A Review of the Regulations and Literature Regarding the
Environmental impacts of Suction Gold Dredges
By
Phillip A. North
U.S. Environmental Protection Agency
Region 10
Alaska Operations Office
April, 1993
-------
-------
Abstract
Pew studies have been published to guide resource managers
who are attemping to mitigate the impacts associated with suction
dredging in streams. This reveiw summarizes and comments on four
articles from peer review journals and four agency reports.
Studies done to date have been limited to low intensity
operations. Both the size of dredge and density on the stream
was low in 'these studies. Impacts to stream fish were severe for
early life stages, eggs and sacfry, while free swimming fish were
not directly affected. The effect of habitat disturbance has
been poorly studied, but may be of short duration under most
circumstances. Changes in stream morphometry was typically of
short duration lasting until the next high flow. Invertebrates-
were displaced but recolonized the disturbed site within the same
season. Water quality was typically temporaly and spatially
restricted to the time and immediate vicinity of the dredge.
Thought more persistant problems may occur under some
circumstances. There is little data in this area. Areas for
future research include impacts in cold climates, long term
affects where mining occurs repeatedly, the impacts of dredges
with large intake diameter.
-------
-------
Introduction
The deregulation of gold prices in the early 1970's and the
following extraordinary rise in the price of gold in the latter
part of that decade resulted in a boom in placer gold mining in
the western states and Alaska. In some areas, such as the gold
bearing regions of California, suction dredging was the
predominant method for extracting gold from stream gravels for
professional miners as we'll as hobbyists. To better understand
the impacts associated with this particular type of stream
disturbance a number of studies have been completed over the last
ten years. These studies have investigated the impacts on stream
biota as well as physical and chemical changes that result from
mining gold from streams with suction dredges.
Suction dredges, most simply, consist of a floating platform
on which a pump and sluice box are mounted, with a suction hose
that reaches to the 'bottom of the stream. The pump is used to
lift gravels from the stream bottom through the hose onto the
sluice box for gold recovery. The intake size of the hose and
the horse power of the engine driving the pump determine the
volume of gravel that a dredge can potentially move. The amount
of material actually moved depends of the skill of the operator
and the conditions in which the operator is working. Intake size
typically ranges from two inches to eleven inches in diameter. A
Few larger dredges, up to 40 cm (16 inches) diameter, are
operated in Alaska. Dredges of 11 and 12 inches are not unusual
on some streams in Alaska. Dredges less than 4 inches are most
common. Dredges with intake nozzle and hose diameters of 6 or
less inches are considered recreational by some governmental
bodies (Alaska Department of Fish and Game); others (many federal
agencies) draw the line at 3 or 4 inches. A recent phone survey
of suction dredge permitting offices of the Alaska Department of
Fish and Game (ADFG) and the U.S. Bureau of Land Management
established an estimate of the number of suction dredges
typically mining on all Alaska streams in the" late 1980's and
early 1990's (Table 1) . There may be many more of the smaller
classes of dredge that are operated on a casual basis and are not
reported to ADFG.
Table 1. Estimated number of dredges permitted for Alaska streams
by the Alaska Department of Fish and Game and the U.S. Bureau of
Land Management (personal communication).
Number of Dredges Intake Diameter (inches)
500-f <4
40 to 60 >4 and <8
• 30 >8
-------
Review of the Literature
The effective action of suction dredges is to excavate
stream bed sediments, often down to bedrock, by lifting them
completely out of the stream and then dropping them back. The
rate that materials settle to the stream bottom depends on
.particle size. Operation of these machines has the potential to
damage stream ecosystems. The four studies that I reviewed from
journals subject to peer review consistently found that when
certain limitations are placed on suction dredge activity the
impacts on the stream ecosystem are local and of short duration.
