Photochemical production of low molecular-weight organic acids in the Rio Negro
Remington, University of Washington, firstname.lastname@example.org
Krusche, CENA, email@example.com
Richey, University of Washington, firstname.lastname@example.org
Souza da Silva, INPA, email@example.com
Brandao da Cunha, INPA, firstname.lastname@example.org
The Amazon river releases more than ten times the amount of carbon by CO2 evasion from water surfaces than is exported to the ocean as TOC and DIC. High CO2 concentrations driving this evasive flux in river channels are thought to derive mostly from in situ respiration of organic carbon, but the sources of this respired carbon remain unresolved. Beginning with the work of Geller (1986, Limnology and Oceanography, 31: 755-764), photochemical production of biologically labile substrates from aquatic humic substances has been widely recognized. In general, low molecular weight organic acids (LMWOAs) and CO2 are produced 10-20 times faster than all other possible photoproducts (Miller and Moran 1997, Limnology and Oceanography, 42(6): 1307-1316). We measured the photochemical production of LMWOAs in the Rio Negro and found it to be 7.5 uM LMWOA-C hr-1. This rate is an order of magnitude greater than measured respiration rates in this river. These results suggest that labile compounds produced during the photochemical degradation of dissolved humic substances may be fueling in situ respiration in the Rio Negro and possibly other rivers throughout the Amazon basin.