Key Connections in Amazon Stream Corridors: Using 15N to Trace N Transformations and Transport
Linda
A.
Deegan, Marine Biological Laboratory, ldeegan@mbl.edu
(Presenting)
Christopher
Neill, Marine Biological Laboratory, cneill@mbl.edu
Reynaldo
L.
Victória, Centro de Energia Nuclear na Agricultura/USP, reyna@cena.usp.br
Christie
L.
Haupert, Marine Biological Laboratory, chaupert@mbl.edu
Victoria
Ballester, Centro de Energia Nuclear na Agricultura/USP, vicky@cena.usp.br
Alex
V.
Krusche, Centro de Energia Nuclear na Agricultura/USP, alex@cena.usp.br
Suzanne
M.
Thomas, Marine Biological Laboratory, sthomas@mbl.edu
Small streams act as important sites in the landscape where nutrients arriving from adjacent uplands are retained, transformed, or released to larger rivers. We are using 15N additions to examine how a change in land use from forest to pasture alters N cycling. Addition of 15N-ammonium to a second order forest stream showed that ammonium was nitrified in the stream channel and that the 15N-nitrate produced traveled long distances downstream. This suggests that N uptake is controlled more by microbial energy demand than by requirements for N. This was consistent with our measurements of high oxygen concentrations, very high ratios of inorganic N:P and low availability of easily used organic matter in forest streams. Under these conditions, forest streams convert ammonium to nitrate and transport nitrate long distances downstream. Mass balance calculations suggest that most N was transported downstream and not retained in the stream. Forest conversion to pasture potentially changes N cycling in small streams by lowering oxygen concentration, raising N:P ratios and increasing available organic matter. We hypothesize that because of these conditions, small pasture streams will have longer transport distances for ammonium and shorter transport distances for nitrate compared to forest streams. Addition of 15N-ammonium to a second order pasture stream was used to compare transport and rates of transformation in pasture to forest streams. These data are being combined with information on the kilometers of channels of different orders and characteristics passing through forest and pasture land-use to model N export at the watershed level.
Submetido por Christie Lynn Haupert em 18-MAR-2004
Tema Científico do LBA: SH (Hidrologia e Química das Águas)