These papers investigated the effects on water quality, channel
morphology, invertebrate abundance and composition, and on the
abundance and distribution of salmonids and sculpins (Griffith
and Andrews 1981, Thomas 1985, Harvey 198.6, Somer and Hassler
1992) . Four additional studies not subject to formal peer
review, investigated the impacts of suction dredges on water
quality, channel morphology, invertebrates and fish (McCleneghan
and Johnson 1983, U.S. Army Corp of Engineers 1985, Hassler et
al. 1986, Huber and Blanchet 1992) . All of the above studies,
were limited to small dredges, the largest being 15 cm . '
(6 inches).
Impacts on Fish
Incubating eggs and very young fish are subject to
entrainment in a suction dredge if mining occurs during the egg
incubation period or when the young fish are still in the gravel.
These life stages have been shown to.be sensitive to mechanical
damage when entrained in a suction dredge (Griffith and Andrews
1981). In a test of sensitivity, un-eyed eggs of cutthroat trout
(Oncorhynchus clarki) were run through an operating dredge. One
hundred percent 'of these eggs were killed. Eyed eggs of
cutthroat and rainbow trout (Oncorhynchus mykiss) also had severe
mortality, 35% and 19% respectively. Similarly, 83% of rainbow
trout sacfry were killed after being run through a suction
dredge. The cause of death in all of these cases was mechanical
damage. The egg membrane was ruptured in the case of both eyed
and un-eyed eggs, and yolk sac was detached in sacfry. - Free
swimming stages of these fish showed no mortality when 'passed
through a running dredge.
While adult fish did not show a sensitivity to entrainment
it is unlikely that they would be sucked into a dredge in the
first place. They have' the ability to avoid entrainment in a
suction dredge by moving to. a safer location. All of the
investigators who examined the impacts of suction dredges on
adult fish concluded that this life stage was not acutely
affected (Harvey 1986, Hassler et al. 1986, Summer and Hassler
.1992). Harvey (1986) found this to be the case for rainbow trout
on streams he studied in California. However, he observed that
-------
the abundance of riffle sculpin (Cottus gulosus), a bottom
dwelling fish, was reduced in dredged stream sections due to a
reduction in suitable habitat. Habitat value was decreased by
increased sedimentation during mining causing a loss of refuge
sites.under boulders. Harvey also observed that trout moved
between locations to find suitable habitat as dredging
progressed. The fish chose were dredge holes as suitable sites.
The fish moved between natural pools in the stream and dredge
holes, presumably choosing the site that provided the best
habitat characteristics. Thomas (1985) noted that during high
flows, following dredging, dredged material moved downstream
filling a pool. Any habitat value the pool might have provided
to fish was lost until suitable flows could again wash the pool
clean of dredged sediments. While adult fish-are not acutely
affectdd by dredging, locally reduced habitat quality may result
in stress to fish until stream habitat recovers.
Aquatic Invertebrates
The existing literature on the effects of suction dredges on
aquatic invertebrates consistently concluded that impacts wetfe
very local and of relatively short duration. Dredging probably
resulted in a displacement of invertebrates rather than
elimination of invertebrates from the ecosystem. However,
investigators witnessed fish feeding on invertebrates discharged
from a dredge (Hassler et al. 1985, Harvey 1986) , so obviously
some did not settle back to the stream bottom. Entrainment
studies by Griffith and Andrews (1981) showed that juvenile life
stages of insects were not sensitive to entrainment. One hundred
percent of juvenile insects survived entrainment in Griffith and
Andrews' tests. The few insects that happened to be emerging
from the juvenile stage at the time of the test were all killed
by passage through the active dredge. All were noted to have
visible injuries. Undoubtedly developing body parts that are
adapted for mobility in the much thinner medium of air are
subject.to greater stress in the relatively dense and turbulent
water conveyed by a suction dredge.
