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.
J Environ Manage. 2018 Jun 1;215:230-238. doi: 10.1016/j.jenvman.2018.03.071.
The extended networks of canals and ditches in agricultural landscapes provide high buffer capacity towards nitrogen (N) excess. Their N mitigation potential depends on several biotic and abiotic factors, among which water velocity is poorly explored and generally omitted from the parameterization of this remarkable ecosystem service. The present work reports new insights on the role of flow velocity in regulating N removal via denitrification in sediments colonized by Phragmites australis. Denitrification was investigated in outdoor mesocosms in the presence and absence of P. australis and over a small range of flow velocity (0-6 cm s) typical of low-gradient water bodies. Simultaneous measurements of NO consumption and N production based on analyses of N:Ar by Membrane Inlet Mass Spectrometry were undertaken. Vegetated sediments were found more efficient in converting NO to N via microbial-mediated denitrification (27-233 mmol N m d) than bare sediments (18-33 mmol N m d). Vegetation provides multiple interfaces, i.e. in the rhizosphere and on epiphytic biofilms, that support the development and activity of bacterial communities responsible for NO dissipation. NO removal and denitrification rates exhibited one order of magnitude raise when water velocity passed from 0 to 6 cm s in vegetated sediments. Indeed, in slow-flow vegetated waterways denitrification may be physically limited and the increase of water velocity enhances the rate of NO supply through the diffusive boundary layer, thereby promoting its consumption and loss from the system. Water velocity should be taken into account as a key factor for management and restoration actions aimed at maximizing the NO buffer capacity of low-flow drainage networks.
农业景观中延伸的运河和沟渠网络为氮（N）过剩提供了高缓冲能力。它们的 N 缓解潜力取决于几个生物和非生物因素，其中水流速度是一个研究甚少且通常被忽略的因素，而水流速度是这种显著生态系统服务功能的参数化的重要因素。本研究报告了关于流速在调节受芦苇（Phragmites australis）定殖的沉积物中反硝化作用去除 N 方面的新见解。在存在和不存在芦苇的情况下，在 0-6 cm s 的小流速范围内（低梯度水体的典型流速），在户外中尺度模型中研究了反硝化作用。通过膜进样质谱分析 N:Ar 进行了同时测量，以研究硝酸盐消耗和 N 生产。与裸沉积物（18-33 mmol N m d）相比，植被沉积物通过微生物介导的反硝化作用将 NO 转化为 N 的效率更高（27-233 mmol N m d）。植被提供了多个界面，即在根际和附生生物膜中，支持负责 NO 耗散的细菌群落的发展和活性。当水流速度从 0 增加到 6 cm s 时，NO 去除和反硝化速率在植被沉积物中提高了一个数量级。实际上，在流速缓慢的植被水道中，反硝化作用可能受到物理限制，而增加水流速度会通过扩散边界层增强 NO 供应的速度，从而促进其消耗和从系统中损失。应将水流速度视为旨在最大化低流速排水网络的 NO 缓冲能力的管理和恢复措施的关键因素。
