The river floodplain interactions is highly dynamic in the Lower Paraná River system due to the important exchange of water in relation to floods, tides and wind action. It is of great interest to study the mutual influence of limnlogical processes occurring at the river itself and within the floodplain, and its relation to the hydrological regime.

The floodplain retained riverine suspended matter. The main nutrient pool of the system consist of the superficial sediment layers representing the sedimentary riverine contribution plus the decomposing macrophyte litter enriched with N.

Bermejo River is an Andean tributary of Paraguay river, and the last is the main tributary of Paraná River. Suspended matter, soluble reactive phosphorous (SRP), and calcium in the Lower Paraná river correlated with the Bermejo River discharge. The equivalences of the conservative ions between the river and the floodplain marshes points the important water exchange between them. Nitrate is the main inorganic N component in the river while ammonia represent the main component in the marshes. Water exchange result in high nitrate inputs of the floodplain. However, because denitrification and detritus and macrophyte uptake, nitrate is depleted within the floodplain.

Low oxygen concentration determines a strong inorganic nitrogen flux from the water to the sediments and inversely an SRP flux from sediments to the water resulting in a low inorganic nitrogen to SRP ratio within the floodplain. Low N/P ratios within macrophyte tissue and fertilization experiments show N limitation within the floodplain, consistent with the ammonia depletion observed in the pore water at the end of the macrophyte growing season. Main processes described are prone to occurred in the whole floodplain extension. The Paraná river floods at the end of the growing period and therefore attenuate the floodplain N deficit. Changes in the hydrologic regime would cause deep changes in the river-floodplains