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     About the Niwot Ridge/Green Lakes Valley (NWT) Long-Term
          Ecological Research (LTER) site

     With an initial set of six sites selected in 1980, the National
Science Foundation established the Long-Term Ecological Research
(LTER) Program to conduct research on long-term ecological phenomena 
in the United States. The present total of 18 sites represents a 
broad array of ecosystems and research emphases. The LTER Network is 
a collaborative effort among over 600 LTER scientists and students 
which extends the opportunities and capabilities of the individual 
sites to promote synthesis and comparative research across sites and 
across ecosystems. The mission of the LTER Network is to conduct and 
facilitate ecological research by (1) understanding general 
ecological phenomena which occur over long temporal and broad 
spatial scales, (2) creating a legacy of well-designed and 
documented long-term experiments and observations for use by future 
generations, (3) conducting major synthesis and theoretical efforts, 
and (4) providing information for the identification and solutions 
of societal problems. LTER sites share a common commitment to 
long-term research on the following core research topics: 
(1) pattern and control of primary production, (2) spatial and
temporal distribution of populations selected to represent trophic
structure, (3) pattern and control of organic matter accumulation
in surface layers and sediments, (4) patterns of inorganic inputs 
and movements of nutrients through soils, groundwater and surface
waters, and (5) patterns and frequency of site disturbances.
[excerpts from "Martin, S. 1993. LTER: National research sites with
common commitment. LTER Network Office, University of Washington,
Seattle. 8pp."]

     Niwot Ridge/Green Lakes Valley is the only LTER site that
includes a cirque glacier and extensive alpine tundra. The area
also features a variety of glacial landforms, glacial lakes and
moraines, cirques and talus slopes, patterned ground and permafrost.  
The entire study site lies above 3,000 m elevation. When compared to
nearby low elevations, it is characterized by low temperatures 
throughout the year, increased solar radiation (and consequently
higher levels of ultraviolet radiation), higher wind velocities,
and an abbreviated growing season. 
     The site is located approximately 35 km west of Boulder,
Colorado and so has a mid-latitude continental climate modified by
high elevation and mountainous relief. Annual mean temperature at
3,743 m is -3.7 degrees C. The January mean temperature is -13.2
degrees C and the July mean is 8.2 degrees C. Mean annual
precipitation is about 930 mm, of which one-third is used in
evapotranspiration, the remainder leaving the system as runoff.
     Precipitation is highly variable temporally - most occurs as
snow during the winter and spring months and annual totals vary
greatly from year to year. The interactions betweens wind, snow, 
and high relief result in a mosaic of snow-free and 
snow-accumulation areas with consequent wide variability in the 
amount and timing of meltwater release. Summer precipitation is also 
highly variable, both temporally and spatially, usually arriving in 
brief convective storms. Thus, the moisture available to the tundra 
plants is very unevenly distributed.
     The headwaters of the three major rives of the southwestern
United States (the Arkansas, Colorado, and Rio Grande) are located
in the Colorado Rockies. The mountain snowpacks provide most of the
water used in human activities in the region, which could have 
serious ramifications if global climate change leads to altered
precipitation patterns in the mountains. However, general 
circulation models usually have lower confidence for precipitation 
than for temperature prediction, and the extrapolation from low 
elevations to the alpine tundra adds further uncertainty. Thus, 
continued analysis of the long-term climate database at the Niwot 
Ridge site is important.
     The significance of snowpack, including patterns of deposition,
the timing of snow, its depth and chemical composition, as well as 
its subsequent disappearence, continue to dominate the biological 
and biogeochemical questions addressed by the NWT LTER. New research 
tools to investigate this variable include a subnivean shelter, used 
to monitor biogeochemical processes within and below the snow, and a
60 m snowfence, used to modify the timing, amount, and duration of
snow. Nitrogen enrichment studies are also be conducted as part of
the recognition that enhanced atmospheric deposition of nitrogen has 
and is occurring in this region.  
     The alpine study area is reached by an unimproved road from
the Mountain Research Station (2,895 m) which leads to within 2 km
of the main tundra research site, the Saddle (3,525 m). The D-1
research site, for which climate records are continuous from 1952, 
lies a further 3 km from the road head. The Martinelli study area 
(3,380 m) is located 1 km southwest of the Saddle, in the forest-
tundra ecotone. The Green Lakes Valley lies immediately south of the 
western half of Niwot Ridge. It includes the Arikaree Glacier at its 
head (3,798 m), and the Wetland, Green Lake 4, and Albion research 
sites. The Green Lakes Valley and Martinelli sites are all within the 
City of Boulder watershed which is closed to public access. Niwot 
Ridge, including the main alpine study site, is part of the Roosevelt 
National Forest and has been designated a Biosphere Reserve (United 
Nations Educational, Scientific and Cultural Organization, UNESCO) 
and an Experimental Ecology Reserve (USDA Forest Service).
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