Nutrient enrichment and climate warming drive carbon production of global lake ecosystems

Underestimating the magnitude of global lake carbon (C) production undermines the evaluation of the terrestrial ecosystem's C sink, which is key to achieving global C balance. Quantifying the potential response of lake net ecosystem productivity (NEP) and associated C production capacity to human activities is critical for evaluating the Earth's C balance. Here, we reveal global spatiotemporal dynamics of lake C production over 20 years across different continents and climate zones, highlighting the role of anthropogenic activity as a driving mechanism. We estimated lake C production using phytoplankton primary productivity from the surface to the estimated euphotic depth (PP_eu) based on chlorophyll-a (Chl-a) content. Economic development has significantly contributed to increases in global lake temperatures and total phosphorus concentrations. This has stimulated increases in annual lake C production, rising from 1.53 Pg C yr⁻¹ in the 2000s to 1.95 Pg C yr⁻¹ in the 2010s. Concurrently, lakes with higher total phosphorus (TP) concentrations (≥ 0.6 mg L⁻¹) exhibited significantly greater PP_eu values of 3.16 g C m⁻² d⁻¹, compared to lakes with lower TP concentrations (≤ 0.1 mg L⁻¹), which showed 1.50 g C m⁻² d⁻¹. Although lake water TP concentrations can reach up to 1 mg L⁻¹, the critical TP concentration (TP_c) at which global lake PP_eu peaks at 4 to 6 g C m⁻² d⁻¹ is approximately 0.5 mg L⁻¹. Exploiting the C sink potential of lakes requires understanding the environmental factors that control metabolic processes; however, there is a lack of effective monitoring and evaluation of the highly heterogeneous and diverse autotrophic C fixation processes in inland waters.