United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
Las Vegas NV89114
Research and Development
EPA/600/S2-86/104 May 1987
SEPA Project Summary
Seasonal Variability in Prickly
Pear Creek Water Quality and
Macroinvertebrate
Communities
Barry P. Baldigo, John R. Baker, Wesley L. Kinney, and Mike Fillinger
Prickly Pear Creek, Montana, was
sampled during four seasons in 1982
and 1983 to attempt to relate biological
responses to fluctuations in discharge,
in-stream toxicity and metal concentra-
tion in the water column. The biota
(macroinvertebrate) were definitely im-
pacted directly downstream from a
metal source during all seasons, but no
definite relationships among discharge,
metal concentration and biological re-
sponse could be established on a sea-
sonal basis.
This Pro/ect Summary was devel-
oped by EPA's Environmental Monitor-
ing Systems Laboratory, Las Vegas,
NV, to announce key findings of the re-
search project that is fully documented
in a separate report of the same title
(see Project Report ordering informa-
tion at back).
Introduction
Prickly Pear Creek, Montana, was
studied by the U.S. EPA Environmental
Monitoring Systems Laboratory, Las
Vegas, Nevada (EMSL-LV), during 1980
through 1983. This stream was of inter-
est because healthy biota were ob-
served throughout much of the system
even though concentrations of zinc,
copper and cadmium exceeded the
acute aquatic life criteria several fold.
Stream surveys and on-site toxicity
tests were conducted to investigate fac-
tors that enable sensitive organisms to
tolerate exposure to waters containing
concentrations of metals well in excess
of acute national aquatic life criteria. Ad-
ditional studies examined persistence
and degradation of metal toxicity in
Prickly Pear Creek as revealed by the
downstream distribution of toxic metals
and the resultant response of the resi-
dent biota.
These studies cited above and others
identified factors that affect organism-
ecosystem toxic responses. However,
not all factors are equally influential in
all aquatic systems, and it is important
to be able to identify the principal fac-
tors controlling metal availability and
toxicity in a given system.
One factor that has generally been ig-
nored in relating metal concentrations
to in-stream toxicity and biological re-
sponses is seasonal variability in flow
and associated changes in water quality
and in the biota. In some waterways,
toxicity may be greatest during periods
of high flow when metals are most sus-
ceptible to mobilization and transport to
surface water (e.g., streams receiving
drainage from mine tailings). Con-
versely, in the same system during low
flow periods, metal loading to the
stream may be minimal, and the toxicity
may be greatly reduced. Knowledge of
these factors is crucial to enable water
managers to make intelligent decisions
regarding the issuance of permits, the
allocation of waste loads, the designa-
tion of beneficial uses, and the estab-
lishment of site-specific criteria and
standards.
Consequently, a study was conducted
on Prickly Pear Creek to assess seasonal
variability in discharge, in water quality,
and in the biota. This summary and the
project report address that study.
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Study Area
Prickly Pear Creek forms its head-
waters in the Elkhorn Mountains ap-
proximately 32 km southeast of Helena,
Montana and flows north for 64 km be-
fore entering Lake Helena and the Mis-
souri River (Figure 1). Tailing and set-
tling ponds remain as prominent
features of historical gold mining opera-
tions within the Corbin and Spring
Creek drainages and release high con-
centrations of zinc, copper, and cad-
mium which are carried into Prickly Pear
Creek. Prickly Pear Creek also under-
went extensive mining operations in the
early 1900's during which time over 75
percent of the stream was subjected to
stream-bed modifications and dredg-
ing.
The present study reach was gener-
ally characterized by riffle flow and cob-
ble and gravel substrate. The Prickly
Peak Creek annual discharge at the U.S.
Geological Survey (USGS) gaging sta-
tion (Figure 1) ranged from 30 to 343
cubic feet per second (cfs) with a mean
of 55 cfs during the 1982 to 1983 water
year. Spring Creek discharge during this
study ranged from approximately 1 to
5 cfs.
Four principal stations on Prickly Pear
Creek and one station on Spring Creek
were utilized in this study (Figure 1).
