Ecological regime shifts weaken sedimentary carbon sequestration in shallow Lake liangzi

[Geoengineering News]

https://www.sciencedirect.com/science/article/pii/S0043135425020767

Authors: Jinglin Hou, Qi Lin, Jiasheng Zhang, Shixin Huang, Yuan Jin, Yanhua Wang, Haibo He, Pierre Taillardat, David Taylor, Ke Zhang, Michael E. Meadows

17 December 2025

Highlights

•A multi-proxy approach revealed long-term transformations in OC sources and molecular composition.

•Eutrophication-driven ecological shifts in shallow lakes reduced OC burial capacity.

•Shallow lake OC sinks are vulnerable to multiple anthropogenic forcings.

•Effective nutrient control is essential to sustain sediment OC burial in shallow eutrophic lakes.

Abstract

Lakes, though covering a minor fraction of Earth’s land surface, are disproportionately important in global carbon cycling and greenhouse gas emissions. Yet how the capacity of sedimentary carbon burial responds to ecological regime shifts remains poorly understood. Here, we reconstruct two centuries of organic carbon (OC) dynamics in Lake Liangzi, a large shallow lake in the middle Yangtze basin, by integrating sediment OC burial rates, stable carbon isotope-based source apportionment (MixSIAR), fluorescence characterization of dissolved organic matter (DOM) using EEM-PARAFAC, and molecular-level analysis using FT-ICR MS. We identify two major ecological transitions. The first, in the 1960s, corresponds to land-use intensification and nutrient enrichment, with sedimentary evidence indicating a shift from a low-productivity state typical of oligotrophic, shallow waters to a high-productivity, macrophyte-algae co-dominated system. The second, since the 2000s, reflects a further ecological shift toward the predominance of phytoplankton and associated enhanced algal-derived inputs and increased humic-like DOM. We reveal that eutrophication-driven shifts from macrophyte-algae coexistence to algal dominance increase labile carbon supply but reduce burial capacity due to intensified microbial mineralization and weakened mineral-associated protection under anoxia. This reduced burial capacity not only weakens long-term carbon sequestration but also potentially enhances greenhouse gas emissions from sediments. These findings indicate that eutrophication-driven ecological shifts fundamentally alter the source composition and diagenetic stability of sedimentary organic matter, diminishing the long-term carbon sequestration capacity of shallow lakes. Effective management should therefore integrate nutrient reduction, hydrological restoration, and ecosystem feedbacks to sustain lacustrine carbon sinks under accelerating environmental change.

Source: ScienceDirect