NASA Ames Global Ecosystem Science

Understanding Change in the Biosphere

1.   NASA-CASA Daily Model

A daily time step version for the soil climate, biogeochemical, and trace gas components of NASA-CASA has been developed and is currently being validated at a number of research sites around the world. In order to better represent localized climate and mineral processes on soil water and nutrient dynamics, several important modifications are made, including development of moisture and heat fluxes through layers in the plant-soil environment, and refinement of microbial responses to wetting-drying episodes. A methane flux component is being tested for northern wetlands sites.

FIGURE CAPTION: Daily Soil Model

1.1.   Major findings

• Model tests in three tropical forest stands over a soil age gradient (ranging from 200 to 185,000 years old) on the island of Hawaii showed that simulations correctly predict the observed difference of an order of magnitude between N2O emission fluxes in the youngest and the oldest forest soils.
• Simulated methane emissions in wetland ecosystems of Alaska and central Canada (BOREAS sites) correctly predict the seasonal range of CH4 flux, along with observed water table depth and soil thaw dynamics.

1.2.   References:

Frolking, S. E., A. R. Moiser, D. S. Ojima, C. Li, W. J. Parton, C. S. Potter, E. Priesack, R. Stenger, C. Haberbosch, P. Dorsch, H. Flessa, and K. A. Smith. 1998. Comparison of N2O emissions from soils at three temperate agricultural sites: Simulations of year-round measurements by four models. Nutrient Cycling in Agroecosystems. (In Press).

Potter C. S., R. H. Riley, and S. A. Klooster. 1997. Simulation modeling of nitrogen trace gas emissions along an age gradient of tropical forest soils. Ecological Modeling. 97(3):179-196.

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