Porewater N and P concentration in a floodplain marsh of the Lower Paraná River.

C VILLAR,; DE CABO, L; VAITHIYANATHAN, P; BONETTO, C.

HYDROBIOLOGIA

Kluwer Academic Publishers

Lugar: Amsterdam; Año: 1999 vol. 392 p. 65 - 71

0018-8158

Abstract Inorganic nitrogen and soluble reactive phosphate  (o-P) concentrations were measured in the water of a marsh and in its interstitial water at two sites, and in the river water of a floodplain marsh of the Lower Parana River. These values were compared with the N and P concentration in sediments and  macrophyte biomass in order to assess nutrient availability, fate and storage capacity.  High variability was found in the interstitital water using a 1 cm resolution device. Nitrate was never detected in the pore water. Depth averaged NH4+ concentrations in the upper 30 cm layer often ranged from N= 1.5 to 1.8 mg  l-1  but showed a pronounced minimum (0.5-0.7 mg  l-1) close to (March 95) or relatively soon after (May 94) the end of the  macrophyte growing season. Soluble phosphate showed a large variation between P= 0.1-1.1 mg l-1 without any discernible seasonal pattern. NH4+ depletion in the pore water concentration and low N/P ratios (3.7 by weigth) within the macrophyte biomass at the end of the growing period suggest that available N limits plant growth. NH4+ and o-P concentrations were 35 and 7 times higher, respectively, in the pore water than in the overlying marsh  suggesting a  permanent flux of nutrients from the sediments. o-P accumulate in the marsh leading to higher concentrations than in the incoming river. NH4+ did not accumulate in the marsh and no significant differences were observed between the river and the marsh water, while the NO3- contributed by the river water was depleted within the marsh, caused probably by coupled nitrification-denitrification at the sediment-water interface. Although an order of magnitude smaller, the pore water pool can supply enough nutrients to build up the macrophyte biomass pool but only if a fast turnover is attained. The Paraná floodplain marsh retains a large amount of nutrients being stored mainly in the sediment compartment.