CARBON DYNAMICS AND SOURCES IN THE PARANA RIVER

The Parana River was sampled and analyzed for carbon and mineral concentrations at the Parana-Santa Fe (Argentina) cross-section (approximately 600 km above the mouth) between March 1981 and November 1984. Within this period, the Parana was affected by an extraordinary flood caused by the 1982 El Nini/Southern Oscillation (ENSO) climatic anomaly. Under such conditions, with a flow 75% higher than the long-term mean, the river exported a total organic C (TOC) load of 8.43 Tg yr-1 (3.0 g m-2 yr-1) of which 89% was accounted for by dissolved organic C (DOC) and the remainder by particulate organic C (POC). Under normal hydrological conditions, however, the Parana has a TOC load that is roughly half of that determined during the ENSO-triggered flood (4.43 Tg yr-1, 1.6 g m-2 yr-1), but with a very different DOC: POC ratio (63: 37). In July-August 1985 the Parand was sampled along a reach of over 1,300 km. At the time of sampling, the Paraguay River supplied approximately 68% of the POC load, 59% of the labile particulate load (LPOC), and 71% of the DOC entering the middle reach of the Parana. Carbohydrates in LPOC appear to become more abundant than amino acids in the lower reaches, probably due a significant input from the floodplain of the Parana.