Stream water chemistry in three meso-scale hydrologic basins in Eastern Amazonia
Ricardo
de O.
Figueiredo, Embrapa Amazônia Oriental, ricardo@cpatu.embrapa.br
(Presenting)
Daniel
Markewitz, The University of Georgia, DMARKE@smokey.forestry.uga.edu
Eric
A.
Davidson, The Woods Hole Research Center, edavidson@whrc.org
Ewerton
da S.
Cunha, Instituto de Pesquisa Ambiental da Amazônia, ewerton@ipam.org.br
Marysol
A. E.
Schuler, Instituto de Pesquisa Ambiental da Amazônia, marysol@ipam.org.br
Patrício
de S.
Silva, Universidade do Estado do Pará, patriciomat@bol.com.br
We are evaluating the effects of land use change on stream water chemistry of three meso-scale (100’s of km2) hydrologic basins near Paragominas, in Eastern Amazonia, which have the following areas and percentages of forested cover: Cinquenta e quatro (Cq) watershed (130 km2) with 18% forest; Sete (St) watershed (150 km2) with 34% forest; and Pajeú (Pj ) watershed (45 km2) with 45% forest. Eleven field campaigns of stream chemistry measurements were conducted from April 2003 to February 2004 along three first-order streams, from their headwaters in remnant mature forests, through pastures, secondary forests, and agricultural fields. The average values across the sampling stations in each stream are (nutrient concentrations in µM): pH (Cq=5.85; St=4.93; Pj=4.60), conductivity (Cq=39.2; St= 30.2; Pj=40.1 µS cm-1), turbidity (Cq=96.4; St=13.84; Pj=14.21 FTU), alkalinity (Cq=158; St=10; Pj=6 µEq L-1), O2 (Cq=4.79; St=6.22; Pj=4.91 mg L-1), Ca2+ (Cq=21; St=8; Pj=12), Mg2+ (Cq=34; St=13; Pj=19), K+ (Cq=48; St=63; Pj=95), Na+ (Cq=82; St=106; Pj=161), NH4+ (Cq=3; St=0.8 ; Pj=0.6), NO3- (Cq=1.5; St=1.0; Pj=1.8), PO43- (Cq=3.6; St=4.7; Pj=3.4), and Cl- (Cq=119; St=166; Pj=299). In all streams turbidity and pH tend to be lower close to the stream headwaters draining the mature forests and increase downstream. All streams also show a peak in turbidity and pH during the rainy season. Among the three streams, turbidity and pH are highest in the most deforested watershed. Concentrations of O2 decrease in the reservoirs, that ranchers commonly construct. Because soils are relatively similar within the study area, we suspect land use conversion is an important factor affecting the observed trends in stream chemistry.
Submetido por Ricardo Figueiredo em 18-MAR-2004
Tema Científico do LBA: SH (Hidrologia e Química das Águas)