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Title Chronic but not acute saltwater intrusion leads to large release of inorganic N in a tidal freshwater marsh
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Sea level rise is expected to increase inundation and saltwater intrusion into many tidal freshwater marshes and forests. Saltwater intrusion may be long-term, as with rising seas, or episodic, as with low river flow or storm surge. We applied continuous (press) and episodic (pulse) treatments of dilute seawater to replicate 2.5 × 2.5 m field plots for three years and measured soil attributes, including soil porewater, oxidation-reduction potential, soil carbon (C), and nitrogen (N) to investigate the effects of continuous and episodic saltwater intrusion and increased inundation on tidal freshwater marsh elemental cycling and soil processes. Continuous additions of dilute seawater resulted in increased porewater chloride, sulfate, sulfide, ammonium, and nitrate concentrations. Plots that received press additions also had lower soil oxidation-reduction potentials beginning in the second year. Episodic additions of dilute seawater during typical low flow conditions (Sept.-Oct.) resulted in transient increases in porewater chloride and sulfate that returned to baseline conditions once dosing ceased. Freshwater additions did not affect porewater inorganic N or soil C or N. Persistent saltwater intrusion in freshwater marshes alters the N cycle by releasing ammonium-N from sorption sites, increasing nitrification and severely reducing N storage in macrophyte biomass. Chronic saltwater intrusion, as is expected with rising seas, is likely to shift tidal freshwater marshes from a sink to a source of N whereas intermittent intrusion from drought may have no long term effect on N cycling.

Contributors Sarah Widney, Dontrece Smith, Ellen Herbert, Joseph P. Schubauer-Berigan, Fan Li, Steven C. Pennings and Christopher B. Craft

Widney, S., Smith, D., Herbert, E., Schubauer-Berigan, J.P., Li, F., Pennings, S.C. and Craft, C.B. 2019. Chronic but not acute saltwater intrusion leads to large release of inorganic N in a tidal freshwater marsh. Science of the Total Environment. 695. (DOI:

Key Words Ammonium, N cycle, Nitrate, Sea level rise, Soil carbon, Sulfate, UGAMI Publication
File Date 2019
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This material is based upon work supported by the National Science Foundation under grants OCE-9982133, OCE-0620959, OCE-1237140 and OCE-1832178. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.