Synergistic Effects of Warming and Internal Nutrient Loading Interfere with the Long-Term Stability of Lake Restoration and Induce Sudden Re-eutrophication

Abstract

Phosphorus (P) precipitation is among the most effective treatments to mitigate lake eutrophication. However, after a period of high effectiveness, studies have shown possible reeutrophication and the return of harmful algal blooms. While such abrupt ecological changes were attributed to the internal P loading, the role of lake warming and its potential synergistic effects with internal loading, thus far, has been understudied. Here, in a eutrophic lake in central Germany, we quantified the driving mechanisms of the abrupt re-eutrophication and cyanobacterial blooms in 2016 (30 years after the first P precipitation). A processbased lake ecosystem model (GOTM-WET) was established using a high-frequency monitoring data set covering contrasting trophic states. Model analyses suggested that the internal P release accounted for 68% of the cyanobacterial biomass proliferation, while lake warming contributed to 32%, including direct effects via promoting growth (18%) and synergistic effects via intensifying internal P loading (14%). The model further showed that the synergy was attributed to prolonged lake hypolimnion warming and oxygen depletion. Our study unravels the substantial role of lake warming in promoting cyanobacterial blooms in re-eutrophicated lakes. The warming effects on cyanobacteria via promoting internal loading need more attention in lake management, particularly for urban lakes.

Lake Water Temperature Modeling in an Era of Climate Change: Data Sources, Models, and Future Prospects

“…Also, important ecological information like the thermal habitat or the solubility of gases can be inferred from the vertical distribution of water temperature (e.g., Butcher et al., 2015; Magee et al., 2019). 1D water temperature models can be easily coupled, or in some cases are already internally coupled, to aquatic ecosystem models (AEM3Ds) to project changes in water quality and ecosystem dynamics (e.g., Andersen et al., 2022; Kong et al., 2023; Ladwig, Hanson, et al., 2021; Salk et al., 2022). In most cases, there is a one‐way coupling between the thermodynamics and the AEM3D, in which the projected vertical diffusivity coefficient is used to infer the transport of water quality variables.…”

“…The progressive warming, depletion of dissolved oxygen, and increase of nutrient concentrations in deep layers have already been observed in numerous lakes worldwide. In many cases, these factors occur simultaneously, posing significant challenges to lake ecosystems (see e.g., Jane et al., 2023; Kong et al., 2023; North et al., 2014; Rempfer et al., 2010; Straile et al., 2003) and highlighting the importance of conducting further research in the field of lake thermal dynamics and regimes.…”

Effects of Dredging on Nitrogen and Phosphorus Storage Patterns and Retention Mechanisms in Column Core Sediments in the Caohai Region of Dianchi Lake

“…The natural water exchange of Dianchi takes up to four years, which provides favorable natural conditions for nutrient retention and lake management. The strong internal nutrient cycling in large shallow lakes and the influence of various aquatic habitats on nutrient retention make lake eutrophication management difficult [11][12][13]. For this study, two areas in the Caohai region-which is the most seriously polluted area of Dianchi Lake-were selected.…”