Abstract In agricultural streams, constructed floodplains have been shown to expand bioreactive surface area and enhance nitrate (NO3−-N) removal via microbial denitrification, thereby reducing export to downstream ecosystems. At the Shatto Ditch Watershed (Indiana, USA), 0.6 km of two-stage ditch was constructed at the watershed outlet in 2007, while an additional 3.7 and 2.7 km were constructed in 2017 and 2018, respectively. We quantified denitrification following floodplain construction using experimental incubations of stream sediments and floodplain soils from Spring 2017 to Spring 2019. We measured dissolved dinitrogen gas (N2) concentrations using membrane inlet mass spectrometry (MIMS) and found that denitrification on unconsolidated stream sediments was minimally impacted by stream dredging during two-stage construction in 2017 and 2018. In contrast, even one year after the 2017 construction, denitrification on floodplain soils fell below detection limits; we finally observed measurable rates in Spring 2019. As predicted, stream sediment denitrification was driven by water column NO3−-N concentration, while organic matter limited denitrification on floodplain soils. Floodplains constructed via the two-stage ditch can increase NO3−-N removal by >20% in agricultural watersheds, representing an effective ecological engineering solution to combat downstream eutrophication. However, our results also show that denitrification on floodplain soils may take longer to recover from construction-related activities as organic matter builds up more slowly over time. As such, lags in the recovery or enhancement of ecosystem function are important to consider when documenting restoration success.

中文翻译：

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通过农业流域两级沟渠对洪泛区恢复后的反硝化作用进行量化

摘要 在农业河流中，人造漫滩已被证明可以扩大生物反应表面积并通过微生物反硝化作用增强硝酸盐 (NO3--N) 的去除，从而减少对下游生态系统的出口。在 Shatto Ditch 流域（美国印第安纳州），2007 年在流域出口处建造了 0.6 公里的两级沟渠，而 2017 年和 2018 年分别建造了 3.7 公里和 2.7 公里。我们使用 2017 年春季至 2019 年春季的溪流沉积物和漫滩土壤的实验孵化来量化洪泛区建设后的反硝化作用。我们使用膜入口质谱法 (MIMS) 测量溶解二氮 (N2) 浓度，发现未固结溪流沉积物的反硝化作用受到的影响最小通过在 2017 年和 2018 年的两阶段施工期间进行河道疏浚。相比之下，即使在 2017 年建设一年后，漫滩土壤的反硝化作用仍低于检测限；我们最终在 2019 年春季观察到了可测量的速率。 正如预测的那样，河流沉积物反硝化作用是由水柱 NO3--N 浓度驱动的，而有机质限制了漫滩土壤的反硝化作用。通过二级沟渠建造的漫滩可以将农业流域中的 NO3--N 去除率提高 20% 以上，是对抗下游富营养化的有效生态工程解决方案。然而，我们的研究结果还表明，随着有机物随着时间的推移积累得更慢，洪泛区土壤的反硝化作用可能需要更长的时间才能从与建筑相关的活动中恢复。因此，