Increased use of phosphorus (P) fertilizers and detergents and intensified livestock production have more than doubled P inputs to human-impacted watersheds over pre-industrial levels. While P fertilizer use and manure application help to maximize crop yields, excess P is lost to runoff, leading to eutrophication of downstream waters. Excess P also accumulates across the landscape, leading to legacies that serve as long-term sources of P to surface waters, even after inputs to the watershed are reduced. Here, we have developed, for the first time, a process-based model, Exploration of Long-tErM Nutrient Trajectories-Phosphorus, designed to capture legacy P accumulation and depletion trajectories along the land-aquatic continuum. To drive the model, we have developed a more than 100-year trajectory of watershed P inputs to the Grand River Watershed (GRW), Canada’s largest watershed draining directly to Lake Erie. Our results first show that net P inputs to the watershed approximately tripled between 1900 and the late-1970s, when P surplus magnitudes peaked at approximately 15 kg ha⁻¹ y⁻¹. During this same period, stream P loads have increased more than fourfold, from 0.11 kg ha⁻¹ y⁻¹ in 1900 to 0.80 kg ha⁻¹ y⁻¹ in the 1970s. Since 1900, the GRW has served as a net P sink, with approximately 96% of net P inputs having been retained within the basin. Future simulations suggest that while 40% reductions in P loading in Lake Erie watersheds are possible under aggressive management scenarios, legacy P will continue to elevate P loads to Lake Erie for many decades to come.

中文翻译：

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超越物质平衡：流域磷的遗产和当前水质政策挑战的演变

磷（P）肥料和清洁剂的使用增加以及畜牧业生产的增加使受人类影响的流域的磷投入比工业化前水平增加了一倍以上。虽然使用磷肥和施肥有助于最大限度地提高作物产量，但过量的磷会流失到径流中，导致下游水域富营养化。过量的磷也会在整个景观中积累，导致作为地表水磷的长期来源的遗留物，即使在流域的输入减少之后也是如此。在这里，我们首次开发了一个基于过程的模型，长期营养轨迹探索 - 磷，旨在捕捉沿陆水连续体的遗留磷积累和消耗轨迹。为了驱动模型，我们已经开发了一个超过 100 年的流域 P 输入到大河流域 (GRW) 的轨迹，该流域是加拿大最大的流域，直接排入伊利湖。我们的结果首先表明，从 1900 年到 1970 年代后期，流域的净磷输入量增加了大约两倍，当时磷过剩量达到峰值，约为 15 千克公顷^-1  y ^-1。在同一时期，河流 P 负荷增加了四倍多，从1900 年的0.11 kg ha ^-1  y ^-1到1970 年代的0.80 kg ha ^-1  y ^-1。自 1900 年以来，GRW 一直充当净 P 汇，大约 96% 的净 P 输入被保留在流域内。未来的模拟表明，虽然在积极的管理方案下，伊利湖流域的磷负荷减少 40% 是可能的，但传统的磷将在未来几十年继续提高伊利湖的磷负荷。