plosives used in the impact areas. Contaminated areas
sition is on the west side within 20 km of the river.
were not mapped by our study and the ecological
Deposits immediately adjacent to the Delta River are
effects of contaminants are poorly understood.
as much as 14 m thick (Pw and Holmes 1964).
In summary, fires have had the largest overall
Organic matter accumulation at the surface greatly
effects (59% of area over 50 years) based on mapping
alters soil properties. Unfortunately, we were not able
of fire occurrences. Channel migration was the second
to map organic (less than 40 cm thick) deposits sepa-
most important cause of disturbance (11% over approxi-
rately because organic thickness was highly variable
mately 200300 years, the general age of mature white
and organic terrain could not be differentiated reliably.
spruce) when compared over the entire area. Human
A map of the thickness of the surface organic horizon
impacts have been negligible (less than 1% over ap-
indicates that depths were highly variable, even within
proximately 50 years), although the effects of muni-
small areas (Fig. 16). Areas that had a higher preva-
tions impact areas and trails have not been adequately
lence of organic deposits included highland moraine
quantified and some fires are caused by human activ-
areas, presumably because of poor drainage and low
ity. Similarly, the effects of thermokarst have been neg-
temperatures, and hilly retransported deposits, presum-
ligible (less than 1% of area over approximately 200
ably because of poor drainage in swales and lack of
300 years).
eolian or fluvial sedimentation. In contrast, areas lack-
ing organic accumulation included rugged mountains,
Ecosections
floodplains, and upland portions of lowland moraines.
Classification and mapping
Although bedrock geology was not used in differ-
Ecosections were differentiated on the basis of geo-
entiating ecosystems, differences in lithology can be
morphic units described from field surveys and features
important in assessing the stability of the surface mate-
large enough or sufficiently distinct to map. Field sur-
rials and the chemistry of the soils. The dominant bed-
veys described stratigraphy for 35 classes (Table A2).
rock types in the study area, as mapped by Wilson et al.
During mapping, some classes were added and some
(1998), include granitic rocks, pelitic and quartoze
field classes were combined, resulting in 32 delineated
schist, Nenana gravel, and coal-bearing rocks (Fig. 17).
types (Fig. 14). A combination of classes identified in
Ecological relationships
field surveys and basic mapping units revealed 38 ter-
restrial and 6 aquatic geomorphic units important on
Ecosections, as differentiated by geomorphic units,
Fort Greely (Table 7). Most of the geomorphic units
are ecologically relevant because they represent areas
were fluvial (22), eolian (3), glacial (4), or organic (5)
with differing erosional and depositional environments,
classes. Classification and mapping were based on the
and, therefore, are affected differentially by natural
geomorphic unit at the surface, although stratigraphic
occurring disturbances. For example, Glaciofluvial
units commonly associated with surface geomorphic
Outwash Active-riverbed Deposits are subject to fre-
units are included in descriptions.
quent deposition and scouring, which prevent estab-
The dominant geomorphic units were lowland loess,
lishment of more than a few pioneer plant species.
hilly retransported deposits, old and young moraines,
Glaciofluvial Outwash Abandoned-riverbed Deposits
and glaciofluvial outwash, indicating the dominance of
lack flooding and sedimentation and, thus, tend to have
glacial and eolian processes (Table 8). Moraine depos-
gravelly, dry soils suitable for xeromorphic species. In
its from the Delta (correlated with Illinoian glaciation)
contrast, low-lying areas with substantial loess depos-
and Donnelly (correlated with Wisconsin glaciation)
its have fine-grained soils that are susceptible to the
glaciations and recent and old glaciofluvial outwash
formation of ice-rich permafrost because of the ther-
cover most of the area. These glacial and glaciofluvial
mal properties of silt. The importance of geomorphic
deposits generally are gravelly in texture, excessively
processes on surface forms and ecological characteris-
to well drained, and dry.
tics has been observed in other regions as well (Jorgenson
Many of these areas were capped with wind-blown
1984, Swanson et al. 1988, Montgomery 1997).
loess. A map of depth to gravel, which provides a gen-
Water body types also differentiate numerous char-
eral indication of loess thickness, reveals that older
acteristics that are ecologically important to inverte-
moraines and glaciofluvial outwash, particularly in ar-
brates, fish, and wildlife. Rivers are fundamentally dif-
eas west of the Delta River, have moderately thick (0.5
ferent from lakes. Glacial rivers have lower water tem-
1.0 m) loess deposits (Fig. 15). The map also reveals,
peratures, higher suspended sediment loads, and higher
however, that the distribution can be very patchy, indi-
mid-summer discharge than nonglacial rivers. Shallow
cating differences in deposition and erosion even at lo-
water tends to melt earlier and become warmer than
cations in proximity. Most of the loess is derived from
deep water. Connected lakes allow better fish passage
the floodplain of the Delta River, and most of the depo-
than isolated lakes. Riverine ponds are prone to flood-
44
Previous Page
