1. Dissolved CO 2 in Small Catchment Streams of Eastern Amazonia Eric A. Davidson 1, Ricardo de O. Figueiredo 2, Daniel Markewitz 3, and Patrício de S. Silva 4 1. The Woods Hole Research Center; 2. Embrapa Amazônia Oriental; 3. The University of Georgia; 4. Universidade do Estado do Pará / CNPq-CTHidro

3. Landsat 1999 scene Three watersheds near Paragominas (Eastern Amazonia) Igarapé 54 (Cq) 137 km 2 ; 18% forest; 1.5 m 3 s -1 Igarapé Sete (St) 161 km 2 ; 34% forest; 2.9 m 3 s -1 Igarapé Pajeú (Pj) 32 km 2 ; 45% forest; 0.3 m 3 s -1 Field campaigns April 2003 to July 2004, from headwaters in remnant mature forests, through pastures, secondary forests, and agricultural fields.

4. Crops Pasture IGARAPÉ DO SETE IGARAPÉ PAJEÚ A view of a farm area between two of the studied streams

5. Water samples were collected from 20 cm below the stream surface using 60cc syringes Syringes were transported to a field laboratory 30 mL of water was injected into a serum bottle with 30 mL of CO 2 –free air and incubated in a water bath for gas and liquid phases to come into equilibrium Headspace CO 2 concentration was determined using LiCor IRGA The pCO 2 in the original streamwater sample was calculated, adjusting for temperature (Henry’s law), acidity (bicarbonate chemistry), and correcting for fugacity.

7. 1 mL CO 2 /L  10,000 ppmv  40  mol CO 2 /L  1300  atm

11. Richey et al. 2002 – Amazon main stem and major tributaries 2,000 – 10,000 ppmv Johnson et al. 2006 – small forested catchment, Mato Grosso 49,000 ppmv in emergent springwater Sousa, 2007 – Acre River, Acre 4,000 ppmv Da Rosa, 2007 – small catchments Igarapé-Açu, Pará 7,500 – 24,000 ppmv near headwaters This study – small catchments in largely deforested area of Pará 15,000 ppmv near headwaters

12. Assume that all water entering the stream has the maximum observed mean pCO 2 Assume that all pCO 2 is evaded to the atmosphere Realize that these assumptions yield maximum possible efflux rates, which is probably an overestimate Mean annual litterfall in the mature forest at Paragominas is 4-5 MgC/ha/yr Efflux of CO 2 from pasture and forest soils is 10-20 MgC/ha/yr Therefore, <1% of the C fixed in the terrestrial system is lost via transport of pCO2 to streams and evasion from the streamTherefore, <1% of the C fixed in the terrestrial system is lost via transport of pCO2 to streams and evasion from the stream

13. Fluxo Vertical e Subsuperficial Fluxo superficial (hortoniano e de retorno) Fluxo superficial por saturação de área Boa Drenagem Drenagem impedida por camada de plintita Sem drenagem, área saturada Latossolo Amarelo Plintossolos Gleissolo Lençol freático plintita (Schuler, 2004) Johnson et al. 2006. Biogeochem. 81:45–57 Where does the stream pCO 2 come from?

14. Soil water in equilibrium with soil atmosphere @ 8% CO 2 @ 25°C, would have pCO 2 ~ 50 mL/L, which is about 3Xs what we measured

15. Assume that all water entering the stream has the maximum observed mean pCO 2 Assume that all pCO 2 is evaded to the atmosphere Realize that these assumptions yield maximum possible efflux rates, which is probably an overestimate Mean annual litterfall in the mature forest at Paragominas is 4-5 MgC/ha/yr Efflux of CO 2 from pasture and forest soils is 10-20 MgC/ha/yr Therefore, ~1% of the C fixed in the terrestrial system is lost via transport of pCO2 to streams and evasion from the streamTherefore, ~1% of the C fixed in the terrestrial system is lost via transport of pCO2 to streams and evasion from the stream 0.06 0.12 0.09

16. 0.004 Mg DOC-C ha -1 yr -1 Markewitz et al. 2004. Ecol. Appl. 14:S177–S199 Inputs of DOC and pCO 2 to streams may be important for aquatic ecology, but are trivial relative to terrestrial C budgets

17. Conclusions Measured pCO 2 concentrations in stream headwaters were consistent with previous reports in the literature for Amazonian streams and rivers If this C originates primarily from primary productivity in terrestrial ecosystems and soil respiration, it is a trivial pathway of CO 2 loss from the terrestrial biosphere, representing no more than 1% of CO 2 efflux from the soil surface on an area-weighted basis. 80-90% of the pCO 2 in headwaters evaded to the atmosphere within 100m downstream