Catchment nutrient export, especially during high flow events, can influence ecological processes in receiving waters by altering nitrogen (N) and phosphorus (P) concentrations and relative amounts (stoichiometry). Event‐scale N and P export dynamics may be significantly altered by land use/land cover (LULC) and season. Consequently, to manage water resources, it is important to understand how LULC and season interact to influence event N and P export. In situ, high‐frequency spectrophotometers allowed us to continuously and concurrently monitor nitrate (NO₃⁻) and soluble reactive P (SRP) concentrations and therefore examine event‐scale NO₃⁻ and SRP export dynamics. Here we analyzed event NO₃⁻ and SRP concentration‐discharge hysteresis patterns and yields for >400 events to evaluate how LULC and seasonality influence event NO₃⁻ and SRP export dynamics in three low‐order watersheds with different primary LULCs (agricultural, forested, and urban). Differences among event NO₃⁻ and SRP hysteresis patterns suggest these nutrients have different source areas and dominant transport pathways that were impacted by both LULC and seasonality. Unexpectedly, we observed similar seasonal patterns in event NO₃⁻:SRP stoichiometry among LULCs, with the most N‐enriched events occurring in spring, and event stoichiometry approaching Redfield N:P ratios in the fall. However, seasonal stoichiometry patterns were driven by unique seasonal NO₃⁻ and SRP export patterns at each site. Overall these findings suggest LULC and seasonality interact to alter the timing and magnitude of event NO₃⁻ and SRP exports, leading to seasonal patterns in event NO₃⁻ to SRP stoichiometry that may influence ecological processes, such as productivity, in receiving waters.

中文翻译：

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土地利用和季节影响事件规模的硝酸盐和可溶性活性磷的出口以及源头集水区的出口化学计量

流域的养分出口，特别是在高流量事件中，可能会通过改变氮（N）和磷（P）的浓度和相对含量（化学计量）来影响接收水域的生态过程。事件规模的氮和磷出口动态可能会因土地利用/土地覆盖（LULC）和季节而发生显着变化。因此，要管理水资源，重要的是要了解土地利用变化量和季节如何相互作用来影响事件N和P的出口。原位，高频分光光度计使我们能够连续且同时监视硝酸盐（NO ₃ ^- ）和可溶性活性磷（SRP）的浓度，并且因此检查事件尺度NO ₃ ^-和SRP出口动力学。在这里，我们分析了事件NO ₃ ^-和SRP浓度-放电履历图案，产量> 400个事件来评估LULC和季节性影响事件NO如何₃ ^-和SRP出口在低3动力学与不同的主LULCs（农业，森林和城市）流域。事件NO之间的差异₃ ^-和SRP迟滞模式表明，这些营养物质具有不同的源区，并且被2 LULC和季节性的影响占主导地位的运输途径。出乎意料的是，我们在事件_3中观察到了类似的季节性模式^-LULC中的：SRP化学计量比，春季发生的N富集事件最多，而秋季的事件化学计量比接近Redfield N：P比率。然而，季节性化学计量模式是由独特的季节性带动NO ₃ ^-和SRP的出口模式在每个站点。总的来说，这些研究结果表明LULC和季节性相互作用改变时间和事件NO的量级₃ ^-和SRP的出口，导致季节性模式在事件NO ₃ ^-对可能影响生态过程，如生产力，在受纳水体SRP化学计量。