Interpreting Dynamic Signatures of Land-water Coupling and In-stream Processes from pCO2: from Small Streams to Big Rivers
Richey, Univ of Washington, firstname.lastname@example.org
Krusche, CENA, email@example.com
Ballester, CENA, firstname.lastname@example.org
The spatial and temporal distributions of dissolved CO2 gas (pCO2, the partial pressure of CO2) in surface waters of tropical river systems is the product of a long sequence of complex biological, hydrological, and geochemical processes. A key gap in our knowledge is how these distributions vary with the hydrograph across a broad range of landscapes and river size. Data from the Rede Beija Rio are extensive, with roughly 20 sites characterizing a wide range of Amazon environments and river orders, from small streams to the Amazon mainstem, with a broad suite of measurements over the period 2004-2006. The results are provocative and have prompted us to rethink the controls that the hydrograph may exert. The distributions of all chemical species are closely associated with the hydrograph. pCO2 tracks the hydrograph almost exactly at all sites. pCO2 at low water ranges from 500 μatm in the Araguaia and Ji-Paraná to 1000 μatm in the Solimões to 2000 μatm in the Rio Negro. High water concentrations exhibit a broader range, from 3000 μatm (Pimento Bueno) to 5000 μatm in the Solimoes and 7000 μatm in the Negro. The highest observed values were 20,000 μatm in the blackwater stream of the Rio Negro, Campinas. Systematic variations in pCO2 relative to other chemical parameters were observed, including O2, DOC, and FPOC. Experiments relating respiration, photo-oxidation, and outgassing to these parameters yield surprises. Initial results of a coupled ydrology/biogeochemistry model provide insight into controlling processes, and a platform for cross-site synthesis and scaling.