Soils Resource
A complete description of the existing soils resource can
be found in the Soil Resource Assessment Report contained in
the analysis file associated with this Environmental
Assessment. Additional characteristics of the herbicides
proposed for use in Alternative 2 are also included in this
report.
Table 9 : Herbicide Characteristics
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Glyphosate
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Triclopyr
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Dicamba
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Picloram
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Leachability
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none
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very little
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moderate
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rapid
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|
Soil decomposition rate
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slow
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rapid
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moderate
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moderate
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Soil half-life (months)
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none
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<1
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1 to 2
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2 to 4
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Alternative 1, No-Action : The No Action
alternative would maintain noxious weed dominated sites
where they currently exist and continue to incur direct
effects on the soil resource. Although no additional
disturbance to the soils on the sites would occur as a
result of physical, biological or chemical control of
noxious weeds, the current levels of compaction and/or the
lack of organic litter and duff would be maintained on these
sites. Lacey et al. (1989) showed that runoff and sediment
yield were higher for sites dominated by spotted knapweed as
compared to sites dominated by bunchgrass types. Sites
dominated by spotted knapweed were shown to have lower
infiltration rates as a result of the structure of live
vegetative cover and the lower levels of litter on the soil
surface.
The persistence and potential spread of noxious weed
populations on these sites would limit and/or decrease the
amount of litter and duff on the soil surface over time as a
result of the lessened resistance of noxious weed biomass to
weathering. The amount of biomass produced by noxious weed
dominated communities does not appear to be significantly
different than that produced by native plant communities,
indicating that the amount of nutrients available for plants
and soil development would not be altered. Direct effects on
soil structure and pH may be altered over time as a result
of the type of biomass produced, although research
quantifying these changes is limited.
Alternative 2 : Alternative 2 proposes to treat
166 noxious weed sites with a variety of chemical (40 sites
- 476 acres), biological (27 sites - 149 acres), manual (98
sites - 901 acres) and prescribed burning (1 site - 5 acres)
treatments. In general, chemical treatments would have some
direct effects in the short term on the soil resource,
biological treatments are expected to have minimal effects
on the soil resource, manual treatments would have minimal
disturbance and potentially beneficial effects on already
disturbed sites, and burning within the Big Marsh meadow
would have limited direct effects on the soil resource.
Chemical Treatments
Four herbicides are proposed for use under this
alternative, including picloram, glyphosate, triclopyr and
dicamba. The effects of herbicide applications on the soil
and groundwater resources relates directly to the type of
herbicide and rate of application, the characteristics of
the soil types present, and the timing and amount of
precipitation following application. The primary elements
examined as potential effects include: 1) the absorption
characteristics and persistence of herbicide residues in the
soil, 2) the effects of herbicides on microbes and, 3) the
likelihood of leaching of herbicide residues into
groundwater systems or the accumulation in overland
flows.
(1) Absorbtion characteristics and
persistence
The persistence of a herbicide is defined as the
length of time that residues of the initial application
remain detectable in the soil. The decay rate, also known
as the half-life, is defined as the length of time for
half of the intitially measured residues to degrade to
other chemical forms in the soil.
The herbicides proposed for application are primarily
degraded by microbes after their adsorption to ionic
sites provided by organic matter or soil colloids,
otherwise known as the cation exchange capacity (CEC) of
the soil. Their persistence and half-life are thus
directly related to the adsorption characteristics of the
herbicide, the cation exchange capacity of the organic
and combined A and A/C mineral soil horizons and the
amount of microbes that are present and active in the
soil horizons in which residues accumulate. Initial
residues may also be lost from a site from dilution by
rainfall and subsquent movement in overland flows.
The adsorption characteristics of the four herbicides
are included in Table 1 in the Soils Report, although an
adsorption factor for triclopyr was not found. The CEC
for soil types on the Forest range from approximately 8
to 20 meq/100g of soil, a figure that is relatively low
due to the minimal amount of clay colloids and relatively
low amounts of organic matter in the mineral soil.
Microbial biomass of a few pumice and ash soils on the
Forest was measured to range from 324 to 345 mg C/kg of
soil (Busse, pers. comm.), suggesting that there are
sufficient amounts present to degrade the herbicide
residues that are not translocated into vegetative roots,
moved offsite by overland flows or degraded by sunlight.
Soil temperatures at the time of application may delay
initial degradation if temperatures are at or below
measurable microbial activity, although temperatures
conducive to microbial activity would be expected to be
reached within the first month of application.
As a result of these factors, the persistence and
decay rates for the herbicides applied are expected to be
consistent with those described in the Herbicide
Information Profiles and research literature, although
monitoring is recommended to measure this for the pumice
and ash soils found locally. Although short-term
substitution of herbicide residues for plant available
nutrients may occur on ionic exchange sites provided by
organic matter or soil colloids, site productivity is not
expected to be altered as a result of these
applications.