Both Thomas (1985) and Harvey (1986) compared the .abundance
of invertebrates in gravels being mined with those above and
below the mined site. Thomas sampled immediately before and
after dredging. She found that the abundance of invertebrates
was significantly decreased due to dredging. Harvey sampled once
per month for a period that included the dredge season. He found
mixed results from dredging, but when there was a difference
between dredged and control sites the dredged site had a lower
abundance of invertebrates. Harvey attributed the general
decrease in abundance of invertebrates at 'mined sites to changes
in substrate. He noted that cobbles were more embedded in fine
sediments after mining than before.
-------
• The difference between Thomas' and Harvey's results may have
been due to difference in study design, specifically the timing
and location of sampling. Thomas' sampling target was the actual
dredged site. Her timing and choice of location were sure to
reflect any disturbance that may have occurred, however locally.
Whereas, Harvey's sampling target was the stream reach. His
timing and location were not juxtaposed to a specific dredging
period or specific location. Some samples that Harvey collected
may have been from sites that remained undisturbed for a long
enough period of time to allow recolonization, or, the site may
never have been dredged, as some of the samples showed no
difference from control sites while others did show a difference.
Given the nature and degree of disturbance, it seems unlikely
that a dredged site will have near normal abundance of
invertebrates immediately after dredging.
Downstream of the mined site neither the abundance (Thomas
1985, Harvey 1986, Somer and Hassler 1992} nor the measure of
diversity of invertebrates appeared to be altered (Harvey 1986,
Somer and Hassler 1992). However, Somer and Hassler using
artificial substrate baskets, found that trophic structure of,_ the
invertebrate community had changed below the 'dredge. Shredders,
those organisms that consume course particulate organic matter
such as leaves on the stream bottom, were more abundant in the
undisturbed stream bed immediately upstream of the dredge. .
Filtering invertebrates, those organisms that filter small
organic particles out of the flowing water column were more
abundant below the dredge outfall where detrital material, after
being removed from the substrate, was suspended in the water
column.
In apparent contradiction of these results, they noted that
organic matter measured during sedimentation sampling was greater
down.stream of the dredges. While this greater mass could be
explained by the displacement of organic material by the dredges
to down stream locations, it does not explain the reduced number
of shredders below the mined sites.
Probably the most significant concern in regard to the
impacts on aquatic invertebrates is the rate at which mined sites
recover the invertebrate fauna. The primary mode of recovery of
the invertebrate fauna in streams is drift from upstream sites.
Rates of recolonization appear to be a function of the length of
stream channel that has been void of invertebrates (Minshall
1983). The longer the affected stream section the more time is
required for complete recovery. If recolonization is slow the
cumulative impacts of suction dredge mining could be significant
over a period of seasons. However, in each of the studies on
suction dredges that investigated this question, the length of
disturbed stream reach was relatively short (on the order of a
,few tens of meters) and recolonization proved to be rapid.
Griffith and Andrews (1981) found that the dredged site was
-------
"substantially recolonized" after 38 days. The abundance within
orders of invertebrates were the same before and after dredging
and "key" taxa were also the same. Harvey (1986) found that
recolonization was complete in terms of numbers of insects within
45 days of dredging. Thomas (1985) sampled the site 30 days
after dredging and found, again, that colonization was
"substantially complete" for most groups. The number of
invertebrates colonizing the artificial substrates used by Somer
and Hassler (1992) did not increase two weeks after the first
sampling. None of these investigators sampled their study site
earlier than the reported time of recolonization. Recolonization
may have occurred sooner than the time reported. It should also
be noted that the artificial substrates used were, as Somer and
Hassler noted, biased because they offer a relatively silt free
substrate for invertebrates to colonize. They therefore should
not be used as an indication of the time for invertebrate
recolonization of the stream substrate.
While, these studies indicate relatively rapid recovery of
aquatic invertebrates from disturbance associated with suction
dredging, the length of times recorded are a substantial part of
the growing season in cold climates. The cumulative impact by
disturbance of successive stream bottom reaches year after year
could deplete the invertebrate fauna in small streams. In many
cases these small headwater streams are the preferred summer
habitat for larger arctic grayling (Thymallus arcticus). Reduced
invertebrate abundance could impact these fish populations.
