Ampe Hannah L, Crumpton William G, Stenback Greg A, Green David I S
Department of Ecology, Evolution and Organismal Biology, Iowa State University, Ames, Iowa, USA.
J Environ Qual. 2025 Sep 15. doi: 10.1002/jeq2.70081.
Although wetland restoration is a promising strategy to reduce nonpoint source nitrogen (N) loads, there is some concern over the potential for increased nitrous oxide (NO) emissions. We examined the production and emission of NO and methane (CH) from wetlands designed to intercept and reduce elevated, nonpoint source nitrate (NO ) loads. We measured NO and CH flux rates at three wetlands subject to a wide range of NO loading rates. Nitrate, dissolved NO, and dissolved CH associated with inflows and outflows were estimated using measured flows and concentrations, and NO and CH emissions were estimated using floating chambers. Nitrate removal, NO production, and CH production were estimated by mass balance analyses. Methane emission rates averaged 1,010 mg m day, similar to rates for restored depressional wetlands, and NO emission rates averaged 4.49 mg m day, similar to rates from cropland. Inflows and outflows contributed little to CH fluxes but were significant components of NO budgets. Dissolved NO loads to the wetlands from inflow streams ranged from 8.1% to 70% of the total NO inputs, and dissolved NO export from the wetlands through outflow to streams ranged from 7.3% to 63% of the total NO outputs. Nitrous oxide production and emission increased with NO loading; however, these wetlands also exhibited very high NO conversion efficiencies, with NO-N production and emission averaging approximately 0.5% of NO removal. The fraction of N loading that would be transformed to NO in these wetlands is much lower than in cropland or downstream riverine systems.
尽管湿地恢复是减少面源氮负荷的一种很有前景的策略，但人们对一氧化二氮（N₂O）排放量增加的可能性仍存在一些担忧。我们研究了旨在拦截和减少升高的面源硝酸盐（NO₃⁻）负荷的湿地中N₂O和甲烷（CH₄）的产生与排放情况。我们在三个承受广泛NO₃⁻负荷率的湿地中测量了N₂O和CH₄通量率。利用测量的流量和浓度估算了与流入和流出相关的硝酸盐、溶解态N₂O和溶解态CH₄，并使用浮动箱估算了N₂O和CH₄排放量。通过质量平衡分析估算了硝酸盐去除量、N₂O产生量和CH₄产生量。甲烷排放率平均为1010毫克/平方米·天，与恢复的洼地湿地的排放率相似，N₂O排放率平均为4.49毫克/平方米·天，与农田的排放率相似。流入和流出对CH₄通量的贡献很小，但却是N₂O收支的重要组成部分。从流入溪流进入湿地的溶解态NO₃⁻负荷占总NO₃⁻输入量的8.1%至70%，通过流出溪流从湿地输出的溶解态NO₃⁻占总NO₃⁻输出量的7.3%至63%。N₂O的产生和排放随NO₃⁻负荷增加而增加；然而，这些湿地也表现出非常高的NO₃⁻转化效率，N₂O-N的产生和排放平均约为NO₃⁻去除量的0.5%。在这些湿地中转化为N₂O的氮负荷比例远低于农田或下游河流系统。