Spring Creek was considered an
"effluent" site (012). Station 011, up-
stream from the confluence of Spring
Creek and Prickly Pear Creek, was used
as a control. Stations 013 and 014 were
designated impact zone sites, and sta-
tion 018 (and occasionally 014) was des-
ignated as a downstream recovery zone
site.
Methods
Invertebrate populations and stream
water metal concentrations from Prickly
Pear Creek control, impact, and recov-
ery sites were sampled during 1982 and
1983. Collections were made during
July and December 1982 and April and
October 1983 to assess seasonal varia-
tions in discharge, temperature, runoff,
metal concentrations, and invertebrate
communities. Water samples were also
collected from Spring Creek during all
seasons, however, invertebrate sam-
ples were only taken during July 1982.
Commonly measured water quality
parameters, were also recorded during
all seasons.
Water Quality
During July 1982, triplicate water
samples for metals analyses were col-
Prickly Pear Creek. Montana
USGS
Figure 1. Station locations on Prickly Pear Creek, Montana.
lected at each station. Because very
little variability among replicates was
observed in these samples, during sub-
sequent samplings single samples were
collected from each station. All metal
samples were preserved with Ultrex
grade HN03 to pH <2.0. July 1982 sam-
ples were analyzed by Inductively Cou-
pled Plasma Optical Emission Spectra-
metric (ICP) methods. The detection
limits of the ICP for all metals except
zinc and copper approached or ex-
ceeded ambient levels in the water
column, during July 1982, hence, the
July data for cadmium, lead, silver and
arsenic should be viewed with this in
mind. For the other three periods zinc
and copper were analyzed by AA Flame;
cadmium, lead, and arsenic via AA Fur
nace; and silver via ICP.
Hydrology
Stream discharge was measured ai
each station during the July and Octo
ber surveys using a Marsh-McBirne>
Model 57 current meter. At each statior
flow at each of 20 intervals along a tran
sect was measured at 6-tenth depth
The December 1982 and the April 198;
discharge was extrapolated from
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and October data and from USGS
gauge values for these periods taken
about 3 km downstream from Station
18.
Macroinvertebrates
A Portable Invertebrate Box Sampler
(PIBS) was used to collect five replicate
samples at each station from riffle zones
of uniform flow and velocity. Samples
were preserved and processed follow-
ing conventional techniques. Sorted in-
vertebrates were identified to the low-
est possible taxon, counted, and the
data entered into computer storage and
tabulated. A reference collection of
identified specimens is maintained at
EMSL-Las Vegas.
Results
Water Quality
Data for metals of concern in Prickly
Pear Creek, i.e. cadmium, lead, zinc,
copper, silver, and arsenic, are summa-
rized in Table 1. This table suggests that
cadmium, lead, silver and arsenic con-
tamination during July 1982 did not
originate from Spring Creek because
control Station (011) concentrations ex-
ceeded those of the effluent (012) and/or
the receiving stream impact zones (sites
013 and 014). This apparent anomaly is
probably attributed to analytical limita-
tions of the ICP instrument used for
analyses of the July 1982 samples. The
three metals that commonly exceeded
National Criteria were Cadmium, Z inc,
and Copper, hence, these results con-
centrate principally on these metals.
Cadmium levels in July of 1982 (Table
1) appeared elevated over those which
occurred during the other three periods,
but were undoubtedly a function of the
analytical methods because the values
reported for July approached the detec-
tion limits of the ICP instrument used for
these analyses. However, cadmium
concentrations measured by AA fur-
nace were clearly elevated in Spring
Creek and impact Station 013 over the
other stations during the other seasons
as well. Spring Creek produced elevated
levels of cadmium in Prickly Pear Creek
impact site 013, but a gradual reduction
to near control (011) levels was ob-
served at sites 014 and 018 (Table 1).
The highest concentrations at all sta-
tions (excluding July 1982) occurred in
October 1983 during low flow. April
(1983) and December (1982) concentra-
tions were considerably lower at the
downstream sites (014, 018) than sum-
mer and fall values. Correlation analysis
Table 1.
