a clinometer .
Kalama Spring s
Site description :
Three outdoor artificial streams, built and owned by the WeyePir use r
Company, were-used to experimentally investigate the response of stream bentho s
to periodic, non-catastrophic disturbance . The streams are fed by Kalama
Springs, a cold-water spring draining into the Kalama•kiver, in Co►1litz Co . ,
Washington . The three streams are designed as a series of alternating pools ah .d
riffles . The riffles are 6-10 cm deep and 1-2 rn wide, in lengths varying fro m
8-16 m . The pools are 30-50 cm deep . Approximately 10% of the flow from Kalam a
Springs is diverted into a series ;of ponds above the streams . Manipulation o f
wiers between the ponds allows .a constant flow to be maintained in each streams,
Substrate of the channels consists of coarse gravel ., 2-4 cm in diameter, whic h
overlays a fine pumice base . Water temperature is 5-7°C throughout the year .
The streams are open, with no riparian canopy .
6
Experimental manipulations :
Disturbance events were simulated in two of the three channels by releasin g
a flood of water from the holding ponds above the channels and by agitating th e
substrate with rakes . In channel 3, disturbances were simulated once every 2
weeks, and in channel 1, once a month . Channel 2 was left unperturbed . Benthi c
invertebrates and algae were monitored biweekly for 3 months following tM e
initial perturbations in the first three riffles below the .holding pond of eac h
stream . Invertebrates were sampled with a modified Hess sampler, and 8-16 tile s
were placed in each riffle to investigate algal colonization patterns . Thi s
experiment was conducted from June to September , 1982 .
7
III . RESULT S
Recovery Patterns In Streams Impacted By Mt . St . Helen s
Habitat constraints :
Although a survey of habitat parameters based on one or two sampling date s
can be misleading, the data provide some indication of constraints imposed b y
the physical setting that may limit the colonization and persistence of benthi c
invertebrate and periphyton populations .
Measurement of such properties as stream gradient and mean channel widt h
and depth provided a means of scaling the study areas so that comparisons coul d
be made . Values that were measured are all fairly similar among the site s
surveyed (Table 2), indicating that comparisons among sites are appropriate .
Water temperatures reflect the time of day and ambient temperatures at sites o n
the dates at which these were measured, and values are included only to indicat e
that these sites were not thermally affected at this time from volcani c
activity . Discharge values that were estimated are not abnormally high, an d
flows at this time of year were probably stable . Peak flows in streams at thes e
elevations generally occur in late sping - early summer and late fall - earl y
winter . Unit stream power, the rate of doing work of a stream per unit o f
'±1_, where p = density of water, g = acceleration of gravity ,
width, equals
w
Q = discharge, s = slope gradient, and w = channel width (Leopold et al . 1964) .
Channel widths of the impacted sites were somewhat greater than width s
typical of streams of low (first to third) order . This sugggests that th e
channel banks of the sites, except where they are controlled locally by bedrock ,
are being continually eroded and re-worked . Because rooted riparian vegetatio n
and large organic debris are absent from most of the sites, the stabilizin g
influence of these elements on channel morphology is likewise absent .
Pfankuch's (1975) rating scheme was used to evaluate channel stability
of
the impacted streams (Appendix 1) . The value of this approach is that ,
particularly in sites experiencing a variety of impacts associated with th e
eruption, many different attributes of the channel banks and bottom ar e
considered, and are scaled relatively in importance to sediment yield . Whe n
making an evaluation, one is less likely to be influenced by a single obviou s
destabilizing factor . Mass wasting, for instance, appears overwhelming in mos t
streams surrounding Mt . St . Helens, but the presence in some sites of large ,
angular rocks and woody debris provided stabilizing influences .
9
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Channel stability of the impacted sites was generally evaluated as poo r
(Table 3), and ranking of scores reflect reasonably well .the type and magnitud e
of impact experienced . Carbonate Springs received a very poor rating . Strea m
power (indicating its potential to move sediments) of the site is high (Table 2) ;
it is a very active, braided channel cutting a floodplain in the avalanche zon e
of Mt . St . Helens . Lower Maratta Creek received the worst 'score . It, too, i s
located in the avalanche zone and received blast deposits . Upper Maratta ,
0 .5 km upstream from the lower site, received a better stability rating . I t
received blast deposits but lies just outside of the landsl=ide area .
