Carbon dynamics and sources in the Parani River

The Paraná River was sampled and analyzed for carbon and mineral concentrations at the Paraná‐Santa Fe (Argentina) cross‐section (∼600 km above the mouth) between March 1981 and November 1984. Within this period, the Paraná was affected by an extraordinary flood caused by the 1982 El Niño/ 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 Paraná 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 Paraná was sampled along a reach of over 1,300 km. At the time of sampling, the Paraguay River supplied ∼68% of the POC load, 59% of the labile particulate load (LPOC), and 71% of the DOC entering the middle reach of the Paraná. 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 Paraná.