S. H. Hiatt

Methane Emissions from Natural Wetlands in the United States: Satellite-Derived Estimation Based on Ecosystem Carbon Cycling

Abstract Wetlands are an important natural source of methane to the atmosphere. The amounts of methane emitted from inundated ecosystems in the United States can vary greatly from area to area. Seasonal temperature, water table dynamics, and carbon content of soils are principal controlling factors. To calculate the effect of wetlands (and their potential conversion to other land uses) on global greenhouse gas emissions, information on area covered by various wetland types is needed, along with verified projections of spatial variation in net methane emissions. Both of these variables are poorly known, and estimates are largely unavailable at the country level. Nationwide satellite datasets for the coterminous United States (excluding Alaska) have been combined with ecosystem model predictions of monthly net carbon exchange with the atmosphere to produce the first detailed mapping of methane fluxes from natural wetlands on a monthly and annual basis. The Carnegie–Ames–Stanford Approach (CASA) model’s pred...

Estimating carbon budgets for U.S. ecosystems

On a global basis, plants and soils may hold more than twice the amount of carbon present in the atmosphere [Geider et al., 2001]. Under increasing atmospheric carbon dioxide (CO2) concentrations and subsequently warming temperatures, these large biogenic pools may change in size [Cox et al., 2000]. Due to a lack of long-term field studies, there is uncertainty as to whether vegetation and soils will act as a net sink or a source of atmospheric CO2 in coming years. It is certain, however, that no retrospective analysis of the U.S. carbon balance will be possible without a comprehensive historical baseline of the sizes of various ecosystem carbon pools and the variability in their net annual increments.

Satellite Data Analysis and Ecosystem Modeling for Carbon Sequestration Assessments in the Western United States

The active management of long-term carbon pools in terrestrial vegetation and soils is an important tool for mitigating the rise in atmospheric CO 2 concentrations. This paper demonstrates the use ofremote sensing, climate records, and a vegetation-soil model National Aeronautics and Space Administration―Carnegie-Ames-Stanford Approach to estimate the past and future carbon balance in vegetation and soils. Using the western United States (WUS) as a case study, we describe spatially detailed (<10-km resolution) terrestrial carbon budgets for ecosystems of the Rocky Mountain and Pacific regions of the country. Net primary production increased on a western region-wide basis during the 1990s to 0.9 ± 0.1 Pg C/year, but the total terrestrial sink in all western U.S. ecosystems did not exceed 0.01 Pg C/year between 1982 and 1997. Over the entire period of 1982―1997, the total estimated net ecosystem production (NEP) flux from WUS ecosystems was 1.3 Pg C lost to the atmosphere (1 Pg = 1 billion metric tons). Forested mountain areas of the Cascades, the Sierra Nevada Range, the northern California Coast Range, and the southern Rockies were estimated as the only consistent ecosystem carbon sinks up to 1997. Most of the remaining vegetated (nondesert) lands of the western states were estimated to lose between 50 and 350 g C m ―2 as net ecosystem fluxes were summed over the period 1982―1997. Future climate scenario tests imply major ecosystem carbon losses in the west will continue in all but the most isolated forest areas of the mountain regions. Carbon pools in surface soils and woody litter pools in all WUS ecosystems are estimated currently at 12 Pg C. These baseline carbon pools are likely to become more susceptible to loss under climate model predictions for the western states over the next 50―100 years.