Differences in rating of the two sites largely reflect difference•,$ in channe l
capacity, especially indexed by width to depth ratios, and in-cutting of th e
lower banks . The bank rock content of bath sites i& fairly high, but mu .chr mor e
mud is present in the lower site .
The Pfankuch scheme does, however, possess limitations, particularly i n
relation to biological activity . It was developed for use in the Rock y
Mountains, and was designed to predict horn likely a channel is to yield'sedimen t
at high flows . The scheme is of ecological importance inasmuch as unstabl e
sediments are of ecological importance . Considerable biological activity ca n
occur, however, in unstable streams .
The major limitation of the Pfankuch scheme for evaluation of
channe l
stability in streams of the Pacific Northwest, and perhaps the entire country ,
is the inadequate emphasis it places on the role of wood debris .
The pretenc e
of wood debris on slopes is rated inn the scheme as a destabilizing facto r
because it increases sediment yields when it is moved . The role large woody
debris plays as a major .structural feature within stream channels (Ke1 . le an d
Swanson 1979, Swanson and Lienkaemper 1978) is not considered . Wood debri s
creates a stepped gradient and although it increases stream power locally ove r
channel drops, it decreases stream power throughout a reach ; this lend s
stability to the channel . The 'control site' surveyed on the upper Kalama Rive r
received a stability rating of good . Even though the site has a high st•rea . m
power (Table 2), the presence of considerable in-channel debris and of roote d
'riparian vegetation provides .a geomorphic control that appears to override it s
capacity to move sediments, and the site stability should probably be rated_, .a s
excellent .
'11
Table 3 . Channel stability evaluation of sites near Mt . St . Helens, winter 1981-82 .
Item Rated
Ape Canyon
Upper Muddy
Upper Maratta
Lower Maratta
Carbonate Spgs .
Swift
Kalam a
UPPER BANK S
Slope
6
6
8
8
6
6
2
Mass Wasting
12
9
12
12
12
12
6
Debris Ja m
Potential
2
2
6
8
2
8
6
Vegetatio n
cover
12
9
12
12
12
6
3
Channe l
capacity •
2
3
2
4
4
4
2
Bank Roc k
content
8
4
4
4
8
8
2
'Obstruction
4
4
8
8
2
6
4
Cutting
12
8
12
16
16
4
4
Deposition
12
6
11
12
16
12
4
Ro c.k
_ Angularity
2
2
1
1
2
1
1
Brightness
2
2
1
1
2
1
1
Consolidation
6
4
6
6
6
4
4
Bottom Siz e
Distrib .
16
16
16
16
16
16
8
Scouring ,
Deposition
24
24
24
24
24
20
12
Moss and Algae
4
3
4
4
3
4
2
(Mood Debris)
+
-
+
+
-
++
++
124
102
127
136
131
112
61
LOWER BANK S
BOTTO M
i
TOTAL SCORE
(Poor)
(Fair)
(Poor)
(Poor)
(Poor)
(Fair) (Good,
4
The presence in the channel bottom of large angular rocks, accordin g . to the
Pfankuch evaluation, is considered to be beneficial as these are not easil y
moved . Small, rounded rocks are destabilizing . More critical, , perhaps, from
a biological perspective, is the presence in the substrate of a divers e
assortment of sediment sizes . Because they can interlock, sediments ar e
probably less likely to shift if they are of different sizes . Substrat e
heterogeneity also prbvides habitat complexity, which is positively correlate d
with biological diversity (Gorman and Karr 1978) . As another approach t o
channel stability evaluation, we plotted the coefficient of variation agains t
mean sediment size (Figure 2) . Large sediment sizes with a small coefficient o f
variation may provide substrate stability, but generally large particle siz e
with a large coefficient of variation is indicative of good substrate stability ,
and small particle sizes with a small coefficient of variation indicate les s
stability . Evaluation of the stability of the study sites ; with the exceptio n
of two outliers, corresponds fairly well with the Pfankuch rating . Uppe r
Maratta, because of its large sediment size, and Lower Maratta, because of th e
large CV, were included among the more stable sites (Figure 2) . The strea m
power of these sites may be too low to affect sediment distribution .
