Leaching of excess nitrogen (N) to groundwater in fertilized landscapes can overwhelm natural biogeochemical processes and cause long-term eutrophication of aquatic systems. We investigated N fate and transport from an intensively managed short-rotation woody crop (Pinus taeda) plantation through the riparian zone of an intermittent, low-gradient blackwater stream. Fertilization of the P. taeda plantation on the uplands resulted in contamination of groundwater with nitrate concentrations between 0.9 and 1.9 mg N L⁻¹. No corresponding increase in nitrate was observed in stream water or shallow groundwater in the riparian zone. Groundwater travel-time modeling predicted that N from near-stream, upland plantation areas should have reached streams during the monitoring period. Two years of measuring N species in well water in contrasting landscape positions (within the plantation, swale, riparian edge, forested hillslope, and valley), indicated rapid nitrate transformation and denitrification within the forested wetland valleys. Denitrification in the shallow groundwater system within the toeslopes and the riparian zone was estimated to have removed > 90% of nitrate. These results highlight the importance of riparian zones as pathways for the removal of N and for controlling downstream N loads.

施肥景观中过量的氮 (N) 浸入地下水可能会破坏自然生物地球化学过程，并导致水生系统长期富营养化。我们研究了集约化管理的短周期木本作物（火炬松）种植园中氮的归宿和传输，穿过间歇性低梯度黑水河的河岸带。高地火炬树种植园的施肥导致地下水污染，硝酸盐浓度在0.9至1.9 mg NL ^-1之间。在河岸地区的溪流水或浅层地下水中没有观察到硝酸盐相应增加。地下水传播时间模型预测，在监测期间，来自近河、高地种植区的氮应该已经到达溪流。两年来在对比景观位置（种植园、洼地、河岸边缘、森林山坡和山谷内）测量井水中的氮形态，表明森林湿地山谷内发生了快速的硝酸盐转化和反硝化。据估计，斜坡和河岸带内浅层地下水系统的反硝化作用已经去除了超过 90% 的硝酸盐。这些结果凸显了河岸带作为氮去除和控制下游氮负荷途径的重要性。