Total Metal Concentrations From Prickly Pear Creek and Spring Creek Sites During
the Four Sampling Periods
Date
011
012
013
014
018
Cadmium
Lead
Zinc
Copper
Silver
Arsenic
07/22/82
12/21/82
04/08/83
10/09/83
07/22/82
12/21/82
04/08/83
10/09/83
07/22/82
12/21/82
04/08/83
10/09/83
07/22/82
12/21/82
04/08/83
10/09/83
07/22/82
12/21/82
04/08/83
10/09/83
07/22/82
12/21/82
04/08/83
10/09/83
13
0.2
<.3
2.0
64
2.4
<1
13
71
21.9
40.5
100
20
<9
11.0
12.0
25
<7
<7
0.6
163
<2
<2
<2
17
5.4
6.0
7.6
29
242.5
246.6
72
2227
1128
1595
2119
119
80.7
67.8
84
24
<7
<7
1.6
90
46.4
26.9
27
19
2.4
2.6
5.0
119
84.3
66.1
30
454
431.1
640.7
580
33
37.0
25.3
28
9
<7
<7
1.9
87
16.7
10.3
6
10
0.7
0.9
4.0
52
16.4
18.1
19
221
212.2
320.9
236
13
22.0
11.7
14
6
<7
<7
0.2
61
4.0
4.5
4
10
0.3
0.2
3.0
51
8.6
5.7
15
128
134.5
138.4
203
15
13.0
<9
12
4
<7
<7
0.1
126
5.3
5.0
10
of USGS gauging station discharge data
and cadmium concentrations produced
correlation coefficients at sites 012 and
018 of r = 0.94 and r = 0.93, respec-
tively.
Very high zinc levels in Spring Creek
<1128to 2227 mj/l) resulted in substan-
tial increases in zinc concentrations in
Prickly Pear Creek (Table 1). Concentra-
tions downstream were progressively
reduced, but they never reached control
site levels. The highest concentrations
of zinc in Spring Creek occurred in July,
the period of highest discharge, and Oc-
tober the lowest discharge period. Dis-
charge values and zinc concentrations
at sites 012 and 018 did not correlate
strongly (r = 0.53 and r = 0.43, respec-
tively).
Copper responded similarly to zinc
(Table 1). Variations in concentrations
between sample periods within the
same sites were not pronounced. Im-
pact site (013) concentrations ranged
from 25 to 37 |o,g/l, approximately twice
the control and final recovery site con-
centrations. July concentrations in
Spring Creek were slightly higher than
those of other seasons (Table 1). Corre-
lation coefficients for copper concentra-
tions and discharge values for stations
012 and 018 were r = 0.11 and r = 0.67,
respectively.
No consistent correlation with dis-
charge (positive or negative) was noted
with these three metals at the other sta-
tions. Spring Creek (012) concentrations
of all three metals correlated positively
with discharge, but possibly this was
extraneous because of the small num-
ber of paired data points.
Hydrology
During July 1982 flow was approxi-
mately two times greater than during
the other three periods. Flow during the
last three sampling periods was essen-
tially uniform and ranged from 38 to
42 cfs at the USGS gauge downstream
from site 018.
Macroinvertebrates
Fifty-two macroinvertebrate taxa
were collected in Prickly Pear Creek dur-
ing the four seasons. Estimates of
Shannon-Wiener diversity (H'), Even-
ness (J) and Simpson's Dominance (D)
are provided in Table 2 for comparison
purposes.
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Table 2. Mean Invertebrate Community Indices From Prickly Pear Creek During the Four Sampling Periods
(Coefficients of Variation [Percent] are Noted in Parentheses).
