Estimates of benthic fluxes of nutrients across the sediment]water interface Guarapiranga reservoir, S˜ao Paulo, Brazil/

Concentration profiles of nutrients dissolved organic carbon, nitrate, nitrite, ammonium and soluble reactive phosphorus. were determined in pore waters from sediment from the Guarapiranga reservoir S˜ao Paulo, Brazil.. Redox potential and acid volatile sulfide measurements on bulk sediment samples were determined in the field and laboratory, respectively. The sediment redox potential ranged from y170 toy220 mV at 0]1 cm and increased to somewhat higher values at 20 cm. The acid volatile sulfide AVS. profile had a bimodal pattern with concentration peaks at 3 cm 27]55 mg kgy1. and 14 cm 70]110 mg kgy1.. Dissolved organic carbon DOC. concentrations increased from the surface 4.7]5.6 mg ly1. to 20 cm values up to 12 mg ly1.. The concentration of ammonium increased significantly with depth, with maximum concentrations occurring at 15 cm; nitrate]nitrite concentrations only increased appreciably at 10 cm. The SRP profiles increased in concentration from the surface to approximately 10-cm depth, with a maximum value of 1200 mg H2PO4y ly1. Benthic fluxes from the sediment into the pore water ranged from 278 to 339 mg cmy2 yeary1 for ammonium ions and from 8 to 18 mg cmy2 yeary1 for SRP. These upward diffusive fluxes correspond to 47]70% and to 10]24% of the total deposition of N and P measured in the reservoir, respectively. The burial rates for N and P in these sediments are 30]54% and 76]89%, respectively.