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<p>Successful global reductions in atmospheric sulfur emissions have transformed freshwater biogeochemistry. However, many lakes still exhibit high sulfate levels despite sulfur emission controls. Here, we demonstrate this shift in Taihu Lake, China’s third-largest freshwater lake, through a comprehensive 25-year hydrochemical record (1999–2023) combined with stable sulfur isotope (δ³⁴S) tracing across water, soils, and sediments. Despite of a 76.2% drop in regional SO₂ emissions after 2015, lake sulfate concentrations decreased by only 18.5%, revealing a pronounced decoupling from atmospheric sources. Generalized additive modeling identified major sulfate sources and regime shifts and isotopic mixing models (IsoSource, validated with Monte Carlo uncertainty propagation) apportioned their current contributions to the lake. Atmospheric deposition remains the largest single source (55.7 ± 4.2%), but non-atmospheric sources collectively contribute 44.3 ± 5.1%, with municipal wastewater emerging as the primary manageable anthropogenic source (27.6 ± 3.8%). This anthropogenic shift creates a clear northwest-southeast lake sulfate gradient, with levels 32.9% higher in urbanized northwest sub-basins that receive over 400&#xa0;million tons of wastewater annually. Watershed soils modulate diffuse inputs: farmland (covering 44.2% of the watershed area) leaches sulfate, which is buffered by organic matter retention. Lake sediments act as the primary sink with over 90% of sulfate reduced in the top 10&#xa0;cm through microbial dissimilatory reduction (α ≈ 1.022). However, this process accelerates phosphorus mobilization via sulfide-driven iron reduction, worsening eutrophication. Our findings identify municipal wastewater as the key controllable sulfate source in the post-emission-reduction era, emphasizing the need for integrated watershed management that targets advanced effluent treatment such as biological sulfate removal to disrupt the sulfate-phosphorus feedback loop and promote ecosystem recovery in eutrophic lakes globally.</p> Graphical Abstract <p></p> <p><?tk 4?>The decoupling of 76.2% decrease in SO₂ emissions after 2015 while only 18.5% reduction in sulfate concentrations in Taihu Lake indicated the increasing dominance of non-atmospheric inputs in this watershed. A notable northwest-southeast spatial SO<sub>4</sub><sup>2−</sup> gradient in lake water and increasing pattern from bottom to surface on sediment profiles were also observed. In the sediment of the major SO<sub>4</sub><sup>2−</sup> sink, over 90% of sulfate undergoes microbial reduction, likely an important driver for internal phosphorus release and potential eutrophication booster. With sulfate isotopic evidence, major SO<sub>4</sub><sup>2−</sup> source contributions were identified, and this highlights an urgent need for adaptive management strategy to gear to the pollutant source shift and internal nutrient loading control.</p>

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Long-Term Variations and Isotopic Evidence Showed Source and Driver Shift of Sulfate During Past Decades in Large Freshwater Taihu Lake, China

  • 期刊论文

  • 发表日期：

    2026年7月6日

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  • Yu Tao,
  • Muhammad Adil,
  • Deng Yixiang,
  • Wang Shaozhi,
  • Xu Gaoying

摘要

Successful global reductions in atmospheric sulfur emissions have transformed freshwater biogeochemistry. However, many lakes still exhibit high sulfate levels despite sulfur emission controls. Here, we demonstrate this shift in Taihu Lake, China’s third-largest freshwater lake, through a comprehensive 25-year hydrochemical record (1999–2023) combined with stable sulfur isotope (δ³⁴S) tracing across water, soils, and sediments. Despite of a 76.2% drop in regional SO₂ emissions after 2015, lake sulfate concentrations decreased by only 18.5%, revealing a pronounced decoupling from atmospheric sources. Generalized additive modeling identified major sulfate sources and regime shifts and isotopic mixing models (IsoSource, validated with Monte Carlo uncertainty propagation) apportioned their current contributions to the lake. Atmospheric deposition remains the largest single source (55.7 ± 4.2%), but non-atmospheric sources collectively contribute 44.3 ± 5.1%, with municipal wastewater emerging as the primary manageable anthropogenic source (27.6 ± 3.8%). This anthropogenic shift creates a clear northwest-southeast lake sulfate gradient, with levels 32.9% higher in urbanized northwest sub-basins that receive over 400 million tons of wastewater annually. Watershed soils modulate diffuse inputs: farmland (covering 44.2% of the watershed area) leaches sulfate, which is buffered by organic matter retention. Lake sediments act as the primary sink with over 90% of sulfate reduced in the top 10 cm through microbial dissimilatory reduction (α ≈ 1.022). However, this process accelerates phosphorus mobilization via sulfide-driven iron reduction, worsening eutrophication. Our findings identify municipal wastewater as the key controllable sulfate source in the post-emission-reduction era, emphasizing the need for integrated watershed management that targets advanced effluent treatment such as biological sulfate removal to disrupt the sulfate-phosphorus feedback loop and promote ecosystem recovery in eutrophic lakes globally.

Graphical Abstract

The decoupling of 76.2% decrease in SO₂ emissions after 2015 while only 18.5% reduction in sulfate concentrations in Taihu Lake indicated the increasing dominance of non-atmospheric inputs in this watershed. A notable northwest-southeast spatial SO42− gradient in lake water and increasing pattern from bottom to surface on sediment profiles were also observed. In the sediment of the major SO42− sink, over 90% of sulfate undergoes microbial reduction, likely an important driver for internal phosphorus release and potential eutrophication booster. With sulfate isotopic evidence, major SO42− source contributions were identified, and this highlights an urgent need for adaptive management strategy to gear to the pollutant source shift and internal nutrient loading control.