Biological Properties :
Overall abundance and diversity of winter assemblages of benthi c
invertebrates in Kalama River relative to the other sites (Table 4) indicat e
that it serves as a reasonable control site .
Composition of the invertebrate fauna present at each site suggests habita t :
conditions and the nature of the food resource base . In Carbonate Springs, onl y
burrowing and/or case-building midges were present (Appendix 2) . This indicate s
that the most likely food resource is fine particulate organic matter (FPOM) ,
which is probably trapped in sediment interstices or in the periphyton film .
The absence of taxa that require stable substrate for attachment, such a s
filter-feeding collectors or large mayfly or caddisfly scrapers, reflect s
substrate instability . That habitat instability may override food resource
-
limitations is suggested by the presence in Carbonate Springs of a fairly hig h
standing crop of chlorophyll-a (Table 4) . The only site in which scrapers wer e
collected is Kalama River, which exhibited slightly lower chlorophyll levels .
Shredders were also abundant and diverse at Kalama River . This reflect s
availability of allochthonous coarse particulate organic matter (CPOM) from th e
13
6
Site
7.
6.
3.
4.
2.
I.
5.
Maotoinvertebrates
Density
Richness
Ka lams
26
Swift
29
U. Maratta
7
L. Maratta
U. Muddy
478
Ape
14
Carbonate Sag, . 9'
14
3
2
1
7
4
7
10
20
Channe l
Stability
Good
Fair
Poor
Poor
Fai r
Poor
Poor
hood
++
++
+
+
+
30
40
Mean Sediment Particle Size (CM) :
Fig . 2 .
Substrate stability indexed by mean particle size and the coefficien t
of variation (CV) . CV = 100 s x
X
Dashed line represents a proposed boundary separating stabl e
and
unstable habitats .
14
VT
1•
a
a)
03 +)
X b
• a)
.O R3
C
1 +-) O ,,
N CM
0
.
CO O 4- L
a
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4- O M -Cl
Ir-1COU O
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Q)
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Y (O E
C Cl)
L U Q) (O d
a) 0 E C 7 a
•I•-)
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C 4- 0 -. a
^a) +) +) Q)
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r- E CO +•) V) ri
W O E
= L •r V)
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▪
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L
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undisturbed riparian zone . A nemourid stonefly was the only shredder found a t
any of the impacted sites . Its food resource probably consists of CPOM burie d
during the eruption and periodically re-excavated as the sediments move about .
The dominant functional group of invertebrates at impacted sites is coile4tors .
Their food source is also derived from buried organic matter as well as fro m
sloughed periphyton . Predators were found only at sites that supported 'a fairl y
high richness of other invertebrate taxa . Because predators are typicall y
long-lived, witp life cycles of one or more years, habitat disruption may als o
prevent their re-establishment in ,impacted stream reaches . The life cycles o f
the dominant taxa (midges) found in the impacted streams are relatively shorter ,
with two or more generations per year .
Apart from burrowing, another strategy enabling persistence in unstabl e
sediments is exhibited by Baetis mayflies, which actively' swim about and utiliz e
FPOM . This was the only species collected at Upper Maratta .
Baetis spp . als o
occurred in Ape Canyon and Upper Muddy .
Taxonomic richness and abundance of the invertebrate fauna appear to b e
fairly closely linked with the evaluation of channel stability of the stud y
sites (Figure 2) . An exception to this relationship is exhibited by Upper
'
Muddy, which has poor stability and a high invertebrate standing crop . No
explanation is readily apparent for this anomaly . Perhaps an unidentifie d
refugia exists nearby that provides a constant source of colonists .
Changes in density (Figure .3) and in taxonomic'rich'ness (Figure 4) o f
invertebrates in Ape Canyon since the 1980 eruption suggest that re establishment of fauna is a temporary phenomenon, and that a succession o f
stable and non-stable cycles may occur in any given reach until the overal l
landscape instability is lessened . Complete recovery of stream communite s
affected by the eruption may be on a time scale of up to 1 0 2 years- or longer .
