Evidence for acclimation of N cycling to episodic N inputs in anthropogenically-affected intertidal salt marsh sediments

Nitrate removal was compared in anthropogenically-impacted and unimpacted salt marsh sediments in microcosms using the acetylene block technique and 15N natural abundance measurements. Potential denitrification rates were greater at the impacted site than the unimpacted site at all added NO3− concentrations (233, 467, or 700 μg N g dw−1). Although the change in concentration of NH4+ over time was small (69–104 μg N g dw−1), the δ15N of accumulated NH4+ increased significantly (0.26–13.22‰), and was more enriched for all NO3− treatments in the impacted sediments than the unimpacted site. The impacted site may be acclimated to episodic N inputs, and based on concentrations and 15N natural abundance had greater denitrification and N cycling than the unimpacted site.