Inhibition of nitrous oxide reduction by a component of Hamilton Harbour sediment

A component of Hamilton Harbour sediment prevented nitrous oxide (N2O) reduction in denitrification assays with a mixed population of endogenous bacteria and a pure culture (HH1) isolated from the sediment. A 5% (v/v) concentration of sediment in nutrient broth caused near maximum inhibition of N2O reduction. Sediment taken from a site closer to pollution sources (Site 906) was twice as inhibitory (as measured by N2O accumulation) as sediment from Site 910, further from pollution sources. N2O persistence was associated with the particulate sediment fraction only. Several heavy metals were tested at in situ concentrations, and ionic cadmium (Cd) and chromium (Cr) caused N2O accumulation. Ashed sediment did not cause N2O accumulation, but did decrease initial nitrate reduction rates with HH1.