Synergistic alleviation of lake eutrophication and carbon emission by macrophyte restoration

Algal blooms induced by eutrophication not only deteriorate water quality but also enhance greenhouse gas emissions. Although the theory of multiple stable states suggests that macrophyte restoration can reverse phytoplankton domination in lakes, associated ecosystem climate benefits are rarely considered. Based on a recent mass balance model, we highlight macrophyte restoration as a promising strategy to synergistically alleviate lake eutrophication and carbon emissions. We found a general decrease in net carbon dioxide equivalents (ΔCO2-eq) after macrophyte restoration, and then we discussed the potential pathways by which macrophyte restoration decreases carbon emissions. It is also noteworthy that such net climate benefits are much more dependent on the applied restoration species and ecosystem management via associated trade-offs between CO2 sequestration and methane (CH4) emissions. Our study emphasizes the significance of macrophyte restoration for its important roles in enhancing water quality and carbon sink in lakes.

Introduction

The prevalence of algal blooms resulting from eutrophication has been causing serious threats to water quality and other ecosystem services.1 Traditionally, this has been primarily attributed to increased nutrient loadings, whereas global warming has recently been shown to deteriorate eutrophication and trigger more frequent or more extensive algal blooms.1 For example, even a slight increase in spring temperatures can result in algal blooms in advance, and higher summer temperatures can promote the outbreak of large-scale algal blooms. Furthermore, although algal blooms may temporarily increase carbon dioxide (CO2) uptake, phytoplankton biomass is easily degraded and may increase the emissions of the more potent greenhouse gas methane (CH4).2 Accordingly, algal blooms not only reduce water quality but also increase the warming potential via greenhouse gas emissions in lakes. With intensified global warming, it is urgent to seek strategies to alleviate eutrophication while also reducing greenhouse gas emissions.

The long-observed regime shifts between a dominance of phytoplankton and macrophytes may offer an opportunity to resolve this enigma in eutrophic lakes.3 In this study, we summarize the positive feedback between algal blooms and carbon emissions and then highlight macrophyte restoration as a plausible strategy to synergistically alleviate lake eutrophication and carbon emissions. Finally, we discuss the potential mechanisms by which macrophyte restoration decreases carbon emissions. This study is therefore of great significance for guiding water purification and carbon sink enhancement in eutrophic lakes.