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Biogeochemical Cycling Of Methyl Bromide In Soils, Ruth Kerwin Varner

Doctoral Dissertations

Tropospheric methyl bromide (CH3Br) is a significant source of ozone (O3) destroying bromine to the stratosphere. Due to this threat, the cessation of the production and use of fumigant CH3Br has been slated for 2005 by the Montreal Protocol nations. This decision was based on CH3Br's relatively long atmospheric lifetime which is estimated from the current understanding of its natural and anthropogenic sources and sinks. The research presented in this dissertation has focused on determining the magnitude and characteristics of the biogeochemical exchange of atmospheric CH3Br with upland and wetland soils to attain a better understanding of these portions of …

Source, Production And Export Of Dissolved Organic Carbon And Nitrogen, Jacqueline A. Aitkenhead-Peterson

Doctoral Dissertations

The purpose of this research was to quantify the major sources of dissolved organic carbon (DOC) and nitrogen (DON) in forest soils and ascertain mechanisms for their production and export to surface waters. To quantify the source of DOC we made use of the on-going litter manipulation study (DIRT) at Harvard Forest, Massachusetts. The organic horizon supplies 74% of DOC to bulk soil solution, 12% is supplied by leaf litter, and 13% from root exudate and decay. In plots with no inputs, DON concentrations were 9% higher than the control plots. When either roots or litter were excluded, DON concentrations …

Carbon And Nitrogen Dynamics Of Northeastern United States Forests In Response To Environmental Stress: Measurements And Models At Local To Regional Scales, Scott V. Ollinger

Doctoral Dissertations

This thesis stems from several ongoing efforts to characterize patterns of productivity and nitrogen cycling in northeastern US forests and to address the effects of nitrogen deposition, tropospheric ozone and rising atmospheric CO2. The work reported on involves two related projects; (1) an ecosystem model analysis that integrates physiological and biogeochemical processes with important environmental variables across the northeast region and (2) a field and remote sensing analysis that examines landscape-level patterns of forest biogeochemistry in the White Mountains of New Hampshire.

Chapter 1 presents a regional analysis of forest productivity using the PnET forest ecosystem model and discusses the …

Modeling Plant-Soil-Atmosphere Carbon Dioxide Exchange Using Optimality Principles, Kevin Patrick Tu

Doctoral Dissertations

The exchange of carbon dioxide (CO2) between terrestrial ecosystems and the atmosphere plays a central role in the ecology of the biosphere and the climate system. Towards quantification of ecosystem-atmosphere CO 2 exchange, a generalized model of plant-soil-atmosphere CO2 exchange (OPTICAL) was described and evaluated using eddy covariance measurements of net ecosystem exchange of CO2 (NEE) in arctic, boreal, temperate, and tropical landscapes. The model requires no calibration and is based on theories of plant resource optimization and plant-soil nutrient feedbacks. The model predicts canopy photosynthetic capacity (Pcmax), canopy photosynthesis (P c), plant respiration (Rp), and soil heterotrophic respiration (RH). …

Soil Hydraulic Controls Over Nitrogen Oxide Emissions And Nitrogen Cycling In Tropical Agriculture, Antje M. Weitz

Doctoral Dissertations

Soils are the major natural source of nitrous oxide (N2O). Intensive land use increased atmospheric concentrations of this greenhouse gas. Soil microbes produce and consume nitrogen oxides (NO, N2O) during the processes of nitrification (aerobic) and denitrification (anaerobic). Micro-scale variability of controlling factors cause nitrification and denitrification to occur simultaneously in soils, resulting in high spatial variability of nitrogen oxide emissions. Fertilization increases nutrient availability and thus N2O fluxes. Forest soils in the humid tropics account for 20--50% of all N2O sources. Expansion and intensification of tropical agriculture is expected to increase atmospheric N2O concentrations.

We measured N2O fluxes from …