Tianxiang Hao

Wetland carbon cycling reflects an intrinsic balance between CO ₂ sequestration and anaerobic methane production, though hydrological drivers remain insufficiently quantified. Here, we synthesize eddy covariance data from 43 natural wetlands spanning diverse climates and hydrological regimes to quantify greenhouse gas (GHG) responses to water table depth (WTD). Both net ecosystem productivity and methane fluxes exhibit consistent unimodal relationships with WTD, peaking at 50 and 60 cm above the surface, respectively. While robust in temperate wetlands, uneven data distribution limits confirming this exact unimodal pattern in tropical and boreal systems. Accounting for GHG temperature sensitivity, 500 years radiative forcing simulations reveal that near surface water tables maximize long term cooling and sustain mitigation efficacy under future warming, whereas deeper or persistently flooded conditions diminish net climate benefits. These findings provide a generalized benchmark for optimizing wetland restoration to advance nature‐based climate solutions.

Soil acidification induced by nitrogen fertilization and atmospheric deposition is widely assumed to deplete soil inorganic carbon (SIC), thereby generating substantial CO ₂ emissions that amplify climate warming. However, national‐scale evidence linking acidification‐driven SIC loss to direct CO ₂ release remains limited. Here we apply a 0.05° proton‐budget framework constrained by atmosphere–soil–vegetation data sets (1980–2020) and extend it to 2050 projections, to quantify acidification‐induced SIC depletion and associated CO ₂ emissions across China's terrestrial ecosystems. As expected, soil acidification emerged as a dominant driver of SIC loss, accounting for ∼30%–56% of total depletion (2.57 ± 0.60 g C m ⁻² yr ⁻¹ or 13.04 ± 3.04 Tg C yr ⁻¹ ), with croplands contributing more than 70% of acidification‐driven losses. Contrary to prevailing assumptions, only 11 ± 3% of depleted SIC (1.52 ± 0.33 Tg C yr ⁻¹ ) was directly emitted as CO ₂ , offsetting merely ∼8% of the carbon sink from natural carbonic acid–driven rock weathering. This contrast arises because SIC‐rich soils are typically circumneutral to alkaline, favoring dissolved bicarbonate export over CO ₂ evasion. Meanwhile, continued policy regulation under the sustainable, low‐carbon, and environmentally friendly development pathway (SSP1‐2.6‐BHE) could further reduce SIC depletion and associated CO ₂ emissions by 36% and 15%, respectively, by 2050. Overall, our findings demonstrate that acidification‐induced SIC depletion does not entirely translate into direct atmospheric CO ₂ release, highlighting the need to explicitly distinguish SIC depletion from gaseous carbon loss in carbon‐cycle and climate assessments.

Chlorine (Cl) is a critical halogen and acidic component that influences atmospheric oxidation capacity, air quality, and acidifies ecosystems. Emission reduction measures in China are expected to similarly reduce Cl deposition as with sulfur (S). However, large knowledge gaps remain regarding the trends and drivers of China's Cl deposition. By integrating data from an observational network and published literature, we developed the first national dataset of Cl wet deposition in China from 1990 to 2020. This dataset revealed that total Cl^- and nonsea-salt (NSS) Cl^- deposition initially increased, reaching an inflection point around 2005, and then decreased, with an overall reduction of approximately 52%. As anticipated, Cl and S deposition decreased synchronously nationwide, attributable to reduced precursor emissions from energy structure adjustments and emission reduction technologies. However, in China's three major urban agglomerations, Cl did not decrease in parallel with S and even increased in the Pearl River Delta at a rate of +8% yr^-1. This mainly stems from rising waste incineration emissions driven by rapid economic and urban development, population and consumption expansion, which offset the mitigation achieved from coal combustion. Our study underscores the effectiveness of emission reduction measures, yet targeted control of emerging anthropogenic Cl pollution sources in urban hotspot areas is urgently needed to achieve regional sustainable development.

