Treesearch

These lakes are moderately sensitive to acid deposition; acidification would require precipitation at least as acidic as that presently found in the more heavily impacted areas of eastern North America. Because most snowpack contaminants are released early in the melting process, seasonal acidification pulses would probably occur at much lower levels of acidic inputs.

The fairy shrimp Branchinecta paludosa is a persistent resident of aestival ponds at high elevation in the Medicine Bow Mountains of southern Wyoming. These populations are far removed from the Arctic tundra habitat that typifies the distribution of the species, and appear to represent the southern margin of the range in North America. All of the records for the northern United States and southern Canada appear to lie along the Central Flyway that is a major migration route for waterfowl and shorebirds that nest in the Arctic. Passive dispersal probably provides for frequent colonization...

Increasing atmospheric concentrations of the three main greenhouse gases-carbon dioxide, methane, and nitrous oxide account for about 70% of anticipated global warming, but the production-consumption budgets are not balanced for any of these gases2. Snow can cover between 44 and 53% of the land area of the Northern Hemisphere3 and may be several metres deep in alpine and sub-alpine regions for more than half the year. Most trace-gas budgets assume that trace-gas exchange stops when soil is snow covered or soil temperatures drop to ~0 °C (refs 4, 5). Thus alpine and sub-alpine soils are...

During the month of February, between 46 and 53% of the land area of the northern hemisphere is snow covered. Continental snowpacks act as chemical reservoirs; pollutants can accumulate in the pack over the entire winter and are released during a relatively short spring melt period. Interactions between the snow and the atmosphere can change the quantities of different chemical species stored in the snow. In addition, snow can retain chemical species to be incorporated into major ice sheets and large glaciers. The record of atmospheric chemistry preserved in this way is important in...

Snowpacks in both Colorado and Wyoming were sampled on 15 dates for total microbial biomass, ratio of bacteria to fungi, and major inorganic ions. Levels of viable microbial biomass remained low throughout the period, peaking at 0.05 micrograms carbon/mi. Microscopic analyses indicated this biomass was composed primarily of bacteria. Fungi were not detected in samples taken at or above treeline. With the exception of one date in early May at the Colorado site, bacteria were confined to a band within the snowpack approximately 20 em above the snow/soil interface. Laboratory incubations...

Controlled exposure of ice to a reactive gas, SO2, demonstrated the importance of the chemical composition of the ice surface on the accumulation of acidity in snow. In a series of bench-scale continuous-flow column experiments run at four temperatures (-1, -8, -30 and -60°C), SO2 was shown to dissolve and to react with other species in the ice-air interfacial region at temperatures approaching the melting point of ice. Experiments consisted of passing air containing SO2 through glass columns packed with 100-ìm ice spheres of varying bulk composition (0-5 ìM H2O2, and 0-1 mM NaCl), and...

The alpine timberline in much of western North America is characterized by a structurally complex transition from subalpine forest to alpine tundra, the forest-tundra ecotone. Trees within the ecotone are typically arrayed across the landscape within clumps or "ribbon forests," elongated strips oriented perpendicular to the prevailing winds. This study describes the structure and reconstructs the development of two study plots, one containing ribbon forest and the other, tree clumps. These data are used to develop a theory of ribbon forest origin and development. The plots are located...

Behavioral responses of Drunella coloradensis nymphs were examined in outdoor experimental stream channels after pH reductions of 7 and 2 pH units below ambient. The severity of pH decline below the ambient of 7.8 influenced the behavior patterns displayed by nymphs. At pH 7.01 (an intermediate pH decline) nymphs sat less frequently and burrowed more than controls. Burrowing behavior frequency returned to control levels and drifting and crawling behaviors increased relative to controls at pH 6.02, Ventilatory behaviors increased with pH decline, but were independent of the severity of...

A simulation model [Salmonid Spawning Analysis Model (SSAM)I was developed as a management tool to evaluate the relative impacts of stream sediment load and water temperature on salmonid egg survival. The model is usefi.il for estimating acceptable sediment loads to spawning habitat that may result from upland development, such as logging and agriculture. Software in common use in the USA were adapted for use in gravel bedded rivers and linked to simulate water temperature (the USFWS Instream Water Temperature, SNTEMP model) and water and sediment routing (the USAE Scour and Deposition in...

Vegetation greenness can be monitored at 1-km resolution for the conterminous United States through data obtained from the Advanced Very High Resolution Radiometer on the NOAA-11 weather satellites. The data are used to calculate biweekly composites of the Normalized Difference Vegetation Index. The resulting composite images are updated weekly and made available to land managers who then calculate and display two measures of percentage vegetation greenness. The images provide a useful method of monitoring the condition of vegetation for fire or range management or other land management...