Long‐term 15N‐nitrogen retention in the vegetated sediments of a New England salt marsh

• Published in: Limnology and oceanography Vol. 39; no. 8; pp. 1878 - 1892
• Main Authors: White, David S., Howes, Brian L.
• Format: Journal Article
• Language: English
• Published: 01-12-1994
• Subjects: Marine; Spartina alterniflora; ANW, USA, New England
• ISSN: 0024-3590; 1939-5590
• DOI: 10.4319/lo.1994.39.8.1878

15N was used in a 7‐yr field study and a laboratory investigation of a single growing season to quantify the amount, timing, and mechanisms of annual N retention and loss in the plant‐sediment system of a short Spartina alterniflora marsh. There was an initial rapid loss of ∼25% of the added 15NH4+ through nitrification‐denitrification at a rate of 25.2 mg N m−2 d−1, with the remaining label being incorporated into plant tissues. Label losses decreased throughout the study as15N was increasingly sequestered in the dead organic N pool. About 40% of the injected label remained after seven growing seasons. Total annual N losses were 7.3–7.6 g N m−2 yr−1 based on 15N losses and estimates of the actively cycling N pool. Export accounted for 26–44% and denitrification for 54–77% of the total N loss. Burial of N in dead belowground organic matter was 3.7–4.1 g N m−2 yr− 1, similar to estimates determined from accretion and total sediment N data. Recycling of N through translocation from aboveground to belowground biomass and remineralization of dead belowground biomass was the major pathway in the sediment N cycle, equivalent to 67–79% of the annual plant N demand. Annual N losses were balanced by inputs, primarily N2 fixation. Long‐term N retention appears to be controlled primarily by the competition for DIN between the plants and bacterial nitrifiers‐denitrifiers and secondarily by the relative incorporation of N into aboveground vs. belowground biomass.