Water Quality
Most water quality studies of the effects of suction gold
dredges on streams focused on turbidity and suspended sediments.
These studies, with some exceptions, largely found that water
quality is impacted for a distance downstream of the dredge
ranging from a few meters to 30 meters (Griffith and Andrews
1981, Thomas 1985, Harvey 1986), after which ^distance, turbidity
and suspended solids return to background levels. In all of
these studies, background turbidity is described as low,
typically less than 1 NTU (nephelometric turbidity unit). One
study found elevated turbidity 123 meters downstream of the
dredge (Somer and Hassler 1992). They reported peak turbidity of
15 NTU and measured the distance downstream was to the point
where turbidity was no longer visible. It would seem that
turbidity in this case was elevated only a few NTU above
background for most of the distance surveyed. The authors
attributed the elevated turbidity to greater content of silt and
clay in the sediments of the mined stream. Five samples taken by
a miner and one by Alaska Department of Environmental
Conservation personnel on the Bluestone River, in western Alaska,
found slightly elevated turbidity 152 meters (500 feet)
downstream of a 25.4 cm (10 inch) dredge. Elevated turbidity at
this distance from the dredge ranged from less than 1 NTU to 4.5
-------
NTU.' It would seem that in most cases water quality recovers
rapidly below a dredge as sediments quickly settle to the stream
bottom. If a miner encountered silts or clay in the stream
substrate water quality problems could be more persistent.
• Somer and Hassler (1992) suggested that .salmon were not
affected by the elevated turbidity and cited studies that found
salmonid growth was reduced at 25 NTU but not below. However
there is evidence that fish feeding, angling, and fishery
management practices can be hampered at turbidity as low as -5 NTU
(Lloyd et al. 1987, Scannell 1988). The cumulative effect of
several dredges in relatively close proximity (150 meters) could
reduce visibility in a stream reach such that fish productivity
would be reduced and human activities hampered.
Hassler et al. (1986) stated that dredges operating within
0.5 km of each other resulted in cumulative impacts on water
quality. However, Huber and Blanchet (1992) found no evidence of
cumulative impacts of mining on water quality in streams of the
Chugach National Forest in Alaska. They monitored streams in the
Forest over a period of three years and found no noticeable v
impact to water quality associated with suction dredges.
A study by the U.S. Army Corps of.Engineers '(1985) on the
Arkansas River of Colorado investigated the fate of metals
suspended and dissolved to the water column by suction gold
dredging. They found that metals largely follow the pattern
observed for sediments. High concentrations of metals are found
at the dredge outfall but they quickly decrease as the sediments,
with which they are bound, settle back to the stream bottom.
They found that zinc and lead continued to exceed Colorado water
quality standards (0.135 mg/1 and 0.008 mg/1 respectively) 15
meters (50 ft) below the dredge and that zinc persisted in excess
of state water quality standards 30.5 meters (100 ft) below the
dredge outfall. While the authors of this study conclude that
suction gold dredge operations on the Arkansas River pose "no
imminent environmental problem", they also suggest that suction
dredging may cause changes in stream chemistry that could cause
an increased risk to stream biota from elevated metal
concentrations. Deposition of discharged sediments and'..
associated metals may make these substances more available to
stream biota.
It should be noted that the Arkansas River flows through an
area where tailings from hardrock mining continually leach metals
into the stream. So care must be taken when extrapolating the
results from this study to other stream^. However, an
investigation of the water quality associated with mining placer
deposits with heavy machinery also found elevated levels of total
and dissolved metals in water discharged from mines (Bjerklie and
LaPerriere 1985). These studies were conducted in streams where
there were no other upstream sources of contamination. A
8
-------
comparison between the impacts associated with these two mining
methods is complicated by the difference in scale between the two
types of operation. Suction dredges typically move much less
material than do placer mining operations that use heavy
machinery. Suction dredges may ordinarily only be able to move
relatively well sorted material which may not have the fine
grained sediments with which metals are often associated. This
may not be a limitation for dredges with a large intake nozzle.
