Why Lake Sediments Matter for the Climate
Beneath the calm surfaces of lakes, sediment layers quietly help determine how much greenhouse gas escapes into the air. This study reveals how lake’s nutrient levels regulate the production of two potent greenhouse gases: nitrous oxide (N₂O), a long-lived heat-trapping gas, and methane (CH4), the main component of natural gas. Understanding these invisible processes shows how farming, fertilizer use, and water-quality policies ripple all the way up to the global climate.
From Drinking Water to Greenhouse Gases
Freshwater lakes supply drinking water, support fisheries and recreation, but they are also major sources of greenhouse gases. As fertilizers and other nitrogen-rich pollutants wash off farmland and cities into lakes, they fuel algal blooms and a process called eutrophication. At the same time, those nutrients feed microorganisms that control whether nitrogen leaves the lake safely as harmless nitrogen gas or leaks out as N₂O, and whether buried organic matter is converted into CH₄. Yet, until now, scientists have not clearly understood how lake’s trophic status determines which gases are produced and through which microbial pathways.
Following Microorganisms Around the World
The authors tracked this question by combining detailed laboratory experiments with a global metagenome-based analysis of lake sediments. They collected metagenome datasets from lakes spanning a wide range of nutrient conditions from oligotrophic to eutrophic levels. Using metagenomics, they read the genetic blueprints of the microorganisms present and tracked key genes linked to nitrogen and CH₄ cycling. They then incubated sediments under carefully controlled conditions, adding specific forms of nitrogen and using inhibitors to turn microbial processes on or off. This allowed them to measure how many N₂O and CH₄ were produced, and to link those rates directly to the underlying mechanism.
Figure 1. Metagenomic analysis linking lake nutrient levels to N₂O and CH₄ production potential.
Two Different N₂O Worlds
In nutrient-rich, eutrophic sediments, organic carbon is plentiful, giving microorganisms the energy they need to carry out complete denitrification—converting reactive nitrogen all the way to harmless N₂ gas. In eutrophic lakes, N₂O arises mainly as a by-product of nitrification, the process where microorganisms oxidize ammonia. When blocked this step with a specific inhibitor, N₂O emissions nearly vanished. In contrast, in nutrient-poor, oligotrophic sediments with little organic carbon, denitrification often stalls halfway. Microorganisms convert nitrate to N₂O but lack the resources to finish the final step, so N₂O generated. Genetic markers mirrored this split: eutrophic sediments were dominated by gene types that favor complete denitrification and strong N₂O consumption, while oligotrophic sediments carried more genes associated with incomplete denitrification and higher N₂O release.
CH₄ Follows a Different Set of Rules
CH₄ told a more complicated story. Across the global dataset, the abundance of genes responsible for CH₄ production in sediments closely tracked genes for nitrogen fixation in specialized microorganisms, suggesting that CH₄-producing archaea often make their own nitrogen fertilizer from N₂ gas. Lab incubations confirmed that supplying N₂ gas boosted both CH₄ production and ammonium levels in sediments. However, unlike N₂O, CH₄-related genes and production rates did not show a clear, consistent shift between nutrient-poor and nutrient-rich lakes. Instead, CH₄ output appears to depend on a broader mix of factors, including temperature, sediment chemistry, lake depth, and how quickly material accumulates on the bottom, making it harder to predict from trophic state alone.
Turning the Nutrient Dial Up and Down
To move beyond snapshots of existing lakes, the authors designed an inventive cross-inoculation experiment. They mixed live microorganisms from a nutrient-poor lake into sterilized sediments from a nutrient-rich lake, and vice versa, creating a gradient from oligotrophic to eutrophic conditions in the lab. As they gradually enriched poor sediments, N₂O production shifted from being driven by incomplete denitrification to being dominated by nitrification, matching the pattern detected in real eutrophic lakes. When they made rich sediments more like low-nutrient ones, the system flipped back. This reversible switch shows that as lakes are pushed along the eutrophication–oligotrophication spectrum by human actions or restoration efforts, the main microbial source of N₂O predictably changes with them.
Figure 2. Cross-inoculation experiments simulating eutrophication/oligotrophication confirm nutrient control over N₂O production.
What This Means for Climate and Lake Management
For a non-specialist, the key finding is that lake’s trophic status strongly controls how N₂O is produced, but have no simple, direct control over CH₄. In eutrophic lakes, cutting back on ammonium inputs or limiting conditions that favor nitrification could sharply reduce N₂O emissions. In oligotrophic or recovering lakes, strategies that keep denitrification running to completion—such as boosting carbon-to- nitrogen ratio or removing accumulated nitrate from sediments—can help prevent N₂O emission. Because global fertilizer use and land development are expected to increase eutrophication in many regions, these findings offer a practical roadmap: by managing the nutrient levels, we can deliberately shift the balance of microbial pathways in sediments and, in turn, curb a significant source of powerful greenhouse gas.
Figure 3. Conceptual model illustrating how nutrient levels regulate N₂O and CH₄ production in lake sediments.
This study was published in Nature Communications entitled "Trophic status strongly regulates nitrous oxide but not methane production in global freshwater lake sediments (https://doi.org/10.1038/s41467-026-72269-z)." Professor Qingyun Yan from the Southern Marine Laboratory is the corresponding author. Associate Professor Yuchun Yang and doctoral student He Zhang from Sun Yat-sen University are co-first authors. Additional contributors include Associate Professor Craig W. Herbold (University of Canterbury, New Zealand), Associate Professor Jie Huang and Professor Yuhe Yu (Institute of Hydrobiology, Chinese Academy of Sciences), and Professors Zhili He and Jianguo He (Southern Marine Laboratory).
This study was supported by the National Natural Science Foundation of China, the Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), and the Ocean Negative Carbon Emissions (ONCE) Program.
