Nitrous Oxide Release from Aerobic Riverine Deposits

Abstract

This study provides: (a) first-known estimates of potential N₂O release from aerobic riverine deposits; (b) evidence that simultaneous measures of gas formation and N-transformations can be used to gain insights into mechanisms controlling N₂O formation in natural environments; and (c) suggestions for improvements in experimental approaches. Nitrous oxide (N₂O) release rates from aerobic benthic deposits of a river into overlying waters showed higher rates for sands of pools (30 to 695 nM m⁻² hr⁻¹) than for gravel deposits of riffles (66 to 274 nM m^–2 hr^−l). N²O production, along with estimates of nitrification rates, indicate some gas production under aerobic nitrifying conditions. Higher N₂O yield as moles of N in N₂O produced per mole of nitrite for sand (0.3 to 15.0%) than gravels (0.1 to 0.3%) deposits suggested that either low nitrification rates or coupled nitrifying-nitrate reducing reactions favor N₂O production. Comparisons of riverine N₂O releases with nearshore marine values for surface sediments indicated that in the sandy river environments gas releases could be higher than some of the marine rates. However, the highest N₂O release rates (~1900 nM m⁻² hr^–l) were for low oxygen, organic rich, and nitrate reducing conditions in marine deposits.