Lake Tegel is an extreme case of restoration: inflow treatment reduced its main external phosphorus (TP) load 40-fold, sharply focused in time, and low-P water flushed the lake volume ≈ 4 times per year. We analysed 35 years of data for the time TP concentrations took to decline from ≈ 700 to 20–30 µg/l, biota to respond and cyanobacteria to become negligible. The internal load proved of minor relevance. After 10 years, TP reached 35–40 µg/l, phytoplankton biomass abruptly declined by 50% and cyanobacteria no longer dominated; yet 10 years later at TP < 20–30 µg/l they were below quantifiable levels. 20–25 years after load reduction, the lake was stably mesotrophic, macrophytes had returned down to 6–8 m, and vivianite now forms, binding P insolubly in the sediment. Bottom-up control of phytoplankton through TP proved decisive. Five intermittent years with a higher external P load caused some ‘re-eutrophication’, delaying recovery by 5 years. While some restoration responses required undercutting thresholds, particularly that of phytoplankton biomass to TP, resilience and hysteresis proved irrelevant. Future research needs to focus on the littoral zone, and for predicting time spans for recovery more generally, meta-analyses should address P load reduction in combination with flushing rates.

中文翻译：

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生态系统组件需要数十年才能应对急剧而急剧的磷负荷减少

泰格尔湖是一个极端的恢复案例：入流处理将其主要的外部磷 (TP) 负荷减少了 40 倍，时间集中，低磷水每年冲刷湖量 ≈ 4 次。我们分析了 35 年的数据，其中 TP 浓度从 ≈ 700 下降到 20-30 µg/l，生物群做出反应，蓝藻变得可以忽略不计。内部负载证明无关紧要。10 年后，TP 达到 35-40 µg/l，浮游植物生物量突然下降 50%，蓝藻不再占主导地位；然而 10 年后，当 TP < 20–30 µg/l 时，它们低于可量化的水平。减荷后20-25年，湖泊中营养稳定，大型植物恢复到6-8 m，现在形成紫云母，将P不溶于沉积物中。通过 TP 自下而上控制浮游植物被证明是决定性的。外部磷负荷较高的五年间断造成了一些“再富营养化”，将恢复延迟了 5 年。虽然一些恢复响应需要降低阈值，特别是浮游植物生物量对 TP 的阈值，但恢复力和滞后被证明是无关紧要的。未来的研究需要关注沿海地区，并且为了更普遍地预测恢复的时间跨度，荟萃分析应该结合冲洗率来解决 P 负荷减少问题。