Research About streams

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Sedimentation and geomorphic changes following the 1980-1983 eruptions of Mount St. Helens

Reduced infiltration and burial of surface roughness elements, together with the loss of root strength and reduced evapotranspiration associated with blast-toppled vegetation have dramatically accelerated erosion of blast-affected hill slopes. Other investigators have found that rill erosion rates were initially higher than the yearly average, but then declined sharply so that rill erosion rates during the second year were only 5 percent of the average first year rate. Initial rates of sheet erosion were substantially higher than the average rate for the year, but the rate of decline was not as pronounced as in the case of rill erosion (Swanson, et al., 1983b).

 

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The herpetofauna of Mount St. Helens: survival and colonization following the 1980 eruption.

This study documents the survival and colonization of reptiles and amphibians in areas impacted by the 1980 eruption of Mount St. Helens. Surveys were conducted at 15 locations, with representative sites in three distinct volcanic impact zones, 1) ashfall, 2) blowdown, and 3) blast, during spring and summer from 1980 through 1991. Twelve species of herptiles (9 amphibians, 3 reptiles) are considered to have survived volcanic influences ranging from the directed blast to the accumulation of ash in otherwise unaltered habitats. These survivors represent most of a hypothetical list of 16 species considered to have occurred in the area before the eruption. Generally, surviving species were characterized by being more aquatic than those not found and this was attributed to the thermal buffering capacity of cool ice and snow covered aquatic systems where individuals were protected from the hot volcanic gases.

 

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Recovery of riparian vegetation at Mount St. Helens

This study documents rates and patterns of vegetation recovery at lakes and streams in the blast zone of the May 1980 eruption. Recovery of streamside vegetation was dominated by plants that resprouted from below ground parts that survived the blast. Depending upon frequencies and intensity of secondary disturbances, revegetation from seeds has become increasingly important. Flooding, battering, and deposition of reworked tephra have extremely important effects on streamside revegetation. Recovery rates are more rapid at greater distances from the volcano where blast effects were less devastating.

 

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Stream channel adjustments in the Smith – Muddy River drainage after the 1980 Mount St. Helens eruptions

Stream channel response to the 1980 eruption of Mount St. Helens has varied widely. Stream channels that received only airfall deposits have shown no significant sedimentation following the eruption. In drainage basins that received both blast and airfall deposits, localized channel modification has been observed. However, as the blast/airfall deposits are predominately sand-sized, they have been quickly removed from the steep low-order channels surrounding the mountain with little net effect on pre-eruption channel morphology. Some subsequent channel modification has resulted in lowered gradient reaches downstream as sediment eroded from upstream hill slopes and stream channels has been redeposited in these reaches. Long-term effects in blast/airfall affected streams appear limited to channels subjected to debris torrents resulting from shallow-seated landsliding and breakup of in-channel debris jams.

 

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Microbiology of thermal vents

Our objectives are to observe, enrich, isolate, and identify bacteria from hot springs in the Mount St. Helens area. If any previously undescribed isolates are found, we will characterize them. In two trips to the area so far, we have observed the following: Cyanobacterial (blue-green algal) mats containing filamentous forms, some with heterocysts; filaments with the appearance of the sulfur oxidizer Beggiatoa or Thiothrix; and numerous rod shaped and coccus shaped bacteria. From anoxic sediment at 60oC, we obtained an enrichment of methanogenic bacteria that appeared similar to Methanobacterium thermoautotrophicum. We also obtained an enrichment of the green non-sulfur photosynthetic bacterium, Chloroflexus. We observed few organisms in a vent at 85oC.

 

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Post eruption studies of ecological recovery of lakes and rivers in the blast zone of Mount St. Helens

This study concentrates on the effects of the May 1980 eruption on Spirit Lake. During and subsequent to the eruption, Spirit Lake received debris avalanche material, timber and other forest vegetation, pyroclastic flows, mudflows, ashfall, and geothermal waters.

 

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Recovery of stream ecosystems following catastrophic disturbances

This study was conducted in the Clearwater basin of Mount St. Helens. Three projects within the study investigate recovery of trout and sculpin populations, tailed frog populations, and invertebrate populations. Trout were studied in the main channel of Clearwater Creek, and the effects of large woody debris in the stream on fish populations were examined. Trout populations were still low as of 1990, being one-tenth to 20% of that in undisturbed stream systems; this appears largely due to interruption of spawning in years following the blast and to continuing lack of spawning habitat. Trout densities were found to be higher in areas with lots of woody debris. The condition of trout was high throughout the stream in years since 1984 presumably due to rapid recovery of high abundance of invertebrate prey. By 1985 sculpin densities were as high as or higher than in undisturbed streams.

 

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Recovery of aquatic insect communities in streams near Mount St. Helens

We have monitored stream insect communities from 1980 to 1988 in Clearwater Creek, Elk Creek, and Ape Canyon. Quantitative and qualitative samples indicate rapid colonization in 1981-82, and then a gradual increase in richness and diversity. Over 200 taxa have now been collected from Ape or Clearwater Creeks.

 

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Ecology of the tadpoles of the tailed frog (Ascaphus truei)

Data on the microhabitat parameters, especially pertaining to flow rate and substrate characteristics, of the stream-inhabiting tadpoles of the tailed frog (Ascaphus truei) were collected at two tributaries of Clearwater Creek at Mount St. Helens, Washington and at Parker Creek on Mary’s Peak, Benton County, Oregon. This is the only tadpole in North America that is highly specialized for maintaining position and feeding from algae while attached to rocks via an enlarged oral disc with many rows of labial teeth. Positions of tadpoles in the streams were correlated with oral morphology and associated anatomy. Because of the length of the larval period of Ascaphus, there are usually 2 to 3 yearly cohorts in the streams at one time. We hypothesized that the interaction of the abilities of the tadpoles to adhere to rocky substrates and the size of the tadpole would result in microhabitat segregation. Whether small or large tadpoles occupied fast versus slow water would depend on the growth pattern of the tadpole (drag) versus the changes of the adhesive abilities with size.

 

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Effects of hillslope erosion on revegetation and sediment influx to the Toutle River

The 1980 eruption of Mount St. Helens covered soils with a tephra blanket and killed the forest tree cover in a 550 km2 area. After the eruption, rates of erosion and plant cover were measured on tephra-covered hill slopes north of the volcano, some of which had been subject to one of three land-management practices. Rill erosion was initially greater than sheetwash, but its importance decreased comparatively quickly. On hill slopes left undisturbed since the eruption, rill erosion and sheetwash underwent a rapid and early decline due to the development of a stable rill network and the exposure and creation of more permeable and less erodible substrates. This decline was independent of plant recovery. Logging of trees downed by the eruption and scarification of the surface in preparation for reforestation slowed erosion, although the effect was small because erosion rates had already slowed substantially by the time these two practices were implemented. An experimental grass seeding program gave rise to a plant cover only after erosion had slowed, and then only in a limited range of environments.

 

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