Nitrogen (N) removal from stormwater runoff prior to its export to sensitive downstream water bodies is a common goal for urban stormwater ponds (SWPs). Denitrification removes nitrate (NO₃⁻) from stormwater runoff by conversion to di-nitrogen gas (N₂), permanently removing reactive N from the ecosystem. Typically, N removal in SWPs is quantified via mass balance approaches, but the internal biogeochemical mechanisms driving N dynamics in these engineered ecosystems are unclear. In this study, we quantified gaseous and dissolved inorganic N fluxes and sediment oxygen demand from sediment cores collected at residential SWPs ranging from 10 to 30 years old in two subtropical cities during the dry and wet seasons. To better understand biogeochemical process rates and drivers within SWP sediments, we exposed sediments to both ambient and elevated (to simulate stormwater runoff) water column nitrate concentrations. Under ambient concentrations, SWP sediments could be either net sources (via N-fixation) or sinks (via denitrification) for N, and net N₂ flux was not significantly affected by background nitrate concentrations, sediment oxygen demand, or age. However, SWP sediments shifted to net denitrification under elevated nitrate conditions. Denitrification (positive net N₂ flux) increased with SWP age, microbial activity, and net nitrate uptake (p < 0.05 for each). These results suggest that while denitrification is N limited under ambient conditions, SWPs have the capacity to rapidly process acute nitrate loading events and remove N from the water column via denitrification.

在雨水径流出口到敏感的下游水体之前从雨水径流中去除氮 (N) 是城市雨水池 (SWP) 的共同目标。反硝化中移除了硝酸盐（NO ₃ ^- ）从通过转化成二氮气雨水径流（N ₂)，从生态系统中永久去除活性氮。通常，SWP 中的 N 去除量通过质量平衡方法进行量化，但在这些工程生态系统中驱动 N 动态的内部生物地球化学机制尚不清楚。在这项研究中，我们量化了两个亚热带城市在旱季和雨季从 10 到 30 年的住宅 SWP 收集的沉积物芯中的气态和溶解无机 N 通量和沉积物需氧量。为了更好地了解 SWP 沉积物中的生物地球化学过程速率和驱动因素，我们将沉积物暴露于环境和升高（以模拟雨水径流）水柱硝酸盐浓度。在环境浓度下，SWP 沉积物可能是 N 的净源（通过固氮）或汇（通过反硝化作用），净 N ₂通量不受背景硝酸盐浓度、沉积物需氧量或年龄的显着影响。然而，在硝酸盐升高的条件下，SWP 沉积物转变为净反硝化。反硝化作用（正净 N ₂通量）随着 SWP 年龄、微生物活动和净硝酸盐吸收而增加（每个 p < 0.05）。这些结果表明，虽然反硝化在环境条件下受 N 限制，但 SWP 有能力快速处理急性硝酸盐负载事件并通过反硝化从水柱中去除 N。