Experimental Simulations of Disturbanc e
Benthic Invertebrates :
Two general trends were observed in the abundance along channels of tax a
that appeared consistently in samples . One trend is that the abundance of som e
taxa was much greater at the termination of the experiment in the unperturbe d
channel (Channel II) than in the two disturbed channels (Figure 5a) . This tren d
was exhibited by a number of taxa, occurring in different functional groups .
16
!I
rI
APE CANYON
E
r
t
1
I
0
1
!
r
0
c
10 0
r
I
I
I
t
I
l
1
I
1
1
I
l
1
1
~
11
I
i
10
1
I
I
I
I
II
I
r
I
1
0
1
•
1
0
5
10
1
1
15
20
Martine Since Eruption
Fig . 3 .
Macroinvertebrate density in Ape Canyon since the eruption (Ma y
1980) of Mt . St . Helens . Except for sample at 19 months, data ar e
from Anderson and Hawkins (unpubl .) .
17
i%
L
•
MI
rp
N ftj
IC)
-
-CI
Q)
N w 0)
I
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•
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+3
QC N
C 01 L0
2
)-2
Cal
ItJ
O.
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S%
0
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rt Z
R7 +Rf3 • r
a
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(U +)
fn
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ip
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a - >
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r
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r t -csa
+.1
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c a)
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f~f •r L
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18
Abundance of Taxa (Control > Disturbed )
6-
asb
Yoraper/a
Plecoptera
600- °' b
Ostracoda-C o
Gr
2
200-
He/icosama
Gastropoda
Gr
b
3-
Simuliidae-C o
,
Ecclisomyia
Trichoptera
Gr
15-
5-
c .
A//oiler/a
Plecopter a
Co
20 V
a, b
Perlodidae
Plecopter a
Pr
b
TurbeHaria-Pr
100-
Channel ]l
Fig . 5a .
Abundance of macroinvertebrate taxa at Kalama Springs three month s
after disturbance simulations, (groups for which control
>
disturbed) . Channels are ordered along an axis of increasin g
disturbance frequency . Co = collector, Sh = shredder, Gr = graze r
(scraper), Pr = predator .
19
Abundance of Taxa (Control > Mud > Most Disturbed )
Poro/eptop'i/ebia I5°
Micrasema
Ephemeroptera
Co
Trichopter a
Sh
50 -
0 150-
Harpactacoid a
Co
300-
a,b
Hydracarino
Acari- P r
I00 -
Sae Hs
Ephemeroptera
Co
2-
5i
-Channel II
Dicranota
Tipulida e
Pr
4
I
II
I
Fig . 5b . Abundance of macroinvertebrate taxa at Kalama Springs three month s
after disturbance simulations, (groups for which control > mod
>
disturbed) . Channels are ordered along an axis of increasin g
disturbance frequency . Co = collector, Sh = shredder, Gr = graze r
(scraper), Pr = predator .
20
a)
L L
( O
to U
a)
L r
a) r
a) C
4) C O
4- M17 U
Rs s
U
N
s
o
+) . L)
C 0 "a
a)
0
II
.
010
N
Q7 V
C
•r r a)
LO U
d L. C
6
rn i-a ms
Cs
( Z W r i w ) ssowOig
r0E OU
co
4
)
r
s v)
b U •r
•r
L
s
d
)
+) 3 a
its L •rC
ms o N L
X
ro 4- a)m aIZ)
}) N L it)
aU
C
i~
o •r
r0 L.
L 0)4 a)
L
U
N
0 La)
a)
~
•I•)
^
}
L (J ) C b
a) C a) L
>
0 -,a •r
I
4-3 rq
L I
O
L r0
N
0
o
(g L ~ u ~
0
A
w • /Jagwnu) ~(4isuaa
a)
CC
v
t
U
rtt E0rt3cD
E v) a) L
o a)U :co
o0a
)L
U a)
0)
a) 0
L a)
V)
L
C4.3
a)
0 V) 0
J:) •r L. _a
11
<-0 Ov)
U
u)
21
Three of these taxa, the snail
Helicosoma, Ostracods ; and the planari a
Orotophela, were very abundant in the unperturbed channel, attaining densities .
of 1800-6000 individuals m- 2 . In some instances, the abundances of taxa wer e
also greater in the moderately perturbed channel (I) than in the frequently
.
perturbed ore (III) (Figure 5b) . Included here are the baetid .mayflies an d
mites that are among the initial colonists- of heavily impacted
streams-
near~ .Mt . _
St . Helens .