Understanding the link between wetland gross primary productivity (GPP) and methane (CH₄) emissions is crucial for global carbon cycle modeling, yet this coupling remains poorly constrained at a global scale due to data limitations. To address this critical gap, we compiled and analyzed the most comprehensive daily scale eddy covariance data set of GPP and CH₄ fluxes. In this analysis, we define this coupling as the slope of the linear fit between carbon fixed by ecosystems and carbon emitted as CH₄. Results indicate that the median lag time between CH₄ emissions and GPP is 24.8 days. In terms of their coupling, for every gram of carbon fixed in wetlands, 0.03 (interquartile range: 0.02-0.05) grams of carbon are released into the atmosphere as CH₄. The upscaling results indicate that the coupling in tropical wetlands is typically larger than in temperate and boreal wetlands, and the CO₂-equivalent emissions of CH₄ surpass the amount of CO₂ absorbed through photosynthesis. These results enhance our understanding of the complex biogeochemical processes that drive CH₄ emissions, offering valuable insights into the interplay between carbon fixation and emissions dynamics in wetland ecosystems.

Atmospheric sulfur (S) deposition, a key component of acid deposition, poses risks to ecosystems, human health, and sustainable development. In China, decades of coal-dominated energy use caused severe S pollution, but recent emission-control policies and energy restructuring have sought to reverse this trend. However, the effectiveness and regional differences in these measures remain insufficiently quantified. Here, we combined continuous observations from 43 monitoring sites (2013–2023), satellite-derived SO₂ vertical column density, and multi-source environmental datasets to construct a high-resolution record of wet S deposition. A random forest model, validated with R² = 0.52 and RMSE = 1.2 kg ha⁻¹ yr⁻¹, was used to estimate fluxes and spatial patterns, while ridge regression and SHAP analysis quantified the relative contributions of emissions, precipitation, and socioeconomic factors. This framework allows us to assess both the environmental and health-related sustainability implications of sulfur deposition. Results show a nationwide decline of more than 50% in wet S deposition during 2013–2023, with two-thirds of sites and 95% of grids showing significant decreases. Historical hotspots such as the North China Plain and Sichuan Basin improved markedly, while some southern provinces (e.g., Guizhou, Hunan, Jiangxi) still exhibited high deposition (>20 kg ha⁻¹ yr⁻¹). Over 90% of the reduction was attributable to emission declines, confirming the dominant effect of sustained policy-driven measures. This study extends sulfur deposition records to 2023, demonstrates the value of integrating ground monitoring with remote sensing and machine learning, and provides robust evidence that China’s emission reduction policies have delivered significant environmental and sustainability benefits. The findings offer insights for region-specific governance and for developing countries balancing economic growth with ecological protection.

Temperature dependence is a crucial parameter in estimating methane (CH₄) fluxes from natural wetlands, yet our understanding of this parameter remains inadequate. Seasonal fluctuations in water levels and ecosystem productivity lead to seasonal differences in CH₄ production and oxidation. We hypothesized the existence of seasonality in the temperature dependence of CH₄ fluxes. To validate this hypothesis, we analysed the FLUXNET‐CH4 dataset to determine the seasonal variation in temperature dependence of CH₄ fluxes. We divided the year into six seasons based on air temperature and assessed the temperature dependence for each season using the apparent activation energy calculated by the Boltzmann–Arrhenius equation. Our results showed that temperature dependence showed a unimodal trend with seasons, with the apparent activation energy peaking in early summer (0.60 eV) and reaching its lowest point in late winter (−0.02 eV). This seasonal pattern of temperature dependence was consistent across wetlands with different vegetation types and hydrological conditions. Modelling of global wetland CH₄ emissions based on seasonal temperature dependences showed a 19% (4%–45%) increase in emission rates under the most severe temperature rise scenario. Our results emphasize the seasonality of temperature dependence, which will help to further improve current and future predictions of wetland CH₄ emissions. Read the free Plain Language Summary for this article on the Journal blog.