The external inputs of nitrogen and phosphorus are crucial driving forces for regime shifts in lakes. However, the altered flow caused by anthropogenic activities and climate change complicates the transition process. Identifying critical nutrient loadings for state transitions and their relationship with flow change has become an increasingly crucial scientific issue for managing lake ecosystems. Lake Dianchi, a shallow plateau lake that suffers from long-term eutrophication and extensive water regulation, was used as a case study to explore the critical nutrient loading under changing flow regimes. To this end, we established the PCLake+ model for Lake Dianchi using the parameters from native submerged macrophytes and long-term observational data. The results showed the following. (1) From 2001 to 2018, the lake's trophic status was moderately eutrophic with slight inter-annual fluctuations, and the most severe period occurred in the summer and autumn. (2) The critical total nitrogen (TN) and total phosphorus (TP) loadings of the lake from the clear-water state dominated by submerged macrophytes to the turbid-water state dominated by algae were 45.89 mg N and 3.53 mg P , respectively. Those from the turbid to the clear state were 26.78 mg N and 2.06 mg P , respectively, which were close to the actual external inputs of TN and TP loadings, indicating that the lake entered a critical period for restoration. (3) The water level and inflow significantly changed the critical TN and TP loadings and impacted the restoration threshold more than degradation. Decreasing water level or increasing water inflow can effectively rise the critical TN and TP loadings of both degradation and restoration, which is conducive to accelerating the evolution of aquatic ecosystems towards a clear-water state dominated by submerged macrophytes.

中文翻译：

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浅层高原滇池动态变化的临界养分负荷模拟

氮和磷的外部输入是湖泊状态转变的关键驱动力。然而，人类活动和气候变化引起的流量变化使转变过程变得复杂。确定状态转变的关键养分负荷及其与流量变化的关系已成为管理湖泊生态系统日益重要的科学问题。滇池是一个长期遭受富营养化和粗放水调节的高原浅水湖泊，本文以滇池为例，探讨水流变化下的临界养分负荷。为此，我们利用原生沉水植物参数和长期观测数据建立了滇池PCLake+模型。结果如下。 （1）2001年至2018年，湖泊营养状况为中度富营养化，年际间波动较小，最严重时期出现在夏秋季节。 （2）湖泊从以沉水植物为主的清水状态到以藻类为主的浊水状态时的临界总氮（TN）和总磷（TP）负荷分别为45.89 mg N和3.53 mg P。从浊态到清态分别为26.78 mg N和2.06 mg P，与实际外部输入的TN和TP负荷接近，表明湖泊进入恢复关键期。 (3) 水位和流入量显着改变了临界TN和TP负荷，对恢复阈值的影响大于退化。降低水位或增加来水量可以有效提高退化和恢复的临界TN和TP负荷，有利于加速水生生态系统向沉水植物为主的清水状态演化。