A second trend was exhibited by a few taxa in which abuncia'rce was greate r
at the termination of the experiment in one or both of the disturbed channel s
than in the unperturbed channel (Figure 5c) . This pattern may represent a
•.
release in numbers, either from the elimination of competitors o r , predators, o r
an increase in resource availability that occurs in the presence o f
non-catastrophic disturbance events . This trend occurred among the orthocla d
midges, which largely dominated the community of the disturbed channels ,
reaching densities of up to 15,000 individuals per m 2 , but it is statisticall y
significant only for biomass (p < .05, ANUVA) and not for density . A n
unidentified orthoclad species occurred in the most frequently perturbed channe l
that was fewer in number but ' much larger in size than the speci-es' inhabitin g
other channels, and this accounts for the greater biomass observed in thi s
channel . The clam Pisidiurnnever occurred in any sample taken from th e
unperturbed channel .
Total density, biomass, and diversity, of the invertebrate assemblages were
-
similar enough among channels prior to disturbance simulations to, make . u s
confident that the differences we observed following .distu .rbance were
attributable to the disturbance regime (Table 5) . Both density and 'diversity o f
the assemblages after the initiation of the disturbance events were higher i n
the channel never perturbed, and were somewhat greater in the channel mor e
frequently perturbed, than in the more moderately perturbed . The diversity in
the moderately perturbed channel (I) declined after one month of disturbanc e
simulations, suggesting that one might observe in this channel a hyperboli c
curve of species diversity over time, , similar to that observed in othe r
successional communities (Connell and'Slatyer 1977) . A decline in di .rsity,•- •
over time was not observed in channel III, probably because - distulbence s
occurred too frequently to allow the colonization of competitiNily superio r
taxa . Biomass following disturbance simulations was -remerkably - 4imilar amon g
22
.4
Table 5 . Community composition parameters of benthic invertebrates prior t o
and after disturbance simulations at Kalama Springs . Values represent ,
means of six samples within each channel .
Channe l
II
I
II I
Increasing Disturbance +
Before Disturbance
Density/0 .1 m 2
3043
346 4
378 .0
386 .9
453 .6 1
1317 .6
1451 .0
1832 .8 '
2989
1343
178 7
Biomass/0 .1 m 2
M .U .I .*
2441
After Disturbance (1 mo . )
Density/0 .1 m 2
Biomass/0 .1 m 2
M .D .I .*
287 .8
333 .0
296 . 8
1447 .1
604 .3
240 .8 1
After Disturbance (3 mos . )
Density/0 .1 m 2
2800
Biomass/0 .1 m 2
M .D .I .*
1758
195 7
246 .4
238 .2
244 . 0
1483 .2
357 .2
240 .8 1
*M .D .I . = McIntosh Diversity Index = N- s E n i 2
i= 1
channels (Table 5) . This suggests that compensatory changes occur in strea m
community structure that act to maintain a constancy, in at least some aspects o f
community function .
The structural resemblance of pairs of channels with each otaier wa s
estimated by use of the Curtis percentage similarity measure, whi€h ranges from '
0 to 100 . A value of 100 indicates complete similarity . Al .] channels wer e
structurally similar prior to disturbance (Table 6) . After three months, channe l
II, the unperturbed channel, was very different from both channels I and III .
Similarity here was altered both because of the dominance of orthoclad midges i n
the disturbed channels and because of the loss in these .channels of some
sensitive taxa, such as the predatory perlodid stoneflies and the grazin g
Invertebrate assemblages were partitioned into functional groups to enable
an assessment and comparison among .channels of the trophic as well as taxonomi c
structure . Functional group designations were assigned according to Merritt an d
Cummins (1979) . The proportional biomass of shredders three months afte r
23
{
Table 6 . Similarity of invertebrate assemblages among channels prior t o
and three months after disturbance simulations at i(alama . Springs .
PS*
Before Disturbance
After Lei s_turbanc e
Channel s
1,2
.769
.28 8
2,3
.806
.42 7
1,3
.941 . .
.835
*PS is the Curtis Percentage Similarity Measure .