More study is clearly needed.
Changes in Channel Morphometry and Sedimentation
In the process of moving stream bottom sediments to extract
gold, suction dredges change the stream channel morphometry.
Channel form, or morphometry, is one element that determines
habitat quality for stream organisms. Suction dredging typically
creates a hole and- pile pattern on the stream bottom as the miner
using a dredge, digs to bedrock, piling sediments behind the
dredge. Use of a suction dredge can channelize a stream as the
miner works the dredge along bedrock, deepening and narrowing a
natural channel. Channelization can eliminate fish habitat by
physically decreasing the area available to fish, by increasing
water velocity, removing cover and by changing riffles and runs
into pool type habitat thereby eliminating areas highly
productive for invertebrates.
Hassler et al. (1986) reported all of these types of channel
change, but they observed that fish move among sites, including
dredge holes, Harvey (1986) made similar observations for trout.
He attributed a reduced abundance of sculpin in the study reach
to loss of suitable habitat due to substrate changes. Hassler et
al. (1986) and Thomas (1985) found that changes in channel
morphometry were typically relatively short in duration. Changes
usually lasted for the season in which dredging occurred. High
flows following dredging redistributed disturbed gravels, though
some dredge holes persisted for more than one season (Hassler et
al. 1986). They also noted that salmon and steelhead spawned on
,a site that had been mined the year before, suggesting that as
long as gravels are redistributed fish spawning may not,, be
affected. As mentioned in the section on the effects on fish,
Thomas noted that gravels disturbed by dredging were washed by
high flows into a downstream pool, eliminating any fish habitat
that may have existed there until sufficiently high flows
recreated the pool.
Dredged sediments may not be redistributed until the
following spring when the ice melts in locations where mining
continues until winter freeze-up, and where winters are very
cold. The impacts of this have not been investigated.
-------
' Another possible threat to the stream channel and therefore
to fish and invertebrate habitat, is using a suction dredge to
mine into the stream bank or by hydraulicly mining the bank.
Hassler et al. (1986) and MeCleneghan and Johnson (1983) surveyed
a combined total of 287 suction gold dredges. They reported that
approximately 7% of these dredges were being operated in such a
way that they were either undercutting the bank or hydraulicly
mining the bank. In all cases the activity observed was illegal,
The impacts associated with this activity are loss of riparian
vegetation and cover, and discharge of silty sediments into the
stream. These impacts have not been quantified for suction
dredges, but mining the area above the active stream channel
creates a condition similar to placer mining with heavy
machinery. These impacts involve sedimentation of the stream
channel and reduced water quality associated with suspended
sediments and elevated levels of metals. Fish and invertebrates .
have been found to be reduced in numbers where wastewater with a
high sediment load is discharged into streams (Bjerklie and
LaPerriere 1985, LaPerriere et al. 1985, Wagener and LaPerriere
1985, Van Nieuwnhuyse and LaPerriere 1986).
\
Existing Regulations
Regulations of Australia, Canada,and most of the western
gold bearing states of the United States were surveyed for
regulation of suction gold dredges. Where suction dredging is
permitted, restrictions are primarily directed toward the
.practices used in operating the dredge as opposed to controlling
the discharge (Table 2). Most of the states and provinces
surveyed had similar regulations. The primary control measures
are size of intake, restriction of the dredge to the active
stream channel, and time windows and stream closures to protect
fish. Additional requirements varied according to management
unit. Canada and Australia had more restrictive regulations than
the United States, with no suction dredging allowed in stream
channels under most circumstances. In Australia suction gold
dredging is not permitted in an active stream- channels (personal
communication). In Canada suction gold dredging is permit only
streams where water quality is already severely degraded
(personal communication).
