Use of 15N Natural Abundance and N Species Concentrations to Assess N-Cycling in Constructed and Natural Coastal Wetlands

Abstract EN

Natural abundance of N stable isotopes used in combination with concentrations may be useful indicators of N-cycling in wetlands.

Concentrations and 15N signatures of NO3 −, NH4 +, and sediment organic nitrogen (SON) were measured in two impacted coastal golf course retention ponds and two natural marshes.

Limited NO3 − was detected in natural site surface water or pore water, but both isotopic signature and concentrations of NO3 − in surface water of impacted sites indicated anthropogenic inputs.

In natural sites, NH4 + concentrations were greatest in deeper pore water and least in surface water, suggesting diffusion predominates.

The natural sites had greater %SON, and 15N indicated that the natural sites also had greater NH4 + released from SON mineralization than impacted sites.

In NO3 −-limited systems, neither concentrations nor 15N natural abundance was able to provide information on N-cycling, while processes associated with NH4 + were better elucidated by using both concentrations and 15N natural abundance.