Picloram
The persistence of picloram has been measured to be
approximately 1 year, although residues have been
retained on sites for longer, especially in arid or cold
regions. The half-life of picloram is generally accepted
to be 2 to 4 months. Picloram residues have a moderate
affinity for ionic sites and are readily degraded by soil
microorganisms. This herbicide is highly soluble and
would be susceptible to dilution in rain water and
subsequent accumulation in overland flows during the
immediate weeks following application.
Glyphosate
The persistence and decay rate of glyphosate in soils
examined in literature that are of similar temperature
regimes and biological activity as the soils located in
the proposed application areas ranges from 3 months to a
year, and 1 to 2 months, respectively (Stark, 1982) and
(Roy, 1989). Glyphosate residues have a very strong
affintity for ionic sites and are unlikely to leach into
groundwater systems. The persistence and rates of decay
for the residues that are held within the organic and
mineral soil horizons are expected to be similar to those
cited in research literature.
Dicamba
The persistence of dicamba is generally lower than the
other herbicides due to its high solubility and rapid
degradation by microbes. The half-life of dicamba is
generally accepted to be 1 to 2 months. Dicamba is not
strongly adsorbed to soil colloids and is readily
dissolved into soil water following initial adsorption to
soil colloids or organic matter sites.
Triclopyr
The persistence of triclopyr is approximately 8 to 10
months, with a half-life of 1 to 3 months. Triclopyr is
weakly adsorbed to organic matter and soil colloids and
can be detached into soil water following initial
adsorption. This herbicide is readily degraded by
microorganisms and is expected to have a half-life and
persistence similar to that described in research
literature.
(2) Effects on Microbes
Direct effects of herbicide application and
persistence include the potential for decreasing
microbial populations or altering species composition of
microorganisms in the soil profile. Three of the
herbicides proposed for use under this alternative are
readily degraded by microorganisms and show moderate to
low levels of toxicity to soil organisms. Dicamba appears
to have the highest level of toxicity to microorganisms.
Research on the direct effects of herbicides on
microorganisms is limited in detail. Additional
information can be found in the Soils Resource Assessment
Report.
(3) Accumulation in groundwater or overland
flow
Herbicide solubility and persistence, soil
permeability and percolation rates, and precipitation
patterns following application are the primary factors in
determining the level of risk for the accumulation of
herbicide residues in groundwater or overland flows.
Buffers included around perennial and intermittent
streams and areas with high seasonal water tables are
intended to reduce the possibility of diluted residues
from reaching a perennial stream or surface body of
water.
Residues of glyphosate that are dissolved in surface
water are subject to rapid degradation as a result of
chemical reactions stimulated by light (USDA Forest
Service 1984). Glyphosate persists for extended periods
of time in groundwater or water in the soil profile where
light is absent. Dilution is the primary process for the
dissipation of this herbicide in groundwater. Glyphosate
is highly unlikely to reach groundwater beneath the
application areas.
Picloram, triclopyr and dicamba are all highly soluble
in water and subject to degradation by sunlight and
microorganisms in surface waters. The half-life of
triclopyr in water exposed to sunlight is less than 24
hours.
Biological Treatments
Treatment of approximately 149 acres would occur with the
release of adult insects whose larvae or adult stages are
capable of targeting noxious weed seeds or plant fibers for
food. A list of these species can be found in the Noxious
Weed, Vegetation and Human Health Assessment Report. The
release of these insects is unlikely to directly affect the
soil resource, although additional competetion may alter
existing soil organism populations. Research literature
addressing competetion and population dynamics with the
addition of species specific insects is limited in
scope.
Manual Treatments
Approximately 901 acres on 98 sites would be physically
treated by pulling or clipping existing noxious weed
species. These treatments would generally have a beneficial
effect on the soil resource by contributing biomass for
decay and eliminating competition for native plant species.
Weed biomass that is pulled or clipped would be left onsite
unless the plants have produced flowers or set seed, in
which case the material would be bagged and disposed off
site. Biomass left on site would initially contribute to
organic matter levels on site that function as surface cover
and would subsequently be available for microbial
degradation into plant available nutrients.
The pulling of plants from specific sites would remove
roots from the soil profile and provide aeration in the
mineral soil rooting zone. The infiltration rates of these
sites may also increase slightly. The majority of the sites
proposed for treatment are disturbed from past activities
and would benefit from any increases in aeration provided
from this operation. Native species that were present on
site or, as in the case of a few of experimental sites,
transplanted or seeded would benefit from these changes in
soil conditions and the reduction of competition for
available water and nutrients.
Prescribed Burning Treatments
The treatment of approximately 5 acres of Big Marsh using
prescribed fire would have limited effects on the soil
resource. Soil productivity is not likely to be
detrimentally affected since burn intensities are unlikely
to be high enough to create a long duration of temperatures
exceeding the volatilization temperatures of inorganic forms
of nutrients in the soil profile. Although the reduction of
reed canary grass composition is the stated goal the
treatment is unlikely to remove all of the live organic
matter on the site, providing production of biomass to
contribute to nutrient recycling in the future.
Alternative 3 : The 40 sites covering
approximately 476 acres which are proposed for chemical
application under alternative 2 would be treated with
biological and manual means under alternative 3. The
potential effects of herbicide residues on soil conditions,
organisms and ground or surface water systems would not
occur under this alternative. The effects of biological and
manual treatments would be similar to those described under
Alternative 2, except over a wider area.
