1. Catastrophic regime shifts in various ecosystems are increasing with the intensification of anthropogenic pressures. Understanding and predicting critical transitions are thus a key challenge in ecology. Previous studies have mainly focused on single environmental drivers (e.g., eutrophication) and early warning signals (EWSs) prior to population collapse. However, how multiple environmental stressors interact to shape ecological behaviour and whether EWSs were detectable prior to the recovery process in lake ecosystems are largely unknown.

2. We present long-term empirical evidence of the critical transition and hysteresis with the combined pressures of climate warming, eutrophication and trophic cascade effects by fish stocking in a subtropical Chinese lake in the Yangtze floodplain. The catastrophic regime shifts are cross-validated by 64-year multi-trophic level monitoring data and paleo-diatom records.

3. We show that EWSs are detectable in both the collapse and recovery trajectories and that including body size information in composite EWSs requires shorter time series data and can improve the predictive ability of regime shifts. Although full recovery has not yet been observed, EWSs prior to recovery provide us with the opportunity to take measures for a clear-water regime.

4. Climate warming and top-down cascade effects have a negative influence on water clarity by altering lower trophic level abundance and body size, which in turn have a negative effect on macrophyte abundance. Furthermore, we identify a shift in the dominant driving forces from bottom-up to top-down after regime shifts, decoupling the relationships between nutrients and biological components and thus decreasing the efficiency of nutrient reduction.

5. Synthesis This study provides new insights into ecological hysteresis under multiple external stressors and improves our understanding of trait-based EWSs in both the collapse and recovery processes in natural freshwater ecosystems. For management practice, our work suggests that slowing down climate warming and weakening the fish predation pressure on food webs are necessary to increase the effectiveness of nutrient reduction in the restoration of lakes.

On July 8, 2010, a 50 cm sediment core was collected in Lake Donghu (30°33′02″ N, 114°21′40″ E) at a water depth of 2 m using a Kajak gravity corer with a 58 mm diameter. The sediment core was sliced at 0.5 cm intervals for dating and diatom analyses. The chronologies of the core were obtained by measuring ²¹⁰Pb and ¹³⁷Cs radionuclide activities in contiguous samples at the State Key Laboratory of Lake Science and Environment of the Chinese Academy of Sciences (CAS), Nanjing, China. A total of 98 sediment samples were prepared for diatom analysis using the standard method (Battarbee, Jones, & Flower, 2001). Diatom species were identified using oil immersion at 1000 magnification under an Olympus microscope (BX51). Diatom concentrations were estimated using DVB microspheres, which are expressed as relative percent abundances.

Paleo-Diatom: This file contains the diatom communities from dated sediment core.

Fish_yield: This file contains the long-term changes of toal fish yield of Lake Donghu.

Long-term_field_observation_phytoplankton: This file contains the long-term field observation data of phytoplankton community (1956-2019).