Nitrogen enrichment alters carbon fluxes in a New England salt marsh

Abstract

Introduction: Nitrogen enrichment of coastal salt marshes can induce feedbacks that alter ecosystem-level processes including primary production and carbon sequestration. Despite the rising interest in coastal blue carbon, the effects of chronic nutrient enrichment on blue carbon processes have rarely been measured in the context of experimental fertilization. Here, we examined the ecosystem-level effects of nitrate (NO3−) enrichment on the greenhouse gas dynamics of a Spartina alterniflora-dominated salt marsh. We measured CO2 and CH4 fluxes using static chambers through two growing seasons in a salt marsh that was nitrogen-enriched for 13 years and compared fluxes to those from a reference marsh. Outcomes: We found that nitrogen enrichment increased gross primary productivity (GPP) by 7.7% and increased ecosystem respiration (Reco) by 20.8%. However, nitrogen enrichment had no discernible effect on net ecosystem exchange (NEE). Taken together, these results suggest that nitrogen-induced stimulation of Reco could transform this salt marsh from a carbon sink into a source of carbon to the atmosphere. Conclusion: Our results complement prior findings of nitrogen enrichment weakening soil structure and organic matter stability in tidal salt marshes, suggesting that increased nutrient inputs have the potential to alter the carbon storage function of these ecosystems through enhanced microbial respiration of previously sequestered carbon.

Keywords

• Spartina alterniflora
• blue carbon
• eutrophication
• gross primary productivity
• net ecosystem exchange
• nitrogen
• ecosystem respiration
• tidal salt marsh