Parameter
Mean Count
Richness
011
411
(53)
21
(36)
July
013
130
(51)
15
(14)
1982
014
103
(86)
10
(43)
December 1982
018
226
(15)
19
(8)
011
578
(21)
27
(10)
013
238
(17)
15
(17)
014
171
(34)
13
(23)
018
230
(23)
16
(19)
011
774
(10)
29
(17)
April 1983
013
460
(9)
19
(20)
014
556
(15)
16
(10)
018
516
(8)
22
(16)
on
298
(17)
20
(16)
October 1983
013
219
(24)
11
(6)
014
126
(33)
15
(26)
018
76
(26)
9
(26)
Diversity (H')
Evenness (J)
Dominance (D)
2.82
(12)
0.67
(9)
0.77
(5)
2.44
(5)
0.64
(9)
0.69
(5)
2.48
(18)
0.79
(11)
0.77
19)
2.92
(7)
0.69
(5)
0.80
(6)
3.36
(4)
0.71
(5)
0.84
(2)
2.59
(8)
0.66
(5)
0.73
(5)
2.90
(11)
0.78
(10)
0.81
(7)
3.12
m
0.79
(2)
0.84
(3)
3.62
(3)
0.75
(5)
0.88
(1)
2.81
(13)
0.66
(7)
0.80
(6)
2.40
(12)
0.60
(12)
0.65
(12)
2.97
(9)
0.67
(7)
0.74
(9)
3.43
(8)
0.79
(4)
0.86
(4)
2.08
(18)
0.60
(18)
0.62
(18)
3.15
(17)
0.81
(13)
0.83
(12)
2.6S
(15)
0.84
(4)
0.82
(7)
Control Zone (Station 011)
Thirty-nine taxa were collected from
the riffles in the control zone during the
four sampling seasons. This station
consistently provided higher mean total
numbers of individual organisms per
sample and higher mean and total num-
ber of taxa per season than the other
sampling stations (Table 2, Figures 2
and 3).
Thirty-two taxa were collected from
the riffle at station 011 during July when
the flow was greatest. The ubiquitous
Baetis tricaudatus was very common,
comprising 38 percent of the total inver-
tebrate numbers at this site. Other com-
mon taxa (6 percent to 30 percent rela-
tive abundance) at this site included the
mayfly, Epeorus longimanus, and the
midge subfamily, Orthocladiinae.
The spring, pre-runoff sampling
(April) produced both the highest total
number of taxa at 37 (Figure 2) and the
highest mean number of taxa per sam-
ple at 29. The highest mean number of
individuals per sample encountered
during the study (n = 774) (Figure 3)
were collected during April at this sta-
tion. The most common organism col-
lected in April was the filter feeding cad-
disfly Arctopsyche grandis, which
comprised 22 percent of the total inver-
tebrate numbers at this site. Other com-
mon taxa in the spring included the
mayfly, Beatis tricaudatus, with a mean
relative abundance of about 16 percent,
and the midge subfamily, Othrocladi-
inae (11 percent), Glossosoma sp.
(9 percent), and Ephemerella tibialis
(8 percent).
The pattern of results for December
was similar to that observed in April,
although the mean total number of indi-
viduals per sample dropped by approxi-
mately one-third (Figure 3). Several rare
or occasional stoneflies captured in
April were not observed in December.
The composition of the dominant func-
tional groups changed little from De-
cember to April.
The macroinvertebrate community at
Station 011 appeared most depressed
during fall (October) sampling. The
mean total number of individuals per
sample was down approximately 60
percent from the spring, (Figure 3) and
total number of taxa (Figure 2) and
mean taxa per sample were reduced by
about one-third. This may be a natural
seasonal occurrence caused by recent
adult emergence and by the inability of
the PIBS net to retain minute nymphal
instars. Nine taxa were found at Station
011 during the study that were not col-
lected at any other station.
Spring Creek (012)
In July (1982) Spring Creek (012) was
sampled to ascertain the presence or
absence of fauna. Only five taxa and a
total of nine organisms were collected
from five replicate samples. These in-
cluded Orthocladiinae midges and a
single stonefly (Chloroperlidae), the
caddisfly, Arctopsyche grandis, the
crane fly, Tipula sp., and the water mite,
Sperchon sp. The low number of taxa
and individuals in Spring Creek reflect
the extremely disturbed nature of the
watershed and the concomitant ele
vated metal levels.
