Department of Environmental Science, Zhejiang University, Hangzhou 310058, China.
Institute of Soil and Water Resources and Environmental Science, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, China.
Water Res. 2022 Sep 1;223:118971. doi: 10.1016/j.watres.2022.118971. Epub 2022 Aug 11.
Photochemically produced reactive intermediates (PPRIs) formed by sunlight-irradiation of natural photosensitizers play critical roles in accelerating biogeochemical cycles on earth surface. Existing PPRI studies mostly focus on bulk phase reactions (e.g., bulk water), with PPRI processes at the environmental interfaces largely unexplored. Here, we report the wetland soil-water interface (SWI) as a widespread but previously unappreciated hotspot for PPRI productions. Massive productions of four important PPRI species (i.e., triplet-state excited organic matter (OM*), singlet oxygen (O), hydrogen peroxide (HO), and hydroxyl radical (OH)) were observed at the SWI. All four PPRI species exhibited higher productions at the SWI than those in bulk water, where OH production was largely elevated by up to one order of magnitude. The enhanced PPRI productions at the SWI were caused by intensified photon absorption and vibrant Fe-mediated redox processes, where the light absorption by less- or non-photoactive soil substances partially offset the enhancement on PPRI productions. Nationwide wetland investigations demonstrate that the SWI was a ubiquitous hotspot for PPRI productions. Simulations on PPRIs-mediated reactions suggest that the enhanced PPRI productions could greatly affect the kinetics and transformation pathways of nutrients and pollutants. Given that the SWI also acts a hotspot for nutrient and pollutant accumulation, incorporating the SWI enhanced PPRI productions into biogeochemical process assessments is pivotal for advancing our understandings on the element cycles and pollutant dynamics in wetlands.
光化学反应产生的活性中间体（PPRIs）是由阳光照射天然光敏剂形成的，在地球表面的生物地球化学循环加速中起着关键作用。现有的 PPRI 研究主要集中在体相反应（例如，体相水）上，而环境界面上的 PPRI 过程在很大程度上尚未得到探索。在这里，我们报告湿地土壤-水界面（SWI）是 PPRI 产生的广泛但以前未被重视的热点。在 SWI 处观察到四种重要的 PPRI 物种（即三重态激发的有机物（OM*）、单线态氧（O）、过氧化氢（HO）和羟基自由基（OH））的大量产生。在 SWI 处，所有四种 PPRI 物种的产生都高于体相水中的产生，其中 OH 的产生大大提高了一个数量级。SWI 处 PPRI 产生的增强是由光子吸收和充满活力的 Fe 介导的氧化还原过程引起的，其中较少或非光活性土壤物质的光吸收部分抵消了对 PPRI 产生的增强。全国性湿地调查表明，SWI 是 PPRI 产生的普遍热点。对 PPRIs 介导的反应的模拟表明，增强的 PPRI 产生可能极大地影响营养物和污染物的动力学和转化途径。鉴于 SWI 也是营养物和污染物积累的热点，将 SWI 增强的 PPRI 产生纳入生物地球化学过程评估对于推进我们对湿地元素循环和污染物动态的理解至关重要。
