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The chemistry of two streams draining kaolinitic soils
Daniel Markewitz (Univ. of Georgia)Ricardo Figueiredo (EMBRAPA)
Eric Davidson (Woods Hole Research Center)Mercedes Bustamante, Lucilia Parron, and Julio
Resende (Univ. de Brasilia)
Objectives:
• To develop a biogeochemical understanding of streams draining watersheds comprised of highly weathered soils in the Amazon and Cerrado.
• Compare seasonal patterns of cation concentrations.
Observation of anomalous patterns of increasing streamwater cation concentrations with increasing stream flow.
Mortatti and Probst 2003, Chemical Geology
Streams (Igarapés):Cq = Igarapé Cinquenta e quatroSt = Igarapé do SetePj = Igarapé Pajeú
Study Area: Fazenda Vitoria, Paragominas, Para
Marques et al., 2003Geoderma
Soilscapes in the Cerrado
Gleissolo Haplico
Plintossolo Argiluvico
Plintossolo Haplico
Latossolo Amarelo0-5 760
5-20 820
20-40 840
40-70 860
70-120 840
0-10 360
10-20 440
20-40 600
40-60 660
60-90 440
90-120 480
Depthcm
Clay g/kg
0-10 380
10-20 480
20-40 580
40-60 600
60-90 620
90-120 600
Microbasin weir
Groundwater well
Soil profile description (Tarcísio Ewerton Rodrigues, EMBRAPA)
Soilscapes in the Eastern Amazon
Soil chemical componentsIn soils of the Fazenda Vitoria and the IBGE
Stream chemical componentsin the Fazenda Vitoria and the IBGE Reserve
Stage Ht x Concentration relationship for Ca
IBGE Reserve
Stage Ht (cm)
0 20 40 60
Ca
(ueq
/L)
0
20
40
60
80
100
120
140 Fazenda Vitoria
Stage Ht (cm)
100 200 300 400
Ca
(ueq
/L)
0
50
100
150
200Ca=41.9 + -0.396 * Ht
r2=0.1
Ca=48.7 + 0.49 * Ht
r2=0.2
Stability diagram
Log (H4SiO4)
-7-6-5-4-3-2-1
Lo
g (
K+
/H+
)
-2
0
2
4
6
Fazenda VitoriaIBGE Reserve
K-mica
Gib
bsi
te
K-feldspar
Kaolinite
Ternary diagram for silicate weathering
Cl+SO40 10 20 30 40 50 60 70 80 90 100
HCO3
0
10
20
30
40
50
60
70
80
90
100
Si
0
10
20
30
40
50
60
70
80
90
100
IBGE ReserveFazenda Vitoria
SO4
0 10 20 30 40 50 60 70 80 90 100
HCO3
0
10
20
30
40
50
60
70
80
90
100
Cl
0
10
20
30
40
50
60
70
80
90
100
IBGE ReserveFazenda Vitoria
Mg0 10 20 30 40 50 60 70 80 90 100
Na+K
0
10
20
30
40
50
60
70
80
90
100
Ca
0
10
20
30
40
50
60
70
80
90
100
IBGE ReserveFazenda Vitoria
Conclusion
• Soil-stream systems in the IBGE do not present anomalous patterns for cation concentrations.
• Both soilscapes are in equilibrium will kaolinite and continue to desilicate.
• Stream cation-anion balances in Fazenda Vitoria are unusually and may be receiving important sea salt inputs.
