We have been measuring tephra/soil erosion rates in the Smith, Bean, Clearwater, Upper Green River areas of the eastern part of the blast zone. Debris slides and debris flows have been inventoried based on field observations and interpretation of aerial photographs for the 1967 to 1984 period. Sheet and rill erosion was measured with arrays of erosion pins. Repeat photography of hillslope, channel, and revegetation changes has been done at a variety of locations. The intensity of measurements has been reduced through time, but all sites could be revisited and longer-term trends in erosion rates estimated.
This preliminary investigation sampled soils in the blast area and blowdown zone in September 1980 for soil arthropods. Predictably, where disruption of pre-eruption ecosystems was most thorough — debris avalanche, pyroclastic flow, blast zone — no soil arthropods survived. In the blowdown zone, by contrast, soil arthropod populations were unaffected largely because they were protected by snow cover at the time of the eruption.
Soils were studied along a disturbance gradient: Pumice Plain, Timberline parking lot, Harmony, Bismark Mtn., Elk Pass, and Fossil Creek Ridge. N03, NH4, N, P, K, Ca, Mg, C were assayed. NO3 and NH4 were also analyzed from resin bags buried at 15 and 30 cm. Soil samples were collected in 1985. Resin bags were buried for 1 year: 1985 – 86, and 1986 -87.
It was hypothesized that tephra from the May 1980 eruption of Mount St. Helens would form an impervious layer, limiting gas exchange (oxygen and carbon dioxide) in the soil. Resulting limited oxygen and excessive carbon dioxide were predicted to affect root and mycorrhizal growth of Pacific silver fir (Abies amabilis) causing higher than normal foliage loss.
Climatic and microclimatic measurements for the summers of 1982 to 1987 were made at three differently disturbed sites around Mount St. Helens. These measurements provided daily information on the physical environment and baseline data for studying the evolution and recolonization of these areas.
Our work has focused on disturbance and recovery of soil, microbial, and plant processes following volcanic disturbance. Particular emphasis was placed on spatial relationships involving the carbon and nitrogen cycles. Comparative studies have been conducted at six sites that were disturbed to varying degrees by the May 1980 eruption of Mount St. Helens. These sites include Butte Camp, Upper Pine Creek, the Lahar on the Muddy River, the former Timberline parking Area, and Meta Lake.
The post-eruption remeasurement of ecology reconnaissance plots installed before 1980 is comprised of five distinct parts. The most basic information was collected on 76 plots relocated during the summer of 1981. Photo points and reconnaissance level plots identical to the pre-eruption plots were installed.
The wetland sampling within the Mount St. Helens National Volcanic Monument is part of a larger study on the Gifford Pinchot National Forest. Information gathered will be used to classify riparian/wetland sites into identifiable ecological units that can be used to understand their environmental characteristics and prescribe appropriate management schemes. Study areas in the Monument are Coldwater Lake, Toutle River debris avalanche, and Goat Marsh Research Natural Area. Sample plots were selected to represent different community types (based on species composition and vegetation structure). Wetlands at Coldwater Lake and Toutle River debris avalanche were created as a result of the May 1980 eruption of Mount St. Helens, and thus can provide unique insight into the development of wetlands and plant succession.
The riparian sampling in the Mount St. Helens vicinity is part of a larger study that extends across the Gifford Pinchot National Forest. Streams sampled on the Mount St. Helens Ranger District are Kalama River, East Fork Fossil Creek, and Pin Creek. The purpose of gathering streamside plot data in this project is to produce a classification of streamside vegetative/geomorphic features. The sampling design is such that plant communities are juxtaposed on their geomorphic surfaces and then related to the stream channel itself. Because this project is being carried out in coordination with a separate Forest Riparian Inventory, we will later be able to relate our riparian information to the aquatic data being collected by the fisheries/hydrology programs.