Extended Abstract (148K)15.13
Effects of land-use change on local energy, water and carbon balances in an Amazonian pasture
Ricardo K. Sakai, SUNY, Albany, NY; and D. R. Fitzjarrald, O. L. L. Moraes, O. C. Acevedo, M. Czikowsky, R. Silva, R. Staebler, K. E. Moore, and D. Spiess
Since September 2000, as part of LBA-ECO, we have been monitoring H, LE, Fc (the CO2 flux) and surface layer profiles of T, q, and [CO2] in a pasture near Santarém, Pará, Brazil. The experiment design is to estimate environmental influences on carbon uptake at this pasture, which was rain forest twenty years previously. Our results then are to be compared with similar measurements made by other groups at an undisturbed forest site and a site at which selective logging occurs. After many years as a cattle pasture, our pasture was burned and ploughed in November 2001 and prepared for rice plantation. In this paper, we report on several aspects of these field measurements, with emphasis on the transient response of Fc to the abrupt change in land use, following the sequence during the first rainy season cycle. Measurements are made on a 20-m tower powered by solar panels that provide 500 W continuously. An eddy covariance system was installed at 8.75 m (3D sonic anemometer and a CO2/H2O gas analyzer). Profile measurements include the wind vector (2-D sonic anemometers at 12.25, 5.73, and 3.12 m), T and q (6.09, 4.14, 2.20 m), and [CO2] (11.81, 5.29, 2.71, and 0.5 m). At the top of the tower (17.76 m) upward and downward solar and terrestrial radiative fluxes are found. Soil temperatures (-0.10, -0.24, -0.50,-1.50, and -2.0 m), soil heat flux (-0.30 m), and soil moisture (-0.30 m) are monitored. Our Linux-based PC records all data, and the are processed and stored at nearly real time. Reasonable estimates of the respiration rate (nocturnal Fc) can only be made by accounting for the "storage" in the stable surface layer. Commonly-used u* criteria and surface layer similarity hypotheses are of little use to describe the nocturnal conditions, since extremely stable surface layer conditions are common. A weak, shallow nocturnal drainage flow is frequently observed. Daytime LE and Fc dependence on soil moisture content is illustrated. Fluxes are composed with respect to position in multiday dry-down sequences. Immediately following burning and plowing, a transient pulse of CO2 emission was observed. Detailed comparison of fluxes during pasture and cultivation phases is presented.
Session 15, Boundary Layers over Heterogeneous Surfaces
Friday, 19 July 2002, 8:30 AM-12:15 PM
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