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 ...
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Transport of Particul<strong>at</strong>e Carbon and Nitrogen in <strong>the</strong> Paraíba do Sul River, Rio deJaneiro, Brazil.Alvaro R. C. Ovalle 1 ; Ricardo de O. Figueiredo 2 and Carlos E. de Rezende 31 Universidade Estadual do Norte Fluminense, Av. Alberto Lamego, 2000, Campos dosGoytacazes, RJ, 28015-620, Brazil; 2 Instituto de Pesquisa Ambiental da Amazônia,Av. Nazaré, 669, Belém, PA, 66035-170, Brazil;ramon@uenf.br; rofig@amazon.com.br; crezende@uenf.brThe study of ecosystems <strong>at</strong> meso-scale w<strong>at</strong>ersheds (>1,000 km 2 ) is a useful tool toevalu<strong>at</strong>e changes <strong>at</strong> regional scale. However, this type of research has not been donefrequently in tropical regions. Therefore, <strong>the</strong>re are few opportunities to compare <strong>the</strong>differences among tropical ecosystems. This paper is an <strong>at</strong>tempt to make availableresults about <strong>the</strong> impacts of land use change <strong>at</strong> regional scale in <strong>the</strong> Atlantic Forest. Thisstudy <strong>at</strong>tempts to identify <strong>the</strong> sources and processes associ<strong>at</strong>ed <strong>with</strong> <strong>the</strong> particul<strong>at</strong>ecarbon and nitrogen transport in <strong>the</strong> basin outlet of Paraíba do Sul River (54,000 km 2 ),in <strong>the</strong> St<strong>at</strong>e of Rio de Janeiro. Suspended particul<strong>at</strong>e m<strong>at</strong>ter (SPM) were collected every15 days from Jan/97 to Jan/98 (n=26), analyzed for elemental (C and N) and carbonisotopic ( 13 C) composition, and fraction<strong>at</strong>ed into fine (FSPM < 63µm) and coarse(CSPM > 63µm) c<strong>at</strong>egories. Vari<strong>at</strong>ions for measured parameters were as follows –Discharge (Q): 402/2351; Suspended Particul<strong>at</strong>e M<strong>at</strong>ter (SPM): 10/153; PC c : 0,92/22,2;PC f : 2,21/5,69; PC t :1,84/6,45; PN c : 0,06/1,45; PN f : 0,18/0,80; PN t : 0,17/0,84 (Q in m 3 /s;SPM in mg.L -1 ; C and N in %); 13 C c : -24,26/-19,80‰; 13 C f : -22,94/-20,40‰; 13 C t :-22,91/-20,62‰. Suspended particul<strong>at</strong>e carbon and nitrogen concentr<strong>at</strong>ions presented<strong>the</strong> same temporal p<strong>at</strong>tern for all granulometric fractions, and an inverse correl<strong>at</strong>ion<strong>with</strong> SPM and Q. The same p<strong>at</strong>tern was observed for 13 C, but not for (C:N) a r<strong>at</strong>io, whichpresented lower values during low discharge. Our results suggest th<strong>at</strong> during low flows<strong>the</strong> phytoplankton biomass contribute more to SPM than do <strong>the</strong> upland eroded soils.Comparing isotopic sign<strong>at</strong>ures of potential sources it was detected th<strong>at</strong> wetland soils, inaddition to m<strong>at</strong>erial from sugar cane production, play an important role in C and Nconcentr<strong>at</strong>ions of <strong>the</strong> SPM transported through <strong>the</strong> river outlet. However, <strong>the</strong> insularlands beside <strong>the</strong> upstream dams function as biogeochemistry barriers to <strong>the</strong> delivery ofelements to <strong>the</strong> ocean.Financial Support: CNPq and Faperj
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