PS
200 E MIN ( N IH, N IK )
s
(NHI + N KI )
-kJ
disturbance was small in all channels (Figure 6) . This was expected, as th e
resource base in the channels is largely autotrdphic . The collector component ,
largely comprised of midges, dominated the disturbed channels ., and a iargei,
relative increase in the predator functional group was observed in .the .
unperturbed channel . The proportional biomass of grazers (scrapers) in the
unperturbed channel was also somewhat larger than in the disturbed channels . .
The functional group structure of the Invertebrates colonizing heavily impacted ,
unstable streams near Mt . St . Helens is similar to that observed in th e
experimentally disturbed streams . Scrapers and predators vau1r in low
abundance in these streams, because the large and stable substrate require1-b y
scrapers for attachement is absent, and the abundance and predictability of foo d
resources required by both groups is low .
Periphyton :
The early colonizing species in all channels was predowimantly Diatoma
hiemale var . mesodon, which forms a gelatinous matrix after one month .
Successive algal taxa included the filamentous xanthophyte Tribonema and th e
chrysophyte Hydrurus foetidus .
Diatoma was most abundant in the mos t
frequently perturbed channel . Chlorophyll-a levels of the periphyto n
assemblages were highly variable within and among channels,_,ranging from 1 .3 t o
over 400 Mg m- 2 . The standing crop of chlorophyll-a was generally greater, bu t
not significantly so, in the unperturbed than in the perturbed channels .
24
N
rO
a
N
0
MI -0
a)
0
L CT)H L
r
}1
r N
C a) • r
O C
•r C
4-) (O N
O
N
u)
E
0
CO
L. ~ .C
a)
EU
> •r
C N
•r
1/)
C
0
a) .
4- V a)
O C a)
rts 3
N .0
t!1 L O
E •F)
O N
•r • r
_o 'Q L
a)
r L >
rO a) a )
C 4.)
04- •4 (O a)
4.)
.
LN L
a..
0
O.
0
C:Lo
25
IV . DISCUSSIO N
A lower density and diversity of invertebrate . fa na, both taxonomically and 16
trophically, were observed in stream channels in wkiich disturbance events wer e
simulated than in•an unperturbed channel . There is some indication, howe%sr• ,
that some community properties, notably biomass, remain constant among differen t .
disturbance regimes .
These findings suggest that non-catastrophic disturbances may not play a
major role in determining stream community structure over ecological time . Non - r - `
catastrophic disturbances in many streams are fairly predictable events, an d
species may have evolved behavioral and other adaptations to deal with them .
Adaptations relevant to competitive situations, be it in usurping resources o r
in withstanding attacks from natural enemies that might be necessary in th e
absence of disturbance, may not have evolved .
We are reluctant to generalize from our findings, however, to dismiss th e
potentially large role that non-catastrophic disturbance may play in streams ,
because . a number of factors not considered in our experiment
will
also affec t
the role disturbance plays . The spatial distribution of disturbance is one o f
these . Effects of non-catastropic disturbance in most streams are patchy i n
nature as some microhabitats are more immune to disruption than others, . A give n
.disturbance regime produces a distribution
of patch ages, and the effect on th e
community is properly the summation of patch . effects . And, critically,_ the
.
exact effect of periodicity . of disturbance events is unresolved . Disturbance s
icalo f
at a rate of once per month, relative to the annual hydrographs ty p
streams in the Pacific Northwest, a-re probably too frequent to allow more slowl y
dispersing colonists to enter a community .
Life history attributes and composition of the invertebrate fauna that wer e
collected in streams severely impacted by the eruption of Mt . St . Helens ar e
similar to those of the invertebrate fauna in the most frequently disturbe d
channel at Kalama Springs . In both cases, communities are dominated by
chironomid midges . Abundances, however, are greatly reduced in the stream s
surrounding Mt . St . Helens, and evidence that the communities are undergoin g
cycles of establishment and denudation in concert with changes in landscap e
geomorphology indicates that catastrophes have different consequences on strea m
communities from other disturbances, and should be distinguished from them .
