One prominent effect of nutrient pollution of surface waters is the mass invasion of floating plants, which can clog waterways, disrupting human use of aquatic systems. These plants are widely vilified and motivate expensive control campaigns, but their presence may be providing a poorly recognized function in the cycling of excess nutrients. The capacity for floating plants to absorb nutrients from surface water has been understood for decades, primarily from their use in constructed wetlands for wastewater treatment. Yet, in natural settings, there has not been to date any effort to quantify whether floating plant invasions represent important pools or fluxes of nutrients relative to those of the river catchments in which they occur. We found that seasonal hydrologic cycles in the Zambezi trap and flush floating plants from river choke points, such as dams and river confluences, on an annual basis. Peak plant biomass at such choke points constitutes a proxy for estimating annual plant-bound nutrient loads. We assessed the significance of floating vegetation as nutrient sinks by comparing annual plant-bound nutrient loading to conventional river nutrient loading (dissolved and particulate) for four tributaries of the Zambezi River in Zambia. We found that the relative importance of floating vegetation was greatest in the more urbanized catchments, such as the Maramba River draining the city of Livingstone, representing approximately 30% and 9% of annual digestible phosphorus and nitrogen flux respectively. We also found plant-bound phosphorus to be important in the Kafue River (19%), draining the industrial town of Kafue and extensive sugarcane plantations. These results demonstrate the great potential of floating plants to take up excess nutrients from natural river systems. Given the importance of hydrology in the life cycle of floating vegetation, controlled dam discharges may have an important role in managing them and their water quality treatment functions.

地表水养分污染的一个突出影响是漂浮植物的大规模入侵，这会堵塞水道，扰乱人类对水生系统的利用。这些植物被广泛诋毁并引发了昂贵的控制活动，但它们的存在可能在过量养分循环中提供了一种鲜为人知的功能。漂浮植物从地表水中吸收养分的能力已经被理解了几十年，主要是因为它们在人工湿地中用于废水处理。然而，在自然环境中，迄今为止还没有任何努力来量化漂浮植物入侵是否代表了相对于它们发生的河流集水区的重要养分池或通量。我们发现赞比西河中的季节性水文循环会从河流阻塞点捕获和冲刷漂浮植物，例如水坝和河流汇合处，每年一次。在这些阻塞点的峰值植物生物量构成了估计每年植物结合养分负荷的代理。我们通过比较赞比亚赞比西河四个支流的年度植物养分负荷与常规河流养分负荷（溶解和颗粒）来评估漂浮植被作为养分汇的重要性。我们发现，漂浮植被在城市化程度更高的流域中的相对重要性最大，例如排出利文斯通市的马兰巴河，分别占年可消化磷和氮通量的 30% 和 9%。我们还发现植物结合磷在 Kafue 河（19%）中很重要，它排干了 Kafue 工业城镇和广泛的甘蔗种植园。这些结果证明了漂浮植物从天然河流系统中吸收多余养分的巨大潜力。鉴于水文在漂浮植被生命周期中的重要性，受控大坝排放可能在管理它们及其水质处理功能方面发挥重要作用。