Use of15NNatural Abundance and N Species Concentrations to Assess N-Cycling in Constructed and Natural Coastal Wetlands

摘要

Natural abundance of N stable isotopes used in combination with concentrations may be useful indicators of N-cycling in wetlands. Concentrations and15Nsignatures ofNO3   −,NH4   +, and sediment organic nitrogen (SON) were measured in two impacted coastal golf course retention ponds and two natural marshes. LimitedNO3   −was detected in natural site surface water or pore water, but both isotopic signature and concentrations ofNO3   −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, and15Nindicated that the natural sites also had greaterNH4   +released from SON mineralization than impacted sites. InNO3   −-limited systems, neither concentrations nor15Nnatural abundance was able to provide information on N-cycling, while processes associated withNH4   +were better elucidated by using both concentrations and15Nnatural abundance.