Dissolved nitrogen and phosphorus dynamics in the lower portion of the paraiba do sul river, campos dos goytacazes, RJ, Brazil

Abstract

The Paraiba do Sitl river lower reach was monitored monthly between August 1995 and July 1996. This study was aimed at evaluating the temporal dynamics of dissolved nitrogen and phosphorus and its main controlling factors. Minimum and maximum obsen'cd values were as follows: N-NO2' - 0.08/0.51; N-NOj' - 21/57; N-NH4+ - 1.4/6.7; DON - 4.9/86.0; DIN -24.5/60.9; P-PO43 - 0.43/1.66; DOP - 0.05/0.92; pH - 6.2/7.8; Dissolved Oxygen - 6.4/10.1; Conductivity - 48/74; Temperature - 20.5/31.1 (Nutrients - μM; Dissolved Oxygen - mg/l; Conductivity - [iS/cm; Temperature - °C). Discharge presented a characteristic seasonal variation, showing a peak in January. Increasing P-PO43, DOP, N-NH4and N-NOi concentrations with increasing discharges could be associated to the partial flooding of intimerons fluvial islands and foodplains and to the agricultural practices of sugar cane crops that during the wet season could transfer nitrogen and phosphorus compounds to the fluvial channel.