Influence of Plant Communities on Denitrification in a Tidal Freshwater Marsh of the Potomac River, United States

• Published in: Journal of environmental quality Vol. 38; no. 2; pp. 618 - 626
• Main Authors: Hopfensperger, Kristine N, Kaushal, Sujay S, Findlay, Stuart E.G, Cornwell, Jeffrey C
• Format: Journal Article
• Language: English
• Published: Madison American Society of Agronomy, Crop Science Society of America, Soil Science Society 01.03.2009; American Society of Agronomy
• Subjects: acetylene; Altitude; ammonia; Ammonium; annuals; autumn; botanical composition; Coastal plains; Community composition; Creeks & streams; Denitrification; Environmental science; Enzymatic activity; enzyme activity; enzyme inhibition; Fresh water; Freshwater; Hypoxia; Land use; land use change; Magnoliopsida; marshes; Mass Spectrometry; Microbiology; National parks; nitrification; nitrogen; Nitrogen - analysis; Nitrogen Compounds - metabolism; nitrogen content; Organic carbon; Organic Chemicals - analysis; Organic matter; perennials; Plant communities; Rivers; Rivers - chemistry; Sand & gravel; Sea level rise; Seasons; sediments; Soil - analysis; Soil erosion; soil organic carbon; Soils; Surface water; Tidal marshes; urban areas; Virginia; Water analysis; wetland plants; wetland soils; Wetlands; Potomac River; Maryland; USA, Maryland, Potomac R; USA
• ISSN: 0047-2425; 1537-2537
• DOI: 10.2134/jeq2008.0220

We investigated whether marsh surface elevation, plant community composition (annuals vs. perennials), and organic matter quantity/quality were associated with differences in denitrification rates in an urban tidal freshwater marsh of the Potomac River, United States. We measured denitrification rates using both denitrification enzyme activity (DEA) with acetylene inhibition (June: n = 38, 3234 ± 303; October: n = 38, 1557 ± 368 ng N g dry soil-1 h-1) and direct N2 flux measurements with membrane inlet mass spectrometry (MIMS) (November: n = 6, 147 ± 24 μmol m-2 h-1). Organic carbon content and nitrate concentrations in soil, and plant community composition were correlated with elevation, but DEA rates did not differ across marsh surface elevation. Soil organic carbon was highest in plots dominated by perennial graminoids, but DEA rates did not differ across plant community types. The DEA rates increased with increasing soil ammonium concentrations and total N content, and DEA rates differed between summer and fall sampling. The MIMS rates did not differ across plant community types, but were correlated with soil organic N content. Denitrification rates suggest that potential N removal at the site could be substantial. In addition, denitrification rates measured in Dyke Marsh were higher than rates for sediments measured in the adjacent Potomac River. Tidal freshwater marshes can represent an important site for denitrification, and factors fostering denitrification should be considered when restoring urban tidal freshwater wetlands as they are faced with pressures from increasing land use change and sea level rise.