Urban stormwater ponds (SWPs) are engineered ecosystems designed to prevent flooding and protect downstream ecosystems by retaining nutrients associated with stormwater runoff, including nitrogen (N). Despite these expectations, multiple studies have found that SWPs have low N removal efficiencies and can be sources of N to downstream ecosystems. To understand mechanisms controlling the fate of N in SWPs, we quantified dinitrogen (N₂) gas saturation to characterize net N₂ exchange as either net denitrification or net N-fixation. We assessed temporal and spatial patterns of N₂ dynamics in fifteen SWPs and six naturally occurring ponds in undisturbed watersheds (Florida, USA) by sampling in two seasons (dry and wet) and from multiple depths of the water column. Samples from SWPs were equally likely to exhibit N₂ supersaturation (net denitrification; 50%) or undersaturation (net N-fixation; 50%). In contrast, the majority (82%) of samples from natural ponds were supersaturated with N₂, indicating net denitrification. The mean SWP air–water N₂ flux was − 1.7 μg N₂-N m⁻² h⁻¹ (range − 500 to 433 μg N₂-N m⁻² h⁻¹), which was lower than clear (40 μg N₂-N m⁻² h⁻¹; range − 68 to 74 μg N₂-N m⁻² h⁻¹) and humic (202 μg N₂-N m⁻² h⁻¹; range 41 to 407 μg N₂-N m⁻² h⁻¹) natural ponds despite considerably higher variation in SWPs. These results indicate that SWPs may have low N removal efficiencies in part due to N-fixation adding new N to the system. Overall, this study shows that SWPs are less effective than natural ponds at removing reactive N from the environment, potentially impacting downstream water quality.

城市雨水池 (SWP) 是经过工程设计的生态系统，旨在通过保留与雨水径流相关的营养物质（包括氮 (N)）来防止洪水并保护下游生态系统。尽管有这些期望，多项研究发现，SWP 的氮去除效率较低，并且可以成为下游生态系统的氮源。为了了解控制 SWP 中 N 命运的机制，我们量化了二氮 (N ₂ ) 气体饱和度，以将净 N ₂ 交换表征为净反硝化或净固氮。我们通过在两个季节（干季和湿季）和水柱的多个深度进行采样，评估了未受干扰流域（美国佛罗里达州）的 15 个 SWP 和 6 个天然池塘的 N ₂ 动态的时间和空间模式。来自 SWP 的样品同样可能表现出 N ₂ 过饱和（净反硝化；50%）或欠饱和（净固氮；50%）。相比之下，来自天然池塘的大多数样品（82%）N ₂ 过饱和，表明存在净反硝化。平均 SWP 空气-水 N ₂ 通量为 − 1.7 µg N ₂ -N m ⁻² h ⁻¹ （范围 − 500 至433 μg N ₂ -N m ⁻² h ⁻¹ )，低于透明 (40 μg N ₂ -N m < b13> h ⁻¹ ；范围 − 68 至 74 µg N ₂ -N m ⁻² h ⁻¹ ）和腐殖质(202 μg N ₂ -N m ⁻² h ⁻¹ ；范围 41 至 407 μg N ₂ -N m ⁻² ) 天然池塘，尽管 SWP 的变化相当大。这些结果表明，SWP 的氮去除效率可能较低，部分原因是固氮向系统中添加了新的氮。 总体而言，这项研究表明，SWP 在去除环境中的活性氮方面不如天然池塘有效，可能会影响下游水质。