A COMPARISON OF 2 NITRIFICATION INHIBITORS USED TO MEASURE NITRIFICATION RATES IN ESTUARINE SEDIMENTS

Nitrification rates were measured using intact sediment cores from Sou th San Francisco Bay and two different nitrification inhibitors: acety lene and methyl fluoride. Sediment oxygen consumption and ammonium and nitrate fluxes were also measured in these cores. Four experiments we re conducted in the spring, and one in the fall of 1993. There was no significant difference in nitrification rates measured using the two i nhibitors, which suggests that methyl fluoride can be used as an effec tive inhibitor of nitrification. Nitrification was positively correlat ed with sediment oxygen consumption and numbers of macrofauna. This su ggests that bioturbation by macrofauna is an important control of nitr ification rates. Irrigation by the tube-dwelling polychaete, Asychis e longata, which dominates the benthic biomass at this location, appears particularly important. Ammonium fluxes out of the sediment were grea test about one week after the spring bloom, while nitrification peaked about one month later.