10
-------
Table 2. Summary of suction gold dredge regulations in gold-bearing states of the western
United States, Canada and Australia.
State
(authority)
Intake Size
Limit
Closures
Restriction to
Active
Channel?
Plan
Required
Spill
Prevent
Chemical
Recovery
Prohibited?
Water
Quality
Limit
Special
Considerations
United States
Oregon
(Dept. of
Env. Qual.)
Alaska
(Dept. of
Fish and
Game)
Arizona
(Dept . of
Env. Qual.)
South
Dakota
(Dept. of
Env . and
Hatrl.
Resrs , )
Wyoming
Guideline
only
(Dept. of
Env. Qual.)
• 4" in state
scenic
waterways .
<= 6"" no need
to file AFMA if
off claim.
No limit.
"Recreational ,
hobby, amateur"
exempt from
regulation ,
<25,Q00 tons
moved requires
"small scale
mining, permit" .
f=Z" requires
letter of
authorization .
>3" requires a
"dozing
permit" .
Window for fish
egg incubation.
Windows for
spawning , egg
incubation and
specific" stream
closures.
No closures.
No closures,
but "critical
areas" may i
require special
cons iteration .
Window for
spawning', trout .
Yes.
Special permit
required for
out~of- stream
mining .
Yes.
No.
No.
Yes.
Ho.
If >6" or
off claim.
Ho.
Thorough
reclamation
plan
required.
Permit
required if
over 3".
Take "care"
not to spill.
No disposal
allowed on
site.
Not
specifically
mentioned, but
covered under
other laws .
Not
specifically
mentioned, but
covered under
other laws.
Not
specifically
mentioned, but
covered under
other laws.
Spills
prohibited.
Yes.
Not
specifically
mentioned,
but covered
under HPDES.
Not
specifically
mentioned.
Prohibition
designated
for "small
scale
mines" .
Hot
specifically
mentioned.
"Minimize"
turbidity,
discharge
to quiet
pool if
practical.
No.
No.
No.
No.
Noise Control.
Special permit
for scenic
waterways .
Special permit
if moving over
50 cubic yards .
Fish Habitat
permit required
if in
anadromous fish
stream or
special site.
Can only
discharge those
substances that
are already
present in the
gravels/soil.
No dredging in
silt or clay.
No dredging in
beaver ponds .
11
-------
Montana
(Dept, of
Health and
Snv. Soi.)
California
(Dept of
Fish and
Game)
Utah
(Dept. of
Satrl. •
Essrs)
Idaho
Colorado
<=4" requires
general permit.
>4" retires
individual
permit
(conditions the
same "for both).
8" limit.
Windows for
spawning .
Windows for
migration and
spawning
specific stream •
closures.
Yes.
Yes.
No.
Plan
required if
one wants
to deviate
from
standard
conditions .
Refers to
Clean Water
Act.
"Precautionary
measures" must
be taken.
Not
specifically
mentioned, but
covered under
other laws .
Yes.
Not
specifically
mentioned .
<=5HTU
over
background
500' down-
stream
No.
Monitoring
retirements
are different
between the SP
and individual
permit.
Special permit
required for
variance from
standard
conditions .
In the process of developing regulations.
5" limit.
Windows for
migration and
spawning .
Specific stream
closures .
Yes.
Ho.
Spill
prevention
included in
permit
conditions .
Yes, but
allowed out
of channel
Permit
conditions
for
turbidity
Prohibited near
campgrounds .
No regulations in place.
Canada
Regulations in Canada are determined by federal law, so all provinces and territories have the same regulations.
Ytikoa and
British
Columbia
No instream suction dredging is allowed unless stream is designated as Type 4 (highly impacted by raining) and water quality limits
for the stream are not violated.
Australia
Victoria,
New South
Wales ,
Queensland
and
Northern
Territory
No instream suction dredging is allowed. Large scale operations have are subject to individual environmental review.
