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TG-08 Abstract

Biogeochemical Consequences of Agricultural Intensification in the Amazon Basin

Carlos Clemente Cerri — CENA - Centro de Energia Nuclear na Agricultura (USP) (SA-PI)
Jerry M. Melillo — Marine Biological Laboratory (US-PI)

Objectives





The objectives of this project are to measure changes in key soil processes and

the fluxes of CO2, N2O, and NO associated with the conversion of tropical rainforest to

pasture in Rond˘nia. In sum, these measurements are intended to provide a comprehensive

quantitative picture of the nature of surface soil element stocks, C and nutrient

dynamics, and trace gas fluxes between soils and the atmosphere during the entire sequence

of land-use change from the initial cutting and burning of native forest, through planting

and establishment of pasture grass and ending with very old continuously-pastured land.

These results will also be used to develop process-based trace gas models.





This research is organized around three questions:







  • Question 1: How does the conversion of forest to pasture

    affect soil physical and chemical properties, C, N and P stocks, and C and N cycling

    rates?






  • Question 2: How does the conversion of forest to pasture

    affect the fluxes of CO2, N2O and NO between the soil and the

    atmosphere, and what are the major controls of these fluxes?








  • Question 3: What is the importance of land-use change to

    trace gas fluxes on the scale of Rond˘nia and of the entire Brazilian Amazon Basin?






We have examined changes in the stocks of C, N and P and the cycling rates of C

and N in pastures three years old and older at Nova Vida. While this work documents

changes to biogeochemical processes over a wide range of pasture ages, it does not capture

the potentially large and important changes that occur in the early stages of forest

clearing and pasture establishment. To understand the dynamics of biogeochemical cycles

immediately after deforestation, our efforts related to this question will focus on the

study of changes in C, N and P stocks and C and N cycling rates in a newly created pasture

at Fazenda Nova Vida.





We will also measure the fluxes of N2O and NO in the forests and in the

established pastures along our existing sequences. Concurrent measurements of N2O, NO and

controlling factors will enable as to predict the ratios of the production of these

important gases under a variety of environmental conditions. We will also perform

plot-level manipulations in a forest and two pastures to examine controls on trace gas

fluxes. We will manipulate soil moisture and fertilize with N and P in a forest site and

pastures cleared in 1987 and 1972. These manipulations designed to study the degree to

which soil moisture and N and P availability control the fluxes of N2O and NO. The

understanding of controls of trace gas fluxes gained from these experiments will be used

by us to construct predictive models that will allow extrapolation to other soil types,

climate regimes and management regimes.





We will use ecosystem models of biogeochemical processes coupled with geographically

referenced information on land-cover and land-use change to estimate the changes in C and

N stocks and the fluxes of CO2, N2O and NO throughout the Brazilian Amazon for the past

two decades. Extant biogeochemistry models will be parameterized by us using results of

our own work in Brazil and the research of others working in Brazil and throughout the

new-world tropics. The biogeochemistry models will be of two types: response function

models such as MBL/TCM and processes-based models such as DNDC. We will then couple these

models with information organized in our geographic information system (GIS) on soils,

climate and ecosystem state (land cover and land use) to estimate gas fluxes.





Contribution to LBA-ECO





This study will contribute in several ways to ongoing interdisciplinary efforts

to understand the current biogeochemical functioning of Amazonia, the influence of the

dominant land-use change on that functioning and how these changes will ultimately

influence the interactions between Amazonia and the Earth's biogeochemical cycles and

climate. First, information derived from field measurements of soil carbon balance and the

fluxes of greenhouse gases (N2O, CO2) following deforestation will provide an invaluable

empirical base from which to build Basin-wide assessments of changes to carbon stocks and

trace gas emissions through the use of GIS and other tools for regional extrapolation.

Second, new information on NO fluxes will contribute to understanding of the current

contribution of intact Amazonian forest to the regulation of atmospheric oxidant balance

and its potential for alteration following land cover conversion. Third, improved

understanding of nutrient and moisture controls on soil trace gas fluxes will permit

construction of process-based models that will improve the ability to predict future

consequences of land-use changes, land management practices and altered climate. Not only

will we contribute information to LBA but also measurements made by others in LBA will

serve as a check on our scaling attempts





Research Team Responsibilities







  • Paul A. Steudler: trace gas fluxes and modeling


  • Jerry M. Melillo: regional and basin wide modeling


  • Christopher Neill: nutrient cycling and C and N stocks


  • Diana Garcia, Post Doctoral: P cycling and stocks and trace gas fluxes


  • Carlos C. Cerri: C and N stocks and regional C modeling






Activities





Our research will be conducted at Fazenda Nova Vida in Rond˘nia where we have been

working for the past six years.







  • Nutrient cycling and trace gas measurements along forest-pasture sequences: 1998-1999


  • Nutrient cycling and trace gas measurements in fertilized and irrigated plots:

    1998-2000


  • Trace gas model development and regional extrapolation: 1999-2000


  • Regional and Basin wide modeling: 1999-2000

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