Department of Life Sciences and Biotechnology, University of Ferrara, Via L. Borsari 46, 44121 Ferrara, Italy.
Department of Life Sciences and Biotechnology, University of Ferrara, Via L. Borsari 46, 44121 Ferrara, Italy.
Chemosphere. 2018 Dec;213:526-532. doi: 10.1016/j.chemosphere.2018.09.079. Epub 2018 Sep 16.
Denitrification associated with emergent macrophytes is a pivotal process underlying the treatment performance of wetlands and slow-flow waterways. Laboratory scale experiments targeting N losses via denitrification in sediments colonized by emergent macrophytes require the use of mesocosms that are necessarily open to the atmosphere. Thus, the proper quantification of N effluxes relies on the accurate characterization of the air-water gas exchanges. In this study, we present a simple approach for direct measurements of the gas transfer velocity, in open-top mesocosms with Phragmites australis, by using argon as a tracer. Different conditions of water velocity (0, 1.5, 3, and 6 cm s) and temperature (8.5, 16, and 28 °C), were tested, along with, for the first time, the presence of emergent vegetation. The outcomes demonstrated that water velocity and temperature are not the only factors regulating aeration at the mesocosm scale. Indeed, the gas transfer velocity was systematically higher, in the range of 42-53%, in vegetated compared to unvegetated sediments. The increase of small-local turbulence patterns created within water parcels moving around plant stems translated into significant modifications of the reaeration process. The adopted approach may be used to improve the accuracy of denitrification measurements by N efflux-based methods in wetland and slow-flow waterway sediments colonized by emergent macrophytes. Moreover, the present outcomes may have multiple implications for whole-system metabolism estimations from which largely depend our understanding of biogeochemical dynamics in inland waters that have strong connections to worldwide issues, such as nitrate contamination and greenhouse gas emissions.
与挺水植物相关的反硝化作用是湿地和缓流水体处理性能的关键过程。针对挺水植物定殖沉积物中通过反硝化作用去除氮的实验室规模实验需要使用开放大气的中尺度模型。因此，氮通量的准确量化依赖于对气-液气体交换的准确描述。在这项研究中，我们提出了一种简单的方法，通过使用氩气作为示踪剂，直接测量开放顶中尺度模型中挺水植物存在时的气体转移速度。测试了不同的水流速度（0、1.5、3 和 6cm/s）和温度（8.5、16 和 28°C）条件，这是首次在挺水植物存在的情况下进行的测试。结果表明，水速和温度并不是调节中尺度模型通气的唯一因素。实际上，在有植被的沉积物中，气体转移速度比无植被的沉积物高 42-53%，这是一个系统的增加。在围绕植物茎移动的水体中小局部湍流模式的增加导致再曝气过程发生显著变化。所采用的方法可用于提高基于氮通量的方法测量湿地和缓流水体中挺水植物定殖沉积物反硝化作用的准确性。此外，本研究结果可能对整个系统代谢估计产生多种影响，而整个系统代谢估计在很大程度上依赖于我们对内陆水域生物地球化学动态的理解，内陆水域与全球范围内的问题（如硝酸盐污染和温室气体排放）密切相关。
