Stream size influences the biogeochemistry of nitrogen in pasture stream channels.
Christie
L.
Haupert, Marine Biological Laboratory, chaupert@mbl.edu
(Presenting)
Linda
A.
Deegan, Marine Biological Laboratory, ldeegan@mbl.edu
Christopher
Neill, Marine Biological Laboratory, cneill@mbl.edu
Alex
V.
Krusche, Centro de Energia Nuclear na Agricultura/USP, alex@cena.usp.br
Reynaldo
L.
Victória, Centro de Energia Nuclear na Agricultura/USP, reyna@cena.usp.br
Victoria
R.
Ballester, Centro de Energia Nuclear na Agricultura/USP, vicky@cena.usp.br
Small streams act as receptors for nutrients arriving from adjacent upland areas, and subsequently transform, retain or release these nutrients to larger rivers. To understand how deforestation and conversion of Amazon forest into pasture alters stream function, we evaluated geomorphology, organic matter stocks and biogeochemical processes of a small (30 L/s) and large (100 L/s) pasture stream in central Rondônia. We conducted two 21-day 15N-ammonium additions to trace transformations and downstream transport of nitrogen and organic matter turnover. The small stream was on average deeper (60-cm) and wider (600-cm) than the large stream (40-cm deep, 350-cm wide). The small stream was bordered by Paspalum grasses that stretched into the stream channel and had organic rich sediments. The large stream was primarily bordered by high soil/sand banks with few grasses growing in the stream channel and had sandy sediments. Grasses growing within 1-m of the edge of both stream channels acquired large amounts of the added 15N (30-130 per mil). Grasses growing further than 1-m from the stream channel border were only present in the small stream and were labeled between 15-30 per mil. Benthic organic matter from the small stream acquired half as much 15N as the large stream. 15N was released from organic matter of both streams at the same rate suggesting organic matter in both streams turned over at roughly equal rates. The small stream retained more nitrogen than the large stream suggesting that alterations in adjacent landscape can have different effects on stream channel biogeochemical processes depending on stream size.
Submetido por Christie Lynn Haupert em 18-MAR-2004
Tema Científico do LBA: SH (Hidrologia e Química das Águas)