Lisa Kellman Lee van Ardenne Glenn R. Guntenspergen Gail L. Chmura 2016 <p><span>We assessed the impact of nutrient additions on greenhouse gas fluxes using dark static chambers in a microtidal and a macrotidal marsh along the coast of New Brunswick, Canada approximately monthly over a year. Both were experimentally fertilized for six years with varying levels of N and P. For unfertilized, N and NPK treatments, average yearly CO</span>₂<span> emissions (which represent only respiration) at the microtidal marsh (13, 19, and 28 mmoles CO</span>₂<span> m</span>^-2<span> hr</span>^-1<span>, respectively) were higher than at the macrotidal marsh (12, 15, and 19 mmoles m</span>^-2<span> hr</span>^-1<span>, respectively, with a flux under the additional high N/low P treatment of 21 mmoles m</span>^-2<span> hr</span>^-1<span>). Response of CH</span>₄<span> to fertilization was more variable. At the macrotidal marsh average yearly fluxes were 1.29, 1.26, and 0.77 μmol CH</span>₄<span> m</span>^-2<span> hr</span>^-1<span> with control, N, and NPK treatments, respectively and 1.21 μmol m</span>^-2<span> hr</span>^-1<span> under high N/low P treatment. At the microtidal marsh CH</span>₄<span>fluxes were 0.23, 0.16, and -0.24 μmol CH</span>₄<span> m</span>^-2<span> hr</span>^-1<span> in control, N, and NPK and treatments, respectively. Fertilization changed soils from sinks to sources of N</span>₂<span>O. Average yearly N</span>₂<span>O fluxes at the macrotidal marsh were -0.07, 0.08, and 1.70, μmol N</span>₂<span>O m</span>^-2<span> hr</span>^-1<span> in control, N, NPK and treatments, respectively and 0.35 μmol m</span>^-2<span> hr</span>^-1<span> under high N/low P treatment. For the control, N, and NPK treatments at the microtidal marsh N</span>₂<span>O fluxes were -0.05, 0.30, and 0.52 μmol N</span>₂<span>O m</span>^-2<span> hr</span>^-1<span>, respectively. Our results indicate that N</span>₂<span>O fluxes are likely to vary with the source of pollutant nutrients but emissions will be lower if N is not accompanied by an adequate supply of P (e.g., atmospheric deposition vs sewage or agricultural runoff). With chronic fertilization the global warming potential of the increased N</span>₂<span>O emissions may be enough to offset the global cooling potential of the C sequestered by salt marshes.</span></p> application/pdf 10.1371/journal.pone.0149937 en PLOS Greenhouse gas fluxes from salt marshes exposed to chronic nutrient enrichment article