I
-------
Summary of Impacts and Discussion
All of "the studies I reviewed came to the same conclusion:
suction gold dredging had localized and short term impacts.
Caveats must be taken into account when coming to this
conclusion:
1. All of these studies, except one involved small dredges,
6 inches or less. The one study that involved a larger
dredge reported only a small amount of data. Five water
samples were taken 500 feet below a six inch dredge and one
sample was taken 500 feet below an 11 inch dredge.
2. All of the studies were done on dredges that were
operating within the restrictions outlined in Table 2 for
Idaho (Griffith and Andrews), California (Harvey, Summer and
Hassler, Hassler et al., McCleneghan and Johnson,), Montana
(Thomas)'or Colorado (U.S. Army Corp of Engineers).
These investigators also offered the suggestion that suction
dredge mining could have more severe effects if: the dredge }
intake size was larger than those they studied; the density of
dredges was greater; and/or if small tributary or headwater
streams were the target of mining, where the stream did not have
flows large enough to redistribute .disturbed gravels.
It appears clear that the eggs and young stages of fish are
susceptible to damage by suction dredging. Periods when dredging
is not allowed, that permit dredging only when eggs and juvenile
fish are not in the gravel, appear to be effective for protection
of these life stages from direct damage by dredges. While adult
fish do not appear at risk to direct mortality, loss of stream
habitat necessary for the survival of fish populations may pose a
more insidious risk. Dredged sites typically appeared to have
recovered over the period of the off season, however, there still
exists some question about quality of rearing^ habitat that
remains. Carefully thought out permit conditions could prevent
loss of stream habitat that would affect fish populations, but
they will have to be monitored for a more conclusive finding.
Based on the investigations reviewed here, a restriction to
mining only in the active stream channel (wetted perimeter at the
time of mining) and limits on the density of dredges on a given
stream could prevent cumulative or long term loss of habitat.
Aquatic invertebrates appear to be impacted only temporarily
at the immediate location of the dredge. As long as the
distances over which recolonizing individual must travel is
relatively short, recovery of the site is likely to be rapid. If
a large section of stream is dredged over a short period of time
impacts could be more persistent. Many dredges focused on
consecutive sections of a stream could create this type of
situation.
13
-------
• Stream morphometry and water quality also appeared to be
impacted only temporarily. Most sediments settle out of the
water column quickly, but changes in turbidity have been noted up
to 152 meters downstream of a dredge. Redistribution of
displaced gravel was observed to occur over the high flow season
following mining,
Impacts associated with disturbance to streams in very cold
climates have not been addressed. Recolonization of disturbed
sites by invertebrates may be prolonged if dredging occurs just
before freeze up. Generations of invertebrates may be eliminated
from a stream reach if the timing of dredging coincides with egg
laying in' 'a given invertebrate species and where there is not
enough time for recolonization before freeze up. If upstream
populations exist from which recolonization can occur then the
local populations will likely return but may be depressed for a
period into the growing season.
In turn this may affect over wintering and the spring time
feeding by fish. Juvenile grayling (Thymallus arcticus) are
known to over winter in water under the ice cover of streams .v
Disturbed portions of the stream may not be recolonized
sufficiently to produce the invertebrate biomass necessary.to
sustain these fish through the winter. Fish may also be affected
downstream of the site because invertebrate drift may be reduced
from upstream disturbances. In the situation where invertebrate
populations are depressed during the spring then fish may not
have an adequate food base in disturbed and adjacent downstream
waters.
Opportunities exist for additional research. Specifically
information is limited or lacking in the following areas: 1. the
timing and implications of the. redistribution of invertebrates,
fish and displaced gravels in stream subject to .very cold
climates; 2. the long term effects on the species and functional
feeding group composition of aquatic insects in heavily mined
streams; 3. the long term impacts on the growth of fish in areas
repeatedly suction dredged; 4. the long term impacts of elevated
levels of metals in stream sediments on benthic biota and fish.
