Hopfensperger Kristine N, Kaushal Sujay S, Findlay Stuart E G, Cornwell Jeffrey C
Univ. of Maryland Center for Environmental Science, Appalachian Lab., Frostburg, MD 21532, USA.
J Environ Qual. 2009 Feb 6;38(2):618-26. doi: 10.2134/jeq2008.0220. Print 2009 Mar-Apr.
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 N(2) flux measurements with membrane inlet mass spectrometry (MIMS) (November: n = 6, 147 +/- 24 mumol 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.
我们调查了在美国波托马克河的一个城市潮汐淡水湿地中，湿地表面高程、植物群落组成（一年生植物与多年生植物）以及有机质数量/质量是否与反硝化速率的差异相关。我们使用乙炔抑制反硝化酶活性（DEA）（6月：n = 38，3234 +/- 303；10月：n = 38，1557 +/- 368纳克氮克干土⁻¹小时⁻¹）和膜进样质谱法（MIMS）直接测量N₂通量（11月：n = 6，147 +/- 24微摩尔米⁻²小时⁻¹）来测定反硝化速率。土壤中的有机碳含量和硝酸盐浓度以及植物群落组成与高程相关，但DEA速率在湿地表面高程上并无差异。在以多年生禾本科植物为主的样地中，土壤有机碳含量最高，但DEA速率在不同植物群落类型间并无差异。DEA速率随土壤铵浓度和总氮含量的增加而升高，且夏季和秋季采样的DEA速率有所不同。MIMS速率在不同植物群落类型间并无差异，但与土壤有机氮含量相关。反硝化速率表明该地点潜在的氮去除量可能很大。此外，在戴克湿地测得的反硝化速率高于在相邻波托马克河沉积物中测得的速率。潮汐淡水湿地可能是反硝化的重要场所，在恢复城市潮汐淡水湿地时应考虑促进反硝化的因素，因为它们面临着土地利用变化增加和海平面上升的压力。
