Date of Award

Winter 1996

Project Type

Dissertation

Program or Major

Earth Sciences

Degree Name

Doctor of Philosophy

First Advisor

Berrien Moore

Abstract

Global biogeochemical processes are being perturbed by human activity, principally that which is associated with industrial activity and expansion of urban and agricultural complexes. Perturbations have manifested themselves at least since the beginning of the 19th Century, and include emissions of CO$\sb2$ and other pollutants from fossil fuel combustion, agricultural emissions of reactive nitrogen, and direct disruption of ecosystem function through land conversion. These perturbations yield local impacts, but there are also global consequences that are the sum of local-scale influences.

Several approaches to understanding the global-scale implications of chemical perturbations to the Earth system are discussed. The lifetime of anthropogenic CO$\sb2$ in the atmosphere is an important concept for understanding the current and future commitment to an altered atmospheric heat budget. The importance of the terrestrial biogeochemistry relative to the lifetime of excess CO$\sb2$ is demonstrated using dynamic, aggregated models of the global carbon cycle. A central theme is the annual flux of carbon into the terrestrial biosphere. Several mechanisms for modification of the natural amount of terrestrial carbon uptake are discussed, focusing on the effects of pollutant deposition; we estimate the historical flux of carbon due to nitrogen deposition, and its sensitivity to assumptions about the details of ecosystem function and to the accuracy of predicted deposition patterns. Further, we introduce the hypothesis that internal biogeochemical regulation results in extreme interannual fluctuations of carbon exchange. This hypothesis is evaluated, and found to be consistent with global data sets of temperature, atmospheric CO$\sb2$ concentrations, and land surface reflectance.

Satellite remote sensing of vegetation amount and function is one of the most important sources of information about the perturbed terrestrial biosphere. Traditional techniques for using optical reflectance data are discussed, and an unconventional algorithm is introduced, based on the inversion of a plant canopy radiative transfer model. The observation of the land surface at multiple angles is critical in this method. Successful model inversions are performed on a transect in the Central African Republic. We extracted biophysical quantities, as well as implicit information about phenology. This technique will be most useful when proposed satellite instruments provide angular reflectance information.

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