| Carbonshed
Study - Niwot Ridge, Colorado |
The oxygen isotopic
composition of atmospheric CO2
is principally affected by CO2
exchange with the terrestrial biosphere and is a potential proxy for
the contribution of terrestrial biomes to the global carbon budget. In
addition, the oxygen isotopic composition of atmospheric CO2
is used to measure many biological and physical processes that
contribute to our understanding of ecosystem ecology, climatology, and
global climate change. Understanding the oxygen isotopic signature of a
biome’s imprint on global CO2
requires
knowing how the isotopic signature is partitioned between respiration
and photosynthesis. This is particularly difficult in mountain regions
since the complex topography creates considerable variation in the
physical characteristics of the region such as temperature, relative
humidity, and δ18O of precipitation
that potentially affects the δ18O
of respired CO2.
Further, δ18O measurements of
nocturnal atmospheric CO2
are confounded by the mixing of locally-respired CO2
with that flowing from higher elevations in the so called
“carbonshed”.
Here are some photos of the research areas. |
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Patchy network of
meadow, aspen, and pine/spruce plant communities in the Rocky Mountains
with Niwot Ridge in background. The snow and hail-capped mountains were
the result of a summer thunderstorm. At lower elevations the storm
brought rain, at mid-elevations hail, and the high elevations saw snow.
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Note
the elk in the bottom left picture. A bull was gathering his harem
around the water source in the bottom of the valley. At least two
satellite bulls are a short distance away.
The Rocky Mountians are
mosiac of plant communities based on differences in aspect, elevation,
edaphic characterisitics. Plants adapt to specific biological,
chemical, and physical environmental conditions. Biological conditions
such as levels of herbivory, associations with other plants in the
commmunity, dispersal abilty, pollination capactity (i.e. correct
pollinators present) affect the survival of a individual or even an
entire plant species in a given area. Chemical conditions such as the
pH of the soil, soil nutrient concentrations, presence of toxins from
environmental pollution or allelopathic properties of other plants
determine the chamical suitability of an area. Temperature and
precipiation together can readily predict the regions that plants will
survive because these two factors affect the type of biome that exists
at the regional scale. However, temperature and precipitation also
affect plant distribution on the local scale. Temperature itself is a
critical physical aspect of an area. The maximum, minimum, the number
of frost-free days, and number of heat units all can determine where a
plant will be able to survive. Temperature can change with elevation
and aspect. North facing slopes are generally cooler than south facing
slopes. If the slope shades the vegetation, then cooler maximum
temperatures and more moist conditions will pervail. Precipitation
varies with physical characterisitics such as the side of the ridge.
Rain shadows or areas of low rainfall exist on the opposition side of
the prevailing direction of weather evewnts bringing precipitation. For
example, the Sierra Nevadas are moist and Death Valley and the White
Mountains of California are in the rain shadow. The Olympic Forest and
Mt Rainier of Washington, while the eastern part of the state is desert
and in the rain shadow because the moisture comes from the Pacific
Ocean. More moist conditions prevail in areas with more direct
sunlight. More areas may have ponderosa pine (Pinus ponderosa)
and grass sparsely covering the ground on the sunny side of a valley.
The other side of the valley will have Engleman's spruce (Abies englemannii),
subalpine fir, alder, and numerous species of shrubs in the understory.
The type of soil (texture, depth, pH, fertility, pattern
of mositure level) also make a huge difference. To understand why
plant species predominate in certain areas and not in others all these
factors have to be considered. |
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Timberline where
subalpine fir and Engleman's spruce can no longer survive the dry,
cold, and inhospitable conditions of high elevations. Alpine areas have
very few frost-free days to allow large trees to produce sufficient
photosynthates to survive the winter (e.g. maintainance/respiration
costs exceed photosynthesis).
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| Placing PVC rings in
the soil to measure night respiration and collect respired CO2.
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| Nederland from across the reservoir at sunset. |
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