50 research outputs found
Biogeochemical processes in sagebrush steppe: Interactions of terrain, vegetation and chemical cycles
Publications, manuscripts in various stages of progress, presentations made at scientific meetings, and undergraduate honor thesis and one Ph.D. dissertation are contained
THE CONTRIBUTION OF ENVIRONMENTAL AMENITIES TO AGRICULTURAL LAND VALUES: HEDONIC MODELLING USING GEOGRAPHIC INFORMATION SYSTEMS DATA
Geographic Information Systems (GIS) data are used in a hedonic model to measure the impact of recreational and scenic amenities on agricultural land values. Results indicate agricultural land values are determined by environmental amenities as well as production attributes. Significant amenity variables included scenic view, elk habitat and fishery productivity.Environmental Economics and Policy, Land Economics/Use,
Estimation of Carbon Sequestration by Combining Remote Sensing and Net Ecosystem Exchange Data for Northern Mixed-Grass Prairie and SagebrushâSteppe Ecosystems
Carbon sequestration was estimated a northern mixed-grass prairie site and a sagebrushâsteppe site in southeastern Wyoming using an approach that integrates remote sensing, CO2 flux measurements, and meteorological data. Net ecosystem exchange (NEE) of CO2 was measured using aircraft and ground flux techniques and was linearly related to absorbed photosynthetically active radiation (APAR). The slope of this relationship is the radiation use efficiency (Δ = 0.51 g C/MJ APAR); there were no significant differences in the regression coefficients between the two sites. Furthermore, ecosystem chamber measurements of total respiration in 1998 and 1999 were used to develop a functional relationship with daily average temperature; the Q10 of the relationship was 2.2. Using the Advanced Very High Resolution radiometer. Normalized Difference Vegetation Index and meteorological data, annual gross primary production and respiration were calculated from 1995 to 1999 for the two sites. Overall, the sagebrushâ steppe site was a net carbon sink, whereas the northern mixed-grass prairie site was in carbon balance. There was no significant relationship between NEE and APAR for a coniferous forest site, indicating this method for scaling up CO2 flux data may be only applicable to rangeland ecosystems. The combination of remote sensing with data from CO2 flux networks can be used to estimate carbon sequestration regionally in rangeland ecosystems
Possible thermochemical disequilibrium in the atmosphere of the exoplanet GJ 436b
The nearby extrasolar planet GJ 436b--which has been labelled as a 'hot
Neptune'--reveals itself by the dimming of light as it crosses in front of and
behind its parent star as seen from Earth. Respectively known as the primary
transit and secondary eclipse, the former constrains the planet's radius and
mass, and the latter constrains the planet's temperature and, with measurements
at multiple wavelengths, its atmospheric composition. Previous work using
transmission spectroscopy failed to detect the 1.4-\mu m water vapour band,
leaving the planet's atmospheric composition poorly constrained. Here we report
the detection of planetary thermal emission from the dayside of GJ 436b at
multiple infrared wavelengths during the secondary eclipse. The best-fit
compositional models contain a high CO abundance and a substantial methane
(CH4) deficiency relative to thermochemical equilibrium models for the
predicted hydrogen-dominated atmosphere. Moreover, we report the presence of
some H2O and traces of CO2. Because CH4 is expected to be the dominant
carbon-bearing species, disequilibrium processes such as vertical mixing and
polymerization of methane into substances such as ethylene may be required to
explain the hot Neptune's small CH4-to-CO ratio, which is at least 10^5 times
smaller than predicted
The Hawaii Infrared Parallax Program. III. 2MASS J0249-0557 c:A Wide Planetary-mass Companion to a Low-mass Binary in the ÎČ Pic Moving Group
We have discovered a wide planetary-mass companion to the Pic moving
group member 2MASSJ02495639-0557352 (M6 VL-G) using CFHT/WIRCam astrometry from
the Hawaii Infrared Parallax Program. In addition, Keck laser guide star
adaptive optics aperture-masking interferometry shows that the host is itself a
tight binary. Altogether, 2MASSJ0249-0557ABc is a bound triple system with an
object separated by AU (40")
from a relatively close ( AU, 0.04") pair of
and objects. 2MASSJ0249-0557AB is
one of the few ultracool binaries to be discovered in a young moving group and
the first confirmed in the Pic moving group ( Myr). The mass,
absolute magnitudes, and spectral type of 2MASSJ0249-0557 c (L2 VL-G) are
remarkably similar to those of the planet Pic b (L2,
). We also find that the free-floating object
2MASSJ2208+2921 (L3 VL-G) is another possible Pic moving group member
with colors and absolute magnitudes similar to Pic b and
2MASSJ0249-0557 c. Pic b is the first directly imaged planet to have a
"twin," namely an object of comparable properties in the same stellar
association. Such directly imaged objects provide a unique opportunity to
measure atmospheric composition, variability, and rotation across different
pathways of assembling planetary-mass objects from the same natal material.Comment: Accepted to AJ, only change is color scheme of figure
Conceptual toolboxes for twenty-first-century ecologists
We ecologists realize that individually we have a variety of interests, knowledge, and skills among us; and we appreciate how those attributes differentially apply to the diverse tasks we address in our various âpracticesâ of ecology. Less obvious to us, however, is the variety of intellectual tools we bring to bear in our practices. In order to understand how members of our discipline âthinkâ as well as âknowâ and âact,â this paper explores how the utility of ecological concepts varies among ecologists and how concepts tend to be lumped into what might be viewed as cognitive âtoolkitsâ for implementing our work. Knowing the character of these metaphorical toolkits helps us to understand the nature of our discipline, to better teach ecology, and to more effectively communicate with one another. We collected âusefulnessâ ratings of 131 normative concepts (i.e., what an ecologist ought to know) through an Ecological Society of America-wide survey and analyzed results through cluster analysis. Ten concept clusters emerged, each having varying numbers of concepts and various degrees of subject matter cohesion. Only some of these resembled commonly recognized specializations in ecology. General descriptors for these clusters are as follows: general ecology, population ecology, community ecology, evolutionary ecology, ecosystem ecology, biogeochemistry, spatial structures, scaling structure and function, cross-system structures, and cross-system dynamics