Pore water N and P concentration in a floodplain marsh of the Lower Paraná River

• Published in: Hydrobiologia 1999-01, Vol.392 (1), p.65-71
• Main Authors: Villar, Carlos, de Cabo, Laura, Vaithiyanathan, Panchabi, Bonetto, Carlos
• Format: Article
• Language: English
• Subjects: Aquatic plants; Argentina, Lower Parana R; Argentina, Parana R; Biomass; Floodplains; Growing season; Marshes; Nitrification; Nutrient availability; Nutrient concentrations; Plant growth; Pore water; Rivers; Sediment-water interface; Sediments; Storage capacity; Water depth
• ISSN: 0018-8158; 1573-5117
• DOI: 10.1023/A:1003505424569

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 Paraná 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 NH^sub 4^^sup +^ concentrations in the upper 30 cm layer often ranged from N = 1.5 to 1.8 mg l^sup -1^, but showed a pronounced minimum (0.5-0.7 mg l^sup -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^sup -1^ without any discernible seasonal pattern. NH^sub 4^^sup +^ depletion in the pore water concentration and low N/P ratios (3.7 by weight) within the macrophyte biomass at the end of the growing period suggest that available N limits plant growth. NH^sub 4^^sup +^ 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. NH^sub 4^^sup +^ did not accumulate in the marsh, and no significant differences were observed between the river and the marsh water, while the NO^sub 3^^sup -^ 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.[PUBLICATION ABSTRACT]