Impact Zone (Stations 013 and
014)
Thirty-three taxa were collected dur
ing the four sampling seasons at Statior
013. The total number of taxa were rela
tiv.ely uniform at this station durinc
April, July, and December (Figure 2)
However, during October the total num
ber of taxa was substantially reduced a
Station 013, and differences in the num
ber of taxa between control Station 01
and impact station were most pro
nounced during the October samplin;
(Figure 2). As was the case at contrc
site 011, the mean number of individu
als per sample was highest in Apri
(n = 460) (Table 2, Figure 3). Decembei
October and July values did not diffe
greatly in terms of numbers of individu
als (Table 2, Figure 3).
Two species, Baetis tricaudatus am
Arctopsyche grandis, predominated a
this station during all sample seasons
Combined, they made up 54 percent o
the total standing crop in July, 65 per
cent in December, 49 percent in April
and 72 percent in October. The onl'
other organisms that contributed sub
stantially were Antocha sp., the Di
amesinae midges, and the caddisfly
Brachycentrus sp.
Twenty-eight taxa were collected dur
ing the four seasons at Station 014, bu
unlike Station 013 no difference in tote
number of taxa was evident on a sea
sonal basis (Figure 2). As was the cas
on the upstream stations, the averag
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40 -i
30 J
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I
s
1
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Pear Creek via Spring Creek near Jeffer-
son City, Montana. Principal metals of
concern were cadmium, copper and
zinc because their concentrations in
Prickly Pear Creek waters exceeded the
national water quality criteria limits for
the protection of aquatic life. Elevated
levels of these three metals were
present in Prickly Pear Creek waters dur-
ing four seasons in the impact zone im-
mediately downstream from the Spring
Creek and Prickly Pear Creek conflu-
ence. Concentrations downstream in
the recovery zone approached, but did
not quite reach, levels in the unim-
pacted control zones.
Stream discharge during the winter,
spring and fall sampling periods was
nearly uniform within each station. Dur-
ing the summer sampling, however,
discharge levels were approximately
twice those during other periods. Dur-
ing this high flow period, the highest
concentrations of the three metals in
Spring Creek water were recorded. Cad-
mium and zinc concentrations reached
their next high levels during October
1983, which was a period of low, stable
flow. No pronounced trends in copper
concentration were apparent on a sea-
sonal or flow related basis.
Macroinvertebrate communities were
definitely affected by the high levels of
metals in the impact zones. Reduction in
numbers of individuals, numbers of
taxa and related parameters were ap-
parent during all seasons in the reach
downstream from the Spring Creek dis-
charge. Recovery of communities to
control station levels was not complete,
but this was judged to be a function of
different habitats in the downstream
reaches rather than a direct impact of
metals. October data were somewhat
anomalous in that the second impact
site showed an increase in total number
of taxa and the recovery site showed a
reduction in number of taxa. In terms of
numbers of individuals, the fall data
were also somewhat anomalous as
total numbers of individuals progres-
sively decreased downstream, reaching
their lowest densities in the recovery
zone.
Additional studies would be needed
to clarify relationships among dis-
charge, seasons, water quality and the
biota. Refinement of hydrological mea-
surements, use of consistent tech-
niques for metals analyses and some
adjustment of sampling periods would
be required to assure a high probability
of success in future studies.
Barry P. Baldigo and John R. Baker are with Lockheed Engineering and
Management Services, Inc., Las Vegas, NV 89109; the EPA author, Wesley
L. Kinney (also the EPA Project Officer, see below), is with the Environmental
Monitoring Systems Laboratory, Las Vegas, NV 89114; and Mike Fillinger
is with Environmental Investigations Services Co., Helena. MT 59601.
The complete report, entitled "Seasonal Variability in Prickly Pear Creek Water
Quality and Macroinvertebrate Communities," (Order No. PB 87-129 300/
AS; Cost: $11.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
P.O. Box 15027
Las Vegas, NV89114
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S2-86/104
OOOQ329 PS
60604
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