A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...
A Look at Amazon Basin Seasonal Dynamics with the Biophysical ... A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...
Organic matter composition of rivers of the Ji-Paraná basin (southwest Amazonbasin) as a function of land use changes.Bernardes, M. C. 1∗ ; R. L. Victoria 1 ; L. A. Martinelli 1 ; A. V. Krusche 1 ; M. Moreira 1 ; J.P. H. B. Ometto 1 ; M. V. R. Ballester 1 ; A. Aufdenkamp 2 ; J. E. Richey 2 ; J. I. Hedges 21 Laboratório de Ecologia Isotópica, Centro de Energia Nuclear na Agricultura,Universidade de São Paulo.2 School of Oceanography, University of Washington, Box 355351, Seattle, WA, USA.Abstract. We investigated the forms and composition of dissolved and particulateorganic matter (OM) in rivers of the Ji-Paraná basin (64.300 km 2 ), Rondonia, whichhas a drainage basin verging the Amazon lowlands, and has been deforested to theextent of approximately 40% in the last three decades, most related to pastureimplementation. The results obtained in this study were compared with otherAmazonian rivers that have their headwaters in the Andean region. We determined aseries of chemical (C,N), biochemical (lignin) and isotopic tracers (δ 13 C and δ 15 N) inthree size classes of organic matter within five sites along Ji-Paraná River and eightmore sites in six tributaries. For Ji-Parana mainstem the land use changes have not yetchanged the compositional characteristics of riverine OM. The coarse fraction (CSS >63 µm) is least degraded and derives primarily from fresh C3 leaves. The fine fraction(FSS > 0.1 µm) is mainly associated with the mineral soil phase, but its ultimatesource appears also to be leaves from forests. This fraction has similar high nitrogencontent as others Amazonian rivers. The ultrafiltered dissolved organic matter(UDOM > 1,000 M.W.) appears to have the same source as the coarse fraction, butthe lignin analysis ([Ad/Al] V ratio) determined as the most degraded of the threefractions, and also with the highest δ 13 C values. However, in smaller catchments withintensive deforestation, the C4 signal has already been detected in the UDOMfraction, with percentage up to 35% and 24% in the Rolim de Moura and Jarutributaries.Key words: organic matter, land-use, Amazon rivers, deforestation, C4 plants,pasture, isotopes and lignin.∗ Author to whom correspondence should be addressed. Caixa Postal 96, CEP 13400-970,Brazil, Fax: 55-19-4349210, e-mail: bernardes@cena.usp.br
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Organic m<strong>at</strong>ter composition of rivers of <strong>the</strong> Ji-Paraná basin (southwest <strong>Amazon</strong>basin) as a function of land use changes.Bernardes, M. C. 1∗ ; R. L. Victoria 1 ; L. A. Martinelli 1 ; A. V. Krusche 1 ; M. Moreira 1 ; J.P. H. B. Ometto 1 ; M. V. R. Ballester 1 ; A. Aufdenkamp 2 ; J. E. Richey 2 ; J. I. Hedges 21 Labor<strong>at</strong>ório de Ecologia Isotópica, Centro de Energia Nuclear na Agricultura,Universidade de São Paulo.2 School of Oceanography, University of Washington, Box 355351, Se<strong>at</strong>tle, WA, USA.Abstract. We investig<strong>at</strong>ed <strong>the</strong> forms and composition of dissolved and particul<strong>at</strong>eorganic m<strong>at</strong>ter (OM) in rivers of <strong>the</strong> Ji-Paraná basin (64.300 km 2 ), Rondonia, whichhas a drainage basin verging <strong>the</strong> <strong>Amazon</strong> lowlands, and has been deforested to <strong>the</strong>extent of approxim<strong>at</strong>ely 40% in <strong>the</strong> last three decades, most rel<strong>at</strong>ed to pastureimplement<strong>at</strong>ion. The results obtained in this study were compared <strong>with</strong> o<strong>the</strong>r<strong>Amazon</strong>ian rivers th<strong>at</strong> have <strong>the</strong>ir headw<strong>at</strong>ers in <strong>the</strong> Andean region. We determined aseries of chemical (C,N), biochemical (lignin) and isotopic tracers (δ 13 C and δ 15 N) inthree size classes of organic m<strong>at</strong>ter <strong>with</strong>in five sites along Ji-Paraná River and eightmore sites in six tributaries. For Ji-Parana mainstem <strong>the</strong> land use changes have not yetchanged <strong>the</strong> compositional characteristics of riverine OM. The coarse fraction (CSS >63 µm) is least degraded and derives primarily from fresh C3 leaves. The fine fraction(FSS > 0.1 µm) is mainly associ<strong>at</strong>ed <strong>with</strong> <strong>the</strong> mineral soil phase, but its ultim<strong>at</strong>esource appears also to be leaves from forests. This fraction has similar high nitrogencontent as o<strong>the</strong>rs <strong>Amazon</strong>ian rivers. The ultrafiltered dissolved organic m<strong>at</strong>ter(UDOM > 1,000 M.W.) appears to have <strong>the</strong> same source as <strong>the</strong> coarse fraction, but<strong>the</strong> lignin analysis ([Ad/Al] V r<strong>at</strong>io) determined as <strong>the</strong> most degraded of <strong>the</strong> threefractions, and also <strong>with</strong> <strong>the</strong> highest δ 13 C values. However, in smaller c<strong>at</strong>chments <strong>with</strong>intensive deforest<strong>at</strong>ion, <strong>the</strong> C4 signal has already been detected in <strong>the</strong> UDOMfraction, <strong>with</strong> percentage up to 35% and 24% in <strong>the</strong> Rolim de Moura and Jarutributaries.Key words: organic m<strong>at</strong>ter, land-use, <strong>Amazon</strong> rivers, deforest<strong>at</strong>ion, C4 plants,pasture, isotopes and lignin.∗ Author to whom correspondence should be addressed. Caixa Postal 96, CEP 13400-970,Brazil, Fax: 55-19-4349210, e-mail: bernardes@cena.usp.br
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