21
Instability of channel banks and bottoms in streams severely impacted by
the eruption appears to pose a major impediment to recovery of benthi c
communities . Until these elements stabilize, communities will consist only of
'
short-lived fugitive-type species that will be swept downstream with eac h
successive' high flow event . Community recovery can perhaps be enhanced b y
management practices that promote channel stability, such as . planting o f
riparian vegetation or introduction of stable substrates into a stream .
4,
28
V . LITERATURE CITE D
Connell, J . H . and R . O . Slatler . 1977 . Mechanisms of sucessian im natura l
communities and their role in community stability and orgeization . Amer .
Natur . 111 :1119-1144 .
Gorman, O . T . and J . R . Karr . 1978 . Habitat structure and stream fi=s h
communities . Ecology 59 :507-515 .
Harper, J . L . 1977 . Population biology of plants . Academic Press, Lonalon. .
Keller, E . A . and F . J . Swanson . 1979 . Effects of large organic material o n
channel form and fluvial processes . Earth Surf . Processes 4 :3'61-3€30 . .
Leopold, L . B ., M . G . Wolman, and J . P . Miller . 1964 . Fluviad processes in
_
geomorphology . W . H . Freemanand Company, San Francisco . 522 p .
Merritt, R . W . . and K . W . Cummins . 1978 . An introduction to the aq,l tie insect s
of North America . Kendall/Hunt, Iowa . 441 p .
Paine, R . T . 1979 . Disaster, catastrophe, and local persistence of the-se a
palm Postelsia palmaeformis .
Science 205 :685-687 .
Pfankuch, D . J . 1975 . Stream reach inventory and channel stability dvairatiom .
U .S .D .A . Forest Service, Northern Reg ion, 26 p .
Rogers, L . E ., W . T . Hinds, and R . L . Buschbom . 1976 . A general weight vs .
length relationship for insects . Ann . Entomol . Soc . Att . 69 :387-389 .
. Swanson, F . J . and G . W . Lienkaemper . 1978 . Physical consequences . of larva
organic debris in Pacific Northwest streams . U . S . Forest Serv . Gen . Tech .
kept . PNW-69, Pac . N . W . .For . Range Exp . Sta . 12 p .
Wetzel, R . G . and G . E . Likens . 1979 . Limnological analyses . W . a, Saunder s
Company, Pa . 357 p .
29
w
VI . APPENDICE S
1. Channel Stability Evaluatio n
2 . Invertebrate Taxa Collected From Stream Impacted B y
Mt . St . Helens, winter 1981-82 .
31
,,
J
.
N
m
N
m
(
m
1
a
+.
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APPENDIX 2 . Invertebrate taxa collected in stream sites impacted by Mt . St .
Helens, winter 1981-82 .
S
Lower Maratt a
Hemipter a
Trichocorixa spp .
Trichopter a
Pseudostenophylax sp .
Di pter a
Simulium sp .
Empidida e
Orthocladiinae spp .
Diamesinae spp .
Other :
Naididae (Uligochaeta )
Ape Canyo n
Ephemeropter a
Baetis bicaudatu s
Baetis tricaudatu s
Plecopter a
Shipsa sp .
Dipter a
Diamesinae spp .
Upper Mudd y
Ephemeropter a
Baetis tricaudatu s
Plecopter a
Malenka sp .
Megarcys sp .
Trichopter a
Rhyacophila sp .
Dipter a
Limnophora sp .
Orthocladiinae spp .
Kalama Rive r
Ephemeropter a
Ephemerella coloradensi s
Drunella sp .
Epeorus longimanu s
Plecopter a
Malenka sp . _
Megarcys sp .
Perlodida e
Trichopter a
Lepidostoma quercin a
Hydatophylax sp .
Pseudostenophylas sp .
,Micrasema sp .
Neotheremma sp .
Rhyacophila sp .
;'Diptera
Dicranota sp .
undetermined Tipulida e
Twinnia sp .
Orthocladiinae spp .
Empididae sp .
Other :
Naididae (Oligochaeta )
Upper Maratt a
Ephemeropter a
Baetis tricaudatu s
$~
Swift Cree k
Dipter a
Orthocladiinae spp .
Diamesinae spp .
undetermined Tipulida e
Other :
Acari (exuvia )
centipede (terrestrial )
Carbonate Spring s
Dipter a
Orthocladiinae spp .
Diamesinae spp .
f
+~.
$ .' 33