Seasonal Patterns of Denitrification and N2O Production in a Southern New England Salt Marsh

Denitrification removes reactive nitrogen (N) from ecosystems by transforming nitrate (NO3-) to dinitrogen (N-2) gas. Incomplete denitrification produces nitrous oxide (N2O), a potent greenhouse gas. In salt marshes, denitrification, N2O production, and N2O yield (the fraction of denitrification that produces N2O) have implications for N load reduction and greenhouse gas emissions. We collected soil cores from three salt marsh zones (low marsh, high marsh, and invasive Phragmites australis) on five sampling dates that spanned the growing season (May through October) to quantify seasonal patterns of potential denitrification, N2O production, and N2O yield. Potential denitrification peaked at the beginning and end of the growing season, with rates several times higher in May and October than in June, but we found no significant differences among salt marsh zones. In contrast, seasonal patterns of potential N2O production depended on marsh zone; N2O production was aseasonal in high marsh and P. australis zones, but in the low marsh, N2O production was lower in July compared to all other months sampled. In this salt marsh, seasonal variation of potential denitrification and N2O production was greater than spatial variation over the marsh zones, highlighting the importance of understanding temporal patterns of salt marsh N cycling.