14
-------
Literature Cited . •
Bjerklie, D. M. and J. D.- La Perriere. 1985. Gold-mining
eff.ects on stream hydrology and water quality, Circle
Quadrangle, Alaska. Water Resources Bulletin,
Vol 21(2):235-243. .
Griffith, J. S. and D. A. Andrews. 1981. Effects of a small
suction dredge on fishes and aquatic invertebrates in Idaho
streams,' North American Journal'of Fisheries Management
1:21-28.
Hassler, T. J., W. L. Somer and G. R. Stern. 1986. Impacts of
suction dredge mining on anadromous fish, invertebrates and
habitat in Canyon Creek, California. Calif. Coop. Fish.
Res. Unit., Humboldt State University, Arcata, California,
Coop. Agreement No. 14-16-0009-1547, Work Order No. 2.
135 pages.
Harvey, B. C. 1986. Effects of suction gold dredging on fish
and invertebrates in two California streams. North American
Journal of Fisheries Management 6:401-409.
Huber, C. and D. Blanchet. 1992. Water quality cumulative
effects of placer mining on the Chugach National Forest,
Kenai Peninsula, 1988-1990. U.S. Forest Service, Chugach
National Forest, Alaska Region. 74 pages.
LaPerriere, J. D., S. .M. Wagener, D. M. Bjerklie. 1985. Gold-
mining effects on heavy metals in streams, Circle
Quadrangle, Alaska. Water Resources Bulletin, Vol
21(2):245-252.
Lloyd, D. S., J. P. Koenings, J..D. LaPerriere. 1987. Effects
of turbidity in fresh waters of Alaska. North American
Journal of Fisheries Management, Vol 7:18-33.
McCleneghan, K. and R. E. Johnson. 1983. Suction dredge gold
mining in the mother lode region of California. California
Department of Fish and Game, Environmental Services- Branch,
Administrative Report 83-1.
Minshall, G. W.,-D. A. Andrews and C. Y. Manual-Faler. 1983.
Application of island biogeographic theory to 'streams:
macroinvertebrate recolonization of the Teton River, Idaho.
in J.R. Barnes and G. 'W. Minshall editors Stream Ecology:
Application and testing of general ecological theory.
Plenum Press, New York.
,Scannell, P. 0. 1988. Effects of elevated sediment levels from
placer mining on survival and behavior of immature Arctic
grayling. Master's thesis. University of Alaska,
Fairbanks, Alaska, USA. 93 pages.
IS
-------
Somer,.W. L. and T. J. Hassier. "1992. Effects of suction-dredge
gold mining on benthic invertebrates • in a Northern
.California Stream. North American Journal of Fisheries
Management 12:244-252.
Thomas, V.' G, 1985. Experimentally determined•impacts of a
small, suction gold dredge on a Montana stream. North
American Journal Fisheries Management 5:480-488.
U.S. Army Corps of Engineers. 1985. Water Quality Study:
Arkansas River above Salida, Colorado. U.S Army Corps of
Engineers, Albuquerque District, P.O. Box 1580, Albuquerque,
New Mexico 87103.
U.S. Environmental Protection Agency. 1991. Regulatory strategy
for controlling small commercial and recreational placer
mining, draft. U.S. Environmental Protection Agency, Office
.of Solid Waste, 2800 Crystal Drive, Crystal Station, Crystal
City, Virginia 20202. EPA Contract No. 68-C8-0066, W.A.
30. SAIC Project No. 1-833-03-630-00. 73 pages.
v
Van Nieuwenhuyse, E. E and J. D. LaPerriere. 1986. Effects of
placer gold mining on primary production in subarctic
streams of Alaska. Water Resources Bulletin.
Vol 22(1):91-99.
Wagener, S. M. and J. D. LaPerriere. 1985. Effects of placer
mining on the invertebrate communities of interior Alaska
streams. Freshwat. Invertebr. Biol., Vol 4(4):208-214
16
------- |