RETURN
Air Quality
Alternative 1, No-Action : There would be no
burning proposed with this alternative, therefore there
would be no direct, indirect, or cumulative effects to air
quality.
Alternatives 2 & 3 : There would be five
acres burned at Big Marsh on the Crescent Ranger District to
determine the effectiveness of burning reed canary grass.
Smoke would be produced but its duration and concentrations
would be slight due to the vegetation (mostly grasses, forbs
and sedges) proposed for burning. Burning would be done in
accordance with the Oregon Smoke Management Plan. These
measures include (1) maintaining satisfactory atmospheric
environments in designated areas and other sensitive areas
consistent with the plan objectives and smoke drift
restrictions, (2) writing a burn plan which includes burning
prescriptions, (3) adhering to smoke management forecasts
and advisories, and (4) limiting smoke impacts to downwind
communities and Class 1 Wildernesses (Diamond Peak and Mt.
Theilson Wildernesses).
There would be no aerial application of herbicides with
this EA.
RETURN
Fisheries
Alternative 1, No-Action : Untreated populations
of noxious weeds in or adjacent to riparian areas would have
the potential to indirectly affect aquatic resources.
Because many noxious weed species are not as effective at
stabilizing soils and preventing erosion as native species,
the displacement of native vegetation increases the
potential for fine sediment into the aquatic environment.
Noxious weed displacement of native riparian vegetation
could also affect the degree of shading and organic material
accumulating in the aquatic systems.
Alternative 2 : Herbicide applications on 40 sites
(476 acres) would have a very low potential to adversely
affect fish and aquatic invertebrate species if applied in
accordance with the mitigation measures identified such as
100 foot no herbicide application areas adjacent to riparian
areas, streams (intermittent and perennial), and high water
table areas. The analysis of herbicide use on riparian
resources and fisheries in the FEIS for Managing Competing
and Unwanted Vegetation concluded that the likelihood of
exposure of fish populations to toxic concentrations of
herbicides used would be low (USDA, 1988). Of the 4
herbicides proposed for use, picloram is moderately toxic to
fish and slightly toxic to aquatic invertebrates. Dicamba is
practically non-toxic to aquatic invertebrates and warmwater
fish, and slightly toxic to coldwater fish (rainbow trout).
Glyphosate is practically non-toxic to fish and aquatic
invertebrates. All four herbicides have low bio-concentation
factors in coldwater fish and are rapidly excreted as the
concentration in the water decreases due to dilution and /
or degradation.
With the implementation of mitigation measures identified
in Chapter 2, short-term entry of biologically significant
levels of herbicides into surface waters should be
prevented.
Biological, prescribed burning and manual treatment
effects are the same as those discussed under Alternative 3
below.
Alternative 3 : There would be no potential for
chemical contamination of fish or invertebrate species
because no herbicides are proposed for use with the
implementation of this alternative. Impacts to fish and
aquatic species from manual treatments would primarily
result from compaction (minor) and runoff events on bare
soils. The amount of acreage treated within a watershed
would be small compared to the overall acreage and impacts
of compaction from other activities such as timber
harvesting. Due to the small area proposed for treatment
with prescribed fire, no degradation of water quality or
fish habitat would result from the burning activities. There
would be no impacts to water quality or fish habitat with
the use of biological control agents. Because biological and
manual treatments take more time for results to be realized,
adverse effects to riparian vegetation and watershed
vegetation diversity would indirectly impact fisheries and
aquatic habitat. The effects would be similar to Alternative
1 but would result in some gains in noxious weed population
control.
Alternatives 2 and 3 : Neither action alternative
would result in substantial adverse impacts on the fisheries
resource due to manual or biological treatments which may
cause increased sedimentation (from compaction) or riparian
vegetation alteration.
RETURN
Hydrology
A discussion on water quality can be found under Issue
3.
During the analysis of this proposal, it was discovered
that public water wells were located within 1 mile of
proposed herbicide treatment sites. Most wells are located
on private lands adjacent to National Forest lands though a
few wells are located on federal lands and administered
under a special use permit. Private companies maintain the
wells and supply water to homeowners in areas not supplied
by city water. Most wells are hundreds of feet deep and
access the large aquifer. There are no restrictions
currently in effect for the use of herbicides within a
specified distance of public water wells. Forest officials
are currently in contact with the private companies and have
notified them of the proposed activities. Mitigation
measures include using only glysophate or manual or
biological treatments within 1/4 mile of public wells.
Forest officials are also in contact with Oregon State
Department of Environmental Quality to insure measures are
implemented to protect public water wells. Based on the
mitigations identified above and in Chapter 2, it is
unlikely that implementation of either Alternative 2 or 3
would result in impacts to public wells. Cumulative impacts
to public water wells could also occur from private
landowners' activities, especially from shallow, unsealed
wells that could allow surface runoff and subsurface flow of
fertilizers or herbicides which may contaminate ground
water.
RETURN
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