Department of Geography, King's College London, London, United Kingdom.
School of Science, Technology and Engineering, University of Suffolk, Ipswich, United Kingdom.
PLoS One. 2019 Mar 13;14(3):e0212690. doi: 10.1371/journal.pone.0212690. eCollection 2019.
River restoration projects focused on altering flow regimes through use of in-channel structures can facilitate ecosystem services, such as promoting nitrogen (N) storage to reduce eutrophication. In this study we use small flux chambers to examine ammonium (NH4+) and nitrate (NO3-) cycling across the sediment-water interface. Paired restored and unrestored study sites in 5 urban tributaries of the River Thames in Greater London were used to examine N dynamics following physical disturbances (0-3 min exposures) and subsequent biogeochemical activity (3-10 min exposures). Average ambient NH4+ concentrations were significantly different amongst all sites and ranged from 28.0 to 731.7 μg L-1, with the highest concentrations measured at restored sites. Average NO3- concentrations ranged from 9.6 to 26.4 mg L-1, but did not significantly differ between restored and unrestored sites. Average NH4+ fluxes at restored sites ranged from -8.9 to 5.0 μg N m-2 sec-1, however restoration did not significantly influence NH4+ uptake or regeneration (i.e., a measure of release to surface water) between 0-3 minutes and 3-10 minutes. Further, average NO3- fluxes amongst sites responded significantly between 0-3 minutes ranging from -33.6 to 97.7 μg N m-2 sec-1. Neither NH4+ nor NO3- fluxes correlated to sediment chlorophyll-a, total organic matter, or grain size. We attributed variations in overall N fluxes to N-specific sediment storage capacity, biogeochemical transformations, potential legacy effects associated with urban pollution, and variations in river-specific restoration actions.
河流修复项目侧重于通过使用河道内结构改变水流模式，从而促进生态系统服务，例如促进氮（N）存储以减少富营养化。在这项研究中，我们使用小型通量室来检测铵（NH4+）和硝酸盐（NO3-）在泥沙-水界面的循环。在大伦敦的泰晤士河的 5 条城市支流中，选择了经过修复和未修复的对比研究点，以研究物理干扰（0-3 分钟暴露）后和随后的生物地球化学活性（3-10 分钟暴露）下的 N 动态。所有地点的平均环境 NH4+浓度差异显著，范围从 28.0 到 731.7 μg L-1，在修复点处测量到的浓度最高。平均 NO3-浓度范围从 9.6 到 26.4 mg L-1，但在修复和未修复的地点之间没有显著差异。修复地点的平均 NH4+通量范围从-8.9 到 5.0 μg N m-2 sec-1，但是修复对 0-3 分钟和 3-10 分钟之间的 NH4+吸收或再生（即释放到地表水的一种度量）没有显著影响。此外，在 0-3 分钟之间，各地点之间的平均 NO3-通量差异显著，范围从-33.6 到 97.7 μg N m-2 sec-1。NH4+和 NO3-通量均与泥沙叶绿素-a、总有机物质或颗粒大小无关。我们将总体 N 通量的变化归因于 N 特定的沉积物存储容量、生物地球化学转化、与城市污染相关的潜在遗留效应，以及河流特定修复措施的变化。
