Data and code for: Regime shifts, trends, and variability of lake productivity at a global scale

Lakes are often described as sentinels of global change. Phenomena like lake eutrophication, algal blooms, or reorganization in community composition belong to the most studied ecosystem regime shifts. But, although regime shifts have been well documented in several lakes, a global assessment of the prevalence of regime shifts is still missing, and, more in general, of the factors altering stability in lake status, is missing. Here, we provide a first global assessment of regime shifts and stability in the productivity of 1,015 lakes worldwide using trophic state index (TSI) time series derived from satellite imagery. We find that 12.8% of the lakes studied show regime shifts whose signatures are compatible with tipping points, while the number of detected regime shifts from low to high TSI has increased over time. Although our results suggest an overall stable picture for global lake dynamics, the limited instability signatures do not mean that lakes are insensitive to global change. Modeling the interaction between lake climatic, geophysical, and socioeconomic features and their stability properties, we find that the probability of a lake experiencing a tipping point increases with human population density in its catchment, while it decreases as the gross domestic product of that population increases. Our results show how quantifying lake productivity dynamics at a global scale highlights socioeconomic inequalities in conserving natural environments.

湖泊常被视作全球变化的哨兵。湖泊富营养化、藻华爆发以及群落结构重组等现象，均为当前研究最为广泛的生态系统状态转换（regime shift）事件。尽管已有诸多湖泊的状态转换事件被详实记录，但目前仍缺乏针对全球范围内状态转换发生普遍性的系统性评估，更遑论对改变湖泊状态稳定性的各类驱动因子的全面解析。本研究基于卫星影像获取的营养状态指数（trophic state index, TSI）时间序列，对全球1015个湖泊的生产力状态转换与稳定性开展了首次全球性评估。研究结果显示，12.8%的受试湖泊出现了符合临界拐点（tipping point）特征的状态转换，且从低营养状态向高营养状态转换的事件数量随时间呈上升趋势。尽管研究结果整体上呈现出全球湖泊动态趋于稳定的图景，但有限的不稳定性信号并不代表湖泊对全球变化不敏感。通过构建湖泊气候、地球物理与社会经济特征及其稳定性属性之间的交互模型，本研究发现，湖泊发生临界拐点的概率随其流域内人口密度的升高而增大，随流域内人口所在地区的国内生产总值（gross domestic product, GDP）提升而降低。本研究结果证实，在全球尺度下量化湖泊生产力动态，能够揭示自然环境保护领域存在的社会经济不平等问题。